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Quantification of Breast Cancer Cell Transmigration across Brain and Lung Microvascular Endothelium

Extravasation is a crucial step during tumor metastasis. Breast cancer cells prefer to extravasate into the lungs and brain. However, where and how tumor cells transmigrate through these organ‐specific endothelial barriers to complete their extravasation remains unclear. Using an in vitro transwell model, we performed a transmigration assay of malignant breast tumor cells (MDA‐MB‐231) through lung or brain microvascular endothelial monolayers under control and pathological conditions. The locations and rates of tumor cell transmigration as well as the changes in structural components of endothelial monolayers were investigated by confocal microscopy. Endothelial monolayer permeability to albumin Palbumin was also quantified under the same conditions. Our results show: 1) More than 95% of transmigration occurs at the joints of endothelial cells instead of cell bodies; 2) Tumor cell adhesion and transmigration degrade endothelial surface glycocalyx and disrupt junctional proteins between adjacent endothelial cells, consequently increasing Palbumin; 3) The transmigration rate of breast tumor cells is higher through the lung endothelial monolayer with higher Palbumin; 4) Both Palbumin and tumor transmigration rates are increased by vascular endothelial growth factor (VEGF) and an inflammatory agent, lipopolysaccharides (LPS) treatments. These results suggest that reinforcing endothelial structural integrity, e.g. preserving surface glycocalyx and junction proteins, is an effective approach for inhibiting tumor extravasation. Supported by NIH SC1CA153325‐01.