Antitumor activity of gold(III)-dithiocarbamato derivatives on prostate cancer cells and xenografts

A promising future of metal-N-heterocyclic carbene complexes in medicinal chemistry: The emerging bioorganometallic antitumor agents

Metal complexes based on N-heterocyclic carbene (NHC) ligands have emerged as promising broad-spectrum antitumor agents in bioorganometallic medicinal chemistry. In recent decades, studies on cytotoxic metal-NHC complexes have yielded numerous compounds exhibiting superior cytotoxicity compared to cisplatin. Although the molecular mechanisms of these anticancer complexes are not fully understood, some potential targets and modes of action have been identified. However, a comprehensive review of their biological mechanisms is currently absent. In general, apoptosis caused by metal-NHCs is common in tumor cells. They can cause a series of changes after entering cells, such as mitochondrial membrane potential (MMP) variation, reactive oxygen species (ROS) generation, cytochrome c (cyt c) release, endoplasmic reticulum (ER) stress, lysosome damage, and caspase activation, ultimately leading to apoptosis. Therefore, a detailed understanding of the influence of metal-NHCs on cancer cell apoptosis is crucial. In this review, we provide a comprehensive summary of recent advances in metal-NHC complexes that trigger apoptotic cell death via different apoptosis-related targets or signaling pathways, including B-cell lymphoma 2 (Bcl-2 family), p53, cyt c, ER stress, lysosome damage, thioredoxin reductase (TrxR) inhibition, and so forth. We also discuss the challenges, limitations, and future directions of metal-NHC complexes to elucidate their emerging application in medicinal chemistry.

A new gold(I) phosphine complex induces apoptosis in prostate cancer cells by increasing reactive oxygen species

Thioredoxin reductase (TrxR) is a pivotal regulator of redox homeostasis. It is frequently overexpressed in various cancer cells, including prostate cancer, making it a promising target for the development of anti-cancer drugs. In this study, we screened a series of newly designed complexes of gold(I) phosphine. Specifically, Compound 5 exhibited the highest cytotoxicity against prostate cancer cells and demonstrated stronger antitumor effects than commonly used drugs, such as cisplatin and auranofin. Importantly, our mechanistic study revealed that Compound 5 effectively inhibits the TrxR system in vitro. Additionally, Compound 5 promoted intracellular accumulation of reactive oxygen species (ROS), leading to mitochondrial dysfunction and irreversible apoptosis in prostate cancer cells. Our in vivo xenograft study further demonstrated that Compound 5 has excellent antitumor activity against prostate cancer cells, but does not cause severe side effects. These findings provide a promising lead Compound for the development of novel antitumor agents targeting prostate cancer and offer a valuable tool for investigating biological pathways involving TrxR and ROS modulation.

The Development of Organotin(IV) N-Ethyl-N-Benzyldithiocarbamate Complexes: A Study on Their Synthesis, Characterization, and Cytocidal Effects on A549 Cell Line

BACKGROUND

Organotin(IV) complexes of dithiocarbamate are vital in medicinal chemistry, exhibiting potential in targeting cancer cells due to their unique properties that enhance targeted delivery. This study aimed to synthesize and characterize organotin(IV) N-ethyl-N-benzyldithiocarbamate complexes (ONBDCs) and evaluate their cytotoxicity against A549 cells, which are commonly used as a model for human lung cancer research.

METHODS

The two ONBDC derivatives - ONBDC 1 (dimethyltin(IV) N-ethyl-N-benzyldithiocarbamate) and ONBDC 2 (triphenyltin(IV) N-ethyl-N-benzyldithiocarbamate) - were synthesized via the reaction of tin(IV) chloride with N-ethylbenzylamine in the presence of carbon disulfide. A range of analytical techniques, including elemental analysis, IR spectroscopy, NMR spectroscopy, UV-Vis spectrometry, TGA/DTA analysis, and X-ray crystallography, was conducted to characterize these compounds comprehensively. The cytotoxic effects of ONBDCs against A549 cells were evaluated using MTT assay.

RESULTS

Both compounds were synthesized and characterized successfully via elemental and spectroscopies analysis. MTT assay revealed that ONBDC 2 demonstrated remarkable cytotoxicity towards A549 cells, with an IC50 value of 0.52 μM. Additionally, ONBDC 2 displayed significantly higher cytotoxic activity against the A549 cell line when compared to the commercially available chemotherapeutic agent cisplatin (IC50: 32 μM).

CONCLUSION

Thus, it was shown that ONBDC 2 could have important anticancer properties and should be further explored as a top contender for creating improved and specialized cancer treatments.

Dinuclear gold(I) complexes based on carbene and diphosphane ligands: bis[2-(dicyclohexylphosphano)ethyl]amine complex inhibits the proteasome activity, decreases stem cell markers and spheroid viability in lung cancer cells

Three new dinuclear gold(I) complexes (1-3) containing a carbene (1,3-Bis(2,6-di-isopropylphenyl)imidazol-2-ylidene (IPr)) and diphosphane ligands [bis(1,2-diphenylphosphano)ethane (Dppe), bis(1,3-diphenylphosphano)propane (Dppp) and bis[2-(dicyclohexylphosphano)ethyl]amine (DCyPA)], were synthesized and characterized by elemental analysis and, ESI-MS, mid FT-IR and NMR spectroscopic methods. The structures of complexes 2 and 3 were determined by X-ray crystallography, which revealed that the complexes are dinuclear having gold(I) ions linearly coordinated. The anticancer activities of the complexes (1-3) were evaluated in lung (A549), breast (MC-F7), prostate (PC-3), osteosarcoma (MG-63) and ovarian (A2780 and A2780cis) cancer models. Growth inhibition by the new complexes was higher than cisplatin in all cell lines tested. The mechanism of action of complex 3 was investigated in A549 cells using 2-dimensional (2D) models and 3D-multicellular tumor spheroids. Treatment of A549 cells with complex 3 caused: the induction of apoptosis and the generation of reactive oxygen species; the cell cycle arrest in the G0/G1 phase; the inhibition of both the proteasome and the NF-kB activity; the down-regulation of lung cancer stem cell markers (NOTCH1, CD133, ALDH1 and CD44). Complex 3 was more active than cisplatin also in 3D models of A549 lung cancer cells.

