An N-hydroxylated derivative of cyanamide that inhibits yeast aldehyde dehydrogenase

Nitroxyl as a Potential Theranostic in the Cancer Arena

Significance: As one-electron reduced molecule of nitric oxide (NO), nitroxyl (HNO) has gained enormous attention because of its novel physiological or pharmacological properties, ranging from cardiovascular protective actions to antitumoricidal effects. Recent Advances: HNO is emerging as a new entity with therapeutic advantages over its redox sibling, NO. The interests in the chemical, pharmacological, and biological characteristics of HNO have broadened our current understanding of its role in physiology and pathophysiology. Critical Issues: In particular, the experimental evidence suggests the therapeutic potential of HNO in tumor pharmacology, such as neuroblastoma, gastrointestinal tumor, ovarian, lung, and breast cancers. Indeed, HNO donors have been demonstrated to attenuate tumor proliferation and angiogenesis. Future Directions: In this review, the generation and detection of HNO are outlined, and the roles of HNO in cancer progression are further discussed. We anticipate that the completion of this review might give novel insights into the roles of HNO in cancer pharmacology and open up a novel field of cancer therapy based on HNO.

A recent history of nitroxyl chemistry, pharmacology and therapeutic potential

Due to the excitement surrounding the discovery of NO as an endogenously generated signalling molecule, a number of other nitrogen oxides were also investigated as possible physiological mediators. Among these was nitroxyl (HNO). Over the past 25 years or so, a significant amount of work by this laboratory and many others has disclosed that HNO possesses unique chemical properties and important pharmacological utility. Indeed, the pharmacological potential for HNO as a treatment for heart failure, among other uses, has garnered this curious molecule a considerable amount of recent attention. This review summarizes the events that led to this recent attention as well as poses important questions that are still to be answered with regards to understanding the chemistry and biology of HNO. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

Development of N-Substituted Hydroxamic Acids with Pyrazolone Leaving Groups as Nitrosocarbonyl Precursors

A novel class of nitrosocarbonyl precursors, N-substituted hydroxamic acids with pyrazolone leaving groups (NHPY), has been synthesized. Under physiological conditions, these compounds generate nitrosocarbonyl intermediates, which upon hydrolysis release nitroxyl (azanone, HNO) in excellent yields. The amount and rate of nitrosocarbonyl generation are dependent on the nature of the pyrazolone leaving groups and significantly on the structural properties of the NHPY donors. Pyrazolones have been found to be efficient nitrosocarbonyl traps, undergoing an N-selective nitrosocarbonyl aldol reaction. This trapping reaction has been used to confirm the involvement of nitrosocarbonyl intermediates in NHPY aqueous decomposition. In addition, NHPY compounds are shown to generate nitrosocarbonyls efficiently under mild basic conditions in organic solvent and may therefore also enjoy synthetic utility.

Development of N-substituted hydroxylamines as efficient nitroxyl (HNO) donors

Due to its inherent reactivity, nitroxyl (HNO), must be generated in situ through the use of donor compounds, but very few physiologically useful HNO donors exist. Novel N-substituted hydroxylamines with carbon-based leaving groups have been synthesized, and their structures confirmed by X-ray crystallography. These compounds generate HNO under nonenzymatic, physiological conditions, with the rate and amount of HNO released being dependent mainly on the nature of the leaving group. A barbituric acid and a pyrazolone derivative have been developed as efficient HNO donors with half-lives at pH 7.4, 37 °C of 0.7 and 9.5 min, respectively.

Optimization of HNO production from N,O-bis-acylated hydroxylamine derivatives

A wide range of N,O-bis-acylated hydroxylamine derivatives with chloro or arenesulfonyl leaving groups, and a related set of N-hydroxy-N-acylsulfonamides, have been synthesized and evaluated for nitroxyl (HNO) production. Mechanistic studies have revealed that the observed aqueous chemistry is more complicated than originally anticipated, and have been used to develop a new series of efficient HNO precursors (4u-4x, 7c-7d) with tunable half-lives.

HNO signaling mechanisms

Due to recent discoveries of important and novel biological activity, nitroxyl (HNO) has become a molecule of significant interest. Although it has been used in the past as a treatment for alcoholism, it is currently being touted as a treatment for heart failure. It is becoming increasingly clear that many of the biological actions of HNO can be attributed to its ability to react with specific thiol- and, possibly, heme-proteins. Herein is discussed the chemistry of HNO with likely biological targets. A particular focus is given to targets associated with the pharmacological utility of HNO as a cardiovascular agent and for the treatment of alcoholism.

Nitroxyl (HNO) signaling

Nitroxyl (HNO) has become a nitrogen oxide of significant interest due to its reported biological activity. The actions of HNO in the cardiovascular system appear to make it a good candidate for therapeutic applications for cardiovascular disorders and other potentially important effects have been noted as well. Although the chemistry associated with this activity has not been firmly established, the propensity for HNO to react with thiols and metals are likely mechanisms. Herein, are described the biological activity of HNO and some of the chemistry of HNO that may be responsible for its biological effects.

