Vitamin D receptor (VDR) ligands are therapeutic agents for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. VDR ligands also show immense potential as therapeutic agents for autoimmune diseases and cancers of skin, prostate, colon, and breast as well as leukemia. However, the major side effect of VDR ligands that limits their expanded use and clinical development is hypercalcemia that develops as a result of the action of these compounds mainly on intestine. In order to discover VDR ligands with less hypercalcemia liability, we sought to identify tissue-selective VDR modulators (VDRMs) that act as agonists in some cell types and lack activity in others. Here, we describe LY2108491 and LY2109866 as nonsecosteroidal VDRMs that function as potent agonists in keratinocytes, osteoblasts, and peripheral blood mononuclear cells but show poor activity in intestinal cells. Finally, these nonsecosteroidal VDRMs were less calcemic in vivo, and LY2108491 exhibited more than 270-fold improved therapeutic index over the naturally occurring VDR ligand 1,25-dihydroxyvitamin D 3 [1,25-(OH) 2 D 3 ] in an in vivo preclinical surrogate model of psoriasis.

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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.

1alpha, 25-Dihydroxyvitamin D3 [1,25-(OH)2D3], the biologically active form of vitamin D, is an important hormone that is critically required for the maintenance of mineral homeostasis and structural integrity of bones. 1,25-(OH)2D3 accomplishes this by facilitating calcium absorption from the gut and by a direct action on osteoblasts, the bone forming cells. Apart form its classical actions on the gut and bone, 1,25-(OH)2D3 and its synthetic analogs also possess potent anti-proliferative, differentiative and immunomodulatory activities. 1,25-(OH)2D3 exerts these effects through vitamin D receptor (VDR), a ligand-dependent transcription factor that belongs to the superfamily of steroid/thyroid hormone/retinoid nuclear receptors. The presence of VDR in various tissues other than gut and bone, along with their ability to exert differentiation, growth inhibitory and anti-inflammatory action, has set the stage for therapeutic exploitation of VDR ligands for the treatment of various inflammatory indications and cancer. However, the use of VDR ligands in clinic is limited by their major dose-related side effect, namely hypercalcemia/hypercalciuria. Efforts are being undertaken to develop vitamin D receptor modulators (VDRMs) that are tissue-selective and/or gene-selective in their action and these ligands may exhibit increased therapeutic indices. This review explores the recent advances in VDR biology, non-secosteroidal VDR ligands and the current and potential clinical applications of VDR ligands in inflammation and cancer.

ICI 204,219 (4-(5-cyclopentyloxycarbonylamino-1-methylindol-3-ylmethy l)-3- methoxy-N-o-tolylsulfonylbenzamide) was designed as a peptide leukotriene (LT) antagonist. The compound is a competitive antagonist of LTD4- and LTE4-induced contraction of guinea pig lung tracheal and parenchymal strips with an apparent negative log molar dissociation constant (KB) of approximately 9.6. ICI 204,219 did not antagonize LTC4-induced contractions of guinea pig trachea when the metabolism of LTC4 to LTD4 and, subsequently, to LTE4 was inhibited. The compound inhibited the binding of [3H]LTD4, [3H]LTE4, and [3H]ICI 198,615 (a potent LT antagonist from a different heterocyclic series) to guinea pig lung parenchymal membranes in a competitive manner, and also inhibited [3H]ICI 198,615 binding to human lung parenchymal membranes. ICI 204,219 did not bind to a variety of other receptors when evaluated at concentrations 1,000- to 10,000-fold higher than the apparent KB value for peptide LT receptors. When administered orally, intravenously, or by aerosol, the compound provided dose-related antagonism of the airway effects of aerosol LTD4 in conscious guinea pigs. ED50 values and pharmacodynamic t1/2 (min) for oral, intravenous and aerosol routes of administration were, respectively: 0.52 mumol/kg, greater than 816 min; 0.046 mumol/kg, 85 min; 5.1 x 10(-6) M, 109 min. ICI 204,219 also produced dose-related inhibition of the effects of LTC4 (aerosol or intravenous administration) on pulmonary mechanics in anesthetized guinea pigs when administered orally, intraduodenally, intravenously, or by aerosol. The compound also reversed bronchospasm produced by LTs. Aerosol ovalbumin antigen-induced bronchospasm in guinea pigs was both inhibited and reversed by ICI 204,219. Lastly, the compound inhibited LTD4-induced increases in cutaneous vascular permeability in guinea pigs, being 1,006- and 679-fold more potent than the first generation LT antagonists LY 171,883 and FPL 55712, respectively. ICI 204,219 is a potent, selective, orally active LT antagonist currently undergoing clinical trials.