The San Diego-based biotech firm Gossamer Bio announced today that it still intends to seek a regulatory path forward with the FDA for its lead drug, seralutinib, despite the treatment narrowly missing its primary goal in a late-stage clinical trial.
The Phase 3 PROSERA study, which evaluated the inhaled drug in patients suffering from pulmonary arterial hypertension (PAH), showed that patients taking seralutinib could walk about 13.3 meters further than those on a placebo after 24 weeks. While the results showed a clear improvement, they fell just short of the strict statistical “p-value” threshold of 0.025 set for the study, landing instead at 0.032.
In the world of clinical trials, missing this target usually makes for a tough conversation with regulators. However, Gossamer leadership pointed to a “compelling signal” in the data, particularly among the sickest patients. In a group of 234 participants classified as intermediate or high-risk, the drug showed a much stronger placebo-adjusted improvement of 20 meters.
“While we are disappointed to have narrowly missed the stringent prespecified statistical threshold… we believe these data clearly demonstrate seralutinib is an active drug,” said Faheem Hasnain, Gossamer’s CEO. He noted that the drug seemed particularly effective in patients with more advanced disease, many of whom were already on three or four other medications.
Pulmonary arterial hypertension is a rare and often fatal condition where high blood pressure in the lung arteries strains the heart. Current treatments often focus on opening up blood vessels, but seralutinib is designed to target the underlying inflammation and tissue scarring that causes the disease to progress.
Beyond the walking test, the study tracked other markers of heart health. One key secondary metric—a blood protein called NT-proBNP that signals heart stress—showed a significant drop in patients using the drug.
On the safety front, the drug was generally well-tolerated. The most common side effect was a cough, reported by 37% of users, which is a known issue with inhaled dry powder medications. About 13% of patients saw an increase in liver enzymes, compared to 1% in the placebo group.
The company is now pausing enrollment in a separate study to analyze these results further, specifically looking at why placebo groups in different parts of the world performed differently. Gossamer plans to sit down with the FDA soon to discuss whether the current data, bolstered by the strong showing in high-risk subgroups, is enough to support an eventual approval.
Despite the company’s optimistic outlook on the future of the drug, the market reacted sharply to the news. Investors appeared focused on the missed primary endpoint rather than the subgroup successes, causing Gossamer Bio’s stock to tumble in early trading following the announcement.
By midday, shares had plummeted roughly 84%, trading at approximately $0.33 as the company became the market’s top loser for the day.
Investors and patients alike are watching closely, as the “narrow miss” leaves the drug’s future in a gray area that only the FDA can clear up.
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