Dual mTORC1/2 inhibition induces anti-proliferative effect in NF1-associated plexiform neurofibroma and malignant peripheral nerve sheath tumor cells

Abstract

Approximately 30-50% of individuals with Neurofibromatosis type 1 develop benign peripheral nerve sheath tumors, called plexiform neurofibromas (PNFs). PNFs can undergo malignant transformation to highly metastatic malignant peripheral nerve sheath tumors (MPNSTs) in 5-10% of NF1 patients, with poor prognosis. No effective systemic therapy is currently available for unresectable tumors. In tumors, the NF1 gene deficiency leads to Ras hyperactivation causing the subsequent activation of the AKT/mTOR and Raf/MEK/ERK pathways and inducing multiple cellular responses including cell proliferation. In this study, three NF1-null MPNST-derived cell lines (90-8, 88-14 and 96-2), STS26T sporadic MPNST cell line and PNF-derived primary Schwann cells were used to test responses to AZD8055, an ATP-competitive “active-site” mTOR inhibitor. In contrast to rapamycin treatment which only partially affected mTORC1 signaling, AZD8055 induced a strong inhibition of mTORC1 and mTORC2 signaling in MPNST-derived cell lines and PNF-derived Schwann cells. AZD8055 induced full blockade of mTORC1 leading to an efficient decrease of global protein synthesis. A higher cytotoxic effect was observed with AZD8055 compared to rapamycin in the NF1-null MPNST-derived cell lines with IC50 ranging from 70 to 140 nM and antiproliferative effect was confirmed in PNF-derived Schwann cells. Cell migration was impaired by AZD8055 treatment and cell cycle analysis showed a G0/G1 arrest. Combined effects of AZD8055 and PD0325901 MEK inhibitor as well as BRD4 (BromoDomain-containing protein 4) inhibitors showed a synergistic antiproliferative effect. These data suggest that NF1-associated peripheral nerve sheath tumors are an ideal target for AZD8055 as a single molecule or in combined therapies.

Novel enriched pathways in superficial malignant peripheral nerve sheath tumours and spindle/desmoplastic melanomas

“…Given their critical role in regulating the AKT-mTOR pathway, the loss of function of NF1 and TSC1/TSC2 identified in our study provides a rationale for investigating mTOR complex (mTORC) inhibitors in both MPNSTs and SDMs [22]. Preclinical studies have suggested a synergistic antiproliferative effect of combined mTORC1/2 and MEK pathway inhibitors or bromo-domain-containing protein 4 inhibitors in cell lines with NF1 deficiency [19]. This…”

“…Our findings corroborate those results by showing deleterious NF1 mutations in the majority of MPNSTs and SDMs analysed. Loss of NF1 can lead to RAS activation and promote signalling along at least two main pathways, the AKT–mammalian target of rapamycin (mTOR) pathway and the mitogen‐activated protein kinase (MAPK) pathway . In our series, NF1 deleterious mutations and/or deep/homozygous deletions were identified in 70% of both SDMs and MPNSTs, with half (35%) of these mutations involving the RAS‐binding domain.…”

Pulmonary hypertension associated with neurofibromatosis type 1

“…Drugs that can inhibit the dysregulation induced by neurofibromin deficiency are potential targets, such as rapamycin, an mTOR inhibitor that has been shown to attenuate PH and neo-intimal formation in rats [62]. A recent study also showed that a stronger inhibition of mTOR by a dual mTORC1/2 inhibitor induced an anti-proliferative effect in NF1-associated plexiform neurofibroma and malignant peripheral nerve sheath tumour cells compared to rapamycin which is only an inhibitor of mTORC1 [63]. Attenuation of the vascular wall proliferation that characterises NF1 using statins (3-hydroxy-3-methylglutarylcoenzyme A reductase inhibitors) is another possible approach, since this class of agent is known to inhibit Ras activity through prevention of its lipid modification [64].…”

Genomic MET amplification occurs early in NF1-related malignant peripheral nerve sheath tumor (MPNST) progression and is a potent therapeutic target

“…NF1-related MPNSTs have been shown to arise from NF1-null myelinating Schwann cells where neurofibromin deficiency results in RAS deregulation (10)(11)(12)(13)(14)(15). Plexiform neurofibromas are the benign precursor of NF1-related MPNSTs and are formed by a recruited admixture of NF1 haploinsufficient cells (fibroblasts, mast cells, and perineurial cells) following an initial NF1-loss-of-heterozygosity event in a peripheral nerve Schwann cell (16)(17)(18). A variety of genomic alterations have been observed in the malignant transformation of benign plexiform neurofibromas into MPNSTs including deleterious mutations that impact cell cycle regulation (CDKN2A), apoptosis (TP53), tumor suppression (PTEN, RASSF1A) and chromatin modification (SUZ12/PRC2 gene family) (19)(20)(21).…”