NF2/merlin is a novel negative regulator of mTOR complex 1, and activation of mTORC1 is associated with meningioma and schwannoma growth

Interaction between PI3K/AKT and Hippo pathways during in vitro follicular activation and response to fragmentation and chemotherapy exposure using a mouse immature ovary model

Understanding and control of the massive and accelerated follicular growth that occurs during in vitro culture of ovarian tissue is a crucial step toward the development of efficient culture systems that offer an attractive alternative to ovarian tissue transplantation for fertility restoration in cancer survivors. One outstanding question focuses on processes that occur prior to cryopreservation, such as tissue sectioning or chemotherapeutic treatment, might exacerbate this follicular activation. Although the PI3K/AKT/mTOR pathway is well known as a major trigger of physiological and chemotherapy-induced follicular activation, studies have shown that disruption of Hippo pathway due to ovarian fragmentation acts as an additional stimulator. This study aimed to characterize the possible interactions between these pathways using post-natal day 3 mouse ovaries cultured for 4 or 48 h. Morphology, gene transcription, and protein levels were assessed to investigate the impact of sectioning or chemotherapy exposure (4-hydroperoxycyclophosphamide [4HC], 3 and 20 μM). The effect of an mTORC1 inhibitor, Everolimus, alone or as a 4HC co-treatment to prevent follicle activation was evaluated. The results showed that organ removal from its physiological environment was as effective as sectioning for disruption of Hippo pathway and induction of follicle activation. Both PI3K/AKT/mTOR and Hippo pathways were involved in chemotherapy-induced follicular activation and responded to fragmentation. Surprisingly, Everolimus was able to prevent the activation of both pathways during chemotherapy exposure, suggesting cross-talk between them. This study underscores the major involvement of PI3K/AKT/mTOR and Hippo pathways in in vitro follicle activation and provides evidence that both can be regulated using mTORC1 inhibitor.

Characterization of a newly established schwannoma cell line from a sporadic vestibular schwannoma patient

A stable, human sporadic vestibular schwannoma cell line is not currently available. By using a lentivirus-mediated transfection from a 41-year-old sporadic vestibular schwannoma patient, primary schwannoma cells were obtained, cultured and immortalized using the hHERT gene. The NF2 gene of the resulting JEI-001 cell line contains a specific Exon 5 mutation. The schwannoma cell origin of this cell line was confirmed using STR techniques and immunocytochemistry. A comparison between the primary tumor tissue and JEI-001 revealed a common mutation of the NF2 gene, which indicated that the JEI-001 cell line had retained most of its original tumor characteristics. The JEI-001 cell line was found to be non-tumorigenic in nude mice, but certain growth features had been altered, resulting in changes such as independence from the Schwann cell growth factors and a higher proliferation rate. This was the first known study to establish cell lines immortalized from human sporadic vestibular schwannoma that had different characteristics from that of HEI-193. This is a novel model system that can be used for the study of NF2 gene functions, in order to elaborate on the biological features of sporadic vestibular schwannoma, even including familial NF2 tumors, and to further explore the molecular pathogenesis and develop new adjuvant therapies.

The pathogenesis of mesothelioma is driven by a dysregulated translatome

Malignant mesothelioma (MpM) is an aggressive, invariably fatal tumour that is causally linked with asbestos exposure. The disease primarily results from loss of tumour suppressor gene function and there are no 'druggable' driver oncogenes associated with MpM. To identify opportunities for management of this disease we have carried out polysome profiling to define the MpM translatome. We show that in MpM there is a selective increase in the translation of mRNAs encoding proteins required for ribosome assembly and mitochondrial biogenesis. This results in an enhanced rate of mRNA translation, abnormal mitochondrial morphology and oxygen consumption, and a reprogramming of metabolic outputs. These alterations delimit the cellular capacity for protein biosynthesis, accelerate growth and drive disease progression. Importantly, we show that inhibition of mRNA translation, particularly through combined pharmacological targeting of mTORC1 and 2, reverses these changes and inhibits malignant cell growth in vitro and in ex-vivo tumour tissue from patients with end-stage disease. Critically, we show that these pharmacological interventions prolong survival in animal models of asbestos-induced mesothelioma, providing the basis for a targeted, viable therapeutic option for patients with this incurable disease.

Transcriptomic Profile Reveals Deregulation of Hearing-Loss Related Genes in Vestibular Schwannoma Cells Following Electromagnetic Field Exposure

Hearing loss (HL) is the most common sensory disorder in the world population. One common cause of HL is the presence of vestibular schwannoma (VS), a benign tumor of the VIII cranial nerve, arising from Schwann cell (SC) transformation. In the last decade, the increasing incidence of VS has been correlated to electromagnetic field (EMF) exposure, which might be considered a pathogenic cause of VS development and HL. Here, we explore the molecular mechanisms underlying the biologic changes of human SCs and/or their oncogenic transformation following EMF exposure. Through NGS technology and RNA-Seq transcriptomic analysis, we investigated the genomic profile and the differential display of HL-related genes after chronic EMF. We found that chronic EMF exposure modified the cell proliferation, in parallel with intracellular signaling and metabolic pathways changes, mostly related to translation and mitochondrial activities. Importantly, the expression of HL-related genes such as NEFL, TPRN, OTOGL, GJB2, and REST appeared to be deregulated in chronic EMF exposure. In conclusion, we suggest that, at a preclinical stage, EMF exposure might promote the transformation of VS cells and contribute to HL.

Phase 0 Clinical Trial of Everolimus in Patients with Vestibular Schwannoma or Meningioma

Inhibition of mTORC1 signaling has been shown to diminish growth of meningiomas and schwannomas in preclinical studies, and clinical data suggest that everolimus, an orally administered mTORC1 inhibitor, may slow tumor progression in a subset of patients with neurofibromatosis type 2 (NF2) with vestibular schwannoma. To assess the pharmacokinetics, pharmacodynamics, and potential mechanisms of treatment resistance, we performed a presurgical (phase 0) clinical trial of everolimus in patients undergoing elective surgery for vestibular schwannoma or meningiomas. Eligible patients with meningioma or vestibular schwannoma requiring tumor resection enrolled on study received everolimus 10 mg daily for 10 days immediately prior to surgery. Everolimus blood levels were determined immediately before and after surgery. Tumor samples were collected intraoperatively. Ten patients completed protocol therapy. Median pre- and postoperative blood levels of everolimus were found to be in a high therapeutic range (17.4 ng/mL and 9.4 ng/mL, respectively). Median tumor tissue drug concentration determined by mass spectrometry was 24.3 pg/mg (range, 9.2-169.2). We observed only partial inhibition of phospho-S6 in the treated tumors, indicating incomplete target inhibition compared with control tissues from untreated patients (P = 0.025). Everolimus led to incomplete inhibition of mTORC1 and downstream signaling. These data may explain the limited antitumor effect of everolimus observed in clinical studies for patients with NF2 and will inform the design of future preclinical and clinical studies targeting mTORC1 in meningiomas and schwannomas.

The biological underpinnings of radiation therapy for vestibular schwannomas: Review of the literature

OBJECTIVE

Radiation therapy is a mainstay in the treatment of numerous neoplasms. Numerous publications have reported good clinical outcomes for primary radiation therapy for Vestibular Schwannomas (VS). However, there are relatively few pathologic specimens of VSs available to evaluate post-radiation, which has led to a relative dearth in research on the cellular mechanisms underlying the effects of radiation therapy on VSs.

