A Phase II Study of Increased-Dose Abiraterone Acetate in Patients With Castration Resistant Prostate Cancer

This is a phase II multicenter trial of Abiraterone Acetate (AA) in patients with progressive prostate cancer despite androgen deprivation with a particular focus on the pharmacokinetic, pharmacodynamic, and pharmacogenomic events occurring at the time of apparent drug resistance. All eligible patients will have baseline (prior to taking the first dose of Abiraterone Acetate 1000mg/daily) measures of routine clinical variables along with measurements of baseline and treatment related changes in testosterone, androgen, and endocrine levels, genotyping of single-nucleotide polymorphisms (SNP) in the selected enzymes known to be directly inhibited by Abiraterone Acetate, and collection of circulating tumor cells. All patients will be requested to consent for biopsies which will be performed prior to treatment and at the time of disease progression on standard dose Abiraterone Acetate therapy. These biopsies will be analyzed for expression of an androgen receptor (AR)-signature as well as for microarray analysis to explore changes in methylation, and expression of CYP17A1 and other androgen synthesis genes. Subjects will then begin daily oral therapy with Abiraterone Acetate 1000mg po daily with physiologic prednisone 5mg BID replacement. No food should be consumed for at least 2 hours before the dose of Abiraterone Acetate and for at least 1 hour after the dose of Abiraterone Acetate is taken. Prostate-specific antigen (PSA) will be followed monthly. Abiraterone Acetate will be supplied by Janssen Services. At the end of the first month, the third month, and then every three months thereafter, Abiraterone Acetate, testosterone, and androgen levels will be followed. Subjects not achieving a greater than or equal to 30% PSA decline at 12 weeks will be taken off study. At the time of progression (defined by RECIST criteria OR by the Prostate Cancer Working Group 2 (PCWG) criteria as a 25% increase in PSA above the nadir and an increase in the absolute value PSA of at least 2ng/dl or back to baseline confirmed at least 2 weeks afterward) for subjects who achieved an initial greater than or equal to 30% PSA decline (referred to as Progressive Disease (PD) #1), subjects will begin taking Abiraterone Acetate 1000 mg po BID. Patients will continue to take prednisone 5mg twice a day (BID) and will continue this therapy until a second progression at which point they will be withdrawn from the study. While 1000 mg po BID is not the FDA recommended dose, it is the dose to be investigated in this study.