中文摘要：

目的研究单次、分次和^125I粒子持续低剂量率照射对结直肠癌CL187细胞生物学效应的影响。方法实验分高剂量率单次照射组（400cGy／min，单次组）、分次照射组（2Gy／次／d，400cGy／min，分次组）和^125I粒子持续低剂量率照射组（2．77cGy／h，^125I组）。3组细胞照射0、2、4和8Gy后，24和48h进行细胞计数和锥虫蓝染色，比较细胞总数和细胞存活率的差异。利用克隆形成实验比较3组细胞增殖能力的差异。通过流式细胞仪检测细胞凋亡。蛋白免疫印迹法分析PHLPP2、PTEN和Bax蛋白表达的变化。结果与单次组和分次组相比，^125I组细胞总数减少（t=34．28和29．48，P〈0．05）、存活细胞比例减少（t=-12．38和-14．61，P〈0．05），细胞克隆形成能力下降，相对生物学效应是1．41。照射后48h细胞凋亡检测发现^125I组细胞凋亡比例增加（t=-15．08和-11．99，P〈0．05）。蛋白免疫印迹法检测发现“’I组Bax表达量升高，PHLPP2和PTEN的表达量3组间差异无统计学意义。结论单次、分次和持续低剂量率照射后细胞PHLPP2蛋白表达水平均升高，但剂量率的高低并不影响其表达水平。不同方式照射后，凋亡相关蛋白Bax的表达水平上升，^125I组升高更加明显，^125I持续低剂量粒子照射可能通过影响凋亡相关蛋白Bax的表达水平实现对结直肠癌CL187细胞的杀伤作用。

英文摘要：

Objective To investigate the effect and underlying mechanism of single, fractioned and continuous low dose rate radiation on CL187 colorectal cancer cell line. Methods CL187 cells were exposed to 6 MV X-rays at a high dose rate of 4 Gy/min and 125I seed at a low dose rate of 2.77 cGy/h with three groups： single dose radiation group （SDR）, fraetioned dose radiation group （FDR） by 2 Gy/f, and continuous low dose rate radiation group （CLDR）. The radiation doses were 0, 2, 4 and 8 Gy. Total cell number and cell viability were determined by trypan blue. Clone forming assay was used to evaluate the cell proliferation ability. The percentage of apoptosis cells was analyzed by flow eytometry. Western blot was used to detect the protein expression levels of PHLPP2, PTEN and Bax. Results Compared with SDR and FDR groups, the total cell number and survival fraction of CLDR group decreased. The relative biological effect （RBE） for 125^I seeds compared with 6 MV X-rays was 1.41. The percentage of apoptosis cells of CLDR group was significantly increased （t= - 15.08, - 11.99, P 〈 0.05 ）. The expression level of Bax increased in CLDR group, while no obvious changes were observed on PHLPP2 and PTEN among three groups. Conclusions The expression level of PHLPP2 increases in SDR, FDR and CLDR group, while it seems that it was not influenced by dose rate. The expression level of Bax increased in three groups, while more colorectal CL187 cells in CLDR group may be killed due to the increase of Bax expression.