Phase 2 trial shows bitopertin reduces protoporphyrin-IX in adults with erythropoietic protoporphyria

BACKGROUND: Erythropoietic protoporphyria is a rare genetic disorder of heme biosynthesis characterized by protoporphyrin-IX accumulation, painful phototoxic reactions, and hepatobiliary disease, for which no disease-modifying therapies are approved. OBJECTIVE: To evaluate the efficacy and safety of bitopertin, an inhibitor of glycine transporter 1, in adults with erythropoietic protoporphyria. METHODS: In this randomized, double-blind, phase 2 study, patients received once-daily oral bitopertin 20 mg, bitopertin 60 mg, or placebo for 17 weeks. The primary endpoint was percentage change from baseline in whole-blood metal-free protoporphyrin-IX levels at day 121. RESULTS: Patients received bitopertin 20 mg (n = 26), 60 mg (n = 25), or placebo (n = 24). At day 121, the percentage change from baseline in whole-blood metal-free protoporphyrin-IX versus placebo was -29.6% (P = .004) with bitopertin 20 mg and -49.8% (P < .001) with bitopertin 60 mg. Bitopertin was associated with a reduced incidence of phototoxic reactions. Bitopertin was well tolerated with no notable safety concerns identified. LIMITATIONS: Small sample size, short follow-up period, and no formal adjustments for between-group multiple-pairwise comparisons. CONCLUSIONS: Bitopertin significantly reduced protoporphyrin-IX levels, showed improved measures of sunlight tolerance, and had a favorable safety profile in patients with erythropoietic protoporphyria.