Expression of oligodendrocyte progenitor cell antigens by gliomas: implications for the histogenesis of brain tumors

Systematic Review of Molecular Targeted Therapies for Adult-Type Diffuse Glioma: An Analysis of Clinical and Laboratory Studies

Gliomas are the most common brain tumor in adults, and molecularly targeted therapies to treat gliomas are becoming a frequent topic of investigation. The current state of molecular targeted therapy research for adult-type diffuse gliomas has yet to be characterized, particularly following the 2021 WHO guideline changes for classifying gliomas using molecular subtypes. This systematic review sought to characterize the current state of molecular target therapy research for adult-type diffuse glioma to better inform scientific progress and guide next steps in this field of study. A systematic review was conducted in accordance with PRISMA guidelines. Studies meeting inclusion criteria were queried for study design, subject (patients, human cell lines, mice, etc.), type of tumor studied, molecular target, respective molecular pathway, and details pertaining to the molecular targeted therapy-namely the modality, dose, and duration of treatment. A total of 350 studies met the inclusion criteria. A total of 52 of these were clinical studies, 190 were laboratory studies investigating existing molecular therapies, and 108 were laboratory studies investigating new molecular targets. Further, a total of 119 ongoing clinical trials are also underway, per a detailed query on clinicaltrials.gov. GBM was the predominant tumor studied in both ongoing and published clinical studies as well as in laboratory analyses. A few studies mentioned IDH-mutant astrocytomas or oligodendrogliomas. The most common molecular targets in published clinical studies and clinical trials were protein kinase pathways, followed by microenvironmental targets, immunotherapy, and cell cycle/apoptosis pathways. The most common molecular targets in laboratory studies were also protein kinase pathways; however, cell cycle/apoptosis pathways were the next most frequent target, followed by microenvironmental targets, then immunotherapy pathways, with the wnt/β-catenin pathway arising in the cohort of novel targets. In this systematic review, we examined the current evidence on molecular targeted therapy for adult-type diffuse glioma and discussed its implications for clinical practice and future research. Ultimately, published research falls broadly into three categories-clinical studies, laboratory testing of existing therapies, and laboratory identification of novel targets-and heavily centers on GBM rather than IDH-mutant astrocytoma or oligodendroglioma. Ongoing clinical trials are numerous in this area of research as well and follow a similar pattern in tumor type and targeted pathways as published clinical studies. The most common molecular targets in all study types were protein kinase pathways. Microenvironmental targets were more numerous in clinical studies, whereas cell cycle/apoptosis were more numerous in laboratory studies. Immunotherapy pathways are on the rise in all study types, and the wnt/β-catenin pathway is increasingly identified as a novel target.

Biological functions of the Olig gene family in brain cancer and therapeutic targeting

The Olig genes encode members of the basic helix-loop-helix (bHLH) family of transcription factors. Olig1, Olig2, and Olig3 are expressed in both the developing and mature central nervous system (CNS) and regulate cellular specification and differentiation. Over the past decade extensive studies have established functional roles of Olig1 and Olig2 in development as well as in cancer. Olig2 overexpression drives glioma proliferation and resistance to radiation and chemotherapy. In this review, we summarize the biological functions of the Olig family in brain cancer and how targeting Olig family genes may have therapeutic benefit.

Brain network mapping and glioma pathophysiology

Adult diffuse gliomas are among the most difficult brain disorders to treat in part due to a lack of clarity regarding the anatomical origins and mechanisms of migration of the tumours. While the importance of studying networks of glioma spread has been recognized for at least 80 years, the ability to carry out such investigations in humans has emerged only recently. Here, we comprehensively review the fields of brain network mapping and glioma biology to provide a primer for investigators interested in merging these areas of inquiry for the purposes of translational research. Specifically, we trace the historical development of ideas in both brain network mapping and glioma biology, highlighting studies that explore clinical applications of network neuroscience, cells-of-origin of diffuse glioma and glioma-neuronal interactions. We discuss recent research that has merged neuro-oncology and network neuroscience, finding that the spatial distribution patterns of gliomas follow intrinsic functional and structural brain networks. Ultimately, we call for more contributions from network neuroimaging to realize the translational potential of cancer neuroscience.

A2B5 Expression in Central Nervous System and Gliomas

A2B5 IgM recognizes c-series gangliosides with three sialic acids. The aim of this review was to focus on A2B5 expression in the central nervous system and gliomas. In brain development, A2B5+ cells are recorded in areas containing multipotent neural stem cells (NSC). In adults, A2B5+ cells persist in neurogenic areas and in white matter where it identifies oligodendrocyte precursor cells (OPCs) but also cells with NSC properties. Although the expression of A2B5 has been widely studied in culture, where it characterizes bipotential glial progenitor cells, its expression in vivo is less characterized mainly because of technical issues. A new interest was given to the NSCs and OPCs since the discovery of cancer stem cells (CSC) in gliomas. Among other cell surface molecules, A2B5 has been identified as an accurate marker to identify glioma CSCs. We and others have shown that all types of gliomas express A2B5, and that only A2B5+ cells, and not A2B5- cells, can generate a tumor after orthotopic implantation in immunocompromised animals. Moreover, A2B5 epitope expression is positively correlated with stemness and tumor growth. This review highlights that A2B5 is an attractive target to tackle glioma CSCs, and a better characterization of its expression in the developing and adult CNS will benefit to a better understanding of gliomagenesis.

Molecular Pathogenesis of Glioblastoma in Adults and Future Perspectives: A Systematic Review

Glioblastoma (GBM) is the most common and malignant tumour of the central nervous system. Recent appreciation of the heterogeneity amongst these tumours not only changed the WHO classification approach, but also created the need for developing novel and personalised therapies. This systematic review aims to highlight recent advancements in understanding the molecular pathogenesis of the GBM and discuss related novel treatment targets. A systematic search of the literature in the PubMed library was performed following the PRISMA guidelines for molecular pathogenesis and therapeutic advances. Original and meta-analyses studies from the last ten years were reviewed using pre-determined search terms. The results included articles relevant to GBM development focusing on the aberrancy in cell signaling pathways and intracellular events. Theragnostic targets and vaccination to treat GBM were also explored. The molecular pathophysiology of GBM is complex. Our systematic review suggests targeting therapy at the stemness, p53 mediated pathways and immune modulation. Exciting novel immune therapy involving dendritic cell vaccines, B-cell vaccines and viral vectors may be the future of treating GBM.

