Selective NTPDase2 expression modulates in vivo rat glioma growth

Research progress on platelets in glioma

ABSTRACT

Gliomas are the most common primary neuroepithelial tumors of the central nervous system in adults, of which glioblastoma is the deadliest subtype. Apart from the intrinsically indestructible characteristics of glioma (stem) cells, accumulating evidence suggests that the tumor microenvironment also plays a vital role in the refractoriness of glioblastoma. The primary functions of platelets are to stop bleeding and regulate thrombosis under physiological conditions. Furthermore, platelets are also active elements that participate in a variety of processes of tumor development, including tumor growth, invasion, and chemoresistance. Glioma cells recruit and activate resting platelets to become tumor-educated platelets (TEPs), which in turn can promote the proliferation, invasion, stemness, and chemoresistance of glioma cells. TEPs can be used to obtain genetic information about gliomas, which is helpful for early diagnosis and monitoring of therapeutic effects. Platelet membranes are intriguing biomimetic materials for developing efficacious drug carriers to enhance antiglioma activity. Herein, we review the recent research referring to the contribution of platelets to the malignant characteristics of gliomas and focusing on the molecular mechanisms mediating the interaction between TEPs and glioma (stem) cells, as well as present the challenges and opportunities in targeting platelets for glioma therapy.

Role and recent progress of P2Y12 receptor in cancer development

P2Y12 receptor (P2Y12R) is an adenosine-activated G protein-coupled receptor (GPCR) that plays a central role in platelet function, hemostasis, and thrombosis. P2Y12R activation can promote platelet aggregation and adhesion to cancer cells, promote tumor angiogenesis, and affect the tumor immune microenvironment (TIME) and tumor drug resistance, which is conducive to the progression of cancers. Meanwhile, P2Y12R inhibitors can inhibit this effect, suggesting that P2Y12R may be a potential therapeutic target for cancer. P2Y12R is involved in cancer development and metastasis, while P2Y12R inhibitors are effective in inhibiting cancer. However, a new study suggests that long-term use of P2Y12R inhibitors may increase the risk of cancer and the mechanism remains to be explored. In this paper, we reviewed the structural and functional characteristics of P2Y12R and its role in cancer. We explored the role of P2Y12R inhibitors in different tumors and the latest advances by summarizing the basic and clinical studies on the effects of P2Y12R inhibitors on tumors.

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.

Nek1-inhibitor and temozolomide-loaded microfibers as a co-therapy strategy for glioblastoma treatment

Malignant glioblastoma (GB) is the predominant primary brain tumour in adults, but despite the efforts towards novel therapies, the median survival of GB patients has not significantly improved in the last decades. Therefore, localised approaches that treat GB straight into the tumour site provide an alternative to enhance chemotherapy bioavailability and efficacy, reducing systemic toxicity. Likewise, the discovery of protein targets, such as the NIMA-related kinase 1 (Nek1), which was previously shown to be associated with temozolomide (TMZ) resistance in GB, has stimulated the clinical development of target therapy approaches to treat GB patients. In this study, we report an electrospun polyvinyl alcohol (PVA) microfiber (MF) brain-implant prepared for the controlled release of Nek1 protein inhibitor (iNek1) and TMZ or TMZ-loaded nanoparticles. The formulations revealed adequate stability and drug loading, which prolonged the drugs' release allowing a sustained exposure of the GB cells to the treatment and enhancing the drugs' therapeutic effects. TMZ-loaded MF provided the highest concentration of TMZ within the brain of tumour-bearing rats, and it was statistically significant when compared to TMZ via intraperitoneal (IP). All animals treated with either co-therapy formulation (TMZ + iNek1 MF or TMZ nanoparticles + iNek1 MF) survived until the endpoint (60 days), whereas the Blank MF (drug-unloaded), TMZ MF and TMZ IP-treated rats' median survival was found to be 16, 31 and 25 days, respectively. The tumour/brain area ratio of the rats implanted with either MF co-therapy was found to be reduced by 5-fold when compared to Blank MF-implanted rats. Taken together, our results strongly suggest that Nek1 is an important GB oncotarget and the inhibition of Nek1's activity significantly decreases GB cells' viability and tumour size when combined with TMZ treatment.

Structure-activity features of purines and their receptors: implications in cell physiopathology

The purine molecular structure consists of fused pyrimidine and imidazole rings. Purines are main pieces that conform the structure of nucleic acids which rule the inheritance processes. Purines also work as metabolic intermediates in different cell functions and as messengers in the signaling pathways throughout cellular communication. Purines, mainly ATP and adenosine (ADO), perform their functional and pharmacological properties because of their structural/chemical characteristics that make them either targets of mutagenesis, mother frameworks for designing molecules with controlled effects (e.g. anti-cancer), or chemical donors (e.g., of methyl groups, which represent a potential chemoprotective action against cancer). Purines functions also come from their effect on specific receptors, channel-linked and G-protein coupled for ATP, and exclusively G-coupled receptors for ADO (also known as ADORAs), which are involved in cell signaling pathways, there, purines work as chemical messengers with autocrine, paracrine, and endocrine actions that regulate cell metabolism and immune response in tumor progression which depends on the receptor types involved in these signals. Purines also have antioxidant and anti-inflammatory properties and participate in the cell energy homeostasis. Therefore, purine physiology is important for a variety of functions relevant to cellular health; thus, when these molecules present a homeostatic imbalance, the stability and survival of the cellular systems become compromised.

Ectonucleotidases in Inflammation, Immunity, and Cancer

Nucleoside triphosphate diphosphohydrolases (NTPDases) are a family of enzymes that hydrolyze nucleotides such as ATP, UTP, ADP, and UDP to monophosphates derivates such as AMP and UMP. The NTPDase family consists of eight enzymes, of which NTPDases 1, 2, 3, and 8 are expressed on cell membranes thereby hydrolyzing extracellular nucleotides. Cell membrane NTPDases are expressed in all tissues, in which they regulate essential physiological tissue functions such as development, blood flow, hormone secretion, and neurotransmitter release. They do so by modulating nucleotide-mediated purinergic signaling through P2 purinergic receptors. NTPDases 1, 2, 3, and 8 also play a key role during infection, inflammation, injury, and cancer. Under these conditions, NTPDases can contribute and control the pathophysiology of infectious, inflammatory diseases and cancer. In this review, we discuss the role of NTPDases, focusing on the less understood NTPDases 2-8, in regulating inflammation and immunity during infectious, inflammatory diseases, and cancer.

Characterization of the Endometrial MSC Marker Ectonucleoside Triphosphate Diphosphohydrolase-2 (NTPDase2/CD39L1) in Low- and High-Grade Endometrial Carcinomas: Loss of Stromal Expression in the Invasive Phenotypes

Ectonucleoside triphosphate diphosphohydrolase-2 (NTPDase2/CD39L1) has been described in human non-pathological endometrium in both epithelial and stromal components without changes along the cycle. It was identified as a stromal marker of basalis. In the present study, we aimed to evaluate NTPDase2 distribution, using immunolabeling and in situ enzyme activity approaches, in endometrial carcinoma (EC) at different tumor grades. NTPDase2 was present in tumor epithelial EC cells, as in the non-pathological endometria, but the expression underwent changes in subcellular distribution and also tended to decrease with the tumor grade. In stroma, NTPDase2 was identified exclusively at the tumor-myometrial junction but this expression was lost in tumors of invasive phenotype. We have also identified in EC samples the presence of the perivascular population of endometrial mesenchymal stem cells (eMSCs) positive for sushi domain containing 2 (SUSD2) and for NTPDase2, already described in non-tumoral endometrium. Our results point to NTPDase2 as a histopathological marker of tumor invasion in EC, with diagnostic relevance especially in cases of EC coexisting with other endometrial disorders, such as adenomyosis, which occasionally hampers the assessment of tumor invasion parameters.

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.

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.

AVNP2 protects against cognitive impairments induced by C6 glioma by suppressing tumour associated inflammation in rats

Glioblastoma is a kind of malignant tumour and originates from the central nervous system. In the last century, some researchers and clinician have noticed that the psychosocial and neurocognitive functioning of patients with malignant gliomas can be impaired. Many clinical studies have demonstrated that part of patients, adults or children, diagnosed with glioblastoma will suffer from cognitive deficiency during their clinical course, especially in long-term survivors. Many nanoparticles (NPs) can inhibit the biological functions of tumours by modulating tumour-associated inflammation, which provokes angiogenesis and tumour growth. As one of the best antiviral nanoparticles (AVNPs), AVNP2 is the 2nd generation of AVNP2 that have been conjugated to graphite-graphene for improving physiochemical performance and reducing toxicity. AVNP2 inactivates viruses, such as the H1N1 and H5N1influenza viruses and even the SARS coronavirus, while it inhibits bacteria, such as MRSA and E. coli. As antimicrobials, nanoparticles are considered to be one of the vectors for the administration of therapeutic compounds. Yet, little is known about their potential functionalities and toxicities to the neurotoxic effects of cancer. Herein, we explored the functionality of AVNP2 on inhibiting C6 in glioma-bearing rats. The novel object-recognition test and open-field test showed that AVNP2 significantly improved the neuro-behaviour affected by C6 glioma. AVNP2 also alleviated the decline of long-term potentiation (LTP) and the decreased density of dendritic spines in the CA1 region induced by C6. Western blot assay and immunofluorescence staining showed that the expressions of synaptic-related proteins (PSD-95 and SYP) were increased, and these findings were in accordance with the results mentioned above. It revealed that the sizes of tumours in C6 glioma-bearing rats were smaller after treatment with AVNP2. The decreased expression of inflammatory factors (IL-1β, IL-6 and TNF-α) by Western blotting assay and ELISA, angiogenesis protein (VEGF) by Western blotting assay and other related proteins (BDNF, NF-ĸB, iNOS and COX-2) by Western blotting assay in peri-tumour tissue indicated that AVNP2 could control tumour-associated inflammation, thus efficiently ameliorating the local inflammatory condition and, to some extent, inhibiting angiogenesis in C6-bearing rats. In conclusion, our results suggested that AVNP2 could have an effect on the peri-tumor environment, obviously restraining the growth progress of gliomas, and eventually improving cognitive levels in C6-bearing rats.

