Altered extracellular ATP, ADP and AMP catabolism in glioma cell lines

Antitumoral Activity of Cecropia Pachystachya Leaves Extract in Vitro and in Vivo Model of Rat Glioma: Brain and Blood Effects

The aim of this study was to investigate the antiglioma effect of Cecropia pachystachya Trécul (CEC) leaves extract against C6 and U87 glioblastoma (GB) cells and in a rat preclinical GB model. The CEC extract reduced in vitro cell viability and biomass. In vivo, the extract decreased the tumor volume approximately 62%, without inducing systemic toxicity. The deficit in locomotion and memory and an anxiolytic-like behaviors induced in the GB model were minimized by CEC. The extract decreased the levels of reactive oxygen species, nitrites and thiobarbituric acid reactive substances and increased the activity of antioxidant enzymes in platelets, sera and brains of GB animals. The activity of NTPDases, 5'-nucleotidase and adenosine deaminase (ADA) was evaluated in lymphocytes, platelets and serum. In platelets, ATP and AMP hydrolysis was reduced and hydrolysis of ADP and the activity of ADA were increased in the control, while in CEC-treated animals no alteration in the hydrolysis of ADP was detected. In serum, the reduction in ATP hydrolysis was reversed by CEC. In lymphocytes, the increase in the hydrolysis of ATP, ADP and in the activity of ADA observed in GB model was altered by CEC administration. The observed increase in IL-6 and decrease in IL-10 levels in the serum of GB animals was reversed by CEC. These results demonstrate that CEC extract is a potential complementary treatment to GB, decreasing the tumor size, while modulating aspects of redox and purinergic systems.

Changes Induced by P2X7 Receptor Stimulation of Human Glioblastoma Stem Cells in the Proteome of Extracellular Vesicles Isolated from Their Secretome

Extracellular vesicles (EVs) are secreted from many tumors, including glioblastoma multiforme (GBM), the most common and lethal brain tumor in adults, which shows high resistance to current therapies and poor patient prognosis. Given the high relevance of the information provided by cancer cell secretome, we performed a proteomic analysis of microvesicles (MVs) and exosomes (EXOs) released from GBM-derived stem cells (GSCs). The latter, obtained from the brain of GBM patients, expressed P2X7 receptors (P2X7Rs), which positively correlate with GBM growth and invasiveness. P2X7R stimulation of GSCs caused significant changes in the EV content, mostly ex novo inducing or upregulating the expression of proteins related to cytoskeleton reorganization, cell motility/spreading, energy supply, protection against oxidative stress, chromatin remodeling, and transcriptional regulation. Most of the induced/upregulated proteins have already been identified as GBM diagnostic/prognostic factors, while others have only been reported in peripheral tumors. Our findings indicate that P2X7R stimulation enhances the transport and, therefore, possible intercellular exchange of GBM aggressiveness-increasing proteins by GSC-derived EVs. Thus, P2X7Rs could be considered a new druggable target of human GBM, although these data need to be confirmed in larger experimental sets.

Investigative needle core biopsies for multi-omics in Glioblastoma

Glioblastoma (GBM) is a primary brain cancer with an abysmal prognosis and few effective therapies. The ability to investigate the tumor microenvironment before and during treatment would greatly enhance both understanding of disease response and progression, as well as the delivery and impact of therapeutics. Stereotactic biopsies are a routine surgical procedure performed primarily for diagnostic histopathologic purposes. The role of investigative biopsies - tissue sampling for the purpose of understanding tumor microenvironmental responses to treatment using integrated multi-modal molecular analyses ('Multi-omics") has yet to be defined. Secondly, it is unknown whether comparatively small tissue samples from brain biopsies can yield sufficient information with such methods. Here we adapt stereotactic needle core biopsy tissue in two separate patients. In the first patient with recurrent GBM we performed highly resolved multi-omics analysis methods including single cell RNA sequencing, spatial-transcriptomics, metabolomics, proteomics, phosphoproteomics, T-cell clonotype analysis, and MHC Class I immunopeptidomics from biopsy tissue that was obtained from a single procedure. In a second patient we analyzed multi-regional core biopsies to decipher spatial and genomic variance. We also investigated the utility of stereotactic biopsies as a method for generating patient derived xenograft models in a separate patient cohort. Dataset integration across modalities showed good correspondence between spatial modalities, highlighted immune cell associated metabolic pathways and revealed poor correlation between RNA expression and the tumor MHC Class I immunopeptidome. In conclusion, stereotactic needle biopsy cores are of sufficient quality to generate multi-omics data, provide data rich insight into a patient's disease process and tumor immune microenvironment and can be of value in evaluating treatment responses.

One sentence summary

Integrative multi-omics analysis of stereotactic needle core biopsies in glioblastoma.

Adenosine metabolism by mesenchymal stromal cells isolated from different human tissues

Mesenchymal stromal cells (MSCs) have unique biological properties and play important functions, which make them attractive tools for cell-based therapies. The basic mechanisms of these cells are not fully understood. However, the adenosinergic pathway contributes to the main effects attributed to MSCs. Adenosine is a highly immunosuppressive molecule and exerts a central role in inflammation by neutralizing the proinflammatory ATP influence. This nucleoside is produced by purinergic signaling, an important physiological pathway for MSCs, which involves proliferation, migration, differentiation, and apoptosis. Therefore, in this study, we analyzed the extracellular AMP hydrolysis and consequent adenosine production, as well as the expression of CD73 and adenosine receptors on the cell surface of MSCs isolated from different human tissues: dermis (D-MSCs), adipose tissue (AD-MSCs), and umbilical cord (UC-MSCs). All cells confirmed their multipotent capacity by adipogenic, osteogenic, and chondrogenic differentiation, as well as the expression of cell surface markers including CD44 + , CD105 + , and CD90 + . All MSCs expressed similar levels of CD73 and CD26 without a statistical difference among the different tissues, whereas ADA expression was lower in AD-MSCs. In addition, A1R and A3R mRNA levels were higher in D-MSCs and AD-MSCs, respectively. Enzymatic assay showed that AD-MSCs have the highest hydrolysis rate of AMP, leading to increased amount of adenosine production. Moreover, despite all MSCs completely hydrolyze extracellular AMP generating adenosine, the pattern of nucleosides metabolism was different. Therefore, although MSCs share certain characteristics as the multilineage potential and immunophenotype, they show different adenosinergic profiles according to tissue origin.

Epidermal melanocytes metabolize extracellular nucleotides by purinergic enzymes

The human epidermal melanocyte (hEM) are melanin-producing cells that provide skin pigmentation and protection against ultraviolet radiation. Although purinergic signaling is involved in skin biology and pathology, the presence of NTPDase members, as well as the rate of nucleotides degradation by melanocytes were not described yet. Therefore, in this study, we analyzed the expression of ectonucleotidases in hEM derived from discarded foreskin of male patients. The expression of purinergic enzymes was confirmed by mRNA and flow cytometry. Among the ectonucleotidases, ectonucleoside triphosphate diphosphohydrolase1 (NTPDase1) and ecto-5´-nucleotidase were the ectoenzymes with higher expressions. The hydrolysis rate for ATP, ADP, and AMP was low in comparison to other primary cells already investigated. The amount of ATP in the culture medium was increased after a scratch wound and decreased to basal levels in 48 h, while the NTPDase1 and P2X7 expressions increased. Therefore, it is possible to suggest that after cell injury, the ATP released by hEM into the extracellular space will be hydrolyzed by ectonucleotidases as the NTPDase1 that will control the levels of nucleotides in the skin micro-environment.

P2Y12 receptor antagonism inhibits proliferation, migration and leads to autophagy of glioblastoma cells

Glioblastoma (GBM) is the most aggressive and lethal among the primary brain tumors, with a low survival rate and resistance to radio and chemotherapy. The P2Y₁₂ is an adenosine diphosphate (ADP) purinergic chemoreceptor, found mainly in platelets. In cancer cells, its activation has been described to induce proliferation and metastasis. Bearing in mind the need to find new treatments for GBM, this study aimed to investigate the role of the P2Y₁₂R in the proliferation and migration of GBM cells, as well as to evaluate the expression of this receptor in patients' data obtained from the TCGA data bank. Here, we used the P2Y₁₂R antagonist, ticagrelor, which belongs to the antiplatelet agent's class. The different GBM cells (cell line and patient-derived cells) were treated with ticagrelor, with the agonist, ADP, or both, and the effects on cell proliferation, colony formation, ADP hydrolysis, cell cycle and death, migration, and cell adhesion were analyzed. The results showed that ticagrelor decreased the viability and the proliferation of GBM cells. P2Y₁₂R antagonism also reduced colony formation and migration potentials, with alterations on the expression of metalloproteinases, and induced autophagy in GBM cells. Changes were observed at the cell cycle level, and only the U251 cell line showed a significant reduction in the ADP hydrolysis profile. TCGA data analysis showed a higher expression of P2Y₁₂R in gliomas samples when compared to the other tumors. These data demonstrate the importance of the P2Y₁₂ receptor in gliomas development and reinforce its potential as a pharmacological target for glioma treatment.

