Trial of Rad-223 Activity in Asymptomatic Patients With mCRPC While on Abiraterone or Enzalutamide Besides AR-V7 Status

Inclusion Criteria: * Subject is an adult ≥ 18 years at the time of informed consent and has signed informed consent before any trial related activities and according to local guidelines. * Subject has histologically confirmed adenocarcinoma of the prostate without neuroendocrine differentiation or small cell features. * Subject has bone metastases due to the prostate cancer and absence of visceral metastases. * Subject has a serum testosterone of ≤ 1.7 nmol/L (or ≤ 50 ng/dL) at screening. * Subject must have received a minimum of 24 weeks of treatment with abiraterone acetate or enzalutamide within its approved label indication and has discontinued use at least four weeks prior to start of study drug at day 1. * Prior use of docetaxel is allowed in castration-naïve patients (maximum of six cycles). * Subject receives and will continue to receive ongoing androgen deprivation with luteinising hormone-releasing hormone (LHRH) analogue therapy throughout the course of the study or has had a bilateral orchiectomy. * Subject is asymptomatic from prostate cancer, defined as patients with the score on brief pain inventory (short form) (BPI-SF) Question #3 must zero and no use of opiate analgesics for prostate cancer-related pain currently or anytime within two weeks prior to screening. * Subject has an Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 at screening. * Subject receiving bisphosphonate or other approved bone-targeting therapy must have been on stable doses for at least four weeks prior to start of study drug at day 1. * Subject has a life expectancy of more than or equal to 12 months. * Subject agrees not to participate in another interventional study while on study drug. * Subject and his female partner who is of childbearing potential must use two acceptable methods of birth control (one of which must include a condom as a barrier method of contraception) starting at screening and continuing throughout the study period and for six months after final study drug administration. Exclusion Criteria: * Subject has received any anti-neoplastic therapy (including ketoconazole and chemotherapy) following abiraterone acetate or enzalutamide discontinuation and prior to start of study drug at day 1. * Subject has known or suspected brain metastases or active leptomeningeal disease. * Subject has concurrent disease or any clinically significant abnormality following the investigator's review of the physical examination and safety laboratory tests at screening, which in the judgment of the investigator would interfere with the subject's participation in this study or evaluation of study results. * Subject has a history of another invasive cancer within three years prior to screening, with the exceptions of non-melanoma skin cancers or a non-infiltrating muscle bladder cancer that have a remote probability of recurrence in the opinion of the investigator in consultation with the medical monitor. * Subject had major surgery within one month prior to screening. * Subject has received investigational therapy within 28 days or 5 half lives, whichever is longer, prior to start of study drug at day 1. * Subject has absolute neutrophil count \< 1,500/μL, platelet count \< 100,000/μL, and hemoglobin \< 6.25 mmol/L (or \< 10 g/dL) at screening (Note: Subjects must not have received any growth factors or blood transfusions within seven days of the hematologic laboratory values obtained at screening). * Subject has total bilirubin \> 1.5 times the upper limit of normal (ULN) at screening, except for subjects with documented Gilbert's syndrome. * Subject has creatinine \> 2.5 mg/dL at screening. * Subject has albumin ≤ 30 g/L (or ≤ 3.0 g/dL) at screening.