Metabolism of 26,27-hexafluoro-1α,25-dihydroxyvitamin D₃and 26,27-hexafluoro1α,23(S)25-trihydroxyvitamin D₃in ROS17/2.8 cells transfected with a plasmid expressing CYP24

1. To clarify the possibility that the metabolism of 26,27-hexafluoro-1 alpha ,25-dihydroxyvitamin D-3 [F-6-1,25(OH)(2)D-3] to 26,27-hexafluoro-1 alpha ,23(S),25-trihydroxyvitamin D-3 [F-6-1,23,25(OH)(3)D-3 and that of F-6-1,23,25(OH)(3)D-3 to 26,27-hexafluoro-23-oxo-1 alpha ,25-dihydroxyvitamin D-3 [F-6-23-oxo-1,25(OH)(2)D-3] are catalysed by 25-hydroxyvitamin D-3 24-hydroxylase (CYP24), ROS17/2.8 cells transfected with a plasmid expressing CYP24 [pSVL-CYP24(+)] and a corresponding blank plasmid [pSLVCYP24R(-)] were used. 2. Incubation of [1 beta-H-3]-F-6-1,25(OH)(2)D-3 for 2 and 5 days with ROS17/2.8 cells transfected with pSVL-CYP24( +) generated a metabolite that co-migrated with authentic F-6-1,23,25(OH)(3)D-3 in both normal phase and reversed-phase HPLC systems. 3. Incubation of [1 beta-H-3]-F-6-1,23,25(OH)(3)D-3 for 5 days with pSVL-CYP24(+)-transfected ROS 17/2.8 cells generated a metabolite that co-migrated with authentic F-6-23-oxo-1,25(OH)(2)D-3. In contrast, the metabolites F-6-1,23,25(OH)(3)D-3 or F-6-23-oxo-1,25(OH)(2)D-3 were not generated in the cells transfected with pSVL-CYP24R(-). 4. The results indicate that CYP24 catalyses the conversion of F-6-1,25(OH)(2)D-3 to F-6-1,23,25(OH)(3)D-3 and that of F-6-1,23,25(OH)(3)D-3 to F-6-23-oxo-1,25 (OH)(2)D-3.