Novel approach to supercritical fluid chromatography-mass spectrometry analysis of metal ions using EDTA complexation

BACKGROUND

Reliable methods enabling detection of metal ions, and especially heavy metals, in different matrices are necessary in various fields such as ecology, pharmaceuticals and toxicology. As some of the currently used methods suffer from spectral and chemical interferences, this study investigates the applicability of SFC-MS/MS for the determination of metal ions.

RESULTS

Effective novel approaches for metal ion analysis using CO2-based mobile phase were developed using three ligands forming metal complexes. As metal-EDTA complexes are prepared by simple addition of EDTA to the solution containing metal ions, this approach to metal ion analysis does not require laborious synthesis and isolation of solid metal-complexes. Besides, two other approaches using diethyldithiocarbamate and acetylacetonate as ligands were compared. Metal complexes of Cu, Co, Cr, Fe, Al, Mn, and Zn with all 3 ligands were synthesized and their identity was confirmed by high-resolution mass spectrometry (HRMS). The suitability of the three developed UHPSFC-MS/MS methods was examined using the determination of calibration range and repeatability of injections. Moreover, the universality of the developed UHPSFC-MS/MS method for the determination of metal-EDTA complexes was proved by analyzing Ni, Bi and Pb as additional metal ions.

SIGNIFICANCE AND NOVELTY

This study demonstrates the extended range of applicability for SFC based separations. For the first time, the possibility to analyze metal complexes with EDTA using a fast and reliable ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS) method is reported. The three developed UHPSFC-MS/MS methods are able to separate DDC, acac, and EDTA complexes of various metals very efficiently (total cycle times of 5, 2, and 3 min, respectively). They offer a fast and green alternative to chromatographic methods commonly used for metal ion analysis.

In vitro and in vivo evaluation of diethyldithiocarbamate with copper ions and its liposomal formulation for the treatment of Staphylococcus aureus and Staphylococcus epidermidis biofilms

Surgical site infections (SSIs) are mainly caused by Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis) biofilms. Biofilms are aggregates of bacteria embedded in a self-produced matrix that offers protection against antibiotics and promotes the spread of antibiotic-resistance in bacteria. Consequently, antibiotic treatment frequently fails, resulting in the need for alternative therapies. The present study describes the in vitro efficacy of the Cu(DDC)₂ complex (2:1 M ratio of diethyldithiocarbamate (DDC^-) and Cu²⁺) with additional Cu²⁺ against S. aureus and S. epidermidis biofilms in models mimicking SSIs and in vitro antibacterial activity of a liposomal Cu(DDC)₂ + Cu²⁺ formulation. The in vitro activity on S. aureus and S. epidermidis biofilms grown on two hernia mesh materials and in a wound model was determined by colony forming unit (CFU) counting. Cu²⁺-liposomes and Cu(DDC)₂-liposomes were prepared, and their antibacterial activity was assessed in vitro using the alamarBlue assay and CFU counting and in vivo using a Galleria mellonella infection model. The combination of 35 μM DDC^- and 128 μM Cu²⁺ inhibited S. aureus and S. epidermidis biofilms on meshes and in a wound infection model. Cu(DDC)₂-liposomes + free Cu²⁺ displayed similar antibiofilm activity to free Cu(DDC)₂ + Cu²⁺, and significantly increased the survival of S. epidermidis-infected larvae. Whilst Cu(DDC)₂ + Cu²⁺ showed substantial antibiofilm activity in vitro against clinically relevant biofilms, its application in mammalian in vivo models is limited by solubility. The liposomal Cu(DDC)₂ + Cu²⁺ formulation showed antibiofilm activity in vitro and antibacterial activity and low toxicity in G. mellonella, making it a suitable water-soluble formulation for future application on infected wounds in animal trials.

