Abstract PR11: Ovarian cancer cells activate the mesothelium in the peritoneal microenvironment promoting fibronectin production and the early steps of metastasis

Abstract

Abstract The main site of ovarian cancer (OvCa) metastasis is the omentum, which is covered by a single layer of mesothelial cells overlaying an extracellular matrix interspersed with fibroblasts (mesothelium). A 3D model of the human peritoneal surface (in vitro), fragments of human omentum (ex vivo), and a mouse xenograft model (in vivo) of OvCa were used to investigate the early effects of cancer cells on the host stromal microenvironment. Our results reveal that fibronectin is overexpressed in the stroma of more than 93% of OvCa omental metastases. OvCa cells induce fibronectin matrix assembly in omental stromal cells, and stimulate fibronectin expression in mesothelial cells. The fibronectin produced by human mesothelial stromal cells promotes OvCa cell adhesion, invasion and proliferation. Inhibition of fibronectin production in mesothelial cells or omental surface cells using a fibronectin specific siRNA decreases OvCa cell adhesion, invasion and proliferation. Genetic knock-down of fibronectin in vitro and in vivo, using fibronectinfl/fl mice, also impaired OvCa cell adhesion/invasion and metastasis. Re-analysis of an Australian OvCa study gene array data set suggested that OvCa, which highly express fibronectin, show co-activation of TGFβ1/Rac1 dependent signaling pathways. Indeed, OvCa cells increase phosphorylation of Smad2/3 in mesothelial cells upon co-culture. Inhibition of TGFβ1 in OvCa cells or inhibition of Smad 3, as well as TGFβRI or TGFβRII, in mesothelial cells resulted in decreased fibronectin production. Moreover, Rac 1 activity was increased upon the co-culture of OvCa and mesothelial cells. Subsequent inhibition of Rac 1 in mesothelial cells led to a decrease in fibronectin secretion. Our data suggest that OvCa cells regulate fibronectin expression in mesothelial cells through a TGFβ1/Rac1 dependent pathway. In vitro and in vivo therapy with a fibronectin inhibitor, ATN161, a peptide derived from the synergy region of fibronectin, reduced OvCa invasion, proliferation and metastasis. In summary, we show that abdominally metastasizing cancer cells induce fibronectin production in the peritoneal and omental microenvironment and that inhibition of this fibronectin-response prevents the first steps of peritoneal metastasis. By understanding the mechanism of OvCa metastasis we will be better able to target cells in the tumor microenvironment (i.e. mesothelial cells, fibroblasts and macrophages) during early ovarian cancer metastasis. This abstract is also presented as Poster A60. Citation Format: Hilary A. Kenny, Chun-Yi Chiang, Andras Ladanyi, Joshy George, David D. Bowtell, Katja Gwin, Andrew Mazar, Ernst Lengyel. Ovarian cancer cells activate the mesothelium in the peritoneal microenvironment promoting fibronectin production and the early steps of metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr PR11.