Single nucleotide polymorphisms of RecQ1, RAD54L, and ATM genes are associated with reduced survival of pancreatic cancer

Clinical relevance of the homologous recombination machinery in cancer therapy

Cancer chemotherapy and radiotherapy kill cancer cells by inducing DNA damage, unless the lesions are repaired by intrinsic repair pathways. DNA double-strand breaks (DSB) are the most deleterious type of damage caused by cancer therapy. Homologous recombination (HR) is one of the major repair pathways for DSB and is thus a potential target of cancer therapy. Cells with a defect in HR have been shown to be sensitive to a variety of DNA-damaging agents, particularly interstrand crosslink (ICL)-inducing agents such as mitomycin C and cisplatin. These findings have recently been applied to clinical studies of cancer therapy. ERCC1, a structure-specific endonuclease involved in nucleotide excision repair (NER) and HR, confers resistance to cisplatin. Patients with ERCC1-negative non-small-cell lung cancer were shown to benefit from adjuvant cisplatin-based chemotherapy. Imatinib, an inhibitor of the c-Abl kinase, has been investigated as a sensitizer in DNA-damaging therapy, because c-Abl activates Rad51, which plays a key role in HR. Furthermore, proteins involved in HR have been shown to repair DNA damage induced by a variety of other chemotherapeutic agents, including camptothecin and gemcitabine. These findings highlight the importance of HR machinery in cancer therapy.

Unique and important consequences of RECQ1 deficiency in mammalian cells

Five members of the RecQ subfamily of DEx-H-containing DNA helicases have been identified in both human and mouse, and mutations in BLM, WRN, and RECQ4 are associated with human diseases of premature aging, cancer, and chromosomal instability. Although a genetic disease has not been linked to RECQ1 mutations, RECQ1 helicase is the most highly expressed of the human RecQ helicases, suggesting an important role in cellular DNA metabolism. Recent advances have elucidated a unique role of RECQ1 to suppress genomic instability. Embryonic fibroblasts from RECQ1-deficient mice displayed aneuploidy, chromosomal instability, and increased load of DNA damage.(1) Acute depletion of human RECQ1 renders cells sensitive to DNA damage and results in spontaneous gamma-H2AX foci and elevated sister chromatid exchanges, indicating aberrant repair of DNA breaks.(2) Consistent with a role in DNA repair, RECQ1 relocalizes to irradiation-induced nuclear foci and associates with chromatin.(2) RECQ1 catalytic activities(3) and interactions with DNA repair proteins(2,4,5) are likely to be important for its molecular functions in genome homeostasis. Collectively, these studies provide the first evidence for an important role of RECQ1 to confer chromosomal stability that is unique from that of other RecQ helicases and suggest its potential involvement in tumorigenesis.

Genetic susceptibility in pancreatic ductal adenocarcinoma

BACKGROUND

The strongest risk factors for pancreatic adenocarcinoma are tobacco smoking and increasing age. However, only a few smokers or elderly individuals develop the disease and genetic factors are also likely to be important.

METHODS

The literature on genetic factors modifying susceptibility to cancer was reviewed, with particular regard to the interindividual variation that exists in the development of pancreatic adenocarcinoma.

RESULTS

Tobacco-derived carcinogen-metabolizing enzyme gene variants have been the main area of study in stratifying the risk of sporadic pancreatic cancer. Inconsistent results have emerged from the few molecular epidemiological studies performed.

CONCLUSION

There is great scope for further investigation of critical pathways and unidentified genetic influences may be revealed. This may eventually allow the identification of individuals at high risk who might be targeted for screening.

Human RECQ1 is a DNA damage responsive protein required for genotoxic stress resistance and suppression of sister chromatid exchanges

