Department of Radiation Oncology, University Hospital Zurich, University of Zurich, Switzerland.
Paul Scherrer Institute, Villigen, Switzerland.
Radiother Oncol. 2015 Sep;116(3):374-80. doi: 10.1016/j.radonc.2015.08.014. Epub 2015 Aug 25.
Non-homologous end-joining (NHEJ) and homologous recombination (HR) contribute to the repair of irradiation-induced DNA double-strand breaks (DSBs). We investigated the impact of the two major DSB repair machineries for cellular survival of human tumor cells in response to proton- and photon-irradiation.
DNA damage repair and cell survival were analyzed in wildtype, HR- and NHEJ-repair-compromised and pharmacologically DNA-PKcs-inhibited human tumor cells in response to clinically relevant, low-linear energy transfer proton- and 200-keV photon-irradiation.
Pharmacological inhibition of DNA-PKcs strongly radiosensitized lung adenocarcinoma and glioblastoma cells to photon- but to a much lower extent to proton-irradiation. Enhanced radiosensitization correlated with strongly delayed repair kinetics with elevated amounts of γH2AX foci after photon-irradiation. Interestingly, we observed reduced phosphorylation of DNA-PKcs at Ser-2056 and Thr-2609 clusters after proton-irradiation compared to photon-irradiation. In contrast, A549 cells depleted of the RAD51 recombinase were markedly hypersensitive to proton-irradiation in comparison with control cells. Likewise, human BRCA2-deficient ovarian carcinoma cells were hypersensitive toward proton- in comparison with photon-irradiation.
A differential DNA damage response with enhanced susceptibility of HR-deficient tumor cells to proton-irradiation and increased sensitivity of photon-irradiated tumor cells to NHEJ inhibitors were demonstrated.
非同源末端连接（NHEJ）和同源重组（HR）有助于修复辐射诱导的 DNA 双链断裂（DSB）。我们研究了两种主要的 DSB 修复机制对人肿瘤细胞在质子和光子照射下细胞存活的影响。
在野生型、HR 和 NHEJ 修复缺陷型以及用药物抑制 DNA-PKcs 的人肿瘤细胞中，分析了 DNA 损伤修复和细胞存活情况，这些细胞对临床相关的低线性能量转移质子和 200keV 光子照射有反应。
药物抑制 DNA-PKcs 强烈增敏肺腺癌细胞和神经胶质瘤细胞对光子的放射敏感性，但对质子的增敏作用要低得多。增强的放射敏感性与明显延迟的修复动力学相关，在光子照射后γH2AX 焦点的数量增加。有趣的是，与光子照射相比，我们观察到在质子照射后，DNA-PKcs 的 Ser-2056 和 Thr-2609 簇的磷酸化减少。相比之下，与对照细胞相比，A549 细胞中 RAD51 重组酶的耗竭使其对质子照射明显敏感。同样，BRCA2 缺陷型卵巢癌细胞对质子照射比光子照射更敏感。
我们证明了 HR 缺陷型肿瘤细胞对质子照射的敏感性增加，以及光子照射的肿瘤细胞对 NHEJ 抑制剂的敏感性增加的差异 DNA 损伤反应。
