MEK inhibitors enhance therapeutic response towards ATRA in NF1 associated malignant peripheral nerve sheath tumors (MPNST) in-vitro.

Susan Fischer-Huchzermeyer,Verena Stahn,Anja Harder,Victor Felix Mautner,Gordon Wilke,Anna Streubel,Anna Dombrowski

doi:10.1371/journal.pone.0187700

Abstract

ObjectiveNeurofibromatosis type 1 (NF1) is a hereditary tumor syndrome characterized by an increased risk of malignant peripheral nerve sheath tumors (MPNST). Chemotherapy of MPNST is still insufficient. In this study, we investigated whether human tumor Schwann cells derived from NF1 associated MPNST respond to all-trans retinoic acid (ATRA). We analyzed effects of ATRA and MEK inhibitor (MEKi) combination therapy.MethodsMPNST cell lines S462, T265, NSF1 were treated with ATRA and MEKi U0126 and PD0325901. We assessed cell viability, proliferation, migration, apoptosis and differentiation as well as mRNA expression of RAR and RXR subtypes and ATRA target genes such as CRABP2, CYP26A1, RARB and PDK1. We also analyzed CRABP2 methylation in cell lines and performed immunohistochemistry of human MPNST specimens.ResultsATRA therapy reduced viability and proliferation in S462 and T265 cells, accompanied by differentiation, apoptosis and reduced migration. NSF1 cells which lacked RXRG expression did not respond to ATRA. We furthermore demonstrated that ATRA signaling was functional for common targets, and that mRNA expression of CRABP2 and its targets was raised by ATRA therapy, whereas alternative pathways via FABP5 were not induced. Finally, combination of ATRA and MEKi demonstrated additively reduced viability of T265 and S462 cells.ConclusionsWe observed therapeutic effects in two of three MPNST cell lines pronounced by combination therapy. These data point to a potentially successful treatment of MPNST by combined application of ATRA and MEK inhibitors such as U0126 or PD0325901.

Highlights

Malignant peripheral nerve sheath tumors are soft tissue sarcomas that typically occur in the setting of Neurofibromatosis type 1 (NF1) [1, 2]
We demonstrated that all-trans retinoic acid (ATRA) signaling was functional for common targets, and that mRNA expression of cellular retinoic acid binding protein 2 (CRABP2) and its targets was raised by ATRA therapy, whereas alternative pathways via fatty acid binding protein 5 (FABP5) were not induced
We observed therapeutic effects in two of three malignant peripheral nerve sheath tumors (MPNST) cell lines pronounced by combination therapy

Summary

Introduction

Malignant peripheral nerve sheath tumors are soft tissue sarcomas that typically occur in the setting of Neurofibromatosis type 1 (NF1) [1, 2]. NF1 associated MPNST develop from benign precursors, so called neurofibromas, the hallmark of the disease [5]. Whereas the first hit of the NF1 gene explains some of the clinical signs, an additional loss-of-function mutation of NF1 is required for the development of tumors, resulting in over activation of RAS signaling. Malignant transformation to MPNST is suggested to require accumulation of additional genetic aberrations. Most common molecular aberrations besides NF1 inactivation are mutations in RB1, SOX9 and MET, homozygous deletion of CDKN2A, INK4A and ARF tumor suppressors and loss of TP53 [12,13,14,15,16]. Different chemotherapeutic regimens have been applied and pre-clinical studies produced promising results, the outcome of patients with MPNST has not been significantly improved over the past decades. Radiotherapy prolongs time to relapse, it does not improve survival [17, 18]

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