Glutamate signaling in benign and malignant disorders: current status, future perspectives, and therapeutic implications

Involvement of metabotropic glutamate receptors in regulation of immune response in the Pacific oyster Crassostrea gigas

Metabotropic glutamate receptors (mGluRs) play a pivotal role in the neuroendocrine-immune regulation. In this study, eight mGluRs were identified in the Pacific Oyster Crassostrea gigas, which were classified into three subfamilies based on genetic similarity. All CgmGluRs harbor variable numbers of PBP1 domains at the N-terminus. The sequence and structural features of CgmGluRs are highly similar to mGluRs in other species. A uniformly upregulated expression of CgmGluRs was observed during D-shaped larval stage compared to early D-shaped larval stage. The transcripts of CgmGluRs were detectable in various tissues of oyster. Different CgmGluR exhibited diverse expression patterns response against different PAMP stimulations, among which CgmGluR5 was significantly downregulated under these stimulations, reflecting its sensitivity and broad-spectrum responsiveness to microbes. Following LPS stimulation, the mRNA expression of CgmGluR5 and CgCALM1 in haemocytes was suppressed within 6 h and returned to normal levels by 12 h. Inhibition of CgmGluR5 activity resulted in a significant reduction in CgCALM1 expression after 12 h. Further KEGG enrichment analysis suggested that CgmGluR5 might modulate calcium ion homeostasis and metabolic pathways by regulating CgCALM1. This research delivers the systematic analysis of mGluR in the Pacific Oyster, offering insights into evolutionary characteristics and immunoregulatory function of mGluR in mollusks.

Expression of mGluR5 in Pediatric Hodgkin and Non-Hodgkin lymphoma-A Comparative Analysis of Immunohistochemical and Clinical Findings Regarding the Association between Tumor and Paraneoplastic Neurological Disease

Autoantibodies targeting the neuronal antigen metabotropic glutamate receptor 5 (mGluR5) have been identified in patients with Ophelia syndrome, which describes a co-occurrence of paraneoplastic limbic encephalitis and Hodgkin lymphoma (HL). Little data exist regarding frequency and function of mGluR5 in HL and its potential role in causing seropositive paraneoplastic disease. We studied a representative cohort of pediatric HL and NHL patients (n = 57) using immunohistochemistry and fluorescence staining to investigate mGluR5 expression. All lymphoma tissues displayed positive mGluR5 staining, with focus on Hodgkin-Reed-Sternberg (H-RS) cells. We did not detect any mGluR5 staining in tumor-free lymph nodes, which is consistent with the absence of GRM5 transcripts in RNA-sequencing data from non-malignant B and T cells. The frequent presence in pediatric lymphoma falls in line with reports of mGluR5 expression and associated tumor progression in other malignancies. We tested for correlation with clinical features, focusing on disease progression and neurological symptoms. Low mGluR5 expression in H-RS cells correlated with young patient age (<15 years) and positive histology for EBV infection. Paraneoplastic or neurological symptoms were found exclusively in HL patients. While an impact of mGluR5 on HL severity remains possible, a prognostic value of mGluR5 expression levels requires further investigation.

Current State of Melanoma Therapy and Next Steps: Battling Therapeutic Resistance

Melanoma is the most aggressive and deadly form of skin cancer due to its high propensity to metastasize to distant organs. Significant progress has been made in the last few decades in melanoma therapeutics, most notably in targeted therapy and immunotherapy. These approaches have greatly improved treatment response outcomes; however, they remain limited in their abilities to hinder disease progression due, in part, to the onset of acquired resistance. In parallel, intrinsic resistance to therapy remains an issue to be resolved. In this review, we summarize currently available therapeutic options for melanoma treatment and focus on possible mechanisms that drive therapeutic resistance. A better understanding of therapy resistance will provide improved rational strategies to overcome these obstacles.

Integrated network pharmacology and metabolomics reveal the action mechanisms of vincristine combined with celastrol against colon cancer

Colon cancer is associated with a high mortality rate. Vincristine (VCR) is a commonly used chemotherapeutic drug. Celastrol (CEL) is an effective component which exerts inhibitory effects on colon cancer. Combination treatment improves resistance to chemotherapeutic drugs and enhances their efficacy. Therefore, we aimed to explore the molecular mechanisms of VCR combined with CEL in colon cancer treatment. We verified the effects of VCR combined with CEL on the proliferation, cell cycle, and apoptosis of HCT-8 cells. Non-targeted metabolomic techniques were used to analyse the changes in cellular metabolites after administration. Finally, network pharmacology technology was used to screen the potential targets and pathways. VCR combined with CEL had synergistic inhibitory effects on HCT-8 colon cancer cells. Cell metabolomics identified 12 metabolites enriched in metabolic pathways, such as the phenylalanine, tyrosine and tryptophan biosynthesis pathways. Network pharmacology revealed that MAPK1, AKT1, PIK3CB, EGFR, and VEGFA were the key targets. Western blotting revealed that VCR combined with CEL activated the P53 pathway by suppressing the PI3K/AKT signalling pathway activation and Bcl-2 expression, promoting the Bax expression. Therefore, VCR combined with CEL potentially treats colon cancer by increasing the apoptosis, improving energy metabolism, and inhibiting PI3K/AKT pathway in colon cancer cells.

Colorectal cancer-associated T cell receptor repertoire abnormalities are linked to gut microbiome shifts and somatic cell mutations

As with many diseases, tumor formation in colorectal cancer (CRC) is multifactorial and involves immune, environmental factors and various genetics that contribute to disease development. Accumulating evidence suggests that the gut microbiome is linked to the occurrence and development of CRC, and these microorganisms are important for immune maturation. However, a systematic perspective integrating microbial profiling, T cell receptor (TCR) and somatic mutations in humans with CRC is lacking. Here, we report distinct features of the expressed TCRβ repertoires in the peripheral blood of and CRC patients (n = 107) and healthy donors (n = 30). CRC patients have elevated numbers of large TCRβ clones and they have very low TCR diversity. The metagenomic sequencing data showed that the relative abundance of Fusobacterium nucleatum (F. nucleatum), Escherichia coli and Dasheen mosaic virus were elevated consistently in CRC patients (n = 97) compared to HC individuals (n = 30). The abundance of Faecalibacterium prausnitzii and Roseburia intestinalis was reduced in CRC (n = 97) compared to HC (n = 30). The correlation between somatic mutations of target genes (16 genes, n = 79) and TCR clonality and microbial biomarkers in CRC had been investigated. Importantly, we constructed a random forest classifier (contains 15 features) based on microbiome and TCR repertoires, which can be used as a clinical detection method to screen patients for CRC. We also analysis of F. nucleatum-specific TCR repertoire characteristics. Collectively, our large-cohort multi-omics data aimed to identify novel biomarkers to inform clinical decision-making in the detection and diagnosis of CRC, which is of possible etiological and diagnostic significance.

