Synthesis, Shedding, and Intercellular Transfer of Human Medulloblastoma Gangliosides: Abrogation by a New Inhibitor of Glucosylceramide Synthase

Abstract: The biological activity of human medulloblastoma tumor gangliosides very likely involves the interaction of these molecules with host cells in the tumor microenvironment. To trace the hypothesized intercellular transfer of shed medulloblastoma gangliosides, we used an in vitro dual-chamber culture system in which the tumor cells, the shed gangliosides, and the target cells to which they might bind would not be perturbed during the transfer process. We observed that under these unmanipulated conditions, gangliosides were shed by the Daoy medulloblastoma cell line (～300 pmol/10⁸ cells/h), traversed the chamber membrane, and stably bound to the target fibroblasts at the very high density of 10⁷ molecules per cell within 48 h. To determine if this substantial intercellular transfer of shed gangliosides, with its potential of modifying target cell function, could be blocked, we evaluated a new inhibitor of glucosylceramide synthase, dl - threo -1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol (PPPP). PPPP (1.0 µ M ) reduced (90%) Daoy cell ganglioside content strikingly, without causing toxicity or inhibiting cell proliferation. Subsequently, ganglioside shedding by the medulloblastoma cells was diminished significantly (to ～50 pmol/10⁸/h), and binding of radiolabeled shed medulloblastoma gangliosides to target fibroblasts was consequently almost completely abrogated. We conclude that the shedding and transfer of potentially biologically active human medulloblastoma gangliosides can be diminished effectively by PPPP.