Molecular Genetic Analysis of the Cytochrome P450-Debrisoquine Hydroxylase Locus and Association with Cancer Susceptibility

Abstract

The cytochrome P450-dependent monooxygenases play a central role in the metabolism of chemical carcinogens. The action of these enzymes can lead to either carcinogen detoxication or activation. Differences in P450 expression in animal models give rise to large differences in susceptibility to chemical carcinogens, so genetic polymorphisms in P450 expression may be expected to be an important factor in individual human susceptibility to cancer. Of particular interest is the genetic polymorphism at the cytochrome P450-debrisoquine/sparteine hydroxylase locus (CYP2D6). Although this is a minor liver P450, its polymorphic expression is associated with the abnormal metabolism of at least 30 therapeutic drugs, including P-blockers and tricyclic antidepressants. Conflicting reports have been made on the association of this polymorphism with cancer susceptibility. This disagreement may be attributable to limitations of the phenotyping assay used to identify affected individuals (poor metabolizers, PMs). In order to clarify these anomalies, we have developed a simple DNA-based assay with which we can identify the majority of PMs. The assay is centered around the primary gene defect responsible for the polymorphism, a G to A transition at the junction of intron 3/exon 4 which results in a frame-shift in the resultant mRNA. The frequency of this mutation is 70-80% in PMs. We have studied the frequency of mutated alleles in a control population and in a wide range of cancer patients. No association between this polymorphism and lung cancer susceptibility was observed; however, in other populations of cancer patients some very interesting shifts were found in the proportion of PMs and heterozygotes from that in the normal population.

Polymorphism of selected enzymes involved in detoxification and biotransformation in relation to lung cancer

“…On the other side, subjects with over-activated CYP2D6 gene showing high cellular levels of debrisoquine 4-hydroxylase were found [52][53][54].…”

CYP 2D6 polymorphism: A predictor of susceptibility and response to chemoradiotherapy in head and neck cancer

“…Poor metabolizers of CYP2D6 may have a higher carcinogen level and potent cell toxicity due to their impaired ability to detoxify the carcinogens. [19,20] Poor metabolizers of CYP2D6 are reported to have a significantly higher incidence of prostatic cancer in North Indian population compared with homozygous and heterozygous extensive metabolizers suggesting that the risk due to CYP2D6 poor metabolizer genotype could be attributed to the lesser detoxification capacity of the carcinogens. [21] Likewise, several fold increase in the risk in alcohol drinking cases with variant genotypes of CYP2D6 have suggested that alcohol possibly interacts with CYP2D6 genotypes in increasing risk.…”

Cytochrome P450 2D6 Polymorphism Is a Molecular Genetic Marker of Liver Cirrhosis Progression

“…PCR was carried out on a Corbett thermal cycler using oligonucleotide primers F: 5'-GCCTTC-GCCAACCACTCCG-3' and R: 5'-AAATCCTGCT CTTCCGAGGC-3' [14]. A 355-b.p.…”