A key step in malignant progression is the acquired ability of tumour cells to escape immune-mediated lysis. A potential mechanism by which tumour cells avoid immune destruction involves the shedding of MHC Class I Chain-Related Protein A (MICA), a Natural Killer (NK) cell-activating ligand, from the tumour cell membrane. Hypoxia has been shown to cause increased MICA shedding; however, this hypoxia-induced effect can be attenuated by pharmacological activation of the cyclic guanosine monophosphate (cGMP)-dependent nitric oxide (NO)-signalling pathway in cancer cells. The primary objective of the present study was to determine whether treatment of tumour-bearing nude mice with the NO-mimetic glyceryl trinitrate (GTN) attenuates in vivo tumour growth and if so, whether this effect is dependent on the presence of an intact NK cell compartment. Results indicated that continuous transdermal administration of GTN (1.8 µg/h) can significantly attenuate the growth of transplanted human DU-145 prostate tumours but that this effect of GTN is lost in mice whose NK-cells have been depleted. Tumours and serum from the mice in this study were analysed to determine whether GTN treatment had any effect on the expression levels of proteins integral to the proposed MICA shedding mechanism; however, the results of these studies were inconclusive. As phosphodiesterase (PDE) inhibition represents a potential method to enhance NO-signalling, experiments were performed to determine whether treatment with the PDE5/6 inhibitor zaprinast could also attenuate hypoxia-induced MICA shedding and decrease in vivo growth of DU-145 tumours. Results demonstrated that treatment with zaprinast (10 mg/kg) significantly attenuates MICA shedding in DU-145 cancer cells and significantly decreases in vivo tumour growth. Taken together, the results of these experiments indicate that GTN attenuates tumour growth by sensitising tumour cells to innate immunity, likely by increasing membrane-associated tumour cell MICA levels through the reactivation of NO-signalling, and that zaprinast decreases tumour growth likely through a similar mechanism. These findings are important because they indicate that agents capable of reactivating NO-signalling, such as NO-mimetics and PDE inhibitors, can potentially be used as immunosensitisers in the treatment and/or prevention of cancer. / Thesis (Master, Anatomy & Cell Biology) -- Queen's University, 2011-04-18 10:43:28.077

Cellular adaptation to conditions of stress is critical to the survival of all organisms. In mammalian cells, reduced oxygen availability, or hypoxia, triggers a myriad of alterations within molecular pathways aimed at ensuring sustained viability and functionality of vital organs. The master regulator of the hypoxic response is the heterodimeric HIF transcription factor, composed of an oxygen-labile HIFalpha subunit and a constitutively expressed and stable HIFbeta(ARNT) subunit. While experiments in mice have demonstrated the indispensability of HIF1alpha/HIF2alpha, unchecked hyperactivation of HIF is associated with pathological complications, such as the development of clear-cell renal cell carcinoma (ccRCC), the most common form of kidney cancer. In particular, overexpression of HIF2alpha has been intimately linked to ccRCC molecular pathogenesis. Here, we report that HIF2alpha overexpression leads to Akt-mediated hyperactivation of Hdm2, resulting in decreased activity of p53 and increased resistance to apoptosis. Significantly, we show that restoration of p53 activity via inhibition of Hdm2 reverses chemoresistance of otherwise refractory ccRCC cells. We also demonstrate that the picornavirus EMCV (Encephalomyocarditis virus) efficiently destroys ccRCC tumour cells in an NF-kappaB- and HIFalpha-dependent manner both in vitro and in a mouse xenograft model. This work provides pre-clinical evidence for the potential use of EMCV in an oncolytic virus-based approach to the treatment of advanced ccRCC. In addition, using a cell biology-based approach we reveal that inhibition of the DNA methyltransferase DNMT1 leads to enhanced HIF promoter-binding affinity and transactivation activity in a manner that is independent of changes in HIFalpha protein levels. This study uncovers a novel HIF regulatory mechanism in mammalian cells. In summary, the work presented here provides insight into the molecular mechanisms governing HIF activity and the effects of HIF on the molecular pathogenesis of ccRCC. Our findings have the potential to provide new therapeutic avenues for the treatment of kidney cancer.

