The purinergic P2X7 receptor (P2X7R) is an ionotropic adenosine triphosphate(ATP) receptor which is closely linked with pathological conditions in the central nervous system (CNS). Gliomas are the most common primary brain tumors with presently no cures. The roles of the P2X7R in these diseases have not been previously studied and in this work, I have used the rat C6 glioma as an experimental model system to investigate expression and function of the P2X7R in vitro and in vivo. The in vitro study has examined expression of the P2X7R in C6 cells and the involvement of this receptor in mediating cell functional responses. C6 glioma cells were found to express the P2X7R at both mRNA and protein levels. The P2X7Ragonist, 2', 3 '-(benzoy1-4-benzoy1)-ATP (BzATP) induced an increase in intracellularCa2+ concentration, an effect which was largely inhibited by periodate-oxidized ATP(OxATP), an irreversible P2X7R antagonist. BzATP treatment of C6 cells also resulted in ethidium bromide dye uptake indicating pore formation was induced byP2X7R activation. Chronic exposure of C6 cells to BzATP showed up-regulation of several pro-inflammatory factors including the chemokines monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8) and the angiogenic factor vascular endothelial growth factor (VEGF) suggesting the P2X7R in C6 cells is involved in mediating inflammation in tumors. In addition, BzATP treatment was found to enhance wound-induced cell migration, an effect which was inhibited in the presence of OxATP, or another P2X7R antagonist, Brilliant Blue G (BBG). The in vivo study examined whether pharmacological modulation of P2X7R with BBG altered tumor growth. C6 glioma cells were implanted into the striatum of rat brain and in situ P2X7R expression was shown to be associated with glioma cells and resident microglia. Preliminary results have indicated that inhibition of P2X7R leads to a reduced volume of brain tumors formed by transplanted C6 cells. The overall results from this study demonstrate the novel finding that C6 glioma cells express functional P2X7R and suggest pharmacological modulation of theP2X7R could serve as an effective strategy to inhibit the development and progression of brain tumors.

The purinergic P2X7 receptor (P2X7R) is an ionotropic adenosine triphosphate(ATP) receptor which is closely linked with pathological conditions in the central nervous system (CNS). Gliomas are the most common primary brain tumors with presently no cures. The roles of the P2X7R in these diseases have not been previously studied and in this work, I have used the rat C6 glioma as an experimental model system to investigate expression and function of the P2X7R in vitro and in vivo. The in vitro study has examined expression of the P2X7R in C6 cells and the involvement of this receptor in mediating cell functional responses. C6 glioma cells were found to express the P2X7R at both mRNA and protein levels. The P2X7Ragonist, 2', 3 '-(benzoy1-4-benzoy1)-ATP (BzATP) induced an increase in intracellularCa2+ concentration, an effect which was largely inhibited by periodate-oxidized ATP(OxATP), an irreversible P2X7R antagonist. BzATP treatment of C6 cells also resulted in ethidium bromide dye uptake indicating pore formation was induced byP2X7R activation. Chronic exposure of C6 cells to BzATP showed up-regulation of several pro-inflammatory factors including the chemokines monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8) and the angiogenic factor vascular endothelial growth factor (VEGF) suggesting the P2X7R in C6 cells is involved in mediating inflammation in tumors. In addition, BzATP treatment was found to enhance wound-induced cell migration, an effect which was inhibited in the presence of OxATP, or another P2X7R antagonist, Brilliant Blue G (BBG). The in vivo study examined whether pharmacological modulation of P2X7R with BBG altered tumor growth. C6 glioma cells were implanted into the striatum of rat brain and in situ P2X7R expression was shown to be associated with glioma cells and resident microglia. Preliminary results have indicated that inhibition of P2X7R leads to a reduced volume of brain tumors formed by transplanted C6 cells. The overall results from this study demonstrate the novel finding that C6 glioma cells express functional P2X7R and suggest pharmacological modulation of theP2X7R could serve as an effective strategy to inhibit the development and progression of brain tumors.

