Implications of the ATR Checkpoint Kinase in Radiation and Targeted Therapies

总结 ATR是人类细胞中DNA损伤反应的主要调节因子。ATR抑制 使癌细胞对辐射和DNA损伤药物敏感，提供了一种有吸引力的策略， 改进放疗和化疗。此外，在具有显著内在 基因组不稳定，ATR的抑制导致大量DNA损伤，从而杀死癌细胞 利用自身基因组的脆弱性确定企业的内在负债 使癌细胞依赖ATR生存将极大地促进ATR的使用 靶向治疗和放射治疗中的抑制剂。几种ATR抑制剂已经在临床试验中 并显示出良好的疗效。然而，尽管初步试验取得了成功， 目前还不清楚ATR抑制剂是否以及如何广泛用于靶向不同类型的基因组 癌细胞的脆弱性最近的研究表明，R环，一组转录 含有DNA：RNA杂交体和置换的单链DNA的中间体是DNA的来源。 癌细胞基因组的不稳定性。在导致这种应用的初步研究中，我们发现 ATR被R环激活，在抑制R环相关DNA中起关键作用， 损害此外，我们发现，癌症相关的RNA剪接因子突变促进R 环形成并使细胞对ATR抑制敏感。这些令人兴奋的发现使我们 假设异常R环积累是癌细胞新的可靶向倾向。 此外，ATR是R环的关键传感器和R环相关DNA的关键抑制子 这使得ATR抑制成为靶向癌细胞的R环易感性的有吸引力的方式。到 这些假设，在目标1，我们将阐明ATR的机制，由R 通过一条之前未知的路径循环在目标2中，我们将确定ATR如何保护 通过三种新的机制，基因组对抗R环。在目标3中，我们将测试ATR是否 抑制剂可以在体外和体内选择性地消除携带高水平R环的癌细胞。 体内，并鉴定标志物以预测肿瘤的R环倾向。此外，我们将调查 放射是否可用于在癌细胞中诱导R环并使高R环肿瘤敏感 ATR抑制剂。总之，这些研究将从机械上解释R环是如何被感知的。 细胞中的ATR，揭示了ATR如何使细胞能够科普R环相关的基因组不稳定性， 并解决ATR是否可以有效地利用癌细胞的R环易感性 治疗中的抑制剂。这些研究不仅将大大促进我们对 R环和ATR信号传导的基础生物学，也改变了ATR抑制剂的使用 靶向治疗和放射治疗。

Summary ATR is a master regulator of the DNA damage response in human cells. Inhibition of ATR sensitizes cancer cells to radiation and DNA-damaging drugs, providing an attractive strategy to improve radiotherapy and chemotherapy. Furthermore, in cancer cells with significant intrinsic genomic instability, inhibition of ATR results in massive DNA damage, thereby killing cancer cells by exploiting the vulnerability of their own genomes. Identification of the intrinsic liabilities of cancer cells that render them reliant on ATR for survival will greatly facilitate the use of ATR inhibitors in targeted therapy and radiotherapy. Several ATR inhibitors are already on clinical trials and showing promising efficacy. However, despite the success of initial trials, it is still largely unknown whether and how ATR inhibitors can be broadly used to target different types of genomic vulnerabilities of cancer cells. Recent studies suggested that R loops, a group of transcription intermediates containing DNA:RNA hybrids and displaced single-stranded DNA, are a source of genomic instability in cancer cells. In the preliminary studies leading to this application, we find that ATR is activated by R loops and it plays a key role in suppressing R loop-associated DNA damage. Furthermore, we show that cancer-associated RNA splicing factor mutations promote R loop formation and render cells sensitive to ATR inhibition. These exciting findings lead us to hypothesize that aberrant R loop accumulation is a new targetable liability of cancer cells. Furthermore, ATR is a key sensor of R loops and a critical suppressor of R loop-associated DNA damage, making ATR inhibition an attractive way to target the R-loop liability of cancer cells. To these hypotheses, in Aim 1, we will elucidate the mechanisms by which ATR is activated by R loops through a previously unknown pathway. In Aim 2, we will determine how ATR protects the genome against R loops through three novel mechanisms. In Aim 3, we will test whether ATR inhibitors can selectively eliminate cancer cells harboring high levels of R loops in vitro and in vivo, and identify markers to predict the R-loop liability of tumors. In addition, we will investigate whether radiation can be used to induce R loops in cancer cells and sensitize R loop-high tumors to ATR inhibitors. Together, these studies will mechanistically explain how R loops are sensed by ATR in cells, reveal how ATR enables cells to cope with R loop-associated genomic instability, and address whether the R-loop liability of cancer cells can be effectively exploited by ATR inhibitors in therapy. These studies will not only significantly advance our understanding of the fundamental biology of R loops and ATR signaling, but also transform the use of ATR inhibitors in targeted therapy and radiotherapy.