HM43239 is an orally active and selective FLT3 inhibitor with IC 50 s of 1.1 nM, 1.8 nM and 1.0 nM for FLT3 WT, FLT3 internal tandem duplication (ITD) and FLT3 D835Y kinases, respectively. HM43239 directly inhibits the kinase activity of FLT3 as a reversible Type I inhibitor and effectively modulates downstream p-STAT5 and p-ERK. HM43239 also demonstrated inhibition of SYK, JAK1/2 and TAK1. HM43239 inhibits the proliferation and induces the apoptosis of leukemic cells [1] [2] [3].