The protective effect of silver nanoparticles' on epithelial cornea cells against ultraviolet is accompanied by changes in calcium homeostasis and a decrease of the P2X7 and P2Y2 receptors.

PURPOSE: The aim of the study was to evaluate the effect of silver nanoparticles hydrocolloids (AgNPs) on human corneal epithelial cells. Epithelial cells form the outermost and the most vulnerable to environmental stimuli layer of the cornea in the eye. Mechanical stress, UV radiation, and pathogens such as bacteria, viruses, and parasites challenge the fragile homeostasis of the eye. To help combat stress, infection, and inflammation wide portfolio of interventions is available. One of the oldest treatments is colloidal silver. Silver nanoparticle suspension in water is known for its anti-bacterial anti-viral and antiprotozoal action. However, AgNPs interact also with host cells, and the character of the interplay between corneal cells and silver seeks investigation. METHODS: The human epithelial corneal cell line (HCE-2) was cultured in vitro, treated with AgNPs, and subjected to UV. The cell's viability, migration, calcium concentration, and expression/protein level of selected proteins were investigated by appropriate methods including cytotoxicity tests, "wound healing" assay, Fluo8/Fura2 AM staining, qRT-PCR, and western blot. RESULTS: Incubation of human corneal cells (HCE-2) with AgNP did not affect cells viability but limited cells migration and resulted in altered calcium homeostasis, decreased the presence of ATP-activated P2X7, P2Y2 receptors, and enhanced the expression of PACAP. Furthermore, AgNPs pretreatment helped restrain some of the deleterious effects of UV irradiation. Interestingly, AgNPs had no impact on the protein level of ACE2, which is important in light of potential SARS-CoV-2 entrance through the cornea. CONCLUSIONS: Silver nanoparticles are safe for corneal epithelial cells in vitro.

Non-radioactive imaging strategies for in vivo immune cell tracking.

In vivo tracking of administered cells chosen for specific disease treatment may be conducted by diagnostic imaging techniques preceded by cell labeling with special contrast agents. The most commonly used agents are those with radioactive properties, however their use in research is often impossible. This review paper focuses on the essential aspect of cell tracking with the exclusion of radioisotope tracers, therefore we compare application of different types of non-radioactive contrast agents (cell tracers), methods of cell labeling and application of various techniques for cell tracking, which are commonly used in preclinical or clinical studies. We discuss diagnostic imaging methods belonging to three groups: (1) Contrast-enhanced X-ray imaging, (2) Magnetic resonance imaging, and (3) Optical imaging. In addition, we present some interesting data from our own research on tracking immune cell with the use of discussed methods. Finally, we introduce an algorithm which may be useful for researchers planning leukocyte targeting studies, which may help to choose the appropriate cell type, contrast agent and diagnostic technique for particular disease study.

Biodistribution PET/CT Study of Hemoglobin-DFO-89Zr Complex in Healthy and Lung Tumor-Bearing Mice.

Proteins, as a major component of organisms, are considered the preferred biomaterials for drug delivery vehicles. Hemoglobin (Hb) has been recently rediscovered as a potential drug carrier, but its use for biomedical applications still lacks extensive investigation. To further explore the possibility of utilizing Hb as a potential tumor targeting drug carrier, we examined and compared the biodistribution of Hb in healthy and lung tumor-bearing mice, using for the first time 89Zr labelled Hb in a positron emission tomography (PET) measurement. Hb displays a very high conjugation yield in its fast and selective reaction with the maleimide-deferoxamine (DFO) bifunctional chelator. The high-resolution X-ray structure of the Hb-DFO complex demonstrated that cysteine ß93 is the sole attachment moiety to the αß-protomer of Hb. The Hb-DFO complex shows quantitative uptake of 89Zr in solution as determined by radiochromatography. Injection of 0.03 mg of Hb-DFO-89Zr complex in healthy mice indicates very high radioactivity in liver, followed by spleen and lungs, whereas a threefold increased dosage results in intensification of PET signal in kidneys and decreased signal in liver and spleen. No difference in biodistribution pattern is observed between naïve and tumor-bearing mice. Interestingly, the liver Hb uptake did not decrease upon clodronate-mediated macrophage depletion, indicating that other immune cells contribute to Hb clearance. This finding is of particular interest for rapidly developing clinical immunology and projects aiming to target, label or specifically deliver agents to immune cells.

