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

The purpose of this study is to evaluate the effects of multiple doses of abiraterone acetate plus prednisone on the pharmacokinetics (study of what the body does to a drug) of single doses of dextromethorphan hydrobromide and theophylline in patients with castration resistant prostate cancer.

This is an open-label (identity of assigned study drug will be known) study of abiraterone acetate plus prednisone in male patients with metastatic castration-resistant prostate cancer. This study will consist of screening, treatment, and follow-up periods, and will have 2 study groups. Patients in Group A and B will receive daily abiraterone acetate (1000 mg) plus prednisone (5 mg) twice daily beginning on Cycle 1 Day 1 until disease progression. Patients in Group A will take dextromethorphan hydrobromide 30 mg administered orally once daily on Day -8 and Day 8 of Cycle 1. Patients in Group B will take theophylline 100 mg administered orally once daily on Day -8 and Day 8 of Cycle 1. Serial pharmacokinetic samples will be collected and safety will be monitored throughout the study.

Eligibility Criteria:
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)