The delta subunit of the GABAA receptor is necessary for the GPT2-promoted breast cancer metastasis

Objectives: Glutamic pyruvate transaminase (GPT2) catalyzes the reversible transamination between alanine and α-ketoglutarate (α-KG) to generate pyruvate and glutamate during cellular glutamine catabolism. The glutamate could be further converted to γ-aminobutyric acid (GABA). However, the role of GPT2 in tumor metastasis remains unclear. Methods: The wound healing and transwell assays were carried out to analyze breast cancer cell migration and invasion in vitro. Gene ontology analysis was utilized following RNA-sequencing to discover the associated molecule function. The mass spectrometry analysis following phosphoprotein enrichment was performed to discover the associated transcription factors. Most importantly, both the tail vein model and Mammary gland conditional Gpt2^-/- spontaneous tumor mouse models were used to evaluate the effect of GPT2 on breast cancer metastasis in vivo. Results: GPT2 overexpression increases the content of GABA and promotes breast cancer metastasis by activating GABA_A receptors. The delta subunit GABRD is necessary for the GPT2/GABA-induced breast cancer metastasis in xenograft and transgenic mouse models. Gpt2 knockout reduces the lung metastasis of the genetic Gpt2^-/- breast cancer in mice and prolongs the overall survival of tumor burden mice. Mechanistically, GPT2-induced GABA_A receptor activation increases Ca²⁺ influx by turning on its associated calcium channel, and the surged intracellular calcium triggers the PKC-CREB pathway activation. The activated transcription factor CREB accelerates breast cancer metastasis by upregulating metastasis-related gene expressions, such as PODXL, MMP3, and MMP9. Conclusion: In summary, this study demonstrates that GPT2 promotes breast cancer metastasis through up-regulated GABA activation of GABA_AR-PKC-CREB signaling, suggesting it is a potential target for breast cancer therapy.

Adaptive and non-adaptive gene expression responses in prostate cancer during androgen deprivation

Androgen deprivation therapy is the cornerstone treatment of advanced prostate cancer. Eventually prostate cancer cells overcome androgen deprivation therapy, giving rise to castration resistant prostate cancer (CRPC) characterized by increased androgen receptor (AR) activity. Understanding the cellular mechanisms leading to CRPC is needed for development of novel treatments. We used long-term cell cultures to model CRPC; a testosterone-dependent cell line (VCaP-T) and cell line adapted to grow in low testosterone (VCaP-CT). These were used to uncover persistent and adaptive responses to testosterone level. RNA was sequenced to study AR-regulated genes. Expression level changed due to testosterone depletion in 418 genes in VCaP-T (AR-associated genes). To evaluate significance for CRPC growth, we compared which of them were adaptive i.e., restored expression level in VCaP-CT. Adaptive genes were enriched to steroid metabolism, immune response and lipid metabolism. The Cancer Genome Atlas Prostate Adenocarcinoma data were used to assess the association with cancer aggressiveness and progression-free survival. Expressions of 47 AR-associated or association gaining genes were statistically significant markers for progression-free survival. These included genes related to immune response, adhesion and transport. Taken together, we identified and clinically validated multiple genes being linked with progression of prostate cancer and propose several novel risk genes. Possible use as biomarkers or therapeutic targets should be studied further.

Implications of a Neuronal Receptor Family, Metabotropic Glutamate Receptors, in Cancer Development and Progression

Cancer is the second leading cause of death, and incidences are increasing globally. Simply defined, cancer is the uncontrolled proliferation of a cell, and depending on the tissue of origin, the cancer etiology, biology, progression, prognosis, and treatment will differ. Carcinogenesis and its progression are associated with genetic factors that can either be inherited and/or acquired and are classified as an oncogene or tumor suppressor. Many of these genetic factors converge on common signaling pathway(s), such as the MAPK and PI3K/AKT pathways. In this review, we will focus on the metabotropic glutamate receptor (mGluR) family, an upstream protein that transmits extracellular signals into the cell and has been shown to regulate many aspects of tumor development and progression. We explore the involvement of members of this receptor family in various cancers that include breast cancer, colorectal cancer, glioma, kidney cancer, melanoma, oral cancer, osteosarcoma, pancreatic cancer, prostate cancer, and T-cell cancers. Intriguingly, depending on the member, mGluRs can either be classified as oncogenes or tumor suppressors, although in general most act as an oncogene. The extensive work done to elucidate the role of mGluRs in various cancers suggests that it might be a viable strategy to therapeutically target glutamatergic signaling.

Nontargeted and targeted metabolomics approaches reveal the key amino acid alterations involved in multiple myeloma

PURPOSE

Multiple myeloma (MM), a kind of malignant neoplasm of clonal plasma cells in the bone marrow, is a refractory disease. Understanding the metabolism disorders and identification of metabolomics pathways as well as key metabolites will provide new insights for exploring diagnosis and therapeutic targets of MM.

METHODS

We conducted nontargeted metabolomics analysis of MM patients and normal controls (NC) using ultra-high-performance liquid chromatography (UHPLC) combined with quadrupole time-of-flight mass spectrometry (Q-TOF-MS) in 40 cases of cohort 1 subjects. The targeted metabolomics analysis of amino acids using multiple reaction monitoring-mass spectrometry (MRM-MS) was also performed in 30 cases of cohort 1 and 30 cases of cohort 2 participants, to comprehensively investigate the metabolomics disorders of MM.

RESULTS

The nontargeted metabolomics analysis in cohort 1 indicated that there was a significant metabolic signature change between MM patients and NC. The differential metabolites were mainly enriched in metabolic pathways related to amino acid metabolism, such as protein digestion and absorption, and biosynthesis of amino acids. Further, the targeted metabolomics analysis of amino acids in both cohort 1 and cohort 2 revealed differential metabolic profiling between MM patients and NC. We identified 12 and 14 amino acid metabolites with altered abundance in MM patients compared to NC subjects, in cohort 1 and cohort 2, respectively. Besides, key differential amino acid metabolites, such as choline, creatinine, leucine, tryptophan, and valine, may discriminate MM patients from NC. Moreover, the differential amino acid metabolites were associated with clinical indicators of MM patients.

CONCLUSIONS

Our findings indicate that amino acid metabolism disorders are involved in MM. The differential profiles reveal the potential utility of key amino acid metabolites as diagnostic biomarkers of MM. The alterations in metabolome, especially the amino acid metabolome, may provide more evidences for elucidating the pathogenesis and development of MM.

Riluzole: A neuroprotective drug with potential as a novel anti‑cancer agent (Review)

Riluzole, a glutamate release inhibitor, has been in use for the treatment of amyotrophic lateral sclerosis for over two decades since its approval by the Food and Drug Administration. Recently, riluzole has been evaluated in cancer cells and indicated to block cell proliferation and/or induce cell death. Riluzole has been proven effective as an anti-neoplastic drug in cancers of various tissue origins, including the skin, breast, pancreas, colon, liver, bone, brain, lung and nasopharynx. While cancer cells expressing glutamate receptors frequently respond to riluzole treatment, numerous types of cancer cell lacking glutamate receptors unexpectedly responded to riluzole treatment as well. Riluzole was demonstrated to interfere with glutamate secretion, growth signaling pathways, Ca²⁺ homeostasis, glutathione synthesis, reactive oxygen species generation and integrity of DNA, as well as autophagic and apoptotic pathways. Of note, riluzole is highly effective in inducing cell death in cisplatin-resistant lung cancer cells. Furthermore, riluzole pretreatment sensitizes glioma and melanoma to radiation therapy. In addition, in triple-negative breast cancer, colorectal cancer, melanoma and glioblastoma, riluzole has synergistic effects in combination with select drugs. In an effort to highlight the therapeutic potential of riluzole, the current study reviewed the effect and outcome of riluzole treatment on numerous cancer types investigated thus far. The mechanism of action and the various molecular pathways affected by riluzole are discussed.

