胶质瘤对MPPa-PDT敏感性研究中ABCG2的作用

背景与目的:三磷酸腺苷结合转运蛋白G超家族成员2(adenosine triphosphate-binding cassette superfamily G member 2,ABCG2)在多种肿瘤细胞中表达,能通过外排抗癌药物参与肿瘤耐药.本研究的目的旨在探讨人胶质瘤细胞对焦脱镁叶绿酸甲酯(pyropheophorbide-a methyl ester,MPPa)介导的光动力疗法(photodynamic therapy,PDT)杀伤效应的敏感性及其与ABCG2的关系.方法:选取处于对数生长期的胶质瘤细胞株U87、A172,分别经MPPa-PDT或MPPa-PDT+烟曲霉毒素C(fumitremorgin C,FTC)处理后,采用CCK-8法检测细胞活性;采用蛋白质]印迹法(Western blot)检测细胞内ABCG2的表达;流式细胞技术法检测未光照前各组细胞内MPPa的含量;AnnexinⅤ-FITC/PI双染流式细胞术检测细胞凋亡率;DCFH-DA染色观察细胞内活性氧(reactive oxygen species,ROS)的产生.结果:MPPa-PDT能抑制A172、U87细胞的活性,且呈一定的光能量依赖性,A172达到半数致死量所需光能量密度为U87的8倍;A172较U87细胞对MPPa-PDT不敏感;A172细胞内高表达的ABCG2影响MPPa在细胞内的聚集;抑制ABCG2后,不仅可以增强MPPa-PDT对A172细胞的杀伤作用,同时可增加MPPa-PDT触发产生的ROS的量及细胞对MPPa的摄取.结论:人胶质瘤细胞株A172对MPPa-PDT相对不敏感,并且产生这种现象的机制可能是ABCG2外排MPPa,减少MPPa的细胞内聚集,进而减弱光敏剂活化后对肿瘤细胞的杀伤作用.

The role of ABCG2 in the sensitivity of glioma to pyropheophorbide-amethyl ester-mediated photodynamic therapy

Background and purpose:Adenosine triphosphate-binding cassette superfamily G member 2 (ABCG2), which has been found over-expressed in a variety of cancer cells, takes part in the drug resistance of cancer through effux of anticancer drugs. The purpose of this study was to investigate the mechanisms of human glioblastoma cells sensitivity to pyropheophorbide-a methyl ester (MPPa)-mediated photodynamic therapy (PDT) eradicating tumour cells and its relationship to ABCG2.Methods:U87 and A172 glioma cell lines in the logarithmic growth phase were selected and exposed to the treatment of MPPa-PDT and MPPa-PDT+fumitremorgin C (FTC) respectively. The cell viability was measured with the use of CCK-8 assay. The expression of ABCG2 was detected by Western blot. The intracellular contents of MPPa in each group without illumination were tested by lfow cytometry. Flow cytometry with AnnexinⅤ-FITC/PI double staining was used to detect the cell apoptotic rate. DCFH-DA staining was used to assess the generation of intracellular reactive oxygen species (ROS).Results:The MPPa-mediated PDT could eradicate A172 and U87 cancer cells in an energy-dependent manner. The light energy density in A172 was 8 times of that in U87 when the cell viability reached median lethal dose after MPPa-mediated PDT. The high expression of ABCG2 in A172 cells affected the accumulation of intracellular MPPa. Inhibition of ABCG2, not only could enhance the eradicating effect of MPPa-PDT on A172 cells, but also could increase the yield of ROS triggered by MPPa-PDT and the accumulation of intracellular MPPa.Conclusion:The human glioblastoma cell line A172 is insensitive to MPPa-mediated PDT. The mechanism may relate to ABCG2, which decreases the MPPa content in cancer cells through effux of MPPa, resulting in decline of cytotoxicity.