Harnessing Microglia and Macrophages for the Treatment of Glioblastoma

Recent advances in biomimetic strategies for the immunotherapy of glioblastoma

Immunotherapy is regarded as one of the most promising approaches for treating tumors, with a multitude of immunotherapeutic thoughts currently under consideration for the lethal glioblastoma (GBM). However, issues with immunotherapeutic agents, such as limited in vivo stability, poor blood-brain barrier (BBB) penetration, insufficient GBM targeting, and represented monotherapy, have hindered the success of immunotherapeutic interventions. Moreover, even with the aid of conventional drug delivery systems, outcomes remain suboptimal. Biomimetic strategies seek to overcome these formidable drug delivery challenges by emulating nature's intelligent structures and functions. Leveraging the variety of biological structures and functions, biomimetic drug delivery systems afford a versatile platform with enhanced biocompatibility for the co-delivery of diverse immunotherapeutic agents. Moreover, their inherent capacity to traverse the BBB and home in on GBM holds promise for augmenting the efficacy of GBM immunotherapy. Thus, this review begins by revisiting the various thoughts and agents on immunotherapy for GBM. Then, the barriers to successful GBM immunotherapy are analyzed, and the corresponding biomimetic strategies are explored from the perspective of function and structure. Finally, the clinical translation's current state and prospects of biomimetic strategy are addressed. This review aspires to provide fresh perspectives on the advancement of immunotherapy for GBM.

Pivotal Role of Cranial Irradiation-Induced Peripheral, Intrinsic, and Brain-Engrafting Macrophages in Malignant Glioma

Malignant (high-grade) gliomas are aggressive intrinsic brain tumors that diffusely infiltrate the brain parenchyma. They comprise of World Health Organization (WHO) grade III and IV gliomas. Ionizing radiation or irradiation (IR) is frequently utilized in the treatment of both primary as well as metastatic brain tumors. On the contrary, macrophages (MΦ) are the most copious infiltrating immune cells of all the different cell types colonizing glioma. MΦ at tumor milieu are referred to as tumor-associated macrophages (TAMΦ). In malignant gliomas milieu, TAMΦ are also polarized into two distinct phenotypes such as M1 TAMΦ or M2 TAMΦ, which are capable of inhibiting or promoting tumor growth, respectively. Cranial-IR such as x- and γ-IR are sufficient to induce the migration of peripherally derived MΦ into the brain parenchyma. The IR facilitate a more immunosuppressive milieu via the stimulation of efferocytosis in TAMΦ, and an upsurge of tumor cell engulfment by TAMΦ exhibited detrimental effect of the anti-tumoral immune response in glioma. The MΦ inside the tumor mass are associated with multiple phenomena that include IR resistance and enrichment of the M2 MΦ after IR is able to facilitate glioblastoma multiforme (GBM) recurrence. Reviews on the role of cranial IR-induced peripheral and brain-engrafting macrophages (BeMΦ) in glioma are lacking. Specifically, most studies on peripheral, intrinsic as well as beMΦ on IR focus on WHO grade III and IV. Thus, this review precisely focuses primary on WHO grade III as well as IV gliomas.

MALT1 protease inhibition restrains glioblastoma progression by reversing tumor-associated macrophage-dependent immunosuppression

MALT1 protease is an intracellular signaling molecule that promotes tumor progression via cancer cell-intrinsic and cancer cell-extrinsic mechanisms. MALT1 has been mostly studied in lymphocytes, and little is known about its role in tumor-associated macrophages. Here, we show that MALT1 plays a key role in glioblastoma (GBM)-associated macrophages. Mechanistically, GBM tumor cells induce a MALT1-NF-κB signaling axis within macrophages, leading to macrophage migration and polarization toward an immunosuppressive phenotype. Inactivation of MALT1 protease promotes transcriptional reprogramming that reduces migration and restores a macrophage "M1-like" phenotype. Preclinical in vivo analysis shows that MALT1 inhibitor treatment results in increased immuno-reactivity of GBM-associated macrophages and reduced GBM tumor growth. Further, the addition of MALT1 inhibitor to temozolomide reduces immunosuppression in the tumor microenvironment, which may enhance the efficacy of this standard-of-care chemotherapeutic. Together, our findings suggest that MALT1 protease inhibition represents a promising macrophage-targeted immunotherapeutic strategy for the treatment of GBM.

Ultrasound-Activated Piezoelectric Nanoparticles Trigger Microglia Activity Against Glioblastoma Cells

Glioblastoma multiforme (GBM) is the most aggressive brain cancer, characterized by a rapid and drug-resistant progression. GBM "builds" around its primary core a genetically heterogeneous tumor-microenvironment (TME), recruiting surrounding healthy brain cells by releasing various intercellular signals. Glioma-associated microglia (GAM) represent the largest population of collaborating cells, which, in the TME, usually exhibit the anti-inflammatory M2 phenotype, thus promoting an immunosuppressing environment that helps tumor growth. Conversely, "classically activated" M1 microglia could provide proinflammatory and antitumorigenic activity, expected to exert a beneficial effect in defeating glioblastoma. In this work, an immunotherapy approach based on proinflammatory modulation of the GAM phenotype is proposed, through a controlled and localized electrical stimulation. The developed strategy relies on the wireless ultrasonic excitation of polymeric piezoelectric nanoparticles coated with GBM cell membrane extracts, to exploit homotypic targeting in antiglioma applications. Such camouflaged nanotransducers locally generate electrical cues on GAM membranes, activating their M1 phenotype and ultimately triggering a promising anticancer activity. Collected findings open new perspectives in the modulation of immune cell activities through "smart" nanomaterials and, more specifically, provide an innovative auspicious tool in glioma immunotherapy.

Interleukin-21 Influences Glioblastoma Course: Biological Mechanisms and Therapeutic Potential

Brain tumors represent a heterogeneous group of neoplasms involving the brain or nearby tissues, affecting populations of all ages with a high incidence worldwide. Among the primary brain tumors, the most aggressive and also the most common is glioblastoma (GB), a type of glioma that falls into the category of IV-grade astrocytoma. GB often leads to death within a few months after diagnosis, even if the patient is treated with available therapies; for this reason, it is important to continue to discover new therapeutic approaches to allow for a better survival rate of these patients. Immunotherapy, today, seems to be one of the most innovative types of treatment, based on the ability of the immune system to counteract various pathologies, including cancer. In this context, interleukin 21 (IL-21), a type I cytokine produced by natural killer (NK) cells and CD4+ T lymphocytes, appears to be a valid target for new therapies since this cytokine is involved in the activation of innate and adaptive immunity. To match this purpose, our review deeply evaluated how IL-21 could influence the progression of GB, analyzing its main biological processes and mechanisms while evaluating the potential use of the latest available therapies.

Uptake of H-ferritin by Glioblastoma stem cells and its impact on their invasion capacity

PURPOSE

Iron acquisition is key to maintaining cell survival and function. Cancer cells in general are considered to have an insatiable iron need. Iron delivery via the transferrin/transferrin receptor pathway has been the canonical iron uptake mechanism. Recently, however, our laboratory and others have explored the ability of ferritin, particularly the H-subunit, to deliver iron to a variety of cell types. Here, we investigate whether Glioblastoma (GBM) initiating cells (GICs), a small population of stem-like cells, are known for their iron addiction and invasive nature acquire exogenous ferritin, as a source of iron. We further assess the functional impact of ferritin uptake on the invasion capacity of the GICs.

METHODS

To establish that H-ferritin can bind to human GBM, tissue-binding assays were performed on samples collected at the time of surgery. To interrogate the functional consequences of H-ferritin uptake, we utilized two patient-derived GIC lines. We further describe H-ferritin's impact on GIC invasion capacity using a 3D invasion assay.

