Different Activation of Mitogen-Activated Protein Kinase and Akt Signaling Is Associated with Aggressive Phenotype of Human Meningiomas

Unveiling a Biomarker Signature of Meningioma: The Need for a Panel of Genomic, Epigenetic, Proteomic, and RNA Biomarkers to Advance Diagnosis and Prognosis

Meningiomas are the most prevalent primary intracranial tumors. The majority are benign but can undergo dedifferentiation into advanced grades classified by World Health Organization (WHO) into Grades 1 to 3. Meningiomas' tremendous variability in tumor behavior and slow growth rates complicate their diagnosis and treatment. A deeper comprehension of the molecular pathways and cellular microenvironment factors implicated in meningioma survival and pathology is needed. This review summarizes the known genetic and epigenetic aberrations involved in meningiomas, with a focus on neurofibromatosis type 2 (NF2) and non-NF2 mutations. Novel potential biomarkers for meningioma diagnosis and prognosis are also discussed, including epigenetic-, RNA-, metabolomics-, and protein-based markers. Finally, the landscape of available meningioma-specific animal models is overviewed. Use of these animal models can enable planning of adjuvant treatment, potentially assisting in pre-operative and post-operative decision making. Discovery of novel biomarkers will allow, in combination with WHO grading, more precise meningioma grading, including meningioma identification, subtype determination, and prediction of metastasis, recurrence, and response to therapy. Moreover, these biomarkers may be exploited in the development of personalized targeted therapies that can distinguish between the 15 diverse meningioma subtypes.

Identification of the Key Immune Cells and Genes for the Diagnostics and Therapeutics of Meningioma

BACKGROUND

Dysregulation of immune infiltration critically contributes to the tumorigenesis and progression of meningiomas. However, the landscape of immune microenvironment and key genes correlated with immune cell infiltration remains unclear.

METHODS

Four Gene Expression Omnibus data sets were included. CIBERSORT algorithm was utilized to analyze the immune cell infiltration in samples. Wilcoxon test, Random Forest algorithm, and Least Absolute Shrinkage and Selection Operator regression were adopted in identifying significantly different infiltrating immune cells and differentially expressed genes (DEGs). Functional enrichment analysis was performed by Kyoto Encyclopedia of Genes and Genomes and Gene Ontology. The correlation between genes and immune cells was evaluated via Spearman's correlation analysis. Receiver Operator Characteristic curve analysis evaluated the markers' diagnostic effectiveness. The mRNA-miRNA and Drug-Gene-Immune cell interaction networks were constructed to identify potential diagnostic and therapeutic targets.

RESULTS

Plasma cells, M1 macrophages, M2 macrophages, neutrophils, eosinophils, and activated NK cells were the significantly different infiltrating immune cells in meningioma. A total of 951 DEGs, associated with synaptic function and structure, ion transport regulation, brain function, and immune-related pathways, were identified. Among 11 hub DEGs, RYR2 and TTR were correlated with plasma cells; SNCG was associated with NK cells; ADCY1 exhibited excellent diagnostic effectiveness; and ADCY1, BMX, KCNA5, SLCO4A1, and TTR could be considered as therapeutic targets.

CONCLUSIONS

ADCY1 can be identified as a diagnostic marker; ADCY1, BMX, KCNA5, SLCO4A1, and TTR are potential therapeutic targets, and their associations with macrophages, neutrophils, NK cells, and plasma cells might impact the tumorigenesis of meningiomas.

Role of pelitinib in the regulation of migration and invasion of hepatocellular carcinoma cells via inhibition of Twist1

BACKGROUND

Overexpression of Twist1, one of the epithelial-mesenchymal transition-transcription factors (EMT-TFs), is associated with hepatocellular carcinoma (HCC) metastasis. Pelitinib is known to be an irreversible epidermal growth factor receptor tyrosine kinase inhibitor that is used in clinical trials for colorectal and lung cancers, but the role of pelitinib in cancer metastasis has not been studied. This study aimed to investigate the anti-migration and anti-invasion activities of pelitinib in HCC cell lines.

METHODS

Using three HCC cell lines (Huh7, Hep3B, and SNU449 cells), the effects of pelitinib on cell cytotoxicity, invasion, and migration were determined by cell viability, wound healing, transwell invasion, and spheroid invasion assays. The activities of MMP-2 and -9 were examined through gelatin zymography. Through immunoblotting analyses, the expression levels of EMT-TFs (Snail1, Twist1, and ZEB1) and EMT-related signaling pathways such as mitogen-activated protein kinases (MAPKs) and Akt signaling pathways were measured. The activity and expression levels of target genes were analyzed by reporter assay, RT-PCR, quantitative RT-PCR, and immunoblotting analysis. Statistical analysis was performed using one-way ANOVA with Dunnett's Multiple comparison tests in Prism 3.0 to assess differences between experimental conditions.

RESULTS

In this study, pelitinib treatment significantly inhibited wound closure in various HCC cell lines, including Huh7, Hep3B, and SNU449. Additionally, pelitinib was found to inhibit multicellular cancer spheroid invasion and metalloprotease activities in Huh7 cells. Further investigation revealed that pelitinib treatment inhibited the migration and invasion of Huh7 cells by inducing Twist1 degradation through the inhibition of MAPK and Akt signaling pathways. We also confirmed that the inhibition of cell motility by Twist1 siRNA was similar to that observed in pelitinib-treated group. Furthermore, pelitinib treatment regulated the expression of target genes associated with EMT, as demonstrated by the upregulation of E-cadherin and downregulation of N-cadherin.

CONCLUSION

Based on our novel finding of pelitinib from the perspective of EMT, pelitinib has the ability to inhibit EMT activity of HCC cells via inhibition of Twist1, and this may be the potential mechanism of pelitinib on the suppression of migration and invasion of HCC cells. Therefore, pelitinib could be developed as a potential anti-cancer drug for HCC.

Innovative treatments for meningiomas

Multi-recurrent high-grade meningiomas remain an unmet medical need in neuro-oncology when iterative surgeries and radiation therapy sessions fail to control tumor growth. Nevertheless, the last 10years have been marked by multiple advances in the comprehension of meningioma tumorigenesis via the discovery of new driver mutations, the identification of activated intracellular signaling pathways, and DNA methylation analyses, providing multiple potential therapeutic targets. Today, Anti-VEGF and mTOR inhibitors are the most used and probably the most active drugs in aggressive meningiomas. Peptide radioactive radiation therapy aims to target SSTR2A receptors, which are strongly expressed in meningiomas, but have an insufficient effect in most aggressive meningiomas, requiring the development of new techniques to increase the dose applied to the tumor. Based on the multiple potential intracellular targets, multiple targeted therapy clinical trials targeting Pi3K-Akt-mTOR and MAP kinase pathways as well as cell cycle and particularly, cyclin D4-6 are ongoing. Recently discovered driver mutations, SMO, Akt, and PI3KCA, offer new targets but are mostly observed in benign meningiomas, limiting their clinical relevance mainly to rare aggressive skull base meningiomas. Therefore, NF2 mutation remains the most frequent mutation and main challenging target in high-grade meningioma. Recently, inhibitors of focal adhesion kinase (FAK), which is involved in tumor cell adhesion, were tested in a phase 2 clinical trial with interesting but insufficient activity. The Hippo pathway was demonstrated to interact with NF2/Merlin and could be a promising target in NF2-mutated meningiomas with ongoing multiple preclinical studies and a phase 1 clinical trial. Recent advances in immune landscape comprehension led to the proposal of the use of immunotherapy in meningiomas. Except in rare cases of MSH2/6 mutation or high tumor mass burden, the activity of PD-1 inhibitors remains limited; however, its combination with various radiation therapy modalities is particularly promising. On the whole, therapeutic management of high-grade meningiomas is still challenging even with multiple promising therapeutic targets and innovations.

