OGX-427 in Metastatic Castrate-Resistant Prostate Cancer With Prostate-Specific Antigen Progression While Receiving Abiraterone

Inclusion Criteria: Subjects must meet ALL of the following criteria to be eligible for inclusion into the study. * Histological or cytological diagnosis of adenocarcinoma of the prostate * Metastatic disease on chest, abdominal, or pelvic computed tomography (CT) scan and/or bone scan * Currently receiving abiraterone acetate and prednisone and meeting the following criteria: * Any PSA decline within 12 weeks from initiation of abiraterone acetate * Currently tolerating abiraterone acetate (1000 mg oral daily) and prednisone (10-20 mg oral daily) * PSA progression, defined as an increase in PSA which is ≥25% above the nadir and an absolute value of ≥2 ng/mL, which is confirmed by a second value ≥2 weeks later. * No evidence of symptomatic or radiographic progression that would require alternative therapy (e.g., needing radiation therapy for pain or significant progression of visceral metastases or \>33% increase in daily opioid use within 2 weeks prior to randomization). * All patients who have not had a surgical orchiectomy must continue treatment with a luteinizing hormone-releasing hormone (LHRH) agonist or antagonist to maintain a castrate level of testosterone. * Patient must fulfill "Prior Therapy" criteria as follows: * Chemotherapy: no more than 1 prior chemotherapy regimen for castrate-resistant prostate cancer (CRPC) is permitted; a minimum of at least 28 days must have passed since the last dose of chemotherapy. * Hormone therapy: hormonal androgen ablation therapy prior to abiraterone is required. * Experimental therapy: prior non-cytotoxic experimental therapy is permitted provided a minimum of at least 14 days has passed since completing therapy. Prior treatment with enzalutamide (MDV3100) is allowed. * Radiation: prior external beam radiation is permitted provided a minimum of at least 14 days have passed since completing radiotherapy (exception for radiotherapy: at least 7 days since completing a single fraction of ≤800 cGy to a restricted field or limited-field radiotherapy to non-marrow bearing area such as an extremity or orbit) at the time of randomization * Must be willing to use effective contraception throughout study treatment and for 3 months after completion of study treatment if able to father a child. * Must be willing not to change (add or subtract) bone protecting therapy (bisphosphonates and/or denosumab) during the study unless changed for toxicity. * Written informed consent must be obtained prior to any protocol-specific procedures being performed. Exclusion Criteria: Subjects meeting ANY of the following exclusion criteria will NOT be eligible for inclusion into the study: * Currently receiving abiraterone acetate in combination with any other anti-cancer agent (except prednisone) * Documented brain metastases, or carcinomatous meningitis, treated or untreated (Brain imaging for asymptomatic patients is not required.) * Cord compression requiring surgery or radiation therapy while on abiraterone treatment * Active second malignancy (including lymphoid malignancies such as chronic lymphocytic leukemia or low grade lymphoma) defined, in general, as requiring anticancer therapy or at high risk of recurrence during the study; not including adequately treated non melanomatous skin cancer or other solid tumors curatively treated with no evidence of disease in \> 3 years * History of allergic reactions to therapeutic antisense oligonucleotides * Active autoimmune disease requiring treatment * Participated in a prior Phase 3 clinical study evaluating custirsen regardless of study arm assignment (i.e., either control or investigational arm), or prior exposure to OGX-427 * Uncontrolled medical conditions such as myocardial infarction, uncontrolled hypertension, stroke or treatment of a major active infection within 3 months of randomization, as well as any significant concurrent medical illness that in the opinion of the Investigator would preclude protocol therapy * Planned concomitant participation in another clinical trial of an experimental agent, vaccine, or device. Concomitant participation in observational studies is acceptable.