Abstract 3188: Forward and reverse signalings of EphB4/EfnB2 are active in epithelial ovarian cancer and are inhibited by dasatinib
Authors: Tomassetti Antonella , Alberti Chiara , Zacchetti Alberto , Guidi Katia , Luison Elena , Ferri Renata , Canevari Silvana 
Published: February 2011

Abstract
Ephrin receptor (Eph) family constitutes the largest subfamily of trans-membrane tyrosine kinases. Their ligands, the ephrins (Efn), are membrane-anchored proteins grouped into two classes: class A ligands which are GPI-anchored proteins; class B ligands which contain a trans-membrane and a cytoplasmic tail. Eph-signaling is termed forward, Efn-signaling is termed reverse. Eph/Efn proteins are expressed in virtually all tissues and they are involved in a number of cellular events during embryonic development such as cell migration, repulsion versus adhesion, and cell to cell communication. In cancers, Eph/Efn involment is controversial. The Eph appeared to exert a suppressive role in colon and breast cancers, and the Eph/Efn signaling has been showed to drive or inhibit invasion via a reciprocal regulatory loop in glioblastomas and prostate cancer. In epithelial ovarian cancers (EOCs) the co-expression of EphB4 and EfnB2 in seventy-two EOC samples was associated to worst prognosis, highlighting a possible autocrine/paracrine activation loop in EOCs. We analyzed the signaling through EphB4/EfnB2 pair in EOC cell lines that express both the receptor and the ligand or only the receptor. To analyze the EphB4 activation we evaluated the EphB4 phosphorylation in growing cells and in cells upon binding of a soluble EfnB2-Fc molecule on cell in suspension. We found that EphB4 is phosphorylated in cells growing in presence of fetal calf serum and is further phosphorylated upon EfnB2-Fc stimulation. Accordingly, treatment of growing EOC cells with the soluble EfnB2-Fc induced a decrease in growth capability, meaning that the ligand in soluble form inhibited the binding of the cell membrane ligand to the receptor. In line with this results, silencing of EphB4 by a specific siRNA pool, inhibited cell growth by impairing cell survival. On the other site, silencing of EfnB2 lead to inhibition of EphB4 and src phosphorylations, followed by FAK phosphorylation and remodeling of focal adhesions. Therefore, in EOC cell lines expressing both the receptor and the ligand forward and reverse signaling of EphB4/EfnB2 were active. In addition, we showed that a panel of EOC cells are sensitive (IC50&lt;10 nM) to the kinase inhibitor dasatinib which has been showed to have the same binding capacity on EphB4 and src. Indeed, dasatinib reduced both EphB4 and src phosphorylation in EOC cells. Ongoing experiments of dasatinib treatment in nude mice bearing OVCAR3 xenografts in the peritoneum showed an increase of the survival rate in the treated animals. These in vitro and in vivo experiments demonstrated for the first time that in EOC cells dasatinib targeted both EphB4 and src kinase thus suggesting dasatinib as a valuable therapy in EOC patients.
Partially supported by FIRB and AIRC.
Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.
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 3188.