Bioactivation of S-methyl N,N-diethylthiolcarbamate to S-methyl N,N-diethylthiolcarbamate sulfoxide. Implications for the role of cytochrome P450

The Promiscuity of Disulfiram in Medicinal Research

Recent efforts to repurpose disulfiram, a drug used in alcohol-aversion therapy for decades, for other diseases suggest the molecule is almost an in vitro panacea: it seems to be effective against various cancers (by multiple mechanisms of action), Alzheimer's disease, obesity and metabolic syndrome, pythiosis, lyme borreliosis, COVID-19, and sepsis. The problem is that the molecule almost does not exist in the body after ingestion and, most importantly, is not the pharmacologically active entity in alcoholic patients, being rather a prodrug. This prodrug is widely and misleadingly used in many in vitro and in vivo experiments regardless of its physiologically reachable concentration or its metabolism in vivo.

Identification of novel dithiocarbamate-copper complexes targeting p97/NPL4 pathway in cancer cells

Dithiocarbamates (DTCs) are simple organic compounds with many applications in industry and medicine. They are potent metal chelators forming complexes with various metal ions, including copper. Recently, bis(diethyldithiocarbamate)-copper complex (CuET) has been identified as a metabolic product of the anti-alcoholic drug Antabuse (disulfiram, DSF), standing behind DSF's reported anticancer activity. Mechanistically, CuET in cells causes aggregation of NPL4 protein, an essential cofactor of the p97 segregase, an integral part of the ubiquitin-proteasome system. The malfunction of p97/NPL4 caused by CuET leads to proteotoxic stress accompanied by heat shock and unfolded protein responses and cancer cell death. However, it is not known whether the NPL4 inhibition is unique for CuET or whether it is shared with other dithiocarbamate-copper complexes. Thus, we tested 20 DTCs-copper complexes in this work for their ability to target and aggregate NPL4 protein. Surprisingly, we have found that certain potency against NPL4 is relatively common for structurally different DTCs-copper complexes, as thirteen compounds scored in the cellular NPL4 aggregation assay. These compounds also shared typical cellular phenotypes reported previously for CuET, including the NPL4/p97 proteins immobilization, accumulation of polyubiquitinated proteins, the unfolded protein, and the heat shock responses. Moreover, the active complexes were also toxic to cancer cells (the most potent in the nanomolar range), and we have found a strong positive correlation between NPL4 aggregation and cytotoxicity, confirming NPL4 as a relevant target. These results show the widespread potency of DTCs-copper complexes to target NPL4 with subsequent induction of lethal proteotoxic stress in cancer cells with implications for drug development.

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.

Investigation of the key chemical structures involved in the anticancer activity of disulfiram in A549 non-small cell lung cancer cell line

Background

Disulfiram (DS), an antialcoholism medicine, demonstrated strong anticancer activity in the laboratory but did not show promising results in clinical trials. The anticancer activity of DS is copper dependent. The reaction of DS and copper generates reactive oxygen species (ROS). After oral administration in the clinic, DS is enriched and quickly metabolised in the liver. The associated change of chemical structure may make the metabolites of DS lose its copper-chelating ability and disable their anticancer activity. The anticancer chemical structure of DS is still largely unknown. Elucidation of the relationship between the key chemical structure of DS and its anticancer activity will enable us to modify DS and speed its translation into cancer therapeutics.

Methods

The cytotoxicity, extracellular ROS activity, apoptotic effect of DS, DDC and their analogues on cancer cells and cancer stem cells were examined in vitro by MTT assay, western blot, extracellular ROS assay and sphere-reforming assay.

Results

Intact thiol groups are essential for the in vitro cytotoxicity of DS. S-methylated diethyldithiocarbamate (S-Me-DDC), one of the major metabolites of DS in liver, completely lost its in vitro anticancer activity. In vitro cytotoxicity of DS was also abolished when its thiuram structure was destroyed. In contrast, modification of the ethyl groups in DS had no significant influence on its anticancer activity.

Conclusions

The thiol groups and thiuram structure are indispensable for the anticancer activity of DS. The liver enrichment and metabolism may be the major obstruction for application of DS in cancer treatment. A delivery system to protect the thiol groups and development of novel soluble copper-DDC compound may pave the path for translation of DS into cancer therapeutics.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4617-x) contains supplementary material, which is available to authorized users.

S-(N, N-diethylcarbamoyl)glutathione (carbamathione), a disulfiram metabolite and its effect on nucleus accumbens and prefrontal cortex dopamine, GABA, and glutamate: a microdialysis study

