Influence of polymorphisms in DNA repair genes XPD, XRCC1 and MGMT on DNA damage induced by gamma radiation and its repair in lymphocytes in vitro

Lymphocyte micronuclei frequencies in skin, haematological, prostate, colorectal and esophageal cancer cases: A systematic review and meta-analysis

Micronucleus (MN) assay has been widely used as a biomarker of DNA damage, chromosomal instability, cancer risk and accelerated aging in many epidemiological studies. In this narrative review and meta-analysis we assessed the association between lymphocyte micronuclei (MNi) and cancers of the skin, blood, digestive tract, and prostate. The review identified nineteen studies with 717 disease subjects and 782 controls. Significant increases in MRi for MNi were observed in the following groups: subjects with blood cancer (MRi = 3.98; 95 % CI: 1.98-7.99; p = 0.000) and colorectal cancer (excluding IBD) (MRi = 2.69; 95 % CI: 1.82-3.98, p < 0.000). The results of this review suggest that lymphocyte MNi are a biomarker of DNA damage and chromosomal instability in people with haematological or colorectal cancers. However, the MRi for lymphocyte MNi in subjects with cancers of skin, prostate, esophagus was not significantly increased. More case-control and prospective studies are warranted to further verify the observed trends and to better understand the role of lymphocyte MNi as a biomarker of cancer risk in blood, skin, digestive tract and prostate.

Micronuclei and Their Association with Infertility, Pregnancy Complications, Developmental Defects, Anaemias, Inflammation, Diabetes, Chronic Kidney Disease, Obesity, Cardiovascular Disease, Neurodegenerative Diseases and Cancer

Micronuclei (MN) are a strong cytogenetic indicator of a catastrophic change in the genetic structure and stability of a cell because they originate from either chromosome breaks or whole chromosomes that have been lost from the main nucleus during cell division. The resulting genetic abnormalities can to lead to cellular malfunction, altered gene expression and impaired regenerative capacity. Furthermore, MN are increased as a consequence of genetic defects in DNA repair, deficiency in micronutrients required for DNA replication and repair and exposure to genotoxic chemicals and ultraviolet or ionising radiation. For all of these reasons, the measurement of MN has become one of the best-established methods to measure DNA damage in humans at the cytogenetic level. This chapter is a narrative review of the current evidence for the association of increased MN frequency with developmental and degenerative diseases. In addition, important knowledge gaps are identified, and recommendations for future studies required to consolidate the evidence are provided. The great majority of published studies show a significant association of increased MN in lymphocytes and/or buccal cells with infertility, pregnancy complications, developmental defects, anaemias, inflammation, diabetes, cardiovascular disease, kidney disease, neurodegenerative diseases and cancer. However, the strongest evidence is from prospective studies showing that MN frequency in lymphocytes predicts cancer risk and cardiovascular disease mortality.

Relevance of XPD polymorphisms to neuroblastoma risk in Chinese children: a four-center case-control study

Neuroblastoma is a lethal tumor that commonly occurs in children. Polymorphisms in XPD reportedly influence risk for several types of cancer, though their roles in neuroblastoma remain unclear. Here we endeavored to determine the relevance of XPD gene polymorphisms and neuroblastoma susceptibility in Chinese children genotyping three XPD polymorphisms (rs3810366, rs13181 and rs238406) in 505 cases and 1070 controls and assessing their contributions to neuroblastoma risk. Overall, we detected no significant association between any single XPD genotype and neuroblastoma risk. When risk genotypes were combined, however, we found that patients with 2-3 risk genotypes were more likely to develop neuroblastoma (adjusted odds ratio =1.31; 95% confidence interval =1.06-1.62, P=0.013) than those with 0-1 risk genotypes. Stratification analysis of rs3810366 revealed significant relationships between the subgroups age ≤18 months and clinical stage I+II+4s and neuroblastoma risk. Moreover, the presence of 2-3 risk genotypes was significantly associated with increased neuroblastoma risk in the subgroups age ≤18 months, male, tumor originated from others, and clinical stage I+II+4s. Our findings provide novel insight into the genetic underpinnings of neuroblastoma and demonstrate that XPD polymorphisms may have a cumulative effect on neuroblastoma risk.

Gene Expression in Parp1 Deficient Mice Exposed to a Median Lethal Dose of Gamma Rays

There is a current interest in the development of biodosimetric methods for rapidly assessing radiation exposure in the wake of a large-scale radiological event. This work was initially focused on determining the exposure dose to an individual using biological indicators. Gene expression signatures show promise for biodosimetric application, but little is known about how these signatures might translate for the assessment of radiological injury in radiosensitive individuals, who comprise a significant proportion of the general population, and who would likely require treatment after exposure to lower doses. Using Parp1^-/- mice as a model radiation-sensitive genotype, we have investigated the effect of this DNA repair deficiency on the gene expression response to radiation. Although Parp1 is known to play general roles in regulating transcription, the pattern of gene expression changes observed in Parp1^-/- mice 24 h postirradiation to a LD_50/30 was remarkably similar to that in wild-type mice after exposure to LD_50/30. Similar levels of activation of both the p53 and NFκB radiation response pathways were indicated in both strains. In contrast, exposure of wild-type mice to a sublethal dose that was equal to the Parp1^-/- LD_50/30 resulted in a lower magnitude gene expression response. Thus, Parp1^-/- mice displayed a heightened gene expression response to radiation, which was more similar to the wild-type response to an equitoxic dose than to an equal absorbed dose. Gene expression classifiers trained on the wild-type data correctly identified all wild-type samples as unexposed, exposed to a sublethal dose or exposed to an LD_50/30. All unexposed samples from Parp1^-/- mice were also correctly classified with the same gene set, and 80% of irradiated Parp1^-/- samples were identified as exposed to an LD_50/30. The results of this study suggest that, at least for some pathways that may influence radiosensitivity in humans, specific gene expression signatures have the potential to accurately detect the extent of radiological injury, rather than serving only as a surrogate of physical radiation dose.

Association of DNA repair gene polymorphisms with the risk of radiation pneumonitis in lung cancer patients

A total of 149 lung cancer patients were recruited to receive intensity modulated radiation therapy (IMRT). The association of developing radiation pneumonitis (RP) with genetic polymorphism was evaluated. The risks of four polymorphic sites in three DNA repair related genes (ERCC1, rs116615:T354C and rs3212986:C1516A; ERCC2, rs13181:A2251C; XRCC1, rs25487:A1196G) for developing grade ≥ 2 RP were assessed respectively. It was observed that ERCC1 T354C SNP had a significant effect on the development of grade ≥ 2 RP (CT/TT vs. CC, adjusted HR = 0.517, 95% CI, 0.285-0.939; adjusted P = 0.030). It is the first time demonstrating that CT/TT genotype of ERCC1 354 was significantly associated with lower RP risk after radio therapy.

