MTOR and prostate cancer: Although the main molecular target of metformin is AMPK [26], several AMPK-dependent and independent mechanisms by which metformin inhibits prostate cancer growth have been reported, such as suppression of cyclin D1 expression [20], mTOR inhibition [27], inhibition of androgen-induced IGF–1 receptor up-regulation [28], and inhibition of lipogenesis [29].