ARID1A is frequently mutated in colorectal cancer (CRC) cells. Loss of ARID1A function compromises DNA damage repair and increases the reliance of tumor cells on ATR-dependent DNA repair pathways. Here, we investigated the effect of ionizing radiation (IR), in combination with ATR inhibitors (ATRi) in CRC cell lines with proficient and deficient ARID1A. The concept of selective vulnerability of ARID1A deficient CRC cells to ATRi was further tested in an ex vivo system by using the ATP-tumor chemosensitivity assay (ATP-TCA) in cells from untreated CRC patients, with and without ARID1A expression. We found selective sensitization upon ATRi treatment as well as after combined treatment with IR (P<0.001), especially in ARID1A deficient CRC cells (P <0.01). Knock-down of ARID1B further increased the selective radiosensitivity effect of ATRi in ARID1A negative cells (P<0.01). Mechanistically, ATRi abrogates the G2 checkpoint (P<0.01) and homologous recombination repair (P<0.01) in ARID1A deficient cells. Most importantly, ex-vivo experiments showed that ATRi had the highest radiosensitizing effect in ARID1A negative cells from CRC patients. Collectively, our results generate pre-clinical and clinical mechanistic rationale for assessing ARID1A defects as a biomarker for ATR inhibitor response as a single agent, or in a synthetic lethal approach in combination with IR.

ARID1A 在结直肠癌 (CRC) 细胞中经常发生突变。ARID1A 功能的丧失会损害 DNA 损伤修复并增加肿瘤细胞对 ATR 依赖性 DNA 修复途径的依赖。在这里，我们研究了电离辐射 (IR) 与 ATR 抑制剂 (ATRi) 组合在具有精通和缺乏 ARID1A 的 CRC 细胞系中的作用。ARID1A 缺陷型 CRC 细胞对 ATRi 的选择性脆弱性的概念在离体通过使用来自未经治疗的 CRC 患者的细胞中的 ATP 肿瘤化学敏感性测定 (ATP-TCA) 系统，有和没有 ARID1A 表达。我们发现 ATRi 治疗以及与 IR 联合治疗后的选择性致敏（P<0.001），尤其是在 ARID1A 缺陷型 CRC 细胞中（P<0.01）。敲低 ARID1B 进一步增加了 ATRi 在 ARID1A 阴性细胞中的选择性放射敏感性效应（P<0.01）。从机制上讲，ATRi 消除了 ARID1A 缺陷细胞中的 G2 检查点 (P<0.01) 和同源重组修复 (P<0.01)。最重要的是，离体实验表明，ATRi 在 CRC 患者的 ARID1A 阴性细胞中具有最高的放射增敏作用。总的来说，我们的结果为评估 ARID1A 缺陷作为 ATR 抑制剂反应的生物标志物作为单一药物或与 IR 结合使用的合成致死方法提供了临床前和临床机制基本原理。