Nitric oxide synthase type 3 is increased in squamous hyperplasia, dysplasia, and squamous cell carcinoma of the head and neck

Expression of cross-tolerance to a wide range of conditions in a human lung cancer cell line after adaptation to nitric oxide

Previously, we have shown that A549, a human lung adenocarcinoma, can be adapted to nitric oxide (NO^●). NO^● is a nitrogen-based free radical that is synthesized by a family of enzymes known as nitric oxide synthases. NO^● has been shown to be overexpressed in patient populations of different cancers. In addition, it has been observed that patients who express high levels of nitric oxide synthases tend to have poorer clinical outcomes than those with low levels of expression. The original cell line A549 (parent) and the adapted A549-HNO (high nitric oxide) cell line serve as a useful model system to investigate the role of NO^● in tumor progression and prognosis. We have previously shown that the A549-HNO-adapted cells grow aggressively when compared to A549-parent cells. Furthermore, we have shown that the A549-HNO-adapted cells exhibit a higher percentage of cell viability when exposed to ultraviolet and X-ray radiation than the A549-parent cells. Cancer patients who develop resistance to one treatment often become resistant to other previously unencountered forms of treatment. This phenomenon is known as cross-tolerance. To determine whether NO^● is a potential cross-tolerance causing agent, we have expanded our research by conducting parallel studies to a variety of other agents and conditions beyond radiation and ultraviolet exposure. We exposed both cell lines to varying levels of chemotherapeutic drugs (taxol and doxorubicin), temperature, pH, calcium chloride, cadmium chloride, copper chloride, sodium chloride, ferrous chloride, and sodium-R-lipoic acid. Our results show that the A549-HNO cells exhibit greater viability than the A549-parent cells when exposed to each of the various conditions. Therefore, NO^● is one potential driving force that can make tumor cells exhibit cross-tolerance.

A549 cells adapted to high nitric oxide show reduced surface CEACAM expression and altered adhesion and migration properties

The migration and adhesion properties of tumors affect their metastatic rate. In the present study, we investigated carcinoembryonic antigen-related cell adhesion molecule (CEACAM) 1, 5, and 6 expression in high nitric oxide (HNO)-adapted lung cancer cells compared to parent cells. We observed high transcript levels of CEACAM 1 (4S, 4L), CEACAM 5, and CEACAM 6 in HNO cells compared to parent cells. However, the surface expression was low in HNO cells. Interestingly, the intracellular protein levels were high for these three CEACAMs. We confirmed these results with immunohistochemical experiments. Further, the adhesion and migration assays showed reduced clumping in HNO-adapted A549 (A549-HNO) cells and faster migration rates, respectively. These results document the altered adhesion and migration properties of cells adapted to HNO. Further, our studies also indicate a dynamic regulation of CEACAM protein expression and surface transport in HNO cells.

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.

Part I-mechanism of adaptation: high nitric oxide adapted A549 cells show enhanced DNA damage response and activation of antiapoptotic pathways

Our previous studies demonstrate that A549, a human lung adenocarcinoma line, could be adapted to the free radical nitric oxide (NO([Symbol: see text])). NO([Symbol: see text]) has been shown to be overexpressed in human tumors. The original cell line, A549 (parent), and the newly adapted A549-HNO (which has a more aggressive phenotype) serves as a useful model system to study the role of NO([Symbol: see text]) in tumor biology. It is well known that DNA damage response (DDR) is altered in cancer cells and NO([Symbol: see text]) is known to cause DNA damage. Modulations in molecular mechanisms involved in DNA damage response in A549-HNO cells can provide better insights into the enhanced growth behavior of these cells. Thus, here, we carried out a series of time course experiments by treating A549 and A549-HNO cells with NO([Symbol: see text]) donor and examining levels of proteins involved in the DDR pathway. We observed induced expression of key components of DDR pathway in A549-HNO cells. The HNO cells showed sustained expression of key proteins involved in both nonhomologous end joining (NHEJ) and homologous recombination pathways, whereas parent cells only expressed low levels of NHEJ pathway proteins. Further with prolonged NO([Symbol: see text]) exposure, ATR, Chk1, and p53 were activated and upregulated in HNO cells. Activation of p53 results in inhibition of apoptosis through induced Mcl1 expression. It also leads to cell cycle modulation. Interestingly, several reports show that cancer stem cells have enhanced expression of proteins involved in DNA damage response and also activated an antiapoptotic response. Our results here suggest that our HNO adapted A549 cells have increased activation of DNA damage response pathway proteins which can lead to better DNA repair function. Enhanced DDR leads to activation of antiapoptosis response and modulation in the cell cycle which may lead to better survival of these cells under harsh conditions. Thus, our present investigation further supports the hypothesis that HNO exposure leads to survival of these cells.

