mGlu3 receptor blockade inhibits proliferation and promotes astrocytic phenotype in glioma stem cells

Disrupted glutamate homeostasis as a target for glioma therapy

Glutamate is the major excitatory neurotransmitter in the central nervous system (CNS). Gliomas, malignant brain tumors with a dismal prognosis, alter glutamate homeostasis in the brain, which is advantageous for their growth, survival, and invasion. Alterations in glutamate homeostasis result from its excessive production and release to the extracellular space. High glutamate concentration in the tumor microenvironment destroys healthy tissue surrounding the tumor, thus providing space for glioma cells to expand. Moreover, it confers neuron hyperexcitability, leading to epilepsy, a common symptom in glioma patients. This mini-review briefly describes the biochemistry of glutamate production and transport in gliomas as well as the activation of glutamate receptors. It also summarizes the current pre-clinical and clinical studies identifying pharmacotherapeutics targeting glutamate transporters and receptors emerging as potential therapeutic strategies for glioma.

Molecular mechanisms of Tetrastigma hemsleyanum Diels&Gilg against lung squamous cell carcinoma: From computational biology and experimental validation

ETHNOPHARMACOLOGICAL RELEVANCE

Tetrastigma hemsleyanum （T. hemsleyanum）, valued in traditional medicine for its potential to boost immunity and combat tumors, contains uncharacterized active compounds and mechanisms. This represents a significant gap in our understanding of its ethnopharmacological relevance.

AIM OF THE STUDY

To involve the mechanism of anti-lung cancer effect of T. hemsleyanum by means of experiment and bioinformatics analysis.

MATERIALS AND METHODS

The anticancer mechanism of T. hemsleyanum against lung squamous carcinoma (LUSC) in zebrafish was investigated. The LUSC model was established by injecting NCI-H2170 cells in the zebrafish and evaluating its anti-tumor efficacy. Next, component targets and key genes were obtained by molecular complex detection (MCODE) analysis and protein-protein interaction (PPI) network analysis. Component analysis of T. hemsleyanum was performed by UPLC-Q-TOF-MS. Molecular docking was used to simulate the binding activities of key potential active components to core targets were simulated using. Prognostic and pan-cancer analyses were then performed to validate the signaling pathways involved in the prognostic genes using gene set enrichment analysis (GSEA). Subsequently, Molecular dynamics simulations were then performed for key active components and core targets. Finally, cellular experiments were used to verify the expression of glutamate metabotropic receptor 3 (GRM3) and glutamate metabotropic receptor 7 (GRM7) in the anticancer effect exerted of T. hemsleyanum.

RESULTS

We experimentally confirmed the inhibitory effect of T. hemsleyanum on LUSC by transplantation of NCI-H2170 cells into zebrafish. There are 20 main compounds in T. hemsleyanum, such as procyanidin B1, catechin, quercetin, and kaempferol, etc. A total of 186 component targets of T. hemsleyanum and sixteen hub genes were screened by PPI network and MCODE analyses. Molecular docking and molecular dynamics simulation results showed that Gingerglycolipid B and Rutin had higher affinity with GRM3 and GRM7, respectively. Prognostic analysis, Pan-cancer analysis and verification experiment also confirmed that GRM3 and GRM7 were targets for T. hemsleyanum to exert anti-tumor effects and to participate in immune and mutation processes. In vitro experiments suggested that the inhibitory effect of T. hemsleyanum on cancer cells was correlated with GRM3 and GRM7.

CONCLUSION

In vivo, in vitro and in silico results confirmed the potential anticancer effects against LUSC of T. hemsleyanum, which further consolidated the claim of its traditional uses.

Metabotropic Glutamate Receptors Type 3 and 5 Feature the "NeuroTransmitter-type" of Glioblastoma: A Bioinformatic Approach

BACKGROUND

Glioblastoma (GBM) represents an aggressive and common tumor of the central nervous system. The prognosis of GBM is poor, and despite a refined genetic and molecular characterization, pharmacological treatment is largely suboptimal.

OBJECTIVE

Contribute to defining a therapeutic line in GBM targeting the mGlu3 receptor in line with the principles of precision medicine.

METHODS

Here, we performed a computational analysis focused on the expression of type 3 and 5 metabotropic glutamate receptor subtypes (mGlu3 and mGlu5, respectively) in high- and low-grade gliomas.

RESULTS

The analysis allowed the identification of a particular high-grade glioma type, characterized by a high expression level of both receptor subtypes and by other markers of excitatory and inhibitory neurotransmission. This so-called neurotransmitter-GBM (NT-GBM) also shows a distinct immunological, metabolic, and vascularization gene signature.

