Debrisoquine oxidation phenotype and susceptibility to lung cancer

Nonsmall-cell lung cancer: chemoprevention studies

Lung cancer is the leading cause of cancer-related death in the world. Tobacco is an addictive agent producing carcinogenic effects that have been extremely difficult to prevent or detect in a curable stage. Important randomized controlled studies have been published in "healthy" smokers (primary prevention); patients with early lesions, such as mucosal dysplasia/metaplasia (secondary prevention); and those who have already had definitive treatment for their first tobacco-related malignancy (tertiary prevention). To date, the results have been generally disappointing. It is critical to remember that lung cancer is usually diagnosed decades after the patient has begun or even stopped smoking. We must intervene with more effective agents or combinations of agents and do it earlier in the process of carcinogenesis. Approximately 10% of patients with lung cancer either never smoked or only were "passive" smokers due to their environment, workplace. These "never-smokers" may actually benefit from retinoids, while current smokers have not benefited from alpha-tocopherol, retinal, N-acetylcysteine, or isotretinoin. Smokers are actually harmed by the concurrent use of beta-carotene. We now have unprecedented knowledge regarding the control of cellular growth and senescence. New diagnostic tools also allow detection of smaller lesions. We must use all our knowledge of the cancer biology, new risk models, more refined intermediate markers, and modern detection tools to focus more clearly on the pathology of lung cancer and design research to ask more probing and relevant questions so we can begin to put an end to the worldwide scourge of this terrible killer.

Association between genetic polymorphisms of the cytochromes P-450 (1A1, 2D6, and 2E1) and the susceptibility to pancreatic cancer

OBJECTIVES

Metabolic activation is a prerequisite for the carcinogenic effect of many carcinogens, and considerable interindividual variation exists in the metabolic capacity to activate the carcinogens. The cytochromes P-450 (CYPs) are responsible for the activation mechanism, and polymorphisms of the CYPs (CYP1A1, CYP2D6, and possibly CYP2E1) are known to be related to increased susceptibility to smoking related Kreyberg type I lung cancer. The aim of this study is to clarify the relationship of genetic polymorphisms of the CYPs to susceptibility to pancreatic cancer, another smoking-related cancer.

METHODS

We analyzed 45 samples from patients with pancreatic cancer and 53 samples from controls. DNA was isolated from blood samples and the CYP1A1, 2D6 and 2E1 genes were amplified by PCR. Analyzing the genotypes of the CYPs by allele-specific PCR or RFLP analysis, we assessed the allele frequencies for each mutation of the CYPs among the patients with pancreatic cancer and the controls.

RESULTS

The allele frequencies for the mutation in the 3'-flanking region of the CYP1A1 among the cases and the controls were 0.31 and 0.36, respectively. The allele frequencies for the exon 7 mutation of the CYP1A1 were 0.16 and 0.23, respectively, but with no statistical significance. The frequencies for the mutant c2 allele of the CYP2E1 were 0.19 and 0.30, respectively, but with no statistical significance. Two persons homozygous for a gene deletion of the CYP2D6 were observed among control subjects; other mutations were not observed among either the patients or controls.

CONCLUSION

We could not find any evidence that polymorphisms of the CYPs are associated with increased susceptibility to pancreatic cancer.

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.

Genotype analysis of the CYP2C19 gene in the Japanese population

A polymorphic CYP2C19 gene was analyzed in 233 Japanese subjects, including 63 with Parkinson's disease, 92 with chronic liver diseases (35 chronic hepatitis, 19 liver cirrhosis, 16 hepatocellular carcinoma, 10 primary biliary cirrhosis and 12 autoimmune hepatitis), 14 with lung cancer (squamous cell carcinoma) and 64 healthy subjects to determine the genotype distributions of the CYP2C19 gene and to investigate its involvement in the diseases. Among Japanese healthy subjects 14.1% are predicted to be poor metabolizers (PM) of mephenytoin. The frequencies of the m1 and the m2 mutations of the CYP2C19 gene in the healthy subjects were 21.9% and 11.7%, respectively. Though the number of patients was small, patients with lung cancer (squamous cell carcinoma) are believed to have reduced enzyme activities of CYP2C19.

