Dual actions of nitric oxide on angiogenesis: possible roles of PKC, ERK, and AP-1

Nitric Oxide‐Based Nanomedicines for Conquering TME Fortress: Say “NO” to Insufficient Tumor Treatment

Almost all cancer treatments are significantly limited by the strong tumor microenvironment (TME) fortress formed by abnormal vasculature, dense extracellular matrix (ECM), multidrug resistance (MDR) system, and immune “cold” environment. In the huge efforts of dismantling the TME fortress, nitric oxide (NO)‐based nanomedicines are increasingly occupying a central position and have already been identified as super “strong polygonal warriors” to dismantle TME fortress for efficient cancer treatment, benefiting from NO's unique physicochemical properties and extremely fascinating biological effects. However, there is a paucity of systematic review to elaborate on the progress and fundamental mechanism of NO‐based nanomedicines in oncology from this aspect. Herein, the key characteristics of TME fortress and the potential of NO in reprogramming TME are delineated and highlighted. The evolution of NO donors and the advantages of NO‐based nanomedicines are discussed subsequently. Moreover, the latest progress of NO‐based nanomedicines for solid tumors is comprehensively reviewed, including normalizing tumor vasculature, overcoming ECM barrier, reversing MDR, and reactivating the immunosuppression TME. Lastly, the prospects, limitations, and future directions on NO‐based nanomedicines for TME manipulation are discussed to provide new insights into the construction of more applicable anticancer nanomedicines.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

Nitric oxide (NO) is a gaseous molecule that has a central role in signaling pathways involved in numerous physiological processes (e.g., vasodilation, neurotransmission, inflammation, apoptosis, and tumor growth). Due to its gaseous form, NO has a short half-life, and its physiology role is concentration dependent, often restricting its function to a target site. Providing NO from an external source is beneficial in promoting cellular functions and treatment of different pathological conditions. Hence, the multifaceted role of NO in physiology and pathology has garnered massive interest in developing strategies to deliver exogenous NO for the treatment of various regenerative and biomedical complexities. NO-releasing platforms or donors capable of delivering NO in a controlled and sustained manner to target tissues or organs have advanced in the past few decades. This review article discusses in detail the generation of NO via the enzymatic functions of NO synthase as well as from NO donors and the multiple biological and pathological processes that NO modulates. The methods for incorporating of NO donors into diverse biomaterials including physical, chemical, or supramolecular techniques are summarized. Then, these NO-releasing platforms are highlighted in terms of advancing treatment strategies for various medical problems.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Nitric Oxide Prevents Glioblastoma Stem Cells' Expansion and Induces Temozolomide Sensitization

Glioblastoma multiforme (GBM) has high mortality and recurrence rates. Malignancy resilience is ascribed to Glioblastoma Stem Cells (GSCs), which are resistant to Temozolomide (TMZ), the gold standard for GBM post-surgical treatment. However, Nitric Oxide (NO) has demonstrated anti-cancer efficacy in GBM cells, but its potential impact on GSCs remains unexplored. Accordingly, we investigated the effects of NO, both alone and in combination with TMZ, on patient-derived GSCs. Experimentally selected concentrations of diethylenetriamine/NO adduct and TMZ were used through a time course up to 21 days of treatment, to evaluate GSC proliferation and death, functional recovery, and apoptosis. Immunofluorescence and Western blot analyses revealed treatment-induced effects in cell cycle and DNA damage occurrence and repair. Our results showed that NO impairs self-renewal, disrupts cell-cycle progression, and expands the quiescent cells' population. Consistently, NO triggered a significant but tolerated level of DNA damage, but not apoptosis. Interestingly, NO/TMZ cotreatment further inhibited cell cycle progression, augmented G0 cells, induced cell death, but also enhanced DNA damage repair activity. These findings suggest that, although NO administration does not eliminate GSCs, it stunts their proliferation, and makes cells susceptible to TMZ. The resulting cytostatic effect may potentially allow long-term control over the GSCs' subpopulation.

Nitric oxide and hormesis

This present paper provides an assessment of the occurrence of nitric oxide (NO)-induced hormetic-biphasic dose/concentration relationships in biomedical research. A substantial reporting of such NO-induced hormetic effects was identified with particular focus on wound healing, tumor promotion, and sperm biology, including mechanistic assessment and potential for translational applications. Numerous other NO-induced hormetic effects have been reported, but require more development prior to translational applications. The extensive documentation of NO-induced biphasic responses, across numerous organs (e.g., bone, cardiovascular, immune, intestine, and neuronal) and cell types, suggests that NO-induced biological activities are substantially mediated via hormetic processes. These observations are particularly important because broad areas of NO biology are constrained by the quantitative features of the hormetic response. This determines the amplitude and width of the low dose stimulation, affecting numerous biomedical implications, study design features (e.g., number of doses, dose spacing, sample sizes, statistical power), and the potential success of clinical trials.

Sildenafil-Induced Revascularization of Rat Hindlimb Involves Arteriogenesis through PI3K/AKT and eNOS Activation

Hypoxia and inflammation play a major role in revascularization following ischemia. Sildenafil inhibits phosphodiesterase-5, increases intracellular cGMP and induces revascularization through a pathway which remains incompletely understood. Thus, we investigated the effect of sildenafil on post-ischemic revascularization. The left femoral artery was ligated in control and sildenafil-treated (25 mg/kg per day) rats. Vascular density was evaluated and expressed as the left/right leg (L/R) ratio. In control rats, L/R ratio was 33 ± 2% and 54 ± 9%, at 7- and 21-days post-ligation, respectively, and was significantly increased in sildenafil-treated rats to 47 ± 4% and 128 ± 11%, respectively. A neutralizing anti-VEGF antibody significantly decreased vascular density (by 0.48-fold) in control without effect in sildenafil-treated animals. Blood flow and arteriolar density followed the same pattern. In the ischemic leg, HIF-1α and VEGF expression levels increased in control, but not in sildenafil–treated rats, suggesting that sildenafil did not induce angiogenesis. PI3-kinase, Akt and eNOS increased after 7 days, with down-regulation after 21 days. Sildenafil induced outward remodeling or arteriogenesis in mesenteric resistance arteries in association with eNOS protein activation. We conclude that sildenafil treatment increased tissue blood flow and arteriogenesis independently of VEGF, but in association with PI3-kinase, Akt and eNOS activation.