A magnetic resonance imaging based radiomics model to predict mitosis cycles in intracranial meningioma

The aim of this study was to develop a magnetic resonance imaging (MRI) based radiomics model to predict mitosis cycles in intracranial meningioma grading prior to surgery. Preoperative contrast-enhanced T1-weighted (T1CE) cerebral MRI data of 167 meningioma patients between 2015 and 2020 were obtained, preprocessed and segmented using the 3D Slicer software and the PyRadiomics plugin. In total 145 radiomics features of the T1CE MRI images were computed. The criterion on the basis of which the feature selection was made is whether the number of mitoses per 10 high power field (HPF) is greater than or equal to zero. Our analyses show that machine learning algorithms can be used to make accurate predictions about whether the number of mitoses per 10 HPF is greater than or equal to zero. We obtained our best model using Ridge regression for feature pre-selection, followed by stepwise logistic regression for final model construction. Using independent test data, this model resulted in an AUC (Area under the Curve) of 0.8523, an accuracy of 0.7941, a sensitivity of 0.8182, a specificity of 0.7500 and a Cohen's Kappa of 0.5576. We analyzed the performance of this model as a function of the number of mitoses per 10 HPF. The model performs well for cases with zero mitoses as well as for cases with more than one mitosis per 10 HPF. The worst model performance (accuracy = 0.6250) is obtained for cases with one mitosis per 10 HPF. Our results show that MRI-based radiomics may be a promising approach to predict the mitosis cycles in intracranial meningioma prior to surgery. Specifically, our approach may offer a non-invasive means of detecting the early stages of a malignant process in meningiomas prior to the onset of clinical symptoms.

Recent advances in the molecular prognostication of meningiomas

Meningiomas are the most common primary intracranial neoplasm. While traditionally viewed as benign, meningiomas are associated with significant patient morbidity, and certain meningioma subgroups display more aggressive and malignant behavior with higher rates of recurrence. Historically, the risk stratification of meningioma recurrence has been primarily associated with the World Health Organization histopathological grade and surgical extent of resection. However, a growing body of literature has highlighted the value of utilizing molecular characteristics to assess meningioma aggressiveness and recurrence risk. In this review, we discuss preclinical and clinical evidence surrounding the use of molecular classification schemes for meningioma prognostication. We also highlight how molecular data may inform meningioma treatment strategies and future directions.

Novel Medical Therapies in Meningiomas

Meningiomas are the most common primary brain tumor in adults and have been historically managed with surgery and radiation therapy. However, in patients with inoperable, recurrent or high-grade tumors, medical therapy is often needed. Traditional chemotherapy and hormone therapy have been largely ineffective. However, with improved understanding of the molecular drivers in meningioma, there has been increasing interest in targeted molecular and immune therapies. In this chapter, we will discuss recent advances in meningioma genetics and biology and review current clinical trials with targeted molecular treatment and other novel therapies.

Identification of key genes of anti-programmed death ligand 1 for meningioma immunotherapy by bioinformatic analysis

Meningioma is one of the most common primary tumors in the central nervous system (CNS). A deeper understanding of its molecular characterization could provide potential therapeutic targets to reduce recurrence. In this study, we attempted to identify specific gene mutations in meningioma for immunotherapy. One GSE43290 dataset was obtained from the Gene Expression Omnibus (GEO) database to find differentially expressed genes (DEGs) between meningioma tissues and normal meninges. In total, 420 DEGs were identified, including 15 up-regulated and 405 down-regulated genes. Functional enrichment analysis showed that these DEGs were mainly enriched in PI3K-Akt signaling pathway, Focal adhesion, and MAPK signaling pathway. We identified 20 hub genes by protein-protein interaction (PPI) analysis. Among the hub genes, the expression of FLT1, CXCL8, JUN, THBS1, FECAM1, CD34, and FGF13 were negatively correlated with Programmed Death Ligand-1 (PD-L1). Additionally, the expression of those genes was co-regulated by miR-155-5p. The findings suggest that miR-155-5p play an important role in the pathogenesis of meningioma and may represent potential therapeutic targets for its anti-PD-L1 immunotherapy.

Co-Targeting MAP Kinase and Pi3K-Akt-mTOR Pathways in Meningioma: Preclinical Study of Alpelisib and Trametinib

Simple Summary

Multi recurrent or high-grade meningiomas remain an unmet medical need in neuro-oncology. Several studies have highlighted the potential therapeutic efficacy of mTor inhibitors to control tumoral growth of meningiomas. However, a positive feedback on AKT oncogenic pathway from these drugs may explain the modest success. Our aim was to target Pi3kinase upstream mTor, and MAP kinase pathway, overactivated in meningiomas, alone or in combined targeting in comparison to mTor targeting. Our in vitro results obtained on three meningioma cell lines and on a large series of fresh human meningiomas, including 35 WHO grade 1, 23 grade 2, and five grade 3, showed that co-targeting Pi3kinase and MAP kinase seemed promising, opening new therapeutic strategies in these tumors.

Abstract

Recurrent or high-grade meningiomas are an unmet medical need. Recently, we demonstrated that targeting mTOR by everolimus was relevant both in vitro and in humans. However, everolimus induces an AKT activation that may impact the anti-proliferative effect of the drug. Moreover, the MAP kinase pathway was shown to be involved in meningioma tumorigenesis. We therefore targeted both the Pi3k-AKT-mTOR and MAP kinase pathways by using combinations of the Pi3k inhibitor alpelisib and the MEK inhibitor trametinib. Our study was performed in vitro on the human meningioma cell lines and on a large series of primary cultures providing from 63 freshly operated meningiomas including 35 WHO grade 1, 23 grade 2, and five grade 3, half of which presented a NF2 genomic alteration. Alpelisib induced a higher inhibitory effect on cell viability and proliferation than everolimus in all cell lines and 32 randomly selected tumors no matter the genomic status, the histological subtype or grade. Trametinib also strongly inhibited cell proliferation and induced AKT activation. Combined treatment with alpelisib plus trametinib reversed the AKT activation induced by trametinib and induced an additive inhibitory effect irrespective of the cell lines or tumor features. Co-targeting pathways seems promising and may be considered particularly for aggressive meningioma.

Identification and Management of Aggressive Meningiomas

Meningiomas are common primary central nervous system tumors derived from the meninges, with management most frequently entailing serial monitoring or a combination of surgery and/or radiation therapy. Although often considered benign lesions, meningiomas can not only be surgically inaccessible but also exhibit aggressive growth and recurrence. In such cases, adjuvant radiation and systemic therapy may be required for tumor control. In this review, we briefly describe the current WHO grading scale for meningioma and provide demonstrative cases of treatment-resistant meningiomas. We also summarize frequently observed molecular abnormalities and their correlation with intracranial location and recurrence rate. We then describe how genetic and epigenetic features might supplement or even replace histopathologic features for improved identification of aggressive lesions. Finally, we describe the role of surgery, radiotherapy, and ongoing systemic therapy as well as precision medicine clinical trials for the treatment of recurrent meningioma.

Chemotherapy and targeted therapies for meningiomas: what is the evidence?

PURPOSE OF REVIEW

Although most meningiomas are slow growing tumors mainly controlled by surgery with or without radiotherapy, aggressive meningiomas that fail these conventional treatments constitute a rare situation, a therapeutic challenge and an unmet need in neuro-oncology.

