Centessa Pharmaceuticals plc (Nasdaq: CNTA), a clinical-stage pharmaceutical company focused on discovering and developing medicines that are transformational for patients, today 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.

“There remains a significant global need for new treatment options for persons with hemophilia B,” said Antoine Yver MD MSc, Chairman of Development of Centessa. “Based on encouraging clinical data from our ongoing Phase 2a study, we believe SerpinPC has the potential to be a first-in-class subcutaneously administered therapy with a differentiated safety profile for persons with hemophilia B, subject to regulatory review and approval.

We are excited to be evaluating the potential of SerpinPC’s novel mechanism of action in the registrational PRESent-2 study. We expect to enroll and dose additional patients across our clinical trial sites and advance toward the interim analysis planned when 36 subjects reach 12 weeks on treatment in Part 1 of the study.”

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.