Activation of NF-kappaB determines the sensitivity of human colon cancer cells to TNFalpha-induced apoptosis

Research progress on nonsteroidal anti-inflammatory drugs in the treatment of pituitary neuroendocrine tumors

Pituitary neuroendocrine tumor is the third most common primary intracranial tumor. Its main clinical manifestations include abnormal hormone secretion symptoms, symptoms caused by tumor compression of the surrounding pituitary tissue, pituitary stroke, and other anterior pituitary dysfunction. Its pathogenesis is yet to be fully understood. Surgical treatment is still the main treatment. Despite complete resection, 10%-20% of tumors may recur. While dopamine agonists are effective in over 90% of prolactinomas, prolonged use and individual variations can lead to increased drug resistance and a gradual decline in efficacy, which ultimately requires surgical intervention. Nonsteroidal anti-inflammatory drugs reduce the production of inflammatory mediator prostaglandins by inhibiting the activity of cyclooxygenase and exert antipyretic, analgesic, antiplatelet, and anti-inflammatory effects. In recent years, many in-depth studies have confirmed the potential of nonsteroidal anti-inflammatory drugs as a preventive and antitumor agent. It has been extensively utilized in the prevention and treatment of various types of cancer. However, their specific mechanisms of action still need to be fully elucidated. This article summarizes recent research progress on the expression of cyclooxygenase in pituitary neuroendocrine tumors and the treatment of nonsteroidal anti-inflammatory drugs. It provides a feasible theoretical basis for further research on pituitary neuroendocrine tumors and explores potential therapeutic targets.

CCL3 Promotes Proliferation of Colorectal Cancer Related with TRAF6/NF-κB Molecular Pathway

Chemokine C-C motif chemokine ligand 3 (CCL3) plays an important role in the invasion and metastasis of malignant tumors. For developing new therapeutic targets and antitumor drugs, the effect of chemokine CCL3 and the related cytokine network on colorectal cancer should be investigated. This study used cell, tissue, and animal experiments to prove that CCL3 is highly expressed in colorectal cancer and confirmed that CCL3 can promote the proliferation of cancer cells, and its expression is closely related to TRAF6/NF-κB molecular pathway. In addition, protein chip technology was used to examine colorectal cancer tissue samples and identify the key factors of chemokine CCL3 and the toll-like receptors/nuclear factor-κB (TLR/NF-κB) pathway in cancer and metastatic lymph nodes. Furthermore, the lentiviral vector technology was employed for transfection to construct interference and overexpression cell lines. The experimental results reveal the mechanism of CCL3 and TNF receptor-associated factor 6 (TRAF6)/NF-κB pathway-related factors and their effects on the proliferation of colon cancer cells. Finally, the expression and significance of CCL3 in colorectal cancer tissues and its correlation with clinical pathology were studied by immunohistochemistry. Also, the results confirmed that CCL3 and C-C motif chemokine receptor 5 (CCR5) were expressed in adjacent tissues, colorectal cancer tissues, and metastatic cancer. The expression level was correlated with the clinical stage and nerve invasion. The expression of chemokine CCL3 and receptor CCR5 was positively correlated with the expression of TRAF6 and NF-κB and could promote the proliferation, invasion, and migration of colorectal cancer cells through TRAF6 and NF-κB.

Anthocyanins Isolated from Vitis coignetiae Pulliat Enhances Cisplatin Sensitivity in MCF-7 Human Breast Cancer Cells through Inhibition of Akt and NF-κB Activation

Anthocyanins isolated from Vitis coignetiae Pulliat (Meoru in Korea) (AIMs) have various anti-cancer properties by inhibiting Akt and NF-κB which are involved in drug resistance. Cisplatin (CDDP) is one of the popular anti-cancer agents. Studies reported that MCF-7 human breast cancer cells have high resistance to CDDP compared to other breast cancer cell lines. In this study, we confirmed CDDP resistance of MCF-7 cells and tested whether AIMs can overcome CDDP resistance of MCF-7 cells. Cell viability assay revealed that MCF-7 cells were more resistant to CDDP treatment than MDA-MB-231 breast cancer cells exhibiting aggressive and high cancer stem cell phenotype. AIMs significantly augmented the efficacy of CDDP with synergistic effects on MCF-7 cells. Molecularly, Western blot analysis revealed that CDDP strongly increased Akt and moderately reduced p-NF-κB and p-IκB and that AIMs inhibited CDDP-induced Akt activation, and augmented CDDP-induced reduction of p-NF-κB and p-IκB in MCF-7 cells. In addition, AIMs significantly downregulated an anti-apoptotic protein, XIAP, and augmented PARP-1 cleavage in CDDP-treated MCF-7 cells. Moreover, under TNF-α treatment, AIMs augmented CDDP efficacy with inhibition of NF-κB activation on MCF-7 cells. In conclusion, AIMs enhanced CDDP sensitivity by inhibiting Akt and NF-κB activity of MCF-7 cells that show relative intrinsic CDDP resistance.