NIK-IKK complex interaction controls NF-κB-dependent inflammatory activation of endothelium in response to LTßR ligation.

NF-κB-inducing kinase (NIK; also known as MAP3K14) is a central regulator of non-canonical NF-κB signaling in response to stimulation of TNF receptor superfamily members, such as the lymphotoxin-ß receptor (LTßR), and is implicated in pathological angiogenesis associated with chronic inflammation and cancer. Here, we identify a previously unrecognized role of the LTßR-NIK axis during inflammatory activation of human endothelial cells (ECs). Engagement of LTßR-triggered canonical and non-canonical NF-κB signaling promoted expression of inflammatory mediators and adhesion molecules, and increased immune cell adhesion to ECs. Sustained LTßR-induced inflammatory activation of ECs was NIK dependent, but independent of p100, indicating that the non-canonical arm of NF-κB is not involved. Instead, prolonged activation of canonical NF-κB signaling, through the interaction of NIK with IκB kinase α and ß (also known as CHUK and IKBKB, respectively), was required for the inflammatory response. Endothelial inflammatory activation induced by synovial fluid from rheumatoid arthritis patients was significantly reduced by NIK knockdown, suggesting that NIK-mediated alternative activation of canonical NF-κB signaling is a key driver of pathological inflammatory activation of ECs. Targeting NIK could thus provide a novel approach for treating chronic inflammatory diseases.

Targeting non-canonical nuclear factor-κB signalling attenuates neovascularization in a novel 3D model of rheumatoid arthritis synovial angiogenesis.

OBJECTIVE: Angiogenesis is crucial in RA disease progression. Lymphotoxin ß receptor (LTßR)-induced activation of the non-canonical nuclear factor-κB (NF-κB) pathway via NF-κB-inducing kinase (NIK) has been implicated in this process. Consequently, inhibition of this pathway may hold therapeutic potential in RA. We describe a novel three-dimensional (3D) model of synovial angiogenesis incorporating endothelial cells (ECs), RA fibroblast-like synoviocytes (RAFLSs) and RA synovial fluid (RASF) to further investigate the contributions of NF-κB in this process. METHODS: Spheroids consisting of RAFLSs and ECs were stimulated with RASF, the LTßR ligands LTß and LIGHT, or growth factor bFGF and VEGF, followed by quantification of EC sprouting using confocal microscopy and digital image analysis. Next, the effects of anginex, NIK-targeting siRNA (siNIK), LTßR-Ig fusion protein (baminercept) and a novel pharmacological NIK inhibitor were investigated. RESULTS: RASF significantly promoted sprout formation, which was blocked by the established angiogenesis inhibitor anginex (P < 0.05). LTß and LIGHT induced significant sprouting (P < 0.05), as did bFGF/VEGF (P < 0.01). siNIK pre-treatment of ECs led to reductions in LTßR-induced vessel formation (P < 0.05). LTßR-Ig not only blocked LTß- or LIGHT-induced sprouting, but also RASF-induced sprouting (P < 0.05). The NIK inhibitor blocked angiogenesis induced by LTß, LIGHT, growth factors (P < 0.05) and RASF (P < 0.01). CONCLUSION: We present a novel 3D model of synovial angiogenesis incorporating RAFLSs, ECs and RASF that mimics the in vivo situation. Using this system, we demonstrate that non-canonical NF-κB signalling promotes neovascularization and show that this model is useful for dissecting relative contributions of signalling pathways in specific cell types to angiogenic responses and for testing pharmacological inhibitors of angiogenesis.

Metastasis Stimulation by Hypoxia and Acidosis-Induced Extracellular Lipid Uptake Is Mediated by Proteoglycan-Dependent Endocytosis.

