Metabolic genetic polymorphisms and susceptibility to lung cancer

Genetic polymorphisms of human cytochrome P450 CYP1A1 in an Egyptian population and tobacco-induced lung cancer

Background

Cytochrome P450 CYP1A1 helps detoxify the potential carcinogens in tobacco smoke, it was reported that polymorphisms in the coding gene result in variation in the expression and activity levels which alter metabolism and clearance of carcinogens and therefore modify cancer risk. In this work, we aimed to identify CYP1A1 gene polymorphisms associated with lung cancer in Egyptian population and to examine the interaction effect with Tobacco smoking in modulating disease risk.

Methods

A case–control study was conducted on 150 unrelated lung cancer patients and 150 unrelated control subjects. Genomic DNA was extracted and sequencing analysis of CYP1A1 gene was performed on ABI PRISM 3100 genetic analyzer.

Results

Three variants in CYP1A1 gene were identified in heterozygous forms in lung cancer patients I462V, T461N and I286T. A combined variant T461N/ I462V associated with lung cancer and those who carried this variant were 2-times more likely to develop lung cancer (OR = 2.03, 95% CI = 1.81-2.29, P = 0.04), specially the non-small cell type (NSCLC) (OR = 2.20, 95% CI = 1.93–2.50, P = 0.02). Wild type was more frequent among smoker controls (83.3%) compared to smoker lung cancer patients (54.8%), P = 0.03. Association studies to examine the interaction effect of identified variants with Tobacco smoking in modulating disease risk showed no significant associations. Identified polymorphisms showed no significant implication on the stage or the prognosis of the disease.

Conclusion

Our findings support that CYP1A1 polymorphisms play a role in the pathogenesis of lung cancer. In Egyptian population, CYP1A1 I462V, T461N and I286T variants were identified among lung cancer patients and combined T461N/ I462V was a risk variant for NSCLC in non smokers.

CYP1A1 gene polymorphisms and smoking status as modifier factors for lung cancer risk

OBJECTIVE

Lung cancer remains the most prevalent malignancy worldwide. Susceptibility to lung cancer has been shown to be modulated by inheritance of polymorphic genes. Several metabolic enzymes are currently under investigation for their possible role in lung cancer susceptibility, including members of the cytochrome P450 (CYP) superfamily. The aim of this work was to identify the correlation between CYP1A1 m1 and m2 polymorphisms and lung cancer risk and figure its interactions with smoking as genetic modifiers in the etiology of lung cancer in the Egyptian population.

MATERIALS AND METHODS

One hundred and ten patients with lung cancer and one hundred and ten controls were enrolled in the study. CYP1A1 m1 and m2 polymorphisms were determined using polymerase chain reaction restriction fragment length polymorphism.

RESULTS

Subjects carrying TC and CC genotypes of CYP1A1 m1 and AG and GG genotypes of CYP1A1 m2 were significantly more likely to develop lung cancer especially squamous cell carcinoma. The proportion of lung cancer attributable to the interaction of smoking and CYP1A1 m1 and CYP1A1 m2 polymorphisms was 32% and 52% respectively.

CONCLUSION

Our results revealed that CYP1A1 m1 and m2 polymorphisms contribute to smoking related lung cancer risk in the Egyptian population.

Correlation of CYP1A1, GSTP1 and GSTM1 gene polymorphisms and lung cancer risk among smokers

Lung cancer is the leading cause of cancer mortality worldwide and tobacco smoking has been established as its biggest risk factor. Cigarette smoke contains several carcinogens. Most of them need to be activated by phase I enzymes, such as cytochrome P450 (CYP), while phase II enzymes, such as glutathione S-transferases are responsible for the detoxification of activated forms. The present study aimed to determine the role of CYP1A1, GSTP1 and GSTM1 gene polymorphisms in smoking-related lung cancer risk. It also aimed to investigate the association of the above polymorphisms with clinicopathological parameters, as well as their effect on survival. One hundred newly diagnosed lung cancer patients with advanced disease and 125 healthy controls with a smoking history participated in the study. The participants were screened for the presence of the following polymorphisms: MspI (CYP1A1), Ile105Val (GSTP1) and GSTM1 deletion. The above polymorphisms were also examined with regards to gender, age, histological type and survival. GSTP1 Ile/Val and GSTM1-null genotypes were associated with increased lung cancer risk and the presence of the combination of the three non-wild-type genotypes increases susceptibility to lung cancer (OR 3.328, 95% CI=1.681-6.587, p=0.001). In the non-small cell lung cancer group, the GSTP1 homozygous variant was significantly associated with increased lung cancer risk (p=0.008) and shorter survival. The results of this study suggest that the GSTP1 Ile/Val genotype and GSTM1 deletion contribute to increased lung cancer susceptibility. Moreover, GSTP1 Val/Val genotype is associated with increased lung cancer risk and shorter survival in non-small cell lung cancer patients.

