In vitro Benzo[a]pyrene Diol Epoxide–Induced DNA Adducts and Risk of Squamous Cell Carcinoma of Head and Neck

Combining Phenotypes of Nucleotide Excision Repair Pathway to Predict the Risk of Head and Neck Squamous Cell Carcinomas in a Chinese Population

Background

Nucleotide excision repair (NER) is pivotal in the development of smoking-related malignancies. Nine core genes (XPA, XPB, XPC, XPD, XPF, XPG, ERCC1, DDB1, and DDB2) are highly involved in the NER process. We combined two phenotypes of NER pathway (NER protein and NER gene mRNA expression) and evaluated their associations with the risks of the head and neck squamous cell carcinomas (HNSCCs) in a Chinese population.

Methods

We conducted a case-control study of 337 HNSCC patients and 285 cancer-free controls by measuring the expression levels of nine core NER proteins and NER gene mRNA in cultured peripheral lymphocytes.

Results

Compared with the controls, cases had statistically significantly lower protein expression levels of XPA (P < 0.001) and lower mRNA expression levels of XPA and XPB (P = 0.005 and 0.001, respectively). After dividing the subjects by controls' medians of expression levels, we found an association between increased risks of HNSCCs and low XPA protein level (P_trend = 0.031), as well as low mRNA levels of XPA and XPB (P_trend = 0.024 and 0.001, respectively). Subsequently, we correlated the two phenotypes and found associations between the NER mRNA and protein levels. Finally, the sensitivity of the expanded model with protein and mRNA expression levels, in addition to demographic variables, on HNSCCs risk was significantly improved.

Conclusions

Combining two phenotypes of NER pathway may be more effective than the model only including one single phenotype for the assessment of risks of HNSCCs.

Associations between expression levels of nine core nucleotide excision repair genes in lymphocytes and risk of head and neck squamous cell carcinomas in a Chinese population

BACKGROUND

Head and neck squamous cell carcinomas (HNSCCs) are one of the most common cancers in the world, and nucleotide excision repair (NER) is involved in HNSCCs susceptibility. We investigated whether mRNA expression levels of nine core NER genes were associated with risk of HNSCCs in a Chinese population.

METHODS

In this study of 251 HNSCC patients and 232 healthy controls, we quantified NER gene mRNA expression levels in cultured peripheral lymphocytes using a quantitative real-time PCR.

RESULTS

Compared with the controls, HNSCC patients had statistically significantly lower expression levels of XPA and XPB (P = 0.029 and 0.001, respectively). After dividing the subjects by the controls' median values of expression levels, we found a dose-dependent association between an increased risk of HNSCCs and low expression levels of XPB (adjusted OR 1.56 and 95% CI 1.07-2.28; P_trend = 0.001). We also identified a significant multiplicative interaction between smoking status as well as alcohol status and mRNA expression levels of XPB (P = 0.014 and 0.042, respectively). Finally, after integrating demographic variables, we found the addition of smoking status and XPB expression levels to the model significantly improved the sensitivity of the expanded model on HNSCC risk.

CONCLUSION

Reduced mRNA expression levels of XPB were associated with an increased risk of HNSCCs in a Chinese population.

Comprehensive Analysis of the Association Between the rs1138272 Polymorphism of the GSTP1 Gene and Cancer Susceptibility

Background: We obtained conflicting results regarding the relationship between the genetic role of the rs1138272 C/T polymorphism of the GSTP1 (Glutathione S-Transferase pi) gene and the risk of various cancers.

Methods: Using the presently available data, a meta-analysis was conducted to comprehensively evaluate the genetic relationship between the GSTP1 rs1138272 polymorphism and cancer susceptibility.

