Gossamer Bio, Inc. (GOSS) Business

Item 1. Business.

Overview

We are a clinical-stage biopharmaceutical company focused on the development and commercialization of seralutinib for the treatment of pulmonary hypertension, or PH, including pulmonary arterial hypertension, or PAH, and PH

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associated with interstitial lung disease, or PH-ILD. Our goal is to be an industry leader in, and to enhance the lives of patients living with, PH. To accomplish this goal, we have assembled a deeply experienced and highly skilled group of industry veterans, scientists, clinicians and key opinion leaders from leading biotechnology and pharmaceutical companies, as well as leading academic centers from around the world. We intend to maintain a scientifically rigorous and inclusive corporate culture where employees strive to bring improved therapeutic options to patients.

Our Team

Our founders and management team have held senior positions at leading biopharmaceutical companies and possess substantial experience and expertise across the spectrum of drug development and commercialization.

Faheem Hasnain is our Co-Founder and has served as our Chief Executive Officer since November 2020 and as our Chairman since our inception. Mr. Hasnain also served as our Chief Executive Officer from our inception through July 2018 and our Executive Chairman from July 2018 through June 2019. Prior to co-founding Gossamer Bio, Mr. Hasnain served as President, CEO and as a Director of Receptos, Inc. from November 2010 to August 2015. Receptos was a public company formed in 2009 focused on developing treatments in immunology and metabolic disorders and was purchased by Celgene Corporation in August 2015. Previously, Mr. Hasnain was the President and Chief Executive Officer and a director of Facet Biotech Corporation, a biology-driven antibody company with a focus in multiple sclerosis and oncology. He held that position from December 2008 until the company's acquisition by Abbott Laboratories in April 2010.

Bryan Giraudo, our Chief Financial Officer and Chief Operating Officer, has extensive biotechnology and medical technology finance experience, having previously served as Senior Managing Director at Leerink Partners and Managing Director at Merrill Lynch, Pierce, Fenner & Smith Incorporated. Bob Smith, our Chief Commercial Officer, has over 30 years of experience in pharmaceuticals, with a strong focus on PAH and rare disease. Prior to Gossamer, Mr. Smith was the National Sales Lead in charge of preparing for the commercial launch of sotatercept for the treatment of PAH in the US at Merck & Co., or Merck. Previously until 2018, Mr. Smith was the Senior Vice President of Sales and an Executive Leadership Team member at Actelion Pharmaceuticals US, Inc., where he spearheaded two successful PAH drug launches, Opsumit (macitentan) and Uptravi (selexipag). Christian Waage, our Executive Vice President, Technical Operations & Administration, has meaningful management biotechnology experience, having previously held various positions at Receptos, most recently as Managing Director after its acquisition by Celgene, and at Ardea Biosciences, Inc. as Vice President, General Counsel. Caryn Peterson, our Executive Vice President, Regulatory Affairs, has considerable experience and regulatory expertise as a Managing Director of Development & Strategic Consulting Associates, as well as management positions leading regulatory affairs at Syndax Pharmaceuticals and FeRx Incorporated.

Our Strategy

Our near-term strategy is to focus our resources on advancing seralutinib for the treatment of PAH and to pursue regulatory alignment and potential approval as efficiently as possible. Based on the totality of data from the Phase 3 PROSERA Study and the Phase 2 TORREY Study, including general consistency across endpoints and within higher risk subgroups, we believe seralutinib demonstrates a risk benefit profile that supports continued regulatory dialogue. Following our February 2026 announcement of topline results from PROSERA, we are prioritizing (i) completing in-depth analyses of the PROSERA dataset, (ii) engaging with the U.S. Food and Drug Administration, or FDA, to obtain feedback regarding potential regulatory paths forward, and (iii) evaluating our strategic options and resource allocation as a company, in addition to strengthening our capital structure. The key elements of our near-term strategy include:

•Obtain FDA feedback and seek to define a regulatory path forward in PAH. We are completing analyses of the PROSERA dataset and plan to engage with the FDA, including through requesting a Type C meeting, to understand their perspective on the totality of the PROSERA and TORREY datasets and potential regulatory paths forward.

•Advance preparations toward a potential NDA submission. We are advancing NDA‑readiness activities and plan to engage with the FDA to clarify the appropriate regulatory path forward. Our decision to submit an NDA, and the timing of any submission, will be informed by ongoing analyses of the PROSERA dataset, the totality of clinical data to date, and FDA feedback.

•Advance toward potential approval while maintaining disciplined resource allocation. If an NDA is submitted and accepted for substantive review, the timing of any FDA action would depend on the applicable review timeline and other factors. While timing remains subject to FDA feedback and other variables, we currently anticipate a potential approval action date by year end 2027.

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•Continue ongoing open-label extension studies: The open-label extension studies remain active, and continued follow‑up is intended to further characterize longer‑term exposure and potential durability of effect.

•Pause SERANATA enrollment while evaluating implications of PROSERA and next steps. While we have paused SERANATA enrollment to support disciplined resource allocation and to evaluate the implications of PROSERA as we engage with regulators, we continue to believe seralutinib may have meaningful potential in fibrotic lung disease, including PH‑ILD, informed in part by the connective tissue disease-associated PAH, or CTD‑APAH, findings in PROSERA.

•Enhance our capital structure through proactive engagement with stakeholders. This includes evaluating a range of potential alternatives related to our outstanding convertible notes to support our strategic priorities. We may also seek to raise additional capital through equity offerings, debt financings or other capital sources to support our strategic priorities.

•Advance RT234 under our option agreement with Respira in a capital‑efficient manner. We intend to continue advancing RT234 pursuant to our option agreement with Respira Therapeutics, which is structured to support limited foundational manufacturing and device readiness activities while preserving our focus and operational resources for seralutinib. We believe RT234 represents a complementary, on‑demand therapeutic opportunity in PAH and PH‑ILD and could be ready to re‑enter clinical development as early as 2027.

Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)

Seralutinib, also known as GB002, is an investigational inhaled, small molecule, platelet-derived growth factor receptor, or PDGFR, colony-stimulating factor 1 receptor, or CSF1R, and c-KIT inhibitor, currently being evaluated in a Phase 3 clinical trial for the treatment of PAH. We believe that seralutinib has the potential to reverse pathological remodeling by addressing mechanisms that underlie PAH. Inhaled seralutinib, which is designed to act on both isoforms of the PDGFR, α and β, as well as the CSF1R and c-KIT pathways, inhibited and reversed cellular overgrowth in lung blood vessels in multiple animal PAH models.

In February 2026, we announced topline results from the 48-week Phase 3 PROSERA Trial in 390 PAH patients. Seralutinib demonstrated a placebo-adjusted improvement in the primary endpoint, six-minute walk distance (6MWD) at Week 24, of 13.3 meters (p = 0.0320), missing the prespecified alpha threshold of 0.025. At Week 24, in this well treated patient population, patients receiving seralutinib had a median change of 28.2 meters from baseline, while patients receiving placebo had a median change from baseline of 13.5 meters. Consistent with the completed Phase 2 TORREY Study, seralutinib delivered a compelling signal in the prespecified intermediate‑ and high‑risk subgroup (n = 234), as defined by the REVEAL 2 Lite Risk Score ≥ 6 at screening, with a 20.0m placebo‑adjusted improvement in 6MWD (nominal p = 0.0207). Three of four key secondary endpoints also demonstrated a nominal p-value below 0.0125 in this subpopulation, underscoring seralutinib’s activity in patients with higher risk. Additional analyses are ongoing.

Additionally, we believe seralutinib may have meaningful potential in fibrotic lung disease, including PH‑ILD. In PROSERA, the subgroup of patients with CTD-APAH (n = 87) demonstrated a placebo‑adjusted improvement in 6MWD at Week 24 of 37.0 meters (nominal p = 0.0104). We believe the biology of connective tissue disease‑associated PAH may be relevant to broader fibrotic lung disease populations, including PH-ILD. CTD APAH has historically been associated with poorer outcomes and less clinical response to PAH therapies compared with idiopathic PAH, and patients may experience higher rates of treatment related adverse events that can limit therapy options. We activated clinical sites and began screening patients for the SERANATA Phase 3 study in PH‑ILD, but following our February 2026 announcement of topline results from PROSERA, we paused enrollment in SERANATA to allow for further evaluation of the PROSERA dataset, including regional variability, and to support disciplined resource allocation as we engage with regulators regarding potential paths forward.

In December 2022, we announced positive topline results from the 24-week Phase 2 TORREY trial in 86 PAH patients. In this well-treated patient population, the seralutinib arm demonstrated a statistically significant, placebo-adjusted improvement of 14.3% in its primary efficacy endpoint, pulmonary vascular resistance, or PVR. In the pre-specified elevated-risk subgroup (REVEAL 2.0 Risk Score ≥ 6), seralutinib showed notable improvements at Week 24 compared to placebo, including a 21.9-meter increase in 6-minute walk distance (6MWD; nominal p = 0.2482), a 23% reduction in

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pulmonary vascular resistance (PVR; nominal p = 0.0134), and a 732 ng/L decrease in NT-proBNP levels (nominal p = 0.0002).

We are completing analyses of the PROSERA dataset and plan to engage with the FDA, including through requesting a Type C meeting, to understand their perspective on the PROSERA and TORREY datasets and potential regulatory paths forward. Across the Phase 2 TORREY and Phase 3 PROSERA studies, we believe that the totality of evidence supports that seralutinib has been generally well tolerated in PAH in heavily treated populations.

In May 2024, we entered into a collaboration agreement with Chiesi. Under the collaboration agreement, we will jointly develop seralutinib with Chiesi. We will lead global development of seralutinib in PAH and PH-ILD and will lead potential commercialization for PAH and PH-ILD in the United States, with both parties contributing 50% of commercial efforts, including performing 50% of the commercialization activities. Chiesi will lead global development in any additional indications and will lead potential commercialization in the United States in any additional indications. Chiesi will also have the exclusive right to commercialize seralutinib outside of the United States. We in-licensed seralutinib from Pulmokine, Inc. The FDA, the European Commission, or EC, and the Pharmaceuticals and Medical Devices Agency, or PMDA, of Japan have granted seralutinib orphan drug designation for the treatment of patients with PAH. Chiesi is currently evaluating the totality of the PROSERA dataset.

Mechanism of Action in PAH

PAH is driven by abnormal cellular proliferation within and around the small blood vessels of the lung that carry blood from the right side of the heart to the lungs. Functional and structural changes in the pulmonary vasculature, known as vascular remodeling, can lead to smooth muscle cell proliferation and migration from the middle layer of the blood vessel into the inner layer. This can result in the development of plexiform and neointimal lesions that can obstruct blood flow. The obstruction of blood flow in the pulmonary vessels can also predispose patients to thrombosis, or blood clots, within these small pulmonary vessels that further blocks blood flow. This progressive obstruction of blood flow from the right side of the heart to the lungs can cause the right ventricle to fail, thus leading to severe breathlessness, reduced exercise tolerance and death. Seralutinib was designed to inhibit multiple kinases that play a role in the pathology of PAH, including PDGFRα/β, CSF1R and c-KIT.

The PDGFR is a tyrosine kinase receptor which, when activated by its agonist, induces cellular proliferation. PDGF expression is known to be particularly important to stimulating smooth muscle cell proliferation in PAH patients. PDGFRs and their ligands are both upregulated in PAH. Upregulated PDGFR signaling results in endothelial cell and fibroblast dysfunction and the proliferation and migration of smooth muscle cells. This effect results in the overgrowth and occlusion of blood vessels in the lung. Kinase inhibitors with activity against the PDGFR pathway have shown the ability to reverse PAH in animal models.

Inhaled seralutinib is designed to act on both isoforms of the PDGFR, α and β. Data from preclinical animal models and human lung histology from PAH patients suggests that it is important to inhibit both of these isoforms of the PDGF receptor. PDGFRα is highly expressed in pulmonary arteriole vascular smooth muscle cells, or PAVSMCs. Inhibiting PDGFRα may help reduce the abnormal cell proliferation of PAVSMCs that results in blood vessel thickening. PDGFRβ is more highly expressed in fibroblasts and myofibroblasts that are involved with the abnormal cell proliferation within the blood vessel that leads to the obstruction of the pulmonary arterioles. We believe inhibiting PDGFRβ is therefore important in decreasing the abnormal cell proliferation of these cell types.

The c-KIT pathway was also identified as an important growth factor involved in pulmonary vascular remodeling, particularly in the cells implicated in perivascular inflammation. An analysis of lung and pulmonary arteriole samples has also shown increased gene expression of c-KIT in idiopathic PAH. C-KIT positive endothelial cells may also secrete PDGF, and perivascular c-KIT positive mast cells have been shown to secrete pro-inflammatory cytokines and tryptase that further contribute to the inflammatory process in PAH.

Mechanistic validation of a PDGFR and c-KIT kinase inhibitor has been observed in clinical trials of imatinib (Gleevec), an oral tyrosine kinase inhibitor with known activity against the PDGFR and c-KIT pathways, which demonstrated proof-of-concept in humans in a Phase 3 clinical trial in PAH. In preclinical models, as compared to imatinib, seralutinib was a more potent inhibitor of the PDGFRα isoform, and seralutinib was a ten-fold more potent inhibitor of the PDGFRβ isoform and c-KIT.

Macrophages have also been identified as one of the most important inflammatory cells in the development and exacerbation of PAH. Macrophages, which express the CSF1 receptor, are now recognized to play an important role in PAH pathology. Activated CSF1R positive macrophages accumulate around pulmonary arterioles in PAH, which have been

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shown in vivo in PAH patients with positron emission tomography. Additionally, macrophage activity in PAH is associated with bone morphogenetic protein receptor type II, or BMPR2, levels. The decrease in BMPR2 characteristic of PAH results in induction of granulocyte-macrophage colony-stimulating factor, or GM-CSF, and macrophage recruitment. Notably, in the BMPR2 knock out mouse, there is significant pulmonary inflammation due to activation of tissue macrophages.

