Inclusion Criteria:

          -  Willing and able to provide written informed consent (ICF) and HIPAA authorization for
             the release of personal health information. A signed informed consent must be obtained
             before screening procedures are performed.

        NOTE: HIPAA authorization may be either included in the informed consent or obtained
        separately.

          -  Males 18 years of age and above

          -  Histological or cytological proof of prostate cancer

          -  Documented progressive mCRPC based on at least one of the following criteria:

               1. PSA progression defined as 25% increase over baseline value with an increase in
                  the absolute value of at least 1.0 ng/mL that is confirmed by another PSA level
                  with a minimum of a 1 week interval and a minimum PSA of 1.0 ng/mL.

               2. Soft-tissue progression defined as an increase ≥ 20% in the sum of the LD of all
                  target lesions based on the smallest sum LD since treatment started or the
                  appearance of one or more new lesions.

               3. Progression of bone disease (evaluable disease) or two or more new bone lesions
                  by bone scan.

          -  Two or more bone lesions

          -  ECOG 0- 1

          -  Normal organ function with acceptable initial laboratory values within 14 days of
             randomization:

               -  Albumin > 30 g/L

               -  ANC ≥ 1.5 x 10^9/L

               -  Hemoglobin ≥ 10 g/dL

               -  Platelet count ≥ 100 x 10^9/L

               -  Creatinine ≤ 1.5 x the institutional upper limit of normal (ULN)

               -  Bilirubin ≤ ULN (unless documented Gilbert's disease)

               -  SGOT (AST) ≤ 1.5 x ULN

               -  SGPT (ALT) ≤ 1.5 x ULN

               -  WBC count ≥ 3 x 10^9/L

          -  Subjects must agree to use a medically acceptable method of birth control (e.g.,
             spermicide in conjunction with a barrier such as a condom) or sexual abstinence for
             the duration of the study, including 30 days after the last dose of study drug. Sperm
             donation is prohibited during the study and for 30 days after the last dose of study
             drug. Female partners must use hormonal or barrier contraception unless postmenopausal
             or abstinent.

          -  Serum testosterone < 50 ng/dL. Subjects must continue primary androgen deprivation
             with an LHRH analogue (agonist or antagonist) if they have not undergone orchiectomy.

          -  All acute toxic effects of any prior treatment have resolved to NCI-CTCAE v4.0 Grade 1
             or less.

          -  Willing and able to comply with the protocol, including follow-up visits and
             examinations

        Exclusion Criteria:

          -  Received any other investigational therapeutic agents or other anticancer therapies
             within 4 weeks prior to randomization.

          -  Received external beam radiotherapy within the 4 weeks prior to randomization.

          -  Has an immediate need for external beam radiotherapy.

          -  Has received any systemic bone-seeking radiopharmaceutical in the past.

          -  Has received any prostate cancer directed chemotherapy in the castration resistant
             setting. Subjects who have received up to 6 prior doses of docetaxel in the castration
             sensitive setting are permitted if they have not experienced disease progression
             within 36 weeks of last treatment with docetaxel.

          -  Has received four or more systemic anticancer regimens for mCRPC.

               -  Treatment with docetaxel or abiraterone for non-castrate metastatic disease is
                  permissible and does not count towards the lines of therapy for mCRPC

               -  A 'line' is a regimen. Combinations of hormones and other types of therapies
                  count as single lines.

          -  Has known Grade ≥3 docetaxel-related toxicities or docetaxel toxicity related dose
             interruption or discontinuation.

          -  Has received blood transfusions or growth factors within the last 4 weeks prior to
             randomization.

          -  Symptomatic nodal disease (i.e., scrotal, penile, or leg edema).

          -  Has visceral metastases with ≥ 3 lung and/or liver metastases or individual lesion ≥2
             cm, as assessed by CT scan or MRI of the chest/abdomen/pelvis within the last 8 weeks
             prior to randomization.

          -  Symptomatic loco-regional disease that causes ongoing Grade 3 or Grade 4 urinary or
             rectal symptoms.

          -  Subjects with a "currently active" second malignancy other than non-melanoma skin
             cancers or non-invasive bladder cancers or other in-situ or non-invasive malignancies.
             Subjects are not considered to have a "currently active" malignancy if they have
             completed therapy and are free of disease for ≥ 3 years.

          -  Has imminent or established cord compression based on clinical findings and/or MRI.

          -  Known bone marrow dysplasia

          -  Has received any of the following in the 4 weeks prior to randomization:
             5-alpha-reductase inhibitors, herbal medications, natural hormonally active foods
             (e.g., phytoestrogens) or other food supplements known to alter PSA in humans

          -  Any other serious illness or medical condition that would, in the opinion of the
             investigator, make this protocol unreasonably hazardous, including but not limited to:

               -  Uncontrolled infection

               -  NYHA III or IV heart failure

               -  Crohn's disease or those with ulcerative colitis who have not undergone a
                  colectomy

               -  Known active infection with HIV, Hepatitis B or Hepatitis C