The pharmacology of nitroxyl (HNO) and its therapeutic potential: not just the Janus face of NO

Nitroxyl (HNO), the 1-electron reduced and protonated congener of nitric oxide (NO), has received recent attention as a potential pharmacological agent for the treatment of heart failure and as a preconditioning agent for the mitigation of ischemia-reperfusion injury. Interest in the pharmacology and biology of HNO has prompted examination, or in some instances reexamination, of many of its chemical properties. Such studies have provided insight into the chemical basis for the biological effects of HNO, although the biochemical mechanisms for many of these effects remain to be established. In this review, a brief description of the biologically relevant chemistry of HNO is given, followed by a more detailed discussion of the pharmacology and potential toxicology of HNO.

The reaction of nitroxyl (HNO) with nitrosobenzene gives cupferron (N-nitrosophenylhydroxylamine)

Nitroxyl (HNO), a penultimate product in the NOS-catalyzed conversion of L-arginine to L-citrulline, generated from Angeli's salt (AS) was determined by trapping it with nitrosobenzene (NB) to produce cupferron. The cupferron thus produced was characterized by complexation with Fe3+, Al3+, Cu2+, or Sn2+. UV/VIS spectra of the solubilized (in CHCl3) precipitates formed from NB and nitroxyl generated from AS in the presence of the iron, aluminum, copper, or tin salts were identical to those of their corresponding cupferron complexes. The identities of the Fe3+ and Cu2+ complexes formed from NB and HNO were further confirmed by their identical retention times on HPLC when compared to authentic Fe3+ and Cu2+ cupferron complexes. It was possible to detect 5 x 10(-6) M of the cupferron Fe3+ complex spectrophotometrically and to measure its production from the nitroxyl generators AS and methanesulfohydroxamic acid (MSHA) in the presence of 10(-4) M NB. The yield of cupferron was 51 and 62% of the amount of nitroxyl possible from AS or MSHA, respectively, after taking into account the relative rates of nitroxyl generation from these donors.

Involvement of nitroxyl (HNO) in the cyanamide-induced vasorelaxation of rabbit aorta

Relaxation of precontracted rabbit aortic rings in vitro by cyanamide, a clinically used alcohol deterrent drug, required catalase and H2O2, suggesting that a bioactivation mechanism was involved. Since the oxidation of cyanamide by catalase/H2O2 had been shown previously to lead to nitroxyl (HNO) generation via the intermediate N-hydroxycyanamide, and aortic ring relaxation was inhibited by the catalase inhibitor, 3-aminotriazole, HNO appears to be responsible for the vasorelaxation mediated by cyanamide. This was further supported by the observation that N,O-dibenzoyl-N-hydroxycyanamide (DBHC), a derivative of N-hydroxycyanamide that releases HNO in the absence of catalase/H2O2, was a potent vasorelaxant, with an EC50 of 4.2 +/- 1.3 x 10(-6) M.

In vivo effects of disulfiram and cyanamide on canine liver aldehyde dehydrogenase isoenzymes as detected by high-performance (pressure) liquid chromatography

Methods for analysis of aldehyde dehydrogenase isoenzymes using high-performance (pressure) liquid chromatography (HPLC) were used to determine in vivo effects of disulfiram and cyanamide on canine liver aldehyde dehydrogenase (ALDH) isoenzymes. Liver ALDH isoenzymes from control and disulfiram- or cyanamide-treated dogs were separated by ion-exchange HPLC, and enzyme activity was detected using a postcolumn reactor. Two major peaks of ALDH activity (peaks I and II) were detected. Varying the composition of the reaction column reagents resulted in alterations in the elution profiles consistent with the kinetic properties of individual isoenzymes (i.e., ALDH IB in peak I and ALDH IIB in peak II), including estimates of the Km for acetaldehyde and the effects of magnesium ions on ALDH activity. Disulfiram treatment decreased both peaks depending on disulfiram dose and length of treatment, with peak I being more sensitive to inactivation than peak II. Reagents containing MgCl2 (1 mM) decreased peak I and increased peak II compared with EDTA (1 mM) for samples from both control and disulfiram-treated animals. These data are consistent with the assignment of the disulfiram-sensitive isoenzyme (ALDH IB) to peak I and the isoenzyme stimulated by magnesium ions (ALDH IIB) to peak II. In vivo cyanamide treatment produced similar decreases in both peaks to a maximum decrease of approximately 30% of control depending on cyanamide dose. Peak I, however, was more sensitive than peak II to in vitro inactivation by cyanamide, which suggests that cytosolic ALDH in the dog (in contrast to other mammals) is more sensitive to inactivation than mitochondrial ALDH.

N,O-diacylated-N-hydroxyarylsulfonamides: nitroxyl precursors with potent smooth muscle relaxant properties

N,O-Diacylated-N-hydroxyarylsulfonamides are capable of slowly releasing nitroxyl (HNO) by simple, non-enzymatic hydrolysis in Krebs solution at 37 degrees C. Release of nitric oxide (NO) was not seen. These compounds were also found to elicit vasorelaxation in rabbit thoracic aorta in vitro, presumably as a result of their ability to release HNO. This effect was enhanced by the addition of superoxide dismutase (SOD). Thus, these results are consistent with previous work indicating that HNO is a potent vasorelaxant.