AMG 386 and Abiraterone for Advanced Prostate Cancer

Background: * Inhibition of angiogenesis, either as a stand-alone approach or in combination with chemotherapy, has demonstrable antitumor efficacy against castration-resistant prostate cancer (CRPC) and there are several antiangiogenic agents that are now in clinical trials in this population of patients. * AMG 386 is a novel peptide-Fc fusion protein. The molecule is a non-glycosylated homodimer engineered by fusing an Immunoglobulin gamma-1 heavy chain constant region, partial (IgG1 Fc) domain to 4 copies of an anti-angiopoietin 2 (Ang2) peptide. AMG 386 sequesters Ang1 and Ang2, thereby preventing their interaction with Tie2 and inhibiting tumor endothelial cell (EC) proliferation and tumor growth. * Abiraterone acetate is a small molecule that irreversibly inhibits Cytochrome P450 17A1 (CYP17), a rate-limiting enzyme in androgen biosynthesis, to block residual androgen synthesis in the adrenal gland and tumor cells. * Previous studies have demonstrated that in vivo alterations of testosterone levels regulate the expression of vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and angiopoietin family members. Dual targeting of the androgen and angiogenic axis represents a novel approach as a potential targeted therapy for patients with metastatic castration-resistant prostate cancer (CRPC). Objectives: -To estimate the treatment effect as measured by progression free survival (PFS) in patients treated with AMG 386 plus abiraterone/prednisone relative to abiraterone/prednisone alone. Eligibility: -Patients with progressive, metastatic CRPC with radiographic evidence of progression after primary therapy (surgery or radiotherapy) and adequate androgen deprivation therapy. Design: * This is an open-label, randomized, phase II multicenter trial with a two-part design and a planned accrual of 88 patients. * An initial run-in phase of AMG 386 will be conducted with 15mg/kg weekly escalating to 30mg/kg weekly to establish the MTD. The decision on declaration of a safe and tolerable dose during this run-in phase will lead to the second part of the study consisting of a randomized comparison of abiraterone/prednisone plus AMG 386 (at the established maximum tolerated dose (MTD)) vs. abiraterone/prednisone alone. * AMG 386 will be administered intravenously every week, on days 1, 8, 15 and 22 of each 28-day cycle. Abiraterone acetate will be self-administered once daily by mouth and prednisone will be self-administered by mouth either twice per day at 5 mg per dose or once per day at 10 mg per dose as the patient prefers.