High-Performance Liquid Chromatographic Analysis of CYP2CSCatalyzed Paclitaxel 6-Hydroxylation

CYP2C8 is a major CYP2C protein expressed in human liver 1 –4 . Considerable interindividual differences (-20-fold) have been observed in hepatic CYP2C8 content (5 ) and a blmodal dlstrlbutlon in CYP2C8 protein amounts m a panel of human liver mlcrosomes has been reported (6 ). Experiments with primary cultures of human hepatocytes have indicated that CYP2C8 is subject to inductton by phenobarbital, dexamethasone, and rifampin (rifampicm) (4 ). Little is known about the function of CYP2C8, although studies with lmmunologically purified or cDNA-expressed CYP2C8 have indicated that this P450 catalyzes the metabohsm of retmol(6 ), retinolc acid (6 ), arachldonic acid (7 , 8 ), carbamazepine (9 ) and paclitaxel (10 –12 ). Oxldatlon of the anticancer drug paclitaxel to 6a-hydroxypachtaxel appears to be selectively catalyzed by CYP2C8 because cDNA-expressed human CYP2C8 is active in this reaction, whereas CYPlA2,2A6, 2B6,2C8, 2C9-Ile359, 2C9-Cys’44, 2C18, 2C19, 2D6, 2EI,3A3,3A4 and 3A5 are inactive (10 –12 ). Paclitaxel Ga-hydroxylase actlvlty may therefore be a potentially useful dlagnostlc catalytic marker for human hepatic CYP2C8 see Note 1 . This chapter describes a high-performance liquid chromatographic (HPLC) assay for the determination of paclltaxel 6α-hydroxylase activity.