Influence of Enzalutamide on Cabazitaxel Pharmacokinetics: a Drug–Drug Interaction Study in Metastatic Castration-resistant Prostate Cancer (mCRPC) Patients

Abstract Purpose: In ongoing clinical research on metastatic castration-resistant prostate cancer (mCRPC) treatment, the potential enhanced efficacy of the combination of taxanes with AR-targeted agents, that is, enzalutamide and abiraterone, is currently being explored. Because enzalutamide induces the CYP3A4 enzyme and taxanes are metabolized by this enzyme, a potential drug–drug interaction needs to be investigated. Experimental Design: Therefore, we performed a pharmacokinetic cross-over study in mCRPC patients who were scheduled for treatment with cabazitaxel Q3W (25 mg/m2). Patients were studied for three consecutive cabazitaxel cycles. Enzalutamide (160 mg once daily) was administered concomitantly after the first cabazitaxel cycle, during 6 weeks. Primary endpoint was the difference in mean area under the curve (AUC) between the first (cabazitaxel monotherapy) and third cabazitaxel cycle, when enzalutamide was added. Results: A potential clinically relevant 22% (95% CI, 9%–34%; P = 0.005) reduction in cabazitaxel exposure was found with concomitant enzalutamide use. The geometric mean AUC0–24h of cabazitaxel was 181 ng*h/mL (95% CI, 150–219 ng*h/mL) in cycle 3 and 234 ng*h/mL (95% CI, 209–261 ng*h/mL) in cycle 1. This combination did not result in excessive toxicity, whereas PSA response was promising. Conclusions: We found a significant decrease in cabazitaxel exposure when combined with enzalutamide. In an era of clinical trials on combination strategies for mCRPC, it is important to be aware of clinically relevant drug–drug interactions. Because recent study results support the use of a lower standard cabazitaxel dose of 20 mg/m2, the clinical relevance of this interaction may be substantial, because the addition of enzalutamide may result in subtherapeutic cabazitaxel exposure. Clin Cancer Res; 24(3); 541–6. ©2017 AACR.