Co-targeting EGFR and mTOR with gefitinib and everolimus in triple-negative breast cancer cells

Abderrahim El Guerrab,Mahchid Bamdad,Corinne Aubel,Frédérique Penault-Llorca,Yves-Jean Bignon

doi:10.1038/s41598-020-63310-2

Abderrahim El Guerrab, Mahchid Bamdad + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-63310-2

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Abstract

Triple-negative breast cancers (TNBC) are unlikely to respond to hormonal therapies and anti-HER2-targeted therapies. TNBCs overexpress EGFR and exhibit constitutive activation of the PI3K/AKT/mTOR signalling pathway. We hypothesized that simultaneously blocking EGFR and mTOR could be a potential therapeutic strategy for the treatment of TNBC. We examined the antitumour activity of the mTOR inhibitor everolimus combined with the EGFR tyrosine kinase inhibitor gefitinib in TNBC cell with or without activating mutations in the PI3K/AKT/mTOR signalling pathway. We demonstrated that everolimus and gefitinib induced synergistic growth inhibition in the PI3K and PTEN-mutant CAL-51 cell line but not in the PTEN-null HCC-1937 cell line. The antiproliferative effect was associated with synergistic inhibition of mTOR and P70S6K phosphorylation, as well as a significant reduction in 4E-BP1 activation in the CAL-51 cell line. We also showed that combination therapy significantly inhibited cell cycle progression and increased apoptosis in this cell line. Gene and protein expression analysis revealed significant downregulation of cell cycle regulators after exposure to combined treatment. Collectively, these results suggested that dual inhibition of mTOR and EGFR may be an effective treatment for TNBC with activating mutations of PI3K.

Highlights

Triple-negative breast cancers (TNBC) are unlikely to respond to hormonal therapies and anti-HER2targeted therapies
The growth inhibitory effects of everolimus and gefitinib were analysed by XTT assay in three TNBC cell lines
We examined the in vitro sensitivity of TNBC cell lines to increasing concentrations (0.1, 1, 10, 100 and 1000 nM) of everolimus alone (Fig. 1A)

Summary

Introduction

Triple-negative breast cancers (TNBC) are unlikely to respond to hormonal therapies and anti-HER2targeted therapies. Gene and protein expression analysis revealed significant downregulation of cell cycle regulators after exposure to combined treatment These results suggested that dual inhibition of mTOR and EGFR may be an effective treatment for TNBC with activating mutations of PI3K. Clinical studies have reported that gefitinib enhanced the growth inhibitory effect of chemotherapies, but the use of gefitinib alone failed to demonstrate significant efficacy[9,10] These disappointing results could be related to the molecular heterogeneity of TNBC, characterized by diverse genetic alterations in EGFR signalling pathways. Triple-negative tumours with overexpression of EGFR exhibit constitutive activation of EGFR-dependent signalling pathways, especially the PI3K/AKT/mTOR pathway Activation of this pathway is involved in tumorigenesis, contributing to apoptosis inhibition, cell cycle progression, drug resistance, cell motility and metastasis[11,12]. Activation of mTOR controls the translation of mRNAs through the activation of eukaryotic translational initiation factor 4E-binding protein (4E-BP1) and ribosomal protein S6 kinase (P70S6K)[15]

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