Organogold(III)-dithiocarbamate compounds and their coordination analogues as anti-tumor and anti-leishmanial metallodrugs

The limited chemical stability of gold(III)-based compounds in physiological environment has been a challenge in drug discovery, and organometallic chemistry might provide the solution to overcome this issue. In this work, four novel cationic organogold(III)-dithiocarbamate complexes of general structure [(C^N)AuIIIDTC]PF6 (C1a - C4a, DTC = dithiocarbamate, L1 - L4, C^N = 2-anilinopyridine) are presented, and compared to their coordination gold(III)-dithiocarbamate analogues [AuIIIDTCCl2] (C1b - C4b), as potential anti-cancer and anti-leishmanial drugs. Most of the complexes effectively inhibited cancer cell growth, notably C3a presented anti-proliferative effect in the nanomolar range against breast cancer (MCF-7 and MDA-MB-231 cells with moderate selectivity. Pro-apoptotic studies on treated MCF-7 cells showed a high population of cells in early apoptosis. Reactivity studies of C3a towards model thiols (N-acetyl-L-cysteine) refer to a possible mode of action involving bonding between the organogold(III)-core and the thiolate. In the scope of neglected diseases, gold complexes are emerging as promising therapeutic alternatives against leishmaniasis. In this regard, all gold(III)-dithiocarbamate complexes presented anti-leishmanial activity against at least one Leishmania species. Complexes C1a, C4a, C1b, C4b were active against all tested parasites with IC50 values varying between 0.12 and 42 μM, and, overall, organometallic compounds presented more intriguing inhibition profiles. For C4a selectivity over 500-fold for L. braziliensis; even higher than the reference anti-leishmanial drug amphotericin B. Overall, our findings revealed that the organogold(III) moiety significantly amplified the anti-cancer and anti-leishmanial effects with respect to the coordination analogues; thus, showing the great potential of organometallic chemistry in metallodrug-based chemotherapy for cancer and leishmaniasis.

Organotin (IV) Dithiocarbamate Compounds as Anticancer Agents: A Review of Syntheses and Cytotoxicity Studies

Organotin (IV) dithiocarbamate has recently received attention as a therapeutic agent among organotin (IV) compounds. The individual properties of the organotin (IV) and dithiocarbamate moieties in the hybrid complex form a synergy of action that stimulates increased biological activity. Organotin (IV) components have been shown to play a crucial role in cytotoxicity. The biological effects of organotin compounds are believed to be influenced by the number of Sn-C bonds and the number and nature of alkyl or aryl substituents within the organotin structure. Ligands target and react with molecules while preventing unwanted changes in the biomolecules. Organotin (IV) dithiocarbamate compounds have also been shown to have a broad range of cellular, biochemical, and molecular effects, with their toxicity largely determined by their structure. Continuing the investigation of the cytotoxicity of organotin (IV) dithiocarbamates, this mini-review delves into the appropriate method for synthesis and discusses the elemental and spectroscopic analyses and potential cytotoxic effects of these compounds from articles published since 2010.

Sulfonamide-Derived Dithiocarbamate Gold(I) Complexes Induce the Apoptosis of Colon Cancer Cells by the Activation of Caspase 3 and Redox Imbalance

Two new families of dithiocarbamate gold(I) complexes derived from benzenesulfonamide with phosphine or carbene as ancillary ligands have been synthesized and characterized. In the screening of their in vitro activity on human colon carcinoma cells (Caco-2), we found that the more lipophilic complexes—those with the phosphine PPh₃—exhibited the highest anticancer activity whilst also displaying significant cancer cell selectivity. [Au(S₂CNHSO₂C₆H₅)(PPh₃)] (1) and [Au(S₂CNHSO₂-p-Me-C₆H₄)(IMePropargyl)] (8) produce cell death, probably by intrinsic apoptosis (mitochondrial membrane potential modification) and caspase 3 activation, causing cell cycle arrest in the G1 phase with p53 activation. Besides this, both complexes might act as multi-target anticancer drugs, as they inhibit the activity of the enzymes thioredoxin reductase (TrxR) and carbonic anhydrase (CA IX) with the alteration of the redox balance, and show a pro-oxidant effect.

Synthesis of carbon-11 radiolabelled transition metal complexes using 11C-dithiocarbamates

A novel radiolabelling method exploiting ¹¹C-dithiocarbamate ligands has been used to generate ¹¹C-labelled Au(I), Au(III), Pd(II) and Pt(II) complexes in high radiochemical yields (71-99%). Labelled complexes were prepared in a rapid one-pot procedure via the substitution reaction of ¹¹C-dithiocarbamate ligands with appropriate transition metal chloride precursors.

In Vitro Cytotoxicity and Apoptosis Inducing Evaluation of Novel Halogenated Isatin Derivatives

BACKGROUND

Isatin (1H-indole-2,3-dione) and its derivatives have been shown their responsibility in a wide range of biological activities. Among the range of beneficial properties, anticancer compounds were the most extensively highlighted and explored.

OBJECTIVE

Herein, we report the targeting effect of halogenated isatin derivatives on cancer cell mitochondria and their antiproliferative mechanism.

METHOD

A series of novel 5-halo-Isatin derivatives consisting 5-Amino-1,3,4-thiadiazole-2-thiol scaffold were synthesized and easily conducted in good yields through a condensation reaction between keto groups of Isatin and primary amine under alcoholic conditions, followed by S-benzylation. The compounds were fully characterized using spectroscopic methods such as 1H-NMR, FTIR, mass spectroscopy and then tested in vitro towards three cancer cell lines HT-29 (colon cancer), MCF-7 (breast cancer) and SKNMC (neuroblastoma). Apoptosis induction was investigated through assessment of caspase 3 and mitochondrial membrane potential.

