Effects of emodin extracted from Chinese herbs on proliferation of non-small cell lung cancer and underlying mechanisms

To aim of this was to observe emodin-mediated cytotoxicity and its influence on Rad51 and ERCC1 expressionin non-small cell lung cancer (NSCLC). NSCLC cells were cultured in vitro with emodin at various concentrations (0, 25, 50, 75 and 100 μmol/L) for 48 h and the proliferation inhibition rate was determined by the MTT method. Then, NSCLC were treated with emodin (SK-MES-1 40 μmol/L, A549 70 μmol/L) or 20 μmol/L U0126 (an ERK inhibitor) for 48 h, or with various concentrations of emodin for 48 h and the protein and mRNA expressions of ERCC1 and Rad51 were determined by RT-PCR and Western blot assay, respectively. Emodin exerted a suppressive effect on the proliferation of NSCLC in a concentration dependent manner. Protein and mRNA expression of ERCC1 and Rad51 was also significantly decreased with the dose. Vacuolar degeneration was observed in A549 and SK-MES-1 cell lines after emodin treatment by transmission electron microscopy. Emodin may thus inhibited cell proliferation in NSCLC cells by downregulation ERCC1 and Rad51.     

恶性胸腔和腹腔积液中ERCC1和BRCA1 mRNA的表达水平与顺铂敏感性的关系

目的:本研究旨在探讨肿瘤特殊转移灶恶性胸腔/腹腔积液中核苷酸切除修复交叉互补组1(excision repair cross-complementing group 1, ERCC1)基因和乳腺癌易感基因1(breast cancer 1, BRCA1)的表达水平与顺铂体外药物敏感性之间的关系.方法:前瞻性收集46例Ⅳ期恶性肿瘤患者的恶性胸腔/腹腔积液,分离出肿瘤细胞后,采用体外药敏试验三磷酸腺苷生物荧光法检测(adenosine triphosphate-bioluminescence assay, ATP-TCA)法检测肿瘤细胞对顺铂的药物敏感性,实时荧光定量PCR检测ERCC1和BRCA1 mRNA的相对表达水平.结果: 在非小细胞肺癌患者的恶性胸腔/腹腔积液中,肿瘤细胞的ERCC1 mRNA相对表达水平与顺铂抗药性呈正相关(P=0.001,r=0.685).非小细胞肺癌患者(P=0.014,r=0.541)和胃癌患者(P=0.002,r=0.625)恶性胸腔/腹腔积液中肿瘤细胞的BRCA 1 mRNA相对表达水平与顺铂抗药性呈正相关.ERCC1和BRCA1对顺铂药物敏感性的影响存在交互作用(所有患者P=0.010;胃癌患者P=0.027).结论:恶性胸腔/腹腔积液中肿瘤细胞的ERCC1和BRCA1 mRNA的相对表达水平与顺铂体外药物敏感性相关.联合检测ERCC1和BRCA1这2种基因较只采用其中一种基因在预测顺铂药物敏感性方面的价值更大.     

Effects of Rad51 on Survival of A549 Cells

Rad51, a key factor in the homologous recombination pathway for the DNA double-strand break repair,plays a vital role in genesis of non-small-cell lung cancer (NSCLC). In recent years, more and more studiesindicate that high expression of Rad51 is of great relevance to resistance of NSCLC to chemotherapeutic agentsand ionizing radiation. However, the underlying molecular mechanisms are poorly understood. In this study,we investigated the role of single Rad51 on cell viability in vitro. Our results show that depletion of endogenousRad51 is sufficient to inhibit the growth of the A549 lung cancer cell line, by accumulating cells in G1 phase andinducing cell death. We conclude that independent Rad51 expression is critical to the survival of A549 cells andcan be an independent prognostic factor in NSCLC patients.     

