Vitamin D receptor as a drug discovery target

1alpha, 25-dihydroxyvitamin D3 [1,25 (OH)(2)D(3)], the active metabolite of vitamin D3, is known for the maintenance of normal skeleton architecture and mineral homeostasis. Apart form these traditional calcemic actions, 1,25 (OH)(3)D(1) and its synthetic analogs are increasingly recognized for their potent anti-proliferative, prodifferentiative and immunomodulatory activities. The calcemic and non-calcemic actions of 1,25 (OH)(2)D(3) and its synthetic analogs are mediated through vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. Physiological and pharmacological actions of 1,25 (OH)(2)D(3) in various systems, along with the detection of VDR in target cells, have indicated potential applications of VDR ligands in inflammation, dermatological indications, osteoporosis, cancers and autoimmune diseases. VDR ligands have shown therapeutic potential in limited clinical trials as well as in animal models of these diseases. As a result, a VDR ligand, calcipotriol is in clinic for psoriasis and another, OCT, [2-oxa-1,25 (OH)(2)D(3)] is being developed as a topical agent for the same indication. Further, 1alpha,-hydroxyvitamin D3 (alphacalcidol), a prodrug of 1,25 (OH)(2)D(3) is in clinic and a synthetic VDR ligand, ED-71, is under consideration for approval in Japan for the treatment of osteoporosis. Interestingly, VDR ligands have shown not only preventive but also potent therapeutic anabolic activities in animal models of osteoporosis. However, the wide spread use of VDR ligands in above-mentioned indications is hampered by their major side effect, namely hypercalcemia. In view of this associated toxicity, synthetic VDR ligands with reduced calcemic potential have been synthesized with the ultimate aim of improving their therapeutic efficacy. This review presents recent advances in VDR biology, novel VDR ligands and therapeutic applications of VDR ligands.