V-PROLI/NO, a prodrug of the nitric oxide donor, PROLI/NO

Chemical Strategies Toward Prodrugs and Fluorescent Probes for Gasotransmitters

Three gaseous molecules are widely accepted as important gasotransmitters in mammalian cells, namely NO, CO and H2S. Due to the pharmacological effects observed in preclinical studies, these three gasotransmitters represent promising drug candidates for clinical translation. Fluorescent probes of the gasotransmitters are also in high demand; however, the mechanisms of actions or the roles played by gasotransmitters under both physiological and pathological conditions remain to be answered. In order to bring these challenges to the attention of both chemists and biologists working in this field, we herein summarize the chemical strategies used for the design of both probes and prodrugs of these three gasotransmitters.

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.

Synthesis and anti-hepatocellular carcinoma activity of novel O2-vinyl diazeniumdiolate-based nitric oxide-releasing derivatives of oleanolic acid

Considering that high levels of nitric oxide (NO) exert anti-cancer effect and the derivatives of oleanolic acid (OA) have shown potent anti-cancer activity, new O²-vinyl diazeniumdiolate-based NO releasing derivatives (5a-l, 11a-l) of OA were designed, synthesized, and biologically evaluated in the present study. These derivatives could release different amounts of NO in liver cells. Among them, 5d, 5i, 5j, 11g, 11h, and 11j released more NO in SMMC-7721 cells and displayed stronger proliferative inhibition against SMMC-7721 and HepG2 cells than OA and other tested compounds. The most active compound 5j showed almost 20-fold better solubility than OA in aqueous solution, released larger amounts of NO in liver cancer cells than that in normal ones, and exhibited potent anti-hepatocellular carcinoma activity but little effect on the normal liver cells. The inhibitory activity against the cancer cells was significantly diminished upon addition of an NO scavenger, suggesting that NO may contribute, at least in part, to the activity of 5j.

Combination of nitric oxide and drug delivery systems: tools for overcoming drug resistance in chemotherapy

Chemotherapeutic drugs have made significant contributions to anticancer therapy, along with other therapeutic methods including surgery and radiotherapy over the past century. However, multidrug resistance (MDR) of cancer cells has remained as a significant obstacle in the achievement of efficient chemotherapy. Recently, there has been increasing evidence for the potential function of nitric oxide (NO) to overcome MDR. NO is an endogenous and biocompatible molecule, contrasting with other potentially toxic chemosensitizing agents that reverse MDR effects, which has raised expectations in the development of efficient therapeutics with low side effects. In particular, nanoparticle-based drug delivery systems not only facilitate the delivery of multiple therapeutic agents, but also help bypass MDR pathways, which are conducive for the efficient delivery of NO and anticancer drugs, simultaneously. Therefore, this review will discuss the mechanism of NO in overcoming MDR and recent progress of combined NO and drug delivery systems.

Visible-Light-Triggered Uncaging of Carbonyl Sulfide for Hydrogen Sulfide (H2S) Release

Generation of hydrogen sulfide (H₂S) is challenging and few methods are capable of localized delivery of this gas. Here, a boron dipyrromethene-based carbamothioate (BDP-H₂S) that is uncaged by visible light of 470 nm to generate carbonyl sulfide (COS), which is rapidly hydrolyzed to H₂S in the presence of carbonic anhydrase, a widely prevalent enzyme, is reported.

Hepatoselective Nitric Oxide (NO) Donors, V-PYRRO/NO and V-PROLI/NO, in Nonalcoholic Fatty Liver Disease: A Comparison of Antisteatotic Effects with the Biotransformation and Pharmacokinetics