Disulfiram (DSF), used for the treatment of alcohol use disorders (AUDs) for over six decades, most recently has shown promise for treating cocaine dependence. Although DSF's mechanism of action in alcohol abuse is due to the inhibition of liver mitochondrial aldehyde dehydrogenase (ALDH2), its mechanism of action in the treatment of cocaine dependence is unknown. DSF is a pro-drug, forming a number of metabolites each with discrete pharmacological actions. One metabolite formed during DSF bioactivation is S-(N, N-diethylcarbamoyl) glutathione (carbamathione) (carb). We previously showed that carb affects glutamate binding. In the present studies, we employed microdialysis techniques to investigate the effect of carb administration on dopamine (DA), GABA, and glutamate (Glu) in the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC), two brain regions implicated in substance abuse dependence. The effect of DSF on DA, GABA, and Glu in the NAc also was determined. Both studies were carried out in male rats. Carb (20, 50, 200 mg/kg i v) in a dose-dependent manner increased DA, decreased GABA, and had a biphasic effect on Glu, first increasing and then decreasing Glu in both the NAc and mPFC. These changes all occurred concurrently. After carb administration, NAc and mPFC carb, as well as carb in plasma, were rapidly eliminated with a half-life for each approximately 4 min, while the changes in DA, GABA, and GLu in the NAc and mPFC persisted for approximately two hours. The maximal increase in carb (Cmax) in the NAc and mPFC after carb administration was dose-dependent, as was the area under the curve (AUC). DSF (200 mg/kg i p) also increased DA, decreased GABA, and had a biphasic effect on Glu in the NAc similar to that observed in the NAc after carb administration. When the cytochrome P450 inhibitor N-benzylimidazole (NBI) (20 mg/kg i p) was administered before DSF dosing, no carb could be detected in the NAc and plasma and also no changes in NAc DA, GABA, and GLu occurred. Changes in these neurotransmitters occurred only if carb was formed from DSF. When NBI was administered prior to dosing with carb, the increase in DA, decrease in GABA, and biphasic effect on GLu was similar to that seen after dosing with carb only. The i p or i v administration of carb showed similar changes in DA, GABA, and GLu, except the time to reach Cmax for DA as well as the changes in GABA, and GLu after i p administration occurred later. The elimination half-life of carb and the area under the curve (AUC) were similar after both routes of administration. It is concluded that carb must be formed from DSF before any changes in DA, GABA, and GLu in the NAc and mPFC are observed. DSF and carb, when administered to rats, co-release DA, GABA, and GLu. Carb, once formed can cross the blood brain barrier and enter the brain. Although inhibition of liver ALDH2 is the accepted mechanism for DSF's action in treating AUDs, the concurrent changes in DA, GABA, and GLu in the NAc and mPFC after DSF administration suggest that changes in these neurotransmitters as a potential mechanism of action not only for AUDs, but also for cocaine dependence cannot be excluded.

Disulfiram metabolite S-methyl-N,N-diethylthiocarbamate quantitation in human plasma with reverse phase ultra performance liquid chromatography and mass spectrometry

Disulfiram has been used extensively for alcohol abuse and may have a role in treatment for cocaine addiction. Recent data suggest that disulfiram may also reactivate latent HIV in reservoirs. Disulfiram has complex pharmacokinetics with rapid metabolism to active metabolites, including S-methyl-N,N-diethylthiocarbamate (DET-Me) which is formed from cytochrome P450 (CYP450). Assessing disulfiram in HIV-infected individuals with a CYP450 inducing drug (e.g., efavirenz) or a CYP450 inhibiting drug (e.g., HIV-1 protease inhibitors) requires an assay that can measure a metabolite that is formed directly via CYP450 oxidation. Therefore, an assay to measure concentrations of DET-Me in human plasma was validated. DET-Me and the internal standard, S-ethyldipropylthiocarbamate (EPTC) were separated by isocratic ultra performance liquid chromatography using a Waters Acquity HSS T3 column (2.1 mm × 100 mm, 1.8 μm) and detection via electrospray coupled to a triple quadrupole mass spectrometer. Multiple reaction monitoring in positive mode was used with DET-Me at 148/100 and the internal standard at 190/128 with a linear range of 0.500-50.0 ng/mL with a 5 min run time. Human plasma (500 μL) was extracted using a solid phase procedure. The interassay variation ranged from 1.86 to 7.74% while the intra assay variation ranged from 3.38 to 5.94% over three days. Representative results are provided from samples collected from subjects receiving daily doses of disulfiram 62.5mg or 250 mg.

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.

Determination of in vivo adducts of disulfiram with mitochondrial aldehyde dehydrogenase

Extensive use for disulfiram (DSF) has been found in the aversion therapy treatment of recovering alcoholics. Although it is known to irreversibly inhibit hepatic aldehyde dehydrogenase (ALDH), the specific mechanism of in vivo inhibition of the enzyme by the drug has not been determined yet. We have demonstrated in this report a novel, but simple and rapid method for structurally characterizing in vivo derived protein-drug adducts by linking on-line sample processing to HPLC-electrospray ionization mass spectrometry (HPLC-MS) and HPLC-tandem mass spectrometry (HPLC-MS/MS). Employing this approach, rats were administered DSF, and their liver mitochondria were isolated and solubilized. Both native and in vivo DSF-treated mitochondrial ALDH (mALDH) were purified in one step with an affinity cartridge. The in vivo DSF-treated mALDH showed 77% inhibition in enzyme activity as compared with that of the control. Subsequently, the control and DSF-inhibited mALDH were both subjected to HPLC-MS analyses. We were able to detect two adducts on DSF-inhibited mALDH, as indicated by the mass increases of approximately 71 and approximately 100 Da. To unequivocally determine the site and structure of these adducts, on-line pepsin digestion-HPLC-MS and HPLC-MS/MS were performed. We observed two new peptides at MH(+) = 973.7 and MH(+) = 1001.8 in the pepsin digestion of DSF-inhibited enzyme. These two peptides were subsequently subjected to HPLC-MS/MS for sequence determination. Both peptides possessed the sequence FNQGQC(301)C(302)C(303), derived from the enzyme active site region, and were modified at Cys(302) by N-ethylcarbamoyl (+71 Da) and N-diethylcarbamoyl (+99 Da) adducts. These findings indicated that N-dealkylation may be an important step in DSF metabolism, and that the inhibition of ALDH occurred by carbamoylation caused by one of the DSF metabolites, most likely S-methyl-N,N-diethylthiocarbamoyl sulfoxide (MeDTC-SO). Finally, there was no evidence of the presence of an intramolecule disulfide bridge modification on the peptide FNQGQCCC.