Preparation and anticancer actions of CuET-nanoparticles dispersed by bovine serum albumin

Diethyldithiocarbamate-copper complex (CuET) shows promising anticancer effect; nonetheless, preclinical evaluations of CuET are hindered due to poor solubility. We prepared bovine serum albumin (BSA)-dispersed CuET nanoparticles (CuET-NPs) to overcome the shortcoming. Results from a cell-free redox system demonstrated that CuET-NPs reacted with glutathione, leading to form hydroxyl radical. Glutathione-mediated production of hydroxyl radicals may help explain why CuET selectively kills drug-resistant cancer cells with higher levels of glutathione. CuET-NPs dispersed by autoxidation products of green tea epigallocatechin gallate (EGCG) also reacted with glutathione; however, the autoxidation products eradicated hydroxyl radicals; consequently, such CuET-NPs exhibited largely compromised cytotoxicity, suggesting that hydroxyl radical is a crucial mediator of CuET anticancer activity. In cancer cells, BSA-dispersed CuET-NPs exhibited cytotoxic activities equivalent to CuET and induced protein poly-ubiquitination. Moreover, the reported powerful inhibition of CuET on colony formation and migration of cancer cells could be replicated by CuET-NPs. These similarities demonstrate BSA-dispersed CuET-NPs is identical to CuET. Thus, we advanced to pilot toxicological and pharmacological evaluations. CuET-NPs caused hematologic toxicities in mice and induced protein poly-ubiquitination and apoptosis of cancer cells inoculated in mice at a defined pharmacological dose. Given high interest in CuET and its poor solubility, BSA-dispersed CuET-NPs pave the way for preclinical evaluations.

[Intervention effects of drugs on GSH and SOD enzyme activity of rats kidney acutely poisoned by nickel carbonyl]

Objective: To evaluate the intervention effect of various drugs on glutathione (GSH) and superoxide dismutase (SOD) enzyme activity of rats kidney with acute nickel carbonyl poisoning. Methods: In January 2019, The 250 SPF male SD rats were randomly divided into normal control group (n=10) , poisoned group (n=40) and treatment groups (n=200) according to the random number table method. And the treatment groups were divided into methylprednisolone group (20 mg/kg) , DDC group (100 mg/kg) , sodium selenite group (10 μmol/kg) , Shenfu huiyang decoction group (0.25 ml) and methylprednisolone combined with DDC group (100 mg/kg) , with 40 mice in each group. Except for the normal control group, rats in the other groups were exposed to nickel carbonyl for 30 min, at 4 h and 30 h after exposure, the rats in each treatment group were intraperitoneally injected with corresponding drugs, and kidney tissues were collected 3 d and 7 d after administration, with 10 mice in each group. The activities of GSH and SOD in kidney were measured by enzyme-linked immunosorbent assay, and using electron microscopy observe ultrastructure changes. Results: Compared to the control group, the activities of GSH and SOD enzyme of poisoned group were significantly decreased at 3 d or 7 d after 4 h or 30 h exposure, and the difference was statistically significant (P=0.000, 0.031, 0.001, 0.033) , the epithelial nuclei of proximal convoluted tubules were pyknosis and lysosome hyperplasia in the cytoplasm. And compared to poisoned group, the activities of GSH and SOD enzyme of methylprednisolone+DDC group were significantly increased at treatment with 7 d after 4 h exposure, the difference was statistically significant (P=0.022, 0.000) , and the activities of GSH and SOD enzyme of methylprednisolone and enzyme of methylprednisolone+DDC group were significantly higher at 7 days than at 3 days, the difference was statistically significant (P=0.020, 0.017, 0.018, 0.033) . The results of electron microscopy showed that the cell nuclei and cytoplasmic organelles of proximal convolute tubule were almost restored to normal tissue level of both methylprednisolone group and methylprednisolone+DDC group. Conclusion: The methylprednisolone and methylprednisolone+DDC have obvious repair effect on renal enzyme activity level of rats with acute nickel carbonyl poisoning, and the treatment effect is better for a long time of medication.

