BRAF activation induces transformation and then senescence in human neural stem cells: a pilocytic astrocytoma model

Increased SOX10, p16, and Cyclin D1 Immunoreactivity Differentiates MAP Kinase-activated Low-grade Gliomas From Piloid Gliosis

Low-grade gliomas and reactive piloid gliosis can present with overlapping features on conventional histology. Given the large implications for patient treatment, there is a need for effective methods to discriminate these morphologically similar but clinically distinct entities. Using routinely available stains, we hypothesize that a limited panel including SOX10, p16, and cyclin D1 may be useful in differentiating mitogen-activated protein (MAP) kinase-activated low-grade gliomas from piloid gliosis. Reviewers blinded to clinical and pathologic data reviewed and quantified immunohistochemical expression patterns across 20 cases of piloid gliosis and 37 cases of MAP kinase-activated low-grade gliomas, including pilocytic astrocytoma and ganglioglioma. The majority of MAP kinase-activated low-grade glioma cases demonstrated extensive immunoreactivity for at least 2 of the 3 immunohistochemical markers, whereas none of the gliosis cases demonstrated significant immunoreactivity for more than one individual immunohistochemical marker. SOX10 and p16 demonstrated the highest individual sensitivity whereas cyclin D1 demonstrated the highest individual specificity to discriminate neoplastic from nonneoplastic cases in this cohort. A composite panel score based on significant immunoreactivity of at least 2 of the 3 markers provided specificity and a positive predictive value of 100% in differentiating MAP kinase-activated low-grade glioma from gliosis, as 0/20 (0%) of gliosis cases were scored positive compared with 24/37 (65%) of MAP kinase-activated low-grade glioma cases. We conclude that while the immunoreactivity of these markers may be suggestive of a low-grade glioma diagnosis, SOX10, p16, and cyclin D1 should be applied in combination to maximize diagnostic value.

Fusion Transcript Detection from Short-Read RNA-Seq

Fusion proteins have been shown to play an important role in many different cancers and other diseases. While the causal mutation can often be found in the genome as a structural variant (SV), differentiating between normal variation within individuals and somatic variants with functional consequences can be time-consuming as well as expensive since it requires a whole-genome sequencing (WGS) method. RNA Sequencing (RNA-Seq) provides a much cheaper and more straightforward approach to the detection of functional somatic events such as overexpression of proto-oncogenes as well as gene fusion. This chapter aims to discuss the utility of RNA-Seq for fusion detection as well as provide a detailed analysis pipeline for the detection of fusion transcripts.

MOST wanted: navigating the MAPK-OIS-SASP-tumor microenvironment axis in primary pediatric low-grade glioma and preclinical models

Understanding the molecular and cellular mechanisms driving pediatric low-grade glioma (pLGG)-the most prevalent brain tumor in children-is essential for the identification and evaluation of novel effective treatments. This review explores the intricate relationship between the mitogen-activated protein kinase (MAPK) pathway, oncogene-induced senescence (OIS), the senescence-associated secretory phenotype (SASP), and the tumor microenvironment (TME), integrating these elements into a unified framework termed the MAPK/OIS/SASP/TME (MOST) axis. This integrated approach seeks to deepen our understanding of pLGG and improve therapeutic interventions by examining the MOST axis' critical influence on tumor biology and response to treatment. In this review, we assess the axis' capacity to integrate various biological processes, highlighting new targets for pLGG treatment, and the need for characterized in vitro and in vivo preclinical models recapitulating pLGG's complexity to test targets. The review underscores the need for a comprehensive strategy in pLGG research, positioning the MOST axis as a pivotal approach in understanding pLGG. This comprehensive framework will open promising avenues for patient care and guide future research towards inventive treatment options.

Dissecting the Natural Patterns of Progression and Senescence in Pediatric Low-Grade Glioma: From Cellular Mechanisms to Clinical Implications

Pediatric low-grade gliomas (PLGGs) comprise a heterogeneous set of low-grade glial and glioneuronal tumors, collectively representing the most frequent CNS tumors of childhood and adolescence. Despite excellent overall survival rates, the chronic nature of the disease bears a high risk of long-term disease- and therapy-related morbidity in affected patients. Recent in-depth molecular profiling and studies of the genetic landscape of PLGGs led to the discovery of the paramount role of frequent upregulation of RAS/MAPK and mTOR signaling in tumorigenesis and progression of these tumors. Beyond, the subsequent unveiling of RAS/MAPK-driven oncogene-induced senescence in these tumors may shape the understanding of the molecular mechanisms determining the versatile progression patterns of PLGGs, potentially providing a promising target for novel therapies. Recent in vitro and in vivo studies moreover indicate a strong dependence of PLGG formation and growth on the tumor microenvironment. In this work, we provide an overview of the current understanding of the multilayered cellular mechanisms and clinical factors determining the natural progression patterns and the characteristic biological behavior of these tumors, aiming to provide a foundation for advanced stratification for the management of these tumors within a multimodal treatment approach.

A multi-institutional series of a novel, recurrent TRIM24::MET fusion-driven infant-type hemispheric glioma reveals significant clinico-pathological heterogeneity

Within the past decade, incremental integration of molecular characteristics into the classification of central nervous system neoplasms increasingly facilitated precise diagnosis and advanced stratification, beyond potentially providing the foundation for advanced targeted therapies. We report a series of three cases of infant-type hemispheric glioma (IHG) involving three infants diagnosed with neuroepithelial tumors of the cerebral hemispheres harboring a novel, recurrent TRIM24::MET fusion. Histopathology showed glial tumors with either low-grade or high-grade characteristics, while molecular characterization found an additional homozygous CDKN2A/B deletion in two cases. Two patients showed leptomeningeal dissemination, while multiple supra- and infratentorial tumor manifestations were found in one case. Following subtotal resection (two cases) and biopsy (one case), treatment intensity of adjuvant chemotherapy regimens did not reflect in the progression patterns within the reported cases. Two patients showed progression after first-line treatment, of which one patient died not responding to tyrosine kinase inhibitor cabozantinib. As the detection of a recurrent TRIM24::MET fusion expands the spectrum of renowned driving fusion genes in IHG, this comparative illustration may indicate a distinct clinico-pathological heterogeneity of tumors bearing this driver alteration. Upfront clinical trials of IHG promoting further characterization and the implementation of individualized therapies involving receptor tyrosine kinase inhibition are required.

An Overview of Optic Pathway Glioma With Neurofibromatosis Type 1: Pathogenesis, Risk Factors, and Therapeutic Strategies

Optic pathway gliomas (OPGs) are most predominant pilocytic astrocytomas, which are typically diagnosed within the first decade of life. The majority of affected children with OPGs also present with neurofibromatosis type 1 (NF1), the most common tumor predisposition syndrome. OPGs in individuals with NF1 primarily affect the optic pathway and lead to visual disturbance. However, it is challenging to assess risk in asymptomatic patients without valid biomarkers. On the other hand, for symptomatic patients, there is still no effective treatment to prevent or recover vision loss. Therefore, this review summarizes current knowledge regarding the pathogenesis of NF1-associated OPGs (NF1-OPGs) from preclinical studies to seek potential prognostic markers and therapeutic targets. First, the loss of the NF1 gene activates 3 distinct Ras effector pathways, including the PI3K/AKT/mTOR pathway, the MEK/ERK pathway, and the cAMP pathway, which mediate glioma tumorigenesis. Meanwhile, non-neoplastic cells from the tumor microenvironment (microglia, T cells, neurons, etc.) also contribute to gliomagenesis via various soluble factors. Subsequently, we investigated potential genetic risk factors, molecularly targeted therapies, and neuroprotective strategies for tumor prevention and vision recovery. Last, potential directions and promising preclinical models of NF1-OPGs are presented for further research. On the whole, NF1-OPGs develop as a result of the interaction between glioma cells and the tumor microenvironment. Developing effective treatments require a better understanding of tumor molecular characteristics, as well as multistage interventions targeting both neoplastic cells and non-neoplastic cells.