Association of the Asp312Asn and Lys751Gln polymorphisms in the XPD gene with the risk of non-Hodgkin's lymphoma: evidence from a meta-analysis

Polymorphisms in DNA repair genes may alter DNA repair capacity and, consequently, lead to genetic instability and carcinogenesis. Several studies have investigated the association of the Asp312Asn and Lys751Gln polymorphisms in the xeroderma pigmentosum complementation group D (XPD) gene with the risk of non-Hodgkin's lymphoma (NHL), but the conclusions have been inconsistent. Therefore, we performed this meta-analysis to more precisely estimate these relationships. A systematic literature search was performed using the PubMed, Embase, and Chinese Biomedical (CBM) databases. Ultimately, 6 studies of Asp312Asn, comprising 3,095 cases and 3,306 controls, and 7 studies of Lys751Gln, consisting of 3,249 cases and 3,676 controls, were included. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the strength of each association. Overall, no association was observed between the Asp312Asn polymorphism and NHL risk (homozygous: OR = 1.11, 95% CI = 0.94-1.32; heterozygous: OR = 1.00, 95% CI = 0.89-1.11; recessive: OR = 1.12, 95% CI = 0.95-1.31; dominant: OR = 1.02, 95% CI = 0.92-1.13; and allele comparison: OR = 1.04, 95% CI = 0.96-1.12) or between the Lys751Gln polymorphism and NHL risk (homozygous: OR = 0.97, 95% CI = 0.83-1.15; heterozygous: OR = 0.96, 95% CI = 0.86-1.06; recessive: OR = 1.00, 95% CI = 0.86-1.16; dominant: OR = 0.96, 95% CI = 0.87-1.06; and allele comparison: OR = 0.98, 95% CI = 0.91-1.05). Furthermore, subgroup analyses did not reveal any association between these polymorphisms and ethnicity, the source of the controls, or the NHL subtype. These results indicated that neither the Asp312Asn nor Lys751Gln XPD polymorphism was related to NHL risk. Large and well-designed prospective studies are required to confirm this finding.

Predictive SNPs for radiation-induced damage in lung cancer patients with radiotherapy: a potential strategy to individualize treatment

In the treatment of lung cancer, radiotherapy has become one of the most important therapies, despite its sometimes unpredictable side effects. As such, identifying lung cancer patients who are at high risk of developing severe radiation-induced damage (mainly radiation pneumonitis and radiation-induced esophageal toxicity) and applying effect intervention or monitoring techniques are important. Although human diversity to a certain amount is explained by clinical and dosimetric factors, the presence of specific genetic determinants also influences the occurrence of radiation-induced damage. Here we summarize the data on mechanisms of radiation pneumonitis and radiation-induced esophageal toxicity supporting the involvement of variances of genes in the evolution of radiation-induced damage. Furthermore, the available evidence from current clinical studies of genetic polymorphisms for the prediction of radiation pneumonitis and radiation-induced esophageal toxicity is discussed. Eventually, this may help to truly individualize radiotherapy, using a personal genetic profile of the most relevant genes for each lung cancer patient.

Potentially functional variants in the core nucleotide excision repair genes predict survival in Japanese gastric cancer patients

Functional genetic variants of DNA repair genes may alter the host DNA repair capacity, and thus influence efficiency of therapies. We genotyped eight potentially functional single nucleotide polymorphisms (SNPs) in genes (i.e. ERCC1, XPA, XPC, XPD and XPG) involved in the nucleotide excision repair (NER) pathway in 496 Japanese gastric cancer patients, and assessed overall survival and recurrence-free survival. The combined effects of risk genotypes of these eight SNPs in Japanese patients were further replicated in 356 North-American gastric cancer patients. In Japanese patients, we found that the XPC rs2228000 TT genotype was associated with shorter overall survival [hazards ratio (HR) = 1.75, 95% confidence interval (95% CI) = 1.07-2.86] and recurrence-free survival (HR = 2.17, 95% CI = 1.19-3.95), compared with CC/CT genotypes, and the XPG rs17655 CC genotype was associated with shorter overall survival (HR = 1.60, 95% CI = 1.08-2.36), compared with GG/CG genotypes. The number of observed risk genotypes in the combined analysis was associated with shorter overall survival and recurrence-free survival in a dose-response manner (P(trend) = 0.006 and P(trend) < 0.000) in Japanese patients; specifically, compared with those with ≤1 risk genotypes, those with ≥2 risk genotypes showed markedly shorter overall survival (HR = 1.79, 95% CI = 1.18-2.70) and recurrence-free survival (HR = 2.80, 95% CI = 1.66-4.73). The association between ≥2 risk genotypes and shorter overall survival was not significant (HR = 1.26, 95% CI = 0.82-1.94) in North-American patients, but the trends were similar in these two groups of patients. These data show that functional SNPs in NER core genes may impact survival in Japanese gastric cancer patients.

ERCC1 and ERCC2 variants predict survival in gastric cancer patients

Purpose

ERCC1 and ERCC2 play critical roles in the nucleotide excision repair pathway that effectively repairs DNA damage induced by chemotherapeutic agents. Therefore, functional single nucleotide polymorphisms (SNPs) in these genes could have an impact on clinical outcomes in cancer patients who received chemotherapy. However, few studies have simultaneously investigated the roles of ERCC1 and ERCC2 SNPs in clinical outcomes in gastric cancer patients.

Experimental Design

We genotyped by the TaqMan assay three common, potentially functional ERCC1 (rs3212986) and ERCC2 SNPs (rs13181 and rs1799793) in 360 gastric cancer patients. We used both Kaplan-Meier tests and Cox proportional hazards models to evaluate the effects of ERCC1 and ERCC2 genotypes and haplotypes on clinical outcomes.

Results

We found that, compared with ERCC2 rs1799793 GG+AG genotypes, the homozygous variant AA genotype was associated with significantly poorer overall survival (OS) (AA vs. GG+AG, log-rank P = 0.012) and significantly higher risk of death (AA vs. GG+AG, Adjusted hazards ratio [HR] 2.13; 95% CI, 1.28 to 3.56; P = 0.004). In combined analyses, patients with any one of the three unfavorable genotypes (i.e. ERCC1 rs3212986 TT, ERCC2 rs13181 GG and rs1799793 AA) had statistically significant hazards of poor prognosis (Adjusted HR, 1.54; 95% CI, 1.06 to 2.25; P = 0.025), compared with those without any unfavorable genotypes. Furthermore, the haplotype A-G-G (rs1799793/rs13181/rs3212986) had a significant impact on OS (Adjusted HR, 1.57; 95% CI, 1.11 to 2.21; P = 0.011), compared with the common haplotype G-T-G.

Conclusion

ERCC1 and ERCC2 functional SNPs may jointly affect OS in Caucasian gastric cancer patients. Additional large prospective studies are essential to confirm our findings.