RESULTS

The most potent compounds of 5b, 5r (IC50 = 18,13 µM) and 5n (IC50 = 20,17 µM) were found to show strong anticancer activity, especially for MCF7 cells. Further anticancer mechanism studies indicated that 5b and 5r induced apoptosis through the intrinsic mitochondrial pathway.

CONCLUSION

This research demonstrated that 5b and 5r have an anticancer property via the modulation of oxidative stress-mediated mitochondrial apoptosis and immune response, which deserves further studies on their clinical applications.

Quantum Chemical Investigations on the Hydrolysis of Gold(III)-Based Anticancer Drugs and Their Interaction with Amino Acid Residues

A comprehensive hydrolysis mechanism of the promising class of Au(III) anticancer drugs [Au(DMDT)Cl₂] (DMDT = N,N-dimethyldithiocarbamate) (R) and [Au(damp)Cl₂] (damp = 2-[(dimethylamino)methyl]phenyl) (R') was done by means of density functional theory (DFT) in combination with the CPCM solvation model to explore the solution behavior and stability under physiological conditions. The activation free energies (ΔG) for the second hydrolysis, R (13.7 kcal/mol) and R' (10.0 kcal/mol) are found to be relatively lower in comparison to the first hydrolysis, and their rate constant values are computed to be 5.62 × 10² and 2.90 × 10⁵ s^-1, respectively. Besides these, the interaction mechanisms of aquated R and R' with the potential protein-binding sites cysteine (Cys) and selenocysteine (Sec) were also investigated in detail. The kinetic study and activation Gibbs free energy profiles reveal that the aquated complexes of R and R' bind more effectively to the Se site of Sec than to the S site of Cys. Intra- and intermolecular hydrogen bonding play a pivotal role in stabilizing the intermediates and transition states involved in the ligand substitution reactions of R and R'. Natural population analysis (NPA) was done to determine the charge distributions on important atoms during the hydrolysis and ligand substitution reactions.

Gold Compounds and the Anticancer Immune Response

Gold compounds are not only well-explored for cytotoxic effects on tumors, but are also known to interact with the cancer immune system. The immune system deploys innate and adaptive mechanisms to protect against pathogens and prevent malignant transformation. The combined action of gold compounds with the activated immune system has shown promising results in cancer therapy through in vivo and in vitro experiments. Gold compounds are known to induce innate immune responses; however, these responses may contribute to adaptive immune responses. Gold compounds play the role of a major hapten that acts synergistically in innate immunity. Gold compounds support cancer cell antigenicity and promote anti-tumor immune response by inducing the release of CRT, ATP, HMGB1, HSP, and NKG2D to enhance immunogenicity. Gold compounds affect various immune cells (including suppressor regulatory T cells), inhibit myeloid derived suppressor cells, and enhance the function and number of dendritic cells. Gold nanoparticles (AuNPs) have potential for improving the effect of immunotherapy and reducing the toxicity and side effects of the treatment process. Thus, AuNPs provide an ideal opportunity for exploring the combination of anticancer gold compounds and immunotherapeutic interventions.

Osmium Arene Germyl, Stannyl, Germanate, and Stannate Complexes as Anticancer Agents

Herein, we describe the synthesis, full spectroscopic characterization, DFT (density functional theory) calculations, and single-crystal X-ray diffraction analyses of a series of osmium arene σ-germyl, germanate, σ-stannyl, and stannate complexes, along with their cytotoxic (anticancer) investigations. The known dimer complexes [OsCl2(η6-C6H6)]2 (1) and [OsCl2(η6-p-cymene)]2 (2) were reacted with PPh3 to form the known mononuclear complex [OsCl2(η6-p-cymene)(PPh3)] (3) and the new complex [OsCl2(η6-C6H6)(PPh3)] (6); complex 3 was reacted with GeCl2·(dioxane) and SnCl2 to afford, by insertion into the Os-Cl bond, the neutral σ-germyl and stannyl complexes [OsCl(η6-p-cymene)(PPh3)(GeCl3)] (7) and [OsCl(η6-p-cymene)(PPh3)(SnCl3)] (11), respectively, as a mixture of enantiomers. Similarly, the reaction of complex 6 with GeCl2·(dioxane) afforded [OsCl(η6-C6H6)(PPh3)(GeCl3)] (9). Complex 2, upon reaction with 1,1-bis(diphenylphosphino)methane (dppm), formed a mixture of [OsCl2(η6-p-cymene)(κ1-dppm)] (4) and [Os(η6-p-cymene)(κ2-dppm)Cl]+Cl- (5) when prepared in acetonitrile and a mixture of 4 and the dinuclear complex [[OsCl2(η6-p-cymene)]2(μ-dppm)] (0) when prepared in dichloromethane. By utilizing either isolated 4 or a mixture of 4 and 5, the synthesis of κ2-dppm germanate and stannate salts, [OsCl(η6-p-cymene)(κ2-dppm)]+GeCl3 - (8) and [OsCl(η6-p-cymene)(κ2-dppm)]+SnCl3 - (10), were accomplished via halide-abstracting reactions with GeCl2·(dioxane) or SnCl2, respectively. All resulting complexes were characterized by means of multinuclear NMR, FT-IR, ESI-MS, and UV/Vis spectroscopy. X-ray diffraction analyses of 4, 8, 9, 10, and 11 were performed and are reported. DFT studies (B3LYP, basis set LANL2DZ for Os, and def2-TZVPP for Sn, Ge, Cl, P, C, and H) were performed on complex 9 and the benzene analogue of complex 11, 11-benzene, to evaluate the structural changes and the effects on the frontier molecular orbitals arising from the substitution of Ge for Sn. Finally, complexes 3 and 7-11 were investigated for potential anticancer activities considering cell cytotoxicity and apoptosis assays against Dalton's lymphoma (DL) and Ehrlich ascites carcinoma (EAC) malignant cancer cell lines. The complexes were also tested against healthy peripheral blood mononuclear cells (PBMCs). All cell lines were also treated with the reference drug cisplatin to draw a comparison with the results obtained from the reported complexes. The study was further corroborated with in silico molecular interaction simulations and a pharmacokinetic study.