Carbonaceous material prepared by pyrolysis of refinery oily sludge for removal of flotation collectors in wastewater

The carbonaceous material (CM) prepared by refinery oily sludge was proposed to remove flotation collectors, butyl xanthate (BX), and diethyldithiocarbamate (DDTC) in synthetic wastewater. The effects of the CM on removal efficiency, adsorption kinetics, and isotherms were experimentally carried out. The surface structure and composition of CM were characterized by BET isotherm, XRD, and SEM-EDS, and the concentration of BX and DDTC was tested by UV-VIS spectrometer. The adsorption behavior and removal mechanism were investigated by zeta potential, ToF-SIMS, FTIR, etc. The removal efficiencies of BX and DDTC were both more than 99%, and the maximum adsorption capacity peaked when the pH of the solution was neutral. The two collectors were heterogeneous adsorption on the surface of CM. BX, DDTC, and related metal compounds were found on the surface of carbonaceous material, confirming the existence of both physical and chemical adsorption, and physical adsorption accounted for the main mechanism. It is proved that BX and DDTC can be removed by carbonaceous material and realize the high-effective utilization of refinery oily sludge.

The repositioned drugs disulfiram/diethyldithiocarbamate combined to benznidazole: Searching for Chagas disease selective therapy, preventing toxicity and drug resistance

Chagas disease (CD) affects at least 6 million people in 21 South American countries besides several thousand in other nations all over the world. It is estimated that at least 14,000 people die every year of CD. Since vaccines are not available, chemotherapy remains of pivotal relevance. About 30% of the treated patients cannot complete the therapy because of severe adverse reactions. Thus, the search for novel drugs is required. Here we tested the benznidazole (BZ) combination with the repositioned drug disulfiram (DSF) and its derivative diethyldithiocarbamate (DETC) upon Trypanosoma cruzi in vitro and in vivo. DETC-BZ combination was synergistic diminishing epimastigote proliferation and enhancing selective indexes up to over 10-fold. DETC was effective upon amastigotes of the BZ- partially resistant Y and the BZ-resistant Colombiana strains. The combination reduced proliferation even using low concentrations (e.g., 2.5 µM). Scanning electron microscopy revealed membrane discontinuities and cell body volume reduction. Transmission electron microscopy revealed remarkable enlargement of endoplasmic reticulum cisternae besides, dilated mitochondria with decreased electron density and disorganized kinetoplast DNA. At advanced stages, the cytoplasm vacuolation apparently impaired compartmentation. The fluorescent probe H2-DCFDA indicates the increased production of reactive oxygen species associated with enhanced lipid peroxidation in parasites incubated with DETC. The biochemical measurement indicates the downmodulation of thiol expression. DETC inhibited superoxide dismutase activity on parasites was more pronounced than in infected mice. In order to approach the DETC effects on intracellular infection, peritoneal macrophages were infected with Colombiana trypomastigotes. DETC addition diminished parasite numbers and the DETC-BZ combination was effective, despite the low concentrations used. In the murine infection, the combination significantly enhanced animal survival, decreasing parasitemia over BZ. Histopathology revealed that low doses of BZ-treated animals presented myocardial amastigote, not observed in combination-treated animals. The picrosirius collagen staining showed reduced myocardial fibrosis. Aminotransferase de aspartate, Aminotransferase de alanine, Creatine kinase, and urea plasma levels demonstrated that the combination was non-toxic. As DSF and DETC can reduce the toxicity of other drugs and resistance phenotypes, such a combination may be safe and effective.

Disulfiram oxy-derivatives induce entosis or paraptosis-like death in breast cancer MCF-7 cells depending on the duration of treatment

BACKGROUND

Dithiocarbamates and derivatives (including disulfiram, DSF) are currently investigated as antineoplastic agents. We have revealed earlier the ability of hydroxocobalamin (vitamin В_12b) combined with diethyldithiocarbamate (DDC) to catalyze the formation of highly cytotoxic oxidized derivatives of DSF (DSFoxy, sulfones and sulfoxides).