The purinergic P2X7 receptor (P2X7R) is an ionotropic adenosine triphosphate(ATP) receptor which is closely linked with pathological conditions in the central nervous system (CNS). Gliomas are the most common primary brain tumors with presently no cures. The roles of the P2X7R in these diseases have not been previously studied and in this work, I have used the rat C6 glioma as an experimental model system to investigate expression and function of the P2X7R in vitro and in vivo. The in vitro study has examined expression of the P2X7R in C6 cells and the involvement of this receptor in mediating cell functional responses. C6 glioma cells were found to express the P2X7R at both mRNA and protein levels. The P2X7Ragonist, 2', 3 '-(benzoy1-4-benzoy1)-ATP (BzATP) induced an increase in intracellularCa2+ concentration, an effect which was largely inhibited by periodate-oxidized ATP(OxATP), an irreversible P2X7R antagonist. BzATP treatment of C6 cells also resulted in ethidium bromide dye uptake indicating pore formation was induced byP2X7R activation. Chronic exposure of C6 cells to BzATP showed up-regulation of several pro-inflammatory factors including the chemokines monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8) and the angiogenic factor vascular endothelial growth factor (VEGF) suggesting the P2X7R in C6 cells is involved in mediating inflammation in tumors. In addition, BzATP treatment was found to enhance wound-induced cell migration, an effect which was inhibited in the presence of OxATP, or another P2X7R antagonist, Brilliant Blue G (BBG). The in vivo study examined whether pharmacological modulation of P2X7R with BBG altered tumor growth. C6 glioma cells were implanted into the striatum of rat brain and in situ P2X7R expression was shown to be associated with glioma cells and resident microglia. Preliminary results have indicated that inhibition of P2X7R leads to a reduced volume of brain tumors formed by transplanted C6 cells. The overall results from this study demonstrate the novel finding that C6 glioma cells express functional P2X7R and suggest pharmacological modulation of theP2X7R could serve as an effective strategy to inhibit the development and progression of brain tumors. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

Glioblastoma multiforme (GBM) is the most aggressive and most common primary brain tumor in adults accounting for 50-60% of primary brain tumors. The prognosis for patients with GBM remains poor and treatment is mainly palliative with a mean survival time of less than one year. Radiotherapy is used extensively in the management of glioblastoma either alone or in combination with surgery and/or chemotherapy. However, this tumor is one of the most resistant tumors to radiotherapy thus limiting the benefit of this form of treatment. <p>Studies have shown that malignant tumors have a high content of glutathione an antioxidant responsible for protecting the cells against damage from free radicals (mainly superoxide, hydroxyl and hydrogen peroxide). It is well established that glutathione, by neutralizing these free radicals plays a major role in radioresistance. Glioblastoma has relatively high levels of glutathione. In this study, by reducing the glutathione content of glioblastoma in a rat model, we were able to investigate the effect of this reduction in enhancing the effect of radiotherapy as a form of treatment for glioblastoma multiforme in a rat model. <p>By injecting L-Buthionine-SR-Sulfoximine (BSO) in to the tumor tissue, the glutathione content of the tumor was reduced by about 70% of its initial value. When administered into the tumors 2 hours prior to radiotherapy the animals so treated had a significantly longer median survival time compared with animals that received radiotherapy alone.

Glioblastoma multiforme (GBM) is the most aggressive and most common primary brain tumor in adults accounting for 50-60% of primary brain tumors. The prognosis for patients with GBM remains poor and treatment is mainly palliative with a mean survival time of less than one year. Radiotherapy is used extensively in the management of glioblastoma either alone or in combination with surgery and/or chemotherapy. However, this tumor is one of the most resistant tumors to radiotherapy thus limiting the benefit of this form of treatment. <p>Studies have shown that malignant tumors have a high content of glutathione an antioxidant responsible for protecting the cells against damage from free radicals (mainly superoxide, hydroxyl and hydrogen peroxide). It is well established that glutathione, by neutralizing these free radicals plays a major role in radioresistance. Glioblastoma has relatively high levels of glutathione. In this study, by reducing the glutathione content of glioblastoma in a rat model, we were able to investigate the effect of this reduction in enhancing the effect of radiotherapy as a form of treatment for glioblastoma multiforme in a rat model. <p>By injecting L-Buthionine-SR-Sulfoximine (BSO) in to the tumor tissue, the glutathione content of the tumor was reduced by about 70% of its initial value. When administered into the tumors 2 hours prior to radiotherapy the animals so treated had a significantly longer median survival time compared with animals that received radiotherapy alone.