Glutaredoxin 2 promotes SP-1-dependent CSPG4 transcription and migration of wound healing NG2 glia and glioma cells: Enzymatic Taoism

Redox regulation of specific cysteines via oxidoreductases of the thioredoxin family is increasingly being recognized as an important signaling pathway. Here, we demonstrate that the cytosolic isoform of the vertebrate-specific oxidoreductase Glutaredoxin 2 (Grx2c) regulates the redox state of the transcription factor SP-1 and thereby its binding affinity to both the promoter and an enhancer region of the CSPG4 gene encoding chondroitin sulfate proteoglycan nerve/glial antigen 2 (NG2). This leads to an increased number of NG2 glia during in vitro oligodendroglial differentiation and promotes migration of these wound healing cells. On the other hand, we found that the same mechanism also leads to increased invasion of glioma tumor cells. Using in vitro (human cell lines), ex vivo (mouse primary cells), and in vivo models (zebrafish), as well as glioblastoma patient tissue samples we provide experimental data highlighting the Yin and Yang of redox signaling in the central nervous system and the enzymatic Taoism of Grx2c.

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CSPG4 promoter binding of the transcription factor SP-1 depends on glutaredoxin 2

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Cytosolic glutaredoxin 2 promotes oligodendrocyte differentiation into NG2 glia

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Migration and wound healing capacity of NG2 glia is increased by glutaredoxin 2

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Glutaredoxin 2 increases invasion of human glioblastoma cells in vitro and in vivo

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.

PDGFRb+ mesenchymal cells, but not NG2+ mural cells, contribute to cardiac fat

Understanding cellular origins of cardiac adipocytes (CAs) can offer important implications for the treatment of fat-associated cardiovascular diseases. Here, we perform lineage tracing studies by using various genetic models and find that cardiac mesenchymal cells (MCs) contribute to CAs in postnatal development and adult homeostasis. Although PDGFRa⁺ and PDGFRb⁺ MCs both give rise to intramyocardial adipocytes, PDGFRb⁺ MCs are demonstrated to be the major source of intramyocardial adipocytes. Moreover, we find that PDGFRb⁺ cells are heterogenous, as PDGFRb is expressed not only in pericytes and smooth muscle cells (SMCs) but also in some subendocardial, pericapillary, or adventitial PDGFRa⁺ fibroblasts. Dual-recombinase-mediated intersectional genetic lineage tracing reveals that PDGFRa⁺PDGFRb⁺ double-positive periendothelial fibroblasts contribute to intramyocardial adipocytes. In contrast, SMCs and NG2⁺ pericytes do not contribute to CAs. These in vivo findings demonstrate that PDGFRb⁺ MCs, but not NG2⁺ coronary vascular mural cells, are the major source of intramyocardial adipocytes.

The Strange Case of Jekyll and Hyde: Parallels Between Neural Stem Cells and Glioblastoma-Initiating Cells

During embryonic development, radial glial precursor cells give rise to neural lineages, and a small proportion persist in the adult mammalian brain to contribute to long-term neuroplasticity. Neural stem cells (NSCs) reside in two neurogenic niches of the adult brain, the hippocampus and the subventricular zone (SVZ). NSCs in the SVZ are endowed with the defining stem cell properties of self-renewal and multipotent differentiation, which are maintained by intrinsic cellular programs, and extrinsic cellular and niche-specific interactions. In glioblastoma, the most aggressive primary malignant brain cancer, a subpopulation of cells termed glioblastoma stem cells (GSCs) exhibit similar stem-like properties. While there is an extensive overlap between NSCs and GSCs in function, distinct genetic profiles, transcriptional programs, and external environmental cues influence their divergent behavior. This review highlights the similarities and differences between GSCs and SVZ NSCs in terms of their gene expression, regulatory molecular pathways, niche organization, metabolic programs, and current therapies designed to exploit these differences.

Genome-wide translation patterns in gliomas: An integrative view

Gliomas are the most frequent tumors of the central nervous system (CNS) and include the highly malignant glioblastoma (GBM). Characteristically, gliomas have translational control deregulation related to overactivation of signaling pathways such as PI3K/AKT/mTORC1 and Ras/ERK1/2. Thus, mRNA translation appears to play a dominant role in glioma gene expression patterns. The, analysis of genome-wide translated transcripts, together known as the translatome, may reveal important information for understanding gene expression patterns in gliomas. This review provides a brief overview of translational control mechanisms altered in gliomas with a focus on the current knowledge related to the translatomes of glioma cells and murine glioma models. We present an integrative meta-analysis of selected glioma translatome data with the aim of identifying recurrent patterns of gene expression preferentially regulated at the level of translation and obtaining clues regarding the pathological significance of these alterations. Re-analysis of several translatome datasets was performed to compare the translatomes of glioma models with those of their non-tumor counterparts and to document glioma cell responses to radiotherapy and MNK modulation. The role of recurrently altered genes in the context of translational control and tumorigenesis are discussed.

Genetic, cellular, and connectomic characterization of the brain regions commonly plagued by glioma

For decades, it has been known that gliomas follow a non-random spatial distribution, appearing more often in some brain regions (e.g. the insula) compared to others (e.g. the occipital lobe). A better understanding of the localization patterns of gliomas could provide clues to the origins of these types of tumours, and consequently inform treatment targets. Following hypotheses derived from prior research into neuropsychiatric disease and cancer, gliomas may be expected to localize to brain regions characterized by functional hubness, stem-like cells, and transcription of genetic drivers of gliomagenesis. We combined neuroimaging data from 335 adult patients with high- and low-grade glioma to form a replicable tumour frequency map. Using this map, we demonstrated that glioma frequency is elevated in association cortex and correlated with multiple graph-theoretical metrics of high functional connectedness. Brain regions populated with putative cells of origin for glioma, neural stem cells and oligodendrocyte precursor cells, exhibited a high glioma frequency. Leveraging a human brain atlas of post-mortem gene expression, we found that gliomas were localized to brain regions enriched with expression of genes associated with chromatin organization and synaptic signalling. A set of glioma proto-oncogenes was enriched among the transcriptomic correlates of glioma distribution. Finally, a regression model incorporating connectomic, cellular, and genetic factors explained 58% of the variance in glioma frequency. These results add to previous literature reporting the vulnerability of hub regions to neurological disease, as well as provide support for cancer stem cell theories of glioma. Our findings illustrate how factors of diverse scale, from genetic to connectomic, can independently influence the anatomic localization of brain dysfunction.

To Become or Not to Become Tumorigenic: Subventricular Zone Versus Hippocampal Neural Stem Cells

Neural stem cells (NSCs) persist in the adult mammalian brain in two neurogenic regions: the subventricular zone lining the lateral ventricles and the dentate gyrus of the hippocampus. Compelling evidence suggests that NSCs of the subventricular zone could be the cell type of origin of glioblastoma, the most devastating brain tumor. Studies in glioblastoma patients revealed that NSCs of the tumor-free subventricular zone, harbor cancer-driver mutations that were found in the tumor cells but were not present in normal cortical tissue. Endogenous mutagenesis can also take place in hippocampal NSCs. However, to date, no conclusive studies have linked hippocampal mutations with glioblastoma development. In addition, glioblastoma cells often invade or are closely located to the subventricular zone, whereas they do not tend to infiltrate into the hippocampus. In this review we will analyze possible causes by which subventricular zone NSCs might be more susceptible to malignant transformation than their hippocampal counterparts. Cellular and molecular differences between the two neurogenic niches, as well as genotypic and phenotypic characteristics of their respective NSCs will be discussed regarding why the cell type originating glioblastoma brain tumors has been linked mainly to subventricular zone, but not to hippocampal NSCs.

