Effects of Fluid Shear Stress on Reactive Oxygen Species Generation, Stemness, and Epithelial-to-Mesenchymal Transition

Most cancer deaths are caused by secondary metastasized tumors initiated by circulating tumor cells (CTCs). These cells are in a dynamic microenvironment where fluid shear stress (FSS) is a prominent force with myriad of consequences, including reactive oxygen species (ROS) generation. It is believed that there exists a correlation between CTCs and cancer stem cells (CSCs) and that this resemblance supports CTCs to survive the metastatic process and proliferate afterwards for colony formation to form a secondary tumor. One stem cell-like quality is the ability to undergo the epithelial-to-mesenchymal transition (EMT). In this study, triple-negative subtype breast cancer MDA-MB-231 and luminal subtype MCF7 cells were subjected to a prolonged FSS in a spinner flask as an in vitro model of CTCs. Post-FSS, the cells were analyzed via flow cytometry and qRT-PCR for ROS generation, CSC, EMT, and Hippo markers. Though MDA-MB-231 did not show a dynamic CSC shift, there were significant changes in ROS, EMT, and Hippo markers (p<0.05). Additionally, MCF7 also showed significant changes in ROS and EMT markers. Notably, both cell lines exhibited the mesenchymal-to-epithelial transition (MET) signature upon recovering from exposure to FSS. These findings indicate that the baseline stemness quality (or lack thereof) and phenotype of each cell line affects how they respond to induced biophysical forces. Furthermore, this shows a possible relationship between mechanotransduction, the Hippo pathway, and the induction of EMT in breast cancer cells.