Furthermore, inflammatory macrophages secrete PDGF and stimulate pulmonary artery smooth muscle cell migration and proliferation, accelerating the feedback loop of inflammation, hyperproliferation and fibrosis that characterize PAH.

Prior PDGF Pathway Development in PAH - The IMPRES Phase 3 Clinical Trial of Imatinib

The IMPRES trial was a Phase 3 clinical trial conducted by Novartis of imatinib (Gleevec) in patients with PAH. Imatinib has known activity against multiple tyrosine kinases, including the PDGFR, c-KIT receptors and Abelson murine leukemia viral oncogene homolog 1, or c-ABL. The trial met its primary endpoint, improvement in 6-minute walk distance, or 6MWD, versus placebo at week 24.

However, systemic adverse events such as bleeding and poor tolerability and frequent drug discontinuation led to a high drop-out rate within the active arm of the trial. Subdural hematomas occurred in eight patients who were also being administered oral anticoagulants during the trial. Novartis withdrew its supplemental regulatory applications in PAH in 2013 and, to our knowledge, did not pursue further development of imatinib in the indication.

Overview of PAH (WHO Group 1 Pulmonary Hypertension)

PAH, classified as World Health Organization, or WHO, Group 1 Pulmonary Hypertension, is a rare disease that is characterized by abnormally high blood pressure in the blood vessels carrying deoxygenated blood from the right side of the heart to the lungs and is progressive and often fatal. Symptoms include shortness of breath at rest or with minimal exertion. Other symptoms include fatigue, chest pain, dizzy spells and fainting. The progressive nature of this disease causes the right side of the heart to work much harder and eventually weaken or fail.

Patients are often evaluated by functional class, which categorizes patients by their ability to carry out physical activity and their symptom severity. Worsening symptoms, and thus higher numbered functional classes, are associated with higher mortality. The four functional classes established by the WHO are detailed below in Table 1.

Table 1. PAH Functional Classes

Additionally, recent medical society guidelines have identified intermediate and high-risk categories of PAH based on several variables including signs of right heart failure, rate of symptom progression, functional class, 6MWD, maximum oxygen consumption and NT-proBNP, which is a biomarker for heart failure and measures of right heart function. One of these risk categorization tools, the REVEAL 2.0 Risk Score, was utilized in the completed Phase 2 TORREY Study.

Multiple PAH-specific treatments have been introduced in the past two decades, however PAH continues to have a high morbidity and mortality. Based on REVEAL registry data, newly diagnosed functional class III and IV patients have 5-year survival rates of 60% and 44%, respectively, while rates for previously diagnosed patients were even lower at 57% and 27%, respectively.

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Overview of PAH Market

PAH most commonly affects women between the ages of 30 and 60. The true incidence and prevalence of PAH are unknown. The estimated PAH patient population in the US is about 50,000 patients, and the estimated patient population in the European Union, or EU, is over 70,000 patients. The number of diagnosed PAH patients continues to increase, and we believe this increase is likely due to enhanced awareness and diagnosis of the disease. Worldwide branded drug sales for therapies used in PAH and PH ILD represent a multi-billion dollar global market.

Treatment Paradigm in PAH

Currently approved PAH therapies consist of three classes of vasodilators and one activin ligand trap therapy. The three classes of vasodilatory therapy are phosphodiesterase type 5, or PDE5, inhibitors (and guanylate cyclase stimulators), ERAs, and prostanoids (and prostacyclin receptor agonists). PDE5 inhibitors are often used in combination with ERAs as an early treatment strategy. In patients who fail to respond to combination therapy of an ERA and a PDE5 inhibitor, it is common practice to add a prostanoid. Prostanoids are also commonly used to treat patients with evidence of right heart failure. The recent introduction of an activin ligand trap therapy (sotatercept) to the market has provided patients with an additional treatment option. While some existing treatments have led to significant improvements in time to clinical worsening and other composite endpoints in PAH patients, there are no cures. The effects of approved PAH therapies, while capable of improving blood flow through the lungs, may eventually be overtaken by the worsening cellular proliferation and arterial remodeling underlying the condition, given the progressive nature of the disease. We believe an agent with the ability to safely reverse pathological remodeling could provide utility across functional classes and risk categories.

Overview of PH-ILD (WHO Group 3 Pulmonary Hypertension)

We believe that seralutinib has potential as a therapeutic treatment for PH-ILD, a subtype of WHO Group 3 Pulmonary Hypertension. PH-ILD is a collection of progressive and often fatal forms of PH that affect the small airways of the lungs. PH-ILD includes PH related to idiopathic pulmonary fibrosis and PH related connective tissue disease-associated interstitial lung disease, amongst other diseases. These diseases are characterized by pulmonary vascular pathology associated with PH, in addition to thickening and scarring of the lung interstitium from interstitial lung disease. While the prevalence of PH-ILD is unknown, we believe PH-ILD is at least as prevalent as PAH. Patients living with PH-ILD generally have a poor disease prognosis and have an increased mortality rate, as compared to PAH patients. We believe seralutinib may have potential in fibrotic lung disease, including PH‑ILD. In PROSERA, the subgroup of patients with CTD‑APAH demonstrated a placebo‑adjusted improvement in 6MWD at Week 24 of 37.0 meters (nominal p=0.0104). We believe the biology of connective tissue disease‑associated disease may be relevant to broader fibrotic lung disease populations, including PH‑ILD. There is only one FDA-approved treatment for PH-ILD, and there are no approved therapies in the EU.

Seralutinib Product Differentiation

Seralutinib is an inhaled kinase inhibitor designed to build on the evidence of efficacy seen in trials of imatinib while overcoming imatinib’s observed systemic safety and tolerability issues and improving on imatinib's kinase inhibitory profile. Seralutinib is designed to have a differentiated selectivity profile as compared to imatinib with increased potency against the PDGFRα isoform, ten-fold higher potency against the PDGFRβ isoform and c-KIT, and no activity against c-ABL or the tyrosine kinase, LCK. Additionally, seralutinib is multiple orders of magnitude more potent against CSF1R, as compared to imatinib. We believe seralutinib has the potential to be a therapeutic option for PH that may provide a:

•    differentiated, anti-proliferative mechanism that addresses the underlying mechanisms of both PAH and PH-ILD;

•    more tolerable safety profile than systemic imatinib; and

•    convenient, simple and portable inhalation delivery system.

Summary of Preclinical Program

Seralutinib inhibits both PDGFR α and β, and it inhibited and reversed cell overgrowth in lung blood vessels in a PAH rat model, which replicates many features of human PAH, including the abnormal cell proliferation that can block the small vessels of the lung. Seralutinib substantially reduced the occlusive lesions in the small lung blood vessels in this model. Additionally, seralutinib demonstrated a statistically significant reduction in right ventricular systolic pressure as compared to placebo.    In a separate rat model of PAH, the SU5416 hypoxia model, seralutinib demonstrated a statistically significant reduction in circulating plasma NT-proBNP as compared to placebo, while the difference between imatinib and placebo was not

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significant for this PAH biomarker. Seralutinib also restored rat lung BMPR2 expression to healthy levels, which was a statistically significant improvement as compared to placebo and imatinib. Irregularities in BMPR2 expression have been linked to PAH.

Clinical Development History of Seralutinib

Summary of Completed Phase 1a Studies

We completed Phase 1a SAD and MAD double-blind, placebo-controlled, randomized studies of orally inhaled seralutinib in 82 healthy adult volunteers. We assessed pharmacokinetics, or PK, parameters and safety. Seralutinib was well-tolerated, and there were no dose-limiting toxicities. No serious adverse events, or SAEs, were reported, and no reported adverse events, or AEs, led to study drug discontinuation. The most common AEs were throat irritation and cough, which were mild in severity and similar in incidence to placebo. Following single and multiple oral inhalations, seralutinib was rapidly absorbed into and cleared from the systemic circulation. Seralutinib exposure increased in a dose-proportional manner following single and multiple dose administration.

Summary of Completed Phase 1b PAH Clinical Trial

In December 2020, we announced topline results from the completed Phase 1b randomized, double-blind, placebo-controlled, multi-center trial of seralutinib in functional class II and III PAH patients. Eight patients completed the two-week blinded portion of the trial. Enrollment for this trial was temporarily paused due to the COVID-19 pandemic but was reopened in the third quarter of 2020. The primary outcome of this 2-week trial was safety and tolerability. Seralutinib was generally well tolerated in PAH patients, and all eight patients completed the 2-week study. There were no SAEs, and the most frequently reported AEs were mild-to-moderate cough and mild headache. Systemic PK was characterized by low systemic exposure and rapid drug clearance in PAH patients, which was consistent with PK data from the Phase 1a studies in healthy volunteers. Target engagement in PAH patients was demonstrated via whole blood CSF1R stabilization assay across all tested dose levels.

Upon completion of the two-week Phase 1b trial, two PAH patients were able to enroll and complete a six-month open label extension trial of seralutinib. Both patients were able to titrate up to the maximum allowed dose, 90 mg twice daily. No SAEs were reported during the extension trial. Both patients demonstrated a decrease in NT-proBNP levels from baseline, and both patients demonstrated an increase in 6MWD from baseline.

Summary of Completed Phase 2 PAH Clinical Trial (TORREY Study)

In December 2022, we announced positive topline results from the completed Phase 2 TORREY Study, a randomized, double-blind, placebo-controlled, multi-center clinical trial in PAH patients. We enrolled 86 functional class II and III PAH patients who were not meeting treatment goal despite background PAH treatment. 57% of enrolled patients were on triple background PAH therapy, and 40% were on double background PAH therapy. Patients on the active arm received seralutinib at doses starting at 60 mg twice daily, and they titrated up to 90 mg twice daily. While the protocol allowed for down-titration to 45 mg twice daily as necessary, the substantial majority of patients on the seralutinib arm were able to achieve and maintain 90 mg twice daily. Patients remained on their background PAH therapies throughout the trial.

Seralutinib demonstrated a statistically significant improvement on the primary endpoint, change from baseline in PVR over a 24-week treatment period. A mean improvement in PVR between the placebo and seralutinib arms of 96.1 dynes × seconds/cm5 (p = 0.0310), equating to a placebo-adjusted improvement of 14.3%, was observed in the study. The p-value is the probability that the difference between two data sets was due to chance. The smaller the p-value, the more likely the differences are not due to chance alone. In general, if the p-value is less than or equal to 0.05, the outcome is considered statistically significant. Improvements in PVR favored the seralutinib arm across all pre-specified patient sub-groups. The key secondary endpoint in the TORREY Study was change from baseline to week 24 in 6MWD. An observed mean difference in 6MWD between placebo and seralutinib of 6.5 meters numerically favored the seralutinib arm. Changes in 6MWD also favored seralutinib in the majority of pre-specified sub-groups. The trial was neither powered nor designed for statistical significance in 6MWD.

Enhanced effects for both PVR and 6MWD were observed in patients with more severe baseline disease, as defined by WHO functional class, or FC, and REVEAL 2.0 Risk Scores. In FC III patients, a 21% placebo-adjusted reduction in PVR (p = 0.0427) and 37-meter placebo-adjusted improvement in 6MWD (p = 0.0476) were observed for the seralutinib arm. In patients with a baseline REVEAL 2.0 Risk Score of 6 or greater, seralutinib demonstrated a 23% placebo-adjusted reduction in PVR (p = 0.0134) and a placebo-adjusted 22-meter improvement in 6MWD (p = 0.2482).

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Seralutinib treatment resulted in a statistically significant reduction in NT-proBNP, a biomarker of right heart stress, as early as 12 weeks, increasing to a placebo-adjusted 408.3 ng/L mean difference at Week 24 (p = 0.0012). This biomarker change was accompanied by clinically relevant and statistically significant changes for seralutinib vs. placebo in key assessments of right heart structure and function, including right atrium area, right ventricle free wall strain and pulmonary artery compliance.

Seralutinib was generally well tolerated in the TORREY study, with treatment emergent adverse events, or TEAEs, reported in 36 (86%) and 41 (93%) of the patients in the placebo and seralutinib arms, respectively. The vast majority of TEAEs reported in the study were mild to moderate in severity. In the seralutinib arm, there was one SAE related to study drug reported, while no SAEs related to study drug were reported in the placebo arm. The most frequently reported TEAE in the study was cough, reported in 16 (38%) and 19 (43%) of the patients in the placebo and seralutinib arms, respectively. Of the 19 patients reporting cough in the seralutinib arm, 17 experienced mild cough, while 2 experienced moderate cough. The most frequently reported TEAEs in the IMPRES Phase 3 study of imatinib in PAH, including nausea, peripheral edema, diarrhea, and vomiting, were observed at substantially lower frequency in the TORREY study, and reported cases were generally well balanced between the seralutinib and placebo arms. No cases of subdural hematoma were reported in the study.

In the TORREY open‑label extension (OLE), participants who continued on seralutinib demonstrated continued improvement in PVR through later follow‑up, with median PVR decreasing from 620 dyne·s/cm⁵ at baseline to 505 at Week 24 and 475 at Week 72. These OLE findings are descriptive and provide additional longer‑term context beyond the 24‑week blinded period.

Summary of Completed Phase 3 PAH Clinical Trial (PROSERA Study)

PROSERA was a randomized, double‑blind, placebo‑controlled, global Phase 3 study in patients with WHO Functional Class II and III PAH on background therapy, randomized 1:1 to seralutinib or placebo and treated for up to 48 weeks. The primary endpoint was change from baseline in 6MWD at Week 24 in the intent‑to‑treat population, with key secondary endpoints including time to clinical worsening, clinical improvement, change in NT‑proBNP, and reduction in REVEAL Lite 2 risk score.

