Triazole BridgedFlavonoid Dimers as Potent, Nontoxic,and Highly Selective Breast Cancer Resistance Protein (BCRP/ABCG2)Inhibitors

The present work describes the syntheses of diverse triazole bridged flavonoid dimers and identifies potent, nontoxic and highly selective BCRP inhibitors. A homodimer, Ac22(Az8)2, with m-methoxycarbonylbenzyloxy substitution at C-3 of the flavone moieties and a bis-triazole-containing linker (21 atoms between the two flavones) showed low toxicity (IC50 towards L929, 3T3 and HFF-1 > 100 µM), potent BCRP-inhibitory activity (EC50 = 1-2 nM) and high BCRP selectivity (BCRP selectivity over MRP1 and P-gp > 455-909). Ac22(Az8)2 inhibits BCRP-ATPase activity, blocks the drug efflux activity of BCRP, elevates the intracellular drug accumulation, and finally restores the drug sensitivity of BCRP-overexpressing cells. It does not down-regulate the surface BCRP protein expression to enhance the drug retention. Therefore, Ac22(Az8)2 and similar flavonoid dimers appear to be promising candidates for further development into combination therapy to overcome MDR cancers with BCRP overexpression.