RESUMO
Objective To investigate the relationship between the p27~(kip1) expression and the change of radiosensitivity of esophageal cancer cells.Methods Radio-resistant cells (EC9706R) were gradually isolated by means of repeated gamma-ray irradiation (6 000 cGy in total) upon human squamous esophageal carcinoma cells (EC9706).The radiosensitivity of these two types of cells was measured by standard colony formation assays,their cell cycle distribution analyzed by flow cytometry respectively,and the p27~(kip1) expression detected by immunocytochemistry.Results As compared with their parent cells,the isolated human squamous esophageal carcinoma cells(EC9706) showed clearly greater radio-resistance(for EC9706R,SF_2=65.71%,D_0=2.20 Gy,D_q=1.61 Gy,N=2.07,and for EC9706,SF_2=46.72％,D_0=1.61 Gy,D_q=0.99 Gy,N=1.85;SF_2,D_0,Dq and N were all higher).As to the cell cycle distribution,the population of G_1 phase cells in EC9706R cells was significantly decreased,but the proportion of S phase cells was significantly increased as compared with the parent cells.Immunocytochemistry revealed that the p27~(kip1) expression of EC9706R cells was clearly lower than that of EC9706 cells.Conclusion Cell phase change due to the decrease of p27~(kip1) expression may be one of the mechanisms of the generation of radio-resistance in esophageal cancer cells.