METHODS

Electron and fluorescent confocal microscopy, molecular biology and conventional biochemical techniques were used to study the morphological and functional responses of MCF-7 human breast cancer cells to treatment with DDC and B_12b alone or in combination.

RESULTS

DDC induces unfolded protein response in MCF-7 cells. The combined use of DDC and B_12b causes MCF-7 cell death. Electron microscopy revealed the separation of ER and nuclear membranes, leading to the formation of both cytoplasmic and perinuclear vacuoles, with many fibers inside. The process of vacuolization coincided with the appearance of ER stress markers, a marked damage to mitochondria, a significant inhibition of 20S proteasome, and actin depolimerization at later stages. Specific inhibitors of apoptosis, necroptosis, autophagy, and ferroptosis did not prevent cell death. A short- time (6-h) exposure to DSFoxy caused a significant increase in the number of entotic cells.

CONCLUSIONS

These observations indicate that MCF-7 cells treated with a mixture of DDC and B_12b die by the mechanism of paraptosis. A short- time exposure to DSFoxy caused, along with paraptosis, a significant activation of the entosis and its final stage, lysosomal cell death.

GENERAL SIGNIFICANCE

The results obtained open up opportunities for the development of new approaches to induce non-apoptotic death of cancer cells by dithiocarbamates.

Molecular diagnostic of toxigenic Corynebacterium diphtheriae strain by DNA sensor potentially suitable for electrochemical point-of-care diagnostic

The presented study is focused on the development of electrochemical genosensor for detection of tox gene fragment of toxigenic Corynebacterium diphtheriae strain. Together with our previous studies it fulfils the whole procedure for fast and accurate diagnostic of diphtheria at its early stage of infection with the use of electrochemical methods. The developed DNA sensor potentially can be used in more sophisticated portable device. After the electrochemical stem-loop probe structure optimization the conditions for real asymmetric PCR (aPCR) product detection were selected. As was shown it was crucial to optimize the magnesium and organic solvent concentrations in detection buffer. Under optimal conditions it was possible to selectively detect as low as 20.8 nM of complementary stand in 5 min or 0.5 nM in 30 min with sensitivity of 12.81 and 0.24 1⋅μM^-1 respectively. The unspecific biosensor response was elucidated with the use of new electrode blocking agent, diethyldithiocarbamate. Its application in electrochemical genosensors lead to significant higher current values and the biosensor response even in conditions with magnesium ion depletion. The developed biosensor selectivity was examined using samples containing genetic material originated from a number of non-target bacterial species which potentially can be present in the human upper respiratory tract.

Co-encapsulation of sodium diethyldithiocarbamate (DETC) and zinc phthalocyanine (ZnPc) in liposomes promotes increases phototoxic activity against (MDA-MB 231) human breast cancer cells

There has been considerable interest in the development of novel photosensitisers for photodynamic therapy (PDT). The use of liposomes as drug delivery systems containing simultaneously two or more drugs is an attractive idea to create a new platform for PDT application. Therefore, the aim of this study was to evaluate the synergistic effect of diethyldithiocarbamate (DETC) and zinc phthalocyanine (PDT) co-encapsulated in liposomes. The reverse-phase evaporation method resulted in the successful encapsulation of DETC and ZnPc in liposomes, with encapsulation efficiencies above 85 %, mean size of 308 nm, and zeta potential of - 36 mV. The co-encapsulation decreased the cytotoxic effects in mouse embryo fibroblast (NIH3T3) cells and inhibited damage to human erythrocytes compared to free DETC + ZnPc. In addition, both the free drugs and co-encapsulated ones promoted more pronounced phototoxic effects on human breast cancer cells (MDA-MB231) compared to treatment with ZnPc alone. This synergistic effect was determined by DETC-induced decreases in the antioxidant enzyme activity of superoxide dismutase (SOD) and glutathione (GSH).

