The vitamin A metabolite retinol is essential for life, and has been shown to exhibit a diverse range of biological functions. Natural as well as synthetic molecules that are structurally related to vitamin A are referred to as retinoids, and typically consist of a polyene chain linking a cyclic end group to a polar end group. Within the cell, retinoids function as signaling molecules, and play important roles in vision, embryonic development, cell proliferation, cell differentiation and immune functions. Vitamin A is stored intracellularly as retinyl esters, which after conversion to retinol, are oxidized to more bioactive retinaldehydes or retinoic acids. The structural abundance of retinoids and subsequent bioactivity allow for a variety of therapeutic applications within the pharmaceutical and cosmetic space.
Chemotherapy and Cancer Prevention
In carcinogenesis, the intracellular levels of retinyl esters are greatly reduced, compromising retinoid signaling. In relation, extensive work has been conducted to examine the efficacy of retinoids to restore signaling for cancer therapy. These studies show retinoids are both chemopreventive and chemotherapeutic, with their activity attributed to abilities to induce cell differentiation, arrest cell proliferation and promote apoptosis in cancer cells.
All-trans retinoic acid, or tretinoin, is the most extensively studied retinoid for cancer therapies, and has been evaluated in clinical trials for the treatment of lymphoma, melanoma, lung cancer, neuroblastoma and leukemia. Retinoids have shown efficacy at preventing the onset and development of cancer, especially precancerous skin lesions. UV irradiation can cause a deficiency of vitamin A; as such, retinoid treatment can prevent aberrant signaling and skin cancer development.