Velocity and inflammatory dependent microvascular adhesion of circulating cancer cells: An in vitro study
Metastasis is the ultimate cause of death among the vast majority of cancer patients. One of the major modes of cancer metastasis is through the circulatory system, also known as haematogenous metastasis. Many of the mechanisms of the haematogenous metastatic cascade remain poorly understood, including the adhesion and extravasation of circulating tumor cells in the vasculature of secondary target organs. Past research in this area has been hampered by poor control of physiological conditions in animal models, and the failure to recapitulate an in vivo-like environment in in vitro models. In this work, a microfluidic device was developed to support the culture and observation of engineered microvasculature with easy control of the environmental characteristics. This device was then used to study the adhesion of circulating cancer cells (MCF7) to an endothelial monolayer (hMVEC) under varying conditions. Adhesion assays with MCF7 in differing biochemical environments and under multiple physiological flow conditions were performed. It was found that pretreatment of the endothelium with TNF-α significantly increase the percent of transiently and firmly adherent cells, while increasing the mean flow velocity within the device significantly reduced the percent of firmly adherent cells and the overall percent of cancer cells interacting with the underlying endothelium. In addition, adhered MCF7 were observed crawling and invading the endothelial monolayer during and after the adhesion experiments. This suggests the formation of integrin bonds between the two cell types. Applying a first order kinetic model to the experimental data, it was found that the decrease in firmly adherent cells with increasing flow rate was mostly due to an increase in the unbinding of cells and not a decrease in the cell binding rate. Further investigation of the unbinding rate revealed time dependence in the likelihood that a firmly adhered cancer cell would detach. Initially cells detached at a high rate corresponding closely with reported values of the reverse kinetic rate of bond formation for E-Selectin. The probability of detachment, at first, decreased quickly with time followed by a slowly decay to a near zero value. The similarity between the initial unbinding rate and the reverse kinetic rate of bond formation for E-selectin suggests that initial firm adhesion may be mediated by selectin bonds. These bonds are then quickly stabilized by stronger receptor-ligand complexes in cancer cells that remain attached for long durations. These findings suggest that the developed microfluidic device and kinetic model of cell adhesion are useful tools in the study of circulating cancer cell attachment to microvasculature and the subsequent extravasation of adhered cells.
Han, Purdue University.
Biomedical engineering|Mechanical engineering
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