CONCLUSION

Our findings might lay the groundwork for a targeted therapy to be specifically applied to this putative novel type of GBM.

Inhibition of metabotropic glutamate receptor III facilitates sensitization to alkylating chemotherapeutics in glioblastoma

Glioblastoma (GBM), the most malignant tumor of the central nervous system, is marked by its dynamic response to microenvironmental niches. In particular, this cellular plasticity contributes to the development of an immediate resistance during tumor treatment. Novel insights into the developmental trajectory exhibited by GBM show a strong capability to respond to its microenvironment by clonal selection of specific phenotypes. Using the same mechanisms, malignant GBM do develop intrinsic mechanisms to resist chemotherapeutic treatments. This resistance was reported to be sustained by the paracrine and autocrine glutamate signaling via ionotropic and metabotropic receptors. However, the extent to which glutamatergic signaling modulates the chemoresistance and transcriptional profile of the GBM remains unexplored. In this study we aimed to map the manifold effects of glutamate signaling in GBM as the basis to further discover the regulatory role and interactions of specific receptors, within the GBM microenvironment. Our work provides insights into glutamate release dynamics, representing its importance for GBM growth, viability, and migration. Based on newly published multi-omic datasets, we explored the and characterized the functions of different ionotropic and metabotropic glutamate receptors, of which the metabotropic receptor 3 (GRM3) is highlighted through its modulatory role in maintaining the ability of GBM cells to evade standard alkylating chemotherapeutics. We addressed the clinical relevance of GRM3 receptor expression in GBM and provide a proof of concept where we manipulate intrinsic mechanisms of chemoresistance, driving GBM towards chemo-sensitization through GRM3 receptor inhibition. Finally, we validated our findings in our novel human organotypic section-based tumor model, where GBM growth and proliferation was significantly reduced when GRM3 inhibition was combined with temozolomide application. Our findings present a new picture of how glutamate signaling via mGluR3 interacts with the phenotypical GBM transcriptional programs in light of recently published GBM cell-state discoveries.

Activation of estrogen receptor beta signaling reduces stemness of glioma stem cells

Glioblastoma (GBM) is the most common and deadliest tumor of the central nervous system. GBM has poor prognosis and glioma stem cells (GSCs) are implicated in tumor initiation and therapy resistance. Estrogen receptor β (ERβ) is expressed in GBM and exhibit tumor suppressive function. However, the role of ERβ in GSCs and the therapeutic potential of ERβ agonists on GSCs remain largely unknown. Here, we examined whether ERβ modulates GSCs stemness and tested the utility of two ERβ selective agonists (LY500307 and Liquiritigenin) to reduce the stemness of GSCs. The efficacy of ERβ agonists was examined on GSCs isolated from established and patient derived GBMs. Our results suggested that knockout of ERβ increased the proportion of CD133+ and SSEA+ positive GSCs and overexpression of ERβ reduced the proportion of GSCs in GBM cells. Overexpression of ERβ or treatment with ERβ agonists significantly inhibited the GSCs cell viability, neurosphere formation, self-renewal ability, induced the apoptosis and reduced expression of stemness markers in GSCs. RNA sequencing analysis revealed that ERβ agonist modulate pathways related to stemness, differentiation and apoptosis. Mechanistic studies showed that ERβ overexpression or agonist treatment reduced glutamate receptor signaling pathway and induced apoptotic pathways. In orthotopic models, ERβ overexpression or ERβ agonists treatment significantly reduced the GSCs mediated tumor growth and improved the mice overall survival. Immunohistochemical studies demonstrated that ERβ overexpression decreased SOX2 and GRM3 expression and increased expression of GFAP in tumors. These results suggest that ERβ activation could be a promising therapeutic strategy to eradicate GSCs.

Bridging the Metabolic Parallels Between Neurological Diseases and Cancer

Despite the many recent breakthroughs in cancer research, oncology has traditionally been seen as a distinct field from other diseases. Recently, more attention has been paid to repurposing established therapeutic strategies and targets of other diseases towards cancer treatment, with some of these attempts generating promising outcomes [1, 2]. Recent studies using advanced metabolomics technologies [3] have shown evidence of close metabolic similarities between cancer and neurological diseases. These studies have unveiled several metabolic characteristics shared by these two categories of diseases, including metabolism of glutamine, gamma-aminobutyric acid (GABA), and N-acetyl-aspartyl-glutamate (NAAG) [4-6]. The striking metabolic overlap between cancer and neurological diseases sheds light on novel therapeutic strategies for cancer treatment. For example, 2-(phosphonomethyl) pentanedioic acid (2-PMPA), one of the glutamate carboxypeptidase II (GCP II) inhibitors that prevent the conversion of NAAG to glutamate, has been shown to suppress cancer growth [6, 7]. These promising results have led to an increased interest in integrating this metabolic overlap between cancer and neurological diseases into the study of cancer metabolism. The advantages of studying this metabolic overlap include not only drug repurposing but also translating existing knowledge from neurological diseases to the field of cancer research. This chapter discusses the specific overlapping metabolic features between cancer and neurological diseases, focusing on glutamine, GABA, and NAAG metabolisms. Understanding the interconnections between cancer and neurological diseases will guide researchers and clinicians to find more effective cancer treatments.

