A Study to Evaluate How Daily Dosing With Enzalutamide Affects the Metabolism of Caffeine and Dextromethorphan in Men With Prostate Cancer

Inclusion Criteria:

* Subject is a male aged 18 years old or older (at screening) with histologically confirmed prostate cancer (all stages) for whom androgen deprivation therapy is indicated (except when indicated in a neoadjuvant/adjuvant setting). Subjects may be on ongoing androgen deprivation therapy with a gonadotropin releasing hormone (GnRH) analogue or have undergone prior bilateral orchiectomy at screening.
* Subject has progressive disease by prostate-specific antigen (PSA) or imaging.
* Subject has received no more than 2 prior chemotherapy regimens.
* Subject has an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
* Male subject must use a condom if having sex with a pregnant woman.
* Male subject and their female spouse/partners who are of childbearing potential must use 2 acceptable methods of birth control starting at screening and continuing throughout the study period and for 3 months after final study drug administration.
* Subject has an estimated life expectancy of at least 6 months.

Exclusion Criteria:

* Subject has confirmed CYP2D6 poor metabolizer, or CYP2D6 ultrarapid metabolizer status based on genotyping analysis.
* Subject has known metastases in the liver or any hepatic disorder that could affect drug metabolism deemed clinically significant by the investigator after discussion with the sponsor.
* Subject has undergone major surgery within 4 weeks prior to day 1.
* Subject received treatment with chemotherapy within 4 weeks prior to enrollment (day 1 visit) or plans to initiate treatment with chemotherapy during the study.
* Subject uses concomitant medications that are potent inducers and/or inhibitors of CYP1A2, CYP2C8, CYP2D6, or CYP3A4.