Retinoids and their biological effects against cancer.

There are more than 4000 natural and synthetic molecules structurally and/or functionally related to vitamin A. Retinoids are a class of these compounds that are structurally associated to vitamin A. The retinoids have a wide spectrum of functions. Retinoic acid, which is the active metabolite of retinol, regulates a wide range of biological processes including development, differentiation, proliferation and apoptosis. It suppresses carcinogenesis in tumorigenic animal models for the skin, oral, lung, breast, bladder, ovarian and prostate. It is important how major retinoids may act in cancer treatment or prevention. The reports have indicated that lower levels of vitamin A in humans may be associated with relative type 1 cytokine dominance and a higher proportion of NK cells. In addition, very low vitamin A levels would be undesirable explaining the essential role of vitamin A in epithelial and general cell maturation and function. However, the cytokine shifts associated with moderately low levels of vitamin A may be in some ways beneficial in an environment where HIV infection, M. tuberculosis infection, or other type 1 infections are highly prevalent and/or when acquired immunity is cooperated. In this review, we intend to describe the biochemical and immunological functions of retinoids against cancer.