Poly(ADP-ribose)ylation (PARylation) by PAR polymerase 1 (PARP1) and PARylation removal by poly(ADP-ribose) glycohydrolase (PARG) critically regulate DNA damage responses; yet, conflicting reports obscure PARG biology and its impact on cancer cell resistance to PARP1 inhibitors. Here, we found that PARG expression is upregulated in many cancers. We employed chemical library screening to identify and optimize methylxanthine derivatives as selective bioavailable PARG inhibitors. Multiple crystal structures reveal how substituent positions on the methylxanthine core dictate binding modes and inducible-complementarity with a PARG-specific tyrosine clasp and arginine switch, supporting inhibitor specificity and a competitive inhibition mechanism. Cell-based assays show selective PARG inhibition and PARP1 hyperPARylation. Moreover, our PARG inhibitor sensitizes cells to radiation-induced DNA damage, suppresses replication fork progression and impedes cancer cell survival. In PARP inhibitor-resistant A172 glioblastoma cells, our PARG inhibitor shows comparable killing to Nedaplatin, providing further proof-of-concept that selectively inhibiting PARG can impair cancer cell survival.

中文翻译：

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选择性小分子 PARG 抑制剂导致复制叉停滞和癌细胞死亡。

PAR 聚合酶 1 (PARP1) 的聚 (ADP-核糖) 化 (PARylation) 和聚 (ADP-核糖) 糖水解酶 (PARG) 的 PARylation 去除严格调节 DNA 损伤反应；然而，相互矛盾的报道掩盖了 PARG 生物学及其对癌细胞对 PARP1 抑制剂耐药性的影响。在这里，我们发现 PARG 表达在许多癌症中上调。我们采用化学库筛选来鉴定和优化甲基黄嘌呤衍生物作为选择性生物可利用 PARG 抑制剂。多个晶体结构揭示了甲基黄嘌呤核心上的取代基位置如何决定结合模式以及与 PARG 特异性酪氨酸扣和精氨酸开关的诱导互补性，支持抑制剂特异性和竞争性抑制机制。基于细胞的测定显示选择性 PARG 抑制和 PARP1 hyperPARylation。而且，我们的 PARG 抑制剂使细胞对辐射诱导的 DNA 损伤敏感，抑制复制叉进展并阻碍癌细胞存活。在 PARP 抑制剂耐药的 A172 胶质母细胞瘤细胞中，我们的 PARG 抑制剂显示出与奈达铂相当的杀伤力，提供了选择性抑制 PARG 可以损害癌细胞存活的进一步概念验证。