Identification of potential classes of glycoligands mediating dynamic endothelial adhesion of human tumor cells.

One critical step of metastasis formation is the extravasation of circulating tumor cells from the bloodstream. This process requires the dynamic interaction of cell adhesion molecules (CAMs) like E-selectin on endothelial cells (ECs) with carbohydrate ligands on tumor cells (TCs). To characterize these glycans in a comprehensible approach, the rolling, tethering and firm adhesion of nine human TC lines on human umbilical vein ECs was analyzed using laminar flow adhesion assays. The TC lines were grouped into three subsets by their canonical E-selectin ligand status (sialyl-Lewis A and X (sLeA/X) +/+, -/+, -/-) and their adhesiveness was compared after enzymatic, pharmacologic, chemical treatment or antibody blockade of the TCs or ECs, respectively. TCs were also screened regarding their glycosyltransferase expression profile. We found that although E-selectin and terminal α2,3-sialic acid largely determined firm adhesion, adhesive events did not exclusively depend on the presence of sLeA and/or sLeX. Two of the three sLeA/X-/- TCs additionally or fully depended on VCAM-1 for firm adhesion. The significance of O-GalNAc- and N-glycans for adhesion varied remarkably among the TCs. The sLeA/X+/+ subset showed glycoprotein-independent adhesion suggesting a role for glycolipids as well. All sLeA/X-/- TCs lacked FUT3 and FUT7 expression as opposed to sLeA/X+/+ or -/+ cell lines. Summarized, the glycans on TCs mediating endothelial adhesion are not as much restricted to sLeA/X as previously assumed. The present study specifically suggests α2,3-linked sialic acid, O-GalNAc glycans, glycosphingolipids, and FUT3/FUT7 products as promising targets for future studies.