Cyclodextrin encapsulation enabling the anticancer repositioning of disulfiram: Preparation, analytical and in vitro biological characterization of the inclusion complexes

Drug repositioning is a high-priority and feasible strategy in the field of oncology research, where the unmet medical needs are continuously unbalanced. Disulfiram is a potential non-chemotherapeutic, adjuvant anticancer agent. However, the clinical translation is limited by the drug's poor bioavailability. Therefore, the molecular encapsulation of disulfiram with cyclodextrins is evaluated to enhance the solubility and stability of the drug. The present work describes for the first time the complexation of disulfiram with randomly methylated-β-cyclodextrin. A parallel analytical andin vitrobiological comparison of disulfiram inclusion complexes with hydroxypropyl-β-cyclodextrin, randomly methylated-β-cyclodextrin and sulfobutylether-β-cyclodextrin is conducted. A significant drug solubility enhancement by about 1000-folds and fast dissolution in 1 min is demonstrated. Thein vitrodissolution-permeation studies and proliferation assays demonstrate the solubility-dependent efficacy of the drug. Throughout the different cancer cell lines' characteristics and disulfiram unspecific antitumoral activity, the inhibitory efficacy of the cyclodextrin encapsulated drug on melanoma (IC50 about 100 nM) and on glioblastoma (IC50 about 7000 nM) cell lines differ by a magnitude. This pre-formulation screening experiment serves as a proof of concept of using cyclodextrin encapsulation as a platform tool for further drug delivery development in repositioning areas.

Localized Sustained Release of Copper Enhances Antitumor Effects of Disulfiram in Head and Neck Cancer

Drug repurposing uses approved drugs as candidate anticancer therapeutics, harnesses previous research and development efforts, and benefits from available clinically suitable formulations and evidence of patient tolerability. In this work, the drug used clinically to treat chronic alcoholism, disulfiram (DSF), was studied for its antitumor efficacy in a copper-dependent manner. The combination of DSF and copper could achieve a tumor cell growth inhibition effect comparable to those of 5-fluorouracil and taxol on head and neck cancer cells. Both bulk dendrimer hydrogel and microsized dendrimer hydrogel particles were utilized for the localized sustained release of copper in the tumor site. The localized sustained release of copper facilitated the tumor inhibition effect following intratumoral injection in a mouse's head and neck cancer model.

Inhibiting the compensatory elevation of xCT collaborates with disulfiram/copper-induced GSH consumption for cascade ferroptosis and cuproptosis

Hepatocellular carcinoma (HCC) is one of the most prevalent malignant tumors and the fourth leading cause of cancer-related death globally, which is characterized by complicated pathophysiology, high recurrence rate, and poor prognosis. Our previous study has demonstrated that disulfiram (DSF)/Cu could be repurposed for the treatment of HCC by inducing ferroptosis. However, the effectiveness of DSF/Cu may be compromised by compensatory mechanisms that weaken its sensitivity. The mechanisms underlying these compensatory responses are currently unknown. Herein, we found DSF/Cu induces endoplasmic reticulum stress with disrupted ER structures, increased Ca2+ level and activated expression of ATF4. Further studies verified that DSF/Cu induces both ferroptosis and cuproptosis, accompanied by the depletion of GSH, elevation of lipid peroxides, and compensatory increase of xCT. Comparing ferroptosis and cuproptosis, it is interesting to note that GSH acts at the crossing point of the regulation network and therefore, we hypothesized that compensatory elevation of xCT may be a key aspect of the therapeutic target. Mechanically, knockdown of ATF4 facilitated the DSF/Cu-induced cell death and exacerbated the generation of lipid peroxides under the challenge of DSF/Cu. However, ATF4 knockdown was unable to block the compensatory elevation of xCT and the GSH reduction. Notably, we found that DSF/Cu induced the accumulation of ubiquitinated proteins, promoted the half-life of xCT protein, and dramatically dampened the ubiquitination-proteasome mediated degradation of xCT. Moreover, both pharmacologically and genetically suppressing xCT exacerbated DSF/Cu-induced cell death. In conclusion, the current work provides an in-depth study of the mechanism of DSF/Cu-induced cell death and describes a framework for the further understanding of the crosstalk between ferroptosis and cuproptosis. Inhibiting the compensatory increase of xCT renders HCC cells more susceptible to DSF/Cu, which may provide a promising synergistic strategy to sensitize tumor therapy and overcome drug resistance, as it activates different programmed cell death.

Disulfiram/Copper Suppresses Cancer Stem Cell Activity in Differentiated Thyroid Cancer Cells by Inhibiting BMI1 Expression

Differentiated thyroid carcinomas (DTCs), which have papillary and follicular types, are common endocrine malignancies worldwide. Cancer stem cells (CSCs) are a particular type of cancer cells within bulk tumors involved in cancer initiation, drug resistance, and metastasis. Cells with high intracellular aldehyde hydrogenase (ALDH) activity are a population of CSCs in DTCs. Disulfiram (DSF), an ALDH inhibitor used for the treatment of alcoholism, reportedly targets CSCs in various cancers when combined with copper. This study reported for the first time that DSF/copper can inhibit the proliferation of papillary and follicular DTC lines. DSF/copper suppressed thyrosphere formation, indicating the inhibition of CSC activity. Molecular mechanisms of DSF/copper involved downregulating the expression of B lymphoma Mo-MLV insertion region 1 homolog (BMI1) and cell cycle-related proteins, including cyclin B2, cyclin-dependent kinase (CDK) 2, and CDK4, in a dose-dependent manner. BMI1 overexpression diminished the inhibitory effect of DSF/copper in the thyrosphere formation of DTC cells. BMI1 knockdown by RNA interference in DTC cells also suppressed the self-renewal capability. DSF/copper could inhibit the nuclear localization and transcriptional activity of c-Myc and the binding of E2F1 to the BMI1 promoter. Overexpression of c-Myc or E2F1 further abolished the inhibitory effect of DSF/copper on BMI1 expression, suggesting that the suppression of c-Myc and E2F1 by DSF/copper was involved in the downregulation of BMI1 expression. In conclusion, DSF/copper targets CSCs in DTCs by inhibiting c-Myc- or E2F1-mediated BMI1 expression. Therefore, DSF is a potential therapeutic agent for future therapy in DTCs.