Cellular adaptation to conditions of stress is critical to the survival of all organisms. In mammalian cells, reduced oxygen availability, or hypoxia, triggers a myriad of alterations within molecular pathways aimed at ensuring sustained viability and functionality of vital organs. The master regulator of the hypoxic response is the heterodimeric HIF transcription factor, composed of an oxygen-labile HIFalpha subunit and a constitutively expressed and stable HIFbeta(ARNT) subunit. While experiments in mice have demonstrated the indispensability of HIF1alpha/HIF2alpha, unchecked hyperactivation of HIF is associated with pathological complications, such as the development of clear-cell renal cell carcinoma (ccRCC), the most common form of kidney cancer. In particular, overexpression of HIF2alpha has been intimately linked to ccRCC molecular pathogenesis. Here, we report that HIF2alpha overexpression leads to Akt-mediated hyperactivation of Hdm2, resulting in decreased activity of p53 and increased resistance to apoptosis. Significantly, we show that restoration of p53 activity via inhibition of Hdm2 reverses chemoresistance of otherwise refractory ccRCC cells. We also demonstrate that the picornavirus EMCV (Encephalomyocarditis virus) efficiently destroys ccRCC tumour cells in an NF-kappaB- and HIFalpha-dependent manner both in vitro and in a mouse xenograft model. This work provides pre-clinical evidence for the potential use of EMCV in an oncolytic virus-based approach to the treatment of advanced ccRCC. In addition, using a cell biology-based approach we reveal that inhibition of the DNA methyltransferase DNMT1 leads to enhanced HIF promoter-binding affinity and transactivation activity in a manner that is independent of changes in HIFalpha protein levels. This study uncovers a novel HIF regulatory mechanism in mammalian cells. In summary, the work presented here provides insight into the molecular mechanisms governing HIF activity and the effects of HIF on the molecular pathogenesis of ccRCC. Our findings have the potential to provide new therapeutic avenues for the treatment of kidney cancer.

Exposure to chronic hypoxia (CH) leads to ventilatory acclimatisation to hypoxia (VAH) which is a time-dependent increase in breathing. This study examined the role of the GABAA receptor in establishing VAH. Rats were exposed to CH or control (normoxic) conditions for 10 days during which the GABAA receptor antagonist, bicuculline, was infused systemically or directly into the nucleus of the solitary tract (NTS). Acute breathing trials were then performed to measure resting ventilation and ventilatory chemoreflexes. Systemic administration of bicuculline caused reductions in breathing during acute hypoxia and acute hypercapnia in the control but not the CH animals. Continuous infusion of bicuculline in to the NTS caused a reduction in the acute hypoxic ventilatory response in animals exposed to CH but not in the control animals. The results indicate that exposure to CH alters the GABAA-mediated regulation of acute ventilatory chemoreflexes both in the NTS and elsewhere in the brain.

With asphyxia, newborns may suffer cardiogenic shock with myocardial dysfunction and dysregulation of vasomotor tone resulting in multiorgan dysfunction. Vasoactive medications are often administered with limited evidence directing clinicians regarding the use of high-dose monotherapy with dopamine relative to combination treatment with dopamine and a second different agent. We hypothesized that the treatment of hypoxia-reoxygenated newborn piglets with combinations of vasoactive medications would improve systemic and regional hemodynamics. Instrumented newborn piglets were subjected to hypoxia-reoxygenation with subsequent infusion of high-dose dopamine or moderate-dose dopamine and one of epinephrine, milrinone or levosimendan. Treatment with high-dose dopamine improved systemic and mesenteric perfusion. The addition of low-dose epinephrine showed some benefits regarding pulmonary hypertension and should a non-catecholamine agent be added to dopamine, milrinone is preferred to levosimendan given benefits to mesenteric perfusion. We conclude that the selection of appropriate vasoactive medical therapy should be directed by the clinical effects desired. / Experimental Surgery

Cell survival in conditions of severe oxygen deprivation depends on a wide variety of biochemical modifications, which result in a large-scale suppression of metabolism, preventing [ATP] from falling to fatally low levels. We investigated whether AMP-activated protein kinase (AMPK) has a role in the coordination of cellular modification during hypoxia, which leads to a regulated state of metabolic suppression in the goldfish (Carassius auratus). Energy charge, AMPK activity, protein and gene expression, as well as the translational capacity and phosphorylation state of a downstream target were measured in goldfish tissues during exposure to hypoxia (-0.3 mg 02/L) for up to 12 h. AMPK activity in the goldfish liver increased by 4-fold at 0.5 h hypoxia and was temporally associated with a —11-fold increase in calculated AMPfree/ATP. No change was observed in total AMPK protein or relative gene expression of identified AMPK isoforms. Changes in AMPK activity were also associated with a decreased rate of protein synthesis and an increase in the phosphorylated form of eukaryotic elongation factor-2 (eEF2; relative to total eEF2). Increases in AMPK activity were not seen in hypoxic goldfish muscle, brain, heart or gill, nor was a significant alteration in cellular energy charge seen in muscle. Still, the present study is the first to show that AMPK activity increases in liver in response to short-term severe hypoxia exposure in a hypoxia-tolerant fish. The decreased rates of protein synthesis, a well known component of metabolic suppression, combined with increased phosphorylation of eEF2, a downstream target of AMPK, potentially implicate the kinase in the cellular effort to suppress metabolism in hypoxia-tolerant species during oxygen deprivation.