ERCC1在非小细胞肺癌中的表达及其与临床病理特征的关系

目的 分析非小细胞肺癌（NSCLC）癌组织中ERCC1的表达状况及其与NSCLC的临床病理特征的关系。方法采用免疫组织化学法检测64例初治中晚期NSCLC患者癌组织中ERCC1基因的表达情况。结果ERCC1表达的阳性率为43．8％，其表达与吸烟有密切关系，在吸烟组中的阳性率（27．8％）显著低于不吸烟组（64．3％）（X^2=8．530，P=0．004）。随着原发灶和疾病分期增加，ERCC1的阳性率有上升的趋势，但组间比较差异均无显著性（均为P〉0．05）。ERCC1在腺癌和低分化癌组中的阳性率分别高于鳞癌和高、中分化组，但差异无显著性（P〉0．05）。ERCC1的表达与年龄、性别和淋巴结转移状况等均未见显著性关联（均为P〉0．05）。结论ERCC1表达与NSCLC的一些临床病理学特征密切相关。     

Effects of gemcitabine on cis-platinum-DNA adduct formation and repair in a panel of gemcitabine and cisplatin-sensitive or -resistant human ovarian cancer cell lines

Gemcitabine (dFdC) can increase the sensitivity of both cisplatin (CDDP)-sensitive and -resistant cell lines. It has been postulated that both formation and repair of platinum-(Pt)-DNA adducts are related to these effects. Therefore, we investigated the effects of dFdC on the formation and repair of Pt-DNA adducts in the human ovarian cancer cell line, A2780, and its CDDP- or dFdC-resistant variants, ADDP and AG6000, which have a different expression of various repair enzymes. Cells were exposed for 1 h to CDDP alone or combined with dFdC in IC50 concentrations, followed by a 1-h exposure to thiourea and, subsequently, by a drug-free period of 1, 3 or 23 h (i.e. 2, 4 or 24 h after CDPP +/- dFdC removal). Pt-DNA adducts were quantified with 32P-post-labeling. The gene expression of the repair enzymes, XPA and XRCC1, was the same in all 3 cell lines but ERCC1, ERCC3 and XPC were 2-6 times higher in AG6000 compared to A2780 cells. In contrast, both ERCC1 and ERCC3 were 10- and 1.5-fold lower in ADDP cells compared to A2780. The mismatch enzyme, MLH1, was lower in ADDP cells. At equally toxic CDDP concentrations, all cell lines formed comparable peak levels of total Pt-DNA adducts (36-48 fmol/microg DNA). However, the time at which peak levels were reached showed large variation. The repair of the adducts was very efficient in the resistant cell lines whereas, in A2780 cells, plateau levels were retained until 24 h after CDDP exposure. In A2780 cells, dFdC shifted the adduct peaks from 4 h to directly after CDDP exposure and increased peak levels by >3.9-fold. dFdC also enhanced the repair of adducts by >1.7-fold and increased the Pt-GG:Pt-AG ratio compared to CDDP alone by >1.4-fold. Overall, dFdC decreased the area under the Pt-DNA adduct-time curve (AUA0-25 h) in A2780 cells by 2.7-fold. In ADDP cells, dFdC shifted the adduct peaks from 2 to 4 h and increased them by >2.2-fold. dFdC also increased the Pt-GG:Pt-AG ratio during the repair process by 1.4-fold. Overall, dFdC increased the AUA0-25 h in ADDP cells by 1.7-fold. In AG6000 cells, dFdC increased the Pt-GG:Pt-AG ratio by 1.6-fold directly after exposure but did not clearly affect the AUA0-25 h. In conclusion, dFdC can affect both Pt-DNA adduct formation and repair, depending on the initial sensitivity of the cells.     