Anticancer Activity and Apoptosis Induction of Gold(III) Complexes Containing 2,2'-Bipyridine-3,3'-dicarboxylic Acid and Dithiocarbamates

Three novel gold(III) complexes (1–3) of general composition [Au(Bipydc)(S₂CNR₂)]Cl₂ (Bipydc = 2,2′-bipyridine-3,3′-dicarboxylic acid and R = methyl for dimethyldithiocarbamate (DMDTC), ethyl for diethyldithiocarbamate (DEDTC), and benzyl for dibenzyldithiocarbamate (DBDTC)) have been synthesized and characterized by elemental analysis, FTIR and NMR spectroscopic techniques. The spectral results confirmed the presence of both the Bipydc and dithiocarbamate ligands in the complexes. The in vitro cytotoxic studies demonstrated that compounds 1–3 were highly cytotoxic to A549, HeLa, MDA-231, and MCF-7 cancer cells with activities much higher (about 25-fold) than cisplatin. In order to know the possible mode of cell death complex 2, [Au(Bipydc)(DEDTC)]Cl₂ was further tested for induction of apoptosis towards the MCF-7 cells. The results indicated that complex 2 induces cell death through apoptosis.

Helenalin Facilitates Reactive Oxygen Species-Mediated Apoptosis and Cell Cycle Arrest by Targeting Thioredoxin Reductase-1 in Human Prostate Cancer Cells

Background

Helenalin is a pseudoguaianolide natural product with anti-cancer activities. This study investigated the underlying mechanism of the anti-prostate cancer effects of helenalin in vitro.

Material/Methods

CCK-8 assay was performed to detect the optimal concentrations of helenalin in DU145 and PC-3 cells. After exposure to helenalin and/or reactive oxygen species (ROS) inhibitor, ROS production was assessed by DCFH-DA staining. Thioredoxin reductase-1 (TrxR1) expression was detected by RT-qPCR and western blot. Moreover, apoptosis and cell cycle were evaluated by flow cytometry. Following TrxR1 knockdown or overexpression, TrxR1 expression, ROS generation, apoptosis, cell cycle, migration, and invasion were examined in cells co-treated with helenalin.

Results

Helenalin distinctly repressed the viability of prostate cancer cells in a concentration-dependent manner. We chose 8 μM and 4 μM as the optimal concentrations of helenalin for DU145 and PC-3 cells, respectively. Helenalin treatment markedly triggered ROS production and lowered TrxR1 expression, which was ameliorated by ROS inhibitor. Exposure to helenalin facilitated apoptosis as well as G0/G1 cell cycle arrest, which was reversed by ROS inhibitor. Helenalin relieved the inhibitory effect of TrxR1 on ROS production. Furthermore, helenalin ameliorated the decrease in apoptosis rate and the shortening of G0/G1 phase as well as the increase in migration and invasion induced by TrxR1 overexpression.

Conclusions

Our findings revealed that helenalin accelerated ROS-mediated apoptosis and cell cycle arrest via targeting TrxR1 in human prostate cancer cells.

Ligand substituent effect on the cytotoxicity activity of two new copper(ii) complexes bearing 8-hydroxyquinoline derivatives: validated by MTT assay and apoptosis in MCF-7 cancer cell line (human breast cancer)

In this study, we have examined the effect of ligand substituent on the structure-cytotoxicity relationships of the MCF-7 cancer cell line (human breast cancer), by two copper(ii) complexes {[Cu(qmbn)(Hqmba)(q)]·NO3·2H2O} (1) and {[Cu(Hqmba)2(q)]·NO3·2H2O} (2) (where, qmbn = 2-(quinolin-8-yloxy)(methyl) benzonitrile (L1); Hqmba = 2-((quinolin-8-yloxy)methyl)benzoic acid (L2) and q = quinolin-8-olate). The structural analysis reveals that both the complexes exhibit distorted octahedral (CuN3O3) configuration which is further corroborated by density functional theory (DFT) calculations. The cytotoxicity impact of ligands (L1 and L2) and complexes (1 and 2) was screened against the MCF-7 cell line (human breast cancer). The MTT assay uptake indicated that the presence of -COOH functionality in complex 2 leads to higher cytotoxicity (lower IC50) than that observed for complex 1 containing a -CN group. This could be due to the strong H-bonding forming propensity of the carboxylic acids. Incubation of MCF-7 cancer cells with IC50 concentrations of 1 and 2 promoted cellular detachments via nuclear condensation and membrane destabilization followed by apoptosis as a result of metal-assisted generation of reactive oxygen species. Flow cytometry analysis showed that 1 and 2 might prompt early apoptosis in MCF-7 cells as the maximum percentage of cells appeared in the LR quadrant. Furthermore, mRNA expression analysis confirmed that both the complexes induced apoptosis in MCF-7 cells. Comparative mRNA expression analysis of complexes with their respective ligands also confirmed the enhanced apoptotic behavior of complexes. Furthermore, molecular docking studies of the complexes have also been performed with the active site of EGFR kinase receptors (major target for any cancer causing agent) due to similar analogues with FDA-approved EGFR inhibitors in order to rationalize its promising cytotoxicity activity.

