Polymorphism of glutathione S-transferase M1 and lung cancer risk among African-Americans and Caucasians in Los Angeles County, California

Genetic polymorphisms in head and neck cancer risk

OBJECTIVE

To assess whether genetic polymorphisms implicated as risk factors for other tobacco-associated malignancies are associated with altered risk of head and neck squamous cell carcinoma.

DESIGN

Case-control study.

SUBJECTS

One hundred sixty patients with head and neck squamous cell carcinoma recruited from a university-based head and neck oncology clinic and 149 population-based controls.

METHODS

Genotyping of the CYP1A1 (Ile462Val), GSTM1 (null), GSTP1 (Ile105Val), GSTT1 (null), and P53 (Arg72Pro) genes was performed by polymerase chain reaction-based techniques on DNA prepared from peripheral blood. In addition, a questionnaire was used to collect demographic information from each subject.

RESULTS

Cases were significantly older (p <.0001) and had significantly greater tobacco use (p <.0001) and were more likely to be male (p <.0001) than were control subjects, thus confirming known risk factors for this disease. When cases and controls were compared by simple chi-square analysis, only the frequency of CYP1A1 (Ile462Val) polymorphism was significantly different between cases and controls (OR =.42; 95% CI =.18-.99; p <.04). However, with a logistic regression model to control for known risk factors, we were unable to demonstrate a significant association with head and neck cancer for any of the polymorphisms tested, including CYP1A1.

CONCLUSIONS

This population fails to identify a relationship between the above-mentioned polymorphisms and head and neck cancer.

Metabolizing enzyme genotype and risk for upper aerodigestive tract cancer

Genetic polymorphisms are associated with a number of enzymes involved in the metabolism of carcinogens important in the induction of upper aerodigestive tract cancer. It has been suggested that such polymorphisms may be linked to cancer susceptibility. Using a case-control molecular epidemiologic approach, the association between many of these genetic polymorphisms and susceptibility to upper aerodigestive tract cancer has been investigated in numerous studies. In this review, we summarize the findings of these studies, analyzing potential associations with upper aerodigestive tract cancer risk in terms of gene:environment interactions, genotype-induced functional defects in enzyme activity and/or expression, and the influence of race on these associations.

GSTM1 genotypes in elderly tumour-free smokers and non-smokers

Cancer is known to be an extremely common disease, with the life-time risks reaching close to 0.5 for men and to 0.4 for women. Hence those individuals, who succeeded to achieve a reasonably old age without a history of malignancy, represent a distinct group of interest, which apparently can be defined as 'tumour-tolerant'. Focus on the genetic features of these subjects may significantly facilitate the research of cancer-predisposing polymorphisms: first, a fundamental understanding of molecular mechanisms conferring the phenomena of cancer resistance appears to be outstandingly important; second, it is promising to involve non-affected geriatric cohorts in the molecular epidemiological studies as a tumour-free control of especial value. Here we analysed the GSTM1 genotype frequencies in the individuals with seemingly different degrees of resistance or susceptibility to neoplasms, such as elderly tumour-free smokers and non-smokers (> or = 75-years-old), healthy middle-aged donors, and lung cancer patients. The proportion of GSTM1-deficient individuals gradually increased from elderly controls (70/157; 45%) to middle-aged ones (77/140; 55%) to lung cancer sufferers (34/58; 59%), showing the minimal estimates in elderly non-affected smokers (35/81; 43%) and the maximal ones in the affected non-smokers (7/7, 100%). These data have led to the two groups of conclusions. First, the broad protective role of GSTM1 has been confirmed in this report. In particular, GSTM1-deficiency appeared to reduce the chances of entering an elderly age without a history of malignancy (OR=0.66 (0.42-1.04); P=0.073). Second, the efficiency of 'tumour patients versus elderly donors' comparative analysis has been exemplified. Indeed, the long-debated fact of overrepresentation of GSTM1(-) genotypes among lung cancer sufferers was clearly demonstrated by comparison of the affected individuals to the geriatric controls (OR=1.76 (0.96-3.23); P=0.068), whereas the same patients failed to produce any convincing deviations towards the middle-aged donors (OR=1.16 (0.63-2.14); P=0.641).

Isothiocyanates, glutathione S-transferase M1 and T1 polymorphisms, and lung-cancer risk: a prospective study of men in Shanghai, China

BACKGROUND

Dietary isothiocyanates inhibit lung carcinogenesis in laboratory animals but human data are limited. Glutathione S-transferases M1 and T1 (GSTM1 and GSTT1) conjugate isothiocyanates leading to more rapid elimination. Common deletion polymorphisms of GSTM1 and GSTT1 abolish enzyme activity. We hypothesised that chemopreventive effects of isothiocyanates might be heightened when enzymes that enhance their elimination are lacking.

METHODS

We examined the relation between total isothiocyanate concentrations in urine, collected before diagnosis, and the subsequent risk of lung cancer among 232 incident cases of lung cancer and 710 matched controls from a cohort of 18,244 men in Shanghai, China, followed from 1986 to 1997. Homozygous deletion of the GSTM1 and GSTT1 genes were determined by PCR.

FINDINGS

Individuals with detectable isothiocyanates in the urine were at decreased risk of lung cancer (smoking-adjusted relative risk for lung cancer=0.65 [95% CI 0.43-0.97]). This protective effect of isothiocyanates was seen primarily among individuals with homozygous deletion of GSTM1 (0.36 [0.20-0.63]) and particularly with deletion of both GSTM1 and GSTT1 (0.28 [0.13-0.57]).

INTERPRETATION

Isothiocyanates appeared to reduce lung-cancer risk in this cohort of Chinese men. Reduction in risk was strongest among persons genetically deficient in enzymes that rapidly eliminate these chemopreventive compounds.

