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Oral bitopertin met all primary and secondary endpoints in the phase 3 APOLLO trial in EPP, cutting PPIX and increasing pain-free time in light.
Bitopertin, an investigational oral glycine transporter 1 (GlyT1) inhibitor, met both co-primary endpoints and all secondary endpoints in the pivotal phase 3 APOLLO trial in adults and adolescents with erythropoietic protoporphyria (EPP), including X-linked protoporphyria (XLP), according to topline results announced October 19, 2026, by Disc Medicine.1
The company plans to resubmit a New Drug Application (NDA) to the US Food and Drug Administration (FDA) by the end of 2026, with a decision anticipated by mid-2027. The results arrive 8 months after the FDA issued a complete response letter for bitopertin, which had been under review for accelerated approval based on reductions in whole-blood metal-free protoporphyrin IX (PPIX) in the phase 2 AURORA and BEACON trials.1,2 The agency indicated APOLLO data would be needed to link PPIX reduction with sunlight-based clinical outcomes.
APOLLO (NCT06910358) was a randomized, double-blind, placebo-controlled trial enrolling 183 patients aged 12 years or older across the United States, Canada, Europe, and Australia.3 Patients were stratified by baseline light tolerance and geography and randomized 1:1 to bitopertin 60 mg or placebo once daily for 6 months.
Bitopertin reduced whole-blood metal-free PPIX from baseline by 41.4% vs placebo (P < .0001). The second co-primary endpoint, average monthly total time in light without pain during month 6, increased by 12.2 hours vs placebo (P = .0010).
Bitopertin also reduced the incidence rate of phototoxic reactions over the 6-month treatment period (P < .0001) and increased cumulative total time in light without pain over 6 months (P < .0001) vs placebo. Among adults, change from baseline in average daily sunlight exposure time to prodrome favored bitopertin (P = .0077).
Exploratory quality-of-life measures were also statistically significant, with improvements in Patient Global Impression of Change (P < .0001) and Patient Global Impression of Severity (P < .0001) scores vs placebo.
Bitopertin was generally well tolerated, with no new safety signals observed. Dizziness was the most commonly reported treatment-emergent adverse event in the bitopertin group, occurring in 50% of patients, and was mild or moderate and generally transient.
No treatment-emergent adverse events above grade 3 were reported. Disc Medicine plans to share more detailed APOLLO data at a future medical conference.
Afamelanotide (Scenesse), a surgically implanted melanocortin 1 receptor agonist, remains the only FDA-approved therapy for EPP. Bitopertin instead targets heme biosynthesis upstream to reduce PPIX production.
Editor's Note: This summary has been edited for grammar and clarity using artificial intelligence tools.
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