7019 Background: Tyrosine kinases (TK) are important for most cellular functions and require stringent control and regulation. C- Kit, a TK and transmembrane receptor for stem cell factor, plays a crucial role in hematopoiesis. Mutations of c-Kit can contribute to AML pathophysiology and have been associated with shorter survival and higher relapse risk following standard AML therapy. On the other hand, responses have been observed following TK inhibitor therapy such as imatinib. Identification of c-Kit or its pathways in AML leukemogenesis and development of new compounds targeting these mutations may therefore hold promise for therapy. Methods: APcK110 is the result of a structure-based design of c-Kit inhibitors and was derived of a set of compounds with favorable IC50 values in a c-Kit kinase assay. Here we present results of the activity and mechanism of action of APcK110. We used the mastocytosis cell line HMC1.1 carrying an activating c-Kit mutation and two AML lines (OCIM2 and OCI/AML3) as well as primary samples from patients with AML. Results: We demonstrate that: (1) APcK110 inhibits proliferation of all three cell lines in a dose dependent fashion using an MTT assay. Inhibition of proliferation is most significant in the SCF-dependent cell line OCI/AML3; (2) inhibition of OCIM2 cells (SCF-responsive) by APcK110 can be enhanced when adding SCF suggesting recruitment of c-Kit-dependent signaling components and increased activity of the c-Kit inhibitor under these circumstances; (3) APcK110 is a more potent inhibitor of OCI/AML3 proliferation than imatinib and dasatininb; (4) using Western immunoblotting, APcK110 decreases levels of phospho-Akt, phospho-Stat3 and 5 in a time- and dose-dependent fashion demonstrating activity of APcK110 on c-Kit downstream signaling pathways; (5) APcK110 induces apoptosis by cleavage of caspase 3 and PARP; (6) APcK110 inhibits proliferation of primary AML cells in a clonogenic assay, but does not affect proliferation of normal controls. Conclusions: APcK110 is a potent inhibitor of AML cell lines and primary samples from patients with AML. Activation of c-Kit or downstream pathways increases activity of APcK110. APcK110 and similar compounds should be evaluated in clinical trials of patients with AML. No significant financial relationships to disclose.