Department of Biochemistry, Indian Institute of Science, Bangalore, India.
Department of Studies in Chemistry, ManasaganFindo-frgotri, University of Mysore, Mysuru, India.
Mol Carcinog. 2020 Jun;59(6):618-628. doi: 10.1002/mc.23186. Epub 2020 Mar 18.
Targeting DNA repair with small-molecule inhibitors is an attractive strategy for cancer therapy. Majority of DNA double-strand breaks in mammalian cells are repaired through nonhomologous end-joining (NHEJ). It has been shown that small-molecule inhibitors of NHEJ can block efficient repair inside cancer cells, leading to cell death. Previously, we have reported that SCR7, an inhibitor of NHEJ can induce tumor regression in mice. Later studies have shown that different forms of SCR7 can inhibit DNA end-joining in Ligase IV-dependent manner. Recently, we have derivatized SCR7 by introducing spiro ring into core structure. Here, we report the identification of a novel inhibitor of NHEJ, named SCR130 with 20-fold higher efficacy in inducing cytotoxicity in cancer cell lines. SCR130 inhibited DNA end-joining catalyzed by rat tissue extract. Specificity analysis revealed that while SCR130 was specific to Ligase IV, it showed minimal or no effect on Ligase III and Ligase I mediated joining. Importantly, SCR130 exhibited the least cytotoxicity in Ligase IV-null cell line as compared with wild type, confirming Ligase IV-specificity. Furthermore, we demonstrate that SCR130 can potentiate the effect of radiation in cancer cells when used in combination with γ-radiation. Various cellular assays in conjunction with Western blot analysis revealed that treatment with SCR130 led to loss of mitochondrial membrane potential leading to cell death by activating both intrinsic and extrinsic pathways of apoptosis. Thus, we describe a novel inhibitor of NHEJ with higher efficacy and may have the potential to be developed as cancer therapeutic.
靶向 DNA 修复的小分子抑制剂是癌症治疗的一种有吸引力的策略。哺乳动物细胞中的大多数 DNA 双链断裂是通过非同源末端连接（NHEJ）修复的。已经表明，NHEJ 的小分子抑制剂可以阻断癌细胞内的有效修复，导致细胞死亡。之前，我们已经报道了 NHEJ 的抑制剂 SCR7 可以在小鼠中诱导肿瘤消退。后来的研究表明，不同形式的 SCR7 可以以依赖 Ligase IV 的方式抑制 DNA 末端连接。最近，我们通过在核心结构中引入螺环来衍生 SCR7。在这里，我们报告了一种新型 NHEJ 抑制剂 SCR130 的鉴定，它在诱导癌细胞系细胞毒性方面的功效比 SCR7 高 20 倍。SCR130 抑制了大鼠组织提取物催化的 DNA 末端连接。特异性分析表明，虽然 SCR130 特异性地针对 Ligase IV，但它对 Ligase III 和 Ligase I 介导的连接几乎没有或没有影响。重要的是，与野生型相比，SCR130 在 Ligase IV 缺失细胞系中表现出最小的细胞毒性，证实了 Ligase IV 的特异性。此外，我们证明，当与 γ 辐射联合使用时，SCR130 可以增强癌细胞中的辐射效应。各种细胞测定结合 Western blot 分析表明，用 SCR130 处理会导致线粒体膜电位丧失，通过激活细胞凋亡的内在和外在途径导致细胞死亡。因此，我们描述了一种新型的 NHEJ 抑制剂，具有更高的功效，并且可能有潜力开发为癌症治疗药物。