Fast and efficient removal of Cr(VI) to ppb level together with Cr(III) sequestration in water using layered double hydroxide interclated with diethyldithiocarbamate

It is still a great challenge to find an eco-friendly, easy-to-synthesize, and cheap adsorbent to rapidly remove Cr(VI) to ppb level in the Cr(VI)-polluted water. Herein, a new layered double hydroxide nanocage intercalated with diethyldithiocarbamate (DDTC-LDH) was fabricated via a facile calcination-rehydration method. The DDTC-LDH rapidly decreased Cr(VI) concentration from 5 to <0.05 mg/L within 35 min, and only a few seconds were required to completely remove it at an initial concentration of 0.5-1 mg/L, primarily attributed to the effective adsorption-reduction of Cr(VI) to Cr(III) by sulfur atoms in CS and CS groups. Attractively, the generated Cr(III) was also quickly removed to below 0.1 mg/L via an opportune Lewis hard-hard interaction with C-SO_x groups produced through CS oxidation. Additionally, Cr(VI) could be removed by DDTC-LDH at a wide pH application range (3.17-10.78) and with weak effects by coexisting anions (Cl^-, NO₃^-, CO₃^2-, SO₄^2-, and PO₄^3-). We systematically analyzed and proposed the mechanisms for Cr(VI) removal by the DDTC-LDH, orderly containing electrostatic attraction, Cr(VI) complexation by sulfur atoms in CS and CS groups, reduction of the Cr(VI) to Cr(III) by the CS and CS groups, and Cr(III) complexation by sulfur atoms in C-SOx groups. Our results provide new insights into the Cr(VI) removal using organosulfur compounds, that is to say, the organosulfur group Lewis hardness increased (from C-S to C-SOx) as the Cr species Lewis hardness increased (from Cr(VI) to Cr(III)), so as to opportunely ensure fast and efficient capture of both Cr(VI) and Cr(III) via Lewis acid-base interactions.

Picomolar-level detection of mercury within non-biological/biological aqueous media using ultra-sensitive polyaniline-Fe3O4-silver diethyldithiocarbamate nanostructure

Mercury as the 3rd most toxic, non-biodegradable, and carcinogenic pollutant can adversely affect the ecosystem and health of living species through its bioaccumulation within the nature that can affect the top consumer in the food chain; therefore, it is vital to sense/remove Hg²⁺ within/from aqueous media using practical approaches. To address this matter, we modified the glassy carbon electrode (GCE) with ultra-sensitive, interconnected, sulfurized, and porous nanostructure consisted of polyaniline-Fe₃O₄-silver diethyldithiocarbamate (PANi-F-S) to enhance the sensitivity, selectivity, and limit of detection (LOD) of the sensor. Obtained results showed that at optimum conditions (i.e., pH value of 7, deposition potential of - 0.8 V, and accumulation time of 120 s), for Hg²⁺ concentration ranging from 0.4 to 60 nM, the modified electrode showing linear relative coefficient of 0.9983, LOD of 0.051 nM, LOQ of 0.14 nM, and sensitivity of 1618.86 μA μM^-1 cm^-2 highlights superior sensitivity of the developed platform until picomolar level. Additionally, the modified electrode showed ideal repeatability, stability, reproducibility, and selectivity (by considering Zn²⁺, Cd²⁺ Pb²⁺, Cu²⁺, Ni²⁺, and Co²⁺ as metal interferences) and recovered more than 99% of the Hg²⁺ ions within non-biological (mineral, tap, and industrial waters) and biological (blood plasma sample) fluids. Graphical abstract.

