Evaluation of Au(III) complexes as Plasmodium falciparum aquaglyceroporin (PfAQP) inhibitors by in silico and in vitro methods

The onset of resistance to artemisinin for malaria treatment has stimulated the quest for novel antimalarial drugs. Herein, the gold(III) coordination complexes Aubipy [Au(bipy)Cl]+ (bipy = 2,2'-bipyridine), Auphen [Au(phen)Cl]+ (phen = phenanthroline), Auterpy [Au(terpy)Cl]2+ (terpy = 2,2';6',2″-terpyridine), and corresponding hydrolyzed species, have been investigated as inhibitors of the Plasmodium falciparum aquaglyceroporin (PfAQP) protein by computational methods. Through an in-silico approach using an Umbrella Sampling protocol to sample how Aubipy, Auphen, and Auterpy permeate through the PfAQP, their permeability coefficients were estimated using the Inhomogeneous Solubility Diffusion (ISD) model with promising results. The efficacy of the gold complexes was then probed by an in vitro assay testing the growth inhibition in chloroquine sensitive and resistant P. falciparum strains. In accordance with the computational data, Auterpy achieved the highest efficiency with an IC50 in the nanomolar range (590 nM) on resistant strain cultures, additionally revealing a good selectivity as compared to its activity against the human aquaglyceroporin 3.

Anticancer Activity of Metallodrugs and Metallizing Host Defense Peptides-Current Developments in Structure-Activity Relationship

This article provides an overview of the development, structure and activity of various metal complexes with anti-cancer activity. Chemical researchers continue to work on the development and synthesis of new molecules that could act as anti-tumor drugs to achieve more favorable therapies. It is therefore important to have information about the various chemotherapeutic substances and their mode of action. This review focuses on metallodrugs that contain a metal as a key structural fragment, with cisplatin paving the way for their chemotherapeutic application. The text also looks at ruthenium complexes, including the therapeutic applications of phosphorescent ruthenium(II) complexes, emphasizing their dual role in therapy and diagnostics. In addition, the antitumor activities of titanium and gold derivatives, their side effects, and ongoing research to improve their efficacy and reduce adverse effects are discussed. Metallization of host defense peptides (HDPs) with various metal ions is also highlighted as a strategy that significantly enhances their anticancer activity by broadening their mechanisms of action.

Interaction of Au(III) with amino acids: a vade mecum for medicinal chemistry and nanotechnology

Au(III) is highly reactive. At odds with its reduced counterpart, Au(I), it is hardly present in structural databases. And yet, it is the starting reactant to form gold nanoclusters (AuNCs) and the constitutive component of a new class of drugs. Its reactivity is a world apart from that of the iso-electronic Pt(II) species. Rather than DNA, it targets proteins. Its interaction with amino acid residues is manifold. It can strongly interact with the residue backbones, amino acid side chains and protein ends, it can form appropriate complexes whose stabilization energy reaches up to more than 40 kcal mol-1, it can affect the pKa of amino acid residues, and it can promote charge transfer from the residues to the amount that it is reduced. Here, quantum chemical calculations provide quantitative information on all the processes where Au(III) can be involved. A myriad of structural arrangements are examined in order to determine the strongest interactions and quantify the amount of charge transfer between protonated and deprotonated residues and Au(III). The calculated interaction energies of the amino acid side chains with Au(III) quantitatively reproduce the experimental tendency of Au(III) to interact with selenocysteine, cysteine and histidine and negatively charged amino acids such as Glu and Asp. Also, aromatic residues such as tyrosine and tryptophan strongly interact with Au(III). In proteins, basic pH plays a role in the deprotonation of cysteine, lysine and tyrosine and strongly increases the binding affinity of Au(III) toward these amino acids. The amino acid residues in the protein can also trigger the reduction of Au(III) ions. Sulfur-containing amino acids (cysteine and methionine) and selenocysteine provide almost one electron to Au(III) upon binding. Tyrosine also shows a considerable tendency to act as a reductant. Other amino acids, commonly identified in Au-protein adducts, such as Ser, Trp, Thr, Gln, Glu, Asn, Asp, Lys, Arg and His, possess a notable reducing power toward Au(III). These results and their discussion form a vade mecum that can find application in medicinal chemistry and nanotech applications of Au(III).

