Characterization of Signal Transduction Abnormalities Revealed Spleen Tyrosine Kinase as a Therapeutic Target in High-risk Precursor B Cell Acute Lymphoblastic Leukemia

Currently, the intensive chemotherapy remains the first line treatment for B cell acute lymphoblastic leukemia (B-ALL). Although these regimens have significantly improved patient outcomes, their use is associated with debilitating morbidities and fatal relapses, highlighting the great need in new agents that target essential survival signals in leukemia. Thus, the overall goal of my project was to gain insights into the signaling abnormalities that regulate aberrant proliferation and survival of B-ALL cells in an effort to identify novel targets in this malignancy. This study demonstrated that pre-B cell receptor (pre-BCR)-independent spleen tyrosine kinase (SYK) activity was required for the survival and proliferation of a p53-/-PrkdcSCID/SCID mouse model of B-ALL. I extended this discovery to human disease, demonstrating that SYK was activated in primary B-ALL, independent of the pre-BCR expression. The small molecule SYK inhibitor fostamatinib (fosta) significantly attenuated proliferation of 79 primary diagnostic B-ALL samples at clinically achievable concentrations. Importantly, fosta treatment reduced dissemination of engrafting B-ALL cells into the spleen, liver, kidney and central nervous system (CNS) in a NOD.Prkdcscid/scidIl2rgtm1Wjl/SzJ xenotransplant model of B-ALL. Analysis of signaling abnormalities using a high-throughput phospho-flow cytometry platform demonstrated that pediatric and adult B-ALL samples exhibit variable basal activation of BCR, iii PI3K/AKT/mTOR, MAPK and JAK/STAT pathways. Importantly, we identified that fosta-mediated inhibition of SYK, PLC2, CRKL and EIF4E phosphorylation in B-ALL was predictive of its anti-leukemic activity, and was distinct from the cellular actions of other small molecule inhibitors of key nodal signaling pathways. Examination of molecular mechanism of fosta action by gene expression profiling revealed transcriptional effects of fosta treatment that included, most notably, potent inhibition of pathways involved in lymphocyte activation and inflammation. In conclusion, this study demonstrates that SYK signaling is crucial for B-ALL survival and provides detailed characterization of cellular and molecular mechanisms of fosta action in B-ALL. These data argue in favor of testing small molecule SYK inhibitors in pediatric and adult B-ALL.Ph