DNA methylation in Schwann cells and in oligodendrocytes

DNA methylation is one of many epigenetic marks, which directly modifies base residues, usually cytosines, in a multiple-step cycle. It has been linked to the regulation of gene expression and alternative splicing in several cell types, including during cell lineage specification and differentiation processes. DNA methylation changes have also been observed during aging, and aberrant methylation patterns have been reported in several neurological diseases. We here review the role of DNA methylation in Schwann cells and oligodendrocytes, the myelin-forming glia of the peripheral and central nervous systems, respectively. We first address how methylation and demethylation are regulating myelinating cells' differentiation during development and repair. We then mention how DNA methylation dysregulation in diseases and cancers could explain their pathogenesis by directly influencing myelinating cells' proliferation and differentiation capacities.

Chondroitin Sulphate Proteoglycan 4 (NG2/CSPG4) Localization in Low- and High-Grade Gliomas

BACKGROUND

Neuron glial antigen 2 or chondroitin sulphate proteoglycan 4 (NG2/CSPG4) is expressed by immature precursors/progenitor cells and is possibly involved in malignant cell transformation. The aim of this study was to investigate its role on the progression and survival of sixty-one adult gliomas and nine glioblastoma (GB)-derived cell lines.

METHODS

NG2/CSPG4 protein expression was assessed by immunohistochemistry and immunofluorescence. Genetic and epigenetic alterations were detected by molecular genetic techniques.

RESULTS

NG2/CSPG4 was frequently expressed in IDH-mutant/1p19q-codel oligodendrogliomas (59.1%) and IDH-wild type GBs (40%) and rarely expressed in IDH-mutant or IDH-wild type astrocytomas (14.3%). Besides tumor cells, NG2/CSPG4 immunoreactivity was found in the cytoplasm and/or cell membranes of reactive astrocytes and vascular pericytes/endothelial cells. In GB-derived neurospheres, it was variably detected according to the number of passages of the in vitro culture. In GB-derived adherent cells, a diffuse positivity was found in most cells. NG2/CSPG4 expression was significantly associated with EGFR gene amplification (p = 0.0005) and poor prognosis (p = 0.016) in astrocytic tumors.

CONCLUSION

The immunoreactivity of NG2/CSPG4 provides information on the timing of the neoplastic transformation and could have prognostic and therapeutic relevance as a promising tumor-associated antigen for antibody-based immunotherapy in patients with malignant gliomas.

Involvement of Heparan Sulfate and Heparanase in Neural Development and Pathogenesis of Brain Tumors

Brain tumors are aggressive and devastating diseases. The most common type of brain tumor, glioblastoma (GBM), is incurable and has one of the worst five-year survival rates of all human cancers. GBMs are invasive and infiltrate healthy brain tissue, which is one main reason they remain fatal despite resection, since cells that have already migrated away lead to rapid regrowth of the tumor. Curative therapy for medulloblastoma (MB), the most common pediatric brain tumor, has improved, but the outcome is still poor for many patients, and treatment causes long-term complications. Recent advances in the classification of pediatric brain tumors reveal distinct subgroups, allowing more targeted therapy for the most aggressive forms, and sparing children with less malignant tumors the side-effects of massive treatment. Heparan sulfate proteoglycans (HSPGs), main components of the neurogenic niche, interact specifically with a large number of physiologically important molecules and vital roles for HS biosynthesis and degradation in neural stem cell differentiation have been presented. HSPGs are composed of a core protein with attached highly charged, sulfated disaccharide chains. The major enzyme that degrades HS is heparanase (HPSE), an important regulator of extracellular matrix (ECM) remodeling which has been suggested to promote the growth and invasion of other types of tumors. This is of clinical interest because GBM are highly invasive and children with metastatic MB at the time of diagnosis exhibit a worse outcome. Here we review the involvement of HS and HPSE in development of the nervous system and some of its most malignant brain tumors, glioblastoma and medulloblastoma.

Chondroitin Sulphate Proteoglycans in the Tumour Microenvironment

Proteoglycans are macromolecules that are essential for the development of cells, human diseases and malignancies. In particular, chondroitin sulphate proteoglycans (CSPGs) accumulate in tumour stroma and play a key role in tumour growth and invasion by driving multiple oncogenic pathways in tumour cells and promoting crucial interactions in the tumour microenvironment (TME). These pathways involve receptor tyrosine kinase (RTK) signalling via the mitogen-activated protein kinase (MAPK) cascade and integrin signalling via the activation of focal adhesion kinase (FAK), which sustains the activation of extracellular signal-regulated kinases 1/2 (ERK1/2).Human CSPG4 is a type I transmembrane protein that is associated with the growth and progression of human brain tumours. It regulates cell signalling and migration by interacting with components of the extracellular matrix, extracellular ligands, growth factor receptors, intracellular enzymes and structural proteins. Its overexpression by tumour cells, perivascular cells and precursor/progenitor cells in gliomas suggests that it plays a role in their origin, progression and neo-angiogenesis and its aberrant expression in tumour cells may be a promising biomarker to monitor malignant progression and patient survival.The aim of this chapter is to review and discuss the role of CSPG4 in the TME of human gliomas, including its potential as a druggable therapeutic target.

The post-surgical era of GBM: How molecular biology has impacted on our clinical management. A review

Glioblastoma (GBM) is the most common glioma in adults, with incidence increasing by 3% per year. According to the World Health Organization Classification of Central Nervous System Tumors, GBM is considered a grade IV tumor due to its malignant behavior. The aim of this review is to summarize the main biological aspects of GBM. In particular, we focused our attention on those alterations which have been proven to have an impact on patients' outcome, mainly in terms of overall survival (OS), or on the tumor response to therapies. We have also analyzed the cellular biology and the interactions between GBM and the surrounding environment.

Clinical-Scale Production of CAR-T Cells for the Treatment of Melanoma Patients by mRNA Transfection of a CSPG4-Specific CAR under Full GMP Compliance

Chimeric antigen receptor (CAR)-T cells already showed impressive clinical regressions in leukemia and lymphoma. However, the development of CAR-T cells against solid tumors lags behind. Here we present the clinical-scale production of CAR-T cells for the treatment of melanoma under full GMP compliance. In this approach a CAR, specific for chondroitin sulfate proteoglycan 4 (CSPG4) is intentionally transiently expressed by mRNA electroporation for safety reasons. The clinical-scale protocol was optimized for: (i) expansion of T cells, (ii) electroporation efficiency, (iii) viability, (iv) cryopreservation, and (v) potency. Four consistency runs resulted in CAR-T cells in clinically sufficient numbers, i.e., 2.4 × 10⁹ CAR-expressing T cells, starting from 1.77x10⁸ PBMCs, with an average expansion of 13.6x, an electroporation efficiency of 88.0% CAR-positive cells, a survival of 74.1% after electroporation, and a viability of 84% after cryopreservation. Purity was 98.7% CD3⁺ cells, with 78.1% CD3⁺/CD8⁺ T cells and with minor contaminations of 1.2% NK cells and 0.6% B cells. The resulting CAR-T cells were tested for cytolytic activity after cryopreservation and showed antigen-specific and very efficient lysis of tumor cells. Although our work is descriptive rather than investigative in nature, we expect that providing this clinically applicable protocol to generate sufficient numbers of mRNA-transfected CAR-T cells will help in moving the field of adoptive cell therapy of cancer forward.