Role of disulfiram in the in vitro inhibition of rat liver mitochondrial aldehyde dehydrogenase

The alcohol aversion therapy drug disulfiram has been shown to inhibit hepatic aldehyde dehydrogenase (ALDH), one of the key enzymes involved in ethanol metabolism. It is believed by some that disulfiram could be one of the active inhibitors in vivo. However, the actual interaction between disulfiram and ALDH remains ambiguous. We report here that when disulfiram inhibited recombinant rat liver mitochondrial ALDH (rlmALDH) in vitro, no significant molecular mass increase was detected during the first 30 min as determined by on-line HPLC-electrospray ionization mass spectrometry (LC-MS). This indicated that the inhibition in vitro was not caused directly by covalent adduct formation on the enzyme. We subsequently subjected both control and disulfiram-inhibited rlmALDH to Glu-C proteolytic digestion. LC-MS analysis of the Glu-C digestion of disulfiram-inhibited enzyme revealed that one peptide of M(r) = 4821, which contained the putative active site of the enzyme, exhibited a mass decrease of 2 amu as compared with the same peptide found in the Glu-C digestion of the control (M(r) = 4823). We believe that the loss of 2 amu indicated that inhibition of rlmALDH in vitro was due to formation of an intramolecular disulfide bond between two of the three adjacent cysteines in the active site, possibly via a very rapid and unstable mixed disulfide interchange reaction. Further confirmation of the intramolecular disulfide bond formation came from the fact that by adding dithiothreitol (DTT) we were able to recover partial enzyme activity. In addition, the peptide of M(r) = 4821 observed in the Glu-C digestion of the disulfiram-treated ALDH reverted to M(r) = 4823 after treatment with DTT, which indicated that the disulfide bond was reduced. We, thereby, conclude that disulfiram inhibited rlmALDH by forming an intramolecular disulfide, possibly via a fast intermolecular disulfiram interchange reaction.

Disulfiram produces a non-carbon disulfide-dependent schwannopathy in the rat

Disulfiram is a dithiocarbamate drug used for alcohol aversion therapy that produces a distal sensorimotor peripheral neuropathy in certain individuals. Because carbon disulfide, a disulfiram metabolite, produces a peripheral neuropathy clinically similar to disulfiram, it has been postulated that disulfiram neuropathy results from CS2 release in vivo. The current study evaluated the morphological changes produced by disulfiram and the contribution of CS2-mediated protein cross-linking to disulfiram-induced neuropathy. Male Sprague-Dawley rats were administered 1% w/w disulfiram in their feed for 2, 4, 5, or 7 wk, and erythrocyte spectrin, hemoglobin, and neurofilament preparations were isolated and the extent of cross-linking assessed by SDS-PAGE, RP-HPLC, and Western blotting, respectively. Spinal cord and peripheral nerve sections were obtained from separate treated animals and assessed by light and electron microscopy. Significant protein cross-linking was only detected in neurofilament preparations obtained after 7 wk of exposure. Morphological changes were observed after 4 wk exposure and consisted of vacuoles within the Schwann cell cytoplasm and segmental demyelination. No neurofilamentous axonal swellings were detected and no significant changes were observed in the CNS. Because disulfiram neuropathy lacks both the morphological changes and intermolecular cross-linking characteristic of CS2, we conclude that disulfiram neuropathy is not mediated by the axonal toxicant CS2; instead, disulfiram appears to be a primary Schwann cell toxicant. Recognition of a diethylcarbamoyl adduct on globin and axonal proteins presents a novel putative neurotoxic mechanism for disulfiram.

Glutathione carbamoylation with S-methyl N,N-diethylthiolcarbamate sulfoxide and sulfone. Mitochondrial low Km aldehyde dehydrogenase inhibition and implications for its alcohol-deterrent action

