Mechanism of action of novel NO-releasing furoxan derivatives of aspirin in human platelets

Design, Synthesis, and Biological Evaluation of a Novel VEGFR-2 Inhibitor Based on a 1,2,5-Oxadiazole-2-Oxide Scaffold with MAPK Signaling Pathway Inhibition

Over the past few decades, the development of broad-spectrum anticancer agents with anti-angiogenic activity has witnessed considerable progress. In this study, a new series of pyrazolo[3,4-d]pyrimidines based on a phenylfuroxan scaffold were designed, synthesized, and evaluated, in terms of their anticancer activities. NCI-60 cell one-dose screening revealed that compounds 12a-c and 14a had the best MGI%, among the tested compounds. The target fluorinated compound 12b, as the most active one, showed better anticancer activity compared to the reference drug sorafenib, with IC50 values of 11.5, 11.6, and 13 µM against the HepG-2, A2780CP, and MDA-MB-231 cell lines, respectively. Furthermore, compound 12b (IC50 = 0.092 µM) had VEGFR-2-inhibitory activity comparable to that of the standard inhibitor sorafenib (IC50 = 0.049 µM). Furthermore, the ability of compound 12b in modulating MAPK signaling pathways was investigated. It was found to decrease the level of total ERK and its phosphorylated form, as well as leading to the down-regulation of metalloproteinase MMP-9 and the over-expression of p21 and p27, thus leading to subG1 cell-cycle arrest and, thus, the induction of apoptosis. Additionally, compound 12b decreased the rate of wound healing in the absence of serum, in comparison to DMSO-treated cells, providing a significant impact on metastasis inhibition. The quantitative RT-PCR results for E-cadherin and N-cadherin showed lower expression of the neuronal N-cadherin and increased expression of epithelial E-cadherin, indicating the ability of 12b to suppress metastasis. Furthermore, 12b-treated HepG2 cells expressed a low level of anti-apoptotic BCL-2 and over-expressed proapoptotic Bax genes, respectively. Using the DAF-FM DA fluorescence probe, compound 12b produced NO intracellularly as efficiently as the reference drug JS-K. In silico molecular docking studies showed a structural similarity through an overlay of 12b with sorafenib. Interestingly, the drug-likeness properties of compound 12b met the expectations of Pfizer's rule for the design of new drug candidates. Therefore, this study presents a novel anticancer lead compound that is worthy of further investigation and activity improvement.

Mechanisms of nitric oxide generation in living systems

In modern chemical and biochemical studies, special attention is paid to molecular systems capable of generating nitric oxide (NO), which is one of the most important signalling molecules in the body and can trigger a whole cascade of reactions. Despite the importance of this molecule, the mechanisms of its formation in living organisms remain a subject of debate. This review combines the most important methods of releasing NO from endogenous and exogenous sources. The history of endogenous NO donors dates back more than 150 years, since the synthesis of nitroglycerin, which remains the standard vasodilator today, even though it is known that it and many other similar compounds lead to the development of a nitrate tolerance. Particular awareness is devoted to the mechanisms of NO formation without the participation of enzymes, since these methods are most important for creating exogenous sources of NO as drugs. The study of NO formation methods is centred on both the creation of new NO donors and understanding the mechanisms of tolerance to them.

Increased bleeding events with the addition of apixaban to the dual anti-platelet regimen for the treatment of patients with acute coronary syndrome: A meta-analysis

BACKGROUND

Dual anti-platelet therapy (DAPT) with aspirin and clopidogrel has been the mainstay of treatment for patients with acute coronary syndrome (ACS). However, the recurrence of thrombotic events, potential aspirin and clopidogrel hypo-responsiveness, and other limitations of DAPT have led to the development of newer oral anti-thrombotic drugs. Apixaban, a new non-vitamin K antagonist, has been approved for use. In this meta-analysis, we aimed to compare the bleeding outcomes observed with the addition of apixaban to DAPT for the treatment of patients with ACS.

METHODS

Online databases including EMBASE, Cochrane Central, http://www.ClinicalTrials.gov, MEDLINE and Web of Science were searched for English based publications comparing the use of apixaban added to DAPT for the treatment of patients with ACS. Different categories of bleeding events and cardiovascular outcomes were assessed. The analysis was carried out by the RevMan software version 5.4. Odds ratios (OR) with 95% confidence intervals (CI) were used to represent the data following analysis.

RESULTS

This research analysis consisted of 4 trials with a total number of 9010 participants. Thrombolysis in myocardial infarction (TIMI) defined major bleeding (OR: 2.45, 95% CI: 1.45-4.12; P = .0008), TIMI defined minor bleeding (OR: 3.12, 95% CI: 1.71-5.70; P = .0002), International society of thrombosis and hemostasis (ISTH) major bleeding (OR: 2.49, 95% CI: 1.80-3.45; P = .00001) and Global Use of Strategies to Open Occluded Arteries (GUSTO) defined severe bleeding (OR: 3.00, 95% CI: 1.56-5.78; P = .01) were significantly increased with the addition of apixaban to DAPT versus DAPT alone in these patients with ACS. However fatal bleeding (OR: 10.96, 95% CI: 0.61-198.3; P = .11) was not significantly different.