Analysis of gene-smoking interaction in lung cancer

The Louisiana Lung Cancer Dataset, consisting of 337 extended pedigrees, is analyzed to determine whether a major Mendelian gene interacts with cumulative tobacco smoking (pack-years). The proportional hazards model is utilized, as it is a natural framework for estimating relative risks while adjusting for variability in age of disease onset. Segregation analyses show evidence that a Mendelian gene is segregating in these families, with the most parsimonious model, including sex, pack-years, pack-years squared, and a dominant major gene. The estimated frequency of the high-risk allele is 2% and carriers are estimated to have relative risk of 17.3 for developing lung cancer, compared to noncarriers. The addition of a gene x pack-years interaction does not significantly improve the fit of the model, indicating that on a multiplicative scale, these two factors independently influence lung cancer risk. Smoking history is missing for 23% of the study subjects and degree of "missingness" depends on disease status, age, and birth-year. To account for the nonrandomness of the missing data, a Markov chain Monte Carlo method for covariate imputation is proposed and implemented. Results from this analysis also support a nonsignificant gene-smoking interaction and an allele frequency of 2%, but a lower genetic relative risk (9.0) compared to the "complete case" analysis.

Biomarkers and molecular epidemiology and chemoprevention of oral carcinogenesis

Chemopreventives are chemicals that prevent the formation of cancers such as oral cancer. They can take the form of nutrients or synthetic molecules, and their fundamental characteristic is that they do not produce disease processes that would result in debilitating symptoms. Current evidence indicates that they function by modifying the oxidative state of transforming cells. Biomarkers can take the form of genetic and molecular indicators, which characterize the function of chemopreventives and cancer processes such as oral carcinogenesis. Biomarkers cannot provide all the required information for risk assessment or possible activity of the chemopreventives. Other methods, such as epidemiological analyses and techniques, must be used to enhance our understanding of the risk for oral cancer in human populations. One common epidemiologic method, the questionnaire, helps to determine the use and carcinogenic potential of tobacco and alcohol during oral carcinogenesis. Genetic and molecular changes in human patient populations may result in a reduction in the number and function of tumor suppressor genes. If these changes are to be assessed, the tissues (e.g., buccal mucosa) must be accessible and harvested in a reliable and consistent manner for the acquisition of DNA, mRNA, and protein. Oral tissues provide sufficient quantities of these molecules and, under stringent conditions, the quality required for the isolation of these molecular constituents. In conjunction with epidemiologic techniques, various genotypic polymorphisms, such as glutathione-S-transferase (GSTM1) or cytochrome P450 (CYP450A1), have indicated a loss in carcinogen detoxification or the processing of internal growth control signals. Biomarkers are composed of a large diverse group of genetic and molecular structures. Some of these biomarkers are indicators for programmed cell death (PCD), while others describe malignant tumor growth. Many of these classes of molecules are oxidative-responsive (e.g., tumor suppressor p53, Bcl-2, growth factors, immune-derived proteins, and death-inducing molecules) and induce PCD by triggering a cascade of cysteine proteases and regulators (e.g., caspases, death receptors). This pathway results in cell-cycle alterations and DNA fragmentation. It is hoped that a detailed knowledge of the processes involved in malignant transformation will better define the biomarker-screening tools for oral cancer. These tools will enhance our ability to predict the incidence of cancer, detect early malignant change, and quantitate chemoprevention during oral carcinogenesis. Chemopreventives such as the retinoids have already demonstrated their ability to suppress potential malignant changes in pre-malignant oral leukoplakias and decrease the incidence of second head-and-neck cancer primaries. It is our hope that this review will increase investigators' interest in developing new screening and detection systems for oral cancer.

Comparison of GSTM polymorphisms and risk for oral cancer between African-Americans and Caucasians

Two members of the mu class of glutathione S-transferase (GST) genes, GSTM1 and GSTM3, have polymorphic alleles which have been associated with altered levels of GST mu protein expression and may be linked to increased risk for several tobacco-related cancers. Oral cancer is a tobacco-related disease that affects African-American men at a significantly higher incidence than Caucasian men. To examine the potential role of GSTM polymorphisms in risk for oral cancer in African-Americans and Caucasians, the prevalences of the GSTM1 null and GSTM3 intron 6 polymorphisms were examined in 63 African-American and 101 Caucasian patients with histologically confirmed primary oral cancer, as well as in 133 African-American and 213 Caucasian matched control subjects. In African-Americans, the odds ratio for oral cancer associated with the GSTM1 (0/0) genotype was 3.1 [95% confidence interval (CI) = 1.1-8.5], with the association between the GSTM1 (0/0) genotype and oral cancer risk strongest in heavy smokers [i.e. > 24 pack-years; odds ratio (OR) = 5.4, 95% CI = 1.2-24]. Using the potentially most protective GSTM1 [+]/GSTM3 (B/B) genotype as the reference group, increased risk for oral cancer was observed in African-Americans with the GSTM1 [+]/GSTM3 [(A/A) + (A/B)] (OR = 2.2, 95% CI = 0.82-6.0), GSTM1 (0/0)/GSTM3 (B/B) (OR = 4.3, 95% CI = 1.1-16), and GSTM1 (0/0)/GSTM3 [(A/A) + (A/B)] (OR = 6.6, 95% CI = 1.2-38) genotypes (P < 0.01, trend test). No significant associations were observed between GSTM genotype and oral cancer risk in Caucasians. These results suggest that the GSTM1 null and GSTM3 intron 6 polymorphisms play an important role in risk for oral cancer among African-Americans and implicates the mu class of GSTs as important tobacco carcinogen detoxifying enzymes in this population.