Gold(I) and Silver(I) Complexes Containing Hybrid Sulfonamide/Thiourea Ligands as Potential Leishmanicidal Agents

Leishmaniasis is a group of parasitic diseases with the potential to infect more than 1 billion people; however, its treatment is still old and inadequate. In order to contribute to changing this view, this work consisted of the development of complexes derived from MI metal ions with thioureas, aiming to obtain potential leishmanicidal agents. The thiourea ligands (HLR) were obtained by reactions of p-toluenesulfohydrazide with R-isothiocyanates and were used in complexation reactions with AgI and AuI, leading to the formation of complexes of composition [M(HLR)2]X (M = Ag or Au; X = NO3- or Cl-). All compounds were characterized by FTIR, 1H NMR, UV-vis, emission spectroscopy and elemental analysis. Some representatives were additionally studied by ESI-MS and single-crystal XRD. Their properties were further analyzed by DFT calculations. Their cytotoxicity on Vero cells and the extracellular leishmanicidal activity on Leishmania infantum and Leishmania braziliensis cells were evaluated. Additionally, the interaction of the complexes with the Old Yellow enzyme of the L. braziliensis (LbOYE) was examined. The biological tests showed that some compounds present remarkable leishmanicidal activity, even higher than that of the standard drug Glucantime, with different selectivity for the two species of Leishmania. Finally, the interaction studies with LbOYE revealed that this enzyme could be one of their biological targets.

Metallacages with 2,6-dipicolinoylbis(N,N-dialkylthioureas) as novel platforms in nuclear medicine for 68Ga, 177Lu and 198Au

BACKGROUND

Heterometallic gold metallacages are of great interest for the incorporation of several cations. Especially in nuclear medicine, those metallacages can serve as a platform for radionuclides relevant for imaging or therapy (e.g. 68Ga or 177Lu). Moreover, the radionuclide 198Au is an attractive beta emitter, for potential application in nuclear medicine. Here, we aim to synthesize a new set of gold metallacages and to study their ability to coordinate to 68Ga, 177Lu and 198Au.

RESULTS

New heterometallic gold metallacages of composition [M{Au(Lmorph-κS)}3] (M = La3+, Tb3+, Lu3+ or Y3+) and [Ga{Au(Lmorph-κS)}2]NO3 have been synthesized from 2,6-dipicolinoylbis(N,N-morpholinylthiourea) (H2Lmorph) with [AuCl(THT)] and the target M3+ metal ions in yields ranging from 33 (Lu) to 62% (Tb). The characterization of the compounds bases on ESI-MS, 1H NMR, IR, EA and single-crystal X-ray diffraction techniques (all except the Ga derivative). Selected gold cages derived from H2Lmorph were compared to previously reported gold cages that were derived from 2,6-dipicolinoylbis(N,N-diethylthiourea) (H2Ldiethyl). The tested metallacages show similar IC50 values close to that of auranofin in four different cancer cell lines (MCF-7, PC-3, U383, U343), e.g. 4.5 ± 0.7 µM for [Ga{Au(Ldiethyl)}2]NO3 on PC-3. The radiolabeling experiments thereof show high radiochemical purities with 68Ga and 198Au and low radiochemical purity with 177Lu.

CONCLUSIONS

The results indicate that these gold metallacages could serve as a novel platform for inclusion of different (radio)nuclides with potential theranostic applications in nuclear medicine.

Gold-Based Coronands as Hosts for M3+ Metal Ions: Ring Size Matters

The controlled, self-assembled synthesis of multinuclear coordination compounds can be performed via different approaches. Frequently, steric, geometric and/or electronic factors located at the ligand systems predefine the way in which metal ions can assemble them to large aggregates. For the compounds in the present paper, also the Pearson's acidities and preferred coordination geometries of the metal ions were used as organization principles. The ligand under study, 2,6-dipicolinoylbis(N,N-diethylthiourea), H₂L1^ethyl, possesses 'soft' sulfur and 'hard' nitrogen and oxygen donors. One-pot reactions of this compound with [AuCl(tht)] (tht = tetrahydrothiophene) and M³⁺ salts (M = Sc, Y, La, Ln, Ga, In) give products with gold-based {Au₃(L1^ethyl)₃}³⁺ or {Au₂(L1^ethyl)₂}²⁺ coronands, which host central M³⁺ ions. The formation of such units is templated by the M³⁺ ions and the individual size of the coronand rings is dependent on the ionic radii of the central ions in a way that small ions such as Ga³⁺ form a [Ga⊂{Au₂(L1^ethyl)₂}]⁺ assembly, while larger ions (starting from Sc³⁺/In³⁺) establish neutral [M⊂{Au₃(L1^ethyl)₃}] units with nine-coordinate central ions.

