Discovery of Potent and Selective Pyrrolo[2,3-d]pyrimidine Derivatives as Fourth-Generation EGFR Inhibitors Targeting Triple Mutations

Three generations of EGFR tyrosine kinase inhibitors (EGFR-TKIs) have shown clinical efficacy in nonsmall cell lung cancer (NSCLC), but acquired resistance mutations─especially the cis-EGFR^T790M/C797S─remain a major challenge. Here, we report the identification of a series of pyrrolo[2,3-d]pyrimidine derivatives that inhibit C797S-mediated EGFR triple mutants. Among them, compound 31r shows subnanomolar IC₅₀ values against Ba/F3 EGFR^{19del/T790M/C797S} and Ba/F3 EGFR^{L858R/T790M/C797S}, while sparing wild-type EGFR. Its binding mode with EGFR^{19del/T790M/C797S} was revealed by a cocrystal structure, providing structural insights into its potency and selectivity. Compound 31r also displays excellent kinome selectivity and drug-like properties, including good metabolic stability (T_1/2 = 5.9 h) and oral bioavailability (F = 24%). Most importantly, 31r significantly suppressed tumor growth in PC-9 EGFR^{19del/T790M/C797S} xenograft models, achieving regression at 80 mg/kg once daily. These results highlight 31r as a promising lead compound for overcoming resistance associated with third-generation EGFR-TKIs and support its further development for drug-resistant NSCLC.