ERCC1 expression by immunohistochemistry and EGFR mutations in resected non-small cell lung cancer

Expression of excision repair cross-complementation group 1 (ERCC1) is important for resistance to platinum agents. Mutations of epidermal growth factor receptor (EGFR) are related to the responsiveness to tyrosine kinase inhibitors in non-small cell lung cancer (NSCLC). This study was performed to determine if ERCC1 expression and EGFR are related to the prognosis of resected NSCLC, and to determine if ERCC1 expression and EGFR mutations are related. We used immunohistochemistry (IHC) to evaluate ERCC1 expression in tumors from 130 patients with curatively resected NSCLC. The median H-score was used as a cut-off for ERCC1 IHC. EGFR mutations were analyzed in exons 18, 19 and 21. ERCC1 expression was detected in tumors from 80 patients (61.5%). ERCC1 was expressed more frequently in smokers and in squamous cell carcinomas. Patients with a positive ERCC1 expression survived longer than ERCC1-negative patients (median overall survival 7.6 years for ERCC1-positive vs. 4.0 years for ERCC1-negative, P=0.046). Subsequent multivariate analysis suggested that ERCC1 expression is an independent prognostic marker of longer survival (hazard ratio: 0.598, 95% confidence interval: 0.357-1.001). EGFR mutations were found in 25 patients (19.2%) but did not affect overall survival. Interestingly, EGFR mutations were more frequent in ERCC1-negative tumors (12.5% in ERCC1-positive vs. 30% in ERCC1-negative tumors, P=0.014). In conclusion, ERCC1 expression was identified as a positive prognostic marker in resected NSCLC. In addition, EGFR mutations were more frequently found in ERCC1-negative tumors.     

Tumor cell kill by c-MYC depletion: role of MYC-regulated genes that control DNA double-strand break repair

MYC regulates a myriad of genes controlling cell proliferation, metabolism, differentiation, and apoptosis. MYC also controls the expression of DNA double-strand break (DSB) repair genes and therefore may be a potential target for anticancer therapy to sensitize cancer cells to DNA damage or prevent genetic instability. In this report, we studied whether MYC binds to DSB repair gene promoters and modulates cell survival in response to DNA-damaging agents. Chromatin immunoprecipitation studies showed that MYC associates with several DSB repair gene promoters including Rad51, Rad51B, Rad51C, XRCC2, Rad50, BRCA1, BRCA2, DNA-PKcs, XRCC4, Ku70, and DNA ligase IV. Endogenous MYC protein expression was associated with increased RAD51 and KU70 protein expression of a panel of cancer cell lines of varying histopathology. Induction of MYC in G(0)-G(1) and S-G(2)-M cells resulted in upregulation of Rad51 gene expression. MYC knockdown using small interfering RNA (siRNA) led to decreased RAD51 expression but minimal effects on homologous recombination based on a flow cytometry direct repeat green fluorescent protein assay. siRNA to MYC resulted in tumor cell kill in DU145 and H1299 cell lines in a manner independent of apoptosis. However, MYC-dependent changes in DSB repair protein expression were not sufficient to sensitize cells to mitomycin C or ionizing radiation, two agents selectively toxic to DSB repair-deficient cells. Our results suggest that anti-MYC agents may target cells to prevent genetic instability but would not lead to differential radiosensitization or chemosensitization.     

Cell cycle association and hypoxia regulation of excision repair cross complementation group 1 protein (ERCC1) in tumor cells of head and neck cancer

Excision repair cross complementation group 1 (ERCC1) is a key component of homologous recombination-based repair of interstrand DNA cross-links (ICLs). As a consequence, ERCC1 mediates resistance to mitomycin C (MMC) and platinum chemotherapeutic agents and may predict treatment failure. Clinical response to MMC or cisplatin (CDDP)-based radiochemotherapy (RCT) was assessed in 106 head and neck squamous cell carcinoma (HNSCC) patients and correlated with cell nuclear immunoreactivity of the mouse monoclonal (clone: 8 F1) ERCC1 antibody in tumor tissue samples. BEAS-2B epithelial and Detroit 562 pharyngeal squamous carcinoma cells were treated with CDDP, MMC, and 5-fluorouracil (5-FU) at 50 % growth inhibitory (IC-50) concentrations. ERCC1 protein synthesis was compared with cell cycle distribution using combined immunocytochemistry and flow cytometry. ERCC1 messenger RNA (mRNA) and protein expression was investigated in normoxic and hypoxic conditions in Detroit 562 cells. Clinically, the nonresponder revealed significantly lower HNSCC tissue ERCC1 immunoreactivity than the responder (p?=?0.0064) or control normal mucosa, which led to further mechanistic investigations. In vitro, control cells and cells treated with cytotoxic agents showed increasing ERCC1 levels from the G1 through S and G2 phases of the cell cycle. In CDDP-treated cells, ERCC1 mRNA and protein expression increased. Under hypoxic conditions, ERCC1 gene expression significantly decreased. Although ERCC1⁺ cells show increased chemoresistance, they might be particularly radiosensitive, representing G2 cell cycle phase and less hypoxic. ERCC1 expression might be indirectly related with some conditions important for RCT treatment, but it is not a clear predictor for its failure in HNSCC patients.     

