P-gp inhibitor 1 is a novel inhibitor reversing P-glycoprotein -mediated multidrug resistance. In Vitro P-gp inhibitor 1 (12k) possesses high potency ( EC 50 =57.9±3.5 nM), low cytotoxicity, and long duration of activity in reversing doxorubicin (DOX) resistance in K562/A02 cells (1 μM, 80 minutes). P-gp inhibitor 1 also boosts the potency of other MDR-related cytotoxic agents with different structures, increases accumulation of DOX, blocks Pgp-mediated Rh123 efflux, and suppresses P-gp ATPase activity in K562/A02 MDR cells (0.1, 1, 5 μM, 1 hour). MCE has not independently confirmed the accuracy of these methods. They are for reference only. Western Blot AnalysisCell Line: K562/A02 cell Concentration: 0.1, 0.5, or 2.0 μM Incubation Time: 72 hours Result: MDR reversal by 12k was not caused by a decreased protein expression but instead most likely due to direct inhibition of P-gp efflux. Form:Solid IC50& Target:P-glycoprotein