Overview--in vitro inhibition of aldehyde dehydrogenase by disulfiram and metabolites

Reactivity and binding mode of disulfiram, its metabolites, and derivatives in SARS-CoV-2 PLpro: insights from computational chemistry studies

The papain-like protease (PL^pro) from SARS-CoV-2 is an important target for the development of antivirals against COVID-19. The safe drug disulfiram (DSF) presents antiviral activity inhibiting PL^pro in vitro, and it is under clinical trial studies, indicating to be a promising anti-COVID-19 drug. In this work, we aimed to understand the mechanism of PL^pro inhibition by DSF and verify if DSF metabolites and derivatives could be potential inhibitors too. Molecular docking, DFT, and ADMET techniques were applied. The carbamoylation of the active site cysteine residue by DSF metabolite (DETC-MeSO) is kinetically and thermodynamically favorable (ΔG^‡ = 3.15 and ΔG =  - 12.10 kcal mol^-1, respectively). Our results strongly suggest that the sulfoxide metabolites from DSF are promising covalent inhibitors of PL^pro and should be tested in in vitro and in vivo assays to confirm their antiviral action.

Disulfiram in glioma: Literature review of drug repurposing

Gliomas are the most common malignant brain tumors. High-grade gliomas, represented by glioblastoma multiforme (GBM), have a poor prognosis and are prone to recurrence. The standard treatment strategy is tumor removal combined with radiotherapy and chemotherapy, such as temozolomide (TMZ). However, even after conventional treatment, they still have a high recurrence rate, resulting in an increasing demand for effective anti-glioma drugs. Drug repurposing is a method of reusing drugs that have already been widely approved for new indication. It has the advantages of reduced research cost, safety, and increased efficiency. Disulfiram (DSF), originally approved for alcohol dependence, has been repurposed for adjuvant chemotherapy in glioma. This article reviews the drug repurposing method and the progress of research on disulfiram reuse for glioma treatment.

The Effect of Disulfiram and Copper on Cellular Viability, ER Stress and ALDH Expression of Human Meningioma Cells

(1) Background: Meningiomas are the most common intracranial tumors in adults; currently there is no effective chemotherapy for malignant meningiomas. The effect of disulfiram (DSF)/Copper (Cu) on meningiomas remains unclear; (2) Methods: The impact of DSF/Cu on cell viability of meningioma adhesion cells (MgACs) and sphere cells (MgSCs) was assessed via MTS assay. The effects of DSF/Cu on intracellular Cu levels, cell senescence, and apoptosis were analyzed using CopperGreen, C12FDG, and Annexin V assays. Intracellular ALDH isoform expression and canonical pathway expression after DSF/Cu treatment were analyzed using mRNA microarray and Ingenuity Pathway Analysis, with further verification through qRT-PCR and immunoblotting; (3) Results: The viability of MgACs and MgSCs were inhibited by DSF/Cu. DSF/Cu increased intracellular Cu levels and cellular senescence. DSF/Cu also induced ER stress in MgACs and activated the PERK/eIF2 pathway for further adaptive response, apoptosis, and autophagy. Finally, DSF/Cu inhibited the expression of different ALDH isoforms in MgACs and MgSCs; (4) Conclusions: DSF/Cu exerts cytotoxic effects against both meningioma cells and stem-like cells and has treatment potential for meningioma.

The interaction of disulfiram and H2S metabolism in inhibition of aldehyde dehydrogenase activity and liver cancer cell growth

Disulfiram (DSF), a sulfur-containing compound, has been used to treat chronic alcoholism and cancer for decades by inactivating aldehyde dehydrogenase (ALDH). Hydrogen sulfide (H₂S) is a new gasotransmitter and regulates various cellular functions by S-sulfhydrating cysteine in the target proteins. H₂S exhibits similar properties to DSF in the sensitization of cancer cells. The interaction of DSF and H₂S on ALDH activity and liver cancer cell survival are not clear. Here it was demonstrated that DSF facilitated H₂S release from thiol-containing compounds, and DSF and H₂S were both capable of regulating ALDH through inhibition of gene expression and enzymatic activity. The supplement of H₂S sensitized human liver cancer cells (HepG2) to DSF-inhibited cell viability. The expression of cystathionine gamma-lyase (a major H₂S-generating enzyme) was lower but ALDH was higher in mouse liver cancer stem cells (Dt81Hepa1-6) in comparison with their parental cells (Hepa1-6), and H₂S was able to inhibit liver cancer stem cell adhesion. In conclusion, these data point to the potential of combining DSF and H₂S for inhibition of cancer cell growth and tumor development by targeting ALDH.

Disulfiram and 6-Thioguanine synergistically inhibit the enzymatic activities of USP2 and USP21

Disulfiram is a promising repurposed drug that, combining with radiation and chemotherapy, exhibits effective anticancer activities in several preclinical models. The cellular metabolites of disulfiram have been established, however, the intracellular targets of disulfiram remain largely unexplored. We have previously reported that disulfiram suppresses the coronaviral papain-like proteases through attacking their zinc-finger domains, suggesting an inhibitory function potentially on other proteases with similar catalytic structures. Ubiquitin-specific proteases (USPs) share a highly-conserved zinc-finger subdomain that structurally similar to the papain-like proteases and are attractive anticancer targets as upregulated USPs levels are found in a variety of tumors. Here, we report that disulfiram functions as a competitive inhibitor for both USP2 and USP21, two tumor-related deubiquitinases. In addition, we also observed a synergistic inhibition of USP2 and USP21 by disulfiram and 6-Thioguanine (6TG), a clinical drug for acute myeloid leukemia. Kinetic analyses revealed that both drugs exhibited a slow-binding mechanism, moderate inhibitory parameters, and a synergistically inhibitory effect on USP2 and USP21, suggesting the potential combinatory use of these two drugs for USPs-related tumors. Taken together, our study provides biochemical evidence for repurposing disulfiram and 6TG as a combinatory treatment in clinical applications.