Novel Disulfiram Derivatives as ALDH1a1-Selective Inhibitors

Aldehyde dehydrogenase-1a1 (ALDH1a1), the enzyme responsible for the oxidation of retinal into retinoic acid, represents a key therapeutic target for the treatment of debilitating disorders such as cancer, obesity, and inflammation. Drugs that can inhibit ALDH1a1 include disulfiram, an FDA-approved drug to treat chronic alcoholism. Disulfiram, by carbamylation of the catalytic cysteines, irreversibly inhibits ALDH1a1 and ALDH2. The latter is the isozyme responsible for important physiological processes such as the second stage of alcohol metabolism. Given the fact that ALDH1a1 has a larger substrate tunnel than that in ALDH2, replacing disulfiram ethyl groups with larger motifs will yield selective ALDH1a1 inhibitors. We report herein the synthesis of new inhibitors of ALDH1a1 where (hetero)aromatic rings were introduced into the structure of disulfiram. Most of the developed compounds retained the anti-ALDH1a1 activity of disulfiram; however, they were completely devoid of inhibitory activity against ALDH2.

Benefits and Toxicity of Disulfiram in Preclinical Models of Nephropathic Cystinosis

Nephropathic cystinosis is a rare disease caused by mutations of the CTNS gene that encodes for cystinosin, a lysosomal cystine/H+ symporter. The disease is characterized by early-onset chronic kidney failure and progressive development of extra-renal complications related to cystine accumulation in all tissues. At the cellular level, several alterations have been demonstrated, including enhanced apoptosis, altered autophagy, defective intracellular trafficking, and cell oxidation, among others. Current therapy with cysteamine only partially reverts some of these changes, highlighting the need to develop additional treatments. Among compounds that were identified in a previous drug-repositioning study, disulfiram (DSF) was selected for in vivo studies. The cystine depleting and anti-apoptotic properties of DSF were confirmed by secondary in vitro assays and after treating Ctns-/- mice with 200 mg/kg/day of DSF for 3 months. However, at this dosage, growth impairment was observed. Long-term treatment with a lower dose (100 mg/kg/day) did not inhibit growth, but failed to reduce cystine accumulation, caused premature death, and did not prevent the development of renal lesions. In addition, DSF also caused adverse effects in cystinotic zebrafish larvae. DSF toxicity was significantly more pronounced in Ctns-/- mice and zebrafish compared to wild-type animals, suggesting higher cell toxicity of DSF in cystinotic cells.

A Tumor Microenvironment-Responsive Theranostic Agent for Synergetic Therapy of Disulfiram-Based Chemotherapy and Chemodynamic Therapy

Despite the fact that chemotherapy has been widely used in the clinical treatment of breast cancer, the toxicity of chemotherapeutics to normal tissues cannot be ignored due to the low specificity. Therefore, due to the non-negligible toxicity of chemotherapeutic agents to normal tissues, tumor microenvironment (TME)-responsive cancer therapy has attracted a great deal of attention. Here, we report a TME-responsive theranostic nanoagent MnOx@PAA@HKUST-1-DSF@BSA fabricated via a layer-by-layer synthesis method. Once endocytosed by tumor cells, the nanoagent can be degraded into Mn²⁺ for magnetic resonance imaging and Cu²⁺ for Fenton-like reaction and chelating with released disulfiram in situ, achieving enhanced chemotherapy. Both in vitro and in vivo experiments demonstrate that the TME-targeted nanoagent can efficiently kill tumor cells. This work provides an alternative option for effective imaging and treatment of breast cancer without collateral damage to normal tissues.

Biodegradable Nanocatalyst with Self-Supplying Fenton-like Ions and H2O2 for Catalytic Cascade-Amplified Tumor Therapy

Therapeutic nanosystems triggered by a specific tumor microenvironment (TME) offer excellent safety and selectivity in the treatment of cancer by in situ conversion of a less toxic substance into effective anticarcinogens. However, the inherent antioxidant systems, hypoxic environment, and insufficient hydrogen peroxide (H₂O₂) in tumor cells severely limit their efficacy. Herein, a new strategy has been developed by loading the chemotherapy prodrug disulfiram (DSF) and coating glucose oxidase (GOD) on the surface of Cu/ZIF-8 nanospheres and finally encapsulating manganese dioxide (MnO₂) nanoshells to achieve efficient DSF-based cancer chemotherapy and dual-enhanced chemodynamic therapy (CDT). In an acidic TME, the nanocatalyst can biodegrade rapidly and accelerate the release of internal active substances. The outer layer of MnO₂ depletes glutathione (GSH) to destroy the reactive oxygen defensive mechanisms and achieves continuous oxygen generation, thus enhancing the catalytic efficiency of GOD to burst H₂O₂. Benefiting from the chelation reaction between the released Cu²⁺ and DSF, a large amount of cytotoxic CuET products is generated, and the Cu⁺ are concurrently released, thereby achieving efficient chemotherapy and satisfactory CDT efficacy. Furthermore, the release of Mn²⁺ can initiate magnetic resonance imaging signals for the tracking of the nanocatalyst.

Differential Cytotoxicity Mechanisms of Copper Complexed with Disulfiram in Oral Cancer Cells

Disulfiram (DSF), an irreversible aldehyde dehydrogenase inhibitor, is being used in anticancer therapy, as its effects in humans are known and less adverse than conventional chemotherapy. We explored the potential mechanism behind the cytotoxicity of DSF-Cu⁺/Cu²⁺ complexes in oral epidermoid carcinoma meng-1 (OECM-1) and human gingival epithelial Smulow-Glickman (SG) cells. Exposure to CuCl₂ or CuCl slightly but concentration-dependently decreased cell viability, while DSF-Cu⁺/Cu²⁺ induced cell death in OECM-1 cells, but not SG cells. DSF-Cu⁺/Cu²⁺ also increased the subG1 population and decreased the G1, S, and G2/M populations in OECM-1 cells, but not SG cells, and suppressed cell proliferation in both OECM-1 and SG cells. ALDH enzyme activity was inhibited by CuCl and DSF-Cu⁺/Cu²⁺ in SG cells, but not OECM-1 cells. ROS levels and cellular senescence were increased in DSF-Cu⁺/Cu²⁺-treated OECM-1 cells, whereas they were suppressed in SG cells. DSF-Cu⁺/Cu²⁺ induced mitochondrial fission in OECM-1 cells and reduced mitochondrial membrane potential. CuCl₂ increased but DSF- Cu²⁺ impaired oxygen consumption rates and extracellular acidification rates in OECM-1 cells. CuCl₂ stabilized HIF-1α expression under normoxia in OECM-1 cells, and complex with DSF enhanced that effect. Levels of c-Myc protein and its phosphorylation at Tyr58 and Ser62 were increased, while levels of the N-terminal truncated form (Myc-nick) were decreased in DSF-Cu⁺/Cu²-treated OECM-1 cells. These effects were all suppressed by pretreatment with the ROS scavenger NAC. Overexpression of c-Myc failed to induce HIF-1α expression. These findings provide novel insight into the potential application of DSF-CuCl₂ complex as a repurposed agent for OSCC cancer therapy.

