Synthesis of peptide-diazeniumdiolate conjugates: towards enzyme activated antitumor agents

Targeted delivery of Nitric Oxide triggered by α-Glucosidase to Ameliorate NSAIDs-induced Enteropathy

Nonsteroidal anti-inflammatory drugs (NSAIDs) increase risks of severe small intestinal injuries. Development of effective therapeutic strategies to overcome this issue remains challenging. Nitric oxide (NO) as a gaseous mediator plays a protective role in small intestinal injuries. However, small intestine-specific delivery systems for NO have not been reported yet. In this study, we reported a small intestine-targeted polymeric NO donor (CS-NO) which was synthesized by covalent grafting of α-glucosidase-activated NO donor onto chitosan. In vitro and in vivo experiments demonstrated that CS-NO could be activated by intestinal α-glucosidase to release NO in the small intestine. Pre-treatment of mice with CS-NO significantly alleviated small intestinal damage induced by indomethacin, as demonstrated by down-regulation of the levels of pro-inflammatory cytokines and chemokines CXCL1/KC. Moreover, CS-NO also attenuated indomethacin-induced gut barrier dysfunction as evidenced by up-regulation of the levels of tight junction proteins and restoration of the levels of goblet cells and MUC2 production. Meanwhile, CS-NO effectively restored the defense function of Paneth cells against pathogens in small intestine. Our present study paves the way to develop NO-based therapeutic strategy for NSAIDs-induced small intestinal injuries.

Glutathione Responsive β-Cyclodextrin Conjugated S-Nitrothiols as a Carrier for Intracellular Delivery of Nitric Oxide

Nitric oxide (NO) exerts multiple functions in many life processes and was of great significance in a variety of biomedical scenarios. However, the mismatches between releasing locations and NO active sites seriously limited the available NO at areas of interest and greatly dampen the overall efficiency of delivery systems. Therefore, in the present study, a NO donor was developed to achieve intracellular delivery and release of NO to overcome the aforementioned challenges. Enhanced uptake and effective intracellular release of NO were realized via β-cyclodextrin (β-CD) mediated endocytosis and high level glutathione (GSH) inside cells, respectively. We demonstrated that intracellularly delivered NO would exert stronger bioeffects than premature release of NO outside targeted cells. Besides, β-CD assisted cellular uptake proved indispensable in maximizing the influence of NO in modulating cellular behavior. These results demonstrated the significance of intracellular delivery and release of NO in improving its bioutilization. The carrier could efficiently inhibit proliferation of SMCs, while promoting the growth of ECs. Such cell-type-differed physiological effects were advantageous in re-endothelialization and might hold great potential in cardiovascular applications.

The renaissance of nitric oxide: from improvement of stability to enhancement of endocytosis

The local generation and intracellular release of NO is no less vital than improving the stability of carriers.

Nitric Oxide Donor-Based Cancer Therapy: Advances and Prospects

The increasing understanding of the role of nitric oxide (NO) in cancer biology has generated significant progress in the use of NO donor-based therapy to fight cancer. These advances strongly suggest the potential adoption of NO donor-based therapy in clinical practice, and this has been supported by several clinical studies in the past decade. In this review, we first highlight several types of important NO donors, including recently developed NO donors bearing a dinitroazetidine skeleton, represented by RRx-001, with potential utility in cancer therapy. Special emphasis is then given to the combination of NO donor(s) with other therapies to achieve synergy and to the hybridization of NO donor(s) with an anticancer drug/agent/fragment to enhance the activity or specificity or to reduce toxicity. In addition, we briefly describe inducible NO synthase gene therapy and nanotechnology, which have recently entered the field of NO donor therapy.

Nitric oxide generating/releasing materials

Harnessing the impressive therapeutic potential of nitric oxide (NO) remains an ongoing challenge. This paper describes several of the current strategies both with respect to the underlying chemistry and physics and to the applications where they have shown promise. Included in this overview are molecular systems such as NONOates that release NO through chemical reactions and delivery vehicles such as nanoparticles that can generate, store, transport and deliver NO and related bioactive forms of NO such as nitrosothiols. Although there has been much positive movement, it is clear that we are only at the early stages of knowing how to precisely produce, transport and deliver to targeted sites therapeutic levels of NO and related molecules.

