An open-label phase II study of bitopertin in adults and adolescents with erythropoietic protoporphyria or X-linked protoporphyria

BACKGROUND: Erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP) are rare genetic disorders characterized by accumulation of protoporphyrin IX (PPIX), painful phototoxic reactions and hepatobiliary disease. No disease-modifying therapies are approved for these conditions. OBJECTIVES: To evaluate the safety and efficacy of bitopertin in adults and adolescents with EPP or XLP. METHODS: BEACON (ACTRN12622000799752) was a phase II, randomized, open-label, parallel-arm study in adult and adolescent participants with EPP or XLP. Participants received an oral, once-daily administration of bitopertin 20 mg or 60 mg for 24 weeks. RESULTS: Twenty-six participants were randomized to 20 mg (n = 14) or 60 mg (n = 12) of bitopertin. The study met its primary efficacy endpoint. Treatment with bitopertin resulted in significant, dose-dependent reductions in PPIX levels compared with baseline at both the 20-mg and 60-mg dose levels (mean -31.7%, SE 7.0; P < 0.001 vs. baseline and mean -57.7%, SE 7.4; P < 0.001 vs. baseline, respectively). Similar efficacy was observed across the adult and adolescent populations. No serious adverse events were reported. Dizziness was the most common adverse event reported with bitopertin, in 9 (64%) and 8 (67%) participants completing the study in the 20-mg and 60-mg dose groups, respectively. CONCLUSIONS: By reducing whole-blood PPIX levels, bitopertin targets the underlying pathophysiology of EPP, resulting in consistent improvements in multiple measures of light tolerance and quality of life. Bitopertin was well tolerated, and most adverse events were mild or moderate in severity.