Radiosensitization by inhibiting DNA-protein kinase and microenvironmental factor

比较了渥曼青霉素在低pH微环境和中性pH微环境中对人肿瘤细胞的放射增敏作用。在照射前2小时用20 μ M渥曼青霉素处理A-172人胶质母细胞瘤细胞、A-549人腺癌细胞和HMV-1人黑素瘤细胞，并检查细胞存活。通过在渥曼青霉素处理之前将细胞暴露于低pH培养基24小时来模拟低pH微环境。本文用脉冲场凝胶电泳法研究了渥曼青霉素对50 Gy照射后DNA双链断裂（dsbs）的修复作用。通过Western blot分析比较了低pH条件下和中性pH条件下DNA依赖性蛋白激酶催化亚基（DNA-PKcs）的表达。渥曼青霉素的放射增敏作用在低pH培养物中比在中性pH培养物中对所有细胞系更大。在低pH值条件下，DNA双链断裂修复的快速再连接组件受到更强烈的抑制，而不是在中性pH值条件下，尽管组间DNA-PKcs表达差异不大。低pH值的培养条件，这是为了模仿积极增殖的实体瘤中的中央肿瘤块的微环境，通过抑制DNA双链断裂修复的快速重新连接组件和通过延长未修复的DNA双链断裂的保留，增强了渥曼青霉素的放射增敏作用。

The radiosensitizing effect of wortmannin on human tumor cells in a low-pH microenvironment was compared with that in a neutral-pH environment. A-172 human glioblastoma cells, A-549 human adenocarcinoma cells, and HMV-I human melanoma cells were treated with 20 uM wortmannin 2 h before irradiation, and cell survival was examined. A low-pH microenvironment was simulated by exposing cells to low-pH culture medium for 24 h before wortmannin treatment. The effect of wortmannin on the repair of DNA double-strand breaks (dsbs) after 50 Gyirradiation in both low-and neutral-pH conditions were measured by pulse-field gel electrophoresis. Expression of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs)in low-pH conditions was also compared with that in neutral-pH conditions was also compared with that in neutral-pH conditions by Western blot analysis. The radiosensitizing effect of wortmannin was greater in low-pH cultures than in neutral-pH cultures for all cell lines. The faster-rejoining component of DNA dsb repair was inhibited more strongly in low-pH than in neutral pH conditions, although there was little difference in DNA-PKcs expression between groups. The low-pH culture condition, which was designed to mimic the microenvironment of the central tumor mass in actively proliferating solid tumors, enhanced the radiosensitizing effect of wortmannin by inhibiting the fast-rejoining component of DNA dsb repair and by prolonging the retention of nonrepaired DNA dsbs.