A bismuth diethyldithiocarbamate compound induced apoptosis via mitochondria-dependent pathway and suppressed invasion in MCF-7 breast cancer cells

Interest in bismuth(III) dithiocarbamate complexes as potential drug candidates is increasing due to their low toxicity compared to other group 15 elements (pnictogen) of the periodic table. Bismuth dithiocarbamate compounds have been reported to induce greater cytotoxicity in various human carcinoma cancer cell lines. Using various in vitro cancer-related assays, we investigated the antiproliferative activity of bismuth diethyldithiocarbamate, denoted as 1, against the MCF-7 human breast adenocarcinoma cell line and the effect on genes that may be involved in antiproliferation, apoptosis, DNA fragmentation, invasion and polyubiquitination functions. In general, 1 exhibited high cytotoxicity in MCF-7 cells, with an IC₅₀ of 1.26 ± 0.02 µM, by inducing the intrinsic apoptotic pathway, as ascertained by measurements of intracellular reactive oxygen species (ROS), caspase activity, the amount of cytochrome c released and the extent of DNA fragmentation and by staining assays that reveal apoptotic cells. In addition, 1 significantly attenuated cell invasion and modulated several cancer-related genes, including PLK2, FIGF, FLT4, PARP4, and HDAC11, as determined via gene expression analysis. The NF-κB signaling pathway was inhibited by 1 upon the activation of Lys48- and Lys63-linked polyubiquitination, thus leading to its degradation via the proteasome. Overall, 1 has the potential to act as an antiproliferative agent and a proteasome inhibitor in estrogen-positive breast cancer.

Reactions of Medicinal Gold(III) Compounds With Proteins and Peptides Explored by Electrospray Ionization Mass Spectrometry and Complementary Biophysical Methods

Electrospray ionization mass spectrometry (ESI MS) is a powerful investigative tool to analyze the reactions of metallodrugs with proteins and peptides and characterize the resulting adducts. Here, we have applied this type of approach to four experimental anticancer gold(III) compounds for which extensive biological and mechanistic data had previously been gathered, namely, Auoxo6, Au₂phen, AuL12, and Aubipyc. These gold(III) compounds were reacted with two representative proteins, i.e., human serum albumin (HSA) and human carbonic anhydrase I (hCA I), and with the C-terminal dodecapeptide of thioredoxin reductase. ESI MS analysis allowed us to elucidate the nature of the resulting metal-protein adducts from which the main features of the occurring metallodrug-protein reactions can be inferred. In selected cases, MS data were integrated and supported by independent ¹HNMR and UV-Vis absorption measurements to gain an overall description of the occurring processes. From data analysis, it emerges that most of the investigated gold(III) complexes, endowed with an appreciable oxidizing character, undergo quite facile reduction to gold(I); the resulting gold(I) species tightly associate with the above proteins/peptides with a remarkable selectivity for free cysteine residues. In contrast, in the case of the less-oxidizing Aubipyc complex, the gold(III) oxidation state is conserved, and a gold(III) fragment still containing the original ligand is found to be associated with the target proteins. It is notable that the C-terminal dodecapeptide of thioredoxin reductase containing the characteristic -Gly-Cys-Sec-Gly metal-binding motif is able in all cases to trigger gold(III)-to-gold(I) reduction. Our investigation allowed us to identify in detail the nature of the gold fragments that ultimately bind the protein targets and determine the exact binding stoichiometry; some insight on the reaction kinetics was also gained. Notably, a few clear correlations could be established between the structure of the metal complexes and the nature of the resulting protein adducts. The mechanistic implications of these findings are analyzed and thoroughly discussed. Overall, the present results set the stage to better understand the real target biomolecules of these gold compounds and elucidate at the atomic level their interaction modes with proteins and peptides.

Regium-π Bonds Are Involved in Protein-Gold Binding

The regium-π interaction is an attractive noncovalent force between group 11 elements (Cu, Ag, and Au) acting as Lewis acids and aromatic surfaces. Herein, we report for the first time experimental (Protein Data Bank analysis) and theoretical (RI-MP2/def2-TZVP level of theory) evidence of regium-π bonds involving Au(I) and aromatic amino acids (Phe, Tyr, Trp, and His). These findings might be important in the field of drug design and for retrospectively understanding the role of gold in proteins.

Cancer cell-selective modulation of mitochondrial respiration and metabolism by potent organogold(iii) dithiocarbamates

Metabolic reprogramming is a key cancer hallmark that has led to the therapeutic targeting of glycolysis. However, agents that target dysfunctional mitochondrial respiration for targeted therapy remains underexplored. We report the synthesis and characterization of ten (10) novel, highly potent organometallic gold(iii) complexes supported by dithiocarbamate ligands as selective inhibitors of mitochondrial respiration. The structure of dithiocarbamates employed dictates the biological stability and cellular cytotoxicity. Most of the compounds exhibit 50% inhibitory concentration (IC50) in the low-micromolar (0.50-2.9 μM) range when tested in a panel of aggressive cancer types with significant selectivity for cancer cells over normal cells. Consequently, there is great interest in the mechanism of action of gold chemotherapeutics, particularly, considering that DNA is not the major target of most gold complexes. We investigate the mechanism of action of representative complexes, 1a and 2a in the recalcitrant triple negative breast cancer (TNBC) cell line, MDA-MB-231. Whole-cell transcriptomics sequencing revealed genes related to three major pathways, namely: cell cycle, organelle fission, and oxidative phosphorylation. 2a irreversibly and rapidly inhibits maximal respiration in TNBC with no effect on normal epithelial cells, implicating mitochondrial OXPHOS as a potential target. Furthermore, the modulation of cyclin dependent kinases and G1 cell cycle arrest induced by these compounds is promising for the treatment of cancer. This work contributes to the need for mitochondrial respiration modulators in biomedical research and outlines a systematic approach to study the mechanism of action of metal-based agents.

Inhibition of Nrf2 might enhance the anti-tumor effect of temozolomide in glioma cells via inhibition of Ras/Raf/MEK signaling pathway

BACKGROUND

Glioblastoma (GBM) is the most common aggressive primary cancer occurring in the brain tissue. GBM accounts 16% of primary brain tumors and half of gliomas. Additionally, the incidence of GBM is increases with aging, and reaches the peak at the age of 75 to 84 years. The survival of patients with GBM remains at a low level, only less than 5% patients diagnosed with GBM survive for 5 years. Temozolomide (TMZ) is a DNA alkylating agent and is currently a first line chemotherapeutic treatment for GBM. TMZ combined with radiation therapy has been shown to prolong the overall survival (OS) to 14.6 months compared with 12.1 months for radiation therapy alone. NF-E2-related factor 2 (Nrf2) is a transcription factor that contains seven functional domains. The binding of Keap1 to Nrf2 is a central regulator of the cellular defense mechanism against environmental stresses.