Imatinib mesylate affects extracellular ATP catabolism and expression of NTPDases in a chronic myeloid leukemia cell line

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm, characterized by the occurrence of the t(9;22)(q34;q11) translocation. First-line therapy for CML consists of treatment with imatinib mesylate, which selectively inhibits the BCR-ABL protein by competing for its ATP-binding site. Adenine nucleotide signaling is modulated by the ectonucleotidases and this pathway is related to tumorigenic processes. Considering the relationship between ATP and cancer, we aimed to evaluate the influence of imatinib mesylate on the expressions and functions of the NTPDase and ecto-5'-nucleotidase (CD73) enzymes in imatinib-sensitive and -resistant K-562 cell lines. mRNA analysis showed that K-562 cells express all ENTPDs and NT5E. However, when treated with imatinib mesylate for 24 h, the expression of ENTPD1, -2, -3 and -5 increased, leading to a higher nucleotides hydrolysis rate. HPLC analysis identified increased ATP degradation in cells after 24 h of treatment, with consequent ADP and AMP formation, corroborating the increase in gene and protein expression of ectonucleotidases as observed in previous results. On the other hand, we observed that imatinib-resistant K-562 cells presented a decrease in nucleotide hydrolysis and expressions of ENTPD1 and -5. These results suggest an involvement of imatinib in modulating ectonucleotidases in CML that will need further investigation. Since these ectonucleotidases have important catalytic activities in the tumor microenvironment, their modulation in CML cells may represent an important therapeutic approach to regulate levels of extracellular adenine nucleotides.

Introduction to Purinergic Signalling in the Brain

ATP is a cotransmitter with glutamate, noradrenaline, GABA, acetylcholine and dopamine in the brain. There is a widespread presence of both adenosine (P1) and P2 nucleotide receptors in the brain on both neurons and glial cells. Adenosine receptors play a major role in presynaptic neuromodulation, while P2X ionotropic receptors are involved in fast synaptic transmission and synaptic plasticity. P2Y G protein-coupled receptors are largely involved in presynaptic activities, as well as mediating long-term (trophic) signalling in cell proliferation, differentiation and death during development and regeneration. Both P1 and P2 receptors participate in neuron-glial interactions. Purinergic signalling is involved in control of cerebral vascular tone and remodelling and has been implicated in learning and memory, locomotor and feeding behaviour and sleep. There is increasing interest in the involvement of purinergic signalling in the pathophysiology of the CNS, including trauma, ischaemia, epilepsy, neurodegenerative diseases, neuropsychiatric and mood disorders, and cancer, including gliomas.

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.

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.

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.

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.

Generation and characterization of polyclonal and monoclonal antibodies to human NTPDase2 including a blocking antibody

Nucleoside triphosphate diphosphohydrolase-2 (NTPDase2) is an ectonucleotidase that modulates P2 receptor activation by hydrolyzing ATP to ADP. In rodents, NTPDase2 is expressed by several specialized cell types such as vascular adventitial cells, neuroglial cells, hepatic portal fibroblasts, gustatory type I cells, and cells within the connective tissues of reproductive and gastrointestinal organs. Much less is known regarding the expression and function of NTPDase2 in humans. Here, we developed specific research tools to study human NTPDase2. We generated mouse monoclonal antibodies and rabbit polyclonal antibodies specific to human NTPDase2 and validated their specificity by western blot, immunocytochemistry, immunohistochemistry, and flow cytometry. In addition, one monoclonal antibody named hN2-D5 _s specifically inhibits human NTPDase2 enzymatic activity but not mouse nor rat NTPDase2. Using these antibodies, NTPDase2 immunoreactivity was detected on glial cells of the human enteric nervous system suggesting a function of the enzyme in intestinal motility. In conclusion, the new antibodies described in our work are novel tools that will enhance future studies of NTPDase2 expression and function in humans.

