MODIFICATION OF 1-ALPHA,25-DIHYDROXYVITAMIN-D(3) METABOLISM BY INTRODUCTION OF 26,26,26,27,27,27-HEXAFLUORO ATOMS IN HUMAN PROMYELOCYTIC LEUKEMIA (HL-60) CELLS - ISOLATION AND IDENTIFICATION OF A NOVEL BIOACTIVE METABOLITE, 26,26,26,27,27,27-HEXAFLUORO-1-ALPHA,23(S),25-TRIHYDROXYVITAMIN-D(3)

To study whether the introduction of fluoro atoms into C-26 and C-27 positions on the 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] molecule could affect metabolism in human promyelocytic leukaemia (HL-60) cells, we compared the metabolism of 26,26,26,27,27,27-hexafluoro-1alpha,25-dihydroxyvitamin D3 [26,27-F6-1alpha,25(OH)2D3] and 1alpha,25(OH)2D3 in HL-60 cells. 26,27-F6-1alpha,25(OH)2D3 was mainly converted into a new bioactive metabolite, 26,26,26,27,27,27-hexafluoro-1alpha,23(S),25-trihydroxyvitamin D3 [26,27-F6-1alpha,23(S),25(OH)3 D3], but not into 26,26,26,27,27,27-hexafluoro-1alpha,24(R),25-trihydroxyvitamin D3 [26,27-F6-1alpha,24(R),25(OH)3D3] in HL-60 cells. 26,27-F6-1alpha,23(S),25(OH)3D3 was identified by combinations of h.p.l.c., u.v. spectroscopy and g.c. mass spectrometry. Evidence is presented that 26,27-F6-1alpha,25(OH)2D2 was metabolized to 26,27-F6-1alpha,23(S),25(OH)3D3 by C-23 hydroxylation as a first step of the metabolism, and the 23-hydroxylated bioactive metabolite was accumulated in the cells, whereas 1alpha,25(OH)2D3 was initially deactivated and metabolized to 1alpha,24(R),25(OH)3D3 by C-24 hydroxylation through a side=chain oxidation pathway resulting in C23-C24 cleavage, yielding 24,25,26,27-tetranor-1alpha,23(OH)2D3 in HL-60 cells. These results show that 26,27-F6-1alpha,25(OH)2D3 and 1alpha,25(OH)2D3 are metabolized by different metabolic pathways in HL-60 cells.