Wang Y, Pantelias G E, Iliakis G
Thomas Jefferson University, Department of Radiation Oncology and Nuclear Medicine, Philadelphia, PA 19107.
Int J Radiat Biol. 1994 Aug;66(2):133-42. doi: 10.1080/09553009414551031.
We measured the contribution of increased DNA double-strand break (dsb) and interphase chromosome break induction in BrdU-mediated radiosensitization in exponentially growing (DNA dsb measurements only) and plateau-phase Chinese hamster ovary cells using an approach developed by Webb et al. (1993). The approach is based on the scavenging capacity of acetone for hydrated electrons, which are thought to react with bromine and form excess DNA and chromosome damage in BrdU-containing cells. In irradiated exponentially growing cells, acetone (1 M) removes the majority of excess DNA dsb induced in the presence of 4 microM BrdU (approximately 40% replacement of thymidine by BrdU), but does not restore cell radiosensitivity to the levels observed in BrdU-free cells. Although BrdU radiosensitizes cells by decreasing both D0 and Dq of the survival curve, acetone only restores D0 to levels measured in BrdU-free cells, but leaves Dq at levels measured in BrdU-containing cells. In plateau-phase cells, acetone removes the majority of excess DNA dsb and interphase chromosome breaks induced in the presence of 4 microM BrdU (approximately 50% replacement of thymidine by BrdU) but has only a small effect on BrdU-mediated radiosensitization to killing. These observations suggest that increased DNA damage production has a variable contribution in BrdU radiosensitization: it constitutes a major, albeit not the sole, component in the radiosensitization of exponentially growing cells, but only a minor component in the radiosensitization of plateau-phase cells. The results suggest that BrdU radiosensitization does not derive exclusively from increased DNA damage induction and support our previous hypothesis invoking repair inhibition/damage fixation as a component in the mechanism of radiosensitization. The results further suggest that repair inhibition is a major component in BrdU radiosensitization in exponentially growing cells, but the main cause of radiosensitization in plateau-phase cells.
我们采用Webb等人（1993年）开发的方法，测量了在指数生长期（仅测量DNA双链断裂）和平期中国仓鼠卵巢细胞中，BrdU介导的放射增敏作用中DNA双链断裂（dsb）增加和间期染色体断裂诱导的贡献。该方法基于丙酮对水合电子的清除能力，水合电子被认为会与溴反应，在含BrdU的细胞中形成过量的DNA和染色体损伤。在受辐照的指数生长期细胞中，丙酮（1 M）可去除在存在4 microM BrdU（约40%的胸腺嘧啶被BrdU取代）时诱导产生的大部分过量DNA双链断裂，但不能将细胞放射敏感性恢复到无BrdU细胞中观察到的水平。尽管BrdU通过降低存活曲线的D0和Dq使细胞放射增敏，但丙酮仅将D0恢复到无BrdU细胞中测量的水平，而Dq仍保持在含BrdU细胞中测量的水平。在平期细胞中，丙酮可去除在存在4 microM BrdU（约50%的胸腺嘧啶被BrdU取代）时诱导产生的大部分过量DNA双链断裂和间期染色体断裂，但对BrdU介导的放射增敏杀伤作用影响较小。这些观察结果表明，DNA损伤产生增加在BrdU放射增敏中具有可变的贡献：它是指数生长期细胞放射增敏的主要成分，尽管不是唯一成分，但在平期细胞放射增敏中只是次要成分。结果表明，BrdU放射增敏并非完全源于DNA损伤诱导增加，支持了我们之前提出的将修复抑制/损伤固定作为放射增敏机制组成部分的假设。结果进一步表明，修复抑制是指数生长期细胞中BrdU放射增敏的主要成分，但却是平期细胞放射增敏的主要原因。