Hypoxia and acidosis are inherent stress factors of the tumor microenvironment and have been linked to increased tumor aggressiveness and treatment resistance. Molecules involved in the adaptive mechanisms that drive stress-induced disease progression constitute interesting candidates of therapeutic intervention. Here, we provide evidence of a novel role of heparan sulfate proteoglycans (HSPG) in the adaptive response of tumor cells to hypoxia and acidosis through increased internalization of lipoproteins, resulting in a lipid-storing phenotype and enhanced tumor-forming capacity. Patient glioblastoma tumors and cells under hypoxic and acidic stress acquired a lipid droplet (LD)-loaded phenotype, and showed an increased recruitment of all major lipoproteins, HDL, LDL, and VLDL. Stress-induced LD accumulation was associated with increased spheroid-forming capacity during reoxygenation in vitro and lung metastatic potential in vivo On a mechanistic level, we found no apparent effect of hypoxia on HSPGs, whereas lipoprotein receptors (VLDLR and SR-B1) were transiently upregulated by hypoxia. Importantly, however, using pharmacologic and genetic approaches, we show that stress-mediated lipoprotein uptake is highly dependent on intact HSPG expression. The functional relevance of HSPG in the context of tumor cell stress was evidenced by HSPG-dependent lipoprotein cell signaling activation through the ERK/MAPK pathway and by reversal of the LD-loaded phenotype by targeting of HSPGs. We conclude that HSPGs may have an important role in the adaptive response to major stress factors of the tumor microenvironment, with functional consequences on tumor cell signaling and metastatic potential. Cancer Res; 76(16); 4828-40. ©2016 AACR.

Global profiling of metabolic adaptation to hypoxic stress in human glioblastoma cells.

Oncogenetic events and unique phenomena of the tumor microenvironment together induce adaptive metabolic responses that may offer new diagnostic tools and therapeutic targets of cancer. Hypoxia, or low oxygen tension, represents a well-established and universal feature of the tumor microenvironment and has been linked to increased tumor aggressiveness as well as resistance to conventional oncological treatments. Previous studies have provided important insights into hypoxia induced changes of the transcriptome and proteome; however, how this translates into changes at the metabolite level remains to be defined. Here, we have investigated dynamic, time-dependent effects of hypoxia on the cancer cell metabolome across all families of macromolecules, i.e., carbohydrate, protein, lipid and nucleic acid, in human glioblastoma cells. Using GC/MS and LC/MS/MS, 345 and 126 metabolites were identified and quantified in cells and corresponding media, respectively, at short (6 h), intermediate (24 h), and prolonged (48 h) incubation at normoxic or hypoxic (1% O2) conditions. In conjunction, we performed gene array studies with hypoxic and normoxic cells following short and prolonged incubation. We found that levels of several key metabolites varied with the duration of hypoxic stress. In some cases, metabolic changes corresponded with hypoxic regulation of key pathways at the transcriptional level. Our results provide new insights into the metabolic response of glioblastoma cells to hypoxia, which should stimulate further work aimed at targeting cancer cell adaptive mechanisms to microenvironmental stress.

Genetically modified human myoblasts with eNOS may improve regenerative ability of myogenic stem cells to infarcted heart.

BACKGROUND: Modern therapies of post infarcted heart failure are focused on perfusion improvement of the injured myocardium. This effect can be achieved by, among other means, implanting stem cells which could be genetically modified with factors inducing the formation of new blood vessels in the post infarction scar area. Combined stem cell and gene therapy seems to be a promising strategy to heal an impaired myocardium. The creation of new blood vessels can be indirectly stimulated via factors inducing vascular endothelial growth factor synthesis, for example endothelial nitric oxide synthase (eNOS). The product of this enzyme, nitric oxide, is a molecule that can influence numerous physiological activities; it can contribute to vasodilation, stimulation of endothelial cell growth, prevention of platelet aggregation and leukocyte adhesion to the endothelium. AIM: To verify the pro-angiogenic and regenerative potential of human primary myoblasts and murine myoblast cell line C2C12 transiently transfected with eNOS gene. METHODS: Stem cells (either human or murine) were maintained in standard in vitro conditions. Next, both types of myoblasts were modified using electroporation and lipofection (human and murine cells), respectively. The efficacy of the transfection method was evaluated using flow cytometry. The concentration of eNOS protein was measured by ELISA immunoassay. The biological properties of modified cells were assessed using an MTT proliferation test and DAPI cell cycle analysis. To verify the influence of oxidative stress on myoblasts, cytometric tests using Annexin V and propidium iodide were applied. To check possible alterations in myogenic gene expression of stem cells transduced by genetic modification, the myogenic regulatory factors were evaluated by real-time PCR. The function of genetic modification was confirmed by a HUVEC capillary sprouting test using myoblasts supernatants. RESULTS: Electroporation turned out to be an efficient transfection method. High amounts of secreted protein were obtained (in the range 2,000 pg/mL) in both cell types studied. Moreover, the functionality of gene overexpression product was confirmed in capillary development assay. Human myoblasts did not exhibit any changes in cell cycle; however, eNOS transfected murine myoblasts revealed a statistically significant reduction in cell cycle ratio compared to controls (p < 0.001). In the case of myogenic gene expression, a decrease in Myogenin level was only detected in the human transfected myoblast population (p < 0.05). CONCLUSIONS: The results of our study may suggest that transplantation of myoblasts overexpressing eNOS could be promising for cell therapy in regenerating the post infarction heart.

