Glioma tumourgenicity is decreased by iNOS knockout: experimental studies using the C6 striatal implantation glioma model

Microglia-Derived Small Extracellular Vesicles Reduce Glioma Growth by Modifying Tumor Cell Metabolism and Enhancing Glutamate Clearance through miR-124

Brain homeostasis needs continuous exchange of intercellular information among neurons, glial cells, and immune cells, namely microglial cells. Extracellular vesicles (EVs) are active players of this process. All the cells of the body, including the brain, release at least two subtypes of EVs, the medium/large EVs (m/lEVs) and small EVs (sEVs). sEVs released by microglia play an important role in brain patrolling in physio-pathological processes. One of the most common and malignant forms of brain cancer is glioblastoma. Altered intercellular communications constitute a base for the onset and the development of the disease. In this work, we used microglia-derived sEVs to assay their effects in vitro on murine glioma cells and in vivo in a glioma model on C57BL6/N mice. Our findings indicated that sEVs carry messages to cancer cells that modify glioma cell metabolism, reducing lactate, nitric oxide (NO), and glutamate (Glu) release. sEVs affect Glu homeostasis, increasing the expression of Glu transporter Glt-1 on astrocytes. We demonstrated that these effects are mediated by miR-124 contained in microglia-released sEVs. The in vivo benefit of microglia-derived sEVs results in a significantly reduced tumor mass and an increased survival of glioma-bearing mice, depending on miR-124.

Protective Role of Natural Products in Glioblastoma Multiforme: A Focus on Nitric Oxide Pathway

In spite of therapeutic modalities such as surgical resection, chemotherapy, and radiotherapy, Glioblastoma Multiforme (GBM) remains an incurable fatal disease. This necessitates further therapeutic options that could enhance the efficacy of existing modalities. Nitric Oxide (NO), a short-lived small molecule, has been revealed to play a crucial role in the pathophysiology of GBM. Several studies have demonstrated that NO is involved in apoptosis, metastasis, cellular proliferation, angiogenesis, invasion, and many other processes implicated in GBM pathobiology. Herein, we elaborate on the role of NO as a therapeutic target in GBM and discuss some natural products affecting the NO signaling pathway.

NOS Expression and NO Function in Glioma and Implications for Patient Therapies

SIGNIFICANCE

Gliomas are central nervous system tumors that primarily occur in the brain and arise from glial cells. Gliomas include the most common malignant brain tumor in adults known as grade IV astrocytoma, or glioblastoma (GBM). GBM is a deadly disease for which the most significant advances in treatment offer an improvement in survival of only ∼2 months.

CRITICAL ISSUES

To develop novel treatments and improve patient outcomes, we and others have sought to determine the role of molecular signals in gliomas. Recent Advances: One signaling molecule that mediates important biologies in glioma is the free radical nitric oxide (NO). In glioma cells and the tumor microenvironment, NO is produced by three isoforms of nitric oxide synthase (NOS), NOS1, NOS2, and NOS3. NO and NOS affect glioma growth, invasion, angiogenesis, immunosuppression, differentiation state, and therapeutic resistance.

FUTURE DIRECTIONS

These multifaceted effects of NO and NOS on gliomas both in vitro and in vivo suggest the potential of modulating the pathway for antiglioma patient therapies. Antioxid. Redox Signal. 26, 986-999.

Investigating the role of tumour cell derived iNOS on tumour growth and vasculature in vivo using a tetracycline regulated expression system

Nitric oxide (NO) is a free radical signalling molecule involved in various physiological and pathological processes, including cancer. Both tumouricidal and tumour promoting effects have been attributed to NO, making its role in cancer biology controversial and unclear. To investigate the specific role of tumour-derived NO in vascular development, C6 glioma cells were genetically modified to include a doxycycline regulated gene expression system that controls the expression of an antisense RNA to inducible nitric oxide synthase (iNOS) to manipulate endogenous iNOS expression. Xenografts of these cells were propagated in the presence or absence of doxycycline. Susceptibility magnetic resonance imaging (MRI), initially with a carbogen (95% O2/5% CO2) breathing challenge and subsequently an intravascular blood pool contrast agent, was used to assess haemodynamic vasculature (ΔR2*) and fractional blood volume (fBV), and correlated with histopathological assessment of tumour vascular density, maturation and function. Inhibition of NO production in C6 gliomas led to significant growth delay and inhibition of vessel maturation. Parametric fBV maps were used to identify vascularised regions from which the carbogen-induced ΔR2* was measured and found to be positively correlated with vessel maturation, quantified ex vivo using fluorescence microscopy for endothelial and perivascular cell staining. These data suggest that tumour-derived iNOS is an important mediator of tumour growth and vessel maturation, hence a promising target for anti-vascular cancer therapies. The combination of ΔR2* response to carbogen and fBV MRI can provide a marker of tumour vessel maturation that could be applied to non-invasively monitor treatment response to iNOS inhibitors.

