Targeting FLT3 Phosphorylation and Signaling in Acute Myeloid Leukemia

• Published in: Blood 2007-11, Vol.110 (11), p.912-912
• Main Authors: Ikeda, Alan K., Judelson, Dejah, Li, Junling, Wei, Ru Qi, Tapang, Paul, Davidsen, Steven K., Albert, Dan H., Glaser, Keith B., Fu, Cecilia, Sakamoto, Kathleen M.
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V110.11.912.912

Children with acute myeloid leukemia (AML) have 50% overall survival despite aggressive chemotherapy and bone marrow transplantation. Similarly, only one third of adults diagnosed with AML will be cured. AML blast cells from approximately 30% of patients express a constitutively active receptor tyrosine kinase, FLT3-ITD, which contains internal tandem duplications in the juxtamembrane domain. Patients with FLT3-ITD have a worse prognosis. ABT-869 is a multi-targeted small molecule inhibitor of receptor tyrosine kinases and is a potent inhibitor of FLT3, c-Kit, and members of the VEGF and PDGF receptor families. We previously demonstrated that ABT-869 in vitro induces apoptosis of AML cell lines harboring the FLT3-ITD and primary AML cells, and in vivo in tumors from MV-411 xenograft models. Phosphorylation of FLT3 and activation of downstream signaling molecules, STAT5 and ERK, were inhibited by ABT-869 in a concentration-dependent manner. Cells were also stained with Annexin V-FITC and propidium iodide, and analyzed using FACS. ABT-869 induced apoptosis, caspase-3 activation, and PARP cleavage after 48 hours. Toxic effects were not observed on normal hematopoietic progenitor cells in methylcellulose-based colony assays at concentrations that were effective in AML cells. To examine the effects of ABT-869 in vivo, we treated SCID mice injected with MV-411 with oral preparations of ABT-869. Complete regression of MV4-11 tumors was observed in mice treated with ABT-869 at 20 and 40 mg/kg/day. No adverse effects were detected in the peripheral blood counts, bone marrow, spleen or liver. Tumors from mice treated with ABT-869 showed decreased proliferation by Ki67 and increased apoptosis by TUNEL staining. We also observed that the mice treated with ABT-869 the day after injection of AML cells remained tumor-free for over 3 months in contrast to the mice receiving the vehicle alone. Inhibition of FLT3 phosphorylation was demonstrated in the tumors from mice treated with ABT-869. ABT-869 also suppresses the growth of Molm-13 (human AML cell line that expresses both FLT3-ITD and wt FLT3) at an IC50 between 1 and 10nM. To examine the effects of ABT-869 in vivo, we employed a murine bone marrow transplantation model. After chemical ablation of the bone marrow, SCID mice were injected with Molm-13 cells through the tail vein to allow engraftment. We observed that mice treated with an oral preparation of ABT-869 at 40 mg/kg/day prevented the engraftment of Molm-13 cel