Phase III, Randomized, Placebo-controlled Study of Once-daily Oral Zibotentan (ZD4054) in Patients with Non-metastatic Castration-resistant Prostate Cancer

Background: Standard treatment options are limited for the management of non-metastatic castration-resistant prostate cancer (CRPC). This study, part of the ENTHUSE (EndoTHelin A USE) phase III programme, evaluated the efficacy and safety of the oral specific endothelin (ET)A receptor antagonist zibotentan vs placebo in patients with non-metastatic CRPC (non-mCRPC).

Methods: This was a multicentre, randomized, double-blind, phase III study. Patients (n=1421) with non-mCRPC and biochemical progression (determined by rising serum PSA levels) were randomized to receive zibotentan 10 mg or placebo once daily. Based on the lack of efficacy signal in another ENTHUSE phase III study, an interim analysis was performed to determine whether the study was likely to achieve the co-primary objectives of improved overall survival (OS) and progression-free survival (PFS).

Results: Criteria for continuation of this study were not met. A total of 79 deaths and 293 progression events were recorded at final data cutoff. Zibotentan-treated patients did not significantly differ from placebo-treated patients for OS (hazard ratio (HR): 1.13; 95% confidence interval (CI): 0.73-1.76, P=0.589) or PFS (HR: 0.89; 95% CI: 0.71-1.12, P=0.330). The most commonly reported adverse events in zibotentan-treated patients were peripheral oedema (37.7%), headache (26.2%) and nasal congestion (24.9%); each occurred with >15% higher incidence than in the placebo group.

Conclusions: This trial was terminated early because of failure at interim analysis of the efficacy data to meet the defined criteria for continuation. Owing to the absence of demonstrable survival benefits in the ENTHUSE clinical studies, zibotentan is no longer under investigation as a potential treatment for prostate cancer.