Discovery of potent and selective HER2 PROTAC degrader based Tucatinib with improved efficacy against HER2 positive cancers

HER2 is a validated therapeutic target for HER2 positive breast cancer and gastric cancer. TKIs have significantly improved the prognosis of patients with HER2 positive cancer. However, the pan-HER TKIs always caused gastrointestinal and skin side effects, and acquired drug resistance inevitable compromised their therapeutic efficacy. Herein, we describe the discovery of the first potent and selective HER2 PROTAC degrader based Tucatinib with improved antitumor activity in vitro and in vivo. The preferred selective HER2 PROTAC, CH7C4, efficiently degraded HER2 with DC₅₀ of 69 nM and D_max of 96%, and inhibited the proliferation of BT-474 cells with IC₅₀ of 0.047 ± 0.006 nM via long lasting HER2 degradation and strong repression of downstream pathway. Moreover, CH7C4 had acceptable pharmacokinetic profiles with a half-life of 5.31 h, and significantly inhibited the growth of BT-474 xenografts in vivo with TGI of 73%. As the first selective HER2 PROTAC degrader with better activity in vitro and in vivo than Tucatinib, CH7C4 provides new insights into the development of new therapeutic strategy for HER2 positive cancer.