Capicua regulates neural stem cell proliferation and lineage specification through control of Ets factors

Capicua (Cic) is a transcriptional repressor mutated in the brain cancer oligodendroglioma. Despite its cancer link, little is known of Cic's function in the brain. We show that nuclear Cic expression is strongest in astrocytes and neurons but weaker in stem cells and oligodendroglial lineage cells. Using a new conditional Cic knockout mouse, we demonstrate that forebrain-specific Cic deletion increases proliferation and self-renewal of neural stem cells. Furthermore, Cic loss biases neural stem cells toward glial lineage selection, expanding the pool of oligodendrocyte precursor cells (OPCs). These proliferation and lineage effects are dependent on de-repression of Ets transcription factors. In patient-derived oligodendroglioma cells, CIC re-expression or ETV5 blockade decreases lineage bias, proliferation, self-renewal, and tumorigenicity. Our results identify Cic as an important regulator of cell fate in neurodevelopment and oligodendroglioma, and suggest that its loss contributes to oligodendroglioma by promoting proliferation and an OPC-like identity via Ets overactivity.

The Role of SVZ Stem Cells in Glioblastoma

As most common primary brain cancer, glioblastoma is also the most aggressive and malignant form of cancer in the adult central nervous system. Glioblastomas are genetic and transcriptional heterogeneous tumors, which in spite of intensive research are poorly understood. Over the years conventional therapies failed to affect a cure, resulting in low survival rates of affected patients. To improve the clinical outcome, an important approach is to identify the cells of origin. One potential source for these are neural stem cells (NSCs) located in the subventricular zone, which is one of two niches in the adult nervous system where NSCs with the capacity of self-renewal and proliferation reside. These cells normally give rise to neuronal as well as glial progenitor cells. This review summarizes current findings about links between NSCs and cancer stem cells in glioblastoma and discusses current therapeutic approaches, which arise as a result of identifying the cell of origin in glioblastoma.

NG2 expression in NG2 glia is regulated by binding of SoxE and bHLH transcription factors to a Cspg4 intronic enhancer

NG2 is a type 1 integral membrane glycoprotein encoded by the Cspg4 gene. It is expressed on glial progenitor cells known as NG2 glial cells or oligodendrocyte precursor cells that exist widely throughout the developing and mature central nervous system and vascular mural cells but not on mature oligodendrocytes, astrocytes, microglia, neurons, or neural stem cells. Hence NG2 is widely used as a marker for NG2 glia in the rodent and human. The regulatory elements of the mouse Cspg4 gene and its flanking sequences have been used successfully to target reporter and Cre recombinase to NG2 glia in transgenic mice when used in a large 200 kb bacterial artificial chromosome cassette containing the 38 kb Cspg4 gene in the center. Despite the tightly regulated cell type- and stage-specific expression of NG2 in the brain and spinal cord, the mechanisms that regulate its transcription have remained unknown. Here, we describe a 1.45 kb intronic enhancer of the mouse Cspg4 gene that directed transcription of EGFP reporter to NG2 glia but not to pericytes in vitro and in transgenic mice. The 1.45 kb enhancer contained binding sites for SoxE and basic helix-loop-helix transcription factors, and its enhancer activity was augmented cooperatively by these factors, whose respective binding elements were found in close proximity to each other. Mutations in these binding elements abrogated the enhancer activity when tested in the postnatal mouse brain.

The Significance of Chondroitin Sulfate Proteoglycan 4 (CSPG4) in Human Gliomas

Neuron glial antigen 2 (NG2) is a chondroitin sulphate proteoglycan 4 (CSPG4) that occurs in developing and adult central nervous systems (CNSs) as a marker of oligodendrocyte precursor cells (OPCs) together with platelet-derived growth factor receptor α (PDGFRα). It behaves variably in different pathological conditions, and is possibly involved in the origin and progression of human gliomas. In the latter, NG2/CSPG4 induces cell proliferation and migration, is highly expressed in pericytes, and plays a role in neoangiogenesis. NG2/CSPG4 expression has been demonstrated in oligodendrogliomas, astrocytomas, and glioblastomas (GB), and it correlates with malignancy. In rat tumors transplacentally induced by N-ethyl-N-nitrosourea (ENU), NG2/CSPG4 expression correlates with PDGFRα, Olig2, Sox10, and Nkx2.2, and with new vessel formation. In this review, we attempt to summarize the normal and pathogenic functions of NG2/CSPG4, as well as its potential as a therapeutic target.

Expression of Oligodendrocyte Precursor Cell Markers in Canine Oligodendrogliomas

Oligodendroglioma is a common brain tumor in dogs, particularly brachycephalic breeds. Oligodendrocyte precursor cells (OPCs) are suspected to be a possible origin of oligodendroglioma, although it has not been well elucidated. In the present study, 27 cases of canine brain oligodendrogliomas were histologically and immunohistochemically examined. The most commonly affected breed was the French Bulldog ( n = 19 of 27, 70%). Seizure was the most predominant clinical sign ( n = 17 of 25, 68%). The tumors were located mainly in the cerebrum, particularly in the frontal lobe ( n = 10 of 27, 37%). All cases were diagnosed as anaplastic oligodendroglioma (AO) and had common histologic features characterized by the proliferation of round to polygonal cells with pronounced atypia and conspicuous mitotic activity (average, 10.7 mitoses per 10 high-power fields). Honeycomb pattern ( n = 5 of 27, 19%), myxoid matrix ( n = 10, 37%), cyst formation ( n = 6, 22%), necrosis ( n = 19, 70%), pseudopalisading ( n = 5, 18.5%), glomeruloid vessels ( n = 16, 59%), and microcalcification ( n = 5, 19%) were other histopathologic features of the present tumors. Immunohistochemically, the tumor cells were positive for Olig2 in all cases and for other markers of OPCs in most cases, including SOX10 ( n = 24 of 27, 89%), platelet-derived growth factor receptor α ( n = 24, 89%), and NG2 ( n = 23, 85%). The present AO also consisted of heterogeneous cell populations that were positive for nestin ( n = 13 of 27, 48%), glial fibrillary acidic protein ( n = 5, 19%), doublecortin ( n = 22, 82%), and βIII-tubulin ( n = 15, 56%). Moreover, cultured AO cells obtained from 1 case retained expression of OPC markers and exhibited multipotent characteristics in a serum culture condition. Overall, the findings suggest that transformed multipotent OPCs may be a potential origin of canine AO.

