Covalent Alkynylpyridopyrimidinones Targeting Cysteine 775 of the Epidermal Growth Factor Receptor Overcome Resistance to Current Therapies.

Inhibitors of epidermal growth factor receptor (EGFR) kinase activity are clinically effective treatments for lung cancers driven by activating mutations in EGFR. Resistance to inhibitors develops over time, frequently through further mutations in the kinase domain. On-target resistance to third-generation inhibitor osimertinib, commonly develops through C797S mutation that prevents covalent binding. There is an urgent need for new treatments for osimertinib-resistant EGFR mutants that retain the advantages of the covalent mechanism. Compounds were designed and synthesized to covalently inhibit EGFR through C775, a further cysteine residue we identified in the orthosteric site. Optimisation of the alkynylpyridopyrimidinone scaffold we discovered led to potent compounds that demonstrate inhibition of EGFR phosphorylation and tumor growth in all EGFR mutant cell lines. The covalent C775 mode-of-action was comprehensively established. This work demonstrates that covalent targeting of C775 is a viable mechanism for the treatment of pan-EGFR mutated cancers, particularly those resistant to current therapies.