Safety and efficacy of pegtibatinase enzyme replacement therapy in adults with classical homocystinuria in the COMPOSE phase 1/2 randomized trial

Abstract

Purpose: Because the standard-of-care treatment for classical homocystinuria (HCU) often cannot achieve adequate metabolic control, the phase 1/2 COMPOSE trial (NCT03406611) evaluated pegtibatinase enzyme replacement therapy.

Methods: Participants with HCU aged 12 to 65 years with elevated total plasma homocysteine (tHcy) receiving standard-of-care treatment were randomized 3:1 into 6 increasing dose cohorts (each n ≈ 4) of subcutaneous pegtibatinase (≤2.5 mg/kg twice weekly [BIW]) or placebo. Primary end points included adverse event incidence and immunogenicity. Secondary end points included tHcy change from baseline to posttreatment (geometric mean of weeks 6-12).

Results: Overall, 24 participants were enrolled. Pegtibatinase was generally well tolerated at all doses with no anaphylaxis or severe immune reactions; 15 participants (62.5%) experienced ≥1 treatment-related treatment-emergent adverse event (most commonly injection-site reactions; 1 serious [acute urticaria]). At the 2 highest doses, substantial tHcy reductions were observed after treatment (relative reduction: 57% for 1.5 mg/kg BIW; 67% for 2.5 mg/kg BIW), and all participants maintained tHcy < 100 μM. One participant receiving 2.5 mg/kg BIW achieved tHcy < 15 μM (normal) and methionine < 14 μM (below normal), enabling increased dietary intact protein intake. Changes in other metabolites aligned with tHcy.

Conclusion: Pegtibatinase was generally well tolerated and substantially reduced tHcy levels, demonstrating potential as a treatment for HCU.

Keywords: COMPOSE; Classical homocystinuria; Enzyme replacement therapy; Pegtibatinase; Total plasma homocysteine.