Radiation Biology Section, Biomedical Physics Department, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia.
Experimental Radiation Oncology Department, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States.
Front Public Health. 2021 Jun 7;9:647563. doi: 10.3389/fpubh.2021.647563. eCollection 2021.
We tested the hypothesis that differences in DNA double-strand break (DSB) repair fidelity underlies differences in individual radiosensitivity and, consequently, normal tissue reactions to radiotherapy. Fibroblast cultures derived from a radio-sensitive (RS) breast cancer patient with grade 3 adverse reactions to radiotherapy were compared with normal control (NC) and hyper-radiosensitive ataxia-telangiectasia mutated (ATM) cells. DSB repair and repair fidelity were studied by Southern blotting and hybridization to repetitive sequence and to a specific 3.2-Mbp I restriction fragment on chromosome 21, respectively. Results for DNA repair kinetics using the I fidelity assay showed significant differences ( < 0.001) with higher levels of misrepaired (misrejoined and unrejoined) DSBs in RS and ATM compared with NC. At 24-h postradiation, the relative fractions of misrepaired DSBs were 10.64, 23.08, and 44.70% for NC, RS, and ATM, respectively. The assay showed significant ( < 0.05) differences in unrepaired DSBs only between the ATM and both NC and RS at the time points of 12 and 24 h. At 24 h, the relative percentages of DSBs unrepaired were 1.33, 3.43, and 12.13% for NC, RS, and ATM, respectively. The comparison between the two assays indicated an average of 5-fold higher fractions of misrepaired (I assay) than unrepaired ( assay) DSBs. In conclusion, this patient with increased radiotoxicity displayed more prominent misrepaired than unrepaired DSBs, suggesting that DNA repair fidelity is a potential marker for the adverse reactions to radiotherapy. More studies are required to confirm these results and further develop DSB repair fidelity as a hallmark biomarker for interindividual differences in radiosensitivity.
我们验证了这样一个假设，即个体间 DNA 双链断裂（DSB）修复保真度的差异是导致放射敏感性差异以及放疗后正常组织反应差异的基础。我们比较了一名放射敏感（RS）乳腺癌患者的成纤维细胞培养物（其对放疗有 3 级不良反应）与正常对照（NC）和超放射敏感共济失调毛细血管扩张突变（ATM）细胞。通过 Southern 印迹杂交和重复序列及特定的 21 号染色体 3.2-Mbp I 限制片段杂交分别研究了 DSB 修复和修复保真度。使用 I 保真度测定法研究 DNA 修复动力学的结果显示，RS 和 ATM 中的错误修复（错误连接和未连接）DSB 水平明显更高（<0.001）。在放射后 24 小时，NC、RS 和 ATM 的错误修复 DSB 相对分数分别为 10.64、23.08 和 44.70%。该测定法仅在 ATM 与 NC 和 RS 之间在 12 和 24 小时时在未修复 DSB 中显示出显著差异（<0.05）。在 24 小时时，NC、RS 和 ATM 的未修复 DSB 相对百分比分别为 1.33、3.43 和 12.13%。两种测定法的比较表明，错误修复（I 测定法）的分数平均比未修复（测定法）的 DSB 高 5 倍。总之，这个放射毒性增加的患者显示出更多的 DSB 错误修复而非未修复，表明 DNA 修复保真度是放疗不良反应的潜在标志物。需要进行更多的研究来确认这些结果，并进一步将 DSB 修复保真度作为放射敏感性个体间差异的标志性生物标志物进行开发。
