Disc Medicine said the U.S. Food and Drug Administration has issued a Complete Response Letter (CRL) for its New Drug Application seeking approval of bitopertin to treat erythropoietic protoporphyria, delaying the potential launch of the investigational therapy.
Bitopertin had been under review through the accelerated approval pathway and was also part of the agency’s Commissioner’s National Priority Voucher pilot program. Accelerated approval allows earlier authorization of medicines based on surrogate biomarkers reasonably likely to predict clinical benefit, particularly in rare or serious diseases.
In its review, the FDA agreed that data from the AURORA and BEACON clinical trials demonstrated that bitopertin significantly reduced whole blood metal-free protoporphyrin IX (PPIX), a key disease biomarker. However, regulators concluded the studies did not establish a clear association between reductions in PPIX and improvements in sunlight-exposure symptoms — a critical measure of patient benefit in erythropoietic protoporphyria.
The agency indicated that results from the ongoing APOLLO study could support a traditional approval instead. The trial is designed to directly evaluate clinical benefit rather than rely primarily on surrogate endpoints.
Company President and CEO John Quisel said the decision would delay approval but not derail the development program. He noted that the company plans to continue working closely with regulators and pursue all possible pathways toward authorization, emphasizing strong support from patients and physicians participating in the APOLLO trial.
Disc Medicine reported that enrollment in the study is expected to be completed in March 2026, earlier than initially planned. A blinded statistical review conducted in January confirmed no change was needed to the trial’s sample size. Top-line results are anticipated in the fourth quarter of the year, after which the company intends to respond to the CRL. An updated regulatory decision could follow by mid-2027.
The company said it ended 2025 with approximately $791 million in cash and investments, providing funding into 2029. Management will discuss the regulatory update with investors during a scheduled conference call.