iNOS as a therapeutic target for treatment of human tumors. Nitric Oxide. 2008;19:217-224. [PMID: 18515106 DOI: 10.1016/j.niox.2008.05.001]

Positron Emission Tomography of Nitric Oxide by a Specific Radical-Generating Dihydropyridine Tracer

Nitric oxide (NO) plays a pivotal role as a biological signaling molecule, presenting challenges in its specific detection and differentiation from other reactive nitrogen and oxygen species within living organisms. Herein, a 18F-labeled (fluorine-18, t1/2 = 109.7 min) small-molecule tracer dimethyl 4-(4-(4-[18F]fluorobutoxy)benzyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate ([18F]BDHP) is developed based on the dihydropyridine scaffold for positron emission tomography (PET) imaging of NO in vivo. [18F]BDHP exhibits a highly sensitive and efficient C-C cleavage reaction specifically triggered by NO under physiological conditions, leading to the production of a 18F-labeled radical that is readily retained within the cells. High uptakes of [18F]BDHP are found within and around NO-generating cells, such as macrophages treated with lipopolysaccharide or benzo(a)pyrene. MicroPET/CT imaging of arthritic animal model mice reveals distinct tracer accumulation in the arthritic legs, showcasing a higher distribution of NO compared with the control legs. In summary, a specific radical-generating dihydropyridine tracer with a unique radical retention strategy has been established for the marking of NO in real-time in vivo.

Myoglobin mutant with enhanced nitrite reductase activity regulates intracellular oxidative stress in human breast cancer cells

Heme proteins play vital roles in regulating the reactive oxygen/nitrogen species (ROS/RNS) levels in cells. In this study, we overexpressed human wild-type (WT) myoglobin (Mb) and its double mutant, F43H/H64A Mb with enhanced nitrite reductase (NIR) activity, in the typical representative triple-negative breast cancer cell, MDA-MB-231 cells. The results showed that the overexpression of F43H/H64A Mb increased the level of nitric oxide (NO) and the degree of oxidative stress, and then activated Akt/MAPK mediated apoptotic cascade, whereas WT Mb showed the opposite effect. This study indicates that Mb plays an important role in maintaining the balance of the cellular redox system and could thus be a valuable target for cancer therapy.

Hepatocellular Protein Arginine Methyltransferase 1 Suppresses Alcohol-Induced Hepatocellular Carcinoma Formation by Inhibition of Inducible Nitric Oxide Synthase

Alcohol is a well-established risk factor for hepatocellular carcinoma (HCC), but the mechanisms by which alcohol promotes liver cancer are not well understood. Studies suggest that ethanol may enhance tumor progression by increasing hepatocyte proliferation and through alcohol-induced liver inflammation. Protein arginine methyltransferase 1 (PRMT1) is the main enzyme responsible for cellular arginine methylation. Asymmetric dimethyl arginine, produced by PRMT1, is a potent inhibitor of nitric oxide synthases. PRMT1 is implicated in the development of several types of tumors and cardiovascular disease. Our previous work has shown that PRMT1 in the liver regulates hepatocyte proliferation and oxidative stress and protects from alcohol-induced liver injury. However, its role in HCC development remains controversial. In this study, we found that hepatocyte-specific PRMT1-knockout mice develop an increased number of tumors in an N-nitrosodiethylamine (DEN) alcohol model of liver tumorigenesis in mice. This effect was specific to the alcohol-related component because wild-type and knockout mice developed similar tumor numbers in the DEN model without the addition of alcohol. We found that in the presence of alcohol, the increase in tumor number was associated with increased proliferation in liver and tumor, increased WNT/β-catenin signaling, and increased inflammation. We hypothesized that increased inflammation was due to increased oxidative and nitrosative stress in knockout mice. By blocking excess nitric oxide production using an inducible nitric oxide synthase inhibitor, we reduced hepatocyte death and inflammation in the liver and prevented the increase in WNT/β-catenin signaling, proliferation, and tumor number in livers of knockout mice. Conclusion: PRMT1 is an important protection factor from alcohol-induced liver injury, inflammation, and HCC development.

Stress hormone-mediated acceleration of breast cancer metastasis is halted by inhibition of nitric oxide synthase

Stress hormones have been shown to be important mediators in driving malignant growth and reducing treatment efficacy in breast cancer. Glucocorticoids can induce DNA damage through an inducible nitric oxide synthase (iNOS) mediated pathway to increase levels of nitric oxide (NO). Using an immune competent mouse breast cancer model and 66CL4 breast cancer cells we identified a novel role of NOS inhibition to reduce stress-induced breast cancer metastasis. On a mechanistic level we show that the glucocorticoid cortisol induces expression of keys genes associated with angiogenesis, as well as pro-tumourigenic immunomodulation. Transcriptomics analysis confirmed that in the lungs of tumour-bearing mice, stress significantly enriched pathways associated with tumourigenesis, some of which could be regulated with NOS inhibition. These results demonstrate the detrimental involvement of NOS in stress hormone signalling, and the potential future benefits of NOS inhibition in highly stressed patients.

The effect of nitric oxide on mitochondrial respiration

This article reviews the interactions between nitric oxide (NO) and mitochondrial respiration. Mitochondrial ATP synthesis is responsible for virtually all energy production in mammals, and every other process in living organisms ultimately depends on that energy production. Furthermore, both necrosis and apoptosis, that summarize the main forms of cell death, are intimately linked to mitochondrial integrity. Endogenous and exogenous •NO inhibits mitochondrial respiration by different well-studied mechanisms and several nitrogen derivatives. Instantaneously, low concentrations of •NO, specifically and reversibly inhibit cytochrome c oxidase in competition with oxygen, in several tissues and cells in culture. Higher concentrations of •NO and its derivatives (peroxynitrite, nitrogen dioxide or nitrosothiols) can cause irreversible inhibition of the respiratory chain, uncoupling, permeability transition, and/or cell death. Peroxynitrite can cause opening of the permeability transition pore and opening of this pore causes loss of cytochrome c, which in turn might contribute to peroxynitrite-induced inhibition of respiration. Therefore, the inhibition of cytochrome c oxidase by •NO may be involved in the physiological and/or pathological regulation of respiration rate, and its affinity for oxygen, which depend on reactive nitrogen species formation, pH, proton motriz force and oxygen supply to tissues.