RESULTS

H-ferritin bound to human GBM tissue at the amount of binding was influenced by sex. GIC lines showed uptake of H-ferritin protein via transferrin receptor. FTH1 uptake correlated with a significant decrease in the invasion capacity of the cells. H-ferritin uptake was associated with a significant decrease in the invasion-related protein Rap1A.

CONCLUSION

These findings indicate that extracellular H-ferritin participates in iron acquisition to GBMs and patient-derived GICs. The functional significance of the increased iron delivery by H-ferritin is a decreased invasion capacity of GICs potentially via reduction of Rap1A protein levels.

Macrophage's role in solid tumors: two edges of a sword

The tumor microenvironment is overwhelmingly dictated by macrophages, intimately affiliated with tumors, exercising pivotal roles in multiple processes, including angiogenesis, extracellular matrix reconfiguration, cellular proliferation, metastasis, and immunosuppression. They further exhibit resilience to chemotherapy and immunotherapy via meticulous checkpoint blockades. When appropriately stimulated, macrophages can morph into a potent bidirectional component of the immune system, engulfing malignant cells and annihilating them with cytotoxic substances, thus rendering them intriguing candidates for therapeutic targets. As myelomonocytic cells relentlessly amass within tumor tissues, macrophages rise as prime contenders for cell therapy upon the development of chimeric antigen receptor effector cells. Given the significant incidence of macrophage infiltration correlated with an unfavorable prognosis and heightened resistance to chemotherapy in solid tumors, we delve into the intricate role of macrophages in cancer propagation and their promising potential in confronting four formidable cancer variants-namely, melanoma, colon, glioma, and breast cancers.

Glioblastoma Microenvironment and Invasiveness: New Insights and Therapeutic Targets

Glioblastoma (GBM) is the most common and malignant primary brain cancer in adults. Without treatment the mean patient survival is approximately 6 months, which can be extended to 15 months with the use of multimodal therapies. The low effectiveness of GBM therapies is mainly due to the tumor infiltration into the healthy brain tissue, which depends on GBM cells' interaction with the tumor microenvironment (TME). The interaction of GBM cells with the TME involves cellular components such as stem-like cells, glia, endothelial cells, and non-cellular components such as the extracellular matrix, enhanced hypoxia, and soluble factors such as adenosine, which promote GBM's invasiveness. However, here we highlight the role of 3D patient-derived glioblastoma organoids cultures as a new platform for study of the modeling of TME and invasiveness. In this review, the mechanisms involved in GBM-microenvironment interaction are described and discussed, proposing potential prognosis biomarkers and new therapeutic targets.

Glioma-associated microglia/macrophages (GAMs) in glioblastoma: Immune function in the tumor microenvironment and implications for immunotherapy

Glioma is a mixed solid tumor composed of neoplastic and non-neoplastic components. Glioma-associated macrophages and microglia (GAMs) are crucial elements of the glioma tumor microenvironment (TME), regulating tumor growth, invasion, and recurrence. GAMs are also profoundly influenced by glioma cells. Recent studies have revealed the intricate relationship between TME and GAMs. In this updated review, we provide an overview of the interaction between glioma TME and GAMs based on previous studies. We also summarize a series of immunotherapies targeting GAMs, including clinical trials and preclinical studies. Specifically, we discuss the origin of microglia in the central nervous system and the recruitment of GAMs in the glioma background. We also cover the mechanisms through which GAMs regulate various processes associated with glioma development, such as invasiveness, angiogenesis, immunosuppression, recurrence, etc. Overall, GAMs play a significant role in the tumor biology of glioma, and a better understanding of the interaction between GAMs and glioma could catalyze the development of new and effective immunotherapies for this deadly malignancy.

Fluoride in the Central Nervous System and Its Potential Influence on the Development and Invasiveness of Brain Tumours-A Research Hypothesis

The purpose of this review is to attempt to outline the potential role of fluoride in the pathogenesis of brain tumours, including glioblastoma (GBM). In this paper, we show for the first time that fluoride can potentially affect the generally accepted signalling pathways implicated in the formation and clinical course of GBM. Fluorine compounds easily cross the blood-brain barrier. Enhanced oxidative stress, disruption of multiple cellular pathways, and microglial activation are just a few examples of recent reports on the role of fluoride in the central nervous system (CNS). We sought to present the key mechanisms underlying the development and invasiveness of GBM, as well as evidence on the current state of knowledge about the pleiotropic, direct, or indirect involvement of fluoride in the regulation of these mechanisms in various tissues, including neural and tumour tissue. The effects of fluoride on the human body are still a matter of controversy. However, given the growing incidence of brain tumours, especially in children, and numerous reports on the effects of fluoride on the CNS, it is worth taking a closer look at these mechanisms in the context of brain tumours, including gliomas.

Ferroptosis in Glioma Immune Microenvironment: Opportunity and Challenge

Glioma is the most common intracranial malignant tumor in adults and the 5-year survival rate of glioma patients is extremely poor, even in patients who received Stupp treatment after diagnosis and this forces us to explore more efficient clinical strategies. At this time, immunotherapy shows great potential in a variety of tumor clinical treatments, however, its clinical effect in glioma is limited because of tumor immune privilege which was induced by the glioma immunosuppressive microenvironment, so remodeling the immunosuppressive microenvironment is a practical way to eliminate glioma immunotherapy resistance. Recently, increasing studies have confirmed that ferroptosis, a new form of cell death, plays an important role in tumor progression and immune microenvironment and the crosstalk between ferroptosis and tumor immune microenvironment attracts much attention. This work summarizes the progress studies of ferroptosis in the glioma immune microenvironment.

Single-Cell Transcriptomics Revealed Subtype-Specific Tumor Immune Microenvironments in Human Glioblastomas

Human glioblastoma (GBM), the most aggressive brain tumor, comprises six major subtypes of malignant cells, giving rise to both inter-patient and intra-tumor heterogeneity. The interaction between different tumor subtypes and non-malignant cells to collectively shape a tumor microenvironment has not been systematically characterized. Herein, we sampled the cellular milieu of surgically resected primary tumors from 7 GBM patients using single-cell transcriptome sequencing. A lineage relationship analysis revealed that a neural-progenitor-2-like (NPC2-like) state with high metabolic activity was associated with the tumor cells of origin. Mesenchymal-1-like (MES1-like) and mesenchymal-2-like (MES2-like) tumor cells correlated strongly with immune infiltration and chronic hypoxia niche responses. We identified four subsets of tumor-associated macrophages/microglia (TAMs), among which TAM-1 co-opted both acute and chronic hypoxia-response signatures, implicated in tumor angiogenesis, invasion, and poor prognosis. MES-like GBM cells expressed the highest number of M2-promoting ligands compared to other cellular states while all six states were associated with TAM M2-type polarization and immunosuppression via a set of 10 ligand–receptor signaling pathways. Our results provide new insights into the differential roles of GBM cell subtypes in the tumor immune microenvironment that may be deployed for patient stratification and personalized treatment.

Emerging Concepts on the Role of Extracellular Vesicles and Its Cargo Contents in Glioblastoma-Microglial Crosstalk

Glioblastoma multiforme is the most common, highly aggressive malignant brain tumor which is marked by highest inter- and intra-tumoral heterogeneity. Despite, immunotherapy, and combination therapies developed; the clinical trials often result into large number of failures. Often cancer cells are known to communicate with surrounding cells in tumor microenvironment (TME). Extracellular vesicles (EVs) consisting of diverse cargo mediates this intercellular communication and is believed to modulate the immune function against GBM. Tumor-associated microglia (TAM), though being the resident innate immune cell of CNS, is known to attain pro-tumorigenic M2 phenotype, and this immunomodulation is aided by extracellular vesicle-mediated transfer of oncogenic, immunomodulatory molecules. Besides, oncogenic proteins, long non-coding RNAs (lncRNAs), are believed to carry oncogenic potential, and therefore, understanding the mechanism leading to microglial dysregulation mediated by GBM-derived extracellular vesicle (GDEV) lncRNAs becomes crucial. This review focuses on current understanding of role of GDEV and lncRNA in microglial dysfunction and its potential as a therapeutic target.