GPCR_LigandClassify.py; a rigorous machine learning classifier for GPCR targeting compounds

The current study describes the construction of various ligand-based machine learning models to be used for drug-repurposing against the family of G-Protein Coupled Receptors (GPCRs). In building these models, we collected > 500,000 data points, encompassing experimentally measured molecular association data of > 160,000 unique ligands against > 250 GPCRs. These data points were retrieved from the GPCR-Ligand Association (GLASS) database. We have used diverse molecular featurization methods to describe the input molecules. Multiple supervised ML algorithms were developed, tested and compared for their accuracy, F scores, as well as for their Matthews' correlation coefficient scores (MCC). Our data suggest that combined with molecular fingerprinting, ensemble decision trees and gradient boosted trees ML algorithms are on the accuracy border of the rather sophisticated deep neural nets (DNNs)-based algorithms. On a test dataset, these models displayed an excellent performance, reaching a ~ 90% classification accuracy. Additionally, we showcase a few examples where our models were able to identify interesting connections between known drugs from the Drug-Bank database and members of the GPCR family of receptors. Our findings are in excellent agreement with previously reported experimental observations in the literature. We hope the models presented in this paper synergize with the currently ongoing interest of applying machine learning modeling in the field of drug repurposing and computational drug discovery in general.

Unveiling the pathogenesis of perineural invasion from the perspective of neuroactive molecules

Perineural invasion (PNI) is characterized by an encounter between the cancer cells and neuronal fibers and holds an extremely poor prognosis for malignant tumors. The exact molecular mechanism behind PNI yet remains to be explored. However, it is worth-noting that an involvement of the neuroactive molecules plays a major part in this process. A complex signaling network comprising the interplay between immunological cascades and neurogenic molecules such as tumor-derived neurotrophins, neuromodulators, and growth factors constitutes an active microenvironment for PNI associated with malignancy. The present review aims at discussing the following points in relation to PNI: a) Communication between PNI and neuroplasticity mechanisms can explain the pathophysiology of poor, short and long-term outcomes in cancer patients; b) Neuroactive molecules can significantly alter the neurons and cancer cells so as to sustain PNI progression; c) Finally, careful manipulation of neurogenic pathways and/or their crosstalk with the immunological molecules implicated in PNI could provide a potential breakthrough in cancer therapeutics.

Inhibition of xCT suppresses the efficacy of anti-PD-1/L1 melanoma treatment through exosomal PD-L1-induced macrophage M2 polarization

Tumor cells increase glutamate release through the cystine/glutamate transporter cystine-glutamate exchange (xCT) to balance oxidative homeostasis in tumor cells and promote tumor progression. Although clinical studies have shown the potential of targeting programmed cell death 1 (PD-1)/programmed death ligand 1 (PD-L1) signaling in melanoma, response rates are low. However, it remains unclear how glutamate metabolism affects anti-PD-1/PD-L1 treatment efficacy in melanoma. Here, we demonstrated that although inhibition of xCT either by pharmacological inhibitor (sulfasalazine [SAS]), approved by US Food and Drug Administration (FDA) for inflammatory diseases, or genetic knockdown induced reactive oxygen species (ROS)-related death in melanoma cells, inhibition of xCT significantly reduced the efficacy of anti-PD-1/PD-L1 immune checkpoint blockade through upregulating PD-L1 expression via the transcription factors IRF4/EGR1, as a consequence, exosomes carrying relatively large amounts of PD-L1 secreted from melanoma cells resulted in M2 macrophage polarization and reduced the efficacy of anti-PD-1/PD-L1 therapy in melanoma. Taken together, our results reveal that inhibition of xCT by SAS is a promising therapeutic strategy for melanoma; on the other hand, SAS treatment blunted the efficacy of anti-PD-1/PD-L1 via exosomal PD-L1-induced macrophage M2 polarization and eventually induced anti-PD-1/PD-L1 therapy resistance.

Novel thienopyrimidine analogues as potential metabotropic glutamate receptors inhibitors and anticancer activity: Synthesis, In-vitro, In-silico, and SAR approaches

There is a continuous need in drug development approach for synthetic anticancer analogues with new therapeutic targets to diminish chemotherapeutic resistance of cancer cells. This study presents new group of synthetic thienopyrimidine analogues (1-9) aims as mGluR-1 inhibitors with anticancer activity. In-vitro antiproliferative assessment was carried out using viability assay against cancer cell lines (MCF-7, A-549 and PC-3) compared to WI-38 normal cell line. Analogues showed variable anticancer activity with IC₅₀ ranging from 6.60 to 121 µg/mL with compound 7b is the most potent analogue against the three cancer cell lines (MCF-7; 6.57 ± 0.200, A-549; 6.31 ± 0.400, PC-3;7.39 ± 0.500 µg/mL) compared to Doxorubicin, 5-Flurouracil and Riluzole controls. Selected compounds were tested as mGluR-1 inhibitors in MCF-7 cell line and results revealed compound 7b induced significant reduction in extracellular glutamate release (IC₅₀; 4.96 ± 0.700 µM) compared to other analogues and next to Riluzole (IC₅₀; 2.80 ± 0.500 µM) of the same suggested mode of action. Furthermore, both cell cycle and apoptosis assays confirmed the potency of compound 7b for early apoptosis of MCF-7 at G₂/M phase and apoptotic positive cell shift to (91.4%) compared to untreated control (19.6%) and Raptinal positive control (51.4%). On gene expression level, compound 7b induced over-expression of extrinsic (FasL, TNF-α and Casp-8), intrinsic (Cyt-C, Casp-3, Bax) apoptotic genes with down-regulation of anti-apoptotic Bcl-2 gene with boosted Bax/Bcl-2 ratio to 2.6-fold increase. Molecular docking and dynamic studies confirmed the biological potency through strong binding and stability modes of 7b where it was faster in reaching the equilibrium point and achieving the stability than Riluzole over 20 ns MD. These results suggest compound 7b as a promising mGluR inhibitory scaffold with anticancer activity that deserves further optimization and in-depth In-vivo and clinical investigations.

Glutamine Uptake via SNAT6 and Caveolin Regulates Glutamine-Glutamate Cycle

SLC38A6 (SNAT6) is the only known member of the SLC38 family that is expressed exclusively in the excitatory neurons of the brain. It has been described as an orphan transporter with an unknown substrate profile, therefore very little is known about SNAT6. In this study, we addressed the substrate specificity, mechanisms for internalization of SNAT6, and the regulatory role of SNAT6 with specific insights into the glutamate-glutamine cycle. We used tritium-labeled amino acids in order to demonstrate that SNAT6 is functioning as a glutamine and glutamate transporter. SNAT6 revealed seven predicted transmembrane segments in a homology model and was localized to caveolin rich sites at the plasma membrane. SNAT6 has high degree of specificity for glutamine and glutamate. Presence of these substrates enables formation of SNAT6-caveolin complexes that aids in sodium dependent trafficking of SNAT6 off the plasma membrane. To further understand its mode of action, several potential interacting partners of SNAT6 were identified using bioinformatics. Among them where CTP synthase 2 (CTPs2), phosphate activated glutaminase (Pag), and glutamate metabotropic receptor 2 (Grm2). Co-expression analysis, immunolabeling with co-localization analysis and proximity ligation assays of these three proteins with SNAT6 were performed to investigate possible interactions. SNAT6 can cycle between cytoplasm and plasma membrane depending on availability of substrates and interact with Pag, synaptophysin, CTPs2, and Grm2. Our data suggest a potential role of SNAT6 in glutamine uptake at the pre-synaptic terminal of excitatory neurons. We propose here a mechanistic model of SNAT6 trafficking that once internalized influences the glutamate-glutamine cycle in presence of its potential interacting partners.

