Interference with DNA repair after ionizing radiation by a pyrrole-imidazole polyamide

Pyrrole-imidazole (Py–Im) polyamides are synthetic non-genotoxic minor groove-binding small molecules. We hypothesized that Py–Im polyamides can modulate the cellular response to ionizing radiation. Pre-treatment of cells with a Py-Im polyamide prior to exposure to ionizing radiation resulted in a delay in resolution of phosphorylated γ-H2AX foci, increase in XRCC1 foci, and reduced cellular replication potential. RNA-sequencing of cell lines exposed to the polyamide showed induction of genes related to the ultraviolet radiation response. We observed that the polyamide is almost 10-fold more toxic to a cell line deficient in DNA ligase 3 as compared to the parental cell line. Alkaline single cell gel electrophoresis reveals that the polyamide induces genomic fragmentation in the ligase 3 deficient cell line but not the corresponding parental line. The polyamide interferes directly with DNA ligation in vitro. We conclude that Py-Im polyamides may be further explored as sensitizers to genotoxic therapies.吡咯-咪唑（Py–Im）聚酰胺是一类人工合成的无遗传毒性的DNA小沟结合小分子。我们提出假说：Py–Im聚酰胺可调节细胞对电离辐射的应答反应。在接受电离辐射照射前用Py–Im聚酰胺预处理细胞，会导致磷酸化γ-H2AX灶点（phosphorylated γ-H2AX foci）的清除延迟、XRCC1灶点数量增加，并降低细胞增殖潜能。对经该聚酰胺处理的细胞系进行RNA测序（RNA-sequencing）分析，发现其诱导了与紫外线辐射应答相关的基因表达。我们观察到，与亲本细胞系相比，该聚酰胺对DNA连接酶3（DNA ligase 3）缺陷型细胞系的毒性高出近10倍。碱性单细胞凝胶电泳（alkaline single cell gel electrophoresis）实验显示，该聚酰胺可在DNA连接酶3缺陷型细胞系中诱导基因组片段化，但在对应的亲本细胞系中无此效应。体外实验证实，该聚酰胺可直接干扰DNA连接过程。综上，我们认为Py–Im聚酰胺有望作为遗传毒性治疗的增敏剂，开展进一步研究。