Celastrol suppresses nitric oxide synthases and the angiogenesis pathway in colorectal cancer

The thunder god vine (Tripterygium wilfordii Hook. F) is traditionally used for inflammation-related diseases in traditional Chinese medicine. In recent years, celastrol (a natural compound from the root of the thunder god vine) has attracted great interest for its potential anticancer activities. The free radical nitric oxide (NO) is known to play a critical role in colorectal cancer growth by promoting tumour angiogenesis. However, how celastrol influences the NO pathway and its mechanism against colorectal cancer is largely unknown. In this study, we investigated the effects and mechanism of celastrol on nitric oxide synthase (NOS) and the angiogenesis pathway in colorectal cancer. Our data show that celastrol inhibited HT-29 and HCT116 cell proliferation, migration, and NOS activity in the cytoplasm. The antiproliferation activity of celastrol was associated with the inhibition of iNOS and eNOS in colorectal cancer cells. Treatment with celastrol inhibited colorectal cancer cell growth and migration, and was associated with suppression of the expression of key genes (TYMP, CDH5, THBS2, LEP, MMP9, and TNF) and proteins (IL-1b, MMP-9, PDGF, Serpin E1, and TIMP-4) involved in the angiogenesis pathway. In addition, combinational use of celastrol with 5-fluorouracil, salinomycin, 1400 W, and L-NIO showed enhanced inhibition of colorectal cancer cell proliferation and migration. In sum, our study suggests that celastrol could suppress colorectal cancer cell growth and migration, likely through suppressing NOS activity and inhibiting the angiogenesis pathway.

Purification and Characterization of a Novel Pentadecapeptide from Protein Hydrolysates of Cyclina sinensis and Its Immunomodulatory Effects on RAW264.7 Cells

In the present study, peptide fractions of Cyclina sinensis hydrolysates, with molecular weight (MW) < 3 kDa and highest relative proliferation rate of murine macrophage cell line RAW 264.7, were purified by a series of chromatographic purification methods, to obtain peptide fractions with immunomodulatory activity. The amino acid sequence of the peptide was identified to be Arg-Val-Ala-Pro-Glu-Glu-His-Pro-Val-Glu-Gly-Arg-Tyr-Leu-Val (RVAPEEHPVEGRYLV) with MW of 1750.81 Da, and the novel pentadecapeptide (named SCSP) was synthesized for subsequent immunomodulatory activity experiments. Results showed the SCSP enhanced macrophage phagocytosis, increased productions of nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β), and up-regulated the protein level of inducible nitric oxide synthase (iNOS), nuclear factor κB (NF-κB), and NOD-like receptor protein 3 (NLRP3) in RAW 264.7 cells. Furthermore, the expression of inhibitor of nuclear factor κB-α (IκB-α) was down-regulated. These findings suggest that SCSP might stimulate macrophage activities by activating the NF-κB signaling pathway and can be used as a potential immunomodulatory agent in functional food or medicine.

Function of miR-146a-5p in Tumor Cells As a Regulatory Switch between Cell Death and Angiogenesis: Macrophage Therapy Revisited

Tumors survive and progress by evading killing mechanisms of the immune system, and by generating a tumor microenvironment (TME) that reprograms macrophages in situ to produce factors that support tumor growth, angiogenesis, and metastasis. We have previously shown that by blocking the translation of the enzyme inducible nitric oxide synthase (iNOS), miR-146a-5p inhibits nitric oxide (NO) production in a mouse renal carcinoma cell line (RENCA), thereby endowing RENCA cells with resistance to macrophage-induced cell death. Here, we expand these findings to the mouse colon carcinoma CT26 cell line and demonstrate that neutralizing miR-146a-5p's activity by transfecting both RENCA and CT26 cells with its antagomir restored iNOS expression and NO production and enhanced susceptibility to macrophage-induced cell death (by 48 and 25%, respectively, p < 0.001). Moreover, miR-146a-5p suppression simultaneously inhibited the expression of the pro-angiogenic protein EMMPRIN (threefolds, p < 0.001), leading to reduced MMP-9 and vascular endothelial growth factor secretion (twofolds and threefolds, respectively, p < 0.05), and reduced angiogenesis, as estimated by in vitro tube formation and scratch assays. When we injected tumors with pro-inflammatory-stimulated RAW 264.7 macrophages together with i.v. injection of the miR-146a-5p antagomir, we found inhibited tumor growth (sixfolds, p < 0.001) and angiogenesis (twofolds, p < 0.01), and increased apoptosis (twofolds, p < 0.01). This combination therapy increased nitrites and reduced TGFβ concentrations in tumor lysates, alleviated immune suppression, and allowed enhanced infiltration of cytotoxic CD8⁺ T cells. Thus, miR-146a-5p functions as a control switch between angiogenesis and cell death, and its neutralization can manipulate the crosstalk between tumor cells and macrophages and profoundly change the TME. This strategy can be therapeutically utilized in combination with the macrophage therapy approach to induce the immune system to successfully attack the tumor, and should be further explored as a new therapy for the treatment of cancer.

Small molecule immuno-oncology therapeutic agents

Treatment of cancer by activation of an antitumor immune response is now a widely practiced and well-accepted approach to therapy. However, despite dramatic responses in some patients, the high proportion of unresponsive patients points to a considerable unmet medical need. Although antibody therapies have led the way, small molecule immuno-oncology agents are close behind. This perspective provides an overview of some of the many small molecule approaches being explored. It encompasses small molecule modulators of validated targets such as programed cell death 1 (PD-1) as well as novel approaches still to be proven clinically.

Clinical significance of HIF-1α expression in gastric malignant transformation in people from high altitude area of Qinghai

AIM

To detect the expression of hypoxia inducible factor-1α (HIF-1α) in gastric malignant transformation in people from high altitude area of Qinghai, China.

METHODS

RT-PCR was used to detect the expression of HIF-1α gene in 7 cell lines and 27 pairs of GC and matched tumor adjacent normal gastric mucosa tissues. Using tissue microarray including 57 normal gastric mucosa tissues, 37 chronic atrophic gastritis tissues, 34 intestinal metaplasia tissues, and 146 gastric cancer (GC) tissues, immunohistochemistry (IHC) was performed to detect the level of HIF-1α protein expression.