Dithiocarbamate prodrugs activated by prostate specific antigen to target prostate cancer

Disulfiram in conjunction with copper has been shown to be a potent anticancer agent. However, disulfiram's therapeutic potential in prostate cancer is hindered by off-target effects due to its reactive and nucleophilic thiol-containing component, diethyldithiocarbamate (DTC). To minimize undesirable reactivity, we have strategically blocked the thiol moiety in DTC with a cleavable p-aminobenzyl (pAB) group linked to peptide substrates recognized by prostate specific antigen (PSA). Here we report the synthesis and evaluation in cancer cell models of two PSA-activatable prodrugs: HPD (Ac-HSSKLQL-pAB-DTC and RPD (RSSYYSL-pAB-DTC). In vitro exposure to PSA was found to trigger activation of HPD and RPD to release diethyldithiocarbamate, and both prodrugs were found to induce toxicity in prostate cancer cells, with HPD showing the most promising selectivity. With copper supplementation, the IC₅₀ of HPD was 1.4 µM in PSA-expressing LNCaP cells, and 11 µM in PC3 cells that do not express PSA. These studies demonstrate the utility of using peptide recognition handles to direct the activity of dithiocarbamate prodrugs for selective cytotoxicity of cancer cells.

Resonance light scattering sensor of the metal complex nanoparticles using diethyl dithiocarbamate doped graphene quantum dots for highly Pb(II)-sensitive detection in water sample

This study was aimed to detect Pb²⁺ using diethyl dithiocarbamate-doped graphene quantum dots (DDTC-GQDs) based pyrolysis of citric acid. The excitation maximum wavelength (λ_max, ex = 337 nm) of the DDTC-GQDs solution was blue shift from bare GQDs (λ_max, ex = 365 nm), with the same emission maximum wavelength (λ_max, em = 459 nm) indicating differences in the desired N, S matrices decorating in the nanoparticles. Their resonance light scattering intensities were peaked at the same λ_max, ex/em = 551/553 nm without any background effect of both ionic strength and masking agent. Under optimal conditions, the linear range was 1.0-10.0 μg L^-1 (R² = 0.9899), limit of detection was 0.8 μg L^-1 and limit of quantification was 1.5 μg L^-1. The precision, expressed as the relative standard deviations, for intra-day and inter-day analyses was 0.87% and 4.47%, respectively. The recovery study of Pb²⁺ for real water samples was ranged between 80.8% and 109.5%. The proposed method was also proved with certified water sample containing 60 μg L^-1 Pb²⁺ giving an excellent accuracy and was then implied satisfactorily for ultra-trace determination of Pb²⁺ in drinking water and tap water samples.

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.

Diethyldithiocarbamate loaded in beeswax-copaiba oil nanoparticles obtained by solventless double emulsion technique promote promastigote death in vitro

Leishmaniasis is considered a neglected tropical disease that represents a Public Health problem due to its high incidence. In the search of new alternatives for Leishmaniasis treatment diethyldithiocarbamate (DETC) has shown an excellent leishmanicidal activity and the incorporation into drug carrier systems, such as solid lipid nanoparticles (SLNs), is very promising. In the present work DETC loaded in beeswax nanoparticles containing copaiba oil were obtained by the double emulsion/melt technique. The nanoparticles were characterized and leishmanicidal activity against L. amazonensis promastigotes forms and cytotoxicity in murine macrophages were evaluated. SLNs presented size below 200 nm, spherical morphology, negative charge surface, high encapsulation efficiency, above 80%, and excellent stability. Moreover, Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) analyses were performed to evaluate the chemical structure and possible interactions between DETC and SLNs. SLNs provided a protection for DETC, decreasing its cytotoxic effects in macrophages, which led to an improvement in the selectivity against the parasites, which almost doubled from free DETC (11.4) to DETC incorporated in SLNs (18.2). These results demonstrated that SLNs had a direct effect on L. amazonensis promastigotes without affect the viability of macrophage cell, can be a promising alternative therapy for the cutaneous treatment of L. amazonensis.

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.