Multiple myeloma (MM) is an incurable haematological malignancy characterised by the clonal proliferation of plasma cells (PCs) within the bone marrow (BM). MM PC survival and expansion is dependent upon an adequate supply of oxygen and nutrients, and increased BM angiogenesis is a critical feature of MM progression. While MM PCs express and secrete a number of angiogenic factors, our current understanding of the precise mechanisms by which MM-induced angiogenesis occurs is incomplete. In this study, we collected specimens from patients with MM and the benign precursor condition MGUS, and demonstrated for the first time that circulating levels of the CXCL12 chemokine positively correlate with the degree of BM angiogenesis. Using conditioned media from a MM PC line, the contribution of MM PC-derived CXCL12 to angiogenesis was also examined and found to strongly induce vascular tube formation in vitro. In several other cell types, hypoxia has been shown to up-regulate CXCL12 expression. Studies investigating the hypoxic regulation of CXCL12 in MM PCs revealed that, while acute hypoxia is unable to stimulate CXCL12 expression, prolonged hypoxia significantly up-regulates CXCL12 mRNA and protein expression. To determine the mechanism(s) responsible for this, over-expression and RNA interference technology was employed to create genetically modified MM cells in which either HIF-1α or HIF-2α were overexpressed or knocked down. These studies showed that HIF-2α is the predominant mediator of the hypoxic induction of CXCL12 in MM PCs. The ability of HIF-2α to bind to the CXCL12 promoter was confirmed using EMSA and ChIP analyses. The role of CXCL12 in in vivo angiogenesis and the contribution of HIF-1α and HIF-2α were also examined. In these studies, transduced MM cells, in which HIF-1α, HIF-2α and CXCL12 were over-expressed or knocked down, were implanted into a vessel-poor, subcutaneous environment in immunocompromised mice. Tumour-induced angiogenesis was assessed after two weeks by measuring the haemoglobin content of excised implants. These studies confirmed that over-expression of CXCL12, HIF-1α and HIF-2α each stimulates a strong angiogenic response. Using the well-characterised CXCR4 antagonist, T140, CXCL12 was found to play a key role in the increased angiogenesis observed in response to HIF-1α and HIF-2α over-expression. These novel studies have shown that CXCL12 is an important mediator of angiogenesis in MM patients, and that aberrant CXCL12 expression by MM PCs is due, in part, to its hypoxic up-regulation mediated predominantly by HIF-2. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1365126 / Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2009

Multiple myeloma (MM) is an incurable haematological malignancy characterised by the clonal proliferation of plasma cells (PCs) within the bone marrow (BM). MM PC survival and expansion is dependent upon an adequate supply of oxygen and nutrients, and increased BM angiogenesis is a critical feature of MM progression. While MM PCs express and secrete a number of angiogenic factors, our current understanding of the precise mechanisms by which MM-induced angiogenesis occurs is incomplete. In this study, we collected specimens from patients with MM and the benign precursor condition MGUS, and demonstrated for the first time that circulating levels of the CXCL12 chemokine positively correlate with the degree of BM angiogenesis. Using conditioned media from a MM PC line, the contribution of MM PC-derived CXCL12 to angiogenesis was also examined and found to strongly induce vascular tube formation in vitro. In several other cell types, hypoxia has been shown to up-regulate CXCL12 expression. Studies investigating the hypoxic regulation of CXCL12 in MM PCs revealed that, while acute hypoxia is unable to stimulate CXCL12 expression, prolonged hypoxia significantly up-regulates CXCL12 mRNA and protein expression. To determine the mechanism(s) responsible for this, over-expression and RNA interference technology was employed to create genetically modified MM cells in which either HIF-1α or HIF-2α were overexpressed or knocked down. These studies showed that HIF-2α is the predominant mediator of the hypoxic induction of CXCL12 in MM PCs. The ability of HIF-2α to bind to the CXCL12 promoter was confirmed using EMSA and ChIP analyses. The role of CXCL12 in in vivo angiogenesis and the contribution of HIF-1α and HIF-2α were also examined. In these studies, transduced MM cells, in which HIF-1α, HIF-2α and CXCL12 were over-expressed or knocked down, were implanted into a vessel-poor, subcutaneous environment in immunocompromised mice. Tumour-induced angiogenesis was assessed after two weeks by measuring the haemoglobin content of excised implants. These studies confirmed that over-expression of CXCL12, HIF-1α and HIF-2α each stimulates a strong angiogenic response. Using the well-characterised CXCR4 antagonist, T140, CXCL12 was found to play a key role in the increased angiogenesis observed in response to HIF-1α and HIF-2α over-expression. These novel studies have shown that CXCL12 is an important mediator of angiogenesis in MM patients, and that aberrant CXCL12 expression by MM PCs is due, in part, to its hypoxic up-regulation mediated predominantly by HIF-2. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1365126 / Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2009