Novel gold(III)-dithiocarbamate complex targeting bacterial thioredoxin reductase: antimicrobial activity, synergy, toxicity, and mechanistic insights

Introduction

Antimicrobial resistance is a pressing global concern that has led to the search for new antibacterial agents with novel targets or non-traditional approaches. Recently, organogold compounds have emerged as a promising class of antibacterial agents. In this study, we present and characterize a (C^S)-cyclometallated Au(III) dithiocarbamate complex as a potential drug candidate.

Methods and results

The Au(III) complex was found to be stable in the presence of effective biological reductants, and showed potent antibacterial and antibiofilm activity against a wide range of multidrug-resistant strains, particularly gram-positive strains, and gram-negative strains when used in combination with a permeabilizing antibiotic. No resistant mutants were detected after exposing bacterial cultures to strong selective pressure, indicating that the complex may have a low propensity for resistance development. Mechanistic studies indicate that the Au(III) complex exerts its antibacterial activity through a multimodal mechanism of action. Ultrastructural membrane damage and rapid bacterial uptake suggest direct interactions with the bacterial membrane, while transcriptomic analysis identified altered pathways related to energy metabolism and membrane stability including enzymes of the TCA cycle and fatty acid biosynthesis. Enzymatic studies further revealed a strong reversible inhibition of the bacterial thioredoxin reductase. Importantly, the Au(III) complex demonstrated low cytotoxicity at therapeutic concentrations in mammalian cell lines, and showed no acute in vivo toxicity in mice at the doses tested, with no signs of organ toxicity.

Discussion

Overall, these findings highlight the potential of the Au(III)-dithiocarbamate scaffold as a basis for developing novel antimicrobial agents, given its potent antibacterial activity, synergy, redox stability, inability to produce resistant mutants, low toxicity to mammalian cells both in vitro and in vivo, and non-conventional mechanism of action.

Next Generation Gold Drugs and Probes: Chemistry and Biomedical Applications

The gold drugs, gold sodium thiomalate (Myocrisin), aurothioglucose (Solganal), and the orally administered auranofin (Ridaura), are utilized in modern medicine for the treatment of inflammatory arthritis including rheumatoid and juvenile arthritis; however, new gold agents have been slow to enter the clinic. Repurposing of auranofin in different disease indications such as cancer, parasitic, and microbial infections in the clinic has provided impetus for the development of new gold complexes for biomedical applications based on unique mechanistic insights differentiated from auranofin. Various chemical methods for the preparation of physiologically stable gold complexes and associated mechanisms have been explored in biomedicine such as therapeutics or chemical probes. In this Review, we discuss the chemistry of next generation gold drugs, which encompasses oxidation states, geometry, ligands, coordination, and organometallic compounds for infectious diseases, cancer, inflammation, and as tools for chemical biology via gold-protein interactions. We will focus on the development of gold agents in biomedicine within the past decade. The Review provides readers with an accessible overview of the utility, development, and mechanism of action of gold-based small molecules to establish context and basis for the thriving resurgence of gold in medicine.

Gold Complexes in Anticancer Therapy: From New Design Principles to Particle-Based Delivery Systems

The discovery of the medicinal properties of gold complexes has fuelled the design and synthesis of new anticancer metallodrugs, which have received special attention due to their unique modes of action. Current research in the development of gold compounds with therapeutic properties is predominantly focused on the molecular design of drug leads with superior pharmacological activities, e.g., by introducing targeting features. Moreover, intensive research aims at improving the physicochemical properties of gold compounds, such as chemical stability and solubility in the physiological environment. In this regard, the encapsulation of gold compounds in nanocarriers or their chemical grafting onto targeted delivery vectors could lead to new nanomedicines that eventually reach clinical applications. Herein, we provide an overview of the state-of-the-art progress of gold anticancer compounds, andmore importantly we thoroughly revise the development of nanoparticle-based delivery systems for gold chemotherapeutics.