Emerging roles of extracellular vesicles in the adaptive response of tumour cells to microenvironmental stress.

Cells are constantly subjected to various types of endogenous and exogenous stressful stimuli, which can cause serious and even permanent damage. The ability of a cell to sense and adapt to environmental alterations is thus vital to maintain tissue homeostasis during development and adult life. Here, we review some of the major phenotypic characteristics of the hostile tumour microenvironment and the emerging roles of extracellular vesicles in these events.

Exosomes reflect the hypoxic status of glioma cells and mediate hypoxia-dependent activation of vascular cells during tumor development.

Hypoxia, or low oxygen tension, is a major regulator of tumor development and aggressiveness. However, how cancer cells adapt to hypoxia and communicate with their surrounding microenvironment during tumor development remain important questions. Here, we show that secreted vesicles with exosome characteristics mediate hypoxia-dependent intercellular signaling of the highly malignant brain tumor glioblastoma multiforme (GBM). In vitro hypoxia experiments with glioma cells and studies with patient materials reveal the enrichment in exosomes of hypoxia-regulated mRNAs and proteins (e.g., matrix metalloproteinases, IL-8, PDGFs, caveolin 1, and lysyl oxidase), several of which were associated with poor glioma patient prognosis. We show that exosomes derived from GBM cells grown at hypoxic compared with normoxic conditions are potent inducers of angiogenesis ex vivo and in vitro through phenotypic modulation of endothelial cells. Interestingly, endothelial cells were programmed by GBM cell-derived hypoxic exosomes to secrete several potent growth factors and cytokines and to stimulate pericyte PI3K/AKT signaling activation and migration. Moreover, exosomes derived from hypoxic compared with normoxic conditions showed increased autocrine, promigratory activation of GBM cells. These findings were correlated with significantly enhanced induction by hypoxic compared with normoxic exosomes of tumor vascularization, pericyte vessel coverage, GBM cell proliferation, as well as decreased tumor hypoxia in a mouse xenograft model. We conclude that the proteome and mRNA profiles of exosome vesicles closely reflect the oxygenation status of donor glioma cells and patient tumors, and that the exosomal pathway constitutes a potentially targetable driver of hypoxia-dependent intercellular signaling during tumor development.

Chondroitin sulfate expression predicts poor outcome in breast cancer.

