Modulation of human Multidrug Resistance Protein (MRP) 1 (ABCC1) and MRP2 (ABCC2) transport activities by endogenous and exogenous glutathione-conjugated catechol metabolites

Members of the multidrug resistance protein (MRP/ABCC) subfamily of ATP-binding cassette proteins transport a wide array of anionic compounds, including sulfate, glucuronide, and glutathione (GSH) conjugates. The present study tested the ATP-dependent vesicular transport of leukotriene C₄ and 17β-estradiol 17-(β-D-glucuronide) (E₂17βG) mediated by the MRP1 and MRP2 transporters in the presence of six potential modulators from three different classes of GSH-conjugated catechol metabolites: the ecstasy metabolite 5-(glutathion-S-yl)-N-methyl-α-methyldopamine (5-GS-N-Me-α-MeDA), the caffeic acid metabolite 2-(glutathion-S-yl)- caffeic acid (2-GS-CA), and four GSH conjugates of 2-hydroxy (OH) and 4-OH estrogens (GS estrogens). MRP1-mediated E₂17βG transport was inhibited in a competitive manner with a relative order of potency of GS estrogens (IC₅₀ <1 μM) > 2-GS-CA (IC₅₀ 3 μM) > 5-GS-N-Me-α-MeDA (IC₅₀ 31 μM). MRP2-mediated transport was inhibited with a similar order of potency, except the 2-hydroxy-4- (glutathion-S-yl)-estradiol and 4-hydroxy-2-(glutathion-S-yl)-estradiol conjugates were approximately 50- and 300-fold less potent, respectively. Transport activity was unaffected by N-acetylcysteine conjugates of N-Me-α-MeDA and CA. The position of GSH conjugation appears important as all four GS estrogen conjugates tested were potent inhibitors of MRP1 transport, but only the 2-hydroxy-1-(glutathion-S-yl)-estradiol and 2-hydroxy-1- (glutathion-S-yl)-estrone conjugates were potent inhibitors of MRP2-mediated transport. In conclusion, we have identified three new classes of MRP1 and MRP2 modulators and demonstrated that one of these, the estrogen conjugates, shows unanticipated differences in their interactions with the two transporters.