Gold(III) Complexes Activity against Multidrug-Resistant Bacteria of Veterinary Significance

The emergence and spread of multidrug-resistant bacteria are a global concern. The lack of new antibiotics in the pipeline points to the need for developing new strategies. In this sense, gold(III) complexes (G3Cs) could be a promising alternative due to their recently described antibacterial activity. The aim of this study was to evaluate the antimicrobial activity of G3Cs alone and in combination with colistin against pathogenic bacteria from veterinary sources. Minimal inhibitory concentration (MIC) values were determined by broth microdilution and compared with clinically relevant antibiotics. Antibiofilm activity was determined by crystal violet staining. Combinations of selected G3Cs with colistin and cytotoxicity in commercial human cell lines were evaluated. Four and seven G3Cs showed antibacterial effect against Gram-negative and Gram-positive strains, respectively, with this activity being higher among Gram-positive strains. The G3Cs showed antibiofilm activity against Gram-negative species at concentrations similar or one to four folds higher than the corresponding MICs. Combination of G3Cs with colistin showed a potential synergistic antibacterial effect reducing concentrations and toxicity of both agents. The antimicrobial and antibiofilm activity, the synergistic effect when combined with colistin and the in vitro toxicity suggest that G3Cs would provide a new therapeutic alternative against multidrug-resistant bacteria from veterinary origin.

Metal-Based Complexes as Potential Anti-cancer Agents

Metal based therapy is no new in biomedical research. In early days the biggest limitation was the inequality among therapeutical and toxicological dosages. Ever since, Barnett Rosenberg discovered cisplatin, a new era has begun to treat cancer with metal complexes. Platinum complexes such as oxaliplatin, cisplatin, and carboplatin, seem to be the foundation of metal/s-based components to challenge malignancies. With an advancement in the biomolemoecular mechanism, researchers have started developing non-classical platinum-based complexes, where a different mechanistic approach of the complexes is observed towards the biomolecular target. Till date, larger number of metal/s-based complexes was synthesized by overhauling the present structures chemically by substituting the ligand or preparing the whole novel component with improved cytotoxic and safety profiles. Howsoever, due to elevated accentuation upon the therapeutic importance of metal/s-based components, a couple of those agents are at present on clinical trials and several other are in anticipating regulatory endorsement to enter the trial. This literature highlights the detailed heterometallic multinuclear components, primarily focusing on platinum, ruthenium, gold and remarks on possible stability, synergism, mechanistic studies and structure activity relationships.

A C∧S-Cyclometallated Gold(III) Complex as a Novel Antibacterial Candidate Against Drug-Resistant Bacteria

The worldwide emergence and spread of infections caused by multidrug-resistant bacteria endangers the efficacy of current antibiotics in the clinical setting. The lack of new antibiotics in the pipeline points to the need of developing new strategies. Recently, gold-based drugs are being repurposed for antibacterial applications. Among them, gold(III) complexes have received increasing attention as metal-based anticancer agents. However, reports on their antibacterial activity are scarce due to stability issues. The present work demonstrates the antibacterial activity of the gold(III) complex 2 stabilized as C∧S-cycloaurated containing a diphenylphosphinothioic amide moiety, showing minimum inhibitory concentration (MIC) values that ranged from 4 to 8 and from 16 to 32 mg/L among Gram-positive and Gram-negative multidrug-resistant (MDR) pathogens, respectively. Complex 2 has a biofilm inhibitory activity of only two to four times than its MIC. We also describe for the first time a potent antibacterial synergistic effect of a gold(III) complex combined with colistin, showing a bactericidal effect in less than 2 h; confirming the role of the outer membrane as a permeability barrier. Complex 2 shows a low rate of internalization in Staphylococcus aureus and Acinetobacter baumannii; it does not interact with replication enzymes or efflux pumps, causes ultrastructural damages in both membrane and cytoplasmic levels, and permeabilizes the bacterial membrane. Unlike control antibiotics, complex 2 did not generate resistant mutants in 30-day sequential cultures. We detected lower cytotoxicity in a non-tumoral THLE-2 cell line (IC50 = 25.5 μM) and no acute toxicity signs in vivo after an i.v. 1-mg/kg dose. The characterization presented here reassures the potential of complex 2 as a new chemical class of antimicrobial agents.