Results: A total of 43 studies including 15,688 cases and 17,143 controls were recruited into our quantitative synthesis. In the overall population, we observed an increased risk of overall cancer cases, compared with unrelated controls, in the genetic models of allele T vs. allele C (P-association = 0.007, OR = 1.17), carrier T vs. carrier C (P-association = 0.035, OR = 1.11), TT vs. CC (P-association = 0.002, OR = 1.45), TT vs. CC+CT (P-association = 0.009, OR = 1.42), and CT+TT vs. CC (P-association = 0.027, OR = 1.13). We detected similar positive results within the Asian population. Additionally, there was a significant increase in the incidence of cancer for Africans under all genetic models (all P-association < 0.05, OR > 1). When targeting the Caucasian population, we detected a positive association with the TT vs. CC and TT vs. CC+CT models in the “Colorectal cancer” (P-association < 0.05, OR < 1) and “Head and neck cancer” (P-association < 0.05, OR > 1) subgroups. For the “Lung cancer” subgroup, we observed a slightly increased risk in Caucasians under the models of allele T vs. allele C, carrier T vs. carrier C, CT vs. CC, and CT+TT vs. CC (P-association < 0.05, OR > 1).

Conclusion: The TT genotype of the GSTP1 rs1138272 polymorphism is likely related to the susceptibility to overall cancer in the Asian and African populations and, specifically, “Colorectal” and “Head and neck” cancers in the Caucasian population. In addition, the CT genotype of the GSTP1 rs1138272 polymorphism may be linked to the risk of lung cancer in Caucasians. Additional evidence is required to confirm this conclusion.

Glutathione S-transferase pi 1 variant and squamous cell carcinoma susceptibility: a meta-analysis of 52 case-control studies

Background

There are several meta-analyses on the genetic relationship between the rs1695 polymorphism within the GSTP1 (glutathione S-transferase pi 1) gene and the risk of different SCC (squamous cell carcinoma) diseases, such as ESCC (oesophageal SCC), HNSCC (head and neck SCC), LSCC (lung SCC), and SSCC (skin SCC). Nevertheless, no unified conclusions have been drawn.

Methods

Herein, an updated meta-analysis was performed to evaluate the probable impact of GSTP1 rs1695 on the susceptibility to different SCC diseases under six genetic models (allele, carrier, homozygote, heterozygote, dominant, and recessive). Three online databases, namely, PubMed, WOS (Web of Science), and Embase (Excerpta Medica Database), were searched.

Results

Initially, we obtained a total of 497 articles. Based on our selection criteria, we eventually included 52 case-control studies (9763 cases/15,028 controls) from 47 eligible articles. As shown in the pooling analysis, there was no difference in the risk of overall SCC disease between cases and controls [allele, P_a (P value of association test) = 0.601; carrier, P_a = 0.587; homozygote, P_a = 0.689; heterozygote, P_a = 0.167; dominant, P_a = 0.289; dominant, P_a = 0.548]. Similar results were obtained after stratification by race (Asian/Caucasian), genotyping, control source, and disease type (ESCC/HNSCC/LSCC/SSCC) (all P_a > 0.05).

Conclusion

The rs1695 polymorphism within the GSTP1 gene is not associated with the risk of overall SCC or a specific SCC type, including ESCC, HNSCC, LSCC, and SSCC.

Filling the gap between chemical carcinogenesis and the hallmarks of cancer: A temporal perspective

BACKGROUND

Cancer is believed to arise through the perturbation of pathways and the order of pathway perturbation events can enhance understanding and evaluation of carcinogenicity. This order has not been examined so far, and this study aimed to fill this gap by attempting to gather evidence on the potential temporal sequence of events in carcinogenesis.

DESIGN

The methodology followed was to discuss first the temporal sequence of hallmarks of cancer from the point of view of pathological specimens of cancer (essentially branched mutations) and then to consider the hallmarks of cancer that one well-known carcinogen, benzo(a)pyrene, can modify.