Screening, Early Detection, and Early Intervention Strategies for Lung Cancer

Screening for lung cancer has been utilized for several decades without demonstrating overall survival benefit. However, recent advances in treatment of lung cancer, improvements in our biologic understanding of lung cancer development, and an increasing population of healthy ex-smokers provide cause for optimism. Several chemoprevention trials suggest that it may be possible to intervene in the oncologic process prior to the development of invasive malignancy, resulting in a delay or reversal of these changes.

"It's the genes, stupid". Molecular bases and clinical consequences of genetic cytochrome P450 2D6 polymorphism

In this review we highlight the information available on the genetic polymorphism of cytochrome P4502D6 expression in man. An absent function of this enzyme is observed in 7-10 percent of the Caucasian population which are referred to as Poor metabolizers as opposed to the remainder of the population (Extensive Metabolizers). More than 30 widely used drugs have been identified as substrates for CYP2D6. Disposition and action of these compounds depend on the individual phenotype. Both the molecular bases of the variable enzyme activity and the consequences for drug therapy are outlined. While mutations on the DNA level have been investigated in great detail larger scale clinical trials are lacking and information on therapeutic consequences of CYP2D6 mediated polymorphic drug oxidation is restricted to case reports. Besides these implications for drug metabolism several lines of evidence indicate that CYP2D6 could be involved in biotransformation of endogenous compounds.

P450 in the rat and man: methods of investigation, substrate specificities and relevance to cancer

1. Considerable evidence has been accumulated that orthologous rat and human P450 forms oxidize numerous chemicals in a highly similar manner, including the detoxication and activation of mutagens and carcinogens. 2. Nevertheless, certain specific substrates of rat P450s are not so well oxidized by the orthologous human forms, and vice versa. 3. Certain mutagens and carcinogens can be activated in a similar way by different (non-orthologous) forms in rat and man, confirming that studies on animals, directed ultimately to man, can be indicative but not predicative of chemical mutagenesis and carcinogenesis.

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.

Genetic differences in drug disposition

Genetic polymorphisms of drug metabolizing enzymes are well recognized. This review presents molecular mechanisms, ontogeny and clinical implications of genetically determined intersubject variation in some of these enzymes. Included are the polymorphic enzymes N-acetyl transferase, cytochromes P4502D6 and 2C, which have been well described in humans. Information regarding other Phase I and Phase II polymorphic pathways, such as glutathione and methyl conjugation and alcohol and acetaldehyde oxidation continues to increase and are also discussed. Genetic factors effecting enzyme activity are frequently important determinants of the disposition of drugs and their efficacy and toxicity. In addition, associations between genetic differences in these enzymes and susceptibility to carcinogens and teratogens have been reported. Ultimately, the application of knowledge regarding these genetic factors of enzyme activity may guide medical therapy and minimize xenobiotic-induced disease.

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.

Advances in mechanisms of activation and deactivation of environmental chemicals

Environmental chemicals are both activated and detoxified by phase I and phase II enzymes. The principal enzymes involved in phase I reactions are the cytochrome P-450s. The phase II enzymes include hydrolase and the conjugative enzymes such as glucuronyltransferases, glutathione transferases, N-acetyltransferase, and sulfotransferase. Although other phase I and phase II enzymes exist, the present review is limited to these enzymes. Once thought to be a single enzyme, multiple cytochrome P-450 enzymes have been purified and characterized from many different species across the evolutionary tree. The application of molecular biology techniques to this field has identified more than 150 cytochrome P-450 genes to date. At least 20-30 cytochrome P-450 enzymes appear to exist in each mammalian species, and many polymorphisms in these enzymes are being identified. The cytochrome P-450 enzymes can now be expressed in recombinant form using cDNA expression systems. The phase II conjugative enzymes add a hydrophilic moiety such as sulfate, glucuronide, or acetate to compounds, which increases their water solubility and facilitates their excretion. However, conjugates of a number of compounds also result in more reactive electrophilic species, which appear to be the ultimate carcinogens. Many of these phase II enzymes also represent families of enzymes, and polymorphisms can affect the ability of these enzymes to metabolize chemicals. Whenever possible, we have reviewed knowledge of the human enzymes involved in particular pathways.

