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Cell Oncol (Dordr). 2019 Aug;42(4):521-536. doi: 10.1007/s13402-019-00443-1. Epub 2019 Apr 13.

The tumor suppressor FOXO3a mediates the response to EGFR inhibition in glioblastoma cells.

Author information

1
Cancer Cell Biology Laboratory, Institut Universitari d'Investigació en Ciències de la Salut (IUNICS), Universitat de les Illes Balears, and Institut d'Investigació Sanitària Illes Balears (IdISBa), Ctra. Valldemossa Km 7,5, Palma, Illes Balears, Spain.
2
Cellomics Unit, Institut Universitari d'Investigació en Ciències de la Salut (IUNICS), Universitat de les Illes Balears, Palma, Illes Balears, Spain.
3
Departament de Química, Universitat de les Illes Balears, Palma, Illes Balears, Spain.
4
Department of Neurosurgery, Hospital Universitari Son Espases, Palma, Illes Balears, Spain.
5
Departament de Biologia Fonamental i Ciències de la Salut, Universitat de les Illes Balears, Palma, Illes Balears, Spain.
6
Cancer Cell Biology Laboratory, Institut Universitari d'Investigació en Ciències de la Salut (IUNICS), Universitat de les Illes Balears, and Institut d'Investigació Sanitària Illes Balears (IdISBa), Ctra. Valldemossa Km 7,5, Palma, Illes Balears, Spain. priam.villalonga@uib.es.
7
Departament de Biologia Fonamental i Ciències de la Salut, Universitat de les Illes Balears, Palma, Illes Balears, Spain. priam.villalonga@uib.es.

Abstract

PURPOSE:

Although EGFR activation is a hallmark of glioblastoma (GBM), anti-EGFR therapy has so far not yielded the desired effects. Targeting PI3K/Akt has been proposed as a strategy to increase the cellular sensitivity to EGFR inhibitors. Here we evaluated the contribution of FOXO3a, a key Akt target, in the response of GBM cells to EGFR inhibition.

METHODS:

FOXO3a activation was assessed by immunofluorescence and gene reporter assays, and by evaluating target gene expression using Western blotting and qRT-PCR. Cellular effects were evaluated using cell viability and apoptosis assays, i.e., Annexin V/PI staining and caspase 3/7 activity measurements. Drug synergism was evaluated by performing isobolographic analyses. Gene silencing experiments were performed using stable shRNA transfections.

RESULTS:

We found that EGFR inhibition in GBM cells led to FOXO3a activation and to transcriptional modulation of its key targets, including repression of the oncogene FOXM1. In addition, we found that specific FOXO3a activation recapitulated the molecular effects of EGFR inhibition, and that the FOXO3a activator trifluoperazine, a FDA-approved antipsychotic agent, reduced GBM cell growth. Subsequent isobolographic analyses of combination experiments indicated that trifluoperazine and erlotinib cooperated synergistically and that their concomitant treatment induced a robust activation of FOXO3a, leading to apoptosis in GBM cells. Using gene silencing, we found that FOXO3a is essential for the response of GBM cells to EGFR inhibition.

CONCLUSIONS:

Our data indicate that FOXO3a activation is a crucial event in the response of GBM cells to EGFR inhibition, suggesting that FOXO3a may serve as an actionable therapeutic target that can be modulated using FDA-approved drugs.

KEYWORDS:

EGFR; Erlotinib; FOXO3a; Glioblastoma; Phenotiazines; Trifluoperazine

PMID:
30980364
DOI:
10.1007/s13402-019-00443-1

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