Pemigatinib

Fibroblast growth factor receptor (FGFR) is a receptor tyrosine kinase involved in activating signalling pathways that promote cell proliferation, survival, and migration, as well as growth arrest and cellular differentiation. The initiation of the FGFR signalling pathway requires the binding of its natural ligand, fibroblast growth factor (FGF). Once FGF binds to the extracellular ligand-binding domain of the receptor, FGFRs dimerize and autophosphorylate the tyrosine residue in the intracellular tyrosine-kinase domain, leading to the activation of the tyrosine kinase. Downstream cascades involve phosphorylation of multiple intracellular signalling proteins, such as phosphatidylinositol 3 kinase (PI3K)-AKT and RAS/mitogen-activated protein kinase (MAPK), and phospholipase Cγ, which activates the protein kinase C pathway. FGFR-mediated pathway ultimately promotes cell growth, differentiation, survival, angiogenesis, and organogenesis, depending on cell type. Expressed in different isoforms in various tissues and cell lines, FGFRs are not constitutively active in normal cells. However, FGFR1, FGFR2, or FGFR3 alterations in certain tumours can lead to constitutive FGFR activation and aberrant FGFR signalling, supporting the proliferation and survival of malignant cells.

Pemigatinib inhibits FGFR1, FGFR2, and FGFR3, blocking their signalling pathways and decreasing cell viability in cancer cell lines with activating FGFR amplification and fusions that resulted in constitutive activation of FGFR signalling. Genetic alterations in FGFR1, FGFR2, and FGFR3 (such as amplification, missense, or fusion mutations in the coding region) leading to constitutive activation of FGFR signalling pathways are observed in various tumours. However, alterations in FGFR genes are demonstrated in selected patients and do not always imply oncogene development. Therefore, it is imperative that fusion or rearrangement of FGFRs are demonstrated through tests prior to initiation of drug therapy.