Cisplatin benefit is predicted by immunohistochemical analysis of DNA repair proteins in squamous cell carcinoma but not adenocarcinoma: theranostic modeling by NSCLC constituent histological subclasses

BackgroundMost non-small-cell lung cancer (NSCLC) patients receive cisplatin-based chemotherapy though clinical response is restricted to a subset of patients. DNA repair protein levels are possible surrogates for cisplatin-induced DNA adduct (and subsequent cell death) repair efficiency and thus molecular determinants of therapeutic efficacy. The International Adjuvant Lung Trial (IALT)-Bio study previously suggested ERCC1 and MSH2 as predictive of cisplatin-based therapeutic benefit.Patients and methodsDNA repair protein expression (XPF, BRCA1, ERCC1, MSH2, p53, PARP1, and ATM) was assessed by immunohistochemistry on a large subset of patients (N = 769) from the IALT trial. Tissue Microarray slides were digitally scanned and signal quantified by user-defined macros. Statistical analyses (univariate and multivariate) of 5-year disease-free survival (DFS) and 5-year overall survival used binary cut-offs (H score low/high expression).ResultsIn patients with squamous cell carcinoma (SCC), ATM, p53, PARP1, ERCC1, and MSH2 displayed significant (borderline) predictive values, mainly on DFS with chemotherapy efficacy limited to low marker levels. Adenocarcinoma (ADC) results were not significant. BRCA1 and XPF were not significant for predictive modeling in either SCC or ADCs.ConclusionHere predictive utility of DNA repair enzymes co-segregates with SCC histology, focusing their predictive value to this histological subclass of NSCLC. Distinct mechanisms of chemotherapeutic response or resistance might exist among histological subclasses of solid tumors.     

切除修复交叉互补基因1表达与非小细胞肺癌患者吉西他滨联合顺铂化疗疗效的相关性

目的探讨非小细胞肺癌(NSCLC)患者肿瘤组织内核苷酸切除修复交叉互补基因1(ERCC1)表达与吉西他滨联合顺铂(GP方案)化疗疗效的相关性。方法采用免疫组化S-P法检测51例Ⅱb～Ⅳ期NSCLC患者肿瘤组织内ERCC1的表达。所有患者接受至少2个周期以上的GP方案化疗,对患者化疗后的中位生存期(MST)及化疗后反应率(RR)进行评估。结果 51例患者ERCC1的阳性表达率为43.14%(22/51)。ERCC1表达阳性组化疗后的RR和MST分别为50.0%、17个月,与阴性组RR(31.04%)、MST(12个月)比较,差异无统计学意义(χ2=1.8877,P=0.1695;χ2=1.6767,P=0.1954)。结论 ERCC1表达阳性的NSCLC患者能从吉西他滨联合顺铂的化疗中受益,调控ERCC1表达逆转耐药的策略,将为肿瘤治疗带来新的方法和途径。     

A model chemosensitivity test examining apoptosis in small specimens of gastric cancer

