A modified host-cell reactivation assay to measure repair of alkylating DNA damage for assessing risk of lung adenocarcinoma

The nicotine-derived nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induces lung adenocarcinoma through formation of DNA adducts. Our previous research on susceptibility to tobacco-induced carcinogenesis focused on benzo[a]pyrene diol epoxide (BPDE) as the in vitro mutagen for phenotype measurements of DNA repair capacity (DRC) in mammalian cells. Here, we present a modified host-cell reactivation (HCR) assay to measure lymphocytic DRC for alkylating DNA damage as is induced by the tobacco-specific nitrosamine, NNK. We substituted dimethyl sulfate (DMS) to create alkylating damage in pCMVluc plasmid DNA and established the damage-repair dose-response curves in both normal and nucleotide excision repair-deficient lymphoblastoid cell lines and in phytohemagglutinin (PHA)-stimulated primary lymphocytes. We then successfully measured the DRC in PHA-stimulated lymphocytes from 48 patients with lung adenocarcinoma and 45 cancer-free controls and tested our hypothesis that lower DRC for alkylating damage is associated with an increased risk of lung adenocarcinoma. The cases exhibited a lower mean DRC than did the controls. A >3-fold increased risk (odds ratio = 3.21; 95% confidence interval = 1.25-8.21) was found for those with DRC levels below the control median. There was no correlation between the DRC measured with this DMS-HCR assay and that from the parallel BPDE-HCR assay. Interestingly, risk increased to >10-fold for those with sub-optimal DRC measured by both DMS- and BPDE-HCR assays. We conclude that variability in DRC is a risk factor for lung cancer and our results provide proof of principle for a new assay that can assess DRC for NNK-induced DNA damage.     

Organ specificity of the bladder carcinogen 4-aminobiphenyl in inducing DNA damage and mutation in mice

Aromatic amines are a widespread class of environmental contaminants present in various occupational settings and tobacco smoke. Exposure to aromatic amines is a major risk factor for bladder cancer development. The etiologic involvement of aromatic amines in the genesis of bladder cancer is attributable to their ability to form DNA adducts, which upon eluding repair and causing mispairing during replication, may initiate mutagenesis. We have investigated the induction of DNA adducts in relation to mutagenesis in bladder and various nontarget organs of transgenic Big Blue mice treated weekly (i.p.) with a representative aromatic amine compound, 4-aminobiphenyl (4-ABP), for six weeks, followed by a six-week recovery period. We show an organ-specificity of 4-ABP in inducing repair-resistant DNA adducts in bladder, kidney, and liver of carcinogen-treated animals, which accords with the bioactivation pathway of this chemical in the respective organs. In confirmation, we show a predominant and sustained mutagenic effect of 4-ABP in bladder, and much weaker but significant mutagenicity of 4-ABP in the kidney and liver of carcinogen-treated mice, as reflected by the elevation of background cII mutant frequency in the respective organs. The spectrum of mutations produced in bladder of 4-ABP-treated mice matches the known mutagenic properties of 4-ABP-DNA adducts, as verified by the preponderance of induced mutations occurring at G:C base pairs (82.9%), with the vast majority being G:C→T:A transversions (47.1%). Our data support a possible etiologic role of 4-ABP in bladder carcinogenesis and provide a mechanistic view on how DNA adduct-driven mutagenesis, specifically targeted to bladder urothelium, may account for organ-specific tumorigenicity of this chemical.     

Altered DNA repair capacity and bleomycin sensitivity as risk markers for non-small cell lung cancer