Exosomes derived from magnesium ion-stimulated macrophages inhibit angiogenesis

Angiogenesis, an essential prerequisite to osteogenesis in bone repair and regeneration, can be mediated by immunoregulation of macrophages. Magnesium and its alloys are promising biodegradable bone implant materials and can affect immunoregulation of macrophages by the degradation products (magnesium ions. Nevertheless, the mechanism of macrophage-derived exosomes stimulated by Mg ions in immunoregulation is still not well understood. Herein, 10-50 mM magnesium ions are shown to inhibit the macrophage viability and proliferation in a dose-dependent manner, but a high concentration results in macrophage apoptosis. The exosomes secreted by macrophages from magnesium ion stimulation inhibit angiogenesis of endothelial cells, as manifested by the suppressed cell viability, proliferation, migration, and tube formation, which arise at least partially from exosome-mediated downregulation of endothelial nitric oxide and the vascular endothelial growth factor. The findings reported in this paper suggest that the bio-functionality of biodegradable magnesium alloys must be considered from the perspective of immunoregulation of macrophage-derived exosomes. Our results also suggest potential cancer therapy by inhibiting tumor-associated angiogenesis.

Anti-Inflammatory Activities of an Anti-Histamine Drug, Loratadine, by Suppressing TAK1 in AP-1 Pathway

Loratadine is an anti-histamine routinely used for treating allergies. However, recent findings have shown that Loratadine may also have anti-inflammatory functions, while their exact mechanisms have not yet been fully uncovered. In this paper, we investigated whether Loratadine can be utilized as an anti-inflammatory drug through a series of in vitro and in vivo experiments using a murine macrophage cell line and an acute gastritis mouse model. Loratadine was found to dramatically reduce the expression of pro-inflammatory genes, including MMP1, MMP3, and MMP9, and inhibit AP-1 transcriptional activation, as demonstrated by the luciferase assay. Therefore, we decided to further explore its role in the AP-1 signaling pathway. The expression of c-Jun and c-Fos, AP-1 subunits, was repressed by Loratadine and, correspondingly, the expression of p-JNK, p-MKK7, and p-TAK1 was also inhibited. In addition, Loratadine was able to reduce gastric bleeding in acute gastritis-induced mice; Western blotting using the stomach samples showed reduced p-c-Fos protein levels. Loratadine was shown to effectively suppress inflammation by specifically targeting TAK1 and suppressing consequent AP-1 signaling pathway activation and inflammatory cytokine production.

Pillars and Gaps of S-Nitrosylation-Dependent Epigenetic Regulation in Physiology and Cancer

Nitric oxide (NO) is a diffusible signaling molecule produced by three isoforms of nitric oxide synthase, which release NO during the metabolism of the amino acid arginine. NO participates in pathophysiological responses of many different tissues, inducing concentration-dependent effect. Indeed, while low NO levels generally have protective effects, higher NO concentrations induce cytotoxic/cytostatic actions. In recent years, evidences have been accumulated unveiling S-nitrosylation as a major NO-dependent post-translational mechanism ruling gene expression. S-nitrosylation is a reversible, highly regulated phenomenon in which NO reacts with one or few specific cysteine residues of target proteins generating S-nitrosothiols. By inducing this chemical modification, NO might exert epigenetic regulation through direct effects on both DNA and histones as well as through indirect actions affecting the functions of transcription factors and transcriptional co-regulators. In this light, S-nitrosylation may also impact on cancer cell gene expression programs. Indeed, it affects different cell pathways and functions ranging from the impairment of DNA damage repair to the modulation of the activity of signal transduction molecules, oncogenes, tumor suppressors, and chromatin remodelers. Nitrosylation is therefore a versatile tool by which NO might control gene expression programs in health and disease.

CXCL13/CXCR5 axis facilitates endothelial progenitor cell homing and angiogenesis during rheumatoid arthritis progression

Angiogenesis is a critical process in the formation of new capillaries and a key participant in rheumatoid arthritis (RA) pathogenesis. The chemokine (C-X-C motif) ligand 13 (CXCL13) plays important roles in several cellular functions such as infiltration, migration, and motility. We report significantly higher levels of CXCL13 expression in collagen-induced arthritis (CIA) mice compared with controls and also in synovial fluid from RA patients compared with human osteoarthritis (OA) samples. RA synovial fluid increased endothelial progenitor cell (EPC) homing and angiogenesis, which was blocked by the CXCL13 antibody. By interacting with the CXCR5 receptor, CXCL13 facilitated vascular endothelial growth factor (VEGF) expression and angiogenesis in EPC through the PLC, MEK, and AP-1 signaling pathways. Importantly, infection with CXCL13 short hairpin RNA (shRNA) mitigated EPC homing and angiogenesis, articular swelling, and cartilage erosion in ankle joints of mice with CIA. CXCL13 is therefore a novel therapeutic target for RA.

The implications of nitric oxide metabolism in the treatment of glial tumors

Glial tumors are the most common intracranial malignancies. Unfortunately, despite such a high prevalence, patients' prognosis is usually poor. It is related to the high invasiveness, tendency to relapse and the resistance of tumors to traditional methods of treatment. An important link in the aspect of these issues may be nitric oxide (NO) metabolism. It is a very complex mechanism with multidirectional effects on the neoplastic process. Depending on the concentration axis, it can both exert pro-tumor action as well as contribute to the inhibition of tumorigenesis. The latest observations show that the control of its metabolism can be very helpful in the development of new methods of treating gliomas, as well as in increasing the effectiveness of the agents currently used. The influence of nitric oxide and nitric oxide synthase (NOS) activity on glioma stem cells seem to be of particular importance. The use of specific inhibitors may allow the reduction of tumor growth and its tendency to relapse. Another important feature of GSCs is their conditioning of glioma resistance to traditional forms of treatment. Recent studies have shown that modulation of NO metabolism can suppress this effect, preventing the induction of radio and chemoresistance. Moreover, nitric oxide is involved in the regulation of a number of immune mechanisms. Adequate modulation of its metabolism may contribute to the induction of an anti-tumor response in the patients' immune system.

