New structure–activity relationships of chalcone inhibitors of breast cancer resistance protein: polyspecificity toward inhibition and critical substitutions against cytotoxicity

Luciana Pereira Rangel,^1,2,* Evelyn Winter,^1,3,* Charlotte Gauthier,¹ Raphaël Terreux,⁴ Louise D Chiaradia-Delatorre,⁵ Alessandra Mascarello,⁵ Ricardo J Nunes,⁵ Rosendo A Yunes,⁵ Tania B Creczynski-Pasa,³ Sira Macalou,¹ Doriane Lorendeau,¹ Hélène Baubichon-Cortay,¹ Antonio Ferreira-Pereira,² Attilio Di Pietro<sup>1

1</sup>Equipe Labellisée Ligue 2013, BMSSI UMR 5086 CNRS/Université Lyon 1, Institut de Biologie et Chimie des Protéines, Lyon, France; ²Department of General Microbiology, Institute of Microbiology, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil; ³Department of Pharmaceutical Sciences, PPGFAR, Federal University of Santa Catarina, Florianopolis, Santa Catarina, Brazil; ⁴Equipe BISI, BMSSI UMR 5086 CNRS/Université Lyon 1, Institut de Biologie et Chimie des Protéines, Lyon, France; ⁵Department of Chemistry, Federal University of Santa Catarina, Florianopolis, Santa Catarina, Brazil

^*These authors contributed equally to this work

Abstract: Adenosine triphosphate-binding cassette subfamily G member 2 (ABCG2) plays a major role in cancer cell multidrug resistance, which contributes to low efficacy of chemotherapy. Chalcones were recently found to be potent and specific inhibitors, but unfortunately display a significant cytotoxicity. A cellular screening against ABCG2-mediated mitoxantrone efflux was performed here by flow cytometry on 54 chalcone derivatives from three different series with a wide panel of substituents. The identified leads, with submicromolar IC₅₀ (half maximal inhibitory concentration) values, showed that the previously identified 2'-OH-4',6'-dimethoxyphenyl, as A-ring, could be efficiently replaced by a 2'-naphthyl group, or a 3',4'-methylenedioxyphenyl with lower affinity. Such a structural variability indicates polyspecificity of the multidrug transporter for inhibitors. At least two methoxyl groups were necessary on B-ring for optimal inhibition, but substitution at positions 3, 4, and 5 induced cytotoxicity. The presence of a large O-benzyl substituent at position 4 and a 2'-naphthyl as A-ring markedly decreased the cytotoxicity, giving a high therapeutic ratio, which constitutes a critical requirement for future in-vivo assays in animal models.

Keywords: ABC transporters, BCRP/ABCG2, cancer chemotherapy, drug transport, inhibitory chalcone derivatives, multidrug resistance transporters.