Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 106 91 Stockholm, Sweden.
Biomedical Physics Division, Faculty of Physics, University of Warsaw, 02-093 Warsaw, Poland.
DNA Repair (Amst). 2023 Oct;130:103554. doi: 10.1016/j.dnarep.2023.103554. Epub 2023 Aug 9.
Cells exposed to densely ionising high and scattered low linear energy transfer (LET) radiation (50 % dose of each) react more strongly than to the same dose of each separately. The relationship between DNA double strand break location inside the nucleus and chromatin structure was evaluated, using high-resolution transmission electron microscopy (TEM) in breast cancer MDA-MB-231 cells at 30 min post 5 Gy. Additionally, response to high and/or low LET radiation was assessed using single (1 ×1.5 Gy) versus fractionated dose delivery (5 ×0.3 Gy). By TEM analysis, the highest total number of γH2AX nanobeads were found in cells irradiated with alpha radiation just prior to gamma radiation (called mixed beam), followed by alpha, then gamma radiation. γH2AX foci induced by mixed beam radiation tended to be surrounded by open chromatin (lighter TEM regions), yet foci containing the highest number of beads, i.e. larger foci representing complex damage, remained in the heterochromatic areas. The γH2AX large focus area was also greater in mixed beam-treated cells when analysed by immunofluorescence. Fractionated mixed beams given daily induced the strongest reduction in cell viability and colony formation in MDA-MB-231 and osteosarcoma U2OS cells compared to the other radiation qualities, as well as versus acute exposure. This may partially be explained by recurring low LET oxidative DNA damage by every fraction together with a delay in recompaction of chromatin after high LET, demonstrated by low levels of heterochromatin marker H3K9me3 at 2 h after the last mixed beam fraction in MDA-MB-231. In conclusion, early differences in response to complex DNA damage may lead to a stronger cell kill induced by fractionated exposure, which suggest a therapeutic potential of combined high and low LET irradiation.
细胞暴露于高剂量密集电离和低剂量散射线（LET）辐射（每种剂量的 50%）比单独接受每种剂量的辐射反应更强烈。使用高分辨率透射电子显微镜（TEM）在乳腺癌 MDA-MB-231 细胞中，在接受 5 Gy 辐射后 30 分钟评估细胞核内 DNA 双链断裂位置与染色质结构之间的关系。此外，通过单次（1×1.5 Gy）与分次剂量（5×0.3 Gy）评估对高和/或低 LET 辐射的反应。通过 TEM 分析，在伽马射线照射之前用阿尔法射线照射的细胞中发现总γH2AX 纳米珠数量最多（称为混合束），其次是阿尔法射线，然后是伽马射线。混合束辐射诱导的γH2AX 焦点往往被开放染色质（较浅的 TEM 区域）包围，但包含最多珠子的焦点，即代表复杂损伤的较大焦点，仍保留在异染色质区域。混合束辐射处理的细胞中γH2AX 大焦点区域也通过免疫荧光分析更大。与其他辐射质量相比，与急性暴露相比，每天给予分次混合束会导致 MDA-MB-231 和骨肉瘤 U2OS 细胞的细胞活力和集落形成下降最强，这可能部分是由于每个分次都会引起低 LET 氧化 DNA 损伤，以及高 LET 后染色质的重新浓缩延迟，这在 MDA-MB-231 中最后一次混合束分次后 2 小时异染色质标记 H3K9me3 水平较低时得到证明。总之，对复杂 DNA 损伤的早期反应差异可能导致分次照射引起更强的细胞杀伤，这表明高和低 LET 联合照射具有治疗潜力。