METHODS

Here we review the latest literature on the complex biological effects of radiation therapy on these benign tumors-including resistance to oxidative stress, mechanisms of DNA damage repair, alterations in normal growth factor pathways, changes in surrounding vasculature, and alterations in immune responses following radiation.

RESULTS

Although VSs are highly radioresistant, radiotherapy is often successful in arresting their growth.

CONCLUSION

By better understanding the mechanisms underlying these effects, we could potentially harness such mechanisms in the future to potentiate the clinical effects of radiotherapy on VSs.

LEVEL OF EVIDENCE

N/A.

Merlin and expanded integrate cell signaling that regulates cyst stem cell proliferation in the Drosophila testis niche

The Drosophila testis is a model organism stem cell niche in which two stem cell populations coordinate together to produce sperm; thus, these stem cells must be balanced in the niche. Merlin, a tumor-suppressor and human disease gene required for contact inhibition of proliferation, is known to limit the proliferation of the somatic cyst stem cells in the testis niche. Expanded encodes a protein that is structurally similar to Merlin in Drosophila, and is semi-redundant with Merlin in multiple tissues. We found that expanded depletion caused similar cyst lineage cell over-proliferation as observed with Merlin, and double mutants showed more severe phenotypes than either gene individually. Thus, these genes have partially redundant functions in the cyst lineage cells of this niche. We also expressed non-phosphorylatable constitutively "tumor suppressing" alleles of Merlin in cyst lineage cells, and surprisingly, we observed a similar cyst lineage over-proliferation phenotype. Merlin is known to impact multiple different signaling pathways to exert its effect on proliferation. We found that the Merlin loss of function phenotype was associated with an increase in MAPK/ERK signaling, consistent with Merlin's established role in transmembrane receptor inhibition. Constitutive Merlin displayed a reduction in both MAPK/ERK signaling and PI3K/Tor signaling. PI3K/Tor signaling is required for cyst cell differentiation, and inhibition of this pathway by Merlin activation phenocopied the Tor cyst lineage loss of function phenotype. Thus, Merlin impacts and integrates the activity of multiple signaling pathways in the testis niche. The ability of Merlin to dynamically change its activity via phosphorylation in response to local contact cues provides an intriguing mechanism whereby the signaling pathways that control these stem cells might be dynamically regulated in response to the division of a neighboring germ cell.

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.

Estrogens in Hepatocellular Carcinoma: Friends or Foes?

Simple Summary

Today, we know that estrogen hormones are required for the development and function of many organs, such as the liver, in both males and females. However, in some circumstances, estrogen excess may be implicated in the appearance of various chronic diseases, including cancer. This review will inspect the results of several studies to better understand the mechanisms responsible for estrogens to change from protective into harmful hormones in human liver.

Abstract

Estrogens are recognized as key players in physiological regulation of various, classical and non-classical, target organs, and tissues, including liver development, homeostasis, and function. On the other hand, multiple, though dispersed, experimental evidence is highly suggestive for the implication of estrogen in development and progression of hepatocellular carcinoma. In this paper, data from our own studies and the current literature are reviewed to help understanding this apparent discrepancy.

Crispr/Cas-based modeling of NF2 loss in meningioma cells

BACKGROUND

Alterations of the neurofibromatosis type 2 gene (NF2) occur in more than fifty percent of sporadic meningiomas. Meningiomas develop frequently in the setting of the hereditary tumor syndrome NF2. Investigation of potential drug-based treatment options has been limited by the lack of appropriate in vitro and in vivo models.

NEW METHODS

Using Crispr/Cas gene editing, of the malignant meningioma cell line IOMM-Lee, we generated a pair of cell clones characterized by either stable knockout of NF2 and loss of the protein product merlin or retained merlin protein (transfected control without gRNA).

RESULTS

IOMM-Lee cells lacking NF2 showed reduced apoptosis and formed bigger colonies compared to control IOMM-Lee cells. Treatment of non-transfected IOMM-Lee cells with the focal adhesion kinase (FAK) inhibitor GSK2256098 resulted in reduced colony sizes. Orthotopic mouse xenografts showed the formation of convexity tumors typical for meningiomas with NF2-depleted and control cells.

COMPARISON WITH EXISTING METHODS

No orthotopic meningioma models with genetically-engineered cell pairs are available so far.

CONCLUSION

Our model based on Crispr/Cas-based gene editing provides paired meningioma cells suitable to study functional consequences and therapeutic accessibility of NF2/merlin loss.

Genetic syndromes predisposing to pediatric brain tumors

The application of high-throughput sequencing approaches including paired tumor/normal sampling with therapeutic intent has demonstrated that 8%-19% of pediatric CNS tumor patients harbor a germline alteration in a classical tumor predisposition gene (NF1, P53). In addition, large-scale germline sequencing studies in unselected cohorts of pediatric neuro-oncology patients have demonstrated novel candidate tumor predisposition genes (ELP1 alterations in sonic hedgehog medulloblastoma). Therefore, the possibility of an underlying tumor predisposition syndrome (TPS) should be considered in all pediatric patients diagnosed with a CNS tumor which carries critical implications including accurate prognostication, selection of optimal therapy, screening, risk reduction, and family planning. The Pediatric Cancer Working Group of the American Association for Cancer Research (AACR) recently published consensus screening recommendations for children with the most common TPS. In this review, we provide an overview of the most relevant as well as recently identified TPS associated with the most frequently encountered pediatric CNS tumors with an emphasis on pathogenesis, genetic testing, clinical features, and treatment implications.

Silencing of SmgGDS, a Novel mTORC1 Inducer That Binds to RHEBs, Inhibits Malignant Mesothelioma Cell Proliferation

Malignant mesothelioma (MM) is an aggressive tumor that typically develops after a long latency following asbestos exposure. Although mechanistic target of rapamycin complex 1 (mTORC1) activation enhances MM cell growth, the mTORC1 inhibitor everolimus has shown limited efficacy in clinical trials of MM patients. We explored the mechanism underlying mTORC1 activation in MM cells and its effects on cell proliferation and progression. Analysis of the expression profiles of 87 MMs from The Cancer Genome Atlas revealed that 40 samples (46%) displayed altered expression of RPTOR (mTORC1 component) and genes immediately upstream that activate mTORC1. Among them, we focused on RHEB and RHEBL1, which encode direct activators of mTORC1. Exogenous RHEBL1 expression enhanced MM cell growth, indicating that RHEB-mTORC1 signaling acts as a pro-oncogenic cascade. We investigated molecules that directly activate RHEBs, identifying SmgGDS as a novel RHEB-binding protein. SmgGDS knockdown reduced mTORC1 activation and inhibited the proliferation of MM cells with mTORC1 activation. Interestingly, SmgGDS displayed high binding affinity with inactive GDP-bound RHEBL1, and its knockdown reduced cytosolic RHEBL1 without affecting its activation. These findings suggest that SmgGDS retains GDP-bound RHEBs in the cytosol, whereas GTP-bound RHEBs are localized on intracellular membranes to promote mTORC1 activation. We revealed a novel role for SmgGDS in the RHEB-mTORC1 pathway and its potential as a therapeutic target in MM with aberrant mTORC1 activation. IMPLICATIONS: Our data showing that SmgGDS regulates RHEB localization to activate mTORC1 indicate that SmgGDS can be used as a new therapeutic target for MM exhibiting mTORC1 activation.

mTOR kinase inhibition disrupts neuregulin 1-ERBB3 autocrine signaling and sensitizes NF2-deficient meningioma cellular models to IGF1R inhibition

