| Objects: To detect the DNA damage and repair caused by X-ray irradiationof human mammary adenocarcinoma sensitive cell line MCF-7 and Adriamycinresistant cell line MCF-7/ADR, analyse the cell cycle distribution andapoptosis rate, and investigate the effect of MDR on the radiosensitivityof the two cell lines. To compare the expression of P-gp, BCRP, GST-πand TopoⅡof MCF-7 and MCF-7/ADR pre-and post-radiotherapy, as wellas pre-and post-reversal treatment administrated after radiotherapy, andinvestigate the effect of radiation on the expression of multidrugresistance proteins.Methods: This study is divided into two parts. In the first part, alkalinesingle cell gel electrophoresis was performed to compare theradiosensitivity and DNA damage repair ability of MCF-7 and MCF-7/ADR.MCF-7 and MCF-7/ADR cell lines were divided into five groups that exposedto 0,2,5,]O, 15Gy X-ray respectively, then cells of each dose group werecollected 0,30,60,180,240 minutes after irradiation. Alkaline single cellgel electrophoresis were performed to detect DNA damage. The comet imagewere analyzed by CASP software; 12,24,48 hours after radiation, the cellcycle distribution and the apoptosis rate were analyzed by flow cytometry.In the second part MCF-7 and MCF-7/ADR cells were treated with fractionated irradiation of 40Gy/16 Fractions/8 Weeks. Cultured the cellsmore than two weeks after the radiotherapy, named them MCF-7/R40 andMCF-7/ADR/R40 respectively. Then 72 hours of reversal treatment of 10μmol/L Verapamil and 1000U/ml IFN were delivered to MCF-7/R40MCF-7/ADR/R40, renamed them with MCF-7/R40-C MCF-7/ADR/ R40-Crespectively. Detected the expression of multidrug resistance proteinspre-and post-radiotherapy, as well as pre-and post-reversaltreatment, using FCM for P-gp and BCRP, and immunohistochemical stainingfor GST-zand TopoⅡ. Statistical analysis data were processed bySPSS11.5 software.Results: 1. (1) For the low dose and media dose(2～10Gy) groups,there weresignificant differences between the Tail Moments of MCF-7 cells andMCF-7/ADR cells with the same dose exposed to (P＜0.05) circumstances,the same X-ray doses of MCF-7 after DNA damage than MCF-7/ADR (P＜0.05 ).(2) There were no significant differences between the TailMoments of MCF-7 cells and MCF-7/ADR cells of the high dose (15Gy)group, (P＞0.05).(3) The half repair time of MCF-7/ADR cells was 45.1±7.1minutes, significantly less than that of MCF-7 cells which was 60.3±5.6 min (P＜0.05).(4) Irradiation caused a G2/M phase block both in MCF-7 andMCF-7/ADR cells. The G2/M phase block was more obvious and disappearedsooner in MCF-7/ADR cells than that of MCF-7 cells; The higher apoptosisrates were shown in MCF-7 cells.2. (1) For MCF-7 cells the expression of P-gp, BCRP and GST-πincreased significantly after radiotherapy (P＜0.05); P-gp and BCRPexpression decreased significantly after reversal therapy (P＜0.05) andwhich had no significant difference compared with that pre-radiotherapy (P＞0.05); while the significant change was not seen in GST-πexpression(P＞0.05); there were no significant change happened in TopoⅡexpressionall along the experiment (P＞0.05).(2) P-gp expression of MCF-7/ADR cells did not changesignificantly after radiotherapy (P＞0.05), while BCRP and GST-πexpression increased significantly (P＜0.05); P-gp and GST-πand BCRPexpression decreased significantly to less than the level ofpre-radiotherapy after reversal therapy(P＜0.05); TopoⅡMCF-7/ADRcells in the expression of radiotherapy, after radiotherapy and afterradiotherapy reverse resistance groups are no significant difference (P＞0.05). Also, there were no significant change happened in TopoⅡexpression all along the experiment (P＞0.05).Oonclusions:1. (1) MCF-7 cells were more radiosensitive than MCF-7/ADRceils because of more DNA damage after exposed to low dose and media dose(2～10Gy) X-ray irradiation;(2) After exposed to high dose of X-ray irradiation (15Gy),MCF-7 and MCF-7/ADR had the same extent of DNA damage, which maybe causedby the sever effect on DNA damage that made the radiosensitivitydifferences between the two cell lines unclear;(3)Sublethal damage repair capacity of MCF-7/ADR cells wasstronger than that of MCF-7 cells.(4)The cell cycle distribution and apoptosis rate weredifferent between the two cell lines, theMCF-7 cells were more sensitiveto radiation than MCF-7/ADR cells.2. (1) Radiation could cause durg resistance in breast cancercells.(2) The changes of P-gp, BCRP, GST-πandTopoⅡexpressionswere different. P-gp, BCRP and GST-πwere relevant to MDR of breast cancer cells, while TopoⅡwas irrelevant to it.(3)Reversal treatment could reverse the changes of somemulticlrug resistance proteins, but its effects needs to be exploredfurther.
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