DNA repair capacity in human peripheral blood lymphocytes was monitored by the repair rate of bleomycin-induced DNA damage using an alkaline single-cell gel electrophoresis assay (comet assay). DNA repair capacity, after 15 min repair time, in lymphocytes of non-small cell lung cancer patients (n = 160) and controls (n = 180) was 67% and 79.3%, respectively (p < 0.0004). Bleomycin sensitivity defined as the tail moment of bleomycin-treated peripheral blood lymphocytes, without allowing time for DNA repair, was significantly higher in lung cancer patients than in tumor-free hospital controls (p < 0.0001). There was no correlation, in either patient or control group, between the bleomycin sensitivity and DNA repair capacity with age or gender. The median values of DNA repair capacity and sensitivity in controls were used as the cut-off points for calculating odds ratios (OR). After adjustment for age, gender and smoking status, the cases vs. controls had reduced DNA repair capacity (OR = 2.1; 95% confidence limit [CL] 1.1-4.0) and increased bleomycin sensitivity (OR = 4; 95% CL 2.2-7.4). For current smokers, the adjusted risk associated with bleomycin sensitivity was 2.3 (95% CL 1.1-4.9). We conclude that our standard comet assay as a phenotypical repair test has sufficient sensitivity and rapidity allowing application to both native and cryopreserved lymphocytes. Bleomycin sensitivity and DNA repair capacity were found to be 2 independent susceptibility markers for non-small cell lung cancer, confirming similar investigations with different marker end points. The latter were much more time consuming than the method used in our study. Thus, the comet assay is more suitable for screening large numbers of individuals in epidemiological studies. Validation of this assay in large prospective studies for the identification of subjects at high risk for non-small cell lung cancer is now warranted.     

High-order interactions among genetic polymorphisms in nucleotide excision repair pathway genes and smoking in modulating bladder cancer risk

Polymorphisms in nucleotide excision repair (NER) genes may cause variations in DNA repair capacity and increase susceptibility to bladder cancer through complex gene-gene and gene-smoking interactions. We applied two data mining approaches to explore high-order gene-gene and gene-environment interactions among 13 polymorphisms in nine major NER genes in 696 bladder cancer patients and 629 controls. Individually, only the XPD D312N variant genotypes exhibited a slightly increased risk for bladder cancer. In classification and regression tree analysis, we observed gene-gene interactions among CCNH V270A, ERCC6 M1097V and RAD23B A249V in ever smokers: smokers with the variant alleles at these three loci had an almost 30-fold increased risk of bladder cancer [odds ratio (OR): 29.6, 95% confidence interval (CI): 9.3-93.7]. When evaluating combined effect of above four single nucleotide polymorphisms, we found a significant gene dosage effect for increased bladder cancer risk with increasing numbers of unfavorable genotypes. Compared with individuals with less than 2 unfavorable genotypes, those with 2 unfavorable genotypes and more than 2 unfavorable genotypes exhibited increased bladder cancer risk with ORs of 1.14 (95% CI: 0.87-1.51) and 2.15 (95% CI: 1.56-2.97), respectively (P < 0.001). The risks were more evident in ever smokers with ORs of 1.43 (95% CI: 1.02-2.01) and 3.40 (95% CI: 2.24-5.15), respectively (P < 0.001). In multifactor dimensionality reduction (MDR) analysis, the five-factor model including smoking, CCNH V270A, ERCC6 M1097V, RAD23B A249V and XPD D312N had the best ability to predict bladder cancer risk. The contributions of these polymorphisms may jointly affect bladder cancer risk through gene-gene and gene-smoking interactions.     

Oxidative DNA damage induced by a metabolite of 2-naphthylamine, a smoking-related bladder carcinogen.

2-Naphthylamine (2-NA), a bladder carcinogen, is contained in cigarette smoke. DNA adduct formation is thought to be a major cause of DNA damage by carcinogenic aromatic amines. We have investigated whether a metabolite of 2-NA, 2-nitroso-1-naphthol (NO-naphthol) causes oxidative DNA damage, using (32)P-labeled DNA fragments. We compared the mechanism of DNA damage induced by NO-naphthol with that by N-hydroxy-4-aminobiphenyl (4-ABP(NHOH)), a metabolite of 4-aminobiphenyl, another smoking-related bladder carcinogen. NO-naphthol caused Cu(II)-mediated DNA damage at T > C > G residues, with non-enzymatic reduction by NADH. Catalase and bathocuproine, a Cu(I)-specific chelator, inhibited the DNA damage, suggesting the involvement of H(2)O(2) and Cu(I). Some free. OH scavengers also attenuated NO-naphthol-induced DNA damage, while free. OH scavengers had no effect on the DNA damage induced by 4-ABP(NHOH). This difference suggests that the reactive species formed by NO-naphthol has more free. OH-character than that by 4-ABP(NHOH). A high-pressure liquid chromatograph equipped with an electrochemical detector showed that NO-naphthol induced 8-oxo-7,8-dihydro-2'-deoxyguanosine formation in the presence of NADH and Cu(II). The oxidative DNA damage by these amino-aromatic compounds may participate in smoking-related bladder cancer, in addition to DNA adduct formation.     