Impact of gallic acid on tumor suppression: Modulation of redox homeostasis and purinergic response in in vitro and a preclinical glioblastoma model

Glioblastoma (GBM) is the deadliest primary brain tumor in adults due to the high rate of relapse with current treatment. Therefore, the search for therapeutic alternatives is urgent. Gallic acid (GA), a potent natural antioxidant, has antitumor and modulatory actions on purinergic signaling. In this study, we investigated the cytotoxic effects of GA on the rat GBM (C6) cell line and on astrocyte culture and analyzed its role in regulating oxidative stress and purinergic enzymes involved in GBM proliferation. Cells were exposed to GA from 50 to 400 µM for 24 and/or 48 h. Next, the effect of GA was evaluated in the preclinical model of GBM. Wistar rats were treated with 50 or 100 mg/kg of GA for 15 days, and cerebral and systemic redox status and degradation of adenine nucleotides and nucleosides in circulating platelets, lymphocytes, and serum were evaluated. Our results demonstrated that GA has selective anti-glioma activity in vitro, without inducing cytotoxicity in astrocyte. Furthermore, GA prevented oxidative stress and changes in the hydrolysis of nucleotides in GBM cells. The anti-glioma effect was also observed in vivo, as GA reduced tumor volume by 90%. Interestingly, GA decreased the oxidative damage induced by a tumor in the brain, serum, and platelets, and, also prevented changes in the degradation of nucleotides and nucleosides in lymphocytes, platelets, and serum. These results indicate, for the first time, the therapeutic potential of GA in a preclinical model of GBM, whose effects may be related to its role in redox and purinergic modulation.

Adenosine Targeting as a New Strategy to Decrease Glioblastoma Aggressiveness

Simple Summary

Given the rising mortality rate caused by GBM, current therapies do not appear to be effective in counteracting tumor progression. The role of adenosine and its interaction with specific receptor subtypes in various physiological functions has been studied for years. Only recently, adenosine has been defined as a tumor-protective target because of its accumulation in the tumor microenvironment. Current knowledge of the adenosine pathway and its involvement in brain tumors would support research in the development of adenosine receptor antagonists that could represent alternative treatments for glioblastoma, used either alone and/or in combination with chemotherapy, immunotherapy, or both.

Abstract

Glioblastoma is the most commonly malignant and aggressive brain tumor, with a high mortality rate. The role of the purine nucleotide adenosine and its interaction with its four subtypes receptors coupled to the different G proteins, A1, A2A, A2B, and A3, and its different physiological functions in different systems and organs, depending on the active receptor subtype, has been studied for years. Recently, several works have defined extracellular adenosine as a tumoral protector because of its accumulation in the tumor microenvironment. Its presence is due to both the interaction with the A2A receptor subtype and the increase in CD39 and CD73 gene expression induced by the hypoxic state. This fact has fueled preclinical and clinical research into the development of efficacious molecules acting on the adenosine pathway and blocking its accumulation. Given the success of anti-cancer immunotherapy, the new strategy is to develop selective A2A receptor antagonists that could competitively inhibit binding to its endogenous ligand, making them reliable candidates for the therapeutic management of brain tumors. Here, we focused on the efficacy of adenosine receptor antagonists and their enhancement in anti-cancer immunotherapy.

Single cell spatial analysis reveals the topology of immunomodulatory purinergic signaling in glioblastoma

How the glioma immune microenvironment fosters tumorigenesis remains incompletely defined. Here, we use single-cell RNA-sequencing and multiplexed tissue-imaging to characterize the composition, spatial organization, and clinical significance of extracellular purinergic signaling in glioma. We show that microglia are the predominant source of CD39, while tumor cells principally express CD73. In glioblastoma, CD73 is associated with EGFR amplification, astrocyte-like differentiation, and increased adenosine, and is linked to hypoxia. Glioblastomas enriched for CD73 exhibit inflammatory microenvironments, suggesting that purinergic signaling regulates immune adaptation. Spatially-resolved single-cell analyses demonstrate a strong spatial correlation between tumor-CD73 and microglial-CD39, with proximity associated with poor outcomes. Similar spatial organization is present in pediatric high-grade gliomas including H3K27M-mutant diffuse midline glioma. These data reveal that purinergic signaling in gliomas is shaped by genotype, lineage, and functional state, and that core enzymes expressed by tumor and myeloid cells are organized to promote adenosine-rich microenvironments potentially amenable to therapeutic targeting.

The crossroads of adenosinergic pathway and epithelial-mesenchymal plasticity in cancer

Epithelial-mesenchymal transition (EMT) is a key mechanism related to tumor progression, invasion, metastasis, resistance to therapy and poor prognosis in several types of cancer. However, targeting EMT or partial-EMT, as well as the molecules involved in this process, has remained a challenge. Recently, the CD73 enzyme, which hydrolyzes AMP to produce adenosine (ADO), has been linked to the EMT process. This relationship is not only due to the production of the immunosuppressant ADO but also to its role as a receptor for extracellular matrix proteins, being involved in cell adhesion and migration. This article reviews the crosstalk between the adenosinergic pathway and the EMT program and the impact of this interrelation on cancer development and progression. An in silico analysis of RNAseq datasets showed that several tumor types have a significant correlation between an EMT score and NT5E (CD73) and ENTPD1 (CD39) expressions, with the strongest correlations in prostate adenocarcinoma. Furthermore, it is evident that the cooperation between EMT and adenosinergic pathway in tumor progression is context and tumor-dependent. The increased knowledge about this topic will help broaden the view to explore new treatments and therapies for different types of cancer.

One-Carbon Metabolism Associated Vulnerabilities in Glioblastoma: A Review

Simple Summary

Glioblastoma tumours are the most malignant and common type of central nervous system tumours. Despite aggressive treatment measures, disease recurrence in patients with glioblastoma is inevitable and survival rates remain low. Glioblastoma cells, like other cancer cells, can leverage metabolic pathways to increase their rate of proliferation, maintain self-renewal, and develop treatment resistance. Furthermore, many of the metabolic strategies employed by cancer cells are similar to those employed by stem cells in order to maintain self-renewal and proliferation. One-carbon metabolism and de novo purine synthesis are metabolic pathways that are essential for biosynthesis of macromolecules and have been found to be essential for tumourigenesis. In this review, we summarize the evidence showing the significance of 1-C-mediated de novo purine synthesis in glioblastoma cell proliferation and tumourigenesis, as well as evidence suggesting the effectiveness of targeting this metabolic pathway as a therapeutic modality.

Abstract

Altered cell metabolism is a hallmark of cancer cell biology, and the adaptive metabolic strategies of cancer cells have been of recent interest to many groups. Metabolic reprogramming has been identified as a critical step in glial cell transformation, and the use of antimetabolites against glioblastoma has been investigated. One-carbon (1-C) metabolism and its associated biosynthetic pathways, particularly purine nucleotide synthesis, are critical for rapid proliferation and are altered in many cancers. Purine metabolism has also been identified as essential for glioma tumourigenesis. Additionally, alterations of 1-C-mediated purine synthesis have been identified as commonly present in brain tumour initiating cells (BTICs) and could serve as a phenotypic marker of cells responsible for tumour recurrence. Further research is required to elucidate mechanisms through which metabolic vulnerabilities may arise in BTICs and potential ways to therapeutically target these metabolic processes. This review aims to summarize the role of 1-C metabolism-associated vulnerabilities in glioblastoma tumourigenesis and progression and investigate the therapeutic potential of targeting this pathway in conjunction with other treatment strategies.