Overcoming cancer therapeutic bottleneck by drug repurposing

Ever present hurdles for the discovery of new drugs for cancer therapy have necessitated the development of the alternative strategy of drug repurposing, the development of old drugs for new therapeutic purposes. This strategy with a cost-effective way offers a rare opportunity for the treatment of human neoplastic disease, facilitating rapid clinical translation. With an increased understanding of the hallmarks of cancer and the development of various data-driven approaches, drug repurposing further promotes the holistic productivity of drug discovery and reasonably focuses on target-defined antineoplastic compounds. The "treasure trove" of non-oncology drugs should not be ignored since they could target not only known but also hitherto unknown vulnerabilities of cancer. Indeed, different from targeted drugs, these old generic drugs, usually used in a multi-target strategy may bring benefit to patients. In this review, aiming to demonstrate the full potential of drug repurposing, we present various promising repurposed non-oncology drugs for clinical cancer management and classify these candidates into their proposed administration for either mono- or drug combination therapy. We also summarize approaches used for drug repurposing and discuss the main barriers to its uptake.

Inactivation of Aldehyde Dehydrogenase by Disulfiram in the Presence and Absence of Lipoic Acid or Dihydrolipoic Acid: An in Vitro Study

The inhibition of aldehyde dehydrogenase (ALDH) by disulfiram (DSF) in vitro can be prevented and/or reversed by dithiothreitol (DTT), which is a well-known low molecular weight non-physiological redox reagent commonly used in laboratory experiments. These observations inspired us to ask the question whether the inhibition of ALDH by DSF can be preserved or abolished also by dihydrolipoic acid (DHLA), which is the only currently known low molecular weight physiological dithiol in the body of humans and other animals. It can even be metaphorized that DHLA is an "endogenous DTT". Lipoic acid (LA) is the oxidized form of DHLA. We investigated the inactivation of ALDH derived from yeast and rat liver by DSF in the presence or absence of LA or DHLA. The results clearly show that DHLA is able both to restore and protect ALDH activity blocked by DSF. The proposed mechanism is discussed.

Anti-alcohol abuse drug disulfiram inhibits human PHGDH via disruption of its active tetrameric form through a specific cysteine oxidation

Due to rising costs and the difficulty to identify new targets, drug repurposing appears as a viable strategy for the development of new anti-cancer treatments. Although the interest of disulfiram (DSF), an anti-alcohol drug, to treat cancer was reported for many years, it is only very recently that one anticancer mechanism-of-action was highlighted. This would involve the inhibition of the p97 segregase adaptor NPL4, which is essential for the turnover of proteins involved in multiple regulatory and stress-response intracellular pathways. However, recently DSF was also reported as one of the first phosphoglycerate dehydrogenase (PHGDH) inhibitors, a tetrameric enzyme catalyzing the initial step of the serine synthetic pathway that is highly expressed in numerous cancer types. Here, we investigated the structure-activity relationships (SAR) of PHGDH inhibition by disulfiram analogues as well as the mechanism of action of DSF on PHGDH via enzymatic and cell-based evaluation, mass spectrometric and mutagenesis experiments.

Hydroxycobalamin catalyzes the oxidation of diethyldithiocarbamate and increases its cytotoxicity independently of copper ions

It is known that some metals (Cu, Zn, Cd, Au) markedly increase the toxic effect of thiocarbamates. It was shown in the present study that hydroxycobalamin (a form of vitamin B12, HOCbl), which incorporates cobalt, significantly enhances the cytotoxicity of diethyldithiocarbamate (DDC), decreasing its IC50 value in tumor cells three to five times. The addition of HOCbl to aqueous DDC solutions accelerated the reduction of oxygen. No hydrogen peroxide accumulation was observed in DDC + HOCbl solutions; however, catalase slowed down the oxygen reduction rate. Catalase as well as the antioxidants N-acetylcysteine (NAC) and glutathione (GSH) partially inhibited the cytotoxic effect of DDC + HOCbl, whereas ascorbate, pyruvate, and tiron, a scavenger of superoxide anion, had no cytoprotective effect. The administration of HOCbl into DDC solutions (> 1 mM) resulted in the formation of a crystalline precipitate, which was inhibited in the presence of GSH. The data of UV and NMR spectroscopy and HPLC and Mass Spectrometry (LC/MS) indicated that the main products of the reaction of DDC with HOCbl are disulfiram (DSF) and its oxidized forms, sulfones and sulfoxides. The increase in the cytotoxicity of DDC combined with HOCbl occurred both in the presence of Cu2+ in culture medium and in nominally Cu-free solutions, as well as in growth medium containing the copper chelator bathocuproine disulfonate (BCS). The results indicate that HOCbl accelerates the oxidation of DDC with the formation of DSF and its oxidized forms. Presumably, the main cause of the synergistic increase in the toxic effect of DDC + HOCbl is the formation of sulfones and sulfoxides of DSF.

Effects of disulfiram on choice behavior in a rodent gambling task: association with catecholamine levels

RATIONALE

Gambling disorder is a growing societal concern, as recognized by its recent classification as an addictive disorder in the DSM-5. Case reports have shown that disulfiram reduces gambling-related behavior in humans.

OBJECTIVES

The purpose of the present study was to determine whether disulfiram affects performance on a rat gambling task, a rodent version of the Iowa gambling task in humans, and whether any changes were associated with alterations in dopamine and/or norepinephrine levels.

METHODS

Rats were administered disulfiram prior to testing on the rat gambling task or prior to analysis of dopamine or norepinephrine levels in brain homogenates. Rats in the behavioral task were divided into two subgroups (optimal vs suboptimal) based on their baseline levels of performance in the rat gambling task. Rats in the optimal group chose the advantageous strategy more, and rats in the suboptimal group (a parallel to problem gambling) chose the disadvantageous strategy more. Rats were not divided into optimal or suboptimal groups prior to neurochemical analysis.

