Objective To investigate the radiosensitivity of stem cells in pancreatic adenocarcinoma PANC‐1 cell line and the possible mechanism of its radiation resistance .Methods Using flow cytometry ,the cells were isolated and sorted into CD44+CD24+ ,CD44-CD24+ ,CD44+CD24- ,and CD44-CD24- .Multi‐target click model was used to fit cell survival curves and deter‐mine the sensitizer enhancement ratio .The apoptosis and cycle distribution of the four cell subsets were determined using flow cy‐tometry ,and the level of ROS was determined by DCFH‐DA probe .Results The ratio of CD44+ and CD24+ in the sorted PANC‐1 cell line was 92 .0% and 4 .7% respectively .Before radiation ,there was no statistically significant difference between four groups (P>0 .05);After treated with 6MV‐X ray ,The ratio of apoptosis was the lowest in CD44+CD24+ (P<0 .01);The percentage G0/G1 cell was the highest in CD44+CD24+ (P<0 .01) ,the sensitizer enhancement ratio of CD44+ CD24- ,CD44-CD24+ and CD44-CD24- were 1 .61 ,1 .81 ,1 .94 ,respectively .The level of ROS in CD44+CD24+ was lower (P<0 .01) .Conclusion Tumor stem cells of pancreatic adenocarcinoma have properties of a lower level of ROS and relative stationary that maybe the reasons of radio resist‐ance .%目的：研究人胰腺癌PANC‐1细胞株中干性细胞放射敏感性，并探讨其放射抗拒的可能机制。方法应用流式细胞仪分选CD44＋CD24＋、CD44－CD24＋、CD44＋CD24－和CD44－CD24－细胞亚群；照射后，计算放射增敏比；利用流式细胞术检测凋亡及周期分布，并结合DCFH‐DA探针检查各亚群活性氧簇（ROS）水平。结果 PANC‐1细胞中CD44＋细胞比例约为92．0％， CD24＋细胞比例约为4．7％。照射前4组凋亡差异无统计学意义（ P＞0．05）；照射后CD44＋ CD24＋的凋亡比例最低（ P＜0．01）。照射前后CD44＋CD24＋的G0／G1期比例最高，显著高于其他3组（ P＜0．01）。照射后CD44＋ CD24－、CD44－CD24＋和CD44－CD24－放射增敏比分别为1．61、1．81、1．94；照射后CD44＋ CD24＋ ROS水平最低，平均荧光强度显著低于其他3组（ P＜0．01）。结论人胰腺癌PANC‐1细胞株中干性细胞大多处于静止期，且低ROS水平，因此考虑胰腺癌干性细胞的放射抗拒与此有关。
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