Adenosine Inhibits Cell Proliferation Differently in Human Astrocytes and in Glioblastoma Cell Lines

Glioblastoma (GBM) is the most common brain primary tumour. Hypoxic regions in GBM are associated to tumour growth. Adenosine accumulates in hypoxic regions and can affect cell proliferation and survival. However, how proliferating GBM cells respond/adapt to increased adenosine levels compared to human astrocytes (HA) is not clarified and was addressed in the present work. GBM cell lines and HA were treated for 3 days with test drugs. Thirty Adenosine (30 µM) caused a 43% ± 5% (P < 0.05) reduction of cell proliferation/viability in HA, through an adenosine receptor-independent mechanism, but had no effect in GBM cell lines U87MG, U373MG and SNB19. Contrastingly, inhibition of adenosine phosphorylation (using the adenosine kinase (ADK) inhibitor 5-iodotubercidin (ITU) (25 µM)), produced a strong and similar decrease on cell proliferation in both HA and GBM cells. The effect of adenosine on HA proliferation/viability was potentiated by 100 µM-homocysteine. Combined application of 30 µM-adenosine and 100 µM-homocysteine reduced the cell proliferation/viability in all three GBM cell lines, but this reduction was much lower than that observed in HA. Adenosine alone did not induce cell death, assessed by lactate dehydrogenase (LDH) release, both in HA and GBM cells, but potentiated the cytotoxic effect of homocysteine in HA and in U87MG and U373MG cells. Results show a strong attenuation of adenosine anti-proliferative effect in GBM cells compared to HA, probably resulting from increased adenosine elimination by ADK, suggesting a proliferative-prone adaptation of tumour cells to increased adenosine levels.

New insights into cytotoxic mechanisms of bozepinib against glioblastoma

Glioblastoma (GBM) is the most frequent and aggressive brain tumor in adults and the current treatments only have a modest effect on patient survival. Recent studies show that bozepinib (BZP), a purine derivative, has potential applications in cancer treatment. The aim of this study was to evaluate the effect of BZP against GBM cells, specially concerning the purinergic system. Thus, GBM cells (C6 and U138 cell lines) were treated with BZP and cell viability, cell cycle, and annexin/PI assays, and active caspase-3 measurements were carried out. Besides, the effect of BZP over the purinergic system was also evaluated in silico and in vitro. Finally, we evaluate the action of BZP against important markers related to cancer progression, such as Akt, NF-κB, and CD133. We demonstrate here that BZP reduces GBM cell viability (IC₅₀ = 5.7 ± 0.3 µM and 12.7 ± 1.5 µM, in C6 and U138 cells, respectively), inducing cell death through caspase-dependent apoptosis, autophagosome formation, activation of NF-κB, without any change in cell cycle progression or on the Akt pathway. Also, BZP modulates the purinergic system, inducing an increase in CD39 enzyme expression and activity, while inhibiting CD73 activity and adenosine formation, without altering CD73 enzyme expression. Curiously, one cycle of treatment resulted in enrichment of GBM cells expressing NF-κB and CD133⁺, suggesting resistant cells selection. However, after another treatment round, the resistant cells were eliminated. Altogether, BZP presented in vitro anti-glioma activity, encouraging further in vivo studies in order to better understand its mechanism of action.

A novel derivatization strategy for profiling phosphate ester/anhydride metabolic network and application on glioma rats using HILIC-MS/MS

Phosphate esters and anhydrides have great significance in the field of biochemical research and medical therapy. The genetic materials (DNA or RNA), most of the coenzymes, many intermediary metabolites, such as nucleotides and glycosyl phosphates in vivo are phosphodiesters, phosphoric acid or phosphates, respectively. It is important to monitor endogenous active phosphate metabolites for investigating many biological processes or drug mechanism. However, the detection and determination of those free active phosphate metabolites are challenged due to their unstable and easily hydrolyzed property and relatively low sensitivity, especially diphosphates and triphosphates. In the current study, we successfully developed a strategy by 3-aminomethyl pyridine (AMPy) derivatization coupled with hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) for simultaneous determination of multiple types of phosphate metabolites with good stability in 48 h and 29 to 126-fold improvement of the limit of detection (LOD). Based on the diagnostic fragment ions of different types of AMPy-derivatized phosphate metabolites, characteristic MRM ion pairs were successfully performed for global profiling of the phosphate metabolites in phosphate ester/anhydride metabolic network, including nucleotide/deoxynucleotide mono/di/triphosphates, glycosyl mono/diphosphates, and other key phosphates, such as 5-phosphoribosyl-1-pyrophosphate (PRPP), SAICARP and FAICARP in HPF, HUVEC and PBMCs cells without standards. The developed strategy greatly expanded the coverage of applying a single derivatization reaction to analyze active phosphate metabolites. Finally, the established method was performed to investigate the phosphate esters and anhydrides based on a glioma rat model. For the first time, phosphate metabolites were comprehensively characterized based on phosphate ester and anhydride metabolic network, covering nucleotide metabolism, glycolysis and pentose phosphate pathways, etc. The results demonstrated that the applicability of the method could be extended to a wider range of active phosphate compounds and could facilitate to related applications in the future studies.

P2Y2 receptor activation promotes esophageal cancer cells proliferation via ERK1/2 pathway

Esophageal cancer is a prominent worldwide illness that is divided into two main subtypes: esophageal squamous cell carcinoma and esophageal adenocarcinoma. Mortality rates are alarming, and the understanding of the mechanisms involved in esophageal cancer development, becomes essential. Purinergic signaling is related to many diseases and among these various types of tumors. Here we studied the effects of the P2Y₂ receptor activation in different types of esophageal cancer. Esophageal tissue samples of healthy controls were used for P2Y₂R expression quantification. Two human esophageal cancer cell lines Kyse-450 (squamous cell carcinoma) and OE-33 (adenocarcinoma) were used to perform in vitro analysis of cell proliferation, migration, adhesion, and the signaling pathways involved in P2Y₂R activation. Data showed that P2Y₂R was expressed in biopsies of patients with ESCC and adenocarcinoma, as well as in the two human esophageal cancer cell lines studied. The RT-qPCR analysis demonstrated that OE-33 cells have higher P2RY2 expression than Kyse-450 squamous cell line. Results showed that P2Y₂R activation, induced by ATP or UTP, promoted esophageal cancer cells proliferation and colony formation. P2Y₂R blockage with the selective antagonist, AR-C 118925XX, led to decreased proliferation, colony formation and adhesion. Treatments with ATP or UTP activated ERK 1/2 pathway in ESCC and ECA cells. The P2Y₂R antagonism did not alter the migration of esophageal cancer cells. Interestingly, the esophageal cancer cell lines presented a distinct profile of nucleotide hydrolysis activity. The modulation of P2Y₂ receptors may be a promising target for esophageal cancer treatment.

The P2X7 Receptor: Central Hub of Brain Diseases

The P2X7 receptor is a cation channel activated by high concentrations of adenosine triphosphate (ATP). Upon long-term activation, it complexes with membrane proteins forming a wide pore that leads to cell death and increased release of ATP into the extracellular milieu. The P2X7 receptor is widely expressed in the CNS, such as frontal cortex, hippocampus, amygdala and striatum, regions involved in neurodegenerative diseases and psychiatric disorders. Despite P2X7 receptor functions in glial cells have been extensively studied, the existence and roles of this receptor in neurons are still controversially discussed. Regardless, P2X7 receptors mediate several processes observed in neuropsychiatric disorders and brain tumors, such as activation of neuroinflammatory response, stimulation of glutamate release and neuroplasticity impairment. Moreover, P2X7 receptor gene polymorphisms have been associated to depression, and isoforms of P2X7 receptors are implicated in neuropsychiatric diseases. In view of that, the P2X7 receptor has been proposed to be a potential target for therapeutic intervention in brain diseases. This review discusses the molecular mechanisms underlying P2X7 receptor-mediated signaling in neurodegenerative diseases, psychiatric disorders, and brain tumors. In addition, it highlights the recent advances in the development of P2X7 receptor antagonists that are able of penetrating the central nervous system.

Biochemical analysis of ectonucleotidases on primary rat vascular smooth muscle cells and in silico investigation of their role in vascular diseases

Vascular smooth muscle cells (VSMCs) exhibit a high degree of plasticity when they undergo the progression from a normal to a disease condition, which makes them a potential target for evaluating early markers and for the development of new therapies. Purinergic signalling plays a key role in vascular tonus control, ATP being an inductor of vasoconstriction, whereas adenosine mediates a vasodilation effect antagonising the ATP actions. The control of extracellular ATP and adenosine levels is done by ectonucleotidases, which represent a potential target to be evaluated in the progression of cardiovascular diseases. In this study, we analysed the basal activity and expression of the ectonucleotidases in aortic rat VSMCs, and we further performed in silico analysis to determine the expression of those enzymes in conditions that mimicked vascular diseases. Cultured in vitro VSMCs showed a prominent expression of Entpd1 followed by Entpd2 and Nt5e (CD73) and very low levels of Entpd3. Slightly faster AMP hydrolysis was observed when compared to ATP and ADP nucleotides. In silico analysis showed that the ectonucleotidases were modulated after induction of conditions that can lead to vascular diseases such as, hypertensive and hypotensive mice models (Nt5e); exposition to high-fat (Entpd1 and Entpd2) or high-phosphate (Nt5e) diet; mechanical stretch (Entpd1, Entpd2 and Nt5e); and myocardial infarction (Entpd1). Our data show that VSMCs are able to efficiently metabolise the extracellular nucleotides generating adenosine. The modulation of Entpd1, Entdp2 and Nt5e in vascular diseases suggests these ectoenzymes as potential targets or markers to be investigated in future studies.

