| 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, and investigate the effect of MDR on theradiosensitivity of the two cell lines. To compare the expression of P-gp,GST-πand TopeⅡof MCF-7 and MCF-7/ADR pre- and post-radiotherapy, aswell as pre- and post-reversal treatment administrated after radiotherapy,and investigate 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 0,2,5,10,15Gy X-rayrespectively, 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. In the second part MCF-7 and MCF-7/ADRcells were treated with fractionated irradiation of 40Gy/16 Fractions/8Weeks. Cultured the cells more than two weeks after the radiotherapy,named them MCF-7/R40 and MCF-7/ADR/R40 respectively. Then 72 hours ofreversal treatment of 10μmol/L Verapamil and 1000U/ml IFN were deliveredto MCF-7/R40 MCF-7/ADR/R40, renamed them with MCF-7/R40-C MCF-F/ADR/R40-C respectively. Detected the expression of multidrug resistanceproteins pre- and post-radiotherapy, as well as pre- and post-reversaltreatment, using FCM for P-gp and immunohistochemical staining for GST- πand TopoⅡ. Statistical analysis data were processed by SPSS11.5software.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).2. (1) For MCF-7 cells the expression of P-gp, GST-πincreasedsignificantly after radiotherapy (P＜0.05); P-gp expression decreasedsignificantly after reversal therapy (P＜0.05) and which had nosignificant 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 TopoⅡexpression allalong the experiment (P＞0.05).(2) P-gp expression of MCF-7/ADR cells did not changesignificantly after radiotherapy (P＞0.05), while GST-πexpressionincreased significantly (P＜0.05); P-gp expression and GST-πexpressiondecreased significantly to less than the level of pre-radiotherapy afterreversal therapy(P＜0.05); TopoⅡMCF-7/ADR cells in the expression ofradiotherapy, after radiotherapy and after radiotherapy reverseresistance groups are no significant difference (P＞0.05). Also, therewere no significant change happened in TopoⅡexpression all along theexperiment (P＞0.05). (3) Reversal treatment could reverse the changes of somemultidrug resistance proteins, but its effects needs to be exploredfurther.Conclusions: 1. (1) MCF-7 cells were more radiosensitive than MCF-7/ADRcells 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.2. (1) Radiation could cause durg resistance in breast cancercells.(2) The changes of P-gp, GST-πand TopoⅡexpressions weredifferent. P-gp and GST-πwere relevant to MDR of breast cancer cells,while TopoⅡwas irrelevant to it.(3) Reversal treatment could reverse the changes of somemultidrug resistance proteins, but its effects needs to be exploredfurther.
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