BACKGROUND

DNA helicases are ubiquitous enzymes that unwind DNA in an ATP-dependent and directionally specific manner. Unwinding of double-stranded DNA is essential for the processes of DNA repair, recombination, transcription, and DNA replication. Five human DNA helicases sharing sequence similarity with the E. coli RecQ helicase have been identified. Three of the human RecQ helicases are implicated in hereditary diseases (Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome) which display clinical symptoms of premature aging and cancer. RECQ1 helicase is the most highly expressed of the human RecQ helicases; however, a genetic disease has yet not been linked to mutations in the RECQ1 gene, and the biological functions of human RECQ1 in cellular DNA metabolism are not known.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we report that RECQ1 becomes phosphorylated upon DNA damage and forms irradiation-induced nuclear foci that associate with chromatin in human cells. Depletion of RECQ1 renders human cells sensitive to DNA damage induced by ionizing radiation or the topoisomerase inhibitor camptothecin, and results in spontaneous gamma-H2AX foci and elevated sister chromatid exchanges, indicating aberrant repair of DNA breaks. Consistent with a role in homologous recombinational repair, endogenous RECQ1 is associated with the strand exchange protein Rad51 and the two proteins directly interact with high affinity.

CONCLUSION/SIGNIFICANCE

Collectively, these results provide the first evidence for a role of human RECQ1 in the response to DNA damage and chromosomal stability maintenance and point to the vital importance of RECQ1 in genome homeostasis.

Human premature aging, DNA repair and RecQ helicases

Genomic instability leads to mutations, cellular dysfunction and aberrant phenotypes at the tissue and organism levels. A number of mechanisms have evolved to cope with endogenous or exogenous stress to prevent chromosomal instability and maintain cellular homeostasis. DNA helicases play important roles in the DNA damage response. The RecQ family of DNA helicases is of particular interest since several human RecQ helicases are defective in diseases associated with premature aging and cancer. In this review, we will provide an update on our understanding of the specific roles of human RecQ helicases in the maintenance of genomic stability through their catalytic activities and protein interactions in various pathways of cellular nucleic acid metabolism with an emphasis on DNA replication and repair. We will also discuss the clinical features of the premature aging disorders associated with RecQ helicase deficiencies and how they relate to the molecular defects.

Polymorphism of the DNA repair enzyme XRCC1 is associated with treatment prediction in anthracycline and cyclophosphamide/methotrexate/5-fluorouracil-based chemotherapy of patients with primary invasive breast cancer

OBJECTIVES

Outcome and survival in anthracycline-based and cyclophosphamide/methotrexate/5-fluorouracil-based chemotherapy of invasive breast cancer are unpredictable. Insights into treatment prediction are expected from studies searching for an association between genetic polymorphisms and treatment outcome effects. A common feature of treatment with chemoreagents is therapeutically induced DNA damage. Therefore, we tested the hypothesis of a relationship between event-free survival and genotype distributions of seven polymorphic DNA repair enzymes and four cell cycle regulators.

BASIC METHODS

This case-case comparison included 180 patients with primary invasive breast cancer diagnosed between 1986 and 2000 and subjected to adjuvant chemotherapy (anthracycline/cyclophosphamide or cyclophosphamide/methotrexate/5-fluorouracil). Ninety-two patients were reported without recurrence and 88 were reported with recurrences or dead. Median clinical follow-up was 61.7 months. Constitutional DNA isolated from archived tissues was genotyped at 19 loci by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Statistical analyses included adjusted risk estimates, Kaplan-Meier analyses, Cox proportional hazard model, and permutation testing.

MAIN RESULTS

Carriers of the XRCC1_1196_AA genotype had a reduced risk for recurrence/death (odds ratio adjusted 0.19; 95% confidence interval: 0.06-0.61), which was observed in survival analyses of all patients (P=0.003) and patients treated with chemotherapy but not radiotherapy (P=0.006). Multivariate analysis confirmed XRCC1 as a potential treatment predictor (hazard ratio 0.62; 95% confidence interval: 0.43-0.89). The result was stable upon permutation testing. No other significant associations were observed.

CONCLUSION

The DNA repair enzyme XRCC1 is a potential treatment predictor for the outcome and survival of anthracycline and cyclophosphamide/methotrexate/5-fluorouracil-based chemotherapy of invasive breast cancer.

Pharmacogenomics of gemcitabine: can genetic studies lead to tailor-made therapy?

Gemcitabine is a deoxycytidine analogue that has a broad spectrum of antitumour activity in many solid tumours including pancreatic cancer. We have recently carried out a pharmacogenomic study in cancer patients treated with gemcitabine, and found that one genetic polymorphism of an enzyme involved in gemcitabine metabolism can cause interindividual variations in the pharmacokinetics and toxicity of this agent. In this paper, we review recent genetic studies of gemcitabine, and discuss the possibility of individualised cancer chemotherapy based on a pharmacogenomic approach.