In February 2026, we announced topline results from PROSERA. At Week 24, seralutinib demonstrated a placebo adjusted improvement in 6MWD of 13.3 meters versus placebo (p = 0.0320), which did not meet the prespecified statistical alpha threshold of 0.025. At Week 24, patients receiving seralutinib had a median change in 6MWD from baseline of 28.2 meters, compared with 13.5 meters for patients receiving placebo.

A key secondary endpoint, change in NT‑proBNP at Week 24, demonstrated an estimated location shift of ‑120.4 ng/L compared with placebo (nominal p = 0.0002) in the overall population, with separation between the arms favoring seralutinib observed starting at Week 4 (-96.0 ng/L; nominal p = 0.0002). Key secondary endpoints time-to-clinical worsening (TTCW), clinical improvement and proportion of patients with a one point or greater reduction in REVEAL Lite 2 Risk Score all favored seralutinib as compared to placebo in the overall population.

In a prespecified subgroup analysis of patients with REVEAL Lite 2 score ≥6 at screening, corresponding to intermediate- and high-risk patients, seralutinib demonstrated a potentially clinically meaningful response profile across the primary and key secondary endpoints. All key secondary endpoints favored seralutinib, with placebo‑adjusted effects including NT‑proBNP at Week 24 (location shift = -265.8 ng/L; nominal p = 0.0002), ≥1‑point improvement in REVEAL Lite 2 risk score at Week 24 (odds ratio = 2.033; nominal p = 0.0083), clinical improvement at Week 24 (odds ratio = 3.318; nominal p = 0.0101), and TTCW through Week 48 (hazard ratio = 0.744; nominal p = 0.4360).

Notably, in patients with CTD‑APAH, seralutinib demonstrated an improvement in six‑minute walk distance, achieving a placebo‑adjusted gain of 37.0 meters at Week 24 (n = 87; nominal p = 0.0104), indicating a potentially strong clinically meaningful treatment effect in this clinically challenging subgroup.

We continue to interrogate our computed tomography (CT) functional respiratory imaging (FRI) exploratory substudy data. Given the exploratory nature of the technology, we are taking the appropriate steps to understand the totality of the data and the utility of the technology.

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Overall, seralutinib was generally well tolerated in the PROSERA Study. TEAEs were reported in 86.5% of patients receiving seralutinib and 80.5% of patients receiving placebo. Treatment-emergent SAEs occurred in 16.0% of patients receiving seralutinib and 18.9% of patients receiving placebo. Transaminase elevations of three times or greater of the upper limit of normal were observed in 13% of patients receiving seralutinib and 1% of patients receiving placebo. In seralutinib treated patients, liver enzyme elevations tended to occur early in treatment, and generally resolved with drug interruption or discontinuation, with rapid recovery reported in observed cases. The most frequently reported adverse event in patients treated with seralutinib was cough, reported in 37.0% of patients.

Summary of Ongoing Open-Label Extensions (Phase 1b, Phase 2 & Phase 3)

Patients from the Phase 1b study, the Phase 2 TORREY Study, and the Phase 3 PROSERA Study continue in ongoing open‑label extension studies of seralutinib, where we are monitoring longer‑term safety and tolerability and where we are further characterizing the durability of clinical response.

Summary of Paused SERANATA Phase 3 Clinical Trial in PH-ILD

Starting in the fourth quarter of 2025, we activated clinical sites and began screening patients for the SERANATA Phase 3 study in PH‑ILD. Following our February 2026 announcement of topline results from PROSERA, we paused enrollment in SERANATA to allow for further evaluation of the PROSERA dataset, including regional variability, and to support disciplined resource allocation as we engage with regulators regarding potential paths forward.

RT234 (Inhaled, On‑Demand PDE5 Inhibitor)

RT234 is an investigational inhaled, as‑needed, or PRN, dry‑powder formulation of vardenafil, a PDE5 inhibitor, being developed for PAH and PH‑ILD. PDE5 inhibitors are an established class with multiple approved oral therapies for chronic use in PAH; however, there are no approved inhaled PDE5 therapies and no approved PRN treatments designed for on‑demand symptom relief in PAH or PH‑ILD. Oral vardenafil is approved for erectile dysfunction. PRN use refers to administration at the time of need, rather than on a scheduled, chronic dosing regimen, with the objective of providing rapid symptom relief. In September 2025, we entered into an option agreement with Respira Therapeutics to acquire RT234. RT234 has completed open‑label Phase 2 clinical trials and is intended to address an unmet need for on‑demand symptom management that may complement existing chronic PH therapies. Current activities by Respira Therapeutics are focused on foundational manufacturing and device readiness, and subject to those ongoing activities, RT234 could reenter clinical development as early as 2027. See Note 14 to our consolidated financial statements included elsewhere in this annual report for additional details regarding the Respira option agreement.

Competition

The biotechnology and pharmaceutical industries are characterized by rapid technological advancement, significant competition and an emphasis on intellectual property. We face potential competition from many different sources, including major and specialty pharmaceutical and biotechnology companies, academic research institutions, governmental agencies and public and private research institutions. Any product candidates that we successfully develop and commercialize will compete with current therapies and new therapies that may become available in the future. Our commercial opportunity could be reduced or eliminated if our competitors develop and commercialize products that are safer, more effective, have fewer or less severe side effects or more convenient than any products that we may develop. Our competitors also may obtain FDA or other regulatory approval for their products more rapidly than we do. We believe that the key competitive factors affecting the success of any of our product candidates will include efficacy, safety profile, convenience, cost, level of promotional activity devoted to them and intellectual property protection.

We expect to face competition for seralutinib and RT234 from existing products and products in development. Seralutinib is a PDGFR, CSF1R and c-KIT inhibitor initially targeted for PAH and PH-ILD patients. We expect competition within the PAH indication will include prostanoids / prostacyclin receptor agonists, including Orenitram (United Therapeutics), Uptravi (Janssen), Tyvaso (United Therapeutics), Yutrepia (Liquidia) and Remodulin (United Therapeutics), and activin ligand traps, including Winrevair (Merck). We also may face some competition from products used as frontline therapy for PAH, such as the oral PDE5 inhibitors, including Revatio (Pfizer Inc.) and Adcirca (United Therapeutics); the sGC stimulator Adempas (Bayer AG); and oral ERAs, including Tracleer (Janssen), Letairis (Gilead Sciences, Inc.) and Opsumit (Janssen); and combination PDE5 inhibitor / ERA therapies, such as Opsynvi (Janssen). We believe that, if approved, seralutinib could be used alongside all classes of approved therapies. PAH is also an active indication for investigational drugs, and we may face competition in the future from L606 (Liquidia / Pharmosa Biopharma Inc.), CS1 (Cereno Scientific), treprostinil palmitil inhalation powder (Insmed, Inc.), ralinepag (United Therapeutics), REGN13335 (Regeneron), HS235 (35Pharma, Inc.), LTP001 (Novartis), APL‑9796 (Apollo Therapeutics Ltd), and ROC‑101 (AllRock Bio, Inc.). Additionally, although not approved for the treatment of PAH, we may face competition from formulations of imatinib, including the one in

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development from Inhibikase Therapeutics. While there are multiple classes of therapies with marketing approval for PAH, there are currently no therapies approved for PRN use to provide rapid, on‑demand symptom relief.

We expect to face competition from Tyvaso (United Therapeutics) and Yutrepia (Liquidia) within the PH-ILD indication, as they are the only approved therapies for PH-ILD in the United States. There are no approved therapies for PH-ILD in the EU. PH-ILD is also an active indication for investigational drugs, and we may face competition in the future from L606 (Liquidia / Pharmosa Biopharma Inc.), sirolimus (OrphAI Therapeutics), treprostinil palmitil inhalation powder (Insmed, Inc.), mosliciguat (Pulmovant, Inc.), mirivadelgat (ForeSee Pharmaceuticals Co., Ltd.), APL‑9796 (Apollo Therapeutics Ltd), and ROC‑101 (AllRock Bio, Inc.). While there is one class of therapy with marketing approval for PH-ILD, there are currently no therapies approved for PRN use to provide rapid, on‑demand symptom relief.

There may be other earlier stage clinical programs that, if approved, would compete with seralutinib. Many of our competitors have substantially greater financial, technical and human resources than we have. Additional mergers and acquisitions in the pharmaceutical industry may result in even more resources being concentrated in our competitors. Competition may increase further as a result of advances made in the commercial applicability of technologies and greater availability of capital for investment in these fields. Our success will be based in part on our ability to build and actively manage a portfolio of drugs that addresses unmet medical needs and creates value in patient therapy.

License and Collaboration Agreements

Pulmokine

In October 2017, we entered into a license agreement, or the Pulmokine Agreement, with Pulmokine, Inc., under which we were granted an exclusive worldwide license and sublicense to certain intellectual property rights owned or controlled by Pulmokine, including intellectual property rights co-owned by Pulmokine and Gilead Sciences, to develop and commercialize seralutinib and certain backup compounds for the treatment, prevention and diagnosis of any and all disease or conditions. On November 26, 2024, Pulmokine became a wholly-owned subsidiary of XOMA Royalty Corporation. We also have the right to sublicense our rights under the Pulmokine Agreement, subject to certain conditions. We are required to use commercially reasonable efforts to develop and commercialize at least one licensed product in the United States and in at least two countries in the European Union.

Under the terms of the Pulmokine Agreement, we made an upfront payment of $5.5 million and milestone payments of $5.0 million and are obligated to make future development and regulatory milestone payments of up to $48 million, which includes a payment of $5.0 million due upon the initiation of a Phase 3 clinical trial in a second indication, commercial milestone payments of up to $45 million, and sales milestone payments of up to $190 million. In January 2024, the Company made a payment of $10.0 million in connection with the initiation of the Phase 3 clinical trial of seralutinib. We are also obligated to pay tiered royalties on sales for each licensed product, at percentages ranging from the mid-single digits to the high single-digits. In addition, if we choose to sublicense or assign to any third parties our rights under the Pulmokine Agreement with respect to a licensed product, or our seralutinib operating subsidiary undergoes a change of control, we must pay to Pulmokine a specified percentage of all revenue to be received in connection with such transaction.

Our royalty obligations and the Pulmokine Agreement will expire on a licensed product-by-licensed product and country-by-country basis on the later of ten years from the date of first commercial sale or when there is no longer a valid patent claim covering such licensed product or specified regulatory exclusivity for the licensed product in such country. The Pulmokine Agreement may be terminated in its entirety either by Pulmokine or by us in the event of an uncured material breach by the other party, in the event the other party is subject to specified bankruptcy, insolvency or similar circumstances, or in the event of a force majeure event under certain circumstances. The agreement may be terminated by Pulmokine if we commence a legal action challenging the validity or enforceability of any licensed patents. We may terminate the agreement, either in its entirety or on a product-by-product basis, in the event of potential safety or efficacy concerns affecting a licensed product.

The intellectual property rights co-owned by Pulmokine and Gilead Sciences are subject to a license agreement, or the Gilead Agreement, between Pulmokine and Gilead Sciences. Under the Gilead Agreement, Pulmokine is required to use commercially reasonable efforts to develop and commercialize at least one licensed product, which obligation can be satisfied through our development efforts required under the Pulmokine Agreement, and to pay Gilead Sciences future regulatory milestone payments and royalties. Upon termination of the Gilead Agreement for any reason, our sublicense under the Pulmokine Agreement will survive provided that we did not cause a material breach that was the basis for such termination and we agree to be bound by the terms of the Gilead Agreement.

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Upon termination of the Pulmokine Agreement for any reason, all rights and licenses granted to us under the agreement will terminate and revert to Pulmokine, and in the event of certain termination events, we would grant Pulmokine worldwide rights to the terminated program.

Chiesi

On May 3, 2024, we, GB002, Inc., our wholly-owned subsidiary, and Gossamer Bio 002 Ltd., our indirect wholly-owned subsidiary, entered into a collaboration agreement with Chiesi. The collaboration is focused on the development and commercialization of seralutinib and licensed products including seralutinib and related licensed compounds, or Licensed Products, in the United States and the rest of the world, or the ROW Territory, for the treatment of PAH and PH-ILD and other indications, as may be permitted under the collaboration agreement.

Pursuant to the collaboration agreement, we granted exclusive, sublicensable (with our consent required in the United States for third party sublicenses) licenses to Chiesi under intellectual property rights controlled by us relating to Licensed Products, for the worldwide development, manufacture and commercialization of seralutinib and Licensed Products for therapeutic, prophylactic and diagnostic uses in humans and animals. The licenses granted to Chiesi are subject to retained rights of our Company for the worldwide development and manufacture of seralutinib and Licensed Products, commercialization of Licensed Products in the United States, and performance of our obligations and exercise of our rights that may be set forth in the global development plan and U.S. commercialization plan, in each case in accordance with the collaboration agreement.

Chiesi granted us a non-exclusive, sublicensable (with Chiesi’s consent required in the US Territory for third party sublicenses) licenses under certain practiced intellectual property rights relating to seralutinib and Licensed Products and arising intellectual property rights, in each case as controlled by Chiesi, for the worldwide development and manufacture of seralutinib and Licensed Product and a co-exclusive license (with Chiesi) to commercialize seralutinib and Licensed Products in the US Territory.