The Pivotal Immunoregulatory Functions of Microglia and Macrophages in Glioma Pathogenesis and Therapy

Gliomas are mixed solid tumors composed of both neoplastic and nonneoplastic cells. In glioma microenvironment, the most common nonneoplastic and infiltrating cells are macrophages and microglia. Microglia are the exact phagocytes of the central nervous system, whereas macrophages are myeloid immune cells that are depicted with ardent phagocytosis. Microglia are heterogeneously located in almost all nonoverlapping sections of the brain as well as the spinal cord, while macrophages are derived from circulating monocytes. Microglia and macrophages utilize a variety of receptors for the detection of molecules, particles, and cells that they engulf. Both microglia and peripheral macrophages interact directly with vessels both in the periphery of and within the tumor. In glioma milieu, normal human astrocytes, glioma cells, and microglia all exhibited the ability of phagocytosing glioma cells and precisely apoptotic tumor cells. Also, microglia and macrophages are robustly triggered by the glioma via the expression of chemoattractants such as monocyte chemoattractant protein, stromal-derived factor-1, and macrophage-colony stimulating factor. Glioma-associated microglia and/or macrophages positively correlated with glioma invasiveness, immunosuppression, and patients' poor outcome, making these cells a suitable target for immunotherapeutic schemes.

Tumor Heterogeneity and Molecular Characteristics of Glioblastoma Revealed by Single-Cell RNA-Seq Data Analysis

Glioblastoma multiforme (GBM) is the most common infiltrating lethal tumor of the brain. Tumor heterogeneity and the precise characterization of GBM remain challenging, and the disease-specific and effective biomarkers are not available at present. To understand GBM heterogeneity and the disease prognosis mechanism, we carried out a single-cell transcriptome data analysis of 3389 cells from four primary IDH-WT (isocitrate dehydrogenase wild type) glioblastoma patients and compared the characteristic features of the tumor and periphery cells. We observed that the marker gene expression profiles of different cell types and the copy number variations (CNVs) are heterogeneous in the GBM samples. Further, we have identified 94 differentially expressed genes (DEGs) between tumor and periphery cells. We constructed a tissue-specific co-expression network and protein-protein interaction network for the DEGs and identified several hub genes, including CX3CR1, GAPDH, FN1, PDGFRA, HTRA1, ANXA2 THBS1, GFAP, PTN, TNC, and VIM. The DEGs were significantly enriched with proliferation and migration pathways related to glioblastoma. Additionally, we were able to identify the differentiation state of microglia and changes in the transcriptome in the presence of glioblastoma that might support tumor growth. This study provides insights into GBM heterogeneity and suggests novel potential disease-specific biomarkers which could help to identify the therapeutic targets in GBM.

Friends with Benefits: Chemokines, Glioblastoma-Associated Microglia/Macrophages, and Tumor Microenvironment

Glioma is the most common primary intracranial tumor and has the greatest prevalence of all brain tumors. Treatment resistance and tumor recurrence in GBM are mostly explained by considerable alterations within the tumor microenvironment, as well as extraordinary cellular and molecular heterogeneity. Soluble factors, extracellular matrix components, tissue-resident cell types, resident or newly recruited immune cells together make up the GBM microenvironment. Regardless of many immune cells, a profound state of tumor immunosuppression is supported and developed, posing a considerable hurdle to cancer cells' immune-mediated destruction. Several studies have suggested that various GBM subtypes present different modifications in their microenvironment, although the importance of the microenvironment in treatment response has yet to be determined. Understanding the microenvironment and how it changes after therapies is critical because it can influence the remaining invasive GSCs and lead to recurrence. This review article sheds light on the various components of the GBM microenvironment and their roles in tumoral development, as well as immune-related biological processes that support the interconnection/interrelationship between different cell types. Also, we summarize the current understanding of the modulation of soluble factors and highlight the dysregulated inflammatory chemokine/specific receptors cascades/networks and their significance in tumorigenesis, cancer-related inflammation, and metastasis.

Cell‑based immunotherapy of glioblastoma multiforme (Review)

Glioblastoma multiforme (GBM) is the most aggressive and lethal primary glial brain tumor. It has an unfavorable prognosis and relatively ineffective treatment protocols, with the median survival of patients being ~15 months. Tumor resistance to treatment is associated with its cancer stem cells (CSCs). At present, there is no medication or technologies that have the ability to completely eradicate CSCs, and immunotherapy (IT) is only able to prolong the patient's life. The present review aimed to investigate systemic solutions for issues associated with immunosuppression, such as ineffective IT and the creation of optimal conditions for CSCs to fulfill their lethal potential. The present review also investigated the main methods involved in local immunosuppression treatment, and highlighted the associated disadvantages. In addition, novel treatment options and targets for the elimination and regulation of CSCs with adaptive and active IT are discussed. Antagonists of TGF-β inhibitors, immune checkpoints and other targeted medication are also summarized. The role of normal hematopoietic stem cells (HSCs) in the mechanisms underlying systemic immune suppression development in cases of GBM is analyzed, and the potential reprogramming of HSCs during their interaction with cancer cells is discussed. Moreover, the present review emphasizes the importance of the aforementioned interactions in the development of immune tolerance and the inactivation of the immune system in neoplastic processes. The possibility of solving the problem of systemic immunosuppression during transplantation of donor HSCs is discussed.

Neuroimmunomodulatory Properties of Flavonoids and Derivates: A Potential Action as Adjuvants for the Treatment of Glioblastoma

Glioblastomas (GBMs) are tumors that have a high ability to migrate, invade and proliferate in the healthy tissue, what greatly impairs their treatment. These characteristics are associated with the complex microenvironment, formed by the perivascular niche, which is also composed of several stromal cells including astrocytes, microglia, fibroblasts, pericytes and endothelial cells, supporting tumor progression. Further microglia and macrophages associated with GBMs infiltrate the tumor. These innate immune cells are meant to participate in tumor surveillance and eradication, but they become compromised by GBM cells and exploited in the process. In this review we discuss the context of the GBM microenvironment together with the actions of flavonoids, which have attracted scientific attention due to their pharmacological properties as possible anti-tumor agents. Flavonoids act on a variety of signaling pathways, counteracting the invasion process. Luteolin and rutin inhibit NFκB activation, reducing IL-6 production. Fisetin promotes tumor apoptosis, while inhibiting ADAM expression, reducing invasion. Naringenin reduces tumor invasion by down-regulating metalloproteinases expression. Apigenin and rutin induce apoptosis in C6 cells increasing TNFα, while decreasing IL-10 production, denoting a shift from the immunosuppressive Th2 to the Th1 profile. Overall, flavonoids should be further exploited for glioma therapy.

The multifaceted mechanisms of malignant glioblastoma progression and clinical implications

With the application of high throughput sequencing technologies at single-cell resolution, studies of the tumor microenvironment in glioblastoma, one of the most aggressive and invasive of all cancers, have revealed immense cellular and tissue heterogeneity. A unique extracellular scaffold system adapts to and supports progressive infiltration and migration of tumor cells, which is characterized by altered composition, effector delivery, and mechanical properties. The spatiotemporal interactions between malignant and immune cells generate an immunosuppressive microenvironment, contributing to the failure of effective anti-tumor immune attack. Among the heterogeneous tumor cell subpopulations of glioblastoma, glioma stem cells (GSCs), which exhibit tumorigenic properties and strong invasive capacity, are critical for tumor growth and are believed to contribute to therapeutic resistance and tumor recurrence. Here we discuss the role of extracellular matrix and immune cell populations, major components of the tumor ecosystem in glioblastoma, as well as signaling pathways that regulate GSC maintenance and invasion. We also highlight emerging advances in therapeutic targeting of these components.

