Tumor Cell-Derived Nitric Oxide Is Involved in the Immune-Rejection of an Immunogenic Murine Lymphoma

Effects of fasting on serial measurements of hyperpolarized [1-(13) C]pyruvate metabolism in tumors

Imaging of the metabolism of hyperpolarized [1-(13) C]pyruvate has shown considerable promise in preclinical studies in oncology, particularly for the assessment of early treatment response. The repeatability of measurements of (13) C label exchange between pyruvate and lactate was determined in a murine lymphoma model in fasted and non-fasted animals. The fasted state showed lower intra-individual variability, although the [1-(13) C]lactate/[1-(13) C]pyruvate signal ratio was significantly greater in fasted than in non-fasted mice, which may be explained by the higher tumor lactate concentrations in fasted animals. These results indicate that the fasted state may be preferable for the measurement of (13) C label exchange between pyruvate and lactate, as it reduces the variability and therefore should make it easier to detect the effects of therapy. © 2016 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.

NOS-2 Inhibition in Phosgene-Induced Acute Lung Injury

Phosgene exposure via an industrial or warfare release produces severe acute lung injury (ALI) with high mortality, characterized by massive pulmonary edema, disruption of epithelial tight junctions, surfactant dysfunction, and oxidative stress. There are no targeted treatments for phosgene-induced ALI. Previous studies demonstrated that nitric oxide synthase 2 (NOS-2) is upregulated in the lungs after phosgene exposure; however, the role of NOS-2 in the pathogenesis of phosgene-induced ALI remains unknown. We previously demonstrated that NOS-2 expression in lung epithelium exacerbates inhaled endotoxin-induced ALI in mice, mediated partially through downregulation of surfactant protein B (SP-B) expression. Therefore, we hypothesized that a selective NOS-2 inhibitor delivered to the lung epithelium by inhalation would mitigate phosgene-induced ALI. Inhaled phosgene produced increases in bronchoalveolar lavage fluid protein, histologic lung injury, and lung NOS-2 expression at 24 h. Administration of the selective NOS-2 inhibitor 1400 W via inhalation, but not via systemic delivery, significantly attenuated phosgene-induced ALI and preserved epithelial barrier integrity. Furthermore, aerosolized 1400 W augmented expression of SP-B and prevented downregulation of tight junction protein zonula occludens 1 (ZO-1), both critical for maintenance of normal lung physiology and barrier integrity. We also demonstrate for the first time that NOS-2-derived nitric oxide downregulates the ZO-1 expression at the transcriptional level in human lung epithelial cells, providing a novel target for ameliorating vascular leak in ALI. Our data demonstrate that lung NOS-2 plays a critical role in the development of phosgene-induced ALI and suggest that aerosolized NOS-2 inhibitors offer a novel therapeutic strategy for its treatment.

CTL induction of tumoricidal nitric oxide production by intratumoral macrophages is critical for tumor elimination

To characterize mechanisms of CTL inhibition within an ocular tumor microenvironment, tumor-specific CTLs were transferred into mice with tumors developing within the anterior chamber of the eye or skin. Ocular tumors were resistant to CTL transfer therapy whereas skin tumors were sensitive. CTLs infiltrated ocular tumors at higher CTL/tumor ratios than in skin tumors and demonstrated comparable ex vivo effector function to CTLs within skin tumors indicating that ocular tumor progression was not due to decreased CTL accumulation or inhibited CTL function within the eye. CD11b(+)Gr-1(+)F4/80(-) cells predominated within ocular tumors, whereas skin tumors were primarily infiltrated by CD11b(+)Gr-1(-)F4/80(+) macrophages (Ms), suggesting that myeloid derived suppressor cells may contribute to ocular tumor growth. However, CD11b(+) myeloid cells isolated from either tumor site suppressed CTL activity in vitro via NO production. Paradoxically, the regression of skin tumors by CTL transfer therapy required NO production by intratumoral Ms indicating that NO-producing intratumoral myeloid cells did not suppress the effector phase of CTL. Upon CTL transfer, tumoricidal concentrations of NO were only produced by skin tumor-associated Ms though ocular tumor-associated Ms demonstrated comparable expression of inducible NO synthase protein suggesting that NO synthase enzymatic activity was compromised within the eye. Correspondingly, in vitro-activated Ms limited tumor growth when co-injected with tumor cells in the skin but not in the eye. In conclusion, the decreased capacity of Ms to produce NO within the ocular microenvironment limits CTL tumoricidal activity allowing ocular tumors to progress.

Exhaled nitric oxide and nitric oxide synthase expression in Hodgkin's disease

Hodgkin's disease (HD) is a malignant lymphoma with frequent mediastinal involvement, characterized by a significant inflammatory infiltration. Exhaled nitric oxide (FENO), is present in healthy humans, and has been proven to be increased in eosinophilic diseases such as allergic asthma. We investigated whether FENO is increased in mediastinal HD and whether NO is produced by lymphoma tissue. To this aim FENO was measured in 56 HD patients, 17 with and 39 without bulky mediastinal involvement, in the period from January 2007 to December 2008. Thirty-seven patients were reassessed after remission. Lymph node biopsies of 10 patients were evaluated for inducible (iNOS) and constitutive (eNOS) nitric oxide synthase expression by immunohistochemistry. FENO resulted significantly related to the mediastinal mass maximum diameter (p=0.009) and was significantly higher in patients with as compared to those without bulky mediastinal disease (38.7 ppb, CI 95% 19.3-58.0, versus 20.7 ppb, CI 95% 16.6-24.7; p=0.009). iNOS and eNOS immunoreactivity was observed in tumour and inflammatory cells (eosinophils and histiocytes). Only in patients with bulky mediastinal HD there was a significant decrease in FENO (from 50.4 ppb CI 95% 18.0-82.8 to 11.1 ppb CI 95% 4.4-17.8, p=0.011). In conclusion, high FENO and NOS expression in lymph-nodes indicate that NO is a component of the inflammatory network of HD. FENO may be proposed for the assessment and follow up of bulky mediastinal HD patients.

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.

Genetic polymorphisms in nitric oxide synthase genes modify the relationship between vegetable and fruit intake and risk of non-Hodgkin lymphoma

Oxidative damage caused by reactive oxygen species and other free radicals is involved in carcinogenesis. It has been suggested that high vegetable and fruit intake may reduce the risk of non-Hodgkin lymphoma (NHL) as vegetables and fruit are rich in antioxidants. The aim of this study is to evaluate the interaction of vegetable and fruit intake with genetic polymorphisms in oxidative stress pathway genes and NHL risk. This hypothesis was investigated in a population-based case-control study of NHL and NHL histologic subtypes in women from Connecticut, including 513 histologically confirmed incident cases and 591 randomly selected controls. Gene-vegetable/fruit joint effects were estimated using unconditional logistic regression model. The false discovery rate method was applied to adjust for multiple comparisons. Significant interactions with vegetable and fruit intake were mainly found for genetic polymorphisms on nitric oxide synthase (NOS) genes among those with diffuse large B-cell lymphoma and follicular lymphoma. Two single nucleotide polymorphisms in the NOS1 gene were found to significantly modify the association between total vegetable and fruit intake and risk of NHL overall, as well as the risk of follicular lymphoma. When vegetables, bean vegetables, cruciferous vegetables, green leafy vegetables, red vegetables, yellow/orange vegetables, fruit, and citrus fruits were examined separately, strong interaction effects were narrowed to vegetable intake among patients with diffuse large B-cell lymphoma. Our results suggest that genetic polymorphisms in oxidative stress pathway genes, especially in the NOS genes, modify the association between vegetable and fruit intake and risk of NHL.

Regulation of nitric oxide signalling by thrombospondin 1: implications for anti-angiogenic therapies

In addition to long-term regulation of angiogenesis, angiogenic growth factor signalling through nitric oxide (NO) acutely controls blood flow and haemostasis. Inhibition of this pathway may account for the hypertensive and pro-thrombotic side effects of the vascular endothelial growth factor antagonists that are currently used for cancer treatment. The first identified endogenous angiogenesis inhibitor, thrombospondin 1, also controls tissue perfusion, haemostasis and radiosensitivity by antagonizing NO signalling. We examine the role of these and other emerging activities of thrombospondin 1 in cancer. Clarifying how endogenous and therapeutic angiogenesis inhibitors regulate vascular NO signalling could facilitate development of more selective inhibitors.

Nitric oxide, apoptosis and macrophage polarization during tumor progression

Decreased oxygen availability evokes adaptive responses, which are primarily under the gene regulatory control of hypoxia inducible factor-1 (HIF-1). Hypoxic cores of a growing tumor cell mass use this signaling circuit to gain access to further blood and nutrient supply that guarantees their continuing growth. Interestingly, NO shares with hypoxia the ability to block prolyl-hydroxylase (PHD) activity, and thus the ability to stabilize hypoxia inducible factor 1 alpha (HIF-1 alpha). Under these conditions NO mimics hypoxia, which might contribute to tumor development. Stimulating/triggering innate immune responses associated with macrophage activation often correlated with iNOS induction and massive NO release, which is known to kill NO-sensitive tumors. However, this safeguard mechanism will only be effective if all tumor cells are eliminated because apoptotic death of tumor cells implies mechanisms to stop macrophages from attacking the survivors. Apoptotic cells release factors, among others sphingosine-1-phosphate (S1P), which reprogram macrophages. Macrophage reprogramming shifts responses from a M1 and thus pro-inflammatory and killing phenotype, to a M2 phenotype, which is anti-inflammatory and pro-angiogenic. These polarized tumor associated macrophages (TAM) are actively contributing to tumor development. Apparently NO uses distinct signaling pathways that could serve as an explanation to understand how NO affects tumor development. Some of these pathways, especially the ability of NO to mimic hypoxia at the level of HIF-1 alpha, as well as the role of macrophage polarization by apoptotic cells with accompanying changes in the iNOS versus arginase ratio and activities, will be discussed to better understand how NO affects tumor growth.