Background. Because chemosensitivity tests usually require a large amount of tissue, they are not used routinely in patients with unresectable gastric cancer. The aim of this study was to investigate whether apoptosis can be used as a sensitivity assay for chemosensitivity in small gastric cancer specimens. Methods. Apoptosis, detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick labeling (TUNEL), was investigated in small specimens of the MKN-1, MKN-45, and TMK-1 human gastric cancer cell lines as a marker of chemosensitivity following exposure to antineoplastic agents. Results. Doxorubicin (DXR), SN-38 (active metabolite of irinotecan), and paclitaxel (Taxol) induced DNA fragmentation in MKN-45 and TMK-1 cells, but not in MKN-1. In contrast, neither 5-fluorouracil (5-FU) nor cisplatin (CDDP) induced DNA fragmentation in any of the three cell lines. Small pieces cut from tumors implanted in nude mice were exposed to the antineoplastic agents in culture medium for 24 h, and the percentage of TUNEL-positive cancer cells (TUNEL positivity) was examined. TUNEL positivity in all three cancers increased after exposure to DXR, SN-38, and Taxol, but not after exposure to CDDP or 5-FU. MKN-45 showed the highest TUNEL positivity with SN-38 and Taxol, and TMK-1 TUNEL positivity was highest with DXR. MKN-45 and TMK-1 were the most sensitive to these three antineoplastic agents in vitro, while MKN-1, with the lowest TUNEL positivity, was the least sensitive to these three antineoplastic agents. TUNEL positivity after exposure to Taxol correlated with the antitumor effects of this compound in an animal model. Conclusion. These results suggest that, in small gastric cancer specimens where apoptosis is implicated, TUNEL positivity may be applicable to a chemosensitivity test. Received: January 28, 2000 / Accepted: April 14, 2000     

High-level expression of Rad51 is an independent prognostic marker of survival in non-small-cell lung cancer patients

High-level expression of Rad51, a key factor in homologous recombination, has been observed in a variety of human malignancies. This study was aimed to evaluate Rad51 expression to serve as prognostic marker in non-small-cell lung cancer (NSCLC). A total of 383 non-small-cell lung tumours were analysed immunohistochemically on NSCLC tissue microarrays. High-level Rad51 expression was observed in 29.4% (100 out of 340) of cases. Patients whose tumours displayed high-level Rad51 expression showed a significantly shorter median survival time of 19 vs 68 months (P<0.0001, log-rank test). Similarly T status, N status, M status, clinical stage and histological tumour grade were significant prognostic markers in univariate Cox survival analysis. Importantly, Rad51 expression (P<0.0001) together with tumour differentiation (P<0.009), clinical stage (P=0.004) and N status (P=0.0001) proved to be independent prognostic parameters in multivariate analysis. Rad51 expression predicted the outcome of squamous cell cancer as well as adenocarcinoma of the lung. Our results suggest that Rad51 expression provides additional prognostic information for surgically treated NSCLC patients. We hypothesise that the decreased survival of NSCLC patients with high-level expression of Rad51 is related to an enhanced propensity of tumour cells for survival, antiapoptosis and chemo-/radioresistance.     

Role of O6-methylguanine-DNA methyltransferase and effect of O6-benzylguanine on the anti-tumor activity of cis-diaminedichloroplatinum(II) in oral cancer cell lines

The DNA repair enzyme O⁶-methylguanine–DNA methyltransferase (MGMT) modulates the effectiveness of alkylating agents. However, the relationship between MGMT and the sensitivities to other agents has not been explored. In the present study, the association between MGMT expression and the cellular sensitivity to the platinum agent, CDDP was examined in four human oral cancer cell lines. CDDP depleted MGMT protein and mRNA levels in all four cell lines. Two cell lines with low MGMT expression were sensitive to an alkylating agent, N-methyl-N′-nitro-N-nitrosoguanidine and CDDP, whereas two other cell lines with high MGMT expression were resistant to both agents. Furthermore, the addition of the MGMT inhibitor, O⁶-benzylguanine (O⁶-BG), invariably enhanced CDDP sensitivity. CDDP depleted MGMT expression, and CDDP sensitivity was enhanced by O⁶-BG. These results provide valuable information about the relationship between MGMT expression and CDDP sensitivity in oral cancer chemotherapy.     