A New Perspective on Cancer Therapy: Changing the Treaded Path?

During the last decade, we have persistently addressed the question, “how can the innate immune system be used as a therapeutic tool to eliminate cancer?” A cancerous tumor harbors innate immune cells such as macrophages, which are held in the tumor-promoting M2 state by tumor-cell-released cytokines. We have discovered that these tumor-associated macrophages (TAM) are repolarized into the nitric oxide (NO)-generating tumoricidal M1 state by the dietary agent curcumin (CC), which also causes recruitment of activated natural killer (NK) cells and cytotoxic T (Tc) cells into the tumor, thereby eliminating cancer cells as well as cancer stem cells. Indications are that this process may be NO-dependent. Intriguingly, the maximum blood concentration of CC in mice never exceeds nanomolar levels. Thus, our results submit that even low, transient levels of curcumin in vivo are enough to cause repolarization of the TAM and recruitment NK cells as well as Tc cells to eliminate the tumor. We have observed this phenomenon in two cancer models, glioblastoma and cervical cancer. Therefore, this approach may yield a general strategy to fight cancer. Our mechanistic studies have so far implicated induction of STAT-1 in this M2→M1 switch, but further studies are needed to understand the involvement of other factors such as the lipid metabolites resolvins in the CC-evoked anticancer pathways.

Glioblastoma: What can we do for these patients today and what will we be able to do in the future?

Glioblastoma multiforme (GBM) is an extremely aggressive primary human brain tumor. The median survival of GBM patients is 15 months in case of completing the modern complex treatment protocol. Chemotherapy can help to extend the life expectancy of patients. GBM treatment resistance is associated with cancer stem cells (CSCs). The present paper analyses the main reasons for ineffectiveness of the existing GBM treatment methods and suggests treating CSCs as a complex phenomenon, resulting from the coordinated interaction of normal stem cells and cancer cells (CCs) in immunosuppressive microsurroundings. The GBM treatment strategy is suggested not for only suppressing strategically important signaling pathways in CCs, but also for regulating interaction between normal stem cells and cancer cells. The paper considers the issue of controlling penetrability of the blood-brain barrier that is one of the main challenges in neuro-oncology. Also, the paper suggests the ways of extending life expectancy of GBM patients today and prospects for the near future.

Reduced Serum sRANKL and sTREM2 Levels in High-Grade Gliomas: Association with Prognosis

INTRODUCTION

High-grade gliomas (HGG), including Glioblastoma multiforme (GBM), account for the majority of primary brain tumors. Nevertheless, prognostic and diagnostic biomarkers are quite limited for HGG. The objective of this study was to investigate the prognostic value of sRANKL and sTREM2 levels in HGG patients.

METHODS

Twelve consecutive patients with HGG, 14 patients with non-glial tumors (non-GT) and 20 age and gender-matched healthy controls were recruited. Overall survival duration of the patients was recorded. Pre-operative serum levels of sRANKL and sTREM2 were measured by ELISA. Tumors of HGG patients were analyzed by immunohistochemical staining for p53 and Ki67 and percentage scores were calculated.

RESULTS

Patients with HGG and non-GT showed lower serum sRANKL and sTREM2 levels than healthy individuals. Levels of sRANKL were inversely correlated with the overall survival of patients (p=0.002, R=0.787), while sTREM2 levels were inversely correlated with p53 score (p=0.018, R=-0.666) but not survival.

CONCLUSION

Brain tumor patients show suppressed levels of glial activity biomarkers in the peripheral circulation. Serum sRANKL levels may serve as a potential prognostic biomarker for HGG.

Plasminogen Activator Urokinase Receptor Implies Immunosuppressive Features and Acts as an Unfavorable Prognostic Biomarker in Glioma

BACKGROUND

Clinical outcomes of patients with glioma are still poor, even after standard treatments, including surgery combined with radiotherapy and chemotherapy. New therapeutic strategies and targets for glioma are urgently needed. Plasminogen activator urokinase receptor (PLAUR), a highly glycosylated integral membrane protein, is reported to modulate plasminogen activation and extracellular matrix degradation in many malignant cancers, but its role in gliomas remains unclear.

METHODS

Glioma samples with mRNA sequencing data and clinical information from the Chinese Glioma Genome Atlas (n = 310) data set and The Cancer Genome Atlas (n = 611) data set were collected for this study. Analyses using Kaplan-Meier plots, time-dependent receiver operating characteristic curves, Cox regression, and nomograms were conducted to evaluate the prognostic performance of PLAUR expression. Analyses using Metascape, ESTIMATE, EPIC, and immunohistochemical staining were performed to reveal the potential biological mechanism. The statistical analysis and graphical work were completed using SPSS, R language, and GraphPad Prism.

RESULTS

PLAUR was highly expressed in phenotypes associated with glioma malignancy and could serve as an independent prognostic indicator. Functional analysis revealed the correlation between PLAUR and immune response. Further studies found that samples with higher PLAUR expression were infiltrated with fewer CD8 T cells and many more M2 macrophages. Strong positive correlation was demonstrated between PLAUR expression and some immunosuppressive markers, including immune checkpoints and cytokines. These findings were also confirmed in patient samples.

CONCLUSION

Our results elucidated the clinical significance and immunosuppressive effect of PLAUR in gliomas, which might provide some clues in glioma immunotherapy.

IMPLICATIONS FOR PRACTICE

Although the efficacy of immunotherapy has been verified in other tumors, its application in glioma is impeded because of the unique microenvironment. Tumor-associated macrophages, which are particularly abundant in a glioma mass, contribute much to the immunosuppressive microenvironment and offer new opportunities in glioma immunotherapy. The results of this study identified plasminogen activator urokinase receptor (PLAUR) expression as a potential marker to predict the infiltration of macrophages and the status of immune microenvironment in patients with glioma, suggesting that treatment decisions could be based on PLAUR level when administering immunotherapeutics. The soluble PLAUR in blood and other body fluids would make this approach easy to implement in the clinic.

Macrophages and microglia: the cerberus of glioblastoma

Glioblastoma (GBM) is the most aggressive and deadliest of the primary brain tumors, characterized by malignant growth, invasion into the brain parenchyma, and resistance to therapy. GBM is a heterogeneous disease characterized by high degrees of both inter- and intra-tumor heterogeneity. Another layer of complexity arises from the unique brain microenvironment in which GBM develops and grows. The GBM microenvironment consists of neoplastic and non-neoplastic cells. The most abundant non-neoplastic cells are those of the innate immune system, called tumor-associated macrophages (TAMs). TAMs constitute up to 40% of the tumor mass and consist of both brain-resident microglia and bone marrow-derived myeloid cells from the periphery. Although genetically stable, TAMs can change their expression profiles based upon the signals that they receive from tumor cells; therefore, heterogeneity in GBM creates heterogeneity in TAMs. By interacting with tumor cells and with the other non-neoplastic cells in the tumor microenvironment, TAMs promote tumor progression. Here, we review the origin, heterogeneity, and functional roles of TAMs. In addition, we discuss the prospects of therapeutically targeting TAMs alone or in combination with standard or newly-emerging GBM targeting therapies.