RESULTS

Even though the sequential order of driving genetic alterations can vary between and within tumours, the main cancer pathways affected are almost ubiquitous and follow a generally common sequence: resisting cell death, insensitivity to antigrowth signals, sustained proliferation, deregulated energetics, replicative immortality and activation of invasion and metastasis. The first 3 hallmarks can be regarded as almost simultaneous while angiogenesis and avoiding immune destruction are perhaps the only hallmarks with a varying position in the above sequence.

CONCLUSIONS

Our review of hallmarks of cancer and their temporal sequence, based on mutational spectra in biopsies from different cancer sites, allowed us to propose a hypothetical temporal sequence of the hallmarks. This sequence can add molecular support to the evaluation of an agent as a carcinogen as it can be used as a conceptual framework for organising and evaluating the strength of existing evidence.

Associations between expression levels of nucleotide excision repair proteins in lymphoblastoid cells and risk of squamous cell carcinoma of the head and neck

Squamous cell carcinoma of head and neck (SCCHN) is one of the most common malignancies worldwide, and nucleotide excision repair (NER) is involved in SCCHN susceptibility. In this analysis of 349 newly diagnosed SCCHN patients and 295 cancer-free controls, we investigated whether expression levels of eight core NER proteins were associated with risk of SCCHN. We quantified NER protein expression levels in cultured peripheral lymphocytes using a reverse-phase protein microarray. Compared with the controls, SCCHN patients had statistically significantly lower expression levels of ERCC3 and XPA (P = 0.001 and 0.001, respectively). After dividing the subjects by controls' median values of expression levels, we found a dose-dependent association between an increased risk of SCCHN and low expression levels of ERCC3 (adjusted OR, 1.75, and 95% CI: 1.26-2.42; P_trend = 0.008) and XPA (adjusted OR, 1.88; 95% CI, 1.35-2.60; P_trend = 0.001). We also identified a significant multiplicative interaction between smoking status and ERCC3 expression levels (P = 0.014). Finally, after integrating demographic and clinical variables, we found that the addition of ERCC3 and XPA expression levels to the model significantly improved the sensitivity of the expanded model on SCCHN risk. In conclusion, reduced protein expression levels of ERCC3 and XPA were associated with an increased risk of SCCHN. However, these results need to be confirmed in additional large studies.

Reduced mRNA expression of nucleotide excision repair genes in lymphocytes and risk of squamous cell carcinoma of the head and neck

Nucleotide excision repair (NER) plays a critical role in the development of smoking-related cancers. We hypothesize that mRNA expression levels of NER genes are associated with risk of the squamous cell carcinoma of head and neck (SCCHN). To test this hypothesis, we conducted a case-control study of 260 SCCHN patients and 246 cancer-free controls by measuring the mRNA expression levels of eight core NER genes in cultured peripheral lymphocytes. Compared with the controls, cases had statistically significantly lower expression levels of DDB1 and ERCC3 (P = 0.015 and 0.041, respectively). Because DDB1 and ERCC3 expression levels were highly correlated, we used DDB1 for further multivariate analyses and modeling. After dividing the subjects by controls' quartiles of expression levels, we found an association between an increased risk of SCCHN and low DDB1 expression levels [adjusted ORs and 95% CIs: 1.92 and 1.11-3.32, 1.48 and 0.85-2.59, 2.00 and 1.15-3.45 for the 2nd-4th quartiles, respectively, compared with the 1st quartile; Ptrend = 0.026]. We also identified a multiplicative interaction between sex and DDB1 expression levels (P = 0.007). Finally, the expanded model with gene expression levels, in addition to demographic and clinical variables, on SCCHN risk was significantly improved, especially among men. In conclusion, reduced DDB1 expression levels were associated with an increased risk of SCCHN. However, these results need to be validated in larger studies.