RESULTS

The expression of HIF-1α at the mRNA level was different in GC cell lines. HIF-1αexpression in AGS, SGC7901, and N87 cells was higher than that in MGC803, BGC823, PAMC82 and MKN45 cells. The level of HIF-1α expression was significantly higher in GC tissues (66.6%, 18/27) compared with normal gastric mucosa tissues (26.3%, 15/57; P < 0.001). IHC data showed that the positive rate of HIF-1α was 64.8% (24/37) in chronic atrophic gastritis tissues, 61.7% (21/34) in intestinal metaplasia tissues, and 56.8% (83/146) in GC tissues, all of which were significantly higher than that in normal tissues (26.3%, 15/57). Expression of HIF-1α was positively associated with age in GC (P < 0.05). Kaplan-Meier analysis showed that patients with a low level of HIF-1α had apparently better survival than those with a high level (P < 0.0001). HIF-1α protein (RR = 3.229, 95%CI: 2.024-5.151) was identified to be an independent risk factor for the outcome of GC patients.

CONCLUSION

High HIF-1α expression is associated with gastric malignant transformation and poor prognosis in high altitude areas.

Radiation enhances the therapeutic effect of Banoxantrone in hypoxic tumour cells with elevated levels of nitric oxide synthase

Banoxantrone (AQ4N) is a prototype hypoxia selective cytotoxin that is activated by haem containing reductases such as inducible nitric oxide synthase (iNOS). In the present study, we evaluate whether elevated levels of iNOS in human tumour cells will improve their sensitivity to AQ4N. Further, we examine the potential of radiation to increase cellular toxicity of AQ4N under normoxic (aerobic) and hypoxic conditions. We employed an expression vector containing the cDNA for human iNOS to transfect human fibrosarcoma HT1080 tumour cells. Alternatively, parental cells were exposed to a cytokine cocktail to induce iNOS gene expression and enzymatic activity. The cells were then treated with AQ4N alone and in combination with radiation in the presence or absence of the iNOS inhibitor N-methyl-L‑arginine. In parental cells, AQ4N showed little difference in toxicity under hypoxic verses normoxic conditions. Notably, cells with upregulated iNOS activity showed a significant increase in sensitivity to AQ4N, but only under conditions of reduced oxygenation. When these cells were exposed to the combination of AQ4N and radiation, there was much greater cell killing than that observed with either modality alone. In the clinical development of hypoxia selective cytotoxins it is likely they will be used in combination with radiotherapy. In the present study, we demonstrated that AQ4N can selectively kill hypoxic cells via an iNOS-dependent mechanism. This hypoxia-selective effect can be augmented by combining AQ4N with radiation without increasing cytotoxicity to well‑oxygenated tissues. Collectively, these results suggest that targeting hypoxic tumours with high levels of iNOS with a combination of AQ4N and radiotherapy could be a useful clinical therapeutic strategy.

Nitric oxide inhibition strategies

Nitric oxide is involved in many physiologic processes. There are efforts, described elsewhere in this volume, to deliver nitric oxide to tissues as a therapy. Nitric oxide also contributes to pathophysiologic processes. Inhibiting nitric oxide or its production can thus also be of therapeutic benefit. This article addresses such inhibitory strategies.

Sterols and triterpenoids as potential anti-inflammatories: Molecular docking studies for binding to some enzymes involved in inflammatory pathways

Triterpenes and sterols are good candidates for the development of anti-inflammatory drugs and use in chemoprevention or chemotherapy of cancer via the interaction with therapeutic targets related to inflammation, such as COX-1 and -2; LOX-5; MPO, PLA2 and i-NOS. In this study, we use molecular docking to evaluate the potential binding of a database of selected sterol and triterpenoid compounds with several skeletons against enzymes related to inflammation to propose structural requirements beneficial for anti-inflammatory activity that can be used for the design of more potent and selective anti-inflammatory and antitumor drugs. Our results suggest that the substitution pattern is important and that there is an important relationship between the class of sterol or triterpenoid skeleton and enzyme binding.

Nitric oxide synthase: non-canonical expression patterns

Science can move ahead by questioning established or canonical views and, so it may be with the enzymes, nitric oxide synthases (NOS). Nitric oxide (NO) is generated by NOS isoforms that are often described by their tissue-specific expression patterns. NOS1 (nNOS) is abundant in neural tissue, NOS2 is upregulated in activated macrophages and known as inducible NOS (iNOS), and NOS3 (eNOS) is abundant in endothelium where it regulates vascular tone. These isoforms are described as constitutive or inducible, but in this perspective we question the broad application of these labels. Are there instances where "constitutive" NOS (NOS1 and NOS3) are inducibly expressed; conversely, are there instances where NOS2 is constitutively expressed? NOS1 and NOS3 inducibility may be linked to post-translational regulation, making their actual patterns activity much more difficult to detect. Constitutive NOS2 expression has been observed in several tissues, especially the human pulmonary epithelium where it may regulate airway tone. These data suggest that expression of the three NOS enzymes may include non-established patterns. Such information should be useful in designing strategies to modulate these important enzymes in different disease states.

Delivery of nitric oxide to the interior of mammalian cell by carbon nanotube: MD simulation

Computer simulations have been performed to study the nanoindentation of phospholipid bilayer by the single-walled armchair carbon nanotube, filled with the nitric oxide molecules. The process has been simulated by means of molecular dynamics (MD) technique at physiological temperature T = 310 K with a constant pulling velocity of the nanotube. The force acting on the nanotube during membrane penetration has been calculated. We show that the indentation by carbon nanotube does not permanently destroy the membrane structure (self-sealing of the membrane occurs). The mobility of nitric oxide molecules during the membrane nanoindentation is discussed.

Nitric oxide synthase 2 (NOS2) expression in histologically normal margins of oral squamous cell carcinoma

The activity of Nitric Oxide Synthase 2 (NOS2) was found in oral squamous cell carcinomas (OSCC) but not in normal mucosa. Molecular changes associated to early carcinogenesis have been found in mucosa near carcinomas, which is considered a model to study field cancerization. The aim of the present study is to analyze NOS2 expression at the histologically normal margins of OSCC.