Immune involvement of the contralateral hemisphere in a glioblastoma mouse model

Background

Glioblastoma (GBM) is the most common and deadliest form of brain cancer in adults. Standard treatment, consisting of surgery and radiochemotherapy, only provides a modest survival benefit and is incapable of combating infiltrating GBM cells in other parts of the brain. New therapies in clinical trials, such as anti-programmed cell death 1 immunotherapy, have so far shown limited success in GBM. Moreover, it is unclear how the growth of GBM suppresses the immune system locally at the site of the brain tumor or if distant sites of tumor cell migration are also involved. Invasive GBM cells in brain tissue beyond the primary tumor limit the use of surgery, thus immunotherapy could be beneficial if activated/suppressed immune cells are present in the contralateral hemisphere.

Methods

Here, we used a syngeneic orthotopic GL26 GBM mouse model and multiparameter fluorescence-activated cell sorting analysis to study the phenotype of resident and infiltrating immune cells in both the brain tumor hemisphere and contralateral hemisphere.

Results

We show that lymphoid cells, including tumor antigen-specific CD8⁺ tumor-infiltrating lymphocytes (TILs) are present in the tumor and are characterized by a tolerogenic phenotype based on high immune checkpoint expression. Massive infiltration of myeloid cells is observed, expressing immune checkpoint ligands, suggesting an immune-dependent coinhibitory axis limiting TIL responses. Surprisingly, these phenotypes are paralleled in the contralateral hemisphere, showing that infiltrating immune cells are also present at distant sites, expressing key immune checkpoints and immune checkpoint ligands.

Conclusion

Whole-brain analysis indicates active immune involvement throughout the brain, both at the site of the primary tumor and in the contralateral hemisphere. Using the right combination and timing, immune checkpoint blockade could have the potential to activate immune cells at the site of the brain tumor and at distant sites, thereby also targeting diffusely infiltrating GBM cells.

Mechanisms of invasion in glioblastoma

PURPOSE OF REVIEW

This review provides an overview of recent updates in understanding the mechanisms by which glioblastoma cells interact with their cellular and molecular partners within the microenvironment.

RECENT FINDINGS

We have now a better knowledge of the cell populations involved in Glioblastoma (GBM) invasion. Recent works discovered the role of new molecular players in GBM invasion, and, most importantly, better models are emerging which better recapitulate GBM invasion.

SUMMARY

Invasive properties of glioblastoma make complete surgical resection impossible and highly invasive cells are responsible for tumor recurrence. In this review, we focus on recent updates describing how invasive cells progress in the surrounding tissue along brain structures. We also provide an overview of the current knowledge on key cells and molecular players within the microenvironment that contribute to the invasive process. VIDEO ABSTRACT.

P4HA1 Down-Regulation Inhibits Glioma Invasiveness by Promoting M1 Microglia Polarization

Background

Polarization of microglia cells in the glioma microenvironment is closely related to the malignant progression and invasion of gliomas. Prolyl 4-hydroxylase subunit α1 (P4HA1) is the rate-limiting subunit of prolyl 4-hydroxylase (P4H). In previous studies, we showed that P4HA1 could promote the proliferation, migration, and invasion of glioma cells, but the specific mechanisms through which this occurs have not been fully elucidated.

Materials and Methods

Interactions between glioma and microglia cells were analyzed using bioinformatics. Then, co-culture models were used to obtain conditioned media. To characterize microglial cell polarization, we used PCR and immunofluorescence. Proliferation and invasion assays were used to explore the biological behavior of glioma cells affected by microglia. Finally, marker expression was detected using immunohistochemistry in glioblastoma multiform (GBM) specimens.

Results

Knockdown of P4HA1 resulted in reduced chemotaxis of microglia toward GBM cells and increased polarization of microglia toward the M1 phenotype. The changed microglial polarization state, in turn, inhibited the proliferation and invasion of GBM cells. Moreover, in GBM tissue specimens, the P4HA1 expression level is negatively correlated with that of the CD86 microglia M1-specific marker.

Conclusion

Our results show that P4HA1 promotes immunosuppressive microenvironment formation by cross-talk between GBM and microglia cells and indirectly increases the aggressiveness of GBM.

A Virus-Mimicking Nucleic Acid Nanogel Reprograms Microglia and Macrophages for Glioblastoma Therapy

Immunotherapy is recognized as one of the most promising approaches to treat cancers. However, its effect in glioblastoma (GBM) treatment is insufficient, which can in part be attributed to the immunosuppressive tumor microenvironment (TME). Microglia and macrophages are the main immune infiltrating cells in the TME of GBM. Unfortunately, instead of initiating the anti-tumor response, GBM-infiltrating microglia and macrophages switch to a tumor-promoting phenotype (M2), and support tumor growth, angiogenesis, and immunosuppression by the release of cytokines. In this work, a virus-mimicking membrane-coated nucleic acid nanogel Vir-Gel embedded with therapeutic miRNA is developed, which can reprogram microglia and macrophages from a pro-invasive M2 phenotype to an anti-tumor M1 phenotype. By mimicking the virus infection process, Vir-Gel significantly enhances the targetability and cell uptake efficiency of the miR155-bearing nucleic acid nanogel. In vivo evaluations demonstrate that Vir-Gel apparently prolongs the circulation lifetime of miR155 and endows it with an active tumor-targeting capability and excellent tumor inhibition efficacy. Owing to its noninvasive feature and effective delivery capability, the virus-mimicking nucleic acid nanogel provides a general and convenient platform that can successfully treat a wide range of diseases.

The Current State of Oncolytic Herpes Simplex Virus for Glioblastoma Treatment

Glioblastoma (GBM) is a lethal primary malignant brain tumor with no current effective treatments. The recent emergence of immuno-virotherapy and FDA approval of T-VEC have generated a great expectation towards oncolytic herpes simplex viruses (oHSVs) as a promising treatment option for GBM. Since the generation and testing of the first genetically engineered oHSV in glioma in the early 1990s, oHSV-based therapies have shown a long way of great progress in terms of anti-GBM efficacy and safety, both preclinically and clinically. Here, we revisit the literature to understand the recent advancement of oHSV in the treatment of GBM. In addition, we discuss current obstacles to oHSV-based therapies and possible strategies to overcome these pitfalls.

Peritumoral Microenvironment in High-Grade Gliomas: From FLAIRectomy to Microglia-Glioma Cross-Talk

Cellular composition and molecular signatures of the glioma core compared with infiltrative margins are different, and it is well known that the tumor edge is enriched in microglia. In this review of the literature, we summarize the role of the peritumoral area in high-grade gliomas (HGGs) from surgical and biological points of view. There is evidence on the dual role of microglia in HGGs-a scavenger-tumoricidal role when microglia are activated in an M1 phenotype and a role favoring tumor growth and infiltration/migration when microglia are activated in an M2 phenotype. Microglia polarization is mediated by complex pathways involving cross-talk with glioma cells. In this scenario, extracellular vesicles and their miRNA cargo seem to play a central role. The switch to a specific phenotype correlates with prognosis and the pathological assessment of a specific microglial setting can predict a patient's outcome. Some authors have designed an engineered microglial cell as a biologically active vehicle for the delivery of intraoperative near-infrared fluorescent dye with the aim of helping surgeons detect peritumoral infiltrated areas during resection. Furthermore, the pharmacological modulation of microglia-glioma cross-talk paves the way to more effective therapies.

Microglia in the Brain Tumor Microenvironment

Microglia are the brain resident phagocytes that act as the primary form of the immune defense in the central nervous system. These cells originate from primitive macrophages that arise from the yolk sac. Advances in imaging and single-cell RNA-seq technologies provided new insights into the complexity of microglia biology.Microglia play an essential role in the brain development and maintenance of brain homeostasis. They are also crucial in injury repair in the central nervous system. The tumor microenvironment is complex and includes neoplastic cells as well as varieties of host and infiltrating immune cells. Microglia are part of the glioma microenvironment and play a critical part in initiating and maintaining tumor growth and spread. Microglia can also act as effector cells in treatments against gliomas. In this chapter, we summarize the current knowledge of how and where microglia are generated. We also discuss their functions during brain development, injury repair, and homeostasis. Moreover, we discuss the role of microglia in the tumor microenvironment of gliomas and highlight their therapeutic implications.