Microglia-Derived Small Extracellular Vesicles Reduce Glioma Growth by Modifying Tumor Cell Metabolism and Enhancing Glutamate Clearance through miR-124

Brain homeostasis needs continuous exchange of intercellular information among neurons, glial cells, and immune cells, namely microglial cells. Extracellular vesicles (EVs) are active players of this process. All the cells of the body, including the brain, release at least two subtypes of EVs, the medium/large EVs (m/lEVs) and small EVs (sEVs). sEVs released by microglia play an important role in brain patrolling in physio-pathological processes. One of the most common and malignant forms of brain cancer is glioblastoma. Altered intercellular communications constitute a base for the onset and the development of the disease. In this work, we used microglia-derived sEVs to assay their effects in vitro on murine glioma cells and in vivo in a glioma model on C57BL6/N mice. Our findings indicated that sEVs carry messages to cancer cells that modify glioma cell metabolism, reducing lactate, nitric oxide (NO), and glutamate (Glu) release. sEVs affect Glu homeostasis, increasing the expression of Glu transporter Glt-1 on astrocytes. We demonstrated that these effects are mediated by miR-124 contained in microglia-released sEVs. The in vivo benefit of microglia-derived sEVs results in a significantly reduced tumor mass and an increased survival of glioma-bearing mice, depending on miR-124.

Molecular docking and dynamic studies of a potential therapeutic target inhibiting glyoxalase system: Metabolic action of the 3, 3 '- [3- (5-chloro-2-hydroxyphenyl) -3-oxopropane-1, 1-diyl] - Bis-4-hydroxycoumarin leads overexpression of the intracellular level of methylglyoxal and induction of a pro-apoptotic phenomenon in a hepatocellular carcinoma model

Methylglyoxal is a dicarbonyl compound recruited as a potential cytotoxic marker, initially presents in cells and considered as a metabolite of the glycolytic pathway. Our aim is to demonstrate the inhibitory effect of 3, 3'-[3-(5-chloro-2-hydroxyphenyl)-3-oxopropane-1, 1-diyl] Bis (4-hydroxycoumarin) on the glyoxalase system, and indirectly its anticancer activity. The docking of OT-55 was conducted by using Flexible docking protocol, ChiFlex and libdock tools inside the active site of Glo-I indicated that both hydrogen bonding and hydrophobic interactions contributed significantly in establishing potent binding with the active site which is selected as a strong inhibitor with high scoring values and maximum Gibbs free energy. Coumarin-liposome formulation was characterized and evaluated in vivo against chemically induced hepatocarcinoma in Wistar rats. After Diethylnitrosamine (DEN) induction, microscopic assessment was realized; precancerous lesions were developed showing an increase of both tumor-associated lymphocyte and multiple tumor acini supported by the blood investigation. Our finding also suggested a preferential uptake of liposomes respectively in liver, kidney, lung, brain and spleen in the DEN-treated animals. OT-55 has also been shown to inhibit the activity of Glo-I in vitro as well as in DEN-treated rats. An abnormal high level of MGO of up to 50% was recorded followed by a reduction in glucose consumption and lactate dehydrogenase production validated in the positive control. MGO generates apoptosis as depicted by focal hepatic lesions. Also, no deleterious effects in the control group were observed after testing our coumarin but rather a vascular reorganization leading to nodular regenerative hyperplasia. Involved in the detoxification process, liver GSH is restored in intoxicated rats, while no changes are seen between controls. At the endothelial cell, OT-55 appears to modulate the release of NO only in the DEN-treated group. OT-55 would behave both as an anticancer agent but also as an angiogenic factor regarding results obtained.

Impaired Vascular Redox Signaling in the Vascular Complications of Obesity and Diabetes Mellitus

Significance: Oxidative stress, a crucial regulator of vascular disease pathogenesis, may be involved in the vascular complications of obesity, systemic insulin resistance (IR), and diabetes mellitus (DM). Recent Advances: Excessive production of reactive oxygen species in the vascular wall has been linked with vascular disease pathogenesis. Recent evidence has revealed that vascular redox state is dysregulated in cases of obesity, systemic IR, and DM, potentially participating in the well-known vascular complications of these disease entities. Critical Issues: The detrimental effects of obesity and the metabolic syndrome on vascular biology have been extensively described at a clinical level. Further, vascular oxidative stress has often been associated with the presence of obesity and IR as well as with a variety of detrimental vascular phenotypes. However, the mechanisms of vascular redox state regulation under conditions of obesity and systemic IR, as well as their clinical relevance, are not adequately explored. In addition, the notion of vascular IR, and its relationship with systemic parameters of obesity and systemic IR, is not fully understood. In this review, we present all the important components of vascular redox state and the evidence linking oxidative stress with obesity and IR. Future Directions: Future studies are required to describe the cellular effects and the translational potential of vascular redox state in the context of vascular disease. In addition, further elucidation of the direct vascular effects of obesity and IR is required for better management of the vascular complications of DM.

Genetic Modifiers of the Breast Tumor Microenvironment

Multiple nonmalignant cell types in the tumor microenvironment (TME) impact breast cancer risk, metastasis, and response to therapy, yet most heritable mechanisms that influence TME cell function and breast cancer outcomes are largely unknown. Breast cancer risk is ∼30% heritable and >170 genetic loci have been associated with breast cancer traits. However, the majority of candidate genes have poorly defined mechanistic roles in breast cancer biology. Research indicates that breast cancer risk modifiers directly impact cancer cells, yet it is equally plausible that some modifier alleles impact the nonmalignant TME. The objective of this review is to examine the list of current breast cancer candidate genes that may modify breast cancer risk and outcome through the TME.

State Estimation of the Time-Varying and Spatially Localized Concentration of Signal Molecules from the Stochastic Adsorption Dynamics on the Carbon Nanotube-Based Sensors and Its Application to Tumor Cell Detection

This paper addresses a problem of estimating time-varying, local concentrations of signal molecules with a carbon-nanotube (CNT)-based sensor array system, which sends signals triggered by monomolecular adsorption/desorption events of proximate molecules on the surfaces of the sensors. Such sensors work on nano-scale phenomena and show inherently stochastic non-Gaussian behavior, which is best represented by the chemical master equation (CME) describing the time evolution of the probabilities for all the possible number of adsorbed molecules. In the CME, the adsorption rate on each sensor is linearly proportional to the local concentration in the bulk phase. State estimators are proposed for these types of sensors that fully address their stochastic nature. For CNT-based sensors motivated by tumor cell detection, the particle filter, which is nonparametric and can handle non-Gaussian distributions, is compared to a Kalman filter that approximates the underlying distributions by Gaussians. In addition, the second-order generalized pseudo Bayesian estimation (GPB2) algorithm and the Markov chain Monte Carlo (MCMC) algorithm are incorporated into KF and PF respectively, for detecting latent drift in the concentration affected by different states of a cell.

