Oncternal Therapeutics, Inc. announced that enrollment has been completed and dosing initiated for the fifth dose cohort of its Phase 1/2 study of ONCT-534 for the treatment of patients with metastatic castration-resistant prostate cancer who are relapsed or refractory to approved androgen receptor pathway inhibitors (ARPI). Patients in the fifth cohort are receiving ONCT-534, the company?s dual-action androgen receptor inhibitor (DAARI), at a dose of 600 mg taken orally once each day. The decision to proceed to this higher dose level was made by the study?s Safety Review Committee (SRC) after reviewing data from the fourth dose level of 300 mg ONCT-534 daily.

An initial update on ONCT-534 safety and efficacy based on prostate-specific antigen (PSA) levels from this study is expected in the third quarter of 2024 and will include data from this 600 mg dose cohort. Study ONCT-534-101 is a Phase 1/2, single-arm, open-label, multi-center study to evaluate the safety and tolerability, pharmacokinetics, and preliminary anti-tumor activity of ONCT-534 in patients with mCRPC who have relapsed or are refractory to approved ARPIs including enzalutamide, abiraterone, apalutamide, and darolutamide. After the safety and tolerability and preliminary antitumor activity of ONCT-534 have been assessed in Phase 1, Phase 2 will commence to further evaluate the safety and antitumor activity of ONCT-534 to support selecting an optimal dose.