Multiple myeloma (MM) is an incurable haematological malignancy characterised by the clonal proliferation of plasma cells (PCs) within the bone marrow (BM). MM PC survival and expansion is dependent upon an adequate supply of oxygen and nutrients, and increased BM angiogenesis is a critical feature of MM progression. While MM PCs express and secrete a number of angiogenic factors, our current understanding of the precise mechanisms by which MM-induced angiogenesis occurs is incomplete. In this study, we collected specimens from patients with MM and the benign precursor condition MGUS, and demonstrated for the first time that circulating levels of the CXCL12 chemokine positively correlate with the degree of BM angiogenesis. Using conditioned media from a MM PC line, the contribution of MM PC-derived CXCL12 to angiogenesis was also examined and found to strongly induce vascular tube formation in vitro. In several other cell types, hypoxia has been shown to up-regulate CXCL12 expression. Studies investigating the hypoxic regulation of CXCL12 in MM PCs revealed that, while acute hypoxia is unable to stimulate CXCL12 expression, prolonged hypoxia significantly up-regulates CXCL12 mRNA and protein expression. To determine the mechanism(s) responsible for this, over-expression and RNA interference technology was employed to create genetically modified MM cells in which either HIF-1α or HIF-2α were overexpressed or knocked down. These studies showed that HIF-2α is the predominant mediator of the hypoxic induction of CXCL12 in MM PCs. The ability of HIF-2α to bind to the CXCL12 promoter was confirmed using EMSA and ChIP analyses. The role of CXCL12 in in vivo angiogenesis and the contribution of HIF-1α and HIF-2α were also examined. In these studies, transduced MM cells, in which HIF-1α, HIF-2α and CXCL12 were over-expressed or knocked down, were implanted into a vessel-poor, subcutaneous environment in immunocompromised mice. Tumour-induced angiogenesis was assessed after two weeks by measuring the haemoglobin content of excised implants. These studies confirmed that over-expression of CXCL12, HIF-1α and HIF-2α each stimulates a strong angiogenic response. Using the well-characterised CXCR4 antagonist, T140, CXCL12 was found to play a key role in the increased angiogenesis observed in response to HIF-1α and HIF-2α over-expression. These novel studies have shown that CXCL12 is an important mediator of angiogenesis in MM patients, and that aberrant CXCL12 expression by MM PCs is due, in part, to its hypoxic up-regulation mediated predominantly by HIF-2. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1365126 / Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2009

Endometrial cancer is one of the most significant gynaecological malignancies that affect women from New Zealand and the rest of the world. One of the critical stages in the development of a tumour is the onset of hypoxia. The malignancy responds by having raised levels of Hypoxia Inducible Factor (HIF) that in turn induces increased production of Vascular Endothelial Growth Factor (VEGF). VEGF is a potent angiogenic factor that will mediate vascular supply of nutrients and oxygen to the developing tumour. The aim of this study was to investigate whether two compounds found in extracts of plant materials, Resveratrol (Resveratrol) and Epigallocatechin gallate (EGCG), altered the levels of VEGF in the supernatant of cultured endometrial cancer cells. Resveratrol is a phytoalexin that is found in many foods, such as grapes, nuts and berries, as well as in high concentrations in some red wines. 100 µM of resveratrol was added to cell cultures for 24 hours. VEGF levels in the supernatant were then analysed using ELISA. Resveratrol was found to have significant inhibitory effects in both primary endometrial cancer cell cultures and immortalised endometrial cancer cell cultures. Resveratrol was also shown to reverse the increase in VEGF caused by the hypoxia mimic cobalt chloride (CoCl₂). Epigallocatechin gallate (EGCG) is an antioxidant catechin extracted from green tea. The effect of EGCG was analysed using the same method as for resveratrol. 100 µM of EGCG was also shown to have a significant inhibitory effect on the level of VEGF in the supernatant of cultured endometrial cancer cells, as well as reducing the effect of CoCl₂. These results suggest that selected food compounds, resveratrol and EGCG, can reduce VEGF levels by inhibiting HIF. Further investigation This may have anti-tumour effects in women with endometrial cancer.