Part I. Molecular and cellular characterization of high nitric oxide-adapted human breast adenocarcinoma cell lines

There is a lack of understanding of the casual mechanisms behind the observation that some breast adenocarcinomas have identical morphology and comparatively different cellular growth behavior. This is exemplified by a differential response to radiation, chemotherapy, and other biological intervention therapies. Elevated concentrations of the free radical nitric oxide (NO), coupled with the up-regulated enzyme nitric oxide synthase (NOS) which produces NO, are activities which impact tumor growth. Previously, we adapted four human breast cancer cell lines: BT-20, Hs578T, T-47D, and MCF-7 to elevated concentrations of nitric oxide (or high NO [HNO]). This was accomplished by exposing the cell lines to increasing levels of an NO donor over time. Significantly, the HNO cell lines grew faster than did each respective ("PARENT") cell line even in the absence of NO donor-supplemented media. This was evident despite each "parent" being morphologically equivalent to the HNO adapted cell line. Herein, we characterize the HNO cells and their biological attributes against those of the parent cells. Pairs of HNO/parent cell lines were then analyzed using a number of key cellular activity criteria including: cell cycle distribution, DNA ploidy, response to DNA damage, UV radiation response, X-ray radiation response, and the expression of significant cellular enzymes. Other key enzyme activities studied were NOS, p53, and glutathione S-transferase-pi (GST-pi) expression. HNO cells were typified by a far more aggressive pattern of growth and resistance to various treatments than the corresponding parent cells. This was evidenced by a higher S-phase percentage, variable radioresistance, and up-regulated GST-pi and p53. Taken collectively, this data provides evidence that cancer cells subjected to HNO concentrations become resistant to free radicals such as NO via up-regulated cellular defense mechanisms, including p53 and GST-pi. The adaptation to NO may explain how tumor cells acquire a more aggressive tumor phenotype.

Part II. Mitochondrial mutational status of high nitric oxide adapted cell line BT-20 (BT-20-HNO) as it relates to human primary breast tumors

Mitochondria combine hydrogen and oxygen to produce heat and adenosine triphosphate (ATP). As a toxic by-product of oxidative phosphorylation (OXPHOS), mitochondria generate reactive oxygen species (ROS). These free radicals may cause damage to mitochondrial DNA (mtDNA) and other molecules in the cell. Nitric oxide (NO) plays an important role in the biology of human cancers, including breast cancer; however, it is still unclear how NO might affect the mitochondrial genome. The aim of the current study is to determine the role of mtDNA in the breast oncogenic process. Using DNA sequencing, we studied one breast cancer cell line as a model system to investigate the effects of oxidative stress. The BT-20 cell line was fully adapted to increasing concentrations of the NO donor DETA-NONOate and is referred to as BT-20-HNO, a high NO (HNO) cell line. The HNO cell line is biologically different from the "parent" cell line from which it originated. Moreover, we investigated 71 breast cancer biopsies and the corresponding noncancerous breast tissues. The free radical NO was able to generate somatic mtDNA mutations in the BT-20-HNO cell line that were missing in the BT-20 parent cell line. We identified two somatic mutations, A4767G and G13481A, which changed the amino acid residues. Another two point mutations were identified in the mtDNA initiation replication site at nucleotide 57 and at the 'hot spot' cytidine-rich D300-310 segment. Furthermore, the NO regulated the mtDNA copy number and selected different mtDNA populations by clonal expansion. Interestingly, we identified eight somatic mutations in the coding regions of mtDNAs of eight breast cancer patients (8/71, 11.2 %). All of these somatic mutations changed amino acid residues in the highly conserved regions of mtDNA which potentially leads to mitochondrial dysfunctions. The other two somatic mtDNA mutations in the displacement loop (D-loop) region [303:315 C(7-8)TC(6) and nucleotide 57] were distributed among 14 patients (14/71, 19.7 %). Importantly, of these 14 patients, six had mutations in the p53 gene. These results validate the BT-20 parent/HNO cell line model system as a means to study ROS damage in mtDNA, as it parallels the results found in a subset of the patient population.

Part III. Molecular changes induced by high nitric oxide adaptation in human breast cancer cell line BT-20 (BT-20-HNO): a switch from aerobic to anaerobic metabolism

Nutrient deprivation and reactive oxygen species (ROS) play an important role in breast cancer mitochondrial adaptation. Adaptations to these conditions allow cells to survive in the stressful microenvironment of the tumor bed. This study is directed at defining the consequences of High Nitric Oxide (HNO) exposure to mitochondria in human breast cancer cells. The breast cancer cell line BT-20 (parent) was adapted to HNO as previously reported, resulting in the BT-20-HNO cell line. Both cell lines were analyzed by a variety of methods including MTT, LDH leakage assay, DNA sequencing, and Western blot analysis. The LDH assay and the gene chip data showed that BT-20-HNO was more prone to use the glycolytic pathway than the parent cell line. The BT-20-HNO cells were also more resistant to the apoptotic inducing agent salinomycin, which suggests that p53 may be mutated in these cells. Polymerase chain reaction (PCR) followed by DNA sequencing of the p53 gene showed that it was, in fact, mutated at the DNA-binding site (L194F). Western blot analysis showed that p53 was significantly upregulated in these cells. These results suggest that free radicals, such as nitric oxide (NO), pressure human breast tumor cells to acquire an aggressive phenotype and resistance to apoptosis. These data collectively provide a mechanism by which the dysregulation of ROS in the mitochondria of breast cancer cells can result in DNA damage.

