A phase 3 study of Gossamer Bio’s seralutinib in pulmonary arterial hypertension (PAH) has missed its primary endpoint, triggering a 77% crash in the biotech’s share price. The company has paused enrollment in another seralutinib study while it digs into the data.
Investigators randomized 390 people with PAH, a condition that limits physical activity, to take seralutinib or placebo on top of background therapy. Seralutinib, an inhaled tyrosine kinase inhibitor, targets growth factor receptors implicated in PAH. Patients walked 6.5 meters farther on seralutinib than placebo in the six-minute walk test in phase 2, but Gossamer bet it could beat that nonsignificant result in phase 3.
The gap between seralutinib and placebo widened in the phase 3 Prosera study, which enrolled sicker patients than the earlier trial did. But the 13.3-meter improvement over placebo fell short of statistical significance and the bar set by Guggenheim Securities analysts going into the readout.
Writing in a note to investors last month, the analysts said the company needed to achieve a 20-meter improvement to succeed. In fact, Gossamer would need to show a 25-meter improvement to give them more confidence in the commercial viability of the drug, they added at the time.
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While Gossamer’s overall dataset fell short of both objectives, the biotech shared subgroup results that suggest seralutinib is more effective in some patients. Limiting the analysis to a prespecified subgroup of 234 intermediate and high-risk patients increased seralutinib’s edge over placebo to 20 meters. Focusing on the 75 patients at North American sites resulted in a 25.9-meter difference.
On a call with analysts to discuss the data, Gossamer Chief Medical Officer Richard Aranda, M.D., said the Prosera outcome is less about a lack of drug activity and more about placebo, particularly in a heavily treated lower-risk population. Patients at Latin American sites performed particularly well on placebo.
Investors focused on the primary endpoint failure, sending Gossamer’s share price down 80% to 44 cents in early trading Monday. Gossamer is hoping the FDA is more positive on the results, and the biotech plans to talk with the regulator about the path forward.
Meanwhile, Gossamer has paused enrollment in a phase 3 trial of seralutinib in pulmonary hypertension associated with interstitial lung disease. The biotech said in this morning’s press release that it hit pause while it investigates regional discrepancies in placebo responses in the PAH data. But Gossamer CEO Faheem Hasnain told analysts on the conference call that there is a financial driver behind the decision.
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“It’s really about resourcing and making sure that our first priority is getting Prosera over the finish line and getting it approved by the FDA. We’re going to go through all of the financials and make sure that we are prioritizing everything for that effect,” Hasnain said.
The biotech expects to end the first quarter with about $105 million in cash.