Metabolic polymorphisms

Polymorphisms have been detected in a variety of xenobiotic-metabolizing enzymes at both the phenotypic and genotypic level. In the case of four enzymes, the cytochrome P450 CYP2D6, glutathione S-transferase mu, N-acetyltransferase 2 and serum cholinesterase, the majority of mutations which give rise to a defective phenotype have now been identified. Another group of enzymes show definite polymorphism at the phenotypic level but the exact genetic mechanisms responsible are not yet clear. These enzymes include the cytochromes P450 CYP1A1, CYP1A2 and a CYP2C form which metabolizes mephenytoin, a flavin-linked monooxygenase (fish-odour syndrome), paraoxonase, UDP-glucuronosyltransferase (Gilbert's syndrome) and thiopurine S-methyltransferase. In the case of a further group of enzymes, there is some evidence for polymorphism at either the phenotypic or genotypic level but this has not been unambiguously demonstrated. Examples of this class include the cytochrome P450 enzymes CYP2A6, CYP2E1, CYP2C9 and CYP3A4, xanthine oxidase, an S-oxidase which metabolizes carbocysteine, epoxide hydrolase, two forms of sulphotransferase and several methyltransferases. The nature of all these polymorphisms and possible polymorphisms is discussed in detail, with particular reference to the effects of this variation on drug metabolism and susceptibility to chemically-induced diseases.

The CYP1A1 gene and cancer susceptibility

A close correlation between cigarette smoking associated lung cancer incidence and an Msp I restriction fragment length polymorphism (RFLP) of the human P-450 1A1 (CYP1A1) gene was found in a Japanese population in terms of genotype frequency and cigarette dose. A Val/Ile codon difference in the primary structure of the CYP1A1 protein (Val-, Ile-type) was in linkage disequilibrium with the Msp I RFLP. A synergistic increase in susceptibility to lung cancer was found when combining genotyping of CYP1A1 and the Mu-class of glutathione S-transferase (GST1). Interindividual variability in the genetic make-up of carcinogen metabolizing enzymes may thus be a key host factor to explain the differences in susceptibility to chemical carcinogenesis among individuals.

Cancer risk related to genetic polymorphisms in carcinogen metabolism and DNA repair

Chemical carcinogenesis involves metabolism in the body of the carcinogen to the ultimate carcinogen and its interaction with DNA. There is considerable interindividual variation in the metabolic ability to activate as well as detoxify the carcinogens and in the ability to repair the carcinogen-DNA adducts. In many cases such differences occur as genetic polymorphisms and form the basis for variation in susceptibility to carcinogens and thereby to cancer risk. The activation mechanism is particularly related to the cytochromes P-450 (CYPs), and four of these are known to activate carcinogens: CYP1A1, CYP1A2, CYP2E1, and CYP3A4. Increased cancer risk has been related to polymorphisms in the CYPs and other activating enzymes. The DNA repair mechanisms show considerable complexity, and deficient repair mechanisms in certain human disorders are clearly related to increased cancer risk. Yet, there is no unambiguous epidemiological evidence available for cancer risk among individuals in general. In vivo methods have to be refined and developed for use in epidemiological studies.

The Role of Pharmacogenetics in Cancer Chemotherapy and the Development of Malignancy

The role of pharmacogenetics in the area of cancer chemotherapy and the development of malignancy has not been well defined. Only four chemotherapeutic agents have been evaluated for toxicity or clinical response based on genetic differences in metabolism. These include 5-fluorouracil, 6-mercaptopurine, amonafide, and cyclophosphamide. Severe toxicity of 5-fluorouracil and amonafide due to individual differences in drug metabolism has been reported in the literature. Tumor response in leukemic children may be associated with genetic differences in metabolism of 6-mercaptorpurine. The development of malignancy may be secondary to an individual's ability to detoxify carcinogens found in the environment. For example, the incidence of bladder cancer appears higher in subjects who have occupational exposure to aromatic amines and the slow acetylator phenotype. Some evidence also exists that smokers who are very extensive metabolizers of debrisoquin may be more prone to developing lung cancer. Strong evidence for an association between other cancer types and pharmacogenetics requires more study.

