GANGLIOSIDES PROTECT HUMAN-MELANOMA CELLS FROM IONIZING RADIATION-INDUCED CLONOGENIC CELL-DEATH

With an experimental model of spontaneous lung metastases of melanoma developed in this laboratory, a range of sublines (variants and clones ) with different metastatic potential and ganglioside expression was e stablished from a single human melanoma cell line M4Be. Using an in vi tro clonogenic assay and provided that cells were cultured for no more than five passages, variations in cellular radioresistance of M4Be an d seven sublines derived from M4Be were detected. This study shows a p ositive correlation between the cell intrinsic radioresistance of M4Be and its seven sublines and their total ganglioside content. More prec isely, the proportion of radioresistant cells in M4Be and the seven su blines correlated with the number of cells determined by flow cytometr y that were positively labelled with a monoclonal antibody directed to GD3 disialoganglioside. Blocking the cellular biosynthesis of ganglio sides with the inhibitor Fumonisin B1 or cleaving with Vibrio cholerae neuraminidase the cell surface ganglioside-bound sialic acid in a rad ioresistant poorly metastatic subline increased its radiosensitivity i n vitro. Ln contrast, enrichment of a radiosensitive metastatic sublin e with exogenous bovine brain GM1 increased its radioresistance in vit ro. These results suggest that, in the radiation dose range important for radioprotection (0-1 Gy), membrane gangliosides radioprotect human melanoma cells in vitro.