Abstract
Vitamin D is a group of seco-steroidal fat-soluble compounds. The two basic forms, vitamin D(2) (ergocalciferol) and vitamin D(3) (cholecalciferol), do not have biological activity. They are converted in the body by a two-step enzymatic hydroxylation into biologically active forms, 1α,25-dihydroxyvitamin D(2) [ercalcitriol, 1,25(OH)(2)D(2)] and 1α,25-dihydroxyvitamin D(3) [calcitriol, 1,25(OH)(2)D(3)], which act as classical steroid hormones. 1,25(OH)(2)D(3) exerts most of its physiological functions by binding to the nuclear vitamin D receptor (VDR), which is present in most body tissues to provide support to a broad range of physiological processes. Vitamin D-liganded VDR controls the expression of many genes. High levels of 1,25(OH)(2)D(3) cause an increase in calcium in the blood, which can lead to harmful hypercalcemia. Several analogs of 1,25(OH)(2)D(3) and 1,25(OH)(2)D(2) have been designed and synthesized with the aim of developing compounds that have a specific therapeutic function, for example, with potent anticancer activity and a reduced toxic calcemic effect. Particular structural modifications to vitamin D analogs have led to increased anticancer activity and reduced calcemic action with the prospect of extending work to provide future innovative therapies.