Inhibition of microglial EZH2 leads to anti-tumoral effects in pediatric diffuse midline gliomas

BACKGROUND

Diffuse intrinsic pontine gliomas (DIPG), within diffuse midline gliomas are aggressive pediatric brain tumors characterized by histone H3-K27M mutation. Small-molecule inhibitors for the EZH2-H3K27 histone methyltransferase have shown promise in preclinical animal models of DIPG, despite having little effect on DIPG cells in vitro. Therefore, we hypothesized that the effect of EZH2 inhibition could be mediated through targeting of this histone modifying enzyme in tumor-associated microglia.

METHODS

Primary DIPG tissues, and cocultures between microglia and patient-derived DIPG or -pediatric high-grade glioma (pHGG) cell lines, were used to establish the H3-K27M status of each cell type. Antisense RNA strategies were used to target EZH2 gene expression in both microglia and glioma cells. Microglia anti-tumoral properties were assessed by gene expression profile, tumor cell invasion capacity, microglial phagocytic activity, and associated tumor cell death.

RESULTS

In primary DIPG tissues, microglia do not carry the H3-K27M mutation, otherwise characteristic of the cancer cells. Activation of a microglial tumor-supportive phenotype by pHGG, independently of their H3-K27M status, is associated with a transient H3K27me3 downregulation. Repression of EZH2 in DIPG cells has no impact on tumor cell survival or their ability to activate microglia. However, repression of EZH2 in microglia induces an anti-tumor phenotype resulting in decreased cancer cell invasion capability, increased microglial phagocytosis, and tumor-related cell death.

CONCLUSIONS

These results indicate that microglia, beyond the tumor cells, contribute to the observed response of DIPG to EZH2 inhibition. Results highlight the potential importance of microglia as a new therapeutic avenue in DIPG.

Distinction of Microglia and Macrophages in Glioblastoma: Close Relatives, Different Tasks?

For decades, it has been known that the tumor microenvironment is significant for glioma progression, namely the infiltration of myeloid cells like microglia and macrophages. Hence, these cell types and their specific tasks in tumor progression are subject to ongoing research. However, the distribution of the brain resident microglia and the peripheral macrophages within the tumor tissue and their functional activity are highly debated. Results depend on the method used to discriminate between microglia and macrophages, whereby this specification is already difficult due to limited options to distinguish between these both cell populations that show mostly the same surface markers and morphology. Moreover, there are indications about various functions of microglia and macrophages but again varying on the method of discrimination. In our review, we summarize the current literature to determine which methods have been applied to differentiate the brain resident microglia from tumor-infiltrated macrophages. Furthermore, we compiled data about the proportion of microglia and macrophages in glioma tissues and ascertained if pro- or anti-tumoral effects could be allocated to one or the other myeloid cell population. Recent research made tremendous efforts to distinguish microglia from recruited macrophages. For future studies, it could be essential to verify which role these cells play in brain tumor pathology to proceed with novel immunotherapeutic strategies.

MiR-181 Family Modulates Osteopontin in Glioblastoma Multiforme

Simple Summary

MicroRNAs can silence a broad set of target genes that may benefit heterogeneous tumors like glioblastoma. We have previously shown that osteopontin has an oncogenic role and may have immune modulatory effects on macrophages. In the current study, we used miRNAs to target osteopontin in tumor cells and modulate immune cells to elicit an antitumor effect. Intravenous delivery of miR-181a to immune competent mice bearing intracranial glioblastoma demonstrated a 22% increase in median survival duration relative to that of control mice. The overexpression of miR-181a in tumor cells led to decreased OPN production and proliferation and increased apoptosis in vitro, and increased survival duration of the mice when compared to its controls. miR-181a controls osteopontin expression in tumor cells by regulating their proliferation and apoptosis.

Abstract

MiRNAs can silence a wide range of genes, which may be an advantage for targeting heterogenous tumors like glioblastoma. Osteopontin (OPN) plays both an oncogenic role in a variety of cancers and can immune modulate macrophages. We conducted a genome wide profiling and bioinformatic analysis to identify miR-181a/b/c/d as potential miRNAs that target OPN. Luciferase assays confirmed the binding potential of miRNAs to OPN. Expression levels of miR-181a/b/c/d and OPN were evaluated by using quantitative real-time PCR and enzyme-linked immunosorbent assay in mouse and human glioblastomas and macrophages that showed these miRNAs were downregulated in Glioblastoma associated CD11b+ cells compared to their matched blood CD14b+ cells. miRNA mimicking and overexpression using lentiviruses showed that MiR-181a overexpression in glioblastoma cells led to decreased OPN production and proliferation and increased apoptosis in vitro. MiR-181a treatment of immune competent mice bearing intracranial glioblastoma demonstrated a 22% increase in median survival duration relative to that of control mice.

Crosstalk between microglia and patient-derived glioblastoma cells inhibit invasion in a three-dimensional gelatin hydrogel model

BACKGROUND

Glioblastoma is the most common and deadly form of primary brain cancer, accounting for more than 13,000 new diagnoses annually in the USA alone. Microglia are the innate immune cells within the central nervous system, acting as a front-line defense against injuries and inflammation via a process that involves transformation from a quiescent to an activated phenotype. Crosstalk between GBM cells and microglia represents an important axis to consider in the development of tissue engineering platforms to examine pathophysiological processes underlying GBM progression and therapy.

METHODS

This work used a brain-mimetic hydrogel system to study patient-derived glioblastoma specimens and their interactions with microglia. Here, glioblastoma cells were either cultured alone in 3D hydrogels or in co-culture with microglia in a manner that allowed secretome-based signaling but prevented direct GBM-microglia contact. Patterns of GBM cell invasion were quantified using a three-dimensional spheroid assay. Secretome and transcriptome (via RNAseq) were used to profile the consequences of GBM-microglia interactions.

RESULTS

Microglia displayed an activated phenotype as a result of GBM crosstalk. Three-dimensional migration patterns of patient-derived glioblastoma cells showed invasion was significantly decreased in response to microglia paracrine signaling. Potential molecular mechanisms underlying with this phenotype were identified from bioinformatic analysis of secretome and RNAseq data.

CONCLUSION

The data demonstrate a tissue engineered hydrogel platform can be used to investigate crosstalk between immune cells of the tumor microenvironment related to GBM progression. Such multi-dimensional models may provide valuable insight to inform therapeutic innovations to improve GBM treatment.

Sphingolipid Metabolism in Glioblastoma and Metastatic Brain Tumors: A Review of Sphingomyelinases and Sphingosine-1-Phosphate

Glioblastoma (GBM) is a primary malignant brain tumor with a dismal prognosis, partially due to our inability to completely remove and kill all GBM cells. Rapid tumor recurrence contributes to a median survival of only 15 months with the current standard of care which includes maximal surgical resection, radiation, and temozolomide (TMZ), a blood-brain barrier (BBB) penetrant chemotherapy. Radiation and TMZ cause sphingomyelinases (SMase) to hydrolyze sphingomyelins to generate ceramides, which induce apoptosis. However, cells can evade apoptosis by converting ceramides to sphingosine-1-phosphate (S1P). S1P has been implicated in a wide range of cancers including GBM. Upregulation of S1P has been linked to the proliferation and invasion of GBM and other cancers that display a propensity for brain metastasis. To mediate their biological effects, SMases and S1P modulate signaling via phospholipase C (PLC) and phospholipase D (PLD). In addition, both SMase and S1P may alter the integrity of the BBB leading to infiltration of tumor-promoting immune populations. SMase activity has been associated with tumor evasion of the immune system, while S1P creates a gradient for trafficking of innate and adaptive immune cells. This review will explore the role of sphingolipid metabolism and pharmacological interventions in GBM and metastatic brain tumors with a focus on SMase and S1P.