Revisit the Candidacy of Brain Cell Types as the Cell(s) of Origin for Human High-Grade Glioma

High-grade glioma, particularly, glioblastoma, is the most aggressive cancer of the central nervous system (CNS) in adults. Due to its heterogeneous nature, glioblastoma almost inevitably relapses after surgical resection and radio-/chemotherapy, and is thus highly lethal and associated with a dismal prognosis. Identifying the cell of origin has been considered an important aspect in understanding tumor heterogeneity, thereby holding great promise in designing novel therapeutic strategies for glioblastoma. Taking advantage of genetic lineage-tracing techniques, performed mainly on genetically engineered mouse models (GEMMs), multiple cell types in the CNS have been suggested as potential cells of origin for glioblastoma, among which adult neural stem cells (NSCs) and oligodendrocyte precursor cells (OPCs) are the major candidates. However, it remains highly debated whether these cell types are equally capable of transforming in patients, given that in the human brain, some cell types divide so slowly, therefore may never have a chance to transform. With the recent advances in studying adult NSCs and OPCs, particularly from the perspective of comparative biology, we now realize that notable differences exist among mammalian species. These differences have critical impacts on shaping our understanding of the cell of origin of glioma in humans. In this perspective, we update the current progress in this field and clarify some misconceptions with inputs from important findings about the biology of adult NSCs and OPCs. We propose to re-evaluate the cellular origin candidacy of these cells, with an emphasis on comparative studies between animal models and humans.

BRAF and MEK Inhibitors Influence the Function of Reprogrammed T Cells: Consequences for Adoptive T-Cell Therapy

BRAF and MEK inhibitors (BRAFi/MEKi), the standard treatment for patients with BRAF^V600 mutated melanoma, are currently explored in combination with various immunotherapies, notably checkpoint inhibitors and adoptive transfer of receptor-transfected T cells. Since two BRAFi/MEKi combinations with similar efficacy are approved, potential differences in their effects on immune cells would enable a rational choice for triple therapies. Therefore, we characterized the influence of the clinically approved BRAFi/MEKi combinations dabrafenib (Dabra) and trametinib (Tram) vs. vemurafenib (Vem) and cobimetinib (Cobi) on the activation and functionality of chimeric antigen receptor (CAR)-transfected T cells. We co-cultured CAR-transfected CD8⁺ T cells and target cells with clinically relevant concentrations of the inhibitors and determined the antigen-induced cytokine secretion. All BRAFi/MEKi reduced this release as single agents, with Dabra having the mildest inhibitory effect, and Dabra + Tram having a clearly milder inhibitory effect than Vem + Cobi. A similar picture was observed for the upregulation of the activation markers CD25 and CD69 on CAR-transfected T cells after antigen-specific stimulation. Most importantly, the cytolytic capacity of the CAR-T cells was significantly inhibited by Cobi and Vem + Cobi, whereas the other kinase inhibitors showed no effect. Therefore, the combination Dabra + Tram would be more suitable for combining with T-cell-based immunotherapy than Vem + Cobi.

Proteoglycans remodeling in cancer: Underlying molecular mechanisms

Extracellular matrix is a highly dynamic macromolecular network. Proteoglycans are major components of extracellular matrix playing key roles in its structural organization and cell signaling contributing to the control of numerous normal and pathological processes. As multifunctional molecules, proteoglycans participate in various cell functions during morphogenesis, wound healing, inflammation and tumorigenesis. Their interactions with matrix effectors, cell surface receptors and enzymes enable them with unique properties. In malignancy, extensive remodeling of tumor stroma is associated with marked alterations in proteoglycans' expression and structural variability. Proteoglycans exert diverse functions in tumor stroma in a cell-specific and context-specific manner and they mainly contribute to the formation of a permissive provisional matrix for tumor growth affecting tissue organization, cell-cell and cell-matrix interactions and tumor cell signaling. Proteoglycans also modulate cancer cell phenotype and properties, the development of drug resistance and tumor stroma angiogenesis. This review summarizes the proteoglycans remodeling and their novel biological roles in malignancies with particular emphasis to the underlying molecular mechanisms.

NG2 Proteoglycan Enhances Brain Tumor Progression by Promoting Beta-1 Integrin Activation in both Cis and Trans Orientations

By physically interacting with beta-1 integrins, the NG2 proteoglycan enhances activation of the integrin heterodimers. In glioma cells, co-localization of NG2 and 31 integrin in individual cells (cis interaction) can be demonstrated by immunolabeling, and the NG2-integrin interaction can be confirmed by co-immunoprecipitation. NG2-dependent integrin activation is detected via use of conformationally sensitive monoclonal antibodies that reveal the activated state of the beta-1 subunit in NG2-positive versus NG2-negative cells. NG2-dependent activation of beta-1 integrins triggers downstream activation of FAK and PI3K/Akt signaling, resulting in increased glioma cell proliferation, motility, and survival. Similar NG2-dependent cis activation of beta-1 integrins occurs in microvascular pericytes, leading to enhanced proliferation and motility of these vascular cells. Surprisingly, pericyte NG2 is also able to promote beta-1 integrin activation in closely apposed endothelial cells (trans interaction). Enhanced beta-1 signaling in endothelial cells promotes endothelial maturation by inducing the formation of endothelial junctions, resulting in increased barrier function of the endothelium and increased basal lamina assembly. NG2-dependent beta-1 integrin signaling is therefore important for tumor progression by virtue of its affects not only on the tumor cells themselves, but also on the maturation and function of tumor blood vessels.

The emerging role of NG2 in pediatric diffuse intrinsic pontine glioma

Diffuse intrinsic pontine gliomas (DIPGs) have a dismal prognosis and are poorly understood brain cancers. Receptor tyrosine kinases stabilized by neuron-glial antigen 2 (NG2) protein are known to induce gliomagenesis. Here, we investigated NG2 expression in a cohort of DIPG specimens (n= 50). We demonstrate NG2 expression in the majority of DIPG specimens tested and determine that tumors harboring histone 3.3 mutation express the highest NG2 levels. We further demonstrate that microRNA 129-2 (miR129-2) is downregulated and hypermethylated in human DIPGs, resulting in the increased expression of NG2. Treatment with 5-Azacytidine, a methyltransferase inhibitor, results in NG2 downregulation in DIPG primary tumor cells in vitro. NG2 expression is altered (symmetric segregation) in mitotic human DIPG and mouse tumor cells. These mitotic cells co-express oligodendrocyte (Olig2) and astrocyte (glial fibrillary acidic protein, GFAP) markers, indicating lack of terminal differentiation. NG2 knockdown retards cellular migration in vitro, while NG2 expressing neurospheres are highly tumorigenic in vivo, resulting in rapid growth of pontine tumors. NG2 expression is targetable in vivo using miR129-2 indicating a potential avenue for therapeutic interventions. This data implicates NG2 as a molecule of interest in DIPGs especially those with H3.3 mutation.

