Abstract 5185: Ovarian cancer cells induce fibronectin production in the peritoneal microenvironment through a TGFβRI-dependent mechanism which promotes the early steps of metastasis

The high mortality rate that results from ovarian cancer (OvCa) is caused by the wide dissemination of cancer cells within the abdominal cavity. OvCa cells metastasize to the peritoneum, which is covered by a single layer of mesothelial cells, and invade into the underlying stroma, composed of extracellular matrices (ECM) including fibronectin (FN) and stromal cells such as fibroblasts. We hypothesize that cancer cells stimulate stromal cells to produce and secrete FN, initiating the metastatic niche. A 3D model of the human peritoneal surface (in vitro), pieces 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 microenvironment. FN expression was investigated in human normal and tumor tissues using tissue microarrays, reverse-phase protein arrays, and preserved tissues. The different model systems and tissues were examined utilizing a number of techniques including; immunohistochemistry, immunofluorescence, ECM extraction, real-time quantitative PCR, and immunoblotting. Our results reveal that FN is overexpressed in the stroma of more than 90% of OvCa metastatic tissues examined. Moreover, total FN expression levels are significantly greater in omental metastases as compared to patient-matched primary tumor tissues. Additionally, the EDA+ fragment of FN is upregulated in OvCa metastases when compared to normal omental tissue. Cancer cell adhesion and proliferation are increased on omental metastases-derived ECM as compared to normal omental-derived ECM, which are significantly inhibited when the interaction between FN and its receptor, integrin α5β1 is blocked. Using the in vitro 3D model, we found that mesothelial cells and fibroblasts are the source of FN, and multiple peritoneal cancer cells induce FN production. Knocking-down FN in mesothelial cells (in vitro), sections of human omentum (ex vivo), and mouse peritoneum (in vivo) perturbs OvCa cell adhesion, invasion, and proliferation. Likewise, treatment with ATN-161, which antagonizes the interaction between FN and its receptor, integrin α5β1, also reduces OvCa cell adhesion, invasion, and proliferation in the 3D omental model (in vitro), and OvCa metastasis in the xenograft model (in vivo). OvCa cells increase phosphorylation and nuclear localization of Smad2/3 in mesothelial cells upon co-culture, and inhibition of Smad 3 as well as TGFβRI in mesothelial cells resulted in decreased FN production. Moreover,