Bleomycin-induced mutagen sensitivity, passive smoking, and risk of breast cancer in Chinese women: a case–control study

Background

It is well recognized that genetic variation as well as environmental factors modulates breast cancer risk. Deficiencies in DNA repair capacity are thought to associate with breast cancer risk. The main aim of this study was to use the mutagen sensitivity assay as an indirect measure of DNA repair capacity to assess breast cancer risk and the relationship between passive smoking and breast cancer risk among women in China.

Methods

We carried out a case–control study, involving 196 Chinese patients with breast cancer and 211 controls without the disease and with no history of cancer. We investigated the association between mutagen sensitivity and breast cancer risk using bleomycin as the mutagen. Mutagen sensitivity was measured by quantifying the chromatid breaks induced by mutagens in short-term cultures of peripheral blood lymphocytes. Nonparametric tests and the Fisher’s exact test were used to determine the statistical significance of the crude case–control comparisons, followed by logistic regression to adjust for important covariates.

Results

The mean number of bleomycin-induced breaks per cell was 0.81 for cases compared with 0.73 for the controls (p = 0.016). A greater number of bleomycin-induced chromosomal breaks per cell was associated with an increased risk of breast cancer (adjusted odds ratio of 1.82, p trend <0.01). The association between bleomycin sensitivity and breast cancer risk was greater for women who were exposed to tobacco smoke (passive smokers). The combination of bleomycin sensitivity and exposure to tobacco smoke increased risk further; women passive smokers with high sensitivity to bleomycin had a 2.77-fold increased risk of breast cancer.

Conclusions

Our data indicate that increased bleomycin-induced mutagen sensitivity is significantly associated with an increased risk of breast cancer among Chinese women. Exposure to passive smoke is also associated with increased breast cancer risk, and the correlation is even greater for women with both longer passive exposure to tobacco smoke and high sensitivity to bleomycin.     

DNA repair gene XRCC3 codon 241 polymorphism, its interaction with smoking and XRCC1 polymorphisms, and bladder cancer risk.

DNA repair efficiency varies among individuals, with reduced repair capacity as a risk factor for various cancers. This variability could be partly explained by allelic variants for different DNA repair genes. We examined the role of a common polymorphism in the XRCC3 gene (codon 241: threonine to methionine change) and bladder cancer risk. This gene plays a role in the homologous recombination pathway, which repairs double-strand breaks. The functional consequences of the XRCC3 codon 241 polymorphism are still unknown. We hypothesized that this polymorphism could affect repair of smoking-associated DNA damage and could thereby affect bladder cancer risk. We genotyped 233 bladder cancer cases and 209 controls who had been frequency matched to cases on age, sex, and ethnicity. We observed little evidence of a positive association between subjects who carried at least one copy of the codon 241 Met allele and bladder cancer (odds ratio: 1.3; 95% confidence interval: 0.9-1.9). Among heavy smokers, individuals with the Met allele had about twice the risk of those without it; however, a test of interaction was not statistically significant (P = 0.26). Previously, we observed in these subjects an association between bladder cancer risk and allelic variants of the XRCC1 gene, which is involved in the repair of base damage and single-strand breaks. In this study, we found some evidence for a gene-gene interaction between the XRCC1 codon 194 and XRCC3 codon 241 polymorphisms (P = 0.09) and some support for a possible gene-gene-smoking three-way interaction (P = 0.08).     

DNA adduct levels in congenic rapid and slow acetylator mouse strains following chronic administration of 4-aminobiphenyl.

