MC-1046 (Impurity A of Calcipotriol) is the C22-23-unsaturated 24-ketone, an active metabolite of the synthetic vitamin D analog calcipotriol (calcipotriene, MC 903). Calcipotriene is a ligand of VDR-like receptors approved for topical dermatological use indicated for the treatment of plaque psoriasis. It is approved by FDA in United States under the trade name Dovonex. Calcipotriol displays minimal effects on calcium homeostasis, and regulates cell differentiation, and proliferation exhibiting antiproliferative activity against human HL-60, HL60/MX2, MCF-7, T47D, SCC-25 and mouse WEHI-3 cancer cell lines. Calcipotriol is an effective anti-proliferative agent when applied topically at high concentrations but it is relatively “noncalcemic” in vivo (administered perorally, intravenously or intraperitoneally) because it can be metabolized by a variety of cells to metabolites with reduced biological activity as was demonstrated in vitro using rat and human cell lines from liver, bone, kidney, and keratinocytes. MC1046 is the initial calcipotriol metabolite which concentration reaches a steady state after 4 h of incubation with cells in vitro whereas the concentration of another major MC 903 metabolite MC1080, C22-23-saturated 24-ketone, continues to increase linearly over the time period tested (20 h). These two metabolites have also been detected in vivo in serum from rats and pigs dosed with MC903. MC1046 has the ability to stimulate e VDRE-mediated human growth hormone production in COS-1 cells co-transfected with pSG5hVDR1/3 and (CT4)4TKGH vectors and also binds to VDR although with lower (1/133) binding affinity compared to calcipotriol.