Pharmacogenetics 2001, 11:597±607 Original article 0960-314X # 2001 Lippincott Williams & Wilkins Polymorphisms in human CYP2C8 decrease metabolism of the anticancer drug paclitaxel and arachidonic acid Ding Dai, Darryl C. Zeldin, Joyce A. Blaisdell, Brian Chanas, Sherry J. Coulter, Burhan I. Ghanayem and Joyce A. Goldstein Laboratories of Pharmacology and Chemistry and Pulmonary and Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA Received 6 November 2000; accepted 12 February 2001 Cytochrome P450 (CYP) 2C8 is the principal enzyme responsible for the metabolism of the anti-cancer drug paclitaxel (Taxol). It is also the predominant P450 responsible for the metabolism of arachidonic acid to biologically active epoxyeicosatrienoic acids (EETs) in human liver and kidney. In this study, we describe two new CYP2C8 alleles containing coding changes: CYP2C8  2 has an Ile 269 Phe substitution in exon 5 and CYP2C8  3 includes both Arg 139 Lys and Lys 399 Arg amino acid substitutions in exons 3 and 8. CYP2C8  2 was found only in African-Americans, while CYP2C8  3 occurred primarily in Caucasians. Neither occurred in Asians. The frequency of the CYP2C8  2 allele was 0.18 in African-Americans, and that of CYP2C8  3 was 0.13 in Caucasians. CYP2C8  1 (wild-type), CYP2C8  2 and CYP2C8  3 cDNAs were expressed in Escherichia coli, and the ability of these enzymes to metabolize both paclitaxel and arachidonic acid was assessed. Recombinant CYP2C8  3 was defective in the metabolism of both substrates. The turnover number of CYP2C8  3 for paclitaxel was 15% of CYP2C8  1. CYP2C8  2 had a two-fold higher K m and two-fold lower intrinsic clearance for paclitaxel than CYP2C8  1. CYP2C8  3 was also markedly defective in the metabolism of arachidonic acid to 11,12- and 14,15-EET (turnover numbers 35±40% that of CYP2C8  1). Thus, CYP2C8  3 is defective in the metabolism of two important CYP2C8 substrates: the anticancer drug paclitaxel and the physiologically important compound arachidonic acid. This polymorphism has important clinical and physiological implications in individuals homozygous for this allele. Pharmacogenetics 11:597±607 # 2001 Lippincott Williams & Wilkins Keywords: CYP2C8 polymovrphisms, site-directed mutagenesis, paclitaxel, arachidonic acid Introduction There is considerable interindividual variation in the way individuals respond to drugs and other xenobio- tics. Much of this variation has been shown to be caused by genetic polymorphisms in the human cytochrome P450 enzymes (CYPs) which both detox- ify and activate drugs (Nebert & Gonzalez, 1987). In addition to the metabolism of drugs and xenobiotics, many of the CYP enzymes can also metabolize physiologically important endogenous compounds such as arachidonic acid (Capdevila et al., 1981). Genetic polymorphisms in CYP enzymes often cause humans to be divided into two distinct populations, poor metabolizers and extensive metabolizers, based on their ability to metabolize certain drugs. The poor metabolizer phenotype can affect the clinical toxicity and/or the ef®cacy of drugs. Polymorphisms in CYPs that metabolize endogenous compounds are also responsible for certain inherited diseases. For exam- ple, polymorphisms of CYP1B1 have been found to be causally related to primary congenital glaucoma (Stoilov et al., 1998; Plasilova et al., 1999). The CYP2Cs are a major subfamily of P450 enzymes that are found primarily in liver, but they are also found in various extrahepatic tissues (Goldstein & de Morais, 1994; Klose, 1999). There are four known human CYP2C enzymes: CYP2C8, CYP2C9, CYP2C18 and CYP2C19 (Romkes et al., 1991). Three of these, CYP2C9, CYP2C19 and CYP2C18, are known to be polymorphic (de Morais et al., 1994a,b; Sullivan-Klose et al., 1996). Func- tional polymorphisms of CYP2C9 and CYP2C19 Correspondence to Dr Joyce A. Goldstein, MD A303, PO Box 12233, NIEHS, RTP, NC 27709, USA Tel: 1 919 541 4495; fax: 1 919 541 3647; e-mail: goldste1@niehs. nih.gov