Revealing the Potential Application of EC-Synthetic Retinoid Analogues in Anticancer Therapy

(1) Background and Aim: All-trans retinoic acid (ATRA) induces differentiation and inhibits growth of many cancer cells. However, resistance develops rapidly prompting the urgent need for new synthetic and potent derivatives. EC19 and EC23 are two synthetic retinoids with potent stem cell neuro-differentiation activity. Here, these compounds were screened for their in vitro antiproliferative and cytotoxic activity using an array of different cancer cell lines. (2) Methods: MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, AV/PI (annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI)), cell cycle analysis, immunocytochemistry, gene expression analysis, Western blotting, measurement of glutamate and total antioxidant concentrations were recruited. (3) Results: HepG2, Caco-2, and MCF-7 were the most sensitive cell lines; HepG2 (ATRA; 36.2, EC19; 42.2 and EC23; 0.74 µM), Caco-2 (ATRA; 58.0, EC19; 10.8 and EC23; 14.7 µM) and MCF-7 (ATRA; 99.0, EC19; 9.4 and EC23; 5.56 µM). Caco-2 cells were selected for further biochemical investigations. Isobologram analysis revealed the combined synergistic effects with 5-fluorouracil with substantial reduction in IC50. All retinoids induced apoptosis but EC19 had higher potency, with significant cell cycle arrest at subG0-G1, -S and G2/M phases, than ATRA and EC23. Moreover, EC19 reduced cellular metastasis in a transwell invasion assay due to overexpression of E-cadherin, retinoic acid-induced 2 (RAI2) and Werner (WRN) genes. (4) Conclusion: The present study suggests that EC-synthetic retinoids, particularly EC19, can be effective, alone or in combinations, for potential anticancer activity to colorectal cancer. Further in vivo studies are recommended to pave the way for clinical applications.

Tumor-induced neurogenesis and immune evasion as targets of innovative anti-cancer therapies

Normal cells are hijacked by cancer cells forming together heterogeneous tumor masses immersed in aberrant communication circuits that facilitate tumor growth and dissemination. Besides the well characterized angiogenic effect of some tumor-derived factors; others, such as BDNF, recruit peripheral nerves and leukocytes. The neurogenic switch, activated by tumor-derived neurotrophins and extracellular vesicles, attracts adjacent peripheral fibers (autonomic/sensorial) and neural progenitor cells. Strikingly, tumor-associated nerve fibers can guide cancer cell dissemination. Moreover, IL-1β, CCL2, PGE2, among other chemotactic factors, attract natural immunosuppressive cells, including T regulatory (Tregs), myeloid-derived suppressor cells (MDSCs), and M2 macrophages, to the tumor microenvironment. These leukocytes further exacerbate the aberrant communication circuit releasing factors with neurogenic effect. Furthermore, cancer cells directly evade immune surveillance and the antitumoral actions of natural killer cells by activating immunosuppressive mechanisms elicited by heterophilic complexes, joining cancer and immune cells, formed by PD-L1/PD1 and CD80/CTLA-4 plasma membrane proteins. Altogether, nervous and immune cells, together with fibroblasts, endothelial, and bone-marrow-derived cells, promote tumor growth and enhance the metastatic properties of cancer cells. Inspired by the demonstrated, but restricted, power of anti-angiogenic and immune cell-based therapies, preclinical studies are focusing on strategies aimed to inhibit tumor-induced neurogenesis. Here we discuss the potential of anti-neurogenesis and, considering the interplay between nervous and immune systems, we also focus on anti-immunosuppression-based therapies. Small molecules, antibodies and immune cells are being considered as therapeutic agents, aimed to prevent cancer cell communication with neurons and leukocytes, targeting chemotactic and neurotransmitter signaling pathways linked to perineural invasion and metastasis.

Osteosarcoma growth suppression by riluzole delivery via iron oxide nanocage in nude mice

Osteosarcomas are the most commonly occurring malignant bone cancer in young individuals. The survival rate of patients with metastatic osteosarcoma is low and has been stagnant for over two decades. We previously demonstrated that the glutamate release inhibitor, riluzole inhibits osteosarcoma cell growth. Towards the development of more effective therapy, we investigated the delivery of riluzole in human metastatic osteosarcoma xenografts in mice. We compared the efficacy of riluzole delivery by intraperitoneally injecting either free riluzole or riluzole released via two different shapes of iron oxide nanoparticles (nanocage or nanosphere) of size 15±2.5 nm. We monitored tumor size using Vernier calipers and bioluminescence assay and found a significant reduction in tumor size in the riluzole-treated groups when injected, either in free form or via nanoparticles, compared to the control groups (PBS, nanosphere or nanocage). Importantly, nanocage-delivered riluzole was most effective in reducing tumor size in the xenograft nude mice. While riluzole delivery induced apoptosis in tumor tissues in all three groups of riluzole-treated animals, it was highest in tumors from the nanocage-delivered riluzole group. Therefore, we conclude that riluzole is an effective drug to reduce tumor size in osteosarcoma and the efficacy of riluzole as a apoptotic and tumor-reducing drug is enhanced when delivered via nanocage.

Integrated molecular analysis of Tamoxifen-resistant invasive lobular breast cancer cells identifies MAPK and GRM/mGluR signaling as therapeutic vulnerabilities

Invasive lobular breast cancer (ILC) is an understudied malignancy with distinct clinical, pathological, and molecular features that distinguish it from the more common invasive ductal carcinoma (IDC). Mounting evidence suggests that estrogen receptor-alpha positive (ER+) ILC has a poor response to Tamoxifen (TAM), but the mechanistic drivers of this are undefined. In the current work, we comprehensively characterize the SUM44/LCCTam ILC cell model system through integrated analysis of gene expression, copy number, and mutation, with the goal of identifying actionable alterations relevant to clinical ILC that can be co-targeted along with ER to improve treatment outcomes. We show that TAM has several distinct effects on the transcriptome of LCCTam cells, that this resistant cell model has acquired copy number alterations and mutations that impinge on MAPK and metabotropic glutamate receptor (GRM/mGluR) signaling networks, and that pharmacological inhibition of either improves or restores the growth-inhibitory actions of endocrine therapy.

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.