CD73 as a target to improve temozolomide chemotherapy effect in glioblastoma preclinical model

Glioblastoma is the most devastating primary brain tumor and effective therapies are not available. Treatment is based on surgery followed by radio and chemotherapy with temozolomide (TMZ), but TMZ increases patient survival only by 2 months. CD73, an enzyme responsible for adenosine production, emerges as a target for glioblastoma treatment. Indeed, adenosine causes tumor-promoting actions and CD73 inhibition increases sensitivity to TMZ in vitro. Here, a cationic nanoemulsion to nasal delivery of siRNA CD73 (NE-siRNA CD73) aiming glioblastoma treatment was employed alone or in combination with TMZ. In vitro, two glioblastoma cell lines (C6 and U138MG) with a chemo-resistant profile were used. Treatment alone with NE-siRNA CD73 reduced C6 and U138MG glioma cell viability by 70% and 25%, respectively. On the other hand, when NE-siRNA + TMZ combined treatment was employed, a reduction of 85% and 33% of cell viability was observed. Notably, treatment with NE-siRNA CD73 of glioma-bearing Wistar rats reduced tumor size by 80%, 60% more than the standard chemotherapy with TMZ, but no synergistic or additive effect was observed in vivo. Additionally, NE-siRNA CD73, TMZ or combined therapy decreased adenosine levels in liquor confirming the importance of this nucleoside on in vivo GB growth. Finally, no hemolytic potential was observed. These results suggest that nasal administration of NE-siRNA CD73 exhibits higher antiglioma effect when compared to TMZ. However, no synergistic or additive in vivo was promoted by the therapeutic regimen employed in this study.

Blockade of CD73 delays glioblastoma growth by modulating the immune environment

Immunotherapy as an approach for cancer treatment is clinically promising. CD73, which is the enzyme that produces extracellular adenosine, favors cancer progression and protects the tumor from immune surveillance. While CD73 has recently been demonstrated to be a potential target for glioma treatment, its role in regulating the inflammatory tumor microenvironment has not yet been investigated. Thus, this study explores the immunotherapeutic value of the CD73 blockade in glioblastoma. The immuno-therapeutic value of the CD73 blockade was evaluated in vivo in immunocompetent pre-clinical glioblastoma model. As such, glioblastoma-bearing rats were nasally treated for 15 days with a siRNA CD73-loaded cationic-nanoemulsion (NE-siRNA CD73R). Apoptosis was determined by flow cytometry using Annexin-V staining and cell proliferation was analyzed by Ki67 expression by immunohistochemistry. The frequencies of the CD4⁺, CD8⁺, and CD4⁺CD25^highCD39⁺ (Treg) T lymphocytes; CD11b⁺CD45^high macrophages; CD11b⁺CD45^low-microglia; and CD206⁺-M2-like phenotypes, along with expression levels of CD39 and CD73 in tumor and tumor-associated immune cells, were determined using flow cytometry, while inflammatory markers associated with tumor progression were evaluated using RT-qPCR. The CD73 blockade by NE-siRNA CD73 was found to induce tumor cell apoptosis. Meanwhile, the population of Tregs, microglia, and macrophages was significantly reduced in the tumor microenvironment, though IL-6, CCL17, and CCL22 increased. The treatment selectively decreased CD73 expression in the GB cells as well as in the tumor-associated-macrophages/microglia. This study indicates that CD73 knockdown using a nanotechnological approach to perform nasal delivery of siRNA-CD73 to CNS can potentially regulate the glioblastoma immune microenvironment and delay tumor growth by inducing apoptosis.

Purinergic Signaling in Glioma Progression

Among the pathological alterations that give tumor cells invasive potential, purinergic signaling is emerging as an important component. Studies performed in in vitro, in vivo and ex vivo glioma models indicate that alterations in the purinergic signaling are involved in the progression of these tumors. Gliomas have low expression of all E-NTPDases, when compared to astrocytes in culture. Nucleotides induce glioma proliferation and ATP, although potentially neurotoxic, does not evoke cytotoxic action on the majority of glioma cells in culture. The importance of extracellular ATP for glioma pathobiology was confirmed by the reduction in glioma tumor size by apyrase, which degrades extracellular ATP to AMP, and the striking increase in tumor size by over-expression of an ecto-enzyme that degrades ATP to ADP, suggesting the effect of extracellular ATP on the tumor growth depends on the nucleotide produced by its degradation. The participation of purinergic receptors on glioma progression, particularly P2X₇, is involved in the resistance to ATP-induced cell death. Although more studies are necessary, the purinergic signaling, including ectonucleotidases and receptors, may be considered as future target for glioma pharmacological or gene therapy.

Role of Infiltrating Microglia/Macrophages in Glioma

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

Nasal Drug Delivery of Anticancer Drugs for the Treatment of Glioblastoma: Preclinical and Clinical Trials

Glioblastoma (GBM) is the most lethal form of brain tumor, being characterized by the rapid growth and invasion of the surrounding tissue. The current standard treatment for glioblastoma is surgery, followed by radiotherapy and concurrent chemotherapy, typically with temozolomide. Although extensive research has been carried out over the past years to develop a more effective therapeutic strategy for the treatment of GBM, efforts have not provided major improvements in terms of the overall survival of patients. Consequently, new therapeutic approaches are urgently needed. Overcoming the blood–brain barrier (BBB) is a major challenge in the development of therapies for central nervous system (CNS) disorders. In this context, the intranasal route of drug administration has been proposed as a non-invasive alternative route for directly targeting the CNS. This route of drug administration bypasses the BBB and reduces the systemic side effects. Recently, several formulations have been developed for further enhancing nose-to-brain transport, mainly with the use of nano-sized and nanostructured drug delivery systems. The focus of this review is to provide an overview of the strategies that have been developed for delivering anticancer compounds for the treatment of GBM while using nasal administration. In particular, the specific properties of nanomedicines proposed for nose-to-brain delivery will be critically evaluated. The preclinical and clinical data considered supporting the idea that nasal delivery of anticancer drugs may represent a breakthrough advancement in the fight against GBM.

Characterization of soluble CD39 (SolCD39/NTPDase1) from PiggyBac nonviral system as a tool to control the nucleotides level

Extracellular ATP (eATP) and its metabolites have emerged as key modulators of different diseases and comprise a complex pathway called purinergic signaling. An increased number of tools have been developed to study the role of nucleotides and nucleosides in cell proliferation and migration, influence on the immune system and tumor progression. These tools include receptor agonists/antagonists, engineered ectonucleotidases, interference RNAs and ectonucleotidase inhibitors that allow the control and quantification of nucleotide levels. NTPDase1 (also called apyrase, ecto-ATPase and CD39) is one of the main enzymes responsible for the hydrolysis of eATP, and purified enzymes, such as apyrase purified from potato, or engineered as soluble CD39 (SolCD39), have been widely used in in vitro and in vivo experiments. However, the commercial apyrase had its effects recently questioned and SolCD39 exhibits limitations, such as short half-life and need of high doses to reach the expected enzymatic activity. Therefore, this study investigated a non-viral method to improve the overexpression of SolCD39 and evaluated its impact on other enzymes of the purinergic system. Our data demonstrated that PiggyBac transposon system proved to be a fast and efficient method to generate cells stably expressing SolCD39, producing high amounts of the enzyme from a limited number of cells and with high hydrolytic activity. In addition, the soluble form of NTPDase1/CD39 did not alter the expression or catalytic activity of other enzymes from the purinergic system. Altogether, these findings set the groundwork for prospective studies on the function and therapeutic role of eATP and its metabolites in physiological and pathological conditions.