Part I. Development of a model system for studying nitric oxide in tumors: high nitric oxide-adapted head and neck squamous cell carcinoma cell lines

The free radical nitric oxide (NO) is over-expressed in many tumors, including head and neck squamous cell carcinomas (HNSCC); however, the role NO plays in tumor pathophysiology is still not well understood. We, herein, report the development of an in vitro model system which can be used to probe the role of NO in the carcinogenesis of HNSCC. Five HNSCC cell lines were adapted to a high NO (HNO) environment by gradually introducing increasing concentrations of DETA-NONOate, a nitrogen-based NO donor, to cell media. The adaptation process was carried out until a sufficiently high enough donor concentration was reached which enabled the HNO cells to survive and grow, but which was lethal to the original, unadapted ("parent") cells. The adapted HNO cells exhibited analogous morphology to the parent cells, but grew better than their corresponding parent cells in normal media, on soft agar, and in the presence of hydrogen peroxide, an oxygen-based free radical donor. These results indicate that the HNO cell lines are unique and possess biologically different properties than the parent cell lines from which they originated. The HNO/parent cell lines developed herein may be used as a model system to better understand the role NO plays in HNSCC carcinogenesis.

Part II. Initial molecular and cellular characterization of high nitric oxide-adapted human tongue squamous cell carcinoma cell lines

It is not understood why some head and neck squamous cell carcinomas, despite having identical morphology, demonstrate different tumor aggressiveness, including radioresistance. High levels of the free radical nitric oxide (NO) and increased expression of the NO-producing enzyme nitric oxide synthase (NOS) have been implicated in tumor progression. We previously adapted three human tongue cancer cell lines to high NO (HNO) levels by gradually exposing them to increasing concentrations of an NO donor; the HNO cells grew faster than their corresponding untreated ("parent") cells, despite being morphologically identical. Herein we initially characterize the HNO cells and compare the biological properties of the HNO and parent cells. HNO/parent cell line pairs were analyzed for cell cycle distribution, DNA damage, X-ray and ultraviolet radiation response, and expression of key cellular enzymes, including NOS, p53, glutathione S-transferase-pi (GST-pi), apurinic/apyrimidinic endonuclease-1 (APE1), and checkpoint kinases (Chk1, Chk2). While some of these properties were cell line-specific, the HNO cells typically exhibited properties associated with a more aggressive behavior profile than the parent cells (greater S-phase percentage, radioresistance, and elevated expression of GST-pi/APE1/Chk1/Chk2). To correlate these findings with conditions in primary tumors, we examined the NOS, GST-pi, and APE1 expression in human tongue squamous cell carcinomas. A majority of the clinical samples exhibited elevated expression levels of these enzymes. Together, the results herein suggest cancer cells exposed to HNO levels can develop resistance to free radicals by upregulating protective mechanisms, such as GST-pi and APE1. These upregulated defense mechanisms may contribute to their aggressive expression profile.

Nitric oxide: perspectives and emerging studies of a well known cytotoxin

The free radical nitric oxide (NO^•) is known to play a dual role in human physiology and pathophysiology. At low levels, NO^• can protect cells; however, at higher levels, NO^• is a known cytotoxin, having been implicated in tumor angiogenesis and progression. While the majority of research devoted to understanding the role of NO^• in cancer has to date been tissue-specific, we herein review underlying commonalities of NO^• which may well exist among tumors arising from a variety of different sites. We also discuss the role of NO^• in human physiology and pathophysiology, including the very important relationship between NO^• and the glutathione-transferases, a class of protective enzymes involved in cellular protection. The emerging role of NO^• in three main areas of epigenetics—DNA methylation, microRNAs, and histone modifications—is then discussed. Finally, we describe the recent development of a model cell line system in which human tumor cell lines were adapted to high NO^• (HNO) levels. We anticipate that these HNO cell lines will serve as a useful tool in the ongoing efforts to better understand the role of NO^• in cancer.

Long-term adaptation of breast tumor cell lines to high concentrations of nitric oxide

Nitric oxide (NO), a free radical, has been implicated in the biology of human cancers, including breast cancer, yet it is still unclear how NO affects tumor development and propagation. We herein gradually adapted four human breast adenocarcinoma cell lines (BT-20, Hs578T, T-47D, and MCF-7) to increasing concentrations of the NO donor DETA-NONOate up to 600 muM. The resulting model system consisted of a set of fully adapted high nitric oxide ("HNO") cell lines that are biologically different from the "parent" cell lines from which they originated. Although each of the four parent and HNO cell lines had identical morphologic appearance, the HNO cells grew faster than their corresponding parent cells and were resistant to both nitrogen- and oxygen-based free radicals. These cell lines serve as a novel tool to study the role of NO in breast cancer progression and potentially can be used to predict the therapeutic response leading to more efficient therapeutic regimens.