RESULTS

Disulfiram administered 2 h, but not 30 min, before the task dose-dependently improved choice behavior in the rats with an initial disadvantageous "gambling-like" strategy, while having no effect on the rats employing an advantageous strategy. The behavioral effects of disulfiram were associated with increased striatal dopamine and decreased striatal norepinephrine.

CONCLUSIONS

These findings suggest that combined actions on dopamine and norepinephrine may be a useful treatment for gambling disorders.

Drug repurposing in cancer

Cancer is a major health issue worldwide, and the global burden of cancer is expected to increase in the coming years. Whereas the limited success with current therapies has driven huge investments into drug development, the average number of FDA approvals per year has declined since the 1990s. This unmet need for more effective anti-cancer drugs has sparked a growing interest for drug repurposing, i.e. using drugs already approved for other indications to treat cancer. As such, data both from pre-clinical experiments, clinical trials and observational studies have demonstrated anti-tumor efficacy for compounds within a wide range of drug classes other than cancer. Whereas some of them induce cancer cell death or suppress various aspects of cancer cell behavior in established tumors, others may prevent cancer development. Here, we provide an overview of promising candidates for drug repurposing in cancer, as well as studies describing the biological mechanisms underlying their anti-neoplastic effects.

Mechanisms of protection against irreversible oxidation of the catalytic cysteine of ALDH enzymes: Possible role of vicinal cysteines

The catalytic mechanism of the NAD(P)⁺-dependent aldehyde dehydrogenases (ALDHs) involves the nucleophilic attack of the essential cysteine (Cys302, mature HsALDH2 numbering) on the aldehyde substrate. Although oxidation of Cys302 will inactivate these enzymes, it is not yet well understood how this oxidation is prevented. In this work we explore possible mechanisms of protection by systematically analyzing the reported three-dimensional structures and amino acid sequences of the enzymes of the ALDH superfamily. Specifically, we considered the Cys302 conformational space, the structure and residues conservation of the catalytic loop where Cys302 is located, the observed oxidation states of Cys302, the ability of physiological reductants to revert its oxidation, and the presence of vicinal Cys in the catalytic loop. Our analyses suggested that: 1) In the apo-enzyme, the thiol group of Cys302 is quite resistant to oxidation by ambient O₂ or mild oxidative conditions, because the protein environment promotes its high pK_a. 2) NAD(P)⁺ bound in the "hydride transfer" conformation afforded total protection against Cys302 oxidation by an unknown mechanism. 3) If formed, the Cys302-sulfenic acid is protected against irreversible oxidation. 4) Of the physiological reductant agents, the dithiol lipoic acid could reduce a sulfenic or a disulfide bond in the ALDHs active site; glutathione cannot because its thiol group cannot reach Cys302, and other physiological monothiols may be ineffective in those ALDHs where their active site cannot sterically accommodate two molecules of the monothiols. 5) Formation of the disulfides Cys301-Cys302, Cys302-Cys304, Cys302-Cys305 and Cys-302-Cys306 in those ALDHs that have these Cys residues is not probable, because of the permitted Cys conformers as well as the conserved structure and low flexibility of the catalytic loop. 6) Only in some ALDH2, ALDH9, ALDH16 and ALDH23 enzymes, Cys303, alone or in conjunction with Cys301, allows disulfide formation. Interestingly, several of these enzymes are mitochondrial.

Phenylacetaldehyde Oxidation by Freshly Prepared and Cryopreserved Guinea Pig Liver Slices: The Role of Aldehyde Oxidase

Phenylacetaldehyde is formed when the xenobiotic and biogenic amine 2-phenylethylamine is inactivated by a monoamine oxidase–catalyzed oxidative deamination. Exogenous phenylacetaldehyde is found in certain foodstuffs such as honey, cheese, tomatoes, and wines. 2-Phenylethylamine can trigger migraine attacks in susceptible individuals and can become fairly toxic at high intakes from foods. It may also function as a potentiator that enhances the toxicity of histamine and tyramine. The present investigation examines the metabolism of phenylacetaldehyde to phenylacetic acid in freshly prepared and in cryopreserved guinea pig liver slices. In addition, it compares the relative contribution of aldehyde oxidase, xanthine oxidase, and aldehyde dehydrogenase in the oxidation of phenylacetaldehyde using specific inhibitors for each oxidizing enzyme. The inhibitors used were isovanillin for aldehyde oxidase, allopurinol for xanthine oxidase, and disulfiram for aldehyde dehydrogenase. In freshly prepared liver slices, phenylacetaldehyde was converted mainly to phenylacetic acid, with traces of 2-phenylethanol being present. Disulfiram inhibited phenylacetic acid formation by 80% to 85%, whereas isovanillin inhibited acid formation to a lesser extent (50% to 55%) and allopurinol had little or no effect. In cryopreserved liver slices, phenylacetic acid was also the main metabolite, whereas the 2-phenylethanol production was more pronounced than that in freshly prepared liver slices. Isovanillin inhibited phenylacetic acid formation by 85%, whereas disulfiram inhibited acid formation to a lesser extent (55% to 60%) and allopurinol had no effect. The results in this study have shown that, in freshly prepared and cryopreserved liver slices, phenylacetaldehyde is converted to phenylacetic acid by both aldehyde dehydrogenase and aldehyde oxidase, with no contribution from xanthine oxidase. Therefore, aldehyde dehydrogenase is not the only enzyme responsible in the metabolism of phenylacetaldehyde, but aldehyde oxidase may also be important and thus its role should not be ignored.

