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Multitargeted tyrosine kinase inhibitors (TKIs) are a new and promising class of therapeutic agents for the treatment of cancer. We are interested in identifying an effective TKI for the treatment of pediatric acute myelogenous leukemia (AML). We evaluated the antitumor activity of four TKIs imatinib, dasatinib, sorafenib and sunitinib in a panel of human AML cell lines, which represent different FAB and cytogenetic subtypes of AML (HL-60, Kasumi-1, KG-1, NB4, ML-2, MV4, THP-1, U937 and Mo7e). Using an MTT assay (72h exposure; 3 independent experiments), sorafenib and sunitinib exhibited more potent anti-proliferative effects in all cell lines than imatinib and dasatinib, which inhibit a narrower spectrum of kinases, with IC50 values ranging 0.0020 μM to 13 μM for the former. The two most sensitive cells lines to sorafenib and sunitinib were Kasumi-1 (IC50 values of 40 nM and 23 nM) and MV4 (IC50 values of 2 nM and 7 nM), which possessed activating mutations of c-KIT and FLT-3 genes, respectively. In a more sensitive cell line (MV4), sorafenib and sunitinib promoted apoptosis (Annexin V + PI staining) in 50% of cells between 0.05 - 0.1 μM (72h exposure; 2 independent experiments) and increased the percentage of cells in G0/G1 phase of the cell cycle; in a less sensitive cell line (NB4; IC50 values of 7 nM and 13 nM), apopotosis was observed in 100% of cells at drug concentrations > 5 μM, but no effect on cell cycle distribution was observed, suggesting that cell cycle arrest may play a role in response to the anti-proliferative effect of these TKIs. Consistent with the presence of an activating mutation, Kasumi-1 and MV4 cells had activated pCKIT and pFLT-3, respectively. The nine AML cell lines showed different levels of constitutive activation of MAPK, PI3K, and STAT signaling pathways by western blot analysis (2 independent experiments). Sorafenib and sunitinib inhibited phosphorylation of the down stream effector protein ERK in the more sensitive cell lines (MV4 and Kasumi-1) and in a cell line with intermediate sensitivity (KG-1; IC50 values 2.7 nM and 1.1 nM)), but not in a cell line of least sensitivity (NB4) at concentrations comparable to IC50 values for anti-proliferative effects; neither sorafenib nor sunitinib exhibited inhibitory effects on pAKT in the four cell lines above. In conclusion, sorafenib and sunitinib showed more potent antitumor effects than imatinib and dasatinib in AML cell lines, with potent activity against cell lines with c-KIT and FLT-3 activating mutations. Further evaluation of TKIs in combination with chemotherapy or other moleculary targeted agents may represent a promising treatment strategy in pediatric AML and warrants further investigation.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA