The anti-cancer properties of gold(III) compounds with dianionic porphyrin and tetradentate ligands

Gold Tripyrrindione: Redox Chemistry and Reactivity with Dichloromethane

The identification of ligands that stabilize Au(III) centers has led to the isolation of complexes for applications in catalysis, gold-based therapeutics, and functional materials. Herein, we report the coordination of gold by tripyrrin-1,14-dione, a linear tripyrrole with the scaffold of naturally occurring metabolites of porphyrin-based protein cofactors (e.g., heme). Tripyrrindione H3TD2 binds Au(III) as a trianionic tridentate ligand to form square planar complex [Au(TD2)(H2O)], which features an adventitious aqua ligand. Two reversible ligand-based oxidations of this complex allow access to the other known redox states of the tripyrrindione framework. Conversely, (spectro)electrochemical measurements and DFT analysis indicate that the reduction of the complex is likely metal-based. The chemical reduction of [Au(TD2)(H2O)] leads to a reactive species that utilizes dichloromethane in the formation of a cyclometalated organo-Au(III) complex. Both the aqua and the organometallic Au(III) complexes were characterized in the solid state by microcrystal electron diffraction (MicroED) methods, which were critical for the analysis of the microcrystalline sample of the organo-gold species. Overall, this study illustrates the synthesis of Au(III) tripyrrindione as well as its redox profile and reactivity leading to gold alkylation chemistry.

Dual Fluorescence and Phosphorescence Emissions from Dye-Modified (NCN)-Bismuth Pincer Thiolate Complexes

We report the synthesis, characterization, and photophysical properties of four new dye-modified (NCN)Bi pincer complexes with two mercaptocoumarin or mercaptopyrene ligands. Their photophysical properties were probed by UV/vis spectroscopy, photoluminescence (PL) studies, and time-dependent density functional theory (TD-DFT) calculations. Absorption spectra of the complexes are dominated by mixed pyrene or coumarin π → π*/n(pS) → pyrene or coumarin π* transitions. While unstable toward reductive elimination of the corresponding disulfide under irradiation at room temperature, the complexes provide stable emissions at 77 K. Under these conditions, coumarin complexes 2 and 4 exhibit exclusively green phosphorescence at 508 nm. In contrast, the emissive properties of pyrene complexes 1 and 3 depend on the excitation wavelength and on sample concentration. Irradiation into the lowest-energy absorption band exclusively triggers red phosphorescence from the pyrenyl residues at 640 nm. At concentrations c < 1 μM, excitation into higher excited electronic states results in blue pyrene fluorescence. With increasing c (1-100 μM), the emission profile changes to dual fluorescence and phosphorescence emission, with a steady increase of the phosphorescence intensity, until at c ≥ 1 mM only red phosphorescence ensues. Progressive red-shifts and broadening of steady-state excitation spectra with increasing sample concentration suggest the presence of static excimers, as we observe it for concentrated solutions of pyrene. Crystalline and powdered samples of 1 indeed show intermolecular association through π-stacking. TD-DFT calculations on model dimers and a tetramer of 1 support the idea of aggregation-induced intersystem crossing (AI-ISC) as the underlying reason for this behavior.

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.

Harnessing the power of gold: advancements in anticancer gold complexes and their functionalized nanoparticles

Cancer poses a formidable challenge, necessitating improved treatment strategies. Metal-based drugs and nanotechnology offer new hope in this battle. Versatile gold complexes and functionalized gold nanoparticles exhibit unique properties like biologically inert behaviour, outstanding light absorption, and heat-conversion abilities. These nanoparticles can be finely tuned for drug delivery, enabling precise and targeted cancer therapy. Their exceptional drug-loading capacity and low toxicity, stemming from excellent stability, biocompatibility, and customizable shapes, make them a promising option for enhancing cancer treatment outcomes and improving diagnostic imaging. Leveraging these attributes, researchers can design more effective and targeted cancer therapeutics. The potential of functionalized gold nanoparticles to advance cancer treatment and diagnostics holds a promising avenue for further exploration and development in the fight against cancer. This review article delves into the finely tuned attributes of functionalized gold nanoparticles, unveiling their potential for application in drug delivery for precise and targeted cancer therapy.

Serum-Stable Gold(III) Bisphosphine Complex Induces Mild Mitochondrial Uncoupling and In Vivo Antitumor Potency in Triple Negative Breast Cancer

The preparation of cyclometalated complexes offers a path to stable materials, catalysts, and therapeutic agents. Here, we explore the anticancer potential of novel biphenyl organogold(III) cationic complexes supported by diverse bisphosphine ligands, Au-1-Au-5, toward aggressive glioblastoma and triple negative breast cancer cells (TNBCs). The [C^C] gold(III) complex, Au-3, exhibits significant tumor growth inhibition in a metastatic TNBC mouse model. Remarkably, Au-3 displays promising blood serum stability over a relevant therapeutic window of 24 h and alteration in the presence of excess L-GSH. The mechanism-of-action studies show that Au-3 induces mitochondrial uncoupling, membrane depolarization, and G1 cell cycle arrest and prompts apoptosis. To the best of our knowledge, Au-3 is the first biphenyl gold-phosphine complex to uncouple mitochondria and inhibit TNBC growth in vivo.

The anti-breast cancer stem cell properties of gold(i)-non-steroidal anti-inflammatory drug complexes

The anti-breast cancer stem cell (CSC) properties of a series of gold(i) complexes comprising various non-steroidal anti-inflammatory drugs (NSAIDs) and triphenylphosphine 1-8 are reported. The most effective gold(i)-NSAID complex 1, containing indomethacin, exhibits greater potency for breast CSCs than bulk breast cancer cells (up to 80-fold). Furthermore, 1 reduces mammosphere viability to a better extent than a panel of clinically used breast cancer drugs and salinomycin, an established anti-breast CSC agent. Mechanistic studies suggest 1-induced breast CSC death results from breast CSC entry, cytoplasm localisation, an increase in intracellular reactive oxygen species levels, cyclooxygenase-2 downregulation and inhibition, and apoptosis. Remarkably, 1 also significantly inhibits tumour growth in a murine metastatic triple-negative breast cancer model. To the best of our knowledge, 1 is the first gold complex of any geometry or oxidation state to demonstrate anti-breast CSC properties.

Selective and rapid extraction of trace amount of gold from complex liquids with silver(I)-organic frameworks

The design of adsorbents for rapid, selective extraction of ultra-trace amounts of gold from complex liquids is desirable from both an environmental and economical point of view. However, the development of such materials remains challenging. Herein, we report the fabrication of two vinylene-linked two-dimensional silver(I)-organic frameworks prepared via Knoevenagel condensation. This material enables selective sensing of gold with a low limit of detection of 60 ppb, as well as selective uptake of ultra-trace gold from complex aqueous mixtures including distilled water with 15 competing metal ions, leaching solution of electronic waste (e-waste), wastewater, and seawater. The present adsorbent delivers a gold adsorption capacity of 954 mg g^-1, excellent selectivity and reusability, and can rapidly and selectively extract ultra-trace gold from seawater down to ~20 ppb (94% removal in 10 minutes). In addition, the purity of recovered gold from e-waste reaches 23.8 Karat (99.17% pure).

Evaluation of the biocompability and corrosion activity of resorbable CaMgZnYbBAu alloys