METHODS

First, Nrf2 overexpression and inhibition models were constructed in U251 cells using transfection. The percentage of viable cells was detected using the MTT assay. Then, the expression of the HO-1 regulator was detected using qPCR, and the concentrations of oxidative stress related factors were detected using ELISAs. The levels of proteins related to oxidative stress and the Ras/Raf/MEK signaling pathway was detected using western blotting analysis.

RESULTS

We initially established Nrf2 inhibition and activation cell models in U251 cells and found that the inhibition of Nrf2 expression decreased the mRNA and protein levels of the anti-oxidative enzymes, as well as the secretion of these enzymes into the cellular microenvironment. These effects might be mediated by the inhibition of Ras/Raf/MEK signaling pathway, leading to the inhibition of cellular proliferation.

CONCLUSIONS

Inhibition of Nrf2 expression might enhance the effect of TMZ on the treatment of GBM and might be a new therapeutic strategy.

Synthesis, characterization and anticancer activity in vitro evaluation of novel dicyanoaurate (I)-based complexes

Molecular structures containing gold, such as auranofin, have been extensively studied in the diagnosis and treatment of many diseases, including cancer treatment. The pharmacological properties of the newly synthesized unique gold-ligand structures have been reported for different cancer cell lines. However, findings on bishydeten-metal salt complexes with gold are rare. In this work, the synthesis of five novel cyanide-bridged coordination compounds having the closed formulae [Ni(bishydeten)][Au(CN)₂]₂ (1), [Cu(bishydeten)][Au(CN)₂]₂ (2), [Zn(bishydeten)₂Au₃(CN)₄][Au₂(CN)₃] (3), [Cd(bishydeten)_0,5]₂[Au(CN)₂]₄.2H₂O (4), and [Cd(bishydeten)₂][Au(CN)₂]₂ (5) (where bisyhdeten = N,N-bis(2-hydroxyethyl)ethylene diamine), and their characterization by elemental, infrared, ESI-MS, X-ray (for 2) and thermic measurement methods were performed. Complexes 1 and 3 are thermally more stable than the other three complexes. For these, pharmacological adequacies were also tested. The nucleic acid and protein binding affinities of the Au (I) compounds were also estimated by spectroscopic and electrophoretic techniques. Au (I) complexes were identified as strong chemotherapeutic with mild cytotoxicity, and they demonstrated a dose-dependent inhibition on the growth of cancer cells with IC50 at 0.11 to 0.47 μM. Investigation of mechanisms of action on cells revealed that Au (I) compounds managed to inhibit cell migration and led to a decrease in cytoskeletal proteins such as CK7 and CK20. However, Au (I) compounds failed to inhibit DNA topoisomerase I. Overall, and we suggest that potent antiproliferative activity, mild cytotoxicity, good solubility, and micromolar dosage of Au (I) compounds containing bisyhdeten-metal derivatives render them the potential focus of further studies as chemotherapeutic agents.

Therapeutic potential of dithiocarbamate supported gold compounds

Chrysotherapy or aurotherapy, the use of gold as medicine, is two thousand years old. Hitherto, numerous diverse gold stabilizing ligands for instance vitamins, pyridine, phosphines, naphthylamine and xanthanes have been developed and their 'chelating effect' in addition to their anti-proliferative properties have been extensively studied. Recent advances in the field of bioinorganic chemistry have led to the design of biologically relevant metal complexes with appropriate fine-tuned ligands such as metallic conjugates of dithiocarbamates (DTCs). DTC compounds have been recognised to possess diverse applications and have demonstrated interesting biological properties. For instance, the chemoprotective and antitumour properties of gold metal ions and DTC compounds respectively, presents an innovative and effective approach to cancer management. This review presents therefore the therapeutic potential of DTC ligand systems as a support for gold compounds. The importance of dithiocarbamate supported gold compounds as potential therapeutic agents is highlighted with emphasis on the therapeutic potential of gold(iii) and gold(i) dithiocarbamate derivatives.

Au(iii)-Proline derivatives exhibiting selective antiproliferative activity against HepG2/SB3 apoptosis-resistant cancer cells

This paper deals with the combination of a proline-based moiety with biologically active gold centers in the oxidation states +1 and +3. In particular, six Au(i)/(iii)-proline dithiocarbamato (DTC) complexes with general formulae [Au(DTC)₂] and [Au^IIIX₂(DTC)] (X = Cl, Br) are reported here. After the synthesis of the ligand and the complexes, all derivatives were characterized via several techniques and tested for their stability in DMSO/water media. This study was focused on the demonstration of a peculiar behavior of Au(iii)-DTC species in solution. Finally, the complexes were screened for their antiproliferative activity against 2 human cancer cell lines, namely HepG2 and HepG2/SB3, taken as models of hepatocellular carcinoma. The latter, chosen for its aggressiveness due to the upregulation of the anti-apoptotic protein SerpinB3, was selectively inhibited in terms of growth by some Au(iii)-DTC complexes.

Antitumor activity of a novel dual functional podophyllotoxin derivative involved PI3K/AKT/mTOR pathway

The progression of cancer through local expansion and metastasis is well recognized, but preventing these characteristic cancer processes is challenging. To this end, a new strategy is required. In this study, we presented a novel dual functional podophyllotoxin derivative, 2-pyridinealdehyde hydrazone dithiocarbamate S-propionate podophyllotoxin ester (PtoxPdp), which inhibited both matrix metalloproteinases and Topoisomerase II. This new podophyllotoxin derivative exhibited significant anti-proliferative, anti-metastatic that correlated with the downregulation of matrix metalloproteinase. In a xenograft animal local expansion model, PtoxPdp was superior to etoposide in tumor repression. A preliminary mechanistic study revealed that PtoxPdp induced apoptosis and autophagy via the PI3K/AKT/mTOR pathway. Furthermore, PtoxPdp could also inhibit epithelial-mesenchymal transition, which was achieved by downregulating both PI3K/AKT/mTOR and NF-κB/Snail pathways. Taken together, our results reveal that PtoxPdp is a promising antitumor drug candidate.

