Selection of Human Ovarian Carcinoma Cells with High Dissemination Potential by Repeated Passage of the Cells in vivo into Nude Mice, and Involvement of Le(x)‐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, III(3)Fucα‐nLc(4)Cer and V(3)Fucα‐nLc(6)Cer 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.