A proposed treatment for pathogenic enveloped viruses having high rates of mutation or replication

Several enveloped viruses, particularly some RNA viruses, have high rates of mutation or replication, which can make them virulent pathogens in humans and other mammals. A proposed treatment could use synthesized proteins to mask pathogenic viral surface proteins to quickly induce an immune attack on specific enveloped viruses by using existing immune cells. One treatment could inject dual‐protein ligand masks into patients' bloodstreams to mask pathogenic surface proteins used to infect mammalian cells. The mammalian immune system already uses an analogous, more complex structure called a pentraxin to neutralize some pathogens by connecting their surface proteins to immune cells. And several types of antiviral peptides have already experimentally demonstrated effectiveness in blocking various viral pathogen infections. These treatments offer advantages, especially for currently untreatable viral pathogens. Furthermore, using dual‐protein ligands and the antigenic memory of some sub‐populations of NK cells would also allow the creation of defacto vaccines based on a host's NK cells, instead of vaccines utilizing CD4 and CD8 α:β T cells, which are limited by the requirement of MHC presentation of the target antigens to α:β T cells. Targeted NK cell vaccines could attack host cells latently or actively infected by intracellular pathogens, even host cells having pathogen downregulated MHC antigen presentation. Eight postulates concerning the effects of pathogen mutation, or change in phenotype from genetic recombination or rearrangement, and replication rates on pathogen vs host dominance are also listed, which should be applicable to viral and non‐viral pathogens.

Microglial lysophosphatidic acid promotes glioblastoma proliferation and migration via LPA1 receptor

Glioblastomas (GBMs) are highly aggressive primary brain tumors characterized by cellular heterogeneity, insensitivity to chemotherapy and poor patient survival. Lysophosphatidic acid (LPA) is a lysophospholipid that acts as a bioactive signaling molecule and plays important roles in diverse biological events during development and disease, including several cancer types. Microglial cells, the resident macrophages of the central nervous system, express high levels of Autotaxin (ATX,Enpp2), an enzyme that synthetizes LPA. Our study aimed to investigate the role of LPA on tumor growth and invasion in the context of microglia-GBM interaction. First, through bioinformatics studies, patient data analysis demonstrated that more aggressive GBM expressed higher levels of ENPP2, which was also associated with worse patient prognosis with proneural GBM. Using GBM-microglia co-culture system we then demonstrated that GBM secreted factors were able to increase LPA₁ and ATX in microglia, which could be further enhanced by hypoxia. On the other hand, interaction with microglial cells also increased ATX expression in GBM. Furthermore, microglial-induced GBM proliferation and migration could be inhibited by pharmacological inhibition of LPA₁ , suggesting that microglial-derived LPA could support tumor growth and invasion. Finally, increased LPA₁ expression was observed in GBM comparing with other gliomas and could be also associated with worse patient survival. These results show for the first time a microglia-GBM interaction through the LPA pathway with relevant implications for tumor progression. A better understanding of this interaction can lead to the development of new therapeutic strategies setting LPA as a potential target for GBM treatment.

Radiation Induced Metabolic Alterations Associate With Tumor Aggressiveness and Poor Outcome in Glioblastoma

Glioblastoma (GBM) is uniformly fatal with a 1-year median survival, despite best available treatment, including radiotherapy (RT). Impacts of prior RT on tumor recurrence are poorly understood but may increase tumor aggressiveness. Metabolic changes have been investigated in radiation-induced brain injury; however, the tumor-promoting effect following prior radiation is lacking. Since RT is vital to GBM management, we quantified tumor-promoting effects of prior RT on patient-derived intracranial GBM xenografts and characterized metabolic alterations associated with the protumorigenic microenvironment. Human xenografts (GBM143) were implanted into nude mice 24 hrs following 20 Gy cranial radiation vs. sham animals. Tumors in pre-radiated mice were more proliferative and more infiltrative, yielding faster mortality (p < 0.0001). Histologic evaluation of tumor associated macrophage/microglia (TAMs) revealed cells with a more fully activated ameboid morphology in pre-radiated animals. Microdialyzates from radiated brain at the margin of tumor infiltration contralateral to the site of implantation were analyzed by unsupervised liquid chromatography-mass spectrometry (LC-MS). In pre-radiated animals, metabolites known to be associated with tumor progression (i.e., modified nucleotides and polyols) were identified. Whole-tissue metabolomic analysis of pre-radiated brain microenvironment for metabolic alterations in a separate cohort of nude mice using ¹H-NMR revealed a significant decrease in levels of antioxidants (glutathione (GSH) and ascorbate (ASC)), NAD⁺, Tricarboxylic acid cycle (TCA) intermediates, and rise in energy carriers (ATP, GTP). GSH and ASC showed highest Variable Importance on Projection prediction (VIPpred) (1.65) in Orthogonal Partial least square Discriminant Analysis (OPLS-DA); Ascorbate catabolism was identified by GC-MS. To assess longevity of radiation effects, we compared survival with implantation occurring 2 months vs. 24 hrs following radiation, finding worse survival in animals implanted at 2 months. These radiation-induced alterations are consistent with a chronic disease-like microenvironment characterized by reduced levels of antioxidants and NAD⁺, and elevated extracellular ATP and GTP serving as chemoattractants, promoting cell motility and vesicular secretion with decreased levels of GSH and ASC exacerbating oxidative stress. Taken together, these data suggest IR induces tumor-permissive changes in the microenvironment with metabolomic alterations that may facilitate tumor aggressiveness with important implications for recurrent glioblastoma. Harnessing these metabolomic insights may provide opportunities to attenuate RT-associated aggressiveness of recurrent GBM.

Pathogenesis of peritumoral hyperexcitability in an immunocompetent CRISPR-based glioblastoma model

Seizures often herald the clinical appearance of gliomas or appear at later stages. Dissecting their precise evolution and cellular pathogenesis in brain malignancies could inform the development of staged therapies for these highly pharmaco-resistant epilepsies. Studies in immunodeficient xenograft models have identified local interneuron loss and excess glial glutamate release as chief contributors to network disinhibition, but how hyperexcitability in the peritumoral microenvironment evolves in an immunocompetent brain is unclear. We generated gliomas in WT mice via in utero deletion of key tumor suppressor genes and serially monitored cortical epileptogenesis during tumor infiltration with in vivo electrophysiology and GCAMP7 calcium imaging, revealing a reproducible progression from hyperexcitability to convulsive seizures. Long before seizures, coincident with loss of inhibitory cells and their protective scaffolding, gain of glial glutamate antiporter xCT expression, and reactive astrocytosis, we detected local Iba1+ microglial inflammation that intensified and later extended far beyond tumor boundaries. Hitherto unrecognized episodes of cortical spreading depolarization that arose frequently from the peritumoral region may provide a mechanism for transient neurological deficits. Early blockade of glial xCT activity inhibited later seizures, and genomic reduction of host brain excitability by deleting MapT suppressed molecular markers of epileptogenesis and seizures. Our studies confirmed xenograft tumor-driven pathobiology and revealed early and late components of tumor-related epileptogenesis in a genetically tractable, immunocompetent mouse model of glioma, allowing the complex dissection of tumor versus host pathogenic seizure mechanisms.