CONCLUSIONS

Addition of the novel oral anticoagulant apixaban to the DAPT regimen significantly increased bleeding and therefore did not show any beneficial effect in these patients with ACS. However, due to the extremely limited data, we apparently have to rely on future larger studies to confirm this hypothesis.

The evolving landscape for cellular nitric oxide and hydrogen sulfide delivery systems: A new era of customized medications

Nitric oxide (NO) and hydrogen sulfide (H2S) are industrial toxins or pollutants; however, both are produced endogenously and have important biological roles in most mammalian tissues. The recognition that these gasotransmitters have a role in physiological and pathophysiological processes has presented opportunities to harness their intracellular effects either through inhibition of their production; or more commonly, through inducing their levels and or delivering them by various modalities. In this review article, we have focused on an array of NO and H2S donors, their hybrids with other established classes of drugs, and the various engineered delivery platforms such a fibers, polymers, nanoparticles, hydrogels, and others. In each case, we have reviewed the rationale for their development.

Binding of adenosine derivatives to carrier proteins may reduce their antiplatelet activity

Adenosine analogues have high affinity and selectivity for adenosine receptors (AR), and exhibit anti-platelet activity. Plasma proteins play an important role in the regulation of platelet function and may influence the action of anti-platelet compounds. Little is known about the interactions of AR agonists with plasma proteins. This study investigates the interplay between AR agonists and plasma proteins and the consequences of those interactions. Surface plasmon resonance was employed together with molecular docking study to determine the binding kinetics of four selected ARagonists (PSB0777, Cl-Ado, MRE0094, UK432097) to several carrier proteins and to clarify the nature of these interactions. The influence of a whole plasma and of some plasma components on the effectiveness of ARagonists in the inhibition of platelet function was assessed by flow cytometry (platelet activation) and ELISA (platelet adhesion). Plasma proteins remarkably diminished the effectiveness of ARagonists in inhibiting platelet activation and adhesion in vitro. ARagonists were found to strongly bind to human serum albumin (HSA) and the protein components of lipoproteins - apolipoproteins; HSA was essential for the binding of water-soluble PSB0777, whereas apolipoproteins were needed for interactions with poorly-water soluble compounds such as UK432097 and MRE0094. In addition, HSA was shown to significantly reduce the effectiveness of PSB0777 in inhibiting ADP-induced platelet activation. In conclusion, HSA and lipoproteins are important carriers for ARagonists, which can affect pharmacodynamics of ARagonists used as platelet inhibitors.

Controlled Delivery of Nitric Oxide for Cancer Therapy

Nitric oxide (NO) is a short-lived, endogenously produced, signaling molecule which plays multiple roles in mammalian physiology. Underproduction of NO is associated with several pathological processes; hence a broad range of NO donors have emerged as potential therapeutics for cardiovascular and respiratory disorders, wound healing, the immune response to infection, and cancer. However, short half-lives, chemical reactivity, rapid systemic clearance, and cytotoxicity have hindered the clinical development of most low molecular weight NO donors. Hence, for controlled NO delivery, there has been extensive effort to design novel NO-releasing biomaterials for tumor targeting. This review covers the effects of NO in cancer biology, NO releasing moieties which can be used for NO delivery, and current advances in the design of NO releasing biomaterials focusing on their applications for tumor therapy.

Design, synthesis, and biological evaluation of novel nitric oxide releasing dehydroandrographolide derivatives

A series of new hybrids of dehydroandrographolide (TAD), a biologically active natural product, bearing nitric oxide (NO)-releasing moieties were synthesized and designated as NO-donor dehydroandrographolide. The biological activities of target compounds were studied in human erythroleukemia K562 cells and breast cancer MCF-7 cells. Biological evaluation indicated that the most active compound I-5 produced high levels of NO and inhibited the proliferation of K562 (IC₅₀ 1.55 μmol·L^-1) and MCF-7 (IC₅₀ 2.91 μmol·L^-1) cells, which were more potent than the lead compound TAD and attenuated by an NO scavenger. In conclusion, I-5 is a novel hybrid with potent antitumor activity and may become a promising candidate for future intensive study.

Complex roles of the old drug aspirin in cancer chemoprevention and therapy

The nonsteroidal anti-inflammatory agent aspirin is widely used for preventing and treating cardiovascular and cerebrovascular diseases. In addition, epidemiologic evidences reveal that aspirin may prevent a variety of human cancers, while data on the association between aspirin and some kinds of cancer are conflicting. Preclinical studies and clinical trials also reveal the therapeutic effect of aspirin on cancer. Although cyclooxygenase is a well-known target of aspirin, recent studies uncover other targets of aspirin and its metabolites, such as AMP-activated protein kinase, cyclin-dependent kinase, heparanase, and histone. Accumulating evidence demonstrate that aspirin may act in different cell types, such as epithelial cell, tumor cell, endothelial cell, platelet, and immune cell. Therefore, aspirin acts on diverse hallmarks of cancer, such as sustained tumor growth, metastasis, angiogenesis, inflammation, and immune evasion. In this review, we focus on recent progress in the use of aspirin for cancer chemoprevention and therapy, and integratively analyze the mechanisms underlying the anticancer effects of aspirin and its metabolites. We also discuss mechanisms of aspirin resistance and describe some derivatives of aspirin, which aim to overcome the adverse effects of aspirin.