Η ΒΥΠ διαθέτει αντίτυπο της διατριβής σε έντυπη μορφή στο βιβλιοστάσιο διδακτορικών διατριβών που βρίσκεται στο ισόγειο του κτιρίου της. / Τα κακοήθη γλοιώματα συνιστούν τον πιο κοινό τύπο καρκίνου του κεντρικού νευρικού συστήματος στους ενήλικες και χαρακτηρίζονται από υψηλό βαθμό αγγειογένεσης και διήθησης στον παρακείμενο φυσιολογικό ιστό. Αν και οι θεραπευτικές προσεγγίσεις που χρησιμοποιούνται περιλαμβάνουν χειρουργική επέμβαση, ακτινοθεραπεία και χημειοθεραπεία, ποσοστό μεγαλύτερο του 90% των ασθενών εμφανίζουν υποτροπή της νόσου και η συνολική επιβίωση είναι εξαιρετικά χαμηλή. Τα παραπάνω γεγονότα εντείνουν την ανάγκη για την εφαρμογή πιο αποτελεσματικών θεραπευτικών σχημάτων, καθώς και την ανακάλυψη νέων μορίων-στόχων για τη θεραπεία του συγκεκριμένου τύπου καρκίνου. Η HARP είναι ένας εκκρινόμενος αυξητικός παράγοντας με μοριακό βάρος 18 kDa που έχει ισχυρή συγγένεια με την ηπαρίνη. Η HARP εκφράζεται κυρίως κατά την εμβρυϊκή ανάπτυξη και απομονώθηκε για πρώτη φορά ως πρωτεΐνη που προάγει την επέκταση των νευριτών στον αναπτυσσόμενο εγκέφαλο. Στην HARP έχει αποδοθεί ένας σημαντικός αριθμός βιολογικών δράσεων, όπως η συμμετοχή της στον πολλαπλασιασμό, στη μετανάστευση και στη διαφοροποίηση των κυττάρων, στο σχηματισμό οστών, στη χονδρογένεση, στη σπερματογένεση, στην ογκογένεση και στην αγγειογένεση. Η HARP εκφράζεται σε διάφορες καρκινικές σειρές από μηνιγγίωμα, νευροβλάστωμα, αστροκυττάρωμα, μελάνωμα, μικροκυτταρικό τύπο καρκίνου του πνεύμονα και γλοιοβλάστωμα. Κλινικές μελέτες έχουν αναφέρει αυξημένα επίπεδα της HARP στον ορό αίματος ασθενών με καρκίνο του κόλον του εντέρου, με καρκίνο του παγκρέατος και με καρκίνο του μαστού. Στην παρούσα μελέτη, προσπαθήσαμε να διερευνήσουμε το ρόλο της HARP στην ανάπτυξη όγκου και στην αγγειογένεση που προκαλούν τα κύτταρα C6, μετασχηματίζοντας τα κύτταρα αυτά με την αντινοηματική αλληλουχία για το cDNA της HARP και καταστέλλοντας την έκφρασή της στα κύτταρα C6. Μείωση της ενδογενούς έκφρασης της πρωτεΐνης της HARP στα κύτταρα C6 (κύτταρα AS-C6) προκάλεσε στατιστικά σημαντική αύξηση στον πολλαπλασιασμό, στην ανάπτυξη των κυττάρων σε τρισδιάστατο περιβάλλον και στη μετανάστευση. Όταν κύτταρα AS-C6 εμβολιάστηκαν σε χοριοαλλαντοϊκή μεμβράνη εμβρύου όρνιθας, οδήγησαν σε σημαντική αύξηση της καρκινικής αγγειογένεσης, σε σύγκριση με τις μεμβράνες που είχαν εμβολιαστεί με μη μετασχηματισμένα κύτταρα C6 ή με κύτταρα C6 που είχαν μετασχηματιστεί μόνο με το πλασμίδιο-φορέα (κύτταρα ΡC-C6). Με παρόμοιο τρόπο, θρεπτικό μέσο καλλιέργειας των κυττάρων AS-C6 προκάλεσε στατιστικά σημαντική αύξηση στον πολλαπλασιασμό, στη μετανάστευση και στο σχηματισμό ψευδαγγείων των ενδοθηλιακών κυττάρων in vitro σε σύγκριση με την επίδραση του θρεπτικού μέσου καλλιέργειας των κυττάρων C6 και ΡC-C6. Η έκφραση της HARP φαίνεται να είναι απαραίτητη για την ανασταλτική δράση αυξημένων ενδοκυτταρικών επιπέδων cAMP στον πολλαπλασιασμό και τη μετανάστευση των κυττάρων C6 και αύξηση των ενδοκυτταρικών επιπέδων cAMP οδήγησε σε αύξηση της έκφρασης και έκκρισης HARP, πιθανά μέσω ενεργοποίησης του μεταγραφικού παράγοντα AP-1. Τέλος, παρατηρήθηκε σημαντική αύξηση των επιπέδων του mRNA και της πρωτεΐνης του αυξητικού παράγοντα των ενδοθηλιακών κυττάρων (vascular endothelial growth factor, VEGF) σε καλλιέργειες των κυττάρων AS-C6 σε σχέση με τα κύτταρα C6 και PC-C6. H HARP βρέθηκε να συν-ανοσοκατακρημνίζεται