Colon cancer chemoprevention by a novel NO chimera that shows anti-inflammatory and antiproliferative activity in vitro and in vivo

The apoptotic inducible effects of salicylic acid on hepatoma cell line: relationship with nitric oxide signaling

Clinical and experimental data suggest that salicylic acid (SA) is tumor preventive and NO has a multitude of effects on tumor biology. Therefore, firstly, the aim of our study is to explore the important role of SA in apoptotic induction of liver cancer cells. Secondly, we investigate whether SA mediates the anti-tumor effects by NO signaling pathway. The liver cancer cell line was treated with different concentrations of SA. Cell proliferation was tested using MTS assay and cell apoptosis was assessed by flow cytometry. NO content and NOS activities were measured by biochemical assay. The anti- or pro-apoptotic regulator gene expressions were analyzed by real-time PCR. Our data illustrated that high concentration of SA significantly inhibited liver cancer cell proliferation accompanied by apoptosis induction. In addition, SA led to the release of NO and the increase of NOS activities in above process. Importantly, SA up-regulated a series of apoptosis-related gene expression and reduced the mRNA level of HMGB1. Meanwhile, we also found that NOS inhibitor L-NAME and NO scavenger cPTIO attenuated the above SA-induced effects. Thus, we provided the evidence that SA exerted anti-tumor effects in liver cancer cell in part mediated by the NO pathway.

HIV-protease inhibitors for the treatment of cancer: Repositioning HIV protease inhibitors while developing more potent NO-hybridized derivatives?

The possible use of HIV protease inhibitors (HIV-PI) as new therapeutic option for the treatment of cancer primarily originated from their success in treating HIV-related Kaposi's sarcoma (KS). While these findings were initially attributed to immune reconstitution and better control of oncogenic viral infections, the number of reports on solid tumors, KS, lymphoma, fibrosarcoma, multiple myeloma and prostate cancer suggest other mechanisms for the anti-neoplastic activity of PIs. However, a major drawback for the possible adoption of HIV-PIs in the therapy of cancer relies on their relatively weak anticancer potency and important side effects. This has propelled several groups to generate derivatives of HIV-PIs for anticancer use, through modifications such as attachment of different moieties, ligands and transporters, including saquinavir-loaded folic acid conjugated nanoparticles and nitric oxide (NO) derivatives of HIV-PIs. In this article, we discuss the current preclinical and clinical evidences for the potential use of HIV-PIs, and of novel derivatives, such as saquinavir-NO in the treatment of cancer.

Prodrugs Bioactivated to Quinones Target NF-κB and Multiple Protein Networks: Identification of the Quinonome

Electrophilic reactive intermediates resulting from drug metabolism have been associated with toxicity and off-target effects and in some drug discovery programs trigger NO-GO decisions. Many botanicals and dietary supplements are replete with such reactive electrophiles, notably Michael acceptors, which have been demonstrated to elicit chemopreventive mechanisms; and Michael acceptors are gaining regulatory approval as contemporary cancer therapeutics. Identifying protein targets of these electrophiles is central to understanding potential therapeutic benefit and toxicity risk. NO-donating NSAID prodrugs (NO-NSAIDs) have been the focus of extensive clinical and preclinical studies in inflammation and cancer chemoprevention and therapy: a subset exemplified by pNO-ASA, induces chemopreventive mechanisms following bioactivation to an electrophilic quinone methide (QM) Michael acceptor. Having previously shown that these NO-independent, QM-donors activated Nrf2 via covalent modification of Keap-1, we demonstrate that components of canonical NF-κB signaling are also targets, leading to the inhibition of NF-κB signaling. Combining bio-orthogonal probes of QM-donor ASA prodrugs with mass spectrometric proteomics and pathway analysis, we proceeded to characterize the quinonome: the protein cellular targets of QM-modification by pNO-ASA and its ASA pro-drug congeners. Further comparison was made using a biorthogonal probe of the "bare-bones", Michael acceptor, and clinical anti-inflammatory agent, dimethyl fumarate, which we have shown to inhibit NF-κB signaling. Identified quinonome pathways include post-translational protein folding, cell-death regulation, protein transport, and glycolysis; and identified proteins included multiple heat shock elements, the latter functionally confirmed by demonstrating activation of heat shock response.