Glutathione S-transferase gene polymorphisms and risk and survival of pancreatic cancer

BACKGROUND

Pancreatic cancer is a multifactorial disease with metastasis-prone and therapy-resistant nature. The authors hypothesized that genetic variants of glutathione S-transferase (GST) affect detoxification of carcinogens and anticancer agents in the human pancreas and, thus, the risk and survival of pancreatic cancer.

METHODS

Genotypes of GSTM1, GSTT1, and GSTP1 were determined in 352 patients with pancreatic ductal adenocarcinoma and in a control group of 315 healthy, non-Hispanic whites (frequency-matched by age and sex). Survival analysis was performed in a subset of 290 patients. Epidemiological and clinical information was obtained. A multiple unconditional logistic regression model, a Cox proportional hazards model, and log-rank tests were used for statistical analysis.

RESULTS

No significant main effects of any of 3 GST genes on the risk of pancreatic cancer were observed. Subgroup analysis showed that older individuals (aged >or=62 years) who carried the GSTP1*C ((105)Val-(114)Val) containing genotype tended to have a reduced risk compared with younger individuals who carried the non-*C genotype (for sex and pack-years of smoking, the adjusted odd ratio was 0.54; 95% confidence interval [95% CI], 0.29-1.02). In a survival analysis of 138 patients who received 5-flurorouracil, patients who carried the GSTP1*C containing genotype had a significantly longer survival than patients who carried the non-*C genotype (multivariate hazard ratio, 0.45; 95% CI, 0.22-0.94).

CONCLUSIONS

The GSTP1*C variant conferred a possible protective effect against pancreatic cancer in older individuals and a significant survival advantage in patients who received 5-florouracil. The current findings must be confirmed before further inferences can be made.

Gene Expression and Polymorphisms of DNA Repair Enzymes: Cancer Susceptibility and Response to Chemotherapy

Platinum compounds play a central role in cancer chemotherapy. Although treatment is limited by side effects, they continue to have widespread application. One of the main aims of clinical or translational research in cancer is the search for genetic factors that could foresee treatment outcomes, in biologic activity and toxic effects. This genetic analysis might allow selection of patients who will have the greatest benefit from chemotherapy. Furthermore, a better knowledge of the underlying molecular profile of the host and the tumor will facilitate screening for lung cancer susceptibility and tailoring of chemotherapy in individual patients, choosing those most likely to respond, adjusting doses more precisely in order to reduce less adverse effects, and establishing safety profiles based on individual genetic analyses. Herein, we discuss current knowledge regarding gene expression and polymorphisms of DNA repair enzymes in regard to cancer susceptibility and response to chemotherapy.

Effects of base excision repair gene polymorphisms on pancreatic cancer survival

To explore the association between single nucleotide polymorphisms of DNA repair genes and overall survival of patients with pancreatic cancer, we conducted a study in 378 cases of pancreatic adenocarcinoma who were treated at The University of Texas M. D. Anderson Cancer Center between February 1999 and October 2004 and were followed up to April 2006. Genotypes were determined using genomic DNA and the MassCode method. Overall survival was analyzed using the Kaplan-Meier plot, log-rank test and Cox regression. We observed a strong effect of the POLB A165G and T2133C genotypes on overall survival. The median survival time (MST) was 35.7 months for patients carrying at least 1 of the 2 homozygous variant POLB GG or CC genotypes, compared with 14.8 months for those carrying the AA/AG or TT/TC genotypes (p = 0.02, log rank test). The homozygous variants of hOGG1 G2657A, APEX1 D148E and XRCC1 R194W polymorphisms all showed a weak but significant effect on overall survival as demonstrated by either log rank test or multivariate COX regression after adjusting for other potential confounders. In combined genotype analysis, a predominant effect of the POLB homozygous variants on survival was observed. When POLB was not included in the model, a slightly better survival was observed among those carrying none of the adverse genotypes than those carrying at least one of the adverse genotypes. These observations suggest that polymorphisms of base excision repair genes significantly affect the clinical outcome of patients with pancreatic cancer. These observations need to be confirmed in a larger study of homogenous patient population.