We agreed to use commercially reasonable efforts to conduct development and commercialization activities in relation to seralutinib and Licensed Products, under the global development plan and U.S. commercialization plan in accordance with the timelines therein. We will continue to lead global development of seralutinib in PAH and PH-ILD, and we and Chiesi will equally share the costs for the activities included in the global development plan for all Licensed Products, with the exception of the PROSERA Phase 3 study, which we will be solely responsible for conducting at our own cost and expense. With respect to each country in the ROW Territory, such obligation to equally share such development costs shall end when regulatory approval is received for a Licensed Product in such country. With respect to United States, the development costs incurred following regulatory approval shall continue to be shared equally. We will lead commercialization for PAH and PH-ILD in the United States, with both parties contributing 50 percent of commercial efforts, including performing 50 percent of the commercialization activities. Chiesi will lead commercialization in the United States in additional indications, and Chiesi will have the exclusive right to commercialize Licensed Products in the ROW Territory. Chiesi further agreed to use commercially reasonable efforts to commercialize Licensed Product in certain specified countries in the ROW Territory following receipt of regulatory approvals. Generally, we will have the right to lead in manufacturing commercial supply of seralutinib and Licensed Products for the United States for PAH and PH-ILD, and, subject to any of our existing obligations of to third party manufacturers, Chiesi will have the right to lead in manufacturing commercial supply of seralutinib and Licensed Products in the ROW Territory, in each case in accordance with the collaboration agreement.

Pursuant to the collaboration agreement, neither party nor its affiliates is permitted to develop or commercialize any compound or product throughout the term whose primary mechanism of action is inhibition of a tyrosine kinase for the treatment of PAH or PH-ILD in the United States or ROW Territory, subject to certain restrictions for the EU and UK.

In consideration and as reimbursement for our development costs, Chiesi agreed to pay us $160.0 million. Additionally, we will be eligible to receive up to $146.0 million in regulatory milestones and $180.0 million in sales milestones. In the United States, the parties agreed to share commercial profits and losses equally. In the ROW Territory, Chiesi will pay us an escalating mid-to-high teens percentage royalty, subject to standard deductions, on net sales of Licensed Product for PAH and additional indications on a Licensed Product-by-Licensed Product and country-by-country basis with such payment obligations beginning on the first commercial sale of Licensed Product in such country and expiring on a country-by-country basis on the latest of (a) the expiration of a valid claim to our patent right in such country, (b) the expiration of regulatory exclusivity, and (c) the date that is 10 years after the first commercial sale of such Licensed Product in such country.

Unless earlier terminated, the collaboration agreement will remain in force until no Licensed Products are being developed or commercialized in the United States and in the ROW Territory, on a country-by-country basis, until no

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royalty terms are in effect for all countries. Either party may terminate the collaboration agreement for the other party’s material breach, subject to a specified notice and cure periods, or due to an insolvency event of the other party. In lieu of termination upon a party’s material breach due to non-payment of development costs within a specified time the non-breaching party may elect an alternative remedy which may involve modifications to their performance and payment obligations. We have the right to terminate by providing written notice in the event Chiesi or its affiliates or sublicensee brings a patent challenge and Chiesi does not take certain steps to withdraw from or cease supporting such challenge. Chiesi may terminate the collaboration agreement for any reason upon prior written notice to us, subject to a notice period.

Manufacturing

We currently rely on multiple third-party manufacturers for the manufacture of seralutinib for preclinical and clinical testing. We intend to rely on third-party contract manufacturers for commercial manufacturing if seralutinib receives marketing approval. Typically, there are multiple sources for all of the materials required for the manufacture of seralutinib. Our manufacturing strategy enables us to more efficiently direct financial resources to the research, development and commercialization of seralutinib rather than diverting resources to internally develop manufacturing facilities. As seralutinib advances through development, we expect to enter into longer-term commercial supply agreements with key suppliers and manufacturers to fulfill and secure our production needs.

Intellectual Property

We strive to protect the proprietary technology, inventions and improvements that are commercially important to our business, including seeking, maintaining, and defending patent rights, whether developed internally or licensed from third parties. We also rely on trade secrets and know-how relating to our proprietary technology and product candidates and continuing innovation to develop, strengthen and maintain our proprietary position. We also plan to rely on data exclusivity, market exclusivity and patent term extensions when available. Our commercial success will depend in part on our ability to obtain and maintain patent and other proprietary protection for our technology, inventions and improvements; to preserve the confidentiality of our trade secrets; to defend and enforce our proprietary rights, including any patents that we may own in the future; and to operate without infringing on the valid and enforceable patents and other proprietary rights of third parties. Intellectual property rights may not address all potential threats to our competitive advantage.

Seralutinib

As of December 31, 2025, with respect to seralutinib, we have exclusively licensed two issued U.S. patents owned by Pulmokine, which are not due to expire before 2037, excluding any additional term for patent term extension; one pending U.S. Patent application, which, if issued, is not due to expire before 2037, excluding any additional term for patent term extension; and a number of patents and pending applications in other jurisdictions, including issued patents in Mexico, Russia, Australia, India, Japan, South Korea, and New Zealand, and pending applications in, Brazil, Canada, China, the European Patent Convention, and New Zealand, which, if issued, are not due to expire before 2037, excluding any additional term for patent term extension. These patents and patent applications are directed to method of use claims. We have also exclusively licensed four issued U.S. patents co-owned by Pulmokine and Gilead Sciences, Inc., which are not due to expire before 2034, excluding any additional term for patent term extension; two pending U.S. patent applications which, if issued, are not due to expire before 2034, excluding any additional term for patent term extension; and a number of patents and pending patent applications in other jurisdictions, including issued patents in Australia, Canada, China, the European Patent Convention, Japan, and Hong Kong. These patents and patent applications are directed to seralutinib compound, formulation and method of use claims. We also own a pending patent application, which, if issued, is not due to expire before 2042, directed to forms of seralutinib, and a pending application, which, if issued, is not due to expire before 2043, directed to combination treatment with seralutinib.

Government Regulation

Government authorities in the United States, at the federal, state and local level, and other countries extensively regulate, among other things, the research, development, testing, manufacture, quality control, approval, labeling, packaging, storage, record-keeping, promotion, advertising, distribution, marketing and export and import of products such as those we are developing. A new drug must be approved by the FDA through the new drug application, or NDA, process before it may be legally marketed in the United States.

Seralutinib is subject to regulation as a combination product, which means that it is composed of both a drug product and device product. If marketed individually, each component would be subject to different regulatory pathways and reviewed by different centers within the FDA. A combination product, however, is assigned to a Center that will have primary jurisdiction over its regulation based on a determination of the combination product’s primary mode of action, which is the

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single mode of action that provides the most important therapeutic action. In the case of seralutinib, the primary mode of action is attributable to the drug component of the product, which means that the FDA’s Center for Drug Evaluation and Research has primary jurisdiction over the premarket development, review and approval. Accordingly, we plan to investigate seralutinib through the Investigational New Drug, or IND, framework and seek approval through the NDA pathway. We do not anticipate that the FDA will require a separate medical device authorization for the device, but this could change during the course of its review of any marketing application that we may submit.

U.S. Drug Development Process

In the United States, the FDA regulates drugs under the federal Food, Drug, and Cosmetic Act, or the FDCA, and its implementing regulations. The process of obtaining regulatory approvals and the subsequent compliance with appropriate federal, state, local and foreign statutes and regulations require the expenditure of substantial time and financial resources. Failure to comply with the applicable U.S. requirements at any time during the product development process, approval process or after approval may subject an applicant to administrative or judicial sanctions. These sanctions could include the FDA’s refusal to approve pending applications, withdrawal of an approval, a clinical hold, warning letters, product recalls, product seizures, total or partial suspension of production or distribution, injunctions, fines, refusals of government contracts, restitution, disgorgement or civil or criminal penalties. Any agency or judicial enforcement action could have a material adverse effect on us.

The process required by the FDA before a drug may be marketed in the United States generally involves the following:

•completion of certain preclinical laboratory tests, animal studies and formulation studies in accordance with Good Laboratory Practice, or GLP, regulations and other applicable regulations;

•submission to the FDA of an IND, which must become effective before human clinical trials may begin;

•approval by an independent institutional review board, or IRB, or ethics committee at each clinical site before each trial may be initiated;

•performance of adequate and well-controlled human clinical trials in accordance with Good Clinical Practice, or GCP, regulations to establish the safety and efficacy of the proposed drug for its intended use;

•submission to the FDA of an NDA;

•satisfactory completion of an FDA advisory committee review, if applicable;

•satisfactory completion of an FDA inspection of the manufacturing facility or facilities at which the drug is produced to assess compliance with current GMP, or cGMP, requirements to assure that the facilities, methods and controls are adequate to preserve the drug’s identity, strength, quality and purity, and potential inspection of selected clinical investigation sites to assess compliance with GCPs; and

•FDA review and approval of the NDA to permit commercial marketing of the product for particular indications for use in the United States.

Once a pharmaceutical candidate is identified for development, it enters the preclinical testing stage. Preclinical tests include laboratory evaluations of product chemistry, toxicity and formulation, as well as animal studies. An IND sponsor must submit the results of the preclinical tests, together with manufacturing information and analytical data, to the FDA as part of the IND. An IND is a request for allowance from the FDA to administer an investigational drug product to humans. The sponsor will also include a protocol detailing, among other things, the objectives of the clinical trial, the parameters to be used in monitoring safety, and the effectiveness criteria to be evaluated, if the clinical trial lends itself to an efficacy evaluation. Some preclinical testing may continue even after the IND is submitted. The IND automatically becomes effective 30 days after receipt by the FDA, unless the FDA, within the 30-day time period, places the clinical trial on a clinical hold. In such a case, the IND sponsor and the FDA must resolve any outstanding concerns before the clinical trial can begin. Clinical holds also may be imposed by the FDA at any time before or during clinical trials due to safety concerns about on-going or proposed clinical trials or non-compliance with specific FDA requirements, and trials may not begin or continue under the IND until the FDA notifies the sponsor that the hold has been lifted. Submission of an IND therefore may or may not result in FDA allowance to begin a clinical trial.

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All clinical trials must be conducted under the supervision of one or more qualified investigators in accordance with GCP regulations, which among other things, include the requirement that all research subjects provide their informed consent in writing for their participation in any clinical trial. Clinical Trials must be conducted under protocols detailing, among other things, the objectives of the trial, dosing procedures, subject selection and exclusion criteria and the safety and effectiveness criteria to be evaluated. Each protocol must be submitted to the FDA as part of the IND as well as any subsequent protocol amendments. While the IND is active, progress reports summarizing the results of the clinical trials and nonclinical studies performed since the last progress report, among other information, must be submitted at least annually to the FDA, and written IND safety reports must be submitted to the FDA and investigators for serious and unexpected suspected adverse events, findings from other studies suggesting a significant risk to humans exposed to the same or similar drugs, findings from animal or in vitro testing suggesting a significant risk to humans, and any clinically important increased incidence of a serious suspected adverse reaction compared to that listed in the protocol or investigator brochure.

Furthermore, an independent IRB at each institution participating in the clinical trial must review and approve each protocol before a clinical trial commences at that institution and must also approve the information regarding the trial and the consent form that must be provided to each trial subject or his or her legal representative, monitor the study until completed and otherwise comply with IRB regulations. The FDA or the sponsor may suspend a clinical trial at any time on various grounds, including a finding that the research subjects or patients are being exposed to an unacceptable health risk. Similarly, an IRB can suspend or terminate approval of a clinical trial at its institution if the clinical trial is not being conducted in accordance with the IRB’s requirements or if the drug has been associated with unexpected serious harm to patients. In addition, some clinical trials are overseen by an independent group of qualified experts organized by the sponsor, known as a data safety monitoring board or committee. Depending on its charter, this group may determine whether a trial may move forward at designated check points based on access to certain data from the trial. There are also requirements governing the reporting of ongoing clinical trials and completed trial results to public registries. Sponsors of certain clinical trials of FDA-regulated products are required to register and disclose specified clinical trial information, which is publicly available at www.clinicaltrials.gov. Information related to the product, patient population, phase of investigation, trial sites and investigators and other aspects of the clinical trial is then made public as part of the registration. Sponsors are also obligated to disclose the results of their clinical trials after completion. Disclosure of the results of these trials can be delayed until the new product or new indication being studied has been approved.

Human clinical trials are typically conducted in three sequential phases that may overlap or be combined:

•Phase 1: The product candidate is initially introduced into healthy human volunteers and tested for safety, dosage tolerance, absorption, metabolism, distribution and excretion and, if possible, to gain an early indication of its effectiveness. In the case of some products for severe or life-threatening diseases, such as cancer, especially when the product may be too inherently toxic to ethically administer to healthy volunteers, the initial human testing is often conducted in patients.

•Phase 2: The product candidate is evaluated in a limited patient population to identify possible adverse effects and safety risks, to preliminarily evaluate the efficacy of the product for specific targeted diseases and to determine dosage tolerance and appropriate dosage.

•Phase 3: The product candidate is further evaluated for dosage, clinical efficacy and safety in an expanded patient population, generally at geographically dispersed clinical study sites. These clinical trials are intended to establish the overall risk-benefit ratio of the product candidate and provide an adequate basis for product labeling.

Post-approval trials, sometimes referred to as Phase 4 studies, may be conducted after initial marketing approval. These trials are used to gain additional experience from the treatment of patients in the intended therapeutic indication. In certain instances, the FDA may mandate the performance of Phase 4 clinical trials as a condition of approval of an NDA.

During the development of a new drug, sponsors are given opportunities to meet with the FDA at certain points. These points may be prior to submission of an IND, at the end of Phase 2, and before an NDA is submitted. Meetings at other times may be requested. These meetings can provide an opportunity for the sponsor to share information about the data gathered to date, for the FDA to provide advice, and/or for the sponsor and the FDA to reach agreement on the next phase of development.