Experimental studies have established that the sulfated glycosaminoglycans heparan sulfate and chondroitin sulfate act as co-receptors of cytokines and growth factors that drive the malignant cell phenotype and the remodelling of the surrounding tumor stroma. However, the clinical relevance of these studies remains ill-defined. The present study investigates the significance of chondroitin sulfate expression in malignant cells and the stroma, respectively, of tumors from two independent cohorts of breast cancer patients (cohort I: 144 patients, 130 evaluable samples; cohort II: 498 patients, 469 evaluable samples; ER-positive patients ~86% in both cohorts). Kaplan-Meier analysis and Cox proportional hazards modelling were used to assess the relationship between chondroitin sulfate and recurrence-free and overall survival. High chondroitin sulfate expression in malignant cells was shown to predict shorter recurrence-free survival (P=0.007, cohort I; P=0.024, cohort II) and overall survival (cohort I: P=0.044; cohort II: P<0.001) in both cohorts. In multivariate analysis, high chondroitin sulfate in malignant cells was shown to be an independent, predictive factor of poor overall survival (cohort I: hazard ratio 2.28: 95% confidence interval 1.08-4.81, P=0.031; cohort II: hazard ratio 1.71: 95% confidence interval 1.23-2.38, P=0.001). However, chondroitin sulfate in the stroma showed no correlation with known markers of tumor aggressiveness or with clinical outcome in either cohort. Our data suggest that high chondroitin sulfate expression in malignant cells is associated with an adverse outcome in patients with primary breast cancer, supporting the idea of a functional and potentially targetable role of chondroitin sulfate in tumor disease.

Hypoxia triggers a proangiogenic pathway involving cancer cell microvesicles and PAR-2-mediated heparin-binding EGF signaling in endothelial cells.

Highly malignant tumors, such as glioblastomas, are characterized by hypoxia, endothelial cell (EC) hyperplasia, and hypercoagulation. However, how these phenomena of the tumor microenvironment may be linked at the molecular level during tumor development remains ill-defined. Here, we provide evidence that hypoxia up-regulates protease-activated receptor 2 (PAR-2), i.e., a G-protein-coupled receptor of coagulation-dependent signaling, in ECs. Hypoxic induction of PAR-2 was found to elicit an angiogenic EC phenotype and to specifically up-regulate heparin-binding EGF-like growth factor (HB-EGF). Inhibition of HB-EGF by antibody neutralization or heparin treatment efficiently counteracted PAR-2-mediated activation of hypoxic ECs. We show that PAR-2-dependent HB-EGF induction was associated with increased phosphorylation of ERK1/2, and inhibition of ERK1/2 phosphorylation attenuated PAR-2-dependent HB-EGF induction as well as EC activation. Tissue factor (TF), i.e., the major initiator of coagulation-dependent PAR signaling, was substantially induced by hypoxia in several types of cancer cells, including glioblastoma; however, TF was undetectable in ECs even at prolonged hypoxia, which precludes cell-autonomous PAR-2 activation through TF. Interestingly, hypoxic cancer cells were shown to release substantial amounts of TF that was mainly associated with secreted microvesicles with exosome-like characteristics. Vesicles derived from glioblastoma cells were found to trigger TF/VIIa-dependent activation of hypoxic ECs in a paracrine manner. We provide evidence of a hypoxia-induced signaling axis that links coagulation activation in cancer cells to PAR-2-mediated activation of ECs. The identified pathway may constitute an interesting target for the development of additional strategies to treat aggressive brain tumors.

Heparan sulfate proteoglycan-mediated polyamine uptake.

The polyamines are polycationic compounds essential for cellular proliferation and transformation. In addition to a well-defined biosynthesis pathway, polyamines are internalized into cells by as yet incompletely defined mechanisms. Numerous reports have shown that efficient polyamine uptake depends on the presence of polyanionic, cell surface-associated heparan sulfate proteoglycans (HSPGs). In this chapter, we provide protocols for studying HSPG-mediated uptake of polyamines in various cell lines, and provide instructions for the use of two different genetic models of HSPG deficiency. We describe the enzymatic reduction of cell surface HSPG through Heparinase III lyase treatment as well as the use of phage display-derived single chain variable fragment (scFv) anti-HS antibodies to block HSPGs at the cell surface. Finally, we provide a protocol for the quantitative verification of loss or reduction of cell surface HSPGs and a detailed description of polyamine uptake measurement.

Combined vascular endothelial growth factor-A and fibroblast growth factor 4 gene transfer improves wound healing in diabetic mice.