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.

Nitric oxide, a double edged sword in cancer biology: Searching for therapeutic opportunities

Nitric oxide (NO) is a pleiotropic molecule critical to a number of physiological and pathological processes. The last decade has witnessed major advances in dissecting NO biology and its role in cancer pathogenesis. However, the complexity of the interactions between different levels of NO and several aspects of tumor development/progression has led to apparently conflicting findings. Furthermore, both anti-NO and NO-based anticancer strategies appear effective in several preclinical models. This paradoxical dichotomy is leaving investigators with a double challenge: to determine the net impact of NO on cancer behavior and to define the therapeutic role of NO-centered anticancer strategies. Only a comprehensive and dynamic view of the cascade of molecular and cellular events underlying tumor biology and affected by NO will allow investigators to exploit the potential antitumor properties of drugs interfering with NO metabolism. Available data suggest that NO should be considered neither a universal target nor a magic bullet, but rather a signal transducer to be modulated according to the molecular makeup of each individual cancer and the interplay with conventional antineoplastic agents.

Uric acid nephrolithiasis: proton titration of an essential molecule?

PURPOSE OF REVIEW

The majority of uric acid nephrolithiasis in humans occurs in the absence of frank hyperuricosuria and is primarily a disease of excessively low urinary pH. Uric acid is substantially less soluble than urate salts so in low urine pH urate is protonated, thus favoring precipitation even under what is considered physiologic concentrations of total urinary uric acid/urate. This commentary examines the rationales behind the existence of uric acid in urine and body fluids in vertebrate evolution.

RECENT FINDINGS

The purpose of uric acid in arthropod, avian and reptilian species is to enable nitrogen excretion in solid state without loss of water. The re-emergence of uric acid in higher primates as an end product of metabolism is intriguing since urea functions perfectly well as a nitrogenous waste. Uric acid must purvey important physiologic functions in primate biology. Numerous roles of uric acid as an antioxidant, immune signaling molecule, and a defender of circulatory integrity have recently been proposed.

SUMMARY

There is little doubt that uric acid serves multiple important functions in higher primates. It is also conceivable, however, that this important molecule when present in the wrong concentration or context can lead to undesirable phenotypes.

The radiosensitizing effect of immunoadjuvant OM-174 requires cooperation between immune and tumor cells through interferon-gamma and inducible nitric oxide synthase

PURPOSE

To explore whether antitumor immunoadjuvant OM-174 can stimulate immune cells to produce interferon-gamma (IFN-gamma) and thereby radiosensitize tumor cells.

METHODS AND MATERIALS

Splenocytes from BALB/c mice were stimulated by OM-174 at plasma-achievable concentrations (0.03-3 mug/mL), and afterward analyzed for the expression and secretion of IFN-gamma by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Stimulated splenocytes were used as a source of IFN-gamma to radiosensitize hypoxic EMT-6 tumor cells through the cytokine-inducible isoform of nitric oxide synthase (iNOS).

RESULTS

OM-174 activated the production of IFN-gamma at high levels that reached 70 ng/mL in normoxia (21% oxygen) and 27 ng/mL in tumor-relevant hypoxia (1% oxygen). This caused up to 2.1-fold radiosensitization of EMT-6 tumor cells, which was associated with the iNOS-mediated production of the radiosensitizing molecule nitric oxide, as confirmed by accumulation of its oxidative metabolite nitrite, Western blot analysis, and reverse transcriptase-polymerase chain reaction. Both iNOS activation and radiosensitization were counteracted by neutralizing antibodies against IFN-gamma. The same mechanism of radiosensitization through the IFN-gamma secretion pathway was identified for IL-12 + IL-18, which are known to mediate IFN-gamma responses. Hypoxia displayed a dual effect on the immune-tumor cell interaction, by downregulating the expression of the IFN-gamma gene while upregulating iNOS at transcriptional level.

CONCLUSION

Immunoadjuvant OM-174 is an efficient radiosensitizer of tumor cells through activation of the IFN-gamma secretion pathway in immune cells. This finding indicates a rationale for combining immunostimulatory and radiosensitizing strategies and extends the potential therapeutic applications of OM-174.