RECENT FINDING

Mutational landscape in recurrent high-grade meningiomas includes mainly NF2 mutation or 22q chromosomal deletion, whereas telomerase reverse transcriptase promoter, BAP-1 and CDK2NA mutations were also found in aggressive meningiomas. Pi3K-Akt-mTOR pathway is currently the most relevant intracellular signaling pathway target in meningiomas with preliminary clinical activity observed. Assessment of drug activity with progression free survival rate at 6 months is challenging in regard to meningioma growth rate heterogeneity, so that 3-dimensional growth rate before and during treatment could be considered in the future to selected new active drugs.

SUMMARY

Despite a low evidence level, some systemic therapies may be considered for patients with recurrent meningioma not amenable to further surgery or radiotherapy. In recurrent high-grade meningioma, everolimus-octreotide combination, bevacizumab, sunitinib and peptide receptor radionuclide therapy exhibit a signal of activity that may justify their clinical use. Despite a lack of clear signal of activity to date, immunotherapy may offer new perspectives in the treatment of these refractory tumors.

Receptor-Tyrosine Kinase Inhibitor Ponatinib Inhibits Meningioma Growth In Vitro and In Vivo

To date, there is no standard-of-care systemic therapy for the treatment of aggressive meningiomas. Receptor tyrosine kinases (RTK) are frequently expressed in aggressive meningiomas and are associated with poor survival. Ponatinib is a FDA- and EMA-approved RTK inhibitor and its efficacy in meningioma has not been studied so far. Therefore, we investigated ponatinib as a potential drug candidate against meningioma. Cell viability and cell proliferation of ponatinib-treated meningioma cells were assessed using crystal violet assay, manual counting and BrdU assay. Treated meningioma cell lines were subjected to flow cytometry to evaluate the effects on cell cycle and apoptosis. Meningioma-bearing mice were treated with ponatinib to examine antitumor effects in vivo. qPCR was performed to assess the mRNA levels of tyrosine kinase receptors after ponatinib treatment. Full-length cDNA sequencing was carried out to assess differential gene expression. IC50 values of ponatinib were between 171.2 and 341.9 nM in three meningioma cell lines. Ponatinib induced G0/G1 cell cycle arrest and subsequently led to an accumulation of cells in the subG1-phase. A significant induction of apoptosis was observed in vitro. In vivo, ponatinib inhibited meningioma growth by 72.6%. Mechanistically, this was associated with downregulation of PDGFRA/B and FLT3 mRNA levels, and mitochondrial dysfunction. Taken together, ponatinib is a promising candidate for targeted therapy in the treatment of aggressive meningioma.

Comprehensive overview of extracellular vesicle proteomics in meningioma: future strategy

Background

Meningioma arising from meninges is one among the various types of brain tumors. Others are, astrocytomas originating from astrocyte, oligodendrogliomas originating from oligodendrocyte, Ependymomas originating from ependymal cells and medulloblastomas originating from neurons. Current knowledge of molecular biology, genetics and epigenetics of meningioma is not sufficient. Therefore, In depth understanding of the mechanism of meningioma formation and progression is needed for its treatment and management. Grade I Grade I meningiomas are majorly classified as grade I, grade II and grade III. Meningioma can be indolent, slow growing or can be invasive and metastatic which can recurre. Grade I meningioma can be removed by surgery in comparison to invasive meningioma which may recurre with high propensity. This property of recurrence is responsible for high morbidity and mortality. Meningioma are majorly classified into three classes namely grade I, grade II, grade III. Protein biomarkers are considered as promising candidates for the diagnosis of meningioma.

Study

Various studies done on differential expression of proteins have shown increased expression of EGFR, NEK9, EPS812, CKAP4, SET and STAT2, in all the three grades of meningioma. Additionally, some proteins like HK2 are overexpressed in grade II and grade III meningioma than in grade I meningioma. Protein Markers, found on extracellular vesicles of different grades of meningioma can serve the same purpose. A test done on a sample of any kind of body fluid like blood, tear, saliva, urine etc. for recognizing the circulating cancer cells or DNA and extracellular vesicles released from them to help detecting the early stage of cancer is known as liquid biopsy. Solid biopsy has several limitations as compared to liquid biopsy. This is because the samples can be easily collected and studied in case of liquid biopsy. Exosomes are related with liquid biopsy and hence provide platform for better diagnosis, prognosis and treatment of any type of cancer including meningioma. Exosomal tetraspanin are important example of exosomal biomarkers. The tetraspanin network is a molecular scaffold which connects various proteins for signal transduction.

Conclusion

This study tells about the utility of proper knowledge of extracellular vesicle proteins and their profiles in different grades, which can help in better understanding of pathogenesis, diagnosis, prognosis and treatment of meningioma. In Addition to use of these proteins as biomarkers, role of exosomes in currently available therapeutic approaches has been discussed.

Mouse Models in Meningioma Research: A Systematic Review

Meningiomas are the most frequent primitive central nervous system tumors found in adults. Mouse models of cancer have been instrumental in understanding disease mechanisms and establishing preclinical drug testing. Various mouse models of meningioma have been developed over time, evolving in light of new discoveries in our comprehension of meningioma biology and with improvements in genetic engineering techniques. We reviewed all mouse models of meningioma described in the literature, including xenograft models (orthotopic or heterotopic) with human cell lines or patient derived tumors, and genetically engineered mouse models (GEMMs). Xenograft models provided useful tools for preclinical testing of a huge range of innovative drugs and therapeutic options, which are summarized in this review. GEMMs offer the possibility of mimicking human meningiomas at the histological, anatomical, and genetic level and have been invaluable in enabling tumorigenesis mechanisms, including initiation and progression, to be dissected. Currently, researchers have a range of different mouse models that can be used depending on the scientific question to be answered.

Current experimental therapies for atypical and malignant meningiomas

INTRODUCTION

Atypical (WHO grade II) and malignant meningiomas (WHO Grade III) are a rare subset of primary intracranial tumors. Given their relatively high recurrence rate after surgical resection and radiotherapy, there has been a recent push to explore other adjuvant treatment options for these treatment-refractory tumors. Recent advances in molecular sequencing of tumors have elucidated new pathways and drug targets which are currently being studied. This article provides a thorough overview of novel investigational therapeutics including targeted therapy, immunotherapy, and new technological modalities for atypical and malignant meningiomas.

METHODS

We performed a comprehensive review of the available literature regarding preclinical and clinical evidence for emerging treatments for high grade meningiomas from 1980 to 2020 including contemporaneous clinical trials.

RESULTS

There is encouraging preclinical evidence regarding the efficacy of the emerging treatments discussed in this article. Several clinical trials are currently recruiting patients to translate targeted molecular therapy for meningiomas. Several clinical studies have suggested a clinical benefit of combinatorial treatment for these treatment-refractory tumors.

CONCLUSION

With numerous active clinical trials for high grade meningiomas, a meaningful improvement in the outcomes for these tumors may be on the horizon.

YAP1-FAM118B Fusion Defines a Rare Subset of Childhood and Young Adulthood Meningiomas

Meningiomas are a central nervous system tumor primarily afflicting adults, with <1% of cases diagnosed during childhood or adolescence. Somatic variation in NF2 may be found in ∼50% of meningiomas, with other genetic drivers (eg, SMO, AKT1, TRAF7) contributing to NF2 wild-type tumors. NF2 is an upstream negative regulator of YAP signaling and loss of the NF2 protein product, Merlin, results in YAP overexpression and target gene transcription. This mechanism of dysregulation is described in NF2-driven meningiomas, but further work is necessary to understand the NF2-independent mechanism of tumorigenesis. Amid our institutional patient-centric comprehensive molecular profiling study, we identified an individual with meningioma harboring a YAP1-FAM118B fusion, previously reported only in supratentorial ependymoma. The tumor histopathology was remarkable, characterized by prominent islands of calcifying fibrous nodules within an overall collagen-rich matrix. To gain insight into this finding, we subsequently evaluated the genetic landscape of 11 additional pediatric and adolescent/young adulthood meningioma patients within the Children's Brain Tumor Tissue Consortium. A second individual harboring a YAP1-FAM118B gene fusion was identified within this database. Transcriptomic profiling suggested that YAP1-fusion meningiomas are biologically distinct from NF2-driven meningiomas. Similar to other meningiomas, however, YAP1-fusion meningiomas demonstrated overexpression of EGFR and MET. DNA methylation profiling further distinguished YAP1-fusion meningiomas from those observed in ependymomas. In summary, we expand the genetic spectrum of somatic alteration associated with NF2 wild-type meningioma to include the YAP1-FAM118B fusion and provide support for aberrant signaling pathways potentially targetable by therapeutic intervention.