Meningiomas (MNs), arising from the arachnoid/meningeal layer, are nonresponsive to chemotherapies, with ∼50% showing loss of the Neurofibromatosis 2 (NF2) tumor suppressor gene. Previously, we established NF2 loss activates mechanistic target of rapamycin complex 1 (mTORC1) and mechanistic target of rapamycin complex 2 (mTORC2) signaling, leading to clinical trials for NF2 and MN. Recently our omics studies identified activated ephrin (EPH) receptor and Src family kinases upon NF2 loss. Here, we report increased expression of several ligands in NF2-null human arachnoidal cells (ACs) and the MN cell line Ben-Men-1, particularly neuregulin-1/heregulin (NRG1), and confirm increased NRG1 secretion and activation of V-ERB-B avian erythroblastic leukemia viral oncogene homolog 3 (ERBB3) receptor kinase. Conditioned-medium from NF2-null ACs or exogenous NRG1 stimulated ERBB3, EPHA2, and mTORC1/2 signaling, suggesting pathway crosstalk. NF2-null cells treated with an ERBB3-neutralizing antibody partially downregulated mTOR pathway activation but showed no effect on viability. mTORC1/2 inhibitor treatment decreased NRG1 expression and downregulated ERBB3 while re-activating pAkt T308, suggesting a mechanism independent of NRG1-ERBB3 but likely involving activation of another upstream receptor kinase. Transcriptomics after mTORC1/2 inhibition confirmed decreased ERBB3/ERBB4 while revealing increased expression of insulin-like growth factor receptor 1 (IGF1R). Drug treatment co-targeting mTORC1/2 and IGF1R/insulin receptor attenuated pAkt T308 and showed synergistic effects on viability. Our findings indicate potential autocrine signaling where NF2 loss leads to secretion/activation of NRG1-ERBB3 signaling. mTORC1/2 inhibition downregulates NRG1-ERBB3, while upregulating pAkt T308 through an adaptive response involving IGF1R/insulin receptor and co-targeting these pathways may prove effective for treatment of NF2-deficient MN.

Merlin cooperates with neurofibromin and Spred1 to suppress the Ras-Erk pathway

The Ras-Erk pathway is frequently overactivated in human tumors. Neurofibromatosis types 1 and 2 (NF1, NF2) are characterized by multiple tumors of Schwann cell origin. The NF1 tumor suppressor neurofibromin is a principal Ras-GAP accelerating Ras inactivation, whereas the NF2 tumor suppressor merlin is a scaffold protein coordinating multiple signaling pathways. We have previously reported that merlin interacts with Ras and p120RasGAP. Here, we show that merlin can also interact with the neurofibromin/Spred1 complex via merlin-binding sites present on both proteins. Further, merlin can directly bind to the Ras-binding domain (RBD) and the kinase domain (KiD) of Raf1. As the third component of the neurofibromin/Spred1 complex, merlin cannot increase the Ras-GAP activity; rather, it blocks Ras binding to Raf1 by functioning as a 'selective Ras barrier'. Merlin-deficient Schwann cells require the Ras-Erk pathway activity for proliferation. Accordingly, suppression of the Ras-Erk pathway likely contributes to merlin's tumor suppressor activity. Taken together, our results, and studies by others, support targeting or co-targeting of this pathway as a therapy for NF2 inactivation-related tumors.

Review of Atypical and Anaplastic Meningiomas: Classification, Molecular Biology, and Management

Although the majority of meningiomas are slow-growing and benign, atypical and anaplastic meningiomas behave aggressively with a penchant for recurrence. Standard of care includes surgical resection followed by adjuvant radiation in anaplastic and partially resected atypical meningiomas; however, the role of adjuvant radiation for incompletely resected atypical meningiomas remains debated. Despite maximum treatment, atypical, and anaplastic meningiomas have a strong proclivity for recurrence. Accumulating mutations over time, recurrent tumors behave more aggressively and often become refractory or no longer amenable to further surgical resection or radiation. Chemotherapy and other medical therapies are available as salvage treatment once standard options are exhausted; however, efficacy of these agents remains limited. This review discusses the risk factors, classification, and molecular biology of meningiomas as well as the current management strategies, novel therapeutic approaches, and future directions for managing atypical and anaplastic meningiomas.

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.

Together we stand, apart we fall: how cell-to-cell contact/interplay provides resistance to ferroptosis

Contextualisation of the new type of cell death called “ferroptosis” opened a completely new avenue for the development of anti-cancer therapies. Cumulative fundamental research dating back to the mid-20th century, crowned by the extraordinary work of the group led by Dr. Stockwell from Columbia University in 2012, finally got its candidature to be applied in the clinical settings. Although the potential for clinical importance is undoubtedly growing every day, as showed by the increasing number of papers dealing with ferroptosis and its applications, long experience of cancer research and treatment taught us that caution is still necessary. The plasticity of the tumour cells, particularly acute, along with its involvement in the resistance mechanisms, that have been seen, to greater or lesser extent, for almost all currently used therapies, represents the biggest fascinations in biomedical research field and also the biggest challenge to achieving cures in cancer patients. Accordingly, the main features of fundamental research have to be vigilance and anticipation. In this review, we tried to summarize the literature data, accumulated in the past couple of years, which point out the pitfalls in which “ferroptosis inducers” can fall if used prematurely in the clinical settings, but at the same time can provide a great advantage in the exhausting battle with cancer resistance. This is the first comprehensive review focusing on the effects of the cell-to-cell contact/interplay in the development of resistance to ferroptosis, while the contribution of cell-born factors has been summarized previously so here we just listed them.

Advances in multidisciplinary therapy for meningiomas

Surgery has long been established as the first-line treatment for the majority of symptomatic and enlarging meningiomas, and evidence for its success is derived from retrospective case series. Despite surgical resection, a subset of meningiomas display aggressive behavior with early recurrences that are difficult to treat. The decision to radically resect meningiomas and involved structures is balanced against the risk for neurological injury in patients. Radiation therapy has largely been used as a complementary and safe therapeutic strategy in meningiomas with evidence primarily stemming from retrospective, single-institution reports. Two of the first cooperative group studies (RTOG 0539 and EORTC 22042) evaluating the outcomes of adjuvant radiation therapy in higher-risk meningiomas have shown promising preliminary results. Historically, systemic therapy has resulted in disappointing results in meningiomas. However, several clinical trials are under way evaluating the efficacy of chemotherapies, such as trabectedin, and novel molecular agents targeting Smoothened, AKT1, and focal adhesion kinase in patients with recurrent meningiomas.

Long-term therapy with Bevacizumab in a young patient affected by NF2. Stop or continue treatment? An update of a case report and review of the literature

Neurofibromatosis type 2 (NF2) is an autosomal dominant condition caused by pathogenic variants in the NF2 gene. To date, cytotoxic chemotherapy has no established role in the treatment of NF-2. Historical case reports of malignant schwannomas have documented responses to chemotherapies with cyclophosphamide, vincristine and doxorubicin, in patients who develop pulmonary metastases. Recently, several studies proposed the use of anti-HER2, anti-EGFR, anti-platelet-derived growth factor receptors. As reported in our previous review of the literature, vascular endothelial growth factor (VEGF) and its receptor VEGFR-1 have been detected in schwannomas with the best results. We described the case of a young patient with NF2 treated for long time with Bevacizumab. Here, we report the update of the previous case report.

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.