4-Aminobiphenyl (4-ABP) is a human and mouse bladder carcinogen. Epidemiological studies have shown that individuals with a slow acetylator phenotype, especially those exposed to high levels of carcinogenic aromatic amines, show an increased susceptibility to bladder cancer. In order to determine if a slow acetylator phenotype results in increased DNA damage, congenic mouse strains C57BL/6J and B6.A-Nat(s), which differ genetically at the acetyltransferase (EC 2.3.1.5) locus as homozygous rapid (Natr/Natr) and homozygous slow (Nat(s)/Nat(s)) acetylators respectively, were continuously administered 4-ABP.HCl (55-300 p.p.m.) in their drinking water for 28 days. The levels of covalently bound N-(deoxyguanosin-8-yl)-4-ABP-DNA adducts, which are believed to be critical for the initiation of tumors, were quantitated in the liver and bladder by 32P-postlabeling analysis. The levels of the hepatic DNA adduct increased with dose in both sexes, but were independent of the mouse acetylator genotype. At comparable doses, however, the levels of DNA adducts were 2-fold higher in the liver of the female as compared to the male animals. The DNA adducts also increased with dose in bladder of the male mice, but in contrast to the liver, the adduct levels were approximately 2-fold lower in the bladder DNA of the female mice. Also in contrast to the liver, the levels of bladder DNA adducts were significantly higher (P < or = 0.03) in the phenotypic rapid acetylator females compared to the slow acetylators at both 75 and 150 p.p.m. doses; the median levels of adducts were 10-20% higher in the phenotypic slow acetylator male bladders compared to their rapid acetylator counterparts. The results of these studies are consistent with the increased carcinogenicity of 4-ABP to the liver of female mice and the bladder of male mice. They further suggest that factors other than acetylator phenotype limit the extent of DNA adduct formation from 4-ABP in these mice.     

Cell cycle checkpoints, DNA damage/repair, and lung cancer risk

Given that defects in cell cycle control and DNA repair capacity may contribute to tumorigenesis, we hypothesized that patients with lung cancer would be more likely than healthy controls to exhibit deficiencies in cell cycle checkpoints and/or DNA repair capacity as gauged by cellular response to in vitro carcinogen exposure. In an ongoing case-control study of 155 patients with newly diagnosed lung cancer and 153 healthy controls, we used the comet assay to investigate the roles of cell cycle checkpoints and DNA damage/repair capability in lung tumorigenesis. The median gamma-radiation-induced and benzo(a)pyrene diol epoxide-induced Olive tail moments, the comet assay parameter for measuring DNA damage, were significantly higher in the case group (5.31 and 4.22, respectively) than in the control group (4.42 and 2.83, respectively; P < 0.001). Higher tail moments of gamma-radiation and benzo(a)pyrene diol epoxide-induced comets were significantly associated with 2.32- and 4.49-fold elevated risks, respectively, of lung cancer. The median gamma-radiation-induced increases of cells in the S and G(2) phases were significantly lower in cases (22.2% and 12.2%, respectively) than in controls (31.1% and 14.9%, respectively; P < 0.001). Shorter durations of the S and G(2) phases resulted in 4.54- and 1.85-fold increased risks, respectively, of lung cancer. Also observed were joint effects between gamma-radiation-induced increases of S and G(2) phase frequencies and mutagen-induced comets. In addition, we found that in controls, the S phase decreased as tail moment increased. This study is significant because it provides the first molecular epidemiologic evidence linking defects in cell cycle checkpoints and DNA damage/repair capacity to elevated lung cancer risk.     

Smoking,DNA repair capacity and risk of nonsmall cell lung cancer

Tobacco-related carcinogens cause a variety of DNA damage that is repaired by different enzymatic pathways, suggesting that DNA repair plays an important role in tobacco-induced carcinogenesis. In a large hospital-based case-control study, we investigated DNA repair capacity (DRC) as a biomarker for susceptibility to nonsmall cell lung cancer (NSCLC) and evaluated the possible interaction between DRC and tobacco smoke in 467 newly diagnosed NSCLC patients and 488 cancer-free controls. We measured DRC in cultured peripheral lymphocytes using the host-cell reactivation assay with a reporter gene damaged by an activated tobacco carcinogen, benzo[a]pyrene diol epoxide. The results showed that current smokers exhibited the highest DRCs as compared to former and nonsmokers both among patients and control subjects. There were no differences of DRC among 3 different histopathologic types of NSCLC. Logistic regression analysis revealed that suboptimal DRC and pack-years smoked were independent predictors of NSCLC risk. The overall 15.5% reduction in DRC observed in the cases (7.84%) compared to the controls (9.28%) (p<0.001) was associated with an approximately 2-fold increased risk of NSCLC (adjusted odds ratio (OR) = 1.85, 95% confidence interval (CI) 1.42-2.42). There was a significant dose-response association between decreased DRC and increased risk of lung cancer. Furthermore, we observed a nonstatistically significant additive but not multiplicative interaction between DRC and pack-years smoked on lung cancer risk, particularly in the histopathologic types of NSCLC other than adenocarcinoma. The results suggest that suboptimal DRC is associated with increased risk of NSCLC and DRC may modulate the risk of lung cancer associated with smoking but the latter needs to be verified in larger studies.     

