A potent and highly selective irreversible HER2 inhibitor for treating HER2-driven cancers

Abstract HER2 amplification and mutations occur frequently in multiple human cancers, including breast, ovarian, gastric and lung cancers. Despite HER2 being one of the earliest oncogenic drivers discovered, HER2 inhibitors have had limited clinical success compared to inhibitors of other kinase oncogenes. This has been attributed to a compensatory mechanism present in HER2-driven cancers that significantly raises the exposure threshold for durable pharmacological inactivation of HER2 signaling in vivo. This requires a therapeutic index far exceeding that of available pan-ERBB and HER2 inhibitors, all of which are hampered by dose-limiting side effects from collateral or residual EGFR inhibition.To address this critical unmet need, we present a novel irreversible HER2 inhibitor, ENT-H1, discovered via artificial intelligence-enabled chemistry. ENT-H1 potently inhibits wild-type and mutated HER2, including the recalcitrant exon 20 insertion mutations, while sparing wild-type EGFR. In a panel of Ba/F3 cells whose growth is driven by HER2 or EGFR expression, ENT-H1 displayed low nanomolar potency across 23 representative HER2 mutations, while showing minimum effect on the growth of Ba/F3 EGFR cells. This exquisite selectivity was confirmed by comparing the sensitivity of cancer cell lines that over-express HER2 (e.g. BT-474 and Calu-3) and EGFR (e.g. A431), and translated into a high in vitro therapeutic index when ENT-H1 was evaluated in a gastrointestinal toxicity assay. In vivo, ENT-H1 demonstrated strong efficacy and better tolerability than benchmark HER2 inhibitors in multiple HER2-amplified or -mutated tumor models, including those bearing HER2 exon 20 insertion mutations (e.g. A775G776insYVMA and G776VC). Treatment with ENT-H1 led to significant tumor regression without causing body-weight loss. In these models, ENT-H1 showed robust and rapid pharmacodynamic effect in reducing phosphorylated HER2 and downstream phosphorylated AKT and ERK levels, confirming that the antitumor effect was a result of targeted inhibition of HER2 oncogenic signaling. Further analysis showed that ENT-H1 concentrations were significantly higher in xenograft tumors than in plasma; this distribution profile has the potential to maximize target engagement in the tumor while minimizing untoward systemic side effects. These data establish that ENT-H1 is a safe and effective HER2 small-molecule inhibitor. With 100-fold selectivity against the highly homologous EGFR and a desirable pharmacokinetic profile, ENT-H1 represents a promising drug candidate to realize the full therapeutic potential of a HER2-targeting agent while avoiding side effects associated with EGFR inhibition. Citation Format: Chunmei Zhao, Lana Kulyk, Iriny Botrous, Kelly Chen, Chang Zhao, Afsheen Banisadr, Mary L. Anderson, Fred Manby, Tom Miller, Chao Zhang, Laurent Gomez, Zhongdong Huang. A potent and highly selective irreversible HER2 inhibitor for treating HER2-driven cancers. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4034.