An update on the CNS manifestations of neurofibromatosis type 2

Neurofibromatosis type II (NF2) is a tumor predisposition syndrome characterized by the development of distinctive nervous system lesions. NF2 results from loss-of-function alterations in the NF2 gene on chromosome 22, with resultant dysfunction of its protein product merlin. NF2 is most commonly associated with the development of bilateral vestibular schwannomas; however, patients also have a predisposition to development of other tumors including meningiomas, ependymomas, and peripheral, spinal, and cranial nerve schwannomas. Patients may also develop other characteristic manifestations such as ocular lesions, neuropathies, meningioangiomatosis, and glial hamartia. NF2 has a highly variable clinical course, with some patients exhibiting a severe phenotype and development of multiple tumors at an early age, while others may be nearly asymptomatic throughout their lifetime. Despite the high morbidity associated with NF2 in severe cases, management of NF2-associated lesions primarily consists of surgical resection and treatment of symptoms, and there are currently no FDA-approved systemic therapies that address the underlying biology of the syndrome. Refinements to the diagnostic criteria of NF2 have been proposed over time due to increasing understanding of clinical and molecular data. Large-population studies have demonstrated that some features such as the development of gliomas and neurofibromas, currently included as diagnostic criteria, may require further clarification and modification. Meanwhile, burgeoning insights into the molecular biology of NF2 have shed light on the etiology and highly variable severity of the disease and suggested numerous putative molecular targets for therapeutic intervention. Here, we review the clinicopathologic features of NF2, current understanding of the molecular biology of NF2, particularly with regard to central nervous system lesions, ongoing therapeutic studies, and avenues for further research.

Therapy of Sporadic and NF2-Related Vestibular Schwannoma

Vestibular schwannoma (VS) is a benign primary brain tumor that occurs sporadic or as part of a genetic syndrome. The most common cause is the mutation of the NF2 tumor suppressor gene that is involved in the production of the protein merlin. Merlin plays a role in cell growth and cell adhesion. In patients with NF2, the VSs arise bilaterally and coincide with other brain tumors. In sporadic VS, the tumor is typically unilateral and does not coincide in combination with other tumors. MRI is the standard imaging technique and can be used to assess the size and aspect of the tumor as well as the progression of disease. The preferred management of large VS in both VS types is surgery with or without adjuvant radiation. The management for the medium- or small-sized VS includes wait and scan, radiotherapy and/or surgery. This choice depends on the preference of the patient and institutional protocols. The outcomes of surgical and radiotherapy treatments are improving due to progress in surgical equipment/approaches, advances in radiation delivery techniques and dose optimizations protocols. The main purpose of the management of VS is preserving function as long as possible in combination with tumor control.

Vestibular Schwannoma: What We Know and Where We are Heading

Vestibular schwannoma (VS) is a Schwann cell-derived tumour arising from the vestibulocochlear nerve. Although benign, it represents a threat to intracranial structures due to mass effect and carries a small risk of malignant transformation. VS therefore represents an important healthcare burden. We review the literature regarding pathogenesis, risk factors, and diagnosis of VS. The current and future potential management strategies are also discussed. A narrative review of all relevant papers known to the authors was conducted. The majority of VS remain clinically stable and do not require interventional procedures. Nevertheless, various surgical techniques exist for removing VS, the most common of which are translabyrinthine and retrosigmoid approaches. Due to surgical risks such as hearing loss, facial nerve dysfunction, post-operative headache, and cerebrospinal fluid leakage, a "watch and rescan" approach is adopted for most patients. Radiotherapy is a useful alternative and has been shown to have a similar response for growth restriction. Due to the heterogeneous nature of VS, there is a lack of consensus regarding management of tumours that are too large for conservative management but too small to indicate surgery. Emerging biologic therapies, such as Bevacizumab, Everolimus, and Lapatinib, as well as anti-inflammatories like aspirin are promising potential treatments; however, long-term evidence of their efficacy is required. The knowledge base regarding VS continues to improve. With increased understanding of the pathogenesis of these tumors, we believe future work should focus on pharmacologic intervention. Biologic therapies aimed toward improved patient outcomes are particularly promising.

Combination therapy with mTOR kinase inhibitor and dasatinib as a novel therapeutic strategy for vestibular schwannoma

Neurofibromatosis type 2 (NF2) is an inherited disorder characterized by bilateral vestibular schwannomas (VS) that arise from neoplastic Schwann cells (SCs). NF2-associated VSs are often accompanied by meningioma (MN), and the majority of NF2 patients show loss of the NF2 tumor suppressor. mTORC1 and mTORC2-specific serum/glucocorticoid-regulated kinase 1 (SGK1) are constitutively activated in MN with loss of NF2. In a recent high-throughput kinome screen in NF2-null human arachnoidal and meningioma cells, we showed activation of EPH RTKs, c-KIT, and SFK members independent of mTORC1/2 activation. Subsequently, we demonstrated in vitro and in vivo efficacy of combination therapy with the dual mTORC1/2 inhibitor AZD2014 and the multi-kinase inhibitor dasatinib. For these reasons, we investigated activated mTORC1/2 and EPH receptor-mediated signaling in sporadic and NF2-associated VS. Using primary human VS cells and a mouse allograft model of schwannoma, we evaluated the dual mTORC1/2 inhibitor AZD2014 and the tyrosine kinase inhibitor dasatinib as monotherapies and in combination. Escalating dose-response experiments on primary VS cells grown from 15 human tumors show that combination therapy with AZD2014 and dasatinib is more effective at reducing metabolic activity than either drug alone and exhibits a therapeutic effect at a physiologically reasonable concentration (~0.1 µM). In vivo, while AZD2014 and dasatinib each inhibit tumor growth alone, the effect of combination therapy exceeds that of either drug. Co-targeting the mTOR and EPH receptor pathways with these or similar compounds may constitute a novel therapeutic strategy for VS, a condition for which there is no FDA-approved pharmacotherapy.

The CREB-binding protein inhibitor ICG-001: a promising therapeutic strategy in sporadic meningioma with NF2 mutations

Background

Meningiomas with Neurofibromin 2 gene mutations (NF2-mutant meningiomas) account for ~40% of the sporadic meningiomas. However, there is still no effective drug treatment for the disease.

Methods

Expression profile of Merlin protein was explored through immunohistochemistry in a meningioma patient cohort (n = 346). A 20-agent library covering a wide range of meningioma relevant targets was tested using meningioma cell lines IOMM-Lee (NF2 wildtype) and CH157-MN (NF2 deficient). Therapeutic effects and biological mechanisms of the identified compound, ICG-001, in NF2-mutant meningiomas were further characterized in vitro and in patient-derived xenograft (PDX) models.

Results

Low Merlin expression was associated with meningioma proliferation and poor clinical outcomes in a large patient series. ICG-001, a cAMP-responsive element binding (CREB)-binding protein (CBP) inhibitor, selectively suppressed tumor growth of cells with low Merlin expression. Besides, ICG-001 mediated CH157-MN and IOMM-Lee growth inhibition primarily through robust induction of the G1 cell-cycle arrest. Treatment with ICG-001 alone significantly reduced the growth of NF2-mutant xenografts in mice, as well. We also provide further evidence that ICG-001 inhibits proliferation of NF2-mutant meningioma cells at least partly through attenuating the FOXM1-mediated Wnt/β-catenin signaling.

Conclusions

This study highlights the importance of ligand-mediated Wnt/β-catenin signaling as well as its drugable potency in NF2-mutant meningioma.

