Chalcogenopyrylium Dyes as Differential Modulators of Organic Anion Transport by Multidrug Resistance Protein 1 (MRP1), MRP2, and MRP4

Multidrug resistance proteins (MRPs) mediate the ATP-dependent efflux of structurally diverse compounds, including anticancer drugs and physiologic organic anions. Five classes of chalcogenopyrylium dyes (CGPs) were examined for their ability to modulate transport of [H-3]estradiol glucuronide (E(2)17 beta G; a prototypical MRP substrate) into MRP-enriched inside-out membrane vesicles. Additionally, some CGPs were tested in intact transfected cells using a calcein efflux assay. Sixteen of 34 CGPs inhibited MRP1-mediated E(2)17 beta G uptake by >50% (IC50 values: 0.7-7.6 mu M). Of 9 CGPs with IC50 values <= 2 mu M, two belonged to class I, two to class III, and five to class V. When tested in the intact cells, only 4 of 16 CGPs (at 10 mu M) inhibited MRP1-mediated calcein efflux by >50% (III-1, V-3, V-4, V-6), whereas a fifth (I-5) inhibited efflux by just 23%. These five CGPs also inhibited [H-3]E(2)17 beta G uptake by MRP4. In contrast, their effects on MRP2 varied, with two (V-4, V-6) inhibiting E(2)17 beta G transport (IC50 values: 2.0 and 9.2 mu M) and two (V-3, III-1) stimulating transport (>2-fold), whereas CGP I-5 had no effect. Strikingly, although V-3 and V-4 had opposite effects on MRP2 activity, they are structurally identical except for their chalcogen atom (Se versus Te). This study is the first to identify class V CGPs, with their distinctive methine or trimethine linkage between two disubstituted pyrylium moieties, as a particularly potent class of MRP modulators, and to show that, within this core structure, differences in the electronegativity associated with a chalcogen atom can be the sole determinant of whether a compound will stimulate or inhibit MRP2.