Insights into the diverse effects of nitric oxide on tumor biology

Among its many roles in cellular biology, nitric oxide (·NO) has long been associated with cancers both as a protumorigenic and as an antitumorigenic agent. The dual nature of this signaling molecule in varied settings is attributable to its temporal and concentration-dependent effects that produce different phenotypes. The steady-state ·NO concentration within the cell is a balance between its rate of enzymatic synthesis from the three nitric oxide synthase (NOS) isoforms and consumption via numerous metabolic pathways and demonstrates strong dependence on the tissue oxygen concentration. NOS expression and ·NO production are often deregulated and associated with numerous types of cancers with dissimilar prognostic outcomes. ·NO influences several facets of tumor initiation and progression including DNA damage, chronic inflammation, angiogenesis, epithelial-mesenchymal transition, and metastasis, to name a few. The role of ·NO as an epigenetic modulator has also recently emerged and has potentially important mechanistic implications in regulating transcription of oncogenes and tumor-suppressor genes. ·NO-derived cellular adducts such as dinitrosyliron complexes and the formation of higher nitrogen oxides further alter its cellular behavior. Among anticancer strategies, the use of NOS as a prognostic biomarker and modulation of ·NO production for therapeutic benefit have gained importance over the past decade. Numerous ·NO-releasing drugs and NOS inhibitors have been evaluated in preclinical and clinical settings to arrest tumor growth. Taken together, ·NO affects various arms of cancer signaling networks. An overview of this complex interplay is provided in this chapter.

A Tunable, Stable, and Bioactive MOF Catalyst for Generating a Localized Therapeutic from Endogenous Sources

The versatile chemical and physical properties of metal organic frameworks (MOFs) have made them unique platforms for the design of biomimetic catalysts, but with only limited success to date due to instability of the MOFs employed in physiological environments. Herein, the use of Cu(II)1,3,5‐Benzene‐tris‐triazole (CuBTTri) is demonstrated for the catalytic generation of the bioactive agent nitric oxide (NO) from endogenous sources, S‐nitrosothiols (RSNOs). CuBTTri exhibits structural integrity in aqueous environments, including phosphate buffered saline (76 h, pH 7.4, 37 °C), cell media used for in vitro testing (76 h, pH 7.4, 37 °C), and fresh citrated whole blood (30 min, pH 7.4, 37 °C). The application of CuBTTri for use in polymeric medical devices is explored through the formation of a composite CuBTTri‐poly by blending CuBTTri into biomedical grade polyurethane matrices. Once prepared, the CuBTTri‐poly material retains the catalytic function towards the generation of NO with tunable release kinetics proportional to the total content of CuBTTri embedded into the polymeric material with a surface flux corresponding to the therapeutic range of 1–100 nm cm−2 min−1, which is maintained even following exposure to blood.

Angiogenesis in gastric mucosa: an important component of gastric erosion and ulcer healing and its impairment in aging

Angiogenesis (also referred to as neovascularization-formation of new blood vessels from existing vessels) is a fundamental process essential for healing of tissue injury and ulcers because regeneration of blood microvessels is a critical requirement for oxygen and nutrient delivery to the healing site. This review article updates the current views on angiogenesis in gastric mucosa following injury and during ulcer healing, its sequential events, the underlying mechanisms, and the impairment of angiogenesis in aging gastric mucosa. We focus on the time sequence and ultrastructural features of angiogenesis, hypoxia as a trigger, role of vascular endothelial growth factor signaling (VEGF), serum response factor, Cox2 and prostaglandins, nitric oxide, and importin. Recent reports indicate that gastric mucosa of aging humans and experimental animals exhibits increased susceptibility to injury and delayed healing. Gastric mucosa of aging rats has increased susceptibility to injury by a variety of damaging agents such as ethanol, aspirin, and other non-steroidal anti-inflammatory drugs because of structural and functional abnormalities including: reduced gastric mucosal blood flow, hypoxia, reduced expression of vascular endothelial growth factor and survivin, and increased expression of early growth response protein 1 (egr-1) and phosphatase and tensin homolog (PTEN). Until recently, postnatal neovascularization was assumed to occur solely through angiogenesis sprouting of endothelial cells and formation of new blood vessels from pre-existing blood vessels. New studies in the last decade have challenged this paradigm and indicate that in some tissues, including gastric mucosa, the homing of bone marrow-derived endothelial progenitor cells to the site of injury can also contribute to neovascularization by a process termed vasculogenesis.

Arginase inhibition enhances angiogenesis in endothelial cells exposed to hypoxia

Hypoxia-induced arginase elevation plays an essential role in several vascular diseases but influence of arginase on hypoxia-mediated angiogenesis is completely unknown. In this study, in vitro network formation in bovine aortic endothelial cells (BAEC) was examined after exposure to hypoxia for 24h with or without arginase inhibition. Arginase activity, protein levels of the two arginase isoforms, eNOS, and VEGF as well as production of NO and ROS were examined to determine the involvement of arginase in hypoxia-mediated angiogenesis. Hypoxia elevated arginase activity and arginase 2 expression but reduced active p-eNOS(Ser1177) and NO levels in BAEC. In addition, both VEGF protein levels and endothelial elongation and network formation were reduced with continued hypoxia, whereas ROS levels increased and NO levels decreased. Arginase inhibition limited ROS, restored NO formation and VEGF expression, and prevented the reduction of angiogenesis. These results suggest a fundamental role of arginase activity in regulating angiogenic function.

Dual inhibition of the vascular endothelial growth factor pathway: a phase 1 trial evaluating bevacizumab and AZD2171 (cediranib) in patients with advanced solid tumors

BACKGROUND

The current study was conducted to evaluate the safety and biological activity of dual inhibition of the vascular endothelial growth factor (VEGF) pathway with combined bevacizumab and cediranib (a VEGF receptor tyrosine kinase inhibitor).

