Abstract 2577: Targeting the Axl tyrosine kinase receptor in pancreatic cancer

With the worst five-year survival rate of any cancer, pancreatic adenocarcinomas now rank as the fourth leading cause of cancer death in adults in the United States. This necessitates increased efforts to identify new leads that will serve as therapeutic targets in our fight against this aggressive cancer. Axl is a TAM family receptor tyrosine kinase involved in multiple aspects of tumorigenesis. Increased expression of Axl is associated with increased oncogenic transformation, cell survival, proliferation, migration, angiogenesis, and cellular adhesion. The oncogenic potential of Axl was first discovered in chronic myelogenous leukemia (CML), but it has been demonstrated to play a role in the progression and metastasis of other cancer types. The known ligand for Axl is the Growth Arrest Specific Gene-6 (Gas6) protein and its binding to Axl leads to Axl autophosphorylation and activation of downstream signaling pathways including MAPK and PI3K/Akt pathways. Furthermore, target validation studies of in vivo cancer models show that inhibition of Axl expression by RNAi blocked tumor growth in those models. Taken together, this information makes Axl kinase an exciting target for small molecule drug discovery. Using HCI-2084, a small molecule Axl kinase inhibitor, we explored the effectiveness of targeting the Axl kinase in pancreatic cancer. HCI-2084 demonstrates low nanomolar (IC50 = 12 nM) activity against the Axl kinase in a biochemical assay with good selectivity for Axl when screened in a kinase panel. In 2D and 3D cell proliferation assays, HCI-2084 significantly inhibited pancreatic cancer cell growth at concentrations as low as 30 nM. In pharmacodynamic endpoint assays, HCI-2084 dramatically inhibited Akt signaling (pAKT S473) downstream of GAS6 stimulation in pancreatic cancer cell lines. Inhibition of Axl autophosphorylation by HCI-2084 was also observed in an Axl-transfected cell line system. Consistent with the known function of Axl, HCI-2084 inhibited Gas6-induced migration and invasion of pancreatic cancer cells in vitro. The proteolytic processing of the extracellular domain of the Axl receptor is a known event downstream of Axl activation and results in the release of soluble Axl (sAxl) into the cell culture media (in vitro) or into the blood stream (in vivo). We hypothesized that sAxl levels could function as a biomarker for target inhibition. Indeed, conditioned media from pancreatic cancer cell lines treated with HCI-2084 showed significant dose-dependent reductions in sAxl levels compared to the vehicle treated controls. Taken together, these results suggest Axl is a potential therapeutic target in pancreatic cancer and that HCI-2084 is an exciting agent to potentially treat this disease. HCI-2084 is currently undergoing evaluation in animal efficacy and pharmacodynamic endpoint studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2577. doi:10.1158/1538-7445.AM2011-2577