Fibroblast growth factor receptors (FGFRs) are tyrosine kinase receptors that play a role in cell proliferation, differentiation, migration, survival, and angiogenesis. Upon binding of extracellular signals, primarily fibroblast growth factors, FGFR dimerizes to promote the phosphorylation of downstream molecules and activation of the Ras-mitogen-activated protein kinase (MAPK) pathway. In some cancers, the FGFR signaling pathway is aberrant and disrupted, leading to unregulated cell proliferation and growth, including malignant cells. Alterations in the FGFR receptors, including mutations, amplifications, and fusions, are associated with a wide array of neoplasms, including prostate, urothelial, ovarian, breast, and liver cancer. In particular, FGFR2 fusion is closely related to intrahepatic cholangiocarcinoma: recent studies show that up to 45% of patients with intrahepatic cholangiocarcinoma exhibited gene rearrangements resulting in FGFR2 fusion proteins. Alterations in FGFR in tumors can lead to constitutive FGFR signaling, supporting the proliferation and survival of malignant cells. Infigratinib is a reversible, non-competitive inhibitor of all four FGFR subtypes – FGFR1, FGFR2, FGFR3, and FGFR4 – that blocks FGFR signaling and inhibits cell proliferation in cancer cell lines with activating FGFR amplification, mutations, or fusions. Out of the four FGFR subtypes, infigratinib has the highest affinity for FGFR1, FGFR2, and FGFR3. Infigratinib binds to the allosteric site between the two kinase lobes of the FGFR – or more specifically, to the ATP-binding cleft. Binding to this cleft prevents autophosphorylation of the receptor and blocks downstream signaling cascades that would otherwise activate MAPK.
Infigratinib is an anti-tumour agent that works to suppress tumour growth in cholangiocarcinoma. It exhibits anti-tumour activity in mouse and rat xenograft models of human tumours with activating FGFR2 or FGFR3 alterations, such as FGFR2-TTC28 or FGFR2-TRA2B fusions. In clinical trials, patients with cholangiocarcinoma who were treated with infigratinib had an overall response rate of 23% – where one patient had a complete response – and a duration of response of 5.5 months, with a range between 0.03 and 28.3 months. Some patients with cancers with FGFR mutations display intrinsic resistance to infigratinib, leading to negligible therapeutic efficacy: investigations are ongoing to target molecular pathways to combat drug resistance.