METHODS

This was a 3 + 3 dose escalation study in patients with advanced solid tumors. Cediranib was given orally daily for 21 days and bevacizumab intravenously every 2 weeks. Pharmacokinetics and correlates (nitric oxide synthase, nitrate oxide, and circulating tumor cells) were assessed.

RESULTS

Fifty-one patients were treated. Dose-limiting toxicities (DLTs) (grade 3-4; graded according to the National Cancer Institute Common Terminology Criteria of Adverse Events [version 3.0]) observed included 1 patient with chest pain, 1 patient with fatigue, 2 patients with thrombocytopenia, 3 patients with hypertension (1 with intracranial hemorrhage), and 1 patient with grade 5 hemoptysis. Moreover, 2 patients presented with grade 3 intracranial bleeding beyond the DLT window. Dose level 2 (cediranib at a dose of 20 mg/day and bevacizumab at a dose of 5 mg/kg every 2 weeks) was selected as the recommended phase 2 dose (RP2D); 17 patients were treated at dose level 2 with 1 DLT and no intracranial bleeding or severe hypertension reported. Pharmacokinetics of cediranib at dose level 3 demonstrated a 46% to 77% increase in area under the curve (0-24 hours) on cycle 1 day 1 compared with historical controls. Four patients attained partial remissions: inflammatory breast cancer (-54%), basal cell carcinoma (-33%), alveolar soft part sarcoma (-33%), and synovial sarcoma (-32%). Patients with a lower circulating tumor cell count (< 30) at the predose period had a longer time to tumor progression (P = .024, log-rank test).

CONCLUSIONS

Cediranib at a dose of 20 mg/day and bevacizumab at a dose of 5 mg/kg every 2 weeks was found to be the RP2D. Activity in several tumor types was noted. Central nervous system bleeding and severe hypertension were observed at doses above the RP2D.

Antiproliferative effects of carbon monoxide on pancreatic cancer

BACKGROUND

Carbon monoxide, the gaseous product of heme oxygenase, is a signalling molecule with a broad spectrum of biological activities. The aim of this study was to investigate the effects of carbon monoxide on proliferation of human pancreatic cancer.

METHODS

In vitro studies were performed on human pancreatic cancer cells (CAPAN-2, BxPc3, and PaTu-8902) treated with a carbon monoxide-releasing molecule or its inactive counterpart, or exposed to carbon monoxide gas (500 ppm/24h). For in vivo studies, pancreatic cancer cells (CAPAN-2/PaTu-8902) were xenotransplanted subcutaneously into athymic mice, subsequently treated with carbon monoxide-releasing molecule (35 mg/kg b.w. i.p./day), or exposed to safe doses of carbon monoxide (500 ppm 1h/day; n = 6 in each group).

RESULTS

Both carbon monoxide-releasing molecule and carbon monoxide exposure significantly inhibited proliferation of human pancreatic cancer cells (p<0.05). A substantial decrease in Akt phosphorylation was observed in carbon monoxide-releasing molecule compared with inactive carbon monoxide-releasing molecule treated cancer cells (by 30-50%, p<0.05). Simultaneously, carbon monoxide-releasing molecule and carbon monoxide exposure inhibited tumour proliferation and microvascular density of xenotransplanted tumours (p<0.01), and doubled the survival rates (p<0.005). Exposure of mice to carbon monoxide led to an almost 3-fold increase in carbon monoxide content in tumour tissues (p=0.006).

CONCLUSION

These data suggest a new biological function for carbon monoxide in carcinogenesis, and point to the potential chemotherapeutic/chemoadjuvant use of carbon monoxide in pancreatic cancer.

Perturbed neural activity disrupts cerebral angiogenesis during a postnatal critical period

During the neonatal period, activity-dependent neural-circuit remodelling coincides with growth and refinement of the cerebral microvasculature. Whether neural activity also influences the patterning of the vascular bed is not known. Here we show in neonatal mice, that neither reduction of sensory input through whisker trimming nor moderately increased activity by environmental enrichment affects cortical microvascular development. Unexpectedly, chronic stimulation by repetitive sounds, whisker deflection or motor activity led to a near arrest of angiogenesis in barrel, auditory and motor cortices, respectively. Chemically induced seizures also caused robust reductions in microvascular density. However, altering neural activity in adult mice did not affect the vasculature. Histological analysis and time-lapse in vivo two-photon microscopy revealed that hyperactivity did not lead to cell death or pruning of existing vessels but rather to reduced endothelial proliferation and vessel sprouting. This anti-angiogenic effect was prevented by administration of the nitric oxide synthase (NOS) inhibitor L-NAME and in mice with neuronal and inducible NOS deficiency, suggesting that excessive nitric oxide released from hyperactive interneurons and glia inhibited vessel growth. Vascular deficits persisted long after cessation of hyperstimulation, providing evidence for a critical period after which proper microvascular patterning cannot be re-established. Reduced microvascular density diminished the ability of the brain to compensate for hypoxic challenges, leading to dendritic spine loss in regions distant from capillaries. Therefore, excessive sensorimotor stimulation and repetitive neural activation during early childhood may cause lifelong deficits in microvascular reserve, which could have important consequences for brain development, function and pathology.

The yin and yang of nitric oxide in cancer progression

Nitric oxide (NO) is a short-lived, pleiotropic molecule that affects numerous critical functions in the body. Presently, there are markedly conflicting findings in the literature regarding NO and its role in carcinogenesis and tumor progression. NO has been shown to have dichotomous effects on cellular proliferation, apoptosis, migration, invasion, angiogenesis and many other important processes in cancer biology. It has been shown to be both pro- and antitumorigenic, depending on the concentration and the tumor microenvironment in question. NO is generated by three isoforms of NO synthase (NOS) that are widely expressed and sometimes upregulated in human tumors. Due to its vast array of physiological functions, it presents a huge challenge to researchers to discover its true potential in cancer biology and consequently, its use in anticancer therapies. In this study, we review the current knowledge in this area, with an emphasis placed on NO modulation as an anticancer therapy, focusing on NO-donating drugs and NOS inhibitors.

