Research paper New, highly potent and non-toxic, chromone inhibitors of the human breast cancer resistance protein ABCG2 Amanda do Rocio Andrade Pires a, 1 , Florine Lecerf-Schmidt b, 1 , Nathalie Guragossian a , Jaqueline Pazinato a , Gustavo Jabor Gozzi a , Evelyn Winter a , Glaucio Valdameri a , Alexander Veale b , Ahc  ene Boumendjel b , Attilio Di Pietro a, 2 , Basile P  er  es b, *, 2 a Equipe Labellis ee Ligue 2014 “M ecanisme et Modulation de la R esistance aux M edicaments”, Universit e Lyon 1, Univ. Lyon, CNRS UMR 5086 Bases Mol eculaires et Structurales des Syst emes Infectieux, IBCP, 7 Passage du Vercors, 69367 Lyon Cedex 07, France b Universit e Grenoble-Alpes/CNRS, D epartement de Pharmacochimie Mol eculaire UMR 5063, F-38041 Grenoble, France article info Article history: Received 21 January 2016 Received in revised form 28 April 2016 Accepted 22 May 2016 Available online 27 June 2016 Keywords: Chromones ABCG2 modulators Chemoresistance Efflux abstract Breast cancer resistance protein (BCRP/ABCG2) is one of the major transporters involved in the efflux of anticancer compounds, contributing to multidrug resistance (MDR). Inhibition of ABCG2-mediated transport is then considered a promising strategy for overcoming MDR in tumors. We recently identi- fied a chromone derivative, namely MBL-II-141 as a selective ABCG2 inhibitor, with relevant in vivo activity. Here, we report the pharmacomodulation of MBL-II-141, with the aim of identifying key phar- macophoric elements to design more potent selective and non-toxic inhibitors. Through rational structural modifications of MBL-II-141, using simple and affordable chemistry, we obtained highly active and easily-made inhibitors of ABCG2. Among the investigated compounds, derivative 4a, was found to be 3-fold more potent than MBL-II-141. It was similarly efficient as the reference inhibitor Ko143 but with the advantage of a lower intrinsic cytotoxicity, and therefore constitutes the best ABCG2 inhibitor ever reported displaying a very high therapeutic ratio. © 2016 Published by Elsevier Masson SAS. 1. Introduction ATP-Binding Cassette (ABC) transporters belong to one of the largest membrane protein superfamily expressed in both pro- karyotic and eukaryotic cells. Acting as ATP-powered pumps, ABC transporters are able to extrude a wide variety of structurally- unrelated compounds from the cells. As expressed in major phys- iological barriers, ABC transporters are crucial for cell detoxification and survival, by effluxing exogenous toxic substances outside the cell. Their overexpression in tumor cells contributes to chemo- resistance through the efflux of anticancer drugs. P-glycoprotein (Pgp/ABCB1) [1], multidrug resistance protein 1 (MRP1/ABCC1) [2] and breast cancer resistance protein (BCRP/ABCG2) [3e5] are so far the three major ABC proteins recognized to strongly contribute to the multidrug resistance developed by cancer cells against cytotoxic drugs. ABCG2 is the most recently ABC transporter identified to be involved in cross-resistance to a wide panel of structurally-unrelated anticancer drugs and other compounds. As opposed to Pgp and MRP1, ABCG2 is a half-transporter which re- quires at least dimerization [6], or even tetramerization [7,8], to be functional. Since its discovery, ABCG2 has attracted intense interest in the MDR context, particularly as a target for the development of new inhibitors to be used in combination with conventional anti- cancer drugs for restoring their efficacy. In the absence of high- resolution structural information regarding ABCG2, the design of new inhibitors is exclusively based on ligand-based drug design [9,10]. Fumitremorgin C (FTC) [11] was the first selective inhibitor re- ported for ABCG2. Unfortunately, it was found to be clinically un- usable due to its high neurotoxicity. Targeting powerful, selective and less toxic inhibitors has led to the design and development of FTC synthetic analogues. In this regard, Ko143 was considered as a reference ABCG2 inhibitor on the basis of its high potency [12,13]; however, its selectivity for ABCG2 versus ABCB1 (P-gp) was recently challenged [14]. Despite the number of known ABCG2 inhibitors [15e22], only very few of them were evaluated in vivo, in animal- * Corresponding author. E-mail address: Basile.Peres@univ-grenoble-alpes.fr (B. P er es). 1 First co-authors. 2 Last co-authors. Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech http://dx.doi.org/10.1016/j.ejmech.2016.05.053 0223-5234/© 2016 Published by Elsevier Masson SAS. European Journal of Medicinal Chemistry 122 (2016) 291e301