Design, Synthesis, and Investigation of Novel Nitric Oxide (NO)-Releasing Prodrugs as Drug Candidates for the Treatment of Ischemic Disorders: Insights into NO-Releasing Prodrug Biotransformation and Hemoglobin-NO Biochemistry

We have developed novel nitric oxide (NO)-releasing prodrugs of efaproxiral (RSR13) for their potential therapeutic applications in a variety of diseases with underlying ischemia. RSR13 is an allosteric effector of hemoglobin (Hb) that decreases the protein's affinity for oxygen, thereby increasing tissue oxygenation. NO, because of its vasodilatory property, in the form of ester prodrugs has been found to be useful in managing several cardiovascular diseases by increasing blood flow and oxygenation in ischemic tissues. We synthesized three NO-donor ester derivatives of RSR13 (DD-1, DD-2, and DD-3) by attaching the NO-releasing moieties nitrooxyethyl, nitrooxypropyl, and 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate, respectively, to the carboxylate of RSR13. In vitro studies demonstrated that the compounds released NO in a time-dependent manner upon being incubated with l-cysteine (1.8-9.3%) or human serum (2.3-52.5%) and also reduced the affinity of Hb for oxygen in whole blood (ΔP50 of 4.9-21.7 mmHg vs ΔP50 of 25.4-32.1 mmHg for RSR13). Crystallographic studies showed RSR13, the hydrolysis product of the reaction between DD-1 and deoxygenated Hb, bound to the central water cavity of Hb. Also, the hydrolysis product, NO, was observed exclusively bound to the two α hemes, the first such HbNO structure to be reported, capturing the previously proposed physiological bis-ligated nitrosylHb species. Finally, nitrate was observed bound to βHis97. Ultraperformance liquid chromatography-mass spectrometry analysis of the compounds incubated with matrices used for the various studies demonstrated the presence of the predicted reaction products. Our findings, beyond the potential therapeutic application, provide valuable insights into the biotransformation of NO-releasing prodrugs and their mechanism of action and into hemoglobin-NO biochemistry at the molecular level.

Targeted prodrug approaches for hormone refractory prostate cancer

Due to the propensity of relapse and resistance with prolonged androgen deprivation therapy (ADT), there is a growing interest in developing non-hormonal therapeutic approaches as alternative treatment modalities for hormone refractory prostate cancer (HRPC). Although the standard treatment for HRPC consists of a combination of ADT with taxanes and anthracyclines, the clinical use of chemotherapeutics is limited by systemic toxicity stemming from nondiscriminatory drug exposure to normal tissues. In order to improve the tumor selectivity of chemotherapeutics, various targeted prodrug approaches have been explored. Antibody-directed enzyme prodrug therapy (ADEPT) and gene-directed enzyme prodrug therapy (GDEPT) strategies leverage tumor-specific antigens and transcription factors for the specific delivery of cytotoxic anticancer agents using various prodrug-activating enzymes. In prostate cancer, overexpression of tumor-specific proteases such as prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) is being exploited for selective activation of anticancer prodrugs designed to be activated through proteolysis by these prostate cancer-specific enzymes. PSMA- and PSA-activated prodrugs typically comprise an engineered high-specificity protease peptide substrate coupled to a potent cytotoxic agent via a linker for rapid release of cytotoxic species in the vicinity of prostate cancer cells following proteolytic cleavage. Over the past two decades, various such prodrugs have been developed and they were effective at inhibiting prostate tumor growth in rodent models; several of these prodrug approaches have been advanced to clinical trials and may be developed into effective therapies for HRPC.

