Development of a new inhibitor of glucosylceramide synthase

Analogs of the potent inhibitor of glucosylceramide (GlcCer) synthase, D-th reo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (P4), based on subst itutions in the palmitoyl group were made by means of a stereo-selective sy nthetic method in order to elucidate the role of the hydrophobic portion in both the inhibitory action toward the enzyme and the biological effects. W hile P4 strongly inhibited GlcCer synthase with an IC50 of 0.5 mu M in vitr o, it also inhibited cell growth by 50% at the concentration of 7 mu M, The shorter N-acyl chain analogs including decanoyl, octanoyl, and hexanoyl gr oups showed similar IC50 values for GlcCer synthase (around 2 mu M), but th e hexanoyl analog exhibited only a slight inhibitory effect on cell growth, showing the dissociation between GlcCer depletion and cell growth. Several compounds which exhibit similar hydrophobicity to the hexanoyl analog of P 4 were subsequently designed. We found that D-threo-1-phenyl-abenzyloxycarb onylamino-3-pyrrolidino-1-propanol (PBPP) was a most potent inhibitor, show ing an IC50 of 0.3 mu M. In cultured cells, PBPP was able to deplete glycos phingolipids without affecting cell growth or the ceramide level.