V-PYRRO/NO [O(2)-vinyl-1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate] and V-PROLI/NO (O2-vinyl-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate), two structurally similar diazeniumdiolate derivatives, were designed as liver-selective prodrugs that are metabolized by cytochrome P450 isoenzymes, with subsequent release of nitric oxide (NO). Yet, their efficacy in the treatment of nonalcoholic fatty liver disease (NAFLD) and their comparative pharmacokinetic and metabolic profiles have not been characterized. The aim of the present work was to compare the effects of V-PYRRO/NO and V-PROLI/NO on liver steatosis, glucose tolerance, and liver fatty acid composition in C57BL/6J mice fed a high-fat diet, as well as to comprehensively characterize the ADME (absorption, distribution, metabolism and excretion) profiles of both NO donors. Despite their similar structure, V-PYRRO/NO and V-PROLI/NO showed differences in pharmacological efficacy in the murine model of NAFLD. V-PYRRO/NO, but not V-PROLI/NO, attenuated liver steatosis, improved glucose tolerance, and favorably modified fatty acid composition in the liver. Both compounds were characterized by rapid absorption following i.p. administration, rapid elimination from the body, and incomplete bioavailability. However, V-PYRRO/NO was eliminated mainly by the liver, whereas V-PROLI/NO was excreted mostly in unchanged form by the kidney. V-PYRRO/NO was metabolized by CYP2E1, CYP2C9, CYP1A2, and CYP3A4, whereas V-PROLI/NO was metabolized mainly by CYP1A2. Importantly, V-PYRRO/NO was a better NO releaser in vivo and in the isolated, perfused liver than V-PROLI/NO, an effect compatible with the superior antisteatotic activity of V-PYRRO/NO. In conclusion, V-PYRRO/NO displayed a pronounced antisteatotic effect associated with liver-targeted NO release, whereas V-PROLI/NO showed low effectiveness, was not taken up by the liver, and was eliminated mostly in unchanged form by the kidney.

Gene expression profiles of NO- and HNO-donor treated breast cancer cells: insights into tumor response and resistance pathways

Nitric oxide (NO) synthase 2 (NOS2), a major inflammatory protein, modulates disease progression via NO in a number of pathologies, including cancer. The role of NOS2-derived NO is not only flux-dependent, which is higher in mouse vs human cells, but also varies based on spatial and temporal distribution both within tumor cells and in the tumor microenvironment. NO donors have been utilized to mimic NO flux conditions and to investigate the effects of varied NO concentrations. As a wide range of effects mediated by NO and other nitrogen oxides such as nitroxyl (HNO) have been elucidated, multiple NO- and HNO-releasing compounds have been developed as potential therapeutics, including as tumor modulators. One of the challenges is to determine differences in biomarker expression from extracellular vs intracellular generation of NO or HNO. Taking advantage of new NO and HNO releasing agents, we have characterized the gene expression profile of estrogen receptor-negative human breast cancer (MDA-MB-231) cells following exposure to aspirin, the NO donor DEA/NO, the HNO donor IPA/NO andtheir intracellularly-activated prodrug conjugates DEA/NO-aspirin and IPA/NO-aspirin. Comparison of the gene expression profiles demonstrated that several genes were uniquely expressed with respect to NO or HNO, such as miR-21, HSP70, cystathionine γ-lyase and IL24. These findings provide insight into targets and pathways that could be therapeutically exploited by the redox related species NO and HNO.

Site-directed delivery of nitric oxide to cancers

Nitric oxide (NO) is a reactive gaseous free radical which mediates numerous biological processes. At elevated levels, NO is found to be toxic to cancers and hence, a number of strategies for site-directed delivery of NO to cancers are in development during the past two decades. More recently, the focus of research has been to, in conjunction with other cancer drugs deliver NO to cancers for its secondary effects including inhibition of cellular drug efflux pumps. Among the various approaches toward site-selective delivery of exogenous NO sources, enzyme activated nitric oxide donors belonging to the diazeniumdiolate category afford unique advantages including exquisite control of rates of NO generation and selectivity of NO production. For this prodrug approach, enzymes including esterase, glutathione/glutathione S-transferase, DT-diaphorase, and nitroreductase are utilized. Here, we review the design and development of various approaches to enzymatic site-directed delivery of NO to cancers and their potential.

O2-sulfonylethyl protected isopropylamine diazen-1-ium-1,2-diolates as nitroxyl (HNO) donors: synthesis, β-elimination fragmentation, HNO release, positive inotropic properties, and blood pressure lowering studies

New types of nonexplosive O(2)-sulfonylethyl protected (-CH(2)CH(2)SO(2)R; R = OMe, NHOMe, NHOBn, Me) derivatives of isopropylamine diazen-1-ium-1,2-diolate (IPA/NO) (2-5) were developed that are designed to act as novel HNO donors. These compounds, with suitable half-lives (6.6-17.1 h) at pH 7.4, undergo a base-induced β-elimination reaction that releases a methyl vinyl sulfone product and the parent IPA/NO anion which subsequently preferentially releases HNO (46-61% range). Importantly, the O(2)-methylsulfonylethyl compound 5 exhibited a significant in vitro inotropic effect up to 283% of the baseline value and increased the rates of contraction and relaxation but did not induce a chronotropic effect. Furthermore, compound 5 (22.5 mg/kg po dose) provided a significant reduction in blood pressure up to 6 h after drug administration. All these data suggest that O(2)-sulfonylethyl protected derivatives of IPA/NO, which are efficient HNO donors, could have potential applications to treat cardiovascular disease(s) such as congestive heart failure.

