Role of asparagine-linked carbohydrates in pulmonary metastasis of B16-F10 murine melanoma cells: implication through glycosylation inhibition by nojirimycin.

N-linked oligosaccharide moieties of cell surface glycoconjugates may be involved in the metastatic potential of tumour cells. Many studies have examined the anti-metastatic properties of inhibitors of carbohydrate synthesis or processing in vitro. However, there has so far been little evidence of such inhibitory factors on metastasis in vivo because of the general high toxicity of the inhibitors. In this study, we found nojirimycin (NM) to be a substantially non-toxic carbohydrate synthesis inhibitor that inhibited the experimental metastasis of B16-F10 melanoma cells not only in vitro but also in vivo. When NM was administered intraperitoneally to syngeneic C57BL/6 mice, the inhibition was dose-dependent, with 40-75% suppression of pulmonary colonization observed after 5 days exposure to NM (at 0.4 or 4 mg/day). An in vitro lectin sensitivity assay showed that NM-treated B16-F10 cells were less susceptible to the lectin concanavalin-A, suggesting alteration or decrease of high mannose-type carbohydrate moieties on the cell surface. Further in vitro analysis of adhesiveness between B16-F10 cells and endothelial cells demonstrated that NM treatment causes reduced binding of B16-F10 cells to endothelial cells. We have also studied the effect of NM on natural killer (NK) cells in mice. NM treatment elicited no substantial increase in the cytotoxic activity of splenic NK cells against YAC-1 target cells. These results indicate that NM acts on the process of adhesion and that specific structures of the cell surface carbohydrate moieties may be involved in the colonization phase of metastasis in vivo.