Environmental exposures and rheumatoid arthritis risk

In addition to rapidly burgeoning data regarding novel genetic risk factors, a growing list of environmental exposures have been implicated in rheumatoid arthritis (RA) susceptibility. Cigarette smoking is chief among the many environmental exposures implicated in disease risk, accounting for approximately one in six new cases of RA, with recent results underscoring the central importance of select gene-smoking interactions in RA development. In this review, we examine data linking several environmental exposures with RA risk, including cigarette smoking, other air pollutants and occupational exposures, reproductive/hormonal influences, alcohol consumption, select infections leading to periodontal disease, and dietary factors. Where applicable, we review the current understanding of biologic mechanisms linking these environmental factors to disease risk.

Gender is a risk factor for lung cancer

Results of epidemiological studies suggest that, after one controls for the number of cigarettes smoked, women have a three times higher risk of getting lung cancer than men. Although the mechanism(s) explaining this gender-dependent difference in lung cancer risk is not known, it is thought that endocrine factors may play an important role. Normal human bronchial epithelial cells contain estrogen receptors and synthesize 17β-estradiol (E(2)) and estrone (E(1)), which can undergo further metabolism into the catechol estrogens, 4-hydroxyestradiol (4-OHE(2)) and 4-hydroxyestrone (4-OHE(1)), respectively. Catechol estrogens are formed from E(2) by the actions of cytochrome p450 1B1 (CYP1B1). CYP1B1 is present in normal human bronchial epithelial) cells, and its activity is increased by cigarette smoking. Both 4-OHE(1) and 4-OHE(2) are mutagenic and carcinogenic and may exert their biological effects by inducing DNA adducts in cancer-related genes, including the tumor suppressor gene p53 and the proto-oncogene K-ras. Women with lung cancer have a different p53 mutational spectrum and a higher frequency of K-ras mutations than do men with lung cancer. Both clinical and basic research studies support the hypothesis that E(2) and cigarette smoking are cofactors in lung carcinogenesis in women. More specifically, cigarette smoke stimulates metabolism of E(2) into the genotoxic metabolites, 4-OHE(1) and 4-OHE(2,) which interact with DNA in cancer-related genes, including the tumor suppressor gene, p53, and the proto-oncogene K-ras, two genes frequently mutated in patients with lung cancer. E(2) may stimulate cellular proliferation and enhance tumor growth.

Just who is at risk? The ethics of environmental regulation

The willingness to view risk as part of daily life has vanished. A risk-averse mindset among environmental regulators engenders confusion between the ethics of intention and the ethics of consequence, leading to the elevation of the precautionary principle with unintended and often unfortunate outcomes. Environmental risk assessment is conservative, but the actual level of conservatism cannot be determined. High-end exposure assumptions and current toxicity criteria from the USEPA, based on linear extrapolation for carcinogens and default uncertainty factors for systemic toxicants, obscure the degree of conservatism in risk assessments. Ideally, one could choose a percentile of the target population to include within environmental standards, but this choice is complicated by the food, pharmaceutical and advertising industries, whose activities, inadvertent or not, often promote maladaptive and unhealthy lifestyle choices. There has lately been much discussion about background exposures and disease processes and their potential to increase the risk from environmental chemicals. Should these background exposures or disease processes, especially those associated with maladaptive individual choices, be included as part of a regulatory risk evaluation? A significant ethical question is whether environmental regulation should protect those pursuing a self-destructive lifestyle that may add to or synergize with otherwise innocuous environmental exposures. Choosing a target percentile of protection would provide an increased level of transparency and the flexibility to choose a higher or lower percentile if such a choice is warranted. Transparency and flexibility will lead to more responsive environmental regulation that balances protection of public health and the stewardship of societal resources.