S-Methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO) and sulfone (DETC-MeSO2) both inhibit rat liver low Km aldehyde dehydrogenase (ALDH2) in vitro and in vivo (Nagendra et al., Biochem Pharmacol 47: 1465-1467, 1994). DETC-MeSO has been shown to be a metabolite of disulfiram, but DETC-MeSO2 has not. Studies were carried out to further investigate the inhibition of ALDH2 by DETC-MeSO and DETC-MeSO2. In an in vitro system containing hydrogen peroxide and horseradish peroxidase, the rate of DETC-MeSO oxidation corresponded to the rate of DETC-MeSO2 formation. Carbamoylation of GSH by both DETC-MeSO and DETC-MeSO2 was observed in a rat liver S9 fraction. Carbamoylation of GSH was not observed in the presence of N-methylmaleimide. In in vitro studies, DETC-MeSO and DETC-MeSO2 were equipotent ALDH2 inhibitors when solubilized mitochondria were used, but DETC-MeSO was approximately four times more potent than DETC-MeSO2 in intact mitochondria. In studies with rats, the dose (i.p. or oral) required to inhibit 50% ALDH2 (ED50) was 3.5 mg/kg for DETC-MeSO and approximately 35 mg/kg for DETC-MeSO2, approximately a 10-fold difference. Furthermore, maximum ALDH2 inhibition occurred 1 hr after DET(-MeSO administration, whereas maximal ALDH2 inhibition occurred 8 hr after DETC-MeSO2 dosing. DETC-MeSO is, therefore, not only a more potent ALDH2 inhibitor than DETC-MeSO2 in vivo, but also in vitro when intact mitochondria are utilized. The in vitro results thus support the in vivo findings. Since oxidation of DETC-MeSO can occur both enzymatically and non-enzymatically, it is possible that DETC-MeSO2 is formed in vivo. DETC-MeSO2, however, is not as effective as DETC-MeSO in inhibiting ALDH2, probably because it has difficulty penetrating the mitochondrial membrane. Thus, even if DETC-MeSO2 is formed in vivo from DETC-MeSO, it is the metabolite DETC-MeSO that is most likely responsible for the inhibition of ALDH2 after disulfiram administration.

Inhibition of human mitochondrial aldehyde dehydrogenase by the disulfiram metabolite S-methyl-N,N-diethylthiocarbamoyl sulfoxide: structural characterization of the enzyme adduct by HPLC-tandem mass spectrometry

S-Methyl-N,N-diethylthiocarbamoyl sulfoxide (MeDTC-SO) is a known metabolite of the aversion therapy drug disulfiram (DSF). MeDTC-SO is also a potent inhibitor of human mitochondrial aldehyde dehydrogenase (hmALDH) with an IC50 of 1.5 microM. Inhibition of the enzyme by MeDTC-SO resulted in the addition of approximately 100 Da to the molecular mass of the intact protein, as determined by on-line HPLC-electrospray ionization MS (LC-MS). Dialysis of the inhibited protein did not reverse the inhibition, and the molecular mass of 54,533 Da (+/- 0.01%) remained unchanged, indicating that a covalent modification of the protein had occurred. Proteolytic digestion of hmALDH under basic conditions using trypsin at pH 7.8 revealed that the adduct was base labile. However, treating the adducted protein with endopeptidase-Glu-C at pH 3.7 produced a peptide adduct at MH+ = 4924, tentatively attributable to a carbamoylated peptide. This peptide contains three adjacent cysteines, one of which has been implicated as a key amino acid in the highly conserved active site region of ALDH. A pepsin digestion of hmALDH carried out at pH 3.7 and subsequent LC-MS analysis revealed an ion at MH2(2+) = 501.5, corresponding to the carbamoylated peptide FNQGQC1C2C3. This peptide contains the same adjacent active site cysteines. This latter peptide was subjected to LC-MS/MS, which enabled us to determine that the site of carbamoylation was at Cys2. The MS/MS product ion data also confirmed the presence of a carbamoyl group as the adduct species.

Disulfiram causes sustained behavioral and biochemical effects in rats

The present experiment examined effects of disulfiram (Antabuse) administration on behavioral measures of nociception (hot plate and tail flick), peripheral muscular performance (grip strength), motivated performance, balance, and coordination (rotorod) in 24 male Sprague-Dawley rats during and 2 wk after an eight-day administration of disulfiram. In addition, peptidylglycine 5(-hydroxylating monooxygenase (PHM) activity in several tissues and levels of alpha-amidated alpha-melanocyte stimulating hormone (alpha-MSH) in the neurointermediate lobe of the pituitary were assayed to evaluate biochemical effects of disulfiram. These particular assays were included because it has been reported that disulfiram affects alpha-amidated peptides via alteration of PHM activity. Decrements in all behavioral measures, except tail flick, occurred after one week of disulfiram administration. Decrements in grip strength continued for the 2 wk after cessation of disulfiram. Dose-related reductions in changes in PHM activity and levels of alpha-MSH were found 2 wk after cessation of disulfiram administration. The time course of the results suggest that changes in PHM activity may underlie decrements in grip strength. The present experiment provides a paradigm for further investigations of effects of alpha-amidated peptides on behavior.

