Enhanced nucleotide excision repair in cisplatin resistant human KB carcinoma cells

We previously reported that enhanced active efflux of cisplatin and increased GSH level were observed in KCP-4 cells. In the present study, KCP-4 cells were found to be cross-resistant to ultraviolet (UV) compared with parental KB-3-1 cells. Enhanced nucleotide excision repair (NER) was verified by time-dependent repair of UV-induced DNA damage. In addition, the amount of platinum bound to DNA after exposure to cisplatin decreased in a time-dependent manner in KCP-4 cells and this was reversed by aphidicolin, a DNA polymerase inhibitor. In stationary phase cultures, aphidicolin increased the sensitivity of KCP-4 cells to cisplatin. The expression of xeroderma pigmentosum complementation group F (XPF), an endonuclease involved in NER, was upregulated in KCP-4 cells. In KCP-4 cells the expression of hMSH6, one of the mismatch repair (MMR) factors, was decreased compared to parental KB-3-1 and revertant KCP-4R cells. However, KCP-4 cells were cross-resistant to oxaliplatin, and microsatellite instability was not observed in them. These findings suggest that the enhanced NER activity for DNA damage caused by cisplatin may be involved in cisplatin resistance in KCP-4 cells.     

核苷酸切除修复交叉互补基因1与卵巢癌顺铂耐药的关系

目的 探讨核苷酸切除修复交叉互补基因1(ERCC1)与卵巢癌顺铂(DDP)耐药的关系.方法 分别应用免疫组化、逆转录聚合酶链反应(RT-PCR)和Western blot检测58例卵巢癌组织和ES-2、SKOV3、COC1、COC1/DDP 4株卵巢癌细胞系中ERCC1基因的表达,分析该基因与DDP化疗耐药的关系,并观察应用RNA干扰技术干扰了ERCC1基因后卵巢癌细胞对DDP敏感性的变化.结果 58例卵巢癌组织中,ERCC1表达阳性者22例,阳性率为37.9%.ERCC1的表达与DDP化疗敏感性有关(P＜0.05),DDP耐药者ERCC1表达的阳性率(57.89%)显著高于敏感者(28.21%,P=0.029).ES-2、SKOV3、COC1、COC1/DDP 4株卵巢癌细胞ERCC1基因的表达与DDP IC50正相关(r=0.932,P＜0.05).RNA干扰ERCC1基因后,ES-2、SKOV3、COC1/DDP细胞对DDP的敏感性分别增加了53.88、5.07、3.75倍.结论 ERCC1基因与卵巢癌DDP耐药有关,RNA干扰ERCC1基因可增强卵巢癌细胞对DDP的敏感性.     

Enhanced cisplatin cytotoxicity by disturbing the nucleotide excision repair pathway in ovarian cancer cell lines

Ovarian cancer is the leading cause of death among women from gynecological malignancies inthe United States. Resistance to the chemotherapeutic agent cisplatin isa major limitation for the successful treatment of ovarian cancer. In an effort to overcome the cisplatin resistance problem in ovarian cancer treatment, we have sought to enhance cisplatin cytotoxicity by perturbing the nucleotide excision repair (NER) pathway. The NER pathway is responsible for repairing cisplatin bound to DNA. Expression of one of the NER components, ERCC1, is correlated with cisplatin drug resistance. Hence, we targeted ERCC1 by antisense RNA methodologies, and we show that we could sensitize a relatively sensitive A2780 cell line and also the highly resistant OVCAR10 cell line to cisplatin by expressing antisense ERCC1 RNA in them as measured with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. The A2780 cell lines expressing antisense ERCC1 had 1.9-8.1-fold enhancements in cisplatin sensitivity. The OVCAR10 antisense ERCC1 cell lines had IC(50) values ranging from 2.28 microM to 2.7 microM cisplatin as compared with 9.52 micro M for control OVCAR10 cells. The OVCAR10 antisense ERCC1 cells also show reduced DNA-damage repair capacity as assessed by host cell reactivation. Furthermore, immunocompromised mice transplanted with the antisense cell lines survived longer than the mice bearing control cells after response to cisplatin treatment. These data suggest that it is possible to substantially enhance the cisplatin cytotoxicity by disturbing the NER pathway in cisplatin-resistant cell lines and to enhance the survival capacity of mice in an ovarian cancer xenograft model.     