Concise review: bullseye: targeting cancer stem cells to improve the treatment of gliomas by repurposing disulfiram

Cancer stem cells (CSCs) are thought to be at the root of cancer recurrence because they resist conventional therapies and subsequently reinitiate tumor cell growth. Thus, targeting CSCs could be the bullseye to successful cancer therapeutics in the future. Brain tumors are some of the most challenging types of cancer to treat and the median survival following the initial diagnosis is 12-18 months. Among the different types of brain tumors, glioblastoma (GBM) is considered the most aggressive and remains extremely difficult to treat. Despite surgery, radiation, and chemotherapy, most patients develop refractory disease. Temozolomide (TMZ) is a chemotherapy used to treat GBM however resistance develops in most patients. The underlying mechanisms for TMZ resistance (TMZ-resistant) involve the expression of DNA repair gene O(6)-methylguanine-DNA methyltransferase. CSC genes such as Sox-2, BMI-1, and more recently Y-box binding protein-1 also play a role in resistance. In order to develop novel therapies for GBM, libraries of small interfering RNAs and off-patent drugs have been screened. Over the past few years, several independent laboratories identified disulfiram (DSF) as an off-patent drug that kills GBM CSCs. Reportedly DSF has several modes of action including its ability to inhibit aldehyde dehydrogenases, E3 ligase, polo-like kinase 1, and NFkB. Due to the fact that GBM is a disease of heterogeneity, chemotherapy with multitargeting properties may be the way of the future. In broader terms, DSF kills CSCs from a range of different cancer types further supporting the idea of repurposing it for "target practice."

Evaluation of the dopamine β-hydroxylase (DβH) inhibitor nepicastat in participants who meet criteria for cocaine use disorder

In the present study, we tested the hypothesis that the potent and selective dopamine-β-hydroxylase (DβH) inhibitor nepicastat would have minimal effects on cardiovascular and pharmacokinetic parameters associated with cocaine administration and would reduce the positive subjective effects produced by cocaine. We conducted a double-blind, placebo-controlled, inpatient study of oral nepicastat (0, 80 and 160mg) concurrent with intravenous (IV) cocaine (0, 10, 20 and 40mg) in non-treatment seeking participants who metcriteria for cocaine use disorder. Safety analyses revealed that nepicastat was well-tolerated and there were no differences in adverse events observed after nepicastat plus cocaine vs. cocaine alone. In addition, the pharmacokinetic properties of cocaine administration were not altered by nepicastat treatment. Cocaine-induced cardiovascular and subjective effects were evaluated for completers in the cohort randomized to nepicastat (n=13) using a within-subjects statistical analysis strategy. Specifically, the cardiovascular and subjective effects of cocaine were assessed in the presence of placebo (0mg), 80mg of nepicastat or 160mg of nepicastat on study Days 4, 8 and 12, respectively. Analyses revealed a main effect of nepicastat to reduce several cocaine-induced positive subjective effects. Taken together, these data indicate that nepicastat is safe when co-administered with cocaine and may suppress its positive subjective effects, and may be viable as a pharmacotherapy for treatment of cocaine use disorder.

Disulfiram/copper causes redox-related proteotoxicity and concomitant heat shock response in ovarian cancer cells that is augmented by auranofin-mediated thioredoxin inhibition

A valuable strategy to develop new therapeutic options for a variety of diseases has been the identification of new targets and applications for already approved drugs, the so-called drug repositioning. Recurrent ovarian cancer is a nearly incurable malignancy for which new and effective treatments are urgently needed. The alcohol-deterring drug disulfiram has been shown to cause preferential cell death in a variety of cancer cells. In this study, it is shown that disulfiram mediates effective cell death in ovarian cancer cells by promoting a pro-oxidative intracellular environment in a copper-dependent mechanism. Within few hours of application, disulfiram caused irreversible cell damage associated with pronounced induction of the inducible heat shock proteins HSP70, HSP40, and HSP32. The small heat shock protein HSP27 was found to be covalently dimerized via oxidized disulfide bonds and precipitated in para-nuclear protein aggregates. Simultaneous inhibition of the cellular thioredoxin system by auranofin further enhanced the cytotoxic effect of disulfiram. These data indeed indicate that the combination of two approved drugs, the anti-alcoholic disulfiram and the anti-rheumatic auranofin, may be of interest for the treatment of recurrent and genotoxic drug-resistant ovarian cancer by inducing a proteotoxic cell death mechanism.

Increased nitroxidative stress promotes mitochondrial dysfunction in alcoholic and nonalcoholic fatty liver disease

Increased nitroxidative stress causes mitochondrial dysfunctions through oxidative modifications of mitochondrial DNA, lipids, and proteins. Persistent mitochondrial dysfunction sensitizes the target cells/organs to other pathological risk factors and thus ultimately contributes to the development of more severe disease states in alcoholic and nonalcoholic fatty liver disease. The incidences of nonalcoholic fatty liver disease continuously increase due to high prevalence of metabolic syndrome including hyperlipidemia, hypercholesterolemia, obesity, insulin resistance, and diabetes. Many mitochondrial proteins including the enzymes involved in fat oxidation and energy supply could be oxidatively modified (including S-nitrosylation/nitration) under increased nitroxidative stress and thus inactivated, leading to increased fat accumulation and ATP depletion. To demonstrate the underlying mechanism(s) of mitochondrial dysfunction, we employed a redox proteomics approach using biotin-N-maleimide (biotin-NM) as a sensitive biotin-switch probe to identify oxidized Cys residues of mitochondrial proteins in the experimental models of alcoholic and acute liver disease. The aims of this paper are to briefly describe the mechanisms, functional consequences, and detection methods of mitochondrial dysfunction. We also describe advantages and limitations of the Cys-targeted redox proteomics method with alternative approaches. Finally, we discuss various applications of this method in studying oxidatively modified mitochondrial proteins in extrahepatic tissues or different subcellular organelles and translational research.

