Abstract B5: Tumor-cell-induced angiopoietin-2 secretion from endothelial cells results in destabilization of the endothelial/smooth muscle cell interaction of blood vessels.

Abstract

Abstract The angiopoietin-Tie2 axis is considered to be a key contributor in tumor associated angiogenesis. Angiopoietin-2 (Ang-2) is an endothelial cell secreted protein that is upregulated by angiogenic stimuli that leads to vessel destabilization by facilitating the disruption of cell-cell contacts between endothelial and periendothelial cells (ie. smooth muscle cells) in the vasculature. Ang-2 is stored in Weibel-Palade bodies and quickly secreted by stimuli such as hypoxia and inflammation; conditions commonly found in solid tumors. In the present study, the effect of renal cell carcinoma tumor cells (Caki-1, Caki-2) on endothelial cell secretion of Ang-2 and the ability to destabilize endothelial-smooth muscle cell co-culture spheroids was evaluated. As anticipated, enzyme-linked immunosorbent assay (ELISA) showed only minimal Ang-2 secretion from Caki tumor cells; 0.02 ng/ml (Caki-1) and 0.005 ng/ml (Caki-2). However, stimulation of endothelial cells with Caki conditioned media showed high levels of Ang-2 secretion from endothelial cells; 1.9 ng/ml (Caki-1) and 3.6 ng/ml (Caki-2), a 95-fold and 720-fold increase respectively. Furthermore, a greater increase in the level of Ang-2 secretion was observed when endothelial cells were stimulated with Caki cells maintained under hypoxic conditions; 3.5 ng/ml (Caki-1) and 5.5 ng/ml (Caki-2), a 1.8-fold and 1.5-fold increase, respectively, compared to cells maintained under normoxic conditions. When media collected from Caki-1 and Caki-2 cells were added to endothelial-smooth muscle cell co-culture spheroids, endothelial cells were rapidly lost from the smooth muscle cell core. Consistent with the levels of Ang-2 secretion, media collected from Caki-2 cells had a greater effect on endothelial cell dissociation from the co-culture spheres than did media from Caki-1 cell culture. This endothelial cell loss was further enhanced when co-culture spheres were exposed to media derived from tumor cell cultures maintained under hypoxic conditions. Using an in vitro endothelial-smooth muscle cell co-culture sphere model we demonstrate that tumor cells can modulate endothelial cell Ang-2 secretion and thereby destabilizing the endothelial cell/smooth muscle cell association of blood vessels. These results support a rationale for targeting Ang-2 as a novel anti-angiogenic strategy in cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B5.