Insights into the diverse effects of nitric oxide on tumor biology

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

Proteomic profiling of nitrosative stress: protein S-oxidation accompanies S-nitrosylation

Reversible chemical modifications of protein cysteine residues by S-nitrosylation and S-oxidation are increasingly recognized as important regulatory mechanisms for many protein classes associated with cellular signaling and stress response. Both modifications may theoretically occur under cellular nitrosative or nitroxidative stress. Therefore, a proteomic isotope-coded approach to parallel, quantitative analysis of cysteome S-nitrosylation and S-oxidation was developed. Modifications of cysteine residues of (i) human glutathione-S-transferase P1-1 (GSTP1) and (ii) the schistosomiasis drug target thioredoxin glutathione reductase (TGR) were studied. Both S-nitrosylation (SNO) and S-oxidation to disulfide (SS) were observed for reactive cysteines, dependent on concentration of added S-nitrosocysteine (CysNO) and independent of oxygen. SNO and SS modifications of GSTP1 were quantified and compared for therapeutically relevant NO and HNO donors from different chemical classes, revealing oxidative modification for all donors. Observations on GSTP1 were extended to cell cultures, analyzed after lysis and in-gel digestion. Treatment of living neuronal cells with CysNO, to induce nitrosative stress, caused levels of S-nitrosylation and S-oxidation of GSTP1 comparable to those of cell-free studies. Cysteine modifications of PARK7/DJ-1, peroxiredoxin-2, and other proteins were identified, quantified, and compared to overall levels of protein S-nitrosylation. The new methodology has allowed identification and quantitation of specific cysteome modifications, demonstrating that nitroxidation to protein disulfides occurs concurrently with S-nitrosylation to protein-SNO in recombinant proteins and living cells under nitrosative stress.

Activation of VCAM-1 and its associated molecule CD44 leads to increased malignant potential of breast cancer cells

VCAM-1 (CD106), a transmembrane glycoprotein, was first reported to play an important role in leukocyte adhesion, leukocyte transendothelial migration and cell activation by binding to integrin VLA-1 (α4β1). In the present study, we observed that VCAM-1 expression can be induced in many breast cancer epithelial cells by cytokine stimulation in vitro and its up-regulation directly correlated with advanced clinical breast cancer stage. We found that VCAM-1 over-expression in the NMuMG breast epithelial cells controls the epithelial and mesenchymal transition (EMT) program to increase cell motility rates and promote chemoresistance to doxorubicin and cisplatin in vitro. Conversely, in the established MDAMB231 metastatic breast cancer cell line, we confirmed that knockdown of endogenous VCAM-1 expression reduced cell proliferation and inhibited TGFβ1 or IL-6 mediated cell migration, and increased chemosensitivity. Furthermore, we demonstrated that knockdown of endogenous VCAM-1 expression in MDAMB231 cells reduced tumor formation in a SCID xenograft mouse model. Signaling studies showed that VCAM-1 physically associates with CD44 and enhances CD44 and ABCG2 expression. Our findings uncover the possible mechanism of VCAM-1 activation facilitating breast cancer progression, and suggest that targeting VCAM-1 is an attractive strategy for therapeutic intervention.

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.

Aspirin inhibits colon cancer cell and tumor growth and downregulates specificity protein (Sp) transcription factors

Acetylsalicylic acid (aspirin) is highly effective for treating colon cancer patients postdiagnosis; however, the mechanisms of action of aspirin in colon cancer are not well defined. Aspirin and its major metabolite sodium salicylate induced apoptosis and decreased colon cancer cell growth and the sodium salt of aspirin also inhibited tumor growth in an athymic nude mouse xenograft model. Colon cancer cell growth inhibition was accompanied by downregulation of Sp1, Sp3 and Sp4 proteins and decreased expression of Sp-regulated gene products including bcl-2, survivin, VEGF, VEGFR1, cyclin D1, c-MET and p65 (NFκB). Moreover, we also showed by RNA interference that β-catenin, an important target of aspirin in some studies, is an Sp-regulated gene. Aspirin induced nuclear caspase-dependent cleavage of Sp1, Sp3 and Sp4 proteins and this response was related to sequestration of zinc ions since addition of zinc sulfate blocked aspirin-mediated apoptosis and repression of Sp proteins. The results demonstrate an important underlying mechanism of action of aspirin as an anticancer agent and, based on the rapid metabolism of aspirin to salicylate in humans and the high salicylate/aspirin ratios in serum, it is likely that the anticancer activity of aspirin is also due to the salicylate metabolite.