Allosteric and Orthosteric Activators of mGluR8 Differentially Affect the Chemotherapeutic-Induced Human Neuroblastoma SH-SY5Y Cell Damage: The Impact of Cell Differentiation State

The participation of group III metabotropic glutamate receptors (mGluRs) in cancer growth and progression is still an understudied issue. Based on our recent data on high expression of mGluR8 in human neuroblastoma SH-SY5Y cells, in this study, we evaluated the effect of an mGluR8-specific positive allosteric modulator (PAM: AZ12216052) and orthosteric agonist [(S)-3,4-DCPG ((S)-3,4-dicarboxyphenylglycine)] on chemotherapeutic (doxorubicin, irinotecan or cisplatin)-evoked cell damage in undifferentiated (UN-) and retinoic acid-differentiated (RA-) SH-SY5Y cells. The data showed that AZ12216052 as well as a group III mGluR antagonist (UBP1112) but not (S)-3,4-DCPG partially inhibited the cell damage evoked by doxorubicin, irinotecan or cisplatin in UN-SH-SY5Y cells. In RA-SH-SY5Y, we observed only a modest protective effect of mGluR8 PAM. In contrast, both types of mGluR8 activators significantly enhanced toxic effects of doxorubicin and irinotecan in RA-SH-SY5Y cells. These data suggest that in undifferentiated neuroblastoma malignant cells, some mGluR8 modulators can decrease cytotoxic effects of chemotherapeutics which exclude them from the group of putative anticancer agents. On the other hand, in SH-SY5Y cells differentiated to a more mature neuron-like phenotype, that is non-malignant cells, the mGluR8 activators can aggravate the chemotherapeutic neurotoxicity which is a well-known undesired effect of these drugs. Our pharmacological data add new observations to the unexplored field of research on the role of mGluR8 in cancer, pointing to complexity of response which could be mediated by particular types of mGluR8 ligands at least in neuroblastoma cells.

Rat Cerebrospinal Fluid Treatment Method through Cisterna Cerebellomedullaris Injection

Drugs that lack the ability to cross the blood-brain barrier (BBB) need to be placed directly into the central nervous system. Our laboratory studies the involvement of the glutamatergic system in the aggressiveness of glioma, and some ligands of glutamate receptors cannot permeate the BBB. Here, glioma-implanted rats were treated by a technique that delivers ligands directly into the cerebrospinal fluid by puncture into the cisterna cerebellomedullaris. Rats were anesthetized and fixed in a rodent stereotactic device. The head was gently tilted downwards at an angle that allowed exposure of the cisterna. Injection into the cisterna was done freehand using a gingival needle coupled to a microsyringe. The efficiency of intracisternal injection was demonstrated using a methylene blue solution. This type of injection is adaptable for any rodent model using small volumes of a variety of other drugs, and is an interesting method for neuroscience studies.

Activation of Grm1 expression by mutated BRaf (V600E) in vitro and in vivo

Our laboratory previously showed that ectopic expression of Grm1 is sufficient to induce spontaneous melanoma formation with 100% penetrance in transgenic mouse model, TG-3, which harbors wild-type BRaf. Studies identified Grm1 expression in human melanoma cell lines and primary to secondary metastatic melanoma biopsies having wild-type or mutated BRaf, but not in normal melanocytes or benign nevi. Grm1 expression was detected in tissues from mice genetically engineered with inducible melanocyte-specific BRaf^V600E. Additionally, stable clones derived from introduction of exogenous BRaf^V600E in mouse melanocytes also showed Grm1 expression, which was not detected in the parental or empty vector-derived cells, suggesting that expression of BRaf^V600E could activate Grm1 expression. Despite aberrant Grm1 expression in the inducible, melanocyte-specific BRaf^V600E mice, no tumors formed. However, in older mice, the melanocytes underwent senescence, as demonstrated previously by others. It was proposed that upregulated p15 and TGFβ contributed to the senescence phenotype. In contrast, in older TG-3 mice the levels of p15 and TGFβ remained the same or lower. Taken together, these results suggest the temporal regulation on the expression of "oncogenes" such as Grm1 or BRaf^V600E is critical in the future fate of the cells. If BRaf^V600E is turned on first, Grm1 expression can be induced, but this is not sufficient to result in development of melanoma; the cells undergo senescence. In contrast, if ectopic expression of Grm1 is turned on first, then regardless of wild-type or mutated BRaf in the melanocytes melanoma development is the consequence.

Glutaminolysis drives membrane trafficking to promote invasiveness of breast cancer cells

The role of glutaminolysis in providing metabolites to support tumour growth is well-established, but the involvement of glutamine metabolism in invasive processes is yet to be elucidated. Here we show that normal mammary epithelial cells consume glutamine, but do not secrete glutamate. Indeed, low levels of extracellular glutamate are necessary to maintain epithelial homoeostasis, and provision of glutamate drives disruption of epithelial morphology and promotes key characteristics of the invasive phenotype such as lumen-filling and basement membrane disruption. By contrast, primary cultures of invasive breast cancer cells convert glutamine to glutamate which is released from the cell through the system Xc- antiporter to activate a metabotropic glutamate receptor. This contributes to the intrinsic aggressiveness of these cells by upregulating Rab27-dependent recycling of the transmembrane matrix metalloprotease, MT1-MMP to promote invasive behaviour leading to basement membrane disruption. These data indicate that acquisition of the ability to release glutamate is a key watershed in disease aggressiveness.

A systems medicine approach for finding target proteins affecting treatment outcomes in patients with non-Hodgkin lymphoma

Autoantibody profiling with a systems medicine approach can help identify critical dysregulated signaling pathways (SPs) in cancers. In this way, immunoglobulins G (IgG) purified from the serum samples of 92 healthy controls, 10 pre-treated (PR) non-Hodgkin lymphoma (NHL) patients, and 20 NHL patients who underwent chemotherapy (PS) were screened with a phage-displayed random peptide library. Protein-protein interaction networks of the PR and PS groups were analyzed and visualized by Gephi. The results indicated AXIN2, SENP2, TOP2A, FZD6, NLK, HDAC2, HDAC1, and EHMT2, in addition to CAMK2A, PLCG1, PLCG2, GRM5, GRIN2B, GRIN2D, CACNA2D3, and SPTAN1 as hubs in 11 and 7 modules of PR and PS networks, respectively. PR- and PS-specific hubs were evaluated in the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Reactome databases. The PR-specific hubs were involved in Wnt SP, signaling by Notch1 in cancer, telomere maintenance, and transcriptional misregulation. In contrast, glutamate receptor SP, Fc receptor-related pathways, growth factors-related SPs, and Wnt SP were statistically significant enriched pathways, based on the pathway analysis of PS hubs. The results revealed that the most PR-specific proteins were associated with events involved in tumor development, while chemotherapy in the PS group was associated with side effects of drugs and/or cancer recurrence. As the findings demonstrated, PR- and PS-specific proteins in this study can be promising therapeutic targets in future studies.

