Interaction of CJZ3, a lomerizine derivative, with ATPase activity of human P-glycoprotein in doxorubicin-resistant human myelogenous leukemia (K562/DOX) cells.

P-Glycoprotein, a 170-180 kDa membrane glycoprotein that mediates multidrug resistance, hydrolyses ATP to efflux a broad spectrum of hydrophobic agents. To observe the interaction of a P-gp reversal agent with P-gp ATPase activity should provide further insights into the mechanisms of P-gp modulator. In this study, we analysed the effect of CJZ3, a lomerizine derivative, on the adenosine triphosphatase (ATPase) activity of human P-glycoprotein. The results showed that the basal P-gp ATPase activity was increased by CJZ3 with half-maximal activity concentration (Km) of 6.8 +/- 1.5 microM, CJZ3 may interact with P-gp with a higher affinity and exhibit a more potent effect than verapamil (Ver). Kinetic analysis indicated a noncompetitive inhibition of Ver-stimulated P-gp ATPase activity and a competitive inhibition of CJX2-stimulated P-gp ATPase activity by CJZ3, moreover, the effect of CsA on CJZ3-stimulated and Ver-stimulated P-gp ATPase activity showed a non-competitive and a competitive inhibition respectively. CJZ3 and CJX2 can bind P-gp either on overlapping sites or distinct but interacting sites, while CJZ3 and Ver as well as CsA can bind P-gp on separated sites in K562/DOX cells.