The Expression Of DNA Repair Genes XRCC1and XRCC3in The Colorectal Cancer AND Prediction Of Genetic Polymorphisms In The Survival Of Advanced Colorectal Cancer Receiving Chemotherapy In The Chinese Population

Background:The incidence of colorectal cancer ranked third in the world’s most common cancer. Compare with developed countries, the incidence of colorectal cancer in China is lower. However, in recent years the morbidity and mortality of colorectal cancer continued to rise with the improvement of people’s living standards, the changes of eating habits and dietary structure and an ageing population. The treatment principle of colorectal cancer is operation with comprehensive therapy, that is on the basis of operation combined with chemotherapy, radiation therapy, and targeted therapy. Because of its insidious onset, often without obvious clinical manifestations and with a slow disease progression, the diagnosis of this disease was usually delayed rendering treatment difficult. Therefore, early diagnosis, early treatment is critical. To investigate the occurrence and development process of colorectal cancer so as to provide a guide for early diagnosis is of importance.The external environment factors and internal factors play a role in tumorigenesis by influencing gene vector DNA. When the body cannot be effectively repair DNA damage, and the damage accumulation to a certain extent cause increased genomic instability, which can cause uncontrolled cell proliferation and differentiation, leading to tumorigenesis. DNA is an important genetic material which play an important role in human life, it stores genetic information of organism’s survival and reproduction. DNA damage occurs spontaneously in some, it must also bear in vivo environment from the physical, chemical, biological and other factors. Therefore, DNA repair failure is an important cause of tumorigenesis. DNA repair system is a large and complex system, and is closely related to all aspects of life activities, however people know little about it. DNA repair mode is divided into mismatch repair (MMR), base excision repair (BER), nucleotide excision repair (NER), homologous recombination (HR) and non-homologous end joining (NHEJ), etc. DNA repair capacity is closely related with tumor susceptibility and tumor chemotherapy sensitivity, it’s also a double-edged sword:the stronger DNA repair capacity always with a low tumor susceptibility, while it also has a resistance to chemotherapy.Platinum (cisplatin or oxaliplatin) in combination with5-fluorourac il (5-Fluorouracil,5-Fu) is currently the first-line treatment of colorectal cancer. Platinum can partial kink or unwinding the strands of DNA, and can prevent DNA polymerase advancing, result in DNA replication, transcription failure, eventually leading to death of tumor cells to achieve the anti-tumor effect. However, it is found in the clinical that the results of the same chemotherapy regimen are very different in sensitivity and side effect among the different colorectal cancer patients, due to the genetic differences about the DNA repair capacity after injury between individuals. Single nucleotide polymorphism (SNP) of DNA repair gene is related with the cell’s DNA repair and cell cycle regulation, it can affects the repair efficiency and increase the risk of suffering from cancer, it also can significantly affect the treatment effect of tumor patients.Human X-ray repair cross-complementing gene1(XRCC1) was the first separated mammalian gene that can influence cell sensitivity to ionizing radiation, it is widely involved in single-strand break repair and base excision repair of DNA damage caused by ionizing radiation and chemical mutagens. XRCC1is a protein directly related to base excision repair and single-strand break repair, and participate in platinum drugs induced DNA repair process, it plays an important role in all kinds of anti-DNA blocking drugs. The coding regions of XRCC1gene have a plurality of SNP which lead amino acid changes, these SNP affect the activity of XRCC1protein. G�'A variation of XRCC1gene Arg399Gln loci result in amino acids Arg�'Gln change encoded by codon399, which may reduce the DNA repair capacity of XRCC1.X-ray repair cross-complementing gene3(XRCC3) is a member of yeast and mammalian cells Rad51family, it can repair DNA double-strand breaks and crosslinking damage caused by oxidative damage, it also plays an important role in double strand break (DSB) repair pathway of homologous recombination (HR). Rad51is a protein in eukaryotes, it plays a key role in the process of DNA damage repair by guiding recombination and interaction. C�'T mutation of XRCC3gene Thr241Met loci result in amino acids Thr�'Met change encoded by codon241. The amino acid base substitution of this gene may participate in the removal of phosphorylation sites, which affects the repair function.Researches about gene expression and polymorphisms of XRCC1and XRCC3genes were extensive, and to some extent, the correlation with survival time of different types of tumors were confirmed, however, little research was about the relationship between the gene expression and polymorphisms of these two genes and the survival period of patients undergoing chemotherapy in colorectal cancer, and the results were divided, so the final conclusion is not clear. Accordingly, we conducted this retrospective analysis, we detected the expression and polymorphism of XRCC1, XRCC3in primary