High-throughput chemical screens identify disulfiram as an inhibitor of human glioblastoma stem cells

Glioblastoma Multiforme (GBM) continues to have a poor patient prognosis despite optimal standard of care. Glioma stem cells (GSCs) have been implicated as the presumed cause of tumor recurrence and resistance to therapy. With this in mind, we screened a diverse chemical library of 2,000 compounds to identify therapeutic agents that inhibit GSC proliferation and therefore have the potential to extend patient survival. High-throughput screens (HTS) identified 78 compounds that repeatedly inhibited cellular proliferation, of which 47 are clinically approved for other indications and 31 are experimental drugs. Several compounds (such as digitoxin, deguelin, patulin and phenethyl caffeate) exhibited high cytotoxicity, with half maximal inhibitory concentrations (IC₅₀) in the low nanomolar range. In particular, the FDA approved drug for the treatment of alcoholism, disulfiram (DSF), was significantly potent across multiple patient samples (IC₅₀ of 31.1 nM). The activity of DSF was potentiated by copper (Cu), which markedly increased GSC death. DSF–Cu inhibited the chymotrypsin-like proteasomal activity in cultured GSCs, consistent with inactivation of the ubiquitin-proteasome pathway and the subsequent induction of tumor cell death. Given that DSF is a relatively non-toxic drug that can penetrate the blood-brain barrier, we suggest that DSF should be tested (as either a monotherapy or as an adjuvant) in pre-clinical models of human GBM. Data also support targeting of the ubiquitin-proteasome pathway as a therapeutic approach in the treatment of GBM.

Cytotoxic effect of disulfiram/copper on human glioblastoma cell lines and ALDH-positive cancer-stem-like cells

Background:

Glioblastoma multiforme (GBM) cells are resistant to anticancer drugs. Cancer stem cells (CSCs) are a key mediator of chemoresistance. We have reported that disulfiram (DS), an aldehyde dehydrogenase (ALDH) inhibitor, targets breast CSC-like cells. In this study, the effect of DS and combination of DS and gemcitabine (dFdC) on GBM cells and GBM stem-like cells was investigated.

Methods:

1-(4,5-Dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), combination index (CI)-isobologram, western blot, luciferase reporter gene assay, electrophoretic mobility-shift assay and ALDH analysis were used in this study.

Results:

Disulfiram is cytotoxic in GBM cell lines in a copper (Cu)-dependent manner. Disulfiram/copper enhances the cytotoxicity of dFdC. Combination index-isobologram analysis indicates a synergistic effect between DS/Cu and dFdC. Disulfiram/copper induces reactive oxygen species (ROS), activates JNK and p38 pathways and inhibits nuclear factor-kappa B activity in GBM cell lines. Disulfiram/copper may trigger intrinsic apoptotic pathway via modulation of the Bcl2 family. Disulfiram/copper abolishes stem-like cell population in GBM cell lines.

Conclusion:

Our findings indicate that the cytotoxicity of DS/Cu and the enhancing effect of DS/Cu on the cytotoxicity of dFdC in GBM stem-like cells may be caused by induction of ROS and inhibition of both ALDH and the NFkB pathway. Both DS and dFdC can traverse the blood–brain barrier. Further study may lead them into GBM chemotherapy.

Disulfiram stimulates dopamine release from noradrenergic terminals and potentiates cocaine-induced dopamine release in the prefrontal cortex

RATIONALE

Disulfiram efficacy in treatment of cocaine addiction is attributed to the inhibition of dopamine-β-hydroxylase and reduction in brain noradrenaline (NA)/dopamine (DA) ratio.

OBJECTIVES

Using microdialysis, we investigated if disulfiram causes DA release from noradrenergic terminals and modifies cocaine-induced DA release.

RESULTS

Disulfiram reduced extracellular NA in the medial prefrontal (mPF) cortex, occipital cortex, accumbens and caudate nuclei, while it markedly increased DA not only in mPF but also in the occipital cortex, despite its scanty dopaminergic afferences, and modestly increased DA in the accumbens and caudate nuclei, despite their dense dopaminergic innervation. Disulfiram-induced DA accumulation was reversed in both cortices by tetrodotoxin infusion and by systemic administration of the α(2)-adrenoceptor agonist clonidine, but was not modified by the α(2)-adrenoceptor antagonist RS 79948 or the D(2)-like agonist quinpirole. Disulfiram prevented cocaine-induced NA release in the mPF cortex and nucleus accumbens, potentiated cocaine-induced DA release in the mPF cortex but failed to modify cocaine effect in the nucleus accumbens. DA release induced by disulfiram-cocaine combination in the mPF cortex was prevented by clonidine but not by quinpirole.

CONCLUSIONS

We suggested that disulfiram, by removing NA-mediated inhibitory control on noradrenergic terminals, causes an unrestrained cocaine-induced DA release from those terminals in the mPF cortex. In the accumbens and caudate nuclei, "allogenic" DA concentration might be clouded by DA originated from dopaminergic terminals. The possible role of "allogenic" DA in disulfiram ability to prevent stress-induced reinstatement of cocaine seeking is discussed.

Post-translational modifications of mitochondrial aldehyde dehydrogenase and biomedical implications

Aldehyde dehydrogenases (ALDHs) represent large family members of NAD(P)+-dependent dehydrogenases responsible for the irreversible metabolism of many endogenous and exogenous aldehydes to the corresponding acids. Among 19 ALDH isozymes, mitochondrial ALDH2 is a low Km enzyme responsible for the metabolism of acetaldehyde and lipid peroxides such as malondialdehyde and 4-hydroxynonenal, both of which are highly reactive and toxic. Consequently, inhibition of ALDH2 would lead to elevated levels of acetaldehyde and other reactive lipid peroxides following ethanol intake and/or exposure to toxic chemicals. In addition, many East Asian people with a dominant negative mutation in ALDH2 gene possess a decreased ALDH2 activity with increased risks for various types of cancer, myocardial infarct, alcoholic liver disease, and other pathological conditions. The aim of this review is to briefly describe the multiple post-translational modifications of mitochondrial ALDH2, as an example, after exposure to toxic chemicals or under different disease states and their pathophysiological roles in promoting alcohol/drug-mediated tissue damage. We also briefly mention exciting preclinical translational research opportunities to identify small molecule activators of ALDH2 and its isozymes as potentially therapeutic/preventive agents against various disease states where the expression or activity of ALDH enzymes is altered or inactivated.