Sublethal concentrations of 17-AAG suppress homologous recombination DNA repair and enhance sensitivity to carboplatin and olaparib in HR proficient ovarian cancer cells

The promise of PARP-inhibitors(PARPis) in the management of epithelial ovarian cancer(EOC) is tempered by the fact that approximately 50% of patients with homologous recombination (HR)-proficient tumors do not respond well to these agents. Combination of PARPis with agents that inhibit HR may represent an effective strategy to enhance their activity in HR-proficient tumors. Using a bioinformatics approach, we identified that heat shock protein 90 inhibitors(HSP90i) may suppress HR and thus revert HR-proficient to HR-deficient tumors. Analysis of publicly available gene expression data showed that exposure of HR-proficient breast cancer cell lines to HSP90i 17-AAG(17-allylamino-17-demethoxygeldanamycin) downregulated HR, ATM and Fanconi Anemia pathways. In HR-proficient EOC cells, 17-AAG suppressed HR as assessed using the RAD51 foci formation assay and this was further confirmed using the Direct Repeat-GFP reporter assay. Furthermore, 17-AAG downregulated BRCA1 and/or RAD51 protein levels, and induced significantly more γH2AX activation in combination with olaparib compared to olaparib alone. Finally, sublethal concentrations of 17-AAG sensitized HR-proficient EOC lines to olaparib and carboplatin but did not affect sensitivity of the HR-deficient OVCAR8 line arguing that the 17-AAG mediated sensitization is dependent on suppression of HR. These results provide a preclinical rationale for using a combination of olaparib/17-AAG in HR-proficient EOC.     

Evidence for in the appearance of mRNAs of nucleotide excision repair genes, in human ovarian cancer tissues

Nucleotide excision repair (NER) is the DNA repair pathway through which cisplatin-DNA intrastrand adduct is repaired. Clinical studies have shown that increased mRNA expression of selected genes involved in the rate-limiting step of NER, appear to be closely associated with clinical resistance to platinum agents. These specific studies have led to the possibility of an assessment of the order in which, the appearance of mRNAs of selected NER genes may occur. Included in this assessment are ERCC1, XPB, CSB, and XPA, studied in 28 ovarian cancer tumor tissue specimens. The study of these four genes, in pairs, from 28 ovarian cancer specimens, results in 168 separate observations. Based on the mRNA expression patterns of these genes in these tissues, it is suggested that ERCC1 mRNA may appear before the mRNA of any of the other genes, in an obligate fashion. This is followed by XPB mRNA; which appears before the mRNA of XPA; which in turn, may appear before CSB. This pattern is consistent with what we have reported previously, in non-malignant human bone marrow specimens from a cohort of 52 patients.     

Cross-talk between nucleotide excision and homologous recombination DNA repair pathways in the mechanism of action of antitumor trabectedin

Trabectedin (Yondelis) is a potent antitumor drug that has the unique characteristic of killing cells by poisoning the DNA nucleotide excision repair (NER) machinery. The basis for the NER-dependent toxicity has not yet been elucidated but it has been proposed as the major determinant for the drug's cytotoxicity. To study the in vivo mode of action of trabectedin and to explore the role of NER in its cytotoxicity, we used the fission yeast Schizosaccharomyces pombe as a model system. Treatment of S. pombe wild-type cells with trabectedin led to cell cycle delay and activation of the DNA damage checkpoint, indicating that the drug causes DNA damage in vivo. DNA damage induced by the drug is mostly caused by the NER protein, Rad13 (the fission yeast orthologue to human XPG), and is mainly repaired by homologous recombination. By constructing different rad13 mutants, we show that the DNA damage induced by trabectedin depends on a 46-amino acid region of Rad13 that is homologous to a DNA-binding region of human nuclease FEN-1. More specifically, an arginine residue in Rad13 (Arg961), conserved in FEN1 (Arg314), was found to be crucial for the drug's cytotoxicity. These results lead us to propose a model for the action of trabectedin in eukaryotic cells in which the formation of a Rad13/DNA-trabectedin ternary complex, stabilized by Arg961, results in cell death.     