Environmental tobacco smoke, genetic susceptibility, and risk of lung cancer in never-smoking women

BACKGROUND

Exposure to environmental tobacco smoke (ETS) is considered to be a major lung cancer risk factor for never smokers. We investigated the hypothesis that never-smoking women who are exposed to ETS and develop lung cancer are a genetically susceptible population.

METHODS

Archival tumor tissues were analyzed from 106 never-smoking women enrolled in a case-control study of ETS (and other personal and environmental factors) and lung cancer risk. We analyzed germline polymorphisms in genes that have been associated with cancer susceptibility and whose products activate (cytochrome P450 1A1 [CYP1A1]) and detoxify (glutathione S-transferases M1 [GSTM1] and T1 [GSTT1]) chemical carcinogens found in tobacco smoke.

RESULTS

When compared with never smokers who had no ETS exposure and developed lung cancer (n = 55), never smokers with exposure to ETS who developed lung cancer (n = 51) were more likely to be deficient in GSTM1 activity (i.e., were GSTM1 null) because of a genetic polymorphism in the GSTM1 gene (odds ratio = 2.6; 95% confidence interval = 1.1-6.1). A statistically significant rising trend in risk occurred with increasing ETS exposure (two-sided P =. 02), reaching a more than sixfold excess risk in those exposed to 55 pack-years of ETS (ETS pack-year = ETS produced by an active smoker, within a confined space such as a room, who smokes one pack of cigarettes a day for a year). No evidence was found of associations between GSTT1 deficiency or the CYP1A1 valine variant and lung cancer risk due to ETS exposure.

CONCLUSIONS

A common genetic polymorphism divides the population of never smokers into two groups of approximately equal size, one (homozygous carriers of the GSTM1 null allele) that has a statistically significant greater risk of lung cancer from ETS than the other (heterozygous or homozygous carriers of the wild-type GSTM1 allele).

Polymorphisms of the GSTM1 and CYP2D6 genes associated with susceptibility to lung cancer in Chinese

The case-control study was conducted to examine the association between GSTM1 null and CYP2D6Ch (T(188)/T) genotypes and lung cancer risk among Chinese of Han nationality living in Guangdong. All 191 subjects were investigated with unitary questionnaire and their DNAs were isolated from peripheral lymphocytes by standard procedures with proteinase K digestion and phenol/chloroform extraction. GSTM1(-) was detected with polymerase chain reaction (PCR) in all 191 subjects, involving 59 lung cancer cases, 59 hospital controls and 73 healthy controls. The frequencies of GSTM1(-) were not significantly different between the cases and the two controls overall. However, among adenocarcinoma of lung, the frequency of GSTM1(-) (76.9%) appeared to be higher than that in controls (49.2%), and the odd radios were 3.42-3.45. The results suggested an elevated risk for adenocarcinoma of lung would be shown by GSTM1(-). Using polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) to detect CYP2D6 T(188)/T genotype in 59 lung cancer patients and 59 hospital controls, it showed no significant difference between the two groups. However, non-smokers with non-T(188)/T (C(188)/C or C(188)/T) genotype showed 3.78-folds increased risk of lung cancer compared with those with T(188)/T genotype (P=0.036). The data did not suggest a substantial interaction effect between GSTM1 and CYP2D6 polymorphisms and the risk of lung cancer. Additionally, among Chinese (Han) of Guangdong, the frequency of CYP2D6 T(188) allele appeared to be 57.2%, and GSTM1(-) to be 51.8%.

Lung cancer risk of the GSTM1 null genotype is enhanced in the presence of the GSTP1 mutated genotype in male Japanese smokers

The potential interaction of GSTM1 and GSTP1 genotypes in pulmonary carcinogenesis was assessed in 382 male Japanese lung cancer patients (127 squamous cell carcinoma, 78 small cell carcinoma, 177 adenocarcinoma) and 257 controls. In smokers (358 cases, 184 controls) the GSTM1 null genotype was more distributed in individuals with at least one GSTP1 mutant allele compared to those without, in lung cancer patients (69.5% vs.53.2%) but not in controls (48.0% vs. 48.5%). No such relationship was detected in non-smokers (24 cases, 73 controls). The estimated relative risk of the GSTM1 null genotype for lung cancer was 2.58 (95%CI = 1.26-5.30) in smokers with the GSTP1 mutant allele while it was 1.17 (95%CI = 0.77-1.79) in those without, suggesting that mutated GSTM1 and GSTP1 genotypes interact to potentiate the risk of lung cancers in Japanese smokers.

Polymorphisms of N-acetyltransferases, glutathione S-transferases, microsomal epoxide hydrolase and sulfotransferases: influence on cancer susceptibility