Synthesis, antiplatelet and antithrombotic activities of resveratrol derivatives with NO-donor properties

Resveratrol (RVT) is a stilbene with a protective effect on the cardiovascular system; however, drawbacks including low bioavailability and fast metabolism limit its efficacy. In this work we described new resveratrol derivatives with nitric oxide (NO) release properties, ability to inhibit platelet aggregation and in vivo antithrombotic effect. Compounds (4a-f) were able to release NO in vitro, at levels ranging from 24.1% to 27.4%. All compounds (2a-f and 4a-f) have exhibited platelet aggregation inhibition using as agonists ADP, collagen and arachidonic acid. The most active compound (4f) showed reduced bleeding time compared to acetylsalicylic acid (ASA) and protected up to 80% against in vivo thromboembolic events. These findings suggest that hybrid resveratrol-furoxan (4f) is a novel lead compound able to prevent platelet aggregation and thromboembolic events.

Nonsteroidal Anti-Inflammatory Therapy: A Journey Toward Safety

The efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) against inflammation, pain, and fever has been supporting their worldwide use in the treatment of painful conditions and chronic inflammatory diseases until today. However, the long-term therapy with NSAIDs was soon associated with high incidences of adverse events in the gastrointestinal tract. Therefore, the search for novel drugs with improved safety has begun with COX-2 selective inhibitors (coxibs) being straightaway developed and commercialized. Nevertheless, the excitement has fast turned to disappointment when diverse coxibs were withdrawn from the market due to cardiovascular toxicity. Such events have once again triggered the emergence of different strategies to overcome NSAIDs toxicity. Here, an integrative review is provided to address the breakthroughs of two main approaches: (i) the association of NSAIDs with protective mediators and (ii) the design of novel compounds to target downstream and/or multiple enzymes of the arachidonic acid cascade. To date, just one phosphatidylcholine-associated NSAID has already been approved for commercialization. Nevertheless, the preclinical and clinical data obtained so far indicate that both strategies may improve the safety of nonsteroidal anti-inflammatory therapy.

Preparation and characterization of DOX loaded keratin nanoparticles for pH/GSH dual responsive release

Smart drug carriers are the current need of the hour in controlled drug delivery applications. In this work, pH and redox dual responsive keratin based drug-loaded nanoparticles (KDNPs) were fabricated through two-step strategies. Keratin nanoparticles were first prepared by desolvation method and chemical crosslinking, followed by electrostatic adsorbing doxorubicin (DOX) to afford drug loaded keratin nanoparticles (KDNPs). The size, size distribution, and morphology of the KDNPs were characterized with dynamic light scattering (DLS) and Scan electronic microscope (SEM). Drug delivery profiles showed that KDNPs exhibited pH and glutathione (GSH) dual-responsive characters. Under tumor tissue/cell microenvironments (more acidic and high GSH level), KDNPs tended to accumulate at the tumor region through a potential enhanced permeability and retention (EPR) effect and perform surface negative-to-positive charge conversion. Hemolysis assay indicated that KDNPs had good blood compatibility. Cellular uptake assay demonstrated that KDNPs could be internalized by A 549 cells through endocytosis. Intriguingly, KDNPs were capable of promoting nitric oxide (NO) release from endogenous donor of S-nitrosoglutathione in the presence of GSH. All of these results demonstrated that keratin based drug carriers had potential for drug/NO delivery and cancer therapy in clinical medicine.

Theoretical investigation of methoxide ion reaction on the 7-methyl-4,6-dinitrobenzofuroxan

Reaction of the methoxide ion on the 7-methyl-4,6-dinitrobenzofuroxan (DNBF) 1 has been studied theoretically by means of DFT/B3LYP technique to interpret the kinetic–thermodynamic competition between the three possible compounds that are carbanion DNBF− 4 and the two complexed forms (2, 3) of the methoxide group in positions 5 and 7, respectively. Optimized geometry, nbo atomic charge distribution, thermodynamic/kinetic parameters (ΔrH°T, ΔrS°T, ΔrG°T, ΔH*, ΔS*, and ΔG*) and IRC path have been calculated for possible products and their transitional states using water as solvent. All obtained ΔrG°T are negative, ranging from −19.16 to −42.87 kcal mol−1 (1 cal = 4.184 J), indicating the possible observation of all products, but the experimenters only detected the anionic form DNBF−. Fukui indices, which were calculated by means of NBO atomic charge distribution, confirm the electrophilicity of the sites C5 and C7. Transition states barriers, ΔG*, are 14.97, 15.16, and 21.94 kcal mol−1 for the three possible products 2, 3, and 4, respectively, in water. As expected, the most stable compound is carbanion, but it also exhibits the highest activation barrier. If this situation formally engenders a double kinetic–thermodynamic competition, the very weak activation energy of the two complexes in C5 and C7 makes improbable the simultaneous detection of the three expected compounds.