Seesaw conformations of Npl4 in the human p97 complex and the inhibitory mechanism of a disulfiram derivative

p97, also known as valosin-containing protein (VCP) or Cdc48, plays a central role in cellular protein homeostasis. Human p97 mutations are associated with several neurodegenerative diseases. Targeting p97 and its cofactors is a strategy for cancer drug development. Despite significant structural insights into the fungal homolog Cdc48, little is known about how human p97 interacts with its cofactors. Recently, the anti-alcohol abuse drug disulfiram was found to target cancer through Npl4, a cofactor of p97, but the molecular mechanism remains elusive. Here, using single-particle cryo-electron microscopy (cryo-EM), we uncovered three Npl4 conformational states in complex with human p97 before ATP hydrolysis. The motion of Npl4 results from its zinc finger motifs interacting with the N domain of p97, which is essential for the unfolding activity of p97. In vitro and cell-based assays showed that the disulfiram derivative bis-(diethyldithiocarbamate)-copper (CuET) can bypass the copper transporter system and inhibit the function of p97 in the cytoplasm by releasing cupric ions under oxidative conditions, which disrupt the zinc finger motifs of Npl4, locking the essential conformational switch of the complex.

Evaluation of Bronopol and Disulfiram as Potential Candidatus Liberibacter asiaticus Inosine 5'-Monophosphate Dehydrogenase Inhibitors by Using Molecular Docking and Enzyme Kinetic

Citrus huanglongbing (HLB) is a destructive disease that causes significant damage to many citrus producing areas worldwide. To date, no strategy against this disease has been established. Inosine 5'-monophosphate dehydrogenase (IMPDH) plays crucial roles in the de novo synthesis of guanine nucleotides. This enzyme is used as a potential target to treat bacterial infection. In this study, the crystal structure of a deletion mutant of CLas IMPDHΔ98-201 in the apo form was determined. Eight known bioactive compounds were used as ligands for molecular docking. The results showed that bronopol and disulfiram bound to CLas IMPDHΔ98-201 with high affinity. These compounds were tested for their inhibition against CLas IMPDHΔ98-201 activity. Bronopol and disulfiram showed high inhibition at nanomolar concentrations, and bronopol was found to be the most potent molecule (Ki = 234 nM). The Ki value of disulfiram was 616 nM. These results suggest that bronopol and disulfiram can be considered potential candidate agents for the development of CLas inhibitors.

Copper-Enriched Prussian Blue Nanomedicine for In Situ Disulfiram Toxification and Photothermal Antitumor Amplification

In situ toxification of less toxic substance for the generation of effective anticarcinogens at the specific tumor tissue has been a novel paradigm for combating cancer. Significant efforts have been recently dedicated to turning clinical-approved drugs into anticancer agents in specific tumor microenvironment by chemical reactions. Herein, a hollow mesoporous Prussian blue (HMPB)-based therapeutic nanoplatform, denoted as DSF@PVP/Cu-HMPB, is constructed by encapsulating alcohol-abuse drug disulfiram (DSF) into the copper-enriched and polyvinylpyrrolidone (PVP)-decorated HMPB nanoparticles to achieve in situ chemical reaction-activated and hyperthermia-amplified chemotherapy of DSF. Upon tumor accumulation of DSF@PVP/Cu-HMPB, the endogenous mild acidity in tumor condition triggers the biodegradation of the HMPB nanoparticle and the concurrent co-releases of DSF and Cu²⁺ , thus forming cytotoxic bis(N,N-diethyl dithiocarbamato)copper(II) complexes (CuL₂ ) via DSF-Cu²⁺ chelating reaction. Moreover, by the intrinsic photothermal-conversion effect of PVP/Cu-HMPBs, the anticancer effect of DSF is augmented by the hyperthermia generated upon near-infrared irradiation, thus inducing remarkable cell apoptosis in vitro and tumor elimination in vivo on both subcutaneous and orthotopic tumor-bearing models. This strategy of in situ drug transition by chemical chelation reaction and photothermal-augmentation provides a promising paradigm for designing novel cancer-therapeutic nanoplatforms.

A disulfiram-loaded electrospun poly(vinylidene fluoride) nanofibrous scaffold for cancer treatment

Disulfiram (DSF), an FDA approved drug for the treatment of alcoholism, has shown its effectiveness against diverse cancer types. Thus, we developed a disulfiram-loaded scaffold using the electrospinning method to enhance the stability of DSF and to facilitate its appropriate distribution to tumor tissues. The drug release profile of the disulfiram-loaded scaffold was examined by high-performance liquid chromatography. We obtained mechanical and morphological characterizations of A549 cells treated with different scaffolds by various techniques to evaluate its antitumor properties. This work revealed that the cells after the treatment with the disulfiram-loaded scaffold exhibited a lower height and a larger elastic modulus compared with the untreated cells and those treated with the neat electrospun fibers. The changes were the indicators of cell apoptosis. Taken collectively, the results indicate that DSF was successfully incorporated into the electrospun fibers, and the disulfiram-loaded scaffold has great potential for inhibiting the regional recurrence of cancer.

