Variation In DNA Repair Capacity Research Articles

Human Variation in DNA Repair, Immune Function, and Cancer Risk.

DNA damage constantly threatens genome integrity, and DNA repair deficiency is associated with increased cancer risk. An intuitive and widely accepted explanation for this relationship is that unrepaired DNA damage leads to carcinogenesis due to the accumulation of mutations in somatic cells. But DNA repair also plays key roles in the function of immune cells, and immunodeficiency is an important risk factor for many cancers. Thus, it is possible that emerging links between inter-individual variation in DNA repair capacity and cancer risk are driven, at least in part, by variation in immune function, but this idea is underexplored. In this review we present an overview of the current understanding of the links between cancer risk and both inter-individual variation in DNA repair capacity and inter-individual variation in immune function. We discuss factors that play a role in both types of variability, including age, lifestyle, and environmental exposures. In conclusion, we propose a research paradigm that incorporates functional studies of both genome integrity and the immune system to predict cancer risk and lay the groundwork for personalized prevention.

Modulation of DNA damage by XPF, XPG and ERCC1 gene polymorphisms in pesticide-exposed agricultural workers of Punjab, North-West India

Inter-individual variations in DNA repair capacity (DRC) for repairing pesticide-induced DNA oxidation damage may influence adverse health outcomes. We aimed to evaluate whether polymorphisms in genes involved in nucleotide excision repair (NER) pathway could modulate DNA damage in pesticide-exposed agricultural workers. Xeroderma pigmentosum group F (XPF) (Arg415Gln, G1244A, rs1800067), xeroderma pigmentosum group G (XPG) (Asp1104His, G3507C, rs17655), excision repair cross complementation group 1 (ERCC1) (3′UTR, C8092A, rs3212986) and ERCC1 (Asn118Asn, C19007T, rs11615) polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique in 225 pesticide-exposed agricultural workers and 225 controls from Punjab, North-West India. The assessment of DNA damage was carried out by alkaline comet assay. Kruskal-Wallis test was used to evaluate the association of gene polymorphisms in NER pathway with DNA damage. Pesticide-exposed agricultural workers carrying variant XPF Gln/Gln (AA) genotype showed higher comet tail length (p < 0.01) than wild type Arg/Arg (GG) genotype. The comet tail length (p < 0.01) was found to be significantly increased in exposed agricultural workers carrying XPG His/His (CC) genotype than wild-type Asp/Asp (GG) genotype. In relation to the individuals carrying wild type ERCC1 3′UTR CC genotype, exposed individuals with variant ERCC1 3′UTR CA genotype showed elevation in the comet tail length (p = 0.029). However, we found no association of ERCC1 Asn118Asn (C19007T) genotype with DNA damage. These results indicate that XPF, XPG and ERCC1 genes of NER pathway may modulate the efficacy of the DNA repair system against pesticide exposure in our population.

&lt;p&gt;Polymorphism of XRCC3 in Egyptian Breast Cancer Patients&lt;/p&gt;

PurposePolymorphisms of DNA repair genes may contribute to variations in DNA repair capacity and subsequent genetic susceptibility to different cancers. In Egypt, breast cancer is the most common cancer among women, representing 18.9% of the total cancer cases. The present study assesses the correlation between X-ray repair cross-complementing group 3 (XRCC3) polymorphism with breast cancer and treatment response in Egyptian female breast cancer patients.Patients and MethodsThis pilot case–control study was conducted on 66 female breast cancer patients and 20 apparently healthy females as a control group. Tumor grading, immunohistostaining of hormone (progesterone and estrogen) receptors and human epidermal growth factor receptor 2 (HER2), and RFLP-PCR for XRCC3 (rs861539) polymorphism were performed. All breast cancer patients received a treatment protocol (after surgery) which was either chemotherapy (anthracyclines followed by paclitaxel or anthracyclines + fluorouracil) or radiotherapy, or both. Disease-free survival (DFS) and overall survival (OS) were recorded.ResultsThe number of patients with a heterozygous allele (GA) was significantly higher in cases of tumor size >20 mm. The A allele was correlated with younger age at diagnosis in both chemotherapy and radiotherapy groups. Poor treatment response and higher mortality rates were significantly associated with AA and GA compared with GG alleles (normal allele). In the chemotherapy group, out of eight patients with the A allele, six showed a poor response to treatment containing fluorouracil.ConclusionXRCC3 rs861539 polymorphism could be associated with lower DFS and OS and poor treatment response. So, we recommend carrying out XRCC3 genotyping before starting treatment to choose the most effective treatment strategy according to XRCC3 polymorphism.

