Asp2215, A Novel Flt3/Axl Inhibitor: Preclinical Evaluation In Acute Myeloid Leukemia (Aml).

7070 Background: Activating mutations in FLT3 receptor tyrosine kinase, characterized by internal tandem duplication (ITD) and tyrosine kinase domain point mutations near position D835, have been identified in up to 30% of AML patients. These mutations are associated with poor prognosis. ASP2215 is a novel small molecule tyrosine kinase inhibitor, currently under clinical trial evaluation. Methods: The kinase inhibition profile was investigated using enzyme assays. Antiproliferative activity was evaluated against several AML cell lines with assessment of the inhibition of pFLT3 and downstream molecules using Western blot and flow cytometry. Antitumor activity was evaluated in nude mice transplanted with MV4-11 AML cells. The pharmacokinetics in xenografted mice was also investigated. Results: Of the 78 tyrosine kinases tested, ASP2215 inhibited FLT3, LTK, ALK, and AXL kinases by over 50% at 1 nM with an IC50 value of 0.29 nM for FLT3, approximately 800-fold more potent than for c-KIT, the inhibition of which is linked to a potential risk of myelosuppression. ASP2215 inhibited the growth of MV4-11 cells, which harbor FLT3-ITD, with an IC50 value of 0.92 nM, accompanied with inhibition of pFLT3, pAKT, pSTAT5, pERK, and pS6. ASP2215 also inhibited the growth of Ba/F3 cells expressing FLT3-ITD and/or FLT3-D835 mutation with similar activity. Colony formation of human granulocyte-macrophage decreased to 58% in response to ASP2215 at 100 nM, more than 100-fold higher than required for MV4-11. In MV4-11 xenografted-mice, the concentration of ASP2215 in tumors was more than 20-fold higher than that in plasma with oral administration of ASP2215 at 10 mg/kg for 4 days. Treatment of ASP2215 for 28 days resulted in dose-dependent inhibition of MV4-11 tumor growth and induced complete tumor regression at more than 6 mg/kg. Further, ASP2215 decreased tumor burden in bone marrow and prolonged the survival of mice intravenously transplanted with MV4-11 cells. Conclusions: ASP2215, a FLT3/AXL inhibitor, showed potent antileukemic activity against AML with either or both FLT3-ITD and FLT3-D835 mutations. These findings support the development of ASP2215 for the potential use in treating AML.