放射治疗广泛应用于晚期结直肠癌（CRC）的管理中。然而，安全辐射剂量限制了其临床疗效。通过干扰DNA修复来使肿瘤细胞对放射治疗敏感是克服这一限制的一种有前景的方法。BRCA1-BARD1复合物已被证明在同源重组（HR）DSB修复中发挥关键作用，其功能可能受到HERC2或BAP1的影响。累积的证据表明，泛素化-去泛素化平衡参与了这些过程，然而，尚未明确这些蛋白质在辐射后HR修复中的相互作用机制。通过活性基于谱学的筛选，我们确定了PT33作为HR修复抑制剂的活性物质。随后，我们揭示了BAP1作为PT33的一个新的分子靶点，通过CRISPR基于去泛素化酶的筛选方法。在机制上，PT33与BAP1的药理性共价抑制导致HERC2与BARD1竞争BRCA1相互作用，干扰HR修复。结果，PT33治疗可以显著提高CRC细胞对放射治疗的敏感性，无论是在体外还是体内。总的来说，这些发现为PT33诱导HR抑制提供了机制基础，并且可能指导有效的治疗策略。© 2023中国制药协会和中国医学科学院药物研究所。Elsevier B.V.生产和托管。

Radiotherapy is widely used in the management of advanced colorectal cancer (CRC). However, the clinical efficacy is limited by the safe irradiated dose. Sensitizing tumor cells to radiotherapy via interrupting DNA repair is a promising approach to conquering the limitation. The BRCA1-BARD1 complex has been demonstrated to play a critical role in homologous recombination (HR) DSB repair, and its functions may be affected by HERC2 or BAP1. Accumulated evidence illustrates that the ubiquitination-deubiquitination balance is involved in these processes; however, the precise mechanism for the cross-talk among these proteins in HR repair following radiation hasn't been defined. Through activity-based profiling, we identified PT33 as an active entity for HR repair suppression. Subsequently, we revealed that BAP1 serves as a novel molecular target of PT33 via a CRISPR-based deubiquitinase screen. Mechanistically, pharmacological covalent inhibition of BAP1 with PT33 recruits HERC2 to compete with BARD1 for BRCA1 interaction, interrupting HR repair. Consequently, PT33 treatment can substantially enhance the sensitivity of CRC cells to radiotherapy in vitro and in vivo. Overall, these findings provide a mechanistic basis for PT33-induced HR suppression and may guide an effective strategy to improve therapeutic gain.© 2023 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V.