Concurrent with clinical trials, companies usually complete additional animal studies and must also develop additional information about the chemistry and physical characteristics of the drug and finalize a process for manufacturing the product in commercial quantities in accordance with cGMP requirements. The manufacturing process must be capable of

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consistently producing quality batches of the product candidate and, among other things, the manufacturer must develop methods for testing the identity, strength, quality and purity of the final drug. In addition, appropriate packaging must be selected and tested and stability studies must be conducted to demonstrate that the product candidate does not undergo unacceptable deterioration over its shelf life.

Regulation of Combination Products in the United States

Certain products may be comprised of components, such as drug components and device components that would normally be regulated under different types of regulatory authorities, and frequently by different centers at the FDA. These products are known as combination products. Specifically, under regulations issued by the FDA, a combination product may be:

•a product comprised of two or more regulated components that are physically, chemically, or otherwise combined or mixed and produced as a single entity;

•two or more separate products packaged together in a single package or as a unit and comprised of drug and device products, device and biological products, or biological and drug products;

•a drug, or device, or biological product packaged separately that according to its investigational plan or proposed labeling is intended for use only with an approved individually specified drug, or device, or biological product where both are required to achieve the intended use, indication, or effect and where upon approval of the proposed product the labeling of the approved product would need to be changed, e.g., to reflect a change in intended use, dosage form, strength, route of administration, or significant change in dose; or

•any investigational drug, or device, or biological product packaged separately that according to its proposed labeling is for use only with another individually specified investigational drug, device, or biological product where both are required to achieve the intended use, indication, or effect.

Under the FDCA and its implementing regulations, the FDA is charged with assigning a center with primary jurisdiction, or a lead center, for review of a combination product. The designation of a lead center generally eliminates the need to receive approvals from more than one FDA component for combination products, although it does not preclude consultations by the lead center with other components of FDA. The determination of which center will be the lead center is based on the “primary mode of action” of the combination product. Thus, if the primary mode of action of a drug-device combination product is attributable to the drug product, the FDA center responsible for premarket review of the drug product would have primary jurisdiction for the combination product. The FDA has also established an Office of Combination Products to address issues surrounding combination products and provide more certainty to the regulatory review process. That office serves as a focal point for combination product issues for agency reviewers and industry. It is also responsible for developing guidance and regulations to clarify the regulation of combination products, and for assignment of the FDA center that has primary jurisdiction for review of combination products where the jurisdiction is unclear or in dispute.

A combination product with a drug primary mode of action generally would be reviewed and approved pursuant to the drug approval processes under the FDCA. In reviewing the NDA application for such a product, however, FDA reviewers in the drug center could consult with their counterparts in the device center to ensure that the device component of the combination product met applicable requirements regarding safety, effectiveness, durability and performance. In addition, under FDA regulations, combination products are subject to cGMP requirements applicable to both drugs and devices, including the Quality System, regulations applicable to medical devices.

NDA Review and Approval Process

The results of product development, including results from preclinical and other non-clinical studies and clinical trials, along with descriptions of the manufacturing process, analytical tests conducted on the chemistry of the drug, proposed labeling and other relevant information are submitted to the FDA as part of an NDA requesting approval to market the product. The submission of an NDA is subject to the payment of substantial user fees; a waiver of such fees may be obtained under certain limited circumstances. The FDA conducts a preliminary review of an NDA within the first 60 days after submission, before accepting the application for filing, to determine whether it is sufficiently complete to permit substantive review. The FDA may request additional information rather than accept an NDA for filing. In this event, the NDA must be resubmitted with the additional information. The resubmitted application also is subject to review before the FDA accepts it for filing.

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Once filed, the FDA reviews an NDA to determine, among other things, whether a product is safe and effective for its intended use and whether its manufacturing is cGMP-compliant to assure and preserve the product’s identity, strength, quality and purity. Under the Prescription Drug User Fee Act, or PDUFA, guidelines that are currently in effect, the FDA has a goal of ten months from the date of “filing” of a standard NDA for a new molecular entity to review and act on the submission. This review typically takes twelve months from the date the NDA is submitted to FDA because the FDA has approximately two months to make a “filing” decision after it the application is submitted.

The FDA may refer an application for a novel drug to an advisory committee. An advisory committee is a panel of independent experts, including clinicians and other scientific experts, that reviews, evaluates and provides a recommendation as to whether the application should be approved and under what conditions. The FDA is not bound by the recommendations of an advisory committee, but it considers such recommendations carefully when making decisions. Before approving an NDA, the FDA will typically inspect the facility or facilities where the product is manufactured. The FDA will not approve an application unless it determines that the manufacturing processes and facilities are in compliance with cGMP requirements and adequate to assure consistent production of the product within required specifications. Additionally, before approving an NDA, the FDA may inspect one or more clinical trial sites to assure compliance with GCP requirements.

After the FDA evaluates an NDA, it will issue an approval letter or a Complete Response Letter. An approval letter authorizes commercial marketing of the drug with prescribing information for specific indications. A Complete Response Letter indicates that the review cycle of the application is complete and the application will not be approved in its present form. A Complete Response Letter usually describes the specific deficiencies in the NDA identified by the FDA and may require additional clinical data or other significant and time consuming requirements related to clinical trials, nonclinical studies or manufacturing. If a Complete Response Letter is issued, the sponsor must resubmit the NDA or, addressing all of the deficiencies identified in the letter, or withdraw the application. Even if such data and information are submitted, the FDA may decide that the NDA does not satisfy the criteria for approval.

If a product receives regulatory approval, the approval may be significantly limited to specific diseases and dosages or the indications for use may otherwise be limited, which could restrict the commercial value of the product. In addition, the FDA may require a sponsor to conduct additional clinical or non-clinical testing, including Phase 4 testing, to further assess a drug’s safety and effectiveness after NDA approval, and may require additional testing and surveillance programs to monitor the safety of approved products. The FDA may also place other conditions on approval including the requirement for a risk evaluation and mitigation strategy, or REMS, to assure the safe use of the drug. If the FDA concludes a REMS is needed, the sponsor of the NDA must submit a proposed REMS, and the FDA will not approve the application without an approved REMS. A REMS could include medication guides, physician communication plans or elements to assure safe use, such as restricted distribution methods, patient registries and other risk minimization tools. Any of these limitations on approval or marketing could restrict the commercial promotion, distribution, prescription or dispensing of products.

In addition, the Pediatric Research Equity Act, or PREA, requires a sponsor to conduct pediatric clinical trials for most drugs, for a new active ingredient, new indication, new dosage form, new dosing regimen or new route of administration. Under PREA, original NDAs and supplements must contain a pediatric assessment unless the sponsor has received a deferral or waiver. The required assessment must evaluate the safety and effectiveness of the product for the claimed indications in all relevant pediatric subpopulations and support dosing and administration for each pediatric subpopulation for which the product is safe and effective. The sponsor or FDA may request a deferral of pediatric clinical trials for some or all of the pediatric subpopulations. A deferral may be granted for several reasons, including a finding that the drug is ready for approval for use in adults before pediatric clinical trials are complete or that additional safety or effectiveness data needs to be collected before the pediatric clinical trials begin. The FDA must send a non-compliance letter to any sponsor that fails to submit the required assessment, keep a deferral current or fails to submit a request for approval of a pediatric formulation.

Orphan Drug Designation

Under the Orphan Drug Act, the FDA may grant orphan designation to a drug intended to treat a rare disease or condition, which is a disease or condition that affects fewer than 200,000 individuals in the United States or, if it affects more than 200,000 individuals in the United States, there is no reasonable expectation that the cost of developing and making a drug product available in the United States for this type of disease or condition will be recovered from sales of the product. Orphan designation must be requested before submitting an NDA. After the FDA grants orphan designation, the identity of the therapeutic agent and its potential orphan use are disclosed publicly by the FDA. Orphan designation does not convey any advantage in or shorten the duration of the regulatory review and approval process.

If a product that has orphan designation subsequently receives the first FDA approval for the disease or condition for which it has such designation, the product is entitled to orphan product exclusivity, which means that the FDA may not approve any other applications to market the same drug for the same approved use or indication within such rare

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disease or condition for seven years, except in limited circumstances, such as a showing of clinical superiority to the product with orphan exclusivity or inability to manufacture the product in sufficient quantities. The designation of such drug also entitles a party to financial incentives such as opportunities for grant funding toward clinical trial costs, tax advantages and user-fee waivers. However, competitors, may receive approval of different products for the indication for which the orphan product has exclusivity or obtain approval for the same product but for a different indication for which the orphan product has exclusivity.

In addition, if an orphan designated product receives marketing approval for a disease or condition broader than what is designated, it may not be entitled to orphan exclusivity. In addition, orphan drug exclusive marketing rights in the United States may be lost if the FDA later determines that the request for designation was materially defective or, as noted above, if the second applicant demonstrates that its product is clinically superior to the approved product with orphan exclusivity within the relevant approved use or indication or the manufacturer of the approved product is unable to assure sufficient quantities of the product to meet the needs relating to the approved use or indication of patients with the rare disease or condition.

Expedited Development and Review Programs

A sponsor may seek approval of its product candidate under programs designed to expedite FDA’s review and approval of new drugs and biological products that meet certain criteria. For example, the FDA has a fast track designation program that is intended to expedite or facilitate the process for reviewing new drug products that meet certain criteria. Specifically, a product candidate is eligible for fast track designation if it is intended to treat a serious or life-threatening disease or condition and demonstrates the potential to address unmet medical needs for the disease or condition. Fast track designation applies to the combination of the product candidate and the specific indication for which it is being studied. The sponsor of a fast track product candidate has opportunities for more frequent interactions with the applicable FDA review team during development. With regard to a fast track product, the FDA may also consider for review sections of the NDA on a rolling basis before the complete application is submitted, if the sponsor provides a schedule for the submission of the sections of the NDA, the FDA agrees to accept sections of the NDA and determines that the schedule is acceptable, and the sponsor pays any required user fees upon submission of the first section of the NDA.

A product candidate intended to treat a serious or life-threatening disease or condition may also be eligible for breakthrough therapy designation to expedite its development and review. A product candidate can receive breakthrough therapy designation if preliminary clinical evidence indicates that the product candidate, alone or in combination with one or more other drugs or biologics, may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development. The designation includes all of the fast track program features, as well as more intensive FDA interaction and guidance beginning as early as Phase 1 and an organizational commitment to expedite the development and review of the product candidate, including involvement of senior managers.

Any NDA for a product candidate submitted to the FDA for approval, including for a product candidate with a fast track designation or breakthrough designation, may also be eligible for other types of FDA programs intended to expedite development and review, such as priority review. An NDA is eligible for priority review if the product candidate is designed to treat a serious or life-threatening disease or condition, and if approved, would provide a significant improvement in safety or effectiveness compared to available alternatives for such disease or condition. The FDA will attempt to direct additional resources to the evaluation of an application designated for priority review in an effort to facilitate the review. The FDA endeavors to review applications with priority review designations within six months of the filing date as compared to ten months for review of new molecular entity NDAs under its current PDUFA review goals.

In addition, depending on the design of the applicable clinical trials, a product candidate may be eligible for accelerated approval. Drug products intended to treat serious or life-threatening diseases or conditions may be eligible for accelerated approval upon a determination that the product has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit, or on a clinical endpoint that can be measured earlier than irreversible morbidity or mortality, that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit, taking into account the severity, rarity, or prevalence of the condition and the availability or lack of alternative treatments. As a condition of approval, the FDA will generally require that a sponsor of a drug receiving accelerated approval perform adequate and well-controlled confirmatory clinical trials and may require that such confirmatory trials be underway prior to granting accelerated approval. In addition, the FDA currently requires as a condition for accelerated approval pre-approval of promotional materials, which could adversely impact the timing of the commercial launch of the product. FDA may withdraw approval of a drug or indication approved under accelerated approval on an expedited basis if, for example, the confirmatory trial fails to verify the predicted clinical benefit of the product or if the sponsor fails to conduct such trials in a timely manner.

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Fast track designation, breakthrough therapy designation, priority review and accelerated approval do not change the standards for approval but may expedite the development or approval process. Even if a product candidate qualifies for one or more of these programs, the FDA may later decide that the product candidate no longer meets the conditions for qualification or decide that the time period for FDA review or approval will not be shortened.

Post-Approval Requirements

Once an approval is granted, the FDA may withdraw the approval if compliance with regulatory standards is not maintained or if problems occur after the product reaches the market. Later discovery of previously unknown problems with a product may result in restrictions on the product or even complete withdrawal of the product from the market. After approval, some types of changes to the approved product, such as adding new indications, certain manufacturing changes and additional labeling claims, are subject to further FDA review and approval. Drug manufacturers and other entities involved in the manufacture and distribution of approved drugs are required to register their establishments with the FDA and certain state agencies, and are subject to periodic unannounced inspections by the FDA and certain state agencies for compliance with cGMP regulations and other laws and regulations. In addition, the FDA may impose a number of post-approval requirements as a condition of approval of an NDA. For example, the FDA may require post-marketing testing, including Phase 4 clinical trials, and surveillance to further assess and monitor the product’s safety and effectiveness after commercialization.

Any drug products manufactured or distributed pursuant to FDA approvals will be subject to pervasive and continuing regulation by the FDA, including, among other things, record-keeping requirements, reporting of adverse experiences with the drug, providing the FDA with updated safety and efficacy information, drug sampling and distribution requirements, complying with certain electronic records and signature requirements, and complying with FDA promotion and advertising requirements. The FDA strictly regulates labeling, advertising, promotion and other types of information on products that are placed on the market and imposes requirements and restrictions on drug manufacturers, such as those related to direct-to-consumer advertising, the prohibition on promoting products for uses or in patient populations that are not described in the product’s approved labeling (known as “off-label use”), industry-sponsored scientific and educational activities, and promotional activities involving the internet.

