Allosteric kinase inhibitors offer a potentially complementary therapeutic strategy to ATP-competitive kinase inhibitors due to their distinct sites of target binding. In this study, we identify and study a mutant-selective EGFR allosteric inhibitor, JBJ-04-125-02, which as a single agent can inhibit cell proliferation and EGFR L858R/T790M/C797S signaling in vitro and in vivo . However, increased EGFR dimer formation limits treatment effi cacy and leads to drug resistance. Remarkably, osimertinib, an ATP-competitive covalent EGFR inhibitor, uniquely and signifi cantly enhances the binding of JBJ-04-125-02 for mutant EGFR. The combination of osimertinib and JBJ-04-125-02 results in an increase in apoptosis, a more effective inhibition of cellular growth, and an increased effi cacy in vitro and in vivo compared with either single agent alone. Collectively, our fi ndings suggest that the combination of a covalent mutant-selective ATP-competitive inhibitor and an allosteric EGFR inhibitor may be an effective therapeutic approach for patients with EGFR -mutant lung cancer. SIGNIFICANCE:The clinical effi cacy of EGFR tyrosine kinase inhibitors (TKI) in EGFR -mutant lung cancer is limited by acquired drug resistance, thus highlighting the need for alternative strategies to inhibit EGFR. Here, we identify a mutant EGFR allosteric inhibitor that is effective as a single agent and in combination with the EGFR TKI osimertinib.

Highlights d A comprehensive degrader molecule (PROTAC) library for KRAS G12C is described d Lead compound degrades GFP-KRAS G12C in a CRBNdependent manner d Challenges and solutions for achieving endogenous KRAS G12C degradation are discussed

Targeted covalent small molecules have shown promise for cancers driven by KRAS G12C. Allosteric compounds that access an inducible pocket formed by movement of a dynamic structural element in KRAS, switch II, have been reported, but these compounds require further optimization to enable their advancement into clinical development. We demonstrate that covalent quinazoline-based switch II pocket (SIIP) compounds effectively suppress GTP loading of KRAS G12C, MAPK phosphorylation, and the growth of cancer cells harboring G12C. Notably we find that adding an amide substituent to the quinazoline scaffold allows additional interactions with KRAS G12C, and remarkably increases the labeling efficiency, potency, and selectivity of KRAS G12C inhibitors. Structural studies using X-ray crystallography reveal a new conformation of SIIP and key interactions made by substituents located at the quinazoline 2-, 4-, and 7-positions. Optimized lead compounds in the quinazoline series selectively inhibit KRAS G12C-dependent signaling and cancer cell growth at sub-micromolar concentrations.

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