Copper (II) complexes of bidentate ligands exhibit potent anti-cancer activity regardless of platinum sensitivity status

Insensitivity to platinum, either through inherent or acquired resistance, is a major clinical problem in the treatment of many solid tumors. Here, we explored the therapeutic potential of diethyldithiocarbamate (DDC), pyrithione (Pyr), plumbagin (Plum), 8-hydroxyquinoline (8-HQ), clioquinol (CQ) copper complexes in a panel of cancer cell lines that differ in their sensitivity to platins (cisplatin/carboplatin) using a high-content imaging system. Our data suggest that the copper complexes were effective against both platinum sensitive (IC50 ~ 1 μM platinum) and insensitive (IC50 > 5 μM platinum) cell lines. Furthermore, copper complexes of DDC, Pyr and 8-HQ had greater therapeutic activity compared to the copper-free ligands in all cell lines; whereas the copper-dependent activities of Plum and CQ were cell-line specific. Four of the copper complexes (Cu(DDC)2, Cu(Pyr)2, Cu(Plum)2 and Cu(8-HQ)2) showed IC50 values less than that of cisplatin in all tested cell lines. The complex copper DDC (Cu(DDC)2) was selected for in vivo evaluation due to its low nano-molar range activity in vitro and the availability of an injectable liposomal formulation. Liposomal (Cu(DDC)2) was tested in a fast-growing platinum-resistant A2780-CP ovarian xenograft model and was found to achieve a statistically significant reduction (50%; p < 0.05) in tumour size. This work supports the potential use of copper-based therapeutics to treat cancers that are insensitive to platinum drugs.

Disulfiram is a slow-binding partial noncompetitive inhibitor of 20S proteasome activity

The alcohol abuse drug disulfiram has also been shown to exhibit potent cell growth inhibitory and anticancer activity. While a number of cellular and animal studies have suggested that disulfiram exhibits its anticancer activity through interaction with the proteasome, direct evidence for inhibition of proteasome activity is lacking. In this study we show that disulfiram potently inhibits the chymotrypsin-like activity of purified human 20S proteasome at low micromolar pharmacological concentrations. The enzyme progress curves displayed characteristics of a slow-binding reaction, similar to that observed for the FDA-approved proteasomal-targeted anticancer drugs bortezomib and carfilzomib. The apparent second order rate constant for reaction with 20s proteasome that was derived from an analysis of the progress curves was about 250-fold smaller than for bortezomib and carfilzomib. The concentration dependence of the enzyme kinetics was consistent with partial noncompetitive inhibition, whereby the putative disulfiram-proteasome adduct retains, partial but decreased enzyme activity. Disulfiram, which is known to have a high affinity for protein thiols, likely reacted with a non-critical cysteine residue, and not at the proteasome substrate binding site.

A binuclear complex constituted by diethyldithiocarbamate and copper(I) functions as a proteasome activity inhibitor in pancreatic cancer cultures and xenografts

It is a therapeutic strategy for cancers including pancreatic to inhibit proteasome activity. Disulfiram (DSF) may bind copper (Cu) to form a DSF-Cu complex. DSF-Cu is capable of inducing apoptosis in cancer cells by inhibiting proteasome activity. DSF is rapidly converted to diethyldithiocarbamate (DDTC) within bodies. Copper(II) absorbed by bodies is reduced to copper(I) when it enters cells. We found that DDTC and copper(I) could form a binuclear complex which might be entitled DDTC-Cu(I), and it had been synthesized by us in the laboratory. This study is to investigate the anticancer potential of this complex on pancreatic cancer and the possible mechanism. Pancreatic cancer cell lines, SW1990, PANC-1 and BXPC-3 were used for in vitro assays. Female athymic nude mice grown SW1990 xenografts were used as animal models. Cell counting kit-8 (cck-8) assay and flow cytometry were used for analyzing apoptosis in cells. A 20S proteasome assay kit was used in proteasome activity analysis. Western blot (WB) and immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays were used in tumor sample analysis. The results suggest that DDTC-Cu(I) inhibit pancreatic cancer cell proliferation and proteasome activity in vitro and in vivo. Accumulation of ubiquitinated proteins, and increased p27 as well as decreased NF-κB expression were detected in tumor tissues of DDTC-Cu(I)-treated group. Our data indicates that DDTC-Cu(I) is an effective proteasome activity inhibitor with the potential to be explored as a drug for pancreatic cancer.