Disposition and metabolism of the specific endothelin A receptor antagonist zibotentan (ZD4054) in healthy volunteers

1. Zibotentan (ZD4054) is a specific endothelin A (ETA) receptor antagonist that is in clinical development for the treatment of castration-resistant prostate cancer (CRPC) and has shown a promising signal for improvement in overall survival compared with placebo in a Phase II study of patients with metastatic CRPC. 2. In this study, the pharmacokinetics, disposition and metabolism of zibotentan were evaluated following administration of a single oral dose of [C-14]-zibotentan 15 mg to six healthy subjects. 3. Zibotentan was rapidly absorbed, with the maximum zibotentan plasma concentration being observed 1 hour after administration. Excretion was rapid with the majority of the dose being excreted in the urine (71-94%). Total recovery of radioactivity over the 5 days of the study was high (mean 93%), with 78% of the dose being recovered within 24 hours. Concentrations of radioactivity in the plasma were similar up to 12 hours post dose, and diverged thereafter, indicating the presence of circulating metabolites. The main circulating component was zibotentan with a number of metabolites being identified in excreta. 4. Zibotentan was well absorbed and was cleared via metabolism and urinary excretion with zibotentan-related material predominantly excreted via the urine.