An image-based, high-throughput screening assay for molecules that induce excess DNA replication in human cancer cells

Previous studies have shown DNA re-replication can be induced in cells derived from human cancers under conditions in which it is not possible for cells derived from normal tissues. Because DNA re-replication induces cell death, this strategy could be applied to the discovery of potential anticancer therapeutics. Therefore, an imaging assay amenable to high-throughput screening was developed that measures DNA replication in excess of four genomic equivalents in the nuclei of intact cells and indexes cell proliferation. This assay was validated by screening a library of 1,280 bioactive molecules on both normal and tumor-derived cells where it proved more sensitive than current methods for detecting excess DNA replication. This screen identified known inducers of excess DNA replication, such as inhibitors of microtubule dynamics, and novel compounds that induced excess DNA replication in both normal and cancer cells. In addition, two compounds were identified that induced excess DNA replication selectively in cancer cells and one that induced endocycles selectively in cancer cells. Thus, this assay provides a new approach to the discovery of compounds useful for investigating the regulation of genome duplication and for the treatment of cancer.

Inhibition of hepatic mitochondrial aldehyde dehydrogenase by carbon tetrachloride through JNK-mediated phosphorylation

The aim of this study was to investigate the mechanism of inhibition of mitochondrial aldehyde dehydrogenase (ALDH2) by carbon tetrachloride (CCl(4)). CCl(4) administration caused marked hepatocyte ballooning and necrosis in the pericentral region. CCl(4) also inhibited hepatic ALDH2 activity in a time-dependent manner without altering the protein level, suggesting ALDH2 inhibition through covalent modifications such as phosphorylation by JNK. To demonstrate phosphorylation, the isoelectric point (pI) of ALDH2 in CCl(4)-exposed rats was compared to that of untreated controls. Immunoblot analysis revealed that immunoreactive ALDH2 bands in CCl(4)-exposed rats were shifted to acidic pI ranges on two-dimensional electrophoresis (2-DE) gels. Incubation with alkaline phosphatase significantly restored the suppressed ALDH2 activity with a concurrent alkaline pI shift of the ALDH2 spots. Both JNK and activated JNK were translocated to mitochondria after CCl(4) exposure. In addition, incubation with catalytically active JNK led to significant inhibition of ALDH2 activity, with an acidic pI shift on 2-DE gels. Furthermore, immunoprecipitation followed by immunoblot analysis with anti-phospho-Ser-Pro antibody revealed phosphorylation of a Ser residue(s) of ALDH2. These results collectively indicate a novel underlying mechanism by which CCl(4) exposure activates JNK, which translocates to mitochondria and phosphorylates ALDH2, contributing to inhibition of ALDH2 activity accompanied by decreased cellular defense capacity and increased lipid peroxidation.

Role of Metabolism in Drug-Induced Idiosyncratic Hepatotoxicity

Rare adverse reactions to drugs that are of unknown etiology, or idiosyncratic reactions, can produce severe medical complications or even death in patients. Current hypotheses suggest that metabolic activation of a drug to a reactive intermediate is a necessary, yet insufficient, step in the generation of an idiosyncratic reaction. We review evidence for this hypothesis with drugs that are associated with hepatotoxicity, one of the most common types of idiosyncratic reactions in humans. We identified 21 drugs that have either been withdrawn from the U.S. market due to hepatotoxicity or have a black box warning for hepatotoxicity. Evidence for the formation of reactive metabolites was found for 5 out of 6 drugs that were withdrawn, and 8 out of 15 drugs that have black box warnings. For the other drugs, either evidence was not available or suitable studies have not been carried out. We also review evidence for reactive intermediate formation from a number of additional drugs that have been associated with idiosyncratic hepatotoxicity but do not have black box warnings. Finally, we consider the potential role that high dosages may play in these adverse reactions.

Complex, unusual conformational changes in kidney betaine aldehyde dehydrogenase suggested by chemical modification with disulfiram

The NAD+-dependent animal betaine aldehyde dehydrogenases participate in the biosynthesis of glycine betaine and carnitine, as well as in polyamines catabolism. We studied the kinetics of inactivation of the porcine kidney enzyme (pkBADH) by the drug disulfiram, a thiol-reagent, with the double aim of exploring the enzyme dynamics and investigating whether it could be an in vivo target of disulfiram. Both inactivation by disulfiram and reactivation by reductants were biphasic processes with equal limiting amplitudes. Under certain conditions half of the enzyme activity became resistant to disulfiram inactivation. NAD+ protected almost 100% at 10 microM but only 50% at 5mM, and vice versa if the enzyme was pre-incubated with NAD+ before the chemical modification. NADH, betaine aldehyde, and glycine betaine also afforded greater protection after pre-incubation with the enzyme than without pre-incubation. Together, these findings suggest two kinds of active sites in this seemingly homotetrameric enzyme, and complex, unusual ligand-induced conformational changes. In addition, they indicate that, in vivo, pkBADH is most likely protected against disulfiram inactivation.

Inhibition of aldehyde detoxification in CNS mitochondria by fungicides

Among the several converging factors leading to Parkinson's disease, epidemiological studies indicate a correlation between Parkinson's disease (PD) with living in a rural area and/or exposure to agricultural pesticides. In this present study, we examined the potential of multiple agricultural pesticides for their ability to inhibit the function of whole, respiring rat brain mitochondria using the oxidation of the neurotoxic lipid-aldehyde trans-4-hydroxy-2-nonenal (HNE) as a biomarker for mitochondrial aldehyde dehydrogenase (ALDH) activity in situ. We chose an arbitrary cutoff concentration of 10 microM of each pesticide. Our data demonstrate that only four of the eighteen compounds tested inhibited oxidation of HNE to trans-4-hydroxy-2-nonenoic acid (HNEAcid). These compounds included rotenone, maneb, mancozeb, and benomyl. Surprisingly, maneb, mancozeb, and benomyl did not inhibit mitochondrial respiration but inhibited the activity of purified rat ALDH2 and rat ALDH5A, enzymes found in brain mitochondria that oxidize HNE and aldehydes derived from neurotransmitters. Our data demonstrate that mitochondrial ALDHs are sensitive targets of pesticide inactivation and that pesticides such as maneb and benomyl can decrease the detoxification of lipid peroxidation derived aldehydes such as HNE and, likely, aldehydes derived from neurotransmitters.

