Biochemical kinase assays for PHI-101 have been performed on 9 different FLT3 mutants and wild type FLT3. Cellular potencies of PHI-101 have also been assessed using various patient-derived AML cells as well as MV4-11, MOLM14 and BaF3 cell lines transformed with human FLT3 mutants including single mutations [FLT3(ITD), FLT3(D835Y)], double or triple mutations [FLT3(ITD/D835Y), FLT3(ITD/F691L), FLT3(ITD/F691L/D835Y)]. PHI-101 possesses excellent in vitro and in vivo activities against not only FLT3 single activating mutations (ITD or TKD mutants) but also FLT3 double (ITD/D835Y or ITD/F691L) and triple (ITD/D835Y/F691L) resistant mutations with no pronounced toxicities. Preclinical evaluation of PHI-101 showed clear evidence of antileukemic activity and improved efficacy in both in vitro and in vivo models.