Zosuquidar is a potent P-glycoprotein (P-gp) inhibitor (Kd = 79 nM). Zosuquidar binds with high affinity to P-glycoprotein and inhibits P-glycoprotein-mediated multidrug resistance (MDR). Restores doxorubicin (Cat. No. 1527) sensitivity in P-gp-expressing multidrug (MDR) resistant cancer cell lines.