OMAHA-4: The purpose of this study is to assess the efficacy and safety of targeted therapy (called opevesostat) plus hormone replacement therapy (HRT) compared to other treatments in people with metastatic castration-resistant prostate cancer (mCRPC) who have had previous treatment with a next-generation hormonal agentA Phase 3, Randomized, Open-label Study of MK-5684 Versus Alternative Abiraterone Acetate or Enzalutamide in Participants With Metastatic Castration-resistant Prostate Cancer (mCRPC) That Progressed On or After Prior Treatment With One Next-generation Hormonal Agent (NHA)

Exclusion

The main exclusion criteria include but are not limited to the following:

• Has presence of gastrointestinal condition
• Is unable to swallow capsules/tablets
• Has history of pituitary dysfunction
• Has poorly controlled diabetes mellitus
• Has a history of active or unstable cardio/cerebro-vascular disease, including thromboembolic events
• Has clinically significant abnormal serum potassium or sodium level
• Has any of the following at screening visit: Hypotension: systolic blood pressure (BP) <110 mmHg, or Uncontrolled hypertension: systolic BP >160mmHg or diastolic blood BP >90 mmHg, in 2 out of the 3 recordings with optimized antihypertensive therapy
• History or family history of long QTc syndrome
• Has a history of seizure(s) within 6 months prior to signing the informed consent (IC) or has any condition that may predispose to seizure within 12 months prior to the date of enrollment
• Has a history of clinically significant ventricular arrhythmias or Mobitz II second degree or third-degree heart block without a permanent pacemaker in place
• Has received a taxane-based chemotherapy and or NHA for metastatic castration-resistant prostate cancer (mCRPC)
• Has not adequately recovered from major surgery or have ongoing surgical complications
• Has received prior treatment with radium for prostate cancer
• Is currently being treated with Cytochrome P450 (CYP450)-inducing antiepileptic drugs for seizures
• Participants on an unstable dose of thyroid hormone therapy within 6 months before the start of the study intervention
• Receives prior radiotherapy within 2 weeks before the first dose of study intervention, or radiation-related toxicities, requiring corticosteroids
• Receives prior systemic anticancer therapy including investigational agents within 4 weeks before the first dose of study intervention
• Has systemic use of strong Cytochrome P450 3A4 (CYP3A4) inducers and P-glycoprotein (P-gp) inhibitors within 2 weeks before the first dose of study intervention
• Has received prior targeted small molecule therapy or NHA treatment within 4 weeks before the first dose of study intervention
• Received a live or live-attenuated vaccine within 30 days before the first dose of study intervention
• Has received an investigational agent or has used an investigational device within 4 weeks prior to study intervention administration
• Has known hypersensitivity to the components or excipients in abiraterone acetate, prednisone or prednisolone, enzalutamide, fludrocortisone, dexamethasone, or opevesostat.
• Has a "superscan" bone scan defined as an intense symmetric activity in the bones and diminished renal parenchymal activity on baseline bone scan such that the presence of additional metastases in the future could not be evaluated
• Has known additional malignancy that is progressing or has required active treatment within the past 3 years
• Diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior the first dose of study medication
• Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Participants with previously treated brain metastases may participate provided they are radiologically stable, (ie, without evidence of progression) for at least 4 weeks as confirmed by repeat imaging performed during study screening, are clinically stable and have not required steroid treatment for at least 14 days prior to the first dose of study intervention
• Has active autoimmune disease that has required systemic treatment in the past 2 years. Replacement therapy is allowed
• Active infection requiring systemic therapy
• Has concurrent active Hepatitis B virus and Hepatitis C virus infection