Calcium-based alloys can be promising candidates for use as biodegradable implants because of attractive properties as mechanical, corrosive, and biocompatible. In the work, the biocompatibility authors discussed the results of the Ca32Mg12Zn38Yb18-xBx (x = 0, 1, 2, 3 at.%) and Ca32Mg12Zn38Yb18-2xBxAux (x = 1, 2 at.%) alloys. The tests were performed using a MTT assay. The corrosion behavior of such Ca-based alloys in PWE fluid at 37 °C was studied and compared with the results in Ringer's solution from previous works. Electrochemical tests were presented by open circuit potential and potentiodynamic curves. Different concentrations of boron and gold in the alloys caused changes in the corrosion results. The best corrosion resistance in PWE solution was observed for the Ca-based alloy with 2 at.% Au due to the lowest value of the corrosion current density (jcorr), equal to 10.6 µA·cm-2. A slightly higher value of jcorr was obtained for the Ca32Mg12Zn38Yb15B3 alloy with the lowest roughness values. The results of the cytotoxicity tests also showed that the alloy with 3 at.% boron was characterized by the highest cell viability. The investigation results discussed in the work allow us to suggest that the presented calcium alloys with 3 at.% of B, and 2 at.% of Au addition may be promising materials for the use in implantology.

Mathematical processing of trading strategy based on long short-term memory neural network model

At present, gold and bitcoin have become mainstream assets in market transactions. Due to the volatility of gold and bitcoin prices, we can buy and sell assets like gold and bitcoin the same way we buy and sell stocks. The research goal of this article is to develop an optimal trading strategy that maximizes our post-trade returns. By studying the relationship between the two, on the one hand, it supplements and enriches the theoretical research on the rate of return of gold and Bitcoin, on the other hand, it provides a certain reference for investors to construct investment strategies. The research on the cointegration relationship between them has important practical significance. At the same time, it has important practical significance for the research on the cointegration relationship between bitcoin and gold.

NIR-emissive, singlet-oxygen-sensitizing gold tetra(thiocyano)corroles

Presented herein are two fully characterized gold tetrathiocyanocorroles representing a potentially significant new class of NIR-emissive 5d-metallocorroles. The four SCN groups on the bipyrrole unit of the corrole exert a powerful electron-withdrawing effect, upshifting both the oxidation and reduction potentials by roughly half a volt relative to their unsubstituted counterparts. That said, the upshift of the LUMO is somewhat higher than that of the HOMO so these complexes also exhibit a smaller HOMO-LUMO gap, as evinced in both electrochemical measurements and Q band energies (∼595 nm relative to ∼571 nm for their SCN-free counterparts). The new compounds exhibit NIR phosphorescence under ambient conditions with emission maxima around 900 nm (compared with 790 nm for simple Au triarylcorroles), phosphorescence quantum yields around 0.3%, phosphorescence lifetimes around 10 μs, and singlet oxygen sensitization with a quantum yield of around 50 ± 5% in solution, together signifying wide-ranging potential applications as triplet photosensitizers in oxygen sensing and photodynamic therapy.

Potential Application of Photosensitizers With High-Z Elements for Synergic Cancer Therapy

The presence of heavy elements in photosensitizers (PS) strongly influences their electronic and photophysical properties, and hence, conjugation of PS with a suitable element is regarded as a potential strategy to improve their photodynamic properties. Moreover, PS conjugated to metal ion or metal complex and heavy atoms such as halogen have attracted considerable attention as promising agents for multimodal or synergistic cancer therapy. These tetrapyrrole compounds depending on the type and nature of the inorganic elements have been explored for photodynamic therapy (PDT), chemotherapy, X-ray photon activation therapy (PAT), and radiotherapy. Particularly, the combination of metal-based PS and X-ray irradiation has been investigated as a promising novel approach for treating deep-seated tumors, which in the case of PDT is a major limitation due to low light penetration in tissue. This review will summarize the present status of evidence on the effect of insertion of metal or halogen on the photophysical properties of PS and the effectiveness of various metal and halogenated PS investigated for PDT, chemotherapy, and PAT as mono and/or combination therapy.