Interactions between cigarette smoking and XPC-PAT genetic polymorphism enhance bladder cancer risk

Inherited polymorphisms in the XPC gene that lead to a reduction in DNA repair capacity may increase susceptibility to bladder cancer. We investigated three polymorphisms of the XPC gene (PAT, Ala499Val and Lys939Gln) in 600 subjects with bladder cancer and in 609 healthy controls by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay in a Chinese Han population. Smoking was associated with a significant increase in the risk for bladder cancer (OR, 2.48; 95% CI, 1.91-3.21). The risk was greater among heavy smokers (OR, 3.09, 95% CI, 2.24-4.25) compared to light smokers (OR, 1.91, 95% CI, 1.37-2.68). In three polymorphisms of XPC, only the XPC-PAT variant genotype exhibited a significantly increased risk for bladder cancer. When the total smoking exposure-gene interaction was examined, the three polymorphisms did not exhibit any significant effect in never smokers but a significant dose-response association in light or heavy smokers. Especially, the bladder cancer risk was significantly elevated among the polymorphisms of XPC-PAT(+/-) (OR, 2.56, 95% CI, 1.56-4.21, p<0.001; OR, 3.41, 95% CI, 2.19-5.29, p<0.001) and XPC-PAT(+/+) (OR, 3. 00, 95% CI, 1.31-6.88, p=0.009; OR, 6. 78, 95% CI, 3.00-15.54, p<0.001) with either light or heavy smoking exposure, respectively. XPC-PAT polymorphisms contribute to the risk for developing bladder cancer and an elevated risk of bladder cancer was significantly associated with the gene-environment (smoking) interaction in a Chinese Han population.     

Double-strand break damage and associated DNA repair genes predispose smokers to gene methylation

Gene promoter hypermethylation in sputum is a promising biomarker for predicting lung cancer. Identifying factors that predispose smokers to methylation of multiple gene promoters in the lung could affect strategies for early detection and chemoprevention. This study evaluated the hypothesis that double-strand break (DSB) repair capacity and sequence variation in genes in this pathway are associated with a high methylation index in a cohort of current and former cancer-free smokers. A 50% reduction in the mean level of DSB repair capacity was seen in lymphocytes from smokers with a high methylation index, defined as three or more of eight genes methylated in sputum, compared with smokers with no genes methylated. The classification accuracy for predicting risk for methylation was 88%. Single nucleotide polymorphisms within the MRE11A, CHEK2, XRCC3, DNA-PKc, and NBN DNA repair genes were highly associated with the methylation index. A 14.5-fold increased odds for high methylation was seen for persons with seven or more risk alleles of these genes. Promoter activity of the MRE11A gene that plays a critical role in recognition of DNA damage and activation of ataxia-telangiectasia mutated was reduced in persons with the risk allele. Collectively, ours is the first population-based study to identify DSB DNA repair capacity and specific genes within this pathway as critical determinants for gene methylation in sputum, which is, in turn, associated with elevated risk for lung cancer.     

Role of TP53 in repair of N-(deoxyguanosin-8-yl)-4-aminobiphenyl adducts in human transitional cell carcinoma of the urinary bladder