Reactive oxygen species-dependent nitric oxide production in reciprocal interactions of glioma and microglial cells

Conditioned mediums (CMs) from glioma cells U87, GBM-8401, and C6 significantly induced iNOS protein and NO production by microglial cells BV-2 but without altering the cell viability or cell-cycle progression of BV2 microglia. Significant increases in intracellular peroxide by U87-CM and C6-CM were detected by a DCHF-DA assay, and vitamin (Vit) C and N-acetyl cysteine (NAC)-reduced intracellular peroxide levels elicited by CMs lead to inhibition of iNOS/NO production The extracellular signal-regulated kinase (ERK) inhibitor, U0126, and c-Jun N-terminal kinase (JNK) inhibitor, SP600125, suppressed U87-CM- and C6-CM-induced iNOS/NO production by respectively blocking phosphorylated ERK (pERK) and JNK (pJNK) protein expressions stimulated by U87-CM and C6-CM. Increased migration of U87 and C6 glioma cells by a co-culture with BV-2 microglial cells or adding the nitric oxide (NO) donor, sodium nitroprusside (SNP) was observed, and that was blocked by adding an NO synthase (NOS) inhibitor, N-nitro L-arginine methyl ester (NAME). Contributions of ROS, pERK, and pJNK to the migration of glioma cells was further demonstrated in a transwell coculture system of U87 and C6 gliomas with BV-2 microglial cells. Furthermore, expressions of tumor necrosis factor (TNF)-α and monocyte chemoattractant protein (MCP)-1 messenger (m)RNA in U87 and C6 cells were detected by an RT-PCR, and TNF-α and MCP-1 induced iNOS protein expression in time- and concentration-dependent manners. Neutralization of TNF-α or MCP-1 in U87-CM and C6-CM using a TNF-α or MCP-1 antibody inhibited iNOS protein expression, and increased intracellular peroxide by TNF-α or MCP-1 was identified in BV-2 cells. The reciprocal activation of glioma cells and microglia via ROS-dependent iNOS/NO elevation at least partially mediated by TNF-α and MCP-1 is elucidated.

Glioma stem cell proliferation and tumor growth are promoted by nitric oxide synthase-2

Malignant gliomas are aggressive brain tumors with limited therapeutic options, and improvements in treatment require a deeper molecular understanding of this disease. As in other cancers, recent studies have identified highly tumorigenic subpopulations within malignant gliomas, known generally as cancer stem cells. Here, we demonstrate that glioma stem cells (GSCs) produce nitric oxide via elevated nitric oxide synthase-2 (NOS2) expression. GSCs depend on NOS2 activity for growth and tumorigenicity, distinguishing them from non-GSCs and normal neural progenitors. Gene expression profiling identified many NOS2-regulated genes, including the cell-cycle inhibitor cell division autoantigen-1 (CDA1). Further, high NOS2 expression correlates with decreased survival in human glioma patients, and NOS2 inhibition slows glioma growth in a murine intracranial model. These data provide insight into how GSCs are mechanistically distinct from their less tumorigenic counterparts and suggest that NOS2 inhibition may be an efficacious approach to treating this devastating disease.

The role of tumour-derived iNOS in tumour progression and angiogenesis

Background:

Progressive tumour growth is dependent on the development of a functional tumour vasculature and highly regulated by growth factors and cytokines. Nitric oxide (NO) is a free radical, produced both by tumour and host cells, and functions as a signalling molecule downstream of several angiogenic factors. Both pro- and antitumourigenic properties have been attributed to NO.