BACKGROUND: Impaired wound healing in diabetes is related to decreased production of growth factors. Hence, gene therapy is considered as promising treatment modality. So far, efforts concentrated on single gene therapy with particular emphasis on vascular endothelial growth factor-A (VEGF-A). However, as multiple proteins are involved in this process it is rational to test new approaches. Therefore, the aim of this study was to investigate whether single AAV vector-mediated simultaneous transfer of VEGF-A and fibroblast growth factor 4 (FGF4) coding sequences will improve the wound healing over the effect of VEGF-A in diabetic (db/db) mice. METHODS: Leptin receptor-deficient db/db mice were randomized to receive intradermal injections of PBS or AAVs carrying ß-galactosidase gene (AAV-LacZ), VEGF-A (AAV-VEGF-A), FGF-4 (AAV-FGF4-IRES-GFP) or both therapeutic genes (AAV-FGF4-IRES-VEGF-A). Wound healing kinetics was analyzed until day 21 when all animals were sacrificed for biochemical and histological examination. RESULTS: Complete wound closure in animals treated with AAV-VEGF-A was achieved earlier (day 19) than in control mice or animals injected with AAV harboring FGF4 (both on day 21). However, the fastest healing was observed in mice injected with bicistronic AAV-FGF4-IRES-VEGF-A vector (day 17). This was paralleled by significantly increased granulation tissue formation, vascularity and dermal matrix deposition. Mechanistically, as shown in vitro, FGF4 stimulated matrix metalloproteinase-9 (MMP-9) and VEGF receptor-1 expression in mouse dermal fibroblasts and when delivered in combination with VEGF-A, enhanced their migration. CONCLUSION: Combined gene transfer of VEGF-A and FGF4 can improve reparative processes in the wounded skin of diabetic mice better than single agent treatment.

Ornithine decarboxylase and extracellular polyamines regulate microvascular sprouting and actin cytoskeleton dynamics in endothelial cells.

The polyamines are essential for cancer cell proliferation during tumorigenesis. Targeted inhibition of ornithine decarboxylase (ODC), i.e. a key enzyme of polyamine biosynthesis, by alpha-difluoromethylornithine (DFMO) has shown anti-neoplastic activity in various experimental models. This activity has mainly been attributed to the anti-proliferative effect of DFMO in cancer cells. Here, we provide evidence that unperturbed ODC activity is a requirement for proper microvessel sprouting ex vivo as well as the migration of primary human endothelial cells. DFMO-mediated ODC inhibition was reversed by extracellular polyamine supplementation, showing that anti-angiogenic effects of DFMO were specifically related to polyamine levels. ODC inhibition was associated with an abnormal morphology of the actin cytoskeleton during cell spreading and migration. Moreover, our data suggest that de-regulated actin cytoskeleton dynamics in DFMO treated endothelial cells may be related to constitutive activation of the small GTPase CDC42, i.e. a well-known regulator of cell motility and actin cytoskeleton remodeling. These insights into the potential role of polyamines in angiogenesis should stimulate further studies testing the combined anti-tumor effect of polyamine inhibition and established anti-angiogenic therapies in vivo.

Magnetic nanoparticle-based isolation of endocytic vesicles reveals a role of the heat shock protein GRP75 in macromolecular delivery.

An increased understanding of cellular uptake mechanisms of macromolecules remains an important challenge in cell biology with implications for viral infection and macromolecular drug delivery. Here, we report a strategy based on antibody-conjugated magnetic nanoparticles for the isolation of endocytic vesicles induced by heparan sulfate proteoglycans (HSPGs), key cell-surface receptors of macromolecular delivery. We provide evidence for a role of the glucose-regulated protein (GRP)75/PBP74/mtHSP70/mortalin (hereafter termed "GRP75") in HSPG-mediated endocytosis of macromolecules. GRP75 was found to be a functional constituent of intracellular vesicles of a nonclathrin-, noncaveolin-dependent pathway that was sensitive to membrane cholesterol depletion and that showed colocalization with the membrane raft marker cholera toxin subunit B. We further demonstrate a functional role of the RhoA GTPase family member CDC42 in this transport pathway; however, the small GTPase dynamin appeared not to be involved. Interestingly, we provide evidence of a functional role of GRP75 using RNAi-mediated down-regulation of GRP75 and GRP75-blocking antibodies, both of which inhibited macromolecular endocytosis. We conclude that GRP75, a chaperone protein classically found in the endoplasmic reticulum and mitochondria, is a functional constituent of noncaveolar, membrane raft-associated endocytic vesicles. Our data provide proof of principle of a strategy that should be generally applicable in the molecular characterization of selected endocytic pathways involved in macromolecular uptake by mammalian cells.