Expression of ERCC1 antisense RNA abrogates gemicitabine-mediated cytotoxic synergism with cisplatin in human colon tumor cells defective in mismatch repair but proficient in nucleotide excision repair.

Gemcitabine, or 2',2'-difluorodeoxycytidine (dFdC) is a new anticancer agent with significant activity against a broad spectrum of tumors either as a single agent or in combination with other active anticancer drugs. Studies in vitro and in vivo have demonstrated that dFdC produces cytotoxic synergism with cisplatin, or cis-diamminedi-choloroplatinum(II) (CDDP); however, the mechanism by which the synergism occurs has not been elucidated. We proposed that the nucleotide excision repair (NER) process, which is responsible for the cellular removal of CDDP-DNA adducts, may be a target for the mechanism of the cytotoxic synergism of dFdC and CDDP. Because the mismatch repair (MMR) pathway is involved in mediating CDDP cytotoxicity, making determination of the role of the NER in the cytotoxic synergism more complicated, and because tumors are often defective in MMR, we selected an NER-proficient, MMR-deficient, CP2.0 human colon carcinoma cell line as a model for this study. By an in vitro repair synthesis assay, we found that dFdC triphosphate (dFdCTP), the active metabolite of dFdC, inhibited the incorporation of [alpha-32P]dATP as well as the incorporation of [alpha-32P]dCTP, suggesting that the repair inhibition by dFdCTP does not result simply from competition for the incorporation site but rather is also due to prevention of chain elongation during the DNA resynthesis process. To determine whether the repair inhibition contributes to the cytotoxic synergism, we examined the effect of the constitutive expression of ERCC1 antisense RNA on the interaction of dFdC and CDDP. CP2.0 cells were transfected with pERCC1/AS, an ERCC1 antisense expression vector; eight hygromycine-resistant clones expressing various levels of the antisense RNA were selected for quantification of and correlation between the repair activity and cytotoxic synergism. The results show that stable expression of ERCC1 antisense RNA down-regulated the level of mRNA and repair activity; the down-regulation of the repair activity significantly correlated with the reduction of the cytotoxic synergism of the two agents. These data provide direct evidence to support the hypothesis that inhibition of the repair of CDDP-induced DNA lesions plays a critical role in dFdC-mediated cytotoxic synergism with CDDP in MMR-deficient tumor cells.     

ERCC1、RRM1和BRCA1在非小细胞肺癌中的表达及预后意义

目的:探讨DNA修复基因家族成员ERCC1、RRM1和BRCA1在非小细胞肺癌(NSCLC)中的表达及预后意义。方法:应用实时荧光定量PCR技术对32例肺癌及16例癌旁组织中ERCC1、RRM1和BRCA1基因的mRNA进行定量检测。用非参数检验、相关分析、Kap lan-M e ier生存曲线和COX多因素回归分析进行统计分析。结果:NSCLC中ERCC1、RRM1和BRCA1在癌组织内表达量显著高于癌旁组织,且在癌内表达具有正相关性;RRM1在肺鳞癌中高于腺癌,但在不同分期中表达无差异;ERCC1和BRCA1在不同病理类型和分期中表达均无差异;RRM1和BRCA1高表达组的生存期明显长于低表达组;COX多因素回归分析示RRM1表达是影响本组患者预后的独立因素。结论:NSCLC中,ERCC1、RRM1和BRCA1在肺癌组织中的表达显著高于癌旁组织,RRM1和BRCA1高表达组的生存期长于低表达组。RRM1和BRCA1可作为判断预后的一种指标。     

Pharmacogenetic role of ERCC1 genetic variants in treatment response of platinum-based chemotherapy among advanced non-small cell lung cancer patients

