20-Hydroxyvitamin D2 is a noncalcemic analog of vitamin D with potent antiproliferative and prodifferentiation activities in normal and malignant cells

Slominski AT, Kim T, Janjetovic Z, Tuckey RC, Bieniek R, Yu e J, Li W, Chen J, Nguyen MN, Tang EK, Miller D, Chen TC, Holick M. 20-hydroxyvitamin D-2 is a noncalcemic analog of vitamin D with potent antiproliferative and prodifferentiation activities in normal and malignant cells. Am J Physiol Cell Physiol 300: C526-C541, 2011. First published December 15, 2010; doi:10.1152/ajpcell. 00203.2010.-20-hydroxyvitamin D-2 [20(OH)D-2] inhibits DNA synthesis in epidermal keratinocytes, melanocytes, and melanoma cells in a dose-and time-dependent manner. This inhibition is dependent on cell type, with keratinocytes and melanoma cells being more sensitive than normal melanocytes. The antiproliferative activity of 20(OH)D-2 is similar to that of 1,25(OH)(2)D-3 and of newly synthesized 1,20(OH)(2)D-2 but significantly higher than that of 25(OH)D-3. 20(OH)D-2 also displays tumorostatic effects. In keratinocytes 20(OH)D-2 inhibits expression of cyclins and stimulates involucrin expression. It also stimulates CYP24 expression, however, to a significantly lower degree than that by 1,25(OH)(2)D-3 or 25(OH)D-3. 20(OH)D-2 is a poor substrate for CYP27B1 with overall catalytic efficiency being 24- and 41-fold lower than for 25(OH)D-3 with the mouse and human enzymes, respectively. No conversion of 20(OH)D-2 to 1,20(OH)(2)D-2 was detected in intact HaCaT keratinocytes. 20(OH)D-2 also demonstrates anti-leukemic activity but with lower potency than 1,25(OH)(2)D-3. The phenotypic effects of 20(OH)D-2 are mediated through interaction with the vitamin D receptor (VDR) as documented by attenuation of cell proliferation after silencing of VDR, by enhancement of the inhibitory effect through stable overexpression of VDR and by the demonstration that 20(OH)D-2 induces time-dependent translocation of VDR from the cytoplasm to the nucleus at a comparable rate to that for 1,25(OH)(2)D-3. In vivo tests show that while 1,25(OH)(2)D-3 at doses as low as 0.8 mu g/kg induces calcium deposits in the kidney and heart, 20(OH)D-2 is devoid of such activity even at doses as high as 4 mu g/kg. Silencing of CY27B1 in human keratinocytes showed that 20(OH)D-2 does not require its transformation to 1,20(OH)(2)D-2 for its biological activity. Thus 20(OH) D-2 shows cell-type dependent antiproliferative and prodifferentiation activities through activation of VDR, while having no detectable toxic calcemic activity, and is a poor substrate for CYP27B1. melanocytes;