Enzalutamide and Metformin Hydrochloride in Treating Patients With Hormone-Resistant Prostate Cancer

This phase I trial studies the side effects and best dose of metformin hydrochloride when given together with enzalutamide in treating patients with prostate cancer that has not responded to previous treatment with hormones. Hormone therapy using enzalutamide may fight prostate cancer by lowering the amount of androgens the body makes and blocking the use of androgens by the tumor cells. Metformin hydrochloride, used for diabetes, may also help kill tumor cells. Giving enzalutamide together with metformin hydrochloride may kill more tumor cells.