In vitro and in vivo modulation of ABCG2 by functionalized aurones and structurally related analogs

Abstract

Over-expression of ABCG2 is linked to multidrug resistance in cancer chemotherapy. We have previously shown that functionalized aurones effectively reduced the efflux of pheophorbide A (an ABCG2 substrate) from ABCG2 over-expressing MDA-MB-231/R (“R”) cells. In the present report, we investigated the functional relevance of this observation and the mechanisms by which it occurs. Aurones and related analogs were investigated for re-sensitization of R cells to mitoxantrone (MX, a chemotherapeutic substrate of ABCG2) in cell-based assays, accumulation of intracellular MX by cell cytometry, interaction with ABCG2 by biochemical assays and in vivo efficacy in MX resistant nude mice xenografts. We found that methoxylated aurones interacted directly with ABCG2 to inhibit efflux activity, possibly by competing for occupancy of one of the substrate binding sites on ABCG2. The present evidence suggests that they are not transported by ABCG2 although they stimulate ABCG2-ATPase activity. Alteration of ABCG2 protein expression was also discounted. One member was found to re-sensitize R cells to MX in both in vitro and in vivo settings. Our study identified methoxylated aurones as promising compounds associated with low toxicities and potent modulatory effects on the ABCG2 efflux protein. Thus, they warrant further scrutiny as lead templates for development as reversal agents of multidrug resistance.

The Effects of Synthetically Modified Natural Compounds on ABC Transporters

“…Ko143 showed highly potent inhibition of BCRP in vitro however in vivo Ko143 exhibited a short plasma half-life of approximately 1 h [ 81 ]. Thereafter, natural compounds including flavonoid scaffolds, aurones, marine products, quinazoline and chalcone moieties and protoflavones have all been modified to investigate BCRP reversibility [ 77 , 78 , 82 , 83 , 84 , 85 ].…”

“…Aurones are a family of flavonoids previously shown to reverse MDR towards mitoxantrone in ABCG2-overexpressing cells [ 83 ]. Mitoxantrone, pheophorbide A and Hoechst 33342 are fluorescent BCRP substrates which can be detected by flow cytometry, allowing direct quantification of BCRP transport activity [ 78 , 83 , 84 ]. Aurone analogues A-2, A-3, I-2, I-3, F-2 and F-3 exhibited considerable cellular accumulation of mitoxantrone, up to levels comparable to fumtremogin C (FTC), a well-defined BCRP inhibitor [ 83 ].…”

“…Mitoxantrone, pheophorbide A and Hoechst 33342 are fluorescent BCRP substrates which can be detected by flow cytometry, allowing direct quantification of BCRP transport activity [ 78 , 83 , 84 ]. Aurone analogues A-2, A-3, I-2, I-3, F-2 and F-3 exhibited considerable cellular accumulation of mitoxantrone, up to levels comparable to fumtremogin C (FTC), a well-defined BCRP inhibitor [ 83 ]. Four methoxylated aurone compounds at 50 nM significantly reduced the IC 50 of mitoxantrone [ 83 ].…”

“…Aurone analogues A-2, A-3, I-2, I-3, F-2 and F-3 exhibited considerable cellular accumulation of mitoxantrone, up to levels comparable to fumtremogin C (FTC), a well-defined BCRP inhibitor [ 83 ]. Four methoxylated aurone compounds at 50 nM significantly reduced the IC 50 of mitoxantrone [ 83 ]. Mitoxantrone was combined with 0.5 µM of a series of chalcone (A-2, A-3, I-2, C-2) compounds and the F-2 aurone compound resulted in complete MDR reversal in resistant cells [ 83 ].…”

“…Four methoxylated aurone compounds at 50 nM significantly reduced the IC 50 of mitoxantrone [ 83 ]. Mitoxantrone was combined with 0.5 µM of a series of chalcone (A-2, A-3, I-2, C-2) compounds and the F-2 aurone compound resulted in complete MDR reversal in resistant cells [ 83 ]. Moreover, I-2 sensitized cells resistant towards mitoxantrone to a higher extent than that observed in control cells [ 83 ].…”