It has become clear that several polymorphisms of human drug-metabolizing enzymes influence an individual's susceptibility for chemical carcinogenesis. This review gives an overview on relevant polymorphisms of four families of drug-metabolizing enzymes. Rapid acetylators (with respect to N-acetyltransferase NAT2) were shown to have an increased risk of colon cancer, but a decreased risk of bladder cancer. In addition an association between a NAT1 variant allele (NAT*10, due to mutations in the polyadenylation site causing approximately two fold higher activity) and colorectal cancer among NAT2 rapid acetylators was observed, suggesting a possible interaction between NAT1 and NAT2. Glutathione S-transferases M1 and T1 (GSTM1 and GSTT1) are polymorphic due to large deletions in the structural gene. Meta-analysis of 12 case-control studies demonstrated a significant association between the homozygous deletion of GSTM1 (GSTM1-0) and lung cancer (odds ratio: 1.41; 95% CI: 1.23-1.61). Combination of GSTM1-0 with two allelic variants of cytochrome P4501A1 (CYP1A1), CYP1A1 m2/m2 and CYP1A1 Val/Val further increases the risk for lung cancer. Indirect mechanisms by which deletion of GSTM1 increases risk for lung cancer may include GSTM1-0 associated decreased expression of GST M3 and increased activity of CYP1A1 and 1A2. Combination of GST M1-0 and NAT2 slow acetylation was associated with markedly increased risk for lung cancer (odds ratio: 7.8; 95% CI: 1.4-78.7). In addition GSTM1-0 is clearly associated with bladder cancer and possibly also with colorectal, hepatocellular, gastric, esophageal (interaction with CYP1A1), head and neck as well as cutaneous cancer. In individuals with the GSTT1-0 genotype more chromosomal aberrations and sister chromatid exchanges (SCEs) were observed after exposure to 1,3-butadiene or various haloalkanes or haloalkenes. Evidence for an association between GSTT1-0 and myelodysplastic syndrome and acute lymphoblastic leukemia has been presented. A polymorphic site of GSTP1 (valine to isoleucine at codon 104) decreases activity to several carcinogenic diol epoxides and was associated with testicular, bladder and lung cancer. Microsomal expoxide hydrolase (mEH) is polymorphic due to amino acid variation at residues 113 and 139. Polymorphic variants of mEH were associated with hepatocellular cancer (His-113 allele), ovarian cancer (Tyr-113 allele) and chronic obstructive pulmonary disease (His-113 allele). Three human sulfotransferases (STs) are regulated by genetic polymorphisms (hDHEAST, hM-PST, TS PST). Since a large number of environmental mutagens are activated by STs an association with human cancer risk might be expected.

Mentholated cigarette smoking and lung-cancer risk

PURPOSE

Menthol smoking may lead to a greater increase in lung-cancer risk than smoking of nonmentholated cigarettes. Mentholation of cigarettes adds additional carcinogenic components to cigarette smoke and increases retention times for cigarette smoke in the lungs. Only two epidemiologic studies have been conducted on menthol smoking and lung cancer, and their results are conflicting. Of note, African American males have much higher rates of lung cancer than Caucasian males despite smoking fewer cigarettes per day. Because the consumption of menthol cigarettes is much more frequent among African Americans, it is of interest to examine the possible association between menthol smoking and lung-cancer risk in this population.

METHODS

We examined the association between menthol cigarette smoking and lung-cancer risk among smokers by comparing 337 incident cases of lung cancer with 478 population controls enrolled in a case-control study of lung cancer. Information on smoking history and other known and potential risk factors for lung cancer, including dietary intake, was obtained by in-person interviews.

RESULTS

The adjusted odds ratios did not differ appreciably between smokers of mentholated cigarettes versus exclusive nonmentholated cigarette smokers in the overall study group of smokers. The odds ratio (OR) for 32 pack-years or more of mentholated vs. nonmentholated cigarettes was 0.90 (95% confidence interval (CI) = 0.38-2.12) in African Americans and 1.06 (95% CI = 0.47-2.36) in Caucasians, and did not differ for either ethnic group (p = 0.98).

CONCLUSIONS

Our results suggest that the lung-cancer risk from smoking mentholated cigarettes resembles the risk from smoking non-mentholated cigarettes. Our data do not support the hypothesis that the increased risk of lung cancer among African Americans is due to the increased prevalence of menthol smoking.

Distinctive structure of the human GSTM3 gene-inverted orientation relative to the mu class glutathione transferase gene cluster

The sequence and exon-intron structure of the human class mu GSTM3 glutathione transferase gene and its orientation with respect to the remainder of the human class mu GSTM gene cluster were determined. The GSTM3 gene is 2847 bp long and is thus considerably shorter than the other class mu genes in the cluster, which range in size from 5325 to 7212 bp. Outside the protein-coding region, the GSTM3 gene does not share significant sequence similarity with other class mu glutathione transferase genes. Identification of overlapping cosmid clones that span the region between GSTM5, the next nearest glutathione transferase gene, and GSTM3 showed that the two genes are about 20,000 bp apart. PCR primers developed from sequences 3'-downstream from the GSTM5 gene were used to identify clones containing the GSTM3 gene. Amplification with these primers showed that the orientation of the GSTM3 gene is 5'-GSTM5-3'-3'-GSTM3-5'. Long-range PCR reactions confirmed this orientation both in the GSTM-YAC2 YAC clone, which contains the five class mu glutathione transferase genes on chromosome 1, and in human DNA. This tail-to-tail orientation is consistent with an evolutionary model of class mu glutathione transferase divergence from a pair of tail-to-tail "M1-like" and "M3-like" class mu glutathione transferase genes that was present at the mammalian radiation to the current organization of multiple head-to-tail M1-like genes tail-to-tail with a single M3-like gene with distinct structural properties and expression patterns.

Genetic susceptibility to tobacco carcinogenesis

Lung cancer risk is thus defined by the balance between metabolic activation and detoxification of xenobiotic compounds and by the efficiency of DNA repair. It is most likely that multiple susceptibility factors must be accounted for to represent the true dimensions of gene-environment interactions. The ability to identify smokers with the highest risks of developing cancer has substantial preventive implications. These subgroups could be targeted for the most intensive screening and smoking cessation interventions and could be enrolled into chemoprevention trials. Studying susceptibility to common cancers and widely prevalent exposures may provide further insights into the basic mechanisms of carcinogenesis. Issues that will need to be addressed in the very near future include risk communication to study subjects and the ethical, legal, and social consequences of such testing.

