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, HEXAFLUORO-1-ALPHA,23(S),25-TRIHYDROXYVITAMIN-D(3)

To study whether the introduction of fluoro atoms into C-26 and C-27 p ositions on the 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] molec ule could affect metabolism in human promyelocytic leukaemia (HL-60) c ells, we compared the metabolism of ,26,27,27,27-hexafluoro-1alpha,25- dihydroxyvitamin D3 [26,27-F6-1alpha,25(OH)2D3] and 1alpha,25(OH)2D3 i n HL-60 cells. 26,27-F6-1alpha,25(OH)2D3 was mainly converted into a n ew bioactive metabolite, 27,27-hexafluoro-1alpha,23(S),25-trihydroxyvi tamin D3 [26,27-F6-1alpha,23(S),25(OH)3 D3], but not into 27,27-hexafl uoro-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 b y combinations of h.p.l.c., u.v. spectroscopy and g.c. mass spectromet ry. Evidence is presented that 26,27-F6-1alpha,25(OH)2D2 was metaboliz ed 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 d eactivated and metabolized to 1alpha,24(R),25(OH)3D3 by C-24 hydroxyla tion through a side=chain oxidation pathway resulting in C23-C24 cleav age, yielding 24,25,26,27-tetranor-1alpha,23(OH)2D3 in HL-60 cells. Th ese results show that 26,27-F6-1alpha,25(OH)2D3 and 1alpha,25(OH)2D3 a re metabolized by different metabolic pathways in HL-60 cells.