Abstract 1807: Characterization of a novel FLT3 inhibitor in AML cell lines

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Acute myeloid leukemia (AML) is a hematologic malignancy that is characterized by increased myeloproliferation and a block in differentiation of progenitor cells, leading to infiltration of immature blasts in the bone marrow and peripheral blood. FMS-like tyrosine kinase-3 (FLT3) is a receptor tyrosine kinase expressed in hematopoietic progenitor cells. Approximately 30% of AML cases harbor a mutation in the FLT3 gene leading to constitutive activation of FLT3. The most commonly observed mutation occurs in the juxtamembrane domain as an internal tandem duplication (FLT3-ITD) of variable length sequence repeats. In addition, activating mutations in the kinase domain are observed in 7-10% of patients. The presence of FLT3-ITD mutations confers a poor prognosis, and thus many studies are directed at developing and testing novel FLT3 inhibitors for the treatment of AML. A number of clinical trials are now underway studying tyrosine kinase inhibitors (TKI) that target FLT3. There have been limitations in the responses observed in patients on these trials related to insufficient achievement of FLT3 inhibition and the development of drug resistance through a variety of mechanisms. This includes resistance conferring point mutations that appear in patients following drug treatment, as well as selection for cells with activation of parallel signaling pathways. Therefore, the search for novel TKIs that overcome some of these mechanisms and the discovery of additional targets for the treatment of AML are necessary to improve the cure rate of this disease. TTT-3002 is a multi-targeted kinase inhibitor that has activity against FLT3-ITD. Here we report the results of the characterization of this compound in a panel of AML cell lines. TTT-3002 has potent activity against FLT3 phosphorylation in FLT3-ITD cell lines at subnanomolar concentrations and significantly decreases cell viability through the induction of apoptosis. Interestingly, TTT-3002 is highly active against cell lines with known activating or resistance mutations in the FLT3 gene, indicating the potential for broad clinical application. Furthermore, through analysis of TTT-3002 potency in cell lines cultured in human plasma preparations from healthy donors, we observed a 10-20 fold shift in IC50 values for FLT3 phosphorylation compared to cell culture media. These results suggest that TTT-3002 has reasonable protein binding, and may require lower doses than many other TKIs to achieve an effective concentration of free drug in plasma. Finally, we have found that 6 mg/kg bid in a solid dosing form is well tolerated in BALB/c mice, and it is sufficient to eliminate luciferase expressing Ba/F3 cells containing a FLT3-ITD mutation after 4 days of treatment. Continual dosing with TTT-3002 significantly prolongs tumor free survival over vehicle control treated mice (p<0.0001, n=10). These findings demonstrate the potential of TTT-3002 as a promising targeted therapeutic in the treatment of AML. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1807. doi:1538-7445.AM2012-1807