Uncovering the Role of N-Acetyl-Aspartyl-Glutamate as a Glutamate Reservoir in Cancer

N-acetyl-aspartyl-glutamate (NAAG) is a peptide-based neurotransmitter that has been extensively studied in many neurological diseases. In this study, we show a specific role of NAAG in cancer. We found that NAAG is more abundant in higher grade cancers and is a source of glutamate in cancers expressing glutamate carboxypeptidase II (GCPII), the enzyme that hydrolyzes NAAG to glutamate and N-acetyl-aspartate (NAA). Knocking down GCPII expression through genetic alteration or pharmacological inhibition of GCPII results in a reduction of both glutamate concentrations and cancer growth. Moreover, targeting GCPII in combination with glutaminase inhibition accentuates these effects. These findings suggest that NAAG serves as an important reservoir to provide glutamate to cancer cells through GCPII when glutamate production from other sources is limited. Thus, GCPII is a viable target for cancer therapy, either alone or in combination with glutaminase inhibition.

Nguyen et al. show that NAAG is more abundant in higher grade cancers and a source of glutamate in cancers expressing GCPII, the enzyme that hydrolyzes NAAG to glutamate and NAA. The results suggest that GCPII is a viable target for cancer therapy, either alone or in combination with glutaminase inhibition.

The Role of Metabotropic Glutamate Receptor 1 Dependent Signaling in Glioma Viability

Glioma refers to malignant central nervous system tumors that have histologic characteristics in common with glial cells. The most prevalent type, glioblastoma multiforme, is associated with a poor prognosis and few treatment options. On the basis of reports of aberrant expression of mGluR1 mRNA in glioma, evidence that melanoma growth is directly influenced by glutamate metabotropic receptor 1 (mGluR1), and characterization of β-arrestin-dependent prosurvival signaling by this receptor, this study investigated the hypothesis that glioma cell lines aberrantly express mGluR1 and depend on mGluR1-mediated signaling to maintain viability and proliferation. Three glioma cell lines (Hs683, A172, and U87) were tested to confirm mGluR1 mRNA expression and the dependence of glioma cell viability on glutamate. Pharmacologic and genetic evidence is presented that suggests mGluR1 signaling specifically supports glioma proliferation and viability. For example, selective noncompetitive antagonists of mGluR1, CPCCOEt and JNJ16259685, decreased the viability of these cells in a dose-dependent manner, and glutamate metabotropic receptor 1 gene silencing significantly reduced glioma cell proliferation. Also, results of an anchorage-independent growth assay suggested that noncompetitive antagonism of mGluR1 may decrease the tumorigenic potential of Hs683 glioma cells. Finally, data are provided that support the hypothesis that a β-arrestin-dependent signaling cascade may be involved in glutamate-stimulated viability in glioma cells and that ligand bias may exist at mGluR1 expressed in these cells. Taken together, the results strongly suggest that mGluR1 may act as a proto-oncogene in glioma and be a viable drug target in glioma treatment.

Targeting metabotropic glutamate receptors in the treatment of primary brain tumors

In spite of the recent advancement in the molecular characterization of malignant gliomas and medulloblastomas, the treatment of primary brain tumors remains suboptimal. The use of small molecule inhibitors of intracellular signaling pathways, inhibitors of angiogenesis, and immunotherapic agents is limited by systemic adverse effects, limited brain penetration, and, in some cases, lack of efficacy. Thus, adjuvant chemo-therapy and radiotherapy still remain the gold standard in the treatment of grade-IV astrocytoma (glioblastoma multiforme) and medulloblastoma. We review evidence that supports the development of mGlu3 receptor antagonists as add-on drugs in the treatment of malignant gliomas. These drugs appear to display pleiotropic effect on tumor cells, affecting proliferation, differentiation, and response to chemotherapy. mGlu1 and mGlu4 receptors could also be targeted by potential anticancer agents in the treatment of malignant gliomas and medulloblastoma, but extensive research is required for target validation.