Porphyrin/Chlorin Derivatives as Promising Molecules for Therapy of Colorectal Cancer

Colorectal cancer (CRC) is a leading cause of cancer-related death. The demand for new therapeutic approaches has increased attention paid toward therapies with high targeting efficiency, improved selectivity and few side effects. Porphyrins are powerful molecules with exceptional properties and multifunctional uses, and their special affinity to cancer cells makes them the ligands par excellence for anticancer drugs. Porphyrin derivatives are used as the most important photosensitizers (PSs) for photodynamic therapy (PDT), which is a promising approach for anticancer treatment. Nevertheless, the lack of solubility and selectivity of the large majority of these macrocycles led to the development of different photosensitizer complexes. In addition, targeting agents or nanoparticles were used to increase the efficiency of these macrocycles for PDT applications. On the other hand, gold tetrapyrrolic macrocycles alone showed very interesting chemotherapeutic activity without PDT. In this review, we discuss the most important porphyrin derivatives, alone or associated with other drugs, which have been found effective against CRC, as we describe their modifications and developments through substitutions and delivery systems.

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.

Medicinal Au(I) compounds targeting urease as prospective antimicrobial agents: unveiling the structural basis for enzyme inhibition

A few gold compounds were recently found to show antimicrobial properties in vitro, holding great promise for the discovery of new drugs to overcome antibiotic resistance. Here, the inhibition of the bacterial virulence factor urease by four Au(I)-compounds, namely Au(PEt₃)Cl, Au(PEt₃)Br, Au(PEt₃)I and [Au(PEt₃)₂]Cl, obtained from the antiarthritic Au(I)-drug Auranofin and earlier reported to act as antimicrobials, is investigated. The three monophosphino Au(I) complexes showed IC₅₀ values in the 30-100 nM range, while the diphosphino Au(I) complex, though being less active, still showed a IC₅₀ value of 7 μM. The structural basis for this inhibition was provided by solving the crystal structures of urease co-crystallized with Au(PEt₃)I and [Au(PEt₃)₂]Cl: at least two Au(I) ions bind the enzyme in a flap domain involved in the catalysis, thus obliterating enzyme activity. Peculiar changes observed in the two structures reveal implications for the mechanism of soft metal binding and enzyme inactivation.

Gold(iii) bis(dithiolene) complexes: from molecular conductors to prospective anticancer, antimicrobial and antiplasmodial agents

The anticancer, antimicrobial and antiplasmodial activities of six gold(iii) bis(dithiolene) complexes were studied. Complexes 1-6 showed relevant anticancer properties against A2780/A2780cisR ovarian cancer cells (IC50 values of 0.08-2 μM), also being able to overcome cisplatin resistance in A2780cisR cells. Complex 1 also exhibited significant antimicrobial activity against Staphylococcus aureus (minimum inhibitory concentration (MIC) values of 12.1 ± 3.9 μg mL-1) and both Candida glabrata and Candida albicans (MICs of 9.7 ± 2.7 and 19.9 ± 2.4 μg mL-1, respectively). In addition, all complexes displayed antiplasmodial activity against the Plasmodium berghei parasite liver stages, even exhibiting better results than the ones obtained using primaquine, an anti-malarial drug. Mechanistic studies support the idea that thioredoxin reductase, but not DNA, is a possible target of these complexes. Complex 1 is stable under biological conditions, which would be important if this compound is ever to be considered as a drug. Overall, the results obtained evidenced the promising biological activity of complex 1, which might have potential as a novel anticancer, antimicrobial and antiplasmodial agent to be used as an alternative to current therapeutics.