Role of cancer-related inflammation in colon cancer

Chronic inflammation is one of the important mechanisms for the development of colon cancer, and the role of cancer-related inflammation (CRI) in tumor development is a hot research topic in recent years. Therefore, it is very important to clarify the effect and regulation of CRI in colon cancer. Accumulating evidence indicates that transcription factors, cytokines, chemokines, cyclooxygenase-2 and microRNAs play key roles in CRI. This review focuses on the research progress about these molecules in colon cancer.

Up-regulation and cytoprotective role of epithelial multidrug resistance-associated protein 1 in inflammatory bowel disease

MRP1 (multidrug resistance-associated protein 1) is well known for its role in providing multidrug resistance to cancer cells. In addition, MRP1 has been associated with both pro- and anti-inflammatory functions in nonmalignant cells. The pro-inflammatory function is evident from the fact that MRP1 is a high affinity transporter for cysteinyl-leukotriene C4 (LTC4), a lipid mediator of inflammation. It remains unexplained, however, why the absence of Mrp1 leads to increased intestinal epithelial damage in mice treated with dextran-sodium sulfate, a model for inflammatory bowel disease (IBD). We found that MRP1 expression is induced in the inflamed intestine of IBD patients, e.g. Crohn disease and ulcerative colitis. Increased MRP1 expression was detected at the basolateral membrane of intestinal epithelial cells. To study a putative role for MRP1 in protecting epithelial cells against inflammatory cues, we manipulated MRP1 levels in human epithelial DLD-1 cells and exposed these cells to cytokines and anti-Fas. Inhibition of MRP1 (by MK571 or RNA interference) resulted in increased cytokine- and anti-Fas-induced apoptosis of DLD-1 cells. Opposite effects, e.g. protection of DLD-1 cells against cytokine- and anti-Fas-induced apoptosis, were observed after recombinant MRP1 overexpression. Inhibition of LTC4 synthesis reduced anti-Fas-induced apoptosis when MRP1 function was blocked, suggesting that LTC4 is the pro-apoptotic compound exported by epithelial MRP1 during inflammation. These data show that MRP1 protects intestinal epithelial cells against inflammation-induced apoptotic cell death and provides a functional role for MRP1 in the inflamed intestinal epithelium of IBD patients.

Endothelin-1 induces NF-kappaB via two independent pathways in human renal tubular epithelial cells

BACKGROUND

Endothelin-1 (ET-1) is a major transcriptional activator of renal proximal tubule cells acting in an autocrine and paracrine manner. In animal studies, ET-1 has been implicated in progressive renal interstitial fibrosis by promoting gene expression, possibly via the inflammatory NF-kappaB signal pathway. While ET-1-dependent mechanisms of signal transduction have been studied mainly in tumor cell lines, we analyzed the mechanism of ET-1-induced, NF-kappaB-mediated target gene activation in proximal tubule cells.

METHODS

Human renal proximal tubule cells were stimulated with ET-1 and gene expression analyzed by protein microarray, Western blot, non-radioactive electromobility shift assay, and quantitative real-time polymerase chain reaction.

RESULTS

Activation of NF-kappaB occurs only via an ET-1-specific type A receptor (not type B as in animals). Induction can be blocked by bosentan, and endothelin-A but not endothelin-B receptor-specific antagonists. Protein microarray screening shows activation of two independent cascades (via the endothelin-A receptor, or via diacylglycerol) leading to NF-kappaB induction. The independent induction is also reflected by target gene expression such as the vascular cell adhesion molecule-1, interleukin-6, and fractalkine at different time points.

CONCLUSION

Thus prohibiting ET-1-mediated gene transcription necessitates blocking of NF-kappaB and diacylglycerol signal transduction in proximal tubule cells.