Genetic susceptibility to radiation-related differentiated thyroid cancers: a systematic review of literature.

The first study establishing exposure to ionizing radiations (IRs) as a risk factor for differentiated thyroid cancer (DTC) was published 70 years ago. Given that radiation exposure causes direct DNA damage, genetic alterations in the different DNA repair mechanisms are assumed to play an important role in long-term IR-induced DNA damage prevention. Individual variations in DNA repair capacity may cause different reactions to damage made by IR exposure. The aim of this review is to recapitulate current knowledge about constitutional genetic polymorphisms found to be significantly associated with DTC occurring after IR exposure. Studies were screened online using electronic databases - only fully available articles, and studies performed among irradiated population or taking radiation exposure as adjustment factors and showing significant results are included. Nine articles were identified. Ten variants in/near to genes in six biological pathways, namely thyroid activity regulations, generic transcription, RET signaling, ATM signaling and DNA repair pathways were found to be associated with radiation-related DTC in these studies. Only seven variants were found to be in interaction with IR exposure in DTC risk. Most of these variants are also associated to sporadic DTC and are not specific to IR-related DTC. In the published studies, no data on children treated with radiotherapy is described. In conclusion, more studies carried out on larger cohorts or on case-control studies with well-documented individual radiation dose estimations are needed to get a comprehensive picture of genetic susceptibility factors involved in radiation-related DTC.

Abstract 1617: Genetic polymorphisms in DNA repair genes XRCC1 and 3 are associated with increased risk of breast cancer in Bangladeshi population

Abstract Background: Breast cancer is the most commonly occurring cancer in women worldwide and its prevalence vary among different ethnic groups. Genetic polymorphisms in DNA repair genes may affect individual variation in DNA repair capacity which may contribute to individual susceptibility for developing various cancers. This study aimed to investigate the contribution of polymorphisms in two DNA repair genes, namely XRCC1 (Arg399Gln, rs25487) and XRCC3 (Thr241Met, rs861539) to breast cancer risk in Bangladeshi females and their role as susceptibility markers. Methods: A case-control study comprising 121 breast cancer patients and 133 healthy volunteers was conducted taking the age, breast feeding status, menopausal status, education etc into account. Genomic DNA isolated from peripheral blood was used to genotype the target polymorphisms using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. Risk-stratified subgroup analyses were conducted to find out the association between the genotypes and age-, menopause-, lactating status-related characteristics of breast cancer patients. Results: A significant positive association was found between XRCC1 (Arg399Gln,) and XRCC3 (Thr241Met) polymorphisms and breast cancer risk in the studied population. In case of XRCC1 Arg399Gln polymorphism, the heterozygous Arg/Gln (G/A) and homozygous Gln/Gln (A/A) genotypes showed 1.78-fold (OR=1.78, 1.0084 to 3.1442, p=0.0467) and 2.41-fold (OR=2.41, 95% CI= 1.0354 to 5.5914, p=0.0413) increased risk of breast cancer, respectively when compared with homozygous Arg/Arg genotype. The presence of any XRCC1 Gln (Arg/Gln or Gln/Gln) was associated with 1.93-fold increased risk (OR=1.93, 95% CI= 1.1574 to 3.2290, p=0.0118). The variant Gln (A) allele also was associated with increased risk of breast cancer (OR=1.78, 95% CI= 1.1885 to 2.6805, p=0.0052). The Gln/Gln genotype was more prevalent in breast cancer cases at ages 55 or above and in menopausal state. In case of XRCC3 (Thr241Met) polymorphism, Thr/Met (C/T) heterozygote, and combined Thr/Met+Met /Met (C/T+T/T) genotypes were significantly associated with 1.85- and 1.89- fold higher risk of breast cancer, respectively (OR=1.85, 95% CI=1.0815 to3.1834, p=0.0248; OR=1.89, 95% CI=1.1199 to 3.1908, p=0.0171, respectively). The variant Met (T) allele showed significant association with increased susceptibility (1.70-fold) to breast cancer (OR=1.70, 95% CI=1.0849 to 2.6172, p= 0.0206). Among breast cancer cases significant differences in genotype frequency were evident in patients with age 55 years or above and with menopause. Conclusion: Our results suggest that XRCC1 (Arg399Gln) and XRCC3 (Thr241Met) polymorphisms are associated with increased risk of breast cancer in Bangladeshi females. In addition, this association was significantly related to age and lactating status. Citation Format: Md. Mustafizur Rahman, Nupur Rani Hawlader, Md. Mostafizur Rahman, Md. Amir Hossain. Genetic polymorphisms in DNA repair genes XRCC1 and 3 are associated with increased risk of breast cancer in Bangladeshi population [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1617.

