A Drug-Drug Interaction Study of Abiraterone Acetate Plus Prednisone With Dextromethorphan and Theophylline in Patients With Metastatic Castration-Resistant Prostate Cancer

Inclusion Criteria:

* Histologically or cytologically confirmed adenocarcinoma of the prostate without neuroendocrine differentiation or small cell histology
* Documented metastatic disease
* Documented prostate specific antigen (PSA) progression according to Prostate Cancer Working Group 2 criteria, with PSA value \>=2 ng/mL despite medical or surgical castration, or prostate cancer progression documented by radiographic progression according to Response Evaluation Criteria In Solid Tumors criteria
* Surgically or medically castrated with testosterone levels of \<50 ng/dL
* Eastern Cooperative Oncology Group (ECOG) Performance Status of \<=2
* Group A only: genomic testing at screening indicating CYP2D6 extensive metabolizer status
* Protocol-defined laboratory values

Exclusion Criteria:

* Serious or uncontrolled co-existent non-malignant disease, including active and uncontrolled infection
* Group A only: genomic testing at screening indicating CYP2D6 non-extensive metabolizer status, or prior treatment with dextromethorphan-containing medication or any medication that is a strong inhibitor or inducer of CYP2D6 within 5 half-lives of that drug or 7 days, whichever is longer, prior to Cycle 1 Day -8
* Group B only: prior treatment with theophylline or any medication that is a strong inhibitor or inducer of CYP1A2 within 5 half-lives of that drug or 7 days, whichever is longer, prior to Cycle 1 Day -8
* Abnormal liver function
* Uncontrolled hypertension (repeated systolic blood pressure \>=160 mmHg, or diastolic blood pressure \>=95 mmHg)
* Active or symptomatic viral hepatitis or chronic liver disease
* Known brain metastasis
* History of pituitary or adrenal dysfunction
* Clinically significant heart disease as evidenced by myocardial infarction, or arterial thrombotic events in the past 6 months, severe or unstable angina, or New York Heart Association Class III or IV heart disease or cardiac ejection fraction measurement of \<50% at baseline
* History of gastrointestinal disorders (medical disorders or extensive surgery) which may interfere with the absorption of the study drug
* Surgery or local prostatic intervention within 28 days of the first dose, and any clinically relevant sequelae from the surgery must have resolved prior to Cycle 1 Day 1
* Radiotherapy or immunotherapy within 28 days, or single fraction of palliative radiotherapy within 14 days of administration of Cycle 1 Day 1
* Any acute toxicities due to prior therapy that have not resolved
* Current enrollment in an investigational drug or device study or participation in such a study within 28 days of Cycle 1 Day 1
* Previous abiraterone acetate or other investigational CYP17 inhibitor (eg, TAK-700)