The effects of physiological fluid shear stress on circulating tumor cells

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The focus of this dissertation is on the effects of physiological fluid shear stress (FSS) on circulating tumor cells (CTCs). FSS occurs on cells both in vitro and in vivo. FSS is typically considered as a major variable in large scale bioprocessing while FSS is assumed to have a negligible role in bench scale culture. In physiological settings, FSS impacts cells in cancer where local, regional, and distant cancers experience FSS through interstitial, lymphatic, and hematological flow, respectively. CTCs in hematological flow experience the highest FSS and are involved in the transit stage of metastasis. One challenge of metastatic cancer is the lack of secondary tumor detection. Detection of CTCs largely relies on the epithelial cell adhesion molecule (EpCAM). CTC phenotype also includes expression of cancer stem cell (CSC) and epithelial to mesenchymal transition (EMT), which are correlated to increased resistance to chemotherapy. The study of FSS using an in vitro model can provide a better understanding on CTC phenotype expression and drug resistance. FSS was first examined using a baseline study with in vitro cell spheroid culture. Spheroids provide better representation of the stem and tumor cell environment than 2D culture. These cells experience FSS during cell dissociation. Since FSS can detrimentally affect cells, a gentler mechanical platform was developed for dissociation. Furthermore, this method, as well as traditional dissociation methods, was tested to study how FSS affects cell viability and expression. This platform was further used to model breast CTCs as suspension cells under FSS. This metastatic model allowed for testing the effects of FSS on CTC phenotype, and it was found that FSS increased CSC and CTC expression. Since an increase in CSC expression is correlated to increased drug resistance, drug resistance on CTCs under FSS was tested with chemotherapy drugs. It was found that the combination of FSS and drug resistance synergistically increases drug resistance expression in the model CTCs, corroborating clinical reports of CTC drug resistance. Finally, the effects of FSS and drug resistance was tested on estrogen receptor positive (ER+) molecular subtype. Collectively, these studies provide a better understanding on CTC behavior during metastasis.

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Bioengineering, Chemical engineering