Effect of artemisinins and other endoperoxides on nitric oxide-related signaling pathway in RAW 264.7 mouse macrophage cells

Artemisinin is the active principle of the Chinese herb Artemisia annua L. In addition to its anti-malarial activity, artemisinin and its derivatives have been shown to exert profound anti-cancer activity. The endoperoxide moiety in the chemical structure of artemisinin is thought to be responsible for the bioactivity. Here, we analyzed the cytotoxicity and the ability of artemisinin, five of its derivatives, and two other endoperoxides to inhibit generation of nitric oxide (NO). In the RAW 264.7 mouse macrophage cell line, the well-established model cell line to analyze NO generation, artesunate revealed the highest ability to inhibit NO production among all compounds tested. In cytotoxicity assays (XTT assay), the IC(50) value of RAW 264.7 cells for artesunate was determined to be 3.1+/-0.7 microM. In order to associate the cytotoxic effects with specific alteration in gene expression related to NO metabolism and signaling, whole genome mRNA microarray analyses were conducted. RAW 264.7 cells were treated with artesunate using DMSO as vehicle control followed by microarray analysis. A total of 36 genes related to NO metabolism and signaling were found to be differentially expressed upon exposure to artesunate. Apart from NO-related genes, the expression of genes associated with other functional groups was also analyzed. Out of 24 functional groups, differential expression was most prominent in genes involved in cell-to-cell signaling and interactions. Further refinement of this analysis showed that the pathways for cAMP-mediated signaling and Wnt/beta-catenin signaling were most closely related to changes in mRNA expression. In conclusion, NO generation and signaling play a role in exhibiting cytotoxic activity of artesunate. In addition, other signaling pathways also contribute to the inhibitory effect of artesunate towards RAW 264.7 cells pointing to a multi-factorial mode of action of artesunate.

Role of nitric oxide in the development of distant metastasis from squamous cell carcinoma

BACKGROUND

Metastasis, the dissemination of malignant cells to distant sites, remains one of the most significant factors responsible for death from cancer. Recent studies have shown some improvement in the rate of distant metastasis (DM) with the addition of chemotherapy to surgery and radiation for treatment of head and neck squamous cell carcinoma (HNSCC). However, diagnosis and treatment at an early stage ultimately leads to a better prognosis. The prediction of which patients will develop metastasis and the selection of treatment most effective at preventing and treating metastasis remains dependent on an incomplete understanding of prognostic factors and the biological and molecular basis for metastatic development. This study was undertaken using an in vivo model to investigate the possible role of nitric oxide (NO) in the development of metastasis from HNSCC. The findings will result in better understanding of the metastatic process for HNSCC, with the potential to develop and implement therapies that could prevent and treat metastasis in patients.

OBJECTIVES/HYPOTHESIS

1) To analyze whether in vivo videomicroscopy (IVVM) is useful for the study of DM from squamous cell carcinoma of the head and neck; 2) with use of IVVM, investigate the effect of the biological mediators NO and interleukin (IL)-1 on the adhesion of circulating human HNSCC cells in the hepatic microcirculation.

STUDY DESIGN

Prospective study using an animal model.

METHODS

Phase 1: athymic nude rats and mice were used for IVVM experiments. The cremaster muscle and liver, used as arterial and venous flow models, were tested to determine whether IVVM was useful for the study of human HNSCC interactions with the microcirculation. A human squamous cell carcinoma cell line (FaDu) labeled with the intracytoplasmic fluorescent marker BCECF-am. was used for all experiments. Videomicroscopic images of FaDu cells in the microcirculation were analyzed for cell adhesion, morphology, deformation, circulation, location of adhesion within the microcirculation, and alteration of microvascular circulation. Phase 2: the effect of IL-1, NO, and NO inhibitors on HNSCC cell adhesion in the hepatic microcirculation of nude mice was analyzed by IVVM. This was followed by histologic determination of the ratio of FaDu cells present for liver area analyzed. Nude mice were treated with 1) IL-1; 2) L-arginine (an NO substrate); or 3) L-N-monomethyl-L-arginine (an NO synthase inhibitor) alone or in combination. These data were analyzed statistically to determine the effect on cell adhesion in the liver.

RESULTS

IVVM provided a method for the study of circulating HNSCC with the microcirculation in both the cremaster and liver models. FaDu cells were arrested at the inflow side of the circulation, with maintenance of cell integrity. L-arginine and IL-1 both increased FaDu cell arrest in the liver above baseline (P = .00008 and P = .03), and the combination of these agents potentiated the effect (P = .000009).

CONCLUSIONS

IVVM allows direct assessment of circulating HNSCC with the microcirculation and is a powerful model for the study of DM. NO and IL-1 play a role in increasing the arrest of HNSCC in the liver and are important in the generation of DM in patients with HNSCC.

In vitro effects of nitric oxide synthase inhibitor L-NAME on oral squamous cell carcinoma: a preliminary study

It has been reported that increased nitric oxide synthase (NOS) expression and nitric oxide (NO) production may play an important role in cancer biology. The aim of this study was to determine the roles of NO in tumour cellular proliferation and DNA or RNA synthesis, and to investigate the therapeutic potential of NOS inhibitors in oral cancer. After exposure to different concentrations of the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), the growth of TSCCa cells, established from a patient with squamous cell carcinoma of the tongue, was evaluated using MTT and crystal violet assay. DNA or RNA synthesis, inducible/endothelial NOS (iNOS/eNOS) mRNA expression and NO production were then examined to determine the possible mechanisms of inhibitory effects of L-NAME on TSCCa cells. L-NAME had an inhibitory effect on TSCCa cell growth in both a concentration- and time-dependent manner. Acridine orange staining revealed that DNA and/or RNA synthesis of TSCCa cells was reduced after treatment with L-NAME. An in situ hybridisation (ISH) study showed clearly that L-NAME down-regulated eNOS and iNOS mRNA expression and this was followed by a decrease in NO production. It is postulated that the NOS/NO pathway may be implicated in cellular proliferation and DNA or RNA synthesis of cancer cells, apart from promoting tumour angiogenesis. Further studies have provided with new insight into the mechanisms by which NOS/NO takes part in oral carcinogenesis, and possible therapeutic interventions based on the NOS/NO pathway for tumour progression control.