Quinone-induced activation of Keap1/Nrf2 signaling by aspirin prodrugs masquerading as nitric oxide

The promising therapeutic potential of the NO-donating hybrid aspirin prodrugs (NO-ASA) includes induction of chemopreventive mechanisms and has been reported in almost 100 publications. One example, NCX-4040 (pNO-ASA), is bioactivated by esterase to a quinone methide (QM) electrophile. In cell cultures, pNO-ASA and QM-donating X-ASA prodrugs that cannot release NO rapidly depleted intracellular GSH and caused DNA damage; however, induction of Nrf2 signaling elicited cellular defense mechanisms including upregulation of NAD(P)H:quinone oxidoreductase-1 (NQO1) and glutamate-cysteine ligase (GCL). In HepG2 cells, the "NO-specific" 4,5-diaminofluorescein reporter, DAF-DA, responded to NO-ASA and X-ASA, with QM-induced oxidative stress masquerading as NO. LC-MS/MS analysis demonstrated efficient alkylation of Cys residues of proteins including glutathione-S-transferase-P1 (GST-P1) and Kelch-like ECH-associated protein 1 (Keap1). Evidence was obtained for alkylation of Keap1 Cys residues associated with Nrf2 translocation to the nucleus, nuclear translocation of Nrf2, activation of antioxidant response element (ARE), and upregulation of cytoprotective target genes. At least in cell culture, pNO-ASA acts as a QM donor, bioactivated by cellular esterase activity to release salicylates, NO(3)(-), and an electrophilic QM. Finally, two novel aspirin prodrugs were synthesized, both potent activators of ARE, designed to release only the QM and salicylates on bioactivation. Current interest in electrophilic drugs acting via Nrf2 signaling suggests that QM-donating hybrid drugs can be designed as informative chemical probes in drug discovery.

Dietary administration of scallion extract effectively inhibits colorectal tumor growth: cellular and molecular mechanisms in mice

Colorectal cancer is a common malignancy and a leading cause of cancer death worldwide. Diet is known to play an important role in the etiology of colon cancer and dietary chemoprevention is receiving increasing attention for prevention and/or alternative treatment of colon cancers. Allium fistulosum L., commonly known as scallion, is popularly used as a spice or vegetable worldwide, and as a traditional medicine in Asian cultures for treating a variety of diseases. In this study we evaluated the possible beneficial effects of dietary scallion on chemoprevention of colon cancer using a mouse model of colon carcinoma (CT-26 cells subcutaneously inoculated into BALB/c mice). Tumor lysates were subjected to western blotting for analysis of key inflammatory markers, ELISA for analysis of cytokines, and immunohistochemistry for analysis of inflammatory markers. Metabolite profiles of scallion extracts were analyzed by LC-MS/MS. Scallion extracts, particularly hot-water extract, orally fed to mice at 50 mg (dry weight)/kg body weight resulted in significant suppression of tumor growth and enhanced the survival rate of test mice. At the molecular level, scallion extracts inhibited the key inflammatory markers COX-2 and iNOS, and suppressed the expression of various cellular markers known to be involved in tumor apoptosis (apoptosis index), proliferation (cyclin D1 and c-Myc), angiogenesis (VEGF and HIF-1α), and tumor invasion (MMP-9 and ICAM-1) when compared with vehicle control-treated mice. Our findings may warrant further investigation of the use of common scallion as a chemopreventive dietary agent to lower the risk of colon cancer.