Glutamic Pyruvate Transaminase GPT2 Promotes Tumorigenesis of Breast Cancer Cells by Activating Sonic Hedgehog Signaling

Increased glutamine metabolism is a hallmark of cancer. Mitochondrial glutamic pyruvate transaminase (GPT2) catalyzes the reversible transamination between alanine and α-ketoglutarate (α-KG), also known as 2-oxoglutarate, to generate pyruvate and glutamate during cellular glutamine catabolism. However, the precise role of GPT2 in tumorigenesis remains elusive. Here, we report that in breast cancer tissue samples and breast cancer cell lines, GPT2 expression level was markedly elevated and correlated with the pathological grades of breast cancers. GPT2 overexpression increased the subpopulation of breast cancer stem cells in vitro and promoted tumorigenesis in mice. GPT2 reduced α-KG level in cells leading to the inhibition of proline hydroxylase 2 (PHD2) activity involved in the regulation of HIF1α stability. Accumulation of HIF1α, resulting from GPT2-α-KG-PHD2 axial, constitutively activates sonic hedgehog (Shh) signaling pathway. Overall, GPT2 promotes tumorigenesis and stemness of breast cancer cells by activating the Shh signaling, suggesting that GTP2 is a potential target for breast cancer therapy.

tsRNA signatures in cancer

Small, noncoding RNAs are short untranslated RNA molecules, some of which have been associated with cancer development. Recently we showed that a class of small RNAs generated during the maturation process of tRNAs (tRNA-derived small RNAs, hereafter "tsRNAs") is dysregulated in cancer. Specifically, we uncovered tsRNA signatures in chronic lymphocytic leukemia and lung cancer and demonstrated that the ts-4521/3676 cluster (now called "ts-101" and "ts-53," respectively), ts-46, and ts-47 are down-regulated in these malignancies. Furthermore, we showed that tsRNAs are similar to Piwi-interacting RNAs (piRNAs) and demonstrated that ts-101 and ts-53 can associate with PiwiL2, a protein involved in the silencing of transposons. In this study, we extended our investigation on tsRNA signatures to samples collected from patients with colon, breast, or ovarian cancer and cell lines harboring specific oncogenic mutations and representing different stages of cancer progression. We detected tsRNA signatures in all patient samples and determined that tsRNA expression is altered upon oncogene activation and during cancer staging. In addition, we generated a knocked-out cell model for ts-101 and ts-46 in HEK-293 cells and found significant differences in gene-expression patterns, with activation of genes involved in cell survival and down-regulation of genes involved in apoptosis and chromatin structure. Finally, we overexpressed ts-46 and ts-47 in two lung cancer cell lines and performed a clonogenic assay to examine their role in cell proliferation. We observed a strong inhibition of colony formation in cells overexpressing these tsRNAs compared with untreated cells, confirming that tsRNAs affect cell growth and survival.

Riluzole exerts distinct antitumor effects from a metabotropic glutamate receptor 1-specific inhibitor on breast cancer cells

Recent evidence suggests that glutamate signaling plays an important role in cancer. Riluzole is a glutamate release inhibitor and FDA-approved drug for the treatment of amyotrophic lateral sclerosis. It has been investigated as an inhibitor of cancer cell growth and tumorigenesis with the intention of repurposing it for the treatment of cancer. Riluzole is thought to act by indirectly inhibiting glutamate signaling. However, the specific effects of riluzole in breast cancer cells are not well understood. In this study, the anti-cancer effects of riluzole were explored in a panel of breast cancer cell lines in comparison to the metabotropic glutamate receptor 1-specific inhibitor BAY 36-7620. While both drugs inhibited breast cancer cell proliferation, there were distinct functional effects suggesting that riluzole action may be metabotropic glutamate receptor 1-independent. Riluzole induced mitotic arrest independent of oxidative stress while BAY 36-7620 had no measurable effect on mitosis. BAY 36-7620 had a more pronounced and significant effect on DNA damage than riluzole. Riluzole altered cellular metabolism as demonstrated by changes in oxidative phosphorylation and cellular metabolite levels. These results provide a better understanding of the functional action of riluzole in the treatment of breast cancer.

Metabotropic glutamate receptor 5 mediates the suppressive effect of 6-OHDA-induced model of Parkinson's disease on liver cancer

Numerous epidemiological studies suggested that there is a variable cancer risk in patients with Parkinson's disease (PD). However, the underlying mechanisms remain unclear. In the present study, the role of metabotropic glutamate receptor 5 (mGluR5) has been investigated in 6-hydroxydopamine (6-OHDA)-induced PD combined with liver cancer both in vitro and in vivo. We found that PD cellular model from 6-OHDA-lesioned MN9D cells suppressed the growth, migration, and invasion of Hepa1-6 cells via down-regulation of mGluR5-mediated ERK and Akt pathway. The application of 2-methyl-6-(phenylethyl)-pyridine and knockdown of mGluR5 further decreased the effect on Hepa-1-6 cells when co-cultured with conditioned media. The effect was increased by (S)-3,5-dihydroxyphenylglycine and overexpression of mGluR5. Moreover, more release of glutamate from 6-OHDA-lesioned MN9D cells suppressed mGluR5-mediated effect of Hepa1-6 cells. Application of riluzole eliminated the increased glutamate release induced by 6-OHDA in MN9D cells and aggravated the suppressive effect on Hepa-1-6 cells. In addition, the growth of implanted liver cancer was inhibited in 6-OHDA induced PD-like rats, and was associated with increased glutamate release in the serum and down-regulation of mGluR5 in tumor tissue. Collectively, these results indicate that selective antagonism of glutamate and mGluR5 has a potentially beneficial effect in both liver cancer and PD, and thus may provide more understanding for the clinical investigation and further an additional therapeutic target for these two diseases.

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.

Osteosarcoma cell proliferation and survival requires mGluR5 receptor activity and is blocked by Riluzole

Osteosarcomas are malignant tumors of bone, most commonly seen in children and adolescents. Despite advances in modern medicine, the poor survival rate of metastatic osteosarcoma has not improved in two decades. In the present study we have investigated the effect of Riluzole on a human and mouse metastatic osteosarcoma cells. We show that LM7 cells secrete glutamate in the media and that mGluR5 receptors are required for the proliferation of LM7 cells. Riluzole, which is known to inhibit glutamate release, inhibits proliferation, induces apoptosis and prevents migration of LM7 cells. This is also seen with Fenobam, a specific blocker of mGluR5. We also show that Riluzole alters the phosphorylation status of AKT/P70 S6 kinase, ERK1/2 and JNK1/2. Thus Riluzole is an effective drug to inhibit proliferation and survival of osteosarcoma cells and has therapeutic potential for the treatment of osteosarcoma exhibiting autocrine glutamate signaling.

Paracrine Induction of HIF by Glutamate in Breast Cancer: EglN1 Senses Cysteine

The HIF transcription factor promotes adaptation to hypoxia and stimulates the growth of certain cancers, including triple-negative breast cancer (TNBC). The HIFα subunit is usually prolyl-hydroxylated by EglN family members under normoxic conditions, causing its rapid degradation. We confirmed that TNBC cells secrete glutamate, which we found is both necessary and sufficient for the paracrine induction of HIF1α in such cells under normoxic conditions. Glutamate inhibits the xCT glutamate-cystine antiporter, leading to intracellular cysteine depletion. EglN1, the main HIFα prolyl-hydroxylase, undergoes oxidative self-inactivation in the absence of cysteine both in biochemical assays and in cells, resulting in HIF1α accumulation. Therefore, EglN1 senses both oxygen and cysteine.

