Antagonistic action of novel 1α,25-dihydroxyvitamin D3-26,23-lactone analogs on 25-hydroxyvitamin-D3-24-hydroxylase gene expression induced by 1α,25-dihydroxyvitamin D3 in human promyelocytic leukemia (HL-60) cells

We have demonstrated that 1 alpha,25-dihydroxyvitamin D-3-26,23-lactone analogs, (23S)- and (23R)-25-dehydro-1 alpha-hydroxyvitamin D-3-26,23-lactone (TEI-9647, TEI-9648, respectively), inhibit HL-60 cell differentiation induced by 1 alpha,25-dihydroxyvitamin D-2 [1 alpha;25(OH)(2)D-3], but not differentiation caused by all-trans retinoic acid (D, Miura ct at, 1999, J. Biol. Chem. 274, 16392), To assess whether the antagonistic actions of TEI-9647 and TEI-9648 in HL-60 cells are related to 1 alpha,25(OH)(2)D-3 breakdown, we investigated their effects on catabolism of 1 alpha,25(OH)(2)D-3. In HL-60 cells, the C-24 but not the C-23 side-chain oxidation pathway of 1 alpha,25(OH)(2)D-3 has been reported, Here we demonstrate that 1 alpha,25(OH)(2)D-3 was metabolized both to 24,25,26,27-tetranor-1 alpha,23-(OH)(2)D-3 and 1 alpha,25(OH)(2)D-3-26,23-lactone; thus HL-60 cells constitutively possess both the 24- and the 23-hydroxylases. Metabolism of 1 alpha,25(OH)(2)D-3 was strongly suppressed by 10(-7) M TEI-9647 or 10(-6) RI:TEI-9648. 1 alpha,25(OH)(2)D-3 alone slightly induced 24-hydroxylase gene expression by 8 h with full enhancement by 24-48 h; this induction was inhibited by 10(-6) M TEI-9647 and 10(-6) M TEI-9648 (86.2 and 31.9%, respectively) 24 h after treatment, However, analogs of TEI-9647 and TEI-9648 without the 25-dehydro functionality induced 24-hydroxylase gene expression. These results indicate that TEI-9647 and TEI-9648 clearly mediate their stereoselective antagonistic actions independent of their actions to block the catabolism of 1 alpha,25(OH)(2)D-3, Therefore, TEI-9647 and TEI-9648 appear to be the first antagonists specific for the nuclear 1 alpha,25(OH)(2)D-3 receptor-mediated genomic actions of 1 alpha,25(OH)(2)D-3 in HL-60 cells, (C)2000AcademicPress.