Potential of Gold Candidates against Human Colon Cancer

Development of novel metallodrugs with pharmacological profile plays a significant role in modern medicinal chemistry and drug design. Metal complexes have shown remarkable clinical results in current cancer therapy. Gold complexes have attained attention due to their high antiproliferative potential. Gold-based drugs are used for the treatment of rheumatoid arthritis. Gold-containing compounds with selective and specific targets are capable to assuage the symptoms of a range of human diseases. Gold (I) species with labile ligands (such as Cl in TEPAuCl) interact with isolated DNA; therefore, this biomolecule has been considered as a target for gold drugs. Gold (I) has a high affinity towards sulfur and selenium. Due to this, gold (I) drugs readily interact with cysteine or selenocysteine residue of the enzyme to form protein-gold(I) thiolate or protein-gold (I) selenolate complexes that lead to inhibition of the enzyme activity. Au(III) compounds due to their square-planner geometriesthe same as found in cisplatin, represent a good source for the development of anti-tumor agents. This article aims to review the most important applications of gold products in the treatment of human colon cancer and to analyze the complex interplay between gold and the human body.

Gold(III) complexes with thiosemicarbazonate ligands as potential anticancer agents: Cytotoxicity and interactions with biomolecular targets

Gold(III) complexes have been studied for the past years due to their anticancer properties and great affinity to biotargets, such as enzymes and proteins, which support their pharmacological applications. Within this scope, in this work the antiproliferative activities of two Au(III)-thiosemicarbazonate complexes, [AuClL₁] (1, L₁: (E,Z)-N-ethyl-N'-(3-nitroso-kN)butan-2-ylidene)carbamohydrazonothioato-k²N²,S) and [Au(Hdamp)L₂]Cl (2, L₂: N-(N'',N''-diethylaminothiocarbonyl)-N'(N''', N'''-dimethylcarbothioamide)benzamidineto-kN,k²S and Hdamp: 2-(N,N-dimethylaminomethyl)-phenyl-C¹), and their affinities to possible biological targets were investigated. Three different tumor cell lines were used to perform the cytotoxicity assays, including one cisplatin-resistant model, and the results showed lower EC₅₀ for 1 over 2 in every case: B16F10 (4.1 μM and 15.6 μM), A431 (4.0 μM and >50 μM) and OVCAR3 (4.2 μM and 24.5 μM). However, a lower toxicity to fibroblast 3T3 cell line was observed for 2 (30.58 μM) when compared to 1 (7.17 μM), resulting in comparable therapeutic indexes. Both complexes presented strong affinity to HSA: they distorted the secondary structure of the protein, as verified by circular dichroism, but 1 additionally presented the apparent fluorescence quenching constant (K_app) ten times greater than 2, which was probably due to the fact of 1 being able to denature HSA. The ethidium bromide displacement assay showed that neither 1 nor 2 are strong DNA intercalators, which is in agreement with what was observed through the UV-vis titration. In both cases, the 260 nm band presented hyperchromism, which can indicate ionic interactions or DNA damage. In fact, 1 was able to damage the pGEM plasmid, similarly to cisplatin, as verified by agarose gel electrophoresis and Atomic Force Microscopy. Biophysical studies in cancer cells model membranes were also performed in order to investigate the interaction of the gold complexes to lipid bilayers and revealed that the compounds interact with the membranes by exhibiting partition coefficients of 10³ order of magnitude. Overall, both complexes were found to be promising candidates for the development of a future anticancer drug against low sensitive or cisplatin resistant tumors.

Unveiling the Potential of Transition Metal Complexes for Medicine: Translational in Situ Activation of Metal-Based Drugs from Bench to in Vivo Applications

The development of metal-based anticancer drugs has been hampered, among other reasons, by their lack of selectivity for cancer cells. In a recent article, Zou and co-workers presented the successful intracellular activation of organogold(I) complexes for potential cancer treatment through Pd(II)-mediated transmetallation, overcoming some off-target activity of novel gold-based drugs. This unique strategy builds the perfect bridge between metallodrug usage and bioorthogonal intracellular catalysis for more advanced and selective therapies. Such an approach will hopefully pave the way for forthcoming studies in medicinal inorganic chemistry.