Prognostic significance of brain invasion in meningiomas: systematic review and meta-analysis

The WHO 2016 classification introduced brain invasion as a standalone criterion for grade II meningioma (GIIM). We systematically reviewed studies published after 2000 and performed a PRISMA-compliant meta-analysis of the hazard ratios (HRs) for progression-free survival (PFS) between brain-invasive and noninvasive meningiomas. In five studies that included both benign and higher-grade meningiomas, brain invasion was a significant risk factor for recurrence (HR = 2.45, p = 0.0004). However, in 3 studies comparing "brain-invasive meningioma with otherwise benign histology (BIOB)" with grade I meningioma, brain invasion was not a significant predictor of PFS (HR = 1.49, p = 0.23). Among GIIM per the WHO 2000 criteria, brain invasion was a significant predictor of shorter PFS than noninvasive GIIM (HR = 3.40, p = 0.001) but not per the WHO 2016 criteria (HR 1.13, p = 0.54), as the latter includes BIOB. Meta-regression analysis of seven studies of grade II meningioma showed that more frequent BIOB was associated with lower HRs (p < 0.0001). Hence, there is no rationale for brain invasion as a standalone criterion for grade II meningioma, although almost all studies were retrospective and exhibited highly heterogeneous HRs due to differences in brain-tumor interface data availability.

A Practical Overview on the Molecular Biology of Meningioma

PURPOSE OF REVIEW

Meningioma is a common intracranial neoplasm currently classified in 15 histologic subtypes across 3 grades of malignancy. First-choice therapy for meningioma is maximum safe resection for grade I tumors, and surgery plus optional and mandatory adjuvant radiotherapy for grade II and III, respectively, given the increased rate of recurrence even in the event of complete resection. The WHO 2016 histopathologic grading of meningioma has been questioned due to subjectivity and its controversial predictive power for recurrence.

RECENT FINDINGS

Novel DNA methylation profiling has simplified classification into six classes that seem to improve prognostic accuracy. We review five main topics of molecular biology research regarding tumorigenesis and natural history of meningioma from the clinician's perspective: the histopathologic diagnostic features and pitfalls of the current tumor classification; the molecular integrated diagnosis supported by identification of genetic alterations and DNA methylation profiling; the general landscape of the various signaling pathways involved in meningioma formation; the pathogenic theories of the peri-tumoral edema present in meningioma and its therapy implications; and a summarized review on the current treatments and plausible targeted therapies directed to meningioma. It seems likely that molecular assessment will be introduced within the next update of the WHO classification of meningiomas, acknowledging the promising value of DNA methylation profiling. This integrated diagnostic protocol will simplify tumor subtype categorization and provide improved accuracy in predicting recurrence and outcome. Although much effort is being done in identifying key gene mutations, and elucidating specific intracellular signaling pathways involved in meningioma tumorigenesis, effective targeted therapies for recurrent meningiomas are still lacking.

Is DNA Methylation a Ray of Sunshine in Predicting Meningioma Prognosis?

Meningioma is the most common intracranial tumor, and recent studies have drawn attention to the importance of further research on malignant meningioma. According to the World Health Organization (WHO) grading, meningioma is classified into 15 subtypes with three grades of malignancy. However, due to a lack of descriptions of molecular subtypes, genetic mutations, or other features, there were deficiencies in the WHO classification. The DNA methylation-based meningioma classification published in 2017 used DNA copy number analysis, mutation profiling, and RNA sequencing to distinguish six clinically relevant methylation classes, which contributed to a better prediction of tumor recurrence and prognosis. Further studies indicated that gene variation and gene mutations, such as those in neurofibromin 2 (NF2) and BRCA1, were related to the high WHO grade, malignant invasion, and recurrence. Among the mutant genes described above, some have been associated with differential DNA methylation. Herein, we searched for articles published in PubMed and Web of Science from January 2000 to May 2020 by entering the keywords “meningioma,” “methylation,” and “gene mutation,” and found a number of published studies that analyzed DNA methylation in meningiomas. In this review, we summarize the key findings of recent studies on methylation status and genetic mutations of meningioma and discuss the current deficits of the WHO grading. We also propose that a methylation-based meningioma classification could provide clues in the assessment of individual risk of meningioma recurrence, which is associated with clinical benefits for patients.

Two-Staged Approach for Giant Hypervascular Meningioma Resection

Introduction:

Giant meningiomas represent very uncommon and challenging tumors. Surgical morbidity is high due to the difficult and complex approaches to devascularize these hypervascular lesions. In the present series, we demonstrate a two-staged approach for surgical resection of giant hypervascular meningiomas.

Patients and Methods:

Four such patients having giant hypervascular meningiomas between July 2017 and June 2019 were taken in the present study. There were two falco-tentorial, one anterior and middle parasagittal and falcine meningioma, and one sphenoid wing with convexity meningioma.

Results:

In the first stage, only the hypervascular bone was removed, and the dura was coagulated and excised. In the definitive stage, usually undertaken 5–8 days following the first surgery, the meningioma was excised, leading to Simpson's Grade 2 excision in two and Grade 3 excision in the remaining two patients. There was one mortality of a previously operated malignant meningioma (histopathologically proven), owing to a cardiac event in the patient, while the other three were discharged without any new neurologic deficit.

Conclusion:

Two-staged approach for giant meningiomas represents a safe and effective surgical management, tolerable for the patient and more comfortable for the neurosurgeon.

Advances in Molecular Classification and Therapeutic Opportunities in Meningiomas

PURPOSE OF REVIEW

Our understanding of the genetic and epigenetic alterations in meningioma and the underlying tumor biology of meningioma has significantly changed over the past decade and resulted in revision of prognostically relevant meningioma subclasses within and beyond the WHO classification of CNS tumors.

RECENT FINDINGS

The 2016 WHO classification of CNS tumors recognizes WHO grade I, II, and III based on histopathological features. Recent work has identified genetic alterations with prognostic implications, including mutations of the TERT promoter, loss of function of the DMD gene, and inactivation of the tumor suppressor BAP-1. Studies of DNA methylation patterns in meningiomas have resulted in a novel and prognostically relevant meningioma subclassification schema. There have been major advances in our understanding of prognostically relevant genetic and epigenetic changes in meningioma which will hopefully allow for improvement in clinical trial design and the development of more effective therapies for meningioma.

Identification of epithelial membrane protein 2 (EMP2) as a molecular marker and correlate for angiogenesis in meningioma

PURPOSE

Although intracranial meningiomas are the most common primary brain tumor in adults, treatment options are few and have traditionally been limited to surgical resection and radiotherapy. Additional targeted therapies and biomarkers are needed, especially as complete surgical resection is frequently not feasible in many patients.

METHODS

Non-pathologic brain tissue from 3 patients undergoing routine autopsies and tumor specimens from 16 patients requiring surgical resection for meningioma were collected. EMP2 protein expression was evaluated by immunohistochemistry and western blot analysis. EMP2 mRNA expression was also investigated using surgical specimens and validated by analysis of several independent NCBI GEO databases.