Cyclometallated Au(iii) dithiocarbamate complexes: synthesis, anticancer evaluation and mechanistic studies

A series of cationic mixed cyclometallated (C^N)Au(iii) dithiocarbamate complexes has been synthesized in good yields [HC^N = 2-(p-t-butylphenyl)pyridine]. The crystal structure of [(C^N)AuS2CNEt2]PF6 (3) has been determined. The cytotoxic properties of the new complexes have been evaluated in vitro against a panel of human cancer cell lines and healthy cells and compared with a neutral mixed (C^C)Au(iii) dithiocarbamate complex (C^C = 4,4'-di-t-butylbiphenyl-2,2'-diyl). The complexes appeared to be susceptible to reduction by glutathione but were stable in the presence of N-acetyl cysteine. The potential mechanism of action of this class of compounds has been investigated by measuring the intracellular uptake of some selected complexes, by determining their interactions with higher order DNA structures, and by assessing the ability to inhibit thioredoxin reductase. The complexes proved unable to induce the formation of reactive oxygen species. The investigations add to the picture of the possible mode of action of this class of complexes.

A novel iron(II) phenanthroline complex exhibits anticancer activity against TFR1-overexpressing esophageal squamous cell carcinoma cells through ROS accumulation and DNA damage

Esophageal squamous cell carcinoma (ESCC) is one of the most common and aggressive cancers worldwide, especially in China, with poor prognosis due to the lack of effective therapeutic strategies. Here, the anticancer effect and pharmacological mechanism of a newly synthesized Fe(II) phenanthroline complex was studied in ESCC. Our data showed that transferrin receptor 1 (TFR1) was specifically overexpressed in ESCC tissues compared to its expression in normal esophageal tissues, a finding further supported by public datasets. The newly synthesized Fe(II) complex was selectively transported into ESCC cells overexpressing TFR1 through TFR1-mediated endocytosis and exhibited anticancer activity in a dose-dependent manner. The mechanistic study elucidated that the Fe(II) complex caused cell cycle arrest at the G0/G1 phase by blocking the CDK4/6-cyclin D1 complex and induced mitochondria-mediated apoptosis. Furthermore, exposure to the Fe(II) complex led to excessive reactive oxygen species (ROS) accumulation by thioredoxin reductase (TrxR) inhibition and DNA double-strand breaks (DSBs), which in turn sequentially activated ATM, CHK1/2 and p53. Moreover, combination treatment with cisplatin and the Fe(II) complex exhibited a synergistic effect in ESCC cells. Taken together, our results initially suggest the potential application of the Fe(II) complex in ESCC chemotherapy, especially for patients with TFR1 overexpression.

Targeting the Thioredoxin System as a Strategy for Cancer Therapy

Thioredoxin reductase (TrxR) participates in the regulation of redox reactions in organisms. It works mainly via its substrate molecule, thioredoxin, to maintain the redox balance and regulate signal transduction, which controls cell proliferation, differentiation, death, and other important physiological processes. In recent years, increasing evidence has shown that the overactivation of TrxR is related to the development of tumors. The exploration of TrxR-targeted antitumor drugs has attracted wide attention and is expected to provide new therapies for cancer treatment. In this perspective, we highlight the specific relationship between TrxR and apoptotic signaling pathways. The cytoplasm and mitochondria both contain TrxR, resulting in the activation of apoptosis. TrxR activity influences reactive oxygen species (ROS) and further regulates the inflammatory signaling pathway. In addition, we discuss representative TrxR inhibitors with anticancer activity and analyze the challenges in developing TrxR inhibitors as anticancer drugs.

Potent In Vitro and In Vivo Anticancer Activity of New Bipyridine and Bipyrimidine Gold (III) Dithiocarbamate Derivatives

We synthesized eight new bipyridine and bipyrimidine gold (III) dithiocarbamate-containing complexes (C1-C8) and tested them in a panel of human cancer cell lines. We used osteosarcoma (MG-63), lung (A549), prostate (PC3 and DU145), breast (MCF-7), ovarian (A2780 and A2780cis, cisplatin- and doxorubicin-resistant), and cervical (ME-180 and R-ME-180, cisplatin resistant) cancer cell lines. We found that C2, C3, C6, and C7 were more cytotoxic than cisplatin in all cell lines tested and overcame cisplatin and doxorubicin resistance in A2780cis and R-ME-180 cells. In the PC3 prostate cancer cell line, the gold (III) complex C6 ([Au₂(BPM)(DMDTC)₂]Cl₄) induced apoptosis and double-stranded DNA breaks, modified cell cycle phases, increased Reactive Oxigen Species (ROS) generation, and reduced thioredoxin reductase and proteasome activities. It inhibited PC3 cell migration and was more cytotoxic against PC3 cells than normal human adipose-derived stromal cells. In mice bearing PC3 tumor xenografts, C6 reduced tumor growth by more than 70% without causing weight loss. Altogether, our results demonstrate the anticancer activity of these new gold (III) complexes and support the potential of C6 as a new agent for prostate cancer treatment.

Mitochondria-Targeting Anticancer Metal Complexes

Background:

Since the serendipitous discovery of the antitumor activity of cisplatin there has been a continuous surge in studies aimed at the development of new cytotoxic metal complexes. While the majority of these complexes have been designed to interact with nuclear DNA, other targets for anticancer metallodrugs attract increasing interest. In cancer cells the mitochondrial metabolism is deregulated. Impaired apoptosis, insensitivity to antigrowth signals and unlimited proliferation have been linked to mitochondrial dysfunction. It is therefore not surprising that mitochondria have emerged as a major target for cancer therapy. Mitochondria-targeting agents are able to bypass resistance mechanisms and to (re-) activate cell-death programs.

