Metformin, a well-known antidiabetic drug, has been reported to inhibit the androgen-dependent proliferation of prostate cancer cells by inhibiting the function of AR and the expression of its target genes; in this process, small heterodimer partner-interacting leucine zipper (SMILE), which is a nuclear receptor coregulator whose protein level can be increased by metformin, competes with SRC-1 to bind AR to inhibit SRC-1-mediated transactivation [106]. This evidence concerns the gene AR and prostate cancer.