The global genomic repair of DNA adducts was examined in human papillary transitional cell carcinoma (TCC) cell lines after exposure to N:-hydroxy-4-acetylaminobiphenyl (N-OH-AABP), the proximate carcinogenic metabolite of the human bladder carcinogen 4-aminobiphenyl (ABP). (32)P-post-labeling analysis of TCC cultures exposed to N-OH-AABP revealed a major adduct, identified as the 3',5'-bisphosphate derivative of N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP). The amount of adduct formation in TCC10 was dependent upon the dose and the duration of exposure and ranged between 1 and 5 adducts/10(7) nucleotides. To test if p53 regulates repair of the dG-C8-ABP adduct in genomic DNA, an isogeneic set of cell lines was obtained by infection of the TCC10 cultures with a retroviral construct expressing a trans-dominant mutant of p53, namely a Val-->Ala mutation at codon 143. The TDM143-TCC10 line expressing the mutant form of p53 was selected. The rate of repair of dG-C8-ABP was compared between TCC10 and TDM143-TCC10 cultures after treatment with 15 microM N-OH-AABP. The rate of disappearance of the adduct was monitored over a period of time after chemical treatment. (32)P-post-labeling analysis of dG-C8-ABP in parental TCC10 showed its rapid removal, the majority of adducts disappearing within 48 h. In contrast to TCC10, TDM143-TCC10 was relatively slower in removal of dG-C8-ABP. After 24 h DNA repair TDM143-TCC10 showed an approximately 3-fold greater amount of dG-C8-ABP compared with TCC10. These results imply that p53 plays a role in the repair of ABP adducts and that in p53 null cells the unrepaired DNA damage could cause accumulation of mutations, which might contribute to increased genomic instability and neoplastic progression.     

DNA repair capacity and lung cancer risk in never smokers.

Besides secondhand smoke exposure, few other risk factors for lung cancer in lifetime never smokers have been identified. We present the estimates of lung cancer risk associated with suboptimal DNA repair capacity (DRC) measured by the host-cell reactivation assay in lifetime never smokers using data from 219 cases and 309 matched controls enrolled in a case-control study. Suboptimal DRC level (below the control median) conferred a significantly increased lung cancer risk in never smokers [odds ratio, 1.92; 95% confidence interval (95% CI), 1.3-2.9; P = 0.0024]. There was a 3.38-fold risk for individuals with DRC below the first quartile (95% CI, 1.8-6.3) compared with individuals with DRC above the third quartile. Secondhand smoke exposure in individuals with DRC below the control median was associated with a 3.81-fold risk of lung cancer (95% CI, 2.3-6.4). A 2.49-fold (95% CI, 1.1-5.6) risk was noted for the joint effects of lung cancer family history in first-degree relatives and suboptimal DRC. Relatives of probands (cases and controls) with lowest DRC (below the first quartile) were significantly more likely to be diagnosed with lung cancer (odds ratio, 2.69; 95% CI, 1.1-6.7) compared with relatives of probands with the most proficient DRC (above the third quartile). Relatives of probands with suboptimal (below the control median) versus proficient DRC also had an earlier age at diagnosis with lung cancer, although the only statistically significant difference was in female relatives (55.4 versus 67.7 years; P = 0.03).     

Environmental tobacco smoke and bladder cancer risk in never smokers of Los Angeles County

Cigarette smoking is a major risk factor for bladder cancer and a prominent point source of 4-aminobiphenyl (4-ABP), a recognized human bladder carcinogen. 4-ABP-hemoglobin (Hb) adducts are established biomarkers of 4-ABP exposure in humans. The role of environmental tobacco smoke (ETS) in the etiology of bladder cancer is largely unknown. As part of a large population-based bladder cancer study in Los Angeles County, California, lifetime exposure to ETS was ascertained for 148 cases and 292 control subjects who had never used any tobacco products over their lifetime. 4-ABP-Hb adducts were quantitatively measured on 230 control subjects. Female lifelong nonsmokers living with two or more smokers during childhood were significantly related to risk of bladder cancer [odds ratio (OR), 3.08; 95% confidence interval (95% CI), 1.16-8.22]. During adulthood, approximately 2-fold risks were seen among women living with a spouse/domestic partner who smoked for > or =10 years or having a coworker who smoked in an indoor environment for > or =10 years. When all sources of ETS exposure were combined, a statistically significant, dose-dependent association (P for trend = 0.03) was noted in women, with the OR for the highest category of ETS exposure being 5.48 (95% CI, 1.06-28.36). Levels of 4-ABP-Hb adducts varied by ETS exposure status among female control subjects. Mean level was lowest in women never exposed to ETS (16.4 pg/g Hb) and highest in those with current ETS exposure (23.6 pg/g Hb). ETS exposure was associated with neither bladder cancer risk nor 4-ABP-Hb adduct levels in male lifelong nonsmokers. In conclusion, ETS is a risk factor for bladder cancer in women who were lifelong nonusers of any tobacco products.     