Broad spectrum detection of DNA damage by Repair Assisted Damage Detection (RADD)

Environmental exposures, reactive by-products of cellular metabolism, and spontaneous deamination events result in a spectrum of DNA adducts that if un-repaired threaten genomic integrity by inducing mutations, increasing instability, and contributing to the initiation and progression of cancer. Assessment of DNA adducts in cells and tissues is critical for genotoxic and carcinogenic evaluation of chemical exposure and may provide insight into the etiology of cancer. Numerous methods to characterize the formation of DNA adducts and their retention for risk assessment have been developed. However, there are still significant drawbacks to the implementation and wide-spread use of these methods, because they often require a substantial amount of biological sample, highly specialized expertise and equipment, and depending on technique, may be limited to the detection and quantification of only a handful of DNA adducts at a time. There is a pressing need for high throughput, easy to implement assays that can assess a broad spectrum of DNA lesions, allowing for faster evaluation of chemical exposures and assessment of the retention of adducts in biological samples. Here, we describe a new methodology, Repair Assisted Damage Detection (RADD), which utilizes a DNA damage processing repair enzyme cocktail to detect and modify sites of DNA damage for a subsequent gap filling reaction that labels the DNA damage sites. This ability to detect and label a broad spectrum of DNA lesions within cells, offers a novel and easy to use tool for assessing levels of DNA damage in cells that have been exposed to environmental agents or have natural variations in DNA repair capacity.

Interaction between APC and Fen1 during breast carcinogenesis.

Aberrant DNA base excision repair (BER) contributes to malignant transformation. However, inter-individual variations in DNA repair capacity plays a key role in modifying breast cancer risk. We review here emerging evidence that two proteins involved in BER - adenomatous polyposis coli (APC) and flap endonuclease 1 (Fen1) - promote the development of breast cancer through novel mechanisms. APC and Fen1 expression and interaction is increased in breast tumors versus normal cells, APC interacts with and blocks Fen1 activity in Pol-β-directed LP-BER, and abrogation of LP-BER is linked with cigarette smoke condensate-induced transformation of normal breast epithelial cells. Carcinogens increase expression of APC and Fen1 in spontaneously immortalized human breast epithelial cells, human colon cancer cells, and mouse embryonic fibroblasts. Since APC and Fen1 are tumor suppressors, an increase in their levels could protect against carcinogenesis; however, this does not seem to be the case. Elevated Fen1 levels in breast and lung cancer cells may reflect the enhanced proliferation of cancer cells or increased DNA damage in cancer cells compared to normal cells. Inactivation of the tumor suppressor functions of APC and Fen1 is due to their interaction, which may act as a susceptibility factor for breast cancer. The increased interaction of APC and Fen1 may occur due to polypmorphic and/or mutational variation in these genes. Screening of APC and Fen1 polymorphic and/or mutational variations and APC/Fen1 interaction may permit assessment of individual DNA repair capability and the risk for breast cancer development. Such individuals might lower their breast cancer risk by reducing exposure to carcinogens. Stratifying individuals according to susceptibility would greatly assist epidemiologic studies of the impact of suspected environmental carcinogens. Additionally, a mechanistic understanding of the interaction of APC and Fen1 may provide the basis for developing new and effective targeted chemopreventive and chemotherapeutic agents.

Polymorphism of the DNA Repair Gene XRCC1 (Arg194Trp) and its role in Colorectal Cancer in Kashmiri Population: a Case Control Study.