A novel method of measuring gas phase nitric oxide concentration in cell cultures

This is the first report on the measurement of nitric oxide (NO) concentrations in the gas phase in a squamous cell culture. The technique may permit the assessment of NO output under conditions that aim to mimic facets of pathology in relatively inaccessible tissues. The primary aim of this study was to devise a method to detect the NO concentration produced by cell cultures in the gas phase of a culture flask. A secondary aim was to determine whether the effect of hypoxia or radiation on NO production in a human squamous cell carcinoma cell culture would be detectable with this technique. The NO concentration was measured off-line using a rapid-response chemiluminescent analyzer. The gas samples were aspirated from cell culture flasks (i) under normal culture conditions, (ii) under conditions of hypoxia and (iii) following radiation of human head and neck squamous cell carcinoma cell line cultures. Elevated levels of the gas phase NO concentration were consistently obtained from the cell culture flasks using this experimental set-up. Hypoxia and radiation diminished NO production.

Expression of endothelial nitric oxide synthase and vascular endothelial growth factor in oral squamous cell carcinoma: its correlation with angiogenesis and disease progression

BACKGROUND

Angiogenesis is a crucial step in the successful growth, invasion, and metastasis of a tumor. It has been popularly accepted that vascular endothelial growth factor (VEGF) is the most potent angiogenic factor in tumor angiogenesis. As another possible star molecule responsible for tumor angiogenesis, the role of nitric oxide (NO) in tumor biology has gained much attention in recent years. The aim of this study was to investigate whether the expression of endothelial nitric oxide synthase (eNOS) and VEGF in oral squamous cell carcinoma (OSCC) is associated with angiogenesis. The present study also made a preliminary exploration of the possible cross-talking existing between eNOS and VEGF during tumor angiogenesis.

METHODS

In this study, expression of eNOS and VEGF were studied immunohistochemically in tissue sections from 40 patients with OSCC and 20 normal controls. To exclude eNOS antibody cross-reactivity with inducible or neuronal nitric oxide (iNOS or nNOS), eNOS expression was confirmed by using an eNOS mRNA in situ hybridization kit. The intratumoral microvessels were highlighted by immunostaining with anti-factor VIII-related antigen monoclonal antibody and counted as well-established methods. Then, chi-square test or Student's t-test was performed to study the correlations between the expression of eNOS and VEGF, microvessel density (MVD), and various clinicopathologic factors.

RESULTS

Both eNOS and VEGF expression significantly increased in OSCC tissues, with a positive rate of 47.5% and 50%, respectively. The average MVD in OSCC tissues was 23.45 per high-power field (HPF), showing an obvious association with lymph node metastasis and clinical stages of patients with OSCC. Either eNOS or VEGF positivity was correlated with vessel involvement and OSCC progression. The mean MVD was significantly higher in eNOS- or VEGF-positive tumors than in eNOS- or VEGF-negative tumors. An obvious, correlation was also seen between eNOS and VEGF expression in OSCC tissues in this study.

CONCLUSIONS

Overexpression of eNOS and VEGF might make an important contribution to the tumor angiogenesis in OSCC. NO generation by eNOS might be implicated in the VEGF-associated angiogenic process. Further investigation of the possible cross-talking between eNOS and VEGF with respect to tumor angiogenesis is necessary.

Nitrosative stress induces DNA strand breaks but not caspase mediated apoptosis in a lung cancer cell line

Background

Key steps crucial to the process of tumor progression are genomic instability and escape from apoptosis. Nitric oxide and its interrelated reactive intermediates (collectively denoted as NO_X) have been implicated in DNA damage and mutational events leading to cancer development, while also being implicated in the inhibition of apoptosis through S-nitrosation of key apoptotic enzymes. The purpose of this study was to explore the interrelationship between NO_X-mediated DNA strand breaks (DSBs) and apoptosis in cultured tumor cell lines.

Methods

Two well-characterized cell lines were exposed to increasing concentrations of exogenous NO_X via donor compounds. Production of NO_X was quantified by the Greiss reaction and spectrophotometery, and confirmed by nitrotyrosine immunostaining. DSBs were measured by the alkaline single-cell gel electrophoresis assay (the COMET assay), and correlated with cell viability by the MTT assay. Apoptosis was analyzed both by TUNEL staining and Annexin V/propidium iodine FACS. Finally, caspase enzymatic activity was measured using an in-vitro fluorogenic caspase assay.

Results

Increases in DNA strand breaks in our tumor cells, but not in control fibroblasts, correlated with the concentration as well as rate of release of exogenously administered NO_X. This increase in DSBs did not correlate with an increase in cell death or apoptosis in our tumor cell line. Finally, this lack of apoptosis was found to correlate with inhibition of caspase activity upon exposure to thiol- but not NONOate-based NO_X donor compounds.