Inhibition of aldehyde dehydrogenase by disulfiram and its metabolite methyl diethylthiocarbamoyl-sulfoxide

Disulfiram (DSF) is presently the only available drug used in the aversion therapy of recovering alcoholics. It acts by inhibiting aldehyde dehydrogenase (ALDH), leading to high blood levels of acetaldehyde. The in vitro inhibition of ALDH by DSF and its metabolites was systematically studied by combined enzyme inhibition assay with direct molecular weight determination of the same sample using electrospray ionization-mass spectrometry (ESI-MS). Enzyme activity was measured after incubating yeast ALDH (yALDH) with excess concentrations of DSF, methyl diethyldithiocarbamate (MeDDC) and methyl diethylthiocarbamoyl-sulfoxide (MeDTC-SO) and then subjected to analysis by ESI-MS. Addition of DSF resulted in complete enzyme inhibition; however, ESI-MS analysis demonstrated no discernible shift in molecular weight, indicating that no intermolecular adduct was formed with the protein. Treatment of yALDH with MeDTC-SO also completely abolished yALDH activity with a concomitant increase of + approximately 100 Da in the molecular mass of the enzyme. This indicated formation of a covalent carbamoyl protein adduct. Furthermore, the effects of dithiothreitol (DTT) were examined on samples of inhibited protein in vitro. At pH 7.5, DTT completely reversed inhibition after DSF treatment. yALDH inhibited by MeDTC-SO could not be recovered by DTT at pH 7.5, but at pH 9 the enzymic activity was fully restored and a mass loss of approximately 100 Da was noted. This observations are consistent with mechanisms where inhibition of yALDH by DSF in vitro involves oxidation of the active site, whereas MeDTC-SO forms a covalent adduct with the protein in vitro resulting in cessation of enzyme activity.

Synthesis and biological evaluation of new diisocyanide- and triisocyanide-99mTc complexes

This paper describes the synthesis of four new polyisocyanides (three diisocyanides and one triisocyanide). The complexation of 99mTc with these ligands is also studied through chromatography and revealed the formation of hexacoordinated 99mTc+1 complexes. Finally, biodistributions of these complexes in mice are given and compared. Heart captations are lower than the ones with [99mTc(MIBI)6]+ but remain constant and a satisfactory lungs clearance, probably due to the metabolization of the ligands, is observed.

S-methyl-N,N-diethylthiocarbamate sulfoxide and S-methyl-N,N-diethylthiocarbamate sulfone, two candidates for the active metabolite of disulfiram

The mechanism of action of disulfiram involves inhibition of hepatic aldehyde dehydrogenase (ALDH). Although disulfiram inhibits ALDH in vitro, it is believed that the drug is too short-lived in vivo to inhibit the enzyme directly. The ultimate inhibitor is thought to be a metabolite of disulfiram. In this study, we examined the effects of S-methyl-N,N-diethylthiocarbamate (MeDTC) sulfoxide and S-methyl-N,N-diethylthiocarbamate sulfone (confirmed and proposed metabolites of disulfiram, respectively) on rat liver mitochondrial low K(m) ALDH. MeDTC sulfoxide and MeDTC sulfone, in 10-min incubations with detergent-solubilized mitochondria, inhibited ALDH activity with an IC50 (mean +/- SD) of 0.93 +/- 0.04 and 0.53 +/- 0.11 microM, respectively, compared with 7.4 +/- 1.0 microM for the parent drug disulfiram. Inhibition by MeDTC sulfone and MeDTC sulfoxide, both at 0.6 microM, was time-dependent, following apparent pseudo-first-order kinetics with a t1/2 of inactivation of 3.5 and 8.8 min, respectively. Dilution of ALDH inhibited by either sulfoxide or sulfone did not restore activity, an indication of irreversible inhibition. Addition of glutathione (50 to 1000 microM) to ALDH before the inhibitors did not alter the inhibition by MeDTC sulfoxide. In contrast, the inhibition by MeDTC sulfone was decreased > 10-fold (IC50 = 6.3 microM) by 50 microM of glutathione and almost completely abolished by 500 microM of glutathione. The cofactor NAD, in a concentration-dependent manner, protected ALDH from inhibition by MeDTC sulfoxide and MeDTC sulfone. In incubations with intact mitochondria, the potency of the two compounds was reversed (IC50 of 9.2 +/- 3.6 and 0.95 +/- 0.30 microM for the MeDTC sulfone and sulfoxide, respectively). Our results suggest that MeDTC sulfone is highly reactive with normal cellular constituents (e.g., glutathione), which may protect ALDH from inhibition, unless this inhibitor is formed very near the target enzyme. In contrast, MeDTC sulfoxide is a better candidate for the ultimate active metabolite of disulfiram, because it is more likely to be sufficiently stable to diffuse from a distant site of formation, such as the endoplasmic reticulum, penetrate the mitochondria, and react with ALDH located in the mitochondrial matrix.

Constitutive nuclear NF kappa B/rel DNA-binding activity of rat thymocytes is increased by stimuli that promote apoptosis, but not inhibited by pyrrolidine dithiocarbamate

Rat thymocytes spontaneously undergo apoptotic death in cell culture, and are also sensitive to the induction of apoptosis by various stimuli. We show that unstimulated thymocytes constitutively express a p50-containing nuclear factor kappa B (NF kappa B)/rel DNA-binding activity in their nuclei. When the cells were fractionated by density-gradient centrifugation this activity was found to be most pronounced in immature CD4+8+ thymocytes, the cell population that undergoes selection by apoptosis in vivo and that is most sensitive to external inducers of apoptosis in vitro. The intensity of the NF kappa B/rel protein-DNA complex was significantly enhanced 30 min after exposing thymocytes to methylprednisolone or etoposide, two agents well known to induce apoptosis in these cells. Expression of this DNA-binding activity therefore correlates with the subsequent occurrence of apoptosis. By analogy to other systems, it has been suggested that antioxidants such as pyrrolidine dithiocarbamate (PDTC) inhibit thymocyte apoptosis by preventing the activation of an NF kappa B/rel transcription factor. However, we have found that etoposide induces a very similar enhancement of the NF kappa B/rel DNA-binding activity in the presence or absence of PDTC, despite a pronounced inhibition of apoptotic DNA fragmentation in the former situation. Dithiocarbamates therefore do not exert their anti-apoptotic activity in thymocytes by inhibiting the activation of this transcription factor.

