Gossamer Bio, Inc. (GOSS)

Gossamer Bio is a clinical-stage biopharmaceutical company focused on developing and commercializing seralutinib for pulmonary hypertension (PH), including pulmonary arterial hypertension (PAH) and PH associated with interstitial lung disease (PH-ILD). The company's stated goal is to be an industry leader in PH. It is led by a management team with prior senior experience at companies such as Receptos, Facet Biotech, Actelion, Merck and Leerink Partners.

Seralutinib (GB002) is an investigational inhaled small-molecule inhibitor of PDGFR (alpha and beta), CSF1R and c-KIT, designed to reverse pathological vascular remodeling. It is meant to build on the efficacy seen with oral imatinib while avoiding its systemic safety and tolerability problems. The company has completed Phase 1a studies in healthy volunteers, a Phase 1b trial, and the Phase 2 TORREY study in 86 PAH patients, which met its primary endpoint of pulmonary vascular resistance. In February 2026 it reported topline results from the 48-week Phase 3 PROSERA trial in 390 PAH patients. The 6-minute walk distance improvement at Week 24 was 13.3 meters, but it missed the prespecified alpha threshold. Larger effects were seen in the intermediate- and high-risk subgroup and in the connective tissue disease-associated PAH subgroup. Near-term priorities include completing PROSERA analyses, seeking FDA feedback (including a Type C meeting), advancing NDA-readiness activities, continuing open-label extension studies, and strengthening the capital structure, including evaluating alternatives for its outstanding convertible notes. Enrollment in the Phase 3 SERANATA study in PH-ILD is paused. The company is also advancing RT234, an on-demand inhaled therapy, under an option agreement with Respira Therapeutics.

The company targets patients with PAH, a rare, progressive and often fatal disease. It estimates about 50,000 PAH patients in the US and more than 70,000 in the EU, and it believes PH-ILD is at least as prevalent. Existing PAH treatments include PDE5 inhibitors, endothelin receptor antagonists, prostanoids and the activin ligand trap sotatercept, none of which is curative. Only one FDA-approved treatment exists for PH-ILD. Seralutinib has orphan drug designation for PAH from the FDA, the European Commission and Japan's PMDA. Gossamer has no approved products.

Gossamer in-licensed seralutinib from Pulmokine, Inc. In May 2024 it entered a collaboration with Chiesi. Gossamer leads global development in PAH and PH-ILD and leads potential US commercialization in those indications, with each party contributing 50% of commercial efforts. Chiesi leads development in any additional indications and holds exclusive commercialization rights outside the United States. Chiesi is currently evaluating the PROSERA dataset.