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.

Catalytic activities of human debrisoquine 4-hydroxylase cytochrome P450 (CYP2D6) expressed in yeast

A 1.57kb BamH1 fragment containing a full-length human debrisoquine 4-hydroxylase cytochrome P450 (CYP2D6) cDNA was inserted into the BglII site of the yeast expression plasmid pMA91 and the resulting recombinant plasmid, PELT1, introduced into Saccharomyces cerevisiae strain AH22. Microsomes prepared from AH22/pELT1 cells gave an absorption maximum at 448 nm and a P450 content of 67 +/- 31 pmol/mg of microsomal protein. No P450 was detectable in microsomes prepared from AH22/pMA91 control cells. A western blot of microsomes prepared from yeast transformed with pELT1 were probed with a monoclonal antibody to CYP2D6 and revealed a strong band with a molecular mass consistent with that of CYP2D6 from human liver microsomes. No corresponding band was observed with microsomes from control yeast transformed with pMA91 alone. Microsomes from AH22/pELT cells showed catalytic activity towards metoprolol (alpha-hydroxylation and O-demethylation, 0.17 and 0.78 nmol/mg protein/h, respectively); and towards sparteine (2- and 5-dehydrogenation, 1.82 and 0.59 nmol/mg protein/h, respectively). The inhibition of metoprolol metabolism by quinidine (Qd) was 200 times more potent than that of quinine (Qn), both for alpha-hydroxylation (Qd IC50 = 0.05 microM; Qn IC50 = 4 microM) and O-demethylation (Qd IC50 = 0.05 microM; Qn IC50 = 4 microM). Negligible metabolism of tolbutamide and S-mephenytoin, substrates of the 2C sub-family, and of p-nitrophenol, a substrate of CYP2E1, was detected, although a trace of the N-deethylated metabolite of lignocaine, thought to be metabolised by CYP3A4, was detected with microsomes from CYP2D6-expressing yeast cells. The results indicate that yeast cells containing human CYP2D6 cDNA express a functionally active form of the enzyme, the immunochemical and catalytic properties of which are consistent with those of human liver.

The human hepatic cytochromes P450 involved in drug metabolism

The cytochromes P450 are a superfamily of hemoproteins that catalyze the metabolism of a large number of xenobiotics and endobiotics. The type and amount (i.e., the animal's phenotype) of the P450s expressed by the animal, primarily in the liver, thus determine the metabolic response of the animal to a chemical challenge. A majority of the characterized P450s involved in hepatic drug metabolism have been identified in experimental animals. However, recently at least 12 human drug-metabolizing P450s have been characterized at the molecular and/or enzyme level. The characterization of these P450s has made it possible to "phenotype" microsomal samples with respect to their relative levels of the various P450s and their metabolic capabilities. The purpose of this review is to compare and contrast the human P450s involved in drug metabolism with their related forms in the rat and other experimental species.

Debrisoquine/sparteine hydroxylation genotype and phenotype: analysis of common mutations and alleles of CYP2D6 in a European population

