Unlocking novel E3 ligases for use in heterobifunctional PROTAC degraders is of high importance to the pharmaceutical industry. Over-reliance on the current suite of ligands used to recruit E3 ligases could limit the potential of their application. To address this, potent ligands for DCAF15 were optimized using cryo-EM supported, structure-based design to improve on micromolar starting points. A potent binder, compound 24, was identified and subsequently conjugated into PROTACs against multiple targets. Following attempts on degrading a number of proteins using DCAF15 recruiting PROTACs, only degradation of BRD4 was observed. Deconvolution of the mechanism of action showed that this degradation was not mediated by DCAF15, thereby highlighting both the challenges faced when trying to expand the toolbox of validated E3 ligase ligands for use in PROTAC degraders and the pitfalls of using BRD4 as a model substrate.

中文翻译：

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E3 连接酶 DCAF15 有效配体的优化及其在异双功能降解剂中的应用评估

解锁用于异双功能 PROTAC 降解剂的新型 E3 连接酶对于制药行业非常重要。过度依赖当前用于招募 E3 连接酶的配体套件可能会限制其应用潜力。为了解决这个问题，使用冷冻电镜支持的基于结构的设计对 DCAF15 的有效配体进行了优化，以改进微摩尔起点。一种有效的结合剂化合物24被鉴定出来，并随后结合到针对多个靶标的 PROTAC 中。在尝试使用 DCAF15 招募 PROTAC 降解多种蛋白质后，仅观察到 BRD4 的降解。作用机制的反卷积表明这种降解不是由 DCAF15 介导的，从而凸显了在尝试扩展用于 PROTAC 降解剂的经过验证的 E3 连接酶配体工具箱时所面临的挑战以及使用 BRD4 作为模型底物的陷阱。