Association between polymorphisms of XRCC1 Arg399Gln and XPD Lys751Gln genes and prognosis of colorectal cancer in a Chinese population

We conducted this study to detect associations between XRCC1 Arg399Gln and XPD Lys751Gln genotypes and survival of colorectal cancer patients treated with 5-FU/oxalipatin chemotherapy. We included 289 Chinese patients with advanced colorectal cancer, who had received 5-FU/oxalipatin chemotherapy as first-line treatment from January 2005 to January 2007. All patients were followed up till Nov. 2011. Genotyping for XRCC1 Arg399Gln and XPD Lys751Gln polymorphisms was based upon duplex polymerase-chain-reaction with the PCR-RFLP method. In our study, we found the XRCC1 399 Gln/Gln genotype to confer significantly higher rates of response to chemotherapy when compared to the Arg/Arg genotype [OR (95% CI)=2.56(1.57-2.55)]. patients with the XPD 751 Gln/Gln genotype had significantly higher rates of response to chemotherapy [OR (95% CI)=1.54(0.87-2.65)] and those with the XRCC1 399 Gln/Gln genotype had a longer average survival time and significantly lower risk of death than did those with the Arg/Arg genotype [HR (95% CI)=0.66(0.36-0.95)]. Similarly, those carrying the XPD 751Gln/Gln genotype had 0.51-fold the risk of death of those with XPD 751Lys/Lys [HR (95% CI)=0.51(0.33-0.94)]. In conclusion, it is suggested that the XRCC1 Arg399Gln and XPD Lys751Gln polymorphisms should be routinely assessed to determine colorectal patients who are more likely to benefit from 5-FU/oxalipatin chemotherapy.

Association of XPD and XRCC1 genetic polymorphisms with hepatocellular carcinoma risk

AIM

XRCC1 and XPD are two major repair genes involved in nucleotide excision repair (NER), which is reported to be associated with risk of several cancers. We explored the association of XRCC1 and XPD polymorphisms with the risk of HCC.

METHODS

A total of 410 cases with HCC and 410 health controls were collected. XRCC1 Arg194Trp, XRCC1 Arg399Gln, XPD Lys751Gln and XPD Asp312Asn genotyping was performed by duplex polymerase-chain-reaction with the confronting-two-pair primer (PCR-CTPP) method.

RESULTS

XRCC1 194Trp/Trp was strongly significantly associated with an increased risk of HCC cancer when compared with the wide-type genotype (OR=2.26, 95% CI=(1.23-5.38). Individuals carrying the XRCC1 399Gln/ Gln showed increased risk of HCC (OR=1.74, 95%CI=1.06-2.74). The XPD 751Gln/Gln and Gln allele genotype were associated with strong elevated susceptibility to HCC (OR=3.51 and 1.42, respectively).

CONCLUSION

These results suggest that polymorphisms in XRCC1 and XPD may have functional significance in risk of HCC.

Evaluation of the in vivo genotoxic effects of gamma radiation on the peripheral blood leukocytes of head and neck cancer patients undergoing radiotherapy

The present study aimed to evaluate the genotoxic effects of ionizing radiation on non-target cells of Head and Neck Squamous Cell Carcinoma (HNSCC) patients exposed to various cumulative doses of gamma rays during radiotherapy. The ten patients (P1-P10) were treated with cobalt 60 gamma radiation (External Beam Radiotherapy) for a period of five to six weeks with a daily fraction of 2Gy for 5 days each week. The genotoxic effects of radiation (single strand breaks - SSBs) in these patients were analyzed using the alkaline single cell gel electrophoresis (SCGE) technique, with the Olive Tail Moment (OTM) as the critical parameter. A sample of each patient's peripheral blood before starting with radiotherapy (pre-therapy) served as the control, and blood collected at weekly time intervals during the course of the radiotherapy served as treated (10, 20, 30, 40, 50 and 60Gy) samples. In vivo radiosensitivity of these patients, as indicated by SSB's after the cumulative radiation doses at the various times, was assessed using Student's t-test. Significant DNA damage relative to the individual patient's pre-therapy baseline data was observed in all patients. Inter-individual variation of the genotoxic effects was analyzed using two-way ANOVA. The correlation between doses for the means of smoker and non-smoker patients was calculated using the Pearson test. The results of this study may indicate the need to reduce the daily radiotherapy dose further to prevent genotoxic effects on non-target cells, thus improving safety. Furthermore, these results may indicate that the estimation of DNA damage following exposure to a gamma radiation, as measured by the comet assay in whole blood leukocytes, can be used to screen human populations for radiation-induced genetic damage at the molecular level.

Polymorphisms of DNA repair pathway genes and cigarette smoking in relation to susceptibility to large artery atherosclerotic stroke among ethnic Chinese in Taiwan

AIM

Cigarette-smoking induced oxidative DNA damage to endothelial cells has been reported to play an etiological role in atherosclerosis development. Individual vulnerability to oxidative stress through smoking exposure and the ability to repair DNA damage, which plays a critical role in modifying the risk susceptibility of large artery atherosclerotic (LAA) stroke, is hypothesized. Thus, we examined the effect of genetic polymorphisms of DNA repair pathway genes and cigarette smoking in relation to risk susceptibility of LAA stroke.

METHODS

We enrolled 116 LAA stroke patients and 315 healthy controls from the Armed Forces Taoyuan General Hospital, Taoyuan, Taiwan. Genotyping of polymorphisms of the OGG1 (Ser326Cys), XRCC1 (Arg399Gln), ERCC2 (Lys751Gln), and ERCC5 (Asp1104His) genes was performed and used to evaluate LAA stroke susceptibility.

RESULTS

Of those non-synonymous polymorphisms, the ERCC2 Lys751Gln variant was found to be associated with LAA stroke risk (OR: 1.69, 95%CI: 1.02-2.86), and this association was more pronounced in smokers, manifesting a 2.73-fold increased risk of LAA stroke (p=0.027). A joint effect on risk elevation of LAA stroke was seen in those patients with OGG1 and ERCC2 polymorphisms (OR: 2.75, 95%CI: 1.26-6.00). Moreover, among smokers carrying the OGG1 Ser326Cys polymorphism, there was a tendency toward an increased risk of LAA stroke in those patients who had a greater number of high-risk genotypes of XRCC1, ERCC2, and ERCC5 polymorphisms (p(trend)=0.010).

CONCLUSION

The susceptible polymorphisms of DNA repair pathway genes may have a modifying effect on the elevated risk of LAA stroke in smokers among ethnic Chinese in Taiwan.

Cytogenetic methods in human biomonitoring: principles and uses

Cellular phenotypes can be applied as biomarkers to differentiate normal from abnormal biological -conditions. Several cytogenetic methods have been developed and allow the accurate detection of such phenotypic changes.Based on their mechanisms of formation, cellular phenotypes may be used either as biomarkers of exposure or as biomarkers of effect. Therefore, it is important that cytogenetic methods implemented in human biomonitoring should be based on a good knowledge of these mechanisms.In this chapter, we aim to review the mechanistic basis, the methodology, and the use in human biomonitoring studies of four major cytogenetic endpoints: sister chromatid exchanges (SCEs), high frequency cells (HFCs), chromosomal aberrations (CAs), and micronuclei (MN). In addition, an overview of potential confounding factors on the induction of these cytogenetic makers is presented. Furthermore, the combination of cytogenetics with molecular methods, which allows chromosome and gene identification on metaphase as well as in interphase cells with high resolution, is discussed. Finally, practical recommendations for an efficient application of these cytogenetic assays and a correct interpretation of the results on the basis of cellular phenotype(s) assessment in human biomonitoring are highlighted.