Soybean lecithin stabilizes disulfiram nanosuspensions with a high drug-loading content: remarkably improved antitumor efficacy

Disulfiram (DSF) has been considered as "Repurposing drug" in cancer therapy in recent years based on its good antitumor efficacy. DSF is traditionally used as an oral drug in the treatment of alcoholism. To overcome its rapid degradation and instability, DSF nanosuspensions (DSF/SPC-NSps) were prepared using soybean lecithin (SPC) as a stabilizer of high drug-loaded content (44.36 ± 1.09%). Comprehensive characterization of the nanosuspensions was performed, and cell cytotoxicity, in vivo antitumor efficacy and biodistribution were studied. DSF/SPC-NSps, having a spherical appearance with particle size of 155 nm, could remain very stable in different physiological media, and sustained release. The in vitro MTT assay indicated that the cytotoxicity of DSF/SPC-NSps was enhanced remarkably compared to free DSF against the 4T1 cell line. The IC50 value decreased by 11-fold (1.23 vs. 13.93 μg/mL, p < 0.01). DSF/SPC-NSps groups administered via intravenous injections exhibited better antitumor efficacy compared to the commercial paclitaxel injection (PTX injection) and had a dose-dependent effect in vivo. Notably, DSF/SPC-NSps exhibited similar antitumor activity following oral administration as PTX administration via injection into a vein. These results suggest that the prepared nanosuspensions can be used as a stable delivery vehicle for disulfiram, which has potential application in breast cancer chemotherapy.

Disulfiram Copper Nanoparticles Prepared with a Stabilized Metal Ion Ligand Complex Method for Treating Drug-Resistant Prostate Cancers

Disulfiram (DSF), an alcohol-aversion drug, has been explored for cancer treatment. Copper diethyldithiocarbamate (Cu(DDC)₂) complex formed by DSF and copper ions is a major active ingredient for its anticancer activity. Direct administration of Cu(DDC)₂ is a promising strategy to enhance the anticancer efficacy of DSF. However, efficient drug delivery remains a significant challenge for Cu(DDC)₂ and hinders its clinical use. In this study, we developed a facile stabilized metal ion ligand complex (SMILE) method to prepare Cu(DDC)₂ nanoparticles (NPs). The SMILE method could prepare Cu(DDC)₂ NPs with different types of stabilizers including 1,2-distearoyl- sn-glycerol-3-phosphoethanolamine-poly(ethylene glycol) (PEG) 2000, d-α-tocopherol PEG 1000 succinate, methoxy PEG 5000- b-poly(l-lactide) 5000, and other generally recognized as safe excipients approved by the US Food and Drug Administration. The optimized formulations demonstrated excellent drug-loading efficiency (close to 100%), high drug concentrations (increased drug concentration by over 200-fold compared to the traditional micelle formulation), and an optimal particle size in the sub-100 nm range. Cu(DDC)₂ NPs exhibited outstanding stability in serum for 72 h and can also be stored at room temperature for at least 1 month. The anticancer effects of Cu(DDC)₂ NP formulations were determined by multiple assays including 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, colony-forming assay, calcein-AM/propidium iodide staining, and others. Cu(DDC)₂ NPs showed excellent activity against drug-resistant prostate cancer cells and other cancer cells with a half-maximal inhibitory concentration (IC₅₀) of around 100 nM. Our study also demonstrated that Cu(DDC)₂ NPs induced cell death in drug-resistant prostate cancer cells (DU145-TXR) through paraptosis, which is a nonapoptotic cell death. To our best knowledge, the SMILE method provides, for the first time, a simple yet efficient process for generating Cu(DDC)₂ NPs with high drug concentration, excellent loading efficiency, and desirable physicochemical properties. This method could potentially address drug delivery challenges of DSF/copper-based chemotherapy and facilitate its clinical translation.

Development of a copper-clioquinol formulation suitable for intravenous use

Clioquinol (CQ) is an FDA-approved topical antifungal agent known to kill cancer cells. This facilitated the initiation of clinical trials in patients with refractory hematologic malignancies. These repurposing efforts were not successful; this was likely due to low intracellular levels of the drug owing to poor absorption and rapid metabolism upon oral administration. CQ forms a sparingly soluble copper complex (Cu(CQ)2) that exhibits enhanced anticancer activity in some cell lines. We have utilized a novel method to synthesize Cu(CQ)2 inside liposomes, an approach that maintains the complex suspended in solution and in a format suitable for intravenous administration. The complex was prepared inside 100-nm liposomes composed of 1,2-distearoyl-sn-glycero-3-phosphocholine/cholesterol (55:45). The therapeutic activity of the resultant formulation was evaluated in two subcutaneous tumor models (glioblastoma and ovarian cancers) but was not active. We also assessed the ability of the Cu(CQ)2 formulation to increase copper delivery to cancer cells in vitro and its potential to be used in combination with disulfiram (DSF). The results suggested that addition of Cu(CQ)2 enhanced cellular copper levels and the activity of DSF in vitro; however, this combination did not result in a statistically significant reduction in tumor growth in vivo. These studies demonstrate that a Cu(CQ)2 formulation suitable for intravenous use can be prepared, but this formulation used alone or in combination with DSF was not efficacious. The methods described are suitable for development formulations of other analogues of 8-hydroxyquinoline which could prove to be more potent.

pH-triggered surface charge-switchable polymer micelles for the co-delivery of paclitaxel/disulfiram and overcoming multidrug resistance in cancer

Multidrug resistance (MDR) remains a major challenge for providing effective chemotherapy for many cancer patients. To address this issue, we report an intelligent polymer-based drug co-delivery system which could enhance and accelerate cellular uptake and reverse MDR. The nanodrug delivery systems were constructed by encapsulating disulfiram (DSF), a P-glyco-protein (P-gp) inhibitor, into the hydrophobic core of poly(ethylene glycol)-block-poly(l-lysine) (PEG-b-PLL) block copolymer micelles, as well as 2,3-dimethylmaleic anhydride (DMA) and paclitaxel (PTX) were grafted on the side chain of l-lysine simultaneously. The surface charge of the drug-loaded micelles represents as negative in plasma (pH 7.4), which is helpful to prolong the circulation time, and in a weak acid environment of tumor tissue (pH 6.5-6.8) it can be reversed to positive, which is in favor of their entering into the cancer cells. In addition, the carrier could release DSF and PTX successively inside cells. The results of in vitro studies show that, compared to the control group, the DSF and PTX co-loaded micelles with charge reversal exhibits more effective cellular uptake and significantly increased cytotoxicity of PTX to MCF-7/ADR cells which may be due to the inhibitory effect of DSF on the efflux function of P-gp. Accordingly, such a smart pH-sensitive nanosystem, in our opinion, possesses significant potential to achieve combinational drug delivery and overcome drug resistance in cancer therapy.