Metabotropic glutamate receptors as a new therapeutic target for malignant gliomas

Metabotropic glutamate receptors (mGluR) are predominantly involved in maintenance of cellular homeostasis of central nervous system. However, evidences have suggested other roles of mGluR in human tumors. Aberrant mGluR signaling has been shown to participate in transformation and maintenance of various cancer types, including malignant brain tumors. This review intends to summarize recent findings regarding the involvement of mGluR-mediated intracellular signaling pathways in progression, aggressiveness, and recurrence of malignant gliomas, mainly glioblastomas (GBM), highlighting the potential therapeutic applications of mGluR ligands. In addition to the growing number of studies reporting mGluR gene or protein expression in glioma samples (resections, lineages, and primary cultures), pharmacological blockade in vitro of mGluR1 and mGluR3 by selective ligands has been shown to be anti-proliferative and anti-migratory, decreasing activation of MAPK and PI3K pathways. In addition, mGluR3 antagonists promoted astroglial differentiation of GBM cells and also enabled cytotoxic action of temozolomide (TMZ). mGluR3-dependent TMZ toxicity was supported by increasing levels of MGMT transcripts through an intracellular signaling pathway that sequentially involves PI3K and NF-κB. Further, continuous pharmacological blockade of mGluR1 and mGluR3 have been shown to reduced growth of GBM tumor in two independent in vivo xenograft models. In parallel, low levels of mGluR3 mRNA in GBM resections may be a predictor for long survival rate of patients. Since several Phase I, II and III clinical trials are being performed using group I and II mGluR modulators, there is a strong scientifically-based rationale for testing mGluR antagonists as an adjuvant therapy for malignant brain tumors.

RNAi for contactin 2 inhibits proliferation of U87-glioma stem cells by downregulating AICD, EGFR, and HES1

Glioblastoma is the most common form of malignant brain tumors and has a poor prognosis. Glioma stem cells (GSCs) are thought to be responsible for the aberrant proliferation and invasion. Targeting the signaling pathways that promote proliferation in GSCs is one of the strategies for glioma treatment. In this study, we found increased expression of contactin 2 (CNTN2) and amyloid β precursor protein (APP) in U87-derived GSCs (U87-GSCs). RNA interference (RNAi) for CNTN2 downregulated the expression of APP intracellular domain (AICD), which is the proteolytic product of APP. Treatment with CNTN2 RNAi inhibited the proliferation of U87-GSCs. CNTN2 RNAi decreased the expression of epidermal growth factor receptor and HES1, which are potential targets of AICD. In summary, inhibition of the CNTN2/APP signaling pathway may repress the proliferation in U87-GSCs via downregulating the expression of HES1 and epidermal growth factor receptor. CNTN2/APP/AICD signaling pathway plays an important role in U87 glial tumorigenesis. Further studies are warranted to elucidate the role of these signaling pathways in other sources of GSCs. Depending on their role in proliferation in other sources of GSCs, members of the CNTN2/APP/AICD signaling pathway may provide novel targets for the development of therapy for glioblastomas.

The miR-487b-3p/GRM3/TGFβ signaling axis is an important regulator of colon cancer tumorigenesis

Molecular targeting is an import strategy to treat advanced colon cancer. The current study demonstrates that expression of GRM3, a metabotropic glutamate receptor mainly expressed in mammalian central nervous system, is significantly upregulated in majority of human colonic adenocarcinomas tested and colon cancer cell lines. Knockdown of GRM3 expression or inhibition of GRM3 activation in colon cancer cells reduces cell survival and anchorage-independent growth in vitro and inhibits tumor growth in vivo. Mechanistically, GRM3 antagonizes TGFβ-mediated activation of protein kinase A and inhibition of AKT. In addition, TGFβ signaling increases GRM3 protein stability and knockdown of GRM3 enhances TGFβ-mediated tumor suppressor function. Further studies indicate that miR-487b-3p directly targets GRM3. Overexpression of miR-487b-3p mimics the effects of GRM3 knockdown and suppresses the tumorigenicity of colon cancer cells in vivo. Expression of miR-487b-3p is decreased in colon adenocarcinomas and inversely correlates with GRM3 expression. Taken together, these studies indicate that upregulation of GRM3 expression is a functionally important molecular event in colon cancer, and that GRM3 is a promising molecular target for colon cancer treatment. This is particularly interesting and important from a therapeutic standpoint because numerous metabotropic glutamate receptor antagonists are available, many of which have been found unsuitable for treatment of neuropsychiatric disorders for reasons such as inability to readily penetrate blood brain barriers. Since GRM3 is upregulated in colon cancer, but rarely expressed in normal peripheral tissues, targeting GRM3 with such agents would not likely cause adverse neurological or peripheral side effects, making GRM3 an attractive and specific molecular target for colon cancer treatment.