Evaluating chromosomal damage in workers exposed to hexavalent chromium and the modulating role of polymorphisms of DNA repair genes

PURPOSE

Welders have been chronically exposed to hexavalent chromium with potential consequences on chromosomal integrity. Our study is focused on the extent of any such chromosomal aberrations with respect to chromium levels in the blood of welders as well as on the tentative modulating role of polymorphisms in DNA repair genes XPD Lys751Gln, XPG Asn114His, XPC Lys939Gln, hOGG1 Ser326Cys and XRCC1 Arg399Gln on chromosomal damage.

METHODS

The study was conducted on 144 individuals consisting of 73 welders exposed to chromium for 10.2 ± 1.67 years and 71 control individuals without known exposures. Chromosomal aberrations, their chromatid-type and chromosome-type aberrations were detected by conventional cytogenetic analysis. XPD, XPG, XPC, hOGG1 and XRCC1 gene polymorphisms were assayed for by Taqman SNP genotyping assay ("Assay-by-Demand") using Real-Time allelic discrimination on AB 7500 equipment. Chromium concentration in the blood was determined by atomic absorption spectrophotometry.

RESULTS

The level of chromium in the blood of welders ranged between 0.032 and 0.182 μmol l(-1) and was significantly higher than that in controls (0.07 ± 0.04 μmol l(-1) vs. 0.03 ± 0.007 μmol l(-1)). Parameters of chromosomal damage were similar in both the exposed and the control individuals (1.89% vs. 1.70% for total chromosomal aberrations, 0.97% vs. 0.88% for chromosome-type and 0.92% vs. 0.80% for chromatid-type, respectively). Chromatid-type of aberrations positively correlated with the level of chromium in the blood (r = 0.28; P = 0.02). Significantly higher total chromosomal aberrations were detected in individuals with homozygous variant polymorphism in XRCC1 Arg399Gln gene as compared to those with heterozygous and homozygous wild-type genotypes (2.20, 1.89 and 1.48%, respectively; P = 0.01). A similar tendency was found for chromatid-type aberrations (1.30% for homozygous variant genotype bearers, 0.94% for those with heterozygous genotype and 0.75% for carriers of homozygous wild-type genotype, respectively; P = 0.04).

CONCLUSIONS

Although no apparent increase in chromosomal damage was recorded in chromium-exposed welders in comparison with controls, genetic make-up in DNA repair genes may increase susceptibility toward adverse effect of chromium.

Heritability of baseline and induced micronucleus frequencies

The scoring of micronuclei (MN) is widely used in biomonitoring and mutagenicity testing as a surrogate marker of chromosomal damage inflicted by clastogenic agents or by aneugens. Individual differences in the response to a mutagenic challenge are known from studies on cancer patients and carriers of mutations in DNA repair genes. However, it has not been studied to which extent genetic factors contribute to the observed variability of individual MN frequencies. Our aim was to quantify this heritable genetic component of both baseline and radiation-induced MN frequencies. We performed a twin study comprising 39 monozygotic (MZ) and 10 dizygotic (DZ) twin pairs. Due to the small number of DZ pairs, we had to recruit controls from which 38 age- and gender-matched random control pairs (CPs) were generated. For heritability estimates, we used biometrical modelling of additive genetic, common environmental, and unique environmental components (ACE model) of variance and direct comparison of variance between the sample groups. While heritability estimates from MZ to DZ comparisons produced inconclusive results, both estimation methods revealed a high degree of heritability (h(2)) for baseline MN frequency (h(2) = 0.68 and h(2) = 0.72) as well as for the induced frequency (h(2) = 0.68 and h(2) = 0.57) when MZ were compared to CP. The result was supported by the different intraclass correlation coefficients of MZ, DZ and CP for baseline (r = 0.63, r = 0.31 and r = 0.0, respectively) as well as for induced MN frequencies (r = 0.79, r = 0.74 and r = 0.0, respectively). This study clearly demonstrates that MN frequencies are determined by genetic factors to a major part. The strong reflection of the genetic background supports the idea that MN frequencies represent an intermediate phenotype between molecular DNA repair mechanisms and the cancer phenotype and affirms the approaches that are made to utilise them as predictors of, for example, cancer risk.

DNA repair enzyme polymorphisms and oxidative stress in a Turkish population with gastric carcinoma

Although the developmental stages of gastric carcinoma are still not clear, the constantly generated reactive oxygen and nitrogen species (ROS/RNS) may contribute to the process of carcinogenesis by interacting with DNA. 8-oxoguanine DNA glycosylase-1 (OGG1) is an enzyme involved in base excision repair of 8-oxoguanine that is one of the premutagenic lesions generated by ROS in DNA. The bulky adducts, are recognized and repaired by nucleotid excision repair (NER) enzymes, including xeroderma pigmentosum C and D (XPC, XPD). Eligible 106 gastric cancer patients and 116 cancer-free individuals constituted the study and control groups, respectively. Association between OGG1 Ser326Cys, XPC Lys939Gln, XPD Lys751Gln polymorphisms and the susceptibility tho cancer and the oxidative stress status were evaluated. DNA was extracted from peripheral blood cells and genotypes were determined by using PCR-RFLP. Serum nitric oxide, albumin concentrations, total antioxidant status and Helicobacter pylori IgG were determined. Serum albumin and nitric oxide of cancer patients were lower than that of the controls (P < 0.05). None of the evaluated polymorphisms or Helicobacter pylori IgG seropositivity associated with increased risk of gastric cancer, despite of the increased oxidative stress in cancer patients.

Association between single-nucleotide polymorphisms of selected genes involved in the response to DNA damage and risk of colon, head and neck, and breast cancers in a Polish population

Single-nucleotide polymorphisms in genes involved in DNA-damage-induced responses are reported frequently to be a risk factor in various cancer types. Here we analysed polymorphisms in 5 genes involved in DNA repair (XPD Asp312Asn and Lys751Gln, XRCC1 Arg399Gln, APE1 Asp148Glu, NBS1 Glu185Gln, and XPA G-4A) and in a gene involved in regulation of the cell-cycle (CCND1 A870G). We compared their frequencies in groups of colon, head and neck, and breast cancer patients, and 2 healthy control groups: (1) matched healthy Polish individuals and (2) a NCBI database control group. Highly significant differences in the distribution of genotypes of the APE1, XRCC1 and CCND1 genes were found between colon cancer patients and healthy individuals. The 148Asp APE1 allele and the 399Gln XRCC1 allele apparently increased the risk of colon cancer (OR = 1.9-2.3 and OR = 1.5-2.1, respectively). Additionally, frequencies of XPD genotypes differed between healthy controls and patients with colon or head and neck cancer. Importantly, no differences in the distribution of these polymorphisms were found between healthy controls and breast cancer patients. The data clearly indicate that the risk of colon cancer is associated with single-nucleotide polymorphism in genes involved in base-excision repair and DNA-damage-induced responses.

