E-selectin binding by pancreatic tumor cells is inhibited by cancer sera

Tumor cells interact with endothelial cells during both intra- and extravasation. Understanding how these interactions are modulated could lead to the development of ways to alter the metastatic potential of tumor cells. Three pancreatic cancer cell lines, SW1990, CAPAN-2 and PANC-I, were examined for their ability to bind to the endothelial cell adhesion molecule E-selectin (ELAM-1). SW1990 cells exhibited highest binding, highest surface expression of the carbohydrate antigens sialylated Lewis(a) (sLe(a)) and sialylated Lewis(x) (sLe(x)) and released the most high m.w. sLe(a) and sLe(x) antigens. Expression of sLe(a) and sLe(x) antigens and binding to E-selectin were reduced by pre-treatment of SW1990 cells with the O-linked glycosylation inhibitor benzyl-alpha-GalNAc but not with the N-linked glycosylation inhibitor tunicamycin. Expression of peptide epitopes associated with MUC1 apomucins was increased by benzyl-alpha-GalNAc. Cell binding was greatly reduced by mucins purified from SW1990 xenografts and by an antibody against sLe(a). An antibody against sLe(x) had a much less marked effect. Sera from pancreatic cancer patients reduced SW1990 cell binding to E-selectin but sera from normals did not. The degree of inhibition was related to the sLe(x) level in the sample. When cancer serum was separated by column chromatography on Sephacryl S-400, the void volume fractions contained most of the sLe(a) and sLe(x) antigens and most of the inhibitory activity to E-selectin binding. Differences in the relative availability of sLe(a) and sLe(x) ligands on serum molecules and on the SW1990 cell surface may account for the differences between antibody and serum inhibition results. Thus SW1990 cell adhesion to E-selectin is mediated by ligands on mucinous glycoproteins, and adhesion can be inhibited by mucins, high blood levels of sLe(x) and reduction of cellular O-linked glycosylation.