Hyperactivation of TORC1 Drives Resistance to the Pan-HER Tyrosine Kinase Inhibitor Neratinib in HER2-Mutant Cancers

We developed neratinib-resistant HER2-mutant cancer cells by gradual dose escalation. RNA sequencing identified TORC1 signaling as an actionable mechanism of drug resistance. Primary and acquired neratinib resistance in HER2-mutant breast cancer patient-derived xenografts (PDXs) was also associated with TORC1 hyperactivity. Genetic suppression of RAPTOR or RHEB ablated P-S6 and restored sensitivity to the tyrosine kinase inhibitor. The combination of the TORC1 inhibitor everolimus and neratinib potently arrested the growth of neratinib-resistant xenografts and organoids established from neratinib-resistant PDXs. RNA and whole-exome sequencing revealed RAS-mediated TORC1 activation in a subset of neratinib-resistant models. DNA sequencing of HER2-mutant tumors clinically refractory to neratinib, as well as circulating tumor DNA profiling of patients who progressed on neratinib, showed enrichment of genomic alterations that converge to activate the mTOR pathway.

Everolimus and Octreotide for Patients with Recurrent Meningioma: Results from the Phase II CEVOREM Trial

PURPOSE

Aggressive meningiomas that progress after surgery/radiotherapy represent an unmet medical need. Strong and constant expression of SSTR2A receptors and activation of the Pi3K/Akt/mTOR pathway have been demonstrated in meningiomas. The combination of everolimus, an mTOR inhibitor, and octreotide, a somatostatin agonist, has shown additive antitumor effect in vitro. The phase II CEVOREM trial investigated the efficacy of this combination on recurrent meningiomas.

PATIENTS AND METHODS

Patients with documented recurrent tumor progression ineligible for further surgery/radiotherapy were eligible to receive octreotide (30 mg/d, day 1) and everolimus (10 mg/d, days 1-28). The primary endpoint was the 6-month progression-free survival rate (PFS6). The secondary endpoints were overall survival, response rate, tumor growth rate according to central review, and safety.

RESULTS

A total of 20 patients were enrolled, including 2 with World Health Organization (WHO) grade I tumors, 10 with WHO grade II tumors, and 8 with WHO grade III tumors; furthermore, 4 patients harbored NF2 germline mutation. The overall PFS6 was 55% [95% confidence interval (CI), 31.3%-73.5%], and overall 6- and 12-month survival rates were 90% (95% CI, 65.6%-97.4%) and 75% (95% CI, 50.0%-88.7%), respectively. A major decrease (>50%) was observed in the growth rate at 3 months in 78% of tumors. The median tumor growth rate decreased from 16.6%/3 months before inclusion to 0.02%/3 months at 3 months (P < 0.0002) and 0.48%/3 months at 6 months after treatment (P < 0.0003).

CONCLUSIONS

The combination of everolimus and octreotide was associated with clinical and radiological activity in aggressive meningiomas and warrants further studies. Decrease in the tumor volume growth rate should be considered a complementary and sensitive endpoint to select potentially effective drugs for recurrent meningiomas.

Contribution of mTOR and PTEN to Radioresistance in Sporadic and NF2-Associated Vestibular Schwannomas: A Microarray and Pathway Analysis

The use of radiation treatment has increased for both sporadic and neurofibromatosis type 2 (NF2)-associated vestibular schwannoma (VS). However, there are a subset of radioresistant tumors and systemic treatments that are seldom used in these patients. We investigated molecular alterations after radiation in three NF2-associated and five sporadically operated recurrent VS after primary irradiation. We compared these findings with 49 non-irradiated (36 sporadic and 13 NF2-associated) VS through gene-expression profiling and pathway analysis. Furthermore, we stained the key molecules of the distinct pathway by immunohistochemistry. A total of 195 differentially expressed genes in sporadic and NF2-related comparisons showed significant differences based on the criteria of p value < 0.05 and a two-fold change. These genes were involved in pathways that are known to be altered upon irradiation (e.g., mammalian target of rapamycin (mTOR), phosphatase and tensin homolog (PTEN) and vascular endothelial growth factor (VEGF) signaling). We observed a combined downregulation of PTEN signaling and an upregulation of mTOR signaling in progressive NF2-associated VS after irradiation. Immunostainings with mTOR and PTEN antibodies confirmed the respective molecular alterations. Taken together, mTOR inhibition might be a promising therapeutic strategy in NF2-associated VS progress after irradiation.

Neratinib degrades MST4 via autophagy that reduces membrane stiffness and is essential for the inactivation of PI3K, ERK1/2, and YAP/TAZ signaling

The irreversible ERBB1/2/4 inhibitor neratinib causes plasma membrane-associated K-RAS to mislocalize into intracellular vesicles liminal to the plasma membrane; this effect is enhanced by HDAC inhibitors and is now a Phase I trial (NCT03919292). The combination of neratinib and HDAC inhibitors killed pancreatic cancer and lymphoma T cells. Neratinib plus HDAC inhibitor exposure was as efficacious as (paclitaxel+gemcitabine) at killing pancreatic cancer cells. Neratinib reduced the phosphorylation of PAK1, Merlin, LATS1/2, AKT, mTOR, p70 S6K, and ERK1/2 which required expression of Rubicon, Beclin1, and Merlin. Neratinib altered pancreatic tumor cell morphology which was associated with MST4 degradation reduced Ezrin phosphorylation and enhanced phosphorylation of MAP4K4 and LATS1/2. Knockdown of the MAP4K4 activator and sensor of membrane rigidity RAP2A reduced basal LATS1/2 and YAP phosphorylation but did not prevent neratinib from stimulating LATS1/2 or YAP phosphorylation. Beclin1 knockdown prevented MST4 degradation, Ezrin dephosphorylation and neratinib-induced alterations in tumor cell morphology. Our findings demonstrate that neratinib enhances LATS1/2 phosphorylation independently of RAP2A/MAP4K4 and that MST4 degradation and Ezrin dephosphorylation may represent a universal trigger for the biological actions of neratinib.

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.

TSC patient-derived isogenic neural progenitor cells reveal altered early neurodevelopmental phenotypes and rapamycin-induced MNK-eIF4E signaling

Background

Tuberous sclerosis complex (TSC) is a neurodevelopmental disorder with frequent occurrence of epilepsy, autism spectrum disorder (ASD), intellectual disability (ID), and tumors in multiple organs. The aberrant activation of mTORC1 in TSC has led to treatment with mTORC1 inhibitor rapamycin as a lifelong therapy for tumors, but TSC-associated neurocognitive manifestations remain unaffected by rapamycin.

Methods

Here, we generated patient-specific, induced pluripotent stem cells (iPSCs) from a TSC patient with a heterozygous, germline, nonsense mutation in exon 15 of TSC1 and established an isogenic set of heterozygous (Het), null and corrected wildtype (Corr-WT) iPSCs using CRISPR/Cas9-mediated gene editing. We differentiated these iPSCs into neural progenitor cells (NPCs) and examined neurodevelopmental phenotypes, signaling and changes in gene expression by RNA-seq.

Results

Differentiated NPCs revealed enlarged cell size in TSC1-Het and Null NPCs, consistent with mTORC1 activation. TSC1-Het and Null NPCs also revealed enhanced proliferation and altered neurite outgrowth in a genotype-dependent manner, which was not reversed by rapamycin. Transcriptome analyses of TSC1-NPCs revealed differentially expressed genes that display a genotype-dependent linear response, i.e., genes upregulated/downregulated in Het were further increased/decreased in Null. In particular, genes linked to ASD, epilepsy, and ID were significantly upregulated or downregulated warranting further investigation. In TSC1-Het and Null NPCs, we also observed basal activation of ERK1/2, which was further activated upon rapamycin treatment. Rapamycin also increased MNK1/2-eIF4E signaling in TSC1-deficient NPCs.

