Disc Medicine Receives FDA Complete Response Letter for Bitopertin EPP Treatment

Disc Medicine received a complete response letter from the FDA on February 13, 2026, regarding bitopertin as a treatment for erythropoietic protoporphyria (EPP). The FDA acknowledged that the AURORA and BEACON studies provided sufficient evidence that bitopertin significantly lowers whole blood metal-free PPIX levels, but concluded the trials did not show evidence of association between percent change in PPIX and sunlight exposure-based endpoints.

The FDA noted there is strong mechanistic and biological plausibility supporting the use of the PPIX biomarker in protoporphyria. However, the agency indicated a need to see the results of the ongoing Phase 3 APOLLO study before making a decision. The FDA stated that results of the APOLLO study could serve as evidence to support traditional approval.

Accelerated approval relies on whether there is evidence of an effect on the proposed surrogate endpoint (percent change in whole blood metal-free PPIX) and whether the proposed surrogate endpoint, including the magnitude of change, is reasonably likely to predict a clinical benefit. On the first point, the FDA agreed that AURORA and BEACON provided sufficient evidence that bitopertin significantly lowers whole blood metal-free PPIX. On the second, based on review of AURORA and BEACON results, the FDA concluded that the trials did not show evidence of association between percent change in PPIX and sunlight exposure-based endpoints, as measured in the trials.

The CEO stated that while efforts at utilizing expedited pathways to get bitopertin to patients quickly have not come to fruition, the company is continuing to pursue all avenues in support of FDA approval. The CEO noted that the complete response letter will delay the potential approval of bitopertin, but expressed confidence in the ongoing APOLLO trial, for which there is significant enthusiasm from the EPP community.

Disc Medicine completed trial enrollment for APOLLO in March 2026, several months earlier than expected, due to significant patient and physician enthusiasm around the trial. A blinded sample size re-estimation of the APOLLO study was conducted in January and no modifications to sample size were needed based on statistical analysis. Topline data from APOLLO is anticipated in Q4 2026.

The company plans to request a Type A meeting to review its approach with the FDA. Upon completion of APOLLO, Disc would then file a response to the complete response letter and expects an updated FDA decision by mid-2027.

Disc Medicine reported approximately $791 million at December 31, 2025 in unaudited cash, cash equivalents, and marketable securities and maintains guidance of providing runway into 2029. The company has a market capitalization of $2.13 billion and is listed on the NASDAQ exchange. The stock has experienced significant volatility, with a 52-week high of $99.5 and a low of $30.82.

Bitopertin is an investigational, clinical-stage, orally administered inhibitor of glycine transporter 1 (GlyT1) that is designed to modulate heme biosynthesis. GlyT1 is a membrane transporter expressed on developing red blood cells and is required to supply sufficient glycine for heme biosynthesis and support erythropoiesis. Disc is developing bitopertin as a potential treatment for a range of hematologic diseases including erythropoietic porphyrias, where it has potential to be the first disease-modifying therapy. Bitopertin has been studied in multiple clinical trials in patients with EPP, including the Phase 2 open-label BEACON trial, the Phase 2 double-blind, placebo-controlled AURORA trial, an open-label extension HELIOS trial, and the confirmatory Phase 3 double-blind, placebo-controlled APOLLO trial.

Bitopertin is an investigational agent and is not approved for use as a therapy in any jurisdiction worldwide. Disc obtained global rights to bitopertin under a license agreement from Roche in May 2021.

Disc Medicine is a clinical-stage biopharmaceutical company focused on the discovery, development, and commercialization of novel treatments for hematologic diseases. The company aims to modify fundamental biological pathways associated with the formation and function of red blood cells, specifically heme biosynthesis and iron homeostasis. Its pipeline includes bitopertin for erythropoietic porphyrias (EPs) including erythropoietic protoporphyria (EPP), X-linked protoporphyria (XLP), and Diamond-Blackfan Anemia (DBA); DISC-0974 for the treatment of anemia of myelofibrosis (MF) and anemia of chronic kidney disease (CKD); and DISC-3405 for the treatment of polycythemia vera (PV) and other hematologic disorders. The company's preclinical programs include DISC-0998.