Targeting Axl Kinase in Hematological Malignancies.

Abstract 2758

Poster Board II-734

Axl kinase, a member of the TAM family and also known as UFO, ARK, and Tyro7, is a receptor tyrosine kinase implicated in tumorigenesis. Overexpression of Axl is associated with increased cellular transformation, cell survival, proliferation, migration, angiogenesis, and adhesion. The oncogenic potential of Axl was first discovered in chronic myelogenous leukemia (CML) and has been shown to play a role in the development of acute myelogenous leukemia (AML) and myelodysplasia. Binding of Growth Arrest Specific Gene-6 (GAS6), a vitamin K-dependent protein and a known ligand for Axl, leads to subsequent phosphorylation events of downstream effecter molecules such as mitogen-activated protein (MAP) kinase and phosphatidyl-inositol (PI)-3 kinase/AKT pathways which are critical in oncogenic transformation. Furthermore, target validation studies of in vivo cancer models show that inhibition of Axl expression by RNA interference blocked tumor growth in those models. Taken together, this information makes Axl kinase an exciting target for small molecule drug discovery. Effectively utilizing SuperGen's proprietary CLIMB“technology, a series of small molecule inhibitors were rapidly discovered and developed for potency and selectivity against Axl. Lead candidate compounds demonstrate low nano-molar IC50 values in an Axl kinase biochemical assay, and focused selectivity for Axl when screened in kinase panels. Likewise, these compounds showed low and sub micro-molar activity from an anti-proliferative leukemia/lymphoma cell-based panel. Similarly, treatment of leukemia cells with these compounds in combination with known chemotherapeutic agents produced results that implicate combinatorial therapies as potentially beneficial treatments for patients suffering from hematological malignancies. In mechanistic, target validation assays, EC50 data from immunoprecipitated western blots of transiently transfected liquid tumor cells showed nano-molar inhibition of phospho-Axl when detecting with an anti-phospho-tyrosine antibody. A western blot panel of leukemia and lymphoma cell lines showed overexpression of Axl in several of these cell lines, further validating Axl as a potential therapeutic target in hematological cancers. Functional cell-based assays using SuperGen's lead compounds also potently inhibited phospho-AKT (S473). We propose that SuperGen's small molecule inhibitors against Axl kinase represent a new class of compounds with potent and selective activity in hematological malignancies.