The role of microglia and P2X7 receptors in gliomas

Gliomas are the most prevalent tumours of the central nervous system and present with high morbidity and mortality. The most common and most aggressive form of glioma is glioblastoma multiforme, of which patients have a median survival time of only 12 to 15 months. Current treatment options are limited and have a small impact on clinical outcome and prognosis. There is accumulating evidence that microglia, the immunocompetent cells of the central nervous system, and the purinergic P2X7 receptor (P2X7R) may contribute to tumour progression and pathology. Importantly, P2X7R on both tumour cells and infiltrating microglia is overexpressed in animal and human glioma cultures. Factors released by glioma cells and P2X7R activation recruit microglia into the largely immunosuppressive tumour microenvironment where they have been demonstrated to contribute to either tumour proliferation or tumour suppression. It is likely that P2X7R mediates a range of microglia effector functions in the glioma setting, potentially increasing tumour growth and proliferation. This review evaluates current evidence on the roles of microglia and P2X7R in glioma pathogenesis. Understanding the nature, mechanisms and outcomes of microglia and P2X7R activation in gliomas is necessary for the development of more therapies with increased efficacy and specificity.

Complex regulation of ecto-5'-nucleotidase/CD73 and A2AR-mediated adenosine signaling at neurovascular unit: A link between acute and chronic neuroinflammation

The review summarizes available data regarding the complex regulation of CD73 at the neurovascular unit (NVU) during neuroinflammation. Based on available data we propose the biphasic pattern of CD73 regulation at NVU, with an early attenuation and a postponed up-regulation of CD73 activity. Transient attenuation of CD73 activity on leukocyte/vascular endothelium and leukocyte/astrocyte surface, required for the initiation of a neuroinflammatory response, may be effectuated either by catalytic inhibition of CD73 and/or by shedding of the CD73 molecule from the cell surface, while postponed induction of CD73 is effectuated by transcriptional up-regulation of Nt5e and posttranslational modifications. Neuroinflammatory conditions are also associated with significant enhancement and gain-of-function of A_2AR-mediated adenosine signaling. However, in contrast to the temporary prevalence of A_2AR over A₁R signaling during an acute inflammatory response, prolonged induction of A_2AR and resulting perpetual CD73/A_2AR coupling may be a contributing factors in the transition between acute and chronic neuroinflammation. Thus, pharmacological targeting of the CD73/A_2AR axis may attenuate inflammatory response and ameliorate neurological deficits in chronic neuroinflammatory conditions.

Activity of ecto-5'-nucleotidase (NT5E/CD73) is increased in papillary thyroid carcinoma and its expression is associated with metastatic lymph nodes

The incidence of papillary thyroid carcinoma (PTC) has been increasing, which raised the interest in its molecular pathways. Although the high expression of ecto-5'-nucleotidase (NT5E) gene expression and NT5E enzymatic activity in several types of cancer is associated with tumor progression, its role in PTC remains unknown. Here, we investigated the AMP hydrolysis in human normal thyroid cells and PTC cells, in primary culture, and the association of NT5E expression with clinical aspects of PTC patients. AMPase activity was higher in thyroid cells isolated from PTC, as compared to normal thyroid (P = 0.0063). Significant correlation was observed between AMPase activity and NT5E levels in primary thyroid cell cultures (r = 0.655, P = 0.029). NT5E expression was higher in PTC than in the adjacent non-malignant thyroid tissue (P = 0.0065) and were positively associated with metastatic lymph nodes (P = 0.0007), risk of recurrence (P = 0.0033), tumor size (P = 0.049), and nodular hyperplasia in the adjacent thyroid parenchyma, when compared to normal thyroid or lymphocytic thyroiditis (P = 0.0146). After adjusting for potential confounders, the malignant/non-malignant paired expression ratio of NT5E mRNA was independently associated with metastatic lymph nodes (P = 0.0005), and tumor size (P=0.0005). In addition, the analysis of PTC described in the TCGA database also showed an association between higher expression of NT5E and metastatic lymph nodes, and tumor microinvasion. These results support the hypothesis that NT5E have a role in PTC microenvironment and might be a potential target for PTC therapy.

Unveiling the Role of Ecto-5'-Nucleotidase/CD73 in Astrocyte Migration by Using Pharmacological Tools

CD73 is a bifunctional glycosylphosphatidylinositol (GPI)-anchored membrane protein which functions as ecto-5′-nucleotidase and a membrane receptor for extracellular matrix protein (ECM). A large body of evidence demonstrates a critical involvement of altered purine metabolism and particularly, increased expression of CD73 in a number of human disorders, including cancer and immunodeficiency. Massive up-regulation of CD73 was also found in reactive astrocytes in several experimental models of human neuropathologies. In all the pathological contexts studied so far, the increased expression of CD73 has been associated with the altered ability of cells to adhere and/or migrate. Thus, we hypothesized that increased expression of CD73 in reactive astrocytes has a role in the process of astrocyte adhesion and migration. In the present study, the involvement of CD73 in astrocyte migration was investigated in the scratch wound assay (SW), using primary astrocyte culture prepared from neonatal rat cortex. The cultures were treated with one of the following pharmacological inhibitors which preferentially target individual functions of CD73: (a) α,β-methylene ADP (APCP), which inhibits the catalytic activity of CD73 (b) polyclonal anti-CD73 antibodies, which bind to the internal epitope of CD73 molecule and mask their surface exposure and (c) small interfering CD73-RNA (siCD73), which silences the expression of CD73 gene. It was concluded that approaches that reduce surface expression of CD73 increase migration velocity and promote wound closure in the scratch wound assay, while inhibition of the enzyme activity by APCP induces redistribution of CD73 molecules at the cell surface, thus indirectly affecting cell adhesion and migration. Application of anti-CD73 antibodies induces a decrease in CD73 activity and membrane expression, through CD73 molecules shedding and their release to the culture media. In addition, all applied pharmacological inhibitors differentially affect other aspects of astrocyte function in vitro, including reduced cell proliferation, altered expression of adenosine receptors and increased expression of ERK1/2. Altogether these data imply that CD73 participates in cell adhesion/migration and transmits extracellular signals through interactions with ECM.

Extracellular ATP is Differentially Metabolized on Papillary Thyroid Carcinoma Cells Surface in Comparison to Normal Cells

The incidence of differentiated thyroid cancer has been increasing. Nevertheless, its molecular mechanisms are not well understood. In recent years, extracellular nucleotides and nucleosides have emerged as important modulators of tumor microenvironment. Extracellular ATP is mainly hydrolyzed by NTPDase1/CD39 and NTPDase2/CD39L1, generating AMP, which is hydrolyzed by ecto-5'-nucleotidase (CD73) to adenosine, a possible promoter of tumor growth and metastasis. There are no studies evaluating the expression and functionality of these ectonucleotidases on normal or tumor-derived thyroid cells. Thus, we investigated the ability of thyroid cancer cells to hydrolyze extracellular ATP generating adenosine, and the expression of ecto-enzymes, as compared to normal cells. We found that normal thyroid derived cells presented a higher ability to hydrolyze ATP and higher mRNA levels for ENTDP1-2, when compared to papillary thyroid carcinoma (PTC) derived cells, which had a higher ability to hydrolyze AMP and expressed CD73 mRNA and protein at higher levels. In addition, adenosine induced an increase in proliferation and migration in PTC derived cells, whose effect was blocked by APCP, a non-hydrolysable ADP analogue, which is an inhibitor of CD73. Taken together, these results showed that thyroid follicular cells have a functional purinergic signaling. The higher expression of CD73 in PTC derived cells might favor the accumulation of extracellular adenosine in the tumor microenvironment, which could promote tumor progression. Therefore, as already shown for other tumors, the purinergic signaling should be considered a potential target for thyroid cancer management and treatment.

GL261 glioma tumor cells respond to ATP with an intracellular calcium rise and glutamate release

Glioblastoma (GBM) is an aggressive brain cancer with an average survival rate of 15 months. The composition of the GBM tumor microenvironment-its pH, the presence of growth and immune factors, neurotransmitters, and gliotransmitters-plays an important role in GBM pathophysiology and facilitates tumor survival and growth. In particular, GBM tumor cells produce glutamate, which is toxic to healthy tissue and is associated with increased tumor invasion into adjacent brain regions. The conditions that lead to this excitotoxic release of glutamate are not completely understood. Previous studies have demonstrated that extracellular ATP is present at high levels in the tumor microenvironment, and that ATP stimulates the release of glutamate from astrocytes in culture. Here we examine the functional effects of extracellular ATP on the GL261 cell line, a model system for high-grade astrocytomas such as GBM. We show that treatment with ATP leads to an immediate, dose-dependent influx of calcium into the cell that is partially inhibited by an antagonist (o-ATP) of the ionotropic ATP receptor P2X7. In addition, GL261 cells respond to extracellular ATP with a dose-dependent release of glutamate. Consistent with other reports, we find that ATP is toxic to GL261 cells at high concentrations. Together, these results provide insight into the mechanisms responsible for glutamate production by tumor cells and inform future studies that will identify how the GBM tumor microenvironment facilitates tumor invasion into healthy areas of the brain.