Genetic polymorphism in cytochrome P450 2D6 (CYP2D6): Population distribution of CYP2D6 activity

Cytochrome P-450 2D6 (CYP2D6) is involved in the metabolism of many therapeutic drugs even though the enzyme represents a small proportion of the total CYP content of human liver. In vivo phenotyping with probe drug substrates such as debrisoquine and dextromethorphan showed a clear separation between poor metabolizers (PM) and extensive metabolizers (EM). This polymorphism may affect susceptibility to environmental disease, as suggested by molecular epidemiologic studies that found an association between CYP2D6 metabolizer phenotype and cancer risk; however, this association is not consistent. There are only a few examples of CYP2D6 involvement in toxicant mechanism of action, but this has not been extensively studied. Gene probe studies documented a number of genetic polymorphisms that underlie CYP2D6 metabolizer phenotypes. The EM group carries the wild-type (*1) or active (*2) variant alleles, while the PM group carries the *3, *4, *5, or *6 alleles, all of which code for a protein that has lower or null CYP2D6 activity. The current analysis characterizes (a) influence of genotype on phenotype based upon in vivo metabolism studies of probe drugs and (b) frequency of the major genotypes in different population groups is also characterized. These data were then incorporated into Monte Carlo modeling to simulate population distributions of CYP2D6 activity. This analysis reproduced the bimodal distributions commonly seen in phenotyping studies of Caucasians and found extensive population variability in enzyme activity, as indicated by the 9- to 56-fold difference between the PM modal median and the total population median CYP2D6 activity. This substantial degree of interindividual variability in CYP function indicates that assessments involving CYP2D6 substrates need to consider the full distribution of enzyme activity in refining estimates of internal dose in health assessments of xenobiotics.

Air pollutants, oxidative stress and human health

Air pollutants have, and continue to be, major contributing factors to chronic diseases and mortality, subsequently impacting public health. Chronic diseases include: chronic obstructive pulmonary diseases (COPD), cardiovascular diseases (CVD), asthma, and cancer. Byproducts of oxidative stress found in air pollutants are common initiators or promoters of the damage produced in such chronic diseases. Such air pollutants include: ozone, sulfur oxides, carbon monoxide, nitrogen oxides, and particulate matter. Interaction between oxidative stress byproducts and certain genes within our population may modulate the expression of specific chronic diseases. In this brief review we attempt to provide some insight into what we currently know about the health problems associated with various air pollutants and their relationship in promoting chronic diseases through changes in oxidative stress and modulation of gene expression. Such insight eventually may direct the means for effective public health prevention and treatment of diseases associated with air pollution and treatment of diseases associated with air pollution.

Green tea consumption is associated with decreased DNA damage among GSTM1-positive smokers regardless of their hOGG1 genotype

The levels of tobacco-related DNA adducts in human tissues reflect a dynamic process that is dependent on the intensity and time of exposure to tobacco smoke, the metabolic balance between activation of detoxification mechanisms, and the removal of adducts by DNA repair and/or cell turnover. Urinary 8-hydroxydeoxyguanosine (8-OHdG) is probably 1 of the most abundant DNA lesions formed during oxidative stress and is proposed as a sensitive biomarker of the overall oxidative DNA damage and repair. We performed this study to determine whether there were differences in increased oxidative stress susceptibility to smoking within the combined GSTM1 and hOGG1 genotypes and the impact of green tea drinking on this. We completed a Phase II randomized, controlled, 3-arm tea intervention trial to study the effect of high consumption of decaffeinated green or black tea or water on urinary 8-OHdG among heavy smokers and to evaluate the roles of GSTM1 and hOGG1 genotypes as effect modifiers. Assessment of urinary 8-OHdG after adjustment for baseline measurements and other potential confounders revealed a significant effect of green tea consumption (P = 0.001). The change from baseline was significant in all GSTM1-positive smokers regardless of their hOGG1 genotype. Our data show that consumption of 4 cups (960 mL) of tea/d is a feasible and safe approach and was associated with a significant decrease in urinary 8-OHdG among green tea consumers. Our finding also suggests that green tea intervention might be effective in decreasing DNA damage in the subgroup of smokers who are GSTM1 positive regardless of their hOGG1 genotype.

