Direct binding of chloroquine to the multidrug resistance protein (MRP) - Possible role for MRP in chloroquine drug transport and resistance in tumor cells

Multidrug resistance protein (MRP) transports a range of compounds that include glutathione S-conjugates, amphiphilic anionic drugs, and natural-product toxins. However, the mechanism of MRP drug binding and transport is presently unclear. We recently demonstrated the direct binding of a quinoline-based photoactive drug, N-{4-[1-hydroxy-2-(dibutylamino)ethyl] quinolin-8-yl}-4-azidosalicylamide (IAAQ), to MRP at a biologically relevant site [Vezmar et at., Biochem Biophys Res Commun 241: 104-111, 1997]. In the present report, we demonstrated that the lysosomotropic or antimalarial drug chloroquine is a substrate for MRP. Specifically, our results showed that chloroquine, similar to leukotriene C-4 (LTC4) and 3-(3-(2-(7-chloro-2-quinolinyl)ethenyl-phenyl)((3-(dimethyl amino-3-oxo propyl)thio)methyl)thio) propanoic acid (MK 571), inhibits the photoaffinity labeling of MRP by IAAQ. Furthermore, cell growth assays showed MRP-expressing multidrug resistant cells (H69/AR and HL60/AR) to be more resistant to chloroquine than their parental cells (i.e., IC50 of 121 mu M versus 28 mu M chloroquine for H-69/AR and H69, respectively). Moreover, MK 571, an LTD, receptor antagonist, reversed the resistance of H69/AR cells to chloroquine. Drug transport studies using [C-14]chloroquine demonstrated that MRP-expressing cells accumulate less drug than the parental drug sensitive cells. The reduced accumulation of [C-14]chloroquine in resistant cells was ATP dependent and was due to enhanced drug efflux. Taken together, the results of this study show that MRP modulates the transport of chloroquine by direct binding. (C) 1998 Elsevier Science Inc.