Cloning and functional characterization of the multidrug resistance-associated protein (MRP1/ABCC1) from the...

The multidrug resistance-associated protein 1 (ABCC1) gene from human (hMRP1), dog (canMRP1), and mouse (muMRP1) all encode proteins that efficiently transport the endogenous MRP1 substrate glutathione-S-leukotriene C(4) and confer resistance to anticancer agents, including vincristine and etoposide. hMRP1 also confers resistance to anthracyclines, whereas this is not true of canMRP1 or muMRP1. To determine whether MRP1 from another animal species used in toxicological studies would be more functionally similar to hMRP1, we cloned and characterized two alleles of the MRP1 homologue from the cynomolgus monkey Macaca fascicularis (monMRP1). The monMRP1 cDNAs encode proteins of 1531 residues that are 98, 90, and 88% identical to hMRP1, canMRP1, and muMRP1, respectively. Stable overexpression of both monMRP1 alleles and hMRP1 in transformed human embryonic kidney cells was achieved using an episomal expression vector. Transporters encoded by both monMRP1 alleles were functionally very similar to hMRP1. monMRP1 conferred an increased resistance to vincristine and etoposide and transported glutathione-S-leukotriene C(4) into membrane vesicles. In addition, MRP1-mediated drug resistance was effectively reversed in monMRP1 and hMRP1 transfectants by LY402913, a new MRP1-selective inhibitor in the class of tricyclic isoxazoles. However, monMRP1 transporters conferred a reduced level of resistance to the anthracyclines doxorubicin, daunorubicin, and epirubicin relative to hMRP1, although resistance levels were significant relative to vector control cells. These functional differences between human and monkey MRP1 transporters will need to be considered when designing pharmacokinetic and toxicological studies for the preclinical evaluation of MRP1 modulators.