DNA双链断裂残留损伤与癌细胞辐射敏感性研究

目的 了解不同组织来源癌细胞株和人体肿瘤组织原代细胞的DNA双链断裂损伤修复的个体差异性,探寻预测癌细胞辐射敏感性的生物指标。方法 ⁶⁰Co γ射线照射诱发DNA损伤,脉冲电场凝胶电泳检测DNA双链断裂损伤修复,细胞克隆形成能力法检测细胞辐射敏感性。结果 8个不同组织来源癌细胞株的辐射敏感性有较大的差异(D₀为0.65~2.15 Gy),不同细胞株20 Gy γ射线照射诱发产生的DNA双链断裂原初损伤有一定的差别,但与细胞辐射抗性无相关性。辐射敏感细胞SX-10的DNA双链断裂修复缺陷发生在早期快速修复相,而A2780细胞的修复缺陷是发生在晚期慢速修复相。20 Gy照射修复2 h后DNA双链断裂残留量与细胞辐射敏感性指标D₀或SF₂值有显著的相关性。不同个体患者脑肿瘤组织原代细胞之间,辐射诱发DNA双链断裂的修复反应存在明显差异,修复2 h后残留损伤的个体差异性分布类似于癌细胞株。结论 DNA双链断裂残留损伤与癌细胞辐射抗性有显著相关性,可作生物指标预测肿瘤组织细胞对放射治疗的反应性。

Correlation between residual level of DNA double-strand breaks and the radiosensitivity of cancer cells

Objective To understand the variation of the DNA double-strand break rejoining capacity among different cultured cancer cell lines and the primary cancer cells from brain cancer patients,and to explore the predictor of radiotherapy responses of cancers. Methods DNA double-strand breaks (DSBs) were induced by 60Co γ-irradiation. Pulsed-field gel electrophoresis was used to analyze the initial production and rejoining of DNA DSBs. Radiosensitivity was determined by in vitro assay of clonogenic-forming capacity. Results A wide variation of radiosensitivity, e.g. The survival parameter of D0 varied from 0.65 to 2.15 Gy, was displayed among the eight cell lines derived from different type of cancers. Although differential level of initial DNA DSBs induced by 20 Gy γ-rays was observed among various cell lines, it was not correlated with the radiosensitivity. The deficiency of DNA DSB rejoining in radiosensitive cell lines was shown either in the early rapid-rejoining phase (SX-10 cells) or in the late slow-rejoining phase (A2780 cells). A significant relationship was observed between the residual level of DNA DSBs measured at 2 h post-20 Gy irradiation and the cellular radioseusitivity (D0 or SF2). The kinetic curves of rejoining DNA DSBs in the primary human brain tumor cells indicated a variation on DSB rejoining capacity among different individual tumor. The residual level of DNA DSBs after 2 h of rejoining post 20 Gy irradiation in primary human brain tumor cells is compatible to the results obtained in vitro culture cancer cell lines. Conclusions The residual level of DNA DSBs is correlated with radioresistance of cancer cells, and the residual DNA damage is a useful parameter in predicting the response of tumor tissue to radiotherapy.