Synthesis of cephalosporin-3'-diazeniumdiolates: biofilm dispersing NO-donor prodrugs activated by β-lactamase

Use of biofilm dispersing NO-donor compounds in combination with antibiotics has emerged as a promising new strategy for treating drug-resistant bacterial biofilm infections. This paper details the synthesis and preliminary evaluation of six cephalosporin-3'-diazeniumdiolates as biofilm-targeted NO-donor prodrugs. Each of the compounds is shown to selectively release NO following reaction with the bacteria-specific enzyme β-lactamase and to trigger dispersion of Pseudomonas aeruginosa biofilms in vitro.

Synthesis and chemical and biological comparison of nitroxyl- and nitric oxide-releasing diazeniumdiolate-based aspirin derivatives

Structural modifications of nonsteroidal anti-inflammatory drugs (NSAIDs) have successfully reduced the side effect of gastrointestinal ulceration without affecting anti-inflammatory activity, but they may increase the risk of myocardial infarction with chronic use. The fact that nitroxyl (HNO) reduces platelet aggregation, preconditions against myocardial infarction, and enhances contractility led us to synthesize a diazeniumdiolate-based HNO-releasing aspirin and to compare it to an NO-releasing analogue. Here, the decomposition mechanisms are described for these compounds. In addition to protection against stomach ulceration, these prodrugs exhibited significantly enhanced cytotoxcity compared to either aspirin or the parent diazeniumdiolate toward nonsmall cell lung carcinoma cells (A549), but they were not appreciably toxic toward endothelial cells (HUVECs). The HNO-NSAID prodrug inhibited cylcooxgenase-2 and glyceraldehyde 3-phosphate dehydrogenase activity and triggered significant sarcomere shortening on murine ventricular myocytes compared to control. Together, these anti-inflammatory, antineoplasic, and contractile properties suggest the potential of HNO-NSAIDs in the treatment of inflammation, cancer, or heart failure.

Effects of nitric oxide-releasing nonsteroidal anti-inflammatory drugs (NONO-NSAIDs) on melanoma cell adhesion

A new class of nitric oxide (NO•)-releasing nonsteroidal anti-inflammatory drugs (NONO-NSAIDs) were developed in recent years and have shown promising potential as NSAID substitutes due to their gentle nature on cardiovascular and gastrointestinal systems. Since nitric oxide plays a role in regulation of cell adhesion, we assessed the potential use of NONO-NSAIDs as anti-metastasis drugs. In this regard, we compared the effects of NONO-aspirin and a novel NONO-naproxen to those exerted by their respective parent NSAIDs on avidities of human melanoma M624 cells. Both NONO-NSAIDs, but not the corresponding parent NSAIDs, reduced M624 adhesion on vascular cellular adhesion molecule-1 (VCAM-1) by 20-30% and fibronectin by 25-44% under fluid flow conditions and static conditions, respectively. Only NONO-naproxen reduced (~56%) the activity of β1 integrin, which binds to α4 integrin to form very late antigen-4 (VLA-4), the ligand of VCAM-1. These results indicate that the diazeniumdiolate (NO•)-donor moiety is critical for reducing the adhesion between VLA-4 and its ligands, while the NSAID moiety can impact the regulation mechanism of melanoma cell adhesion.

Fifty years of diazeniumdiolate research. From laboratory curiosity to broad-spectrum biomedical advances

Here I show that a “pure” research project, seemingly totally lacking in practical application when it was first published, can years later spark a whole new scientific field with the potential to revolutionize clinical practice. A 1961 publication describing adducts of nitric oxide (NO) with certain nucleophiles attracted little notice at the time, but later work showing that the adducts could be hydrolyzed to regenerate the NO in bioactive form has provided the foundation for a host of biomedical applications. Crucial to the discovery of widely used tools for studying NO’s chemical biology as well as for the design of a variety of promising therapeutic advances has been the increasingly detailed understanding of the physicochemical properties of these “diazeniumdiolates” (also known as NONOates).

Novel β-galactosidase-specific O2-glycosylated diazeniumdiolate probes

Three β-galactosidase-specific nitric-oxide-releasing diazeniumdiolate conjugated probes were prepared as a prelude to studies of new potential molecular MRI imaging agents. A glycosylated derivative, 2e, designed to be trafficked across cell membranes, was also prepared. We report, in detail, the synthesis and characterization of these probes. In addition, the release of diazeniumdiolate from the probes by β-galactosidase-catalyzed hydrolysis was used to estimate their efficacy as serum-stable, specific NO donors.

