Proteolysis targeting chimeras (PROTACs) represent a new class of promising therapeutic modalities. PROTACs hijack E3 ligases and the ubiquitin-proteasome system (UPS), leading to selective degradation of the target proteins. However, only a very limited number of E3 ligases have been leveraged to generate effective PROTACs. Herein, we report that the KEAP1 E3 ligase can be harnessed for targeted protein degradation utilizing a highly selective, noncovalent small-molecule KEAP1 binder. We generated a proof-of-concept PROTAC, MS83, by linking the KEAP1 ligand to a BRD4/3/2 binder. MS83 effectively reduces protein levels of BRD4 and BRD3, but not BRD2, in cells in a concentration-, time-, KEAP1- and UPS-dependent manner. Interestingly, MS83 degrades BRD4/3 more durably than the CRBN-recruiting PROTAC dBET1 in MDA-MB-468 cells and selectively degrades BRD4 short isoform over long isoform in MDA-MB-231 cells. It also displays improved antiproliferative activity than dBET1. Overall, our study expands the limited toolbox for targeted protein degradation.

中文翻译：

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利用 E3 连接酶 KEAP1 进行靶向蛋白质降解

蛋白水解靶向嵌合体 (PROTAC) 代表了一类新的有前途的治疗方式。PROTAC 劫持 E3 连接酶和泛素-蛋白酶体系统 (UPS)，导致目标蛋白的选择性降解。然而，只有非常有限的 E3 连接酶被用来产生有效的 PROTAC。在此，我们报道了 KEAP1 E3 连接酶可用于利用高选择性、非共价小分子 KEAP1 结合物进行靶向蛋白质降解。我们通过将 KEAP1 配体连接到 BRD4/3/2 结合物生成了概念验证 PROTAC，MS83。MS83 以浓度、时间、KEAP1 和 UPS 依赖性方式有效降低细胞中 BRD4 和 BRD3 的蛋白质水平，但不降低 BRD2 的蛋白质水平。有趣的是，MS83 在 MDA-MB-468 细胞中比招募 CRBN 的 PROTAC dBET1 更持久地降解 BRD4/3，并且在 MDA-MB-231 细胞中选择性地降解 BRD4 短亚型而不是长亚型。它还显示出比 dBET1 更好的抗增殖活性。总的来说，我们的研究扩展了靶向蛋白质降解的有限工具箱。