Theoretical and experimental reinvestigation of methoxide ion reaction with 7-methyl 4-nitro benzofuroxan

DFT/B3LYP theoretical study has been performed in order to interpret the kinetic-thermodynamic competition between compounds obtained by reaction of the methoxide ion on the 7-methyl 4-nitro benzofuroxan. Geometry, atomic charge distribution, transition states, IRC path, thermodynamic, and kinetic parameters ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]*, [Formula: see text]*, and [Formula: see text]*) have been calculated for all possible products. In gaseous state or in the presence of water as solvent, all [Formula: see text] values were found to be negative, ranging from [Formula: see text]12.54[Formula: see text]kcal mol[Formula: see text] to [Formula: see text]29.85[Formula: see text]kcal mol[Formula: see text] in water, indicating that all possible products should form spontaneously. Those values indicated the possible observation of all products but experimenters only detect simultaneously two [Formula: see text]-complexes in C5 and C7 among three possibilities. The Fukui indices obtained by NBO atomic charge distribution confirm the super electrophilicity of those two sites. For transition states barriers, [Formula: see text]* ranged from 18.98[Formula: see text]kcal mol[Formula: see text] to 42.12[Formula: see text]kcal mol[Formula: see text] in gaseous state and from 18.59[Formula: see text]kcal mol[Formula: see text] to 24.22[Formula: see text]kcal mol[Formula: see text] in water. The unexpected result of our calculations is that the most stable compound is the unobserved carbanion but it also exhibits the highest activation barrier. Our results indicated the existence of two consecutive kinetic/thermodynamic competitions that occur in separate periods. The simultaneous observation of the three compounds is impossible because compound 4 occurs as a trace at the time compound 2 disappears completely. Experimental reinvestigation of the studied reaction leads by a very slow process to the earlier unobserved carbanion. Reaction mechanisms were also discussed on the basis of IRC calculations.

Oxadiazole-2-oxides may have other functional targets, in addition to SjTGR, through which they cause mortality in Schistosoma japonicum

BACKGROUND

Schistosomiasis is one of the world's major public health problems. Besides praziquantel (PZQ), there is currently no other effective treatment against schistosomiasis. The development of new antischistosomal agents to curb the emergence of PZQ resistance should be a high priority. Oxadiazole-2-oxides have been identified as potential antischistosomal reagents, with thioredoxin glutathione reductase (TGR) being one of their molecular targets.

METHODS

To develop novel treatment reagents against Schistosoma japonicum, 30 novel oxadiazole-2-oxides were synthesised and their antischistosomal activities on juvenile and adult S. japonicum were evaluated in vitro and in vivo. Their inhibitory activities against S. japonicum thioredoxin glutathione reductase (SjTGR) were also analysed.

RESULTS

Most of the oxadiazole-2-oxides showed good juvenile and adult S. japonica killing activities in vitro. However, the antischistosomal effects of these compounds were not positively correlated with either their inhibition of SjTGR, or with nitric oxide (NO) release. Compounds 4a, 4b, 7c, 13, 16 and 20 resulted in 87.7%, 83.1%, 87.1%, 84.6%, 90.8% and 69.5%, respectively, mortality in the adult worms, when used to treat infected mice at schistosomula stage. These mortality rates were similar to or higher than that of artemisinin. Furthermore, compounds 4a and 16 resulted in 66.7% and 69.4% reductions in the worm burdens, respectively, when infected mice were treated at the adult worm stage. These treatment effects were similar to PZQ. No differences in activity of the oxadiazole-2-oxides against female and male adult worms were observed. The toxicity of the oxadiazole-2-oxides on mammalian cells appeared to be similar to, or less than, that of PZQ.

CONCLUSIONS

The antischistosomal activity of the oxadiazole-2-oxides does not depend on NO production or the inhibition of SjTGR activity. There may be other functional targets of the oxadiazole-2-oxides in S. japonicum. Several of the novel oxadiazole-2-oxides synthesised in this study could be used to develop novel antischistosomal drugs and explore potential molecular targets.

Synthesis and Preliminary Evaluation of N-Oxide Derivatives for the Prevention of Atherothrombotic Events

Thrombosis is the main outcome of many cardiovascular diseases. Current treatments to prevent thrombotic events involve the long-term use of antiplatelet drugs. However, this therapy has several limitations, thereby justifying the development of new drugs. A series of N-oxide derivatives (furoxan and benzofuroxan) were synthesized and characterized as potential antiplatelet/antithrombotic compounds. All compounds (3a,b, 4a,b, 8a,b, 9a,b, 13a,b and 14a,b) inhibited platelet aggregation induced by adenosine-5-diphosphate, collagen, and arachidonic acid. All compounds protected mice from pulmonary thromboembolism induced by a mixture of collagen and epinephrine; however, benzofuroxan derivatives (13a,b and 14a,b) were the most active compounds, reducing thromboembolic events by up to 80%. N-oxide derivative 14a did not induce genotoxicity in vivo. In conclusion, 14a has emerged as a new antiplatelet/antithrombotic prototype useful for the prevention of atherothrombotic events.