Four different mutations of the cytochrome P450 CYP2D6 gene associated with the poor metabolizer phenotype (PM) of the debrisoquine/sparteine polymorphism were analyzed by Xba I restriction fragment length polymorphism (RFLP) analysis and a polymerase chain reaction (PCR)-based DNA amplification method in DNA of 394 healthy European subjects; 341 of these were phenotyped by sparteine or debrisoquine administration and urinary metabolic ratios (MR). Our study demonstrates the efficiency of the PCR-test for phenotype prediction; 96.4% of individuals were correctly predicted, i.e., 100% of the extensive metabolizers (EMs) and 86.0% of the poor metabolizers (PMs). In contrast, Xba I RFLP analysis was far less informative, predicting the phenotype in only 26.8% of PMs. By combining both DNA tests, the prediction rate of the PM phenotype increased to 90.6%. A point mutation at a splice-site consensus sequence termed D6-B represented the most common mutant CYP2D6 gene and accounted for more than 75% of mutant alleles. In addition, other known mutations such as D6-D (14%), D6-A (5%), and the rare D6-C mutation bring the identified mutant alleles to greater than 95% of all mutant PM-alleles. Most of Xba I 44-kb alleles were confirmed as mutant alleles carrying the D6-B mutation. However, 9.7% did not have this mutation and may express a functional CYP2D6 gene. Moreover, all Xba I 16 + 9-kb alleles contained the D6-B mutation. Heterozygous EM individuals had a significantly higher MR when compared to homozygous EMs. Genotyping provides an important advantage for investigations of the influence of CYP2D6 activity on drug therapy and its association with certain diseases.

Oxidative polymorphism of debrisoquine is not related to human colo-rectal cancer

The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio greater than 12.6, were classified as poor metabolisers of DBQ (n.s.). No difference was found in the distribution of the frequencies of the MR of DBQ between patients and controls. It is concluded that polymorphic oxidation of DBQ is not related to the risk of developing colo-rectal cancer in human beings.

Lack of a relationship between the polymorphism of debrisoquine oxidation and lung cancer

1. Determination of debrisoquine oxidation phenotype was carried out in 119 healthy subjects, 135 patients with chronic bronchitis and 153 patients with lung cancer, all of Caucasian origin. 2. A non-Gaussian distribution of the log D/HD ratio was observed in the three groups. 3. Assuming an antimode of 1.12, the proportion of PMs was found to be 6.7% in healthy subjects, 8.9% in chronic bronchitics and 6.5% in patients with lung cancer. These differences were not significant. 4. The presence of a lung tumour itself had no influence on phenotype in a group of 14 patients who were phenotyped before and after surgery. 5. We conclude that a link between debrisoquine phenotype and lung cancer is unlikely.

Clinical consequences of polymorphic drug oxidation

Many characters are genetically regulated as polymorphisms. This means that discrete groups are seen within the distribution of a certain character. Drug metabolism is no exception and the polymorphism of acetylation is recognised since the 50's. Polymorphic drug oxidation was discovered in the 70's and has been extensively studied. There are two fully established polymorphisms in drug oxidation named as the debrisoquine/sparteine and the s-mephenytoin hydroxylation polymorphisms. The metabolism of a number of important drugs cosegregates with that of debrisoquine. Among these drugs are beta-blockers, antiarrhythmics, tricyclic antidepressants and neuroleptics. Apart from accumulation of parent drug and active metabolite, also reduced formation of active metabolite occur for some drugs in slow metabolisers. There are, however, few cases where the presence of polymorphic drug metabolism is of significant disadvantage. The polymorphisms will add to variability in drug clearance but the potential clinical importance should be evaluated for each drug. The cytochrome P-450 isozyme responsible for debrisoquine hydroxylation is of high affinity-low capacity character, which means that it can be saturated under certain circumstances. This will decrease the difference in drug metabolic rate between rapid and low metabolisers as will inhibitors of the debrisoquine isozyme like cimetidine, quinidine and propafenone. The debrisoquine isozyme is not readily inducible. In cases where a major metabolic route or the formation of an active metabolite are polymorphically controlled, knowledge about a patient's oxidator status might be of practical value for dose adjustments especially if there is a narrow therapeutic ratio or an established concentration-effect relationship. For some drugs it is difficult to differentiate between insufficient therapeutic effect and symptoms of overdosage. Tricyclic antidepressants and neuroleptics meet some of these criteria and patients who get recurrent treatment may benefit if the physician has knowledge about debrisoquine metabolic phenotype. Otherwise, the clinical consequences of polymorphisms in drug oxidation seem so far to be limited, considering that a number of disease conditions have not shown any clear association with oxidation status. The polymorphisms in drug metabolism should be considered as a part of natural variability which could in fact be larger with other drugs that do not show polymorphic elimination.