Molecular epidemiology of lung cancer

Lung cancer occurs through a complex multistage process that results from the combination of carcinogen exposure and genetic susceptibilities. The primary etiology of lung cancer is tobacco smoking, but an understanding of why some smokers develop lung cancer, and others do not, remains unclear. Current studies focus on genetic susceptibilities to lung cancer, and how they modify the effects of tobacco smoke carcinogens. New assays are being developed to study other contributors to cancer risk, such as interindividual differences in DNA repair. There is current evidence to suggest that the risk of lung cancer for women, compared to men, is higher for the same level of smoking. Several biological differences for the types of lung cancer have been observed in women and men. Also, there appear to be differences in lung cancer between Caucasians and African-Americans. Molecular epidemiology tools are uniquely suited to study these biological differences. These studies will improve cancer risk assessments and focus cancer prevention strategies. Other studies also are focusing on tobacco addiction, in order to lead to improved smoking cessation strategies.

Genetic polymorphisms of human N-acetyltransferase, cytochrome P450, glutathione-S-transferase, and epoxide hydrolase enzymes: relevance to xenobiotic metabolism and toxicity

In this review, an overview is presented of the current knowledge of genetic polymorphisms of four of the most important enzyme families involved in the metabolism of xenobiotics, that is, the N-acetyltransferase (NAT), cytochrome P450 (P450), glutathione-S-transferase (GST), and microsomal epoxide hydrolase (mEH) enzymes. The emphasis is on two main topics, the molecular genetics of the polymorphisms and the consequences for xenobiotic metabolism and toxicity. Studies are described in which wild-type and mutant alleles of biotransformation enzymes have been expressed in heterologous systems to study the molecular genetics and the metabolism and pharmacological or toxicological effects of xenobiotics. Furthermore, studies are described that have investigated the effects of genetic polymorphisms of biotransformation enzymes on the metabolism of drugs in humans and on the metabolism of genotoxic compounds in vivo as well. The effects of the polymorphisms are highly dependent on the enzyme systems involved and the compounds being metabolized. Several polymorphisms are described that also clearly influence the metabolism and effects of drugs and toxic compounds, in vivo in humans. Future perspectives in studies on genetic polymorphisms of biotransformation enzymes are also discussed. It is concluded that genetic polymorphisms of biotransformation enzymes are in a number of cases a major factor involved in the interindividual variability in xenobiotic metabolism and toxicity. This may lead to interindividual variability in efficacy of drugs and disease susceptibility.

Molecular epidemiology of human cancer risk: gene-environment interactions and p53 mutation spectrum in human lung cancer

The p53 tumour suppressor gene is at the crossroads of a network of cellular pathways including cell cycle checkpoints, DNA repair, chromosomal segregation, and apoptosis. These pathways have evolved to maintain the stability of the genome during cellular stress from DNA damage, hypoxia, and activated oncogenes. The high frequency of p53 mutations in human cancer is a reflection of the importance of p53 involvement in this network of pathways during human carcinogenesis. An electronic database containing p53 mutations from more than 9000 cancers (http:/(/)www.iarc.fr/p53/homepage.html) can be used to generate hypotheses for further clinical, epidemiological, and laboratory investigations. For example, one can hypothesize that (a) p53 mutations vary in their pathobiological significance; (b) cellular content influences the selection of p53 mutations in clonally derived cancers; (c) the location and type of mutation within the p53 gene provide clues to functional domains in the gene product; and (d) the p53 mutation spectrum can be a molecular link between aetiological agents and human cancer. This review will focus on the role of p53 and cancer susceptibility genes in the molecular pathogenesis and epidemiology of human lung cancer.

Polymorphisms in xenobiotic conjugation and disease predisposition

Low activity of arylamine N-acetyltransferase 2 (slow NAT2) was consistently associated with urinary bladder cancer risk. The increased cancer risk attributable to slow NAT2 was more significant when taking gene-environment interactions and gene-gene interactions into account. In urinary bladder, slow NAT2 was no risk factor in subjects who never smoked but became increasingly relevant with increasing lifetime dose of tobacco smoke expressed by an odds ratio of 2.7 for slow NAT2 in extensive smokers. The functional impact of some arylamine N-acetyltransferase 1 variants is controversial. It was published that the NAT1 allele 10 was associated with high enzyme activity and that there was an overrepresentation of carriers of NAT1*10 in bladder and colon cancer, but we could only detect a moderately elevated activity of NAT1*10 and an underrepresentation of fast NAT1 alleles in bladder cancer. Recently, a C/A-polymorphism in intron 1 of cytochrome P450 1A2 was associated with high inducibility and persons with this high inducibility variant were overrepresented in bladder cancer, but only if they were smokers or if they had slow NAT2 genotypes. Numerous studies have shown that glutathione S-transferase M1 deficiency (GSTM1*0/0) increases the risk for lung and bladder cancer but the overall risk attributable to GSTM1*0/0 was only around 1.3 according to meta-analyses. The GSTM1*0/0 genotype appears to be the best established metabolic susceptibility factor. Several independent experimental approaches showed that GSTM1 decreases mutagenicity of reactive epoxides and it was shown that carriers of GSTM1*0/0 were at increased risk for several types of cancer and other diseases. There are also studies which showed no effects of GSTM1, a result which is compatible with the assumption that GSTM1*0/0 is a susceptibility factor of moderate strength. GSTM1*0/0 may, however, become a dominant risk factor in certain gene-gene combinations such as the combination with highly active CYP1A1 gene variants or in combination with specific types of exposure. Specific precautions have to be taken in the design of molecular epidemiological studies on risk factors with moderate strength; some requirements for high quality molecular epidemiological studies will be discussed in this article. Molecular epidemiology is an increasingly powerful approach to understand carcinogenesis and may be used in the future to individualize cancer prevention strategies.

Polymorphic CYP genes and disease predisposition--what have the studies shown so far?