IFN-γ Regulates Donor CD8 T Cell Expansion, Migration, and Leads to Apoptosis of Cells of a Solid Tumor

We previously reported that IFN-gamma secreted by donor cytotoxic T cell 1 (Tc1) cells was the most important factor in promoting EG7 (an OVA transfection the EL4 thymoma) rejection in mice. In this study, we show that the ability of the host to respond to Tc1-secreted IFN-gamma is critical for promoting acute tumor rejection, while host production of IFN-gamma is not important. CFSE-labeled wild-type and IFN-gamma-deficient Tc1 cells divide rapidly in secondary lymphoid organs, indicating no defect in rate of cell division. However, wild-type Tc1 cells accumulate to significantly greater numbers in the tumor than deficient Tc1 cells. Hosts injected with wild-type Tc1 effectors had more T cells within the tumor at day 4, had higher levels of MCP-1, IFN-gamma-inducible protein-10, MIP-1alpha, and MIP-1beta mRNA transcripts, had greater numbers of CD11b+ and Gr-1+ cells within the tumor, and had massive regions of tumor cell apoptosis as compared with IFN-gamma knockout Tc1 cell-treated hosts. NO has a cytostatic effect on EG7 growth in vitro, and NO is important for tumor eradication by day 22. These observations are compatible with a model in which the donor CD8 Tc1 effectors expand rapidly in the host, migrate to the tumor site, and induce the secretion of a number of chemokines that in turn recruit host cells that then attack the tumor.

Genetic polymorphisms of eNOS, hormone receptor status, and survival of breast cancer

The endothelial cell-specific form of nitric oxide synthase (eNOS) may play an important role in tumor progression via angiogenesis or apoptosis. We studied eNOS -786T > C and 894G > T (Glu298Asp), two functionally significant SNPs, in relation to hazard of breast cancer recurrence or death in 873 women with incident, non-metastatic breast cancer, recruited from two teaching hospitals in Seoul, Korea, 1995-2002. Hazards were estimated by Cox proportional hazard models, in relation to genotype, adjusting for hormone receptor status, lymph node involvement, and tumor size. Women carriers of the eNOS -786C allele had significantly increased hazards of breast cancer recurrence or death, compared with women having the TT genotype (HR = 2.1, 95% CI = 1.03-4.33); risks increased up to 3-fold in ER positive cases (HR = 3.2, 95% CI = 0.95-10.50). The hazard was also increased in eNOS 894T carriers, however, it did not reach statistical significance (HR = 1.8, 95% CI = 0.85-3.93). The combined genotypes containing -786C or 894T was associated with a 2.5-fold risk, compared to the TT-GG genotypes, the most dominant genotype combination (95% CI = 1.29-4.68), with the greatest risks in ER positive cases (HR = 4.9, 95% CI = 1.31-18.36). These results indicate that the eNOS -786C polymorphism, and possibly the 894T polymorphism, are associated with breast cancer recurrence and death, particularly in women with ER positive tumors.

Immune cell-induced synthesis of NO and reactive oxygen species in lymphoma cells causes their death by apoptosis

Induction of apoptosis in a lymphoma cell line using immune cell-conditioned medium, etoposide or an nitric oxide (NO) donor, resulted in the production of reactive oxygen species (ROS). Agents that inhibited NO production or scavenged ROS or species formed by reaction of NO with ROS, protected the cells from apoptosis. These data support the suggestion that immune rejection of an immunogenic derivative of this lymphoma in vivo involves the induced synthesis of both NO and ROS by the tumour cells.

Monitoring T-lymphocyte trafficking in tumors undergoing immune rejection

Activated T cells, isolated from animals that had rejected a tumor (E.G7-OVA) expressing chicken ovalbumin, were labeled with citrated superparamagnetic iron oxide nanoparticles at an intracellular iron concentration of up to 0.5 pg/cell. Injection of these labeled T cells into animals bearing E.G7-OVA tumors undergoing immune rejection resulted in tumor infiltration of these cells, which was detectable as a heterogeneous decrease in intensity in T(2)-weighted MR images. T-cell infiltration was confirmed by immunohistochemical staining of tumor sections obtained postmortem and was shown to colocalize with iron that had been stained using Prussian blue. Tumor rejection was correlated with the uptake of labeled T cells, since the infiltration of labeled T cells was only observed in those tumors that went on to regress. This technique should assist in the elucidation of those factors that are important in mediating tumor immune rejection.

Uric acid promotes tumor immune rejection

Uric acid released from dying cells has been shown recently to act as a danger signal for the immune system, stimulating dendritic cell maturation and enhancing T-cell responses to foreign antigens. Stimulation of dendritic cell maturation by uric acid has been proposed as a mechanism by which the immune system could generate responses against tumors. We show here that uric acid levels are elevated in tumors undergoing immune rejection and that the inhibition of uric acid production, by systemic administration of allopurinol, or the removal of uric acid, by administration of uricase, delayed tumor immune rejection, whereas subcutaneous administration of crystalline uric acid enhanced the rejection process.