Nitric oxide-releasing polymeric furoxan conjugates

Polymeric nitric oxide (NO) donors were prepared by the conjugation of the azide-containing furoxans and poly(ethylene glycol) having an alkyne end groupviathe copper-catalyzed Huisgen cycloaddition.

Mechanisms of aggregation inhibition by aspirin and nitrate-aspirin prodrugs in human platelets

Objectives

Aspirin is the mainstay of anti-platelet therapy in the secondary prevention of cardiovascular disease. However, problems with aspirin safety and resistance demand clinical strategies based on multiple pharmacological approaches. Prodrugs of aspirin may offer beneficial effects in terms of gastro-intestinal safety and multiple pharmacological approaches. However, the pharmacological profile of aspirin prodrugs in human platelets has not been completed yet. We aimed to compare the effects of aspirin and prodrugs of aspirin (1–5) on human platelet aggregation stimulated by ADP and collagen and associated receptor expression (GPIIb/IIIa and P-selectin) in platelet-rich plasma (PRP) and washed platelets (WP).

Methods

As aspirin is released from prodrugs following esterase hydrolysis we studied the expression and activity of butyrylcholineterase (BuChE) and carboxyesterase (CE) in plasma and platelets. The mechanism of prodrug-induced platelet aggregation inhibition was explored by studying the effects of plasma and purified human BuChE on aggregation. Finally, the relative contribution of nitric oxide (NO) bioactivity to nitrate-containing prodrugs of aspirin-induced inhibition of aggregation was determined using 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ,) a selective inhibitor of the soluble guanylyl cyclase.

Key findings

ST0702, 2, a nicotinic acid-aspirin codrug was equipotent with aspirin with respect to inhibition of collagen-induced platelet aggregation. Compound 4, a NO releasing aspirin was the most potent inhibitor of ADP-induced platelet aggregation, an effect partially reversed by ODQ. The platelet inhibitory effects of aspirin prodrugs were time-dependent as the maximal inhibitory effects against collagen-induced aggregation were achieved by aspirin at 2 min, 1 at 5 min and ST0702 at 15 min. The aspirin prodrugs were significantly less potent in WP than in PRP and the reverse was true of aspirin. In the presence of complete BuChE inhibition in PRP, there was almost complete loss of aspirin prodrug, but not aspirin anti-aggregatory activity. Interestingly, CE activity was observed in WP and platelet lysate with pNPA substrate. Accordingly, 1 and ST0702 retained 50% and 100% anti-aggregatory activity at maximal concentrations in WP, which was attenuated in the presence of esterase inhibitor phenylmethylsulphonyl fluoride.

Conclusions

The inhibitory effect of aspirin prodrugs in PRP is due to prodrug activation by BuChE. In contrast, the platelet-inhibitory effects of aspirin prodrugs in WP may be mediated through the activity of platelet CE. Compound 4, a NO-containing aspirin prodrug, may exert dual inhibitory effects in platelets. Thus, aspirin prodrugs effectively inhibit human platelet aggregation and as such may be an alternative to conventional aspirin.

Interaction characteristics with bovine serum albumin and retarded nitric oxide release of ZCVI₄-2, a new nitric oxide-releasing derivative of oleanolic acid

ZCVI₄-2 is a newly developed furoxan-based nitric oxide-releasing derivative of oleanolic acid. It exhibited strong cytotoxicity against human hepatocellular carcinoma (HCC) in vitro and significantly inhibited the growth of HCC tumors in vivo. However, its low aqueous solubility and toxicity due to the fast release of nitric oxide (NO) in blood challenged its formulation. In the present investigation, the interaction characteristics of ZCVI₄-2 with bovine serum albumin (BSA) were studied by fluorescence spectrometry, synchronous fluorescence spectra and Fourier transform-infrared (FT-IR). It was found that ZCVI₄-2 concentration, temperature and pH had significant effect on the interactions. ZCVI₄-2 was able to bind BSA with high affinity, low temperature and neutral pH favor the binding. The interaction exhibited to be a spontaneous and exothermic process. ZCVI₄-2 was buried in the hydrophobic pocket in subdomain IIB of BSA and the exact binding site was around 3.83 nm in average from Trp²¹². The NO releasing characteristics of nanocomplexes were compared with ZCVI₄-2 solution by Griess Reagent Method. It was found that the release of NO from ZCVI₄-2/BSA nanocomplexes was retarded significantly, thus making ZCVI₄-2 into a BSA-bound nanocomplexes had the great potential to lower the toxicity due to the absence of organic solvents and surfactants and meanwhile the sustained release of NO.