Multi-Targeted Anticancer Activity of Imidazolate Phosphane Gold(I) Compounds by Inhibition of DHFR and TrxR in Breast Cancer Cells

A class of phosphane gold(I) compounds, made of azoles and phosphane ligands, was evaluated for a screening on the regards of Breast Cancer cell panels (BC). The compounds possess N-Au-P or Cl-Au-P bonds around the central metal, and they differ for the presence of aprotic or protic polar groups in the azoles and/or the phosphane moieties to tune their hydrophilicity. Among the six candidates, only the compounds having the P-Au-N environment and not displaying neither the hydroxyl nor carboxyl groups in the ligands were found active. The compounds were screened by MTT tests in SKBR3, A17, and MDA-MB231 cancer cells, and two compounds (namely the 4,5-dicyano-imidazolate-1yl-gold(I)-(triphenylphosphane, 5, and 4,5-dichloro-imidazolate-1yl-gold(I)-triphenylphosphane, 6) were found very cytotoxic, with the most active with an IC₅₀ value of 3.46 μM in MDA-MB231 cells. By performing enzymatic assays in the treated cells lysates, the residual enzymatic activity of dihydrofolate reductase (DHFR) has been measured after cell treatment for 4 or 12 h in comparison with control cells. Upon 12 h of treatment, the activity of DHFR was significantly reduced in both SKBR3 and A17 cells by compounds 5 and 6, but not in human MDA-MB231 cells; interestingly, it was found remarkably high after 4 h of treatment, revealing a time dependence for the DHFR enzymatic assays. The DHFR inhibition data have been compared to those for the thioredoxin reductase (TrxR), the most recognized molecular target for gold compounds. For this latter, similar residual activities (i.e., 37 and 49% for the match of SKBR3 cells and compound 5 or 6, respectively) were found. Binding studies on the regards of ct-DNA (calf-thymus-DNA) and of plasma transporters proteins, such as BSA (bovine serum albumin) and ATF (apo transferrin), were performed. As expected for gold compounds, the data support strong binding to proteins (K_sv values range: 1.51 ÷ 2.46 × 10⁴ M⁻¹) and a weaker interaction with ct-DNA's minor groove (K_sv values range: 1.55 ÷ 6.12 × 10³ M⁻¹).

Preclinical Gold Complexes as Oral Drug Candidates to Treat Leishmaniasis Are Potent Trypanothione Reductase Inhibitors

The drugs currently used to treat leishmaniases have limitations concerning cost, efficacy, and safety, making the search for new therapeutic approaches urgent. We found that the gold(I)-derived complexes were active against L. infantum and L. braziliensis intracellular amastigotes with IC₅₀ values ranging from 0.5 to 5.5 μM. All gold(I) complexes were potent inhibitors of trypanothione reductase (TR), with enzyme IC₅₀ values ranging from 1 to 7.8 μM. Triethylphosphine-derived complexes enhanced reactive oxygen species (ROS) production and decreased mitochondrial respiration after 2 h of exposure, indicating that gold(I) complexes cause oxidative stress by direct ROS production, by causing mitochondrial damage or by impairing TR activity and thus accumulating ROS. There was no cross-resistance to antimony; in fact, SbR (antimony-resistant mutants) strains were hypersensitive to some of the complexes. BALB/c mice infected with luciferase-expressing L. braziliensis or L. amazonensis and treated orally with 12.5 mg/kg/day of AdT Et (3) or AdO Et (4) presented reduced lesion size and parasite burden, as revealed by bioimaging. The combination of (3) and miltefosine allowed for a 50% reduction in miltefosine treatment time. Complexes 3 and 4 presented favorable pharmacokinetic and toxicity profiles that encourage further drug development studies. Gold(I) complexes are promising antileishmanial agents, with a potential for therapeutic use, including in leishmaniasis caused by antimony-resistant parasites.

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.

Cu(ii)-induced twisting of the biphenyl core: exploring the effect of structure and coordination environment of biphenyl-based chiral copper(ii) complexes on interaction with calf-thymus DNA

Biphenyl core-based clip-like receptors get twisted after complexation with Cu²⁺. The extent of interaction of the optically active complexes with ct-DNA varies depending on the structure and coordination environment.

From coins to cancer therapy: Gold, silver and copper complexes targeting human topoisomerases

Cancer is a complex issue and, even though the prevention basics and therapy have been implemented, it is still the second leading death cause worldwide. With the hope to discover new powerful and safer molecules to fight cancer, many researchers focused their attention on metal-based compounds, starting from the most famous and successfully employed anticancer drug, i.e. cisplatin. The current article aims to report the most recent discoveries about the use of gold, silver and copper complexes as antitumor agents, highlighting their influences on important enzymes, namely human topoisomerases. The latter are fundamental for the cell life and, if overexpressed, strongly implicated in cancer onset and progression. The identification of lead complexes targeting human topoisomerases and gifted with the appropriate chemical and pharmacological properties represents a fecund starting point to obtain new and more effective anticancer molecules.