Nitric oxide release is not required to decrease the ulcerogenic profile of nonsteroidal anti-inflammatory drugs

The objective of this work was to evaluate the biological properties of a new series of nitric oxide-releasing nonsteroidal anti-inflammatory drugs (NO-NSAIDs) possessing a tyrosol linker between the NSAID and the NO-releasing moiety (PROLI/NO); however, initial screening of ester intermediates without the PROLI/NO group showed the required (desirable) efficacy/safety ratio, which questioned the need for NO in the design. In this regard, NSAID ester intermediates were potent and selective COX-2 inhibitors in vitro, showed equipotent anti-inflammatory activity compared to the corresponding parent NSAID, but showed a markedly reduced gastric toxicity when administered orally. These results provide complementary evidence to challenge the currently accepted notion that hybrid NO-NSAIDs exert their cytoprotective effects by releasing NO. Results obtained in this work constitute a good body of evidence to initiate a debate about the future replacement of NSAID prodrugs for unprotected NSAIDs (possessing a free carboxylic acid group) currently in clinical use.

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).

Structurally Diverse Nitric Oxide-Releasing Poly(propylene Imine) Dendrimers

Structurally diverse secondary amine-functionalized poly(propylene imine) (PPI) dendrimers capable of tunable nitric oxide (NO) release were synthesized in a straightforward, one-step manner using ring-opening or conjugate-addition reactions with propylene oxide (PO), styrene oxide (SO), acrylonitrile (ACN), poly(ethylene glycol) methyl ether acrylate (average Mn = 480) (PEG) or 1,2-epoxy-9-decene (ED). N-Diazeniumdiolate nitric oxide donors were formed on the resulting secondary amine-functionalized G2-G5 PPI dendrimers by reaction with NO gas in basic solution. The NO storage and release kinetics for the resulting dendritic scaffolds were diverse (0.9-3.8 μmol NO/mg totals and 0.3 to 4.9 h half lives), illustrating the importance of the exterior chemical modification (e.g., steric environments, hydrophobicity, etc.) on diazeniumdiolate stability/decomposition. Tunable NO release was demonstrated by combining two donor systems on the exterior of one macromolecular scaffold. Additionally, a mathematical model was developed that allows for the simulation of dual NO release kinetics using the NO release data from the two single NO donor systems. The approaches described herein extend the range and scope of NO-releasing macromolecular scaffolds by unlocking a series of materials for use as dopants in biomedical polymers or stand-alone therapeutics depending on the exterior modification.

Nitric oxide donor, V-PROLI/NO, provides protection against arsenical induced toxicity in rat liver cells: requirement for Cyp1a1

Arsenic is a cancer chemotherapeutic but hepatotoxicity can be a limiting side effect. O(2)-vinyl 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (V-PROLI/NO) is a nitric oxide (NO) donor prodrug and metabolized by liver cytochromes P450 (CYP450) to release NO. The effects of V-PROLI/NO pretreatment on the toxicity of arsenic (as NaAsO(2)) were studied in a rat liver cell line (TRL 1215). The cells acted upon the prodrug to release NO, as assessed by nitrite levels, in a time-dependent fashion to maximal levels of 8-fold above basal levels. Pretreatment with V-PROLI/NO markedly reduced arsenic cytolethality which was directly related to the level of NO produced by V-PROLI/NO treatment. Cyp1a1 expression was directly related to the level of NO production and to reduced arsenic cytotoxicity. V-PROLI/NO pretreatment markedly reduced arsenic-induced apoptosis and suppressed phosphorylation of JNK1/2. V-PROLI/NO pretreatment facilitated additional increases in arsenic-induced metallothionein, a metal-binding protein important in arsenic tolerance. Thus, V-PROLI/NO protects against arsenic toxicity in rat liver cells, reducing cytolethality, apoptosis and dysregulation of MAPKs, through generation of NO formed after metabolism by liver cell enzymes, possibly including Cyp1a1. CYP450 required for NO production from V-PROLI/NO treatment in the rat and human appears to differ as we have previously studied the ability of V-PROLI/NO to prevent arsenic toxicity in human liver cells where it reduced toxicity apparently through a CYP2E1-mediated metabolic mechanism. None-the-less, it appears that both rat and human liver cells act upon V-PROLI/NO via a CYP450-related mechanism to produce NO and subsequently reduce arsenic toxicity.