BRAFV600E promotes anchorage-independent growth but inhibits anchorage-dependent growth in hTERT/Cdk4-Immortalized normal human bronchial epithelial cells

Certain oncogenes, including mutant RAS and BRAF, induce a type of senescence known as oncogene-induced senescence (OIS) in normal cells in a cell-type-specific manner. OIS serves as a barrier to transformation by activated oncogenes. Our previous studies showed that mutant KRASV12 did not efficiently induce OIS in an hTERT/Cdk4-immortalized normal human bronchial epithelial cell line (HBEC3), but it did enhance both anchorage-dependent and anchorage-independent growth. In this study, we investigated whether mutant BRAF, a well-known inducer of OIS, could trigger OIS in HBEC3 cells. We also assessed the impact of mutant BRAF on the growth of HBEC3 cells, as no previous studies have examined this using a normal bronchial epithelial cell line model. We established an HBEC3 cell line, designated as HBEC3-BIN, that expresses mutant BRAFV600E in a doxycycline-regulated manner. Unlike our previous finding that KRASV12 upregulated both pERK and pAKT, mutant BRAFV600E upregulated pERK but not pAKT in HBEC3-BIN cells. Similar to KRASV12, BRAFV600E did not efficiently induce OIS. Interestingly, while BRAFV600E inhibited colony formation in anchorage-dependent conditions, it dramatically enhanced colony formation in anchorage-independent conditions in HBEC3-BIN. In HBEC3 cells without BRAFV600E or KRASV12 expression, p21 was only detected in the cytoplasm, and its localization was not altered by the expression of BRAFV600E or KRASV12. Next-generation sequencing analysis revealed an enrichment of gene sets known to be involved in carcinogenesis, including IL3/JAK/STAT3, IL2, STAT5, and the EMT pathway. Our results indicate that, unlike KRASV12, which promoted both, BRAFV600E enhances anchorage-independent growth but inhibits anchorage-dependent growth of HBEC3. This contrast may result from differences in activation signaling in the downstream pathways. Furthermore, HBEC3 cells appear to be inherently resistant to OIS, which may be partly due to the fact that p21 remains localized in the cytoplasm upon expression of BRAFV600E or KRASV12.

Pediatric low-grade glioma models: advances and ongoing challenges

Pediatric low-grade gliomas represent the most common childhood brain tumor class. While often curable, some tumors fail to respond and even successful treatments can have life-long side effects. Many clinical trials are underway for pediatric low-grade gliomas. However, these trials are expensive and challenging to organize due to the heterogeneity of patients and subtypes. Advances in sequencing technologies are helping to mitigate this by revealing the molecular landscapes of mutations in pediatric low-grade glioma. Functionalizing these mutations in the form of preclinical models is the next step in both understanding the disease mechanisms as well as for testing therapeutics. However, such models are often more difficult to generate due to their less proliferative nature, and the heterogeneity of tumor microenvironments, cell(s)-of-origin, and genetic alterations. In this review, we discuss the molecular and genetic alterations and the various preclinical models generated for the different types of pediatric low-grade gliomas. We examined the different preclinical models for pediatric low-grade gliomas, summarizing the scientific advances made to the field and therapeutic implications. We also discuss the advantages and limitations of the various models. This review highlights the importance of preclinical models for pediatric low-grade gliomas while noting the challenges and future directions of these models to improve therapeutic outcomes of pediatric low-grade gliomas.

DNA methylation landscapes in DIPG reveal methylome variability that can be modified pharmacologically

Background

Diffuse intrinsic pontine glioma (DIPG) is a uniformly lethal brainstem tumor of childhood, driven by histone H3 K27M mutation and resultant epigenetic dysregulation. Epigenomic analyses of DIPG have shown global loss of repressive chromatin marks accompanied by DNA hypomethylation. However, studies providing a static view of the epigenome do not adequately capture the regulatory underpinnings of DIPG cellular heterogeneity and plasticity.

Methods

To address this, we performed whole-genome bisulfite sequencing on a large panel of primary DIPG specimens and applied a novel framework for analysis of DNA methylation variability, permitting the derivation of comprehensive genome-wide DNA methylation potential energy landscapes that capture intrinsic epigenetic variation.

Results

We show that DIPG has a markedly disordered epigenome with increasingly stochastic DNA methylation at genes regulating pluripotency and developmental identity, potentially enabling cells to sample diverse transcriptional programs and differentiation states. The DIPG epigenetic landscape was responsive to treatment with the hypomethylating agent decitabine, which produced genome-wide demethylation and reduced the stochasticity of DNA methylation at active enhancers and bivalent promoters. Decitabine treatment elicited changes in gene expression, including upregulation of immune signaling such as the interferon response, STING, and MHC class I expression, and sensitized cells to the effects of histone deacetylase inhibition.

Conclusions

This study provides a resource for understanding the epigenetic instability that underlies DIPG heterogeneity. It suggests the application of epigenetic therapies to constrain the range of epigenetic states available to DIPG cells, as well as the use of decitabine in priming for immune-based therapies.

A new subtype of diffuse midline glioma, H3 K27 and BRAF/FGFR1 co-altered: a clinico-radiological and histomolecular characterisation

Diffuse midline gliomas (DMG) H3 K27-altered are incurable grade 4 gliomas and represent a major challenge in neuro-oncology. This tumour type is now classified in four subtypes by the 2021 edition of the WHO Classification of the Central Nervous System (CNS) tumours. However, the H3.3-K27M subgroup still appears clinically and molecularly heterogeneous. Recent publications reported that rare patients presenting a co-occurrence of H3.3K27M with BRAF or FGFR1 alterations tended to have a better prognosis. To better study the role of these co-driver alterations, we assembled a large paediatric and adult cohort of 29 tumours H3K27-altered with co-occurring activating mutation in BRAF or FGFR1 as well as 31 previous cases from the literature. We performed a comprehensive histological, radiological, genomic, transcriptomic and DNA methylation analysis. Interestingly, unsupervised t-distributed Stochastic Neighbour Embedding (tSNE) analysis of DNA methylation profiles regrouped BRAFV600E and all but one FGFR1MUT DMG in a unique methylation cluster, distinct from the other DMG subgroups and also from ganglioglioma (GG) or high-grade astrocytoma with piloid features (HGAP). This new DMG subtype harbours atypical radiological and histopathological profiles with calcification and/or a solid tumour component both for BRAFV600E and FGFR1MUT cases. The analyses of a H3.3-K27M BRAFV600E tumour at diagnosis and corresponding in vitro cellular model showed that mutation in H3-3A was the first event in the oncogenesis. Contrary to other DMG, these tumours occur more frequently in the thalamus (70% for BRAFV600E and 58% for FGFR1MUT) and patients have a longer overall survival with a median above three years. In conclusion, DMG, H3 K27 and BRAF/FGFR1 co-altered represent a new subtype of DMG with distinct genotype/phenotype characteristics, which deserve further attention with respect to trial interpretation and patient management.

Optimizing preclinical pediatric low-grade glioma models for meaningful clinical translation

Pediatric low-grade gliomas (pLGGs) are the most common brain tumor in young children. While they are typically associated with good overall survival, children with these central nervous system tumors often experience chronic tumor- and therapy-related morbidities. Moreover, individuals with unresectable tumors frequently have multiple recurrences and persistent neurological symptoms. Deep molecular analyses of pLGGs reveal that they are caused by genetic alterations that converge on a single mitogenic pathway (MEK/ERK), but their growth is heavily influenced by nonneoplastic cells (neurons, T cells, microglia) in their local microenvironment. The interplay between neoplastic cell MEK/ERK pathway activation and stromal cell support necessitates the use of predictive preclinical models to identify the most promising drug candidates for clinical evaluation. As part of a series of white papers focused on pLGGs, we discuss the current status of preclinical pLGG modeling, with the goal of improving clinical translation for children with these common brain tumors.

Cellular senescence in glioma

INTRODUCTION

Glioma is the most common primary brain tumor and is often associated with treatment resistance and poor prognosis. Standard treatment typically involves radiotherapy and temozolomide-based chemotherapy, both of which induce cellular senescence-a tumor suppression mechanism.

DISCUSSION

Gliomas employ various mechanisms to bypass or escape senescence and remain in a proliferative state. Importantly, senescent cells remain viable and secrete a large number of factors collectively known as the senescence-associated secretory phenotype (SASP) that, paradoxically, also have pro-tumorigenic effects. Furthermore, senescent cells may represent one form of tumor dormancy and play a role in glioma recurrence and progression.

CONCLUSION

In this article, we delineate an overview of senescence in the context of gliomas, including the mechanisms that lead to senescence induction, bypass, and escape. Furthermore, we examine the role of senescent cells in the tumor microenvironment and their role in tumor progression and recurrence. Additionally, we highlight potential therapeutic opportunities for targeting senescence in glioma.

