Enzalutamide With or Without Radium Ra 223 Dichloride in Patients With Metastatic, Castration-Resistant Prostate Cancer

PRIMARY OBJECTIVES: I. To evaluate changes in prostate cancer bone involvement induced by enzalutamide alone or in combination with radium Ra 223 dichloride (radium 223), specifically extent of prostate cancer infiltration, androgen receptor (AR) signaling and hormone levels, hematopoietic composition, apoptosis and proliferation. II. To evaluate the immune activation of enzalutamide alone, or with radium 223. SECONDARY OBJECTIVES: I. To describe the adverse event profile for the combination in this patient population. II. Rate of undetectable prostate specific antigen (PSA) nadir, PSA and alkaline phosphatase changes, rate of symptomatic skeletal events at 12 months, and rate of PSA and radiographic progression at 12 months. OUTLINE: Patients are randomized to 1 of 2 arms. ARM I: Patients receive enzalutamide orally (PO) daily on days 1-28. Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. Patients also receive radium Ra 223 dichloride intravenously (IV) on day 1. Treatment repeats every 28 days for up to 6 courses in the absence of disease progression or unacceptable toxicity. ARM II: Patients receive enzalutamide as in Arm I. Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up every 3 months for 1.5 years.