The pilot phase of the NIH Chemical Genomics Center

The NIH Chemical Genomics Center (NCGC) was the inaugural center of the Molecular Libraries and Screening Center Network (MLSCN). Along with the nine other research centers of the MLSCN, the NCGC was established with a primary goal of bringing industrial technology and experience to empower the scientific community with small molecule compounds for use in their research. We intend this review to serve as 1) an introduction to the NCGC standard operating procedures, 2) an overview of several of the lessons learned during the pilot phase and 3) a review of several of the innovative discoveries reported during the pilot phase of the MLSCN.

Phenylsulfonylfuroxans as modulators of multidrug-resistance-associated protein-1 and P-glycoprotein

A series of furoxan derivatives were studied for their ability to interact with P-gp and MRP1 transporters in MDCK cells overexpressing these proteins. 3-Phenylsulfonyl substituted furoxans emerged as the most interesting compounds. All of them were capable of inhibiting P-gp, and a few also were capable of inhibiting MRP1. Substituents at the 4-position of 3-phenylsulfonylfuroxan scaffold were able to modulate the selectivity and the intensity of inhibition. In some cases, they reverted MRP1 inhibitor activity, namely, they were capable of potentiating MRP1 dependent efflux. When compounds 16 and 17 were coadministered with doxorubicin, they restored a high degree of the activity of the antibiotic. Preliminary immunoblotting studies carried out on these two compounds indicate that they are capable of nitrating P-gp, which in this form is likely unable to efflux the antibiotic.

Evaluation of the antioxidant properties of N-acetylcysteine in human platelets: prerequisite for bioconversion to glutathione for antioxidant and antiplatelet activity

N-Acetylcysteine (NAC) is a frequently used "antioxidant" in vitro, but the concentrations applied rarely correlate with those encountered with oral dosing in vivo. Here, we investigated the in vitro antioxidant and antiplatelet properties of NAC at concentrations (10-100 microM) that are achievable in plasma with tolerable oral dosing. The impact of NAC pretreatment (2 hours) on aggregation of platelets from healthy volunteers in response to thrombin and adenosine diphosphate and on platelet-derived nitric oxide (NO) was examined. NAC was found to be a weak reducing agent and a poor antioxidant compared with glutathione (reduced form) (GSH). However, platelets treated with NAC showed enhanced antioxidant activity and depression of reactive oxygen species generation associated with increases in intraplatelet GSH levels. An approximately 2-fold increase in NO synthase-derived nitrite was observed with 10 microM NAC treatment, but the effect was not concentration dependent. Finally, NAC significantly reduced both thrombin-induced and adenosine diphosphate-induced platelet aggregation. NAC should be considered a weak antioxidant that requires prior conversion to GSH to convey antioxidant and antithrombotic benefit at therapeutically relevant concentrations. Our results suggest that NAC might be an effective antiplatelet agent in conditions where increased oxidative stress contributes to heightened risk of thrombosis but only if the intraplatelet machinery to convert it to GSH is functional.

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.

Structure mechanism insights and the role of nitric oxide donation guide the development of oxadiazole-2-oxides as therapeutic agents against schistosomiasis

Schistosomiasis is a chronic parasitic disease affecting hundreds of millions of individuals worldwide. Current treatment depends on a single agent, praziquantel, raising concerns of emergence of resistant parasites. Here, we continue our explorations of an oxadiazole-2-oxide class of compounds we recently identified as inhibitors of thioredoxin glutathione reductase (TGR), a selenocysteine-containing flavoenzyme required by the parasite to maintain proper cellular redox balance. Through systematic evaluation of the core molecular structure of this chemotype, we define the essential pharmacophore, establish a link between the nitric oxide donation and TGR inhibition, determine the selectivity for this chemotype versus related reductase enzymes, and present evidence that these agents can be modified to possess appropriate drug metabolism and pharmacokinetic properties. The mechanistic link between exogenous NO donation and parasite injury is expanded and better defined. The results of these studies verify the utility of oxadiazole-2-oxides as novel inhibitors of TGR and as efficacious antischistosomal agents.

A novel hybrid aspirin-NO-releasing compound inhibits TNFalpha release from LPS-activated human monocytes and macrophages

Background

The cytoprotective nature of nitric oxide (NO) led to development of NO-aspirins in the hope of overcoming the gastric side-effects of aspirin. However, the NO moiety gives these hybrids potential for actions further to their aspirin-mediated anti-platelet and anti-inflammatory effects. Having previously shown that novel NO-aspirin hybrids containing a furoxan NO-releasing group have potent anti-platelet effects, here we investigate their anti-inflammatory properties. Here we examine their effects upon TNFα release from lipopolysaccharide (LPS)-stimulated human monocytes and monocyte-derived macrophages and investigate a potential mechanism of action through effects on LPS-stimulated nuclear factor-kappa B (NF-κB) activation.