RESULTS

EMP2 mRNA expression levels were found to be higher in meningioma relative to non-pathologic meninges (P = 0.0013) and brain (P = 0.0011). Concordantly, strong EMP2 protein expression was demonstrated in 100% of meningioma specimens from all 16 patients, with no observable protein expression in normal brain tissue samples from 3 subjects (P < 0.001). EMP2 expression was confirmed by western blot analysis in five samples, with EMP2 protein intensity positively correlating with histologic staining score (R² = 0.780; P = 0.047). No association was found between EMP2 mRNA or protein levels and WHO grade or markers of proliferation. However, EMP2 expression was positively associated with an angiomatous pattern on histologic evaluation (P = 0.0597), VEGF-A mRNA expression (P < 0.001), and clinical markers of tumor vascularity such as operative blood loss (P = 0.037).

CONCLUSIONS

EMP2 is not found in normal brain tissue, yet has shown consistently high mRNA and protein expression in meningiomas, and may serve as a useful molecular marker for these tumors.

Constitutive activation of the EGFR-STAT1 axis increases proliferation of meningioma tumor cells

Background

Meningiomas are the most frequent primary brain tumors of the central nervous system. The standard of treatment is surgery and radiotherapy, but effective pharmacological options are not available yet. The well-characterized genetic background stratifies these tumors in several subgroups, thus increasing diversification. We identified epidermal growth factor receptor–signal transducer and activator of transcription 1 (EGFR–STAT1) overexpression and activation as a common identifier of these tumors.

Methods

We analyzed STAT1 overexpression and phosphorylation in 131 meningiomas of different grades and locations by utilizing several techniques, including Western blots, qPCR, and immunocytochemistry. We also silenced and overexpressed wild-type and mutant forms of the gene to assess its biological function and its network. Results were further validated by drug testing.

Results

STAT1 was found widely overexpressed in meningioma but not in the corresponding healthy controls. The protein showed constitutive phosphorylation not dependent on the JAK–STAT pathway. STAT1 knockdown resulted in a significant reduction of cellular proliferation and deactivation of AKT and ERK1/2. STAT1 is known to be activated by EGFR, so we investigated the tyrosine kinase and found that EGFR was also constitutively phosphorylated in meningioma and was responsible for the aberrant phosphorylation of STAT1. The pharmaceutical inhibition of EGFR caused a significant reduction in cellular proliferation and of overall levels of cyclin D1, pAKT, and pERK1/2.

Conclusions

STAT1–EGFR-dependent constitutive phosphorylation is responsible for a positive feedback loop that causes its own overexpression and consequently an increased proliferation of the tumor cells. These findings provide the rationale for further studies aiming to identify effective therapeutic options in meningioma.

Recent Advances in Meningioma Immunogenetics

Meningiomas are relatively common, and typically benign intracranial tumors, which in many cases can be cured by surgical resection. However, less prevalent, high grade meningiomas, grow quickly, and recur frequently despite treatment, leading to poor patient outcomes. Across tumor grades, subjective guidelines for histological analysis can preclude accurate diagnosis, and an insufficient understanding of recurrence risk can cloud the choice of optimal treatment. Improved diagnostic and prognostic markers capable of discerning between the 15 heterogeneous WHO recognized meningioma subtypes are necessary to improve disease management and identify new targeted drug treatments. In this review, we show the advances in molecular profiling and immunophenotyping of meningiomas, which may lead to the development of new personalized therapeutic strategies.

Protein Kinase A Distribution in Meningioma

Deregulation of intracellular signal transduction pathways is a hallmark of cancer cells, clearly differentiating them from healthy cells. Differential intracellular distribution of the cAMP-dependent protein kinases (PKA) was previously detected in cell cultures and in vivo in glioblastoma and medulloblastoma. Our goal is to extend this observation to meningioma, to explore possible differences among tumors of different origins and prospective outcomes. The distribution of regulatory and catalytic subunits of PKA has been examined in tissue specimens obtained during surgery from meningioma patients. PKA RI subunit appeared more evenly distributed throughout the cytoplasm, but it was clearly detectable only in some tumors. RII was present in discrete spots, presumably at high local concentration; these aggregates could also be visualized under equilibrium binding conditions with fluorescent 8-substituted cAMP analogues, at variance with normal brain tissue and other brain tumors. The PKA catalytic subunit showed exactly overlapping pattern to RII and in fixed sections could be visualized by fluorescent cAMP analogues. Gene expression analysis showed that the PKA catalytic subunit revealed a significant correlation pattern with genes involved in meningioma. Hence, meningioma patients show a distinctive distribution pattern of PKA regulatory and catalytic subunits, different from glioblastoma, medulloblastoma, and healthy brain tissue. These observations raise the possibility of exploiting the PKA intracellular pathway as a diagnostic tool and possible therapeutic interventions.

The Role of Merlin/NF2 Loss in Meningioma Biology

Mutations in the neurofibromin 2 (NF2) gene were among the first genetic alterations implicated in meningioma tumorigenesis, based on analysis of neurofibromatosis type 2 (NF2) patients who not only develop vestibular schwannomas but later have a high incidence of meningiomas. The NF2 gene product, merlin, is a tumor suppressor that is thought to link the actin cytoskeleton with plasma membrane proteins and mediate contact-dependent inhibition of proliferation. However, the early recognition of the crucial role of NF2 mutations in the pathogenesis of the majority of meningiomas has not yet translated into useful clinical insights, due to the complexity of merlin's many interacting partners and signaling pathways. Next-generation sequencing studies and increasingly sophisticated NF2-deletion-based in vitro and in vivo models have helped elucidate the consequences of merlin loss in meningioma pathogenesis. In this review, we seek to summarize recent findings and provide future directions toward potential therapeutics for this tumor.

New molecular targets in meningiomas: the present and the future

PURPOSE OF REVIEW

Meningiomas, the most common primary brain tumor, have historically been managed with surgery and radiation. Traditional chemotherapy has not been effective. Fortunately, recent advances in genetic sequencing have led to an improved understanding of the molecular drivers in meningioma. This article aims to discuss the diagnostic and therapeutic implications of recently discovered genetic alterations in meningiomas.

RECENT FINDINGS

Many of the recently discovered genetic alterations correlate with distinct clinical phenotypes. SMO, AKT and PIK3CA mutations are enriched in the anterior skull base. KLF4 mutations are specific for secretory histology, and BAP1 alterations are common in progressive rhabdoid meningiomas. Alterations in TERT, DMD and BAP1 correlate with poor clinical outcomes. Importantly, the discovery of clinically actionable alterations in a number of genes, including SMO, AKT1 and PIK3CA, has opened up novel potential avenues for therapeutic management of meningiomas. Overexpression of PD-L1 in higher grade meningiomas also provides preclinical support for the investigation of checkpoint blockade.

SUMMARY

The discovery of genetic alterations has improved our understanding of the natural history and classification of meningiomas. Clinical trials with several novel agents targeting driver mutations are currently accruing patients and they can lead to better treatment strategies.

An integrated genomic analysis of anaplastic meningioma identifies prognostic molecular signatures

Anaplastic meningioma is a rare and aggressive brain tumor characterised by intractable recurrences and dismal outcomes. Here, we present an integrated analysis of the whole genome, transcriptome and methylation profiles of primary and recurrent anaplastic meningioma. A key finding was the delineation of distinct molecular subgroups that were associated with diametrically opposed survival outcomes. Relative to lower grade meningiomas, anaplastic tumors harbored frequent driver mutations in SWI/SNF complex genes, which were confined to the poor prognosis subgroup. Aggressive disease was further characterised by transcriptional evidence of increased PRC2 activity, stemness and epithelial-to-mesenchymal transition. Our analyses discern biologically distinct variants of anaplastic meningioma with prognostic and therapeutic significance.

