A Dichloropropionamide-Substituted Diaminopyrimidine EGFR-TKI Overcomes Osimertinib Resistance in NSCLC via Dual Anchoring at Ser797 and Met793

The tertiary C797S mutation in the EGFR tyrosine kinase domain disrupts osimertinib binding, driving resistance in NSCLC. We designed a series of novel diaminopyrimidine derivatives to establish the interaction with Ser797. H8b potently inhibited EGFR L858R/T790M/C797S kinase with an IC 50 of 3.86 nM (30-fold lower than osimertinib) and suppressed both double mutant NCI-H1975 and triple mutant H1975-M3 cells with IC 50 s of 0.03 μM and 0.57 μM (14- and 11-fold reductions over osimertinib, respectively). Cocrystal X-ray analysis revealed that H8b forms a “two-point tethering” in the ATP pocket with a hydrogen bond between its dichloropropionamide oxygen and Ser797, complemented by a hydrogen bond between terminal N of the piperazine ring and Phe795. Mechanistically, H8b suppressed EGFR phosphorylation and downstream AKT, STAT3, and MAPK signaling, inhibiting proliferation, invasion, and migration. In vivo, H8b achieved 71.15% tumor inhibition in H1975-M3 xenografts. This study identifies H8b as a promising EGFR-TKI overcoming C797S-mediated resistance.