The Effect of Cage Shape on Nanoparticle-Based Drug Carriers: Anticancer Drug Release and Efficacy via Receptor Blockade Using Dextran-Coated Iron Oxide Nanocages

Although a range of nanoparticles have been developed as drug delivery systems in cancer therapeutics, this approach faces several important challenges concerning nanocarrier circulation, clearance, and penetration. The impact of reducing nanoparticle size on penetration through leaky blood vessels around tumor microenvironments via enhanced permeability and retention (EPR) effect has been extensively examined. Recent research has also investigated the effect of nanoparticle shape on circulation and target binding affinity. However, how nanoparticle shape affects drug release and therapeutic efficacy has not been previously explored. Here, we compared the drug release and efficacy of iron oxide nanoparticles possessing either a cage shape (IO-NCage) or a solid spherical shape (IO-NSP). Riluzole cytotoxicity against metastatic cancer cells was enhanced 3-fold with IO-NCage. The shape of nanoparticles (or nanocages) affected the drug release point and cellular internalization, which in turn influenced drug efficacy. Our study provides evidence that the shape of iron oxide nanoparticles has a significant impact on drug release and efficacy.

Ionotropic glutamate receptors: Which ones, when, and where in the mammalian neocortex

A multitude of 18 iGluR receptor subunits, many of which are diversified by splicing and RNA editing, localize to >20 excitatory and inhibitory neocortical neuron types defined by physiology, morphology, and transcriptome in addition to various types of glial, endothelial, and blood cells. Here we have compiled the published expression of iGluR subunits in the areas and cell types of developing and adult cortex of rat, mouse, carnivore, bovine, monkey, and human as determined with antibody- and mRNA-based techniques. iGluRs are differentially expressed in the cortical areas and in the species, and all have a unique developmental pattern. Differences are quantitative rather than a mere absence/presence of expression. iGluR are too ubiquitously expressed and of limited use as markers for areas or layers. A focus has been the iGluR profile of cortical interneuron types. For instance, GluK1 and GluN3A are enriched in, but not specific for, interneurons; moreover, the interneurons expressing these subunits belong to different types. Adressing the types is still a major hurdle because type-specific markers are lacking, and the frequently used neuropeptide/CaBP signatures are subject to regulation by age and activity and vary as well between species and areas. RNA-seq reveals almost all subunits in the two morphofunctionally characterized interneuron types of adult cortical layer I, suggesting a fairly broad expression at the RNA level. It remains to be determined whether all proteins are synthesized, to which pre- or postsynaptic subdomains in a given neuron type they localize, and whether all are involved in synaptic transmission. J. Comp. Neurol. 525:976-1033, 2017. © 2016 Wiley Periodicals, Inc.

Chronic but not acute immobilization stress stably enhances hippocampal CA1 metabotropic glutamate receptor dependent Long-Term Depression

Acute stress has been shown to facilitate but not increase metabotropic glutamate receptor (mGluR) mediated Long-Term Depression (LTD) in the hippocampus. However, the effect of chronic stress on mGluR dependent LTD has not been investigated. Moreover, whether stress leads to a transient modification LTD threshold or a more stable change in synaptic plasticity needs to be addressed. In the present study, we have explored the effects of both a ten-day long and a single day immobilization stress protocol on mGluR-LTD at the CA3:CA1synapse in the hippocampus of adult male Sprague-Dawley rats, a day after applying stress. Bath application of the selective group 1 mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) promoted robust LTD in hippocampal slices from control (i.e. un-stressed) animals. Administration of immobility stress for two hours per day for ten days significantly elevated this LTD to a level almost twice that of control, when observed 24h following the last stress event. Acute stress i.e. a single day of two hours of immobilization, however, failed to significantly enhance LTD, 24h later. These results demonstrate for the first time, that repeated exposure to stress, but not a single stress event, is required to bring about a stable alteration in mGluR mediated synaptic plasticity.

Glutamate release inhibitor, Riluzole, inhibited proliferation of human hepatocellular carcinoma cells by elevated ROS production

Liver cancer is one of the common malignancies in many countries and an increasing cause of cancer death. Despite of that, there are few therapeutic options available with inconsistent outcome, raising a need for developing alternative therapeutic options. Through a drug repositioning screening, we identified and investigated the action mechanism of the Riluzole, an amyotrophic lateral sclerosis (ALS) drug, on hepatocellular carcinoma (HCC) therapy. Treatment of the Riluzole leads to a suppression of cell proliferation in liver primary cancer cells and cancer cell lines. In addition, Riluzole induced caspase-dependent apoptosis and G2/M cell cycle arrest in SNU449 and Huh7 cell lines. In a line with the known function of glutamate release inhibitor, we found Riluzole-treated cells have increased the level of inner cellular glutamate that in turn decrease the glutathione (GSH) level and finally augment the reactive oxygen species (ROS) production. We confirm this finding in vivo by showing the Riluzole-induced GSH and ROS changes in a Huh7 xenograft cancer model. Altogether, these data suggest the anti-cancer effect of Riluzole on hepatocellular carcinoma and the suppression of glutamate signaling might be a new target pathway for HCC therapy.

Zebrafish Get Connected: Investigating Neurotransmission Targets and Alterations in Chemical Toxicity

Neurotransmission is the basis of neuronal communication and is critical for normal brain development, behavior, learning, and memory. Exposure to drugs and chemicals can alter neurotransmission, often through unknown pathways and mechanisms. The zebrafish (Danio rerio) model system is increasingly being used to study the brain and chemical neurotoxicity. In this review, the major neurotransmitter systems, including glutamate, GABA, dopamine, norepinephrine, serotonin, acetylcholine, histamine, and glutamate are surveyed and pathways of synthesis, transport, metabolism, and action are examined. Differences between human and zebrafish neurochemical pathways are highlighted. We also review techniques for evaluating neurological function, including the measurement of neurotransmitter levels, assessment of gene expression through transcriptomic analysis, and the recording of neurobehavior. Finally examples of chemical toxicity studies evaluating alterations in neurotransmitter systems in the zebrafish model are reviewed.

Autocrine glutamatergic transmission for the regulation of embryonal carcinoma stem cells

Glutamate behaves as the principal excitatory neurotransmitter in the vertebrate central nervous system and recently demonstrates intercellular signaling activities in periphery cancer cells. How the glutamatergic transmission is organized and operated in cancer stem cells remains undefined. We have identified a glutamatergic transmission circuit in embryonal carcinoma stem cells. The circuit is organized and operated in an autocrine mechanism and suppresses the cell proliferation and motility. Biological analyses determined a repertoire of glutamatergic transmission components, glutaminase, vesicular glutamate transporter, glutamate NMDA receptor, and cell membrane excitatory amino-acid transporter, for glutamate biosynthesis, package for secretion, reaction, and reuptake in mouse and human embryonal carcinoma stem cells. The glutamatergic components were also identified in mouse transplanted teratocarcinoma and in human primary teratocarcinoma tissues. Released glutamate acting as the signal was directly quantified by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Genetic and pharmacological abolishment of the endogenously released glutamate-induced tonic activation of the NMDA receptors increased the cell proliferation and motility. The finding suggests that embryonal carcinoma stem cells can be actively regulated by establishing a glutamatergic autocrine/paracrine niche via releasing and responding to the transmitter.