Opportunities and challenges in tumor angiogenesis research: back and forth between bench and bed

Angiogenesis is essential for tumor growth and metastasis. Many signaling pathways are involved in regulating tumor angiogenesis, with the vascular endothelial growth factor pathway being of particular interest. The recognition of the heterogeneity in tumor vasculature has led to better predictions of prognosis through differential analyses of the vasculature. However, the clinical benefits from antiangiogenic therapy are limited, because many antiangiogenic agents cannot provide long-term survival benefits, suggesting the development of drug resistance. Activation of the hypoxia and c-Met pathways, as well as other proangiogenic factors, has been shown to be responsible for such resistance. Vessel co-option could be another important mechanism. For future development, research to improve the efficacy of antiangiogenic therapy includes (a) using tumor-derived endothelial cells for drug screening; (b) developing the drugs focusing on specific tumor types; (c) developing a better preclinical model for drug study; (d) developing more accurate biomarkers for patient selection; (e) targeting the c-Met pathway or other pathways; and (f) optimizing the dose and schedule of antiangiogenic therapy. In summary, the future of antiangiogenic therapy for cancer patients depends on our efforts to develop the right drugs, select the right patients, and optimize the treatment conditions.

Regulatory effects of the JAK3/STAT1 pathway on the release of secreted phospholipase A₂-IIA in microvascular endothelial cells of the injured brain

Background

Secreted phospholipase A₂-IIA (sPLA₂-IIA) is an inducible enzyme released under several inflammatory conditions. It has been shown that sPLA₂-IIA is released from rat brain astrocytes after inflammatory stimulus, and lipopolysaccharide (LPS) and nitric oxide (NO) have been implicated in regulation of this release. Here, brain microvascular endothelial cells (BMVECs) were treated with LPS to uncover whether sPLA₂-IIA was released, whether nitric oxide regulated this release, and any related signal mechanisms.

Methods

Supernatants were collected from primary cultures of BMVECs. The release of sPLA₂-IIA, and the expression of inducible nitric oxide synthase (iNOS), phospho-JAK3, phospho-STAT1, total JAK3 and STAT1, β-actin, and bovine serum albumin (BSA) were analyzed by Western blot or ELISA. NO production was calculated by the Griess reaction. sPLA₂ enzyme activity was measured with a fluorometric assay. Specific inhibitors of NO (L-NAME and aminoguanidine, AG), JAK3 (WHI-P154,WHI), STAT1 (fludarabine, Flu), and STAT1 siRNA were used to determine the involvement of these molecules in the LPS-induced release of sPLA₂-IIA from BMVECs. Nuclear STAT1 activation was tested with the EMSA method. The monolayer permeability of BMVECs was measured with a diffusion assay using biotinylated BSA.

Results

Treatment of BMVECs with LPS increased the release of sPLA₂-IIA and nitrite into the cell culture medium up to 24 h. Pretreatment with an NO donor, sodium nitroprusside, decreased LPS-induced sPLA₂-IIA release and sPLA₂ enzyme activity, and enhanced the expression of iNOS and nitrite generation after LPS treatment. Pretreatment with L-NAME, AG, WHI-P154, or Flu notably reduced the expression of iNOS and nitrite, but increased sPLA₂-IIA protein levels and sPLA₂ enzyme activity. In addition, pretreatment of the cells with STAT1 siRNA inhibited the phosphorylation of STAT1, iNOS expression, and nitrite production, and enhanced the release of sPLA₂-IIA. Pretreatment with the specific inhibitors of NOS, JAK2, and STAT3 decreased the permeability of BMVECs. In contrast, inhibition of sPLA₂-IIA release increased cell permeability. These results suggest that sPLA₂-IIA expression is regulated by the NO-JAK3-STAT1 pathway. Importantly, sPLA₂-IIA augmentation could protect the LPS-induced permeability of BMVECs.

Conclusion

Our results demonstrate the important action of sPLA₂-IIA in the permeability of microvascular endothelial cells during brain inflammatory events. The sPLA₂ and NO pathways can be potential targets for the management of brain MVEC injuries and related inflammation.

Redox balance dynamically regulates vascular growth and remodeling

Vascular growth and remodeling responses entail several complex biochemical, molecular, and cellular responses centered primarily on endothelial cell activation and function. Recent studies reveal that changes in endothelial cell redox status critically influence numerous cellular events that are important for vascular growth under different conditions. It has been known for some time that oxidative stress actively participates in many aspects of angiogenesis and vascular remodeling. Initial studies in this field were largely exploratory with minimal insight into specific molecular mechanisms and how these responses could be regulated. However, it is now clear that intracellular redox mechanisms involving hypoxia, NADPH oxidases (NOX), xanthine oxidase (XO), nitric oxide and its synthases, and intracellular antioxidant defense pathways collectively orchestrate a redox balance system whereby reactive oxygen and nitrogen species integrate cues controlling vascular growth and remodeling. In this review, we discuss key redox regulation pathways that are centrally important for vascular growth in tissue health and disease. Important unresolved questions and issues are also addressed that requires future investigation.

Chronic inhibition of epidermal growth factor receptor tyrosine kinase and extracellular signal-regulated kinases 1 and 2 (ERK1/2) augments vascular response to limb ischemia in type 2 diabetic mice

Type 2 diabetes is a key risk factor for ischemia-dependent pathology; therefore, a significant medical need exists to develop novel therapies that increase the formation of new vessels. We explored the therapeutic potential of epidermal growth factor receptor tyrosine kinase (EGFRtk) and extracellular signal-regulated kinase 1/2 (ERK1/2) inhibition in impaired ischemia-induced neovascularization in type 2 diabetes. Unilateral femoral artery ligation was performed in diabetic (db(-)/db(-)) and their control (db(-)/db(+)) mice for 4 weeks, followed by treatments with EGFRtk and ERK1/2 inhibitors (AG1478, 10 mg/kg/day and U0126, 400 μg/kg/day, respectively) for 3 weeks. Neovascularization, blood flow recovery, vascular and capillary density, and endothelial nitric oxide synthase activity were significantly impaired and were associated with enhanced EGFRtk and ERK1/2 activity in db(-)/db(-) mice. EGFRtk and ERK1/2 inhibitors did not have any effect in control mice, while in db(-)/db(-) mice there was a significant increase in neovascularization, blood flow recovery, vascular and capillary density, endothelial nitric oxide synthase activity, and were associated with a decrease in EGFRtk and ERK1/2 activity. Our data demonstrated that the inhibition of EGFRtk and ERK1/2 restored ischemia-induced neovascularization and blood flow recovery in type 2 diabetic mice. Thus, EGFRtk and ERK1/2 could be possible targets to protect from ischemia-induced vascular pathology in type 2 diabetes.