Combining disulfiram and poly(l-glutamic acid)-cisplatin conjugates for combating cisplatin resistance

A poly(l-glutamic acid) graft polyethylene glycol-cisplatin complex (PGA-CisPt) performs well in reducing the toxicity of free cisplatin and greatly enhances the accumulation and retention of cisplatin in solid tumors. However, there is a lack of effective treatment options for cisplatin-resistant tumors. A major reason for this is the dense PEG shell, which ensures that the PGA-CisPt maintains a long retention time in the blood that may result in it bypassing the tumor cells or failing to be endocytosed within the tumor microenvironment. Consequently, the cisplatin from PGA-CisPt is released to the extracellular space in the presence of cisplatin-resistant tumor cells and the resistant problem to free cisplatin still valid. Therefore, we devised a strategy to combat the resistance of cisplatin in the tumor microenvironment using nanoparticles-loaded disulfiram (NPs-DSF) as a modulator. In vitro, cisplatin, in combination with DSF, had a synergistic effect and decreased cell survival rate of cisplatin-resistant A549DDP cells. This effect was also observed when combining PGA-CisPt with NPs-DSF. Similarly, in Balb/C nude mice with A549DDP xenografts, NPs-DSF improved PGA-CisPt effectiveness in inhibiting tumor growth while maintaining low toxicity. Our data demonstrate that DSF reduces intracellular glutathione (GSH) levels, inhibits NFκB activity, and modulates the expression of apoptosis-related proteins Bcl-2 and Bax, thereby improves the effectiveness of cisplatin in resistant cell lines. Here, we provide a promising method for overcoming cisplatin resistance in tumors, while maintaining the in vivo benefits of the PGA-CisPt complex.

[A disulfiram-alcohol reaction after inhalation of a salbutamol aerosol: a plausible interaction?]

An asthmatic patient (male, aged 47) being treated for his alcohol dependence complained of experiencing mild symptoms of disulfiram-alcohol reaction after using of pressurised metered-dose inhaler containing ethanol. It has been reported in the literature that the disulfiram-alcohol reaction may occur after a patient has been exposed to only minimal amounts of ethanol. This is why, in daily practice, physicians are generally reluctant to prescribe preparations containing ethanol and why they usually switch patients to an alternative. However, close evaluation of the biopharmaceutical and pharmacokinetic aspects of ethanol suggests that subjective disulfiram-alcohol reactions following the use of inhalers containing ethanol cannot be explained rationally from a clinical pharmacological perspective.

Smart pH-sensitive and temporal-controlled polymeric micelles for effective combination therapy of doxorubicin and disulfiram

The combination of a chemotherapeutic drug with a multidrug resistance (MDR) modulator has emerged as a promising strategy for treating MDR cancer. To ensure two drugs could be simultaneously delivered to tumor region at the optimum ratio, and the MDR modulator could be released earlier and faster than the chemotherapeutic drug to inactivate P-glycoprotein (P-gp) and subsequently inhibit the pumping out of the chemotherapeutic drug, a smart pH-sensitive polymeric micelles system with high drug loading and precise drug ratio was designed and prepared by conjugating doxorubicin (DOX) to poly(styrene-co-maleic anhydride) (SMA) derivative with adipic dihydrazide (ADH) through a acid-cleavable hydrazone bond, and then encapsulating disulfiram (DSF), a P-gp inhibitor as well as an apoptosis inducer, into the micelles formed by the self-assembly of SMA-ADH-DOX (SAD) conjugate. The pH-sensitive polymeric micelles system enabled a temporal release of two drugs: encapsulated DSF was released fast to inhibit the activity of P-gp and restore cell apoptotic signaling pathways, while conjugated DOX was released in a sustained and pH-dependent manner and highly accumulated in drug resistant cells to exert therapeutic effect, due to the inactivation of P-gp by DSF. The smart co-delivery system was very effective in enhancing the cytotoxicity by increasing the intracellular accumulation of DOX and promoting the apoptotic response, and showed the most effective inhibitory effect on the growth of drug-resistant breast cancer xenografts as compared to other combinations of both drugs. In a word, this smart co-delivery system has significant promise for the clinical therapy of MDR cancer.

The enzymatic activity of human aldehyde dehydrogenases 1A2 and 2 (ALDH1A2 and ALDH2) is detected by Aldefluor, inhibited by diethylaminobenzaldehyde and has significant effects on cell proliferation and drug resistance

There has been a new interest in using aldehyde dehydrogenase (ALDH) activity as one marker for stem cells since the Aldefluor flow cytometry-based assay has become available. Diethylaminobenzaldehyde (DEAB), used in the Aldeflour assay, has been considered a specific inhibitor for ALDH1A1 isoform. In this study, we explore the effects of human ALDH isoenzymes, ALDH1A2 and ALDH2, on drug resistance and proliferation, and the specificity of DEAB as an inhibitor. We also screened for the expression of 19 ALDH isoenzymes in K562 cells using TaqMan Low Density Array (TLDA). We used lentiviral vectors containing the full cDNA length of either ALDH2 or ALDH1A2 to over express the enzymes in K562 leukemia and H1299 lung cancer cell lines. Successful expression was measured by activity assay, Western blot, RT-PCR, and Aldefluor assay. Both cell lines, with either ALDH1A2 or ALDH2, exhibited higher cell proliferation rates, higher clonal efficiency, and increased drug resistance to 4-hydroperoxycyclophosphamide and doxorubicin. In order to study the specificity of known ALDH activity inhibitors, DEAB and disulfiram, we incubated each cell line with either inhibitor and measured the remaining ALDH enzymatic activity. Both inhibitors reduced ALDH activity of both isoenzymes by 65-90%. Furthermore, our TLDA results revealed that ALDH1, ALDH7, ALDH3 and ALDH8 are expressed in K562 cells. We conclude that DEAB is not a specific inhibitor for ALDH1A1 and that Aldefluor assay is not specific for ALDH1A1 activity. In addition, other ALDH isoenzymes seem to play a major role in the biology and drug resistance of various malignant cells.