Association of TGF-β1 and XPD polymorphisms with severe acute radiation-induced esophageal toxicity in locally advanced lung cancer patients treated with radiotherapy

PURPOSE

Radiation-induced esophageal toxicity (RIET) is a dose-limiting toxicity in lung cancer patients receiving radiotherapy. Accumulating evidence indicates that DNA repair and the cytokine pathways play essential roles in radiation-induced diseases. Genetic polymorphisms of genes in these pathways may affect gene function and/or gene expression and lead to different treatment-related esophageal toxicity.

MATERIALS AND METHODS

This study investigated the association of 21 polymorphisms in 14 genes, with the occurrence of ≥ grade 2 acute RIET. Genotypes were analyzed among 213 stage III lung cancer patients receiving radiotherapy.

RESULTS

We used Cox proportional hazard model to examine the effects of genotypes on ≥ grade 2 acute RIET risk and Kaplan-Meier estimator to compare effects of different genotypes on such risk. Multivariate analysis showed that CT or TT genotype of TGF-β1-509C/T polymorphism was associated with a significantly higher RIET risk (adjusted hazard ratio [HR]=2.47; 95% confidence interval (CI)=1.17-5.24; P=0.018, or HR=3.86; 95% CI=1.50-9.92; P=0.005), respectively, compared with the CC genotype. Moreover, Lys/Gln+Gln/Gln genotypes of XPD Lys751Gln polymorphism were also associated with a significantly decreased RIET risk (adjusted HR=0.55; 95% CI=0.32-0.96; P=0.030).

CONCLUSIONS

This report, for the first time, examined the influence of inherited variation in the DNA repair and the cytokine pathways on RIET.

Polymorphisms of COMT and XPD and risk of esophageal squamous cell carcinoma in a population of Yili Prefecture, in Xinjiang, China

OBJECTIVE

To investigate polymorphisms of COMT (Rs4680) and XPD (Rs13181) and risk of esophageal squamous cell carcinoma (ESCC) in a population from Yili Prefecture, Xinjiang, China.

METHODS

A hospital-based case-control study was designed. Genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Odds ratios (OR) and 95% confidence intervals (CI) were analysed using unconditional logistic regression.

RESULTS

An increased risk of ESCC was discovered with COMT in relation to the frequency of the presence of the A allele (Rs4680; OR 1.30, 95% CI 1.00-1.68). An individual with combined COMT 158 (Val/Met or Met/Met) and XPD 751 (Lys/Gln or Gln/Gln) genotype had an increased ESCC risk.

CONCLUSIONS

Polymorphic variation in COMT Val158Met and XPD Lys751Gln may be important for ESCC susceptibility.

Influence of XRCC1 Genetic Polymorphisms on Ionizing Radiation-Induced DNA Damage and Repair

It is well known that ionizing radiation (IR) can damage DNA through a direct action, producing single- and double-strand breaks on DNA double helix, as well as an indirect effect by generating oxygen reactive species in the cells. Mammals have evolved several and distinct DNA repair pathways in order to maintain genomic stability and avoid tumour cell transformation. This review reports important data showing a huge interindividual variability on sensitivity to IR and in susceptibility to developing cancer; this variability is principally represented by genetic polymorphisms, that is, DNA repair gene polymorphisms. In particular we have focussed on single nucleotide polymorphisms (SNPs) of XRCC1, a gene that encodes for a scaffold protein involved basically in Base Excision Repair (BER). In this paper we have reported and presented recent studies that show an influence of XRCC1 variants on DNA repair capacity and susceptibility to breast cancer.

Pharmacogenetic analysis in neoadjuvant chemoradiation for rectal cancer: high incidence of somatic mutations and their relation with response

Aims: The identification of predictive markers of response to chemoradiotherapy treatment remains a promising approach for patient management in order to obtain the best response with minor side effects. Initially, we investigated whether the analysis of several markers previously studied and others not yet evaluated could predict response to 5-fluorouracil- and capecitabine-based neoadjuvant treatment in locally advanced rectal cancer. Methods & materials: We studied germline and tumoral samples of 65 stage II/III rectal patients. A panel of pharmacogenetic markers was genotyped in paired peripheral blood samples and rectal cancer tumors. Results: Our results seem to confirm the previously described association of thymidylate synthase and the prediction of chemoradiotherapy response in rectal cancer. However, it failed to confirm the clinical utility proposed for XRCC1, ERCC1, ERCC2, MTHFR and EGFR polymorphisms in blood/germline samples. Subsequently, with the aim of improving prediction of individual response and assessing the role of studied polymorphisms in response to treatment, we determined if changes in tumor response to these markers could predict clinical outcome. We found a high degree of changes between germline and tumor samples, mainly somatic mutations without microsatellite instability, and a minor frequency of loss-of-heterozygosity events. In tumoral samples, XRCC1 appeared to be significantly associated (p = 0.006) with downstaging of the tumor (odds ratio: 7.93; 95% CI: 1.03–60.83), but the increasing of TYMS low-expression alleles contradict the previous results observed in germline samples. Conclusion: The detection of somatic mutations in rectal cancer tumors led us to re-evaluate the utility of the tests performed in blood samples for these polymorphisms in rectal cancer. Furthermore, studies aimed at assessing the influence of pharmacogenetic markers in treatment response performed in blood samples should take into account the particular pattern of hypermutability present in each tumor type. We hypothesize that different patterns of hypermutability present in each tumor type would be related to the different results in association studies related to response to the treatment.

Nucleotide excision repair polymorphisms and survival outcome for patients with metastatic breast cancer

PURPOSE

Inter-individual variations in treatment efficacy may be influenced by polymorphisms in DNA repair genes. We investigated the association of 3 functional polymorphisms in the nucleotide excision repair (NER) pathway with survival outcome of 95 patients with metastatic breast cancer (MBC) treated with DNA-damaging chemotherapy.

METHODS

ERCC1 8092 C/A, ERCC2 Asp312Asn and ERCC2 Lys751Gln were determined using Taqman-based genotyping assays. Genotype associations with breast cancer-specific survival (BCSS) and progression-free survival (PFS) were evaluated using Kaplan-Meier estimates and hazard ratios calculated using Cox regression analysis. Tests for trend were conducted by calculating P-values for the HR coefficient in proportional hazards regression models.