Dithiocarbamates induce apoptosis in thymocytes by raising the intracellular level of redox-active copper

Dithiocarbamates are metal-chelating compounds that can exert either pro-oxidant or antioxidant effects in different situations. They have recently been found to potently inhibit apoptotic cell death, an activity attributed to their antioxidant action. However, when thymocytes were exposed to pyrrolidine dithiocarbamate, an oxidation of the glutathione pool occurred within 90 min. Longer incubation resulted in cell shrinkage, chromatin fragmentation, glutathione depletion, and eventual cell lysis, which is typical of apoptosis in these cells. These changes were inhibited by inclusion of non-permeable metal chelators in the incubation medium, suggesting that pyrrolidine dithiocarbamate exerts its toxic effect by transporting a redox-active metal into the cell. This was directly confirmed when sustained 8-fold elevations of intracellular copper were detected after addition of pyrrolidine dithiocarbamate. In agreement with this, supplementation of the incubation medium with submicromolar concentrations of copper significantly potentiated pyrrolidine dithiocarbamate toxicity. We conclude that pyrrolidine dithiocarbamate exerts a powerful pro-oxidant effect on thymocytes due to its ability to transport external redox-active copper into cells. The resulting increase in glutathione disulfide may also explain the temporary anti-apoptotic activity of this compound described in other systems.

Peptide alpha-amidation: differential regulation by disulfiram and its metabolite, diethyldithiocarbamate

The rate limiting step in the alpha-amidation of bioactive peptides is catalyzed by peptidylglycine-alpha-hydroxylating mono-oxygenase (PHM; EC 1.14.17.3). Sustained treatment with disulfiram (Antabuse), the disulfide dimer of diethyldithiocarbamate (DDC), inhibits PHM in vivo, causing tissue levels of alpha-amidated peptides to decrease. As a compensatory response, PHM protein is modified in such a way that its activity is increased when assayed under optimal conditions in a test tube. Because disulfiram is rapidly reduced to DDC in vivo, this investigation sought to determine if metabolic transformation plays a role in the effects of disulfiram treatment on alpha-amidation. While disulfiram treatment reduced concentrations of alpha-amidated peptides in the pituitary neurointermediate lobe and brain, DDC treatment did not, even at comparatively high doses. Both treatments increased the activity of PHM extracted from the neurointermediate pituitary and assayed under optimal copper conditions in vitro. Only disulfiram treatment elicited an increase in PHM activity extracted from cardiac atrium. It is concluded that the activity of PHM is regulated in a tissue specific fashion and that not all of the actions of disulfiram require its metabolism to DDC.

S-methyl N,N-diethylthiocarbamate sulfone, a potential metabolite of disulfiram and potent inhibitor of low Km mitochondrial aldehyde dehydrogenase

Disulfiram inhibits hepatic aldehyde dehydrogenase (ALDH) causing an accumulation of acetaldehyde after ethanol ingestion. It is thought that disulfiram is too short-lived in vivo to directly inhibit ALDH, but instead is biotransformed to reactive metabolites that inhibit the enzyme. S-Methyl N,N-diethylthiocarbamate (MeDTC) sulfoxide has been identified in the blood of animals given disulfiram and is a potent inhibitor of ALDH (Hart and Faiman, Biochem Pharmacol 46: 2285-2290, 1993). MeDTC sulfone is a logical metabolite of MeDTC sulfoxide. Therefore, we investigated the effects of MeDTC sulfone on the activity of rat hepatic low Km mitochondrial ALDH, the major enzyme in the metabolism of acetaldehyde. MeDTC sulfone inhibited the low Km mitochondrial ALDH in vitro with an IC50 of 0.42 +/- 0.04 microM (mean +/- SD, N = 5) compared with disulfiram, which had an IC50 of 7.5 +/- 1.2 microM under the same conditions. The inhibition of ALDH by MeDTC sulfone was time dependent. The decline in ALDH activity followed pseudo first-order kinetics with an apparent half-life of 2.1 min at 0.6 microM MeDTC sulfone. Inhibition of ALDH by MeDTC sulfone was apparently irreversible; dilution of the inhibited enzyme did not restore lost activity. The substrate (acetaldehyde, 80 microM) and cofactor (NAD, 0.5 mM) together completely protected ALDH from inhibition by MeDTC sulfone; substrate alone partially protected the enzyme. Addition of either thiol-containing compound glutathione (GSH) or dithiothreitol (DTT) to MeDTC sulfone before incubation with the enzyme increased the IC50 of MeDTC sulfone by 7- to 14-fold. Neither GSH nor DTT could restore lost ALDH activity after exposure of the enzyme to MeDTC sulfone. Results of these studies indicate that MeDTC sulfone, a potential metabolite of disulfiram, is a potent, irreversible inhibitor of low Km mitochondrial ALDH.