Genetic polymorphisms in DNA repair genes may influence individual variation in DNA repair capacity, which may be associated with risk of developing cancer. For colorectal cancer the importance of mutations in mismatch repair genes has been extensively documented. In this study we focused on the Arg194Trp polymorphism of the DNA repair gene XRCC1, involved in base excision repair (BER) and its role in colorectal cancer in Kashmiri population. A case-control study was conducted including 100 cases of colorectal cancer, and 100 hospital-based age- and sex-matched healthy controls to examine the role of XRCC1 genetic polymorphisms in the context of colorectal cancer risk for the Kashmiri population. Genotype analysis of XRCC1 Arg194Trp was conducted with a restriction fragment length polymorphism (RFLP) method. The overall association between the XRCC1 polymorphism and the CRC cases was found to be significant (p<0.05) with both the heterozygous genotype (Arg/Trp) as well as homozygous variant genotype (Trp/Trp) being moderately associated with the elevated risk for CRC [OR=2.01 (95% CI=1.03-3.94) and OR=5.2(95% CI=1.42-19.5)] respectively. Our results suggest an increased risk for CRC in individuals with XRCC1 Arg194Trp polymorphism suggesting BER repair pathway modulates the risk of developing colorectal cancer in the Kashmiri population.

Polymorphism of the XRCC3 gene and risk of gastric cancer in a Kashmiri population

DNA repair plays a critical role in protecting the genome of the cell from the insults of cancer-causing agents. Genetic polymorphisms in DNA repair genes may influence individual variation in DNA repair capacity, which may be associated with the risk of developing cancer. Inherited polymorphisms of DNA repair genes may contribute to variations in DNA repair capacity and genetic susceptibility to different cancers. The X-ray repair complementing defective repair in Chinese hamster cells 3 (XRCC3) gene is a member of the RAD51 gene family. It encodes an important protein that functions in the homologous recombination repair of a DNA double-strand break. For gastric cancer, the importance of mutations in mismatch repair genes has been well documented, but less is known about other DNA repair pathways in gastric carcinogenesis. In this study, we have focused on the XRCC3 gene, involved in homologous recombinational repair. The Kashmir valley has an increased incidence of gastric cancer and its etiology has not been understood fully as yet. As the Kashmiri population is ethnically and demographically different from that in other parts of the world, the aim of this study was to determine whether a single nucleotide polymorphism of the XRCC3 gene (Thr241Met) of exon 7 can influence the risk of gastric cancer in the population. As many as 80 histopathologically confirmed gastric cancer cases and 70 healthy controls, age, sex, and ethnicity matched for known genotypes of XRCC3 exon 7 were studied. We genotyped for this variant using PCR-restriction fragment length polymorphisms. The XRCC3 genotype and allele frequencies were not significantly different between cases and controls (P=0.92 for the genotype; P=0.72 for the allele). The XRCC3 241Met allele frequency (6.6%) was significantly lower in healthy Kashmiri controls than reported previously in healthy US White controls (38.9%). Compared with the XRCC3 241Thr/Thr genotype, the variant XRCC3 241Thr/Met and Met/Met genotypes were not associated with an increased risk of gastric cancer (adjusted odds ratio=1.19; 95% confidence interval=0.44-3.18). These findings suggest that polymorphisms of XRCC3 Thr241Met may not play a role in the etiology of gastric cancer. Further studies with a larger number of participants and simultaneous measurement of different polymorphisms in DNA repair genes in the same pathway are needed.

Polymorphisms of homologous recombination RAD51, RAD51B, XRCC2, and XRCC3 genes and the risk of prostate cancer.

Genetic polymorphisms in DNA repair genes may induce individual variations in DNA repair capacity, which may in turn contribute to the risk of cancer developing. Homologous recombination repair (HRR) plays a critical role in maintaining chromosomal integrity and protecting against carcinogenic factors. The aim of the present study was to evaluate the relationship between prostate cancer risk and the presence of single nucleotide polymorphisms (SNPs) in the genes involved in HRR, that is, RAD51 (rs1801320 and rs1801321), RAD51B (rs10483813 and rs3784099), XRCC2 (rs3218536), and XRCC3 (rs861539). Polymorphisms were analyzed by PCR-RFLP and Real-Time PCR in 101 patients with prostate adenocarcinoma and 216 age- and sex-matched controls. A significant relationship was detected between the RAD51 gene rs1801320 polymorphism and increased prostate cancer risk. Our results indicate that the RAD51 gene rs1801320 polymorphism may contribute to prostate cancer susceptibility in Poland.

