Identification of Major CYP2C9 and CYP2C19 Polymorphisms by Fluorescence Resonance Energy Transfer Analysis

Abstract

CYP2C9 and CYP2C19 monooxygenases (EC 1.14.14.1) are responsible for the metabolism of a variety of drugs and other xenobiotics, including proton pump inhibitors, certain tricyclic antidepressants, barbiturates, beta-blockers, nonsteroidal antiinflammatory drugs, warfarin, and others (1). More than 12 variants of CYP2C9 and CYP2C19 are known, some of which can be linked to altered drug metabolism and to potential severe side effects (2)(3). CYP2C9*2 (430C→T), CYP2C9*3 (1075A→C), CYP2C19*2 (681G→A), CYP2C19*3 (636G→A), and CYP2C19*4 (1A→G) account for >90% of Caucasian poor-metabolizer alleles (nucleotide changes in parentheses after the allele) (4)(5). The nucleotide changes in the CYP2C9*2 and CYP2C9*3 alleles lead to changes in the amino acid sequence (R144C for CYP2C9*2 and I359L for CYP2C9*3 ) and thus to decreased enzyme activity. In the case of CYP2C19*2 , * 3 , and * 4 , the nucleotide changes lead to a splicing defect, stop codon, and GTG initiation codon, respectively, and therefore to a protein with no activity. We developed a new assay based on fluorescence resonance energy transfer (FRET). We labeled oligonucleotides with donor and acceptor fluorophores for mutation detection and applied this assay to the LightCycler (Roche Diagnostics). Single base alterations can be identified on the basis of different melting temperatures ( T ms), and we used this method to screen genotypes of healthy unrelated individuals from Southern Germany. We report a robust and swift genotyping assay to permit analysis of major CYP2C9 and CYP2C19 alleles within 60 min of blood collection for each allele. This assay can be used in routine clinical practice to provide guidance for dose adjustments of drugs metabolized by CYP2C9/19. We examined 189 healthy males and females from a Human Pharmacology Unit for participation in various clinical research trials. After giving written informed consent, these individuals were genotyped for CYP2C9*2 , CYP2C9*3 , …