TG101348: A Dual-Acting JAK2/FLT3 Small Molecule Kinase Inhibitor for the Treatment of AML.

A number of genetic mutations have been identified in the development of acute myeloid leukemia (AML), including mutations in the proto-oncogene N-RAS, p53, c-Kit and the FMS-like receptor tyrosine kinase 3 (FLT3). FLT3 plays an important role in the formation of early stem/progenitor cells during hematopoietic development. FLT3 is mutated in ∼30% of AMLs, with internal tandem duplications (ITD) in the juxtamembrane region being the most common (FLT3-ITD). This results in constitutive activation of FLT3 kinase activity and patients harboring such mutations do not respond well to conventional treatments and demonstrate poor clinical prognosis. There is growing evidence that the JAK/STAT pathway may also contribute to the etiology of AML. For instance, the JAK2 V617F point mutation driving various chronic myeloproliferative disorders (MPDs) has recently been detected in de novo AMLs and STAT3/5 phosphorylation is commonly elevated in AML patients. We have developed TG101348, a selective JAK2/FLT3 small molecule inhibitor which has the potential to treat both MPDs and AML. In in vitro based assays, TG101348 was capable of inhibiting the proliferation of human AML cell lines representing a variety of mutations. In AML cell lines carrying mutations in N-RAS such as KG-1, HL-60, and THP-1, EC₅₀s ranged from ∼300 nM-1000 nM. In TF-1a AML cells, which harbor a mutation in p53, TG101348 demonstrated an EC₅₀ of 493 nM. Most interestingly, for these cell lines, FLT3/VEGFR2 specific small molecule inhibitors such SU5416 were significantly less effective, demonstrating EC₅₀s that were generally >10-fold higher. TG101348 was most potent against the FLT3-ITD positive cells lines, MV411 (EC₅₀=57 nM) and MOLM13 (EC₅₀=69 nM). In MV411 cells, TG101348 functionally inhibited FLT3 autophosphorylation, and phosphorylation of downstream intermediates including STAT5, ERK, and AKT. In a human MV411 xenograft models, oral administration (120mg/kg, BID) of TG101348 resulted in complete regression of the subcutaneously implanted MV411 tumors. Taken together, these data suggest that the dual-acting JAK2/FLT3 kinase inhibitor TG101348 may have a therapeutic advantage in that it has the capacity to block multiple pathways critical for dysregulated cell proliferation and survival in AML.