ERCC1 and ERCC2 haplotype modulates induced BPDE-DNA adducts in primary cultured lymphocytes

Background

Benzo[a]pyrene(B[a]P), and its ultimate metabolite Benzo[a]pyrene 7,8-diol 9,10-epoxide (BPDE), are classic DNA damaging carcinogens. DNA damage caused by BPDE is normally repaired by Nucleotide Excision Repair (NER), of which ERCC1 and ERCC2/XPD exert an indispensable role. Genetic variations in ERCC1 and ERCC2 have been related to DNA repair efficiency. In this study we used lymphocytes from healthy individuals to show that polymorphisms in ERCC1 and ERCC2 are directly associated with decreased DNA repair efficiency.

Methods

ERCC1 (rs3212986 and rs11615) and ERCC2 (rs13181, rs1799793 and rs238406) were genotyped in 818 healthy Han individuals from the northeast of China. BPDE induced DNA adducts in lymphocytes were assessed by high performance liquid chromatography (HPLC) in 282 randomly selected participants. The effect of ERCC1 rs3212986 and ERCC2 rs238406 on DNA damage caused by B[a]P was assessed with a modified comet assay.

Results

We found that the variant genotypes of ERCC1 rs3212986 and ERCC2 rs238406 were associated with the high levels of BPDE-DNA adducts. Especially ERCC1 rs3212986 A-allele variant was significantly associated with the high BPDE-DNA adducts. Haplotype analysis showed that the ERCC1 haplotype AC (OR = 2.36, 95% CI = 1.84–2.97), ERCC2 haplotype AGA (OR = 1.51, 95% CI = 1.06–2.15) and haplotype block AGAAC (OR = 5.28, 95% CI = 2.95–9.43), AGCAC (OR = 1.35 95% CI = 1.13–1.60) were linked with high BPDE-DNA adducts. In addition, we found that the combined minor alleles of ERCC1 rs3212986 and ERCC2 rs238406 were associated with a reduced DNA repair capacity.

Conclusions

Our results suggest that the variant genotypes of ERCC1 rs3212986 and ERCC2 rs238406 are associated with decreased repair efficiency of BPDE induced DNA damage, and may be predictive for an individual’s DNA repair capacity in response to environmental carcinogens.

Excision repair of BPDE-adducts in human lymphocytes: diminished capacity associated with ERCC1 C8092A (rs3212986) polymorphism

Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), a metabolite of Benzo[a]pyrene (B[a]P), is a high-risk factor for development of a number of cancers. DNA damage caused by BPDE is normally repaired by Nucleotide Excision Repair system of which ERCC1 exerts an important role. We investigated whether two single nucleotide polymorphisms in ERCC1 (C19007T; rs11615 and C8092A; rs3213986) affected the repair efficacy of BPDE-DNA adducts. We collected peripheral blood of 780 healthy individuals from the northeast of China and detected the genotypes of rs11615 and rs3213986. The amount of induced BPDE-DNA adducts in lymphocytes from 117 randomly selected participants was assessed by HPLC. Presence of BPDE-DNA adducts in nucleus of lymphocytes was visualized using the modified comet assay. ERCC1 and CAST (3' adjacent gene of ERCC1) mRNA expression levels were quantified after in vitro exposure to BPDE. We found that the minor A allele in rs3212986 was related to higher levels of BPDE-DNA adducts and holistic marking DNA damage (P < 0.01). Haplotype CA (rs11615 and rs3213986) was also associated with an elevated risk of high BPDE-DNA adduct levels (OR = 1.801, 95 % CI of OR 1.191-2.724). Interestingly, in participants with AA genotype for rs3213986, CAST mRNA level was decreased compared to individuals with the homozygous CC genotype. Our findings suggests that ERCC1 C8092A (rs3213986) is associated with a diminished capacity of repairing BPDE-DNA adducts and may be used as a valid biomarker to predict an individual's risk to develop cancer upon exposure to environmental carcinogens.