Glutathione S-transferase M1 (GSTM1) polymorphisms and lung cancer: a literature-based systematic HuGE review and meta-analysis

Multiple genes have been studied for potential associations with lung cancer. The gene most frequently associated with increased risk has been glutathione S-transferase M1 (GSTM1). The glutathione S-transferase enzyme family is known to catalyze detoxification of electrophilic compounds, including carcinogens, therapeutic drugs, environmental toxins, and products of oxidative stress. In this review, the authors summarize the available evidence associating lung cancer with the GSTM1 gene. They describe results from an updated meta-analysis of 98 published genetic association studies investigating the relation between the GSTM1 null variant and lung cancer risk including 19,638 lung cancer cases and 25,266 controls (counting cases and controls in each study only once). All studies considered, the GSTM1 null variant was associated with an increased risk of lung cancer (odds ratio (OR) = 1.22, 95% confidence interval (CI): 1.14, 1.30), but no increase in risk was seen (OR = 1.01, 95% CI: 0.91, 1.12) when only the five largest studies (>500 cases each) were considered. Furthermore, while GSTM1 null status conferred a significantly increased risk of lung cancer to East Asians (OR = 1.38, 95% CI: 1.24, 1.55), such a genotype did not confer increased risk to Caucasians. More data regarding the predictive value of GSTM1 genetic testing are needed before population-based testing may be reasonably considered.

Do genetic factors protect for early onset lung cancer? A case control study before the age of 50 years

BACKGROUND

Early onset lung cancer shows some familial aggregation, pointing to a genetic predisposition. This study was set up to investigate the role of candidate genes in the susceptibility to lung cancer patients younger than 51 years at diagnosis.

METHODS

246 patients with a primary, histologically or cytologically confirmed neoplasm, recruited from 2000 to 2003 in major lung clinics across Germany, were matched to 223 unrelated healthy controls. 11 single nucleotide polymorphisms of genes with reported associations to lung cancer have been genotyped.

RESULTS

Genetic associations or gene-smoking interactions was found for GPX1(Pro200Leu) and EPHX1(His113Tyr). Carriers of the Leu-allele of GPX1(Pro200Leu) showed a significant risk reduction of OR = 0.6 (95% CI: 0.4-0.8, p = 0.002) in general and of OR = 0.3 (95% CI:0.1-0.8, p = 0.012) within heavy smokers. We could also find a risk decreasing genetic effect for His-carriers of EPHX1(His113Tyr) for moderate smokers (OR = 0.2, 95% CI:0.1-0.7, p = 0.012). Considered both variants together, a monotone decrease of the OR was found for smokers (OR of 0.20; 95% CI: 0.07-0.60) for each protective allele.

CONCLUSION

Smoking is the most important risk factor for young lung cancer patients. However, this study provides some support for the T-Allel of GPX1(Pro200Leu) and the C-Allele of EPHX1(His113Tyr) to play a protective role in early onset lung cancer susceptibility.

Risk of non-small cell lung cancer and the cytochrome P4501A1 Ile462Val polymorphism

OBJECTIVE

The Ile462Val substitution in the cytochrome P450 1A1 gene (CYP1A1) results in increased enzymatic activity. Preliminary data suggesting a link between this polymorphism and lung cancer risk in Caucasians are inconsistent, reflecting small sample sizes and the relatively low frequency of the variant.

METHODS

The data set consisted of 1050 primary non-small cell lung cancer cases and 581 controls, a large homogenous population designed specifically to address previous inconsistencies. Patients were genotyped using a PCR-RFLP technique.

RESULTS

Carriers of the valine allele, CYP1A1*2C, (Ile/Val or Val/Val genotypes) were significantly over-represented in non-small cell lung cancer compared to controls (OR=1.9; 95% CI=1.2-2.9; p=0.005) when adjusted for confounders, particularly in women (OR=4.6; 95% CI=1.7-12.4; p=0.003). The valine variant was statistically significantly over-represented in cases of lung cancer younger than the median age (64 years) (OR=2.5; 95% CI=1.3-4.8; p=0.005) and cases with less than the median cumulative tobacco-smoke exposure (46 pack-years) (OR=2.4; 95% CI=1.3-4.7; p=0.007).