Discovery of previously unknown problems or the failure to comply with the applicable regulatory requirements may result in restrictions on the marketing of a product or withdrawal of the product from the market as well as possible civil or criminal sanctions. Failure to comply with the applicable U.S. requirements at any time during the product development process, approval process or after approval, may subject an applicant or manufacturer to administrative or judicial civil or criminal sanctions and adverse publicity. FDA sanctions could include refusal to approve pending applications, withdrawal of an approval, clinical holds on post-approval clinical trials, warning or untitled letters, product recalls, product seizures, total or partial suspension of production or distribution, injunctions, fines, refusals of government contracts, mandated corrective advertising or communications with doctors, debarment, restitution, disgorgement of profits, or civil or criminal penalties.

Marketing Exclusivity

Market exclusivity provisions under the FDCA can delay the submission or the approval of certain marketing applications. The FDCA provides a five-year period of non-patent data exclusivity within the United States to the first applicant to obtain approval of an NDA for a new chemical entity. A drug is a new chemical entity if the FDA has not previously approved any other new drug containing the same active moiety, which is the molecule or ion responsible for the action of the drug substance. During the exclusivity period, the FDA may not approve or even accept for review an abbreviated new drug application, or ANDA, or an NDA submitted under Section 505(b)(2), or 505(b)(2) NDA, submitted by another company for another drug based on the same active moiety, regardless of whether the drug is intended for the same indication as the original innovative drug or for another indication, where the applicant does not own or have a legal right of reference to all the data required for approval. However, an application may be submitted after four years if it contains a certification of patent invalidity or non-infringement to one of the patents listed with the FDA by the innovator NDA holder.

The FDCA alternatively provides three years of non-patent exclusivity for an NDA, or supplement to an existing NDA if new clinical investigations, other than bioavailability studies, that were conducted or sponsored by the applicant are deemed by the FDA to be essential to the approval of the application, for example new indications, dosages or strengths of an existing drug. This three-year exclusivity covers only the modification for which the drug received approval on the basis of the new clinical investigations and does not prohibit the FDA from approving ANDAs or 505(b)(2) NDAs for drugs containing the active agent for the original indication or condition of use. Five-year and three-year exclusivity will not delay the submission or approval of a full NDA. However, an applicant submitting a full NDA would be required to conduct or obtain a right of reference to all of the preclinical studies and adequate and well-controlled clinical trials necessary to demonstrate safety and effectiveness.

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Pediatric exclusivity is another type of marketing exclusivity available in the United States. Pediatric exclusivity provides for an additional six months of marketing exclusivity attached to an existing period of regulatory exclusivity or patent term if a sponsor conducts clinical trials in children in response to a written request from the FDA. The issuance of a written request does not require the sponsor to undertake the described clinical trials. In addition, orphan drug exclusivity, as described above, may offer a seven-year period of marketing exclusivity, except in certain circumstances.

U.S. Coverage and Reimbursement

Significant uncertainty exists as to the coverage and reimbursement status of any product candidate for which we may seek regulatory approval. Sales in the United States will depend, in part, on the availability of sufficient coverage and adequate reimbursement from third-party payors, which include government health programs such as Medicare, Medicaid, TRICARE and the Veterans Administration, as well as managed care organizations and private health insurers. Prices at which we or our customers seek reimbursement for seralutinib can be subject to challenge, reduction or denial by third-party payors.

The process for determining whether a third-party payor will provide coverage for a product is typically separate from the process for setting the reimbursement rate that the payor will pay for the product. A third-party payor’s decision to provide coverage for a product does not imply that an adequate reimbursement rate will be available. Additionally, in the United States there is no uniform policy among payors for coverage or reimbursement. Third-party payors often rely upon Medicare coverage policy and payment limitations in setting their own coverage and reimbursement policies, but also have their own methods and approval processes. Therefore, coverage and reimbursement for products can differ significantly from payor to payor. If coverage and adequate reimbursement are not available, or are available only at limited levels, successful commercialization of, and obtaining a satisfactory financial return on, any product we develop may not be possible.

Third-party payors are increasingly challenging the price and examining the medical necessity and cost-effectiveness of medical products and services, in addition to their safety and efficacy. In order to obtain coverage and reimbursement for any product that might be approved for marketing, we may need to conduct expensive studies in order to demonstrate the medical necessity and cost-effectiveness of any products, which would be in addition to the costs expended to obtain regulatory approvals. Third-party payors may not consider seralutinib to be medically necessary or cost-effective compared to other available therapies, or the rebate percentages required to secure favorable coverage may not yield an adequate margin over cost or may not enable us to maintain price levels sufficient to realize an appropriate return on our investment.

Healthcare Reform

In the United States and some foreign jurisdictions, there has been, and we expect there will continue to be, several legislative and regulatory changes and proposed changes regarding the healthcare system that could prevent or delay marketing approval of product candidates, restrict or regulate post-approval activities, and affect the profitable sale of product candidates.

Among policy makers and payors in the United States and elsewhere, there is significant interest in promoting changes in healthcare systems with the stated goals of containing healthcare costs, improving quality and/or expanding access. In the United States and elsewhere, the pharmaceutical industry has been a particular focus of these efforts and has been significantly affected by major legislative and regulatory initiatives. We expect that current laws and regulations, as well as other healthcare reform measures that may be adopted in the future, may result in more rigorous coverage criteria and additional downward pressure on the price that we may receive for seralutinib. In particular, there have been and continue to be a number of initiatives at the U.S. federal and state levels that seek to reduce healthcare costs and improve the quality of healthcare.

For example, in 2010, the ACA was enacted in the United States. Among the provisions of the ACA of importance to seralutinib, the ACA: established an annual, nondeductible fee on any entity that manufactures or imports specified branded prescription drugs and biologic agents; extended manufacturers’ Medicaid rebate liability to covered drugs dispensed to individuals who are enrolled in Medicaid managed care organizations; established a new Patient-Centered Outcomes Research Institute to oversee, and established a Center for Medicare and Medicaid Innovation at CMS to test innovative payment and service delivery models to lower Medicare and Medicaid spending.

Since its enactment, there have been judicial and political challenges to certain aspects of the ACA. On June 17, 2021, the U.S. Supreme Court dismissed the most recent judicial challenge to the ACA brought by several states without specifically ruling on the constitutionality of the ACA.

Further, there has been heightened governmental scrutiny in the United States of pharmaceutical pricing practices in light of the rising cost of prescription drugs. Such scrutiny has resulted in several recent congressional inquiries and

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proposed and enacted federal and state legislation designed to, among other things, bring more transparency to product pricing, review the relationship between pricing and manufacturer patient programs, and reform government program reimbursement methodologies for products.

The Inflation Reduction Act, or IRA, was enacted in 2022. This statute marks the most significant action by Congress with respect to the pharmaceutical industry since adoption of the ACA in 2010. Among other things, the IRA requires manufacturers of certain drugs to engage in price negotiations with Medicare, with prices that can be negotiated subject to a cap; imposes rebates under Medicare Part B and Medicare Part D to penalize price increases that outpace inflation (first due in 2023); redesigns the Medicare Part D benefit (beginning in 2024); and replaces the Part D coverage gap discount program with a new manufacturer discount program (beginning in 2025). CMS has published the negotiated prices for the initial ten drugs, which became effective in 2026, and the subsequent 15 drugs, which will first be effective in 2027. CMS has also published the next set of 15 drugs that will be subject to negotiation. The IRA permits the Secretary of the Department of Health and Human Services (HHS) to implement many of these provisions through guidance, as opposed to regulation, for the initial years. HHS has and will continue to issue and update guidance as these programs are implemented, although the Medicare drug price negotiation program is currently subject to legal challenges. The impact of the IRA on us and the pharmaceutical industry cannot yet be fully determined, but is likely to be significant.

In addition, the One Big Beautiful Bill Act, which was enacted in July 2025, imposes significant reductions in the funding of the Medicaid program. Such reductions are expected to decrease the number of persons enrolled in Medicaid and reduce the services covered by Medicaid, which could adversely affect our ability to generate revenue, attain profitability or commercialize seralutinib.

Furthermore, the Trump administration is pursuing a two-fold strategy to reduce drug costs in the U.S. While it is unclear whether and how the Trump proposals will be implemented, the Trump policies are likely to have a negative impact on the pharmaceutical industry and on our ability to receive adequate revenues for seralutinib. On the one hand, President Trump has threatened to impose significant tariffs on pharmaceutical manufacturers that do not adopt pricing policies such as most favored nation pricing, which would tie the price for drugs in the U.S. to the lowest price in a group of other countries. In response, multiple manufacturers have reportedly entered into confidential pricing agreements with the federal government. On the other hand, the Trump administration is pursuing traditional regulatory pathways to impose drug pricing policies, and published two proposed regulations in December 2025, referred to as Globe and Guard. If finalized, these regulations would implement mandatory payment models under which manufacturers of eligible drugs would be required to pay rebates to the federal government on a portion of the units of their drugs that are reimbursed by Medicare, with the rebate amount based on most favored nation pricing. Imposing a rebate in the U.S. that is based on drug prices outside the U.S. would mark a drastic and unprecedented shift in the U.S. pharmaceutical market, and while the impact of the Globe and Guard proposed regulations, if finalized, cannot yet be determined, it is likely to be significant. Even regulatory proposals or executive actions that are ultimately deemed unlawful could negatively impact the U.S. pharmaceutical sector and our business. In addition, pharmaceutical pricing and marketing has long been the subject of considerable discussion in Congress and among policymakers, and it is possible that Congress could enact additional laws that negatively affect the pharmaceutical industry.

At the state level, legislatures have increasingly passed legislation and implemented regulations designed to control pharmaceutical and biological product pricing, including price or patient reimbursement constraints, discounts, restrictions on certain product access and marketing cost disclosure, drug price reporting and other transparency measures, and, in some cases, designed to encourage importation from other countries and bulk purchasing. Some states have enacted legislation creating so-called prescription drug affordability boards, which ultimately may attempt to impose price limits on certain drugs in these states, and at least one state board is imposing an upper payment limit. States are also seeking to implement general, across the board price caps for pharmaceuticals, or are seeking to regulate drug distribution. Legally mandated price controls on payment amounts by third-party payors or other restrictions could harm our business, results of operations, financial condition and prospects. In addition, regional healthcare authorities and individual hospitals are increasingly using bidding procedures to determine what pharmaceutical products and which suppliers will be included in their prescription drug and other healthcare programs. This could reduce the ultimate demand for seralutinib, if approved, or put pressure on our product pricing, which could negatively affect our business, results of operations, financial condition and prospects.

In the EU, similar political, economic and regulatory developments may affect our or Chiesi's ability to profitably commercialize, or co-commercialize, seralutinib, if approved. For instance, on December 13, 2021, Regulation No 2021/2282 on Health Technology Assessment, or HTA, amending Directive 2011/24/EU, was adopted. The Regulation entered into force in January 2022 and has been applicable since January 2025, with phased implementation based on the type of product, i.e. oncology and advanced therapy medicinal products as of 2025, orphan medicinal products as of 2028, and all other medicinal products by 2030. The Regulation intends to boost cooperation among EU member states in assessing health

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technologies, including new medicinal products, and provide the basis for cooperation at the EU level for joint clinical assessments in these areas. It will permit EU member states to use common HTA tools, methodologies, and procedures across the EU, working together in four main areas, including joint clinical assessment of the innovative health technologies with the highest potential impact for patients, joint scientific consultations whereby developers can seek advice from HTA authorities, identification of emerging health technologies to identify promising technologies early, and continuing voluntary cooperation in other areas. Individual EU member states will continue to be responsible for assessing non-clinical (e.g., economic, social, ethical) aspects of health technology, and making decisions on pricing and reimbursement.

We expect that healthcare reform measures that may be adopted in the future may result in more rigorous coverage criteria, new payment methodologies and additional downward pressure on the price that we receive for any approved product. Any reduction in reimbursement from Medicare or other government programs may result in a similar reduction in payments from private payors.

Healthcare Fraud and Abuse Laws and Compliance Requirements

Federal, state and foreign healthcare laws and regulations restrict business practices in the biopharmaceutical industry. These laws include anti-kickback and false claims laws and regulations, and transparency laws and regulations.

The federal Anti-Kickback Statute prohibits, among other things, individuals or entities from knowingly and willfully offering, paying, soliciting or receiving remuneration, directly or indirectly, overtly or covertly, in cash or in kind to induce or in return for purchasing, leasing, ordering or arranging for or recommending the purchase, lease or order of any item or service reimbursable under Medicare, Medicaid or other federal healthcare programs. A person or entity does not need to have actual knowledge of this statute or specific intent to violate it in order to have committed a violation.

The federal civil and criminal false claims laws, including the civil False Claims Act, prohibit, among other things, any individual or entity from knowingly presenting, or causing to be presented, a false claim for payment to the federal government or knowingly making, using or causing to be made or used a false record or statement material to a false or fraudulent claim to the federal government. In addition, the government may assert that a claim including items or services resulting from a violation of the federal Anti-Kickback Statute constitutes a false or fraudulent claim for purposes of the civil False Claims Act.

The federal Health Insurance Portability and Accountability Act of 1996, or HIPAA, created additional federal civil and criminal statutes that prohibit, among other things, knowingly and willfully executing a scheme to defraud any healthcare benefit program. Similar to the federal Anti-Kickback Statute, A person or entity does not need to have actual knowledge of this statute or specific intent to violate it in order to have committed a violation.