Brain invasion in meningiomas-clinical considerations and impact of neuropathological evaluation: a systematic review

With the release of the 2016 edition of the World Health Organization (WHO) Classification of Central Nervous System Tumors, brain invasion in meningiomas has been added as a stand-alone criterion for atypia and can therefore impact grading and indirectly adjuvant therapy. Regarding this rising clinical importance, we have reviewed the current knowledge about brain invasion with emphasis on its implications on current and future clinical practice. We found various definitions of brain invasion and approaches for evaluation in surgically obtained specimens described over the past decades. This heterogeneity is reflected by weak correlation with prognosis and remains controversial. Similarly, associated clinical factors are largely unknown. Preoperative, imaging-guided detection of brain invasion is unspecific, and intraoperative assessment using standard and new high-magnification microscopic techniques remains imprecise. Despite the increasing knowledge about molecular alterations of the tumor/ brain surface, pharmacotherapeutic options targeting brain invasive meningiomas are lacking. Finally, we summarize the impact of brain invasion on histopathological grading in the WHO classifications of brain tumors since 1979.In conclusion, standardized neurosurgical sampling and neuropathological analyses could improve diagnostic reliability and reproducibility of future studies. Further research is needed to improve pre- and intraoperative visualization of brain invasion and to develop adjuvant, targeted therapies.

Frequent AKT1E17K mutations in skull base meningiomas are associated with mTOR and ERK1/2 activation and reduced time to tumor recurrence

Background

Skull base meningiomas are considered to be difficult for surgical treatment. We wondered whether genetic alterations recently identified in benign non-NF2-mutated World Health Organization (WHO) grade I meningiomas are related to clinical features of skull base meningiomas and whether druggable signaling pathways are activated.

Methods

We analyzed 93 skull base meningiomas (82 WHO grade I, 11 WHO grade II) for mutations of hot spots or the most relevant exons of AKT1, KLF4/TRAF7, SMO, PI3K, and the TERT promoter.

Results

The AKT1E17K mutation was present in 31% of patients and was related to meningothelial histology. AKT1E17K had a negative effect on the time to tumor recurrence. Analyses of activated signaling proteins revealed among AKT1E17K tumors a significantly higher rate of phospho-mammalian target of rapamycin (mTOR) and phospho-p70S6K+ tumors. AKT1E17K tumors with immunoexpression of phospho-extracellular signal-regulated kinase 1 or 2 (ERK1/2) were characterized by significantly shorter time to tumor recurrence compared with AKT1wt tumors expressing phospho-ERK1/2 (P = .046). KLF4 mutations (K409Q) were present in 11.8% of cases, with significant association to the secretory/transitional subtype (P < .001). The presence of the KLF4 K409Q mutation was associated with favorable outcome. One phosphatidylinositol-3 kinase (PI3K) mutation but no SMO or TERT promoter mutation was found.

Conclusions

AKT1E17K mutation is frequent in skull base meningiomas, results in activation of the mTOR and ERK1/2 signaling pathways, and has negative impact on tumor recurrence. Patients with skull base meningiomas with AKT1E17K mutation might benefit from additional treatment targeting the mTOR pathway. Generally, the PI3K-Akt-mTOR axis might be a potential target for kinase inhibitors in these tumors.

New drug candidates for treatment of atypical meningiomas: An integrated approach using gene expression signatures for drug repurposing

Background

Atypical meningiomas are common central nervous system neoplasms with high recurrence rate and poorer prognosis compared to their grade I counterparts. Surgical excision and radiotherapy remains the mainstay therapy but medical treatments are limited. We explore new drug candidates using computational drug repurposing based on the gene expression signature of atypical meningioma tissue with subsequent analysis of drug-generated expression profiles. We further explore possible mechanisms of action for the identified drug candidates using ingenuity pathway analysis (IPA).

Methods

We extracted gene expression profiles for atypical meningiomas (12 samples) and normal meningeal tissue (4 samples) from the Gene Expression Omnibus, which were then used to generate a gene signature comprising of 281 differentially expressed genes. Drug candidates were explored using both the Board Institute Connectivity Map (cmap) and Library of Integrated Network-Based Cellular Signatures (LINCS). Functional analysis of significant differential gene expression for drug candidates was performed with IPA.

Results

Using our integrated approach, we identified multiple, already licensed, drug candidates such as emetine, verteporfin, phenoxybenzamine and trazodone. Analysis with IPA revealed that these drugs target signal cascades potentially relevant in pathogenesis of meningiomas, particular examples are the effect on ERK by trazodone, MAP kinases by emetine, and YAP-1 protein by verteporfin.

Conclusion

Gene expression profiling and use of drug expression profiles have yielded several plausible drug candidates for treating atypical meningioma, some of which have already been suggested by preceding studies. Although our analyses suggested multiple anti-tumour mechanisms for these drugs, further in vivo studies are required for validation.

Importance of the study

To our knowledge this is the first study which combines relatively new, yet established computational techniques to identify additional treatments for a difficult to manage cerebral neoplasm. Beyond proposing already approved drug candidates in the management of atypical meningioma the study highlights the promise held by computational techniques in improving our management strategies.

Advances in meningioma genetics: novel therapeutic opportunities

Meningiomas currently are among the most frequent intracranial tumours. Although the majority of meningiomas can be cured by surgical resection, ∼20% of patients have an aggressive clinical course with tumour recurrence or progressive disease, resulting in substantial morbidity and increased mortality of affected patients. During the past 3 years, exciting new data have been published that provide insights into the molecular background of meningiomas and link sites of tumour development with characteristic histopathological and molecular features, opening a new road to novel and promising treatment options for aggressive meningiomas. A growing number of the newly discovered recurrent mutations have been linked to a particular clinicopathological phenotype. Moreover, the updated WHO classification of brain tumours published in 2016 has incorporated some of these molecular findings, setting the stage for the improvement of future therapeutic efforts through the integration of essential molecular findings. Finally, an additional potential classification of meningiomas based on methylation profiling has been launched, which provides clues in the assessment of individual risk of meningioma recurrence. All of these developments are creating new prospects for effective molecularly driven diagnosis and therapy of meningiomas.

Global epigenetic profiling identifies methylation subgroups associated with recurrence-free survival in meningioma

Meningioma is the most common primary brain tumor and carries a substantial risk of local recurrence. Methylation profiles of meningioma and their clinical implications are not well understood. We hypothesized that aggressive meningiomas have unique DNA methylation patterns that could be used to better stratify patient management. Samples (n = 140) were profiled using the Illumina HumanMethylation450BeadChip. Unsupervised modeling on a training set (n = 89) identified 2 molecular methylation subgroups of meningioma (MM) with significantly different recurrence-free survival (RFS) times between the groups: a prognostically unfavorable subgroup (MM-UNFAV) and a prognostically favorable subgroup (MM-FAV). This finding was validated in the remaining 51 samples and led to a baseline meningioma methylation classifier (bMMC) defined by 283 CpG loci (283-bMMC). To further optimize a recurrence predictor, probes subsumed within the baseline classifier were subject to additional modeling using a similar training/validation approach, leading to a 64-CpG loci meningioma methylation predictor (64-MMP). After adjustment for relevant clinical variables [WHO grade, mitotic index, Simpson grade, sex, location, and copy number aberrations (CNAs)] multivariable analyses for RFS showed that the baseline methylation classifier was not significant (p = 0.0793). The methylation predictor, however, was significantly associated with tumor recurrence (p < 0.0001). CNAs were extracted from the 450k intensity profiles. Tumor samples in the MM-UNFAV subgroup showed an overall higher proportion of CNAs compared to the MM-FAV subgroup tumors and the CNAs were complex in nature. CNAs in the MM-UNFAV subgroup included recurrent losses of 1p, 6q, 14q and 18q, and gain of 1q, all of which were previously identified as indicators of poor outcome. In conclusion, our analyses demonstrate robust DNA methylation signatures in meningioma that correlate with CNAs and stratify patients by recurrence risk.

