Reversal of Multidrug Resistance by 7-O-Benzoylpyripyropene A in Multidrug-Resistant Tumor Cells.

7-O-Benzoylpyripyropene A (7-O-BzP), a semi-synthetic analog of pyripyropene, was investigated for its reversing effect on multidrug-resistant (MDR) tumor cells. 7-O-BzP (6.25 microg/ml) completely reversed resistance against vincristine and adriamycin in vincristine-resistant KB cells (VJ-300) and adriamycin-resistant P388 cells (P388/ADR), respectively. 7-O-BzP alone had no effect on the growth of drug sensitive and drug-resistant cells. 7-O-BzP (6.25 microg/ml) significantly enhanced accumulation of [3H]vincristine in VJ-300 cells and completely inhibited the binding of [3H]azidopine to the P-glycoprotein in VJ-300 cells and P388/ADR cells. The result suggests that 7-O-BzP effectively reverses P-glycoprotein-related MDR by interacting directly with P-glycoprotein in drug resistant VJ-300 and P388/ADR cells.