Chiesi retreats from Gossamer PAH programme after Phase 3 miss
Italian pharmaceutical group Chiesi has returned all development and commercial rights to seralutinib to Gossamer Bio, ending a pulmonary arterial hypertension partnership originally valued at up to $486 million.
Why it matters: The withdrawal removes a potentially important respiratory asset from Chiesi’s pipeline after the drug missed the primary endpoint of its pivotal Phase 3 trial.
Zoom in: Chiesi will pay Gossamer a final $5 million under the termination agreement. Gossamer does not have to repay Chiesi and will regain worldwide rights to the inhaled drug.
- Chiesi will retain a capped royalty on any future worldwide sales, alongside undisclosed payments if seralutinib reaches specified regulatory and commercial milestones.
Backstory: The original 2024 agreement included $160 million in research and development reimbursements, up to $146 million in regulatory milestones and another $180 million tied to sales. The partners had planned to split US profits equally, while Chiesi controlled commercialisation outside the U.S.
How it works: Seralutinib is an inhaled inhibitor of PDGFR, CSF1R and c-KIT, targeting signalling pathways linked to the narrowing and remodelling of blood vessels in pulmonary arterial hypertension.
Yes, but: In February, the 390-patient PROSERA study showed a placebo-adjusted improvement of 13.3 metres in the six-minute walk test after 24 weeks, but its p-value of 0.032 missed the prespecified statistical threshold of 0.025.
- Chiesi said the decision followed its evaluation of the development programme and the Phase 3 results. The company stressed that respiratory medicine remains a strategic pillar, with its efforts focused on asthma, chronic obstructive pulmonary disease and other respiratory conditions.
What’s next: Gossamer is not abandoning the drug. After a June meeting with the US Food and Drug Administration, the biotech said the agency viewed the magnitude and statistical significance of the Phase 3 effect as issues for review rather than barriers to filing.
- Gossamer plans to submit a US approval application in September, combining PROSERA with confirmatory Phase 2 evidence and other analyses. If accepted, the application could receive an FDA decision in the third quarter of 2027.
The bottom line: Chiesi has limited its exposure to a programme carrying significant regulatory and commercial risk, while preserving a smaller financial interest should Gossamer succeed in taking seralutinib to market.
Also notable: The refocus will also help strengthen Chiesi’s recent expansion in rare diseases, including its $1.9 billion acquisition of KalVista Pharmaceuticals, the largest takeover in the Italian company’s history.
