Abstract 2531: Benzofuran derivatives as a novel class of mTOR signaling inhibitors

Abstract

Abstract Background: Current clinical development of rapalogues is impaired by toxicity when combined with chemotherapy or targeted therapies. Furthermore, the antiproliferative activity of rapalogues appears to be limited by various molecular mechanisms of resistance in cancer cells.. Experimental evidences have suggested that specific mTORC1 inhibition using rapalogues may be hampered by a negative feedback loop that results in PI3K activation due to a lack of mTORC2 inhibition. Thus, new generations of drugs targeting either PI3K or PI3K and mTOR kinases may avoid the intrinsic weakness of rapalogues. The aim of our study was to evaluate the antiproliferative activity of a set of 70 new benzofuran derivatives (BFD) in a panel of cancer cell lines and to characterise their molecular mechanism of action. Materials and Methods: Cytotoxic effects of 70 benzofuran derivatives were determined in the HNSCC cell line SQ20B using MTT assay after 72 hours of drug exposure. Activity of the best candidates was assessed on a panel of 10 cancer cell lines of different origins. Protein expression and phoshorylation after exposure to BFD were assessed by western blot. Target identification was realised by pull-down assay. Results: Cytotoxicity of BFD1, the first benzofuran derivative compound, was assessed on a panel of human colon (HT29, HCT116, Colo205, HCC2998), ovarian (OVCAR3, IGROV1), lung (HOP62, HOP92), breast (MCF7 and MDA-MB-231), prostate (DU145) and head and neck (SQ20B) cancer cell lines; SQ20B cells were the most sensitive with an IC50 of 40µM. Structure Activity Relationship (SAR) studies led to the synthesis of 69 derivatives with stepwise increased cytotoxicity against SQ20B cells. Early lead compounds BFD22 and BFD27 were shown to inhibit the phosphorylation of S6 ribosomal protein, target of mTORC1, in a dose dependent manner. In addition, phosphorylation of AKT (Ser473) was increased after exposure to high doses of BFD27, suggesting a specific inhibition of mTORC1 but not mTORC2. In contrast, the derivatives BFD56 and BFD62 were more cytotoxic and displayed potent inhibition of mTOR targets p-S6, p-4EBP1 and p-AKT, suggesting that those compounds also targeted mTORC2 activity. IC50s of 5 best compounds were compared with commercially available mTOR inhibitors everolimus and OZI-027. Compound BFD27 was then selected for the design of an affinity ligand to identify the molecular target of this class of compounds by pull-down assays. Western blot analysis showed that BFD27 interacted with mTOR but not other proteins that belong to the same signaling pathway, such as Akt, Rictor, Raptor, PI3K and PDK1 suggesting that mTOR is the target of this class of compounds. Conclusion: We identified a new class of benzofurane derivative compounds that interacts with the complex mTORC1 to inhibit its activity. SAR studies led to the optimization of mTOR inhibition and increased cytotoxicities. Citation Format: Marie Serova, Christophe Salomé, Vanessa Narbonne, Nigel Ribeiro, Frédéric Thuaud, Eric Raymond, Armand de Gramont, Laurent Desaubry. Benzofuran derivatives as a novel class of mTOR signaling inhibitors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2531. doi:10.1158/1538-7445.AM2014-2531