BRAF Mutations in CNS Tumors-Prognostic Markers and Therapeutic Targets

Gliomas are a heterogeneous group of brain tumors with limited therapeutic options. However, identification of BRAF V600E mutations in a subset of gliomas has provided a genomic-targeted approach for management of these diseases. In this review, we aimed to review the role of BRAF V600E in gliomagenesis, to characterize concurrent genomic alterations and their potential prognostic implications, and to review comprehensively the efficacy data of BRAF inhibitors (combined or not with MEK inhibitors) for the treatment of low- and high-grade gliomas. We also provide a summary of the toxicity of these agents and describe resistance mechanisms that may be circumvented by alternative genomic approaches. Although the efficacy of targeted therapy for management of BRAF V600E-mutant gliomas has mostly been assessed in small retrospective and phase 2 studies with heterogeneous populations, the data generated so far are a proof of concept that genomic-directed therapies improve outcomes of patients with refractory/relapsed glioma and underpin the need of comprehensive genomic assessments for these difficult-to-treat diseases. In the future, the role of targeted therapy in the first-line setting and of genomic-directed therapies to overcome resistance mechanisms should be assessed in well-designed clinical trials.

Unlocking the power of precision medicine for pediatric low-grade gliomas: molecular characterization for targeted therapies with enhanced safety and efficacy

In the past decade significant advancements have been made in the discovery of targetable lesions in pediatric low-grade gliomas (pLGGs). These tumors account for 30-50% of all pediatric brain tumors with generally a favorable prognosis. The latest 2021 WHO classification of pLGGs places a strong emphasis on molecular characterization for significant implications on prognosis, diagnosis, management, and the potential target treatment. With the technological advances and new applications in molecular diagnostics, the molecular characterization of pLGGs has revealed that tumors that appear similar under a microscope can have different genetic and molecular characteristics. Therefore, the new classification system divides pLGGs into several distinct subtypes based on these characteristics, enabling a more accurate strategy for diagnosis and personalized therapy based on the specific genetic and molecular abnormalities present in each tumor. This approach holds great promise for improving outcomes for patients with pLGGs, highlighting the importance of the recent breakthroughs in the discovery of targetable lesions.

Cancer Stem Cells in Tumours of the Central Nervous System in Children: A Comprehensive Review

Cancer stem cells (CSCs) are a subgroup of cells found in various kinds of tumours with stem cell characteristics, such as self-renewal, induced differentiation, and tumourigenicity. The existence of CSCs is regarded as a major source of tumour recurrence, metastasis, and resistance to conventional chemotherapy and radiation treatment. Tumours of the central nervous system (CNS) are the most common solid tumours in children, which have many different types including highly malignant embryonal tumours and midline gliomas, and low-grade gliomas with favourable prognoses. Stem cells from the CNS tumours have been largely found and reported by researchers in the last decade and their roles in tumour biology have been deeply studied. However, the cross-talk of CSCs among different CNS tumour types and their clinical impacts have been rarely discussed. This article comprehensively reviews the achievements in research on CSCs in paediatric CNS tumours. Biological functions, diagnostic values, and therapeutic perspectives are reviewed in detail. Further investigations into CSCs are warranted to improve the clinical practice in treating children with CNS tumours.

Evaluating the safety of perioperative dexamethasone treatment: A retrospective analysis of a single center pediatric low-grade glioma cohort

In addition to surgical management, corticosteroids have proven to be beneficial in the management of acute symptoms related to CNS tumors, and have been widely used for many decades, with dexamethasone (DM) representing the most commonly used agent. However, lately published in vitro data possibly indicates a DM-induced suppression of oncogene-induced senescence (OIS) in a preclinical pediatric low-grade glioma (pLGG) model, which, alongside data associating perioperative DM treatment with reduced event-free survival in adult glioma, raises questions concerning the safety of DM treatment in pLGG. A total of 172 patients with pLGG were retrospectively analyzed concerning the impact of perioperative DM application on postoperative short- and long-term tumor growth velocity and progression-free survival (PFS). Three-dimensional volumetric analyses of sequential MRI follow-up examinations were used for assessment of tumor growth behavior. Mean follow-up period accounted for 60.1 months. Sixty-five patients (45%) were perioperatively treated with DM in commonly used doses. Five-year PFS accounted for 93% following gross-total resection (GTR) and 57% post incomplete resection (IR). Comparison of short- and long-term postoperative tumor growth rates in patients with vs without perioperative DM application showed no significant difference (short-term: 0.022 vs 0.023 cm³ /month, respectively; long-term: 0.019 vs 0.023 cm³ /month, respectively). Comparison of PFS post IR (5-year-PFS: 65% vs 55%, respectively; 10-year-PFS: 52% vs 53%, respectively) and GTR (5- and 10-years-PFS: 91% vs 92%, respectively) likewise showed similarity. This data emphasizes the safety of perioperative DM application in pLGG, adding further evidence for decision making and requested future guidelines.

BH3 mimetics targeting BCL-XL impact the senescent compartment of pilocytic astrocytoma

BACKGROUND

Pilocytic astrocytoma (PA) is the most common pediatric brain tumor and a mitogen-activated protein kinase (MAPK)-driven disease. Oncogenic MAPK-signaling drives the majority of cells into oncogene-induced senescence (OIS). While OIS induces resistance to antiproliferative therapies, it represents a potential vulnerability exploitable by senolytic agents.

METHODS

We established new patient-derived PA cell lines that preserve molecular features of the primary tumors and can be studied in OIS and proliferation depending on expression or repression of the SV40 large T antigen. We determined expression of anti-apoptotic BCL-2 members in these models and primary PA. Dependence of senescent PA cells on anti-apoptotic BCL-2 members was investigated using a comprehensive set of BH3 mimetics.

RESULTS

Senescent PA cells upregulate BCL-XL upon senescence induction and show dependency on BCL-XL for survival. BH3 mimetics with high affinity for BCL-XL (BCL-XLi) reduce metabolic activity and induce mitochondrial apoptosis in senescent PA cells at nano-molar concentrations. In contrast, BH3 mimetics without BCL-XLi activity, conventional chemotherapy, and MEK inhibitors show no effect.

CONCLUSIONS

Our data demonstrate that BCL-XL is critical for survival of senescent PA tumor cells and provides proof-of-principle for the use of clinically available BCL-XL-dependent senolytics.

p16 Immunohistochemical Expression as a Surrogate Assessment of CDKN2A Alteration in Gliomas Leading to Prognostic Significances

CDKN2A is a tumor suppressor gene encoding the p16 protein, a key regulator of the cell cycle. CDKN2A homozygous deletion is a central prognostic factor for numerous tumors and can be detected by several techniques. This study aims to evaluate the extent to which immunohistochemical levels of p16 expression may provide information about CDKN2A deletion. A retrospective study was conducted in 173 gliomas of all types, using p16 IHC and CDKN2A fluorescent in situ hybridization. Survival analyses were performed to assess the prognostic impact of p16 expression and CDKN2A deletion on patient outcomes. Three patterns of p16 expression were observed: absence of expression, focal expression, and overexpression. Absence of p16 expression was correlated with worse outcomes. p16 overexpression was associated with better prognoses in MAPK-induced tumors, but with worse survival in IDH-wt glioblastomas. CDKN2A homozygous deletion predicted worse outcomes in the overall patient population, particularly in IDH-mutant 1p/19q oligodendrogliomas (grade 3). Finally, we observed a significant correlation between p16 immunohistochemical loss of expression and CDKN2A homozygosity. IHC has strong sensitivity and high negative predictive value, suggesting that p16 IHC might be a pertinent test to detect cases most likely harboring CDKN2A homozygous deletion.

