Simultaneous inhibition of driver and effector kinases promotes potent growth arrest of AML cells in vitro and in viv

Acute myelogenous leukemia (AML) is caused by successive mutations acquired in hematopoietic progenitor cells that lead to the overpopulation of the bone marrow and peripheral blood by immature myeloid cells. The overall survival rate with current therapy is 25%, which decreases steadily with patient age. While numerous genetic alterations occur in AML, mutations to the FMS-like tyrosine kinase 3 (FLT3) are the most common, occurring in 30% of patients. Two types of FLT3 mutations occur in AML: internal tandem duplications (ITDs) and tyrosine kinase domain point mutations. FLT3 mutations drive AML pathogenesis and numerous small molecule kinase inhibitors have been designed as therapeutics for FLT3-mutated AML. However, these FLT3 inhibitors have had limited clinical success owing to lack of potency in vivo, toxicity, or short duration of response due to the development of resistance.;Constitutively active FLT3 links to multiple downstream tyrosine kinases that are critical for AML cell survival and proliferation. Gene silencing studies have shown that several of these FLT3-associated kinases are individually crucial for FLT3 oncogenic potential, including SYK, FES, and the myeloid Src-family kinase, HCK. These previous observations raised the hypothesis that a small molecule inhibitor with a selectivity profile targeting FLT3 plus these associated kinases may be a potent AML drug lead with reduced propensity for acquired resistance. To test this hypothesis, we screened a library of N-phenylbenzamide compounds and identified a compound with three-digit nanomolar activity against each of these AML-associated kinases in vitro. Remarkably, this compound (TL02-59) inhibited FLT3-ITD+ cell growth in the picomolar range. Furthermore, TL02-59 demonstrated efficacy against primary AML bone marrow samples and a mouse xenograft model of AML. To explore the full range of targets for TL02-59, we performed a KINOMEscan assay and determined the expression of the TL02-59 target kinases in primary AML bone marrow samples. We discovered that while myeloid Src-family kinases HCK, LYN and FGR are critical to TL02-59 efficacy, inhibition of SYK, FES and the Ser/Thr kinases p38alpha and TAOK3 also plays a role. Future work will explore the advantages of this potent, multi-targeted kinase inhibitor in combating acquired resistance in AML.