Methods

Peripheral venous blood was drawn from the antecubital fossa of human volunteers. Mononuclear cells were isolated and cultured. The resultant differentiated macrophages were treated with pharmacologically relevant concentrations of either a furoxan-aspirin (B8, B7; 10 μM), their respective furazan NO-free counterparts (B16, B15; 10 μM), aspirin (10 μM), existing nitroaspirin (NCX4016; 10 μM), an NO donor (DEA/NO; 10 μM) or dexamethasone (1 μM), in the presence and absence of LPS (10 ng/ml; 4 h). Parallel experiments were conducted on undifferentiated fresh monocytes. Supernatants were assessed by specific ELISA for TNFα release and by lactate dehydrogenase (LDH) assay for cell necrosis. To assess NF-κB activation, the effects of the compounds on the loss of cytoplasmic inhibitor of NF-κB, IκBα (assessed by western blotting) and nuclear localisation (assessed by immunofluorescence) of the p65 subunit of NF-κB were determined.

Results

B8 significantly reduced TNFα release from LPS-treated macrophages to 36 ± 10% of the LPS control. B8 and B16 significantly inhibited monocyte TNFα release to 28 ± 5, and 49 ± 9% of control, respectively. The B8 effect was equivalent in magnitude to that of dexamethasone, but was not shared by 10 μM DEA/NO, B7, the furazans, aspirin or NCX4016. LDH assessment revealed none of the treatments caused significant cell lysis. LPS stimulated loss of cytoplasmic IκBα and nuclear translocation of the p65 NF-κB subunit was inhibited by the active NO-furoxans.

Conclusion

Here we show that furoxan-aspirin, B8, significantly reduces TNFα release from both monocytes and macrophages and suggest that inhibition of NF-κB activation is a likely mechanism for the effect. This anti-inflammatory action highlights a further therapeutic potential of drugs of this class.

Searching for new NO-donor aspirin-like molecules: a new class of nitrooxy-acyl derivatives of salicylic acid

A new class of products in which the phenol group of salicylic acid is linked to alkanoyl moieties bearing nitrooxy functions has been synthesized and studied for their polyvalent actions. The products were stable in acid and neutral media, while they were hydrolyzed in human serum. Their half-lives were dependent upon the structure of alkanoyl moieties. The products showed anti-inflammatory activities similar to aspirin when tested in the carrageenan-induced paw edema assay in the rat. Interestingly, unlike aspirin, they showed reduced or no gastrotoxicity in a lesion model in rats at equimolar doses. A number of them were able to inhibit platelet aggregation induced by collagen in human platelet-rich plasma. All of the products were capable of relaxing rat aortic strips precontracted with phenylephrine in a concentration-dependent manner. Selected members of this new class of nonsteroidal anti-inflammatory drugs might represent possible safer alternatives to aspirin in different clinical settings.

Multitarget drugs: Focus on the NO-donor hybrid drugs

The article addresses the design of multitarget drugs, namely, compounds capable of interacting with more than one target simultaneously. These agents could be useful tools in the therapy of complex diseases such as cardiovascular and inflammatory diseases. An interesting case of multitarget compounds are nitric oxide (NO)-donor hybrids, structures which combine the physiological properties of NO with those of a lead drug. In particular, the authors discuss the symbiotic approach used to design NO-donor nonsteroidal anti-inflammatory drugs (NO-NSAIDs) and NO-donor antioxidants. The former could be useful agents in the treatment of anti-inflammatory diseases being devoid of gastro- and cardiotoxicity, the latter could be a valid approach to the treatment of many cardiovascular diseases.

Recent developments in nitric oxide donor drugs

During the 1980s, the free radical, nitric oxide (NO), was discovered to be a crucial signalling molecule, with wide-ranging functions in the cardiovascular, nervous and immune systems. Aside from providing a credible explanation for the actions of organic nitrates and sodium nitroprusside that have long been used in the treatment of angina and hypertensive crises respectively, the discovery generated great hopes for new NO-based treatments for a wide variety of ailments. Decades later, however, we are still awaiting novel licensed agents in this arena, despite an enormous research effort to this end. This review explores some of the most promising recent advances in NO donor drug development and addresses the challenges associated with NO as a therapeutic agent.

Bioactivation of nitroglycerin by ascorbate

Bioactivation of nitroglycerin (GTN) into an activator of soluble guanylate cyclase (sGC) is essential for the vasorelaxant effect of the drug. Besides several enzymes that catalyze GTN bioactivation, the reaction with cysteine is the sole nonenzymatic mechanism known so far. Here we show that a reaction with ascorbate results in GTN bioactivation. In the absence of ascorbate, GTN did not affect the activity of purified sGC. However, the enzyme was activated to approximately 20% of maximal NO-stimulated activity by GTN in the presence of 10 mM ascorbate with an EC(50) value of 27.3 +/- 4.9 microM GTN. The EC(50) value of ascorbate was 0.11 +/- 0.011 mM. Activation of sGC was sensitive to oxyhemoglobin, superoxide, and a heme-site enzyme inhibitor. GTN had no effect when ascorbate was replaced by 1000 U of superoxide dismutase per milliliter. Ascorbate is known to reduce inorganic nitrite to NO. In the presence of 10 mM ascorbate, approximately 30 microM nitrite caused the same increase in sGC activity as 0.3 mM GTN. Determination of ascorbate-driven 1,2- and 1,3-glycerol dinitrate formation indicated that a 140 nM concentration of products was generated from 0.3 mM GTN within 10 min, excluding nitrite as a relevant intermediate. Our results suggest that a reaction between GTN and ascorbate or an ascorbate-derived species yields an activator of sGC with NO-like chemical properties. This reaction may contribute to GTN bioactivation in blood vessels under conditions of GTN tolerance and ascorbate supplementation.

