Inside And Outside The Irradiation Induced Dna Strand Breaks And Repair In The Treatment Of Tumors

DNA strand breakage and repair ,as well as opoptosis induced by internall and external irradiation play an important role in the field of radiation oncology. They are the most important aspects that can be used pbtentially in clinic in order to interfere radiation effects by means of moleculles biology. The comet assay is a quick, simple, sensitive, reliable, newly advanced method of measuring DNA strand breakage. At present, the scope of its applications is covered from investigation of physicochemical behavior of DNA, through studies of cellular responses to DNA damage, to biomonitoring of human populations. In our study, the neutral and alkaline comet assay were applied to detect DNA strand breaks in peripheral blood lymphocytes after in vitro external irradiation, in vivo internal exposure, arid in radiation workers, in tumor patients untreated and treated with radiotherapy, as well as in irradiated tumor cell lines. Surely, the comet assay is a biomarker of future cancer risk and a predictor of intrinsic radiosensitivity for tumor cells. The main content of this thesis is as follows: 1. Effects of DNA single?and double-strand breaks in mice peripheral blood lymphocytes induced by γ-rays irradiation were analyzed by neutral and alkaline comet assay. Results indicated that γ-rays caused the increase of DNA migration length in the lymphocytes in the dose-dependent manner. 2. Effects of DNA single-strand breaks in rats peripheral blood lymphocytes induced by internal exposure with fission-bebris nuclides were analyzed by alkaline comet assay. It shown that fission-bebris nuclids caused the increase of DNA migration length in the lymphocytes in the dose-dependent manner. It should be noted that comet assay not only can be applied to monitor DNA single-band double-strand breaks in vivo or in vitro, but also can be used as a newly biological dosimeter. 3. DNA single-strand breaks in peripheral blood lymphocytes of 20 normal pepol e, 17 workers exposed to external irradiation, 28 unirradiated and 19 irradiated patients with malignant tumor were studied by comet assay. Both the percentage 5 of comet cells and the DNA migration length of workers, patients in contact with γ-rays were higher than those nornBl people (P<0. 01). It is expected that the cornet assay may be a relevant biomarker of radiation suspectiable and future cancer risk. 4. The relationship between intrinsic radiosensitivity for tuixr cells and radiation-induced initial DNA double-strand breaks (DSBs), DSB repair in three tumor cell lines:K562: LS-T-17 and C6 can be established by the neutral comet assay. It was found that there was a close association of initial DSBs and the del ivered dose; that is the larger the dose, the severer the 1)88. For the same single dose according to a descending order, the different initial DSBs and intrinsic radiosensitivity measured using a clonogenic assay ranked as: K562> LS-T 117>C6, while the capacity of DBS repair did as C6>LS-T-17>K562. The results suggest both radiation-induced initial DSBs and DSB repair correlated with intrinsic radiosensitivity to a certain extent,especially can be used as potential predictors of intrinsic radiosensitivity for tumor cells. 5. The relationship between intrinsic radiosensitivity for tumor cells and radiation-induced initial DNA single-strand breaks(SSBs),SSB repair in three tumor cell 1ines:K562 LS-T-117 and C6 β-ray b...