Molecular Heterogeneity in BRAF-Mutant Gliomas: Diagnostic, Prognostic, and Therapeutic Implications

Over the last few decades, deciphering the alteration of molecular pathways in brain tumors has led to impressive changes in diagnostic refinement. Among the molecular abnormalities triggering and/or driving gliomas, alterations in the MAPK pathway reign supreme in the pediatric population, as it is encountered in almost all low-grade pediatric gliomas. Activating abnormalities in the MAPK pathway are also present in both pediatric and adult high-grade gliomas. Across those alterations, BRAF p.V600E mutations seem to define homogeneous groups of tumors in terms of prognosis. The recent development of small molecules inhibiting this pathway retains the attention of neurooncologists on BRAF-altered tumors, as conventional therapies showed no significant effect, nor prolonged efficiency on the high-grade or low-grade unresectable forms. Nevertheless, tumoral heterogeneity and especially molecular alteration(s) associated with MAPK-pathway abnormalities are not fully understood with respect to how they might lead to the specific dismal prognosis of those gliomas and/or affect their response to targeted therapies. This review is an attempt to provide comprehensive information regarding molecular alterations related to the aggressiveness modulation in BRAF-mutated gliomas and the current knowledge on how to use those targeted therapies in such situations.

Rare adult pilocytic astrocytoma of the septum pellucidum with novel RIN2::BRAF fusion

Pilocytic astrocytoma is mostly a pediatric tumor with the majority of patients under age 20. Although tumors can occur throughout neuraxis, most tumors are in the cerebellum and optic chiasm. Pilocytic astrocytoma in unusual locations is often associated with different genetic alterations than the classic KIAA1549::BRAF fusion. We report a rare adult pilocytic astrocytoma of the septum pellucidum that presented with progressive headache. A detailed genomic evaluation found a fusion between BRAF and a novel partner RIN2, a gene overexpressed in both low-grade glioma and glioblastoma. The RIN2::BRAF transcript encodes a chimeric protein containing a dimerization domain SH2 and an intact kinase domain, consistent with a prototypic oncogenic kinase rearrangement. In addition, we discuss the potential oncogenic mechanisms of BRAF signaling and its implication in targeted therapy with kinase inhibitors.

BRAF-mediated brain tumors in adults and children: A review and the Australian and New Zealand experience

The mitogen-activated protein kinase (MAPK) pathway signaling pathway is one of the most commonly mutated pathways in human cancers. In particular, BRAF alterations result in constitutive activation of the rapidly accelerating fibrosarcoma-extracellular signal-regulated kinase-MAPK significant pathway, leading to cellular proliferation, survival, and dedifferentiation. The role of BRAF mutations in oncogenesis and tumorigenesis has spurred the development of targeted agents, which have been successful in treating many adult cancers. Despite advances in other cancer types, the morbidity and survival outcomes of patients with glioma have remained relatively stagnant. Recently, there has been recognition that MAPK dysregulation is almost universally present in paediatric and adult gliomas. These findings, accompanying broad molecular characterization of gliomas, has aided prognostication and offered opportunities for clinical trials testing targeted agents. The use of targeted therapies in this disease represents a paradigm shift, although the biochemical complexities has resulted in unexpected challenges in the development of effective BRAF inhibitors. Despite these challenges, there are promising data to support the use of BRAF inhibitors alone and in combination with MEK inhibitors for patients with both low-grade and high-grade glioma across age groups. Safety and efficacy data demonstrate that many of the toxicities of these targeted agents are tolerable while offering objective responses. Newer clinical trials will examine the use of these therapies in the upfront setting. Appropriate duration of therapy and durability of response remains unclear in the glioma patient cohort. Longitudinal efficacy and toxicity data are needed. Furthermore, access to these medications remains challenging outside of clinical trials in Australia and New Zealand. Compassionate access is limited, and advocacy for mechanism of action-based drug approval is ongoing.

Pediatric diffuse hemispheric glioma H3 G34-mutant with gains of the BRAF locus: An illustrative case

Diffuse hemispheric glioma, H3 G34-mutant, is a recently recognized distinct high-grade glioma with a dismal prognosis. In addition to the H3 G34 missense mutation, numerous genetic events have been identified in these malignant tumors, including ATRX, TP53, and, rarely, BRAF genes. There are only a few reports to date that have identified BRAF mutations in diffuse hemispheric glioma, H3 G34-mutant. Moreover, to our knowledge, gains of the BRAF locus have yet to be described. Here, we present a case of an 11-year-old male with a diffuse hemispheric glioma, H3 G34-mutant, found to have novel gains of the BRAF locus. Furthermore, we emphasize the current genetic landscape of diffuse hemispheric glioma, H3 G34-mutant, and implications of an aberrant BRAF signaling pathway.

Detection and genomic analysis of BRAF fusions in Juvenile Pilocytic Astrocytoma through the combination and integration of multi-omic data

BACKGROUND

Juvenile Pilocytic Astrocytomas (JPAs) are one of the most common pediatric brain tumors, and they are driven by aberrant activation of the mitogen-activated protein kinase (MAPK) signaling pathway. RAF-fusions are the most common genetic alterations identified in JPAs, with the prototypical KIAA1549-BRAF fusion leading to loss of BRAF's auto-inhibitory domain and subsequent constitutive kinase activation. JPAs are highly vascular and show pervasive immune infiltration, which can lead to low tumor cell purity in clinical samples. This can result in gene fusions that are difficult to detect with conventional omics approaches including RNA-Seq.

METHODS

To this effect, we applied RNA-Seq as well as linked-read whole-genome sequencing and in situ Hi-C as new approaches to detect and characterize low-frequency gene fusions at the genomic, transcriptomic and spatial level.

RESULTS

Integration of these datasets allowed the identification and detailed characterization of two novel BRAF fusion partners, PTPRZ1 and TOP2B, in addition to the canonical fusion with partner KIAA1549. Additionally, our Hi-C datasets enabled investigations of 3D genome architecture in JPAs which showed a high level of correlation in 3D compartment annotations between JPAs compared to other pediatric tumors, and high similarity to normal adult astrocytes. We detected interactions between BRAF and its fusion partners exclusively in tumor samples containing BRAF fusions.

CONCLUSIONS

We demonstrate the power of integrating multi-omic datasets to identify low frequency fusions and characterize the JPA genome at high resolution. We suggest that linked-reads and Hi-C could be used in clinic for the detection and characterization of JPAs.

Resection extent and BRAF V600E mutation status determine postoperative tumor growth velocity in pediatric low-grade glioma: results from a single-center cohort analysis

PURPOSE

Despite excellent long-term overall survival rates, pediatric low-grade gliomas (pLGG) show high variety of clinical behavior regarding progress or senescence post incomplete resection (IR). This study retrospectively analyzes tumor growth velocity (TGV) of pLGG before surgery and after IR to investigate the impact of surgical extent, tumor location and molecular BRAF status on postoperative residual tumor growth behavior.

METHODS

Of a total of 172 patients with pLGG receiving surgical treatment, 107 underwent IR (66%). Fifty-three vs 94 patients could be included in the pre- and post-operative cohort, respectively, and were observed over a mean follow-up time of 40.2 vs 60.1 months. Sequential three-dimensional MRI-based tumor volumetry of a total of 407 MRI scans was performed to calculate pre- and postoperative TGV.

RESULTS

Mean preoperative TGV of 0.264 cm3/month showed significant deceleration of tumor growth to 0.085 cm3/month, 0.024 cm3/month and -0.016 cm3/month after 1st, 2nd, and 3rd IR, respectively (p < 0.001). Results remained significant after excluding patients undergoing (neo)adjuvant treatment. Resection extent showed correlation with postoperative reduction of TGV (R = 0.97, p < 0.001). ROC analysis identified a residual cut-off tumor volume > 2.03 cm3 associated with a higher risk of progress post IR (sensitivity 78,6%, specificity 76.3%, AUC 0.88). Postoperative TGV of BRAF V600E-mutant LGG was significantly higher than of BRAF wild-type LGG (0.123 cm3/month vs. 0.016 cm3/month, p = 0.047).

CONCLUSION

This data suggests that extensive surgical resection may impact pediatric LGG growth kinetics post incomplete resection by inducing a significant deceleration of tumor growth. BRAF-V600E mutation may be a risk factor for higher postoperative TGV.

Use of Trametinib in Children and Young Adults With Progressive Low-Grade Glioma and Glioneuronal Tumors

Low-grade gliomas/glioneuronal tumors comprise one-third of all pediatric-type CNS tumors. These tumors are generally caused by activating mutations in the mitogen-activated protein kinase (MAPK) pathway. Targeted drugs, such as trametinib, have shown promise in other cancers and are being utilized in low-grade gliomas. A retrospective chart review was conducted to evaluate radiographic response, visual outcomes, tolerability, and durability of response in progressive circumscribed low-grade gliomas treated with trametinib. Eleven patients were treated with trametinib. The best radiographic response was 2/11 partial response, 3/11 minor response, 3/11 stable disease, and 3/13 progressive disease. In the patients with partial or minor response, the best response was seen after longer durations of therapy; 4 of 5 best responses occurred after at least 9 months of therapy with a median of 21 months. Patients with optic pathway tumors showed at least stable vision throughout treatment, with 3 having improved vision on treatment. Trametinib is effective and well-tolerated in patients with progressive low-grade glioma. Best responses were seen after a longer duration of therapy in those with a positive response. Patients with optic pathway lesions showed stable to improved vision while on treatment.