Synthetic 2-aryl-3-((piperidin-1-yl)ethyl)thiazolidin-4-ones exhibit selective in vitro antitumoral activity and inhibit cancer cell growth in a preclinical model of glioblastoma multiforme

Glioblastoma multiforme (GBM) is the worst form of primary brain tumor, which has a high rate of infiltration and resistance to radiation and chemotherapy, resulting in poor prognosis for patients. Recent studies show that thiazolidinones have a wide range of pharmacological properties including antimicrobial, anti-inflammatory, anti-oxidant and anti-tumor. Here, we investigate the effect antiglioma in vitro of a panel of sixteen synthetic 2-aryl-3-((piperidin-1-yl)ethyl)thiazolidin-4-ones where 13 of these decreased the viability of glioma cells 30-65% (100 μM) compared with controls. The most promising compounds such as 4d, 4l, 4m and 4p promoted glioma reduction of viability greater than 50%, were further tested at lower concentrations (12.5, 25, 50 and 100 μM). Also, the data showed that the compounds 4d, 4l, 4m and 4p induced cell death primarily through necrosis and late apoptosis mechanisms. Interestingly, none of these 2-aryl-3-((piperidin-1-yl)ethyl)thiazolidin-4-ones were cytotoxic for primary astrocytes, which were used as a non-transformed cell model, indicating selectivity. Our results also show that the treatment with sub-therapeutic doses of 2-aryl-3-((piperidin-1-yl)ethyl)thiazolidin-4-ones (4d, 4l and 4p) reduced in vivo glioma growth as well as malignant characteristics of implanted tumors such as intratumoral hemorrhage and peripheral pseudopalisading. Importantly, 2-aryl-3-((piperidin-1-yl)ethyl)thiazolidin-4-ones treatment did not induce mortality or peripheral damage to animals. Finally, 2-aryl-3-((piperidin-1-yl)ethyl)thiazolidin-4-ones also changed the nitric oxide metabolism which may be associated with reduced growth and malignity characteristics of gliomas. These data indicates for the first time the therapeutic potential of synthetic 2-aryl-3-((piperidin-1-yl)ethyl)thiazolidin-4-ones to GBM treatment.

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.

Involvement of purinergic system in the release of cytokines by macrophages exposed to glioma-conditioned medium

Macrophages are involved in cancer progression. M1 macrophages have an antitumor effect, whereas M2 phenotype are associated with tumor growth. The progression of gliomas involves the participation of an inflammatory microenvironment. Adenosine triphosphate (ATP) can act as pro-inflammatory signal, whereas adenosine has opposite properties. The biological effects of extracellular nucleotides/nucleosides mediated by purinergic receptors are controlled by ectonucleotidases. In the present work, we evaluated whether glioma-conditioned medium (GL-CM) modulates macrophage differentiation and the participation of ATP and adenosine in the release of pro-and anti-inflammatory cytokines by these cells. The results show that macrophages exposed to GL-CM were modulated to an M2-like phenotype. HPLC analysis of GL-CM demonstrated the presence of significant amounts of ATP and its metabolites. Macrophages exposed to GL-CM presented decreased ATP and AMP hydrolysis and increased IL-10 and MCP-1 secretion, effects that were diminished by P1 or P2 antagonists. GL-CM did not alter the release of IL-6 by macrophages, although treatment with ATP promoted an increase in the release of IL-6, which was prevented by a P2X7 antagonist. In summary, we found that A2A and P2X7 activation is necessary for IL-10, MCP-1, and IL-6 release by macrophages exposed to GL-CM, which, in turn, modulates the macrophages to M2-phenotype. The present study establishes a relationship between M2-like polarization, cytokine release and purinergic receptor activation in macrophages exposed to GL-CM. Therefore, the data presented herein contributes to advancing in the field of cancer-related inflammation and point specific purinergic receptors as targets for modulation of the phenotype of glioma-associated macrophages.

P2X7 receptor as predictor gene for glioma radiosensitivity and median survival

Glioblastoma multiforme (GBM) is considered the most lethal intracranial tumor and the median survival time is approximately 14 months. Although some glioma cells present radioresistance, radiotherapy has been the mainstay of therapy for patients with malignant glioma. The activation of P2X7 receptor (P2X7R) is responsible for ATP-induced death in various cell types. In this study, we analyzed the importance of ATP-P2X7R pathway in the radiotherapy response P2X7R silenced cell lines, in vivo and human tumor samples. Both glioma cell lines used in this study present a functional P2X7R and the P2X7R silencing reduced P2X7R pore activity by ethidium bromide uptake. Gamma radiation (2Gy) treatment reduced cell number in a P2X7R-dependent way, since both P2X7R antagonist and P2X7R silencing blocked the cell cytotoxicity caused by irradiation after 24h. The activation of P2X7R is time-dependent, as EtBr uptake significantly increased after 24h of irradiation. The radiotherapy plus ATP incubation significantly increased annexin V incorporation, compared with radiotherapy alone, suggesting that ATP acts synergistically with radiotherapy. Of note, GL261 P2X7R silenced-bearing mice failed in respond to radiotherapy (8Gy) and GL261 WT-bearing mice, that constitutively express P2X7R, presented a significant reduction in tumor volume after radiotherapy, showing in vivo that functional P2X7R expression is essential for an efficient radiotherapy response in gliomas. We also showed that a high P2X7R expression is a good prognostic factor for glioma radiosensitivity and survival probability in humans. Our data revealed the relevance of P2X7R expression in glioma cells to a successful radiotherapy response, and shed new light on this receptor as a useful predictor of the sensitivity of cancer patients to radiotherapy and median survival.