Vascular endothelial growth factor gene polymorphisms associated with prognosis for patients with gastric cancer

BACKGROUND

The present study analyzed vascular endothelial growth factor (VEGF) gene polymorphisms and their impact on the prognosis for patients with gastric cancer.

PATIENTS AND METHODS

Five hundred and three consecutive patients with surgically resected gastric adenocarcinoma were enrolled in the present study. The genomic DNA was extracted from paraffin-embedded tissue and four VEGF (-460T > C, -116G > A, +405G > C, and +936C > T) gene polymorphisms were determined using a polymerase chain reaction-restriction fragment length polymorphism assay.

RESULTS

The survival analysis showed no association of three VEGF gene polymorphisms with the prognosis. For the +936C > T polymorphism, the T/T genotype, however, had a worse overall survival (OS) compared with the C/C genotype (P = 0.037). The -460 T/C or C/C genotype was a poor prognostic factor in patients with stage 0 or I gastric cancer (OS: hazard ratio (HR) = 3.96, disease-free survival (DFS): HR = 4.87). In the haplotype analysis, the CACC haplotype was associated with a significantly worse survival when compared with the TGGC haplotype (OS: HR = 1.72, DFS: HR = 1.73).

CONCLUSIONS

VEGF gene polymorphisms were found to be an independent prognostic marker for patients with gastric cancer. Consequently, the analysis of VEGF gene polymorphisms can help identify patient subgroups at high risk of a poor disease outcome.

The genomics revolution and radiotherapy

The expansion of our knowledge through the Human Genome Project has been accompanied by the development of new high-throughput techniques, which provide extensive capabilities for the analysis of a large number of genes or the whole genome. These assays can be carried out in various clinical samples at the DNA (genome), RNA (transcriptome) or protein (proteome) level. There is a belief that this genomic revolution, i.e. sequencing of the human genome and developments in high-throughput technology, heralds a future of personalised medicine. For clinical oncology, this progress should increase the possibility of predicting individual patient responses to radiotherapy. This review highlights some of the work involving sparsely ionising radiation and the new technologies.

RECQL, a member of the RecQ family of DNA helicases, suppresses chromosomal instability

The mouse gene Recql is a member of the RecQ subfamily of DEx-H-containing DNA helicases. Five members of this family have been identified in both humans and mice, and mutations in three of these, BLM, WRN, and RECQL4, are associated with human diseases and a cellular phenotype that includes genomic instability. To date, no human disease has been associated with mutations in RECQL and no cellular phenotype has been associated with its deficiency. To gain insight into the physiological function of RECQL, we disrupted Recql in mice. RECQL-deficient mice did not exhibit any apparent phenotypic differences compared to wild-type mice. Cytogenetic analyses of embryonic fibroblasts from the RECQL-deficient mice revealed aneuploidy, spontaneous chromosomal breakage, and frequent translocation events. In addition, the RECQL-deficient cells were hypersensitive to ionizing radiation, exhibited an increased load of DNA damage, and displayed elevated spontaneous sister chromatid exchanges. These results provide evidence that RECQL has a unique cellular role in the DNA repair processes required for genomic integrity. Genetic background, functional redundancy, and perhaps other factors may protect the unstressed mouse from the types of abnormalities that might be expected from the severe chromosomal aberrations detected at the cellular level.

Mechanisms of RecQ helicases in pathways of DNA metabolism and maintenance of genomic stability

Helicases are molecular motor proteins that couple the hydrolysis of NTP to nucleic acid unwinding. The growing number of DNA helicases implicated in human disease suggests that their vital specialized roles in cellular pathways are important for the maintenance of genome stability. In particular, mutations in genes of the RecQ family of DNA helicases result in chromosomal instability diseases of premature aging and/or cancer predisposition. We will discuss the mechanisms of RecQ helicases in pathways of DNA metabolism. A review of RecQ helicases from bacteria to human reveals their importance in genomic stability by their participation with other proteins to resolve DNA replication and recombination intermediates. In the light of their known catalytic activities and protein interactions, proposed models for RecQ function will be summarized with an emphasis on how this distinct class of enzymes functions in chromosomal stability maintenance and prevention of human disease and cancer.

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