Human induced pluripotent stem cell engineering establishes a humanized mouse platform for pediatric low-grade glioma modeling

A major obstacle to identifying improved treatments for pediatric low-grade brain tumors (gliomas) is the inability to reproducibly generate human xenografts. To surmount this barrier, we leveraged human induced pluripotent stem cell (hiPSC) engineering to generate low-grade gliomas (LGGs) harboring the two most common pediatric pilocytic astrocytoma-associated molecular alterations, NF1 loss and KIAA1549:BRAF fusion. Herein, we identified that hiPSC-derived neuroglial progenitor populations (neural progenitors, glial restricted progenitors and oligodendrocyte progenitors), but not terminally differentiated astrocytes, give rise to tumors retaining LGG histologic features for at least 6 months in vivo. Additionally, we demonstrated that hiPSC-LGG xenograft formation requires the absence of CD4 T cell-mediated induction of astrocytic Cxcl10 expression. Genetic Cxcl10 ablation is both necessary and sufficient for human LGG xenograft development, which additionally enables the successful long-term growth of patient-derived pediatric LGGs in vivo. Lastly, MEK inhibitor (PD0325901) treatment increased hiPSC-LGG cell apoptosis and reduced proliferation both in vitro and in vivo. Collectively, this study establishes a tractable experimental humanized platform to elucidate the pathogenesis of and potential therapeutic opportunities for childhood brain tumors.

Signaling pathways and therapeutic approaches in glioblastoma multiforme (Review)

Glioblastoma multiforme (GBM) is the most aggressive type of primary brain tumor and is associated with a poor clinical prognosis. Despite the progress in the understanding of the molecular and genetic changes that promote tumorigenesis, effective treatment options are limited. The present review intended to identify and summarize major signaling pathways and genetic abnormalities involved in the pathogenesis of GBM, as well as therapies that target these pathways. Glioblastoma remains a difficult to treat tumor; however, in the last two decades, significant improvements in the understanding of GBM biology have enabled advances in available therapeutics. Significant genomic events and signaling pathway disruptions (NF‑κB, Wnt, PI3K/AKT/mTOR) involved in the formation of GBM were discussed. Current therapeutic options may only marginally prolong survival and the current standard of therapy cures only a small fraction of patients. As a result, there is an unmet requirement for further study into the processes of glioblastoma pathogenesis and the discovery of novel therapeutic targets in novel signaling pathways implicated in the evolution of glioblastoma.

Heterogeneity and excitability of BRAFV600E-induced tumors is determined by Akt/mTOR-signaling state and Trp53-loss

BACKGROUND

Developmental brain tumors harboring BRAFV600E somatic mutation are diverse. Here, we describe molecular factors that determine BRAFV600E-induced tumor biology and function.

METHODS

Intraventricular in utero electroporation in combination with the piggyBac transposon system was utilized to generate developmental brain neoplasms, which were comprehensively analyzed with regard to growth using near-infrared in-vivo imaging, transcript signatures by RNA sequencing, and neuronal activity by multielectrode arrays.

RESULTS

BRAF  V600E expression in murine neural progenitors elicits benign neoplasms composed of enlarged dysmorphic neurons and neoplastic astroglia recapitulating ganglioglioma (GG) only in concert with active Akt/mTOR-signaling. Purely glial tumors resembling aspects of polymorphous low-grade neuroepithelial tumors of the young (PLNTYs) emerge from BRAFV600E alone. Additional somatic Trp53-loss is sufficient to generate anaplastic GGs (aGGs) with glioneuronal clonality. Functionally, only BRAFV600E/pAkt tumors intrinsically generate substantial neuronal activity and show enhanced relay to adjacent tissue conferring high epilepsy propensity. In contrast, PLNTY- and aGG models lack significant spike activity, which appears in line with the glial differentiation of the former and a dysfunctional tissue structure combined with reduced neuronal transcript signatures in the latter.

CONCLUSION

mTOR-signaling and Trp53-loss critically determine the biological diversity and electrical activity of BRAFV600E-induced tumors.

Role of the Skin Microenvironment in Melanomagenesis: Epidermal Keratinocytes and Dermal Fibroblasts Promote BRAF Oncogene-Induced Senescence Escape in Melanocytes

Simple Summary

Melanoma is a deadly skin cancer caused by the uncontrolled proliferation of melanocytes, a population of specialized cells that produce the skin pigment melanin. An aberrant proliferation of melanocytes is common, manifesting as new moles, and these lesions often remain benign. Only a small fraction of these aberrant melanocytes transition to melanoma (i.e., melanomagenesis). The factors that drive this transition are not fully understood. Recent studies have suggested that other cells—specifically, keratinocytes that make up the upper skin layers and fibroblasts, which are non-specialized cells within the deeper layers of the skin—also contribute to melanomagenesis. Here, employing microscale models that mimicked the skin microenvironment, we investigated the effect of crosstalk between melanocytes as well as keratinocytes and fibroblasts on melanomagenesis. Our findings show that keratinocyte- and fibroblast-derived factors can inhibit the mechanisms that prevent an uncontrolled melanocyte proliferation and contribute to melanomagenesis. Thus, targeting skin microenvironment-derived factors is a potential strategy to prevent melanomagenesis.

Abstract

BRAF^V600E is the most common mutation driver in melanoma. This mutation is known to cause a brief burst of proliferation followed by growth arrest and senescence, which prevent an uncontrolled cell proliferation. This phenomenon is known as oncogene-induced senescence (OIS) and OIS escape is thought to lead to melanomagenesis. Much attention has been focused on the melanocyte-intrinsic mechanisms that contribute to senescence escape. Additional genetic events such as the loss of tumor suppressor PTEN and/or epigenetic changes that contribute to senescence escape have been described. However, the role of the skin microenvironment—specifically, the role of epidermal keratinocytes—on melanomagenesis is not fully understood. In this study, we employ a microfluidic platform to study the interaction between melanocytes expressing the BRAF^V600E mutation as well as keratinocytes and dermal fibroblasts. We demonstrate that keratinocytes suppress senescence-related genes and promote the proliferation of transformed melanocytes. We also show that a keratinocyte-conditioned medium can alter the secretion of both pro- and anti-tumorigenic factors by transformed melanocytes. In addition, we show that melanocytes and keratinocytes from donors of white European and black African ancestry display different crosstalks; i.e., white keratinocytes appear to promote a more pro-tumorigenic phenotype compared with black keratinocytes. These data suggest that keratinocytes exert their influence on melanomagenesis both by suppressing senescence-related genes in melanocytes and by affecting the balance of the melanocyte-secreted factors that favor tumorigenesis.

Immune deconvolution and temporal mapping identifies stromal targets and developmental intervals for abrogating murine low-grade optic glioma formation

BACKGROUND

Brain tumor formation and progression are dictated by cooperative interactions between neoplastic and non-neoplastic cells. This stromal dependence is nicely illustrated by tumors arising in the Neurofibromatosis type 1 (NF1) cancer predisposition syndrome, where children develop low-grade optic pathway gliomas (OPGs). Using several authenticated Nf1-OPG murine models, we previously demonstrated that murine Nf1-OPG growth is regulated by T cell function and microglia Ccl5 production, such that their inhibition reduces tumor proliferation in vivo. While these interactions are critical for established Nf1-OPG tumor growth, their importance in tumor formation has not been explored.

METHODS

A combination of bulk and single-cell RNA mouse optic nerve sequencing, immunohistochemistry, T cell assays, and pharmacologic and antibody-mediated inhibition methods were used in these experiments.