Phase IIa clinical trial of curcumin for the prevention of colorectal neoplasia

Curcumin is derived from the spice tumeric and has antiinflammatory and antineoplastic effects in vitro and in animal models, including preventing aberrant crypt foci (ACF) and adenomas in murine models of colorectal carcinogenesis. Inhibiting the production of the procarcinogenic eicosanoids prostaglandin E₂ (PGE₂) and 5-hydroxyeicosatetraenoic acid (5-HETE) can suppress carcinogenesis in rodents. Curcumin reduces mucosal concentrations of PGE₂ (via inhibition of cyclooxygenases 1 and 2) and 5-HETE (via inhibition of 5-lipoxygenase) in rats. Although preclinical data support curcumin activity in many sites, the poor bioavailability reported for this agent supports its use in the colorectum. We assessed the effects of oral curcumin (2 g or 4 g per day for 30 days) on PGE₂ within ACF (primary endpoint), 5-HETE, ACF number, and proliferation in a nonrandomized, open-label clinical trial in 44 eligible smokers with eight or more ACF on screening colonoscopy. We assessed pre- and posttreatment concentrations of PGE₂ and 5-HETE by liquid chromatography tandem mass spectroscopy in ACF and normal-tissue biopsies; ACF number via rectal endoscopy; proliferation by Ki-67 immunohistochemistry; and curcumin concentrations by high-performance liquid chromatography in serum and rectal mucosal samples. Forty-one subjects completed the study. Neither dose of curcumin reduced PGE₂ or 5-HETE within ACF or normal mucosa or reduced Ki-67 in normal mucosa. A significant 40% reduction in ACF number occurred with the 4-g dose (P < 0.005), whereas ACF were not reduced in the 2-g group. The ACF reduction in the 4-g group was associated with a significant, five-fold increase in posttreatment plasma curcumin/conjugate levels (versus pretreatment; P = 0.009). Curcumin was well tolerated at both 2 g and 4 g. Our data suggest that curcumin can decrease ACF number, and this is potentially mediated by curcumin conjugates delivered systemically.

GT-094, a NO-NSAID, inhibits colon cancer cell growth by activation of a reactive oxygen species-microRNA-27a: ZBTB10-specificity protein pathway

Ethyl 2-((2,3-bis(nitrooxy)propyl)disulfanyl)benzoate (GT-094) is a novel nitric oxide (NO) chimera containing an nonsteroidal anti-inflammatory drug (NSAID) and NO moieties and also a disulfide pharmacophore that in itself exhibits cancer chemopreventive activity. In this study, the effects and mechanism of action of GT-094 were investigated in RKO and SW480 colon cancer cells. GT-094 inhibited cell proliferation and induced apoptosis in both cell lines and this was accompanied by decreased mitochondrial membrane potential (MMP) and induction of reactive oxygen species (ROS), and these responses were reversed after cotreatment with the antioxidant glutathione. GT-094 also downregulated genes associated with cell growth [cyclin D1, hepatocyte growth factor receptor (c-Met), epidermal growth factor receptor (EGFR)], survival (bcl-2, survivin), and angiogenesis [VEGF and its receptors (VEGFR1 and VEGFR2)]. Results of previous RNA interference studies in this laboratory has shown that these genes are regulated, in part, by specificity protein (Sp) transcription factors Sp1, Sp3, and Sp4 that are overexpressed in colon and other cancer cell lines and not surprisingly, GT-094 also decreased Sp1, Sp3, and Sp4 in colon cancer cells. GT-094-mediated repression of Sp and Sp-regulated gene products was due to downregulation of microRNA-27a (miR-27a) and induction of ZBTB10, an Sp repressor that is regulated by miR-27a in colon cancer cells. Moreover, the effects of GT-094 on Sp1, Sp3, Sp4, miR-27a, and ZBTB10 were also inhibited by glutathione suggesting that the anticancer activity of GT-094 in colon cancer cells is due, in part, to activation of an ROS-miR-27a:ZBTB10-Sp transcription factor pathway.

Differential inhibitory effects of the polyphenol ellagic acid on inflammatory mediators NF-kappaB, iNOS, COX-2, TNF-alpha, and IL-6 in 1,2-dimethylhydrazine-induced rat colon carcinogenesis

Dietary polyphenols have been found to possess preventive and therapeutic potential against several types of cancers. We investigated the effect of ellagic acid on colon cancer induced by 1,2-dimethylhydrazine in rats. Male Wistar albino rats were divided into four groups. Group 1 served as control, group 2 rats received ellagic acid 60 mg/kg bodyweight/every day p.o. throughout the experiment. Rats from groups 3 and 4 were given subcutaneous (s.c.) injections of 1,2-dimethylhydrazine (20 mg/kg body weight) once a week for the first 15 weeks; rats in group 4 received ellagic acid as in group 2 after the last injection of 1,2-dimethylhydrazine and continued till the end of the experimental period of 30 weeks. 1,2-dimethylhydrazine-induced rats exhibited alterations in cancer tumour markers [5'-nucleotidase (5'-ND), gamma glutamyl transpeptidase (gamma-GT), carcinoembryonic antigen (CEA), alphafetoprotein (AFP) and cathepsin-D (CD)]; pathophysiological markers [alkaline phosphatase (ALP) and lactate dehydrogenase (LDH)] and oral administration of ellagic acid restored the levels of these marker enzymes. Nuclear factor-kappa B (NF-kappaB) actively involved in the regulation of both pro-inflammatory proteins [inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2)] and pro-inflammatory cytokines [tumour necrosis factor (TNF)-alpha and interleukin (IL)-6] and in our study 1,2-dimethylhydrazine-induced group exhibited elevated expressions of all these inflammatory proteins. Ellagic acid administration reduced the expressions of NF-kappaB, COX-2, iNOS, TNF-alpha and IL-6 as confirmed by immunohistochemical, immunoblot and immunofluorescence analysis during 1,2-dimethylhydrazine-induced colon carcinogenesis. In conclusion, ellagic acid demonstrates anti-inflammatory property by iNOS, COX-2, TNF-alpha and IL-6 down-regulation due to inhibition of NF-kappaB and exerts its chemopreventive effect on colon carcinogenesis.

