Project Summary/Abstract New targeted therapies are urgently needed for acute myeloid leukemia (AML), where little progress has been made in improving long-term patient survival despite significant inroads into understanding the molecular pathogenesis of this disease. We previously discovered spleen tyrosine kinase (SYK) as a new target in AML, with FLT3-ITD a biomarker of response to SYK inhibitors in AML cells. These findings become immediately translatable as numerous SYK inhibitors are entering clinical trials for patients with cancer, including AML. The translation of SYK inhibitors to the clinic for patients with AML is the focus of this project. In Aim 1 of this proposal, we will study SYK activation in AML cell lines and patient blasts to determine whether SYK activation promotes resistance to current AML therapy. In this Aim, we will also determine whether SYK inhibitors synergize with drugs currently used to treat patients with AML, both in vitro and in vivo, to inform second- generation SYK inhibitor clinical trials. In Aim 2, we will test specific hypotheses and conduct unbiased functional genomic studies to identify resistance mechanisms to SYK inhibitors in AML. We expect that these experiments will inform new drug combinations for testing with SYK inhibitors. Aim 3 will focus on performing the correlative biology studies for two Phase I/II clinical trials testing SYK inhibitors in patients with AML. In this Aim, we will use next-generation sequencing of panels of leukemia-associated genes, immunohistochemistry and intracellular phospho-specific flow cytometry to measure activated SYK, BH3 profiling, and gene expression signature assays to identify biomarkers of response to SYK inhibitors and to confirm target inhibition using AML samples from patients treated on the clinical trial. At the completion of this study, we expect to confirm on-target, anti-leukemia activity of a SYK inhibitor in patients with AML and to inform second- generation clinical trials through the identification of drug combinations with SYK inhibitors and through the identification of biomarkers of response in patients with AML treated with a SYK inhibitory drug.