RESULTS

We show that T cells and microglia are the main non-neoplastic immune cell populations in both murine and human LGGs. Moreover, we demonstrate that CD8+ T cells, the predominant LGG-infiltrating lymphocyte population, are selectively recruited through increased Ccl2 receptor (Ccr4) expression in CD8+, but not CD4+, T cells, in a NF1/RAS-dependent manner. Finally, we identify the times during gliomagenesis when microglia Ccl5 production (3-6 weeks of age) and Ccl2-mediated T cell infiltration (7-10 weeks of age) occur, such that temporally-restricted Ccl2 or Ccl5 inhibition abrogates tumor formation >3.5 months following the cessation of treatment.

CONCLUSIONS

Collectively, these findings provide proof-of-concept demonstrations that targeting stromal support during early gliomagenesis durably blocks murine LGG formation.

Treatment of BRAF V600E mutated ganglioglioma of the third ventricle with dabrafenib

Background:

Ganglioglioma (GG) of the third ventricle is rare. Surgical excision of tumors in this location is associated with high morbidity due to nearby eloquent brain centers. Alternative treatments, when available, should be considered to reduce risks of surgical treatment.

Case Description:

We present the case of a 21-year-old female diagnosed with a BRAF V600E mutated GG of the third ventricle. After an endoscopic biopsy and insertion of a ventriculoperitoneal shunt, the patient was started on the BRAF inhibitor dabrafenib, as an alternative to surgery or radiation. Nearly 2 years after starting dabrafenib, her tumor appearance on serial magnetic resonance imaging is stable, and she has maintained a good quality of life with no new neurological symptoms.

Conclusion:

The disease control thus far suggests targeted medical therapy of GG of the third ventricle with BRAF inhibitors may have efficacy and should be a considered treatment modality.

The Role of Psychologic Stress in Cancer Initiation: Clinical Relevance and Potential Molecular Mechanisms

The hypothesis that the physiologic response to psychologic stress influences the initiation of cancer is highly controversial. The link between initiating stressors, the psychologic stress response, and disease is plausible, considering that the stress response is associated with defined physiologic outcomes and molecular mechanisms. In light of this, we review the clinical relevance of psychologic stress on the risk of cancer, and we propose potential molecular pathways that may link the stress response to early stages of malignant cell transformation.

Opportunities and Challenges in Stem Cell Aging

Studying aging, as a physiological process that can cause various pathological phenotypes, has attracted lots of attention due to its increasing burden and prevalence. Therefore, understanding its mechanism to find novel therapeutic alternatives for age-related disorders such as neurodegenerative and cardiovascular diseases is essential. Stem cell senescence plays an important role in aging. In the context of the underlying pathways, mitochondrial dysfunction, epigenetic and genetic alterations, and other mechanisms have been studied and as a consequence, several rejuvenation strategies targeting these mechanisms like pharmaceutical interventions, genetic modification, and cellular reprogramming have been proposed. On the other hand, since stem cells have great potential for disease modeling, they have been useful for representing aging and its associated disorders. Accordingly, the main mechanisms of senescence in stem cells and promising ways of rejuvenation, along with some examples of stem cell models for aging are introduced and discussed. This review aims to prepare a comprehensive summary of the findings by focusing on the most recent ones to shine a light on this area of research.

Reimagining Pilocytic Astrocytomas in the Context of Pediatric Low-Grade Gliomas

Pediatric low-grade gliomas (pLGGs) are the most common brain tumor in children, and are associated with life-long clinical morbidity. Relative to their high-grade adult counterparts or other malignant childhood brain tumors, there is a paucity of authenticated preclinical models for these pediatric low-grade gliomas and an incomplete understanding of their molecular and cellular pathogenesis. While large scale genomic profiling efforts have identified the majority of pathogenic driver mutations, which converge on the MAPK/ERK signaling pathway, it is now appreciated that these events may not be sufficient by themselves for gliomagenesis and clinical progression. In light of the recent World Health Organization reclassification of pLGGs, and pilocytic astrocytoma (PA) in particular, we review our current understanding of these pediatric brain tumors, provide a conceptual framework for future mechanistic studies, and outline the challenges and pressing needs for the pLGG clinical and research communities.

Conditional reprogramming culture conditions facilitate growth of lower-grade glioma models

BACKGROUND

The conditional reprogramming cell culture method was developed to facilitate growth of senescence-prone normal and neoplastic epithelial cells, and involves co-culture with irradiated fibroblasts and the addition of a small molecule Rho kinase (ROCK) inhibitor. The aim of this study was to determine whether this approach would facilitate the culture of compact low-grade gliomas.

METHODS

We attempted to culture 4 pilocytic astrocytomas, 2 gangliogliomas, 2 myxopapillary ependymomas, 2 anaplastic gliomas, 2 difficult-to-classify low-grade neuroepithelial tumors, a desmoplastic infantile ganglioglioma, and an anaplastic pleomorphic xanthoastrocytoma using a modified conditional reprogramming cell culture approach.

RESULTS

Conditional reprogramming resulted in robust increases in growth for a majority of these tumors, with fibroblast conditioned media and ROCK inhibition both required. Switching cultures to standard serum containing media, or serum-free neurosphere conditions, with or without ROCK inhibition, resulted in decreased proliferation and induction of senescence markers. Rho kinase inhibition and conditioned media both promoted Akt and Erk1/2 activation. Several cultures, including one derived from a NF1-associated pilocytic astrocytoma (JHH-NF1-PA1) and one from a BRAF p.V600E mutant anaplastic pleomorphic xanthoastrocytoma (JHH-PXA1), exhibited growth sufficient for preclinical testing in vitro. In addition, JHH-NF1-PA1 cells survived and migrated in larval zebrafish orthotopic xenografts, while JHH-PXA1 formed orthotopic xenografts in mice histopathologically similar to the tumor from which it was derived.

CONCLUSIONS

These studies highlight the potential for the conditional reprogramming cell culture method to promote the growth of glial and glioneuronal tumors in vitro, in some cases enabling the establishment of long-term culture and in vivo models.

BRAFnon-V600E more frequently co-occurs with IDH1/2 mutations in adult patients with gliomas than in patients harboring BRAFV600E but without a survival advantage

BACKGROUND

The effects of BRAF^non-V600E and BRAF^V600E on the outcomes and the molecular characteristics of adult glioma patients are unknown and need to be explored, although BRAF^V600E has been extensively studied in pediatric glioma.

METHODS

Co-occurring mutations and copy number alterations of associated genes in the MAPK and p53 pathways were investigated using data from The Cancer Genome Atlas (TCGA) public database retrieved by cBioPortal. The prognosis of available adult glioma cohorts with BRAF^V600E and BRAF^non-V600E mutations were also investigated.

RESULTS

Ninety patients with BRAF^V600E or BRAF^non-V600E were enrolled in this study, and data from 52 nonredundant patients were investigated. Glioblastoma multiform was the most common cancer type, with BRAF ^non-V600E and BRAF^V600E. TP53 (56.00% vs. 7.41%), IDH1/2 (36.00% vs. 3.70%), and ATRX (32.00% vs. 7.41%) exhibited more mutations in BRAF^non-V600E than in BRAF^V600E, and TP53 was an independent risk factor (56.00% vs. 7.41%). Both BRAF^non-V600E and BRAF^V600E frequently overlapped with CDKN2A/2B homozygous deletions (HDs), but there was no significant difference. Survival analysis showed no difference between the BRAF ^non-V600E and BRAF^V600E cohorts, even after excluding the survival benefit of IDH1/2 mutations and considering the BRAF^non-V600E mutations in the glycine-rich loop (G-loop) and in the activation segment. The estimated mean survival of patients with BRAF^non-V600E & IDH1/2^WT with mutations in the G-loop groups was the shortest.

CONCLUSIONS

BRAF^non-V600E exhibited a stronger association with IDH1/2 mutations than BRAF^V600E, but no survival advantage was found.

Synergistic activity of mTORC1/2 kinase and MEK inhibitors suppresses pediatric low-grade glioma tumorigenicity and vascularity

BACKGROUND

Pediatric low-grade glioma (pLGG) is the most common childhood brain tumor. Many patients with unresectable or recurrent/refractory tumors have significant lifelong disability. The majority of pLGG have mutations increasing the activity of the Ras/mitogen-activated protein kinase (MAPK) pathway. Activation of mammalian target of rapamycin (mTOR) is also a hallmark of pLGG. We therefore hypothesized that the dual target of rapamycin complexes 1 and 2 (TORC1/2) kinase inhibitor TAK228 would synergize with the mitogen-activated extracellular signal-regulated kinase (MEK) inhibitor trametinib in pLGG.