Ionotropic glutamate receptor expression in human white matter

Glutamate is the key excitatory neurotransmitter of the central nervous system (CNS). Its role in human grey matter transmission is well understood, but this is less clear in white matter (WM). Ionotropic glutamate receptors (iGluR) are found on both neuronal cell bodies and glia as well as on myelinated axons in rodents, and rodent WM tissue is capable of glutamate release. Thus, rodent WM expresses many of the components of the traditional grey matter neuron-to-neuron synapse, but to date this has not been shown for human WM. We demonstrate the presence of iGluRs in human WM by immunofluorescence employing high-resolution spectral confocal imaging. We found that the obligatory N-methyl-d-aspartic acid (NMDA) receptor subunit GluN1 and the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluA4 co-localized with myelin, oligodendroglial cell bodies and processes. Additionally, GluA4 colocalized with axons, often in distinct clusters. These findings may explain why human WM is vulnerable to excitotoxic events following acute insults such as stroke and traumatic brain injury and in more chronic inflammatory conditions such as multiple sclerosis (MS). Further exploration of human WM glutamate signalling could pave the way for developing future therapies modulating the glutamate-mediated damage in these and other CNS disorders.

Impact of Feeding Strategies on the Scalable Expansion of Human Pluripotent Stem Cells in Single-Use Stirred Tank Bioreactors

: The routine application of human pluripotent stem cells (hPSCs) and their derivatives in biomedicine and drug discovery will require the constant supply of high-quality cells by defined processes. Culturing hPSCs as cell-only aggregates in (three-dimensional [3D]) suspension has the potential to overcome numerous limitations of conventional surface-adherent (two-dimensional [2D]) cultivation. Utilizing single-use instrumented stirred-tank bioreactors, we showed that perfusion resulted in a more homogeneous culture environment and enabled superior cell densities of 2.85 × 10⁶ cells per milliliter and 47% higher cell yields compared with conventional repeated batch cultures. Flow cytometry, quantitative reverse-transcriptase polymerase chain reaction, and global gene expression analysis revealed a high similarity across 3D suspension and 2D precultures, underscoring that matrix-free hPSC culture efficiently supports maintenance of pluripotency. Interestingly, physiological data and gene expression assessment indicated distinct changes of the cells' energy metabolism, suggesting a culture-induced switch from glycolysis to oxidative phosphorylation in the absence of hPSC differentiation. Our data highlight the plasticity of hPSCs' energy metabolism and provide clear physiological and molecular targets for process monitoring and further development. This study paves the way toward more efficient GMP-compliant cell production and underscores the enormous process development potential of hPSCs in suspension culture.

SIGNIFICANCE

Human pluripotent stem cells (hPSCs) are a unique source for the, in principle, unlimited production of functional human cell types in vitro, which are of high value for therapeutic and industrial applications. This study applied single-use, clinically compliant bioreactor technology to develop advanced, matrix-free, and more efficient culture conditions for the mass production of hPSCs in scalable suspension culture. Using extensive analytical tools to compare established conditions with this novel culture strategy, unexpected physiological features of hPSCs were discovered. These data allow a more rational process development, providing significant progress in the field of translational stem cell research and medicine.

1,25-Dihydroxyvitamin D induces the glutamate transporter SLC1A1 and alters glutamate handling in non-transformed mammary cells

Genomic profiling of immortalized human mammary epithelial (hTERT-HME1) cells identified several metabolic genes, including the membrane glutamate transporter, SLC1A1, as 1,25-dihydroxyvitamin D3 (1,25D) regulated. In these studies we have surveyed the effects of 1,25D on known glutamate transporters and evaluated its impact on cellular glutamate handling. We confirm that expression of SLC1A1 and all of its known transcript variants are significantly upregulated in hTERT-HME1 cells following 1,25D treatment. Expression of the full-length cognate protein, EAAT3, is correspondingly increased in 1,25D treated hTERT-HME1 cells. Under the same conditions, the expression of two other glutamate transporters--SLC1A6 (EAAT4) and SLC1A2 (EAAT2 or GLT-1)--is enhanced by 1,25D while that of SLC1A3 (EAAT1 or GLAST) and SLC7A11 (xCT) is decreased. Glutamate is not essential for growth of hTERT-HME1 cells, and supplemental glutamate (up to 0.5 mM) does not abrogate the growth inhibitory effects of 1,25D. These data suggest that extracellular glutamate is not a major contributor to cellular energy metabolism in hTERT-HME1 cells under basal conditions and that the growth inhibitory effects of 1,25D are not secondary to its effects on glutamate handling. Instead, the effects of 1,25D on glutamate transporters translated to a decrease in cellular glutamate concentration and an increase in media glutamate concentration, suggesting that one or more of these transporters functions to export glutamate in response to 1,25D exposure. The reduced cellular glutamate concentration may also reflect its incorporation into the cellular glutathione (GSH) pool, which is increased upon 1,25D treatment. In support of this concept, the expression of GCLC (which codes for the rate-limiting enzyme in GSH synthesis) and genes which generate reducing equivalents in the form of NADPH (ie, G6PD, PGD, IDH2) are elevated in 1,25D-treated cells. Taken together, these data identify 1,25D as a physiological regulator of multiple membrane glutamate transporters that impacts on overall cellular glutamate handling.

Heart Alterations after Domoic Acid Administration in Rats

Domoic acid (DA) is one of the best known marine toxins, causative of important neurotoxic alterations. DA effects are documented both in wildlife and experimental assays, showing that this toxin causes severe injuries principally in the hippocampal area. In the present study we have addressed the long-term toxicological effects (30 days) of DA intraperitoneal administration in rats. Different histological techniques were employed in order to study DA toxicity in heart, an organ which has not been thoroughly studied after DA intoxication to date. The presence of DA was detected by immunohistochemical assays, and cellular alterations were observed both by optical and transmission electron microscopy. Although histological staining methods did not provide any observable tissue damage, transmission electron microscopy showed several injuries: a moderate lysis of myofibrils and loss of mitochondrial conformation. This is the first time the association between heart damage and the presence of the toxin has been observed.

[The cancer paradigm in pulmonary arterial hypertension: towards anti-remodeling therapies targeting metabolic dysfunction?]

Pulmonary arterial hypertension (PAH) is a rare, complex and multifactorial disease in which pulmonary vascular remodeling plays a major role ending in right heart failure and death. Current specific therapies of PAH that mainly target the vasoconstriction/vasodilatation imbalance are not curative. Bi-pulmonary transplantation remains the only option in patients resistant to current therapies. It is thus crucial to identify novel vascular anti-remodeling therapeutic targets. This remodeling displays several properties of cancer cells, especially overproliferation and apoptosis resistance of pulmonary vascular cells, hallmarks of cancer related to the metabolic shift known as the "Warburg effect". The latter is characterized by a shift of ATP production, from oxidative phosphorylation to low rate aerobic glycolysis. In compensation, the cancer cells exhibit exacerbated glutaminolysis thus resulting in glutamine addiction, necessary to their overproliferation. Glutamine intake results in glutamate production, a molecule at the crossroads of energy metabolism and cancer cell communication, thus contributing to cell proliferation. Accordingly, therapeutic strategies targeting glutamate production, its release into the extracellular space and its membrane receptors have been suggested to treat different types of cancers, not only in the central nervous system but also in the periphery. We propose that similar strategies targeting glutamatergic signaling may be considered in PAH, especially as they could affect not only the vascular remodeling but also the right heart hypertrophy known to involve the glutaminolysis pathway. Ongoing studies aim to characterize the involvement of the glutamate pathway and its receptors in vascular remodeling, and the therapeutic potential of specific molecules targeting this pathway.