The federal Physician Payments Sunshine Act requires certain manufacturers of drugs, devices, biologics and medical supplies for which payment is available under Medicare, Medicaid or the Children’s Health Insurance Program, with specific exceptions, to report annually to CMS information related to payments or other transfers of value made to physicians (defined to include doctors, dentists, optometrists, podiatrists and chiropractors), certain non-physician providers including physician assistants and nurse practitioners, and teaching hospitals, and applicable manufacturers and applicable group purchasing organizations to report annually to CMS ownership and investment interests held by physicians (as defined by statute) and their immediate family members.

Similar state, local and foreign laws and regulations may also restrict business practices in the biopharmaceutical industry, such as state anti-kickback and false claims laws, which may apply to business practices, including but not limited to, research, distribution, sales and marketing arrangements and claims involving healthcare items or services reimbursed by non-governmental third-party payors, including private insurers, or by patients themselves; state laws that require pharmaceutical companies to comply with the pharmaceutical industry’s voluntary compliance guidelines and the relevant compliance guidance promulgated by the federal government, or otherwise restrict payments that may be made to healthcare providers and other potential referral sources; state laws and regulations that require drug manufacturers to file reports relating to pricing and marketing information or which require tracking gifts and other remuneration and items of value provided to physicians, other healthcare providers and entities; and state and local laws that require the registration of pharmaceutical sales representatives.

Foreign laws and regulations may be broader in scope than the provisions described above and may apply regardless of payor. These laws and regulations may differ from one another in significant ways, thus further complicating compliance efforts. For instance, in the EU, many EU member states have adopted specific anti-gift statutes that further limit commercial practices for medicinal products, in particular vis-à-vis healthcare professionals and organizations. Additionally, there has been a recent trend of increased regulation of payments and transfers of value provided to healthcare professionals or

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entities and many EU member states have adopted national “Sunshine Acts” which impose reporting and transparency requirements (often on an annual basis), similar to the requirements in the United States, on pharmaceutical companies. Certain countries also mandate implementation of commercial compliance programs, or require disclosure of marketing expenditures and pricing information.

Efforts to ensure compliance with applicable healthcare laws and regulations can involve substantial costs. Violations of healthcare laws can result in significant penalties, including the imposition of significant civil, criminal and administrative penalties, damages, monetary fines, disgorgement, individual imprisonment, possible exclusion from participation in Medicare, Medicaid and other U.S. and foreign healthcare programs, integrity oversight and reporting obligations, contractual damages, reputational harm, diminished profits and future earnings, and curtailment or restructuring of operations.

U.S. Data Privacy and Security Laws

Numerous state and federal laws, regulations and standards govern the collection, use, access to, confidentiality and security of health-related and other personal information, and could apply now or in the future to our operations or the operations of our partners. In the United States, numerous federal and state laws and regulations, including data breach notification laws, health information privacy and security laws, and federal and state consumer protection laws and regulations that govern the collection, use, disclosure, and protection of health-related and other personal information could apply to our operations or the operations of our partners. Failure to comply with these laws, where applicable, can result in the imposition of significant civil and/or criminal penalties and private litigation. Privacy and security laws, regulations, and other obligations are constantly evolving, may conflict with each other to make compliance efforts more challenging, and can result in investigations, proceedings, or actions that lead to significant penalties and restrictions on data processing.

Foreign Regulation

In order to market any product outside of the United States, we need to comply with numerous and varying regulatory requirements of other countries and jurisdictions regarding quality, safety and efficacy and governing, among other things, clinical trials, marketing authorization, or MA, commercial sales and distribution of our products.

Whether or not we obtain FDA approval for a product, we would need to obtain the necessary approvals by the comparable foreign regulatory authorities before we can commence clinical trials or marketing of the product in foreign countries and jurisdictions. Although many of the issues discussed above with respect to the United States apply similarly in the context of EU, the approval process varies between countries and jurisdictions and can involve additional product testing and additional administrative review periods. The time required to obtain approval in other countries and jurisdictions might differ from and be longer than that required to obtain FDA approval. Regulatory approval in one country or jurisdiction does not ensure regulatory approval in another, but a failure or delay in obtaining regulatory approval in one country or jurisdiction may negatively impact the regulatory process in others.

Failure to comply with applicable foreign regulatory requirements, may be subject to, among other things, fines, suspension or withdrawal of regulatory approvals, product recalls, seizure of products, operating restrictions and criminal prosecution.

Non-clinical studies and clinical trials

Similar to the U.S., the various phases of non-clinical and clinical research in the EU are subject to significant regulatory controls.

Non-clinical studies are performed to demonstrate the health or environmental safety of new chemical or biological substances. Non-clinical (pharmaco-toxicological) studies must be conducted in compliance with the principles of good laboratory practice, or GLP, as set forth in EU Directive 2004/10/EC (unless otherwise justified for certain particular medicinal products, e.g., radio-pharmaceutical precursors for radio-labeling purposes). In particular, non-clinical studies, both in vitro and in vivo, must be planned, performed, monitored, recorded, reported and archived in accordance with the GLP principles, which define a set of rules and criteria for a quality system for the organizational process and the conditions for non-clinical studies. These GLP standards reflect the Organization for Economic Co-operation and Development requirements.

Certain countries outside of the United States have a similar process that requires the submission of a clinical trial application, or CTA, much like the IND prior to the commencement of human clinical trials. Clinical trials of medicinal products in the EU must be conducted in accordance with EU and national regulations and the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use, or ICH, guidelines on GCP as well as the

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applicable regulatory requirements and the ethical principles that have their origin in the Declaration of Helsinki. If the sponsor of the clinical trial is not established within the EU, it must appoint an EU entity to act as its legal representative. The sponsor must take out a clinical trial insurance policy, and in most EU countries, the sponsor is liable to provide ‘no fault’ compensation to any study subject injured in the clinical trial.

The regulatory landscape related to clinical trials in the EU has been subject to recent changes. The EU Clinical Trials Regulation, or CTR, which was adopted in April 2014 and repeals the EU Clinical Trials Directive, became applicable on January 31, 2022. Unlike directives, the CTR is directly applicable in all EU member states without the need for member states to further implement it into national law. The CTR notably harmonizes the assessment and supervision processes for clinical trials throughout the EU via a Clinical Trials Information System, which contains a centralized EU portal and database.

While the EU Clinical Trials Directive required a separate CTA to be submitted in each member state in which the clinical trial takes place, to both the competent national health authority and an independent ethics committee, much like the FDA and IRB respectively, the CTR introduces a centralized process and only requires the submission of a single application for multi-center trials. The CTR allows sponsors to make a single submission to both the competent authority and an ethics committee in each member state, leading to a single decision per member state. The CTA must include, among other things, a copy of the trial protocol and an investigational medicinal product dossier containing information about the manufacture and quality of the medicinal product under investigation. The assessment procedure of the CTA has been harmonized as well, including a joint assessment by all member states concerned, and a separate assessment by each member state with respect to specific requirements related to its own territory, including ethics rules. Each member state’s decision is communicated to the sponsor via the centralized EU portal. Once the CTA is approved, clinical trial development may proceed.

The CTR transition period ended on January 31, 2025, and all clinical trials (and related applications) are now fully subject to the provisions of the CTR.

Medicines used in clinical trials must be manufactured in accordance with Good Manufacturing Practices, or GMP. Other national and EU-wide regulatory requirements may also apply.

Marketing Authorization

To market a medicinal product in the EU, we must obtain a MA. To obtain regulatory approval of an investigational medicinal product under EU regulatory systems, we must submit a MA application, or MAA. The process for doing this depends, among other things, on the nature of the medicinal product. There are two types of MAs:

•“Centralized MAs” are issued by the EC through the centralized procedure, based on the opinion of the Committee for Medicinal Products for Human Use, or CHMP, of the European Medicines Agency, or EMA, and are valid throughout the EU. The centralized procedure is mandatory for certain types of products, such as: (i) medicinal products derived from biotechnology medicinal products, (ii) designated orphan medicinal products, (iii) advanced therapy medicinal products, or ATMPs, and (iv) medicinal products containing a new active substance indicated for the treatment certain diseases, such as HIV/AIDS, cancer, neurodegenerative diseases, diabetes, auto-immune and other dysfunctions and viral diseases. The centralized procedure is optional for products containing a new active substance not yet authorized in the EU, or for products that constitute a significant therapeutic, scientific or technical innovation or which are in the interest of public health in the EU.

•“National MAs” are issued by the competent authorities of the EU member states, only cover their respective territory, and are available for products not falling within the mandatory scope of the centralized procedure. Where a product has already been authorized for marketing in an EU member state, this national MA can be recognized in another member state through the mutual recognition procedure. If the product has not received a national MA in any member state at the time of application, it can be approved simultaneously in various member states through the decentralized procedure. Under the decentralized procedure an identical dossier is submitted to the competent authorities of each of the member states in which the MA is sought, one of which is selected by the applicant as the reference member state.

Under the above described procedures, before granting the MA, the regulatory authorities make an assessment of the risk-benefit balance of the product on the basis of scientific criteria concerning its quality, safety and efficacy.

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Under the centralized procedure the maximum timeframe for the evaluation of a MAA by the EMA is 210 days. In exceptional cases, the CHMP might perform an accelerated review of a MAA in no more than 150 days (not including clock stops). Innovative products that target an unmet medical need and are expected to be of major public health interest may be eligible for a number of expedited development and review programs, such as the PRIority MEdicines, or PRIME, scheme, which provides incentives similar to the breakthrough therapy designation in the U.S. In March 2016, the EMA launched an initiative, the PRIME scheme, a voluntary scheme aimed at enhancing the EMA’s support for the development of medicines that target unmet medical needs. It is based on increased interaction and early dialogue with companies developing promising medicines, to optimize their product development plans and speed up their evaluation to help them reach patients earlier. Product developers that benefit from PRIME designation can expect to be eligible for accelerated assessment but this is not guaranteed. Many benefits accrue to sponsors of product candidates with PRIME designation, including but not limited to, early and proactive regulatory dialogue with the EMA, frequent discussions on clinical trial designs and other development program elements, and accelerated MAA assessment once a dossier has been submitted. Importantly, a dedicated contact and rapporteur from the CHMP is appointed early in the PRIME scheme facilitating increased understanding of the product at EMA’s committee level. An initial meeting initiates these relationships and includes a team of multidisciplinary experts at the EMA to provide guidance on the overall development and regulatory strategies.

Moreover, in the EU, a “conditional” MA may be granted in cases where all the required safety and efficacy data are not yet available. The conditional MA is subject to conditions to be fulfilled for generating the missing data or ensuring increased safety measures. It is valid for one year and has to be renewed annually until fulfillment of all the conditions. Once the pending studies are provided, it can become a “standard” MA. However, if the conditions are not fulfilled within the timeframe set by the EMA, the MA ceases to be renewed. Furthermore, MA may also be granted “under exceptional circumstances” when the applicant can show that it is unable to provide comprehensive data on the efficacy and safety under normal conditions of use even after the product has been authorized and subject to specific procedures being introduced. This may arise in particular when the intended indications are very rare and, in the present state of scientific knowledge, it is not possible to provide comprehensive information, or when generating data may be contrary to generally accepted ethical principles. This MA is close to the conditional MA as it is reserved to medicinal products to be approved for severe diseases or unmet medical needs and the applicant does not hold the complete data set legally required for the grant of a MA. However, unlike the conditional MA, the applicant does not have to provide the missing data and will never have to. Although the MA “under exceptional circumstances” is granted definitively, the risk-benefit balance of the medicinal product is reviewed annually and the MA is withdrawn in case the risk-benefit ratio is no longer favorable.

MAs have an initial duration of five years. After these five years, the authorization may be renewed for an unlimited period on the basis of a reevaluation of the risk-benefit balance.

Data and marketing exclusivity

In the EU, new products authorized for marketing, or reference products, generally receive eight years of data exclusivity and an additional two years of market exclusivity upon MA. If granted, the data exclusivity period prevents generic or biosimilar applicants from relying on the preclinical and clinical trial data contained in the dossier of the reference product when applying for a generic or biosimilar MA in the EU during a period of eight years from the date on which the reference product was first authorized in the EU. During the additional two‑year period of market exclusivity, a generic or biosimilar MAA can be submitted, and the innovator’s data may be referenced, but no generic or biosimilar product can be marketed until 10 years have elapsed from the initial MA of the reference product in the EU. The overall 10-year market exclusivity period can be extended to a maximum of eleven years if, during the first eight years of those 10 years, the MA holder obtains an authorization for one or more new therapeutic indications which, during the scientific evaluation prior to their authorization, are held to bring a significant clinical benefit in comparison with existing therapies. However, there is no guarantee that a product will be considered by the EU’s regulatory authorities to be a new chemical entity, and products may not qualify for data exclusivity.

Pediatric development

In the EU, MAAs for new medicinal product candidates have to include the results of trials conducted in the pediatric population, in compliance with a pediatric investigation plan, or PIP, agreed with the EMA’s Pediatric Committee, or PDCO. The PIP sets out the timing and measures proposed to generate data to support a pediatric indication of the product candidate for which MA is being sought. The PDCO can grant a deferral of the obligation to implement some or all of the measures of the PIP until there are sufficient data to demonstrate the efficacy and safety of the product in adults. Further, the obligation to provide pediatric clinical trial data can be waived by the PDCO when these data is not needed or appropriate because the product is likely to be ineffective or unsafe in children, the disease or condition for which the product is intended occurs only in adult populations, or when the product does not represent a significant therapeutic benefit over existing treatments for pediatric patients. Once the MA is obtained in all EU member states and study results are included in the product

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information, even when negative, the product is eligible for six months’ supplementary protection certificate extension (if any is in effect at the time of approval) or, in the case of orphan medicinal products, a two year extension of the orphan market exclusivity is granted.