P2X and P2Y receptors—role in the pathophysiology of the nervous system

Purinergic signalling plays a crucial role in proper functioning of the nervous system. Mechanisms depending on extracellular nucleotides and their P2 receptors also underlie a number of nervous system dysfunctions. This review aims to present the role of purinergic signalling, with particular focus devoted to role of P2 family receptors, in epilepsy, depression, neuropathic pain, nervous system neoplasms, such as glioma and neuroblastoma, neurodegenerative diseases like Parkinson’s disease, Alzheimer’s disease and multiple sclerosis. The above-mentioned conditions are associated with changes in expression of extracellular ectonucleotidases, P2X and P2Y receptors in neurons and glial cells, as well as releasing considerable amounts of nucleotides from activated or damaged nervous tissue cells into the extracellular space, which contributes to disturbance in purinergic signalling. The numerous studies indicate a potential possibility of using synthetic agonists/antagonists of P2 receptors in treatment of selected nervous system diseases. This is of particular significance, since numerous available agents reveal a low effectiveness and often produce side effects.

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.

2-Hexylthio-β,γ-CH2-ATP is an effective and selective NTPDase2 inhibitor

NTPDase2 catabolizes nucleoside triphosphates and consequently, through the interaction of nucleotides with P2 receptors, controls multiple biological responses. NTPDase2 inhibitors could modulate responses induced by nucleotides in thrombosis, inflammation, cancer, etc. Here we developed a set of ATP analogues as potential NTPDase inhibitors and identified a subtype-selective and potent NTPDase2 inhibitor, 2-hexylthio-β,γ-methylene-ATP, 2. Analogue 2 was stable to hydrolysis by NTPDase1, -2, -3, and -8. It inhibited hNTPDase2 with Ki 20 μM, while only marginally (5-15%) inhibiting NTPDase1, -3, and -8. Homology models of hNTPDase1 and -2 were constructed. Docking and subsequent linear interaction energy (LIE) simulations provided a correlation with r2=0.94 between calculated and experimental inhibition data for the triphosphate analogues considered in this work. The origin of selectivity of 2 for NTPDase2 over NTPDase1 is the thiohexyl moiety of 2 which is favorably located within a hydrophobic pocket, whereas in NTPDase1 it is exposed to the solvent.

NTPDase3 and ecto-5'-nucleotidase/CD73 are differentially expressed during mouse bladder cancer progression

According to the World Health Organization, bladder cancer is the seventh most common cancer among men in the world. The current treatments for this malignancy are not efficient to prevent the recurrence and progression of tumors. Then, researches continue looking for better therapeutic targets which can end up in new and more efficient treatments. One of the recent findings was the identification that the purinergic system was involved in bladder tumorigenesis. The ectonucleotidases, mainly ecto-5'-nucleotidase/CD73 have been revealed as new players in cancer progression and malignity. In this work, we investigated the NTPDase3 and ecto-5'-nucleotidase/CD73 expression in cancer progression in vivo. Bladder tumor was induced in mice by the addition of 0.05 % of N-butyl-N-(hydroxybutyl)-nitrosamine (BBN) in the drinking water for 4, 8, 12, 18, and 24 weeks. After this period, mice bladders were removed for histopathology analysis and immunofluorescence assays. The bladder of animals which has received BBN had alterations, mainly inflammation, in initial times of tumor induction. After 18 weeks, mice's bladder has developed histological alterations similar to human transitional cell carcinoma. The cancerous urothelium, from mice that received BBN for 18 and 24 weeks, presented a weak immunostaining to NTPDase3, in contrast to an increased expression of ecto-5'-nucleotidase/CD73. The altered expression of NTPDase3 and ecto-5'-nucleotidase/CD73 presented herein adds further evidence to support the idea that alterations in ectonucleotidases are involved in bladder tumorigenesis and reinforce the ecto-5'-nucleotidase/CD73 as a future biomarker and/or a target for pharmacological therapy of bladder cancer.

