Identification and characterization of highly potent and specific FLT3 kinase inhibitors effective against FLT3-driven leukemia in culture and in vivo

5990 Mutations resulting in constitutive activation of the receptor tyrosine kinase FLT3 occur in 25-40% of patients with Acute Myeloid Leukemia (AML) and correlate with poor prognosis. Although several ATP-competitive inhibitors of FLT3 have progressed into the clinic, recent experience suggests that increases in compound potency and specificity may be necessary for the use of small molecule inhibitors of FLT-3 in AML treatment. To this end, we have identified and characterized a series of compounds that have high affinity for wild type and mutant forms of FLT3 observed in human AML (K d range: 0.15 - 50 nM). This series of compounds also demonstrates remarkable specificity for the kinases FLT3, KIT and/or PDGFR (confirmed across a broad panel of up to 170 independent kinase assays). The AML-derived human cell line MV4;11 expresses a commonly observed Internal Tandem Duplication (ITD) mutation that results in constitutive activation of FLT3 and FLT3-driven proliferation. Exposure of MV4;11 cells to these compounds demonstrates dose-dependent inhibition of both proliferation and FLT3 receptor autophosphorylation (IC 50 range: 0.2 - 50 nM). The compounds are orally bioavailable and have favorable pharmacokinetic properties in mice. Preliminary xenograft studies in nude mice show that the compounds have potent anti-tumor effects in MV4;11 solid tumor and leukemia models.