Polymorphisms in DNA damage binding protein 2 (DDB2) and susceptibility of primary lung cancer in the Chinese: a case-control study

DNA damage binding protein 2 (DDB2) is one of the major DNA repair proteins involved in the nucleotide excision repair (NER) pathway. Mutations in the DDB2 gene can cause a repair-deficiency syndrome xeroderma pigmentosum group E. Because tobacco carcinogens can cause DNA damage that is repaired by NER and suboptimal NER capacity is reported to be associated with lung cancer risk, we hypothesized that common variants in the DDB2 gene are associated with lung cancer risk. To test this hypothesis, we conducted a case-control study of 1010 patients with incident lung cancer and 1011 cancer-free controls and genotyped two DDB2 single nucleotide polymorphisms (SNPs) (rs830083 and rs3781620) that are in linkage disequilibrium with other untyped SNPs. We found that compared with the rs830083CC, subjects carrying the heterozygous rs830083CG genotype had a significantly 1.31-fold increased risk of lung cancer [95% confidence interval (CI) 1.08-1.60] and those carrying the homozygous rs830083GG genotype had a non-significantly 1.22-fold elevated risk (95% CI 0.89-1.67). In addition, effects of the combined rs830083CG/GG variant genotypes were more evident in young subjects, heavy smokers and subjects with a positive family history of cancer. These findings indicate, for the first time, that the DDB2 rs830083 polymorphism may contribute to the etiology of lung cancer. Further functional studies on this SNP and/or related variants are warranted to elucidate the underlying molecular mechanisms of the association.     

Polymorphisms in DNA repair genes, smoking, and pancreatic adenocarcinoma risk

Base excision repair and nucleotide excision repair are vital responses to multiple types of DNA damage, including damage from tobacco exposure. Single-nucleotide polymorphisms (SNP) in these pathways may affect DNA repair capacity and therefore influence risk for cancer development. We performed a clinic-based, case-control study comprising 481 consecutive patients with confirmed pancreatic adenocarcinoma and 625 healthy controls. Allele and genotype frequencies for 16 SNPs in DNA repair genes ERCC1, XPD/ERCC2, XPC, XPF/ERCC4, OGG1, and XRCC1 were compared after adjusting for age, sex, and smoking history. Subgroup analysis by sex and smoking history was performed. Carriers of one or two XPF/ERCC4 minor alleles at R415Q had decreased risk of pancreatic adenocarcinoma compared with those who had two major alleles [odds ratio (OR), 0.59; 95% confidence interval (95% CI), 0.40-0.85]. Heavy smokers (>40 pack-years) had increased risk for cancer if they were carriers of at least one minor allele for XPD/ERCC2 at D312N (OR, 2.78; 95% CI, 1.28-6.04) or D711D (OR, 2.19; 95% CI, 1.01-4.73). No other significant differences in risk were identified. Minor alleles in DNA repair genes XPF/ERCC4 and XPD/ERCC2 were associated with altered risk for pancreatic cancer.     

Genetic instability in bladder cancer assessed by the comet assay

BACKGROUND: Latent genetic instability has been associated with an increased risk for several cancers. We used the comet assay (single-cell gel electrophoresis) to assess whether genetic instability, as reflected by susceptibility to DNA damage, was associated with the risk of bladder cancer in a case-control study. METHODS: We used the comet assay to measure baseline and benzo[a]pyrene diol epoxide (BPDE)- and gamma-radiation-induced DNA damage in individual peripheral blood lymphocytes from 114 incident case patients with bladder cancer and 145 matched healthy control subjects. All subjects provided personal information, including smoking history. DNA damage was visualized with the comet assay and quantified by the Olive tail moment parameter, a relative measure. Multivariable analysis was used to assess relative risks for bladder cancer associated with DNA damage. All statistical tests were two-sided. RESULTS: Baseline levels of DNA damage were statistically significantly higher in case patients (tail moment = 1.40) than in control subjects (tail moment = 1.21) (difference = 0.19, 95% confidence interval [CI] = 0.04 to 0.32; P =.015), as were gamma-radiation-induced (tail moment = 4.76 versus 4.22; difference = 0.54, 95% CI = 0.11 to 0.96; P =.013) and BPDE-induced (tail moment = 4.06 versus 3.45; difference = 0.61, 95% CI = 0.23 to 0.99; P =.002) DNA damage. When data were dichotomized at the median value for DNA damage in control subjects and adjusted for age, sex, ethnicity, and smoking status, an increased estimated relative risk of bladder cancer was statistically significantly associated with DNA damage at baseline (odds ratio [OR] = 1.84, 95% CI = 1.07 to 3.15) and after gamma-radiation (OR = 1.81, 95% CI = 1.04 to 3.14) but not after BPDE treatment (OR = 1.69, 95% CI = 0.98 to 2.93). CONCLUSION: Latent genetic instability as measured by the comet assay is associated with an increased estimated relative risk of bladder cancer.     