Conclusions

Genotoxicity appears to be highly interrelated with both the concentration and kinetic delivery of NO_X. Moreover, alterations in cell apoptosis can be seen as a consequence of the explicit mechanisms of NO_X delivery. These findings lend credence to the hypothesis that NO_X may play an important role in tumor progression, and underscores potential pitfalls which should be considered when developing NO_X-based chemotherapeutic agents.

Hypoxic inducible factor 1alpha, extracellular signal-regulated kinase, and p53 are regulated by distinct threshold concentrations of nitric oxide

NO produced in tumors can either positively or negatively regulate growth. To examine this dichotomy, effects of NO concentration and duration on the posttranslational regulation of several key proteins were examined in human breast MCF7 cells under aerobic conditions. We found that different concentration thresholds of NO appear to elicit a discrete set of signal transduction pathways. At low steady-state concentrations of NO (<50 nM), extracellular signal-regulated kinase (ERK) phosphorylation was induced via a guanylate cyclase-dependent mechanism. Hypoxic inducible factor 1alpha (HIF-1alpha) accumulation was associated with an intermediate amount of NO (>100 nM), whereas p53 serine 15 phosphorylation occurred at considerably higher levels (>300 nM). ERK phosphorylation was transient during NO exposure. HIF-1alpha stabilization paralleled the presence of NO, whereas p53 serine 15 phosphorylation was detected during, and persisted after, NO exposure. The dose-dependent effects of synthetic NO donors were mimicked by activated macrophages cocultured with MCF7 cells at varying ratios. ERK and HIF-1alpha activation was similar in breast cancer cell lines either mutant (MB231) or null (MB157) in p53. The stabilization of HIF-1alpha by NO was not observed with increased MCF7 cell density, demonstrating the interrelationship between NO and O(2) consumption. The findings show that concentration and duration of NO exposure are critical determinants in the regulation of tumor-related proteins.

The role of nitric oxide in oral diseases

Although previously regarded as a toxic pollutant gas, nitric oxide (NO) is a short-lived molecule that plays a key role in many physiological and pathological processes. It is produced in vivo from the amino acid L-arginine by a complex family of enzymes termed nitric oxide synthase (NOS). Since its discovery as a biological messenger in 1987, NO has been implicated in many disease processes, ranging from septic shock to cancer. It is a highly reactive free radical and causes concentration-dependent conformational changes in proteins, enzymes and DNA, predominantly by its reaction with transition metals and thiol residues. Although high concentrations of NO are cytotoxic, the levels produced in many human cancers possibly facilitate tumour growth and dissemination. The interest in this molecule by scientists and clinicians involved with the oral cavity and head and neck regions is fairly recent, and only a tiny minority of 50,000 papers currently cited on NO relate to diseases in this anatomical area. This review gives an overview of NO, outlining its basic chemistry, formation by NOS and its possible roles in the oral diseases studied to date. The implications for possible therapeutic manipulation of NO are also discussed.

Expression of glutathione s-transferase pi in benign mucosa, Barrett's metaplasia, and adenocarcinoma of the esophagus

BACKGROUND

Glutathione s-transferase pi (GSTpi) is an enzyme that provides cellular protection against redox-mediated damage by free radicals, which have been implicated in carcinogenesis.

METHODS

Forty-three consecutive specimens from 19 patients were reviewed to identify samples of squamous mucosa, Barrett's metaplasia, adenocarcinoma, and peritumoral inflammation. Serial sections were stained with an anti-GSTpi polyclonal antibody, and GSTpi expression was quantified for each histologic group.

RESULTS

GSTpi expression was diminished in peritumoral mononuclear inflammatory cells (p <.001) compared with squamous epithelium, Barrett's metaplasia, or adenocarcinoma. Barrett's metaplasia exhibited decreased GSTpi expression compared with squamous mucosa (p =.045). GSTpi expression by >50% of adenocarcinoma cells was associated with an increased risk (2.25x) of disease at last follow-up.

CONCLUSIONS

GSTpi is prominently expressed in esophageal squamous mucosa and adenocarcinoma. Mononuclear cells may be susceptible to oxidative damage secondary to weak GSTpi production. GSTpi may protect the tumor cells themselves from the cytotoxic effects of free radicals. The biochemical role of GSTpi expression in malignant transformation deserves further investigation.

Role of nitric oxide in tumour progression with special reference to a murine breast cancer model

Nitric oxide (NO) is a potent bioactive molecule produced in the presence of NO synthase (NOS) enzymes, which mediates numerous physiological functions under constitutive conditions. Sustained overproduction of NO (and NO-reaction products), typically under inductive conditions, can lead to cell cycle arrest and cellular apoptosis. Furthermore, carcinogenesis may result from mutational events following NO-mediated DNA damage and hindrance to DNA repair (e.g., mutation of tumour-suppressor gene p53). In a majority of human and experimental tumours, tumour-derived NO appears to stimulate tumour progression; however, for a minority of tumours, the opposite has been reported. This apparent discrepancy may be explained by differential susceptibility of tumour cells to NO-mediated cytostasis or apoptosis, and the emergence of NO-resistant and NO-dependent clones. NO-resistance may be mediated by p53 inactivation, and upregulation of cyclo-oxygenase-2 and heat shock protein 70 (HSP70). In a murine mammary tumour model, tumour-derived NO promoted tumour growth and metastasis by enhancing invasive, angiogenic, and migratory capacities of tumour cells. Invasion stimulation followed the altered balance of matrix metalloproteases and their inhibitors; migration stimulation followed activation of guanylate cyclase and MAP kinase pathways. Selective NOS inhibitors may have a therapeutic role in certain cancers.