Degradation of the thiocarbamate herbicide EPTC (S-ethyl dipropylcarbamothioate) and biosafening by Rhodococcus sp. strain NI86/21 involve an inducible cytochrome P-450 system and aldehyde dehydrogenase

Determination of the N-terminal sequences of two EPTC (S-ethyl dipropylcarbamothioate)-induced proteins from thiocarbamate-degrading Rhodococcus sp. strain NI86/21 resolved by two-dimensional electrophoresis enabled the localization of the respective structural genes on two distinct DNA fragments. One of these strongly induced proteins is a NAD(+)-dependent dehydrogenase active on aliphatic aldehydes. The second protein was identified as a cytochrome P-450 enzyme. The cytochrome P-450 gene represents the first member of a new family, CYP116. Downstream of the cytochrome P-450 gene, two genes for a [2Fe-2S] ferredoxin (rhodocoxin) and a ferredoxin reductase are located. A putative regulatory gene encoding a new member of the AraC-XylS family of positive transcriptional regulators is divergently transcribed from the cytochrome P-450 gene. By hybridization, it was demonstrated that the aldehyde dehydrogenase gene is widespread in the Rhodococcus genus, but the components of the cytochrome P-450 system are unique to Rhodococcus sp. strain NI86/21. Overexpression in Escherichia coli was achieved for all of these proteins except for the regulatory protein. Evidence for the involvement of this cytochrome P-450 system in EPTC degradation and herbicide biosafening for maize was obtained by complementation experiments using EPTC-negative Rhodococcus erythropolis SQ1 and mutant FAJ2027 as acceptor strains. N dealkylation by cytochrome P-450 and conversion of the released aldehyde into the corresponding carboxylic acid by aldehyde dehydrogenase are proposed as the reactions initiating thiocarbamate catabolism in Rhodococcus sp. strain NI86/21. In addition to the major metabolite N-depropyl EPTC, another degradation product was identified, EPTC-sulfoxide.

Inhibition of rat liver low Km aldehyde dehydrogenase by thiocarbamate herbicides. Occupational implications

S-Methyl N,N-diethylthiolcarbamate (DETC-Me) is a metabolite formed during the bioactivation of disulfiram. The formation of its corresponding sulfoxide, S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO), from DETC-Me is required for low Km mitochondrial aldehyde dehydrogenase (ALDH2, EC 1.2.1.3) inhibition. DETC-Me is similar in structure to thiocarbamate herbicides with the general structure R1R2NC(O)SR3. Representative herbicides studied were n-propyl, n-propylthiocarbamate ethyl ester (EPTC), molinate, vernolate, ethiolate and butylate. All of these thiocarbamate herbicides inhibited rat liver ALDH2 in vivo. The dose of these thiocarbamates that inhibited rat liver ALDH2 by 50% (ID50) when administered 8 hr before determination of ALDH2, was found to be 5.2, 3.1, 1.6, 12, and 174 mg/kg, respectively. These thiocarbamates were ineffective rat liver ALDH2 inhibitors in vitro, unless rat liver microsomes and an NADPH-generating system were added to the incubation. The respective thiocarbamate sulfoxides were formed when the thiocarbamates were incubated with liver microsomes and an NADPH-generating system. The thiocarbamate sulfoxides all inhibited rat liver ALDH2 in vitro. An equimolar dose of molinate and molinate sulfoxide inhibited rat liver ALDH2 in vivo to the same degree. Molinate-treated rats challenged with ethanol exhibited a disulfiram-like ethanol reaction. In conclusion, thiocarbamate herbicides inhibit ALDH2, probably due to the formation of their sulfoxide, and therefore have the potential to produce a disulfiram-like ethanol reaction in an unsuspecting population.

Photolysis of sulfiram: a mechanism for its disulfiram-like reaction

Sulfiram, a drug applied topically to treat scabies, produces effects similar to those of disulfiram after subsequent ingestion of ethanol. Disulfiram, used in aversion therapy in the treatment of alcoholism, inhibits hepatic aldehyde dehydrogenase (ALDH) causing an accumulation of acetaldehyde after ethanol ingestion. The increased tissue levels of acetaldehyde cause a spectrum of undesirable side-effects including flushing, nausea, vomiting, and tachycardia, which are referred to as the disulfiram reaction. Previous studies have shown that in vitro sulfiram is a very weak inhibitor of ALDH, but solutions of sulfiram markedly increase in potency with time. In the present study, fresh solutions of sulfiram were exposed to fluorescent room light under ambient conditions and analyzed at timed intervals by HPLC. At least eight products, including disulfiram, were formed in the light-exposed sulfiram solutions, but not in solutions kept in the dark. Structural characterization of two of the photolysis products was obtained by on-line microbore HPLC-mass spectrometry (mu LC-MS) and on-line microbore HPLC-tandem mass spectrometry (mu LC-MS/MS) using continuous flow-liquid secondary ion mass spectrometry (CF-LSIMS) as the primary ionization method. Sulfiram was converted to disulfiram at an initial rate of 0.7%/hr, and the formation of disulfiram correlated with the increase in ALDH inhibition in vitro. The results of this investigation show that while sulfiram is a weak inhibitor of ALDH in vitro, it is readily photoconverted to disulfiram, a very potent inhibitor of ALDH, which may explain the adverse reaction to ethanol after sulfiram therapy.