The excision repair cross-complementation group 1 (ERCC1) plays an essential role in DNA repair and has been linked to resistance to platinum-based anticancer drugs among advanced non-small cell lung cancer (NSCLC) patients. We systematically evaluate whether ERCC1 Asn118Asn and C8092A genetic variants are associated with treatment response of platinum chemotherapy. We preformed a meta-analysis using ten eligible cohort studies (including 11 datasets) with a total of 1,252 NSCLC patients to summarize the existing data on the association between the ERCC1 Asn118Asn and C8092A polymorphisms and response to platinum regiments. Odds ratio or hazard ratio with 95% confidence interval were calculated to estimate the correlation. We found that neither ERCC1 C8092A polymorphism nor Asn118Asn variant is associated with different response of platinum-based treatment among advanced NSCLC patients. Additionally, these two genetic variants are not related to treatment response in either Caucasian patients or Asian patients. Our meta-analysis indicates that the ERCC1 Asn118Asn and C8092A polymorphisms may not be good prognostic biomarkers for platinum-based chemotherapy in patients with stage III-IV NSCLC.     

DNA repair as a determinant of tumour chemosensitivity

Differently from target-based anticancer drugs, molecular mechanisms of actions are not well-known in many of the classical antineoplastic agents. With the exception of vinca alkaloids and taxanes, all of the classical antineoplastic agents work on DNA metabolism in cells and can therefore be categorised as 'DNA metabolism inhibitor'. Cellular sensitivity against these drugs largely depends on various activities in DNA metabolism, particularly in DNA repair. However, DNA repair as a determinant of drug sensitivity had long received little attention. DNA mismatch repair (MMR) is now regarded as an important determinant to alter cellular sensitivities against various drugs including fluoropyrimidines, platinum compounds and topoisomerase inhibitors. However, molecular mechanisms of this connection are still unknown. In particular, the relationship between MMR and 5-fluorouraci (l 5-FU) sensitivity is now being approached by examining the tumour MMR status and clinical outcomes in colorectal cancer patients treated with 5-FU-based adjuvant chemotherapies. However, reported results lack consistency, possibly due to the methodological problems in assays used to determine the MMR status. On the other hand, nucleotide excision repair (NER) is also regarded as an important determinant of cisplatin (CDDP) sensitivity. Expression of ERCC 1, a component of this complex multi-protein system, has been reported to be a determinant of prognosis in CDDP-treated non-small-cell lung cancer patients. In order to establish the significance of DNA repair as a determinant of tumour chemosensitivity, further basic studies, particularly ones approached from biochemical viewpoints, are required. Clinical studies supported by accurate assay techniques are also needed.     

The role of celecoxib in Rad51 expression and cell survival affected by gefitinib in human non-small cell lung cancer cells

Celecoxib (Celebrex^R) is a cyclooxygenase-2 (COX-2) selective inhibitor and gefitinib (Iressa^R, ZD1839) is a selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor for human non-small cell lung cancer (NSCLC). The addition of celecoxib to gefitinib to prolong the survival of patients with NSCLC still remains controversial and needs to be investigated. The Rad51 protein is essential for homologous recombination repair, and is overexpressed in chemo- or radioresistant carcinomas. In this study, we characterize the role of celecoxib in the cytotoxicity, ERK1/2 activation and Rad51 expression affected by gefitinib in NSCLC cells. We show that celecoxib can enhance the cytotoxicity induced by gefitinib in NSCLC cells. Treatment with celecoxib alone has no effect on the ERK1/2 activation, Rad51 mRNA and protein levels, however, combined treatment with gefitinib results in a significant reduction of phospho-ERK1/2 and Rad51 protein levels, and triggers the degradation of Rad51 via a 26S proteasome-dependent pathway. Expression of constitutively active MKK1/2 vectors (MKK1/2-CA) significantly rescues the decreased ERK1/2 activity, and restores Rad51 protein levels and cell survival under co-treatment with gefitinib and celecoxib. Furthermore, blocking ERK1/2 activation by U0126 (MKK1/2 inhibitor) and knocking down Rad51 expression by transfection with small interfering RNA of Rad51 can enhance the cytotoxicity of celecoxib.