Biological Activity of Au(III) Complexes

The earliest therapy use of gold compounds dated in 2500 AD. In 1960s gold compounds were used in the treatment of rheumatoid arthritis, discoid lupus erythematosus, etc. Although the compounds of Au(I) are well-known and used in the modern medicine, new complexes of Au(III) and ligands with different donor atoms are synthetized and examined for their biological (antitumor, antimicrobial) activity. So far conducted studies show that complexes with Au(III) as central metal ions have greater activity compared with free ligands. Future syntheses should be based on the increase of biological activity with complexes that have necessary stability under physiological conditions.

Organometallic Gold(III) Complex [Au(Hdamp)(L14)]+ (L1 = SNS-Donating Thiosemicarbazone) as a Candidate to New Formulations against Chagas Disease

Chagas disease remains a serious public health concern with unsatisfactory treatment outcomes due to strain-specific drug resistance and various side effects. To identify new therapeutic drugs against Trypanosoma cruzi, we evaluated both the in vitro and in vivo activity of the organometallic gold(III) complex [Au(III)(Hdamp)(L1⁴)]Cl (L1 = SNS-donating thiosemicarbazone), henceforth denoted 4-Cl. Our results demonstrated that 4-Cl was more effective than benznidazole (Bz) in eliminating both the extracellular trypomastigote and intracellular amastigote forms of the parasite without cytotoxic effects on mammalian cells. In in vivo assays, 4-Cl in PBS solution loses the protonation and becomes the 4-neutral. 4-Neutral reduced parasitaemia and tissue parasitism in addition to protecting the liver and heart from tissue damage at 2.8 mg/kg/day. All these changes resulted in the survival of 100% of the mice treated with the gold complex during the acute phase. Analyzing the surviving animals of the acute infection, the parasite load after 150 days of infection was equivalent to those treated with the standard dose of Bz without demonstrating the hepatotoxicity of the latter. In addition, we identified a modulation of interferon gamma (IFN-γ) levels that may be targeting the disease's positive outcome. To the best of our knowledge, this is the first gold organometallic study that shows promise in an in vivo experimental model against Chagas disease.

Efficient Gold(I) Acyclic Diaminocarbenes for the Synthesis of Propargylamines and Indolizines

Mononuclear gold(I) acyclic diaminocarbenes (ADCs) were prepared by the reaction of 1,2-cyclohexanediamine with the corresponding isocyanide complexes [AuCl(CNR)] (R = Cy, t Bu). The three-component coupling of aldehydes, amines, and alkynes was investigated by using these gold(I) ADC complexes. The new gold(I) metal complexes are highly efficient catalysts for the synthesis of propargylamines and indolizines in the absence of solvent and in mild conditions. This method affords the corresponding final products with excellent yields in short reaction times. Additionally, chiral gold(I) complexes with ADCs have been prepared and tried in the enantioselective synthesis of propargylamines.

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.

New insights in Au-NHCs complexes as anticancer agents

Within the research field of antitumor metal-based agents alternative to platinum drugs, gold(I/III) coordination complexes have always been in the forefront due mainly to the familiarity of medicinal chemists with gold compounds, whose application in medicine goes back in the ancient times, and to the rich chemistry shown by this metal. In the last decade, N-heterocyclic carbene ligands (NHC), a class of ligands that largely resembles the chemical properties of phosphines, became of interest for gold(I) medicinal applications, and since then, the research on NHC-gold(I/III) coordination complexes as potential antiproliferative agents boosted dramatically. Different classes of gold(I/III)-NHC complexes often showed an outstanding in vitro antiproliferative activity, however up to now very few in vivo data have been reported to corroborate the in vitro results. This review summarizes all achievements in the field of gold (I/III) complexes comprising NHC ligands proposed as potential antiproliferative agents in the period 2004-2016, and critically analyses biological data (mainly IC₅₀ values) in relation to the chemical structures of Au compounds. The state of art of the in vivo studies so far described is also reported.