Inducible nitric oxide synthase expression and its prognostic significance in colorectal cancer

Nitric oxide synthases (NOS) are expressed in colorectal cancer. The aim of this study was to examine the inducible NOS (iNOS) expression in colorectal cancer and to investigate its prognostic relevance. Tissue sections of primary tumors from 132 patients undergoing curative resection for colorectal cancer were immunohistochemically examined for iNOS expression. The expression pattern of iNOS was correlated with various clinicopathological characteristics and survival. iNOS immunoreactivity was observed in the cytoplasm of tumor epithelial cells in 60 patients (45.5%) and positively correlated with lymph node involvement (p = 0.019). No significant correlation was found between iNOS expression and various clinicopathological characteristics, including age, gender, tumor location, tumor size, tumor grade, T stage, and Union International Contra la Cancrum (UICC) stage. Survival analysis showed a significant correlation between iNOS-positive tumors and poor disease-specific survival (p < 0.0001), with independent prognostic significance in multivariate analysis (HR = 4.42; p < 0.0001). Patients with stage II disease and iNOS-positive tumors had significantly worse disease-specific survival than those with iNOS-negative tumors (p < 0.0001). In addition, patients with stage III disease and iNOS-positive tumors had significantly worse disease-specific survival than those with iNOS-negative tumors (p = 0.001). The ability of iNOS to predict outcome in colorectal cancer patients may be independent of other known prognostic factors, providing a new molecular marker with significant potential for clinical utility.

Anti-inflammatory agents as cancer therapeutics

Cancer prevention sometimes referred to as tertiary prevention or chemoprevention makes use of specific xenobiotics or drugs to prevent, delay, or retard the development of cancer. Over the last two decades or so cancer prevention has made significant strides. For example, prevention of lung cancer through smoking cessation; cervical cancer prevention through regular Pap smear tests; colon cancer prevention through screening colonoscopy; and prostate cancer reductions by prostate-specific antigen measurements in conjunction with regular prostate examinations. The seminal epidemiological observation that nonsteroidal anti-inflammatory drugs (NSAIDs) prevent colon and other cancers has provided the impetus to develop novel chemoprevention approaches against cancer. To that end, a number of "designer drugs" have been synthesized that are in different stages of development, evaluation, and deployment. Some include the cyclooxygenase-2-specific inhibitors (coxibs), nitric oxide-releasing NSAIDs (NO-NSAIDs and NONO-NSAIDs), hydrogen sulfide-releasing NSAIDs, modulators of the lipoxygenase pathway, prostanoid receptor blockers, and chemokine receptor antagonists. In addition to these novel agents, there are also a host of naturally occurring compounds/micronutrients that have chemopreventive properties. This chapter reviews these classes of compounds, their utility and mechanism(s) of action against the background of mediators that link inflammation and cancer.

Reduced susceptibility to azoxymethane-induced aberrant crypt foci formation and colon cancer in growth hormone deficient rats

OBJECTIVES

To evaluate the role of GH in colon carcinogenesis, we examined the formation of aberrant crypt foci (ACFs) and tumor development in wild type (WT) and GH-deficient, spontaneous dwarf rats (SDRs) exposed to the carcinogen azoxymethane (AOM).

DESIGN

ACF were quantified by stereomicroscopy and tumor number and weights were recorded for each animal. Cell proliferation was measured by vincristine metaphase arrest, flow cytometry, and bromodeoxyuridine (BrdU) incorporation. Apoptosis was measured by TUNEL staining and cleaved caspase-3 immunohistochemistry. IGF-I was measured by radioimmunoassay (RIA). Hexokinase activity was measured by spectrophotometric assay. PARP cleavage, and IGF-IR, and p27(kip/cip) expression were measured by Western blotting.

