The Axl receptor tyrosine kinase is an adverse prognostic factor and a therapeutic target in esophageal adenocarcinoma.

Esophageal adenocarcinoma (EAC) arises in the backdrop of reflux-induced metaplastic phenomenon known as Barrett esophagus. The prognosis of advanced EAC is dismal, and there is an urgent need for identifying molecular targets for therapy. Serial Analysis of Gene Expression (SAGE) was performed on metachronous mucosal biopsies from a patient who underwent progression to EAC during endoscopic surveillance. SAGE confirmed significant upregulation of Axl "tags" during the multistep progression of Barrett esophagus to EAC. In a cohort of 92 surgically resected EACs, Axl overexpression was associated with shortened median survival on both univariate (p < 0.004) and multivariate (p < 0.036) analysis. Genetic knockdown of Axl receptor tyrosine kinase (RTK) function was enabled in two EAC lines (OE33 and JH-EsoAd1) using lentiviral short hairpin RNA (shRNA). Genetic knockdown of Axl in EAC cell lines inhibited invasion, migration, and in vivo engraftment, which was accompanied by downregulation in the activity of the Ral GTPase proteins (RalA and RalB). Restoration of Ral activation rescued the transformed phenotype of EAC cell lines, suggesting a novel effector mechanism for Axl in cancer cells. Pharmacological inhibition of Axl was enabled using a small molecule antagonist, R428 (Rigel Pharmaceuticals). Pharmacological inhibition of Axl with R428 in EAC cell lines significantly reduced anchorage-independent growth, invasion and migration. Blockade of Axl function abrogated phosphorylation of ERBB2 (Her-2/neu) at the Tyr877 residue, indicative of receptor crosstalk. Axl RTK is an adverse prognostic factor in EAC. The availability of small molecule inhibitors of Axl function provides a tractable strategy for molecular therapy of established EAC.

Preclinical characterization of Aurora kinase inhibitor R763/AS703569 identified through an image-based phenotypic screen.

PURPOSE: Aurora kinases play a key role in mitotic progression. Over-expression of Aurora kinases is found in several human cancers and correlated with histological malignancy and clinical outcomes. Therefore, Aurora kinase inhibitors should be useful in the treatment of cancers. METHODS: Cell-based screening methods have an advantage over biochemical approaches because hits can be optimized to inhibit targets in the proper intracellular context. We developed a novel Aurora kinase inhibitor R763/AS703569 using an image-based phenotypic screen. The anti-proliferative effect was examined in a panel of tumor cell lines and primary cells. The efficacy was determined in a broad panel of xenograft models. RESULTS: R763/AS703569 inhibits Aurora kinases, along with a limited number of other kinases including FMS-related tyrosine kinase 3 (FLT3), and has potent anti-proliferative activity against many cell types accompanying unique phenotypic changes such as enlarged cell size, endoreduplication and apoptosis. The endoreduplication cycle induced by R763/AS703569 was irreversible even after the compound was withdrawn from the culture. Oral administration of R763/AS703569 demonstrated marked inhibition of tumor growth in xenograft models of pancreatic, breast, colon, ovarian, and lung tumors and leukemia. An acute myeloid leukemia cell line MV4-11, which carries a FLT3 internal tandem duplication mutation, is particularly sensitive to R763/AS703569 in vivo. CONCLUSIONS: R763/AS703569 is a potent inhibitor of Aurora kinases and exhibited significant anti-proliferative activity against a wide range of tumor cells both in vitro and in vivo. Inhibition of Aurora kinases has the potential to be a new addition to the treatment of cancers.