The Role of NG2 Proteoglycan in Glioma

Neuron glia antigen-2 ((NG2), also known as chondroitin sulphate proteoglycan 4, or melanoma-associated chondroitin sulfate proteoglycan) is a type-1 membrane protein expressed by many central nervous system (CNS) cells during development and differentiation and plays a critical role in proliferation and angiogenesis. ‘NG2’ often references either the protein itself or the highly proliferative and undifferentiated glial cells expressing high levels of NG2 protein. NG2 glia represent the fourth major type of neuroglia in the mammalian nervous system and are classified as oligodendrocyte progenitor cells by virtue of their committed oligodendrocyte generation in developing and adult brain. Here, we discuss NG2 glial cells as well as NG2 protein and its expression and role with regards to CNS neoplasms as well as its potential as a therapeutic target for treating childhood CNS cancers.

Stability and activity of MCSP-specific chimeric antigen receptors (CARs) depend on the scFv antigen-binding domain and the protein backbone

Chimeric antigen receptor (CAR)-modified T cells emerged as effective tools in the immunotherapy of cancer but can produce severe on-target off-tissue toxicities. This risk can conceivably be overcome, at least partially, by transient transfection. The design of CARs, however, has so far not been optimized for use in non-permanent T cell modification. Here we compared the performance of T cells modified with three different first- and second-generation CARs, each specific for MCSP (HMW-MAA) which is commonly expressed by melanoma cells. Upon RNA transfer, the expression of all receptors was limited in time. The second-generation CARs, which combined CD28-CD3ζ signaling, were expressed at higher levels and more prolonged than first-generation CARs with CD3ζ only. The CD28 domain increased the cytokine production, but had only an indirect effect on the lytic capacity, by prolonging the CAR expression. Especially for the second-generation CARs, the scFv clearly impacted the level and duration of CAR expression and the T cell performance. Thus, we identified a CAR high in both expression and anti-tumor cell reactivity. T cells transfected with this CAR increased the mean survival time of mice after challenge with melanoma cells. To facilitate clinical application, this CAR was used to redirect T cells from late-stage melanoma patients by RNA transfection. These T cells mediated effective antigen-specific tumor cell lysis and release of pro-inflammatory cytokines, even after cryoconservation of the transfected T cells. Taken together, the analysis identified a CAR with superior anti-melanoma performance after RNA transfer which is a promising candidate for clinical exploration.

Theranostic impact of NG2/CSPG4 proteoglycan in cancer

NG2/CSPG4 is an unusual cell-membrane integral proteoglycan widely recognized to be a prognostic factor, a valuable tool for ex vivo and non-invasive molecular diagnostics and, by virtue of its tight association with malignancy, a tantalizing therapeutic target in several tumour types. Although the biology behind its involvement in cancer progression needs to be better understood, implementation of NG2/CSPG4 in the routine clinical practice is attainable and has the potential to contribute to an improved individualized management of cancer patients. In this context, its polymorphic nature seems to be particularly valuable in the effort to standardize informative diagnostic procedures and consolidate forcible immunotherapeutic treatment strategies. We discuss here the underpinnings for this potential and highlight the benefits of taking advantage of the intra-tumour and inter-patient variability in the regulation of NG2/CSPG4 expression. We envision that NG2/CSPG4 may effectively be exploited in therapeutic interventions aimed at averting resistance to target therapy agents and at interfering with secondary lesion formation and/or tumour recurrence.

Cell of origin for malignant gliomas and its implication in therapeutic development

Malignant glioma remains incurable despite tremendous advancement in basic research and clinical practice. The identification of the cell(s) of origin should provide deep insights into leverage points for one to halt disease progression. Here we summarize recent studies that support the notion that neural stem cell (NSC), astrocyte, and oligodendrocyte precursor cell (OPC) can all serve as the cell of origin. We also lay out important considerations on technical rigor for further exploring this subject. Finally, we share perspectives on how one could apply the knowledge of cell of origin to develop effective treatment methods. Although it will be a difficult battle, victory should be within reach as along as we continue to assimilate new information and facilitate the collaboration among basic scientists, translational researchers, and clinicians.

Diversified expression of NG2/CSPG4 isoforms in glioblastoma and human foetal brain identifies pericyte subsets

NG2/CSPG4 is a complex surface-associated proteoglycan (PG) recognized to be a widely expressed membrane component of glioblastoma (WHO grade IV) cells and angiogenic pericytes. To determine the precise expression pattern of NG2/CSPG4 on glioblastoma cells and pericytes, we generated a panel of >60 mouse monoclonal antibodies (mAbs) directed against the ectodomain of human NG2/CSPG4, partially characterized the mAbs, and performed a high-resolution distributional mapping of the PG in human foetal, adult and glioblastoma-affected brains. The reactivity pattern initially observed on reference tumour cell lines indicated that the mAbs recognized 48 immunologically distinct NG2/CSPG4 isoforms, and a total of 14 mAbs was found to identify NG2/CSPG4 isoforms in foetal and neoplastic cerebral sections. These were consistently absent in the adult brain, but exhibited a complementary expression pattern in angiogenic vessels of both tumour and foetal tissues. Considering the extreme pleomorphism of tumour areas, and with the aim of subsequently analysing the distributional pattern of the NG2/CSPG4 isoforms on similar histological vessel typologies, a preliminary study was carried out with endothelial cell and pericyte markers, and with selected vascular basement membrane (VBM) components. On both tumour areas characterized by 'glomeruloid' and 'garland vessels', which showed a remarkably similar cellular and molecular organization, and on developing brain vessels, spatially separated, phenotypically diversified pericyte subsets with a polarized expression of key surface components, including NG2/CSPG4, were disclosed. Interestingly, the majority of the immunolocalized NG2/CSPG4 isoforms present in glioblastoma tissue were present in foetal brain, except for one isoform that seemed to be exclusive of tumour cells, being absent in foetal brain. The results highlight an unprecedented, complex pattern of NG2/CSPG4 isoform expression in foetal and neoplastic CNS, discriminating between phenotype-specific and neoplastic versus non-neoplastic variants of the PG, thus opening up vistas for more selective immunotherapeutic targeting of brain tumours.

