Results from a phase I study of enzalutamide in combination with docetaxel in men with prostate cancer.

Abstract

5066 Background: Enzalutamide (ENZA) is a novel androgen receptor (AR) inhibitor that prolongs survival in men with metastatic castration-resistant prostate cancer (mCRPC) who had received prior docetaxel (DOC). DOC also prolongs survival in mCRPC and also appears to have anti-tumor effects mediated through the androgen-receptor axis, providing a compelling rationale for combining the two agents. CYP3A4 plays a role in DOC clearance and is induced by ENZA. We therefore conducted a phase I study to explore the PK and safety profiles of this combination. Methods: This study (NCT01565928) evaluated the safety and pharmacokinetics (PK) of DOC co-administered with ENZA in men with mCRPC on androgen deprivation therapy. Pts received DOC (75 mg/m2) by 1-h infusion every 3 weeks with corticosteroids. ENZA (160 mg/d) was started 24 h after the first DOC infusion. Plasma PK samples were collected for 24 h after Cycle (C) 1 and C2 DOC infusions to enable within-subject comparisons of DOC PK ± ENZA. A sample size of 18 pts able to receive ≥ 2 full doses of DOC was specified for PK analyses. Results: Twenty-two pts were enrolled, 4 did not receive 2 full doses of DOC. As of 21 Sept 2012, preliminary PK and C1 and C2 safety data were available from 15 pts. The median age was 65 (range 46-80 yrs); 11 had ECOG performance status 1 (vs 0). Prior primary therapy included surgery (n=2), radiation (n=4) or both (n=5); median PSA was 44.7ng/mL (1.9-585). ANC<1000/mm3 was reported in 14 pts (1 febrile neutropenia), other adverse events in ≥4 pts included fatigue (11), dyspnea (6), alopecia (5), peripheral neuropathy (5), anemia (4) and dysgueusia (4). No seizures were reported. Preliminary PK data (n=15) show similar DOC exposure (within 20%) for DOC in combination with ENZA vs. DOC alone.Final PK and updated tolerability and efficacy data beyond Cycle 2 will be presented. Conclusions: In mCRPC pts, ENZA does not appear to affect tolerability of DOC or have a clinically meaningful impact on DOC PK. Clinical trial information: NCT01565928.