Identification of the Acetamide-Chalcone Derivative That Selectively Inhibits ABCG2 Transport Activity

Multidrug resistance (MDR) remains a major obstacle to effective cancer chemotherapy, often driven by the overexpression of ABC transporters such as ABCG2. In this study, we identified the synthetic chalcone derivative, B5, as a selective ABCG2 inhibitor. Among the 20 chalcone analogs evaluated, B5, bearing an acetamide group at R1 and an ethoxy substituent at R2, was the only compound that produced more than 50% inhibition of ABCG2-mediated Hoechst 33342 transport at 10 μM, while showing no activity against ABCB1. B5 exhibited an IC₅₀ of 2.7 μM for ABCG2 inhibition, consistent with the low-micromolar potency reported for chalcone-based ABCG2 modulators. Furthermore, B5 effectively reversed ABCG2-mediated resistance to the chemotherapeutic agent SN-38 in ABCG2-overexpressing cells, thereby restoring drug sensitivity. Notably, B5 was noncytotoxic at concentrations up to 5 μM and did not exhibit differential cytotoxicity between parental and ABCG2-overexpressing cells, suggesting that it was not efficiently transported under the experimental conditions. ATPase assays revealed that B5 stimulated, rather than inhibited, ABCG2 ATPase activity, a behavior previously reported for chemically distinct ABCG2 inhibitors. Molecular docking and molecular dynamics simulations suggested that B5 bound within the central inhibitor-binding cavity of ABCG2, forming π-π interactions with Phe439 and hydrophobic contacts with Val546, although with a lower interaction frequency than the reference inhibitor Ko143. This binding mode, together with the physicochemical properties of B5, suggested that the electron-donating acetamide group enhanced its inhibitory activity, potentially by facilitating hydrogen-bonding interactions within the binding pocket. Collectively, these findings identified B5 as a promising lead compound for the development of selective ABCG2 inhibitors and provided structural insights to support the rational design of more potent analogs capable of overcoming MDR in cancer.