CONCLUSIONS

These new data establish an association between the CYP1A1 Ile462Val polymorphism and the risk of developing non-small cell lung cancer, especially among women.

Biomonitoring of inhaled complex mixtures--ambient air, diesel exhaust and cigarette smoke

Human biomonitoring comprises the determination of biomarkers in body-fluids, cells and tissues. Biomarkers are generally assigned to one of three classes, namely, biomarkers of exposure, effect or susceptibility. Since biomarkers represent steps in an exposure-disease continuum, their application in epidemiological studies ('molecular epidemiology') shows promise. However, to be a predictor of disease, a biomarker has to be validated. Validation criteria for a biomarker include intrinsic qualities such as specificity, sensitivity, knowledge of background in the population, existence of dose-response relationships, degree of inter- and intra-individual variability, knowledge of the kinetics, confounding and modifying factors. In addition, properties of the sampling and analytical procedures are of relevance, including constraints and non-invasiveness of sampling, stability of sample as well as simplicity, high sensitivity, specificity and speed of the analytical method. It is of particular importance to prove by suitable studies that the biomarker of exposure indicates the actual exposure, the biomarker of effect strongly predicts the actual risk of disease and the biomarker of susceptibility actually modifies the risk. Biomonitoring of the exposure to complex mixtures such as polluted ambient air, diesel exhaust or tobacco smoke is a particular challenge since these exposures have many constituents in common and many people were exposed to more than one of these mixtures. Data on the exposure to polycyclic aromatic hydrocarbons (PAH) and benzene from ambient air, diesel exhaust and tobacco smoke will be presented. In addition, some source-specific biomarkers such as nitro-arenes and nicotine metabolites as well as their application in population groups will be discussed. The second part of the presentation addresses the application of biomarkers for assessing so called 'potentially reduced exposure products' (PREPs). According to a recent report of the Institute of Medicine (USA), "reducing risk of disease by reducing exposure to tobacco toxicants is feasible" and "surrogate biological markers that are associated with tobacco-related diseases could be used to offer guidance as to whether or not PREPs are likely to be risk-reducing." In general, the same validation criteria apply as discussed above. In addition, it is suggested that a panel of biomarkers should be used, representing both smoke phases (gas and particulate phase) and the various chemical classes of smoke constituents (e.g., carbonyls, benzene, PAH, tobacco-specific nitrosamines, aromatic amines). Also, a panel of biomarkers of effect should cover the major known adverse effects of smoking (e.g., oxidative stress, inflammatory processes, lipid peroxidation, lipometabolic disorders, mutagenic effects). Biomarkers of nicotine and carbon monoxide uptake are of interest for evaluating the smoking and inhalation behavior, respectively. Finally, suitable study designs for evaluating PREPs are discussed. It is concluded that suitable biomarkers for assessing the exposure to complex mixtures such as ambient air, diesel exhaust and tobacco smoke as well as for evaluating the exposure-reducing properties of PREPs are already available. Future efforts should focus on the development and validation of biomarkers of effect.

Will nicotine genetics and a nicotine vaccine prevent cigarette smoking and smoking-related diseases?

Hall argues that the preventive use of genetic and vaccine biotechnologies is a superficially attractive tobacco policy option of doubtful efficacy, cost-effectiveness, and ethicality.

After Helsinki: a multidisciplinary review of the relationship between asbestos exposure and lung cancer, with emphasis on studies published during 1997-2004