Synthesis of new 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines: a search for novel nitric oxide donor anti-inflammatory agents

A group of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines possessing a variety of substituents (Me, CO2Et, H, N=O) attached to the 1,2,3,6-tetrahydropyridyl N(1)-nitrogen atom were synthesized and evaluated as anti-inflammatory agents. Structure-activity relationship data showed that the N-methyl-1,2,3,6-tetrahydropyridyl moiety is a suitable bioisosteric replacement for the tolyl moiety in celecoxib. The most potent compound 4-[5-(1-methyl-1,2,3,6-tetrahydropyridin-4-yl)-3-trifluoromethylpyrazol-1-yl]benzenesulfonamide (ED(50)=61.2 mg/kg po) exhibited an anti-inflammatory activity between that of the reference drugs celecoxib (ED(50)=10.8 mg/kg po) and aspirin (ED(50)=128.7 mg/kg po). The synthesis of model hybrid nitric oxide donor N-diazen-1-ium-1,2-diolate derivatives of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines requires further investigation since the reaction of 1,2,3,6-tetrahydropyridines with nitric oxide furnished the undesired N-nitroso-1,2,3,6-tetrahydrohydropyridyl product rather than the desired N-diazen-1-ium-1,2-diolate-1,2,3,6-tetrahydropyridyl product.

Novel (E)-2-(aryl)-3-(4-methanesulfonylphenyl)acrylic ester prodrugs possessing a diazen-1-ium-1,2-diolate moiety: Design, synthesis, cyclooxygenase inhibition, and nitric oxide release studies

A novel group of hybrid nitric oxide-releasing anti-inflammatory drugs (11) possessing a 1-(N,N-diethylamino)diazen-1-ium-1,2-diolate, or 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate, nitric oxide (.NO) donor moiety attached via a one-carbon methylene spacer to the carboxylic acid group of (E)-3-(4-methanesulfonylphenyl)-2-(phenyl)acrylic acids were synthesized. These ester prodrugs (11) all exhibited in vitro inhibitory activity against the cyclooxygenase-2 (COX-2) isozyme (IC(50)=0.94-31.6 microM range). All compounds released .NO upon incubation with phosphate buffer (PBS) at pH 7.4 (3.2-11.3% range). In comparison, the percentage of .NO released was significantly higher (48.6-75.3% range) when these hybrid ester prodrugs were incubated in the presence of rat serum. These incubation studies suggest that both .NO and the parent anti-inflammatory (E)-3-(4-methanesulfonylphenyl)-2-(phenyl)acrylic acid would be released upon in vivo cleavage by non-specific serum esterases. O(2)-[(E)-2-(4-Acetylaminophenyl)-3-(4-methanesulfonylphenyl)acryloyloxymethyl]-1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (11f) is a moderately potent (IC(50)=0.94 microM) and selective (SI>104) COX-2 inhibitor that released 73% of the theoretical maximal release of two molecules of .NO/molecule of the parent hybrid ester prodrug upon incubation with rat serum. Hybrid ester .NO-donor prodrugs offer a potential drug design concept for the development of anti-inflammatory drugs that are devoid of adverse ulcerogenic and/or cardiovascular side effects.

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.

