MOLECULAR MECHANISMS OF HEAT INDUCED RADIOSENSITIZATION

热疗越来越多地与放射治疗结合使用， 治疗人类恶性肿瘤。 将这两者结合起来的理由是， 用于治疗癌症的临床方案中的模式依赖于 热辐射敏感性和优先杀死细胞的观察， 对辐射有抵抗力 分子解析 热辐射增敏的潜在机制可能提供信息 可用于开发这种组合治疗方案。 长 因此，本提案的长期目标是确定 热诱导现象背后的分子过程 放射增敏并阐明所涉及的机制。 中央 这一建议所依据的假设是，热使细胞对 通过增加DNA双链转化的可能性进行辐射 断裂（DSB）至致死性染色体畸变。 在增强的 假定DNA双链断裂转化为染色体畸变的概率为 由染色质结构和功能的改变引起， 急性暴露于热后发生，和/或通过减少 修复的功效。 染色质结构和功能的改变， 用于解释预辐照暴露诱导的放射增敏作用 在43-45.5摄氏度加热，可能导致结构不稳定， 辐射的DNA分子，或减少的可及性， 辐射诱导的DNA双链断裂修复酶， 残留的染色体损伤 修复系统的功效降低 主要用于解释辐射后暴露引起的放射增敏 加热到41-43摄氏度。 DNA双链断裂在热辐射增敏中的重要性将用 显示出修复该损伤的能力降低的辐射敏感突变体， 而DNA双链断裂转化为染色体损伤的改变， 通过测量，一方面，DNA双链断裂的诱导和修复， 使用非解旋过滤器洗脱技术或脉冲场凝胶 另一方面，诱导和修复染色体 利用早熟染色体技术对间期细胞的损伤 冷凝（PCC）。 具体而言，将进行实验， CHO辐射敏感突变体热辐射增敏作用研究 （xrs-5）和V-79（irs-1，irs-2，irs-3）细胞显示出不同的能力， 修复DNA dsb，在细胞水平上观察到的效果将是 与修复缺陷的程度相关， DNA和染色体修复的热量。 此外，实验将 进行了调查热辐射增敏修复熟练 细胞，并将热对诱导的影响，特别是 修复DNA（dsb）和染色体的辐射损伤。 所获得的结果有望评估DNA双链断裂在 热辐射增敏现象，并将其结合起来构建 这一现象背后的分子过程模型。

Hyperthermia is increasingly used in conjunction with radiotherapy for the treatment of human malignancy. The rationale for combining these two modalities in clinical protocols for the treatment of cancer rests on the observation that heat radiosensitizes and kills preferentially cells that are resistant to radiation alone. Elucidation of the molecular mechanism(s) underlying heat radiosensitization might provide information useful in the development of such combined treatment protocols. The long term objective of the present proposal is, therefore, to identify the molecular processes that underlie the phenomenon of heat induced radiosensitization and to elucidate the mechanism(s) involved. The central hypothesis on which this proposal rests is that heat sensitizes cells to radiation by increasing the probability of conversion of DNA double strand breaks (dsb) to lethal chromosome aberrations. The enhancement in the conversion probability of DNA dsb to chromosome aberrations is assumed to be caused either by alterations in chromatin structure and function, known to occur after acute exposures to heat, and/or by a reduction in the efficacy of repair. Alterations in chromatin structure and function, invoked to explain radiosensitization induced by pre-irradiation exposure to heat at 43-45.5 degrees C, may lead either to structural instability of irradiated DNA molecules, or to a decrease in the accessibility of radiation induced DNA dsb to repair enzymes that results in an increase in residual chromosome damage. Reduction in the efficacy of the repair system is mainly invoked to explain radiosensitization by postirradiation exposure to heat at 41-43 degrees C. The importance of DNA dsb in heat radiosensitization will be evaluated with radiation sensitive mutants showing reduced ability to repair this lesion, whereas alterations in the conversion of DNA dsb to chromosome damage will be assessed by measuring, on the one hand, induction and repair of DNA dsb using the non-unwinding filter elution technique or pulse field gel electrophoresis and, on the other hand, induction and repair of chromosome damage in interphase cells using the technique of premature chromosome condensation (PCC). Specifically, experiments will be carried out to investigate heat radiosensitization in radiation sensitive mutants of CHO (xrs-5) and V-79 (irs-1, irs-2, irs-3) cells that show different ability to repair DNA dsb, and the effect observed at the cell level will be correlated with the degree of repair deficiency as well as with the effect of heat on DNA and chromosome repair. Furthermore, experiments will be carried out to investigate heat radiosensitization in repair proficient cells and to correlate the effect of heat on the induction and particularly on the repair of radiation damage in the DNA (dsb) and the chromosomes. The results obtained are expected to evaluate the importance of DNA dsb in the phenomenon of heat radiosensitization and will be combined to construct models of the molecular processes underlying this phenomenon.