Vitamin D analogs as anti-carcinogenic agents.
Deltanoids are the class of compounds comprising all natural and synthetic vitamin D molecules. The anti-proliferative, pro-differentiation, and pro-apoptotic properties of deltanoids have garnered interest in the fields of cancer chemoprevention and chemotherapy. The naturally occurring, biologically active form of vitamin D, 1,25(OH)2D3, causes hypercalcemia at pharmacologically relevant doses which forms a major obstacle in the clinical development of this compound. Design of new deltanoids has shown promise in separating the beneficial effects from the toxic effects. The Vitamin D receptor (VDR) is a major target for deltanoid design, and the structural features of deltanoid binding have been described. Effective compounds must also exhibit beneficial pharmacokinetic properties in vivo, and the plasma vitamin D binding protein (DBP) is likely to play an important role in the success of deltanoids in the clinic. Further, dual strategies of avoiding vitamin D toxicity through altering the dosing schedule and using less toxic deltanoids are in development. The three main categories of structural modification to the vitamin D backbone include the C,D-ring, the A-ring, and the C,D-ring side chain, and the ways each area has impacted efficacy and toxicity have been described through structure-activity relationships (SARs). Lastly, there is evidence that deltanoids can enhance the activity of other chemopreventive agents. The use of a cocktail approach will be discussed as a potential avenue for deltanoids in chemoprevention and chemotherapy.