Disc Medicine and FDA Reach Agreement to Resubmit Bitopertin After Earlier Rejection

Disc Medicine has reached an agreement with the U.S. Food and Drug Administration to resubmit its rare blood disorder drug bitopertin for approval, with the agency allowing the use of the company's Phase 3 APOLLO trial to support a new regulatory filing. The agreement comes four months after the FDA rejected bitopertin in February, citing concerns about the adequacy of the surrogate endpoint used in earlier trials.

In its February rejection letter, the FDA questioned the adequacy of the surrogate endpoint used in Disc's Phase 2 trial—percent change in whole-blood metal-free protoporphyrin IX—as a reasonable predictor of clinical benefit for treating erythropoietic protoporphyria, a rare blood disorder characterized by sensitivity to light. The FDA's complete response letter indicated that while two trials confirmed bitopertin's benefit in lowering protoporphyrin IX levels, there were "uncertainties" regarding whether lower levels correlated with meeting sunlight exposure endpoints.

Following a meeting with the FDA, Disc Medicine announced that the agency will allow the use of its ongoing Phase 3 APOLLO trial to support a resubmission. The FDA wrote that a resubmission would require an adequate and well-controlled Phase 3 trial measuring clinical outcomes, not indicators. APOLLO, which was already launched at the time of the rejection, now provides a potential path to full approval. If successful, the drug could be on track for a mid-2027 decision.

The regulatory setback has had significant financial impacts for Disc Medicine. Disc's stock is down approximately 15% in 2026 as of late February. The company's Chief Financial Officer sold 11,156 shares for approximately $720,000 in open-market transactions in February, accounting for 13.52% of direct holdings. Disc also announced in February it was cutting 20% of its workforce due to the FDA rejection. The company's Q4 FY 2025 earnings report showed a net loss for the entire fiscal year that doubled compared to the previous year. Disc Medicine, a clinical-stage biotechnology company, currently has a market capitalization of $2.51 billion, 142 employees, and a trailing twelve-month net loss of $212.18 million.

Bitopertin is an orally available molecule that works by blocking the glycine transporter 1, a protein involved in the production of hemoglobin. Erythropoietic protoporphyria is a rare disorder characterized by sensitivity to sunlight and some artificial lights, with patients suffering from severe pain upon exposure and potential liver and gallbladder complications.

Disc had previously received a Commissioner's National Priority Voucher, a ticket that drastically speeds up decision timelines, but the faster review did not lead to approval. The regulatory alignment follows recent high-level exits at the FDA, including the departure of the former director of the Center for Biologics Evaluation and Research and the former FDA Commissioner.