Inhibition of experimental metastasis of murine Lewis lung carcinoma by an inhibitor of glucosylceramide synthase and its possible mechanism of action.

In view of the increasing evidence that glucosphingolipids (GSLs) on tumor cell surfaces play an important role in tumor metastasis, an inhibitor of glucosylceramide synthase, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP) was used to evaluate the role of GSLs in this respect. Treatment of Lewis lung carcinoma cells with 5 microM D-PDMP resulted in a time-dependent marked decrease in levels of all cellular GSLs (glucosylceramide, lactosylceramide, ceramide trihexoside, globoside, and ganglioside GM3). By 6 days, the total GSL content was reduced to approximately 20% of the level in the untreated control cells and at the same time the lung-colonizing capacity of the PDMP-treated cells in inoculated mice was greatly reduced. Closely associated with the degree of GSL depletion, the ability of the cells to invade reconstituted basement membranes in vitro was also reduced, suggesting that GSLs in tumor cell membranes modulate the cell surface interaction with basement membrane components. In order to assess a possible contribution of the defective capacities to drug-induced suppression of experimental metastasis and invasion, we tested the effect of D-PDMP on attachment and migration to laminin and fibronectin and found that the inhibitor specifically reduced the laminin-mediated attachment and migration, whereas it had no effect on fibronectin-mediated attachment and migration. These effects of the inhibitor on lung colonizing capacity in vivo and the invasion, adhesion, and migration properties of the cells in vitro were reversible within 24 h after removal of the drug. By contrast, L-PDMP (the enantiomeric form of D-PDMP), which has no inhibitory activity on glucosylceramide synthesis, did not cause any of the changes produced by D-PDMP. Together, these results suggest that GSLs in tumor cell membranes are essential for the metastatic spread of tumor cells through basement membranes, modulating the interaction of laminin and its receptors.