ESSA Pharma Announces First Patient Dosed In Phase 1/2 Clinical Trial Of EPI-7386 In Combination With Enzalutamide In Patients With Metastatic Castration-Resistant Prostate Cancer

ESSA Pharma Inc.

("ESSA" or the "Company"), a clinical-stage pharmaceutical company focused on developing novel therapies for the treatment of prostate cancer, today announced the first patient dosed in the Company-sponsored Phase 1/2 study to evaluate the safety, tolerability and preliminary efficacy of ESSA's lead product candidate, EPI-7386, a first-in-class N-terminal domain androgen receptor inhibitor, in combination with Astellas Pharma Inc.'s ("Astellas") and Pfizer Inc.'s ligand-binding domain androgen receptor inhibitor, enzalutamide, in patients with metastatic castration-resistant prostate cancer ("mCRPC"). "The initiation of this combination trial with Astellas is a watershed moment for ESSA as we investigate the potential clinical benefit of inhibiting the androgen receptor through two independent pathways in the treatment of patients with mCRPC who have not yet received treatment with a second-generation antiandrogen drug," said Dr. David. R. Parkinson, Chief Executive Officer, ESSA Pharma Inc. "Combining our two therapies will simultaneously target both ends of the androgen receptor. In preclinical models, we have seen that combining EPI-7386 with current antiandrogens can lead to deeper and broader inhibition of androgen biology. This Phase 1/2 trial marks the first of a series of clinical studies to evaluate EPI-7386 in combination with current antiandrogen therapies in patients with mCRPC, with additional Phase 1/2 combination trials anticipated to begin in 2022." The Phase 1/2 clinical trial (NCT05075577) begins with an initial phase 1 portion wherein the doses of each drug are adjusted followed by a phase 2 portion wherein the single agent enzalutamide is compared to the combination of enzalutamide and EPI-7386. The phase 1 study is expected to enroll up to 30 mCRPC patients who have not yet been treated with second-generation antiandrogen therapies. The goal of the phase 1 portion of the study is to evaluate the safety and tolerability of the drug combination and establish the recommended phase 2 doses for EPI-7386 and enzalutamide when dosed in combination. The phase 2 study is expected to enroll 120 mCRPC patients who have not yet been treated with second-generation antiandrogen therapies. The goal of the phase 2 part of the study is to evaluate the safety, tolerability and antitumor activity of EPI-7386 in combination with a fixed dose of enzalutamide compared with enzalutamide as a single agent.