Correlation between base-excision repair gene polymorphisms and levels of in-vitro BPDE-induced DNA adducts in cultured peripheral blood lymphocytes

In vitro benzo[a]pyrene diol epoxide (BPDE)-induced DNA adducts in cultured peripheral lymphocytes have been shown to be a phenotypic biomarker of individual’s DNA repair phenotype that is associated with cancer risk. In this study, we explored associations between genotypes of base-excision repair genes (PARP1 Val762Ala, APEX1 Asp148Glu, and XRCC1 Arg399Gln) and in vitro BPDE-induced DNA adducts in cultured peripheral blood lymphocytes in 706 cancer-free non-Hispanic white subjects. We found that levels of BPDE-induced DNA adducts were significantly higher in ever smokers than in never smokers and that individuals with the Glu variant genotypes (i.e., Asp/Glu and Glu/Glu) exhibited lower levels of BPDE-induced DNA adducts than did individuals with the common Asp/Asp homozygous genotype (median RAL levels: 32.0 for Asp/Asp, 27.0 for Asp/Glu, and 17.0 for Glu/Glu, respectively; P_trend = 0.030). Further stratified analysis showed that compared with individuals with the common APEX1-148 homozygous Asp/Asp genotype, individuals with the APEX1-148Asp/Glu genotype or the Glu/Glu genotype had a lower risk of having higher-level adducts (adjusted OR = 0.60, 95% CI: 0.36–0.98 and adjusted OR = 0.47, 95% CI: 0.26–0.86, respectively; P_trend = 0.012) among smokers. Such an effect was not observed in non-smokers. However, there was no significant interaction between the APEX1 Asp148Glu polymorphism and smoking exposure in this study population (P = 0.512). Additional genotype-phenotype analysis found that the APEX1-148Glu allele had significantly increased expression of APEX1 mRNA in 270 Epstein-Barr virus-transformed lymphoblastoid cell lines, which is likely associated with more active repair activity. Our findings suggest that the functional APEX1-148Glu allele is associated with reduced risk of having high levels of BPDE-induced DNA adducts mediated with high levels of mRNA expression.

Assays to determine DNA repair ability

DNA repair is crucial to the integrity of the human genome since mammalian cells are continuously exposed to different chemical and physical genotoxic agents. To counteract the lesions induced by these agents, organisms have developed a number of highly conserved repair mechanisms involving numerous protein complexes grouped in several different repair pathways. The importance of studying the individual capacity to repair DNA damage lies in the observation that deficient repair mechanisms of the genome have been linked to the presence of large number of diseases and cancer, and alterations in these mechanisms may also alter the susceptibility of individuals exposed to a particular mutagen. This review focused on the current knowledge of different assays developed to evaluate DNA repair capacity (DRC). These assays, which are grouped into five major categories, have been successfully applied in (1) in vitro studies, (2) epidemiological studies in patients with cancer or other different pathologies, and (3) environmentally or occupationally exposed populations. Nevertheless, some of the limitations include high interlaboratory variability and difficulty to implement the assays on a large scale. The selection of an adequate DRC assay needs to be made on the basis of the objective raised for its application and taking into account a number of determining factors, namely, (1) speed and cost, (2) type of DNA repair to be evaluated, and (3) sample availability.

A single nucleotide polymorphism in the alcohol dehydrogenase 7 gene (alanine to glycine substitution at amino acid 92) is associated with the risk of squamous cell carcinoma of the head and neck

BACKGROUND

The authors conducted a hospital-based study of 1110 patients with squamous cell carcinoma of the head and neck (SCCHN) and a control group of 1129 patients to replicate the associations reported by a recent, large European study between 2 potentially functional single nucleotide polymorphisms (SNPs) of the alcohol dehydrogenase (ADH) genes, a substitution in ADH1B at amino acid 48 from arginine to histidine (R48H) (reference SNP number [rs]1229984; guanine to adenine [G-->A]) and a substitution in ADH7 at amino acid 92 from alanine to glycine (A92G) (rs1573496; cytosine to guanine [C-->G]), and the risk of squamous cell carcinoma of the head and neck (SCCHN).

