Introduction:

Resistance to androgen receptor (AR) pathway inhibitors (ARPI; e.g., abiraterone, enzalutamide) in metastatic castration-resistant prostate cancer (mCRPC) may be driven by preservation of AR signaling through various mechanisms. Enhancer of zeste homolog 2 (EZH2) is implicated in the pathogenesis of prostate cancer and ARPI resistance. Combining ARPI with therapies that modulate alternative signaling pathways, including epigenetic modifiers such as EZH2, could be a promising treatment approach to overcome resistance. Mevrometostat (PF-06821497) is a potent and selective small molecule EZH2 inhibitor. Results from the dose-escalation period of a phase 1 study (NCT03460977) showed promising activity for mevrometostat combined with enzalutamide, with a manageable adverse-event profile in abiraterone-exposed patients with mCRPC (Schweizer MT, et al. J Clin Oncol. 2024;42(16_suppl):5061). The current trial aims to evaluate radiographic progression-free survival (rPFS), overall survival (OS), and safety of mevrometostat plus enzalutamide compared with standard of care in patients with mCRPC previously treated with abiraterone.

Methods:

MEVPRO-1 (registry#) is a global, open-label, phase 3 trial in patients with mCRPC aged ≥18 years with progression on/after ≥12 weeks abiraterone, castration testosterone levels ≤50 ng/dL, ECOG performance status 0–2, and life expectancy ≥6 months. Approximately 600 patients will be randomized 1:1 to receive mevrometostat (875mg BD with food) with enzalutamide (160mg QD), or physician’s choice of enzalutamide (160mg QD) or docetaxel (75mg/m² intravenously every 21d). Randomization will be stratified by previous docetaxel in metastatic castration-sensitive setting, physician’s choice of comparator (enzalutamide/docetaxel), and presence of hepatic metastases.

The primary endpoint is BICR-assessed rPFS per RECIST 1.1 (soft tissue) and PCWG3 (bone) assessed by blinded central radiology review. Key secondary endpoint is OS. Secondary endpoints include anti-tumor activity, safety, pharmacokinetics, ctDNA, and patient-reported outcomes. Stratified log-rank P-values, HRs, and 95% CIs will be estimated using a stratified Cox proportional hazard model, and Kaplan–Meier analysis will summarize time-to-event endpoints.

Results:

Conclusion:

Funding: This study is sponsored by Pfizer Inc. Enzalutamide for the study will be provided by Astellas Pharma Inc. Medical writing and editorial support were provided by Michelle Mancher, MPH, Allison TerBush, PhD, and Rosie Henderson, MSc, of Onyx (a division of Prime, London, UK), and funded by Pfizer Inc.