Prodrugs of cyanamide as (long-acting) alcohol deterrent agents

Transcriptional activation of budding yeast DDI2/3 through chemical modifications of Fzf1

DDI2 and DDI3 (DDI2/3) are two identical genes in Saccharomyces cerevisiae encoding cyanamide (CY) hydratase. They are not only highly induced by CY, but also by a DNA-damaging agent methyl methanesulfonate (MMS), and the regulatory mechanism is unknown. In this study, we performed a modified genome-wide genetic synthetic array screen and identified Fzf1 as a zinc-finger transcriptional activator required for CY/MMS-induced DDI2/3 expression. Fzf1 binds to a DDI2/3 promoter consensus sequence CS2 in vivo and in vitro, and this interaction was enhanced in response to the CY treatment. Indeed, experimental over production of Fzf1 alone was sufficient to induce DDI2/3 expression; however, CY and MMS treatments did not cause the accumulation or apparent alteration in migration of cellular Fzf1. To test a hypothesis that Fzf1 is activated by covalent modification of CY and MMS, we performed mass spectrometry of CY/MMS-treated Fzf1 and detected a few modified lysine residues. Amino acid substitutions of these residues revealed that Fzf1-K70A completely abolished MMS-induced and reduced CY-induced DDI2/3 expression, indicating that the Fzf1-K70 methylation activates Fzf1. This study collectively reveals a novel regulatory mechanism by which Fzf1 is activated by chemical modifications and in turn induces the expression of its target genes for detoxification.

Mechanisms of inhibition of aldehyde dehydrogenase by nitroxyl, the active metabolite of the alcohol deterrent agent cyanamide

Nitroxyl, produced in the bioactivation of the alcohol deterrent agent cyanamide, is a potent inhibitor of aldehyde dehydrogenase (AIDH); however, the mechanism of inhibition of AlDH by nitroxyl has not been described previously. Nitroxyl is also generated from Angeli's salt (Na2N2O3) at physiological pH, and, indeed, Angeli's salt inhibited yeast AlDH in a time- and concentration-dependent manner, with IC50 values under anaerobic conditions with and without NAD+ of 1.3 and 1.8 microM, respectively. Benzaldehyde, a substrate for AlDH, competitively blocked the inhibition of this enzyme by nitroxyl in the presence of NAD+, but not in its absence, in accord with the ordered mechanism of this reaction. The sulfhydryl reagents dithiothreitol (5 mM) and reduced glutathione (10 mM) completely blocked the inhibition of AlDH by Angeli's salt. These thiols were also able to partially restore activity to the nitroxyl-inhibited enzyme, the extent of reactivation being dependent on the pH at which the inactivation occurred. This pH dependency indicates the formation of two inhibited forms of the enzyme, with an irreversible form predominant at pH 7.5 and below, and a reversible form predominant at pH 8.5 and above. The reversible form of the inhibited enzyme is postulated to be an intra-subunit disulfide, while the irreversible form is postulated to be a sulfinamide. Both forms of the inhibited enzyme are derived via a common N-hydroxysulfenamide intermediate produced by the addition of nitroxyl to active site cysteine thiol(s).

Novel prodrugs of cyanamide that inhibit aldehyde dehydrogenase in vivo

S-Methylisothiourea (4), when administered to rats followed by a subsequent dose of ethanol, gave rise to a 119-fold increase in ethanol-derived blood acetaldehyde (AcH) levels-a consequence of the inhibition of hepatic aldehyde dehydrogenase (A1DH)-when compared to control animals not receiving 4. The corresponding O-methylisourea was totally inactive under the same conditions, suggesting that differential metabolism may be a factor in this dramatic difference between the pharmacological effects of O-methylisourea and 4 in vivo. The S-n-butyl- and S-isobutylisothioureas (8 and 9, respectively) at doses equimolar to that of 4 were nearly twice as effective in raising ethanol-derived blood AcH, while S-allylisothiourea (10) was slightly less active. However, blood ethanol levels of all experimental groups were indistinguishable from controls. Pretreatment of the animals with 1-benzylimidazole, a known inhibitor of the hepatic mixed function oxidases, followed sequentially by either 8, 9, or 10 plus ethanol, reduced blood AcH levels by 66-88%, suggesting that the latter compounds were being oxidatively metabolized to a common product that led to the inhibition of AcH metabolism. In support of this, when 8 was incubated in vitro with rat liver microsomes coupled to catalase and yeast A1DH, the requirement for microsomal activation for the inhibition of A1DH activity was clearly indicated. We suggest that S-oxidation is involved and that the S-oxides produced in vivo inhibited A1DH directly, or spontaneously released cyanamide, an inhibitor of A1DH. Indeed, incubation of 8 with rat liver microsomes and NADPH gave rise to cyanamide as metabolite, identified as its dansylated derivative. Cyanamide formation was minimal in the absence of coenzyme. Extending the side chain was detrimental, since S-benzylisothiourea (11) and S-n-hexadecylisothiourea (12) were toxic, the latter producing extensive necrosis of the liver and kidneys when administered to rats.

Pharmacokinetics of cyanamide in dog and rat

A pharmacokinetic study of cyanamide, an inhibitor of aldehyde dehydrogenase (E.C. 1.2.1.3) has been made in the beagle dog and Sprague-Dawley rat. Cyanamide plasma levels were determined by a sensitive high performance liquid chromatographic assay, specific for cyanamide. In the dog, i.v. administration of cyanamide at 1, 2 and 4 mg kg-1, produced a dose-dependent pharmacokinetic behaviour. Statistically significant changes were observed in plasma clearance values (12.6 to 19.7 mL kg-1 min-1), half life values (39 to 61 min) and mean residence times (50 to 79 min). Peak plasma concentrations, after oral administration of 4 mg kg-1 were achieved at 30 min and oral bioavailability was about 65%. In the rat after i.v. or oral administration, cyanamide (2 mg kg-1) had a half life of 30 min, a total plasma clearance of 117 mL kg-1 min-1 and a mean residence time of 26 min. Oral bioavailability was about 69%.

Cyanamide given ICV or systemically to the rat alters subsequent alcohol drinking

Cyanamide or disulfiram serves to suppress volitional intake of alcohol presumably because of the toxic build-up of acetaldehyde dehydrogenase (AIDH). However, the presence of acetaldehyde systemically favors the in vivo synthesis of addictive-like metabolites in the brain which in turn enhance alcohol drinking. The purpose of this investigation, therefore, was to determine whether cyanamide administered to the rat, which did not have access to alcohol during treatment, would nevertheless affect the subsequent preference for alcohol. In the first experiment, cannulae were implanted bilaterally above the cerebral ventricle of 33 adult male Sprague-Dawley rats so that an artificial CSF or a solution of cyanamide could be infused intracerebroventricularly (ICV). Following post-operative recovery, each rat was tested for its alcohol preference by offering it water and a solution of ethyl alcohol which was increased over 8 days from 3-20%. After a single test concentration of alcohol (range of 5-9%) was selected for each individual animal presented with water over a 5-day interval, cyanamide was infused in a volume of 2.5 microliters per side three times daily for 4 days in one of the following total doses: 0.03, 0.1, 0.3, 0.5 or 1.0 mg. A second five-day preference test was run, and 6 weeks following cyanamide infusions a final 3-20% alcohol preference screen was run over 8 days. The results showed that a long-term, dose-dependent increase or decrease in alcohol intake occurred in those rats reactive to the drug.(ABSTRACT TRUNCATED AT 250 WORDS)