Establishment of heparan sulphate deficient primary endothelial cells from EXT-1(flox/flox) mouse lungs and sprouting aortas.

Angiogenesis is a hallmark of expanding tissue e.g. during embryogenesis and wound healing in physiology as well as in diseases such as cancer and atherosclerosis. Key steps of the angiogenic process involve growth factor-mediated stimulation of endothelial cell sprouting and tube formation. Heparan sulphate proteoglycans (HSPGs) have been implicated as important co-receptors of several pro-angiogenic proteins. The importance of HSPGs in physiology was underscored by the finding that knockout of the gene encoding HS polymerase, EXT-1, resulted in early embryonic lethality. Here, we describe the establishment of HS-deficient endothelial cells from sprouting aortas as well as from the lungs of EXT-1(flox/flox) mice. Recombination of the loxP-flanked EXT-1 locus by Cre-expressing adenovirus was demonstrated at the mRNA level. Moreover, depletion of HS polysaccharides was verified by flow cytometry and fluorescence microscopy methodology using phage display-derived anti-HS antibodies. In summary, we provide a genetic model to unravel the functional role of HSPGs specifically in primary endothelial cells during early steps of angiogenesis. Our studies are applicable to most loxP-based transgenic mouse strains, and may thus be of general importance in the angiogenesis field.

The polyamines regulate endothelial cell survival during hypoxic stress through PI3K/AKT and MCL-1.

Hypoxia-dependent angiogenesis is an inherent feature of solid tumors, and a better understanding of the molecular mechanisms of hypoxic cell-death should provide additional targets for cancer therapy. Here, we show a novel role of the polyamines in endothelial cell (EC) survival during hypoxia. Polyamine depletion by specific inhibition of ornithine decarboxylase was shown to protect ECs from hypoxia-induced apoptosis. Inhibition of the polyamines resulted in a significant induction of PI3K/AKT and its down-stream target MCL-1, i.e. an anti-apoptotic member of the BCL-2 family. Specific inhibitors of PI3K reversed the decrease of hypoxia-induced apoptosis as well as the induction of MCL-1 in polyamine-deprived cells. Moreover, siRNA-mediated down-regulation of MCL-1 was found to counter-act the protective effect of polyamine inhibition. We conclude that the polyamines regulate hypoxia-induced apoptosis in ECs through PI3K/AKT and MCL-1 dependent pathways. Our results may have important implications for the modulation of hypoxia-driven neovascularization.

Hypoxia-mediated induction of the polyamine system provides opportunities for tumor growth inhibition by combined targeting of vascular endothelial growth factor and ornithine decarboxylase.

Hypoxia is a hallmark of solid tumors, which may offer opportunities for targeted therapies of cancer; however, the mechanisms that link hypoxia to malignant transformation and tumor progression are not fully understood. Here, we show that up-regulation of the polyamine system promotes cancer cell survival during hypoxic stress. Hypoxia was found to induce polyamine transport and the key enzyme of polyamine biosynthesis, ornithine decarboxylase (ODC), in a variety of cancer cell lines. Increased ODC protein expression was shown in hypoxic, GLUT-1-expressing regions of tumor spheroids and experimental tumors, as well as in clinical tumor specimens. Hypoxic induction of the polyamine system was dependent on antizyme inhibitor (i.e., a key positive regulator of ODC and polyamine transport), as shown by RNA interference experiments. Interestingly, depletion of the polyamines during hypoxia resulted in increased apoptosis, which indicates an essential role of the polyamines in cancer cell adaptation to hypoxic stress. These results were supported by experiments in an in vivo glioma tumor model, showing significantly enhanced antitumor effects of the antiangiogenic, humanized anti-vascular endothelial growth factor (VEGF) antibody bevacizumab when used in combination with the well-established, irreversible inhibitor of ODC, alpha-difluoromethylornithine. Our results provide important insights into the hypoxic stress response in malignant cells and implicate combined targeting of VEGF and ODC as an alternative strategy to treat cancer disease.