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

Renate Wagner,Ramón Colomer,Peter Lanzerstorfer,Nastasia Wilfinger-Lutz,Michael Wuczkowski,Karin Nowikovsky,Gerald Stübiger,Emmanouil Karteris,Daniel Veigel,María Luz López-Rodríguez,Christian F Singer,Peter Valent,Bellinda Benhamú,Julian Weghuber,Thomas W Grunt

doi:10.18632/oncotarget.14591

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.

Highlights

Ovarian cancer (OC) represents the most lethal malignancy of the female reproductive system [1,2,3]
Acetyl-CoA carboxylase converts acetyl-CoA to malonyl-CoA. Both intermediates are used by fatty acid synthase (FASN) to generate the saturated fatty acid (FA) palmitic acid (PA (16 : 0)), which is the source for most other lipids including monounsaturated FA (MUFA) oleic acid (OA (18 : 1(9Z)))
We demonstrate that addition of exogenous OA, unlike PA, partially abolishes FASNinhibitor-mediated growth arrest and apoptosis (Figure 1B, 1C)

Summary

Introduction

Ovarian cancer (OC) represents the most lethal malignancy of the female reproductive system [1,2,3]. Many OCs harbor hyperactive oncogenic drivers in the ERBBphosphatidylinositol 3-kinase(PI3K)-mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway. They exhibit ‘PI3Kness’ and are sensitive to drugs that target this pathway [5, 6]. ERBB-PI3K-mTORC1 controls diverse cellular functions including proliferation, survival, growth, migration, autophagy, angiogenesis, metabolism, and energy balance [7]. Thereby, the TSC1/2 tumor suppressor complex loses its ability to block RHEB–the upstream activator of mTORC1–and enables mTORC1 downstream signaling. TSC1/2 functions as a regulator of cell homeostasis. It receives activating inputs from REDD1 (DDIT4, RTP801) and AMPK–two sensors of nutritive and energetic shortage, which counteract AKT-mediated induction of mTORC1 and block cell proliferation

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