The anti-diabetic drug metformin inhibits prostate cancer cell growth and reduces AR protein levels. Prostate cancer and immortalized benign prostate epithelial cells were treated with increasing concentrations of metformin. After 96 h cell numbers were counted and AR levels determined by western blot. (A), AR-positive cell lines, (B), AR negative cell lines, and (C), immortalized benign prostate epithelial cell lines. (D, E), AR protein levels determined by quantification of western blot bands in AR positive cell lines. Each experiment was repeated at least 3 times. Representative western blot flouroscan images are shown in (E). Statistical significant differences are indicated as *, p < 0.05; **, p <0.01 and ***, p < 0.001.