ESSA Pharma Announces First Patient Dosed in a Phase 1/2 Clinical Trial of EPI-7386 in Combination with Enzalutamide in Patients with Metastatic Castration-Resistant Prostate Cancer

HOUSTON and VANCOUVER, BC, Jan. 19, 2022 /PRNewswire/ - ESSA Pharma Inc. (NASDAQ: EPIX) ("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. 

About EPI-7386
EPI-7386 is an investigational, highly-selective, oral, small molecule inhibitor of the N-terminal domain of the androgen receptor. EPI-7386 is currently being studied in a Phase 1 clinical trial (NCT04421222) in men with metastatic castration-resistant prostate cancer whose tumors have progressed on current standard-of-care therapies. The Phase I clinical trial of EPI-7386 began in calendar Q3 of 2020 following FDA allowance of ESSA's Investigational New Drug application and Health Canada acceptance. EPI-7386 is also currently being studied in a Phase 1/2 clinical trial (NCT05075577) in mCRPC patients who have not yet been treated with second-generation antiandrogen therapies. The U.S. FDA has granted Fast Track designation to EPI-7386 for the treatment of adult male patients with mCRPC resistant to standard-of-care treatment. ESSA retains all rights to EPI-7386 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 www.essapharma.com and follow us on Twitter under @ESSAPharma.

About Prostate Cancer
Prostate cancer is the second-most commonly diagnosed cancer among men and the fifth most common cause of male cancer death worldwide (Globocan, 2018). Adenocarcinoma of the prostate is dependent on androgen for tumor progression and depleting or blocking androgen action has been a mainstay of hormonal treatment for over six decades. Although tumors are often initially sensitive to medical or surgical therapies that decrease levels of testosterone, disease progression despite castrate levels of testosterone can lead to mCRPC. The treatment of mCRPC patients has evolved rapidly over the past ten years. Despite these advances, many patients with mCRPC fail or develop resistance to existing treatments, leading to continued disease progression and limited survival rates.

Forward-Looking Statement Disclaimer This release contains certain information which, as presented, constitutes "forward-looking information" within the meaning of the Private Securities Litigation Reform Act of 1995 and/or applicable Canadian securities laws. Forward-looking information involves statements that relate to future events and often addresses expected future business and financial performance, containing words such as "anticipate", "believe", "plan", "estimate", "expect", and "intend", statements that an action or event "may", "might", "could", "should", or "will" be taken or occur, or other similar expressions and includes, but is not limited to, statements regarding the the combination of EPI-7386 and enzalutamide simultaneously targeting both ends of the androgen receptor, the combination of EPI-7386 with current antiandrogens leading to deeper and broader inhibition of androgen biology, the anticipated timeline of additional Phase 1/2 combination trials, and the methodology, goals and details of the Phase 1/2 clinical trial.

Forward-looking statements and information are subject to various known and unknown risks and uncertainties, many of which are beyond the ability of ESSA to control or predict, and which may cause ESSA's actual results, performance or achievements to be materially different from those expressed or implied thereby. Such statements reflect ESSA's current views with respect to future events, are subject to risks and uncertainties and are necessarily based upon a number of estimates and assumptions that, while considered reasonable by ESSA as of the date of such statements, are inherently subject to significant medical, scientific, business, economic, competitive, political and social uncertainties and contingencies. In making forward looking statements, ESSA may make various material assumptions, including but not limited to (i) the accuracy of ESSA's financial projections; (ii) obtaining positive results of clinical trials; (iii) obtaining necessary regulatory approvals; and (iv) general business, market and economic conditions.

Forward-looking information is developed based on assumptions about such risks, uncertainties and other factors set out herein and in ESSA's Quarterly Report on Form 10-Q dated August 16, 2021 under the heading "Risk Factors", a copy of which is available on ESSA's profile on EDGAR at www.sec.gov.com  and on the SEDAR website at www.sedar.com, and as otherwise disclosed from time to time on ESSA's EDGAR and SEDAR profiles. Forward-looking statements are made based on management's beliefs, estimates and opinions on the date that statements are made and ESSA undertakes no obligation to update forward-looking statements if these beliefs, estimates and opinions or other circumstances should change, except as may be required by applicable United States and Canadian securities laws. Readers are cautioned against attributing undue certainty to forward-looking statements.

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