Abstract 6956: Overcoming stress induced therapy resistance in triple negative breast cancer with the MNK inhibitor EB1

Abstract INTRODUCTION. Therapy resistance and the evasion from immune based therapies represent main caveats of current cancer treatments and both processes critically rely on the activation of stress response pathways, which activate the kinases MNK1/2. While MNKs are non-essential kinases, phosphorylation of eIF4E at S209 is required for oncogenic transformation and correlates with worse prognosis in several human tumors. Targeting MNKs has therefore evolved as a non-toxic strategy in oncology, to improve the efficacy of current treatments. We have identified with EB1 the first in-class Type-II inhibitor of the kinases MNK1/2 with a superior mode of action (Bou-Petit et al, JMC, 2022). OBJECTIVES. We have previously postulated that targeting MNKs sensitizes cells to therapy induced cellular stress (Martinez et al. PLOSone, 2015). In this work, we describe the impact of EB1 on cell fate in the context of cellular stress and delineate the underling signaling pathways. METHODOLOGY. The cell line MDA-MB231 was used as model of triple negative breast cancer (TNBC) and results were confirmed in MDA-MB468 and HS578T cells. Effects on cell growth of EB1 alone and in combination with cellular stress or therapeutic agents were studied through crystal violet assay. Alterations in signaling pathways were studied by western blot. Electron and confocal microscopy were used to analyze changes in cellular organelles and their activity. Functional assays on protein translation and the autophagy-lysosomal pathway complement the study. Main results obtained with EB1 were compared to the siRNA mediated knock-down of MNKs and eFT-508 (eFFECTOR Therapeutics, Inc.) as the most advanced Type I MNK inhibitor. RESULTS. Cell growth assays demonstrate enhanced activity of EB1 in combination with cellular stress or therapeutic agents. Concomitantly, stress response pathways were hyper-activated in the presence of EB1 and protein translation was diminished. Microscopic analysis reveal alterations in the morphology autophagosome/lysosome structures, particularly under cellular stress. Analysis of signaling pathways revealed furthermore a link to the PI3K/AKT/mTOR signaling pathway in stress-compromised cells upstream of protein translation and autophagy. Remarkably, the observed phenotypes could only be observed with EB1 but not with eFT508, suggesting that the mode of action of MNK inhibitors is relevant in this context. CONCLUSIONS. We demonstrate here that the MNK inhibitor EB1 affects breast cancer cells particularly under cellular stress conditions. We propose that EB1 might represent a novel therapeutic opportunity, to combat cellular stress induced therapy resistance. This might be of particular importance for the treatment of TNBC, in which good initial responses to systemic therapies are in most of cases followed by therapy resistance and tumor relapse. Citation Format: Marta Cano-Galietero, Elena Muro-Blanc, Sara Garcia-Ortega, Adriana Martínez Cifuentes, José Ignacio Borrell Bilbao, Stefan Hummer, Santiago Ramón y Cajal. Overcoming stress induced therapy resistance in triple negative breast cancer with the MNK inhibitor EB1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6956.