The risk of lung and urinary bladder cancers was reported to be increased in individuals who carried high risk genotypes in either cytochrome P450 (CYP)1A1, CYP2E1 or glutathione S-transferase (GST)M1, and the combined genotype of both CYP1A1 and GSTM1 enzymes have an enhanced tendency of risk to lung cancer more significantly. On the other hand, gene-environmental interactions have to be considered precisely, and are indicated to be more pronounced at lower levels of cigarette exposure in which the susceptibility to lung cancer increased in the case of individuals with some mutated alleles. In each category, however, there are several confused and controversial results. These early predictions of genetic disposition for the incidence of such severe disease as cancer may prompt them to receive early examination and diagnosis and to expect a complete cure from the diseases for their life.

Combined effect of polymorphic GST genes on individual susceptibility to lung cancer

Glutathione S-transferases (GSTs) are known to take part in detoxification of many potentially carcinogenic compounds. Therefore, polymorphisms of the GST genes have been considered as potentially important modifiers of individual risk of environmentally induced cancers. The association between lack of glutathione S-transferase M1 gene (GSTM1 null genotype) and susceptibility to smoking-related lung cancer has been actively studied, with contradictory results. In contrast, little is known about the more recently found polymorphisms in GSTM3, GSTP1 and GSTT1 genes with respect to individual responses to environmental exposures. In this study, we determined the genotype distribution of all these genes, and their combinations, among 208 Finnish lung cancer patients and 294 population controls. None of the genotypes studied had a statistically significant effect on lung cancer risk, when studied separately. However, a significant association was observed for concurrent lack of the GSTM1 and GSTT1 genes and susceptibility to squamous cell carcinoma. For that cell type, the risk was more than 2-fold when compared with that of individuals having other genotype combinations (OR = 2.3; 95% CI = 1.0-5.3; p = 0.05). Moreover, the risk was mostly attributable to patients with smoking history of 40 pack-years or less (OR = 2.9; 95% CI = 1.1-7.7; p = 0.03). In contrast, this genotype combination did not affect the risk for other histological types of lung cancer, and the other genotype combinations had no effects on individual susceptibility to this malignancy. The overall role of GST polymorphisms in modifying the lung cancer risk may therefore be more limited than has been so far anticipated.

Alcoholic beverage consumption and lung cancer risk among residents of Los Angeles County

Although studies generally support a positive association between alcohol consumption and lung-cancer risk, the relationship between specific alcoholic beverages and lung-cancer risk has been inconsistent. We examined recent and past alcoholic beverage intake among 261 incident cases and 615 population controls enrolled in a lung-cancer case-control study of African Americans and Caucasians in Los Angeles County between 1991 and 1994. An in-person interview elicited information about past alcohol intake from ages 30 to 40 y, smoking, other lung-cancer risk factors, as well as recent intake of alcohol, and recent dietary intake. An association was observed between recent hard-liquor consumption and lung-cancer risk. The odds ratio (OR) for 1 or more drinks (1.5 oz or 0.051 mL) per day of hard liquor compared with infrequent liquor drinking (0-3 drinks per month), adjusted for smoking, the matching factors, saturated fat and other alcoholic beverages was 1.87 [95% confidence interval (CI) = 1.02-3.42]. No appreciable association was observed for total alcohol, whereas small inverse associations were observed for beer and wine, although confidence intervals were wide. An elevated lung-cancer risk was also observed for past liquor consumption (between ages 30 and 40 y). The adjusted OR for 1 or more drinks per day of liquor compared with infrequent drinkers was 1.83 (95% CI = 1. 06-3.15). Confounding of the association between alcohol and lung cancer by smoking was apparent. Although we devoted considerable efforts to adjusting for smoking in our analyses, residual confounding is still possible because smoking and alcohol are closely associated. In addition, case-control studies including this study should be viewed with caution because of possible selection bias. An increased risk of lung cancer might occur with moderate drinking of hard liquor but confirmation is required in larger studies.

Characterization of the human class Mu glutathione S-transferase gene cluster and the GSTM1 deletion

A partial physical map has been constructed of the human class Mu glutathione S-transferase genes on chromosome 1p13.3. The glutathione S-transferase genes in this cluster are spaced about 20 kilobase pairs (kb) apart, and arranged as 5'-GSTM4-GSTM2-GSTM1-GSTM5-3'. This map has been used to localize the end points of the polymorphic GSTM1 deletion. The left repeated region is 5 kb downstream from the 3'-end of the GSTM2 gene and 5 kb upstream from the beginning of the GSTM1 gene; the right repeated region is 5 kb downstream from the 3'-end of the GSTM1 and 10 kb upstream from the 5'-end of the GSTM5 gene. The GSTM1-0 deletion produces a novel 7.4-kb HindIII fragment with the loss of 10.3- and 11.4-kb HindIII fragments. The same novel fragment was seen in 13 unrelated individuals (20 null alleles), suggesting that most GSTM1-0 deletions involve recombinations between the same two regions. We have cloned and sequenced the deletion junction that is produced at the GSTM1-null locus; the 5'- and 3'-flanking regions are more than 99% identical to each other and to the deletion junction sequence over 2.3 kb. Because of the high sequence identity between the left repeat, right repeat, and deletion junction regions, the crossing over cannot be localized within the 2.3-kb region. The 2.3-kb repeated region contains a reverse class IV Alu repetitive element near one end of the repeat.