Therapeutic effects of nitric oxide-aspirin hybrid drugs

This review examines the therapeutic potential and mechanisms of action of drugs known as nitric oxide (NO)-aspirins. Drugs of this class have an NO-releasing moiety joined by ester linkage to the aspirin molecule. NO-aspirins have the capability to release NO in addition to retaining the cyclooxygenase-inhibitory action of aspirin. The protective nature of NO led to the development of NO-aspirins in the hope that they might avoid the gastric side effects associated with aspirin. However, it has become apparent that the drug-derived NO instills potential for a wide range of added beneficial effects over the parent compound. In this review, the authors focus on the analgesic, anti-inflammatory, cardiovascular and chemopreventative actions of compounds of this emerging drug class.

Modulation of prostaglandin activity, part 1: prostaglandin inhibition in the management of nonrheumatologic diseases: immunologic and hematologic aspects

Prostaglandins (PGs) are active biologic substances that are involved in a wide range of physiologic processes; when their production is out of balance, they are factors in the pathogenesis of illness. Modulation of PGs by inhibition or stimulation is promising for the management of various conditions. PG inhibitors are widely used to relieve pain and inflammation in patients with rheumatologic disease. Interest in the use of PG inhibitors to prevent cancer and cardiovascular events is growing. More than 27 y ago, investigators found that PG depresses antibody production in vivo; reduces serum iron, hemoglobin, and leukoid series in bone marrow during acute and chronic blood loss; reduces albumin during antigenic stimulation; suppresses hypercalcemia after bleeding; and reduces fasting blood sugar and hyperglycemia after ether anesthesia and bleeding. Chronic conditions that produce large quantities of PGs are associated with immunosuppression and secondary anemia. Investigators in the present study hypothesized (1) that the overproduction of PGs is responsible for immunosuppression and secondary anemia in conditions associated with increased PG synthesis, such as pathologic inflammation, malignancy, trauma, and injury, and (2) that PG inhibitors reverse immunosuppression and secondary anemia, thereby enhancing the immune response. This is supported by many reports that show the immunosuppressive effects of PGs and their role in the immunosuppression associated with pathologic inflammation, burns, trauma, and tumors. Inhibition of PGs can be achieved through the use of synthetic medicines and natural products. This article reviews the effects of PGs and inhibition of increased synthesis of PGs on the lymphoid system, hematologic indices, and bone marrow elements in trauma, injury, burns, and tumors. The Medline database (1966-2006) was used in this study. Investigators in the present study and others have provided evidence that shows the involvement of PGs in immunosuppression and secondary anemia, as well as the efficacy of inhibited overproduction of PGs in many pathologic conditions other than rheumatologic disease.

A novel electron paramagnetic resonance-based assay for prostaglandin H synthase-1 activity

Background

Prostaglandin H₂ synthase (PGHS) is the enzyme that catalyses the two-stage conversion of arachidonic acid to prostaglandin H₂ (PGH₂) prior to formation of prostanoids that are important in inflammation. PGHS isozymes (-1 and -2) are the target for nonsteroidal anti-inflammatory drugs (NSAIDs).

Given the rekindled interest in specific anti-inflammatory PGHS inhibitors with reduced unwanted side effects, it is of paramount importance that there are reliable and efficient techniques to test new inhibitors. Here, we describe a novel in vitro electron paramagnetic resonance (EPR)-based assay for measuring the activity of PGHS-1.

Methods

We validated a novel in vitro PGHS-1 activity assay based on the oxidation of spin-trap agent, 1-hydroxy-3-carboxy-pyrrolidine (CPH) to 3-carboxy-proxy (CP) under the action of the peroxidase element of PGHS-1. This quantifiable spin-adduct, CP, yields a characteristic 3-line electron paramagnetic (EPR) spectrum.

Results

The assay is simple, reproducible and facilitates rapid screening of inhibitors of PGHS-1. Aspirin (100 μM, 1 mM) caused significant inhibition of spin-adduct formation (72 ± 11 and 100 ± 16% inhibition of control respectively; P < 0.05). Indomethacin (100 μM) also abolished the signal (114 ± 10% inhibition of control; P < 0.01). SA and the PGHS-2-selective inhibitor, NS398, failed to significantly inhibit spin-adduct generation (P > 0.05).

Conclusion

We have demonstrated and validated a simple, reproducible, quick and specific assay for detecting PGHS-1 activity and inhibition. The EPR-based assay described represents a novel approach to measuring PGHS activity and provides a viable and competitive alternative to existing assays.