Effects of long term nitrite therapy on functional recovery in experimental ischemia model

Our data have shown that nitrite therapy can rescue the ischemic brain when injected <3h after cerebral ischemic-reperfusion (I/R) injury and its effects can be prolonged to 4.5h in combination with memantine. We investigated whether or not long-term nitrite therapy is beneficial in ischemic brains. Sodium nitrite (1-100 μg/kg ip) or saline were administered to rats subjected to focal I/R injury for 7 days beginning 24h after I/R. Behavioral tests for 5 weeks revealed better functional recovery in the high-dose nitrite group than the control group. Other nitrite groups with relatively low doses showed no functional benefits. Hemispheric atrophy was attenuated by approximately 30% in the high-dose nitrite group. High-dose nitrite therapy also reduced inflammatory cytokine levels and caspase activity in the subacute period, and increased BrdU(+)MAP2(+) and BrdU(+)laminin(+) cells, and vascular density in the 5-week ischemic brain. Long-term nitrite therapy, when initiated 24h after I/R, corrected the subacute hostile environment, induced tissue and vascular regeneration, and improved functional recovery. Early and subsequent long term nitrite therapy may be effective in the management for ischemic stroke patients.

Inorganic nitrite and chronic tissue ischaemia: a novel therapeutic modality for peripheral vascular diseases

Ischaemic tissue damage represents the ultimate form of tissue pathophysiology due to cardiovascular disease, which is the leading cause of morbidity and mortality across the globe. A significant amount of basic research and clinical investigation has been focused on identifying cellular and molecular pathways to alleviate tissue damage and dysfunction due to ischaemia and subsequent reperfusion. Over many years, the gaseous molecule nitric oxide (NO) has emerged as an important regulator of cardiovascular health as well as protector against tissue ischaemia and reperfusion injury. However, clinical translation of NO therapy for these pathophysiological conditions has not been realized for various reasons. Work from our laboratory and several others suggests that a new form of NO-associated therapy may be possible through the use of nitrite anion (sodium nitrite), a prodrug which can be reduced to NO in ischaemic tissues. In this manner, nitrite anion serves as a highly selective NO donor in ischaemic tissues without substantially altering otherwise normal tissue. This surprising and novel discovery has reinvigorated hopes for effectively restoring NO bioavailability in vulnerable tissues while continuing to reveal the complexity of NO biology and metabolism within the cardiovascular system. However, some concerns may exist regarding the effect of nitrite on carcinogenesis. This review highlights the emergence of nitrite anion as a selective NO prodrug for ischaemic tissue disorders and discusses the potential therapeutic utility of this agent for peripheral vascular disease.

Different responsiveness of endothelial cells to vascular endothelial growth factor and basic fibroblast growth factor added to culture media under gravity and simulated microgravity

When incubated under simulated microgravity (s-microg), endothelial cells (EC) form tubular structures that resemble vascular intimas. This delayed formation of 3D EC structures begins between the 5th and 7th day of culturing EC under conditions of s-microg, when double-row cell assemblies become visible. With the aim of learning about this initial phase of tubular structure formation, we found that NFkappaBp65 protein content was similar in all cell populations, but gene and protein expression of phosphokinase A catalytic subunit, phosphokinase Calpha, and extracellular signal-regulated kinases 1 and 2 was altered in cells cultured under s-microg. Apoptosis remained below 30% in all EC cultures. In contrast to controls, the 7-day-old s-microg cultures contained 3D aggregates with proliferating cells, enhanced numbers of necrotic cells, and osteopontin-negative EC as well as supernatants with reduced quantities of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), soluble TNFRSF5, TNFSF5, intercellular adhesion molecule-1, tumor necrosis factor receptor 2, IL-18, complement C3, and von Willebrand factor. VEGF and/or bFGF (10 ng/mL) application influenced the accumulation of proteins in supernatants more profoundly under 1 g than under s-microg. These findings provide evidence that phosphokinase Calpha plays a key role in tube formation. Improving the interaction of VEGF and/or bFGF with EC under s-microg could enhance the engineering of vascular intimas.

Pharmacotherapy for end-stage coronary artery disease

IMPORTANCE OF THE FIELD

Coronary artery disease remains the leading cause of mortality in the industrialized world. Despite advances in surgical and catheter-based interventions, a select number of patients remain with no options for invasive therapy. The goal of this review is to discuss the current status of pharmacotherapeutic interventions to treat end-stage coronary artery disease.

AREAS COVERED IN THIS REVIEW

Literature review on the topic of therapeutic angiogenesis from 1980 to 2009.

WHAT THE READER WILL GAIN

Insight into current therapeutic strategies employed to manage end-stage coronary artery disease.

TAKE HOME MESSAGE

A promising approach focuses on augmenting the endogenous angiogenic response to chronic myocardial ischemia via the use of growth factors.

Targeting nitric oxide for cancer therapy

A blueprint for the ideal anticancer molecule would include most of the properties of nitric oxide (NO•), but the ability to exploit these characteristics in a therapeutic setting requires a detailed understanding of the biology and biochemistry of the molecule. These properties include the ability of NO• to affect tumour angiogenesis, metastasis, blood flow and immuno surveillance. Furthermore NO• also has the potential to enhance both radio- and chemotherapy. However, all of these strategies are dependent on achieving appropriate levels of NO•, since endogenous levels of NO• appear to have a clear role in tumour progression. This review aims to summarize the role of NO• in cancer with particular emphasis on how the properties of NO• can be exploited for therapy.

Gene therapy via inducible nitric oxide synthase: a tool for the treatment of a diverse range of pathological conditions

Nitric oxide (NO(.)) is a reactive nitrogen radical produced by the NO synthase (NOS) enzymes; it affects a plethora of downstream physiological and pathological processes. The past two decades have seen an explosion in the understanding of the role of NO(.) biology, highlighting various protective and damaging modes of action. Much of the controversy surrounding the role of NO(.) relates to the differing concentrations generated by the three isoforms of NOS. Both calcium-dependent isoforms of the enzyme (endothelial and neuronal NOS) generate low-nanomolar/picomolar concentrations of NO(.). By contrast, the calcium-independent isoform (inducible NOS (iNOS)) generates high concentrations of NO(.), 2-3 orders of magnitude greater. This review summarizes the current literature in relation to iNOS gene therapy for the therapeutic benefit of various pathological conditions, including various states of vascular disease, wound healing, erectile dysfunction, renal dysfunction and oncology. The available data provide convincing evidence that manipulation of endogenous NO(.) using iNOS gene therapy can provide the basis for future clinical trials.