CCL8 secreted by tumor-associated macrophages promotes invasion and stemness of glioblastoma cells via ERK1/2 signaling

Tumor-associated macrophages (TAMs) constitute a large population of glioblastoma and facilitate tumor growth and invasion of tumor cells, but the underlying mechanism remains undefined. In this study, we demonstrate that chemokine (C-C motif) ligand 8 (CCL8) is highly expressed by TAMs and contributes to pseudopodia formation by GBM cells. The presence of CCL8 in the glioma microenvironment promotes progression of tumor cells. Moreover, CCL8 induces invasion and stem-like traits of GBM cells, and CCR1 and CCR5 are the main receptors that mediate CCL8-induced biological behavior. Finally, CCL8 dramatically activates ERK1/2 phosphorylation in GBM cells, and blocking TAM-secreted CCL8 by neutralized antibody significantly decreases invasion of glioma cells. Taken together, our data reveal that CCL8 is a TAM-associated factor to mediate invasion and stemness of GBM, and targeting CCL8 may provide an insight strategy for GBM treatment.

Elevated expression of DOK3 indicates high suppressive immune cell infiltration and unfavorable prognosis of gliomas

Docking protein 3 has been implicated in immune response, including interferon-β production in macrophage and plasma cell differentiation. And its importance in lung adenocarcinoma has been reported. However, studies about its role in gliomas are rare. In this study, we explored the clinical and prognostic characteristics of DOK3 expression in 921 glioma samples. Kaplan-Meier survival analysis and Cox regression analysis verified the independent unfavorable prognostic value and high prognostic accuracy of DOK3 expression for overall survival. Functional analysis with Database for Annotation, Visualization and Integrated Discovery (DAVID) and Gene Set Enrichment Analysis (GSEA) implied the involvement of DOK3 in immune related responses. Immune cell infiltration analysis with online tools, CIBERSORT and EPIC, showed that samples with higher DOK3 expression were infiltrated with much more macrophages. DOK3 was also found to be strongly positively correlated with marker genes of tumor-associated macrophages and M2 macrophages, not M1. Results of immunohistochemical staining also demonstrated that samples with higher DOK3 expression level were infiltrated with more microglia/macrophages and immunosuppressive M2 macrophages. In summary, our results demonstrated the correlation between high DOK3 expression level and malignant progression of gliomas, and the possible involvement of DOK3 in immunosuppressive responses in gliomas.

Demeclocycline Reduces the Growth of Human Brain Tumor-Initiating Cells: Direct Activity and Through Monocytes

Myeloid cells that infiltrate into brain tumors are deactivated or exploited by the tumor cells. We previously demonstrated that compromised microglia, monocytes, and macrophages in malignant gliomas could be reactivated by amphotericin-B to contain the growth of brain tumorinitiating cells (BTICs). We identified meclocycline as another activator of microglia, so we sought to test whether its better-tolerated derivative, demeclocycline, also stimulates monocytes to restrict BTIC growth. Monocytes were selected for study as they would be exposed to demeclocycline in the circulation prior to entry into brain tumors to become macrophages. We found that demeclocycline increased the activity of monocytes in culture, as determined by tumor necrosis factor-α production and chemotactic capacity. The conditioned medium of demeclocycline-stimulated monocytes attenuated the growth of BTICs generated from human glioblastoma resections, as evaluated using neurosphere and alamarBlue assays, and cell counts. Demeclocycline also had direct effects in reducing BTIC growth. A global gene expression screen identified several genes, such as DNA damage inducible transcript 4, frizzled class receptor 5 and reactive oxygen species modulator 1, as potential regulators of demeclocycline-mediated BTIC growth reduction. Amongst several tetracycline derivatives, only demeclocycline directly reduced BTIC growth. In summary, we have identified demeclocycline as a novel inhibitor of the growth of BTICs, through direct effect and through indirect stimulation of monocytes. Demeclocycline is a candidate to reactivate compromised immune cells to improve the prognosis of patients with gliomas.

Development of an Immune Infiltration-Related Prognostic Scoring System Based on the Genomic Landscape Analysis of Glioblastoma Multiforme

Introduction: Glioblastoma multiforme (GBM) is the most common deadly brain malignancy and lacks effective therapies. Immunotherapy acts as a promising novel strategy, but not for all GBM patients. Therefore, classifying these patients into different prognostic groups is urgent for better personalized management.

Materials and Methods: The Cell type Identification by Estimating Relative Subsets of RNA Transcripts (CIBERSORT) algorithm was used to estimate the fraction of 22 types of immune-infiltrating cells, and least absolute shrinkage and selection operator (LASSO) Cox regression analysis was performed to construct an immune infiltration-related prognostic scoring system (IIRPSS). Additionally, a quantitative predicting survival nomogram was also established based on the immune risk score (IRS) derived from the IIRPSS. Moreover, we also preliminarily explored the differences in the immune microenvironment between different prognostic groups.

Results: There was a total of 310 appropriate GBM samples (239 from TCGA and 71 from CGGA) included in further analyses after CIBERSORT filtering and data processing. The IIRPSS consisting of 17 types of immune cell fractions was constructed in TCGA cohort, the patients were successfully classified into different prognostic groups based on their immune risk score (p = 1e-10). What's more, the prognostic performance of the IIRPSS was validated in CGGA cohort (p = 0.005). The nomogram also showed a superior predicting value. (The predicting AUC for 1-, 2-, and 3-year were 0.754, 0.813, and 0.871, respectively). The immune microenvironment analyses reflected a significant immune response and a higher immune checkpoint expression in high-risk immune group.

Conclusion: Our study constructed an IIRPSS, which maybe valuable to help clinicians select candidates most likely to benefit from immunological checkpoint inhibitors (ICIs) and laid the foundation for further improving personalized immunotherapy in patients with GBM.

A Proposed Treatment Approach to Treat Lethal Mutating Cancers

A proposed treatment using dual-peptide ligand masks, that are functional extensions to existing analogous mammalian immune system structures, to bind to cancer cell surface proteins and stop mutating cancers that could evade presently used engineered immune cell therapies. One treatment injects the dual-peptide ligand masks into the blood stream of patients, and another treatment injects the dual-peptide ligand masks into localized cancers to bind to cancer cell surface proteins. The mammalian immune system has long used analogous, but more complex structures called pentraxins to physically link various types of pathogens to immune cells for neutralization. This treatment approach offers potential advantages in increased binding adaptability to mutations in the surface proteins of cancer cells, and potentially lower treatment cost compared to engineered immune cell treatments against cancer, especially against mutating cancer cells, even compared to extremely specific and costly monoclonal antibody treatments or engineered T cell treatments.

Role of Infiltrating Microglia/Macrophages in Glioma

In this chapter we describe the state of the art knowledge of the role played by myeloid cells in promoting and supporting the growth and the invasive properties of a deadly brain tumor, glioblastoma. We provide a review of the works describing the intercellular communication among glioma and associated microglia/macrophage cells (GAMs) using in vitro cellular models derived from mice, rats and human patients and in vivo animal models using syngeneic or xenogeneic experimental systems. Special emphasis will be given to 1) the timing alteration of brain microenvironment under the influence of glioma, 2) the bidirectional communication among tumor and GAMs, 3) possible approaches to interfere with or to guide these interactions, with the aim to identify molecular and cellular targets which could revert or delay the vicious cycle that favors tumor biology.

Dual-peptide ligand masks: a proposed treatment approach to stop prion disease dementias

Prion disease dementias are currently not practically treatable. However, a proposed treatment approach using specifically targeted dual-peptide ligand masks can mask prion surface proteins and treat specific prion diseases. Different approaches might be used to treat these prion diseases. One treatment introduces genetically modified cells into the gastrointestinal tract or other locations to produce dual-peptide ligand masks; and another treatment introduces only the dual-peptide ligand masks into the center of prion infections to mask prion surface proteins. An independent group introduced genetically modified therapeutic bacteria into large numbers of mammals, including several human volunteers, with safe and effective experimental results, without long-term colonization by the bacteria, which experimentally supports the feasibility of the first treatment. These approaches offer several advantages compared with other potential treatments against prion diseases in humans.