Department of Oncology, University of Oxford, Oxford, United Kingdom.
CRUK/MRC Oxford Institute for Radiation Oncology, University of Oxford, Oxford, United Kingdom.
Cancer Res. 2021 Apr 15;81(8):2128-2141. doi: 10.1158/0008-5472.CAN-20-2860. Epub 2021 Jan 28.
Inhibition of IGF receptor (IGF1R) delays repair of radiation-induced DNA double-strand breaks (DSB), prompting us to investigate whether IGF1R influences endogenous DNA damage. Here we demonstrate that IGF1R inhibition generates endogenous DNA lesions protected by 53BP1 bodies, indicating under-replicated DNA. In cancer cells, inhibition or depletion of IGF1R delayed replication fork progression accompanied by activation of ATR-CHK1 signaling and the intra-S-phase checkpoint. This phenotype reflected unanticipated regulation of global replication by IGF1 mediated via AKT, MEK/ERK, and JUN to influence expression of ribonucleotide reductase (RNR) subunit RRM2. Consequently, inhibition or depletion of IGF1R downregulated RRM2, compromising RNR function and perturbing dNTP supply. The resulting delay in fork progression and hallmarks of replication stress were rescued by RRM2 overexpression, confirming RRM2 as the critical factor through which IGF1 regulates replication. Suspecting existence of a backup pathway protecting from toxic sequelae of replication stress, targeted compound screens in breast cancer cells identified synergy between IGF inhibition and ATM loss. Reciprocal screens of ATM-proficient/deficient fibroblasts identified an IGF1R inhibitor as the top hit. IGF inhibition selectively compromised growth of ATM-null cells and spheroids and caused regression of ATM-null xenografts. This synthetic-lethal effect reflected conversion of single-stranded lesions in IGF-inhibited cells into toxic DSBs upon ATM inhibition. Overall, these data implicate IGF1R in alleviating replication stress, and the reciprocal IGF:ATM codependence we identify provides an approach to exploit this effect in ATM-deficient cancers. SIGNIFICANCE: This study identifies regulation of ribonucleotide reductase function and dNTP supply by IGFs and demonstrates that IGF axis blockade induces replication stress and reciprocal codependence on ATM. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/8/2128/F1.large.jpg.
抑制 IGF 受体 (IGF1R) 会延迟辐射诱导的 DNA 双链断裂 (DSB) 的修复，这促使我们研究 IGF1R 是否会影响内源性 DNA 损伤。在这里，我们证明 IGF1R 抑制会产生受 53BP1 体保护的内源性 DNA 损伤，表明存在复制不足的 DNA。在癌细胞中，IGF1R 的抑制或耗尽会延迟复制叉的前进，同时激活 ATR-CHK1 信号和 S 期内检查点。这种表型反映了 IGF1 通过 AKT、MEK/ERK 和 JUN 介导的对全局复制的意外调节，从而影响核糖核苷酸还原酶 (RNR) 亚基 RRM2 的表达。因此，IGF1R 的抑制或耗竭会下调 RRM2，从而影响 RNR 功能并扰乱 dNTP 供应。通过 RRM2 的过表达可以挽救 IGF1R 抑制或耗竭导致的叉进展延迟和复制应激的标志性特征，这证实了 RRM2 是 IGF1 调节复制的关键因素。由于怀疑存在保护复制应激毒性后果的备用途径，我们在乳腺癌细胞中进行了靶向化合物筛选，发现 IGF 抑制与 ATM 缺失之间存在协同作用。在 ATM 功能正常/缺失成纤维细胞中的相互筛选确定了 IGF1R 抑制剂为最佳命中物。IGF 抑制选择性地损害 ATM 缺失细胞和球体的生长，并导致 ATM 缺失异种移植物的消退。这种合成致死效应反映了 IGF 抑制细胞中的单链损伤在 ATM 抑制后转化为毒性 DSB。总的来说，这些数据表明 IGF1R 缓解了复制应激，并且我们确定的 IGF:ATM 相互依赖提供了一种利用 ATM 缺失癌症中这种效应的方法。意义：本研究鉴定了 IGF 对核糖核苷酸还原酶功能和 dNTP 供应的调节作用，并证明 IGF 轴阻断会诱导复制应激和对 ATM 的相互依赖性。图形摘要：http://cancerres.aacrjournals.org/content/canres/81/8/2128/F1.large.jpg。
