Recommended Phase 2 dose regimen identified as masofaniten 600mg BID combined with enzalutamide 160mg QD

Phase 2 head-to-head portion of the study to commence enrollment immediately

Updated Phase 1 results selected for a poster presentation at ESMO 2023

SOUTH SAN FRANCISCO, CA, USA and VANCOUVER, Canada I September 18, 2023 I ESSA Pharma Inc. (“ESSA”, or the “Company”) (NASDAQ: EPIX), a clinical-stage pharmaceutical company focused on developing novel therapies for the treatment of prostate cancer, today announced the initiation of the Phase 2 portion of its Phase 1/2 study evaluating its lead candidate, masofaniten (formerly known as EPI-7386), a first-in-class N-terminal domain androgen receptor inhibitor, in combination with Astellas and Pfizer’s antiandrogen enzalutamide in patients with metastatic castration-resistant prostate cancer (“mCRPC”) naïve to second-generation antiandrogens.

Updated results from the first four cohorts of patients from the Phase 1 dose escalation portion of the Phase 1/2 study have been selected for a poster presentation at the upcoming European Society of Medical Oncology (“ESMO”) Congress taking place October 20-24, 2023, in Madrid, Spain.

“Initiation of the randomized Phase 2 portion of this study investigating the combination of masofaniten and enzalutamide (the “Combination”) is a significant milestone for ESSA and we look forward to reporting updated results from the Phase 1 dose equilibration portion of the study next month at ESMO 2023,” stated David Parkinson, M.D., President and CEO of ESSA. “The favorable safety profile observed to date with the Combination has led the safety review board to agree that we can proceed forward into the head-to-head comparison portion of the study with the dose regimen studied in Cohort 4 as our recommended Phase 2 dose. We look forward to further elucidating the Combination’s potential to improve long-term clinical benefit for patients with mCRPC. We plan to provide guidance for timing of the public disclosure of initial data once the Phase 2 portion has been underway for several months.”

The Phase 2 dose expansion portion of the study is a two-arm, randomized, open-label study (NCT05075577) that will evaluate the safety, tolerability and preliminary efficacy of masofaniten, and is expected to enroll approximately 120 patients. Patients will continue to receive androgen deprivation therapy and will be randomized 2:1 to receive either the combination of masofaniten (600mg twice-daily (“BID”)) and enzalutamide (160mg once daily (“QD”)) or enzalutamide (160mg QD) as a single agent. Patients may remain on study treatment as long as they are tolerating treatment without disease progression based on RECIST v1.1 and/or Prostate Cancer Clinical Trials Working Group 3 (PCWG3) criteria.

Details for the ESMO 2023 Presentation

Title: Phase 1/2 Trial of Oral EPI-7386 in Combination with Enzalutamide (Enz) Compared to Enz Alone in Metastatic Castration-Resistant Prostate Cancer (mCRPC) Subjects: Current Phase 1 (P1) results
Speaker: Andrew L. Laccetti
Presentation #: 1813P
Date: Sunday, October 22, 2023

About Masofaniten

Masofaniten (formerly known as EPI-7386) is a first-in-class investigational, highly selective, oral, small molecule inhibitor of the N-terminal domain (“NTD”) of the androgen receptor (“AR”). Masofaniten’s unique mechanism of action disrupts the AR signaling pathway, the primary pathway that drives prostate cancer growth, by selectively binding to the NTD, a region of the AR that is not currently targeted by other therapies. Masofaniten is currently being studied in an open-label, randomized Phase 2 clinical trial (NCT05075577) in combination with enzalutamide in patients with metastatic castration-resistant prostate cancer (mCRPC) naïve to second-generation antiandrogens. ESSA is also conducting a Phase 1 monotherapy study (NCT04421222) in patients with mCRPC whose tumors have progressed on standard-of-care therapies. The U.S. Food and Drug Administration has granted Fast Track designation to masofaniten for the treatment of adult male patients with mCRPC resistant to standard-of-care treatment. ESSA retains all rights to masofaniten worldwide.

About ESSA Pharma Inc.

ESSA is a clinical-stage pharmaceutical company focused on developing novel and proprietary therapies for the treatment of patients with prostate cancer. For more information, please visit, and follow us on Twitter and LinkedIn.