Nitric oxide and apoptosis during human head and neck squamous cell carcinoma development

PURPOSE

Apoptosis index (AI), Bcl-2, and Bax have shown prognostic significance in head and neck squamous cell carcinoma (HNSCCa). Other areas of research have implicated nitric oxide (NO) or its various intermediate species in both proapoptotic and antiapoptotic processes. We have previously shown that NO-generating enzymes are significantly increased during the stepwise progression to HNSCCa. The aim of this study was to explore the interrelationship of NO and a known consequence of NO-related oxidative stress, apoptosis, during this step-wise process.

MATERIALS AND METHODS

Formalin fixed-paraffin embedded tissue samples of 10 normal oral mucosa, 15 reactive/dysplastic lesions, and 17 HNSCCa lesions studied previously were subjected to the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP labeling (TUNEL) assay as well as immunohistochemical staining against Bcl-2, Bax, and p53. Patient charts were reviewed and clinical data were compared. The study pathologist (G.K.H) reviewed these slides blinded to patient identifiers or clinical data. The number of immunopositive cell nuclei or staining intensity was graded, noting the pattern of immunostaining. These staining characteristics were compared with the results of immunostaining previously obtained for endothelial constitutive NO synthase (ecNOS) and nitrotyrosine.

RESULTS

Compared with normal oral mucosa, the AI, Bcl-2, Bax, Bcl-2/Bax intensity and frequency ratios, and mutant p53 intensity significantly changed in reactive/dysplastic and HNSCCa lesions (P <.001 for all). Correlations between the staining characteristics of the antigens studied are presented. Furthermore, perilesional inflammatory cells showed staining in the TUNEL assay.

CONCLUSIONS

In a set of tissue samples previously well characterized, these new findings implicate a link between NO and the induction of apoptotic cell death in HNSCCa development.

Expression of nitric oxide synthase type 3 in reflux-induced esophageal lesions

BACKGROUND

The expression of endothelial constitutive nitric oxide synthase (NOS3) by squamous dysplasia and carcinomas of the head and neck has previously been described. We sought to compare NOS3 expression in squamous mucosa, glandular metaplasia, and adenocarcinoma of the esophagus.

METHODS

Forty paraffin-embedded specimens from 20 patients with adenocarcinoma were stained with anti-NOS3 monoclonal antibody. The percentage of cells stained and the intensity of staining were determined for squamous epithelium, metaplasia, and adenocarcinoma. Staining characteristics were statistically analyzed according to clinical variables.

RESULTS

NOS3 expression was significantly higher in adenocarcinoma and squamous epithelium compared with glandular metaplasia. Among the carcinomas, larger tumor size (T3/4), nodal positivity, and advanced TNM stage (III/IV) significantly correlated with increased NOS3 expression.

CONCLUSIONS

NOS3 is expressed in reflux-induced lesions of the esophagus. Glandular metaplasia shows basal levels of NOS3 that significantly increase with malignant transformation and tumor progression. The role of free radicals in carcinogenesis is being actively studied.

Does type II nitric oxide synthase expression correlate with cellular proliferation in oral squamous cell carcinoma and dysplasia?

BACKGROUND

Nitric oxide (NO) has been implicated both in tumor progression and inhibition. This study investigated whether type II nitric oxide synthase (NOS2) expression correlated with cell proliferation in oral squamous cell carcinoma (OSCC) and dysplasia.

METHODS

Paraffin-embedded tissue samples of normal oral mucosa, OSCC, and dysplasia were assessed immunohistochemically using monoclonal antibodies to NOS2 and Ki-67 antigen. We used Western blotting to confirm NOS2 antibody specificity and protein expression in select cases.

RESULTS

NOS2 staining was increased in OSCC relative to normal oral mucosa, in which no expression was found. Both NOS2 expression and Ki-67 indices independently correlated with grade of dysplasia (p < .001) but not with the degree of tumor differentiation. A positive correlation was found between NOS2 expression and Ki-67 in cases of mild and moderate dysplasia (p < .001), but not in severe dysplasia and OSCC.

CONCLUSIONS

No correlation exists between Ki-67 and NOS2 expression in severe dysplasia and OSCC. The findings suggest that the level of NO produced by NOS2 is insufficient to affect cellular proliferation in these conditions. The mechanism of NOS2 activation and the consequences of its expression remain to be fully explained.

Correlation between type II nitric oxide synthase and p53 expression in oral squamous cell carcinoma

Prolonged nitric oxide (NO) production by the enzyme type II nitric oxide synthase (NOS2) has been implicated in angiogenesis and metastasis of human cancers. In animal models, wild-type p53 (but not mutant) protein results in down-regulation of NOS2 expression, which reduces both tumour growth and dissemination. In the current study, we aimed to find out whether a correlation was present in oral squamous cell carcinoma. Fifty-six cases of squamous cell carcinoma were assessed immunohistochemically using antibodies to NOS2 and p53 (clone DO-7). We also confirmed NOS2 protein expression in selected cases using immunoblotting. The results were correlated with clinicopathological findings. Statistical analysis showed a significant relationship between p53 and NOS2 expression (P= 0.001). No relationship was found between size of tumour or histological degree of differentiation, and NOS2 expression in the primary tumour.