RESULTS

ACFs detected by stereomicroscopy were markedly reduced ( approximately 85%) in SDRs vs. WT rats at 10, 25, and 28 weeks after AOM. Tumor incidence, number, and weight also were reduced in SDR vs. WT animals. AOM treatment increased cell proliferation in the distal colon (where tumors occur) of WT rats but not SDRs, and these changes corresponded to increased ACF and tumor formation. Apoptosis rates were similar in AOM-treated WT and SDRs. Alterations in serum IGF-I levels may contribute to differences in the proliferative response to AOM and decreased ACF formation in SDR vs. WT rats.

CONCLUSIONS

We conclude that early neoplastic lesions (ACFs) were reduced in GH-deficient animals. This effect corresponds with differences in AOM-induced proliferation, but not apoptosis. These data indicate that GH is required for the full effect of AOM on colon ACF and tumor development, and that the SDR rat is a promising model for studies regarding the role of GH/IGF system in the initiation and promotion of colon cancer.

Comparative methods for analysis of protein covalent modification by electrophilic quinoids formed from xenobiotics

Conjugation of biotin and fluorophore tags is useful for assaying covalent protein modification. Oxidative bioactivation of selective estrogen receptor modulators (SERMs) yields reactive quinoid electrophiles that covalently modify proteins, and bioactivation is associated with carcinogenic and chemopreventive effects. Identification of the protein targets of electrophilic metabolites is of general importance for xenobiotics. Four methodologies using SERM derivatized biotin/fluorophore tags were compared for purification and quantification: (1) covert oxidatively activated tags (COATags; SERM conjugated to biotin); (2) dansylTags (SERM conjugated to fluorophore); and azidoTags (SERM azide derivatives) in a two-step conjugation to biotin, using either (3) Staudinger ligation or (4) click chemistry. All synthetic derivatives retained the estrogen receptor ligand characteristics of the parent SERMs. Model proteins with bioactivation by tyrosinase in buffer or cell lysates and liver proteins with in situ bioactivation in rat primary hepatocytes were studied by immunoassay and fluorescence. Comparison showed that the azidoTag/Staudinger method was sensitive but nonspecific, the azidoTag/click methodology had low sensitivity, and the dansylTag methodology failed to detect modified proteins in hepatocytes. The COATag methodology was judged superior, detecting 5 ng of modified protein in vitro and identifying protein targets in hepatocytes. In metabolism studies in rat liver microsomes, the azide group was metabolically labile, which was a contributing factor in not selecting the azidoTag methodology in the oxidative environments required for bioactivation. For study of the protein targets of electrophilic metabolites formed by in situ oxidative bioactivation, the COATag is both sensitive and specific and does not appear to suffer from poor cell permeability.

NSAIDs and the colon

PURPOSE OF REVIEW

To better understand the effects of NSAIDs on the colon.

RECENT FINDINGS

An epidemiological study has confirmed that NSAIDs increase the risk of hospitalizations for lower gastrointestinal complications, though the estimated rate of hospitalization was lower than that for upper gastrointestinal complications. Proton-pump inhibitors were associated with reduction in hospitalizations for upper but not lower gastrointestinal complications. Current research on cyclooxygenase (COX) inhibition in patient and animal models suggests that COX-1 and COX-2 may have different roles in the exacerbation of inflammatory bowel disease. Epidemiological research on the chemoprevention of colorectal cancer with aspirin suggests that the positive effect of risk reduction is only observed after long-term treatment. The search for targets of chemopreventive drugs is ongoing. COX-2 inhibition still seems preferred option, as the effects observed with aspirin (the only chemopreventive agent with some apparent future) are more profound only in tumors and cells expressing COX-2. Other molecules such as nitric oxide NSAIDs, especially nitric oxide aspirin, are under intensive experimental research.

SUMMARY

NSAID use increases the risk of hospitalizations due to complications in the lower gastrointestinal tract. By inhibiting COX-2 or other tumorigenic targets, NSAIDs, especially aspirin or new aspirin derivates, may prevent colon cancer in selected populations.