STAT3 activation and risk of recurrence in meningiomas

Several studies have suggested that activation of signal transducer and activator of transcription 3 (STAT3) is associated with initiation, progression and metastasis of numerous types of malignancy. However, the role of the Janus kinase-interleukin 6-STAT3 signaling pathway in the pathogenesis and recurrence of meningiomas is unknown. The present study evaluated STAT3 activation by western blotting and immunohistochemistry and assessed its association with Ki-67 labeling in 13 cases of meningioma in which frozen tissue and ≥5.5-year follow-up information were available, and in formalin-fixed meningioma tissues from 14 cases with an 8.4-year follow-up. The results of the western blot analysis indicated that STAT3 phosphorylation was markedly higher in grade II meningiomas compared with that in grade I, with mean densitometric values of 8.6 and 1.7 following normalization to actin, respectively. High STAT3 phosphorylation/activation was identified in 2 of 3 recurrent World Health Organization (WHO) grade I meningiomas and 0 of 3 non-recurrent meningiomas. Strong STAT3 phosphorylation/activation signal was also found in 2 of 4 recurrent grade II meningiomas and 1 of 3 non-recurrent cases. According to the immunohistochemistry results, phospho-STAT3 was not increased in WHO grade II tumors compared with that in grade I tumors, and was not significantly different between recurrent and non-recurrent cases. Ki-67 labeling was significantly increased in grade II vs. grade I tumors, and was also significantly increased in recurrent compared with non-recurrent grade I meningiomas. The results of the current study suggest that, while detection of phosphorylated/activated STAT3 may be useful in isolated cases, identifying activation may be of little value in predicting recurrence.

Receptor tyrosine kinase inhibition by regorafenib/sorafenib inhibits growth and invasion of meningioma cells

Systemic chemotherapeutic treatment for unresectable and/or aggressive meningiomas is still unsatisfying. PDGF receptor (PDGFR)-mediated activation of mitogenic signalling has been shown to be active in meningiomas. Therefore, we evaluate in vitro and in vivo the effects of inhibiting PDGFR using the clinically well-characterised tyrosine kinase inhibitors sorafenib or regorafenib in meningioma models. IOMM-Lee meningioma cells were used to assess cytotoxic effects, inhibition of proliferation, induction of apoptosis, as well as inhibition of migration and motility by sorafenib and regorafenib. Using an orthotopic mouse xenograft model, growth inhibition as monitored by magnetic resonance imaging, and overall survival of sorafenib- or regorafenib-treated mice compared with control animals was determined. Treatment of malignant IOMM-Lee cells resulted in significantly reduced cell survival and induction of apoptosis following regorafenib and sorafenib treatment. Western blots showed that both drugs target phosphorylation of p44/42 ERK via downregulation of the PDGFR. Both drugs additionally showed significant inhibition of cell motility and invasion. In vivo, mice with orthotopic meningioma xenografts showed a reduced volume (n.s.) of signal enhancement in MRI (mainly tumour) following sorafenib and regorafenib treatment. This was translated in a significantly increased overall survival time (p ≤ 0.05) for regorafenib-treated mice. Analyses of in vivo-grown tumours demonstrated again reduced PDGFR expression and expression/phosphorylation of p44/42. Sorafenib and regorafenib show antitumour activity in vitro and in vivo by targeting PDGFR and p44/42 ERK signalling.

Genomic landscape of intracranial meningiomas

Meningiomas are the most common primary intracranial neoplasms in adults. Current histopathological grading schemes do not consistently predict their natural history. Classic cytogenetic studies have disclosed a progressive course of chromosomal aberrations, especially in high-grade meningiomas. Furthermore, the recent application of unbiased next-generation sequencing approaches has implicated several novel genes whose mutations underlie a substantial percentage of meningiomas. These insights may serve to craft a molecular taxonomy for meningiomas and highlight putative therapeutic targets in a new era of rational biology-informed precision medicine.

Genetic/molecular alterations of meningiomas and the signaling pathways targeted

Meningiomas are usually considered to be benign central nervous system tumors; however, they show heterogenous clinical, histolopathological and cytogenetic features associated with a variable outcome. In recent years important advances have been achieved in the identification of the genetic/molecular alterations of meningiomas and the signaling pathways involved. Thus, monosomy 22, which is often associated with mutations of the NF2 gene, has emerged as the most frequent alteration of meningiomas; in addition, several other genes (e.g., AKT1, KLF4, TRAF7, SMO) and chromosomes have been found to be recurrently altered often in association with more complex karyotypes and involvement of multiple signaling pathways. Here we review the current knowledge about the most relevant genes involved and the signaling pathways targeted by such alterations. In addition, we summarize those proposals that have been made so far for classification and prognostic stratification of meningiomas based on their genetic/genomic features.

p38MAPK activation and DUSP10 expression in meningiomas

The mitogen activated protein kinase (MAPK) p38MAPK has been implicated in regulation of cell proliferation and apoptosis. However, expression, activation and regulation has not been studied in meningiomas, to our knowledge. p38MAPK is regulated, in part, by dual specificity phosphatases (DUSP) that inactivate signaling by dephosphorylation. DUSP10 is also a likely participant in regulating meningioma proliferation. Five fetal and an adult human leptomeninges and 37 meningioma cultures (MC) were evaluated for DUSP10 as well as phosphorylation of its substrates p38MAPK and p44/42MAPK by western blot and DUSP10 expression by polymerase chain reaction. Platelet derived growth factor-BB (PDGF-BB), transforming growth factor B1 (TGFB1) and cerebrospinal fluid effects on DUSP10 and signaling were also studied in vitro. DUSP10 and phospho-p38MAPK and phospho-p44/42MAPK were detected in all six leptomeninges. DUSP10 was detected in 13 of 17 World Health Organization grade I, 11 of 14 grade II and four of six grade III meningiomas. Phospho-p38MAPK was detected in nine of 17 grade I, two of six grade II, and four of six grade III meningiomas. In the majority of meningiomas DUSP10 expression correlated inversely with phosphorylation of p38MAPK. PDGF-BB increased DUSP10 in MC2 and MC4 and weakly in MC3. TGFB1 increased phosphorylation of p38MAPK and caspase 3 activation. Thus p38MAPK and DUSP10 likely participate in the pathogenesis of meningiomas.

Medical Management of Meningiomas: Current Status, Failed Treatments, and Promising Horizons

Meningiomas are benign tumors of the central nervous system, with low recurrence risk for World Health Organization (WHO) grade I lesions but a high risk for WHO grade II and III lesions. Current standard treatments include maximum safe surgical resection when indicated and radiation. Only three systemic therapies alpha-interferon, somatostatin receptor agonists, and vascular endothelial growth factor inhibitors are currently recommended by the National Comprehensive Cancer Network for treatment of recurrent meningioma. This paper aims to review medical approaches in the treatment of meningiomas.