Despite an extensive literature, the relationship between asbestos exposure and lung cancer remains the subject of controversy, related to the fact that most asbestos-associated lung cancers occur in those who are also cigarette smokers: because smoking represents the strongest identifiable lung cancer risk factor among many others, and lung cancer is not uncommon across industrialised societies, analysis of the combined (synergistic) effects of smoking and asbestos on lung cancer risk is a more complex exercise than the relationship between asbestos inhalation and mesothelioma. As a follow-on from previous reviews of prevailing evidence, this review critically evaluates more recent studies on this relationship--concentrating on those published between 1997 and 2004--including lung cancer to mesothelioma ratios, the interactive effects of cigarette smoke and asbestos in combination, and the cumulative exposure model for lung cancer induction as set forth in The Helsinki Criteria and The AWARD Criteria (as opposed to the asbestosis-->cancer model), together with discussion of differential genetic susceptibility/resistance factors for lung carcinogenesis by both cigarette smoke and asbestos. The authors conclude that: (i) the prevailing evidence strongly supports the cumulative exposure model; (ii) the criteria for probabilistic attribution of lung cancer to mixed asbestos exposures as a consequence of the production and end-use of asbestos-containing products such as insulation and asbestos-cement building materials--as embodied in The Helsinki and AWARD Criteria--conform to, and are further consolidated by, the new evidence discussed in this review; (iii) different attribution criteria (e.g., greater cumulative exposures) are appropriate for chrysotile mining/milling and perhaps for other chrysotile-only exposures, such as friction products manufacture, than for amphibole-only exposures or mixed asbestos exposures; and (iv) emerging evidence on genetic susceptibility/resistance factors for lung cancer risk as a consequence of cigarette smoking, and potentially also asbestos exposure, suggests that genotypic variation may represent an additional confounding factor potentially affecting the strength of association and hence the probability of causal contribution in the individual subject, but at present there is insufficient evidence to draw any meaningful conclusions concerning variation in asbestos-mediated lung cancer risk relative to such resistance/susceptibility factors.

Mouse models for human lung cancer

In recent years several new mouse models for lung cancer have been described. These include models for both non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC). Tumorigenesis in these conditional mouse tumor models can be initiated in adult mice through Cre-recombinase-induced activation of oncogenic mutations in a subset of the cells. They present a marked improvement over mouse models that depend on carcinogen induction of tumors. These models permit us to study the consecutive steps involved in initiation and progression and allow us to address questions like the cell of origin, and the role of cancer stem cells in the maintenance of these tumors. They now need to be validated as suitable preclinical models for intervention studies in which questions with respect to therapy response and resistance can be addressed.

Lung cancer susceptibility and polymorphisms of glutathione-S-transferase genes in Hong Kong

OBJECTIVE

To study the potential role of genetic polymorphisms of glutathione-S-transferases GSTM1, GSTT1 and GSTP1 in susceptibility to lung cancer in Hong Kong Chinese.

METHODS

229 consecutive incident patients with a histological diagnosis of lung cancer from a regional hospital and 197 healthy population-based controls were recruited for this study between July 1999 and June 2001. Genetic polymorphisms of GSTT1 and GSTM1 were determined using PCR-based technique.

RESULTS

The frequencies of GSTT1 and GSTM1 null genotypes were 51.8 and 59.4% in healthy controls and 63 and 54.7%, respectively, in lung cancer patients. GSTP1 Val105/Val105 genotype was found in only 1% of healthy controls. The risk for lung cancer with GSTT1 null genotype was significantly higher, adjusted odds ratio (OR) 1.69, 95% confidence interval (CI) 1.12-2.56, compared with those with the GSTT1 genotype; the increase in risk was found only in non-smokers. GSTM1 null genotype, combined GSTT1 and GSTM1 null genotype and GSTP1 Val105/Val105 genotype did not confer any increase risk for lung cancer.

CONCLUSION

GSTT1 null genotype is associated with an increased risk for lung cancer in non-smoking Chinese in Hong Kong.

Genotoxicity of tobacco smoke and tobacco smoke condensate: a review

This report reviews the literature on the genotoxicity of mainstream tobacco smoke and cigarette smoke condensate (CSC) published since 1985. CSC is genotoxic in nearly all systems in which it has been tested, with the base/neutral fractions being the most mutagenic. In rodents, cigarette smoke induces sister chromatid exchanges (SCEs) and micronuclei in bone marrow and lung cells. In humans, newborns of smoking mothers have elevated frequencies of HPRT mutants, translocations, and DNA strand breaks. Sperm of smokers have elevated frequencies of aneuploidy, DNA adducts, strand breaks, and oxidative damage. Smoking also produces mutagenic cervical mucus, micronuclei in cervical epithelial cells, and genotoxic amniotic fluid. These data suggest that tobacco smoke may be a human germ-cell mutagen. Tobacco smoke produces mutagenic urine, and it is a human somatic-cell mutagen, producing HPRT mutations, SCEs, microsatellite instability, and DNA damage in a variety of tissues. Of the 11 organ sites at which smoking causes cancer in humans, smoking-associated genotoxic effects have been found in all eight that have been examined thus far: oral/nasal, esophagus, pharynx/larynx, lung, pancreas, myeoloid organs, bladder/ureter, uterine cervix. Lung tumors of smokers contain a high frequency and unique spectrum of TP53 and KRAS mutations, reflective of the PAH (and possibly other) compounds in the smoke. Further studies are needed to clarify the modulation of the genotoxicity of tobacco smoke by various genetic polymorphisms. These data support a model of tobacco smoke carcinogenesis in which the components of tobacco smoke induce mutations that accumulate in a field of tissue that, through selection, drive the carcinogenic process. Most of the data reviewed here are from studies of human smokers. Thus, their relevance to humans cannot be denied, and their explanatory powers not easily dismissed. Tobacco smoke is now the most extreme example of a systemic human mutagen.