Anti-inflammatory, antiproliferative, and cytoprotective activity of NO chimera nitrates of use in cancer chemoprevention

Nonsteroidal anti-inflammatory drugs (NSAIDs) have shown promise in colorectal cancer (CRC), but they are compromised by gastrotoxicity. NO-NSAIDs are hybrid nitrates conjugated to an NSAID designed to exploit the gastroprotective properties of NO bioactivity. The NO chimera ethyl 2-((2,3-bis(nitrooxy)propyl)disulfanyl)benzoate (GT-094), a novel nitrate containing an NSAID and disulfide pharmacophores, is effective in vivo in rat models of CRC and is a lead compound for design of agents of use in CRC. Preferred chemopreventive agents possess 1) antiproliferative and 2) anti-inflammatory actions and 3) the ability to induce cytoprotective phase 2 enzymes. To determine the contribution of each pharmacophore to the biological activity of GT-094, these three biological activities were studied in vitro in compounds that deconstructed the structural elements of the lead GT-094. The anti-inflammatory and antiproliferative actions of GT-094 in vivo were recapitulated in vitro, and GT-094 was seen to induce phase 2 enzymes via the antioxidant responsive element. In the variety of colon, macrophage-like, and liver cell lines studied, the evidence from structure-activity relationships was that the disulfide structural element of GT-094 is the dominant contributor in vitro to the anti-inflammatory activity, antiproliferation, and enzyme induction. The results provide a direction for lead compound refinement. The evidence for a contribution from the NO mimetic activity of nitrates in vitro was equivocal, and combinations of nitrates with acetylsalicylic acid were inactive.

Problematic detoxification of estrogen quinones by NAD(P)H-dependent quinone oxidoreductase and glutathione-S-transferase

Estrogen exposure through early menarche, late menopause, and hormone replacement therapy increases the risk factor for hormone-dependent cancers. Although the molecular mechanisms are not completely established, DNA damage by quinone electrophilic reactive intermediates, derived from estrogen oxidative metabolism, is strongly implicated. A current hypothesis has 4-hydroxyestrone-o-quinone (4-OQE) acting as the proximal estrogen carcinogen, forming depurinating DNA adducts via Michael addition. One aspect of this hypothesis posits a key role for NAD(P)H-dependent quinone oxidoreductase (NQO1) in the reduction of 4-OQE and protection against estrogen carcinogenesis, despite two reports that 4-OQE is not a substrate for NQO1. 4-OQE is rapidly and efficiently trapped by GSH, allowing measurement of NADPH-dependent reduction of 4-OQE in the presence and absence of NQO1. 4-OQE was observed to be a substrate for NQO1, but the acceleration of NADPH-dependent reduction by NQO1 over the nonenzymic reaction is less than 10-fold and at more relevant nanomolar concentrations of substrate is less than 2-fold. An alternative detoxifying enzyme, glutathione-S-transferase, was observed to be a target for 4-OQE, rapidly undergoing covalent modification. These results indicate that a key role for NQO1 and GST in direct detoxification of 4-hydroxy-estrogen quinones is problematic.

Solid tumor physiology and hypoxia-induced chemo/radio-resistance: novel strategy for cancer therapy: nitric oxide donor as a therapeutic enhancer

Hypoxia exists in solid tumor tissues due to abnormal vasculature, vascular insufficiency, treatment or malignancy related anemia, and low intratumor blood flow. Hypoxic status in solid tumor promotes accumulation of hypoxia-inducible factor-1 alpha which is promptly degraded by proteasomal ubiquitination under normoxic conditions. However, under hypoxic conditions, the ubiquitination system for HIF-1 alpha is inhibited by inactivation of prolyl hydroxylase which is responsible for hydroxylation of proline in the oxygen-dependent degradation domain of HIF-1 alpha. HIF-1 alpha is an important transcriptional factor that codes for hundreds of genes involved in erythropoiesis, angiogenesis, induction of glycolytic enzymes in tumor tissues, modulation of cancer cell cycle, cancer proliferation, and cancer metastasis. Hypoxia and accumulation of HIF-1 alpha in solid tumor tissues have been reported to associate with resistance to chemotherapy, radiotherapy, and immunotherapy and poor prognosis. Production of vascular endothelial growth factor (VEGF) in cancer cells is regulated by the activated HIF-1 mediated system. An increase in VEGF levels subsequently induces HIF-1 alpha accumulation and promotes tumor metastasis by angiogenesis. Recently, angiogenesis targeting therapy using humanized VEGF antibody and VEGF receptor tyrosine kinase inhibitors have been used in solid cancer therapy. Nitric oxide (NO) is a unique chemical gaseous molecule that plays a role as a chemical messenger involved in vasodilator, neurotransmitter, and anti-platelet aggregation. In vivo, NO is produced and released from three different isoforms of NO synthase (NOS) and from exogenously administered NO donors. In cancer science, NO has been mainly discussed as an oncogenic molecule over the past decades. However, NO has recently been noted in cancer biology associated with cancer cell apoptosis, cancer cell cycle, cancer progression and metastasis, cancer angiogenesis, cancer chemoprevention, and modulator for chemo/radio/immuno-therapy. The presence and activities of all the three isoforms of NOS and were detected in cancer tissue components such as cancer cells, tumor-associated macrophages, and vascular endothelium. Overexpression of iNOS in cancer tissues has been reported to associate with poor prognosis in patients with cancers. On the other hand, NO donors such as nitroglycerin have been demonstrated to improve the effects of cancer therapy in solid cancers. Nitroglycerin has been used safely for a long time as a potent vasodilator for the treatment of ischemic heart diseases or heart failure. Therefore, we think highly of clinical use of nitroglycerin as a novel cancer therapy in combination with anticancer drugs for improvement of cancer therapeutic levels. In this review article, we demonstrate the unique physiological characteristics of malignant solid tumors, several factors in solid tumors resulting in resistance for cancer therapies, and the effects of NO from NOS or exogenous NO-donating drugs on malignant cells. Furthermore, we refer to promising therapeutic roles of NO and NO-donating drugs for novel treatments in solid tumors.

