ESSA Pharma Updates Phase 1 Masofaniten (EPI-7386) Data at 2024 ASCO GU Symposium

The combination treatment of masofaniten and enzalutamide has shown promising results in patients with metastatic castration-resistant prostate cancer (mCRPC), demonstrating both safety and significant reductions in prostate-specific antigen (PSA) levels. ESSA Pharma Inc., a clinical-stage pharmaceutical company, has been actively presenting their findings, most recently at the 2024 ASCO Genitourinary Cancers Symposium.

Masofaniten, also known as EPI-7386, is an innovative N-terminal domain androgen receptor inhibitor. This first-in-class small molecule disrupts androgen receptor signaling, which is crucial in driving prostate cancer growth. The Phase 1/2 clinical study has been exploring masofaniten's efficacy in conjunction with enzalutamide. This combination therapy continues to be well tolerated by patients, with many achieving deep and durable declines in PSA levels.

In the Phase 1 dose escalation study, a total of 18 patients were enrolled. The study's results indicated that across the various dosing cohorts, 88% of patients achieved over a 50% reduction in PSA levels. Specifically, 81% of patients achieved a 90% reduction, and 69% reached this milestone in under 90 days. Furthermore, 63% of patients saw their PSA levels drop to less than 0.2ng/mL. Despite the data still maturing, the median time to PSA progression currently stands at 16.6 months.

The Phase 2 dose expansion part of the trial is designed to provide a comparative analysis between the combination therapy and single-agent enzalutamide. It's currently ongoing, with patient enrollment happening across numerous sites in the USA, Canada, and Australia, and plans to extend to European locations.

Masofaniten has demonstrated an ability to achieve clinically relevant exposure levels even in conjunction with the full labeled dose of enzalutamide. This is despite enzalutamide reducing the exposure levels of masofaniten. The trial has confirmed that masofaniten combined with enzalutamide is well tolerated. The most common side effects were mild, but a Grade 3 rash was observed in one patient, prompting an expansion of the cohort for further observation. No dose-limiting toxicities were identified, and the recommended doses for Phase 2 have been set at 600 mg of masofaniten twice daily and 160 mg of enzalutamide once daily.

Masofaniten is a highly selective oral inhibitor targeting the androgen receptor's N-terminal domain. It’s currently in a Phase 2 clinical trial in combination with enzalutamide for patients with mCRPC who haven't been treated with second-generation antiandrogens. Additionally, there’s an ongoing Phase 1 study of masofaniten as a monotherapy in patients whose cancer has progressed despite standard treatments. The U.S. Food and Drug Administration has granted Fast Track designation to masofaniten for treating mCRPC patients resistant to standard care.

ESSA Pharma Inc. remains dedicated to advancing novel therapies for prostate cancer, continuing their clinical developments and providing updates on their progress.