A selective inhibitor of acid ceramidase (IC50 = 79 nM for rat acid ceramidase); reduces acid ceramidase activity and induces intracellular accumulation of various ceramide species in SW403 colon and LNCaP prostate cancer cells; induces apoptosis in SW403 cells without inhibiting DNA synthesis (IC50 = 1,212 mM for human thymidylate synthetase); reduces acid ceramidase activity and increases ceramide accumulation in mouse lung and brain at 10 and 30 mg/kg