Abstract 5367: DNA repair capacity, gene expression and epigenomic profiles in bladder cancer

Abstract In Europe, bladder cancer (BC) is the sixth most commonly diagnosed tumor and the second most common cause of death among patients with genitourinary tract malignancies. The ability to repair DNA damage is strongly associated with the risk of cancer and inter-individual variation in DNA repair capacity (DRC) might account for different susceptibility of developing cancer. DRC represents a complex marker comprising the sum of several factors such as gene variants, gene expression, stability of gene products, and effect of inhibitors/stimulators. Individuals with low DRC will tend to accumulate more damage than those who have a better ability to repair such damage. This variability is modulated by the genetic background to which SNPs/haplotype combinations in DNA repair genes, as well as epigenetic regulation are likely to contribute. Phenotypic assays to evaluate DNA repair activity (in particular NER comet assay, H2AX phosphorylation and micronucleus assay) were performed on cryopreserved lymphocytes from 159 cases (collected before treatment) and 159 controls matched by age and smoking habits, enrolled in Turin Bladder Cancer Study (TBCS). We aimed at studying the relationship between DRC (evaluated by comet assay, micronuclei and H2AX phosphorylation assay) and bladder cancer integrating, gene expression and epigenetic profile data (methylation levels and microRNA expression). In particular, we performed an integrated analysis on the genotype/phenotype correlation in a population of bladder cancer cases and controls provided with detailed description of the follow-up for response to therapy/recurrence/survival. This integrated approach will help in elucidating the role of DRC (and its determinants) as predictive and prognostic marker and to identify combined biomarkers to be measured in blood cells as non-invasive predictive method. Citation Format: Barbara Pardini, Alessandra Allione, Simonetta Guarrera, Valentina Turinetto, Giovanni Fiorito, Fabio Rosa, Alessia Russo, Federica Modica, Claudia Giachino, Paolo Vineis, Carlotta Sacerdote, Giuseppe Matullo. DNA repair capacity, gene expression and epigenomic profiles in bladder cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5367. doi:10.1158/1538-7445.AM2014-5367

Inter-individual variation in DNA repair capacity: a need for multi-pathway functional assays to promote translational DNA repair research.

Why does a constant barrage of DNA damage lead to disease in some individuals, while others remain healthy? This article surveys current work addressing the implications of inter-individual variation in DNA repair capacity for human health, and discusses the status of DNA repair assays as potential clinical tools for personalized prevention or treatment of disease. In particular, we highlight research showing that there are significant inter-individual variations in DNA repair capacity (DRC), and that measuring these differences provides important biological insight regarding disease susceptibility and cancer treatment efficacy. We emphasize work showing that it is important to measure repair capacity in multiple pathways, and that functional assays are required to fill a gap left by genome wide association studies, global gene expression and proteomics. Finally, we discuss research that will be needed to overcome barriers that currently limit the use of DNA repair assays in the clinic.

Association between polymorphisms at promoters of XRCC5 and XRCC6 genes and risk of breast cancer

Variation in DNA repair genes is one of the mechanisms that may lead to variation in DNA repair capacity. Ku, a heterodimeric DNA-binding complex, is directly involved in repair of DNA double-strand breaks. Ku consists of two subunits, Ku70 and Ku80, which are encoded by the XRCC6 and XRCC5 genes, respectively. In the present study, we investigated whether common genetic variant in variable number of tandem repeats (VNTR) XRCC5 and T-991C XRCC6 was associated with an altered risk of breast cancer. The present study included 407 females with breast cancer and 395 age frequency-matched controls which were randomly selected from the healthy female blood donors. The XRCC5 and XRCC6 polymorphisms were determined using PCR-based methods. For XRCC5 polymorphism, in comparison with the 1R/1R genotype, the 0R/0R genotype increased breast cancer risk (OR 9.55, 95%CI 1.19-76.64, P = 0.034). The 1R/3R genotype compared with 1R/1R genotype decreased the risk of breast cancer (Fisher's exact test P = 0.015). There was no association between T-991C polymorphism of XRCC6 and breast cancer risk. Mean of age at diagnosis of breast cancer for 0, 1, 2, 3, and >4 repeat in XRCC5 were 39.2, 41.9, 44.3, 45.8, and 47.3 years, respectively. The Kaplan-Meier survival analysis revealed that the number of repeat was associated with age at diagnosis of breast cancer (log rank statistic = 13.90, df = 4, P = 0.008). The findings of the present study revealed that either breast cancer risk or age at diagnosis of breast cancer was associated with the VNTR polymorphism at promoter region of XRCC5.