METHODS

Multivariate logistic regression was used to calculate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). False-positive report probabilities (FPRPs) also were calculated for significant findings.

RESULTS

The ADH7 A92G GG and combined CG + GG genotypes were associated with a decreased risk of SCCHN (GG: adjusted OR, 0.32; 95% CI, 0.13-0.82; CG + GG: adjusted OR, 0.74; 95% CI, 0.59-0.94; FPRP, .098) compared with the CC genotype. This association was also evident in subgroups of older patients (aged >57 years), men, former smokers, patients with oral cancer, and patients with N) lymph node status (P < .05 for all); however, such associations were not observed for the ADH1B R48H SNP.

CONCLUSIONS

The current results support the ADH7 A92G SNP as a marker for the risk of SCCHN in non-Hispanic white populations.

Glutathione S-transferase polymorphisms and risk of second primary malignancy after index squamous cell carcinoma of the head and neck

Glutathione S-transferases (GST) detoxify carcinogens in tobacco smoke, which plays a major role in development of not only squamous cell carcinoma of the head and neck (SCCHN) but also second primary malignancy (SPM) after index SCCHN. We hypothesized that GSTM1 null, GSTT1 null, GSTP1 Ile(105)Val, and GSTP1 Ala(114)Val polymorphisms would individually and, more likely, collectively show an association with risk of SPM after index SCCHN. One thousand three hundred seventy-six incident SCCHN patients were prospectively recruited between May 1996 and December 2006, genotyped, and followed for SPM development. One hundred ten patients (8%) developed SPM: 43 (39%) second SCCHN, 38 (35%) other tobacco-associated sites, and 29 (26%) other non-tobacco-associated sites. Patients with GSTP1 Ile(105)Val polymorphism had a statistically significant association with risk of SPM development (adjusted hazard ratio, 1.7; 95% confidence interval, 1.1-2.5). However, no statistically significant associations were observed with GSTM1, GSTT1, or GSTP1 Ala(114)Val polymorphisms. After combining risk genotypes for all four polymorphisms, rates of SPM development with 0 to 1, 2, 3, and 4 risk genotypes were 6.4%, 8.4%, 10.9%, and 15.1%, respectively, and a stepwise increase in SPM risk was observed with increasing number of risk genotypes (P = 0.004 for trend). Patients with 3 to 4 risk genotypes had a 1.7-fold increased risk for SPM compared with patients with 0 to 2 risk genotypes (hazard ratio, 1.70; 95% confidence interval, 1.2-2.5). This large prospective cohort study supports a modestly increased risk of SPM after index SCCHN with GSTP1 Ile(105)Val polymorphism and an even greater risk of SPM with multiple combined GST risk genotypes.

DNA repair phenotype and cancer susceptibility--a mini review

DNA repair is a complicated biological process, consisting of several distinct pathways, that plays a fundamental role in the maintenance of genomic integrity. The very important field of DNA repair and cancer risk has developed rapidly in the past decades. In this review of selected published data from our laboratory, we describe mostly our work on the study of phenotypic markers of nucleotide excision repair (NER), as measured by the benzo(a)pyrene diol epoxide (BPDE)/ultraviolet (UV)-induced mutagen sensitivity assays, BPDE-induced adduct assay, host cell reactivation (HCR)-DNA repair capacity (DRC) assay, reverse transcription-polymerase chain reaction (RT-PCR) assay and reverse-phase protein lysate microarray (RPP) assay, by using peripheral blood lymphocytes in a series of molecular epidemiological studies. Results of our studies suggest that individuals with reduced DRC have an elevated cancer risk. This finding needs additional validation by other investigators, and we also discussed issues in conducting this kind of research in the future.