Rad51在同源重组中作用及其与肿瘤关系的研究进展

目的：总结国内外关于同源重组因子Rad51在人类肿瘤发生、发展中的作用,以及其在肿瘤治疗中应用的研究现状。方法：应用Medline及CNKI期刊全文数据库检索系统,以＂同源重组、Rad51和肿瘤＂为关键词,检索1993-01-2009-05的相关文献,共检索到英文文献374篇和中文文献14篇。纳入标准：1）同源重组在DNA修复中的作用;2）Rad51及其相关蛋白在同源重组中的作用和机制;3）Rad51蛋白的表达调控,4）Rad51在人类肿瘤发生、发展中的作用和机制以及以Rad51为靶点的治疗策略。根据纳入标准,精选86篇文献,最后32篇文献纳入分析。结果：Rad51蛋白是参与DNA同源重组性修复的关键因子,Rad51蛋白的高水平表达会导致体内DNA同源重组性修复能力的增强,而同源重组机制的功能失调常会导致基因组不稳定和肿瘤的发生。还有许多研究发现,Rad51蛋白表达升高所导致DNA修复能力的增强会导致肿瘤细胞对放疗、化疗和靶向治疗等多种治疗产生耐受。体外研究表明,下调Rad51蛋白表达水平可有效逆转肿瘤耐药和对放疗产生耐受。结论：Rad51是体内参与同源重组性DNA修复的关键因子,Rad51的功能失调与肿瘤的发生、发展以及治疗耐受密切相关,Rad51将会是未来肿瘤临床治疗中重要的潜在靶点。     

Impaired homologous recombination DNA repair and enhanced sensitivity to DNA damage in prostate cancer cells exposed to anchorage-independence

During metastases, cancer cells are temporarily exposed to the condition in which interactions with extracellular environment can be restricted (anchorage-independence). We demonstrate that the sensitivity of prostate cancer cell lines, DU145 and PC-3, to genotoxic treatment (cisplatin and gamma-irradiation) increased several folds when cells were forced to grow in anchorage-independence. This enhanced drug sensitivity was associated with a severe impairment of homologous recombination-directed DNA repair (HRR). The mechanism involves Rad51, which is the major enzymatic component of HRR. The protein level of Rad51 and its recruitment to DNA double-strand breaks (DSBs) were both attenuated. Rad51 deficiency in anchorage-independence was not associated with Rad51 promoter activity, and was not compensated by a constitutive overexpression of Rad51 cDNA. Instead, Rad51 protein level and its ability to colocalize with DSBs were restored in the presence of proteosome inhibitors, or when cells from the suspension cultures were allowed reattachment. Presented results indicate that anchorage-independence sensitizes prostate cancer cells to genotoxic agents; however, it also attenuates faithful component of DNA repair by targeting stability of Rad51. This temporal attenuation of HRR may contribute to the accumulation mutations after DNA damage, and possibly the selection of new adaptations in cells, which survived genotoxic treatment.     

Rad5 1在同源重组中作用及其与肿瘤关系的研究进展

目的:总结国内外关于同源重组因子Rad51在人类肿瘤发生、发展中的作用,以及其在肿瘤治疗中应用的研究现状。方法:应用Medline及CNKI期刊全文数据库检索系统,以同源重组、Rad51和肿瘤为关键词,检索1993-01-2009-05的相关文献,共检索到英文文献374篇和中文文献14篇。纳入标准:1)同源重组在DNA修复中的作用;2)Rad51及其相关蛋白在同源重组中的作用和机制;3)Rad51蛋白的表达调控,4)Rad51在人类肿瘤发生、发展中的作用和机制以及以Rad51为靶点的治疗策略。根据纳入标准,精选86篇文献,最后32篇文献纳入分析。结果:Rad51蛋白是参与DNA同源重组性修复的关键因子,Rad51蛋白的高水平表达会导致体内DNA同源重组性修复能力的增强,而同源重组机制的功能失调常会导致基因组不稳定和肿瘤的发生。还有许多研究发现,Rad51蛋白表达升高所导致DNA修复能力的增强会导致肿瘤细胞对放疗、化疗和靶向治疗等多种治疗产生耐受。体外研究表明,下调Rad51蛋白表达水平可有效逆转肿瘤耐药和对放疗产生耐受。结论:Rad51是体内参与同源重组性DNA修复的关键因子,Rad51的功能失调与肿瘤的发生...     