The Nitric Oxide Prodrug V-PROLI/NO Inhibits Cellular Uptake of Proline

V-PYRRO/NO is a well studied nitric oxide (NO) prodrug which has been shown to protect human liver cells from arsenic, acetaminophen, and other toxic assaults in vivo. Its proline-based analogue, V-PROLI/NO, was designed to be a more biocompatible form that decomposes to the naturally occurring metabolites of proline, NO, and glycolaldehyde. Like V-PYRRO/NO, this cytochrome P450-activated prodrug was previously assumed to passively diffuse through the cellular membrane. Using (14)C-labeled proline in a competition assay, we show that V-PROLI/NO is transported through proline transporters into multiple cell lines. A fluorescent NO-sensitive dye (DAF-FM diacetate) and nitrite excretion indicated elevated intracellular NO release after metabolism over V-PYRRO/NO. These results also allowed us to predict and design a more permeable analogue, V-SARCO/NO. We report a proline transporter-based strategy for the selective transport of NO prodrugs that may have enhanced efficacy and aid in development of further NO prodrugs with increased permeability.

Glycosylated PROLI/NO derivatives as nitric oxide prodrugs

GlcNAc-PROLI/NO prodrugs that are activated by N-acetylglucosaminidase to release nitric oxide (NO) are described. A classical acid-amine coupling is used to bifunctionalize these PROLI/NO prodrugs, which on activation generate up to 4 mol of NO, a peptide residue, and an N-acetylglucosamine residue. Many of the prodrugs synthesized are efficient sources of intracellular NO.

Aryl bis(diazeniumdiolates): potent inducers of S-glutathionylation of cellular proteins and their in vitro antiproliferative activities

A number of bis(diazeniumdiolates) that we designed to release up to 4 mol of nitric oxide (NO) and that are structural analogues of the NO prodrug and anticancer lead compound O(2)-{2,4-dinitro-5-[4-(N-methylamino)benzoyloxy]phenyl} 1-(N,N-dimethylamino)diazen-1-ium-1,2- diolate (PABA/NO) were synthesized and studied. A majority of these compounds yielded higher levels of NO, were better inhibitors of proliferation of a number of cancer cell lines, and more rapidly induced substantially increased levels of S-glutathionylation of cellular proteins in comparison with PABA/NO. In most cases, the antiproliferative activity and extents of S-glutathionylation correlated well with levels of intracellular NO release. We report bis(diazeniumdiolates) to be a class of S-glutathionylating agents with potent antiproliferative and S-glutathionylating activity.

V-PROLI/NO, a nitric oxide donor prodrug, protects liver cells from arsenic-induced toxicity

Inorganic arsenic shows great promise in human cancer chemotherapy, although hepatotoxicity is a major limiting side-effect. O(2)-Vinyl 1-[2-(Carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (V-PROLI/NO) [Correction added after publication 19 December 2008: 1-[2-(Carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (V-PROLI/NO) was corrected to O(2)-Vinyl 1-[2-(Carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (V-PROLI/NO)] is a nitric oxide (NO) donor prodrug that is metabolized by liver cytochromes P450 to release NO. Other NO-releasing agents have been shown to mitigate arsenic toxicity. Thus, the effects of V-PROLI/NO pretreatment on the toxicity of inorganic arsenic (as NaAsO(2)) were studied in vitro in a human liver (HepG2) cell line. HepG2 cells acted upon the prodrug to release NO, as assessed by nitrite levels, in a dose- and time-dependent fashion to maximal levels of 57-fold above control levels. In cells pretreated with V-PROLI/NO (200 microM, 24 h) then exposed to arsenic for an additional 24 h, arsenic was much less toxic (LC(50) = 151.9 +/- 5.9 microM) than in control cells (LC(50) = 90.5 +/- 6.5 microM) and the reduced cytolethality was directly related to the level of NO produced. V-PROLI/NO also increased CYP2E1 transcriptional expression in a dose-dependent manner and CYP2E1 expression was directly related to the level of NO produced and the reduction in arsenic cytotoxicity. V-PROLI/NO pretreatment markedly reduced arsenic-induced apoptosis as measured by DNA fragmentation. Pretreatment with V-PROLI/NO suppressed phosphorylation of JNK1/2 after arsenic exposure. Arsenic increased metallothionein, a metal-binding protein important in arsenic tolerance, and V-PROLI/NO pretreatment caused additional increases in metallothionein levels. Thus, the prodrug, V-PROLI/NO, protects against arsenic toxicity in cultured human liver cells, reducing cytolethality, apoptosis and dysregulation of mitogen-activated protein kinases, through generation of NO formed after metabolism by liver cell enzymes, possibly including CYP2E1.