P2Y14 receptor activation decreases interleukin-6 production and glioma GL261 cell proliferation in microglial transwell cultures

Gliomas are rich in extracellular nucleotides that modulate glioma cell production of multiple cytokines including interleukin (IL)-6, which strongly contributes to glioma cell proliferation. However, little is known about how nucleotide signaling modulates microglial/macrophage (MG/MP) cytokine production in the context of gliomas, nor how MG/MP purinergic P2 receptor expression changes in the tumor micro-environment. We hypothesized that: (1) expression of key P2Y receptors will be augmented in glioma-derived MG/MP, and (2) selective activation of these receptors in vitro will regulate microglial production of IL-6 and glioma cell proliferation. We tested these hypotheses using the murine GL261 glioma model. Compared to MG/MP isolated from the normal brain tissue, CD11b⁺ cells isolated from GL261 tumors expressed higher levels of several P2 receptors, including P2Y14 receptors. To evaluate microglial P2Y14 receptor function in the context of tumor cells, we first cultured N9 microglia in transwells with GL261 cells and found that microglial P2Y14 mRNA levels were similarly increased in transwell cultures. GL261 cells did not express detectable P2Y14 levels either when they were cultured alone or in transwell cultures with N9 cells. Selective P2Y14 receptor activation with UDP-glucose (UDPG) did not affect IL-6 levels in either cell type cultured alone, but in transwell cultures, UDPG decreased IL-6 protein levels in the medium. Application of conditioned medium from UDPG-treated microglia reduced GL261 cell proliferation. Together, these data suggest that P2Y14 receptors may be a key a receptor involved in glioma cell-MG/MP communication in the tumor environment.

Glioma sensitive or chemoresistant to temozolomide differentially modulate macrophage protumor activities

BACKGROUND

Glioblastomas are the most devastating brain tumor characterized by chemoresistance development and poor prognosis. Macrophages are a component of tumor microenvironment related to glioma malignancy. The relation among inflammation, innate immunity and cancer is accepted; however, molecular and cellular mechanisms mediating this relation and chemoresistance remain unresolved.

OBJECTIVE

Here we evaluated whether glioma sensitive or resistant to temozolomide (TMZ) modulate macrophage polarization and inflammatory pathways associated. The impact of glioma-macrophage crosstalk on glioma proliferation was also investigated.

METHODS

GL261 glioma chemoresistance was developed by exposing cells to increasing TMZ concentrations over a period of 6months. Mouse peritoneal macrophages were exposed to glioma-conditioned medium or co-cultured directly with glioma sensitive (GL) or chemoresistant (GLTMZ). Macrophage polarization, in vitro and in vivo glioma proliferation, redox parameters, ectonucleotidase activity and ATP cytotoxicity were performed.

RESULTS

GLTMZ cells were more effective than GL in induce M2-like macrophage polarization and in promote a strong immunosuppressive environment characterized by high IL-10 release and increased antioxidant potential, which may contribute to glioma chemoresistance and proliferation. Interestingly, macrophage-GLTMZ crosstalk enhanced in vitro and in vivo proliferation of chemoresistant cells, decreased ectonucleotidase activities, which was followed by increased macrophage sensitivity to ATP induced death.

CONCLUSIONS

Results suggest a differential macrophage modulation by GLTMZ cells, which may favor the maintenance of immunosuppressive tumor microenvironment and glioma proliferation.

GENERAL SIGNIFICANCE

The induction of immunosuppressive environment and macrophage education by chemoresistant gliomas may be important for tumor recovery after chemotherapy and could be considered to overcome chemoresistance development.

Evidence for purine nucleoside phosphorylase (PNP) release from rat C6 glioma cells

Intracellular purine turnover is mainly oriented to preserving the level of triphosphate nucleotides, fundamental molecules in vital cell functions that, when released outside cells, act as receptor signals. Conversely, high levels of purine bases and uric acid are found in the extracellular milieu, even in resting conditions. These compounds could derive from nucleosides/bases that, having escaped to cell reuptake, are metabolized by extracellular enzymes similar to the cytosolic ones. Focusing on purine nucleoside phosphorylase (PNP) that catalyzes the reversible phosphorolysis of purine (deoxy)-nucleosides/bases, we found that it is constitutively released from cultured rat C6 glioma cells into the medium, and has a molecular weight and enzyme activity similar to the cytosolic enzyme. Cell exposure to 10 μM ATP or guanosine triphosphate (GTP) increased the extracellular amount of all corresponding purines without modifying the levels/activity of released PNP, whereas selective activation of ATP P2Y₁ or adenosine A_2A metabotropic receptors increased PNP release and purine base formation. The reduction to 1% in oxygen supply (2 h) to cells decreased the levels of released PNP, leading to an increased presence of extracellular nucleosides and to a reduced formation of xanthine and uric acid. Conversely, 2 h cell re-oxygenation enhanced the extracellular amounts of both PNP and purine bases. Thus, hypoxia and re-oxygenation modulated in opposite manner the PNP release/activity and, thereby, the extracellular formation of purine metabolism end-products. In conclusion, extracellular PNP and likely other enzymes deputed to purine base metabolism are released from cells, contributing to the purinergic system homeostasis and exhibiting an important pathophysiological role.

Polyphosphate as a donor of high-energy phosphate for the synthesis of ADP and ATP

Here, we studied the potential role of inorganic polyphosphate (polyP) as an energy source for ADP and ATP formation in the extracellular space. In SaOS-2 cells, we show that matrix vesicles are released into the extracellular space after incubation with polyP. These vesicles contain both alkaline phosphatase (ALP) and adenylate kinase (AK) activities (mediated by ALPL and AK1 enzymes). Both enzymes translocate to the cell membrane in response to polyP. To distinguish the process(es) of AMP and ADP formation during ALP hydrolysis from the ATP generated via the AK reaction, inhibition studies with the AK inhibitor A(5')P5(5')A were performed. We found that ADP formation in the extracellular space occurs after enzymatic ATP synthesis. After exposure to polyP, a significant increase of the ADP level was observed, which is likely to be been catalyzed by ALP. This increase is not due to an intensified ATP release via exocytosis. The ATP level in the extracellular space of SaOS-2 cells is strongly increased in response to polyP, very likely mediated by the AK. We propose that the ALP and AK enzymes are involved in the extracellular ADP and ATP synthesis.

Roles of purinergic P2X7 receptor in glioma and microglia in brain tumors

This review considers evidence suggesting that activation of the ionotropic purinergic receptor P2X₇ (P2X₇R) is a contributing factor in the growth of brain tumors. Importantly, expression of P2X₇R may be upregulated in both glioma cells and in immune responding microglial cells with possible differential effects on tumor progression. The recruitment of immune cells into tumor regions may not only be involved in supporting an immunosuppressive environment aiding tumor growth but activated microglia could secrete inflammatory factors promoting neoangiogenesis in expanding tumors. The subtype P2X₇R exhibits a number of unique properties including activation of the receptor in pathological conditions associated with developing brain tumors. In particular, the tumor microenvironment includes elevated levels of ATP required for activation of P2X₇R and the sustained tumor and immune cell P2X₇R-mediated responses which in total contribute to overall tumor growth and viability. Studies on cultured rat and human glioma show marked increases in expression of P2X₇R and enhanced cell mobility relative to control. Glioma cell animal models demonstrate enhanced expression of P2X₇R in both glioma and microglia with antagonism of receptor showing differential effects on tumor growth. Overall, P2X₇R activation is associated with a complexity of modulatory actions on tumor growth in part due to ubiquitous expression of the receptor in glioma and immune responsive cells.

Extracellular Nucleotide Hydrolysis in Dermal and Limbal Mesenchymal Stem Cells: A Source of Adenosine Production

Human Limbal (L-MSCs) and Dermal Mesenchymal Stem Cell (D-MSCs) possess many properties that increase their therapeutic potential in ophthalmology and dermatology. It is known that purinergic signaling plays a role in many aspects of mesenchymal stem cells physiology. They release and respond to purinergic ligands, altering proliferation, migration, differentiation, and apoptosis. Therefore, more information on these processes would be crucial for establishing future clinical applications using their differentiation potential, but without undesirable side effects. This study evaluated and compared the expression of ecto-nucleotidases, the enzymatic activity of degradation of extracellular nucleotides and the metabolism of extracellular ATP in D-MSCs and L-MSCs, isolated from discard tissues of human skin and sclerocorneal rims. The D-MSCs and L-MSCs showed a differentiation potential into osteogenic, adipogenic, and chondrogenic lineages and the expression of markers CD105⁺ , CD44⁺ , CD14^- , CD34^- , CD45^- , as expected. Both cells hydrolyzed low levels of extracellular ATP and high levels of AMP, leading to adenosine accumulation that can regulate inflammation and tissue repair. These cells expressed mRNA for ENTPD1, 2, 3, 5 and 6, and CD73 that corresponded to the observed enzymatic activities. Thus, considering the degradation of ATP and adenosine production, limbal MSCs are very similar to dermal MSCs, indicating that from the aspect of extracellular nucleotide metabolism L-MSCs are very similar to the characterized D-MSCs. J. Cell. Biochem. 118: 2430-2442, 2017. © 2017 Wiley Periodicals, Inc.