Ectonucleotidase expression profile and activity in human cervical cancer cell lines

Cervical cancer is the third most frequent cancer in women worldwide. Adenine nucleotide signaling is modulated by the ectonucleotidases that act in sequence, forming an enzymatic cascade. Considering the relationship between the purinergic signaling and cancer, we studied the E-NTPDases, ecto-5'-nucleotidase, and E-NPPs in human cervical cancer cell lines and keratinocytes. We evaluated the expression profiles of these enzymes using RT-PCR and quantitative real-time PCR analysis. The activities of these enzymes were examined using ATP, ADP, AMP, and p-nitrophenyl-5'-thymidine monophosphate (p-Nph-5'-TMP) as substrate, in a colorimetric assay. The extracellular adenine nucleotide hydrolysis was estimated by HPLC analysis. The hydrolysis of all substrates exhibited a linear pattern and these activities were cation-dependent. An interesting difference in the degradation rate was observed between cervical cancer cell lines SiHa, HeLa, and C33A and normal imortalized keratinocytes, HaCaT cells. The mRNA of ecto-5'-nucleotidase, E-NTPDases 5 and 6 were detectable in all cell lines, and the dominant gene expressed was the Entpd 5 enzyme, in SiHa cell line (HPV16 positive). In accordance with this result, a higher hydrolysis activity for UDP and GDP nucleotides was observed in the supernatant of the SiHa cells. Both normal and cancer cells presented activity and mRNAs of members of the NPP family. Considering that these enzymes exert an important catalytic activity, controlling purinergic nucleotide concentrations in tumors, the presence of ectonucleotidases in cervical cancer cells can be important to regulate the levels of extracellular adenine nucleotides, limiting their effects.

P2Y receptors in the mammalian nervous system: pharmacology, ligands and therapeutic potential

P2Y receptors for extracellular nucleotides are coupled to activation of a variety of G proteins and stimulate diverse intracellular signaling pathways that regulate functions of cell types that comprise the central nervous system (CNS). There are 8 different subtypes of P2Y receptor expressed in cells of the CNS that are activated by a select group of nucleotide agonists. Here, the agonist selectivity of these 8 P2Y receptor subtypes is reviewed with an emphasis on synthetic agonists with high potency and resistance to degradation by extracellular nucleotidases that have potential applications as therapeutic agents. In addition, the recent identification of a wide variety of subtype-selective antagonists is discussed, since these compounds are critical for discerning cellular responses mediated by activation of individual P2Y receptor subtypes. The functional expression of P2Y receptor subtypes in cells that comprise the CNS is also reviewed and the role of each subtype in the regulation of physiological and pathophysiological responses is considered. Other topics include the role of P2Y receptors in the regulation of blood-brain barrier integrity and potential interactions between different P2Y receptor subtypes that likely impact tissue responses to extracellular nucleotides in the CNS. Overall, current research suggests that P2Y receptors in the CNS regulate repair mechanisms that are triggered by tissue damage, inflammation and disease and thus P2Y receptors represent promising targets for the treatment of neurodegenerative diseases.

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 P2X(7), 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.

Purines, purinergic receptors, and cancer

Purines were long thought to be restricted to the intracellular compartment, where they are used for energy transactions, nucleic acid synthesis, and a multiplicity of biochemical reactions. However, it is now clear that both adenosine and adenosine triphosphate are (i) abundant biochemical components of the tumor microenvironment, (ii) potent modulators of immune cell responses and cytokine release, and (iii) key players in host-tumor interaction. Moreover, both ATP and adenosine directly affect tumor cell growth. Adenosine is a powerful immunosuppressant (mainly acting at A2A receptors) and a modulator of cell growth (mainly acting at A3 receptors). ATP is a proinflammatory (acting at P2Y1, P2Y2, P2Y4, P2Y6, and P2Y12, and at P2X4 and P2X7 receptors), an immunosuppressant (acting at P2Y11), and a growth-promoting agent (acting at P2Y1, P2Y2, and P2X7 receptors). This complex signaling network generates an array of inhibitory and stimulatory responses that affect immune cell function, tumor growth, and metastatic dissemination. Investigation of purinergic signaling has increased our understanding of the tumor microenvironment and opened new and exciting avenues for the development of novel therapeutics.

Ectonucleotidases in tumor cells and tumor-associated immune cells: an overview

Increasing evidence points out that genetic alteration does not guarantee the development of a tumor and indicates that complex interactions of tumor cells with the microenvironment are fundamental to tumorigenesis. Among the pathological alterations that give tumor cells invasive potential, disruption of inflammatory response and the purinergic signaling are emerging as an important component of cancer progression. Nucleotide/nucleoside receptor-mediated cell communication is orchestrated by ectonucleotidases, which efficiently hydrolyze ATP, ADP, and AMP to adenosine. ATP can act as danger signaling whereas adenosine, acts as a negative feedback mechanism to limit inflammation. Many tumors exhibit alterations in ATP-metabolizing enzymes, which may contribute to the pathological events observed in solid cancer. In this paper, the main changes occurring in the expression and activity of ectonucleotidases in tumor cells as well as in tumor-associated immune cells are discussed. Furthermore, we focus on the understanding of the purinergic signaling primarily as exemplified by research done by the group on gliomas.