Conclusion

MEK-ERK and MNK-eIF4E pathways regulate protein translation, and our results suggest that aberrant translation distinct in TSC1/2-deficient NPCs could play a role in neurodevelopmental defects. Our data showing upregulation of these signaling pathways by rapamycin support a strategy to combine a MEK or a MNK inhibitor with rapamycin that may be superior for TSC-associated CNS defects. Importantly, our generation of isogenic sets of NPCs from TSC patients provides a valuable platform for translatome and large-scale drug screening studies. Overall, our studies further support the notion that early developmental events such as NPC proliferation and initial process formation, such as neurite number and length that occur prior to neuronal differentiation, represent primary events in neurogenesis critical to disease pathogenesis of neurodevelopmental disorders such as ASD.

The clinical characteristics and molecular mechanism of pituitary adenoma associated with meningioma

BACKGROUND

Pituitary adenoma and meningioma are the most common benign tumors in the central nervous system. Pituitary adenoma associated with meningioma (PAM) is a rare disease and the clinical features and mechanisms of PAM are unclear.

METHODS

We summarized the clinical data of 57 PAM patients and compared with sporadic pituitary adenoma (SPA) and sporadic meningioma (SM). 5 pituitary adenomas of PAM and 5 SPAs were performed ceRNA microarray. qRT-PCR, Western Blot, siMEN1 and rapamycin inhibition experiment were validated for ceRNA microarray.

RESULTS

Clinical variable analyses revealed that significant correlations between PAM and female sex as well as older age when compared with SPA and significant correlations between PAM and transitional meningioma as well as older age when compared with SM. Additionally, the characteristics of PAM were significantly different for MEN1 patients. Functional experiments showed lower expression of MEN1 can upregulate mTOR signaling, in accordance with the result of ceRNA microarray. Rapamycin treatment promotes apoptosis in primary pituitary adenoma and meningioma cells of PAM.

CONCLUSIONS

MEN1 plays an important role in PAM by upregulating mTOR signaling pathway. Rapamycin represents a potential therapeutic strategy for PAM in the future.

Persistent Oxidative Stress in Vestibular Schwannomas After Stereotactic Radiation Therapy

OBJECTIVE

Stereotactic radiation therapy is increasingly used to treat vestibular schwannomas (VSs) primarily and to treat tumor remnants following microsurgery. Little data are available regarding the effects of radiation on VS cells. Tyrosine nitrosylation is a marker of oxidative stress following radiation in malignant tumors. It is not known how long irradiated tissue remains under oxidative stress, and if such modifications occur in benign neoplasms such as VSs treated with significantly lower doses of radiation. We immunostained sections from previously radiated VSs with an antibody that recognizes nitrosylated tyrosine residues to assess for ongoing oxidative stress.

STUDY DESIGN

Immunohistochemical analysis.

METHODS

Four VSs, which recurred after excision, were treated with stereotactic radiation therapy. Ultimately each tumor required salvage reresection for regrowth. Histologic sections of each tumor before and after radiation were immunolabeled with a monoclonal antibody specific to nitrotyrosine and compared. Two VSs that underwent reresection of a growing tumor remnant without previous radiation therapy served as additional controls.

RESULTS

Irradiated tumors enlarged in volume by 3.16 to 8.62 mL following radiation. Preradiation sections demonstrated little to no nitrotyrosine immunostaining. Three of four of irradiated VSs demonstrated increased nitrotyrosine immunostaining in the postradiation sections compared with preradiation tumor sections. Nonirradiated VSs did not label with the antinitrotyrosine antibody.

CONCLUSIONS

VSs exhibit oxidative stress up to 7 years after radiotherapy, yet these VSs continued to enlarge. Thus, VSs that grow following radiation appear to possess mechanisms for cell survival and proliferation despite radiation-induced oxidative stress.

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.

EPH receptor signaling as a novel therapeutic target in NF2-deficient meningioma

Background

Meningiomas are the most common primary brain tumor in adults, and somatic loss of the neurofibromatosis 2 (NF2) tumor suppressor gene is a frequent genetic event. There is no effective treatment for tumors that recur or continue to grow despite surgery and/or radiation. Therefore, targeted therapies that either delay tumor progression or cause tumor shrinkage are much needed. Our earlier work established mammalian target of rapamycin complex mTORC1/mTORC2 activation in NF2-deficient meningiomas.

Methods

High-throughput kinome analyses were performed in NF2-null human arachnoidal and meningioma cell lines to identify functional kinome changes upon NF2 loss. Immunoblotting confirmed the activation of kinases and demonstrated effectiveness of drugs to block the activation. Drugs, singly and in combination, were screened in cells for their growth inhibitory activity. Antitumor drug efficacy was tested in an orthotopic meningioma model.

Results

Erythropoietin-producing hepatocellular receptor tyrosine kinases (EPH RTKs), c-KIT, and Src family kinase (SFK) members, which are biological targets of dasatinib, were among the top candidates activated in NF2-null cells. Dasatinib significantly inhibited phospho-EPH receptor A2 (pEPHA2), pEPHB1, c-KIT, and Src/SFK in NF2-null cells, showing no cross-talk with mTORC1/2 signaling. Posttreatment kinome analyses showed minimal adaptive changes. While dasatinib treatment showed some activity, dual mTORC1/2 inhibitor and its combination with dasatinib elicited stronger growth inhibition in meningiomas.

Conclusion

Co-targeting mTORC1/2 and EPH RTK/SFK pathways could be a novel effective treatment strategy for NF2-deficient meningiomas.

Clinical potential of meningioma genomic insights: a practical review for neurosurgeons

Meningiomas are among the most common intracranial pathological conditions, accounting for 36% of intracranial lesions treated by neurosurgeons. Although the majority of these lesions are benign, the classical categorization of tumors by histological type or World Health Organization (WHO) grade has not fully captured the potential for meningioma progression and recurrence. Many targeted treatments have failed to generate a long-lasting effect on these tumors. Recently, several seminal studies evaluating the genomics of intracranial meningiomas have rapidly changed the understanding of the disease. The importance of NF2 (neurofibromin 2), TRAF7 (tumor necrosis factor [TNF] receptor-associated factor 7), KLF4 (Kruppel-like factor 4), AKT1, SMO (smoothened), PIK3CA (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha), and POLR2 (RNA polymerase II subunit A) demonstrates that there are at least 6 distinct mutational classes of meningiomas. In addition, 6 methylation classes of meningioma have been appreciated, enabling improved prediction of prognosis compared with traditional WHO grades. Genomic studies have shed light on the nature of recurrent meningioma, distinct intracranial locations and mutational patterns, and a potential embryonic cancer stem cell-like origin. However, despite these exciting findings, the clinical relevance of these findings remains elusive. The authors review the key findings from recent genomic studies in meningiomas, specifically focusing on how these findings relate to clinical insights for the practicing neurosurgeon.