RESULTS

ERCC2 Lys751Gln was significantly associated with BCSS (median: 24.8 months for AA/AC combined and 14.2 months for CC, HR: 1.9 (95% CI 1.06-3.26)). Median BCSS decreased with increasing number of designated adverse genotypes for the 3 polymorphisms (P (trend) = 0.003). Risk estimates for PFS were nonsignificantly elevated and were significantly elevated for BCSS for patients with 2 (HR = 2.21, 95% CI: 1.04-4.72) or 3 (HR = 6.67, 95% CI: 2.19-20.29) adverse genotypes. In treatment subgroup analysis, risk estimates for BCSS were significantly elevated for patients with 3 adverse genotypes treated with cyclophosphamide, mitoxantrone and vinblastine (HR: 11.9, 95% CI 1.77-79.51) and P (trend) = 0.02 for increasing number of adverse genotypes. Risk of progression was significantly increased for patients with 1 adverse genotype treated with cyclophosphamide, mitoxantrone and carboplatin (HR: 3.5, 95% CI 1.19-10.6) and P (trend) = 0.02 for increasing number of adverse genotypes.

CONCLUSION

Polymorphisms in NER pathway may impact survival outcome for patients with MBC following treatment with DNA-damaging chemotherapy. These results provide support for a polygenic pathway approach for assessing the prognostic and predictive potential of polymorphisms in treatment outcome.

Association of single nucleotide polymorphisms in ATM, GSTP1, SOD2, TGFB1, XPD and XRCC1 with clinical and cellular radiosensitivity

PURPOSE

To examine the association of polymorphisms in ATM (codon 158), GSTP1 (codon 105), SOD2 (codon 16), TGFB1 (position -509), XPD (codon 751), and XRCC1 (codon 399) with fibrosis and also individual radiosensitivity.

METHODS AND MATERIALS

Retrospective analysis with 69 breast cancer patients treated with breast-conserving radiotherapy; total dose delivered was restricted to vary between 54 and 55Gy. Fibrosis was evaluated according to LENT/SOMA score. DNA was extracted from blood samples; cellular radiosensitivity was measured using the G0 assay and polymorphisms by PCR-RFLP and MALDI-TOF, respectively.

RESULTS

Twenty-five percent of all patients developed fibrosis of grade 2 or 3. This proportion tends to be higher in patients being polymorphic in TGFB1 or XRCC1 when compared to patients with wildtype genotype, whereas for ATM, GSTP1, SOD2 and XPD the polymorphic genotype appears to be associated with a lower risk of fibrosis. However, none of these associations are significant. In contrast, when a risk score is calculated based on all risk alleles, there was significant association with an increased risk of fibrosis (per risk allele odds ratio (ORs)=2.09, 95% confidence interval (CI): 1.32-3.55, p=0.0005). All six polymorphisms were found to have no significant effect on cellular radiosensitivity.

CONCLUSIONS

It is most likely that risk for radiation-induced fibrosis can be assessed by a combination of risk alleles. This finding needs to be replicated in further studies.

XPD codon 312 and 751 polymorphisms, and AFB1 exposure, and hepatocellular carcinoma risk

BACKGROUND

Genetic polymorphisms in DNA repair genes may influence individual variation in DNA repair capacity, which may be associated with risk of hepatocellular carcinoma (HCC) related to the exposure of aflatoxin B1 (AFB1). In this study, we have focused on the polymorphisms of xeroderma pigmentosum complementation group D (XPD) codon 312 and 751 (namely Asp312Asn and Lys751Gln), involved in nucleotide excision repair.

METHODS

We conducted a case-control study including 618 HCC cases and 712 controls to evaluate the associations between these two polymorphisms and HCC risk for Guangxi population by means of TaqMan-PCR and PCR-RFLP analysis.

RESULTS

We found that individuals featuring the XPD genotypes with codon 751 Gln alleles (namely XPD-LG or XPD-GG) were related to an elevated risk of HCC compared to those with the homozygote of XPD codon 751 Lys alleles [namely XPD-LL, adjusted odds ratios (ORs) were 1.75 and 2.47; 95% confidence interval (CIs) were 1.30-2.37 and 1.62-3.76, respectively]. A gender-specific role was evident that showed an higher risk for women (adjusted OR was 8.58 for XPD-GG) than for men (adjusted OR = 2.90 for XPD-GG). Interestingly, the interactive effects of this polymorphism and AFB1-exposure information showed the codon 751 Gln alleles increase the risk of HCC for individuals facing longer exposure years (Pinteraction = 0.011, OR = 0.85). For example, long-exposure-years (> 48 years) individuals who carried XDP-GG had an adjusted OR of 470.25, whereas long-exposure-years people with XDP-LL were at lower risk (adjusted OR = 149.12). However, we did not find that XPD codon 312 polymorphism was significantly associated with HCC risk.

CONCLUSION

These findings suggest that XPD Lys751Gln polymorphism is an important modulator of AFB1 related-HCC development in Guangxi population.

Recognition of O6MeG lesions by MGMT and mismatch repair proficiency may be a prerequisite for low-dose radiation hypersensitivity

Low-dose hyper-radiosensitivity (HRS) is the phenomenon whereby cells exposed to radiation doses of less than approximately 0.5 Gy exhibit increased cell killing relative to that predicted from back-extrapolating high-dose survival data using a linear-quadratic model. While the exact mechanism remains to be elucidated, the involvement of several molecular repair pathways has been documented. These processes in turn are also associated with the response of cells to O6-methylguanine (O6MeG) lesions. We propose a model in which the level of low-dose cell killing is determined by the efficiency of both pre-replicative repair by the DNA repair enzyme O6-methylguanine methyltransferase (MGMT) and post-replicative repair by the DNA mismatch repair (MMR) system. We therefore hypothesized that the response of cells to low doses of radiation is dependent on the expression status of MGMT and MMR proteins. MMR (MSH2, MSH6, MLH1, PMS1, PMS2) and MGMT protein expression signatures were determined in a panel of normal (PWR1E, RWPE1) and malignant (22RV1, DU145, PC3) prostate cell lines and correlated with clonogenic survival and cell cycle analysis. PC3 and RWPE1 cells (HRS positive) were associated with MGMT and MMR proficiency, whereas HRS negative cell lines lacked expression of at least one (MGMT or MMR) protein. MGMT inactivation had no significant effect on cell survival. These results indicate a possible role for MMR-dependent processing of damage produced by low doses of radiation.

Chromosomal aberrations in railroad transit workers: effect of genetic polymorphisms

Complex chemical mixtures are transported by train from Russia to Finland for further shipment. Here, we studied if exposure to genotoxic components among these substances could affect chromosomal aberrations (CAs) in peripheral lymphocytes of workers handling the tank cars. An initial survey among 48 railroad workers and 39 referents (male smokers and nonsmokers) showed an elevation of CAs. A campaign was started to reduce exposures through preventive measures. Five years later, 51 tank car workers and 40 age-matched referents (all nonsmoking men) were studied for CAs and genetic polymorphisms of xenobiotic metabolism (EPHX1, GSTM1, GSTP1, GSTT1, NAT1, NAT2), DNA repair (ERCC2, ERCC5, XPA, XPC, XRCC1, XRCC3), and folate metabolism (MTHFR, MTR). No increase in CAs was seen in the exposed group, suggesting that the preventive measures had been successful. However, a positive association existed between exposure duration and CA level among the exposed subjects. The level of chromosome-type breaks was actually lower in the exposed workers than the referents, particularly among MTHFR wild-type homozygotes or XRCC3 codon 241 variant allele carriers, suggesting modulation of CA frequency by folate metabolism and DNA repair. An interaction was observed between the occupational exposure and MTHFR, EPHX1, and MTR genotypes in determining CA level. The NAT2, ERCC2 exon 10, and XRCC1 codon 194 polymorphisms also affected CA frequency. Our findings suggest that handling of tank cars containing complex chemical mixtures poses a genotoxic risk, which may be reduced by preventive measures. Several genetic polymorphisms seem to modify the genotoxic effect or baseline CA level.

