A PROTAC-inspired bifunctional small molecule recruits CDK6 to target EYA2 degradation and suppress breast tumor growth.

Cyclin-dependent kinase 6 (CDK6) has been reported to exert tumor-suppressive functions through its non-enzymatic activity and promotes the degradation of the oncogenic driver EYA2. This suggests a potential strategy for targeted protein degradation by exploiting endogenous protein-protein interactions. Here, we report the design and synthesis of a bifunctional small molecule, EC21, capable of simultaneously engaging CDK6 and EYA2. Structure-guided design based on the reported binding modes of palbociclib and the EYA2 inhibitor ETC-616 enabled the identification of EC21 as a lead compound. Biological studies demonstrated that EC21 effectively reduced EYA2 protein levels in breast cancer cells in a time- and concentration-dependent manner through a ubiquitin-proteasome-dependent process. Mechanistic investigations indicated that EC21 enhances the interaction between CDK6 and EYA2, thereby promoting EYA2 degradation. Functional analyses further revealed that EC21 disrupts DNA damage repair pathways and significantly suppresses breast cancer cell proliferation. Importantly, EC21 exhibited pronounced antitumor activity in a syngeneic breast cancer mouse model and reduced EYA2 protein levels in tumor tissues without apparent toxicity. Collectively, these findings demonstrate that pharmacological stabilization of the CDK6-EYA2 interaction represents a feasible strategy for inducing EYA2 degradation and provides a potential therapeutic approach for EYA2-driven breast cancer.