Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Oxford OX3 7DQ, UK.
Nitric Oxide. 2013 Nov 1;34:47-55. doi: 10.1016/j.niox.2013.04.005. Epub 2013 Apr 26.
Nitric oxide (NO) is a very effective radiosensitizer of hypoxic mammalian cells, at least as efficient as oxygen in enhancing cell death in vitro. NO may induce cell death through the formation of base lesions which are difficult to repair, and if they occur within complex clustered damage common to ionizing radiation, they may lead to replication-induced DNA strand breaks. It has previously been shown that 8-azaguanine and xanthine result from the reaction of guanine radicals with nitric oxide. We have now shown that adenine radicals also react with NO to form hypoxanthine and 8-azaadenine. Cells irradiated in exponential growth in the presence of NO are twice as radiosensitive compared to those irradiated in anoxia alone, whereas confluent cells are less radiosensitive to (•)NO. In addition, the numbers of DNA double strand breaks observed as γH2AX staining following radiosensitization by NO, are higher in exponential cells than in confluent cells. DNA damage, detected as 53BP1 foci, is also higher in HF-19 cells expressing Cyclin A, a marker for cells in S and G2 phases of the cell cycle, following radiosensitization by NO. RAD51 foci are highest in V79-4 cells irradiated in the presence of NO compared to in anoxia, 24h after radiolysis. This work presents evidence that radiosensitization of cells by NO is in part through the formation of specific DNA damage, difficult to repair, which in dividing cells may induce the formation of stalled replication forks and as a consequence replication-induced DNA strand breaks which may lead to cell death.
一氧化氮 (NO) 是一种非常有效的缺氧哺乳动物细胞放射增敏剂，至少与氧一样有效，可增强体外细胞死亡。NO 可能通过形成难以修复的碱基损伤诱导细胞死亡，如果这些损伤发生在电离辐射常见的复杂聚集损伤中，则可能导致复制诱导的 DNA 链断裂。先前已经表明，8-氮鸟嘌呤和黄嘌呤是鸟嘌呤自由基与一氧化氮反应的产物。我们现在已经表明，腺嘌呤自由基也与 NO 反应形成次黄嘌呤和 8-氮杂腺嘌呤。与单独缺氧照射相比，在存在 NO 的指数生长中照射的细胞对放射增敏的敏感性增加了一倍，而汇合细胞对 (•)NO 的放射敏感性降低。此外，在用 NO 进行放射增敏后，作为 γH2AX 染色观察到的 DNA 双链断裂数量，在指数细胞中比在汇合细胞中更高。在用 NO 进行放射增敏后，作为 53BP1 焦点检测到的 DNA 损伤在表达细胞周期 S 和 G2 期标志物细胞周期蛋白 A 的 HF-19 细胞中也更高。与缺氧相比，在用 NO 辐照后 24 小时，RAD51 焦点在 V79-4 细胞中最高。这项工作提供了证据表明，NO 对细胞的放射增敏作用部分是通过形成特定的 DNA 损伤，难以修复，在分裂细胞中，这些损伤可能导致停滞的复制叉的形成，并且作为后果，复制诱导的 DNA 链断裂，可能导致细胞死亡。
