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目的 探讨二甲双胍对肺癌A549细胞的放射增敏作用及其潜在的机制.方法 采用CCK-8法检测不同浓度二甲双胍对A549细胞的抑制作用,计算IC50值;细胞克隆形成实验检测二甲双胍联合放疗的增敏作用;流式细胞仪检测细胞周期及细胞凋亡;免疫印迹法检测DNA损伤蛋白γ-H2AX,DNA修复蛋白DNA-PK,Ku80,Ku70的表达.结果 我们发现5mM浓度的二甲双胍增强了A549细胞的放射敏感性.克隆形成实验结果显示放疗联合5 mM二甲双胍24小时后细胞存活分数(SF值)为1.39,单纯放疗组SF值为0.1;流式细胞技术结果显示6Gy放疗联合5 mM二甲双胍组24小时后G2/M期比例为8％,早期凋亡率为34.9％,而单纯放疗组G2/M期比例为26％,早期凋亡率为10.6％.免疫印迹结果显示5 mM二甲双胍与6 Gy放射联合作用于A549细胞24小时,二甲双胍能够上调DNA损伤蛋白γ-H2AX表达,下调DNA修复蛋白DNA-PK,Ku70及Ku80表达(P＜0.01).结论 体外实验中,我们发现二甲双胍增敏放疗的机制是降低放疗相关的G2检查点及抑制DNA损伤修复.“,”Objective To explore the possibility that mefformin enhance radiosensitivity and its potential mechanism in lung cancer A.549 cells.Methods CCK8 assay was conducted to determine the IC50 value of mefformin in A549 cell.The radiosensitizing effect of mefformin in A549 cell on survival curve after radiation were detected by cell colony assay.Flow cytometry with Annexin V-PI staining was used to assess the apoptosis and cell cycle arrest.The expression of DNA damage proteinγ-H2AX and DNA repair protein,such as DNA-PK,Ku80,Ku70,were detected by Western Blot analysis.Results We found that mefformin at 5mM concemtration enhanced the radiosensitivity of A549 cell.Cell colony assay showed that the cell survival fraction (SF) was 1.39 after radiation combined with 5 mM metformin for 24 hours,and the SF value was 0.1 in radiation alone group.Flow cytometry showed that the ratio of G2/M phase after 6Gy combined with 5mM metformin group was 8％,the early apoptotic rate was 34.9％,but its ratio of 6Gy was 26％,the early apoptotic rate was 10.6％.Western blot showed that metformin significantly down-regulated the expression of DNA repair protein such as DNA-PK,Ku70 and Ku80 and up-regulated the expression of DNA damage repairγ-H2AX protein after 6Gy combined with 5 mM mefformin for 24 hours (P ＜ 0.01).Conclusion In vitro,we found that the mechanism about radiosensitivity of metformin was to reduce G2 checkpoint and inhibit DNA damage repair.