Familial Syndromes Involving Meningiomas Provide Mechanistic Insight Into Sporadic Disease

Currently, there is an incomplete understanding of the molecular pathogenesis of meningiomas, the most common primary brain tumor. Several familial syndromes are characterized by increased meningioma risk, and the genetics of these syndromes provides mechanistic insight into sporadic disease. The best defined of these syndromes is neurofibromatosis type 2, which is caused by a mutation in the NF2 gene and has a meningioma incidence of approximately 50%. This finding led to the subsequent discovery that NF2 loss-of-function occurs in up to 60% of sporadic tumors. Other important familial diseases with increased meningioma risk include nevoid basal cell carcinoma syndrome, multiple endocrine neoplasia 1 (MEN1), Cowden syndrome, Werner syndrome, BAP1 tumor predisposition syndrome, Rubinstein-Taybi syndrome, and familial meningiomatosis caused by germline mutations in the SMARCB1 and SMARCE1 genes. For each of these syndromes, the diagnostic criteria, incidence in the population, and frequency of meningioma are presented to review the relevant clinical information for these conditions. The genetic mutations, molecular pathway derangements, and relationship to sporadic disease for each syndrome are described in detail to identify targets for further investigation. Familial syndromes characterized by meningiomas often affect genes and pathways that are also implicated in a subset of sporadic cases, suggesting key molecular targets for therapeutic intervention. Further studies are needed to resolve the functional relevance of specific genes whose significance in sporadic disease remains to be elucidated.

Collecting ducts carcinoma: An orphan disease. Literature overview and future perspectives

Collecting ducts carcinoma (CDC) is a rare and aggressive histological subtype of renal cancer accounting for only 1% of renal tumors. Usually patients present in bad clinical conditions due to a symptomatic disease with synchronous metastasis. Due to the rarity of CDC, data from prospective trials evaluating the best treatment for these patients are limited. The prognosis is poor with a median overall survival of around 11 months for patients with metastatic disease. The best treatment option today is considered a doublet chemotherapy with platinum salt plus gemcitabine as a result from a prospective phase II trial, but survival outcomes remain unsatisfactory. The interest in the in-depth understanding the biology of this orphan disease is growing, leading to find potential new biological-driven treatment approaches. Here we review the up-to-date literature evidences to address the best management of this rare and unfavorable clinical condition.

CHL1 suppresses tumor growth and metastasis in nasopharyngeal carcinoma by repressing PI3K/AKT signaling pathway via interaction with Integrin β1 and Merlin

Deletion of Chromosome 3p is one of the most frequently detected genetic alterations in nasopharyngeal carcinoma (NPC). We reported the role of a novel 3p26.3 tumor suppressor gene (TSG) CHL1 in NPC. Down-regulation of CHL1 was detected in 4/6 of NPC cell lines and 71/95 (74.7%) in clinical tissues. Ectopic expressions of CHL1 in NPC cells significantly inhibit colony formation and cell motility in functional study. By up-regulating epithelial markers and down-regulating mesenchymal markers CHL1 could induce mesenchymal-epithelial transition (MET), a key step in preventing tumor invasion and metastasis. CHL1 could also cause the inactivation of RhoA/Rac1/Cdc42 signaling pathway and inhibit the formation of stress fiber, lamellipodia, and filopodia. CHL1 could co-localize with adhesion molecule Integrin-β1, the expression of CHL1 was positively correlated with Integrin-β1 and another known tumor suppressor gene (TSG) Merlin. Down-regulation of Integrin-β1 or Merlin was significantly correlated with the poor survival rate of NPC patients. Further mechanistic studies showed that CHL1 could directly interact with integrin-β1 and link to Merlin, leading to the inactivation of integrin β1-AKT pathway. In conclusion, CHL1 is a vital tumor suppressor in the carcinogenesis of NPC.

Phosphorylation of Merlin by Aurora A kinase appears necessary for mitotic progression

Although Merlin's function as a tumor suppressor and regulator of mitogenic signaling networks such as the Ras/rac, Akt, and Hippo pathways is well-documented, in mammals as well as in insects, its role during cell cycle progression remains unclear. In this study, using a combination of approaches, including FACS analysis, time-lapse imaging, immunofluorescence microscopy, and co-immunoprecipitation, we show that Ser-518 of Merlin is a substrate of the Aurora protein kinase A during mitosis and that its phosphorylation facilitates the phosphorylation of a newly discovered site, Thr-581. We found that the expression in HeLa cells of a Merlin variant that is phosphorylation-defective on both sites leads to a defect in centrosomes and mitotic spindles positioning during metaphase and delays the transition from metaphase to anaphase. We also show that the dual mitotic phosphorylation not only reduces Merlin binding to microtubules but also timely modulates ezrin interaction with the cytoskeleton. Finally, we identify several point mutants of Merlin associated with neurofibromatosis type 2 that display an aberrant phosphorylation profile along with defective α-tubulin-binding properties. Altogether, our findings of an Aurora A-mediated interaction of Merlin with α-tubulin and ezrin suggest a potential role for Merlin in cell cycle progression.

COX2 expression is associated with proliferation and tumor extension in vestibular schwannoma but is not influenced by acetylsalicylic acid intake

Acetylsalicylic acid has been linked to a lower risk for different cancer types, presumably through its inhibitory effect on cyclooxygenase 2. This has also been investigated in vestibular schwannomas with promising results suggesting an antiproliferative effect and recently the intake has been recommended for vestibular schwannomas as a conservative treatment option. We constructed tissue microarrays from paraffin-embedded tissue samples of 1048 vestibular schwannomas and analyzed the expression of cyclooxygenase 2 and the proliferation marker MIB1 (Molecular Immunology Borstel) via immunohistochemistry together with clinical data (age, gender, tumor extension, prior radiotherapy, neurofibromatosis type 2, tumor recurrence, cyclooxygenase 2 responsive medication). Univariate analysis showed that cyclooxygenase 2 expression was increased with age, female gender, prior radiotherapy and larger tumor extension. MIB1 expression was also associated with higher cyclooxygenase 2 expression. Schwannomas of neurofibromatosis type 2 patients had lower cyclooxygenase 2 levels. Use of acetylsalicylic acid, non-steroidal anti-inflammatory drugs, glucocorticoids or other immunosuppressants did not show differences in cyclooxygenase 2 or MIB1 expression. Instead, cyclooxygenase 2 expression increases with tumor extension while MIB1 expression is not associated with tumor size. Overall, cyclooxygenase 2 expression is associated with proliferation but not influenced by regular intake of acetylsalicylic acid or other cyclooxygenase 2-responsive medications. Acetylsalicylic acid intake does not alter cyclooxygenase 2 expression and has no antiproliferative effect in vestibular.

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.

Expression of NF2 Modulates the Progression of BRAFV600E Mutated Thyroid Cancer Cells

BACKGROUND

We previously reported the frequent neurofibromatosis 2 (NF2) gene mutations in anaplastic thyroid cancers in association with the BRAF^V600E mutation. We aimed to investigate the role of NF2 in thyroid cancer with BRAF mutation.

METHODS

To identify the function of NF2 in thyroid cancers, we investigated the changes in cell proliferation, colon formation, migration and invasion of thyroid cancer cells (8505C, BHT101, and KTC-1) with BRAF^V600E mutation after overexpression and knock-down of NF2. We also examined how cell proliferation changed when NF2 was mutagenized. Human NF2 expression in papillary thyroid carcinoma (PTC) was analyzed using the The Cancer Genome Atlas (TCGA) data.

RESULTS

First, NF2 was overexpressed in 8505C and KTC-1 cells. Compared to control, NF2 overexpressed group of both thyroid cancer cells showed significant inhibition in cell proliferation and colony formation. These results were also confirmed by cell migration and invasion assay. After knock-down of NF2 in 8505C cells, there were no significant changes in cell proliferation and colony formation, compared with the control group. However, after mutagenized S288* and Q470* sites of NF2 gene, the cell proliferation increased compared to NF2 overexpression group. In the analysis of TCGA data, the mRNA expression of NF2 was significantly decreased in PTCs with lateral cervical lymph node (LN) metastasis compared with PTCs without LN metastasis.