Orphan designation

The criteria for designating an “orphan medicinal product” in the EU are similar in principle to those in the United States. A medicinal product may be designated as orphan if its sponsor can establish that (1) the product is intended for the diagnosis, prevention or treatment of a life threatening or chronically debilitating condition (2) either (a) such condition affects not more than five in 10,000 persons in the EU when the application is made, or (b) the product, without the benefits derived from the orphan status, would not generate sufficient return in the EU to justify the necessary investment; and (3) there exists no satisfactory method of diagnosis, prevention or treatment of the condition in question that has been authorized for marketing in the EU or, if such method exists, the product will be of significant benefit to those affected by that condition.

In the EU, an application for designation as an orphan product can be made any time prior to the filing of an MAA. Orphan designation entitles a party to incentives such fee reductions or fee waivers, protocol assistance, and access to the centralized procedure. Upon grant of a MA, orphan medicinal products are entitled to a ten-year period of market exclusivity for the approved therapeutic indication, which means that the regulatory authorities cannot accept another MAA, or grant a MA, or accept an application to extend a MA for a similar product for the same indication for a period of ten years. The period of market exclusivity is extended by two years for orphan medicinal products that have also complied with an agreed PIP. No extension to any supplementary protection certificate can be granted on the basis of pediatric studies for orphan indications. Orphan designation does not convey any advantage in, or shorten the duration of, the regulatory review and approval process.

The orphan exclusivity period may, however, be reduced to six years if, at the end of the fifth year, it is established that the product no longer meets the criteria for orphan designation, for example because the product is sufficiently profitable not to justify market exclusivity, or where the prevalence of the condition has increased above the threshold. Granting of an authorization for another similar orphan medicinal product can happen at any time if: (i) the second applicant can establish that its product, although similar to the authorized product, is safer, more effective or otherwise clinically superior, (ii) inability of the applicant to supply sufficient quantities of the orphan medicinal product or (iii) where the applicant consents to a second orphan medicinal product application. A company may voluntarily remove a product from the orphan register.

Post-Approval Requirements

Similar to the United States, both MA holders and manufacturers of medicinal products are subject to comprehensive regulatory oversight by the EMA, the EC and/or the competent regulatory authorities of the member states. The holder of a MA must establish and maintain a pharmacovigilance system and appoint an individual qualified person for pharmacovigilance, or QPPV, who is responsible for establishment and maintenance of that system, and oversees the safety profiles of medicinal products and any emerging safety concerns. Key obligations include expedited reporting of suspected serious adverse reactions and submission of periodic safety update reports, or PSURs.

All new MAA must include a risk management plan, or RMP describing the risk management system that the company will put in place and documenting measures to prevent or minimize the risks associated with the product. The regulatory authorities may also impose specific obligations as a condition of the MA. Such risk-minimization measures or post-authorization obligations may include additional safety monitoring, more frequent submission of PSURs, or the conduct of additional clinical trials or post-authorization safety studies.

The advertising and promotion of medicinal products is also subject to laws concerning promotion of medicinal products, interactions with physicians, misleading and comparative advertising and unfair commercial practices. All advertising and promotional activities for the product must be consistent with the approved summary of product characteristics, and therefore all off-label promotion is prohibited. Direct-to-consumer advertising of prescription medicines is also prohibited in the EU. Although general requirements for advertising and promotion of medicinal products are established under EU directives, the details are governed by regulations in each member state and can differ from one country to another.

The aforementioned EU rules are generally applicable in the European Economic Area, or EEA, which consists of the 27 EU member states plus Norway, Liechtenstein and Iceland.

Failure to comply with EU and member state laws that apply to the conduct of clinical trials, manufacturing approval, MA of medicinal products and marketing of such products, both before and after grant of the MA, manufacturing of pharmaceutical products, statutory health insurance, bribery and anti-corruption or with other applicable regulatory

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requirements may result in administrative, civil or criminal penalties. These penalties could include delays or refusal to authorize the conduct of clinical trials, or to grant MA, product withdrawals and recalls, product seizures, suspension, withdrawal or variation of the MA, total or partial suspension of production, distribution, manufacturing or clinical trials, operating restrictions, injunctions, suspension of licenses, fines and criminal penalties.

Regulation of Combination Products in the EU

The EU regulates medical devices and medicinal products separately, through different legislative instruments, and the applicable requirements will vary depending on the type of drug-device combination product. EU guidance has been published to help manufacturers select the right regulatory framework.

Drug-delivery products intended to administer a medicinal product where the medicinal product and the device form a single integral product are regulated as medicinal products in the EU. The EMA is responsible for evaluating the quality, safety and efficacy of MAAs submitted through the centralized procedure, including the safety and performance of the medical device in relation to its use with the medicinal product. The EMA or the EU member state national competent authority will assess the product in accordance with the rules for medicinal products described above but the device part must comply with the Medical Devices Regulation (including the general safety and performance requirements provided in Annex I). MAA must include – where available – the results of the assessment of the conformity of the device part with the Medical Devices Regulation contained in the manufacturer’s EU declaration of conformity of the device or the relevant certificate issued by a notified body. If the MAA does not include the results of the conformity assessment and where for the conformity assessment of the device, if used separately, the involvement of a notified body is required, the competent authority must require the applicant to provide a notified body opinion on the conformity of the device.

By contrast, in case of drug-delivery products intended to administer a medicinal product where the device and the medicinal product do not form a single integral product (but are e.g. co-packaged), the medicinal product is regulated in accordance with the rules for medicinal products described above while the device part is regulated as a medical device and will have to comply with all the requirements set forth by the Medical Devices Regulation.

The characteristics of non-integral devices used for the administration of medicinal products may impact the quality, safety and efficacy profile of the medicinal products. To the extent that administration devices are co-packaged with the medicinal product or, in exceptional cases, where the use of a specific type of administration device is specifically provided for in the product information of the medicinal product, additional information may need to be provided in the MAA for the medicinal product on the characteristics of the medical device(s) that may impact on the quality, safety and/or efficacy of the medicinal product.

The requirements regarding quality documentation for medicinal products when used with a medical device, including single integral products, co-packaged and referenced products, are outlined in the EMA guideline of July 22, 2021, which became applicable as of January 1, 2022.

The aforementioned EU rules are generally applicable in the EEA.

Brexit and the Regulatory Framework in the United Kingdom

Since the end of the Brexit transition period on January 1, 2021, and the implementation of the Windsor Framework on January 1, 2025, the United Kingdom, or UK, has not generally been directly subject to EU laws with respect to medicinal products. The EU laws that have been transposed into UK law through secondary legislation remain applicable in Great Britain (England, Scotland and Wales), or GB, however, new legislation such as the (EU) CTR is not generally applicable in GB. Whilst the EU-UK Trade and Cooperation Agreement, or TCA, includes the mutual recognition of GMP inspections of manufacturing facilities for medicinal products and GMP documents issued, it does not contain wholesale mutual recognition of UK and EU pharmaceutical regulations and product standards.

The UK Medicines and Medical Devices Act 2021 has introduced delegated powers in favor of the Secretary of State or an ‘appropriate authority’ to amend or supplement existing regulations in the area of medicinal products and medical devices. This allows new rules to be introduced in the future by way of secondary legislation, which aims to allow flexibility in addressing regulatory gaps and future changes in the fields of human medicines, clinical trials and medical devices.

Since January 1, 2021, the Medicines and Healthcare products Regulatory Agency, or MHRA, has been the UK’s standalone medicines and medical devices regulator. As a result of the Northern Ireland Protocol, different rules applied in Northern Ireland than in GB; broadly, Northern Ireland continued to follow the EU regulatory regime. However, on January 1, 2025, an arrangement called the “Windsor Framework” came into effect and reintegrated Northern Ireland under the regulatory authority of the MHRA with respect to medicinal products. The Windsor Framework removes EU licensing

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processes, and EU labelling and serialization requirements in relation to Northern Ireland, and introduces a UK-wide licensing process for medicinal products.

MAs in the UK are governed by the Human Medicines Regulations (SI 2012/1916), as amended. Under the terms of the Windsor Framework, these MAs became valid for the whole of the UK from January 1, 2025. In order to use the centralized procedure to obtain an MA that will be valid throughout the EEA, companies must be established in the EEA. Therefore, since Brexit, companies established in the UK can no longer use the EU centralized procedure and instead an EEA entity must hold any centralized MAs. In order to obtain a UK MA to commercialize products in the UK, an applicant must be established in the UK and must follow one of the UK national authorization procedures or one of the remaining post-Brexit international cooperation procedures. Applications are governed by the Human Medicines Regulations (SI 2012/1916), as amended, and are made electronically through the MHRA Submissions Portal. The MHRA has introduced changes to national licensing procedures, including procedures to prioritize access to new medicinal products that will benefit patients, including a 150-day assessment (subject to clock-stops) and a rolling review procedure. In addition, an international recognition procedure, or IRP, has been in place since January 1, 2024, whereby the MHRA will have regard to decisions on the approval of MAs made by the EMA and certain other regulators when determining an application for a new UK MA. Pursuant to the IRP, the MHRA will take into account the expertise and decision-making of trusted regulatory partners (i.e. the regulators in Australia, Canada, Switzerland, Singapore, Japan, the U.S. and the EU). The MHRA will conduct a targeted assessment of IRP applications but retain the authority to reject applications if the evidence provided is considered insufficiently robust. The IRP allows medicinal products approved by such trusted regulatory partners that meet certain criteria to undergo a fast-tracked MHRA review to obtain and/or update an MA in the UK. Applications should be decided within a maximum of 60 days if there are no major objections identified that cannot be resolved within such 60-day period and the approval from the trusted regulatory partner selected has been granted within the previous 2 years or if there are such major objections identified or such approval has not been granted within the previous 2 years within 110 days. Applicants can submit initial MAAs to the IRP but the procedure can also be used throughout the lifecycle of a product for post-authorization procedures including line extensions, variations and renewals. In the UK, the initial duration of an MA is five years and following renewal will be valid for an unlimited period unless the MHRA decides on justified grounds relating to pharmacovigilance, to proceed with only one additional 5-year renewal. Any authorization which is not followed by the actual placing of the medicinal product on the market in the UK within 3 years shall cease to be in force.

There is no pre-MA orphan designation in the UK. Instead, the MHRA reviews applications for orphan designation in parallel to the corresponding MA application. The criteria are essentially the same, but have been tailored for the market, i.e., the prevalence of the condition in the UK, rather than the EU, must not be more than five in 10,000. Should an orphan designation be granted, the period or market exclusivity will be set from the date of first approval of the product in the UK.

The UK regulatory framework in relation to clinical trials is derived from the now-repealed EU Clinical Trials Directive (as implemented into UK law, through the Medicines for Human Use (Clinical Trials) Regulations 2004, as amended). In April 2025, the UK government introduced the Medicines for Human Use (Clinical Trials) Amendment Regulations 2024. The amendment, which will take effect from April 2026, aims to provide a more flexible regime to make it easier to conduct clinical trials in the UK, increase the transparency of clinical trials conducted in the UK and make clinical trials more patient centered.

Foreign Data Privacy and Security Laws

We are also subject to laws and regulations in non-U.S. countries governing data privacy and the protection of personal data, including health-related data. Laws and regulations in the EU and other jurisdictions apply broadly to the collection, use, storage, disclosure, processing and security of personal data, and have generally become more stringent over time. Privacy and security laws, regulations, and other obligations are constantly evolving, may conflict with each other to complicate compliance efforts, and can result in investigations, proceedings, or actions that lead to significant civil and/or criminal penalties and restrictions on data processing.

Human Capital

We have assembled a deeply experienced and highly skilled group of industry veterans, scientists, clinicians and key opinion leaders from leading biotechnology and pharmaceutical companies, as well as leading academic centers from around the world. Our employees are a team of highly dedicated, passionate individuals who pride themselves on a culture of respect, humility, transparency, inclusion, dedication, collaboration and fun. Our ultimate goal is to enhance and extend the lives of patients.

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Our philosophy is to offer a comprehensive compensation and benefits package to support our greatest assets, our people, and our human capital resources objectives include, as applicable, identifying, attracting, retaining and motivating our highly qualified management and our clinical, scientific and other employees and consultants. The principal purposes of our equity and cash incentive plans are to attract, retain and motivate personnel through the granting of stock-based and cash-based compensation awards, in order to align our interests and the interests of our stockholders with those of our employees and consultants.

As of March 10, 2026, we had 161 full-time employees and 1 part-time employee. Of those 162 employees, 32, or 20%, have a Ph.D. or M.D., and 95, or 59%, are women. None of our employees are represented by labor unions or covered by collective bargaining agreements. We consider our relationship with our employees to be good.

Corporate Information

We were incorporated under the laws of the state of Delaware on October 26, 2015 under the name FSG, Bio, Inc. and changed our name to Gossamer Bio, Inc. in 2017. Our principal executive offices are located at 3115 Merryfield Row, Suite 120, San Diego, California 92121, and our telephone number is (858) 684-1300.

Available Information

Our internet address is www.gossamerbio.com. Our investor relations website is located at http://ir.gossamerbio.com. We make available free of charge on our investor relations website under “filings” our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, our directors’ and officers’ Section 16 reports and any amendments to those reports as soon as reasonably practicable after filing or furnishing such materials to the US Securities and Exchange Commission, or SEC. They are also available for free on the SEC’s website at www.sec.gov. We use our investor relations website as a means of disclosing material non-public information and for complying with our disclosure obligations under Regulation FD. Investors should monitor such website, in addition to following our press releases, SEC filings and public conference calls and webcasts. Information relating to our corporate governance is also included on our investor relations website. The information in or accessible through the SEC and our website are not incorporated into, and are not considered part of, this filing. Further, our references to the URLs for these websites are intended to be inactive textual references only.