Genetic Polymorphisms in DNA Repair Genes XRCC4 and XRCC5 and Aflatoxin B1–related Hepatocellular Carcinoma

Genetic polymorphisms in DNA repair genes may influence individual variation in DNA repair capacity and may play an important role in carcinogenesis. We investigated the role of genetic polymorphisms at XRCC4 codon 247 (rs3734091, XRCC4P) and XRCC5 codon 180 (rs80309960, XRCC5P) in liver cancer (hepatocellular carcinoma) caused by aflatoxin B1 (AFB1). A hospital-based case-control study, including 1499 liver cancer cases and 2045 controls without any liver disease, was conducted in a high aflatoxin exposure area in the Guangxi region of China to assess the relationship between these two polymorphisms and aflatoxin-related liver cancer risk and prognosis. Genotypes, mRNA levels, and the hot-spot mutation of TP53 gene (TP53M) related to AFB1 exposure was tested using TaqMan-PCR technique. XRCC4 protein level was analyzed by immunohistochemistry. For XRCC4P and XRCC5P, only XRCC4P modified liver cancer risk. Compared with the homozygote of XRCC4 codon 247 Ala alleles (XRCC4-AA), the genotypes of XRCC4 codon 247 Ser alleles (namely XRCC4-AS or -SS) increased liver cancer risk (odds ratio [OR] = 1.35 and 2.02, respectively). Significant interactive effects between risk genotypes (OR > 1) and aflatoxin exposure status were also observed in the joint effects analysis. Moreover, this polymorphism was associated not only with lower XRCC4 expression levels but also with higher AFB1-DNA adduct levels and increasing TP53M and portal vein tumor risk. Additionally, XRCC4P modified the recurrence-free survival and overall survival of cases, especially under conditions of high aflatoxin exposure. XRCC4P may be a genetic modifier for the risk and outcome of hepatocellular carcinoma induced by AFB1 exposure.

DNA Repair Deficiency as a Susceptibility Marker for Spontaneous Lymphoma in Golden Retriever Dogs: A Case-Control Study

There is accumulating evidence that an individual’s inability to accurately repair DNA damage in a timely fashion may in part dictate a predisposition to cancer. Dogs spontaneously develop lymphoproliferative diseases such as lymphoma, with the golden retriever (GR) breed being at especially high risk. Mechanisms underlying such breed susceptibility are largely unknown; however, studies of heritable cancer predisposition in dogs may be much more straightforward than similar studies in humans, owing to a high degree of inbreeding and more limited genetic heterogeneity. Here, we conducted a pilot study with 21 GR with lymphoma, 20 age-matched healthy GR and 20 age-matched healthy mixed-breed dogs (MBD) to evaluate DNA repair capability following exposure to either ionizing radiation (IR) or the chemical mutagen bleomycin. Inter-individual variation in DNA repair capacity was evaluated in stimulated canine lymphoctyes exposed in vitro utilizing the G2 chromosomal radiosensitivity assay to quantify clastogen-induced chromatid-type aberrations (gaps and breaks). Golden retrievers with lymphoma demonstrated elevated sensitivity to induction of chromosome damage following either challenge compared to either healthy GR or MBD at multiple doses and time points. Using the 75th percentile of chromatid breaks per 1,000 chromosomes in the MBD population at 4 hours post 1.0 Gy IR exposure as a benchmark to compare cases and controls, GR with lymphoma were more likely than healthy GR to be classified as “sensitive” (odds ratio = 21.2, 95% confidence interval 2.3-195.8). Furthermore, our preliminary findings imply individual (rather than breed) susceptibility, and suggest that deficiencies in heritable factors related to DNA repair capabilities may be involved in the development of canine lymphoma. These studies set the stage for larger confirmatory studies, as well as candidate-based approaches to probe specific genetic susceptibility factors.