Chronic sodium nitrite therapy augments ischemia-induced angiogenesis and arteriogenesis

Chronic tissue ischemia due to defective vascular perfusion is a hallmark feature of peripheral artery disease for which minimal therapeutic options exist. We have reported that sodium nitrite therapy exerts cytoprotective effects against acute ischemia/reperfusion injury in both heart and liver, consistent with the model of bioactive NO formation from nitrite during ischemic stress. Here, we test the hypothesis that chronic sodium nitrite therapy can selectively augment angiogenic activity and tissue perfusion in the murine hind-limb ischemia model. Various therapeutic doses (8.25-3,300 mug/kg) of sodium nitrite or PBS were administered. Sodium nitrite significantly restored ischemic hind-limb blood flow in a time-dependent manner, with low-dose sodium nitrite being most effective. Nitrite therapy significantly increased ischemic limb vascular density and stimulated endothelial cell proliferation. Remarkably, the effects of sodium nitrite therapy were evident within 3 days of the ischemic insult demonstrating the potency and efficacy of chronic sodium nitrite therapy. Sodium nitrite therapy also increased ischemic tissue nitrite and NO metabolites compared to nonischemic limbs. Use of the NO scavenger carboxy PTIO completely abolished sodium nitrite-dependent ischemic tissue blood flow and angiogenic activity consistent with nitrite reduction to NO being the proangiogenic mechanism. These data demonstrate that chronic sodium nitrite therapy is a recently discovered therapeutic treatment for peripheral artery disease and critical limb ischemia.

Thrombospondin-1 stimulates platelet aggregation by blocking the antithrombotic activity of nitric oxide/cGMP signaling

Platelet alpha-granules constitute the major rapidly releasable reservoir of thrombospondin-1 in higher animals. Although some fragments and peptides derived from thrombospondin-1 stimulate or inhibit platelet aggregation, its physiologic function in platelets has remained elusive. We now show that endogenous thrombospondin-1 is necessary for platelet aggregation in vitro in the presence of physiologic levels of nitric oxide (NO). Exogenous NO or elevation of cGMP delays thrombin-induced platelet aggregation under high shear and static conditions, and exogenous thrombospondin-1 reverses this delay. Thrombospondin-1-null murine platelets fail to aggregate in response to thrombin in the presence of exogenous NO or 8Br-cGMP. At physiologic concentrations of the NO synthase substrate arginine, thrombospondin-1-null platelets have elevated basal cGMP. Ligation of CD36 or CD47 is sufficient to block NO-induced cGMP accumulation and mimic the effect of thrombospondin-1 on aggregation. Exogenous thrombospondin-1 also reverses the suppression by NO of alphaIIb/beta3 integrin-mediated platelet adhesion on immobilized fibrinogen, mediated in part by increased GTP loading of Rap1. Thrombospondin-1 also inhibits cGMP-mediated activation of cGMP-dependent protein kinase and thereby prevents phosphorylation of VASP. Thus, release of thrombospondin-1 from alpha-granules during activation provides positive feedback to promote efficient platelet aggregation and adhesion by overcoming the antithrombotic activity of physiologic NO.

Down-regulation of matrix metalloproteinase-9 expression by nitric oxide in lipopolysaccharide-stimulated rat primary astrocytes

Immunologically activated astrocytes over-express matrix metalloproteinase-9 (MMP-9) and nitric oxide (NO). Because they have both beneficial and detrimental effects on the pathophyiological outcomes of several neurological diseases, their expression should be tightly regulated in the CNS. NO can modify the activity of other proteins either by directly modifying protein structure or regulating the expression of target proteins. In this study, we investigated the role of NO on the expression of MMPs in rat primary astrocytes. Rat primary astrocytes were stimulated with lipopolysaccharide (LPS), resulting in the over-expression of both MMP-9 and NO. Inhibition of NO production using nitric oxide synthase inhibitor, Nomega-nitro-l-arginine methyl ester (l-NAME), further increased MMP-9 expression, suggesting NO inhibits MMP-9 expression. In line with this observation, exogenous addition of NO donor, sodium nitroprusside (SNP) or S-nitroso-N-acetylpenicillamine (SNAP), inhibited MMP-9 expression in astrocytes. The inhibitory effect of NO was mediated by the down-regulation of mRNA and protein levels of MMP-9 but not by the direct modification of the enzymatic activity of MMP-9. The effect of NO on MMP-9 expression was mimicked by dibutyryl-cGMP and inhibited by PKG inhibitor KT5823, suggesting NO regulates MMP-9 expression via guanylate cyclase-PKG pathway. Finally, SNP or dibutyryl-cGMP inhibited the activation of ERK1/2 in LPS-stimulated astrocytes, which is an essential regulator of MMP-9 expression in astrocytes. The regulation of MMP-9 expression by NO may confer additional levels of fine-tuning of the level of MMP-9 during brain inflammatory conditions.

Tumor Necrosis Factor Receptor 2–Mediated Tumor Suppression Is Nitric Oxide Dependent and Involves Angiostasis

Tumor necrosis factor (TNF) binds to two different receptors. Although most of its functions are attributed to TNF receptor 1 (TNFR1), the independent role of TNFR2 is still largely unknown. Using TNFR single or double knock-out mice, we show here that the expression of TNFR2 alone on host cells was sufficient to suppress the growth of TNF-secreting tumors in both immune competent and T/B lymphocyte-deficient severe combined immunodeficiency (SCID) mice. Histologic studies showed that TNF recruited, via TNFR2, large numbers of macrophages and efficiently inhibited angiogenesis in the tumor. In vitro, TNF activated TNFR1-deficient macrophages to produce nitric oxide (NO). Treatment of TNFR1 knock-out mice with L-NAME, a specific NO synthase inhibitor, almost completely eliminated TNF-induced angiostasis and tumor suppression. Moreover, L-NAME acted only during the first few days of tumor growth. Our results show for the first time that TNFR2 expressed on host innate immune cells is sufficient to mediate the antitumor effect of TNF, and NO is necessary for this process, possibly by inhibition of angiogenesis in the tumor.