Methods:

Web-based literature searching tools such as SciFinder were used to search for reports on cytotoxic metal complexes that are taken up by the mitochondria and interact with mitochondrial DNA or mitochondrial proteins, disrupt the mitochondrial membrane potential, facilitate mitochondrial membrane permeabilization or activate mitochondria-dependent celldeath signaling by unbalancing the cellular redox state. Included in the search were publications investigating strategies to selectively accumulate metallodrugs in the mitochondria.

Results:

This review includes 241 references on antimitochondrial metal complexes, the use of mitochondria-targeting carrier ligands and the formation of lipophilic cationic complexes.

Conclusion:

Recent developments in the design, cytotoxic potency, and mechanistic understanding of antimitochondrial metal complexes, in particular of cyclometalated Au, Ru, Ir and Pt complexes, Ru polypyridine complexes and Au-N-heterocyclic carbene and phosphine complexes are summarized and discussed.

In vitro and in vivo anti-tumor activity of two gold(III) complexes with isoquinoline derivatives as ligands

Two gold(III) complexes of isoquinoline derivatives: [Au(L¹)Cl₂] (Au1) and [Au(L²)Cl₂] (Au2) have been prepared and characterized. Au1 and Au2 exhibited greater cytotoxicity than their corresponding ligands and cisplatin against T-24 cells. Both complexes arrested cell cycle at S-phase by upregulation of p53, p27, and p21, and downregulation of cyclin A and cyclin E. The depolarization of the mitochondrial membrane potential, generation of ROS, and stimulated Ca²⁺ release activated the caspase cascade and ultimately caused apoptosis by increasing the levels of Bax and Bak, and decreasing the levels of Bcl-2 and Bcl-xl. Cell apoptosis was achieved via mitochondria mediated pathways. The in vivo studies of Au1 and Au2 demonstrated that they were safer than cisplatin and could effectively inhibit tumor growth.

Organometallic gold(iii) complexes with hybrid SNS-donating thiosemicarbazone ligands: cytotoxicity and anti-Trypanosoma cruzi activity

Stable organogold(iii) compounds of the composition [Au^III(Hdamp)(L1)]Cl are formed from reactions of [AuCl₂(damp)] with H₂L1 (damp^- = dimethylaminomethylphenyl; H₂L1 = N'-(diethylcarbamothioyl)benzimidothiosemicarbazides). The cationic complexes can be neutralized by reactions with weak bases under the formation of [Au^III(damp)(L1)] compounds. The structures of the products show interesting features like relatively short AuH contacts between the methylene protons of the Hdamp ligand and the gold(iii) ions. Preliminary biological studies on the uncoordinated compounds H₂L1 and their gold complexes indicate considerable cytotoxicity for the [Au^III(Hdamp)(L1)]Cl complexes against MCF-7 cells. The in vitro trypanocidal activity was evaluated against the intracellular form of Trypanosoma cruzi. The organometallic complexes display a remarkable activity, which is dependent on the alkyl substituents of the thiosemicarbazone building blocks of the ligands. One representative of the cationic [Au^III(Hdamp)(L1)]Cl complexes, where H₂L1 contains a dimethylthiosemicarbazide building block, shows a trypanocidal activity against the intracellular amastigote form in the same order of magnitude as that of the standard drug benznidazole. Furthermore, no appreciable toxicity to mice spleen cells is observed for this compound resulting in a therapeutic index of about 30, which strongly recommends it as a promising candidate for the development of a future antiparasitic drug.

Gold-Based Medicine: A Paradigm Shift in Anti-Cancer Therapy?

A new era of metal-based drugs started in the 1960s, heralded by the discovery of potent platinum-based complexes, commencing with cisplatin [(H₃N)₂PtCl₂], which are effective anti-cancer chemotherapeutic drugs. While clinical applications of gold-based drugs largely relate to the treatment of rheumatoid arthritis, attention has turned to the investigation of the efficacy of gold(I) and gold(III) compounds for anti-cancer applications. This review article provides an account of the latest research conducted during the last decade or so on the development of gold compounds and their potential activities against several cancers as well as a summary of possible mechanisms of action/biological targets. The promising activities and increasing knowledge of gold-based drug metabolism ensures that continued efforts will be made to develop gold-based anti-cancer agents.

New bipyridine gold(III) dithiocarbamate-containing complexes exerted a potent anticancer activity against cisplatin-resistant cancer cells independent of p53 status

We synthesized, characterized and tested in a panel of cancer cell lines, nine new bipyridine gold(III) dithiocarbamate-containing complexes. In vitro studies demonstrated that compounds 1, 2, 4, 5, 7 and 8 were the most cytotoxic in prostate, breast, ovarian cancer cell lines and in Hodgkin lymphoma cells with IC₅₀ values lower than the reference drug cisplatin. The most active compound 1 was more active than cisplatin in ovarian (A2780cis and 2780CP-16) and breast cancer cisplatin-resistant cells. Compound 1 determined an alteration of the cellular redox homeostasis leading to increased ROS levels, a decrease in the mitochondrial membrane potential, cytochrome-c release from the mitochondria and activation of caspases 9 and 3. The ROS scavenger NAC suppressed ROS generation and rescued cells from damage. Compound 1 resulted more active in tumor cells than in normal human Mesenchymal stromal cells. Gold compounds were active independent of p53 status: exerted cytotoxic effects on a panel of non-small cell lung cancer cell lines with different p53 status and in the ovarian A2780 model where the p53 was knocked out. In conclusion, these promising results strongly indicate the need for further preclinical evaluation to test the clinical potential of these new gold(III) complexes.

Gold(i) and gold(iii) phosphine complexes: synthesis, anticancer activities towards 2D and 3D cancer models, and apoptosis inducing properties

Herein we report the synthesis of gold(i) and gold(iii) complexes of tris(4-methoxyphenyl)phosphine and tris(2,6-dimethoxyphenyl)phosphine and their anticancer activity towards 2D and 3D cancer models.