Modifying Effect of Smoking on GSTM1 and NAT2 in Relation to the Risk of Bladder Cancer in Mongolian Population: A Case-Control Study

Objectives: Tobacco smoking is the predominant risk factor for bladder cancer as it contains cancer-causing chemicals. However, genetic factors may play important role in response towards chemical carcinogens. In this study we aim to investigate genetic polymorphisms of glutathione S-transferase M1 (GSTM1) and N-acetyltransferase 2 (NAT2) as determinants of bladder cancer risk, independently and in combination with tobacco use in the Mongolian population. Materials and Methods: The current study was a hospital-based case-control study including 60 histologically confirmed bladder cancer patients and 60 cancer-free controls. PCR-RFLP assay was used to determine the presence of GSTM1 and NAT2 polymorphisms in bladder cancer patients and controls. GSTM1 and NAT2 were tested using binary logistical regression analysis with adjustment or stratification according to the smoking. Results: There were 46 men and 14 women diagnosed with bladder cancer, with mean age was 58±4. The controls included 37 men and 23 women with a mean age of 57±3. The frequency of GSTM1 null genotype was higher in controls (71.67%) than in bladder cancer patients (58.33%) without statistical significance (OR=0.5534; 95% CI=0.2586-1.1843), (p=0.128). The NAT2 low acetylator phenotype was more common in patients with bladder cancer (15%) than in controls (5%). Furthermore, individuals with NAT2 low acetylator phenotype had a nearly 3.35-fold increased risk to develop bladder cancer (OR=3.35; 95% CI=0.8604-13.0657), (p=0.081) while the risk was even higher when combined with null GSTM1 genotype (OR=4; 95% CI=0.4459-37.5308), (p=0.213) but there was no statistical significance. Prevalence of smoking in bladder cancer patients was higher than controls and increased significantly the risk of bladder cancer (OR=8.31; 95% CI=3.66-18.88). Smokers with GSTM1 null genotype were at 5-fold higher risk of bladder cancer (OR=5.0; 95% CI=1.55-16.16), (p=0.007) while NAT2 low acetylator phenotype increased bladder cancer risk by 20-fold (OR=20.5; 95% CI=2.33-80.86), (p=0.006). Conclusion: The current study shows that tobacco smokers with the NAT2 low acetylator phenotype and GSTM1 null genotype have the highest risk of bladder cancer in the Mongolian population.     

Risk assessment in first degree female relatives of breast cancer patients using the alkaline Comet assay

First degree female relatives (FDFRs) of breast cancer patients have been reported to have a 2- to 3-fold increase in breast cancer risk as compared with the general population. Assessment of genetic instability (DNA damage and repair efficiency) is an important parameter concerning mutagenesis and carcinogenesis. In an attempt to identify individuals at high risk of breast cancer in the FDFRs of breast cancer patients, two tests were used: the alkaline Comet assay on leucocytes and the micronucleus test (MNT) on buccal epithelial cells. In addition to FDFRs, two other categories of subjects were included: breast cancer patients and controls. The Comet assay was used to study basal DNA damage, DNA susceptibility to a mutagen (N-methyl N-nitro N-nitrosoguanidine) and DNA repair efficiency. In addition, the MNT served as an indicator of chromosome breakage/aneuploidy. A significant increase in DNA damage (basal and after treatment with a mutagen, as well as after allowing repair to take place) and micronucleus frequency was observed from controls to FDFRs and from FDFRs to breast cancer patients. There was considerable variability in the subjects with respect to both of these parameters. Outliers identified among the FDFRs based on 3 SD limits of DNA damage and micronucleus frequency were considered as high risk individuals.