CONCLUSION

Our study suggests that NF2 might play a role as a tumor suppressor in thyroid cancer with BRAF mutation. More studies are needed to elucidate the mechanism how NF2 acts in thyroid cancer with BRAF mutation.

2016 Children's Tumor Foundation conference on neurofibromatosis type 1, neurofibromatosis type 2, and schwannomatosis

Organized and hosted by the Children's Tumor Foundation (CTF), the Neurofibromatosis (NF) conference is the premier annual gathering for clinicians and researchers interested in neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and schwannomatosis (SWN). The 2016 edition constituted a blend of clinical and basic aspects of NF research that helped in clarifying different advances in the field. The incorporation of next generation sequencing is changing the way genetic diagnostics is performed for NF and related disorders, providing solutions to problems like genetic heterogeneity, overlapping clinical manifestations, or the presence of mosaicism. The transformation from plexiform neurofibroma (PNF) to malignant peripheral nerve sheath tumor (MPNST) is being clarified, along with new management and treatments for benign and premalignant tumors. Promising new cellular and in vivo models for understanding the musculoskeletal abnormalities in NF1, the development of NF2 or SWN associated schwannomas, and clarifying the cells that give rise to NF1-associated optic pathway glioma were presented. The interaction of neurofibromin and SPRED1 was described comprehensively, providing functional insight that will help in the interpretation of pathogenicity of certain missense variants identified in NF1 and Legius syndrome patients. Novel promising imaging techniques are being developed, as well as new integrative and holistic management models for patients that take into account psychological, social, and biological factors. Importantly, new therapeutic approaches for schwannomas, meningiomas, ependymomas, PNF, and MPNST are being pursued. This report highlights the major advances that were presented at the 2016 CTF NF conference.

TARBP2-Enhanced Resistance during Tamoxifen Treatment in Breast Cancer

Tamoxifen is the most widely used hormone therapy in estrogen receptor-positive (ER+) breast cancer, which accounts for approximately 70% of all breast cancers. Although patients who receive tamoxifen therapy benefit with respect to an improved overall prognosis, resistance and cancer recurrence still occur and remain important clinical challenges. A recent study identified TAR (HIV-1) RNA binding protein 2 (TARBP2) as an oncogene that promotes breast cancer metastasis. In this study, we showed that TARBP2 is overexpressed in hormone therapy-resistant cells and breast cancer tissues, where it enhances tamoxifen resistance. Tamoxifen-induced TARBP2 expression results in the desensitization of ER+ breast cancer cells. Mechanistically, tamoxifen post-transcriptionally stabilizes TARBP2 protein through the downregulation of Merlin, a TARBP2-interacting protein known to enhance its proteasomal degradation. Tamoxifen-induced TARBP2 further stabilizes SOX2 protein to enhance desensitization of breast cancer cells to tamoxifen, while similar to TARBP2, its induction in cancer cells was also observed in metastatic tumor cells. Our results indicate that the TARBP2-SOX2 pathway is upregulated by tamoxifen-mediated Merlin downregulation, which subsequently induces tamoxifen resistance in ER+ breast cancer.

Proteomic analysis discovers the differential expression of novel proteins and phosphoproteins in meningioma including NEK9, HK2 and SET and deregulation of RNA metabolism

Background

Meningioma is the most frequent primary intracranial tumour. Surgical resection remains the main therapeutic option as pharmacological intervention is hampered by poor knowledge of their proteomic signature. There is an urgent need to identify new therapeutic targets and biomarkers of meningioma.

Methods

We performed proteomic profiling of grade I, II and III frozen meningioma specimens and three normal healthy human meninges using LC-MS/MS to analyse global proteins, enriched phosphoproteins and phosphopeptides. Differential expression and functional annotation of proteins was completed using Perseus, IPA® and DAVID. We validated differential expression of proteins and phosphoproteins by Western blot on a meningioma validation set and by immunohistochemistry.

Findings

We quantified 3888 proteins and 3074 phosphoproteins across all meningioma grades and normal meninges. Bioinformatics analysis revealed commonly upregulated proteins and phosphoproteins to be enriched in Gene Ontology terms associated with RNA metabolism. Validation studies confirmed significant overexpression of proteins such as EGFR and CKAP4 across all grades, as well as the aberrant activation of the downstream PI3K/AKT pathway, which seems differential between grades. Further, we validated upregulation of the total and activated phosphorylated form of the NIMA-related kinase, NEK9, involved in mitotic progression. Novel proteins identified and validated in meningioma included the nuclear proto-oncogene SET, the splicing factor SF2/ASF and the higher-grade specific protein, HK2, involved in cellular metabolism.

Interpretation

Overall, we generated a proteomic thesaurus of meningiomas for the identification of potential biomarkers and therapeutic targets.

Fund

This study was supported by Brain Tumour Research.

High p-mTOR expression is associated with recurrence and shorter disease-free survival in atypical meningiomas

Due to their widely variable clinical behavior, the post-surgical treatment of atypical meningiomas is controversial. Therefore, prognostic factors able to identify high-risk cases, which may benefit from adjuvant treatments, are warranted. Mammalian target of rapamycin (mTOR) belongs to the PI3K-AKT pathway. Its phosphorylated form (p-mTOR Ser2448) is involved in cell growth, differentiation and tumorigenesis. The aim of this study was to evaluate p-mTOR Ser2448 expression and its eventual correlation with clinicopathological features, recurrence, or disease-free survival (DFS), in atypical meningiomas. p-mTOR immunohistochemical expression was analyzed in 48 atypical meningiomas and correlated with clinicopathological parameters and with DFS. Eighty-one percent of atypical meningiomas expressed p-mTOR Ser2448. High immuno-expression was significantly associated with recurrences (P = 0.01) and lower DFS (P = 0.01). The presence of brain invasion, high mitotic index plus sheeting, and Simpson grade were significant and independent prognostic variables at multivariate analysis. p-mTOR Ser2448 is expressed in atypical meningiomas. High expression predicts development of recurrences and shorter DFS in patients affected by these tumors. Since p-mTOR Ser2448 is a target of anti-neoplastic drugs, evaluation of its expression may be used, not only to identify atypical meningiomas at higher risk of recurrence, but also to select those to submit to adjuvant targeted chemotherapy.

The Hippo pathway effector Taz is required for cell morphogenesis and fertilization in zebrafish

Hippo signaling is a critical pathway that integrates extrinsic and intrinsic mechanical cues to regulate organ size. Despite its essential role in organogenesis, little is known about its role in cell fate specification and differentiation. Here, we unravel a novel and unexpected role of the Hippo pathway effector Taz (wwtr1) in controlling the size, shape and fate of a unique cell in the zebrafish ovary. We show that wwtr1 mutant females are infertile. In teleosts, fertilization occurs through the micropyle, a funnel-like opening in the chorion, formed by a unique enlarged follicle cell, the micropylar cell (MC). We describe here, for the first time, the mechanism that underlies the differentiation of the MC. Our genetic analyses show that Taz is essential for MC fate acquisition and subsequent micropyle formation in zebrafish. We identify Taz as the first bona fide MC marker and show that Taz is specifically and strongly enriched in the MC precursor. Altogether, we performed the first genetic and molecular characterization of the MC and propose that Taz is a key regulator of MC fate.This article has an associated 'The people behind the papers' interview.

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.