HM43239 is an orally active small molecule inhibitor of FLT3 that selectively inhibits not only FLT3 wild type, ITD mutants or TKD mutations, but also FLT3 ITD/TKD double mutations. 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, known to be involved in tumor cell proliferation and/or differentiation HM43239 monotherapy induced dose-dependent regression of tumor growth in FLT3 wild-type and FLT3 mutated leukemia cancer cell line.