Polymorphic oxidation of debrisoquine in lung cancer patients

The molecular epidemiology of lung cancer

One in ten tobacco smokers develops bronchogenic carcinoma over a lifetime. The study of susceptibility of an individual and a population to lung cancer traditionally has been limited to the study of tobacco smoke dose and family history of cancer. New insights into lung carcinogenesis have made the study of molecular markers of risk possible in human populations in the emerging field of molecular epidemiology. This review summarizes data addressing the relationships of human lung cancer to polymorphisms of phase I procarcinogen-activating and phase II-deactivating enzymes and intermediate biomarkers of DNA mutation, such as DNA adducts, oncogene and tumor suppressor gene mutation, and polymorphisms. These parameters are reviewed as they relate to tobacco smoke exposure, procarcinogen metabolizing polymorphisms, and the presence of lung cancer. Problem areas in biomarker validation, such as cross-sectional data interpretation; tissue source, race, statistical power, and ethical implications are addressed.

The sparteine/debrisoquine (CYP2D6) oxidation polymorphism and the risk of lung cancer: a meta-analysis

OBJECTIVE

To examine the association between the sparteine/debrisoquine (CYP2D6) oxidation polymorphism and the risk of lung cancer.

METHOD

Meta-analysis of case-control studies using a random effects model. The "Main outcome measure" was the odds ratio for the risk of lung cancer, using extensive metabolisers as the reference group.

RESULTS

Thirteen studies were identified. The studies were too heterogeneous to be pooled the size of the odds ratio increased with the sample size. When the analysis was restricted to the largest studies, there was no difference in risk between poor and extensive metabolisers (odds ratio 0.95, 95% confidence interval 0.68-1.33).

CONCLUSION

No association was found between the CYP2D6 oxidation polymorphism and lung cancer risk when sample size bias was taken into account.

Thioether excretion, urinary mutagenicity, and metabolic phenotype in smokers

In 81 healthy individuals (51 smokers and 30 nonsmokers) biological indicators of internal exposure to electrophiles derived from tobacco smoke through metabolism were evaluated. Subgroups of smokers have been established in relation to the amount and type of tobacco smoked. Acetylator and hydroxylator phenotypes have been used as biomarkers of genetically determined susceptibility to cancer development. Urinary concentrations of thioethers (UT) and mutagenicity, with S9 mix for microsomal activation (MI-S9), were higher in smokers in relation to the level of tobacco consumption, but not to the type of tobacco. The "Slow acetylators-rapid oxidizers" category was not significant from the "rapid acetylators-rapid oxidizers" for values of UT and MI-S9. Data suggest that the biomarkers of exposure used in this study lack the necessary specificity to ascertain genetically determined susceptibility to cancer induced by tobacco smoking.

Drug metabolizing enzymes related to laboratory medicine: cytochromes P-450 and UDP-glucuronosyltransferases

Many studies on drug metabolism have been carried out during the last decades using protein purification, molecular cloning techniques and analysis of polymorphisms at phenotype and genotype levels. These researchers led to a better understanding of the role of drug metabolizing enzymes in the biotransformation of drugs, pollutants or foreign compounds and of their use in laboratory medicine. The metabolic processes commonly involved in the biotransformation of xenobiotics have been classified into functionalization reaction (phase I reactions), which implicate lipophilic compounds. These molecules are modified via monooxygenation, dealkylation, reduction, aromatization, hydrolysis and can be substrates for the phase II reactions, often called conjugation reactions as they conjugate a functional group with a polar, endogenous compound. This review, devoted to cytochromes P-450 (CYP) and UDP-glucuronosyltransferases (UGT), describes essentially the genetic polymorphisms found in humans, their clinical consequences and the methods to assess the phenotypes or genotypes, with a view to studying the interindividual differences in drug monooxygenation and drug glucuronidation. Variations in drug glucuronidation reported here focused essentially on variations due to physiological factors, induction, drug interactions and genetic factors in disorders such as Gilbert's Syndrome and Crigler-Najjar type I and II diseases.

Dextromethorphan test for evaluation of congenital predisposition to lung cancer

We report the results of an investigation conducted in 992 healthy control subjects (854 adults and 138 adolescents) and in 116 subjects with lung cancer (LC) for the purpose of detecting those individuals with a possible genetic predisposition to lung cancer. The test consists of the oral administration of 64 mumol of dextromethorphan (DMP) with collection of urine samples over the following 8-h period and urine assay of the drug (DMP) and its main metabolite, dextrorphan (DOP). The ratio of the urinary concentrations of DMP to those of DOP is called the metabolic ratio (DMP/DOP) and is inversely proportional to the DMP demethylation rate. The pattern of the metabolic ratio (Log10 DMP/DOP) allowed, using a maximum likelihood approach, the identification of three subpopulations in the 854 control subjects (adults): (1) probable homozygous extensive metabolizers with Log10 DMP/DOP < -1.74 (73.1 percent); (2) probable heterozygous intermediate metabolizers with Log10 DMP/DOP in the -1.74 to -0.40 range (22.3 percent); and (3) probable homozygous poor metabolizers with Log10 DMP/DOP > -0.4 (4.6 percent). Most of the patients with LC (89 percent) were probable homozygous extensive metabolizers. As the latter have a cancer risk that is 2.54-fold greater than that of intermediate metabolizers (95 percent confidence interval [CI]: 1.37 to 4.73) and 7.43-fold greater than that of poor metabolizers (95 percent CI: 1.01 to 54.5), their identification by means of the DMP test may be particularly useful for subjects exposed to environmental and occupational carcinogens. The phenotype test used is similar to that of the debrisoquin test, but presents the advantage that DMP is a widely used, harmless drug with a faster and simpler urinary assay procedure.

Mutant genes of cytochrome P-450IID6, glutathione S-transferase class Mu, and arylamine N-acetyltransferase in lung cancer patients

Epidemiological studies suggested a protective effect of certain phenotypes of polymorphic foreign-compound-metabolizing enzymes in some types of cancer. Poor metabolizers (PM) of debrisoquine 4-hydroxylase (cytochrome P-450IID6, CYP2D6) were found to be underrepresented among patients with lung cancer. Recent advances in molecular genetic characterization of CYP2D6, glutathione S-transferase (GST) class Mu, and arylamine N-acetyltransferase enabled genotypical determination of mutant alleles in lung cancer patients. Restriction fragment length polymorphism (RFLP) with a cDNA gene probe of CYP2D6 was analyzed in 79 lung cancer patients who were phenotyped with debrisoquine. Mutant alleles were detected by allele-specific polymerase chain reaction (PCR). In the same individuals, genotype of GST class Mu was analyzed by PCR and correlated with ex vivo activity of glutathione conjugation towards trans-stilbene oxide. RFLP patterns allowed discrimination between the slow and fast genotype of N-acetyltransferase as well as the heterozygotes. Three phenotypical PMs of debrisoquine (3.8%) were confirmed by PCR and RFLP. No PM could be unambiguously recognized only by RFLP patterns. The PMs were characterized by PCR and RFLP as carriers of the 29B/29B (n = 1), 29A/29B (n = 1), and 29A/44 (n = 1) mutant alleles. Higher debrisoquine hydroxylase activities were found in the homozygous EMs, who possess two active genes, as compared to heterozygous EMs, who have only one active gene. The patients with phenotypically impaired GST Mu activity were confirmed as such by PCR. A complete correspondence between phenotyping of N-acetyltransferase (with caffeine) and genotyping was found. The new genetic techniques proved to be powerful tools for molecular-epidemiological studies aimed at establishing host factors of cancer susceptibility.