Hetero- and homoleptic binuclear gold(I)-thiolate and -halide complexes - ligand exchange kinetics and supramolecular structures

Heteroleptic and homoleptic binuclear Au(I) complexes [Au2(μ-PAnP)(SPh)(X)] (X = Cl^- or Br^-), [Au2(μ-PAnP)(SPh)2] and [Au2(μ-PAnP)(SPhCO2H)2] (SPh = benzenethiolate and SPhCO₂H = 4-thiolatobenzoic acid) containing the bridging diphosphine, 9,10-bis(diphenylphosphino)anthracene (PAnP), were synthesized and characterized by single crystal X-ray diffraction. [Au2(μ-PAnP)(SPh)2] exists as a monomer in its crystals but [Au2(μ-PAnP)(SPhCO2H)2] polymerizes into zig-zag chains via intermolecular hydrogen bonding. [Au2(μ-PAnP)(SPh)(Cl)] forms cyclophane-like dimers of C_i symmetry in crystals via intermolecular aurophilic interactions (Au-Au distance = 3.3081(5) Å). Recrystallization of [Au2(μ-PAnP)(SPh)(Br)] invariably led to crystals composed of [Au2(μ-PAnP)(SPh)(Br)] and [Au2(μ-PAnP)(Br)2]. Despite the chemically different P atoms in the heteroleptic [Au2(μ-PAnP)(SPh)(Cl)] and [Au2(μ-PAnP)(SPh)(Br)], solutions of the complexes show only a single signal in their ³¹P{¹H} NMR spectra at room temperature which resolved into two singlets of equal intensity at 183 K. Identical signals which show the same thermal behavior were observed in solutions of [Au2(μ-PAnP)(SPh)2] and [Au2(μ-PAnP)(X)2] in 1 : 1 molar ratios, indicating that there are three exchanging species, [Au2(μ-PAnP)(SPh)(X)], [Au2(μ-PAnP)(SPh)2] and [Au2(μ-PAnP)(X)2], in solution. A solution of [Au2(μ-PAnP)(Cl)2] and [Au2(μ-PAnP)(Br)2] in 1 : 1 molar ratio shows two singlets, implying that the exchange is not due to the dissociation of either PAnP or halide ligands, but rather it involves the exchange of the thiolate and the halide ligands (SPh^- ↔ X^-). A mixture of [(PPh3)Au(SPh)] and [(PPh3)Au(Cl)] (1 : 1 molar ratio) showed only one signal in its room temperature ³¹P{¹H} NMR spectrum, indicating that the ligand exchange can happen intermolecularly. Self-exchange of SPh^- ligands is possible as the room temperature ³¹P NMR spectrum of a mixture of [Au2(μ-PAnP)(SPh)2] and [Au2(μ-PAnP)(SPhCO2H)2] displayed only one signal. The rate constants of the exchange were determined by fitting the line shapes of the ³¹P NMR signals at different temperatures. The activation energies (E_as), obtained from Arrhenius plots, for the SPh^- ↔ Cl^- and SPh^- ↔ Br^- exchange are 36.9 ± 0.7 and 33.7 ± 1.0 kJ mol^-1, respectively. The activation enthalpy and activation entropy, obtained from Eyring plots, for the SPh^- ↔ Cl^- and SPh^- ↔ Br^- exchange are 35.0 ± 0.7 kJ mol^-1 and -25.7 ± 3.2 J K^-1, and 32.0 ± 1.0 kJ mol^-1 and -21.8 ± 4.7 J K^-1, respectively. Based on the kinetic results, two possible mechanisms were proposed for the reactions.

Computational Studies of Au(I) and Au(III) Anticancer MetalLodrugs: A Survey

Owing to the growing hardware capabilities and the enhancing efficacy of computational methodologies, computational chemistry approaches have constantly become more important in the development of novel anticancer metallodrugs. Besides traditional Pt-based drugs, inorganic and organometallic complexes of other transition metals are showing increasing potential in the treatment of cancer. Among them, Au(I)- and Au(III)-based compounds are promising candidates due to the strong affinity of Au(I) cations to cysteine and selenocysteine side chains of the protein residues and to Au(III) complexes being more labile and prone to the reduction to either Au(I) or Au(0) in the physiological milieu. A correct prediction of metal complexes' properties and of their bonding interactions with potential ligands requires QM computations, usually at the ab initio or DFT level. However, MM, MD, and docking approaches can also give useful information on their binding site on large biomolecular targets, such as proteins or DNA, provided a careful parametrization of the metal force field is employed. In this review, we provide an overview of the recent computational studies of Au(I) and Au(III) antitumor compounds and of their interactions with biomolecular targets, such as sulfur- and selenium-containing enzymes, like glutathione reductases, glutathione peroxidase, glutathione-S-transferase, cysteine protease, thioredoxin reductase and poly (ADP-ribose) polymerase 1.