Disulfiram irreversibly aggregates betaine aldehyde dehydrogenase--a potential target for antimicrobial agents against Pseudomonas aeruginosa

In the human pathogen Pseudomonas aeruginosa, betaine aldehyde dehydrogenase (PaBADH) may play the dual role of assimilating carbon and nitrogen from choline or choline precursors--abundant at infection sites--and producing glycine betaine, which protects the bacterium against the high-osmolality stress prevalent in the infected tissues. This tetrameric enzyme contains four cysteine residues per subunit and is a potential drug target. In our search for specific inhibitors, we mutated the catalytic Cys286 to alanine and chemically modified the recombinant wild-type and the four Cys-->Ala single mutants with thiol reagents. The small methyl-methanethiosulfonate inactivated the enzymes without affecting their stability while the bulkier dithionitrobenzoic acid (DTNB) and bis[diethylthiocarbamyl] disulfide (disulfiram) induced enzyme dissociation--at 23 degrees C--and irreversible aggregation--at 37 degrees C. Of the four Cys-->Ala mutants only C286A retained its tetrameric structure after DTNB or disulfiram treatments, suggesting that steric constraints arising upon the covalent attachment of a bulky group to C286 resulted in distortion of the backbone configuration in the active site region followed by a severe decrease in enzyme stability. Since neither NAD(P)H nor betaine aldehyde prevented disulfiram-induced PaBADH inactivation or aggregation, and reduced glutathione was unable to restore the activity of the modified enzyme, we propose that disulfiram could be a useful drug to combat infection by P. aeruginosa.

Transient release of oxygenated volatile organic compounds during light-dark transitions in Grey poplar leaves

In this study, we investigated the prompt release of acetaldehyde and other oxygenated volatile organic compounds (VOCs) from leaves of Grey poplar [Populus x canescens (Aiton) Smith] following light-dark transitions. Mass scans utilizing the extremely fast and sensitive proton transfer reaction-mass spectrometry technique revealed the following temporal pattern after light-dark transitions: hexenal was emitted first, followed by acetaldehyde and other C(6)-VOCs. Under anoxic conditions, acetaldehyde was the only compound released after switching off the light. This clearly indicated that hexenal and other C(6)-VOCs were released from the lipoxygenase reaction taking place during light-dark transitions under aerobic conditions. Experiments with enzyme inhibitors that artificially increased cytosolic pyruvate demonstrated that the acetaldehyde burst after light-dark transition could not be explained by the recently suggested pyruvate overflow mechanism. The simulation of light fleck situations in the canopy by exposing leaves to alternating light-dark and dark-light transitions or fast changes from high to low photosynthetic photon flux density showed that this process is of minor importance for acetaldehyde emission into the Earth's atmosphere.

Oxidation of 4-hydroxy-2-nonenal by succinic semialdehyde dehydrogenase (ALDH5A)

Elevated levels of 4-hydroxy-trans-2-nonenal (HNE) are implicated in the pathogenesis of numerous neurodegenerative disorders. Although well-characterized in the periphery, the mechanisms of detoxification of HNE in the CNS are unclear. HNE is oxidized to a non-toxic metabolite in the rat cerebral cortex by mitochondrial aldehyde dehydrogenases (ALDHs). Two possible ALDH enzymes which might oxidize HNE in CNS mitochondria are ALDH2 and succinic semialdehyde dehydrogenase (SSADH/ALDH5A). It was previously established that hepatic ALDH2 can oxidize HNE. In this work, we tested the hypothesis that SSADH oxidizes HNE. SSADH is critical in the detoxification of the GABA metabolite, succinic semialdehyde (SSA). Recombinant rat SSADH oxidized HNE and other alpha,beta-unsaturated aldehydes. Inhibition and competition studies in rat brain mitochondria showed that SSADH was the predominant oxidizing enzyme for HNE but only contributed a portion of the total oxidizing activity in liver mitochondria. In vivo administration of diethyldithiocarbamate (DEDC) effectively inhibited (86%) ALDH2 activity but not HNE oxidation in liver mitochondria. The data suggest that a relationship between the detoxification of SSA and the neurotoxic aldehyde HNE exists in the CNS. Furthermore, these studies show that multiple hepatic aldehyde dehydrogenases are able to oxidize HNE.

Identification of the human liver enzymes involved in the metabolism of the antimigraine agent almotriptan

Almotriptan is a novel highly selective 5-hydroxytryptamine(1B/1D) agonist developed for the acute oral treatment of migraine. The in vitro metabolism of almotriptan has been investigated using human liver subcellular fractions and cDNA-expressed human enzymes, to study the metabolic pathways and identify the enzymes responsible for the formation of the major metabolites. Specific enzymes were identified by correlation analysis, chemical inhibition studies, and incubation with various cDNA expressed human enzymes. Human liver microsomes and S9 fraction metabolize almotriptan by 2-hydroxylation of the pyrrolidine group to form a carbinolamine metabolite intermediate, a reaction catalyzed by CYP3A4 and CYP2D6. This metabolite is further oxidized by aldehyde dehydrogenase to the open ring gamma-aminobutyric acid metabolite. Almotriptan is also metabolized at the dimethylaminoethyl group by N-demethylation, a reaction that is carried out by five different cytochrome P450s, flavin monooxygenase-3 mediated N-oxidation, and MAO-A catalyzed oxidative deamination to form the indole acetic acid and the indole ethyl alcohol derivatives of almotriptan. The use of human liver mitochondria confirmed the contribution of MAO-A to the metabolism of almotriptan. Both, the gamma-aminobutyric acid and the indole acetic acid metabolites have been found to be the major in vivo metabolites of almotriptan in humans. In addition, different clinical trials conducted to study the effects of CYP3A4, CYP2D6, and MAO-A on the pharmacokinetics of almotriptan confirmed the involvement of these enzymes in the metabolic clearance of this drug and that no dose changes are required in the presence of inhibitors of these enzymes.

