New players from the old chalcone scaffold: Synthesis, identification, and characterization of new potent ABCG2 inhibitors.

The ABCG2 transporter is an efflux pump that can transport various anticancer drugs and is strongly associated with multidrug resistance (MDR) in cancer. A promising strategy to combat MDR mediated by this transporter is through functional inhibition. However, there are currently no potent selective ABCG2 inhibitors in clinical trials. Chalcone, a privileged scaffold, can be easily synthesized to produce a wide array of derivatives with diverse biological applications. Notably, chalcone derivatives have been identified as inhibitors of ABC transporters, including ABCG2. In this study, we synthesized and evaluated a series of twenty chalcone derivatives as potential ABCG2 inhibitors. Out of these, ten compounds were found to completely inhibit ABCG2 transport activity. Among them, compounds 10, 19, and 20 demonstrated particularly high potency, with EC values (compound concentrations giving a half-maximal inhibition) of 0.34, 0.83, and 0.94 μM, respectively. These three promising chalcone derivatives selectively inhibited ABCG2, enhanced the binding of the 5D3 conformational antibody, and exhibited low cytotoxicity, with estimated IG values (compound concentrations giving a half-maximal cell viability) exceeding 50 μM. The therapeutic ratio (TR), calculated as the ratio of IG to EC values, revealed that 10 had a TR greater than 147, nearly 3-fold higher than those of 19 (greater than 60) and 20 (greater than 53). Modeling studies, while biased towards the conformation of the selected starting compound, successfully reproduced relevant interactions with residues Phe439 and Asn436, which are consistent with ABCG2 inhibition. Finally, 10 was shown to chemosensitize cell lines that overexpress ABCG2, effectively overcoming the MDR phenotype mediated by this transporter.