Effects of cytochrome P450 inhibitors on peroxidase activity

OBJECTIVES

Of several enzymes metabolizing xenobiotics, cytochrome P450 (CYP) and peroxidase enzymes seem to be most important. One of the major challenges in studies investigating metabolism of xenobiotics is to resolve which of these two groups of enzymes is predominant to metabolize individual xenobiotic compounds. Utilization of selective inhibitors of CYP and peroxidase enzymes might be a useful tool to identify the contribution of these enzymes to metabolism of xenobiotics in samples, where both types of enzymes are present. The aim of this study was to investigate specificities of several known CYP inhibitors to these enzymes; whether they inhibit only the CYP enzymes and do not inhibit peroxidases.

METHODS

Since the oxidation of o-anisidine catalyzed by a model peroxidase used, horseradish peroxidase (HRP), is a two-substrate reaction, the inhibition potential of tested chemicals was studied with respect to both peroxidase substrates, o-anisidine and hydrogen peroxide. Initial velocities of o-anisidine oxidation by HRP under various conditions were determined spectrophotometrically.

RESULTS

The CYP inhibitors metyrapone, troleandomycine, disulfiram, sulfaphenazole, quinidine and 1-aminobenzotriazole do not inhibit o-anisidine oxidation catalyzed by HRP. In contrast, ketoconazole, diethyldithiocarbamate, ellipticine, α-naphtoflavone, proadifen SKF525A, piperonylbutoxide, were found to inhibit not only the CYPs, but also the HRP-mediated oxidation of o-anisidine. Interestingly, α-naphtoflavone inhibits oxidation of o-anisidine by HRP with respect to H2O2, but not with respect to o-anisidine. Diethyldithiocarbamate is the most potent peroxidase inhibitor of o-anisidine oxidation with Ki with respect to o-anisidine of 10 μM and Ki with respect to H2O2 of 60 μM, being even the better peroxidase inhibitor than the classical "peroxidase inhibitor" - propyl gallate (Ki with respect to o-anisidine of 60 μM and Ki with respect to H2O2 of 750 μM).

CONCLUSIONS

The results of the present study demonstrate that 1-aminobenzotriazole, a potent inhibitor of various CYP enzymes, seems to be the best candidate suitable for utilization in studies evaluating participation of CYP enzymes in metabolism of xenobiotics in various complex biological materials containing both CYP and peroxidase enzymes. Moreover, precaution to prevent misinterpretation of results is necessary in cases when proadifen SKF525A, piperonylbutoxide, diethyldithiocarbamate, ketoconazole, α-naphtoflavone and ellipticine are used in similar studies (as CYP inhibitors in various complex biological materials containing both CYP and peroxidase enzymes), since these chemicals can except of CYP enzymes inhibit also peroxidase-mediated reactions.

Determination of disulfiram by micellar liquid chromatography in illicit preparations

Presently, disulfiram is used in aversion therapy for recovering alcoholics. It acts by inhibiting aldehyde dehydrogenase, leading to high blood levels of acetaldehyde. A simple direct injection micellar liquid chromatographic procedure was developed to determine disulfiram in illicit preparations (ayurvedic, herbal, divine ash, and traditional medicine), as well as in pharmaceuticals and biological samples (urine). After application of a predictive optimization strategy, the proposed method was developed using a 0.1 M sodium dodecyl sulfate-butanol 4% (v/v) buffered to pH 7 as the mobile phase at a flow rate of 1 mL/min, an octyl silyl (C8) 150 mm column, and diode array detection at 248 nm. Under the above conditions, the analysis time was below 8 min. Validation studies were based on U.S. Food and Drug Administration guidelines. The LOD (3 x SD criterion) was 15 ng/mL and LOQ (10 x SD criterion) was 70 ng/mL for disulfiram. The intraday and interday precisions were below 3.5%, recoveries were in the range of 97-102%, and robustness was below 3%. The optimized and validated micellar liquid chromatographic method was successfully applied to the determination of disulfiram in ayurvedic, herbal, divine ash, and other samples. The procedure developed could also be used in the fields of QC, routine analysis, and pharmacokinetic studies.

[Peculiarities of detection and evaluation of the persistence of tetraethyltiuram disulfide in the biological material]

Optimal conditions for the identification and quantitative determination of tetraethyltiuram disulfide in "fresh" and putrefactive tissues of cadaverous liver are described for the purpose of TLC, HPLC, and IK-spectrophotometry following extraction of the compound of interest with ethyl acetate and its purification on a silicagel L column, 40/100 mcm. The persistence of tetraethyltiuram disulfide in the cadaverous tissues was evaluated. It was shown that the period during which tetraethyltiuram disulfide can be detected in the autopsied tissues decreases from 203 to 28 days with a rise in temperature from -15 degrees C to +36 degrees C.

PKC sulfhydryl targeting by disulfiram produces divergent isozymic regulatory responses that accord with the cancer preventive activity of the thiuram disulfide

The protein kinase C (PKC) isozyme family plays key roles in cell growth regulation and influences neoplastic disease development and progression. For example, PKCepsilon is oncogenic, and PKCdelta tumor-suppressive. PKC isozymes are characterized by distinct activation mechanisms entailing phosphatidylserine-dependent cofactor binding to the regulatory domain. Evidence is now emerging that redox signaling offers another platform of PKC regulation. We have established that PKC isozymes are regulated by S-thiolation, a posttranslational modification entailing disulfide linkage of low-molecular-weight species to select protein sulfhydryls. Our recent studies demonstrate that physiologically occurring disulfides with cysteinyl constituents, e.g., cystine, regulate cellular PKC isozymes by S-thiolation-triggered mechanisms. This report shows that PKC isozymes are also molecular targets of a chemically distinct class of disulfides. Disulfiram is a thiuram disulfide with potent cancer preventive activity in in vivo models of chemical carcinogenesis. Our results indicate that PKC Sthiolation by disulfiram induces differential regulatory effects on PKC isozymes that correlate with the cancer preventive activity of the drug. The implication of these findings is that PKC-regulatory effects of thiuram disulfides may offer a useful pharmacological guide for development of disulfiram analogues with superior cancer preventive activity.