Water-Soluble Gold(III)-Metformin Complex Alters Mitochondrial Bioenergetics in Breast Cancer Cells

Chemical control of mitochondrial dynamics and bioenergetics can unravel fundamental biological mechanisms and therapeutics for several diseases including, diabetes and cancer. We synthesized stable, water-soluble gold(III) complexes (Auraformin) supported by biguanide metformin or phenylmetformin for efficacious inhibition of mitochondrial respiration. The new compounds were characterized following the reaction of [C N]-cyclometalated gold(III) compounds with respective biguanides. Auraformin is solution stable in a physiologically relevant environment. We show that auraformin decreases mitochondrial respiration efficiently in comparison to the clinically used metformin by 100-fold. The compound displays significant mitochondrial uptake and induces antiproliferative activity in the micromolar range. Our results shed light on the development of new scaffolds as improved inhibitors of mitochondrial respiration.

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.

Pectin-Coated Plasmonic Nanoparticles for Photodynamic Therapy: Inspecting the Role of Serum Proteins

Plasmonic metal nanoparticles (NPs) can be used as enhancers of the efficiency of standard photosensitizers (PSs) in photodynamic therapy (PDT). Protein corona, the adsorption layer that forms spontaneously around NPs once in contact with biological fluids, determines to a great extent the efficiency of PDT. In this work, we explore the possibility that pectin-coated Au NPs (Au@Pec NPs) could act as adjuvants in riboflavin (Rf)-based PDT by comparing the photodamage in HeLa cells cultured in the presence and in the absence of the NPs. Moreover, we investigate the impact that the preincubation of Rf and Au@Pec NPs (or Ag@Pec NPs) at two very different serum concentrations could have on cell's photodamage. Because reactive oxygen species (ROS) precursors are the excited states of the PS, the effect of proteins on the photophysics of Rf and Rf/plasmonic NPs was studied by transient absorption experiments. The beneficial effect of Au@Pec NPs in Rf-based PDT on HeLa cells cultured under standard serum conditions was demonstrated for the first time. However, the preincubation of Rf and Au@Pec NPs (or Ag@Pec NPs) with serum has undesirable results regarding the enhancement of Rf-based PDT. In this sense, we also verified that more concentrated protein conditions result in lower amounts of the triplet excited state of Rf and thus an expected lower production of ROS, which are the key elements for PDT's efficacy. These findings point out the relevance of serum concentration in the design of in vitro cell culture experiments carried out to determine the best way to combine and use potential sensitizers with plasmonic NPs to develop more effective PDTs.

Unraveling Halogen Effects in Supramolecular Polymerization

Halogens play a crucial role in numerous natural processes and synthetic materials due to their unique physicochemical properties and the diverse interactions they can engage in. In the field of supramolecular polymerization, however, halogen effects remain poorly understood, and investigations have been restricted to halogen bonding or the inclusion of polyfluorinated side groups. Recent contributions from our group have revealed that chlorine ligands greatly influence molecular packing and pathway complexity phenomena of various metal complexes. These results prompted us to explore the role of the halogen nature on supramolecular polymerization, a phenomenon that has remained unexplored to date. To address this issue, we have designed a series of archetypal bispyridyldihalogen Pt^II complexes bearing chlorine (1), bromine (2), or iodine (3) and systematically compared their supramolecular polymerization in nonpolar media using various experimental methods and theory. Our studies reveal a remarkably different supramolecular polymerization for the three compounds, which can undergo two competing pathways with either slipped (kinetic) or parallel (thermodynamic) molecular packing. The halogen exerts an inverse effect on the energetic levels of the two self-assembled states, resulting in a single thermodynamic pathway for 3, a transient kinetic species for 2, and a hidden thermodynamic state for 1. This seesaw-like bias of the energy landscape can be traced back to the involvement of the halogens in weak N-H···X hydrogen-bonding interactions in the kinetic pathway, whereas in the thermodynamic pathway the halogens are not engaged in the stabilizing interaction motif but rather amplify solvophobic effects.

