(447e) Notch Signaling Inhibition Increases E-Selectin Ligand Activity and Alters Cell Migration of Mesenchymal-like Breast Cancer Cells

Activation of Notch signaling has been shown to promote cell migration properties and hematogenous metastasis by inducing a dramatic phenotypic change in breast cancer cells via the epithelial-to-mesenchymal transition (EMT). In response to these findings, Notch signaling inhibitors are being explored as therapeutics to prevent EMT in cancers. However, research examining the effects of Notch inhibitors on the activity of sialofucosylated ligands used by circulating tumor cells to adhere to selectin-expressing vascular cells during metastasis is lacking. We hypothesize that Notch signaling leads to changes in expression of functional selectin ligands on epithelial-like and mesenchymal-like breast cancer cells. We first investigated the use of an indirect Notch signaling inhibitor (DAPT) on modifying E-selectin ligand activity of breast cancer cell lines by shear flow adhesion assays performed at physiological bone marrow shear stress. DAPT exposure to mesenchymal-like MDA-MB-231 and induced mesenchymal-like MDA-MB-468 (induced by exogenous epidermal growth factor) breast cancer cells increased E-selectin ligand activity. Furthermore, induced mesenchymal-like MDA-MB-468 cells after DAPT exposure demonstrated E-selectin ligand activity similar to that of epithelial-like MDA-MB-468 cells. That is, DAPT treatment of breast cancer cells led to impaired notch signalling that consequently resulted in epithelial-like characteristics and increased E-selectin ligand activity. These results are consistent with our previous work demonstrating that epithelial-like and mesenchymal-like phenotypes determine activity of functional E-selectin ligands in breast cancer cells, in that epithelial cells display high E-selectin ligand activity while mesenchymal cells display little or no ligand activity. Investigation of the effects of DAPT on P-selectin and L-selectin ligand activities of breast cancer cells are currently on-going. In addition to selectin ligand function, cell migration ability was assessed using wound closure assays. Mesenchymal-like MDA-MB-468 cells exposed to DAPT exhibited decreased migration compared to mesenchymal-like MDA-MB-468 cells exposed to the DMSO diluent control, whereas mesenchymal-like MDA-MB-231 cells demonstrated no difference in migration compared to DMSO exposed cells. Altogether, our results suggest Notch inhibition may both increase fluid-shear resistant adhesion and alter migration ability of mesenchymal-like breast cancer cells, and that pharmacologic factors present in the blood might impact the metastatic potential of cancer cells via regulating cellular phenotypes.