Deficient nucleotide excision repair capacity enhances human prostate cancer risk

Prostate cancer (CaP) is the most commonly diagnosed non-skin cancer and the second leading cause of cancer death in American men. The etiology of CaP is not fully understood. Because most of the DNA adducts generated by some CaP-related carcinogens, including polycyclic aromatic hydrocarbons, heterocyclic amines, and pesticides, are removed by the nucleotide excision repair (NER) pathway, we pilot tested the hypothesis that CaP is associated with deficient NER capacity (NERC), measured by a plasmid-based host reactivation assay. Using cryopreserved lymphocytes collected in an ongoing, clinic-based case-control study, our results showed that the mean NERC was significantly lower (P = 0.03) in 140 cases (mean +/- SD, 8.06 +/- 5.17) than in 96 controls (9.64 +/- 5.49). There was a significant association between below-median NERC and CaP risk: odds ratio (OR), 2.14; 95% confidence interval (CI), 1.19-3.86, after adjustment for age, race/ethnicity, smoking history, benign prostatic hyperplasia, and family history. This association was stronger in younger (<60 years of age) subjects (OR, 3.98; 95% CI, 1.13-14.02) compared with older (> or = 60) subjects (OR, 1.74; 95% CI, 0.90-3.37). When we stratified NERC values by quartiles of controls, there was a significant dose-dependent association between lower NERC and elevated CaP risk (p (test for linear trend), 0.01). Compared with the highest quartile of NERC as the referent group, the adjusted ORs for the 75th, 50th, and 25th quartiles were: 1.09 (95% CI, 0.46-2.59); 1.81 (95% CI, 0.77-4.27); and 2.63 (95% CI, 1.17-5.95), respectively. This pilot study is the first direct evidence associating deficient NERC with human CaP risk.     

Patterns of genomic loss of heterozygosity predict homologous recombination repair defects in epithelial ovarian cancer

Background:

Defects in BRCA1, BRCA2, and other members of the homologous recombination pathway have potential therapeutic relevance when used to support agents that introduce or exploit double-stranded DNA breaks. This study examines the association between homologous recombination defects and genomic patterns of loss of heterozygosity (LOH).

Methods:

Ovarian tumours from two independent data sets were characterised for defects in BRCA1, BRCA2, and RAD51C, and LOH profiles were generated. Publically available data were downloaded for a third independent data set. The same analyses were performed on 57 cancer cell lines.

Results:

Loss of heterozygosity regions of intermediate size were observed more frequently in tumours with defective BRCA1 or BRCA2 (P=10⁻¹¹). The homologous recombination deficiency (HRD) score was defined as the number of these regions observed in a tumour sample. The association between HRD score and BRCA deficiency was validated in two independent ovarian cancer data sets (P=10⁻⁵ and 10⁻²⁹), and identified breast and pancreatic cell lines with BRCA defects.

Conclusion:

The HRD score appears capable of detecting homologous recombination defects regardless of aetiology or mechanism. This score could facilitate the use of PARP inhibitors and platinum in breast, ovarian, and other cancers.     

外源性p53基因增加卵巢癌细胞对顺铂的敏感性

 目的 探讨外源性ｐ５３基因转染对人卵巢癌细胞株的化疗敏感性的影响。方法用脂质体介导的转染技术，将人野生型ｐ５３基因的真核表达载体导入不表达ｐ５３的卵巢癌ＳＫＯＶ－３细胞中，经Ｇ４１８筛选，Ｎｏｒｔｈｅｒｎｂｌｏｔ及Ｗｅｓｔｅｒｎｂｌｏｔ鉴定后，观察其对顺铂作用后的 ＳＫＯＶ－３细胞的集落形成及凋亡的影响。结果 外源性Ｐ５３基因在转染细胞中有效表达，并增强了顺铂对ＳＫＯＶ－３细胞集落形成的抑制作用及促进了顺铂诱导的细胞凋亡。结论 外源性ｐ５３基因能增加卵巢癌细胞对顺铂的敏感性，两者联合作用能更大程度地杀灭肿瘤细胞。     

Role of eIF3a in regulating cisplatin sensitivity and in translational control of nucleotide excision repair of nasopharyngeal carcinoma

