Centessa Pharmaceuticals plc announced the dosing of the first subject in its registrational PRESent-2 study of SerpinPC for the treatment of hemophilia B without inhibitors. The dosing phase of PRESent-2 follows a minimum 12-week observation period during which prospective baseline data of the subject’s disease status under their current therapy are collected to support regulatory review of the benefit and risk profile of SerpinPC. SerpinPC is an investigational subcutaneously administered novel inhibitor of activated protein C (APC) being developed as a potential treatment for hemophilia B, with or without inhibitors.

The PRESent-2 study (AP-0102) is a Phase 2b, global, open-label, seamless adaptive design study to investigate the efficacy and safety of subcutaneous dosing of SerpinPC every week, every 2 weeks, or every 4 weeks in approximately 120 adult (aged 18 to =65 years) or adolescent (aged =12 to <18 years) male subjects with severe hemophilia A (with or without inhibitors) or moderately severe to severe hemophilia B (without inhibitors). PRESent-2 consists of 3 parts: a 24-week randomized dose-justification phase (Part 1), a 24-week dose-confirmatory phase (Part 2), and a further 24-week extension phase (Part 3) for subjects who complete either Part 1 or Part 2. Subjects must have undergone a minimum period of prospective observation (at least 12 weeks for Part 1 or 24 weeks for Part 2) under their current therapy (either on-demand or prophylaxis factor replacement) before switching to SerpinPC treatment. The primary efficacy endpoint for the study is the rate of treated bleeds (expressed as an annualized bleeding rate (ABR)) in the observation period compared to the first 24 weeks treated with SerpinPC.

The Company expects to begin dosing in its registrational PRESent-3 (AP-0103) study for subjects with hemophilia B with inhibitors this year.