Genetic polymorphisms in human drug-metabolizing enzymes: potential uses of reverse genetics to identify genes of toxicological relevance

The human mind was engaged with fundamental questions on the nature of heredity long before the study of genetics became a scientific discipline. Many traits, such as height, eye color, blood pressure, or cancer susceptibility, have been known to run in families, although the genes or combination of genes that underlie these observable characteristics remain unknown in most cases. Differences in susceptibility to environmental agents in humans are likewise determined by variations in genetic background--genetic polymorphisms. In this article, we review the current status of studies on human polymorphisms in drug-metabolizing enzymes and discuss various approaches to the analysis of genetic polymorphisms. We expect that in the near future, novel methods in genetic analysis of human populations will be likely to play a key role in the identification of genes of toxicological relevance.

Molecular epidemiology and retinoid chemoprevention of head and neck cancer

Head and neck cancer is a major worldwide health problem; it has been estimated that approximately 900,000 people were diagnosed with this disease in 1995. Patients are generally treated with surgery and/or radiation therapy. Treatment, especially of patients with early stage (I or II) head and neck squamous cell carcinoma, is often successful. A serious concern, however, is the fact that these patients subsequently develop second primary tumors at an annual rate of 4%-7%. Molecular analyses of premalignant and malignant tissues have produced strong evidence that clonal genetic alterations occur during the early stage of aerodigestive tract carcinogenesis. Although the roles of tobacco and diet in head and neck carcinogenesis have been the subjects of epidemiologic investigations for many years, it has only recently become possible to integrate information regarding genetic susceptibility factors into the development of comprehensive risk models for these cancers. The molecular and epidemiologic studies provide the foundation on which clinical trials can be designed to evaluate the role of retinoids and other compounds in the reversal of premalignancy and the prevention of second primary tumors (i.e., in chemoprevention). This translational approach has led to studies of the utility of intermediate end point markers, such as the nuclear retinoic acid receptors, in chemoprevention strategies. Given the rapid advances occurring in this area of research, it may soon be possible to use these biomarkers to identify patients who are most at risk for developing head and neck cancer and who are most likely to benefit from chemopreventive interventions.

GSTM1 gene polymorphism as a possible marker for susceptibility to head and neck cancers among Japanese smokers

Increased risk of lung cancer has been reported in individuals with glutathione S-transferase M1 (GSTM1) gene deletion, with limited evidence for head and neck (HN) cancer. Here, we report the results of a case-control study in Japanese HN cancer patients (n = 158) and community controls (n = 174). GSTM1 null genotype (GSTM1(-)) was distributed more in smoker patients than in control subjects (56.7% vs. 48.5%) but not in non-smoker patients (48.3%). In smokers, GSTM1(-) was detected at increased frequency in non-larynx cancer (62.7%, odds ratio 1.77, 95% CI 1.04-3.01) but not in larynx cancer (48.1%). In larynx cancer GSTM1(-) was presented at higher frequency in patients < 60 years old than in those > or = 60 years old (78.6% vs. 36.8%). These findings suggest that the GSTM1 gene polymorphism potentially modifies the risk for HN cancer depending on smoking history, the region of cancer and age.

Helicobacter pylori infection and genetic polymorphisms for cancer-related genes in gastric carcinogenesis

The development of gastric cancer is a multistep process that is multi-factorial. An association with the Helicobacter pylori infections, gastric atrophy and gastric cancer has received recent attention. The objective of this study was to elucidate the risk factors for gastric cancer by using molecular epidemiological techniques for genetic susceptibility, gastric atrophy and serum markers including H pylori infection. We used an age- and gender-matched case-control study, where patients with benign gastric lesions were the controls. Low serum pepsinogen I levels (cut-off < 50 ng/mL) and low pepsinogen I/pepsinogen II ratios (cut-off < 3.0) were significantly associated with the risk of gastric cancer (odds ratio [OR] = 3.53: 95% confidence interval [CI] = 2.46-5.09 and OR = 4.73: 3.26-6.88, respectively). However, seropositivity of serum immunoglobulin G (IgG) antibody against H pylori (OR = 1.09: 0.74-1.61) was not associated with gastric cancer, even when analyzed by age greater than or less then 50 years. Specific genotypes of the cytochrome p450 2E1 (CYP2E1) RsaI polymorphism and glutathione-S-transferase (GST) M1 gene deletion were determined but were not associated with gastric cancer; however, a Lmyc genetic polymorphism was associated with gastric cancer (OR = 1.55: 1.03-2.34). Therefore, in this Japanese study, atrophic mucosal change, indicated by serum pepsinogen levels, is a possible risk factor for gastric cancer.

Analysis of L-myc and GSTM1 genotypes in Chinese non-small cell lung carcinoma patients

The genotypes of L-myc and GSTM1 genes were studied in normal lung tissues of 98 non-small cell lung carcinoma (NSCLC) patients from Hong Kong using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) techniques. Results showed a statistical difference in L-myc genotypes between Chinese and African Americans (P = 0.02). A significant deficit in heterozygotes resulting in the departure from Hardy-Weinberg equilibrium in lung cancer female patients was detected (0.01 < P < 0.02). There were significant differences in survival times in patients having L-L and S-S genotypes, with shorter survival times in the patients with L-L genotypes (0.01 < P < 0.05). Data on age, size of tumor, histological types, and lymph node metastasis showed no significant association with L-myc genotype. The survival time in the GSTM1-negative (null gene) group was significantly different from the GSTM1 positive group between 16 and 24 months after operation (0.01 < P < 0.05). There was no significant difference in the distribution of GSTM1 genotypes between Chinese and Caucasian Americans.

Familial risks of squamous cell carcinoma of the head and neck: retrospective case-control study

OBJECTIVE

To determine the contribution of inheritance to the incidence of squamous cell carcinoma of the head and neck.

DESIGN

Historical cohort study. First degree relatives of cases with squamous cell carcinoma of the head and neck made up the exposed cohort and first degree relatives of spouses of cases made up the comparison unexposed cohort.