Translational control at the initiation step has been recognized as a major and important regulatory mechanism of gene expression. Eukaryotic initiation factor-3a (eIF3a), a putative subunit of the eIF3 complex, has recently been shown to have an important role in regulating the translation of a subset of mRNAs and is found to correlate with the prognosis of cancers. In this study, using nasopharyngeal carcinoma (NPC) cells as a model system, we tested the hypothesis that eIF3a negatively regulates the synthesis of nucleotide excision repair (NER) proteins, and, in turn, cellular response to treatments with DNA-damaging agents such as cisplatin (cis-dichlorodiammine platinum(II) (CDDP)). We found that a CDDP-sensitive sub-clone S16 isolated through limited dilution from an NPC cell line CNE-2 has increased eIF3a expression. Knocking down its expression in S16 cells increased cellular resistance to CDDP, NER activity and synthesis of the NER proteins XPA, XPC, RAD23B and RPA32. Altering eIF3a expression also changed the cellular response to CDDP and UV treatment in other NPC cell lines. Taken together, we conclude that eIF3a has an important role in the CDDP response and in NER activity of NPCs by suppressing the synthesis of NER proteins.     

Exploiting the homologous recombination DNA repair network for targeted cancer therapy

Genomic instability is a characteristic of cancer cells. In order to maintain genomic integrity, cells have evolved a complex DNA repair system to detect, signal and repair a diversity of DNA lesions. Homologous recombination (HR)-mediated DNA repair represents an error-free repair mechanism to maintain genomic integrity and ensure high-fidelity transmission of genetic information. Deficiencies in HR repair are of tremendous importance in the etiology of human cancers and at the same time offer great opportunities for designing targeted therapeutic strategies. The increase in the number of proteins identified as being involved in HR repair has dramatically shifted our concept of the proteins involved in this process: traditionally viewed as existing in a linear and simple pathway, today they are viewed as existing in a dynamic and interconnected network. Moreover, exploration of the targets within this network that can be modulated by small molecule drugs has led to the discovery of many effective kinase inhibitors, such as ATM, ATR, DNA-PK, CHK1, and CHK2 inhibitors. In preclinical studies, these inhibitors have been shown to sensitize cancer cells to chemotherapy and radiation therapy. The most exciting discovery in the field of HR repair is the identification of the synthetic lethality relationship between poly (ADP-ribose) polymerase (PARP) inhibitors and HR deficiency. The promises of clinical applications of PARP inhibitors and the concept of synthetic lethality also bring challenges into focus. Future research directions in the area of HR repair include determining how to identify the patients most likely to benefit from PARP inhibitors and developing strategies to overcome resistance to PARP inhibitors.     

Arsenic trioxide and cisplatin synergism increase cytotoxicity in human ovarian cancer cells: Therapeutic potential for ovarian cancer

Drug resistance is a major concern in the successful treatment of ovarian cancer. In the present study we report a combinational drug regime using arsenic trioxide (ATO) and cisplatin (CDDP) to increase therapeutic potentiality in ovarian cancer cells. ATO-mediated growth inhibition and apoptosis in human suspension ovarian cancer COC1 cells were evaluated by MTT assay and annexin V assay using flow cytometry, respectively. cDNA arrays were performed to screen ATO-mediated gene expression. Treatment of COC1 cells with ATO alone resulted in growth inhibition and apoptosis with a dose-and time-dependent fashion; further cDNA arrays showed that 34 genes (23 up-regulated genes and 11 down-regulated genes) may strongly associate with the antiproliferative and pro-apoptotic effects induced by ATO. Furthermore, Chou–Talalay analysis was used to evaluate the combinational effect of ATO and CDDP as well as dose-reduction index (DRI) in a panel of ovarian cancer cells including CDDP-sensitive and -resistant cell lines. The combination index (CI) analysis indicated that the interaction effect of ATO/CDDP exhibited a wide range of synergism in all the adherent ovarian cancer cells (A2780, IGROV-1, SKOV-3, and R182) as well as 0.93 to 0.69 for IC₅₀ to IC₉₀ in suspension COC1 cells where CI < 1, =1, and >1, define synergism, additive effect, and antagonism, respectively. More intriguingly, the combination of ATO and CDDP yielded favorable DRIs ranging from 1.23-fold to 13.51-fold dose reduction. These results suggest that ATO and its combination with CDDP present therapeutic potential for ovarian cancer, and deserve further preclinical and clinical studies. ( Cancer Sci 2009; 100: 2459–2464)