👤 N Bardeesy

Pan-fibroblast growth factor receptor (FGFR) inhibitors, targeting FGFR1-3 or FGFR1-4, are Food and Drug Administration-approved for FGFR2-driven cholangiocarcinoma. However, acquired resistance and dose-limiting toxicities from systemic FGFR inhibition constrain efficacy. Lirafugratinib (RLY-4008), a first-in-class FGFR2-selective inhibitor with activity against resistance-associated FGFR2 kinase domain mutations, shows promise in patients with FGFR2-altered solid tumors (ReFocus trial, NCT04526106). Defining acquired resistance mechanisms to selective FGFR2 targeting is essential for therapeutic development. Circulating tumor DNA (ctDNA) samples from 28 patients treated with lirafugratinib (16 FGFR inhibitor-naive, 12 FGFR inhibitor-refractory) were analyzed using targeted next-generation sequencing. Genomic alterations observed were compared with those reported in prior studies of pan-FGFR inhibitor resistance and validated in preclinical models. Polyclonal FGFR2 kinase domain mutations and receptor tyrosine kinase-mitogen activated protein kinase (RTK-MAPK) bypass alterations emerged as common lirafugratinib resistance mechanisms in the FGFR inhibitor-naive context (8/16 and 9/16 patients, respectively). Resistance profiles differed markedly from pan-FGFR inhibitors, with decreased FGFR2 V565F/L and N550H/K mutations, increased M538I and L618F mutations, and more frequent RTK-MAPK bypass alterations. The variant allele fraction was typically higher for FGFR2 kinase domain mutations, consistent with these alterations serving as primary resistance drivers. Preclinical studies confirmed differential sensitivity of these FGFR2 mutations to lirafugratinib. Importantly, lirafugratinib demonstrated clinical efficacy in the FGFR inhibitor-refractory setting, with ctDNA dynamics showing resolution of multiple FGFR2 mutations and persistence or emergence of others. Lirafugratinib retains activity against multiple mutations that confer clinical resistance to pan-FGFR inhibitors. However, diverse resistance mechanisms, including various kinase domain mutations and RTK-MAPK bypass alterations, remain challenges in the treatment of FGFR2-altered tumors, even with selective FGFR2 kinase inhibition. Show less

FGFR2 and FGFR3 show oncogenic activation in many cancer types, often through chromosomal fusion or extracellular domain mutation. FGFR2 and FGFR3 alterations are most prevalent in intrahepatic cholangiocarcinoma (ICC) and bladder cancers, respectively, and multiple selective reversible and covalent pan-FGFR tyrosine kinase inhibitors (TKI) have been approved in these contexts. However, resistance, often due to acquired secondary mutations in the FGFR2/3 kinase domain, limits efficacy. Resistance is typically polyclonal, involving a spectrum of different mutations that most frequently affect the molecular brake and gatekeeper residues (N550 and V565 in FGFR2). Here, we characterize the activity of the next-generation covalent FGFR inhibitor, KIN-3248, in preclinical models of FGFR2 fusion+ ICC harboring a series of secondary kinase domain mutations, in vitro and in vivo. We also test select FGFR3 alleles in bladder cancer models. KIN-3248 exhibits potent selectivity for FGFR1-3 and retains activity against various FGFR2 kinase domain mutations, in addition to being effective against FGFR3 V555M and N540K mutations. Notably, KIN-3248 activity extends to the FGFR2 V565F gatekeeper mutation, which causes profound resistance to currently approved FGFR inhibitors. Combination treatment with EGFR or MEK inhibitors potentiates KIN-3248 efficacy in vivo, including in models harboring FGFR2 kinase domain mutations. Thus, KIN-3248 is a novel FGFR1-4 inhibitor whose distinct activity profile against FGFR kinase domain mutations highlights its potential for the treatment of ICC and other FGFR-driven cancers. Show less