Pathophysiology of astroglial purinergic signalling

Astrocytes are fundamental for central nervous system (CNS) physiology and are the fulcrum of neurological diseases. Astroglial cells control development of the nervous system, regulate synaptogenesis, maturation, maintenance and plasticity of synapses and are central for nervous system homeostasis. Astroglial reactions determine progression and outcome of many neuropathologies and are critical for regeneration and remodelling of neural circuits following trauma, stroke, ischaemia or neurodegenerative disorders. They secrete multiple neurotransmitters and neurohormones to communicate with neurones, microglia and the vascular walls of capillaries. Signalling through release of ATP is the most widespread mean of communication between astrocytes and other types of neural cells. ATP serves as a fast excitatory neurotransmitter and has pronounced long-term (trophic) roles in cell proliferation, growth, and development. During pathology, ATP is released from damaged cells and acts both as a cytotoxic factor and a proinflammatory mediator, being a universal "danger" signal. In this review, we summarise contemporary knowledge on the role of purinergic receptors (P2Rs) in a variety of diseases in relation to changes of astrocytic functions and nucleotide signalling. We have focussed on the role of the ionotropic P2X and metabotropic P2YRs working alone or in concert to modify the release of neurotransmitters, to activate signalling cascades and to change the expression levels of ion channels and protein kinases. All these effects are of great importance for the initiation, progression and maintenance of astrogliosis-the conserved and ubiquitous glial defensive reaction to CNS pathologies. We highlighted specific aspects of reactive astrogliosis, especially with respect to the involvement of the P2X(7) and P2Y(1)R subtypes. Reactive astrogliosis exerts both beneficial and detrimental effects in a context-specific manner determined by distinct molecular signalling cascades. Understanding the role of purinergic signalling in astrocytes is critical to identifying new therapeutic principles to treat acute and chronic neurological diseases.

Overexpression of NTPDase2 in gliomas promotes systemic inflammation and pulmonary injury

Gliomas are the most common and devastating type of primary brain tumor. Many non-neoplastic cells, including immune cells, comprise the tumor microenvironment where they create a milieu that appears to dictate cancer development. ATP and the phosphohydrolytic products ADP and adenosine by activating P2 and P1 receptors may participate in these interactions among malignant and immune cells. Purinergic receptor-mediated cell communication is closely regulated by ectonucleotidases, such as by members of the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family, which hydrolyze extracellular nucleotides. We have shown that gliomas, unlike astrocytes, exhibit low NTPDase activity. Furthermore, ATP induces glioma cell proliferation and the co-administration of apyrase decreases progression of injected cells in vivo. We have previously shown that NTPDase2 reconstitution dramatically increases tumor growth in vivo. Here we evaluated whether NTPDase2 reconstitution to gliomas modulates systemic inflammatory responses. We observed that NTPDase2 overexpression modulated pro-inflammatory cytokine production and platelet reactivity. Additionally, pathological alterations in the lungs were observed in rats bearing these tumors. Our results suggest that disruption of purinergic signaling via ADP accumulation creates an inflammatory state that may promote tumor spread and dictate clinical progression.

Ectonucleotidases CD39 and CD73 on OvCA cells are potent adenosine-generating enzymes responsible for adenosine receptor 2A-dependent suppression of T cell function and NK cell cytotoxicity

The ectonucleotidases CD39 and CD73 degrade immune stimulatory ATP to adenosine that inhibits T and NK cell responses via the A(2A) adenosine receptor (ADORA2A). This mechanism is used by regulatory T cells (T(reg)) that are associated with increased mortality in OvCA. Immunohistochemical staining of human OvCA tissue specimens revealed further aberrant expression of CD39 in 29/36 OvCA samples, whereas only 1/9 benign ovaries showed weak stromal CD39 expression. CD73 could be detected on 31/34 OvCA samples. While 8/9 benign ovaries also showed CD73 immunoreactivity, expression levels were lower than in tumour specimens. Infiltration by CD4(+) and CD8(+) T cells was enhanced in tumour specimens and significantly correlated with CD39 and CD73 levels on stromal, but not on tumour cells. In vitro, human OvCA cell lines SK-OV-3 and OaW42 as well as 11/15 ascites-derived primary OvCA cell cultures expressed both functional CD39 and CD73 leading to more efficient depletion of extracellular ATP and enhanced generation of adenosine as compared to activated T(reg). Functional assays using siRNAs against CD39 and CD73 or pharmacological inhibitors of CD39, CD73 and ADORA2A revealed that tumour-derived adenosine inhibits the proliferation of allogeneic human CD4(+) T cells in co-culture with OvCA cells as well as cytotoxic T cell priming and NK cell cytotoxicity against SK-OV3 or OAW42 cells. Thus, both the ectonucleotidases CD39 and CD73 and ADORA2A appear as possible targets for novel treatments in OvCA, which may not only affect the function of T(reg) but also relieve intrinsic immunosuppressive properties of tumour and stromal cells.