Genetic polymorphisms in RAD23B and XPC modulate DNA repair capacity and breast cancer risk in Puerto Rican women

Studies have shown that DNA repair capacity (DRC) is significantly decreased in breast cancer patients, but the molecular causes of inter-individual variation in DRC are unknown. We hypothesized that genetic variation in the nucleotide excision repair pathway genes can modulate DRC and breast cancer risk in Puerto Rican women. A total of 228 breast cancer cases and 418 controls were recruited throughout Puerto Rico. For all study participants, eight single nucleotide polymorphisms (SNPs) in the genes XPC, XPD, and RAD23B were genotyped using a TaqMan PCR, and the DRC levels of UV induced-DNA damage was measured in peripheral lymphocytes using a host cell reactivation assay. After adjustment for confounders, RAD23B rs1805329 (Ala249Val) was found to be significantly associated with breast cancer risk under all models tested (P < 0.001). There was also a significant association between breast cancer risk and RAD23B rs10739234 (intronic) under the recessive model (P = 0.003, OR: 2.72, 95% CI: 1.40-5.30). In cases, there was a statistically significant difference in mean DRC per genotype for RAD23B rs1805329 (P < 0.001) and XPC rs2607775 (P = 0.002). When we modeled the combined effect of multiple SNPs that each independently affected DRC on cancer risk, we observed incremental augmentations in risk with increasing number of risk genotypes at those loci (P overall model <0.001). The increase in adverse genotypes was also correlated with a progressive decrease in DRC values. Our data indicate an additive effect of the NER SNPs on DRC and breast cancer risk in Puerto Rican women.

DNA Repair Genes XRCC1, XRCC3, XPD, and OGG1 Polymorphisms among the Central Region Population of Saudi Arabia

DNA repair is one of the central defense mechanisms against mutagenic exposures. Inherited SNPs of DNA repair genes may contribute to variations in DNA repair capacity and susceptibility to cancer. Due to the presence of these variants, inter-individual and ethnic differences in DNA repair capacity have been established in various populations. Saudi Arabia harbors enormous genetic and cultural diversity. In the present study we aimed to determine the genotype and allele frequencies of XRCC1 Arg399Gln (rs25487), XRCC3 Thr241Met (rs861539), XPD Lys751Gln (rs13181), and OGG1 Ser326Cys (rs1052133) gene polymorphisms in 386 healthy individuals residing in the central region of Saudi Arabia and compare them with HapMap and other populations. The genotype and allele frequencies of the four DNA repair gene loci in central Saudi population showed a distinctive pattern. Furthermore, comparison of polymorphisms in these genes with other populations also showed a unique pattern for the central Saudi population. To the best of our knowledge, this is the first report that deals with these DNA repair gene polymorphisms among the central Saudi population.

DNA Repair Gene Polymorphisms at XRCC1, XRCC3, XPD, and OGG1 Loci in the Hyderabad Population of India

DNA repair is one of the crucial defense mechanism against mutagenic exposure. Inherited SNPs of DNA repair genes may contribute to variation in DNA repair capacity and susceptibility to cancer. Due to the presence of these variants, inter-individual and ethnic differences in DNA repair capacity have been established in various populations. India harbors enormous genetic and cultural diversity. In the present study we aimed to determine the genotypes and allele frequencies of XRCC1 Arg399Gln (rs25487), XRCC3 Thr241Met (rs861539), XPD Lys751Gln (rs13181), and OGG1 Ser326Cys (rs1052133) gene polymorphisms in 186 healthy individuals residing in the Hyderabad region of India and to compare them with HapMap and other populations. The genotype and allele frequency distribution at the four DNA repair gene loci among Hyderabad population of India revealed a characteristic pattern. Comparison of these gene polymorphisms with other populations revealed a distinctiveness of Hyderabad population from the Deccan region of India. To the best of our knowledge, this is the first report of such DNA repair gene polymorphisms in the Deccan Indian population.

