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 c
DNA
-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.