Overexpression of high mobility group (HMG) B1 and B2 proteins directly correlates with the progression of squamous cell carcinoma in skin

High mobility group B (HMGB) chromosomal proteins, which plays important role in cancer and inflammation, were followed at various stages of the squamous cell carcinoma of skin. Present results were analyzed by histopathology, BrdU assay, immunohistochemistry, western blot and RT-PCR, which indicate that at early stages of tumorigenesis, expression of HMGB (B1, B2), raised only by about 20%. However, the advanced (> or =12 weeks) tumors showed significant (> or =80%) increase in HMG levels. Using skin cancer model, we demonstrated that high levels of HMGB directly correlate with the extent of neoplastic changes, and it appears that HMGB is an effective stimulus for cell differentiation, tumor progression, and metastatic invasion.

Chromosome instability and risk of squamous cell carcinomas of head and neck

In 895 subjects with squamous cell carcinoma of the head and neck (SCCHN) and 898 cancer-free controls matched by age, sex, and ethnicity, we validated our previous finding that mutagen sensitivity as measured by the frequency of chromatid breaks in vitro induced by benzo[a]pyrene diol epoxide (BPDE) is an independent risk factor for SCCHN. Using a previously established concentration of 4 micromol/L BPDE to treat short-term cultured primary lymphocytes for 5 hours, we evaluated chromatid breaks in 50 well-spread metaphases for each blood sample. The mean frequency of BPDE-induced chromatid breaks was significantly higher in cases than in controls in non-Hispanic Whites (P = 0.0003) but not in other ethnic groups (P = 0.549 for Hispanic Americans and 0.257 for African Americans). The odds ratio associated with risk of SCCHN for the frequency of chromatid breaks greater than median value of controls was 1.56 (95% confidence interval, 1.27-1.91) in non-Hispanic Whites (767 cases and 763 controls) after adjustment for age, sex, smoking status, and drinking status. When the quartiles of the controls were used as the cutoff values, there was a dose response between the degree of mutagen sensitivity and risk of SCCHN in non-Hispanic Whites (P(trend) = 0.0001). However, none of these associations in non-Hispanic Whites was identified in Hispanic Americans (69 cases and 70 controls) or African Americans (59 cases and 65 controls), possibly because of the small samples of these ethnic groups or ethnic difference in genetic variation, which needs to be confirmed in future studies.

Functional variants of the NEIL1 and NEIL2 genes and risk and progression of squamous cell carcinoma of the oral cavity and oropharynx

PURPOSE

Human DNA glycosylases NEIL1 and NEIL2 participate in oxidized base excision repair and protect cells from DNA damage. NEIL1 (MIM:608844) and NEIL2 (MIM:608933) variants may affect their protein functions, leading to altered cell death and carcinogenesis. To date, only one reported study has investigated the association between NEIL1 and NEIL2 polymorphisms and cancer risk.

EXPERIMENTAL DESIGN

Genotype and haplotypes of the NEIL1 NT_010194.16:g.46434077G>T (rs7182283) and g.46438282C>G (rs4462560) and NEIL2 NT_077531.3:g.4102971C>G (rs804270) polymorphisms were determined for 872 patients with newly diagnosed squamous cell carcinomas of the oral cavity and oropharynx (SCCOOP) and 1,044 cancer-free non-Hispanic white control subjects frequency-matched by age and sex. Crude and adjusted odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using multivariate logistic regression, and false-positive report probabilities were also calculated.

RESULTS

We found no overall differences in the frequencies of alleles, genotypes, and haplotypes of NEIL1 g.46434077G>T and NEIL1 g.46438282C>G polymorphisms between cases and controls. However, the NEIL2 g.4102971CC genotype was associated with a significantly increased risk of SCCOOP (adjusted OR, 1.30; 95% CI, 1.02-1.65); this increase in risk was the highest among current alcohol drinkers (adjusted OR, 1.87; 95% CI, 1.28-2.72), particularly in patients with oropharyngeal cancer (adjusted OR, 1.35; 95% CI, 1.04-1.76). The NEIL2 g.4102971CC genotype was also significantly associated with SCCOOP of advanced stages.

