PGP and leukemia: Mifepristone, the antiprogestin also known as RU-486, can enhance vincristine and Adriamycin sensitivity in drug-resistant gastric cancer, hepatoma, and leukemia cells (Table 1V) [184,185], and fittingly, mifepristone is a P-gp antagonist [185] as well as a ceramide glycosylation blocker in drug-resistant cells [192].