Inactivation of betaine aldehyde dehydrogenase from Pseudomonas aeruginosa and Amaranthus hypochondriacus L. leaves by disulfiram

Betaine aldehyde dehydrogenase (BADH) activity might be crucial for the growth of the human pathogen Pseudomonas aeruginosa under conditions of infection and therefore appears to be a suitable target for antimicrobial agents. As a first step in the search for BADH inhibitors, we have tested the effects of the known aldehyde dehydrogenase inhibitor disulfiram (DSF) on the activity of P. aeruginosa and Amaranthus hypochondriacus (amaranth) leaf BADHs. DSF totally inactivated both enzymes in a time- and dose-dependent manner. In the case of the Pseudomonas enzyme, inactivation kinetics were monophasic with a second-order inactivation rate constant at pH 6.9 of 4.9+/-0.4 M(-1) s(-1), whereas the plant enzyme was inactivated in a biphasic process with second-order inactivation rate constants at pH 7.5 of 6.8+/-0.6 and 0.33+/-0.04 M(-1) s(-1). At pH 8.8, the second-order rate constants for inactivation of the bacterial enzyme was 1 x 10(3) M(-1) s(-1), which compare well with that reported for human liver mitochondrial aldehyde dehydrogenase (ALDH2), the target of DSF inhibition in the aversion therapy of alcoholism. Both BADHs were inactivated faster in the presence of NAD(P)(+) than in its absence, whereas NAD(P)H and betaine aldehyde protected the bacterial, but increased the inactivation rate of the plant enzyme. The inactivated enzymes were reactivated by dithiothreitol, but not by a high concentration of the physiological reductant glutathione. The high in vitro sensitivity of the Pseudomonas BADH to DSF, particularly in the presence of NAD(P)(+), together with the lack of reversibility of DSF modification by glutathione, makes this inhibitor a potential antimicrobial agent and suggests that it might be worth testing its effects and those of its metabolites in vivo, under culture conditions in which the activity of BADH is required for growth of the bacteria.

Novel competitive irreversible inhibitors of aldehyde dehydrogenase (ALDH1): restoration of chemosensitivity of L1210 cells overexpressing ALDH1 and induction of apoptosis in BAF(3) cells overexpressing bcl(2)

4-Amino-4-methyl-pent-2-ynthioc acid S-methyl ester (ampal thiolester: ATE) was used as a lead compound to synthesise new amino-substituted derivatives of alpha, beta acetylenic thiolester compounds as inhibitors of aldehyde dehydrogenase 1, (ALDH1). Of these compounds, the dimethyl derivative (DIMATE) was a competitive irreversible inhibitor (K(i) approximately 280 microM) of baker's yeast ALDH1 in vitro showing 80% inhibition at 400 microM when preincubated with the enzyme for 30min, whereas the trimethyl ammonium and the morpholine derivatives showed only 15% inhibition at 600 microM even after 60min preincubation. ATE inhibited ALDH1 activity in ALDH1-transfected L1210 T cells resistant to hydroperoxycyclophosphamide (HCPA) and inhibited growth synergistically in the presence of HCPA. In non-transfected L1210 counterparts ATE did not potentiate growth inhibition by HCPA. DIMATE was a 30-100-fold more effective growth inhibitor than ATE. Endogenous ALDH1 activities of BAF(3) cells over-expressing different levels of bcl(2) (0-100%) were similar (16-20mU/mg protein) and were all inhibited by DIMATE, reaching 20-30% at 4 microM. Up to 4 microM no apoptosis, as measured by DNA-fragmentation was observed, but at 8 and 10 microM DIMATE, DNA-fragmentation increased concomitantly with ALDH1 inhibition. No DNA-fragmentation was observed with ALDH1 irreversible inhibitors devoid of a thiolester group or with thiolesters which were not inhibitors of ALDH1. It was seen only with competitive irreversible inhibitors having the methanethiol and enzyme-inhibitory moieties. The methanethiol putatively released from DIMATE by ALDH1 esterase activity plays a role, albeit undefined, in lowering intramitochondrial glutathione levels which decreased by 47% as DNA-fragmentation increased.

Modulation of the reactivity of the essential cysteine residue of betaine aldehyde dehydrogenase from Pseudomonas aeruginosa

Betaine aldehyde dehydrogenase (BADH) catalyses the irreversible NAD(P)(+)-dependent oxidation of betaine aldehyde to glycine betaine. In the human opportunistic pathogen Pseudomonas aeruginosa this reaction is an obligatory step in the assimilation of carbon and nitrogen when bacteria are growing in choline or choline precursors. As with every aldehyde dehydrogenase studied so far, BADH possesses an essential cysteine residue involved in the formation of the intermediate thiohemiacetal with the aldehyde substrate. We report here that the chemical modification of this residue is conveniently measured by the loss in enzyme activity, which allowed us to explore its reactivity in a pH range around neutrality. The pH dependence of the observed second-order rate constant of BADH inactivation by methyl methanethiosulphonate (MMTS) suggests that at low pH values the essential cysteine residue exists as thiolate by the formation of an ion pair with a positively charged residue. The estimated macroscopic pK values are 8.6 and 4.0 for the free and ion-pair-forming thiolate respectively. The reactivity towards MMTS of both thiolate forms is notably lower than that of model compounds of similar pK, suggesting a considerable steric inhibition by the structure of the protein. Binding of the dinucleotides rapidly induced a significant and transitory increment of thiolate reactivity, followed by a relatively slow change to an almost unreactive form. Thus it seems that to gain protection against oxidation without compromising catalytic efficiency, BADH from P. aeruginosa has evolved a complex and previously undescribed mechanism, involving several conformational rearrangements of the active site, to suit the reactivity of the essential thiol to the availability of coenzyme and substrate.