A glycosylated nitric oxide donor, beta-Gal-NONOate, and its site-specific antitumor activity

So far, nitric oxide (NO) donors have been applied to various aspects of antitumor therapy. To selectively sensitize tumor cells and avoid unwanted side effects, we recently synthesized a beta-galactosidase-activatable NO-releasing compound, beta-galactosyl-pyrrolidinyl diazeniumdiolate (beta-Gal-NONOate). In this study, we first verified its superiority over its parent diazeniumdiolate (NONOate) in terms of targeted intracellular NO-releasing and antitumor activity with 9L/LacZ cells (rat glioma cell line 9L with transformed LacZ gene) in vitro. beta-Gal-NONOate only released NO when hydrolyzed by induced beta-galactosidase in 9L/LacZ cells, which led to its more powerful cytotoxicity than that of NONOate. The results showed that beta-Gal-NONOate produced higher NO levels than NONOate in 9L/LacZ cells at equal concentration, and hence induced optimal NO levels for antitumor activity. However, in 9L cells, beta-Gal-NONOate showed less toxicity than NONOate. Therefore, it is demonstrated that beta-Gal-NONOate is a site-specific prodrug for targeting NO intracellularly as a beta-galactosidase-sensitive NO donor, and it is also expected to be a promising probe in numerous experimental settings and a potential therapeutic drug for antitumor treatment.

Sialated diazeniumdiolate: a new sialidase-activated nitric oxide donor

A new sialated diazeniumdiolate has been synthesized, and the glycosylation product was exclusively an alpha anomer. This new nitric oxide donor exhibited significantly improved stability as compared to its parent diazeniumdiolate salts, and it could be efficiently hydrolyzed by neuraminidase to release nitric oxide with a K(m) of 0.14 mM. The sialic acid-NO conjugate would be a valuable prodrug that targets NO to influenza viruses.

Controlled photochemical release of nitric oxide from O2-substituted diazeniumdiolates

Diazeniumdiolates are a well-established class of nitric oxide (NO) donors that have been employed in a wide variety of biochemical and pharmacological investigations. To provide a means of targeting NO release, photosensitive precursors to diazeniumdiolates have been developed and are reviewed here. After a brief description of diazeniumdiolate chemistry and the potential uses of photosensitive precursors to NO, three different classes of phototriggered diazeniumdiolates are discussed: 2-nitrobenzyl derivatives, meta-substituted benzyl derivatives, and naphthylmethyl and naphthylallyl derivatives. In addition, the photochemistry of diazeniumdiolate salts themselves is covered.

Progress toward clinical application of the nitric oxide-releasing diazeniumdiolates

Diazeniumdiolates, compounds of structure R(1)R(2)NN(O)=NOR(3), which have also been called NONOates, have proven useful for treating an increasing diversity of medical disorders in relevant animal models. Here, I review the chemical features that make them such excellent starting points for designing materials capable of targeting reliable and controllable fluxes of bioactive NO for in vitro and in vivo applications. This is followed by a consideration of recent proof-of-concept studies that underscore what I believe to be the substantial clinical promise of such materials. Examples covered include progress toward inhibiting restenosis after angioplasty, preparing thromboresistant medical devices, reversing vasospasm, and relieving pulmonary hypertension. Together with a very recent report describing the beneficial effects of diazeniumdiolate therapy in a patient with acute respiratory distress syndrome, the results of the animal experiments support the prediction that a broad selection of problems in clinical medicine can be solved by judiciously mining the enormous variety of possible R(1)R(2)NN(O)=NOR(3) structures.

Synthesis of beta-lactamase activated nitric oxide donors

In order to achieve site specific delivery of NO, we designed conjugates of cephalosporin with NO donors. NO donors such as cupferron and SIN-1 were evaluated as potential choices for conjugates. Cephalosporin conjugated with SIN-1 demonstrated promising beta-lactamase dependent NO releasing ability.

Nitric oxide donor drugs: current status and future trends

Nitric oxide synthesised in endothelial cells that line blood vessels has a wide range of functions that are vital for maintaining a healthy cardiovascular system. Reduced nitric oxide availability is implicated in the initiation and progression of many cardiovascular diseases and delivery of supplementary nitric oxide to help prevent disease progression is an attractive therapeutic option. Nitric oxide donor drugs represent a useful means of systemic nitric oxide delivery and organic nitrates have been used for many years as effective therapies for symptomatic relief from angina. However, nitrates have limitations and a number of alternative nitric oxide donor classes have emerged since the discovery that nitric oxide is a crucial biological mediator. This review focuses on novel advances and possible future directions in nitric oxide donor drug development.