Prostate cancer is the second most common cancer among men and the leading cause of death after lung cancer. Development of hormone-refractory disease is a crucial step for prostate cancer progression for which an effective treatment option is currently unavailable. Therefore, there is a need for new agents that can efficiently target cancer cells, decrease tumor growth, and thereby extend the survival of patients in late-stage castration-resistant prostate cancer. In the current study, a novel heterodinuclear copper(II)Mn(II) Schiff base complex combined with P85 was used to evaluate anticancer activity against prostate cancer in vitro and in vivo. Cell proliferation and cytotoxicity were evaluated by cell viability, gene, and protein expression assays in vitro. Results showed that the heterodinuclear copper(II)Mn(II) complex–P85 combination decreased cell proliferation by upregulating the apoptotic gene expressions and blocking the cell proliferation-related pathways. Tramp-C1-injected C57/B16 mice were used to mimic a prostate cancer model. Treatment combination of Schiff base complex and P85 significantly enhanced the cellular uptake of chemicals (by blocking the drug transporters and increased life time), suppressed tumor growth, and decreased tumor volume steadily over the course of the experiments. Overall, heterodinuclear copper(II)Mn(II) complex–P85 showed remarkable anticancer activity against prostate cancer in in vitro and in vivo.