Key Inclusion Criteria:

          1. A diagnosis of adenocarcinoma of the prostate confirmed by histologic or cytologic
             evidence and with a documented medical history of either:

               -  High-risk, mCSPC defined as having at least two of three risk factors at the
                  baseline (Day 1) visit:

                    -  Total Gleason score of ≥ 6;

                    -  Presence of ≥ 2 metastatic lesions on bone scan;

                    -  Evidence of measurable visceral metastases with exception of hepatic
                       metastases.

               -  mCRPC defined as disease progression despite maintaining castration levels of
                  testosterone with androgen deprivation therapy:

                    -  An increase in prostate-specific antigen ≥ 25% and ≥ 2 ng/mL above the
                       nadir, confirmed by 2 measurements at least 3 weeks apart, and;

                    -  The progression of pre-existing disease as evidenced either by worsening
                       symptoms and/or enlarged metastatic lesions; and/or;

                    -  The development of new metastases.

          2. Currently receiving standard-of-care treatment of leuprolide acetate [3-, 4-, or
             6-month injections (intramuscular Lupron or subcutaneous Eligard)] and abiraterone
             1000 mg once daily plus prednisone 5 mg once daily for participants with mCSPC or
             twice daily for participants with mCRPC and in whom abiraterone has been well
             tolerated (that is, without evidence of hepatotoxicity requiring dose adjustment for
             abiraterone) for a minimum of 12 weeks prior to initiation of the study treatment
             period.

        Key Exclusion Criteria:

          1. Received treatment with a gonadotropin-releasing hormone receptor agonist or
             antagonist in combination with abiraterone plus prednisone in high-risk mCSPC
             participants for a total duration > 24 months or in mCRPC participants for a total
             duration > 6 months.

          2. Abnormal clinical laboratory test value(s) suggestive of clinically unstable
             underlying disease or a clinical laboratory test value(s) at the screening visit or
             prior to the baseline (Day 1) visit including:

               -  Serum alanine aminotransferase and/or aspartate aminotransferase > upper limit of
                  normal (ULN) (confirmed twice during screening at least 14 days apart);

               -  Total bilirubin > ULN (unless values are consistent with Gilbert's syndrome for
                  which the total bilirubin cannot exceed > 3x ULN);

               -  Serum creatinine > 2.0 mg/dL;

               -  Potassium < 3.5 milliequivalents/liter;

               -  Platelets < 100 × 10^3/microliter (μL);

               -  Hemoglobin < 10.0 grams/dL;

               -  Leukocytes < 3 × 10^3/μL;

               -  Absolute neutrophil count < 1.5 × 10^3/μL;

               -  Hemoglobin A1c > 8%.

          3. A medical history within 6 months prior to the screening visit of the following
             (myocardial infarction; unstable angina; unstable symptomatic ischemic heart disease;
             New York Heart Association class III or IV heart failure; thromboembolic event[s]) and
             any other significant cardiac conditions.

          4. An abnormal electrocardiogram finding

          5. Uncontrolled hypertension

          6. Hypotension

          7. Bradycardia