Insulin-like growth factor binding protein 3 (IGFBP-3) potentiates TRAIL-induced apoptosis of human colorectal carcinoma cells through inhibition of NF-kappaB

There is growing evidence that the insulin-like growth factor-binding protein 3 (IGFBP-3) can have IGF-independent effects on cell growth. However, despite the fact that IGFBP-3 has been reported to be both antiproliferative and proapoptotic, the molecular mechanisms underlying the action of IGFBP-3 have not been elucidated. We report that although addition of IGFBP-3 (either synthetic or secreted protein) had no effect on cell survival, IGFBP-3 (100 ng/ml) significantly enhanced TNF-related apoptosis-inducing ligand (TRAIL)-induced cell death in colonic carcinoma-derived cell lines (20-30% depending on cell line), whereas it had no effect on the survival of the TRAIL-resistant adenoma-derived cells. Both addition of IGFBP-3 protein to cell cultures or enforced expression of IGFBP-3 in the HT29 carcinoma cell line inhibited nuclear factor kappa B (NF-kappaB) activation in response to the induction of apoptosis by TRAIL. We propose that IGFBP-3 is a non-toxic NF-kappaB inhibitor, which could be used as an adjuvant in the treatment of colon cancer.

Inhibition of transcription factor NF-kappaB signaling proteins IKKbeta and p65 through specific cysteine residues by epoxyquinone A monomer: correlation with its anti-cancer cell growth activity

Transcription factor NF-kappaB is constitutively active in many human chronic inflammatory diseases and cancers. Epoxyquinone A monomer (EqM), a synthetic derivative of the natural product epoxyquinol A, has previously been shown to be a potent inhibitor of tumor necrosis factor-alpha (TNF-alpha)-induced activation of NF-kappaB, but the mechanism by which EqM inhibits NF-kappaB activation was not known. In this report, we show that EqM blocks activation of NF-kappaB by inhibiting two molecular targets: IkappaB kinase IKKbeta and NF-kappaB subunit p65. EqM inhibits TNF-alpha-induced IkappaBalpha phosphorylation and degradation by targeting IKKbeta, and an alanine substitution for Cys179 in the activation loop of IKKbeta makes it resistant to EqM-mediated inhibition. EqM also directly inhibits DNA binding by p65, but not p50; moreover, replacement of Cys38 in p65 with Ser abolishes EqM-mediated inhibition of DNA binding. Pretreatment of cells with reducing agent dithiothreitol dose-dependently reduces EqM-mediated inhibition of NF-kappaB, further suggesting that EqM directly modifies the thiol group of Cys residues in protein targets. Modifications of the exocyclic alkene of EqM substantially reduce EqM's ability to inhibit NF-kappaB activation. In the human SUDHL-4 lymphoma cell line, EqM inhibits both proliferation and NF-kappaB DNA binding, and activates caspase-3 activity. EqM also effectively inhibits the growth of human leukemia, kidney, and colon cancer cell lines in the NCI's tumor cell panel. Among six colon cancer cell lines, those with low amounts of constitutive NF-kappaB DNA-binding activity are generally more sensitive to growth inhibition by EqM. Taken together, these results suggest that EqM inhibits growth and induces cell death in tumor cells through a mechanism that involves inhibition of NF-kappaB activity at multiple steps in the signaling pathway.

Inactivation of nuclear factor kappaB by soy isoflavone genistein contributes to increased apoptosis induced by chemotherapeutic agents in human cancer cells

Cancer chemotherapeutic strategies commonly require multiple agents. However, use of multiple agents contributes to added toxicity resulting in poor treatment outcome. Thus, combination chemotherapy must be optimized to increase tumor response and at the same time lower its toxicity. Chemotherapeutic agents are known to induce nuclear factor kappaB (NF-kappaB) activity in tumor cells, resulting in lower cell killing and drug resistance. In contrast, genistein has been shown to inhibit the activity of NF-kappaB and the growth of various cancer cells without causing systemic toxicity. We therefore investigated whether the inactivation of NF-kappaB by genistein before treatment of various cancer cells with chemotherapeutic agents could lead to better tumor cell killing as tested by in vitro studies using gene transfections and also by animal studies. PC-3 (prostate), MDA-MB-231 (breast), H460 (lung), and BxPC-3 (pancreas) cancer cells were pretreated with 15 to 30 micromol/L genistein for 24 hours and then exposed to low doses of chemotherapeutic agents for an additional 48 to 72 hours. We found that 15 to 30 micromol/L genistein combined with 100 to 500 nmol/L cisplatin, 0.5 to 2 nmol/L docetaxel, or 50 ng/mL doxorubicin resulted in significantly greater inhibition of cell growth and induction of apoptosis compared with either agent alone. Moreover, we found that the NF-kappaB activity was significantly increased within 2 hours of cisplatin and docetaxel treatment and that the NF-kappaB inducing activity of these agents was completely abrogated in cells pretreated with genistein. These results were also supported, for the first time, by animal experiments, p65 cDNA transfection and p65 small interfering RNA studies, which clearly showed that a specific target (NF-kappaB) was affected in vivo. Collectively, our results clearly suggest that genistein pretreatment inactivates NF-kappaB and may contribute to increased growth inhibition and apoptosis induced by cisplatin, docetaxel, and doxorubicin in prostate, breast, lung, and pancreatic cancer cells. Theses results warrant carefully designed clinical studies investigating the combination of soy isoflavones and commonly used chemotherapeutic agents for the treatment of human cancers.