Gender and lung cancer

Although lung cancer is the leading cause of cancer death among men and women in the United States, female smokers appear to be at increased risk. After controlling for the number of cigarettes smoked, female sex imparts a significant, independent risk for most histologic types of lung cancer. Cigarette smoking, genetics, and endocrine factors may interact to contribute to the disparity in lung cancer risk between the sexes. Estrogens have direct and indirect actions in the lung, and estrogen has been implicated in lung carcinogenesis in female smokers. This review of the literature will focus on endocrine factors and tobacco carcinogens as risk factors for lung cancer in women.

Candidate gene polymorphisms in solid cancers

Accumulation of information from scientific advances in genetics and biotechnology has accelerated research investigating the inherent individual variation in disease susceptibility and severity. Gene polymorphisms, in particular single nucleotide polymorphisms, are being evaluated for their role in multi-factorial diseases such as cancer and inflammation. Most surgical diseases are multi-factorial and a better understanding and utilization of the information gained from such studies by clinicians/surgeons is likely to favorably influence patient outcome. In this article, we illustrate the types of genetic variation and the complexities involved in their study and discuss their potential in predicting both the occurrence and outcomes of solid cancers.

Effect of a 4-Month Tea Intervention on Oxidative DNA Damage among Heavy Smokers

Glutathione S-transferase (GST), a member of the phase II group of xenobiotic metabolizing enzymes, has been intensively studied at the levels of phenotype and genotype. The GST mu 1 (GSTM1) and GST theta 1 (GSTT1) genes have a null-allele variant in which the entire gene is absent. The null genotype for both enzymes has been associated with many different types of tumors. The aim of this study was to determine the possible differences in increased oxidative stress susceptibility to smoking within the GSTM1 and GSTT1 genotypes and the impact of high tea drinking on this. We designed a Phase II randomized, controlled, three-arm tea intervention trial to study the effect of high consumption (4 cups/day) of decaffeinated green or black tea, or water on oxidative DNA damage, as measured by urinary 8-hydroxydeoxyguanosine (8-OHdG), among heavy smokers over a 4-month period and to evaluate the roles of GSTM1 and GSTT1 genotypes as effect modifiers. A total of 133 heavy smokers (100 females and 33 males) completed the intervention. GSTM1 and GSTT1 genotype statuses were determined with a PCR-based approach. Multiple linear regression models were used to estimate the main effects and interaction effect of green and black tea consumption on creatinine-adjusted urinary 8-OHdG, with or without adjustment for potential confounders. Finally, we studied whether the effect of treatment varied by GSTM1 and GSTT1 status of the individual. Although there were no differences in urinary 8-OHdG between the groups at baseline, the between-group 8-OHdG levels at month 4 were statistically significant for GSTM1-positive smokers (P = 0.05) and GSTT1-positive smokers (P = 0.02). GSTM1-positive and GSTT1-positive smokers consuming green tea showed a decrease in urinary 8-OHdG levels after 4 months. Assessment of urinary 8-OHdG after adjustment for baseline measurements and other potential confounders revealed significant effect for green tea consumption (P = 0.001). The change from baseline was significant in both GSTM1-positive (t = -2.99; P = 0.006) and GSTT1-positive (P = 0.004) green tea groups, but not in the GSTM1-negative (P = 0.07) or GSTT1-negative (P = 0.909) green tea groups. Decaffeinated black tea consumption had no effect on urinary 8-OHdG levels among heavy smokers. Our data show that consumption of 4 cups of tea/day is a feasible and safe approach and is associated with a significant decrease in urinary 8-OHdG among green tea consumers after 4 months of consumption. This finding also suggests that green tea intervention may be effective in the subgroup of smokers who are GSTM1 and/or GSTT1 positive.

