FLT3

Class

Covalent small molecule kinase inhibitor

Pathway

FLT3 signal transduction

FLT3 (FMS-like tyrosine kinase 3) is a cell-surface receptor tyrosine kinase expressed mainly on early blood-forming (hematopoietic) progenitor cells. Its natural ligand, FLT3 ligand, binds the receptor and triggers dimerization and autophosphorylation, activating downstream signaling cascades—chiefly the RAS/MAPK and PI3K/AKT pathways, along with STAT5—that promote cell survival and proliferation. In a substantial proportion of acute myeloid leukemia (AML) cases, FLT3 carries activating mutations, most commonly internal tandem duplications (ITD) or point mutations in the kinase domain, that lock the receptor into a constitutively active state independent of ligand binding. This drives uncontrolled proliferation of leukemic blasts and is associated with a more aggressive disease course. Small-molecule kinase inhibitors that occupy the ATP-binding pocket of FLT3 block this constitutive signaling, reducing the proliferative and survival drive of the malignant clone. Because FLT3 signaling also has physiological roles in normal blood cell development, inhibiting it can affect healthy hematopoiesis, which is a consideration in how these agents are used. FLT3 inhibition is a well-established mechanism in AML treatment strategies, illustrating the broader principle of targeting an oncogenic kinase driver while managing effects on the normal tissue compartment that depends on the same signaling node.