με τον VEGF σε θρεπτικό μέσο καλλιέργειας των κυττάρων C6 και pC-C6, το οποίο υποδηλώνει μια άμεση αλληλεπίδραση μεταξύ των δύο αυτών αυξητικών παραγόντων. Συνοψίζοντας, τα αποτελέσματα της παρούσας εργασίας προτείνουν ότι ο αυξητικός παράγοντας HARP έχει αρνητικό ρόλο στη ρύθμιση της ανάπτυξη όγκου και της αγγειογένεση που επάγουν τα κύτταρα C6, πιθανά ρυθμίζοντας την έκφραση ή/και τη διαθεσιμότητα άλλων αυξητικών παραγόντων. / Malignant gliomas, the most common type of brain tumors in adults, present a remarkable degree of neovascularisation and invasiveness into surrounding tissues. Although combinations of surgery, radiotherapy and chemotherapy are used, more than 90% of the patients experience local recurrence and their survival is extremely low. These facts stress the need for more effective therapeutic strategies and new targets for tumour therapy. Heparin affin regulatory peptide (HARP), also known as pleiotrophin or heparin-binding growth-associated molecule, is an 18-kDa secreted growth factor that has high affinity for heparin. HARP is mainly expressed during embryonic development, in early postnatal rat and bovine brain and was first isolated as a major neurite outgrowth-promoting protein of developing brain. Since then, a number of biological activities have been well established for HARP, such as its role in cellular proliferation, migration and differentiation and its involvement in bone formation, chondrogenesis, spermatogenesis, tumor growth and angiogenesis. HARP is expressed in various cancer cell lines, derived from meningiomas, neuroblastomas, astrocytomas, melanomas, small cell lung cancer (SCLC) cell lines and glioblastomas. Clinical studies have shown elevated serum levels and tumor expression of HARP in patients with colon, stomach, pancreatic and breast cancer. Ιn the present study, we tried to elucidate the role of HARP in the growth and angiogenicity of C6 glioma cells by using an antisense strategy for inhibition of HARP expression in rat C6 glioma cells. Decrease of the expression of endogenous HARP protein in C6 cells (AS-C6 cells) significantly increased proliferation rate and anchorage-independent growth of cells. Implantation of AS-C6 cells onto chicken embryo chorioallantoic membranes resulted in a significant increase of tumor-induced angiogenesis, compared with those induced by non transfected or C6 cells transfected with the plasmid alone (PC-C6 cells). In the same line, conditioned medium from AS-C6 cells significantly increased endothelial cell proliferation, migration and tube formation in vitro compared with the effect of C6 or PC-C6 cells. HARP expression is required for cAMP-induced inhibition of C6 cell proliferation and migration and cAMP increased the expression and secretion of HARP by C6 cells, possibly through activation of Activator Protein 1. Finally, a significant increase in vascular endothelial growth factor (VEGF) mRNA and protein levels were observed in cultures of AS-C6 cells compared with C6 or PC-C6 cells. HARP was co-immunoprecipitated with VEGF from the conditioned medium of C6 and PC-C6 cells, which indicates a direct interaction between the two factors. Collectively, these data suggest that HARP negatively regulates tumor growth and angiogenesis induced by C6, possibly through regulation of the expression or/and activation of other growth factors.