Expression of inducible nitric oxide synthase and p53 in oral epithelial dysplasia

AIM

Nitric oxide (NO) has been studied in a variety of human cancers and is implicated in both tumor promotion and inhibition. Downregulation of the enzyme iNOS by wild-type p53 (but not mutant) protein has been shown to occur in normal cells and some tumors, but the relationship has not been reported in oral epithelial dysplasia.

METHODS AND RESULTS

An immunohistochemical study was conducted with antibodies to iNOS and p53 (clone DO-7) in 36 cases of oral dysplasia of varying severity. Statistical analysis showed a significant correlation between iNOS staining and grade of dysplasia (P <.001) and between p53 and iNOS staining (P <.001).

CONCLUSIONS

This preliminary study has shown that iNOS expression correlates with severity of dysplasia, and it is also increased in those cases showing positive staining for p53. Further research is required to fully establish the relationship between iNOS and p53 in both dysplasia and oral squamous cell carcinoma.

Glutathione S-transferase pi in squamous cell carcinoma of the head and neck

OBJECTIVES/HYPOTHESIS

Oxidative/reductive (redox) DNA damage from radical species such as nitric oxide (NO*) are increasingly being implicated in the development of cancer. Moreover, redox-protective cellular mechanisms, such as glutathione S-transferase, may determine cellular susceptibility to this redox-mediated damage.

METHODS

Formalin-fixed, paraffin-embedded tissue samples of 11 normal oral mucosa, 15 reactive/dysplastic lesions, and 131 head and neck squamous cell carcinomas (HNSCCs) were immunohistochemically stained using a polyclonal antibody against glutathione S-transferase pi (GST-pi). Slides were reviewed in a blinded fashion by the study pathologist (G.K.H.) and intensity was graded, noting the pattern of immunostaining. These staining characteristics were compared with those obtained using monoclonal antibodies against endothelial constitutive nitric oxide synthase (ecNOS) and nitrotyrosine, a marker of NO*'s pathological nitrosylation of proteins on serial sections of the same tissue. Patient charts were reviewed and clinical data collected.

RESULTS

The expression of GST-pi was significantly increased in reactive/dysplastic and HNSCC samples compared with normal squamous mucosa (P < .001 for both). Furthermore, among the carcinomas the expression of GST-pi was significantly increased in higher-grade lesions (P < .02). The expression of GST-pi correlated highly with the expression of ecNOS and nitrotyrosine (P < .0001 for both).

CONCLUSIONS

These findings demonstrate that GST-pi is upregulated in conjunction with the NO*-generating ecNOS isoform and implicate GST-pi in protecting HNSCC from the cytotoxic effects of high concentrations of NO* found in the tumor bed.

Does expression of inducible nitric oxide synthase correlate with severity of oral epithelial dysplasia?

The small molecule nitric oxide (NO) has generated an exponential amount of research since its discovery as a biological messenger in 1987. It has a vast number of actions, many of which are poorly understood. It has been studied in a variety of human cancers and has been implicated both in tumour promotion and inhibition. Although NO is produced by three distinct isoforms of the enzyme nitric oxide synthase (NOS), most cancer research is directed towards the calcium-independent form, iNOS which following induction, produces much higher quantities of NO than the other two. In this study the expression of iNOS is assessed by immunohistochemistry in 26 cases of oral epithelial dysplasia ranging in severity from mild to severe. iNOS staining was found in all 26 cases of dysplasia with the degree of staining correlating to the severity of dysplasia (p < 0.001). There was no iNOS staining seen in adjacent normal epithelium. The possible role of iNOS in the complex transformation from dysplasia to invasive oral cancer and the clinical applications are discussed.

The yin and yang of nitric oxide: reflections on the physiology and pathophysiology of NO

Nitric oxide (NO.) is an arginine-derived nitrogen-based radical that is rapidly becoming one of the most important molecular species to be discovered. Over the past decade, an explosion of evidence has revealed the extreme complexity of function of this seemingly simple inorganic molecule. It is now evident that NO. demonstrates a functional dualism, playing a pivotal role in numerous physiologic and pathophysiologic processes. Whether this molecule is beneficial or detrimental is dependent upon the tissue of generation, the level of production, the oxidative/reductive (redox) environment in which this radical is generated, and the presence or absence of NO. transduction elements. Nitric oxide is generated by three independent isoenzymes that resemble the p-450 enzyme superfamily in both form and function. It ultimately alters enzymatic function through covalent modification, redox interactions, and interactions with metallic functional centers. This radical is a key figure in a number of pathophysiologic processes by means of similar yet uncoordinated interactions. In consideration of the already broad spectrum of roles attributed to NO., it seems highly likely that this molecule will be implicated in an ever widening variety of functions relative to the practice of otolaryngology-head and neck surgery. This article reviews the enzymology, signal transduction mechanisms, physiology, and pathophysiology of NO. as it pertains to head and neck cancer.