Multi-level suppression of receptor-PI3K-mTORC1 by fatty acid synthase inhibitors is crucial for their efficacy against ovarian cancer cells

// Renate Wagner 1, 2 , Gerald Stubiger 2, 3, 4 , Daniel Veigel 1, 2 , Michael Wuczkowski 3, 4 , Peter Lanzerstorfer 5 , Julian Weghuber 5 , Emmanouil Karteris 6 , Karin Nowikovsky 1, 2 , Nastasia Wilfinger-Lutz 1, 2 , Christian F. Singer 7 , Ramon Colomer 8 , Bellinda Benhamu 9 , Maria Luz Lopez-Rodriguez 9 , Peter Valent 2, 10, 11 , Thomas W. Grunt 1, 2, 11 1 Division of Oncology, Department of Medicine I, Medical University Vienna, Vienna, Austria 2 Comprehensive Cancer Center, Medical University Vienna, Vienna, Austria 3 Department of Biomedical Imaging and Image-guided Therapy, Medical University Vienna, Vienna, Austria 4 Center for Biomarker Research in Medicine, Graz, Austria 5 University of Applied Sciences Upper Austria, School of Engineering and Environmental Sciences, Wels, Austria 6 Department of Biosciences, School of Health Sciences and Social Care, Brunel University London, Uxbridge, UK 7 Department of Obstetrics/Gynecology, Medical University Vienna, Vienna, Austria 8 Department of Medical Oncology, Hospital Universitario La Princesa and Spanish National Cancer Research Center (CNIO), Clinical Research Program, Madrid, Spain 9 Departamento de Quimica Organica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, Madrid, Spain 10 Division of Hematology and Hemostaseology, Department of Medicine I, Medical University Vienna, Vienna, Austria 11 Ludwig Boltzmann Cluster Oncology, Medical University Vienna, Vienna, Austria Correspondence to: Thomas W. Grunt, email: thomas.grunt@meduniwien.ac.at Keywords: AMPK, fatty acid synthase (FASN), lipids, mTORC1, REDD1 Received: February 24, 2016      Accepted: December 24, 2016      Published: January 10, 2017 ABSTRACT Receptor-PI3K-mTORC1 signaling and fatty acid synthase (FASN)-regulated lipid biosynthesis harbor numerous drug targets and are molecularly connected. We hypothesize that unraveling the mechanisms of pathway cross-talk will be useful for designing novel co-targeting strategies for ovarian cancer (OC). The impact of receptor-PI3K-mTORC1 onto FASN is already well-characterized. However, reverse actions–from FASN towards receptor-PI3K-mTORC1–are still elusive. We show that FASN-blockade impairs receptor-PI3K-mTORC1 signaling at multiple levels. Thin-layer chromatography and MALDI-MS/MS reveals that FASN-inhibitors (C75, G28UCM) augment polyunsaturated fatty acids and diminish signaling lipids diacylglycerol (DAG) and phosphatidylinositol 3,4,5-trisphosphate (PIP3) in OC cells (SKOV3, OVCAR-3, A2780, HOC-7). Western blotting and micropatterning demonstrate that FASN-blockers impair phosphorylation/expression of EGF-receptor/ERBB/HER and decrease GRB2–EGF-receptor recruitment leading to PI3K-AKT suppression. FASN-inhibitors activate stress response-genes HIF-1α-REDD1 (RTP801/DIG2/DDIT4) and AMPKα causing mTORC1- and S6-repression. We conclude that FASN-inhibitor-mediated blockade of receptor-PI3K-mTORC1 occurs due to a number of distinct but cooperating processes. Moreover, decrease of PI3K-mTORC1 abolishes cross-repression of MEK-ERK causing ERK activation. Consequently, the MEK-inhibitor selumetinib/AZD6244, in contrast to the PI3K/mTOR-inhibitor dactolisib/NVP-BEZ235, increases growth inhibition when given together with a FASN-blocker. We are the first to provide deep insight on how FASN-inhibition blocks ERBB-PI3K-mTORC1 activity at multiple molecular levels. Moreover, our data encourage therapeutic approaches using FASN-antagonists together with MEK-ERK-inhibitors.