Background: The tumor microenvironment contains high levels of immunosuppressive adenosine, which binds to and activates the A_2a and A_2b receptors (R) on immune cells, resulting in an ineffective anti-tumor immune response. Extracellular adenosine is primarily produced by the enzyme CD73. In prostate cancer (PC), the activity of prostatic acid phosphatase produces additional adenosine. AB928 is the first clinical-stage small molecule dual antagonist of both A_2aR and A_2bR, which is highly potent, pharmacodynamically active, and has been well tolerated in dose escalation studies as a single agent or in combination with chemo/immunotherapy. Targeting the adenosine pathway in combination with standard of care regimens may have a more profound effect on activating and inducing sustained anti-tumor immunity. Methods: This Phase 1b/2, open-label, multi-cohort platform study will evaluate the efficacy and safety of AB928 combination therapy in participants with metastatic castrate resistant PC (mCRPC). Each cohort will independently assess AB928 plus AB122 (anti-PD-1 antibody) in combination with standard of care (SOC; enzalutamide, docetaxel) or AB928 plus AB680 (CD73 inhibitor) with or without AB122. Cohort eligibility is informed by prior treatment history. In Ph1b, up to 15 participants will receive investigational products at the single-agent recommended dose with SOC per label guidance. Provided safety and activity stopping criteria are not met, further accrual will proceed in Ph2 and, depending on treatment cohort, may involve randomization to enzalutamide or docetaxel; crossover to experimental therapy will be allowed following progression on control treatment. Investigator-assessed antitumor response (radiologic, prostate specific antigen) will follow PCWG3 criteria. Conclusions: This Ph1b/2 study is the first to target the adenosine axis using a dual A_2aR/A_2bR antagonist (AB928) together with a small molecule CD73 inhibitor (AB680), anti-PD-1 antibody (AB122), and SOC for mCRPC. Study enrollment is proceeding in the United States; results will be shared in upcoming scientific conferences.