STUDY DESIGN

Eleven biopsy specimens of OSCC containing histologically normal margins (HNM) were analyzed. Ten biopsies of normal oral mucosa were used as controls. The activity of NOS2 was determined by immunohistochemistry. Salivary nitrate and nitrite as well as tobacco and alcohol consumption were also analyzed. The Chi-squared test was applied.

RESULTS

Six out of the eleven HNM from carcinoma samples showed positive NOS2 activity whereas all the control group samples yielded negative (p=0.005). No statistically significant association between enzyme expression and tobacco and/or alcohol consumption and salivary nitrate and nitrite was found.

CONCLUSION

NOS2 expression would be an additional evidence of alterations that may occur in a state of field cancerization before the appearance of potentially malignant morphological changes.

The emerging immunological role of post-translational modifications by reactive nitrogen species in cancer microenvironment

Under many inflammatory contexts, such as tumor progression, systemic and peripheral immune response is tailored by reactive nitrogen species (RNS)-dependent post-translational modifications, suggesting a biological function for these chemical alterations. RNS modify both soluble factors and receptors essential to induce and maintain a tumor-specific immune response, creating a “chemical barrier” that impairs effector T cell infiltration and functionality in tumor microenvironment and supports the escape phase of cancer. RNS generation during tumor growth mainly depends on nitric oxide production by both tumor cells and tumor-infiltrating myeloid cells that constitutively activate essential metabolic pathways of l-arginine catabolism. This review provides an overview of the potential immunological and biological role of RNS-induced modifications and addresses new approaches targeting RNS either in search of novel biomarkers or to improve anti-cancer treatment.

Anti-inflammatory effects of 81 chinese herb extracts and their correlation with the characteristics of traditional chinese medicine

Inducible nitrogen oxide synthase (iNOS) is the primary contributor of the overproduction of nitric oxide and its inhibitors have been actively sought as effective anti-inflammatory agents. In this study, we prepared 70% ethanol extracts from 81 Chinese herbs. These extracts were subsequently evaluated for their effect on nitrogen oxide (NO) production and cell growth in LPS/IFNγ-costimulated and unstimulated murine macrophage RAW264.7 cells by Griess reaction and MTT assay. Extracts of Daphne genkwa Sieb.et Zucc, Caesalpinia sappan L., Iles pubescens Hook.et Arn, Forsythia suspensa (Thunb.) Vahl, Zingiber officinale Rosc, Inula japonica Thunb., and Ligusticum chuanxiong Hort markedly inhibited NO production (inhibition > 90% at 100 μg/mL). Among active extracts (inhibition > 50% at 100 μg/mL), Rubia cordifolia L., Glycyrrhiza glabra L., Iles pubescens Hook.et Arn, Nigella glandulifera Freyn et Sint, Pueraria lobata (Willd.) Ohwi, and Scutellaria barbata D. Don displayed no cytotoxicity to unstimulated RAW246.7 cells while increasing the growth of LPS/IFNγ-costimulated cells. By analyzing the correlation between their activities and their Traditional Chinese Medicine (TCM) characteristics, herbs with pungent flavor displayed potent anti-inflammatory capability. Our study provides a series of potential anti-inflammatory herbs and suggests that herbs with pungent flavor are candidates of effective anti-inflammatory agents.

Inhibition of Raf-MEK-ERK and hypoxia pathways by Phyllanthus prevents metastasis in human lung (A549) cancer cell line

BACKGROUND

Lung cancer constitutes one of the malignancies with the greatest incidence and mortality rates with 1.6 million new cases and 1.4 million deaths each year. Prognosis remains poor due to deleterious development of multidrug resistance resulting in less than 15% lung cancer patients reaching five years survival. We have previously shown that Phyllanthus induced apoptosis in conjunction with its antimetastastic action. In the current study, we aimed to determine the signaling pathways utilized by Phyllanthus to exert its antimetastatic activities.

METHODS

Cancer 10-pathway reporter array was performed to screen the pathways affected by Phyllanthus in lung carcinoma cell line (A549) to exert its antimetastatic effects. Results from this array were then confirmed with western blotting, cell cycle analysis, zymography technique, and cell based ELISA assay for human total iNOS. Two-dimensional gel electrophoresis was subsequently carried out to study the differential protein expressions in A549 after treatment with Phyllanthus.

RESULTS

Phyllanthus was observed to cause antimetastatic activities by inhibiting ERK1/2 pathway via suppression of Raf protein. Inhibition of this pathway resulted in the suppression of MMP2, MMP7, and MMP9 expression to stop A549 metastasis. Phyllanthus also inhibits hypoxia pathway via inhibition of HIF-1α that led to reduced VEGF and iNOS expressions. Proteomic analysis revealed a number of proteins downregulated by Phyllanthus that were involved in metastatic processes, including invasion and mobility proteins (cytoskeletal proteins), transcriptional proteins (proliferating cell nuclear antigen; zinc finger protein), antiapoptotic protein (Bcl2) and various glycolytic enzymes. Among the four Phyllanthus species tested, P. urinaria showed the greatest antimetastatic activity.

CONCLUSIONS

Phyllanthus inhibits A549 metastasis by suppressing ERK1/2 and hypoxia pathways that led to suppression of various critical proteins for A549 invasion and migration.

The radiosensitizing effect of CpG ODN107 on human glioma cells is tightly related to its antiangiogenic activity via suppression of HIF-1α/VEGF pathway

Malignant glioma displays invasive growth and is difficult to be completely excised; surgery combined with subsequent radiotherapy is a standard treatment for patients. CpG oligodeoxynucleotides (CpG ODN) can enhance radiotherapeutic effect in some tumors. Angiogenesis is crucial for tumor progression and metastasis. Anti-angiogenic strategy thus may be effective for tumor treatment. Herein, the antiangiogenic activity and radiosensitizing effect of CpG ODN107 on glioma were investigated. Our results showed that the growth of glioma cell line U87 was significantly inhibited by CpG ODN107 (10μg/ml) in combination with irradiation (5Gy) in vitro. In orthotopic implantation model of nude mice, the survival rate of mice significantly increased after treatment with CpG ODN107 (0.083mg/kg) in combination with radiotherapy (10Gy) as compared with treatment with local radiotherapy alone. CpG ODN107 in combination with radiotherapy significantly decreased microvessel density (MVD), VEGF level and HIF-1α expression in orthotopic implantation glioma. In conclusion, CpG ODN107 significantly increased the radiosensitivity of U87 human glioma cells in vitro and in vivo. The radiosensitizing effect of CpG ODN 107 is tightly related to its anti-angiogenic activity via suppression of HIF-1α/VEGF pathway.