Disulfiram, an old drug with new potential therapeutic uses for human cancers and fungal infections

Disulfiram, a drug used to treat alcoholism, has recently been indicated to play a primary as well as an adjuvant role in the treatment of many cancers and in the reversal of fungal drug-resistance. This review discusses the molecular mechanism of action of disulfiram and its potential use in the treatment of human cancers and fungal infections.

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.

Preparation and in vivo ocular absorption studies of disulfiram solid dispersion

Disulfiram, a dimer of diethyldithiocarbamate (DDC) which is a strong radical scavenger, is known to prevent cataract development. However, disulfiram is hardly absorbed from the cornea and its bioavailability is extremely low. In this study, we attempted to prepare disulfiram solid dispersion for the improvement of ocular bioavailability. Solid dispersions of disulfiram were prepared by either an evaporation method or a spray-drying method, using polyvinylpyrrolidone (PVP) as a carrier. Preparations were analyzed by scanning electron microscopy, powder X-ray diffractometry and differential scanning calorimetry, and confirmed to be a solid dispersion. The particle size of the solid dispersion prepared by the spray-drying method was smaller than the preparation by the evaporation method (spray-drying: 3.3+/-0.04 microm, evaporation: 34.3+/-18.0 microm). An in vivo ocular absorption experiment was conducted by instilling solid dispersions to rabbit eye and measuring the DDC in the aqueous humor. After instillation of disulfiram and PVP physical mixture, DDC was not detected in the aqueous humor. On the other hand, DDC appeared in the aqueous humor after the instillation of a solid dispersion. Maximal concentration and the area under the aqueous humor concentration-time curve were greater in the solid dispersion prepared by the spray-drying method than the preparation by the evaporation method. Disulfiram solid dispersion, especially prepared by the spray-drying method, improved ocular bioavailability.

Zinc ejection as a new rationale for the use of cystamine and related disulfide-containing antiviral agents in the treatment of AIDS

The highly conserved and mutationally intolerant retroviral zinc finger motif of the HIV-1 nucleocapsid protein (NC) is an attractive target for drug therapy due to its participation in multiple stages of the viral replication cycle. A literature search identified cystamine, thiamine disulfide, and disulfiram as compounds that have been shown to inhibit HIV-1 replication by poorly defined mechanisms and that have electrophilic functional groups that might react with the metal-coordinating sulfur atoms of the retroviral zinc fingers and cause zinc ejection. 1H NMR studies reveal that these compounds readily eject zinc from synthetic peptides with sequences corresponding to the HIV-1 NC zinc fingers, as well as from the intact HIV-1 NC protein. In contrast, the reduced forms of disulfiram and cystamine, diethyl dithiocarbamate and cysteamine, respectively, were found to be ineffective at zinc ejection, although cysteamine formed a transient complex with the zinc fingers. Studies with HIV-1-infected human T-cells and monocyte/macrophage cultures revealed that cystamine and cysteamine possess significant antiviral properties at nontoxic concentrations, which warrant their consideration as therapeutically useful anti-HIV agents.

Diethyl dithiocarbamate-induced decomposition of S-nitrosothiols

Diethyl dithiocarbamate (DDC) has been used extensively as an inhibitor of CuZn superoxide dismutase (SOD) in the study of superoxide and nitric oxide. Addition of DDC to solutions of the endogenous NO adduct S-nitrosoglutathione (GSNO) causes a rapid decrease in GSNO with concomitant formation of nitrite, nitrate, disulfuram, oxidized glutathione, and mixed disulfide. Nitric oxide and superoxide appear to be produced in the process. Product formation is best explained by a radical mechanism in which S-nitrosation of DDC facilitates disulfide formation following homolytic cleavage. S-Nitrosocysteine and S-nitroso-N-acetylpenicillamine are likewise unstable in the presence of DDC. These findings may complicate interpretation of experiments in which DDC is used to alter NO-mediated responses. Some biological actions of DDC may result from SNO elimination rather than SOD inactivation. Moreover, apparent DDC-induced potentiation of superoxide effects may derive from O2- produced during the conversion of SNO to NO.

Characterization of intermediates in the oxidation of zinc fingers in human immunodeficiency virus type 1 nucleocapsid protein P7

Oxidants targeted toward inactivation of the nucleocapsid zinc finger protein are under development as antiviral agents, especially for use against human immunodeficiency virus. In the present study, electrospray ionization-mass spectrometry is used to follow in situ the progress of the reactions of 2,2'-dithiodipyridine and disulfiram with recombinant nucleocapsid protein p7 (Ncp7) from human immunodeficiency virus-1 at pH 7.4. Both reagents react with the two zinc fingers in the protein, resulting in the ejection of two zinc ions and the formation of oxidized apo-Ncp7 with three intramolecular disulfide bonds. The ejection of zinc by 2,2'-dithiodipyridine occurs in two steps. Alkylation of unreacted cysteine residues with N-ethylmaleimide after a 2-min reaction with 2,2'-dithiodipyridine reveals that the carboxyl-terminal zinc finger is disrupted first. Cys-49, Cys-36, and, to a lesser extent, Cys-39 are all shown to be target residues for initial electrophilic attack. In the reaction of disulfiram with Ncp7, ejection of the two zinc ions also occurs in two steps; however, the fully oxidized apo-Ncp7 is formed more rapidly. Thus, after a 40-min reaction, 45% of native Ncp7 is oxidized by 2,2'-dithiodipyridine, whereas 75% is oxidized by disulfiram.

Elicitation thresholds for thiuram mix using petrolatum and ethanol/sweat as vehicles

An estimate of amounts of thiurams that may be released from rubber gloves into synthetic sweat, has previously been generated. These amounts should be compared to elicitation thresholds of patch tests performed with serial dilutions of thiuram mix using synthetic sweat as vehicle. Because of solubility properties of thiurams in aqueous media, such dilutions cannot directly be prepared. In this study, a stem solution was prepared in ethanol. This solution was then further diluted with synthetic sweat. Thiuram mix 0.5 w/v% was the most concentrated solution in ethanol achievable. The patch test reactions were compared to reactions to serial dilutions using petrolatum as vehicle. The experiment revealed that endpoint dilution with synthetic sweat was not achieved in this study. The threshold for elicitation of positive patch test reactions seemed to be lower for ethanol/sweat as vehicle compared to petrolatum: 32% reacted to ethanol/synthetic sweat 0.001 mg/cm2 compared to 14% reacting to thiuram in pet. 0.002 mg/cm2. Based on these results, synthetic sweat may be considered a more relevant medium for threshold finding studies than petrolatum. Because of expected instability of the aqueous solutions, petrolatum is probably a more suitable vehicle for routine testing. The study does not permit final conclusions concerning acceptable thresholds for leachable thiurams in rubber gloves, but it is likely that an acceptable threshold would be substantially less than 0.001 mg/ cm2.

