Abstract 5756: The receptor tyrosine kinase EPHB4 has tumor suppressor activities in intestinal tumorigenesis

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Colorectal cancer is the second cause of cancer related death in the western world and although the genetic and molecular mechanisms involved in initiation and progression of these tumors is among the best characterized, there are significant gaps in our understanding of this disease. The family of receptor tyrosine kinases EPH and their Ephrin ligands regulate cell proliferation, migration and attachment. An important role in colorectal carcinogenesis is emerging for some of its members. In this study we used animal models and analysis of large tumor collections to investigate the possible role of EPHB4 as a new tumor suppressor gene in colorectal cancer. Modulation of EPHB4 levels in colon cancer cell lines resulted in significant growth differences in vitro and in a xenograft model, with low levels of EPHB4 associated with faster growth. In addition, using a genetic model of intestinal tumorigenesis where Apc mutations lead to initiation of the tumorigenic process (Apcmin mice), we show that inactivation of a single allele of EphB4 results in: a) higher proliferation both in the normal epithelium and intestinal tumors, b) significantly larger tumors in the small intestine and c) a 10-fold increase in the number of tumors in the large intestine. This was associated with a 25% reduction in the lifespan of Apcmin mice (p<0.0001). Gene expression analysis demonstrated that EphB4 inactivation causes a profound transcriptional reprogramming affecting genes involved in cell proliferation, remodeling of the extracellular matrix and cell attachment to the basement membrane, among other functional groups of genes. Importantly, in agreement with the expression profiling experiments, using an in vitro assay we demonstrate that loss of EPHB4 in colon cancer cells results in a significantly increased potential to invade through a complex extracellular matrix. In addition, using archived human colorectal tumors we investigated the possible association between EPHB4 levels and patient prognosis. In a series of 252 cases, we found that EPHB4 expression is frequently reduced or lost in colorectal tumors. Patients with low EPHB4 tumor levels had significantly shorter survival than patients in the high EPHB4 group (Logrank test p<0.01; median survival of 1.8 and over 9 years, respectively). Moreover, we demonstrate that EPHB4 promoter hypermethylation is a common mechanism of EPHB4 inactivation. Collectively, these results indicate that EPHB4 has tumor suppressor activities in colorectal cancer and that tumor expression of this tyrosine kinase can be used to predict patient prognosis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5756.