Biomechanical regulation of cancer metastasis

Metastasis is the ultimate cause of most cancer-related deaths. As such, it is critical to understand the processes that control the spread of cancer through the body. To metastasize, cancer cells must leave the primary tumor, access the circulatory system, adhere to the endothelium of the metastatic site, and migrate out into the surrounding tissue. A major limitation in the discovery and development of drugs that prevent the spread of cancer is a lack of high throughput in vitro assays that accurately recreate the cell-cell interactions and mechanical forces that occur during cancer cell adhesion and exit from the vasculature at the secondary site. Here we study cancer cell adhesion in the presence of physiologic shear stress and the effects of mechanical strain on cancer progression and metastasis. We developed an adhesion assay to investigate cancer cell adhesion in the presence of shear stress. Adhesion assays performed under flow yield markedly different results from static adhesion assays. Treatment of breast cancer cells with integrin inhibitors demonstrated that these compounds had minimal effect on cancer cell adhesion to endothelial cells under static conditions, whereas under shear many of these compounds significantly reduced adhesion of cancer cells. A static adhesion assay of breast cancer cells to various types of ECM showed higher adhesion of the less aggressive MCF-7 cell line in comparison to the more aggressive MDA-MB-231 cell line. In contrast, flow incorporating assays showed increased adhesion of the MDA-MB-231 cell line. Finally, a high throughput screen using a kinase inhibitor library of 80 compounds identified seven hits, several of which were multiple hits for the same target, in the shear assay, whereas no hits were found in the same assay performed under static conditions. This assay was then modified to read cancer cell adhesion in real time, enabling the investigation of cancer cell adhesion kinetics to several ECM with various drug treatments. Cancer cell adhesion had a complex relationship with shear stress, cancer cell line, and ECM. Application of mechanical strain effects cancer cell signaling and function. Cyclic mechanical strain reduced proliferation and increased drug resistance in MDA-MB-231 breast cancer cells. Mechanical strain increased Yap/Taz nuclear localization, while decreasing nuclear phosphorylated Smad 2/3. Mechanical strain increased adhesion to endothelial cells while decreasing transmigration through an endothelial monolayer. These findings were supported by RNA sequencing data. The addition of shear stress to adhesion assays in a high throughput device enabled rapid investigation of inhibitors of cancer cell adhesion while more accurately recapitulating conditions within the body. Application of mechanical strain altered cancer cell proliferation, drug resistance, adhesion and invasion. Biophysical forces are present throughput the tumor microenvironment and play an important role in regulating cancer metastasis and progression