Design, Synthesis, and Biological Evaluation of Indolin-2-one Derivatives as Novel Covalent Pan-FGFR Inhibitors for Overcoming Clinical Resistance

Oncogenic FGFR alterations drive the development of multiple cancers. However, acquired resistance to clinically approved inhibitors mediated by gatekeeper and molecular brake mutations poses a major therapeutic challenge. Herein, we describe the structure-based discovery of (Z)-3-(amino(phenyl)methylene)indolin-2-one derivatives as potent covalent pan-FGFR inhibitors. The representative compound, 9v, displayed high potency against FGFR1/2/3/4 (IC50 = 8.6, 5.4, 4.4, and 6.9 nM, respectively) and potent antiproliferative effects across a panel of FGFR-driven cancer cell lines (IC50 = 0.3−6.1 nM). Notably, 9v retained high efficacy against common resistance mutations, including the gatekeeper (FGFR1 V561M, FGFR2 V564F, and FGFR3 V555M) and “molecular brake” (FGFR2 N549K) variants, with IC50 values of <0.1 nM. Covalent modification of FGFR3 by 9v was confirmed through MALDI-TOF-MS and LC−MS/MS-based site mapping. Furthermore, 9v exhibited significant antitumor efficacy in an RT112/84 bladder cancer xenograft model, providing a promising strategy to overcome resistance in FGFR-targeted therapy.