Selection of Human Ovarian Carcinoma Cells with High Dissemination Potential by Repeated Passage of the Cells in vivo into Nude Mice, and Involvement of Lex-determinant in the Dissemination Potential

Cells of the human tumor cell line RMG-1, derived from a clear-cell adenocarcinoma of the ovary, were injected intraperitoneally into nude mice, and the cells obtained from the tumor nodules in the mesenterium were found to form a larger number of, and larger-sized, tumor nodules than the original RMG-1 cells. The RMG-1-h cells, transferred into culture from the tumor nodules after a 4th in vivo passage, showed a dissemination potential as high as that of cells disseminating directly from the tissues, and exceedingly higher than that of RMG-1 cells. To assess the molecular bases of the different biological properties of RMG-1 and RMG-1-h cells, we compared the content and expression of various carbohydrate antigens in both cells. The chromosomal profile of RMG-1-h cells revealed their human origin and was identical to that of the original RMG-1 cells. In contrast to the broad histogram for the Le^x-bearing cells among RMG-1 cells in flow cytometry, the weakly and moderately positive cells toward anti-Le^x antibody were found to be eliminated from the histogram for the RMG-1-h cells, resulting in the enrichment of cells strongly expressing Le^x, which may account for the high dissemination potential. In addition, the adhesion of RMG-1 cells to mesothelial cells was found to be significantly inhibited by pretreatment of the cells with anti-Le^x antibody, indicating Le^x-mediated cell-to-cell interaction between ovarian cancer cells and mesothelial cells. By TLC-immunostaining, two Le^x-glycolipids, III³Fucα-nLc₄Cer and V³Fucα-nLc₆Cer were detected in both RMG-1 and RMG-1-h cells, and their total concentrations were not significantly different from each other. However, the hydrophobic moieties of Le^x-glycolipids in RMG-1-h cells were different from those in RMG-1 cells, suggesting that a difference in the structure of the hydrophobic moieties of Le^x is partly involved in the enhanced reactivity of RMG-1-h cells toward anti-Le^x antibody. Thus, the high dissemination potential of ovarian cancer cells was shown to be mediated by the Le^x-determinant and the Le^x-bearing cells are enriched by repeated in vivo passage of the cells into nude mice.