Relationships between acute reactions to radiotherapy in head and neck cancer patients and parameters of radiation-induced DNA damage and repair in their lymphocytes

PURPOSE

To study the relationship between lymphocyte radiosensitivity measured in vitro and acute reactions to radiotherapy in patients with head and neck cancer.

MATERIALS AND METHODS

Acute reactions were measured in 34 patients using the Dische scale. Lymphocyte radiosensitivity was measured using the alkaline comet assay, the micronucleus assay, the nuclear division index and morphological assessment of apoptosis.

RESULTS

There was a weak, statistically significant correlation between in vitro radiosensitivity measured as the rate of DNA damage repair and the cumulative radiation dose exerting the maximum acute reaction scored (r = -0.366, p = 0.039, n = 34). Subgroup analyses showed that for patients with a low level of radiation-induced DNA damage there was a statistically significant relationship between lymphocyte radiosensitivity measured as inhibition of proliferation and acute toxicity (r = -0.621, p = 0.007, n = 18). For patients with a high level of residual DNA damage, there was a relationship between lymphocyte radiosensitivity measured using the micronucleus assay and acute toxicity (r = -0.597, p = 0.023, n = 14).

CONCLUSIONS

Combining two measures of radiosensitivity improves the ability to correlate in vitro lymphocyte radiosensitivity and acute radiotherapy toxicity data.

Association of single nucleotide polymorphisms in SOD2, XRCC1 and XRCC3 with susceptibility for the development of adverse effects resulting from radiotherapy for prostate cancer

The objective of this study was to determine whether an association exists between certain single nucleotide polymorphisms (SNPs), which have previously been linked with adverse normal tissue effects resulting from radiotherapy, and the development of radiation injury resulting from radiotherapy for prostate cancer. A total of 135 consecutive patients with clinically localized prostate cancer and a minimum of 1 year of follow-up who had been treated with radiation therapy, either brachytherapy alone or in combination with external-beam radiotherapy, with or without hormone therapy, were genotyped for SNPs in SOD2, XRCC1 and XRCC3. Three common late tissue toxicities were investigated: late rectal bleeding, urinary morbidity, and erectile dysfunction. Patients with the XRCC1 rs25489 G/A (Arg280His) genotype were more likely to develop erectile dysfunction after irradiation than patients who had the G/G genotype (67% compared to 24%; P=0.048). In addition, patients who had the SOD2 rs4880 T/C (Val16Ala) genotype exhibited a significant increase in grade 2 late rectal bleeding compared to patients who had either the C/C or T/T genotype for this SNP (8% compared to 0%; P=0.02). Finally, patients with the combination of the SOD2 rs4880 C/T genotype and XRCC3 rs861539 T/C (Thr241Met) genotype experienced a significant increase in grade 2 late rectal bleeding compared to patients without this particular genotypic arrangement (14% compared to 1%; P=0.002). These results suggest that SNPs in the SOD2, XRCC1 and XRCC3 genes are associated with the development of late radiation injury in patients treated with radiation therapy for prostate adenocarcinoma.

Inherited susceptibility to bleomycin-induced micronuclei: correlating polymorphisms in GSTT1, GSTM1 and DNA repair genes with mutagen sensitivity

Susceptibility to DNA damage varies among individuals and sensitivity to bleomycin (BLM) may reflect the inter-individual differences. BLM sensitivity in part may be explained by inherited differences in DNA repair genes. We investigated the association between genetic polymorphisms in the GSTT1, GSTM1, XPD, XRCC1 and XRCC3 genes and the levels of spontaneous and BLM-induced DNA damage in peripheral blood lymphocytes from 200 healthy, unexposed individuals. The investigation of BLM sensitivity on cancer- or disease-free subjects and not occupationally exposed to known mutagen represents the strengths of the present study, as the detection of genetic damage is not biased by any disease- and occupational-related factor. The micronucleus (MN) assay was used to detect the spontaneous and BLM-induced genetic damage whereas, genotype analysis was carried out using methods based on polymerase chain reaction. Poisson regression analysis showed that subject's age, gender and smoking status had no effect on the spontaneous and BLM-induced MN frequencies. Genotype analysis revealed a clear association between GSTT1-null and XPD polymorphisms and both spontaneous and BLM-induced MN frequencies, whereas the effect of the XRCC1 polymorphism was marginally significant only with regard to spontaneous MN frequency. Genotype analysis did not reveal a clear association between the other studied SNPs (GSTM1 and XRCC3) and MN frequencies. Poisson regression analysis revealed no association between the score of protective alleles and the frequency of spontaneous MN. However, an increased number of protective alleles was significantly associated with a lower frequency of BLM-induced MN (P=0.0003). This finding highlights the genetic basis for BLM sensitivity, which could be a valid and useful surrogate for identifying genotypes that might increase susceptibility in population exposed to carcinogens. Further investigations in a large sample size and including more SNPs, reflecting the complexity of DNA repair machinery, might lead to the identification of a genetic profile responsible for the susceptibility to genotoxicants, with a far-reaching long-term impact on primary prevention and early detection of disease associated genes.

Genetic polymorphisms and micronucleus formation: a review of the literature

The formation of micronuclei (MN) is extensively used in molecular epidemiology as a biomarker of chromosomal damage, genome instability, and eventually of cancer risk. The occurrence of MN represents an integrated response to chromosome-instability phenotypes and altered cellular viabilities caused by genetic defects and/or exogenous exposures to genotoxic agents. The present article reviews human population studies addressing the relationship between genetic polymorphisms and MN formation, and provides insight into how genetic variants could modulate the effect of environmental exposures to genotoxic agents, host factors (gender, age), lifestyle characteristics (smoking, alcohol, folate), and diseases (coronary artery disease, cancer). Seventy-two studies measuring MN frequency either in peripheral blood lymphocytes or exfoliated cells were retrieved after an extensive search of the MedLine/PubMed database. The effect of genetic polymorphisms on MN formation is complex, influenced to a different extent by several polymorphisms of proteins or enzymes involved in xenobiotic metabolism, DNA repair proteins, and folate-metabolism enzymes. This heterogeneity reflects the presence of multiple external and internal exposures, and the large number of chromosomal alterations eventually resulting in MN formation. Polymorphisms of EPHX, GSTT1, and GSTM1 are of special importance in modulating the frequency of chromosomal damage in individuals exposed to genotoxic agents and in unexposed populations. Variants of ALDH2 genes are consistently associated with MN formation induced by alcohol drinking. Carriers of BRCA1 and BRCA2 mutations (with or without breast cancer) show enhanced sensitivity to clastogens. Some evidence further suggests that DNA repair (XRCC1 and XRCC3) and folate-metabolism genes (MTHFR) also influence MN formation. As some of the findings are based on relatively small numbers of subjects, larger scale studies are required that include scoring of additional endpoints (e.g., MN in combination with fluorescent in situ hybridization, analysis of nucleoplasmic bridges and nuclear buds), and address gene-gene interactions.

