Original article Benzofuran derivatives as a novel class of inhibitors of mTOR signaling Christophe Salomé a , Vanessa Narbonne a , Nigel Ribeiro a , Frédéric Thuaud a , Maria Serova b , Armand de Gramont b , Sandrine Faivre b , Eric Raymond b , Laurent Désaubry a, * a Therapeutic Innovation Laboratory, UMR7200, CNRS/Université de Strasbourg, Illkirch, France b Department of Medical Oncology, Beaujon University Hospital, INSERM U728/AP-HP, Clichy, France article info Article history: Received 26 November 2013 Received in revised form 20 December 2013 Accepted 21 December 2013 Available online 2 January 2014 Keywords: Benzofuran Cytotoxicity mTOR mTORC1 abstract High-throughput screening (HTS) hit 1 was previously identified as an inhibitor of the Akt/mTOR (Akt/ mammalian target of rapamycin) signaling, which is a major target in oncology. The cytotoxicity of 1 was determined on a panel of human cancer cells lines with an IC 50 comprised between 30 and 140 mM. Subsequent structureeactivity relationship (SAR) studies led us to the identification of compounds that displayed an enhanced cytotoxicity. We demonstrated also that these molecules directly bind to mTOR complex 1 (mTORC1) and inhibit its kinase activity. Ó 2013 Elsevier Masson SAS. All rights reserved. 1. Introduction The AKT/mammalian target of rapamycin (mTOR) pathway is considered as one of the most commonly activated and deregulated signaling pathways in human cancer [1e3]. Rapamycin (sirolimus), a naturally occurring macrolide, was the first identified potent in- hibitor of mTOR. This kinase is associated with other proteins in two molecular complexes: mTORC1 and mTORC2. Rapamycin binds to the cytosolic immunophilin protein FKBP12 (FK-binding protein 12), which selectively inhibits mTORC1, without interacting with mTORC2. Several rapamycin derivatives (rapalogues) such as tem- sirolimus, everolimus and deforolimus, are currently commercial- ized to treat cancers. Temsirolimus and everolimus have been approved for the first- and second-line treatment, respectively, of patients with clear renal cell carcinomas. Moreover, temsirolimus was also approved for the treatment of mantle cell lymphoma. Current clinical development of rapalogues was impaired by toxicity when combined with chemotherapy and several targeted therapies [1e3]. Furthermore, the antiproliferative activity of rapalogues appears to be limited by various molecular mechanisms of resistance in cancer cells combined to a lack of mTORC2 complex inhibition. Novel anticancer drugs designed to overcome potential mech- anisms of resistance to rapalogues are currently in development [1]. Several companies have identified drugs that inhibit mTOR by competing with adenosine triphosphate (ATP) into the ATP-binding sites. These compounds do not require FKBP12 to bind with mTOR and, thereby, inhibit both mTORC1 and mTORC2 complexes. Some of these molecules do not only inhibit mTOR, but also phosphati- dylinositide 3-kinases (PI3K). Several specific mTOR inhibitors and dual PI3K/mTOR inhibitors are currently investigated in phase III trials. Compound 1 (also known as ChemBridge 5219657, Fig. 1) was identified in a high-throughput screen as an inhibitor of Akt/mTOR signaling [4,5]. In 786-O renal carcinoma cells, 1 blocked Akt/ mTOR-induced nuclear export of the transcription factor FOXO1a (IC 50 ¼ 20 mM) and cell proliferation (IC 50 ¼ 10 mM) by an un- identified mechanism downstream of Akt. The privileged structure of benzofurans, which is uncommon among the known inhibitors of the Akt/mTOR cascade, prompted us to define the structural requirements of 1 for its antiproliferative effects and to examine the pharmacological potential of this new class of cytostatic agents. Herein, we report the first SAR study on 1 and our efforts to identify its mechanism of action. * Corresponding author. Tel.: þ33 368 854 141; fax: þ33 368 854 310. E-mail address: desaubry@unistra.fr (L. Désaubry). Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech 0223-5234/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.ejmech.2013.12.020 European Journal of Medicinal Chemistry 74 (2014) 41e49