Biology and clinical management challenges in meningioma

Meningiomas are the most frequently occurring intracranial tumors. They are characterized by a broad spectrum of histopathologic appearance. Molecular alterations driving meningioma development, which affect the NF2 gene, are found in roughly 50% of patients. Rare genetic events in benign meningiomas are mutations in TRAF7, KLF4, AKT1, and SMO; all of these mutations are exclusive of NF2 alterations. Progression to a clinically aggressive meningioma is linked to inactivation of CDKN2A/B genes, and a plethora of signaling molecules have been described as activated in meningiomas, which supports the concept of successful clinical use of specific inhibitors. Established treatments include surgical resection with or without radiotherapy delivered in a single fraction, a few large fractions (radiosurgery), or multiple fractions (fractionated radiotherapy). For recurrent and aggressive tumors, inhibitors of the vascular endothelial growth factor (VEGF) pathway, such as vatalinib, bevacizumab, and sunitinib, showed signs of activity in small, uncontrolled studies, and prospective clinical studies will test the efficacy of the tetrahydroisoquinoline trabectedin and of SMO and AKT1 inhibitors.

Role of Merlin/NF2 inactivation in tumor biology

Merlin (Moesin-ezrin-radixin-like protein, also known as schwannomin) is a tumor suppressor protein encoded by the neurofibromatosis type 2 gene NF2. Loss of function mutations or deletions in NF2 cause neurofibromatosis type 2 (NF2), a multiple tumor forming disease of the nervous system. NF2 is characterized by the development of bilateral vestibular schwannomas. Patients with NF2 can also develop schwannomas on other cranial and peripheral nerves, as well as meningiomas and ependymomas. The only potential treatment is surgery/radiosurgery, which often results in loss of function of the involved nerve. There is an urgent need for chemotherapies that slow or eliminate tumors and prevent their formation in NF2 patients. Interestingly NF2 mutations and merlin inactivation also occur in spontaneous schwannomas and meningiomas, as well as other types of cancer including mesothelioma, glioma multiforme, breast, colorectal, skin, clear cell renal cell carcinoma, hepatic and prostate cancer. Except for malignant mesotheliomas, the role of NF2 mutation or inactivation has not received much attention in cancer, and NF2 might be relevant for prognosis and future chemotherapeutic approaches. This review discusses the influence of merlin loss of function in NF2-related tumors and common human cancers. We also discuss the NF2 gene status and merlin signaling pathways affected in the different tumor types and the molecular mechanisms that lead to tumorigenesis, progression and pharmacological resistance.

Oncogenic PI3K mutations are as common as AKT1 and SMO mutations in meningioma

BACKGROUND

Meningiomas are the most common primary intracranial tumor in adults. Identification of SMO and AKT1 mutations in meningiomas has raised the possibility of targeted therapies for some patients. The frequency of such mutations in clinical cohorts and the presence of other actionable mutations in meningiomas are important to define.

METHODS

We used high-resolution array-comparative genomic hybridization to prospectively characterize copy-number changes in 150 meningiomas and then characterized these samples for mutations in AKT1, KLF4, NF2, PIK3CA, SMO, and TRAF7.

RESULTS

Similar to prior reports, we identified AKT1 and SMO mutations in a subset of non-NF2-mutant meningiomas (ie, ∼9% and ∼6%, respectively). Notably, we detected oncogenic mutations in PIK3CA in ∼7% of non-NF2-mutant meningiomas. AKT1, SMO, and PIK3CA mutations were mutually exclusive. AKT1, KLF4, and PIK3CA mutations often co-occurred with mutations in TRAF7. PIK3CA-mutant meningiomas showed limited chromosomal instability and were enriched in the skull base.

CONCLUSION

This work identifies PI3K signaling as an important target for precision medicine trials in meningioma patients.

Group I Paks as therapeutic targets in NF2-deficient meningioma

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder characterized by the development of multiple tumors in the central nervous system, most notably schwannomas and meningiomas. Mutational inactivation of NF2 is found in 40-60% of sporadic meningiomas, but the molecular mechanisms underlying malignant changes of meningioma cells remain unclear. Because group I p21-activated kinases (Paks) bind to and are inhibited by the NF2-encoded protein Merlin, we assessed the signaling and anti-tumor effects of three group-I specific Pak inhibitors - Frax597, 716 and 1036 - in NF2-/- meningiomas in vitro and in an orthotopic mouse model. We found that these Pak inhibitors suppressed the proliferation and motility of both benign (Ben-Men1) and malignant (KT21-MG1) meningiomas cells. In addition, we found a strong reduction in phosphorylation of Mek and S6, and decreased cyclin D1 expression in both cell lines after treatment with Pak inhibitors. Using intracranial xenografts of luciferase-expressing KT21-MG1 cells, we found that treated mice showed significant tumor suppression for all three Pak inhibitors. Similar effects were observed in Ben-Men1 cells. Tumors dissected from treated animals exhibited an increase in apoptosis without notable change in proliferation. Collectively, these results suggest that Pak inhibitors might be useful agents in treating NF2-deficient meningiomas.

KINOMIC ALTERATIONS IN ATYPICAL MENINGIOMA

BACKGROUND

We sought to profile Atypical Meningioma in a high-throughput manner to better understand the altered signaling within these tumors and specifically the kinases altered in recurrent atypical meningioma. Kinomic Profiles could be used to identify prognostic biomarkers for responders/non-responders to classify future patients that are unlikely to benefit from current therapies. Directly these results could be used to identify drug-actionable kinase targets as well.

METHODS

Peptide-substrate microarray kinase activity analysis was conducted with a PamStation^®12 analyzing the tyrosine kinome in each tumor kinetically against ~144 target peptides. These data were then analyzed relative to clinical outcome (e.g., tumor recurrence).

RESULTS

3 major clusters of atypical meningiomas were identified with highly variant peptides primarily being targets of EGFR family, ABL, BRK and BMX kinases. Kinomic analysis of recurrent atypical meningiomas indicated patterns of increased phosphorylation of BMX, TYRO3 and FAK substrates as compared to non-recurrent tumors.

CONCLUSION

The atypical meningiomas profiled here exhibited molecular sub-clustering that may have phenotypic corollaries predictive of outcome. Recurrent tumors had increases in kinase activity that may predict resistance to current therapies, and may guide selection of directed therapies. Taken together these data further the understanding of kinomic alteration in atypical meningioma, and the processes that may not only mediate recurrence, but additionally may identify kinase targets for intervention.

MKP-3 regulates PDGF-BB effects and MAPK activation in meningioma cells

Autocrine platelet derived growth factor-BB (PDGF-BB) and cerebrospinal fluid, which also contains PDGF, stimulate proliferation of leptomeningeal and meningioma cells, in part, by activation of the Raf-1-MEK-1-MAPK pathway. The negative regulators of this activation are not known. However, PDGF receptors and p44/42 MAPK are regulated, in part, by mitogen activated kinase phosphatase 3 (MKP-3) and Src homology carboxyl terminus protein (SHP-2). Six fetal and one adult human leptomeninges specimens and 22 meningiomas were evaluated for MKP-3, SHP-2, and phospho-SHP-2 as well as activation/phosphorylation of MEK1/2, p44/42 MAPK, Akt and signal transducer and activator of transcription 3 (STAT3) by western blot and MKP3 expression by polymerase chain reaction. PDGF-BB and cerebrospinal fluid effects on these phosphatases and signaling were also studied in vitro. MKP-3 and phospho-p44/42 MAPK were detected in all or six of seven leptomeninges, respectively. MKP-3 was detected in six of eight World Health Organization grade I and II meningiomas. Three of four grade I and five of five grade II with no or low MKP-3 had high levels of phospho-p44/42MAPK. MKP3 was not detected in four of six grade III meningiomas. These had high levels of phospho-p44/42MAPK. SHP2 was found in all leptomeninges and meningiomas while phospho-SHP-2 was found in 11 to 33% of grade I-III meningiomas. Reduced MKP-3 may facilitate PDGF-BB autocrine and paracrine mitogenic effects in a subpopulation of higher grade meningiomas by increasing phospho-p44/42 MAPK.