Both the ability of malignant cells to form multicellular aggregates via homotypic or heterotypic aggregation and their adhesion to the endothelium are important if not critical during early stages of
cancer metastasis. The
tumor-associated
carbohydrate Thomsen-Friedenreich antigen (
T antigen) and
beta-galactoside binding
lectins (
galectins) have been implicated in
tumor cell adhesion and tissue invasion. In this study, we demonstrate the involvement of
T antigen in both homotypic aggregation of MDA-MB-435 human
breast carcinoma cells and their adhesion to the endothelium. The
T antigen-specific
peptide P-30 (HGRFILPWWYAFSPS) selected from a bacteriophage display library was able to inhibit spontaneous homotypic aggregation of MDA-MB-435 cells up to 74% in a dose-dependent manner. Because
T antigen has beta-
galactose as a terminal
sugar, the expression profile of
beta-galactoside-binding
lectins (
galectins) in MDA-MB-435 cells was studied. Our data indicated the abundant expression of [35S]
methionine/
cysteine-labeled
galectin-1 and
galectin-3 in this cell line, which suggested possible interactions between
galectins and
T antigen. As revealed by
laser confocal microscopy, both
galectin-1 and
galectin-3 also participate in the adhesion of the MDA-MB-435 cells to the endothelium. We observed the clustering of
galectin-3 on endothelial cells at the sites of the contact with
tumor cells, consistent with its possible interaction with
T antigen on
cancer cells The
galectin-1 signal, however, strongly accumulated at the sites of cell-cell contacts predominantly on
tumor cells. The
T antigen-specific P-30 significantly (50%) inhibited this adhesion, which indicated that
T antigen participates in the adhesion of MDA-MB-435
breast cancer cells to the endothelium. The ability of synthetic
P-30 to inhibit both the spontaneous homotypic aggregation of MDA-MB-435 cells and their adhesion to the endothelium (>70 and 50%, respectively) suggests its potential functional significance for antiadhesive
therapy of
cancer metastasis.