Unconjugated bilirubin induces apoptosis in colon cancer cells by triggering mitochondrial depolarization

Bilirubin is the principal end product of heme degradation. Prompted by epidemiologic analyses demonstrating an inverse correlation between serum bilirubin levels and cancer mortality, we examined the effect(s) of bilirubin on the growth and survival of colon adenocarcinoma cells. Adenocarcinoma cell monolayers were treated with bilirubin over a range of bilirubin:BSA molar ratios (0-0.6), and viability was assessed colorimetrically. Apoptosis was characterized by TUNEL assay, annexin V staining and caspase-3 activation. The mechanism(s) by which bilirubin induces apoptosis was investigated by Western blotting for cytochrome c release, assaying for caspase-8 and caspase-9 activation and for mitochondrial depolarization by JC-1 staining. The direct effect of bilirubin on the membrane potential of isolated mitochondria was evaluated using light-scattering and fluorescence techniques. Bilirubin decreased the viability of all colon cancer cell lines tested in a dose-dependent manner. Cells exhibited substantial apoptosis when exposed to bilirubin concentrations ranging 0-50 microM, as demonstrated by an 8- to 10-fold increase in TUNEL and annexin V staining and in caspase-3 activity. Bilirubin treatment evokes specific activation of caspase-9, enhances cytochrome c release into the cytoplasm and triggers the mitochondrial permeability transition in colon cancer monolayers. Additionally, bilirubin directly induces the depolarization of isolated rat liver mitochondria, an effect that is not inhibited by cyclosporin A. Bilirubin stimulates apoptosis of colon adenocarcinoma cells in vitro through activation of the mitochondrial pathway, apparently by directly dissipating mitochondrial membrane potential. As this effect is triggered at concentrations normally present in the intestinal lumen, we postulate a physiologic role for bilirubin in modulating colon tumorigenesis.

Apoptosis-inducing effect of chemotherapeutic agents is potentiated by soy isoflavone genistein, a natural inhibitor of NF-kappaB in BxPC-3 pancreatic cancer cell line

Cancer chemotherapeutic strategies should be devised to provide higher tumor response and lower toxicity for combination chemotherapy. Genistein has been shown to inhibit the growth of various cancer cells in vitro and in vivo without toxicity to normal cells. The antitumor effects of genistein could be in part due to inactivation of NF-kappaB activity. In contrast, chemotherapeutic agents inadvertently induce NF-kappaB activity, which may lead to chemoresistance. In this study, we investigated whether the inactivation of NF-kappaB by genistein would enhance the efficacy of chemotherapeutic agents. BxPC-3 pancreatic cancer cells were pretreated with 30 micromol/L genistein for 24 hours and then exposed to lower concentrations of chemotherapeutic agents for an additional 24 hours. Cell growth inhibition assay, apoptosis assay, and NF-kappaB EMSA were performed. The combination of 30 micromol/L genistein with 1 nmol/L docetaxel or 100 nmol/L cisplatin elicited significantly greater inhibition of cell growth compared with either agent alone. The combination treatment induced more apoptosis in BxPC-3 cells compared with single agents. Moreover, the NF-kappaB activity was significantly increased within 2 hours of docetaxel or cisplatin treatment, and the NF-kappaB-inducing activity of these agents was completely abrogated in cells pretreated with genistein. These results clearly suggest that genistein pretreatment, which inactivates NF-kappaB activity, together with other cellular effects of genistein, may contribute to increased cell growth inhibition and apoptosis inducing effects of nontoxic doses of docetaxel and cisplatin, which could be a novel strategy for the treatment of pancreatic cancer.