METHODS

We tested TAK228 and trametinib in patient-derived pLGG cell lines harboring drivers of pLGG including BRAFV600E and neurofibromatosis type 1 loss. We measured cell proliferation, pathway inhibition, cell death, and senescence. Synergy was analyzed via MTS assay using the Chou-Talalay method. In vivo, we tested for overall survival and pathway inhibition and performed immunohistochemistry for proliferation and vascularization. We performed a scratch assay and measured angiogenesis protein activation in human umbilical vein endothelial cells (HUVECs).

RESULTS

TAK228 synergized with trametinib in pLGG at clinically relevant doses in all tested cell lines, suppressing proliferation, inducing apoptosis, and causing senescence in a cell line-dependent manner. Combination treatment increased median survival by 70% and reduced tumor volume compared with monotreatment and control cohorts. Vascularization of tumors decreased as measured by CD31 and CD34. Combination treatment blocked activation of focal adhesion kinase (FAK) and sarcoma proto-oncogene non-receptor tyrosine kinase (SRC) in HUVEC cells and reduced HUVEC migration compared with each drug alone.

CONCLUSIONS

The combination of TAK228 and trametinib synergized to suppress the growth of pLGG. These agents synergized to reduce tumor vascularity and endothelial cell growth and migration by blocking activation of FAK and SRC.

Evidence of the Cellular Senescence Stress Response in Mitotically Active Brain Cells-Implications for Cancer and Neurodegeneration

Cellular stress responses influence cell fate decisions. Apoptosis and proliferation represent opposing reactions to cellular stress or damage and may influence distinct health outcomes. Clinical and epidemiological studies consistently report inverse comorbidities between age-associated neurodegenerative diseases and cancer. This review discusses how one particular stress response, cellular senescence, may contribute to this inverse correlation. In mitotically competent cells, senescence is favorable over uncontrolled proliferation, i.e., cancer. However, senescent cells notoriously secrete deleterious molecules that drive disease, dysfunction and degeneration in surrounding tissue. In recent years, senescent cells have emerged as unexpected mediators of neurodegenerative diseases. The present review uses pre-defined criteria to evaluate evidence of cellular senescence in mitotically competent brain cells, highlights the discovery of novel molecular regulators and discusses how this single cell fate decision impacts cancer and degeneration in the brain. We also underscore methodological considerations required to appropriately evaluate the cellular senescence stress response in the brain.

TORC1/2 kinase inhibition depletes glutathione and synergizes with carboplatin to suppress the growth of MYC-driven medulloblastoma

Medulloblastoma is the most common malignant pediatric brain tumor. Tumors having high levels of c-MYC have the worst clinical prognosis, with only a minority of patients surviving. To address this unmet clinical need, we generated a human neural stem cell model of medulloblastoma that recapitulated the most aggressive subtype phenotypically and by mRNA expression profiling. An in silico analysis of these cells identified mTOR inhibitors as potential therapeutic agents. We hypothesized that the orally bioavailable TORC1/2 kinase inhibitor TAK228 would have activity against MYC-driven medulloblastoma. TAK228 inhibited mTORC1/2, decreased cell growth and caused apoptosis in high-MYC medulloblastoma cell lines. Comprehensive metabolic profiling of medulloblastoma orthotopic xenografts showed upregulation of glutathione compared to matched normal brain. TAK228 suppressed glutathione production. Because glutathione is required to detoxify platinum-containing chemotherapy, we hypothesized that TAK228 would cooperate with carboplatin in medulloblastoma. TAK228 synergized with carboplatin to inhibit cell growth and induce apoptosis and extended survival in orthotopic xenografts of high-MYC medulloblastoma. Brain-penetrant TORC1/2 inhibitors and carboplatin may be an effective combination therapy for high-risk medulloblastoma.

ESC-sEVs Rejuvenate Aging Hippocampal NSCs by Transferring SMADs to Regulate the MYT1-Egln3-Sirt1 Axis

Tissue stem cell senescence leads to stem cell exhaustion, which results in tissue homeostasis imbalance and a decline in regeneration capacity. However, whether neural stem cell (NSC) senescence occurs and causes neurogenesis reduction during aging is unknown. In this study, mice at different ages were used to detect age-related hippocampal NSC (H-NSC) senescence, as well as the function and mechanism of embryonic stem cell-derived small extracellular vesicles (ESC-sEVs) in rejuvenating H-NSC senescence. We found a progressive cognitive impairment, as well as age-related H-NSC senescence, in mice. ESC-sEV treatment significantly alleviated H-NSC senescence, recovered compromised self-renewal and neurogenesis capacities, and reversed cognitive impairment. Transcriptome analysis revealed that myelin transcription factor 1 (MYT1) is downregulated in senescent H-NSCs but upregulated by ESC-sEV treatment. In addition, knockdown of MYT1 in young H-NSCs accelerated age-related phenotypes and impaired proliferation and differentiation capacities. Mechanistically, ESC-sEVs rejuvenated senescent H-NSCs partly by transferring SMAD family members 4 (SMAD4) and 5 (SMAD5) to activate MYT1, which downregulated egl-9 family hypoxia inducible factor 3 (Egln3), followed by activation of hypoxia inducible factor 2 subunit α (HIF-2α), nicotinamide phosphoribosyl transferase (NAMPT), and sirtuin 1 (Sirt1) successively. Taken together, our results indicated that H-NSC senescence caused cellular exhaustion, neurogenesis reduction, and cognitive impairment during aging, which can be reversed by ESC-sEVs. Thus, ESC-sEVs may be promising therapeutic candidates for age-related diseases.

Characterizing temporal genomic heterogeneity in pediatric low-grade gliomas

Recent discoveries have provided valuable insight into the genomic landscape of pediatric low-grade gliomas (LGGs) at diagnosis, facilitating molecularly targeted treatment. However, little is known about their temporal and therapy-related genomic heterogeneity. An adequate understanding of the evolution of pediatric LGGs' genomic profiles over time is critically important in guiding decisions about targeted therapeutics and diagnostic biopsy at recurrence. Fluorescence in situ hybridization, mutation-specific immunohistochemistry, and/or targeted sequencing were performed on paired tumor samples from primary diagnostic and subsequent surgeries. Ninety-four tumor samples from 45 patients (41 with two specimens, four with three specimens) from three institutions underwent testing. Conservation of BRAF fusion, BRAF^V600E mutation, and FGFR1 rearrangement status was observed in 100%, 98%, and 96% of paired specimens, respectively. No loss or gain of IDH1 mutations or NTRK2, MYB, or MYBL1 rearrangements were detected over time. Histologic diagnosis remained the same in all tumors, with no acquired H3K27M mutations or malignant transformation. Changes in CDKN2A deletion status at recurrence occurred in 11 patients (42%), with acquisition of hemizygous CDKN2A deletion in seven and loss in four. Shorter time to progression and shorter time to subsequent surgery were observed among patients with acquired CDKN2A deletions compared to patients without acquisition of this alteration [median time to progression: 5.5 versus 16.0 months (p = 0.048); median time to next surgery: 17.0 months versus 29.0 months (p = 0.031)]. Most targetable genetic aberrations in pediatric LGGs, including BRAF alterations, are conserved at recurrence and following chemotherapy or irradiation. However, changes in CDKN2A deletion status over time were demonstrated. Acquisition of CDKN2A deletion may define a higher risk subgroup of pediatric LGGs with a poorer prognosis. Given the potential for targeted therapies for tumors harboring CDKN2A deletions, biopsy at recurrence may be indicated in certain patients, especially those with rapid progression.

Genetic and genomic alterations differentially dictate low-grade glioma growth through cancer stem cell-specific chemokine recruitment of T cells and microglia

BACKGROUND

One of the clinical hallmarks of low-grade gliomas (LGGs) arising in children with the neurofibromatosis type 1 (NF1) cancer predisposition syndrome is significant clinical variability with respect to tumor growth, associated neurologic deficits, and response to therapy. Numerous factors could contribute to this clinical heterogeneity, including the tumor cell of origin, the specific germline NF1 gene mutation, and the coexistence of additional genomic alterations. Since human specimens are rarely acquired, and have proven difficult to maintain in vitro or as xenografts in vivo, we have developed a series of Nf1 mutant optic glioma mouse strains representing each of these contributing factors.

