Discovery of CZY43 as a new small-molecule degrader of pseudokinase HER3.

The pseudokinase HER3 emerges as a promising anti-cancer target, especially for HER2-driven breast cancer and EGFR-mediated non-small cell lung cancer. However, it is challenging to target HER3 by ATP-competitive small molecules because HER3 is catalytically impaired. Herein, we report the discovery of a series of HER3 degraders by connecting a HER3 binder bosutinib with a hydrophobic tag adamantane. The optimal compound CZY43 effectively induced HER3 degradation in dose- and time-dependent manners in breast cancer SKBR3 cells. Mechanistic studies revealed compound CZY43 to induce HER3 degradation via autophagy. Importantly, compound CZY43 potently inhibited HER3-dependent signaling, cancer cell growth and cell adhesion, and was more potent than bosutinib. This study further suggested that HER3 can be modulated by small-molecule degraders, and compound CZY43 can serve as a lead compound for further optimization.