Increased NF-kappaB DNA binding but not transcriptional activity during apoptosis induced by the COX-2-selective inhibitor NS-398 in colorectal carcinoma cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit colorectal neoplasia, an effect that is associated with their ability to induce apoptosis. Although NSAIDs have been reported to inhibit NF-κB, more recent studies show activation of NF-κB by NSAIDs. NF-κB commonly shows antiapoptotic activity and is implicated in the therapeutic resistance of cancer cells. The effects of highly COX-2-selective NSAIDs such as NS-398 on NF-κB in colorectal tumour cells have not been reported. Therefore, we addressed whether NF-κB has a role in NS-398-induced apoptosis of colorectal cancer cells. Treatment of HT-29 colorectal carcinoma cells with doses of NS-398 (50–75 μM) known to induce apoptosis had no effect on NF-κB for up to 48 h. However after 72 and 96 h NF-κB DNA-binding activity was increased by NS-398, in parallel with apoptosis induction. NS-398-treated HT-29 cells showed increased p50 homodimer binding and an induction of p50/p65 heterodimers, as demonstrated by supershift assay. However, although NS-398 increased NF-κB DNA binding it did not increase NF-κB-dependent reporter activity and inhibition of NF-κB DNA binding did not enhance NS-398-induced apoptosis. This indicates that NF-κB activated by NS-398 is transcriptionally inactive and is an encouraging result for the use of COX-2-selective NSAIDs not only in chemoprevention but also as novel therapies for colon cancer.

Apc+/Min colonic epithelial cells express TNF receptors and ICAM-1 when they are co-cultured with large intestine intra-epithelial lymphocytes

Adenomatous polyposis coli (APC) functions are involved in the heterotypic interactions occurring between intestinal epithelial cells (IECs) and intra-epithelial lymphocytes (IELs). These interactions may be of interest in cancer prevention, since recent data provide evidence for lymphocyte mediated immunosurveillance of epithelial cancers. The present study attempts to determine if APC inactivation induces changes in the cross-talk between IEC and large intestine IEL (LI-IEL) through intercellular adhesion molecule (ICAM-1)/leukocyte function-associated (LFA-1) interactions. Mouse Apc+/+ and Apc+/Min colonocytes were co-cultivated with LI-IEL. When co-cultured with LI-IEL Apc+/Min IEC but not Apc+/+ IEC expressed high levels of ICAM-1. The presence of ICAM-1 was linked to TNFalpha production in both co-cultures and TNFR expression only in co-cultivated Apc+/Min IEC. Finally, butyrate enhanced the expression of ICAM-1 in Apc+/Min IEC co-cultured with LI-IEL, and the secretion of TNFalpha by both types of co-cultures. These events could participate in determining the Apc+/Min IEC immunogenicity under different in vivo conditions.

Phosphorylation of Akt/PKB is required for suppression of cancer cell apoptosis and tumor progression in human colorectal carcinoma

BACKGROUND

Akt/protein kinase B (PKB), which is included in phosphatidyl inositol-3-OH kinase (PI3K) signaling, controls many intracellular processes, such as the suppression of apoptosis and the promotion of the cell cycle. Therefore, the authors investigated phosphorylated Akt (Ser473) in colorectal carcinomas to reveal the role of PI3K signaling during the development of colorectal carcinoma.

METHODS

Expression of phosphorylated Akt (Ser473) in two colon carcinoma cell lines (DLD-1 and Colo205) and 65 human colorectal carcinomas was analyzed using western blotting and immunohistochemistry, respectively. Growth inhibition and induction of apoptosis caused by LY294002, a specific inhibitor of PI3K, were also examined in these cell lines. In tumor samples, the level of cell proliferation activity (Ki-67) and number of apoptotic bodies (single stranded DNA) were determined by counting positive cells.

RESULTS

LY294002 significantly affected the proliferation and apoptosis of Colo205 cells, suggesting an association with the low phosphorylation level of Akt protein. Immunohistochemic analysis showed that 46% of the tumors had a high level of expression of phosphorylated Akt with a close association with Ki-67 proliferative activity (P < 0.001) and the number of apoptotic bodies (P < 0.001). Akt phosphorylation was also correlated with some clinicopathologic parameters of the malignancies, including depth of invasion, infiltration to venous vessels, lymph node metastasis, and clinicopathologic stage.

