Effect of multidrug resistance-reversing agents on transporting activity of human canalicular multispecific organic anion transporter

The canalicular multispecific organic anion transporter (cMOAT), also termed MRP2, is a recently identified ATP-binding cassette transporter. We previously established stable human cMOAT cDNA-transfected cells, LLC/cMOAT-1 from LLC-PK1 cells, and LLC/CMV cells that were transfected with an empty vector. We found that LLC/cMOAT-1 cells have increased resistance to vincristine (VCR), 7-ethyl-10-hydroxycamptothecin, and cisplatin but not to etoposide. The multidrug resistance-reversing agents cyclosporin A (CsA) and 2-[4-(diphenylmethyl)-1-piperazinyl]-5-(trans-4,6-dimethyl-1,3,2-dioxaphosphorinan-2-yl)-2,6-dimethyl-4-(3-nitrophenyl)-3-pyridinecarboxylate P-oxide (PAK-104P) almost completely reversed the resistance to VCR, 7-ethyl-10-hydroxy-camptothecin, and cisplatin of LLC/cMOAT-1 cells; and DL-buthionine(S,R)-sulfoximine, (3'-oxo-4-butenyl-4-methyl-threonine(1), (valine(2)) cyclosporin (PSC833), and 3-([{3-(2-[7-chloro-2-quinolinyl] ethenyl)phenyl}-{(3-dimethylamino-3-oxopropyl)-thio}- methyl]thio)propanoic acid (MK571) partially reversed the resistance to these drugs. CsA and PAK-104P at 10 mu M enhanced the accumulation of VCR in LLC/cMOAT-1 cells almost to the level in LLC/CMV cells without the agents. The efflux of VCR from LLC/cMOAT-1 cells was enhanced compared with LLC/CMV cells and inhibited by CsA and PAK-104P. Transport of leukotriene C-4 (LTC4) and S-(2, 4-dinitrophenyl) glutathione also was studied with membrane vesicles prepared from these cells. LTC4 and S-( 2, 4-dinitrophenyl) glutathione were actively transported into membrane vesicles prepared from LLC/cMOAT-1 cells. The K-m and V-max values for the uptake of LTC4 by the LLC/cMOAT-1 membrane vesicles were 0.26 +/- 0.05 mu M and 7.48 +/- 0.67 pmol/min/mg protein, respectively. LTC4 transport was competitively inhibited by PAK-104P, CsA, MK571, and PSC833, with K-i values of 3.7, 4.7, 13.1, and 28.9 mu M, respectively. These findings demonstrate that cMOAT confers a novel drug-resistance phenotype. CsA and PAK-104P may be useful for reversing cMOAT-mediated drug resistance in tumors.