Disc Medicine Reports Positive Phase 3 Bitopertin Results in EPP

WATERTOWN, Mass. — October 19, 2026

APOLLO Trial Demonstrates Improvements in Primary Endpoints

The randomized, double-blind Phase 3 APOLLO trial enrolled 183 patients aged 12 years and older with EPP or XLP across the United States, Canada, Europe and Australia. Participants were randomized 1:1 to receive oral bitopertin at 60 mg once daily or placebo for six months, with stratification based on baseline light tolerance and geography. Bitopertin achieved statistically significant results on both co-primary endpoints. Whole-blood metal-free PPIX decreased by 41.4% versus placebo (p<0.0001), while average monthly total time in light without pain during month six increased by 12.2 hours versus placebo (p=0.0010). PPIX accumulation is central to EPP disease biology, and reducing its levels may help address the underlying mechanism responsible for light-induced symptoms. Disc said the results provide clinical evidence linking modulation of heme biosynthesis to improvements in disease severity. The company plans to present more detailed findings and additional analyses at a future medical conference.

Secondary Endpoints and Patient-Reported Outcomes Also Improve

The trial met all secondary endpoints, including a statistically significant reduction in the incidence rate of phototoxic reactions over the six-month treatment period (p<0.0001) and an increase in cumulative total time spent in light without pain (p<0.0001). Among adults, bitopertin also improved the change from baseline in average daily sunlight exposure time before the onset of prodromal symptoms (p=0.0077). Exploratory quality-of-life measures showed statistically significant improvements in Patient Global Impression of Change (PGIC) and Patient Global Impression of Severity (PGIS) scores, both with p<0.0001. Bitopertin was generally well-tolerated. Dizziness was the most commonly reported treatment-emergent adverse event in the bitopertin group, occurring in 50% of participants; events were described as mild or moderate and generally transient. No treatment-emergent adverse events above Grade 3 were reported. Disc said no new safety signals were observed in the study. The results build on earlier clinical investigations of bitopertin, including the Phase 2 BEACON and AURORA trials and the HELIOS open-label extension study.

Bitopertin Targets Heme Biosynthesis as Disc Plans FDA Resubmission

Bitopertin is an investigational oral inhibitor of glycine transporter 1 (GlyT1) designed to modulate heme biosynthesis. GlyT1 is expressed on developing red blood cells and supplies glycine required for heme production and erythropoiesis. EPP and XLP are rare disorders associated with abnormalities in heme biosynthesis that lead to accumulation of photoactive PPIX. Exposure to sunlight can trigger severe pain, burning sensations, swelling and, in some cases, blistering or disfigurement. PPIX accumulation can also affect the hepatobiliary system and cause complications including gallstones, cholestasis and liver damage. Patients often rely on extensive sunlight avoidance, protective clothing and pain management, which can substantially affect daily activities and quality of life. Disc obtained global rights to bitopertin from Roche in May 2021 and is investigating its potential in EPP and other hematologic diseases. Following the positive APOLLO results, the company intends to resubmit its NDA by year-end 2026. Bitopertin remains investigational and is not approved for use in any jurisdiction worldwide. Its safety and efficacy for EPP will be subject to regulatory review.

Source::Disc Medicine,press release