Macrophage-tumor cell interactions regulate the function of nitric oxide

Tumor cell-macrophage interactions change as the tumor progresses, and the generation of nitric oxide (NO) by the inducible nitric oxide synthase (iNOS) plays a major role in this interplay. In early stages, macrophages employ their killing mechanisms, particularly the generation of high concentrations of NO and its derivative reactive nitrogen species (RNS) to initiate tumor cell apoptosis and destroy emerging transformed cells. If the tumor escapes the immune system and grows, macrophages that infiltrate it are reprogramed in situ by the tumor microenvironment. Low oxygen tensions (hypoxia) and immunosuppressive cytokines inhibit iNOS activity and lead to production of low amounts of NO/RNS, which are pro-angiogenic and support tumor growth and metastasis by inducing growth factors (e.g., VEGF) and matrix metalloproteinases (MMPs). We review here the different roles of NO/RNS in tumor progression and inhibition, and the mechanisms that regulate iNOS expression and NO production, highlighting the role of different subtypes of macrophages and the microenvironment. We finally claim that some tumor cells may become resistant to macrophage-induced death by increasing their expression of microRNA-146a (miR-146a), which leads to inhibition of iNOS translation. This implies that some cooperation between tumor cells and macrophages is required to induce tumor cell death, and that tumor cells may control their fate. Thus, in order to induce susceptibility of tumors cells to macrophage-induced death, we suggest a new therapeutic approach that couples manipulation of miR-146a levels in tumors with macrophage therapy, which relies on ex vivo stimulation of macrophages and their re-introduction to tumors.

Mechanism-based triarylphosphine-ester probes for capture of endogenous RSNOs

Nitrosothiols (RSNOs) have been proposed as important intermediates in nitric oxide (NO^•) metabolism, storage, and transport as well as mediators in numerous NO-signaling pathways. RSNO levels are finely regulated, and dysregulation is associated with the etiology of several pathologies. Current methods for RSNO quantification depend on indirect assays that limit their overall specificity and reliability. Recent developments of phosphine-based chemical probes constitute a promising approach for the direct detection of RSNOs. We report here results from a detailed mechanistic and kinetic study for trapping RSNOs by three distinct phosphine probes, including structural identification of novel intermediates and stability studies under physiological conditions. We further show that a triarylphosphine-thiophenyl ester can be used in the absolute quantification of endogenous GSNO in several cancer cell lines, while retaining the elements of the SNO functional group, using an LC–MS-based assay. Finally, we demonstrate that a common product ion (m/z = 309.0), derived from phosphine–RSNO adducts, can be used for the detection of other low-molecular weight nitrosothiols (LMW-RSNOs) in biological samples. Collectively, these findings establish a platform for the phosphine ligation-based, specific and direct detection of RSNOs in biological samples, a powerful tool for expanding the knowledge of the biology and chemistry of NO^•-mediated phenomena.

NPM-ALK up-regulates iNOS expression through a STAT3/microRNA-26a-dependent mechanism

NPM-ALK chimeric oncogene is aberrantly expressed in an aggressive subset of T-cell lymphomas that frequently occurs in children and young adults. The mechanisms underlying the oncogenic effects of NPM-ALK are not completely elucidated. Inducible nitric oxide synthase (iNOS) promotes the survival and maintains the malignant phenotype of cancer cells by generating NO, a highly active free radical. We tested the hypothesis that iNOS is deregulated in NPM-ALK(+) T-cell lymphoma and promotes the survival of this lymphoma. In line with this possibility, an iNOS inhibitor and NO scavenger decreased the viability, adhesion, and migration of NPM-ALK(+) T-cell lymphoma cells, and an NO donor reversed these effects. Moreover, the NO donor salvaged the viability of lymphoma cells treated with ALK inhibitors. In further support of an important role of iNOS, we found iNOS protein to be highly expressed in NPM-ALK(+) T-cell lymphoma cell lines and in 79% of primary tumours but not in human T lymphocytes. Although expression of iNOS mRNA was identified in NPM-ALK(+) T-cell lymphoma cell lines and tumours, iNOS mRNA was remarkably elevated in T lymphocytes, suggesting post-transcriptional regulation. Consistently, we found that miR-26a contains potential binding sites and interacts with the 3'-UTR of iNOS. In addition, miR-26a was significantly decreased in NPM-ALK(+) T-cell lymphoma cell lines and tumours compared with T lymphocytes and reactive lymph nodes. Restoration of miR-26a in lymphoma cells abrogated iNOS protein expression and decreased NO production and cell viability, adhesion, and migration. Importantly, the effects of miR-26a were substantially attenuated when the NO donor was simultaneously used to treat lymphoma cells. Our investigation of the mechanisms underlying the decrease in miR-26a in this lymphoma revealed novel evidence that STAT3, a major downstream substrate of NPM-ALK tyrosine kinase activity, suppresses MIR26A1 gene expression.

Mitochondrial-targeting nitrooxy-doxorubicin: a new approach to overcome drug resistance

In previous studies, we showed that nitric oxide (NO) donors and synthetic doxorubicins (DOXs) modified with moieties containing NO-releasing groups--such as nitrooxy-DOX (NitDOX) or 3-phenylsulfonylfuroxan-DOX (FurDOX)--overcome drug resistance by decreasing the activity of ATP-binding cassette (ABC) transporters that can extrude the drug. Here, we have investigated the biochemical mechanisms by which NitDOX and FurDOX exert antitumor effects. Both NitDOX and FurDOX were more cytotoxic than DOX against drug-resistant cells. Interestingly, NitDOX exhibited a faster uptake and an extranuclear distribution. NitDOX was preferentially localized in the mitochondria, where it nitrated and inhibited the mitochondria-associated ABC transporters, decreased the flux through the tricarboxylic acid cycle, slowed down the activity of complex I, lowered the synthesis of ATP, induced oxidative and nitrosative stress, and elicited the release of cytochrome c and the activation of caspase-9 and -3 in DOX-resistant cells. We suggest that NitDOX may represent the prototype of a new class of multifunctional anthracyclines, which have cellular targets different from conventional anthracyclines and greater efficacy against drug-resistant tumors.