NO-donating NSAIDs and cancer: an overview with a note on whether NO is required for their action

Nitric oxide-donating nonsteroidal anti-inflammatory drugs (NO-NSAIDs) consist of a conventional NSAID to which an NO-releasing moiety is attached covalently, often via a spacer molecule. NO-NSAIDs represent an emerging class of compounds with chemopreventive properties against a variety of cancers, demonstrated in preclinical models including cell culture systems and animal tumor models; their potential efficacy in humans has not been assessed. Their mechanism of action appears complex and involves the generation of reactive oxygen species, suppression of microsatellite instability in mismatch repair-deficient cells, and modulation of several signaling cascades that culminate in inhibited cell renewal and enhanced apoptosis. NO, long appreciated to be able to protect from and also promote cancer, is released form NO-NSAIDs and constitutes their defining property. Existing data are consistent with the notion that NO may mediate their anticancer effect. In addition there is evidence that long-term administration of NO-donating compounds is not associated with increased incidence of colon cancer. Whether NO release is required for the anticancer effect of NO-NSAIDs has being questioned by recent data indicating that, at least in the case of NO-aspirin, the NO-releasing moiety may serve as a leaving group while the spacer actually being the moiety responsible for its pharmacological action. Regardless of mechanistic issues, these compounds promise to contribute to the control of cancer.

Nitrates and NO-NSAIDs in cancer chemoprevention and therapy: in vitro evidence querying the NO donor functionality

Properties of the NO-ASA family of NO-donating NSAIDs (NO-NSAIDs), notably NCX 4016 (mNO-ASA) and NCX 4040 (pNO-ASA), reported in more than one hundred publications, have included positive preclinical data in cancer chemoprevention and therapy. Evidence is presented that the antiproliferative, the chemopreventive (antioxidant/electrophile response element (ARE) activation), and the anti-inflammatory activity of NO-ASA in cell cultures is replicated by X-ASA derivatives that are incapable of acting as NO donors. pBr-ASA and mBr-ASA are conisogenic with NO-ASA, but are not NO donors. The biological activity of pNO-ASA is replicated by pBr-ASA; and both pNO-ASA and pBr-ASA are bioactivated to the same quinone methide electrophile. The biological activity of mNO-ASA is replicated by mBr-ASA; mNO-ASA and mBr-ASA are bioactivated to different benzyl electrophiles. The observed activity is likely initiated by trapping of thiol biomolecules by the quinone and benzyl electrophiles, leading to depletion of GSH and modification of Cys-containing sensor proteins. Whereas all NO-NSAIDs containing the same structural "linker" as NCX 4040 and NCX 4016 are anticipated to possess activity resulting from bioactivation to electrophilic metabolites, this expectation does not extend to other linker structures. Nitrates require metabolic bioactivation to liberate NO bioactivity, which is often poorly replicated in vitro, and NO bioactivity provided by NO-NSAIDs in vivo provides proven therapeutic benefits in mitigation of NSAID gastrotoxicity. The in vivo properties of X-ASA drugs await discovery.