Twenty-seven chalcogenopyrylium derivatives varying in the heteroatom of the pyrylium core and substituents at the 2-, 4-, and 6-positions were examined for their effect on human MRP1-mediated uptake of tritiated estradiol glucuronide into inside-out membrane vesicles, their affinity for and ability to stimulate the ATPase activity of purified human P-glycoprotein (P-gp)-His(10), and their ability to promote uptake of calcein AM and vinblastine in multidrug-resistant cells. Differences in their effects on MRP1 and P-gp activity were noted, and a second set of thiopyrylium compounds with systematic substituent changes was examined to refine these differences further. Derivatives with tert-butyl substituents in the 2- and 6-positions had the lowest inhibitory activity toward both transporters. Derivatives with thioamide functionality in the 4-position were more active against MRP1 than derivatives with amide functionality. Conversely, derivatives with amide functionality in the 4-position were more active in P-gp than derivatives with thioamide functionality.

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 [ 3 H]estradiol glucuronide (E 2 17bG; 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 17bG uptake by >50% (IC 50 values: 0.7-7.6 mM). Of 9 CGPs with IC 50 values £2 mM, 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 mM) 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 [ 3 H]E 2 17bG uptake by MRP4. In contrast, their effects on MRP2 varied, with two (V-4, V-6) inhibiting E 2 17bG transport (IC 50 values: 2.0 and 9.2 mM) 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.