Impact of tumor blood flow modulation on tumor sensitivity to the bioreductive drug banoxantrone

We investigated the hypoxia-dependent cytotoxicity of AQ4N (banoxantrone) using a panel of 13 cancer cell lines and studied its relationship to the expression of the quinone reductase DT-diaphorase (NQO1), which is widely found in cancer cells. We also investigated pharmacologic treatments that increase tumor hypoxia in vivo and their impact on AQ4N chemosensitivity in a solid tumor xenograft model. AQ4N showed ≥ 8-fold higher cytotoxicity under hypoxia than normoxia in cultures of 9L rat gliosarcoma and H460 human non-small-cell lung carcinoma cells but not for 11 other human cancer cell lines. DT-diaphorase protein levels and AQ4N chemosensitivity were poorly correlated across the cancer cell line panel, and AQ4N chemosensitivity was not affected by DT-diaphorase inhibitors. The vasodilator hydralazine decreased tumor perfusion and increased tumor hypoxia in 9L tumor xenografts, and to a lesser extent in H460 tumor xenografts. However, hydralazine did not increase AQ4N-dependent antitumor activity. Combination of AQ4N with the angiogenesis inhibitor axitinib, which increases 9L tumor hypoxia, transiently increased antitumor activity but with an increase in host toxicity. These findings indicate that the capacity to bioactivate AQ4N is not dependent on DT-diaphorase and is not widespread in cultured cancer cell lines. Moreover, the activation of AQ4N cytotoxicity in vivo requires tumor hypoxia that is more extensive or prolonged than can readily be achieved by vasodilation or by antiangiogenic drug treatment.

Endogenously produced nitric oxide mitigates sensitivity of melanoma cells to cisplatin

Melanoma patients experience inferior survival after biochemotherapy when their tumors contain numerous cells expressing the inducible isoform of NO synthase (iNOS) and elevated levels of nitrotyrosine, a product derived from NO. Although several lines of evidence suggest that NO promotes tumor growth and increases resistance to chemotherapy, it is unclear how it shapes these outcomes. Here we demonstrate that modulation of NO-mediated S-nitrosation of cellular proteins is strongly associated with the pattern of response to the anticancer agent cisplatin in human melanoma cells in vitro. Cells were shown to express iNOS constitutively, and to generate sustained nanomolar levels of NO intracellularly. Inhibition of NO synthesis or scavenging of NO enhanced cisplatin-induced apoptotic cell death. Additionally, pharmacologic agents disrupting S-nitrosation markedly increased cisplatin toxicity, whereas treatments favoring stabilization of S-nitrosothiols (SNOs) decreased its cytotoxic potency. Activity of the proapoptotic enzyme caspase-3 was higher in cells treated with a combination of cisplatin and chemicals that decreased NO/SNOs, whereas lower activity resulted from cisplatin combined with stabilization of SNOs. Constitutive protein S-nitrosation in cells was detected by analysis with biotin switch and reduction/chemiluminescence techniques. Moreover, intracellular NO concentration increased significantly in cells that survived cisplatin treatment, resulting in augmented S-nitrosation of caspase-3 and prolyl-hydroxylase-2, the enzyme responsible for targeting the prosurvival transcription factor hypoxia-inducible factor-1α for proteasomal degradation. Because activities of these enzymes are inhibited by S-nitrosation, our data thus indicate that modulation of intrinsic intracellular NO levels substantially affects cisplatin toxicity in melanoma cells. The underlying mechanisms may thus represent potential targets for adjuvant strategies to improve the efficacy of chemotherapy.

Established Principles and Emerging Concepts on the Interplay between Mitochondrial Physiology and S-(De)nitrosylation: Implications in Cancer and Neurodegeneration

S-nitrosylation is a posttranslational modification of cysteine residues that has been frequently indicated as potential molecular mechanism governing cell response upon redox unbalance downstream of nitric oxide (over)production. In the last years, increased levels of S-nitrosothiols (SNOs) have been tightly associated with the onset of nitroxidative stress-based pathologies (e.g., cancer and neurodegeneration), conditions in which alterations of mitochondrial homeostasis and activation of cellular processes dependent on it have been reported as well. In this paper we aim at summarizing the current knowledge of mitochondria-related proteins undergoing S-nitrosylation and how this redox modification might impact on mitochondrial functions, whose impairment has been correlated to tumorigenesis and neuronal cell death. In particular, emphasis will be given to the possible, but still neglected implication of denitrosylation reactions in the modulation of mitochondrial SNOs and how they can affect mitochondrion-related cellular process, such as oxidative phosphorylation, mitochondrial dynamics, and mitophagy.

STAT3-iNOS Signaling Mediates EGFRvIII-Induced Glial Proliferation and Transformation

Malignant gliomas, including glioblastoma multiforme, constitute the most common and aggressive primary brain tumors in adults. The transcription factor signal transducer and activator of transcription 3 (STAT3) plays an essential role in glioblastoma pathogenesis downstream of the major oncogenic protein epidermal growth factor receptor variant III (EGFRvIII). However, the critical gene targets of STAT3 that mediate EGFRvIII-induced glial transformation have remained unknown. Here, we identify inducible nitric oxide synthase (iNOS) as a novel target gene of STAT3 in EGFRvIII-expressing mouse astrocytes. Endogenous STAT3 occupies the endogenous iNOS promoter and stimulates iNOS transcription in EGFRvIII-expressing astrocytes. STAT3 does not appear to control iNOS transcription in astrocytes deficient in the major glioblastoma tumor suppressor protein phosphatase and tensin homolog (PTEN), suggesting that STAT3 regulates iNOS transcription specifically in EGFRvIII-expressing astrocytes. Importantly, inhibition of iNOS by distinct approaches, including knockdown by RNA interference, reduces cell population growth and invasiveness of EGFRvIII-expressing astrocytes. In addition, upon iNOS knockdown or administration of a small-molecule inhibitor of iNOS, EGFRvIII-expressing astrocytes form smaller tumors in vivo. These findings suggest that inhibition of iNOS may have potential therapeutic value for EGFRvIII-activated brain tumors.