Modulation of DNA damage/DNA repair capacity by XPC polymorphisms

XPC, a key protein in the nucleotide excision repair (NER) pathway, recognizes damaged DNA and initiates NER. Genetic variations in the XPC gene might be associated with altered DNA repair capacities (DRC). In this study, we genotyped three XPC polymorphisms, Ala499Val (C-->T), PAT (-/+) and Lys939Gln (A-->C), and measured the DNA damage/DRC by alkaline comet assay challenged by BPDE and gamma-radiation in 476 healthy subjects. We also evaluated the associations between DNA damage/DRC and genotypes of XPC polymorphisms. Compared with the XPC Lys939Gln homozygous wild type (AA) subjects, subjects with the variant alleles (AC and CC) had significantly higher DNA damages induced by BPDE (Median and 95% confidence interval [CI]: 3.16 (3.01-3.44) vs. 2.88 (2.51-3.05), P=0.01), and gamma-radiation (4.18 (3.94-4.44) vs. 3.71 (3.49-4.04), P=0.01). However, subjects with the variant alleles (CT and TT) of Ala499Val exhibited a 8.6% and 13.1% decrease in DNA damages induced by BPDE (P=0.05) and gamma-radiation (P=0.001), respectively. Significant correlations were found between genotypes and induced DNA damages in XPC Lys939Gln (For BPDE: R=0.12, P=0.01; for gamma-radiation: R=0.094, P=0.046) and Ala499Val (For BPDE: R=-0.11, P=0.03; for gamma-radiation: R=-0.16, P=0.0009). The haplotypes "T-A" (in the order of Ala499Val-PAT-Lys939Gln) was associated with the lowest DNA damages. Our results suggested that the DRC of host cells might be modulated by specific XPC polymorphisms.

Polymorphism in nucleotide excision repair gene XPC correlates with bleomycin-induced chromosomal aberrations

Chromosomal aberrations (CAs) are important genetic alterations in the development and progression of the majority of human cancers. The frequency with which such alterations occur depends to a large extent on polymorphisms of DNA-repair genes and in genes coding for xenobiotic metabolizing enzymes, which are involved in the processes of activation and inactivation of xenobiotics. The frequency of bleomycin (BLM)-induced CAs is an indirect measure of the effectiveness of DNA repair mechanisms, and a predictor of environment-related risk of cancer. Our study was conducted on the human peripheral blood lymphocytes of 82 healthy volunteers. The aim of the study was to elucidate whether the frequency of BLM-induced CAs is correlated with polymorphisms of selected genes involved in different mechanisms of DNA repair such as: XRCC1 [base excision repair]; XPA, XPC, XPG, XPD, XPF, ERCC1 [nucleotide excision repair], NBS1, RAD51, XRCC2, XRCC3, RAD51, and BRCA1 [homologous recombination], as well as in genes encoding xenobiotic metabolizing enzymes, such as CYP1A, CYP2E1, NAT2, GSTT1, and EPHX (mEH). Our study indicated that, of the polymorphisms studied, only XPC (exon 15 and intron 11) is associated with BLM-induced CAs, suggesting a role of the NER pathway in the repair of BLM-induced chromosomal aberrations.

Telomere length modulates human radiation sensitivity in vitro

The molecular basis of the interindividual differences of normal individuals to ionizing radiation is poorly understood. Several studies in telomerase KO mice with short telomeres have uncovered an inverse relationship between telomere length and radiation sensitivity. The present work aims to determine if chromosome radiosensitivity is correlated with telomere length in healthy individuals. With this purpose, individual radiosensitivity was determined by the micronucleus assay in peripheral blood lymphocytes from two groups of individuals of the same age but with highly heterogeneous telomere length, selected from a population of 181 individuals where we previously measured telomere length. Our study demonstrates that telomere length modulates chromosome in vitro radiosensitivity in healthy individuals as the group with short telomeres presented higher frequencies of ionizing radiation-induced micronuclei when compared to the long telomeres group. This result supports the conclusion that individual telomere length acts as biomarker of individual chromosome instability upon exposure to ionizing radiation.

Influence of polymorphisms at loci encoding DNA repair proteins on cancer susceptibility and G2 chromosomal radiosensitivity

Sixteen candidate polymorphisms (13 SNPs and 3 microsatellites) in nine genes from four DNA repair pathways were examined in 83 subjects, comprising 23 survivors of childhood cancer, their 23 partners, and 37 offspring, all of whom had previously been studied for G(2) chromosomal radiosensitivity. Genotype at the Asp148Glu SNP site in the APEX gene of the base excision repair (BER) pathway was associated with childhood cancer in survivors (P = 0.001, significant even after multiple test adjustment), due to the enhanced frequency of the APEX Asp148 allele among survivors in comparison to that of their partners. Analysis of variance (ANOVA) of G(2) radiosensitivity in the pooled sample, as well as family-based association test (FBAT) of the family-wise data, showed sporadic suggestions of associations between G(2) radiosensitivity and polymorphisms at two sites (the Thr241Met SNP site in the XRCC3 gene of the homologous recombinational pathway by ANOVA, and the Ser326Cys site in the hOGG1 gene of the BER pathway by FBAT analysis), but neither of these remained significant after multiple-test adjustment. This pilot study provides an intriguing indication that DNA repair gene polymorphisms may underlie cancer susceptibility and variation in radiosensitivity.

Xeroderma pigmentosum group D 751 polymorphism as a predictive factor in resected gastric cancer treated withchemo-radiotherapy

AIM: To evaluate the potential association of xeroderma pigmentosum group D (XPD) codon 751 variant with outcome after chemo-radiotherapy in patients with resected gastric cancer.

METHODS: We used PCR-RFLP to evaluate the genetic XPD Lys751Gln polymorphisms in 44 patients with stage III (48%) and IV (20%) gastric cancer treated with surgery following radiation therapy plus 5-fluorouracil/leucovorin based chemotherapy.

RESULTS: Statistical analysis showed that 75% (12 of 16) of relapse patients showed Lys/Lys genotype more frequently (P = 0.042). The Lys polymorphism was an independent predictor of high-risk relapse-free survival from Cox analysis (HR: 3.07, 95% CI: 1.07-8.78, P = 0.036) and Kaplan-Meir test (P = 0.027, log-rank test).

CONCLUSION: XPD Lys751Gln polymorphism may be an important marker in the prediction of clinical outcome to chemo-radiotherapy in resected gastric cancer patients.