CONCLUSIONS

Polymorphisms of the NEIL2 gene may be markers for risk and progression of SCCOOP, particularly in patients with oropharyngeal cancer. Larger studies are needed to confirm our findings.

Molecular techniques and genetic alterations in head and neck cancer

It is well known that cellular DNA alterations can lead to the formation of cancer, and there has been much discovery in the pathways involved in the development of head and neck squamous cell carcinoma (HNSCC). With novel genome-wide molecular assays, our ability to detect these abnormalities has increased. We now have a better understanding of the molecular complexity of HNSCC, but there is still much research to be done. In this review, we discuss the well described genetic alterations and touch on the newer findings, as well as some of the future directions of head and neck cancer research.

Genotypes and haplotypes of ERCC1 and ERCC2/XPD genes predict levels of benzo[a]pyrene diol epoxide-induced DNA adducts in cultured primary lymphocytes from healthy individuals: a genotype-phenotype correlation analysis

Benzo[a]pyrene diol epoxide (BPDE)-induced DNA adducts are a risk factor for tobacco-related cancers. Excision repair cross-complementing complementation group 1 (ERCC1) and excision repair cross-complementing complementation group 2/xeroderma pigmentosum D (ERCC2/XPD) participate in the nucleotide excision repair (NER) pathway that removes BPDE-DNA adducts; however, few studies have provided population-based evidence for this association. Therefore, we assayed for levels of in vitro BPDE-induced DNA adducts and genotypes of single-nucleotide polymorphisms (SNPs) of the NER genes ERCC1 (rs3212986 and rs11615) and ERCC2/XPD (rs13181, rs1799793 and rs238406) in 707 healthy non-Hispanic whites. The linear trend test of increased adduct values in never to former to current smokers was statistically significant (P(trend) = 0.0107). The median DNA adduct levels for the ERCC2 rs1799793 GG, GA and AA genotypes were 23, 29 and 30, respectively (P(trend) = 0.057), but this trend was not observed for other SNPs. After adjustment for covariates, adduct values larger than the median value were significantly associated with the genotypes ERCC1 rs3212986TT [odds ratio (OR) = 1.89, 95% confidence interval (CI) = 1.03-3.48] and ERCC2/XPD rs238406AA (OR = 0.64, 95% CI = 0.41-0.99) and rs238406CA (OR = 0.63, 95% CI = 0.45-0.89) compared with their corresponding wild-type homozygous genotypes. The results of haplotype analysis further suggested that haplotypes CAC and CGA of ERCC2/XPD, TC of ERCC1 and CACTC of ERCC2/XPD and ERCC1 were significantly associated with high levels of DNA adducts compared with their most common haplotypes. Our findings suggest that the genotypes and haplotypes of ERCC1 and ERCC2/XPD may have an effect on in vitro BPDE-induced DNA adduct levels.

Genetic and environmental factors in head and neck cancer genesis

Head and neck squamous cell carcinoma (HNSCC) include squamous cell carcinomas of the oral cavity, pharynx, and larynx. Epidemiologic data suggest that the etiology and pathogenesis of HNSCC are influenced by environmental and lifestyle-related factors, such as tobacco use, ethanol consumption, papilloma virus infection, dietary factors and exposure to toxic substances. DNA repair systems and carcinogen-metabolizing enzymes can increase the risk for HNSCC but no definite causal mechanism has been demonstrated. There are several well-characterized entities that are associated with risk and prognosis of head and neck cancer, including Lynch-II syndrome, Bloom syndrome, Fanconi's anemia, xeroderma pigmentosum, ataxia telangiectasia, and Li-Fraumeni syndrome. This review aims to present the current status in our understanding of HNSCC and highlight controversies relating to the role of several factors in the genesis of the cancer.