SETTING

Ear, nose, and throat clinic in a large metropolitan teaching hospital.

SUBJECTS

1429 first degree relatives of 242 index cases of squamous cell carcinoma of the head and neck; as controls, 934 first degree relatives of the spouses of 156 index cases.

MAIN OUTCOME MEASURES

Relative risk of developing squamous cell carcinoma in first degree relatives of cases compared with risk in first degree relatives of spouses.

RESULTS

The adjusted relative risk for developing head and neck cancer if the index case had squamous cell carcinoma of the head and neck was 3.79 (95% confidence interval 1.11 to 13.0). There were no significantly increased risks associated with a family history of cancer at other sites. The adjusted relative risk for squamous cell carcinoma of the head and neck was 7.89 (1.50 to 41.6) in first degree relatives of patients with multiple primary head and neck tumours.

CONCLUSIONS

These data suggest that genetic factors are important in the aetiology of head and neck cancer, in particular for patients with multiple primary cancers. Given the prolonged exposure of these subjects to carcinogens, these genetic factors may have a role in modifying carcinogen activity or in host resistance to carcinogens. Inherited factors may be important in persons with environmentally induced cancers.

Ultrarapid metabolizers of debrisoquine: characterization and PCR-based detection of alleles with duplication of the CYP2D6 gene

Up to 7% of Caucasians may demonstrate ultrarapid metabolism of debrisoquine due to inheritance of alleles with duplicated functional CYP2D6 genes. Here we describe the genomic organization of the duplicated CYP2D6 genes in the 42 kb XbaI allele. We postulate that this duplication originates from a homologous, unequal cross-over event which involved two 29 kb XbaI wild-type alleles, and had break points within a 2.8 kb direct repeat (CYP-REP) flanking the CYP2D6 gene. Moreover, we have designed two different PCR assays for detection of alleles with duplicated CYP2D6 genes. Both assays correctly identified 29 out of 29 subjects positive for the 42 kb XbaI allele. No false negative or false positive reactions were observed.

Genetic polymorphisms of the cancer related gene and Helicobacter pylori infection in Japanese gastric cancer patients. An age and gender matched case-control study

BACKGROUND

Gastric cancer is a multistage process, each caused by numerous factors. The objective of this study was to elucidate the risk factors for gastric cancer by using molecular epidemiologic techniques and serum markers.

METHODS

Serum pepsinogen I levels, pepsinogen I/pepsinogen II (I/II) ratios, serum IgG antibody against Helicobacter pylori (H. pylori), and genetic polymorphisms of cytochrome p450 2E1 (CYP2E1), glutathione-S-transferase M1 (GSTM1), and L-myc protooncogenes were analyzed in 82 persons with gastric cancer and in 151 age- and sex-matched controls, who were selected from 208 gastric cancer patients and 375 noncancer patients, respectively. Statistical analysis was performed to elucidate which risk factors for gastric cancer were contributing the most to gastric carcinogenicity.

RESULTS

Serum pepsinogen I level (odds ratio [OR] = 1.81; 95% confidence interval [CI], 1.04-3.16) and pepsinogen I/II ratios (OR = 3.09; 95% CI, 1.74-5.49) were significantly associated with gastric cancer risk in a case-control study. Seropositivity of serum IgG antibody against H. pylori (OR = 1.25; 95% CI, 0.84-1.85) and specific genotypes of a L-myc genetic polymorphism (OR = 1.33; 95% CI, 0.59-2.99) were more commonly observed in gastric cancer cases, but this was not statistically significant. Specific genotypes of the CYP2E1 RsaI polymorphism and GSTM1 gene deletion were not associated with gastric cancer.

CONCLUSIONS

Atrophic mucosal change, indicated by serum pepsinogen levels, is possible a risk factor for gastric cancer. H. pylori infection and genetic polymorphisms of CYP2E1, L-myc, and GSTM1 genetic polymorphisms were not risk factors in this study.

Genetic susceptibility to cancer from exogenous and endogenous exposures

The past four decades of epidemiological research have yielded valuable information on the risks of populations to environmental exposures such as tobacco, asbestos, and dietary components. Prevention efforts have been focused on large-scale population-based interventions to minimize exposure to such external carcinogens. While some cancers are beginning to show a decline from changing environmental exposures, hormone-related cancers, such as breast and prostate, are becoming more prevalent. The development of these cancers appears to be closely related to endogenous exposures to circulating steroid hormones. Although prevention trials using antihormone agents are proving successful in some instances, the long-term control of these cancers necessitates a clearer understanding of the metabolism and transport of the relevant hormone in vivo. The revolution in molecular biology has provided powerful genetic tools for evaluating mechanisms of cancer causation as well as the potential to better define individual susceptibility. Using tobacco exposure as an example, we and others have demonstrated that polymorphisms in genes controlling aromatic amine metabolism provide at least a partial explanation for ethnic and individual susceptibility to bladder cancer. Similar studies have examined genetic polymorphisms in the metabolism of tobacco smoke and lung cancer risk, red meat and colorectal cancer, and aflatoxin and liver cancer. Our current studies have pursued a similar paradigm of genetic polymorphism and individual cancer susceptibility in prostate and breast carcinogenesis. We are evaluating polymorphisms in the steroid 5 alpha-reductase type II and androgen receptor genes in relation to prostate cancer based on the evidence that intracellular dihydrotestosterone is the critical "carcinogen." We are pursuing genetic polymorphisms affecting estradiol metabolism, including those in the 17 beta-hydroxysteroid dehydrogenase 2 and estrogen receptor genes as they relate to susceptibility to breast cancer. The potential role of a polymorphism in the cytochrome P450c 17 alpha gene in both breast and prostate cancers is also being examined.