ESSA Pharma Ends Phase 2 Study of Masofaniten and Enzalutamide in Metastatic Castration-Resistant Prostate Cancer

ESSA Pharma Inc., a clinical-stage pharmaceutical company specializing in innovative treatments for prostate cancer, has decided to discontinue its Phase 2 clinical trial. This trial was evaluating the efficacy of masofaniten in combination with enzalutamide compared to enzalutamide alone in patients with metastatic castration-resistant prostate cancer who had not received second-generation antiandrogens previously.

The decision to halt the trial was made after a thorough interim review of safety, pharmacokinetics, and efficacy data. The review indicated that patients receiving enzalutamide monotherapy, which is the current standard treatment, showed higher than anticipated rates of PSA90 response. This response rate was significantly better than that observed historically. Moreover, the combination of masofaniten and enzalutamide did not demonstrate a clear efficacy advantage over enzalutamide alone.

A futility analysis further confirmed that the trial was unlikely to meet its primary endpoint, leading to the conclusion that continuing the study would not be beneficial. The combination treatment was well-tolerated, with a safety profile similar to that seen in earlier Phase 1 studies, and no new safety concerns were identified.

David Parkinson, MD, President and CEO of ESSA, emphasized the company's commitment to providing significant clinical benefits to patients while maintaining a strong safety profile. He acknowledged that the decision to terminate the trial was difficult but necessary given the data. Parkinson expressed gratitude to all partners, investigators, employees, patients, and their families for their involvement in the clinical trials.

Richard Glickman, Chairman of the Board of Directors of ESSA, noted that the company is focusing on capital preservation. ESSA will initiate a strategic review process to explore and evaluate various options aimed at maximizing shareholder value.

The Phase 2 study was an open-label, two-arm randomized trial intended to enroll 120 patients, with 80 patients in the combination arm and 40 in the enzalutamide-only arm. The efficacy interim analysis included 52 patients who had at least one PSA measurement post-baseline, and 41 patients who completed at least three months of follow-up. These patients were from clinical sites in the United States, Canada, Australia, and France. The primary endpoint was the proportion of patients achieving PSA90, with secondary endpoints including PSA50 response and other PSA-based measures.

In light of the interim findings, ESSA also plans to conclude its remaining clinical studies involving masofaniten, either as a monotherapy or in combination with other treatments.

Financially, as of September 30, 2024, ESSA reported cash reserves and short-term investments totaling $126.8 million, with a net working capital of $124.3 million. The company has no long-term debt and had 44,388,551 common shares issued and outstanding.

The terminated Phase 2 study was part of the larger Phase 1/2 clinical program investigating masofaniten, a first-in-class investigational oral small molecule inhibitor of the androgen receptor. The U.S. Food and Drug Administration has granted Fast Track designation to masofaniten for treating adult male patients with metastatic castration-resistant prostate cancer who are resistant to standard treatments.

ESSA Pharma Inc. remains focused on developing proprietary therapies for prostate cancer, continually seeking ways to optimize clinical outcomes and patient safety in its ongoing research efforts.