Identifying molecular regulators of ovarian tumor cell attachment to peritoneal mesothelial cells under shear stress using an ex-vivo microfluidic model

Ovarian cancer metastasis is unique in that the primary tumor and the initial metastatic site, the peritoneal mesothelial layer, share the same cavity. Early spread of ovarian cancer involves tumor cell shedding from primary ovarian tumors, which then circulate throughout the abdominal cavity to attach and invade mesothelium covering the abdominal organs. During peritoneal migration, ovarian tumor cells are also exposed to ascitic fluid, and the influence of this fluid flow on tumor cell attachment to mesothelium is poorly understood. To address this problem, we developed and characterized a robust microfluidic device incorporating ovarian tumor cell attachment to mesothelial cells in the presence of fluid flow. Mesothelial cells are cultured within the microfluidic device for 48 hours, and ovarian cancer cells are introduced at fixed flow rates for 7 minutes. Using live cell video imaging and analysis, we can quantify the extent of tumor cell adhesion. We find that factor(s) secreted by ovarian tumor cells significantly increase tumor cell adhesion to mesothelium. To identify candidate molecules modulating this cell-cell communication, we performed bulk mRNA sequencing of mesothelial cells treated with ovarian tumor cell culture supernatant and proteomics of the ovarian tumor cell secreted media. From these analyses, we have identified numerous potential candidate molecules. One of these molecules, cadherin-12, is downregulated in mesothelial cells in response to tumor cell culture supernatant exposure both in vitro and in vivo. Genetic depletion of cadherin-12 in mouse peritoneal mesothelial cells results in altered mesothelial barrier function, fibroblastic differentiation, and increased tumor cell adhesion to mesothelium. Our results suggest that cadherin-12 plays a role in maintaining peritoneal mesothelial integrity and is manipulated by some factor(s) secreted by ovarian tumor cells during early ovarian cancer metastasis.