Gossamer Bio submits seralutinib NDA after Phase 3 endpoint miss
The FDA will decide whether to file the application for review after PROSERA's walking-distance gain missed its preset statistical cutoff.
Adrian Kessler
An FDA filing decision is now the next test for seralutinib, after Gossamer Bio, Inc. NASDAQGOSS said on Wednesday it had submitted its first new drug application for the pulmonary arterial hypertension treatment. Its pivotal trial missed a prespecified p-value cutoff of 0.025 despite a 13.3-metre gain over placebo on a walking test.
The Sept. 23 release says Gossamer filed the application in September using Phase 3 PROSERA as its main controlled study, with Phase 2 TORREY and other analyses as supporting evidence. Gossamer said the FDA's June pre-submission meeting minutes treated PROSERA's statistical strength and effect size as issues for the full review rather than reasons to reject the application at filing.
Gossamer is a small-cap San Diego drug developer focused on inhaled seralutinib for pulmonary hypertension. It has not said the FDA has accepted the application for review. Gossamer shares NASDAQGOSS closed at US$10.99 on Nasdaq at 4:00:01 p.m. EDT on Wednesday.
The Main Trial Missed Its Preset Threshold
The Feb. 23 PROSERA readout reported 390 patients with pulmonary arterial hypertension, randomized between 197 receiving seralutinib and 193 receiving placebo. At week 24, the estimated treatment effect over placebo was 13.3 metres on the six-minute walk test. Its p value of 0.0320 missed the study's prespecified 0.025 threshold.
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A prespecified group of 234 patients at intermediate or high risk had a 20.0-metre placebo-adjusted gain, which Gossamer cited as supportive. Because the overall primary endpoint missed its threshold, the company said p values for the key secondary endpoints could not be evaluated for statistical significance. That leaves the FDA to judge the full data package rather than a straightforward positive pivotal result.
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The safety readout showed liver-enzyme elevations at least three times the upper limit of normal in 13 per cent of seralutinib patients versus 1 per cent on placebo. Gossamer described overall tolerability as consistent with prior experience; the imbalance remains part of the benefit-risk assessment.
"After an NDA is received, the FDA has 60 days to decide whether to file it so it can be reviewed," the agency says in its drug review guide.
Filing would begin a substantive review of efficacy, safety and manufacturing; it would not establish that seralutinib can be marketed. Gossamer expects a filing decision later in 2026 and had previously described a possible third-quarter 2027 approval decision if the application is accepted.
A PAH Rival Has Fresh Label Data
Merck & Co., Inc. NYSEMRK said on Sept. 22 that the FDA had added its HYPERION trial to the U.S. label for Winrevair, an approved pulmonary arterial hypertension treatment. In newly diagnosed adults on background therapy, the trial measured a 76 per cent reduction in clinical-worsening risk versus placebo. That endpoint and population differ from Gossamer's walking-distance study, but the label update places a fresh comparator beside any future seralutinib launch.
The iShares Biotechnology ETF NASDAQIBB closed at US$210.81 on Nasdaq at 4:00:01 p.m. EDT on Tuesday.
Gossamer reported US$57.0 million in cash, equivalents and marketable securities at June 30 in its Aug. 13 results. It expected that balance to fund operations into the first quarter of 2027, a narrower window than the possible approval timing it outlined.
The next dated step is the FDA's filing decision within 60 days of receiving the September application, putting the call in October or November 2026. That decision will determine whether seralutinib enters substantive FDA review.
