HM43239 is a potent, orally bioavailable, and selective Type I FLT3 inhibitor with low nM IC50 values against FLT3 WT, ITD, and D835Y mutants. It effectively blocks downstream signaling (p-STAT5, p-ERK) and inhibits proliferation while inducing apoptosis in leukemic cells in vitro, supporting its research application in acute myeloid leukemia (AML).