[Construction of A eukaryotic expression vector carrying the iNOS gene and its effect on A549 lung cancer cells]

背景与目的

iNOS与NO介导的抗肿瘤效应有关。本研究旨在构建pVAX-iNOS载体并转染A549肺癌细胞，检测其基因的表达并初步探讨iNOS基因表达增高后对A549肺癌细胞的抗肿瘤作用。

方法

应用RT-PCR方法扩增人iNOS编码序列的CDS片段，构建pVAX-iNOS载体后转染肺癌A549细胞，通过RT-PCR和Western blot方法检测目的基因的表达；采用MTT法、Hoechst 3235染色和划痕实验分别检测iNOS高表达在体外对肺癌A549细胞增殖、凋亡和迁移作用的影响。

结果

真核表达质粒载体pVAX-iNOS构建成功，iNOS蛋白在转染后的A549细胞中表达升高。pVAX-iNOS转染A549肺癌细胞后能明显诱导细胞发生凋亡并抑制肿瘤细胞的生长和迁移。

结论

本研究成功构建pVAX-iNOS真核表达质粒，高表达iNOS能明显抑制A549细胞的增殖、迁移并促进细胞发生凋亡。本研究有望为临床治疗肺癌提供一个新的有效策略。

Feasibility and dosimetry studies for 18F-NOS as a potential PET radiopharmaceutical for inducible nitric oxide synthase in humans

Nitric oxide (NO), the end product of the inducible form of NO synthase (iNOS), is an important mediator of a variety of inflammatory diseases. Therefore, a radiolabeled iNOS radiopharmaceutical for assessing iNOS protein concentration as a marker for its activity would be of value to the study and treatment of NO-related diseases. We recently synthesized an (18)F-radiolabeled analog of the reversible NOS inhibitor, 2-amino-4-methylpyridine ((18)F-NOS), and confirmed its utility in a murine model of lung inflammation. To determine its potential for use in humans, we measured (18)F-NOS myocardial activity in patients after orthotopic heart transplantation (OHT) and correlated it with pathologic allograft rejection, tissue iNOS levels, and calculated human radiation dosimetry.

METHODS

Two groups were studied-a kinetic analysis group and a dosimetry group. In the kinetic analysis group, 10 OHT patients underwent dynamic myocardial (18)F-NOS PET/CT, followed by endomyocardial biopsy. Myocardial (18)F-NOS PET was assessed using volume of distribution; standardized uptake values at 10 min; area under the myocardial moment curve (AUMC); and mean resident time at 5, 10, and 30 min after tracer injection. Tissue iNOS levels were measured by immunohistochemistry. In the dosimetry group, the biodistribution and radiation dosimetry were calculated using whole-body PET/CT in 4 healthy volunteers and 12 OHT patients. The combined time-activity curves were used for residence time calculation, and organ doses were calculated with OLINDA.

RESULTS

Both AUMC at 10 min (P < 0.05) and tissue iNOS (P < 0.0001) were higher in patients exhibiting rejection than in those without rejection. Moreover, the (18)F-NOS AUMC at 10 min correlated positively with tissue iNOS at 10 min (R(2) = 0.42, P < 0.05). (18)F-NOS activity was cleared by the hepatobiliary system. The critical organ was the bladder wall, with a dose of 95.3 μGy/MBq, and an effective dose of 15.9 μSv/MBq was calculated.

CONCLUSION

Myocardial (18)F-NOS activity is increased in organ rejection (a condition associated with increased iNOS levels) and correlates with tissue iNOS measurements with acceptable radiation exposure. Although further modifications to improve the performance of (18)F-NOS are needed, these data show the feasibility of PET of iNOS in the heart and other tissues.

Protein S-nitrosylation and cancer

Protein S-nitrosylation is a covalent post-translational modification through coupling of a nitric oxide (NO) moiety with the reactive thiol group of a protein cysteine residue to form an S-nitrosothiol (SNO). S-nitrosylation is a key mechanism in the transmission of NO-based cellular signals in the vital cellular processes, including transcription regulation, DNA repair, and apoptosis. Contemporary research has implicated dysregulation of S-nitrosylation in severe pathological events, including cancer onset, progression, and treatment resistance. The S-nitrosylation status may be directly linked to many cancer therapy outcomes as well as therapeutic-resistance, emphasizing the need to develop S-nitrosylation-related anti-cancer therapeutics. The role of S-nitrosylated proteins in the development and progression of cancer are varied, generating a critical need for a thorough review of the current dynamic research in this area.

Natural and synthetic α,β-unsaturated carbonyls for NF-κB inhibition

BACKGROUND

The nuclear transcription factor NF-κB has gained considerable importance due to its major involvement in inflammation and constitutive activity in malignant cells. It is induced by a variety of stimuli and controls the expression of several proteins involved in biological processes. Numerous natural products and synthesized organic molecules have been reported to inhibit NF-κB and have played an integral role in identifying implicated pathways. Prominent among them are the sesquiterpene lactones, polyphenolic enones and other α,β-unsaturated carbonyl-containing molecules, particularly α-methylene-γ-butyrolactones.

DISCUSSION

This mini-review provides an introductory overview of some of the associated pathways involving NF-κB in cancer and discusses the structures and mode of action of natural α,β-unsaturated carbonyl-containing inhibitors and their synthetic counterparts. A review of the recent methods for the synthesis of α-alkylidene-γ-butyrolactones is also provided, with the aim of arousing the interest of synthetic chemists for the design and development of novel NF-κB inhibitors.

CONCLUSIONS

Modulating damaging effects without harming the inflammatory and immune responses are crucial parameters for developing NF-κB inhibitors. Examination of novel α,β-unsaturated carbonyls and the further discovery of simple methods to prepare such molecules should lead to the identification of site-specific inhibitors.

Transcriptional regulation of inducible nitric oxide synthase gene therapy: targeting early stage and advanced prostate cancer

BACKGROUND

Using the tumour type specific human osteocalcin (hOC) promoter, we have previously reported strong promoter activation in hormone independent prostate cancer cells in vitro. In the present study, we present a comparative study of the tissue specific promoter prostate specific membrane antigen (PSMA), and the tumour-type specific hOC promoter driving the inducible nitric oxide synthase (iNOS) transgene using both in vitro and in vivo models.