A Purinergic Trail for Metastases

Nucleotides and nucleosides have emerged as important modulators of tumor biology. Recently acquired evidence shows that, when these molecules are released by cancer cells or surrounding tissues, they act as potent prometastatic factors, favoring tumor cell migration and tissue colonization. Therefore, nucleotides and nucleosides should be considered as a new class of prometastatic factors. In this review, we focus on the prometastatic roles of nucleotides and discuss future applications of purinergic signaling modulation in view of antimetastatic therapies.

Platelets from glioblastoma patients promote angiogenesis of tumor endothelial cells and exhibit increased VEGF content and release

Glioblastoma multiforme (GBM) is the most common and fatal intracranial cancer in humans and exhibits intense and aberrant angiogenesis that sustains its malignancy and involves several angiogenic signals. Among them, vascular endothelial growth factor (VEGF) plays a key role and is overexpressed in GBM. Different cells appear to act as triggers of the aberrant angiogenesis, and, among them, platelets act as key participants. In order to provide further insights into the platelet features and angiogenic role in GBM, this study investigated the effects of platelet releasate on GBM-derived endothelial cells (GECs) and the levels of VEGF and endostatin, as pro- and anti-angiogenic components of platelet releasate from GBM patients. We demonstrate for the first time that: 1) platelet releasate exerts powerful pro-angiogenic effect on GECs, suggesting it might exert a role in the aberrant angiogenesis of GBM; 2) ADP and thrombin stimulation leads to significantly higher level of VEGF, but not of endostatin, in the releasate of platelets from GBM patients than those from healthy subjects; and 3) the intraplatelet concentrations of VEGF were significantly elevated in GBM patients as compared to controls. Moreover, we found a direct correlation between platelet-released VEGF and overall survival in our patient cohort. Although preliminary, these findings prompt further investigations to clarify the biologic relevance of platelet VEGF in GBM and prospective studies for screening GBM patients for anti-VEGF therapy and/or to optimize this treatment.

Methotrexate up-regulates ecto-5'-nucleotidase/CD73 and reduces the frequency of T lymphocytes in the glioblastoma microenvironment

Glioblastoma multiforme (GBM) is a deadly cancer characterized by a pro-tumoral immune response. T-regulatory (Treg) lymphocytes suppress effector immune cells through cytokine secretion and the adenosinergic system. Ecto-5'-nucleotidase/CD73 plays a crucial role in Treg-mediated immunosuppression in the GBM microenvironment (GME). Methotrexate (MTX) is an immunosuppressive drug that can increase the extracellular concentration of adenosine. In this manuscript, C6 GBM cells were treated with 1.0 μM MTX, and ecto-5'-nucleotidase/CD73 expression and extracellular AMP metabolism were analyzed in vitro. For in vivo studies, rats with implanted GBM were treated for 10 days with MTX-loaded lipid-core nanocapsules (MTX-LNCs, 1 mg/kg/day). The activity of ectonucleotidase and the expression of NTPDase1/CD39 and ecto-5'-nucleotidase/CD73 were measured. The frequencies of T lymphocytes (CD3(+)CD4(+), CD3(+)CD8(+), and CD4(+)CD25(high)CD39(+)) were quantified. In vitro, treatment with MTX increased CD73 expression and activity in C6 cells, which is in agreement with higher levels of extracellular adenosine. In vivo, MTX-LNC treatment increased CD39 expression on CD3(+)CD8(+) lymphocytes. In addition, MTX-LNC treatment up-regulated CD73 expression in tissue isolated from GBM, a finding that is in agreement with the higher activity of this enzyme. More specifically, the treatment increased CD73 expression on CD3(+)CD4(+) and CD3(+)CD8(+) lymphocytes. Treatment with MTX-LNCs decreased the frequencies of T-cytotoxic, T-helper, and Treg lymphocytes in the GME. Although more studies are necessary to better understand the complex cross-talk mediated by supra-physiological concentrations of adenosine in the GME, these studies demonstrate that MTX treatment increases CD73 enzyme expression and AMP hydrolysis, leading to an increase in adenosine production and immunosuppressive capability.

1,3-Dinitrobenzene neurotoxicity - Passage effect in immortalized astrocytes

Age-related disturbances in astrocytic mitochondrial function are linked to loss of neuroprotection and decrements in neurological function. The immortalized rat neocortical astrocyte-derived cell line, DI-TNC1, provides a convenient model for the examination of cellular aging processes that are difficult to study in primary cell isolates from aged brain. Successive passages in culture may serve as a surrogate of aging in which time-dependent adaptation to culture conditions may result in altered responses to xenobiotic challenge. To investigate the hypothesis that astrocytic mitochondrial homeostatic function is decreased with time in culture, low passage DI-TNC1 astrocytes (LP; #2-8) and high passage DI-TNC1 astrocytes (HP; #17-28) were exposed to the mitochondrial neurotoxicant 1,3-dinitrobenzene (DNB). Cells were exposed in either monoculture or in co-culture with primary cortical neurons. Astrocyte mitochondrial membrane potential, morphology, ATP production and proliferation were monitored in monoculture, and the ability of DI-TNC1 cells to buffer K(+)-induced neuronal depolarization was examined in co-cultures. In HP DI-TNC1 cells, DNB exposure decreased proliferation, reduced mitochondrial membrane potential and significantly decreased mitochondrial form factor. Low passage DI-TNC1 cells effectively attenuated K(+)-induced neuronal depolarization in the presence of DNB whereas HP counterparts were unable to buffer K(+) in DNB challenge. Following DNB challenge, LP DI-TNC1 cells exhibited greater viability in co-culture than HP. The data provide compelling evidence that there is an abrupt phenotypic change in DI-TNC1 cells between passage #9-16 that significantly diminishes the ability of DI-TNC1 cells to compensate for neurotoxic challenge and provide neuroprotective spatial buffering. Whether or not these functional changes have an in vivo analog in aging brain remains to be determined.

Ecto-5'-nucleotidase CD73 modulates the innate immune response to influenza infection but is not required for development of influenza-induced acute lung injury

Extracellular nucleotides and nucleosides are important signaling molecules in the lung. Nucleotide and nucleoside concentrations in alveolar lining fluid are controlled by a complex network of surface ectonucleotidases. Previously, we demonstrated that influenza A/WSN/33 (H1N1) virus resulted in increased levels of the nucleotide ATP and the nucleoside adenosine in bronchoalveolar lavage fluid (BALF) of wild-type (WT) C57BL/6 mice. Influenza-induced acute lung injury (ALI) was highly attenuated in A1-adenosine receptor-knockout mice. Because AMP hydrolysis by the ecto-5'-nucleotidase (CD73) plays a central role in and is rate-limiting for generation of adenosine in the normal lung, we hypothesized that ALI would be attenuated in C57BL/6-congenic CD73-knockout (CD73-KO) mice. Infection-induced hypoxemia, bradycardia, viral replication, and bronchoconstriction were moderately increased in CD73-KO mice relative to WT controls. However, postinfection weight loss, pulmonary edema, and parenchymal dysfunction were not altered. Treatment of WT mice with the CD73 inhibitor 5'-(α,β-methylene) diphosphate (APCP) also had no effect on infection-induced pulmonary edema but modestly attenuated hypoxemia. BALF from CD73-KO and APCP-treated WT mice contained more IL-6 and CXCL-10/IFN-γ-induced protein 10, less CXCL-1/keratinocyte chemoattractant, and fewer neutrophils than BALF from untreated WT controls. BALF from APCP-treated WT mice also contained fewer alveolar macrophages and more transforming growth factor-β than BALF from untreated WT mice. These results indicate that CD73 is not necessary for development of ALI following influenza A virus infection and suggest that tissue-nonspecific alkaline phosphatase may be responsible for increased adenosine generation in the infected lung. However, they do suggest that CD73 has a previously unrecognized immunomodulatory role in influenza.