Validation of the nucleotide excision repair comet assay on cryopreserved PBMCs to measure inter-individual variation in DNA repair capacity

Inter-individual susceptibility to mutagens/carcinogens can be assessed by either genotyping DNA repair genes in different pathways or phenotyping DNA repair capacity (DRC) at the molecular or cellular level. Due to the large number of known DNA repair genes, and the interactions between repair pathways, phenotyping is becoming the preferred approach to measure DRC, and reliable assays are therefore increasingly needed. The use of a cellular phenotype comet assay for the nucleotide excision repair (NER) pathway using benzo[a]pyrene diol epoxide (BPDE) has been described in previous papers, but no thorough evaluation of its applicability in large genotype-phenotype studies has been presented. Our aim was to evaluate the possibility of using cryopreserved instead of fresh peripheral blood mononuclear cells (PBMCs) to evaluate intra- and inter-assay variation, and inter-individual variation, for the aphidicolin (APC)-block NER comet assay. Moreover, we measured the variation for the designated internal standard (K562 erythroleukaemia cell line) and we evaluated the feasibility to use lymphoblastoid cell lines (LCLs) as surrogate of PBMCs. Our results showed a low intra-assay [coefficient of variation (CV) 19.9%] and inter-assay (CV 32.3%) variation, with a good inter-individual variation (122 subjects, mean ± standard deviation 7.38 ± 4.99; range 0.66-26.14; CV 67.63%). A significant correlation between results derived from cryopreserved and fresh PBMCs from the same individuals was found (10 subjects, r = 0.62, P = 0.05). Results from LCLs and cryopreserved PBMCs from the same subjects showed an inverse significant correlation (10 subjects, r = -0.712, P = 0.02). K562 cells as internal standard showed low intra-assay variation. In the present study the APC-block NER comet assay on cryopreserved PBMCs seemed to be a reliable method to measure DRC variation in epidemiological studies; LCLs were not a good surrogate in this assay.

Abstract 3108: Exploring base excision repair variants as potential defining events in cancer patient populations and characterization of models for pre-clinical studies

Abstract Background Deficiencies in base excision repair (BER) may increase the cell's dependence on alternative repair pathways and so define a patient population for novel inhibitors of DNA damage repair. Notably, cancer associated molecular events in DNA polymerase beta (POLα) have been described in various disease backgrounds including colorectal cancer (CRC), gastric, breast and prostate (1-5). Although functional consequence has been linked to certain POLα mutations and splice variants, their prevalence in defined disease segments remains largely undefined. Aim We set out to ascertain the prevalence of POLα deficiencies in CRC, and subsequently investigated protein and gene expression profiling as alternative methods for defining BER defects in cancer. Methods/Results A comprehensive study of clinical (CRC; N=64), tumour explant (CRC; N=36) and cell line (mixed origin; N=280) samples revealed that cancer-associated mutations in the polymerase encoding domain of POLα (1-3) are not common events in CRC. Additionally, a previously described splice variant of POLα lacking part of the polymerase domain (3-4), was assayed and found to be expressed at similar levels in CRC and normal tissue. This would suggest that expression of the POLα splice variant is not a defining element of CRC in western populations. Expression profiling using Fluidigm Taqman revealed a subset of BER genes more highly expressed in CRC clinical samples and mixed cell lines compared with normal tissue. While protein expression profiles did not reflect relative gene expression in selected cell line models, we observed an additional low molecular weight band in a subset of cells profiled for POLB expression. Furthermore, we report variations in the expression of the scaffold protein XRCC1 in colorectal and breast cell lines and propose that this could also provide a mechanism for variation in DNA repair capacity. Summary Although from our studies sequencing and transcript analysis of POLα do not provide suitable markers of BER deficiency in CRC, we report aberrant banding patterns in POLα by Western blotting and variation in XRCC1 protein expression in a subset of cell lines analyzed. We hypothesize that these variants may confer a BER deficient phenotype. 1. Lang, T. et al. (2004Proc. Natl Acad. Sci. USA, 101, 6074-6079. 2. Tan, Xiao-Hui, et al Cancer Letters: 2005: 220: 101-114 3. Wang, L et al Cancer Research, 1992; 52:4824-4827 4. Bhattacharyya, N. et al. (1997) Proc. Natl Acad. Sci. USA, 94, 10324-10329 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3108. doi:1538-7445.AM2012-3108