Effects of bacterial cell surface polysaccharides on cell adhesion and cancer metastasis

Endothelial cells cover inside of the vascular walls. These cells are known to have important functions in cancer metastasis. In the first stage of metastasis, sialyl Le(a) and Le(x) carbohydrates of cancer cells interact with endothelial cell leukocyte adhesion molecule-1 (ELAM-1) on endothelial cells (rolling). In this study, we tried to develop new cancer metastasis inhibitors by hampering this rolling step. Polysaccharides from a bacterium, Streptococcus agalactiae,have very similar structures to sialyl Le(a) and Le(x). The polysaccharides contain NeuNAc-Gal-GlcNAc trisaccharide which is a common structure of sialyl Lewis carbohydrates, but do not contain branched fucose residue. We partially purified the bacterial polysaccharides and investigated the effects on adhesion between endothelial cells and cancer cells (HL60 and Colo201). In the presence of the polysaccharides, adhesion between endothelial and cancer cells was reduced to 15-60% of that without the polysaccharides. This seems to be due to competitive inhibitory activities of these bacterial polysaccharides on the cell adhesion. This result suggests that these polysaccharides and their derivatives can be used for development of new cancer metastasis inhibitors.