Association of a functional tandem repeats in the downstream of human telomerase gene and lung cancer

Chemoprevention has been widely explored as a promising strategy for controlling the incidence of lung cancer, the leading cause of cancer-related death. To maximize the benefit of lung cancer chemoprevention, it is important to identify individuals at high risk for the disease. The genetic background has been shown to play an important role in one's risk of developing lung cancer. We report here the identification of a polymorphic tandem repeats minisatellite (termed MNS16A) in the downstream region of the human telomerase gene. This minisatellite is located upstream of an antisense transcript from the human telomerase gene locus and was demonstrated to have promoter activity. The promoter activity was significantly lower in the construct containing the shorter repeats, suggesting that the MNS16A variant may have a relevance of functionality. To explore the role of this novel polymorphism in lung cancer, we conducted a pilot hospital-based case-control study by identifying the MNS16A genotype with genomic DNA from 53 lung cancer patients and 72 cancer-free controls. We found four different alleles and classified them as shorter (S) or longer (L) on the functional basis of the length of the repeats in the controls. The MNS16A genotype distributions of the SS, SL, and LL genotypes were 11, 32, and 57%, respectively, in the cases, and 14, 40, and 46%, respectively, in the controls. Compared with the SS+SL genotype, the LL genotype was associated with greater than twofold increased risk of lung cancer (odds ratio=2.18; 95% confidence interval=0.92, 5.20) after adjustment for age, sex, ethnicity, and smoking status, suggesting a potential role of MNS16A in lung cancer susceptibility. Larger studies are needed to verify our findings.

Lung cancer andCYP1A1 orGSTM1 polymorphisms

Most chemical carcinogens are metabolized and activated in vivo by phase I enzymes including the microsomal cytochromes P450 and epoxide hydroxylases. The carcinogens and their metabolites are detoxified by phase II enzymes that in clude various transferases such as glutathion-S-transferases (GST). Increasing numbers of studies have demonstrated the association of the polymorphisms inGSTM1 (a member of GST) andCYP1A1 genes with the susceptibility to lung cancer. Subsequently, the polymorphisms appear to be important biomarkers that provide information for assessment of exposure and total burden of environmental carcinogens. Therefore, the investigation of the polymorphisms in these genes will provide information not only for the prediction of individual cancer risk but also for the prevention of cancer. In this review, we will summarize the polymorphisms in theGSTM1 andCYP1A1 genes and their relation to lung cancer susceptibility.

A T2517C polymorphism in the GSTM4 gene is associated with risk of developing lung cancer

The human Mu class Glutathione S-Transferases is a family of genes encoding phase II detoxifying enzymes thus playing a significant role in the detoxification of potential carcinogens. While there are many contradicting reports on the association of GSTM1 polymorphisms and cancer development, no studies exist to date describing polymorphisms in GSTM4. We have identified a new C-T polymorphism in intron 6 of the GSTM4 gene (T2517C, Genebank sequence accession number X68677) and termed the allele carrying T at this position allele *A and the allele carrying C, allele *B. Screening a population sample in Merseyside, England, revealed 23 carriers of the *B allele out of 156 healthy control individuals but only 12 carriers of the *B allele out of 163 individuals with lung cancer (O.R.=2.23, Fisher's test P=0.026). The polymorphism did not demonstrate any associations with tumour type, gender, and age at presentation. This is the first report on the implication of a polymorphism in the GSTM4 gene in lung cancer risk. Further studies are required to investigate the relation of this polymorphism to cancer risk to substantiate these findings.

The genetics of tobacco use: methods, findings and policy implications

Research on the genetics of smoking has increased our understanding of nicotine dependence, and it is likely to illuminate the mechanisms by which cigarette smoking adversely effects the health of smokers. Given recent advances in molecular biology, including the completion of the draft sequence of the human genome, interest has now turned to identifying gene markers that predict a heightened risk of using tobacco and developing nicotine dependence