Natural and synthetic retinoids in prostate cancer

Prostate cancer (PCa) is the most common cancer for men in Europe, North America, and some parts of Africa. Initially, growth of prostate cancer is usually androgen-dependent, but often it becomes androgen-independent after androgen-deprivation therapy. Managing hormone-refractory prostate carcinoma remains a difficult challenge for clinicians. Retinoids, vitamin A and its synthetic analogs are one of the most studied class of chemopreventive drugs for PCa. Retinoids play a key role in several vital functions as vision and development, and also exert anti-proliferative actions. Anti-proliferative effects of retinoids rely on the regulation of many biological processes, including differentiation, cell proliferation, and apoptosis. Retinoid actions are mediated by two classes of nuclear proteins called retinoic acid (RARalpha,beta and gamma and retinoic alpha,beta and gamma receptors, which are ligand-regulated transcription factors. Effects of both all-trans-retinoic acid (RA), the natural active derivative of vitamin A, and its synthetic derivatives, on prostate gland or prostate cell lines implicate retinoids in the regulation of prostate growth and suppression of PCa development. Deficient retinoid availability and action at the cellular level because of either decreased content or altered metabolism in PCa cells can play a key role in abnormal cellular differentiation pathways, and the loss of anti-proliferative effects. Here we review the in vitro and in vivo effects of retinoids in PCa.