METHODS

Optic glioma stem cells (o-GSCs) were generated from this collection of Nf1 genetically engineered mice, and analyzed for their intrinsic growth properties, as well as the production of chemokines that could differentially attract T cells and microglia.

RESULTS

The observed differences in Nf1 optic glioma growth are not the result of cell autonomous growth properties of o-GSCs, but rather the unique patterns of o-GSC chemokine expression, which differentially attract T cells and microglia. This immune profile collectively dictates the levels of chemokine C-C ligand 5 (Ccl5) expression, the key stromal factor that drives murine Nf1 optic glioma growth.

CONCLUSIONS

These findings reveal that genetic and genomic alterations create murine LGG biological heterogeneity through the differential recruitment of T cells and microglia by o-GSC-produced chemokines, which ultimately determine the expression of stromal factors that drive tumor growth.

Clinical Relevance of BRAF V600E Mutation Status in Brain Tumors with a Focus on a Novel Management Algorithm

The possible application of BRAF-targeted therapy in brain tumors is growing continuously. We have analyzed clinical strategies that address BRAF activation in primary brain tumors and verified current recommendations regarding screening for BRAF mutations. There is preliminary evidence for a range of positive responses in certain brain tumor types harboring the BRAF V600E mutation. National Comprehensive Cancer Network Guidelines for central nervous system cancers recommend screening for the BRAF V600E mutation in pilocytic astrocytoma, pleomorphic xanthoastrocytoma, and ganglioglioma. We suggest additional testing in glioblastomas WHO grade IV below the age of 30 years, especially those with epithelioid features, papillary craniopharyngiomas, and pediatric low-grade astrocytomas. BRAF-targeted therapy should be limited to the setting of a clinical trial. If the patient harboring a V600E mutation does not qualify for a trial, multimodality treatment is recommended. Dual inhibition of both RAF and MEK is expected to provide more potent and durable effects than anti-BRAF monotherapy. First-generation RAF inhibitors should be avoided. Gain-of-function mutations of EGFR and KIAA fusions may compromise BRAF-targeted therapy. BRAF alterations that result in MAPK pathway activation are common events in several types of brain tumors. BRAF V600E mutation emerges as a promising molecular target. The proposed algorithm was designed to help oncologists to provide the best therapeutic options for brain tumor patients.

Rapid Recurrence and Anaplastic Transformation of a Pilocytic Astrocytoma in an Elderly Patient: Case Report and Review of the Literature

BACKGROUND

Rapid recurrence of a pilocytic astrocytoma with anaplastic transformation is extremely rare. The case of an elderly patient with a cerebellar pilocytic astrocytoma with anaplastic transformation during short-term follow-up is reported.

CASE DESCRIPTION

An 83-year-old woman presented initially with dizziness and a gait deviation to the right. Magnetic resonance imaging demonstrated a homogeneously enhanced mass in the right cerebellar hemisphere, and the tumor was subtotally removed by right suboccipital craniotomy. Histologic examination showed that the tumor cells contained eosinophilic cytoplasm and spindle-shaped processes with Rosenthal fibers and eosinophilic granular bodies, diagnosed as a typical pilocytic astrocytoma (PA). The MIB-1 index was <1%. The patient did not receive postoperative adjuvant radiation and chemotherapy. Two months after surgery, magnetic resonance imaging showed growth of the residual tumor adjacent to the fourth ventricle, causing obstructive hydrocephalus. She underwent surgery again, and the tumor was totally removed. Histologic findings showed mitotic cells and increased cellularity compared with the primary tumor, which was compatible with anaplastic transformation of PA with a MIB-1 index of 50%. Postoperatively, she was observed with best supportive care without postoperative adjuvant therapy. Nine months after the second operation, she died due to tonsillar herniation and obstructive hydrocephalus caused by a recurrent tumor. An autopsy was performed.

CONCLUSIONS

It is extremely rare, as in the present case, that a cerebellar PA in an elderly patient recurs rapidly with anaplastic transformation, despite deferred postoperative adjuvant therapy including radiation and chemotherapy. A novel molecular-targeted therapy is needed for anaplastic PA showing aggressive biological behavior.

A Cell-Based MAPK Reporter Assay Reveals Synergistic MAPK Pathway Activity Suppression by MAPK Inhibitor Combination in BRAF-Driven Pediatric Low-Grade Glioma Cells

Pilocytic astrocytomas as well as other pediatric low-grade gliomas (pLGG) exhibit genetic events leading to aberrant activation of the MAPK pathway. The most common alterations are KIAA1549:BRAF fusions and BRAF^V600E and NF1 mutations. Novel drugs targeting the MAPK pathway (MAPKi) are prime candidates for the treatment of these single-pathway diseases. We aimed to develop an assay suitable for preclinical testing of MAPKi in pLGGs with the goal to identify novel MAPK pathway-suppressing synergistic drug combinations. A reporter plasmid (pDIPZ) with a MAPK-responsive ELK-1-binding element driving the expression of destabilized firefly luciferase was generated and packaged using a lentiviral vector system. Pediatric glioma cell lines with a BRAF fusion (DKFZ-BT66) and a BRAF^V600E mutation (BT-40) background, respectively, were stably transfected. Modulation of the MAPK pathway activity by MAPKi was measured using the luciferase reporter and validated by detection of phosphorylated protein levels. A screening of a MAPKi library was performed, and synergy of selected combinations was calculated. Screening of a MAPKi library revealed MEK inhibitors as the class inhibiting the pathway with the lowest IC₅₀s, followed by ERK and next-generation RAF inhibitors. Combination treatments with different MAPKi classes showed synergistic effects in BRAF fusion as well as BRAF^V600E mutation backgrounds. Here, we report a novel reporter assay for medium- to high-throughput preclinical drug testing in pLGG cell lines. The assay confirmed MEK, ERK, and next-generation RAF inhibitors as potential treatment approaches for KIAA1549:BRAF and BRAF^V600E-mutated pLGGs. In addition, the assay revealed that combination treatments synergistically suppressed MAPK pathway activity.

Pediatric Low-Grade Gliomas

Brain tumors constitute the largest source of oncologic mortality in children and low-grade gliomas are among most common pediatric central nervous system tumors. Pediatric low-grade gliomas differ from their counterparts in the adult population in their histopathology, genetics, and standard of care. Over the past decade, an increasingly detailed understanding of the molecular and genetic characteristics of pediatric brain tumors led to tailored therapy directed by integrated phenotypic and genotypic parameters and the availability of an increasing array of molecular-directed therapies. Advances in neuroimaging, conformal radiation therapy, and conventional chemotherapy further improved treatment outcomes. This article reviews the current classification of pediatric low-grade gliomas, their histopathologic and radiographic features, state-of-the-art surgical and adjuvant therapies, and emerging therapies currently under study in clinical trials.

ESC-sEVs Rejuvenate Senescent Hippocampal NSCs by Activating Lysosomes to Improve Cognitive Dysfunction in Vascular Dementia

Vascular dementia (VD) is one of the most common types of dementia, however, the intrinsic mechanism is unclear and there is still lack of effective medications. In this study, the VD rats exhibit a progressive cognitive impairment, as well as a time-related increasing in hippocampal neural stem cells (H-NSCs) senescence, lost and neurogenesis decline. Then, embryonic stem cell-derived small extracellular vesicles (ESC-sEVs) are intravenously injected into VD rats. ESC-sEVs treatment significantly alleviates H-NSCs senescence, recovers compromised proliferation and neuron differentiation capacity, and reverses cognitive impairment. By microarray analysis and RT-qPCR it is identified that several miRNAs including miR-17-5p, miR-18a-5p, miR-21-5p, miR-29a-3p, and let-7a-5p, that can inhibit mTORC1 activation, exist in ESC-sEVs. ESC-sEVs rejuvenate H-NSCs senescence partly by transferring these miRNAs to inhibit mTORC1 activation, promote transcription factor EB (TFEB) nuclear translocation and lysosome resumption. Taken together, these data indicate that H-NSCs senescence cause cell depletion, neurogenesis reduction, and cognitive impairment in VD. ESC-sEVs treatment ameliorates H-NSCs senescence by inhibiting mTORC1 activation, and promoting TFEB nuclear translocation and lysosome resumption, thereby reversing senescence-related neurogenesis dysfunction and cognitive impairment in VD. The application of ESC-sEVs may be a novel cell-free therapeutic tool for patients with VD, as well as other aging-related diseases.