ESSA Pharma Inc. announced the presentation of updated clinical data from the first two cohorts of the Phase 1/2 study of ESSA's lead candidate EPI-7386 in combination with enzalutamide in patients with metastatic castration-resistant prostate cancer ("mCRPC"). Data will be presented in a poster format at the 2022 Prostate Cancer Foundation ("PCF") Scientific Retreat, taking place October 27-29, 2022 in Carlsbad, CA. In the multicenter, open-label Phase 1/2 dose escalation study, seven mCRPC patients naïve to second generation antiandrogens were enrolled in the first two cohorts, with escalating doses of EPI-7386 and a fixed 120mg once a day (QD) dose of enzalutamide.

The study permitted one prior line of chemotherapy. Pharmacokinetic results from these first two cohorts demonstrated that enzalutamide exposure was minimally impacted by EPI-7386 while exposures of EPI-7386 were reduced by coadministration with enzalutamide, but remained in the clinically relevant range as suggested by preclinical xenograft studies. The safety of the combination was favorable with a safety profile consistent with second-generation antiandrogens and no dose limiting toxicities observed.

One of the patients in the first cohort discontinued after one cycle of dosing due to a strong CYP3A inducer concomitant medication which lowered exposures to both EPI-7386 and enzalutamide and was therefore not evaluable for efficacy. Anti-tumor activity in the remaining six patients enrolled demonstrated that four of six of these patients achieved a PSA90 by 12 weeks of dosing and five of six patients to date have achieved a PSA90.