colorectal cancer patients respectively, we also detected the expression of antigen Ki-67in tumor which closely related to tumor cell proliferation so as to explore the effect of base excision repair and homologous recombination repair in colorectal cancer, as well as the relationship between them and Ki-67, we also try to explore the relationship between the SNP of XRCC1, XRCC3and the platinum-based chemotherapy efficacy. We hope this research can provide a theoretical basis for efficacy improvement of individualized medication in colorectal cancer patients. Part Ⅰ The expression of XRCC1/XRCC3and Ki-67protein in human colorectal carcinoma and some of clinical factors of colorectal carcinomaObjective:To investigate the expression of XRCC1, XRCC3and Ki-67in colorectal cancer and in normal intestinal mucosa tissue, in order to investigate their roles in colorectal cancer and the relationship between each other.Methods:The expression of XRCC1, XRCC3and Ki-67in432colorectal cancer cases and matching normal intestinal mucosa tissues was assayed by immunohistochemical staining. We analyzed their roles in the development of colorectal cancer and we also investigated the relationship among the clinical pathological parameters in colorectal cancer patients.Result:The expression of XRCC1, XRCC3and Ki-67in colorectal cancer tissues was significantly higher than that of normal intestinal mucosa tissue, and the difference was statistically significant (P<0.05). The expression of XRCC3in colorectal cancer tissues was positively associated with the expression of Ki-67protein (P<0.05). The expression of XRCC1, XRCC3and Ki-67in colorectal cancers had no significant correlation with the patients’ age, gender, as well as histological grade, clinical stage (P>0.05).Conclusion:(1) The expression of XRCC1protein in colorectal cancers is increased.(2) The expression of XRCC3protein in colorectal cancers is increased.(3) The expression of Ki-67protein in colorectal cancers is increased significantly.(4) The expression of XRCC1protein in colorectal cancers has no significant correlation with the expression of XRCC3protein, it is indicated the independence of their repair function.(5) The expression of Ki-67protein in colorectal cancer tissues is positively associated with the expression of XRCC3protein, which indicate XRCC3protein may have synergism with Ki-67protein in the occurrence and development of the colorectal cancer.(6) The expression of XRCC1, XRCC3and Ki-67in colorectal cancers have no significant correlation with the patients’ age, gender, as well as histological grade, clinical stage. Part Ⅱ Genetic polymorphisms of DNA repair genes XRCC1and XRCC3are Correlated with the survival of colorectal cancer patients treated with oxaliplatin-based chemotherapyObjective:To investigate the relationship between the genetic polymorphisms of XRCC1Arg399Gln and XRCC3Thr241Met and the survival time of colorectal cancer patients treated with oxaliplatin-based chemotherapy.Methods:The prospective study was conducted with394cases treated with oxaliplatin-based chemotherapy. All the patients were followed-up from May2007to May2012, XRCC1and XRCC3Genotype polymorphisms was based upon PCR-RFLP method.Results:(1) In the394cases of colorectal cancer patients, the cases of carrying Arg/Arg, Arg/Gln, Gln/Gln genotype in XRCC1Arg399Gln loci were184cases (46.7%),155cases (39.3%)、55cases (14.0%) Effective rate of chemotherapy in colorectal cancer patients carrying XRCC1399Arg/Arg genotype was significantly higher than other genotype carriers (P<0.05).(2) In the394cases of colorectal cancer patients, the cases of carrying Thr/Thr, Thr/Met, Met/Met genotype in XRCC3Thr241Met loci were299cases (75.9%)、68cases (17.3%)、27cases (6.9%). These three genotypes in colorectal cancer patients with chemotherapy response rates were32.4%、30.9%、22.2%, no significant difference between the three (P>0.05).(3) Using the combined low-risk genotypes (XRCC1399Arg/Arg and XRCC3241Thr/Thr) as the referent group, the combination of XRCC1399Gln allele and XRCC3241Met allele showed a significantly lose association with five years survival rate of colorectal cancer(OR=5.24,95%CI=2.65-10.36).(4) XRCC1Gln/Gln, XRCC3Thr/Met and Met/Met genotype and of colorectal cancer survival rates are negatively correlated.(5) The gene polymorphism of XRCC1Arg399Gln and XRCC3Thr241Met had no significant correlation with colorectal cancer patients’ gender, age, tumor location, tumor size, mesenteric lymph node metastasis and TNM stages state (P>0.05). Conclusion:(1) The result shows XRCC1399Arg/Arg genotype may be associated with receiving oxaliplatin-base chemotherapy in patients with colorectal cancer survival recent positive correlation.(2) The result shows XRCC1399Gln/Gln genotype may be associated with receiving oxaliplatin-base chemotherapy in patients with colorectal cancer survival recent negative correlation.(3) The combination of XRCC1399Gln allele and XRCC3241Met allele showed a significantly strong association with death risk of colorectal cancer, the multiple effect of DNA repair gene polymorphisms may have interaction on the prognosis of colorectal cancer.(4) Indicates XRCC3241polymorphisms with oxaliplatin chemotherapy irrelevant.(5) The gene polymorphism of XRCC1Arg399Gln and XRCC3Thr241Met have no significant correlation with colorectal cancer patients’ gender, age, tumor location, tumor size, mesenteric lymph node metastasis and TNM stages state.