Ecto-5'-Nucleotidase Overexpression Reduces Tumor Growth in a Xenograph Medulloblastoma Model

Background

Ecto-5’-nucleotidase/CD73 (ecto-5’-NT) participates in extracellular ATP catabolism by converting adenosine monophosphate (AMP) into adenosine. This enzyme affects the progression and invasiveness of different tumors. Furthermore, the expression of ecto-5’-NT has also been suggested as a favorable prognostic marker, attributing to this enzyme contradictory functions in cancer. Medulloblastoma (MB) is the most common brain tumor of the cerebellum and affects mainly children.

Materials and Methods

The effects of ecto-5’-NT overexpression on human MB tumor growth were studied in an in vivo model. Balb/c immunodeficient (nude) 6 to 14-week-old mice were used for dorsal subcutaneous xenograph tumor implant. Tumor development was evaluated by pathophysiological analysis. In addition, the expression patterns of adenosine receptors were verified.

Results

The human MB cell line D283, transfected with ecto-5’-NT (D283hCD73), revealed reduced tumor growth compared to the original cell line transfected with an empty vector. D283hCD73 generated tumors with a reduced proliferative index, lower vascularization, the presence of differentiated cells and increased active caspase-3 expression. Prominent A₁ adenosine receptor expression rates were detected in MB cells overexpressing ecto-5’-NT.

Conclusion

This work suggests that ecto-5’-NT promotes reduced tumor growth to reduce cell proliferation and vascularization, promote higher differentiation rates and initiate apoptosis, supposedly by accumulating adenosine, which then acts through A₁ adenosine receptors. Therefore, ecto-5’-NT might be considered an important prognostic marker, being associated with good prognosis and used as a potential target for therapy.

Multidrug Resistance-Associated Protein 2 Expression Is Upregulated by Adenosine 5'-Triphosphate in Colorectal Cancer Cells and Enhances Their Survival to Chemotherapeutic Drugs

Extracellular adenosine 5’-triphosphate (ATP) is a signaling molecule that induces a plethora of effects ranging from the regulation of cell proliferation to modulation of cancerous cell behavior. In colorectal cancer, ATP was reported to stimulate epithelial cell proliferation and possibly promote resistance to anti-cancer treatments. However, the exact role of this danger-signaling molecule on cancerous intestinal epithelial cells (IECs) in response to chemotherapeutic agents remains unknown. To address how ATP may influence the response of cancerous IECs to chemotherapeutic agents, we used Caco-2 cells, which display enterocyte-like features, to determine the effect of ATP on the expression of multidrug resistance-associated protein 2 (MRP2). Gene and protein expression were determined by quantitative real-time PCR (qRT-PCR) and Western blotting. Resistance to etoposide, cisplatin and doxorubicin was determined by MTT assays in response to ATP stimulation of Caco-2 cells and in cells for which MRP2 expression was down-regulated by shRNA. ATP increased the expression of MRP2 at both the mRNA and protein levels. MRP2 expression involved an ATP-dependent stimulation of the MEK/ERK signaling pathway that was associated with an increase in relative resistance of Caco-2 cells to etoposide. Abolition of MRP2 expression using shRNA significantly reduced the protective effect of MRP2 toward etoposide as well as to cisplatin and doxorubicin. This study describes the mechanism by which ATP may contribute to the chemoresistance of cancerous IECs in colorectal cancer. Given the heterogeneity of colorectal adenocarcinoma responses to anti-cancer drugs, these findings call for further study to understand the role of P2 receptors in cancer drug therapy and to develop novel therapies aimed at regulating P2 receptor activity.

Mesenchymal stem cells from different murine tissues have differential capacity to metabolize extracellular nucleotides

Mesenchymal stem cells (MSCs) have shown a great potential for cell-based therapy and many different therapeutic purposes. Despite the recent advances in the knowledge of MSCs biology, their biochemical and molecular properties are still poorly defined. Ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) and ecto-5'-nucleotidase (eNT/CD73) are widely expressed enzymes that hydrolyze extracellular nucleotides, generating an important cellular signaling cascade. Currently, studies have evidenced the relationship between the purinergic system and the development, maintenance, and differentiation of stem cells. The objective of this study is to identify the NTPDases and eNT/CD73 and compare the levels of nucleotide hydrolysis on MSCs isolated from different murine tissues (bone marrow, lung, vena cava, kidney, pancreas, spleen, skin, and adipose tissue). MSCs from all tissues investigated expressed the ectoenzymes at different levels. In MSCs from pancreas and adipose tissue, the hydrolysis of triphosphonucleosides was significantly higher when compared to the other cells. The diphosphonucleosides were hydrolyzed at a higher rate by MSC from pancreas when compared to MSC from other tissues. The differential nucleotide hydrolysis activity and enzyme expression in these cells suggests that MSCs play different roles in regulating the purinergic system in these tissues. Overall MSCs are an attractive adult-derived cell population for therapies, however, the fact that ecto-nucleotide metabolism can affect the microenvironment, modulating important events, such as immune response, makes the assessment of this metabolism an important part of the characterization of MSCs to be applied therapeutically.

Nucleotide receptors control IL-8/CXCL8 and MCP-1/CCL2 secretions as well as proliferation in human glioma cells

Glioma cells release cytokines to stimulate inflammation that facilitates cell proliferation. Here, we show that Lipopolysaccharide (LPS) treatment could induce glioma cells to proliferate and this process was dependent on nucleotide receptor activation as well as interleukin-8 (IL-8/CXCL8) secretion. We observed that extracellular nucleotides controlled IL-8/CXCL8 and monocyte chemoattractant protein 1 (MCP-1/CCL2) release by U251MG and U87MG human glioma cell lines via P2X7 and P2Y6 receptor activation. The LPS-induced release of these cytokines was also modulated by purinergic receptor activation since IL-8 and MCP-1 release was decreased by the nucleotide scavenger apyrase as well as by the pharmacological P2Y6 receptor antagonists suramin and MRS2578. In agreement with these observations, the knockdown of P2Y6 expression decreased LPS-induced IL-8 release as well as the spontaneous release of IL-8 and MCP-1, suggesting an endogenous basal release of nucleotides. Moreover, high millimolar concentrations of ATP increased IL-8 and MCP-1 release by the glioma cells stimulated with suboptimal LPS concentration which were blocked by P2X7 and P2Y6 antagonists. Altogether, these data suggest that extracellular nucleotides control glioma growth via P2 receptor-dependent IL-8 and MCP-1 secretions.

Biochemical and cytogenetic analysis of brain tissues in different grades of glioma patients

Background

Glioma, a neoplasm of neuroglial cells, is the most common type of brain tumor, constituting more than 50% of all brain tumors.

Purpose

This report summarizes the current knowledge regarding the clinical utility of biochemical enzyme markers for both diagnostic and therapeutic purposes in different grades of glioma.

Methods

Sixty patients with different grades of glioma include glioblastoma multiforme (n=20), Anaplastic astrocytoma (n=10). Oligodendroglioma (n=10). Ependymoma (n=10), Pilocytic astrocytoma (n=10) and patients with benign lesions (n=5) served as controls. Activity of antioxidants and marker enzymes were assayed in all grades followed by karyotyping.

Results

Activities of antioxidant enzymes reduced significantly (p<0.05) compared to controls except CAT, GST that showed marked increase (p<0.05) in accordance with malignancy. CK, Na-K⁺ ATPases, 5'-Nucleotidases showed marked increase in grade IV. Similarly, Mg2-ATPase, Ca2+ATPases showed significant increase in grade III.

Conclusion

The clinical importance for classification and treatment of glioma is governed by biochemical enzyme markers. The study of enzymes supported by related chromosomal changes is anticipated to provide better appreciation of biological properties in different grades of glioma.

Purinergic signalling and cancer

Receptors for extracellular nucleotides are widely expressed by mammalian cells. They mediate a large array of responses ranging from growth stimulation to apoptosis, from chemotaxis to cell differentiation and from nociception to cytokine release, as well as neurotransmission. Pharma industry is involved in the development and clinical testing of drugs selectively targeting the different P1 nucleoside and P2 nucleotide receptor subtypes. As described in detail in the present review, P2 receptors are expressed by all tumours, in some cases to a very high level. Activation or inhibition of selected P2 receptor subtypes brings about cancer cell death or growth inhibition. The field has been largely neglected by current research in oncology, yet the evidence presented in this review, most of which is based on in vitro studies, although with a limited amount from in vivo experiments and human studies, warrants further efforts to explore the therapeutic potential of purinoceptor targeting in cancer.