Influence of cellular ganglioside depletion on tumor formation

Background: Gangliosides are immunosuppressive cell surface molecules that are often present in high concentrations in and shed actively by tumor cells. These molecules inhibit the antitumor immune response that is implicated in tumor rejection. We therefore determined the ability of tumor cells pharmacologically depleted of gangliosides to form tumors in mice. Methods: We tested a ganglioside-rich subline of B16 murine melanoma, MEB4, and MEB4 cells that had been depleted of endogenous gangliosides by incubation with 0.5 mu M 1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol, a specific inhibitor of the enzyme glucosylceramide synthase, Tumor formation was assessed twice a week for 10 weeks after the intradermal injection of tumor cells, and metastatic potential was assessed 4 weeks after tail vein injection of tumor cells. All P values are from two-sided tests. Results: Reduction of the ganglioside content of MEB4 cells, which was not cytotoxic to cells and did not inhibit cell proliferation in vitro, markedly reduced their ability to form tumors. Only 40% of the mice given an intradermal injection of 10(5) ganglioside-depleted MEB4 cells developed tumors compared with 100% of the mice given an injection of 105 control MEB4 cells (P<.001), Ganglioside depletion also reduced metastasis: A mean of five pulmonary metastases was detected per mouse given an injection of 2 x 10(5) ganglioside-depleted MEB4 cells compared with a mean of 25 per mouse given an injection of 2 x 105 control MEB4 cells. Conclusion: Tumor cells with a pharmacologically decreased concentration of gangliosides produce fewer tumors in mice than do untreated cells, suggesting that pharmacologic depletion of gangliosides should be explored further as a therapeutic approach to cancer.