Differential activities of 1 alpha,25-dihydroxy-16-ene-vitamin D-3 analogsand their 3-epimers on human promyelocytic leukemia (HL-60) cell differentiation and apoptosis

To clarify physiological role of the carbon 3 (C-3) epimerization of 1 alph a ,25(OH)(2)D-3 and biologic significance of a 3-epi metabolite of 1 alpha ,25(OH)(2)D-3, we examined biologic activities of the 3- epimers of 1 alpha ,25(OH)(2)D-3 and 1 alpha ,25(OH)(2)-16-ene-D-3 analogs in terms of modula tion of cell cycle phase distribution and cell-surface CD11b antigen expres sion of HL-60 cells, transactivation of vitamin D target genes in transfect ed cells, stimulation of VDR/RXR alpha heterodimer formation in a rabbit re ticulocyte lysates transcription/translation system, stimulation of VDR/RXR alpha /VDRE complex formation, and induction of HL-60 cell apoptosis. The analogs tested here were I) 1 alpha ,25(OH)(2)D-3, 2) 1 alpha ,25(OH)(2)-3- epi-D-3, 3) 1 alpha ,25(OH)(2)-16-ene-D-3, 4) 1 alpha ,25(OH)(2)-16-ene-3-e pi-D-3, 5) 1 alpha ,25(OH)(2)-16-ene-23-yne-hexafluoro(F-6)-D-3, 6) 1 alpha ,25(OH)(2)-16-ene-23-yne-hexafluoro(F-6)-3-epi-D-3, 7) 1 alpha ,25-(OH)(2) -16-ene-20-epi-23-yne-D-3. and 8) 1 alpha ,25(OH)(2)16-ene-20-epi-23-yne-3- epi-D-3. When compared to the 3-natural (beta) analogs, the 3-epi (alpha) a nalogs were biologically significantly less active. The findings support th e hypothesis that the C-3 epimerization is an inactivation pathway of la,25 (OH),D, and its analogs in vitamin D target tissues. We also found that the 3-epi analogs, but not the 3-natural (P) analogs, were the potent inducers of apoptosis of HL-60 cells. These results suggest that the analogs could be divided into two groups, in which the 3-epi analogs were the potent indu cers of apoptosis of HL-60 cells, and the 3-natural analogs were the potent modulators of HL-60 cell growth and differentiation. This is the first rep ort demonstrating that the 3-epimerization of the hydroxyl group at C-3 of the A-ring of 1 alpha ,25(OH)(2)D-3 plays an important role to modulate HL- 60 cell differentiation and apoptosis. (C) 2001 Elsevier Science Inc. All r ights reserved.