Glioblastoma-initiating cells: relationship with neural stem cells and the micro-environment

Glioblastoma multiforme (GBM, WHO grade IV) is the most common and lethal subtype of primary brain tumor with a median overall survival of 15 months from the time of diagnosis. The presence in GBM of a cancer population displaying neural stem cell (NSC) properties as well as tumor-initiating abilities and resistance to current therapies suggests that these glioblastoma-initiating cells (GICs) play a central role in tumor development and are closely related to NSCs. However, it is nowadays still unclear whether GICs derive from NSCs, neural progenitor cells or differentiated cells such as astrocytes or oligodendrocytes. On the other hand, NSCs are located in specific regions of the adult brain called neurogenic niches that have been shown to control critical stem cell properties, to nourish NSCs and to support their self-renewal. This “seed-and-soil” relationship has also been adapted to cancer stem cell research as GICs also require a specific micro-environment to maintain their “stem cell” properties. In this review, we will discuss the controversies surrounding the origin and the identification of GBM stem cells and highlight the micro-environment impact on their biology.

A novel, diffusely infiltrative xenograft model of human anaplastic oligodendroglioma with mutations in FUBP1, CIC, and IDH1

Oligodendroglioma poses a biological conundrum for malignant adult human gliomas: it is a tumor type that is universally incurable for patients, and yet, only a few of the human tumors have been established as cell populations in vitro or as intracranial xenografts in vivo. Their survival, thus, may emerge only within a specific environmental context. To determine the fate of human oligodendroglioma in an experimental model, we studied the development of an anaplastic tumor after intracranial implantation into enhanced green fluorescent protein (eGFP) positive NOD/SCID mice. Remarkably after nearly nine months, the tumor not only engrafted, but it also retained classic histological and genetic features of human oligodendroglioma, in particular cells with a clear cytoplasm, showing an infiltrative growth pattern, and harboring mutations of IDH1 (R132H) and of the tumor suppressor genes, FUBP1 and CIC. The xenografts were highly invasive, exhibiting a distinct migration and growth pattern around neurons, especially in the hippocampus, and following white matter tracts of the corpus callosum with tumor cells accumulating around established vasculature. Although tumors exhibited a high growth fraction in vivo, neither cells from the original patient tumor nor the xenograft exhibited significant growth in vitro over a six-month period. This glioma xenograft is the first to display a pure oligodendroglioma histology and expression of R132H. The unexpected property, that the cells fail to grow in vitro even after passage through the mouse, allows us to uniquely investigate the relationship of this oligodendroglioma with the in vivo microenvironment.

p53 isoform profiling in glioblastoma and injured brain

The tumor suppressor p53 has been found to be the most commonly mutated gene in human cancers; however, the frequency of p53 mutations varies from 10 to 70% across different cancer types. This variability can partly be explained by inactivating mechanisms aside from direct genomic polymorphisms. The p53 gene encodes 12 isoforms, some of which can modulate full-length p53 activity in cancer. In this study, we characterized p53 isoform expression patterns in glioblastoma, gliosis, non-tumor brain and neural progenitor cells by SDS-PAGE, immunoblot, mass spectrometry and reverse transcription-PCR. We found that the most consistently expressed isoform in glioblastoma, Δ40p53, was uniquely expressed in regenerative processes, such as those involving neural progenitor cells and gliosis compared with tumor samples. Isoform profiling of glioblastoma tissues revealed the presence of both Δ40p53 and full-length p53, neither of which were detected in non-tumor cerebral cortex. Upon xenograft propagation of tumors, p53 levels increased. The variability of overall p53 expression and relative levels of isoforms suggest fluctuations in subpopulations of cells with greater or lesser capacity for proliferation, which can change as the tumor evolves under different growth conditions.

MAPK pathway activation in pilocytic astrocytoma

Pilocytic astrocytoma (PA) is the most common tumor of the pediatric central nervous system (CNS). A body of research over recent years has demonstrated a key role for mitogen-activated protein kinase (MAPK) pathway signaling in the development and behavior of PAs. Several mechanisms lead to activation of this pathway in PA, mostly in a mutually exclusive manner, with constitutive BRAF kinase activation subsequent to gene fusion being the most frequent. The high specificity of this fusion to PA when compared with other CNS tumors has diagnostic utility. In addition, the frequency of alteration of this key pathway provides an opportunity for molecularly targeted therapy in this tumor. Here, we review the current knowledge on mechanisms of MAPK activation in PA and some of the downstream consequences of this activation, which are now starting to be elucidated both in vitro and in vivo, as well as clinical considerations and possible future directions.

On the origin of glioma

Glioma is the most frequent primary brain tumor of adults that has a presumably glial origin. Although our knowledge regarding molecular mechanisms and signaling pathways involved in gliomagenesis has increased immensely during the past decade, high-grade glioma remains a lethal disease with dismal prognosis. The failure of current therapies has to a large extent been ascribed the functional heterogeneity of glioma cells. One reason for this heterogeneity is most certainly the large number of variations in genetic alterations that can be found in high-grade gliomas. Another factor that may influence glioma heterogeneity could be the cell type from which the glioma is initiated. The cell of origin for glioma is still undefined, and additional knowledge about this issue may prove critical for a more complete understanding of glioma biology. Based on information from patients, developmental biology, and experimental glioma models, the most putative target cells include astrocytes, neural stem cells, and oligodendrocyte precursor cells, which are all discussed in more detail in this article. Animal modeling of glioma suggests that these three cell types have the capability to be the origin of glioma, and we have reason to believe that, depending on the initiating cell type, prognosis and response to therapy may be significantly different. Thus, it is essential to explore further the role of cellular origin in glioma.

The cellular origin for malignant glioma and prospects for clinical advancements

Glioma remains incurable despite great advancements in medicine. Targeting the cell of origin for gliomas could bring great hope for patients. However, as a collection of diverse diseases, each subtype of glioma could derive from a distinct cell of origin. To resolve such a complex problem, one must use multiple research approaches to gain deep insights. Here we review current evidence regarding the cell of origin from clinical observations, whole-genome molecular pathology and glioma animal models. We conclude that neural stem cells, glial progenitors (including oligodendrocyte progenitor cells) and astrocytes could all serve as cells of origin for gliomas, and that cells incurring initial mutations (cells of mutation) might not transform, while their progeny cells could instead transform and act as cells of origin. Further studies with multidisciplinary approaches are needed to link each subtype to a particular cell of origin, and to develop effective therapies that target the signaling network within these cells.

Roles of NG2 glial cells in diseases of the central nervous system

NG2 cells are a novel distinct class of central nervous system (CNS) glial cells, characterized by the expression of the chondroitin sulfate proteoglycan NG2. They have been detected in a variety of human CNS diseases. As morphological, physiological and biomolecular studies of NG2 cells have been conducted, their roles have been gradually revealed. Research on cellular and molecular mechanisms in the pathophysiological state was built on the preliminary findings of their physiological functions; and in turn, this helps to clarify their physiological roles and leads to the identification of novel therapeutic targets. This review summarizes recent findings regarding the potential roles of NG2 cells in traumatic brain injury, multiple sclerosis, glioma, epilepsy, Alzheimer's disease and electroconvulsive therapy for depression.

