Gossamer Bio Advances Seralutinib Phase 3 Trials with PROSERA Results Expected February 2026
Key Insights
Gossamer Bio completed enrollment of 390 patients in the pivotal PROSERA Phase 3 study evaluating seralutinib for pulmonary arterial hypertension (search), with topline results expected in February 2026.
The company activated the first clinical site for the registrational SERANATA Phase 3 study in pulmonary hypertension associated with interstitial lung disease (search), planning to enroll approximately 480 patients.
Seralutinib, an inhaled PDGFR (search), CSF1R (search) and c-KIT (search) inhibitor, is being developed in collaboration with Chiesi Group (search) for two distinct pulmonary hypertension indications.
Gossamer Bio has reached a critical milestone in its late-stage clinical development program, completing enrollment for the pivotal PROSERA Phase 3 study evaluating seralutinib in pulmonary arterial hypertension (search) (PAH) and initiating its second registrational trial for pulmonary hypertension associated with interstitial lung disease (search) (PH-ILD). The company expects to announce topline results from PROSERA in February 2026.
PROSERA Phase 3 Study Nears Completion
The PROSERA study enrolled 390 WHO Functional Class II and III PAH patients in a double-blind, placebo-controlled, global registrational clinical trial. Patients are randomized 1:1 to receive either seralutinib or placebo on top of background PAH therapy, with blinded treatment administered for up to 48 weeks.
The primary endpoint measures change in six-minute walk distance (6MWD) from baseline compared to placebo at week 24. Key secondary endpoints include time to clinical worsening compared to placebo up to week 48, alongside additional secondary and exploratory endpoints evaluating safety and tolerability.
"We are proud to be progressing through the final stages of the PROSERA Phase 3 Study. This is a pivotal moment for our team, and I am continually impressed by the focus, diligence, and professionalism that everyone brings to this important work," said Faheem Hasnain, Chairman, Co-Founder, and CEO of Gossamer Bio.
SERANATA Study Launches for PH-ILD Indication
Gossamer Bio activated the first clinical site for the SERANATA Phase 3 study in the fourth quarter of 2025, marking the initiation of its second registrational program. The 24-week, randomized, double-blind, placebo-controlled global trial will enroll approximately 480 PH-ILD patients.
The SERANATA study employs a 1:1:1 randomization to three arms: 90mg seralutinib twice-daily, 120mg seralutinib twice-daily, or placebo. The primary endpoint evaluates change in 6MWD from baseline compared to placebo at week 24, with key secondary endpoints including time to clinical worsening and change from baseline in forced vital capacity (FVC).
"We are encouraged by the engagement from the PH-ILD community as we begin to activate the first clinical sites in the SERANATA Phase 3 study," Hasnain noted. "We are grateful for the opportunity to collaborate closely with physicians and patients to better understand the challenges for those living with this challenging and under-treated disease."
Seralutinib Mechanism and Development Partnership
Seralutinib (GB002) is an inhaled inhibitor targeting PDGFR (search), CSF1R (search) and c-KIT (search) pathways. The drug candidate is being developed through a global collaboration agreement between Gossamer Bio and the Chiesi Group (search), focusing on two distinct pulmonary hypertension indications.
Recent scientific presentations at the European Respiratory Society Congress 2025 demonstrated seralutinib's potential mechanisms of action, including targeting fibrotic pathways in idiopathic pulmonary fibrosis (search) through single-cell transcriptomics evidence and demonstrating in vitro reduction of vascular inflammatory drivers underlying pulmonary hypertension.
Financial Position and Strategic Expansion
As of September 30, 2025, Gossamer Bio maintained cash, cash equivalents and marketable securities totaling $180.2 million. The company expects these resources will be sufficient to fund operating and capital expenditures into 2027.
The company also entered into a strategic option agreement on September 24th to acquire Respira Therapeutics (search) and its inhaled vardenafil formulation for as-needed use in pulmonary hypertension. The option can be exercised through issuance of 1.5 million Gossamer Bio shares, representing less than 1% of outstanding shares. If exercised, Gossamer does not expect to commence further clinical trials for this asset until at least 2027.
Third quarter 2025 financial results showed revenue from the Chiesi collaboration of $13.3 million, including $9.2 million in cost reimbursement revenue, compared to $9.5 million in the same period of 2024. Research and development expenses increased to $45.5 million from $34.9 million year-over-year, reflecting the advancement of both Phase 3 programs.