CONCLUSIONS

The phosphorylated Akt level can monitor cell growth and resistance to apoptosis, indicating that activation of Akt plays an important role during the progression of colorectal carcinomas by helping promote cell growth and rescue cells from apoptosis. These findings also suggest the possibility of using LY294002 for treatment of colorectal carcinoma.

Control of cell cycle exit and entry by protein kinase B-regulated forkhead transcription factors

AFX-like Forkhead transcription factors, which are controlled by phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) signaling, are involved in regulating cell cycle progression and cell death. Both cell cycle arrest and induction of apoptosis are mediated in part by transcriptional regulation of p27(kip1). Here we show that the Forkheads AFX (FOXO4) and FKHR-L1 (FOXO3a) also directly control transcription of the retinoblastoma-like p130 protein and cause upregulation of p130 protein expression. Detailed analysis of p130 regulation demonstrates that following Forkhead-induced cell cycle arrest, cells enter G(0) and become quiescent. This is shown by a change in phosphorylation of p130 to G(0)-specific forms and increased p130/E2F-4 complex formation. Most importantly, long-term Forkhead activation causes a sustained but reversible inhibition of proliferation without a marked increase in apoptosis. As for the activity of the Forkheads, we also show that protein levels of p130 are controlled by endogenous PI3K/PKB signaling upon cell cycle reentry. Surprisingly, not only nontransformed cells, but also cancer cells such as human colon carcinoma cells, are forced into quiescence by Forkhead activation. We therefore propose that Forkhead inactivation by PKB signaling in quiescent cells is a crucial step in cell cycle reentry and contributes to the processes of transformation and regeneration.

Cyclooxygenase-independent actions of cyclooxygenase inhibitors

Several studies have demonstrated unequivocally that certain nonsteroidal anti-inflammatory drugs (NSAIDs) such as sodium salicylate, sulindac, ibuprofen, and flurbiprofen cause anti-inflammatory and antiproliferative effects independent of cyclooxygenase activity and prostaglandin synthesis inhibition. These effects are mediated through inhibition of certain transcription factors such as NF-kappaB and AP-1. The respective NSAIDs might interfere directly with the transcription factors, but their effects are probably mediated predominantly through alterations of the activity of cellular kinases such as IKKbeta, Erk, p38 MAPK, or Cdks. These effects apparently are not shared by all NSAIDs, since indomethacin failed to inhibit NF-kappaB and AP-1 activation as well as Erk and Cdk activity. In contrast, indomethacin was able to activate PPARgamma, which was not affected by sodium salicylate or aspirin. The differences in cyclooxygenase-independent mechanisms may have consequences for the specific use of these drugs in individual patients because additional effects may either enhance the efficacy or reduce the toxicity of the respective compounds.

Nitric oxide disrupts H2O2-dependent activation of nuclear factor kappa B. Role in sensitization of human tumor cells to tumor necrosis factor-alpha -induced cytotoxicity

Tumor necrosis factor alpha (TNF-alpha) exerts its effect by two distinct signaling pathways. It can trigger cytotoxicity in sensitive target cells. TNF-alpha can also promote nuclear factor kappaB (NF-kappaB) activity and regulate the expression of genes that interfere with apoptosis and thus conferring resistance to several apoptotic stimuli. We have observed that interferon-gamma (IFN-gamma) sensitizes human ovarian carcinoma cell lines to TNF-alpha-mediated apoptosis and further, IFN-gamma induces the expression of the inducible nitric-oxide synthase (iNOS) and the generation of nitric oxide (NO). This study examines the role of NO in the sensitization of the ovarian carcinoma cell line AD10 to TNF-alpha-mediated cytotoxicity. Treatment of AD10 cells with the NOS inhibitor l-NMA blocked the IFN-gamma-dependent sensitization whereas NO donors (S-nitroso-N-acetylpenicillamine) sensitized these cells to TNF-alpha cytotoxicity. Analysis of the activation status of NF-kappaB upon treatment with NO donors confirmed the inhibitory role of NO on both the NF-kappaB DNA-binding property and its activation. Moreover, the inhibition of NF-kappaB nuclear translocation by NO donors directly correlated with the intracellular concentration of H(2)O(2) and was reversed by the addition of exogenous H(2)O(2). These findings show that NO might interfere with TNF-alpha-dependent NF-kappaB activation by interacting with O(2) and reducing the generation of H(2)O(2), a potent NF-kappaB activator. Therefore, NO-mediated disruption of NF-kappaB activation results in the removal of anti-apoptotic/resistance signals and sensitizes tumor cells to cytotoxic cytokines like TNF-alpha.