Methods:

The expression of the inducible isoform of NO synthase (iNOS) was knocked down in the C6 glioma cell line using constitutive expression of antisense RNA, and the effect of tumour-derived NO on tumour progression and angiogenesis was investigated.

Results:

Tumours in which iNOS expression was decreased displayed significantly reduced growth rates compared with tumours derived from parental C6 cells. Quantitative non-invasive magnetic resonance imaging and fluorescence microscopy of tumour uptake of Hoechst 33342, and haematoxylin and eosin staining, revealed significantly impaired vascular development and function in antisense iNOS tumours compared with control in vivo, primarily associated with the more necrotic tumour core. Decreased iNOS expression had no effect on tumour VEGF expression.

Conclusion:

Nitric oxide derived from tumour iNOS is an important modulator of tumour progression and angiogenesis in C6 gliomas and further supports the therapeutic strategy of inhibiting iNOS for the treatment of cancer.

Induced nitric oxide synthase as a major player in the oncogenic transformation of inflamed tissue

Nitric oxide (NO) is a free radical that is involved in the inflammatory process and carcinogenesis. There are four nitric oxide synthase enzymes involved in NO production: induced nitric oxide synthase (iNOS), endothelial NO synthase (eNOS), neural NO synthase (nNOS), and mitochondrial NOS. iNOS is an inducible and key enzyme in the inflamed tissue. Recent literatures indicate that NO as well as iNOS and eNOS can modulate cancer-related events including nitro-oxidative stress, apoptosis, cell cycle, angio-genesis, invasion, and metastasis. This chapter focuses on linking NO/iNOS/eNOS to inflammation and carcinogenesis from experimental evidence to potential targets on cancer prevention and treatment.

Essential role of the JAK/STAT1 signaling pathway in the expression of inducible nitric-oxide synthase in intestinal epithelial cells and its regulation by butyrate

Nitric oxide (NO) is a highly reactive free radical that modulates tumorigenesis through its ability to regulate cell proliferation, cell death, migration and angiogenesis. Although the role of NO has been well studied in inflammatory cells, much less is known about the regulation of NO production in epithelial cells. We demonstrated that in intestinal epithelial cells the expression of inducible NO synthase (iNOS), the critical enzyme in the synthesis of NO, is synergistically stimulated by bacterial lipopolysaccharide (LPS) and interferon gamma (IFNgamma) or by the combination of tumor necrosis factor (TNF) and IFNgamma at the transcriptional level. Expression of iNOS and the production of NO in response to LPS/IFNgamma were significantly increased upon induction of oncogenic K-Ras, underlying frequently elevated expression of iNOS in colon cancer. Silencing of STAT1, a major transcription factor involved in signaling by IFNgamma, or pharmacological inhibition of JAKs, kinases that phosphorylate STATs, prevented the induction of iNOS and the production of NO in response to stimulation of cells with LPS/IFNgamma or TNF/IFNgamma, underscoring the importance of the intact JAK/STAT signaling in the regulation of iNOS expression in intestinal epithelial cells. Butyrate, a histone deacetylase (HDAC) inhibitor and a dietary chemopreventive agent, decreased NO production in macrophages and in intestinal myofibroblasts, consistent with its anti-inflammatory activity. In contrast, in intestinal epithelial cells, butyrate significantly enhanced the expression of iNOS and the production of NO in response to treatment with LPS/IFNgamma. Despite the fact that, like butyrate, three structurally unrelated inhibitors of HDAC activity, trichostatin A, suberoylanilide hydroxamic acid, and apicidin, induced acetylation of H3 and H4 in epithelial cells, they failed to increase the production of NO, demonstrating that butyrate regulates NO production in epithelial cells in an HDAC-independent manner. The ability of butyrate to regulate the production of NO in a variety of cell types is likely to underlie its potent chemopreventive and anti-inflammatory activity.

The role of nitric oxide in tumour progression

Nitric oxide (NO) and nitric oxide synthases are ubiquitous in malignant tumours and are known to exert both pro- and anti-tumour effects. We summarize our current understanding of the role of NO in tumour progression, especially in relation to angiogenesis and vascular functions. We also discuss potential strategies for cancer treatment that modulate NO production and/or its downstream signalling pathways.