Inhibitory effects of mixed disulfides from disulfiram on the metabolism and genotoxicity of N-nitrosodiethylamine

Disulfiram (CAS 97-77-8, DSF), a potent anticarcinogenic compound, is known to form mixed disulfides with sulfhydryl group containing amino acids or proteins in vivo. In the present study the stabilities of two mixed disulfides which may arise in the metabolism of disulfiram, i.e. S-(N,N-diethyldithiocarbamoyl)-N-acetyl-L-cysteine (AC-DDTC) and S-(N,N-diethyldithiocarbamoyl)-L-glutathione (GS-DDTC) in phosphate buffer (pH 7.2) and in rat liver subcellular fractions were investigated as well as their influences on the glutathione (GSH)-related detoxifying system, on the metabolism of [14C] N-nitrosodiethylamine (NDEA) and on the genotoxic activity of NDEA in rats. Both substances were stable in buffer and in microsomes but were degraded in cytosol showing a half life of 4.7 h (AC-DDTC) and 3.2 h (GS-DDTC). Addition of GSH to the incubation media accelerated the degradation of mixed disulfides in cytosol. In vivo administration of AC-DDTC and GS-DDTC (1.7 mmol/kg i.p.) led to an increase in hepatic GSH content and to an inhibition of the activity of NDEA deethylase. Both mixed disulfides inhibited the metabolism of NDEA. After a 28 mg/kg i.p. dose of [14C] NDEA only 0.4% was excreted unchanged in the urine. Pretreatment with AC-DDTC and GS-DDTC caused a 10 to 20 fold increase in the amount of NDEA excreted in the urine. The occurrence of DNA single strand breaks in rat liver cells induced by NDEA was completely neutralized by the pretreatment with AC-DDTC.

Simultaneous structure-activity determination of disulfiram photolysis products by on-line continuous-flow liquid secondary ion mass spectrometry and enzyme inhibition assay

Disulfiram (DSF) is used in the treatment of recovering alcoholics and exerts its effect by inhibiting the enzyme aldehyde dehydrogenase (ALDH). We analyzed a mixture of products derived photochemically from DSF with on-line microbore HPLC-continuous-flow liquid secondary ion mass spectrometry (HPLC-CF-LSI-MS). By utilizing the post-HPLC column split of solvent flow, a small proportion (ca. 5%) was sent directly into the mass spectrometer, and the remainder was collected. Simultaneous MS analysis and enzyme inhibition studies on ALDH were then possible. Furthermore, using HPLC-CF-LSI-MS-MS, we were able to structurally characterize an interesting sulfine compound that inhibited ALDH.

Antioxidant action of sodium diethyldithiocarbamate: reaction with hydrogen peroxide and superoxide radical

The oxidation of sodium diethyldithiocarbamate (DDC) by hydrogen peroxide or superoxide radicals has been investigated. Hydrogen peroxide oxidizes DDC, leading to the formation of a hydrated form of disulfiram, a dimer of DDC having a disulfide group. In equimolar conditions, the overall process appears as a first-order reaction (k = 0.025 +/- 0.005 s-1), the first step being a second-order reaction (k = 5.0 +/- 0.1 mol-1.1.s-1). No radical intermediate was observed in this process. In the presence of an excess of any of the reagents, the hydrated form of disulfiram transforms into different products corresponding to the fixation of oxygen by sulfur atoms or replacement of C = S group by ketone function, in the presence of an excess of hydrogen peroxide. Superoxide anions (produced by steady-state 60Co gamma-radiolysis) oxidize DDC, yielding similar products to those obtained with hydrogen peroxide with a maximum oxidation G-value of 0.3 mumol.J-1. The rate constant k(O2.- + DDC) is equal to 900 mol-1.1.s-1.

Identification of novel glutathione conjugates of disulfiram and diethyldithiocarbamate in rat bile by liquid chromatography-tandem mass spectrometry. Evidence for metabolic activation of disulfiram in vivo

Recent studies have shown that the inhibitory effects of disulfiram and diethyldithiocarbamate (DDTC) (to which disulfiram is rapidly reduced in vivo) on the liver mitochondrial low-Km form of aldehyde dehydrogenase (ALDH) may be mediated by a reactive metabolite(s) of these compounds. In order to investigate the nature of such electrophilic intermediates in vivo, the present study was carried out with the goal of detecting and identifying their respective glutathione (GSH) conjugates in the bile of rats dosed ip with either disulfiram (75 mg kg-1) or sodium DDTC (114 mg kg-1). By means of highly selective screening strategies based on coupled liquid chromatography-tandem mass spectrometry techniques, one major and four minor GSH adducts were identified as common biliary metabolites of disulfiram and DDTC. The major conjugate, whose excretion into bile over 4 h accounted for ca. 1% of the dose of either precursor, was identified as S-(N,N-diethylcarbamoyl)glutathione (SDEG). In vitro experiments with synthetic SDEG demonstrated that this carbamate thioester derivative is chemically stable in aqueous media under physiological conditions and does not carbamoylate nucleophiles such as cysteine. Consistent with these findings, SDEG failed to inhibit yeast ALDH in vitro. The minor GSH conjugates in bile were identified as S-(N,N-diethylthiocarbamoyl)glutathione, S-(N-ethyl-carbamoyl)glutathione, S-(N-ethylthiocarbamoyl)glutathione, and S-[N-(carboxymethyl)-N- ethylcarbamoyl]glutathione, the structures of which indicate that metabolic oxidation takes place at the thiono sulfur group and at each of the carbon atoms of disulfiram and DDTC.(ABSTRACT TRUNCATED AT 250 WORDS)