Synthesis, mechanistic studies, and anti-proliferative activity of glutathione/glutathione S-transferase-activated nitric oxide prodrugs

Nitric oxide (NO) prodrugs such as O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) are a growing class of promising NO-based therapeutics. Nitric oxide release from the anti-cancer lead compound, JS-K, is proposed to occur through a nucleophilic aromatic substitution by glutathione (GSH) catalyzed by glutathione S-transferase (GST) to form a diazeniumdiolate anion that spontaneously releases NO. In this study, a number of structural analogues of JS-K were synthesized and their chemical and biological properties were compared with those of JS-K. The homopiperazine analogue of JS-K showed anti-cancer activity that is comparable with that of JS-K but with a diminished reactivity towards both GSH and GSH/GST; both the aforementioned compounds displayed no cytotoxic activity towards normal renal epithelial cell line at concentrations where they significantly diminished the proliferation of a panel of renal cancer cell lines. These properties may prove advantageous in the further development of this class of nitric oxide prodrugs as cancer therapeutic agents.

Cell-permeable esters of diazeniumdiolate-based nitric oxide prodrugs

Although O(2)-(2,4-dinitrophenyl) derivatives of diazeniumdiolate-based nitric oxide (NO) prodrugs bearing a free carboxylic acid group were activated by glutathione to release NO, these compounds were poor sources of intracellular NO and showed diminished antiproliferative activity against human leukemia HL-60 cells. The carboxylic acid esters of these prodrugs, however, were found to be superior sources of intracellular NO and potent inhibitors of HL-60 cell proliferation.

Synthesis, nitric oxide release, and anti-leukemic activity of glutathione-activated nitric oxide prodrugs: Structural analogues of PABA/NO, an anti-cancer lead compound

Diazeniumdiolate anions and their prodrug forms are reliable sources of nitric oxide (NO) that have generated interest as promising therapeutic agents. A number of structural analogues of O(2)-(2,4-dinitro-5-(4-(N-methylamino)benzoyloxy)phenyl) 1-(N,N-dimethylamino)diazen-1-ium-1,2-diolate (PABA/NO), an anti-cancer lead compound that is designed to release NO upon activation by glutathione, were prepared. The nitric oxide release patterns of these O(2)-(2,4-dinitrophenyl) diazeniumdiolates in the presence of glutathione were tested and it was found that in the absence of competing pathways, these compounds release nearly quantitative amounts of NO. The ability of PABA/NO and its structural analogues to inhibit human leukemia cell proliferation was determined and it was found that compounds releasing elevated amounts of NO displayed superior cytotoxic effects.

Second-generation aspirin and indomethacin prodrugs possessing an O(2)-(acetoxymethyl)-1-(2-carboxypyrrolidin-1-yl)diazenium-1,2-diolate nitric oxide donor moiety: design, synthesis, biological evaluation, and nitric oxide release studies

The carboxylic acid group of the anti-inflammatory (AI) drugs aspirin and indomethacin was covalently linked to the 1-(2-carboxypyrrolidin-1-yl)diazen-1-ium-1,2-diolate ion via a one-carbon methylene spacer to obtain two new hybrid prodrugs. The aspirin prodrug ( 23) was a 2.2-fold more potent AI agent than aspirin, whereas the indomethacin prodrug ( 26) was about 1.6-fold less potent than indomethacin. Prodrugs 23 and 26 slowly released nitric oxide (NO) upon dissolution in phosphate buffer at pH 7.4 (1.1 mol of NO/mol of compound after 43 h), but the rate and the extent of NO release were higher (1.9 mol of NO/mol of compound in 3 min or less) when the compounds were incubated in the presence of porcine liver esterase. In vivo ulcer index (UI) studies showed that the aspirin prodrug 23 (UI = 0.7) and indomethacin prodrug 26 (UI = 0) were substantially less ulcerogenic than the parent drugs aspirin (UI = 51) and indomethacin (UI = 64).

Synthesis and in vitro anti-leukemic activity of structural analogues of JS-K, an anti-cancer lead compound

Structural analogues of JS-K, an anti-cancer lead compound, were prepared and their in vitro anti-leukemic activity was determined. The rate of nitric oxide release from the corresponding diazeniumdiolate anions did not appear to affect the anti-leukemic activity of the prodrug forms. Two compounds with potent inhibitory activity and a potentially favorable toxicological profile were identified.