Metabolism of debrisoquine and susceptibility to breast cancer

There may exist an association between the genetically determined oxidation status of the antihypertensive agent debrisoquine (DEB) and the propensity to develop tumours. The metabolism of DEB is extensive in 90% of healthy subjects (metabolic ratio = MR = 0-12.6; MR = % DEB excreted divided by % 4-hydroxy-DEB excreted) and poor in 10% (MR greater than 12.6). In patients with cancer of the lung, urinary bladder, and gastrointestinum, the percentage of high metabolizers is increased to greater than 98%. The poor metabolizer mode is almost devoid of cancer patients. It was investigated whether breast cancer patients show a similar association with respect to the oxidative status of DEB. 108 breast cancer patients and 123 women with benign gynecologic disorders received 1 tablet of 10 mg DEB orally in the evening. Urine was collected for the subsequent 8 hrs and analysed for its content of DEB and its main urinary metabolite 4-OH-DEB by means of HPLC. No decreased amount of poor metabolizers was seen in the cancer group.

Is there a link between debrisoquine oxidation phenotype and lung cancer susceptibility?

A link between debrisoquine oxidation phenotype and lung cancer susceptibility has been evoked by some authors but not confirmed by others. For this reason, we compared the frequency of debrisoquine poor metabolizer phenotype in 91 Belgian patients with lung cancer to that studied in 167 healthy Belgian subjects. No significant difference was observed in our study. These results do not support the existence of this link.

Polymorphic oxidation of debrisoquine in lung cancer patients

Oxidative polymorphism of debrisoquine (DBQ) was assessed in 84 patients (81 male) with histologically proven bronchogenic carcinoma and in 143 healthy male smokers. 80 (95%) patients and 133 (93%) controls, with a metabolic ratio (MR) below 12.6, were classified as extensive metabolisers of DBQ (no significant difference between patients and controls). Only 1 of the 73 patients with epidermoid or microcytic carcinomas was classified as a poor metaboliser (PM) (P = 0.031 compared with controls). 63 patients (75%) and 110 controls (77%) showed a very fast oxidative rate, with MR values under 1 (not significant). The EM phenotype of DBQ might be a secondary genetic risk factor for developing bronchogenic carcinoma in male smokers.

Identification of the primary gene defect at the cytochrome P450 CYP2D locus

The mammalian cytochrome P450-dependent monooxygenase system is involved in the metabolism of drugs and chemical carcinogens. The role of these enzymes in toxicological response is exemplified by an autosomal recessive polymorphism at the cytochrome P450 CYP2D6 debrisoquine hydroxylase locus which results in the severely compromised metabolism of at least 25 drugs, and which in some cases can lead to life-threatening side-effects. In addition, this polymorphism, which affects 8-10% of the caucasian population, has been associated with altered susceptibility to lung and bladder cancer. Here we report the identification of the primary mutation responsible for this metabolic defect and the development of a simple DNA-based genetic assay to allow both the identification of most individuals at risk of drug side-effects and clarification of the conflicting reports on the association of this polymorphism with cancer susceptibility.

Cytochrome P450dbl phenotypes in malignant and benign breast disease

129 female patients with breast cancer and 79 controls undergoing biopsy for benign breast conditions had debrisoquine hydroxylator phenotype established. 129 female hospital patients with known hydroxylator phenotype were used as another control group. The breast cancer cases differed significantly from the benign controls in their debrisoquine phenotype, with 10% being poor metabolisers compared with none of the controls (P less than 0.01). However, while a comparison of the distributions of metabolic ratio (an inverse measure of debrisoquine metabolism) of breast cancer patients and hospital controls showed a significant difference by rank, there was no significant difference in the proportion of poor metabolisers in these two groups. The cases with benign disease differed from the hospital controls in both metabolic ratio distribution (P less than 0.001) and frequency of poor metabolisers (P less than 0.05). Although there was a shift in metabolic ratio distribution, debrisoquine hydroxylator phenotype was not a genetic marker for breast cancer. Why no patients undergoing biopsies for benign conditions were poor metabolisers is unknown.