Diethyldithiocarbamate methyl ester sulfoxide, an inhibitor of rat liver mitochondrial low Km aldehyde dehydrogenase and putative metabolite of disulfiram

S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO) is a potent inhibitor of rat liver mitochondrial low Km aldehyde dehydrogenase (ALDH2) both in vivo and in vitro, and has been proposed to be the metabolite responsible for ALDH2 inhibition by disulfiram. Diethyldithiocarbamate methyl ester (DDTC-Me), a key intermediate in the metabolism of disulfiram, has been shown to be bioactivated by microsomal monooxygenases to diethyldithiocarbamate methyl ester sulfoxide (DDTC-Me sulfoxide). Studies were conducted to determine if DDTC-Me sulfoxide was also an active metabolite of disulfiram and inhibitor of ALDH2. DDTC-Me sulfoxide inhibited ALDH2 in vitro with an IC50 of 10 microM, and in vivo with an ID50 of 31 mg/kg (170 mumol/kg). Maximal ALDH2 inhibition in vivo was observed 8 hr after the administration of 45.2 mg/kg DDTC-Me sulfoxide, with ALDH2 activity returning to control levels after 48 hr. Although DDTC-Me sulfoxide inhibited ALDH2 in vivo, DDTC-Me sulfoxide was not detected in plasma from rats treated with either disulfiram (75 mg/kg), DDTC-Me (122.25 mg/kg), or DDTC-Me sulfoxide (45.2 mg/kg). However, DDTC-Me and S-methyl N,N-diethylthiolcarbamate (DETC-Me) were detected in plasma from rats treated with DDTC-Me sulfoxide. In rats treated with DDTC-Me sulfoxide and challenged with ethanol, a small increase of approximately microM in blood acetaldhyde and an inconsistent drop in blood pressure was observed. In conclusion, DDTC-Me sulfoxide inhibited ALDH2 in vitro and in vivo, was less potent than DETC- MeSO, and was not detected after disulfiram administration.

S-methyl N,N-diethylthiolcarbamate sulfone, an in vitro and in vivo inhibitor of rat liver mitochondrial low Km aldehyde dehydrogenase

S-Methyl N,N-diethylthiolcarbamate sulfone (DETC-Me sulfone) was investigated for its rat liver mitochondrial low Km aldehyde dehydrogenase (ALDH2) inhibitory properties. DETC-Me sulfone inhibited ALDH2 in vitro (IC50 = 3.8 microM) and in vivo (ID50 = 170 mumol/kg; 31 mg/kg). Maximum inhibition (60%) of ALDH2 was observed 8 hr after DETC-Me sulfone administration. In addition, incubation of S-methyl N,N-diethylthiolcarbamate (DETC-Me) or S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-Me sulfoxide) with rat liver microsomes and an NADPH-generating system failed to produce DETC-Me sulfone. Furthermore, DETC-Me sulfone could not be detected in plasma from rats treated with either DETC-Me sulfoxide or DETC-Me sulfone. In conclusion, DETC-Me sulfone inhibited ALDH2 in vitro and in vivo. However, there was no evidence suggesting that DETC-Me sulfoxide was metabolized to DETC-Me sulfone.

Role of flavin-dependent monooxygenases and cytochrome P450 enzymes in the sulfoxidation of S-methyl N,N-diethylthiolcarbamate

Disulfiram is bioactivated to S-methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO), the metabolite proposed to be responsible for the action of disulfiram as an aldehyde dehydrogenase inhibitor. This bioactivation process includes a reduction, an S-methylation, and two successive oxidations. Sulfur-containing functional groups are substrates for cytochrome P450 enzymes or flavin-containing monooxygenases (FMO). In the present study, we investigated the contribution of these monooxygenases to the formation of DETC-MeSO from its immediate precursor S-methyl N,N-diethylthiolcarbamate (DETC-Me). Liver microsomes obtained from mature male rats were incubated with DETC-Me. The formation of DETC-MeSO was blocked completely by solubilization of the microsomes with the detergent Emulgen 911, or by the presence of the cytochrome P450 inhibitor 1-benzylimidazole. However, thermal-inactivation of FMO resulted in only a partial loss in DETC-MeSO formation. Liver microsomes from phenobarbital-treated rats showed a 4- to 5-fold increase in the rate of formation of DETC-MeSO, compared with controls. Liver microsomes from pyrazole-treated rats showed a 50% decrease in the sulfoxidation of DETC-Me compared with controls. In a purified reconstituted system, cytochrome P450 2B1 (CYP2B1) catalyzed the formation of DETC-MeSO at a rate of 51 nmol DETC-MeSO formed/min/nmol cytochrome P450. Antibodies to CYP2B1 caused a 60% inhibition of DETC-MeSO formation by liver microsomes from phenobarbital-treated rats. These results suggest that in male rat liver microsomes, cytochrome P450 plays a major role in catalyzing the sulfoxidation of DETC-Me, whereas FMO plays a minor role (< 10%). Also, in liver microsomes from phenobarbital-treated rats, CYP2B1 is the major catalyst for the sulfoxidation of DETC-Me.