METHODS

In vitro cytotoxicity was assessed by clonogenic assay. Quantification of nitric oxide expression was determined by the Griess test. In vivo anti-tumour efficacy was determined by tumour growth delay following direct intra-tumoural injection of the constructs into PC3 xenografts. In addition, tumours were dissected post mortem and examined for morphological differences as well as changes in apoptotic protein expression.

RESULTS

PSMA/iNOS produced cytotoxicity in both androgen dependant and independent cell lines. Nitric oxide quantification confirmed that increased cytotoxicity was directly associated with nitric oxide production. Tumour growth delays were observed in all groups treated with the iNOS-expressing constructs ranging from 10.7 days for the hOC/iNOS single dose treatment group to a maximum of 52.2 days for the hOC/iNOS multiple dose group. Intra-tumoural assessment of iNOS and cleaved poly (ADP-ribose) polymerase protein expression demonstrated a significant up-regulation of both proteins, indicating cytotoxicity mediated through the intrinsic apoptotic pathway.

CONCLUSIONS

Highly significant tumour growth delay coupled with no detrimental side-effects were observed following treatment with the PSMA/iNOS and hOC/iNOS constructs. We consider that these findings provide a basis for the development of systemically delivered PSMA/iNOS or hOC/iNOS targeting early stage and advanced prostate cancer.

NO to breast: when, why and why not?

Nitric oxide is a pleiotropic ancestral molecule, which elicits beneficial effect in many physiological settings but is also tenaciously expressed in numerous pathological conditions, particularly breast tumors. Nitric oxide is particularly harmful in adipogenic milieu of the breast, where it initiates and promotes tumorigenesis. Epidemiological studies have associated populations at a greater risk for developing breast cancer, predominantly estrogen receptor positive tumors, to express specific polymorphic forms of endothelial nitric oxide synthase, that produce sustained low levels of nitric oxide. Low sustained nitric oxide generates oxidative stress and inflammatory conditions at susceptible sites in the heterogeneous microenvironment of the breast, where it promotes cancer related events in specific cell types. Inflammatory conditions also stimulate inducible nitric oxide synthase expression, which dependent on the microenvironment, could promote or inhibit mammary tumors. In this review we re-examine the mechanisms by which nitric oxide promotes initiation and progression of breast cancer and address some of the controversies in the field.

Loss of inducible nitric oxide synthase expression in the mouse renal cell carcinoma cell line RENCA is mediated by microRNA miR-146a

Tumor-associated macrophages can potentially kill tumor cells via the high concentrations of nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS); however, tumor-associated macrophages actually support tumor growth, as they are skewed toward M2 activation, which is characterized by low amounts of NO production and is proangiogenic. We show that the mouse renal cell carcinoma cell line, RENCA, which, on stimulation, expresses high levels of iNOS mRNA, loses its ability to express the iNOS protein. This effect is mediated by the microRNA miR-146a, as inhibition of RENCA cells with anti-miR- 146a restores iNOS expression and NO production (4.8 ± 0.4 versus 0.3 ± 0.1 μmol/L in uninhibited cells, P < 0.001). In vivo, RENCA tumor cells do not stain for iNOS, while infiltrating tumor-associated macrophages showed intense staining, and both cell types expressed iNOS mRNA. Restoring iNOS protein expression in RENCA cells using anti-miR-146a increases macrophage-induced death of RENCA cells by 73% (P < 0.01) in vitro and prevents tumor growth in vivo. These results suggest that, in addition to NO production by macrophages, tumor cells must produce NO to induce their own deaths, and some tumor cells may use miR-146a to reduce or abolish endogenous NO production to escape macrophage-mediated cell death. Thus, inhibiting miR-146a may render these tumor cells susceptible to therapeutic strategies, such as adoptive transfer of M1-activated macrophages.

Integrin-linked kinase is involved in TNF-alpha-induced inducible nitric-oxide synthase expression in myoblasts

Tumor necrosis factor-alpha (TNF-alpha) is a pleiotropic cytokine produced by activated macrophages. Nitric oxide (NO) is a highly reactive nitrogen radical implicated in inflammatory responses. We investigated the signaling pathway involved in inducible nitric oxide synthase (iNOS) expression and NO production stimulated by TNF-alpha in cultured myoblasts. TNF-alpha stimulation caused iNOS expression and NO production in myoblasts (G7 cells). TNF-alpha-mediated iNOS expression was attenuated by integrin-linked kinase (ILK) inhibitor (KP392) and siRNA. Pretreatment with Akt inhibitor, mammalian target of rapamycin (mTOR) inhibitor (rapamycin), NF-kappaB inhibitor (PDTC), and IkappaB protease inhibitor (TPCK) also inhibited the potentiating action of TNF-alpha. Stimulation of cells with TNF-alpha increased ILK kinase activity. TNF-alpha also increased the Akt and mTOR phosphorylation. TNF-alpha mediated an increase of NF-kappaB-specific DNA-protein complex formation, p65 translocation into nucleus, NF-kappaB-luciferase activity was inhibited by KP392, Akt inhibitor, and rapamycin. Our results suggest that TNF-alpha increased iNOS expression and NO production in myoblasts via the ILK/Akt/mTOR and NF-kappaB signaling pathway.

Electron flow through metalloproteins

Electron transfers in photosynthesis and respiration commonly occur between metal-containing cofactors that are separated by large molecular distances. Understanding the underlying physics and chemistry of these biological electron transfer processes is the goal of much of the work in our laboratories. Employing laser flash-quench triggering methods, we have shown that 20A, coupling-limited Fe(II) to Ru(III) and Cu(I) to Ru(III) electron tunneling in Ru-modified cytochromes and blue copper proteins can occur on the microsecond timescale both in solutions and crystals; and, further, that analysis of these rates suggests that distant donor-acceptor electronic couplings are mediated by a combination of sigma and hydrogen bonds in folded polypeptide structures. Redox equivalents can be transferred even longer distances by multistep tunneling, often called hopping, through intervening amino acid side chains. In recent work, we have found that 20A hole hopping through an intervening tryptophan is several hundred-fold faster than single-step electron tunneling in a Re-modified blue copper protein.