Disc Medicine announced on October 19 that bitopertin, its oral GlyT1 inhibitor, met all primary and secondary endpoints in APOLLO, the pivotal Phase 3 trial in adults and adolescents with erythropoietic protoporphyria (EPP), including X-linked protoporphyria. Whole blood metal free protoporphyrin IX (PPIX), the toxic metabolite whose accumulation causes the disease’s painful reactions to light, fell 41.4 percent relative to placebo (p<0.0001). The second co-primary endpoint, total time in light without pain, rose by 12.2 hours at month six against placebo (p=0.0010). Secondary endpoints, including fewer phototoxic reactions and improved light tolerance measures, were also positive, as were exploratory quality of life endpoints. The drug was generally well tolerated with no new safety signals; dizziness was the most common treatment related side effect. Disc shares rose more than 35 percent on the day.
The context is a regulatory reversal eight months old. In February 2026 the FDA issued a complete response letter refusing accelerated approval: the agency accepted that bitopertin lowers PPIX but found no demonstrated link in the earlier AURORA and BEACON trials between PPIX reduction and sunlight tolerance, and pointed to APOLLO as the study that could support traditional approval. APOLLO was designed to answer that objection directly by pairing the biomarker with time in light and phototoxic reaction endpoints, and on the company’s topline it has.
EPP has one marketed therapy, Clinuvel’s Scenesse implant, which works by increasing skin melanin rather than reducing PPIX production, and LEO Pharma’s dersimelagon is also in regulatory review. Bitopertin, which Disc licensed from Roche after Roche abandoned it in schizophrenia, would be the first oral, disease modifying entrant if approved. Disc plans to resubmit its new drug application by the end of 2026, with an FDA decision anticipated by mid 2027. Leerink Partners analyst Thomas Smith wrote that the results “substantially” address the concerns in the complete response letter; Jefferies’ Roger Song put the market opportunity at 1 billion to 2 billion dollars.
The discipline is the same as for any topline. The effect sizes are the company’s, the full dataset is unpublished, and the February letter shows this FDA division reads the biomarker to clinical benefit link strictly. But the trial the agency asked for has now reported, on both halves of the question it posed.