Extracellular ATP reduces tumor sphere growth and cancer stem cell population in glioblastoma cells

Glioblastoma is the most aggressive tumor in the CNS and is characterized by having a cancer stem cell (CSC) subpopulation essential for tumor survival. The purinergic system plays an important role in glioma growth, since adenosine triphosphate (ATP) can induce proliferation of glioma cells, and alteration in extracellular ATP degradation by the use of exogenous nucleotidases dramatically alters the size of gliomas in rats. The aim of this work was to characterize the effect of the purinergic system on glioma CSCs. Human U87 glioma cultures presented tumor spheres that express the markers of glioma cancer stem cells CD133, Oct-4, and Nanog. Messenger RNA of several purinergic receptors were differently expressed in spheres when compared to a cell monolayer not containing spheres. Treatment of human gliomas U87 or U343 as well as rat C6 gliomas with 100 μM of ATP reduced the number of tumor spheres when grown in neural stem cell medium supplemented with epidermal growth factor and basic fibroblast growth factor. Moreover, ATP caused a decline in the number of spheres observed in culture in a dose-dependent manner. ATP also reduces the expression of Nanog, as determined by flow cytometry, as well as CD133 and Oct-4, as analyzed by flow cytometry and RT-PCR in U87 cells. The differential expression of purinergic receptor in tumor spheres when compared to adherent cells and the effect of ATP in reducing tumor spheres suggest that the purinergic system affects CSC biology and that ATP may be a potential agonist for differentiation therapy.

Cuprizone-induced demyelination in CNP::GFP transgenic mice

Cuprizone (bis-cyclohexanone oxaldihydrazone) was previously shown to induce demyelination in white matter enriched brain structures. In the present study we used the cuprizone demyelination model in transgenic mice expressing the enhanced green fluorescent protein (GFP) under the 2'-3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) promoter. The use of these particular transgenic mice allows easy detection of cells belonging to the entire oligodendroglial (OLG) lineage, ranging from OLG precursors to mature myelinating OLGs. We were able to evaluate the precise extent of oligodendroglial cell damage and recovery within the murine adult central nervous system (CNS) after inducing demyelination by acute cuprizone intoxication. A generalized loss of GFP+ cells was observed after cuprizone exposure and correlated with a decline in myelin basic protein (MBP) expression. OLGs were depleted in many brain areas that were previously thought to be unaffected by cuprizone treatment. Thus, in addition to the well-known cuprizone effects on the medial corpus callosum, we also found a loss of GFP+ cells in most brain structures, particularly in the caudatus putamen, cortex, anterior commissure, olfactory bulb, hippocampus, optic chiasm, brainstem, and cingulum. Loss of GFP+ cells was accompanied by extensive astrogliosis and microglial activation, although neurons were not affected. Interestingly, cuprizone-treated animals showed both activation of GFAP expression and a higher proliferation rate in subventricular zone cells. A week after cuprizone removal from the diet, GFP+ oligodendroglial cells began repopulating the damaged structures. GFP expression precedes that of MBP and allows OLG detection before myelin restoration.

Characterization of ATP-induced cell death in the GL261 mouse glioma

Gliomas have one of the worst prognosis among cancers. Their resistance to cell death induced by endogenous neurotoxic agents, such as extracellular ATP, seems to play an important role in their pathobiology since alterations in the degradation rate of extracellular ATP drastically affects glioma growth in rats. In the present work we characterized the mechanisms of cell death induced by extracellular ATP in a murine glioma cell line, GL261. ATP and BzATP, a P2X7 agonist, induced cell death at concentrations that are described to activate the P2X7 receptor in mouse. oATP, an antagonist of P2X7, blocked the ATP-induced cell death. Agonists of purinergic receptors expressed in GL261 such as adenosine, ADP, UTP did not cause any cell death, even at mM concentrations. A sub-population of cells more sensitive to ATP expressed more P2X7 when compared to a less sensitive subpopulation. Accordingly, RNA interference of the P2X7 receptor drastically reduced ATP-induced cell death, suggesting that this receptor is necessary for this effect. The mechanism of ATP-induced cell death is predominantly necrotic, since cells presented shrinkage accompanied by membrane permeabilization, but not apoptotic, since no phosphatidylserine externalization or caspase activity was observed. These data show the importance of P2X7 in ATP-induced cell death and shed light on the importance of ATP-induced cell death in glioma development.