Expression of the progenitor marker NG2/CSPG4 predicts poor survival and resistance to ionising radiation in glioblastoma

Glioblastoma (GBM) is a highly aggressive brain tumour, where patients respond poorly to radiotherapy and exhibit dismal survival outcomes. The mechanisms of radioresistance are not completely understood. However, cancer cells with an immature stem-like phenotype are hypothesised to play a role in radioresistance. Since the progenitor marker neuron-glial-2 (NG2) has been shown to regulate several aspects of GBM progression in experimental systems, we hypothesised that its expression would influence the survival of GBM patients. Quantification of NG2 expression in 74 GBM biopsies from newly diagnosed and untreated patients revealed that 50% express high NG2 levels on tumour cells and associated vessels, being associated with significantly shorter survival. This effect was independent of age at diagnosis, treatment received and hypermethylation of the O(6)-methylguanine methyltransferase (MGMT) DNA repair gene promoter. NG2 was frequently co-expressed with nestin and vimentin but rarely with CD133 and the NG2 positive tumour cells harboured genetic aberrations typical for GBM. 2D proteomics of 11 randomly selected biopsies revealed upregulation of an antioxidant, peroxiredoxin-1 (PRDX-1), in the shortest surviving patients. Expression of PRDX-1 was associated with significantly reduced products of oxidative stress. Furthermore, NG2 expressing GBM cells showed resistance to ionising radiation (IR), rapidly recognised DNA damage and effectuated cell cycle checkpoint signalling. PRDX-1 knockdown transiently slowed tumour growth rates and sensitised them to IR in vivo. Our data establish NG2 as an important prognostic factor for GBM patient survival, by mediating resistance to radiotherapy through induction of ROS scavenging enzymes and preferential DNA damage signalling.

NG2 expression in glioblastoma identifies an actively proliferating population with an aggressive molecular signature

Glioblastoma multiforme (GBM) is the most common type of primary brain tumor and a highly malignant and heterogeneous cancer. Current conventional therapies fail to eradicate or curb GBM cell growth. Hence, exploring the cellular and molecular basis of GBM cell growth is vital to develop novel therapeutic approaches. Neuroglia (NG)-2 is a transmembrane proteoglycan expressed by NG2+ progenitors and is strongly linked to cell proliferation in the normal brain. By using NG2 as a biomarker we identify a GBM cell population (GBM NG2+ cells) with robust proliferative, clonogenic, and tumorigenic capacity. We show that a significant proportion (mean 83%) of cells proliferating in the tumor mass express NG2 and that over 50% of GBM NG2+ cells are proliferating. Compared with the GBM NG2- cells from the same tumor, the GBM of NG2+ cells overexpress genes associated with aggressive tumorigenicity, including overexpression of Mitosis and Cell Cycling Module genes (e.g., MELK, CDC, MCM, E2F), which have been previously shown to correlate with poor survival in GBM. We also show that the coexpression pattern of NG2 with other glial progenitor markers in GBM does not recapitulate that described in the normal brain. The expression of NG2 by such an aggressive and actively cycling GBM population combined with its location on the cell surface identifies this cell population as a potential therapeutic target in a subset of patients with GBM.

Targeting the NG2/CSPG4 proteoglycan retards tumour growth and angiogenesis in preclinical models of GBM and melanoma

Aberrant expression of the progenitor marker Neuron-glia 2 (NG2/CSPG4) or melanoma proteoglycan on cancer cells and angiogenic vasculature is associated with an aggressive disease course in several malignancies including glioblastoma multiforme (GBM) and melanoma. Thus, we investigated the mechanism of NG2 mediated malignant progression and its potential as a therapeutic target in clinically relevant GBM and melanoma animal models. Xenografting NG2 overexpressing GBM cell lines resulted in increased growth rate, angiogenesis and vascular permeability compared to control, NG2 negative tumours. The effect of abrogating NG2 function was investigated after intracerebral delivery of lentivirally encoded shRNAs targeting NG2 in patient GBM xenografts as well as in established subcutaneous A375 melanoma tumours. NG2 knockdown reduced melanoma proliferation and increased apoptosis and necrosis. Targeting NG2 in two heterogeneous GBM xenografts significantly reduced tumour growth and oedema levels, angiogenesis and normalised vascular function. Vascular normalisation resulted in increased tumour invasion and decreased apoptosis and necrosis. We conclude that NG2 promotes tumour progression by multiple mechanisms and represents an amenable target for cancer molecular therapy.

Platelet-derived growth factor receptor (PDGFR) expression in primary spinal cord gliomas

Abnormal signaling through the platelet-derived growth factor receptor (PDGFR) has been proposed as a possible mechanism of spinal cord glioma initiation and progression. However, the extent of PDGFR expression in human spinal cord gliomas remains unknown. In this study we perform immunohistochemical analysis of PDGFRα expression in a series of 33 primary intramedullary spinal cord gliomas of different types and grades. PDGFRα was seen to be expressed in a significant subset of these tumors across all major glioma types including ependymoma, oligodendroglioma, pilocytic astrocytoma, astrocytoma, and glioblastoma. These results support the hypothesis that growth factor signaling through the PDGFR may be important for the development of at least a subset of human spinal cord gliomas. Further studies investigating the prognostic significance of PDGFR expression as well as the role of PDGF signaling on the development of intramedullary spinal cord gliomas are warranted.

Genetic modeling of gliomas in mice: new tools to tackle old problems

The recently published comprehensive profiles of genomic alterations in glioma have led to a refinement in our understanding of the molecular events that underlie this cancer. Using state-of-the-art genomic tools, several laboratories have created and characterized accurate genetically engineered mouse models of glioma based on specific genetic alterations observed in human tumors. These in vivo brain tumor models faithfully recapitulate the histopathology, etiology, and biology of gliomas and provide an exceptional experimental system to discover novel therapeutic targets and test therapeutic agents. This review focuses on mouse models of glioma with a special emphasis on genetically engineered models developed around key genetic glioma signature mutations in the PDGFR, EGFR, and NF1 genes and pathways. The resulting animal models have provided insight into many fundamental and mechanistic facets of tumor initiation, maintenance and resistance to therapeutic intervention and will continue to do so in the future.

Non-stem cell origin for oligodendroglioma

Malignant astrocytic brain tumors are among the most lethal cancers. Quiescent and therapy-resistant neural stem cell (NSC)-like cells in astrocytomas are likely to contribute to poor outcome. Malignant oligodendroglial brain tumors, in contrast, are therapy sensitive. Using magnetic resonance imaging (MRI) and detailed developmental analyses, we demonstrated that murine oligodendroglioma cells show characteristics of oligodendrocyte progenitor cells (OPCs) and are therapy sensitive, and that OPC rather than NSC markers enriched for tumor formation. MRI of human oligodendroglioma also suggested a white matter (WM) origin, with markers for OPCs rather than NSCs similarly enriching for tumor formation. Our results suggest that oligodendroglioma cells show hallmarks of OPCs, and that a progenitor rather than a NSC origin underlies improved prognosis in patients with this tumor.