Abstract A11: Redistribution of endothelial junction protein PECAM-1 and MMP activity are important for transmigration of breast tumor cells across lung endothelial monolayer in-vitro
Authors: Low Pin Yan , Yap Celestial , Lim Yaw Chyn 
Published: June 2012

Abstract
The ability of tumor cells to escape the circulation is essential to the establishment of secondary malignancy. The occurrence of metastases in a particular secondary site is influenced by differences in the barriers present at each such site, as well as the unique organ-specific microenvironments. One of the preferred metastatic sites for breast cancer is lung and our study aims to identify in vitro the interactions between breast tumor cells and lung endothelium that may be important in the metastatic process.
In this study, we used in vitro tumor binding assays and the transwell assay system to examine the adhesive interactions of breast tumor cells (MDA-MB-231, MCF-7) and subsequent transmigration across monolayers of endothelial cells. In addition, we compared breast cancer cell interactions with endothelial cells isolated from different organ sites, namely human lung (FLEC), saphenous vein (SVEC), and umbilical cord vein (HUVEC).
To determine the mechanisms facilitating transmigration, we examined, using immunofluorescent staining, the distribution of the endothelial junction protein, PECAM-1, on tumor cell-bound endothelial monolayers. The role of matrix metalloproteinases (MMPs) in the transendothelial migration process was examined via various MMP(s) inhibitors.
FLEC were able to bind both the highly invasive MDA-MB-231 and the non-metastasising MCF-7 cells with similar efficiency. However, more MDA-MB-231 transmigrated the FLEC monolayer as compared to MCF-7.
Bound MDA-MB-231 cells were more effective at disrupting FLEC junction integrity, resulting in the formation of ‘gaps’ at cellular junctions with loss of PECAM-1 expression. Treatment with broad spectrum MMPs inhibitor (GM6001) and specific MMP2, 3, 8 inhibitors (OA-HY, MMP3 inhibitor II, MMP8 inhibitor I respectively) resulted in a reduction in MDA-MB-231 transmigration across the FLEC monolayer. A yet unidentified MMP(s) secreted by MDA-MB-231 and FLEC-derived MMP2 contributed to the observed ‘gap’ formation. In comparison, MDA-MB-231 transmigration across HUVEC and SVEC monolayers were significantly less efficient compared to FLEC monolayer. The resistance of HUVEC and SVEC to MDA-MB-231 transmigration correlated to significantly less disruption of junction integrity and gap formation by bound MDA-MB-231.
Our data suggest that disruption of endothelial junction integrity, due to redistribution of PECAM-1 and MMP activity, contributes to breast tumor cell transmigration across lung endothelial monolayer. The decreased interaction of breast tumor cells with HUVEC and SVEC suggests that breast tumor cells preferentially interact with lung endothelial cells, thus resulting in the lung being a common site of metastasis in breast cancer.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A11.