Synergetic anticancer activity of gold porphyrin appended to phenyl tin malonate organometallic complexes

The discovery of novel anticancer chemotherapeutics is fundamental to treat cancer more efficiently. Towards this goal, two dyads consisting of a gold porphyrin appended to organotin(iv) entities were synthesized and their physicochemical and biological properties were characterized. One dyad contains a gold porphyrin connected to a tin(iv) cation via a malonate and two phenyl ligands (AuP-SnPh₂), while the other contains two tin(iv) cations each chelated to one carboxylic acid group of the malonate and three phenyl ligands (AuP-Sn₂Ph₆). The mode of chelation of Sn(iv) to the malonate was elucidated by IR spectroscopy and ¹¹⁹Sn NMR. In the solid state, the complexes exist as coordination polymers in which the tin is penta-coordinated and bridged to two different malonate units. In solution the chemical shifts of ¹¹⁹Sn signals indicate that the tin complexes are in the form of monomeric species associated with a tetra-coordinated tin cation. The therapeutic potential of these new compounds was assessed by determining their cytotoxic activities on human breast cancer cells (MCF-7) and on healthy human fibroblasts (FS 20-68). The study reveals that the dyads are more potent anticancer drugs than the mixture of their individual components (gold porphyrin and reference tin complexes). Therefore, the covalent link of organotin complexes to a gold porphyrin induces a synergistic cytotoxic effect. The dyad AuP-SnPh₂ shows high cytotoxicity (0.13 μM) against MCF-7 along with good selectivity for cancer cells versus healthy cells. Finally, it was also shown that the dyad AuP-Sn₂Ph₆ exhibits a very high anticancer activity (LC₅₀ = 0.024 μM), but the presence of two tin units induces strong cytotoxicity on healthy cells too (LC₅₀ = 0.032 μM). This study underscores, thus, the potential of the association of gold porphyrin and organotin complexes to develop anticancer metallo-drugs.

Methionine oxidation of proteins analyzed by affinity capillary electrophoresis in presence of silver(I) and gold(III) ions

Oxidative damage of biopharmaceuticals during manufacturing and storage is a key concern throughout pharmaceutical development. However, few simple and robust analytical methods are available for the determination of oxidation sites. Here, the potential of affinity capillary electrophoresis (ACE) in the separation of proteins with oxidized methionine (Met) residues is shown. Silver(I) and gold(I) ions have the attribute to selectively form complexes with thioethers over sulfoxides. The addition of these ions to the BGE leads to a selective complexation of Met residues and, thus, to a change of charge allowing separation of species according to the different oxidation states of Met. The mechanisms of these interactions are discussed and binding constants for peptides containing Met with silver(I) are calculated. Additionally, the proposed method can be used as an indicator of oxidative stress in large proteins. The presented technique is easily accessible, economical, and has rapid analysis times, adding new approaches to the analytical toolbox of Met sulfoxide detection.

Au(III) complexes with tetradentate-cyclam-based ligands

Chiral cyclam (1,4,8,11-tetraazacyclotetradecane) derivatives were synthesized stepwise from chiral mono-Boc-1,2-diamines and (dialkyl)malonyl dichloride via open diamide-bis(N-Boc-amino) intermediates (65-91%). Deprotection and ring closure with a second malonyl unit afforded the cyclam tetraamide precursors (80-95%). The new protocol allowed the preparation of the target cyclam derivatives (53-59%) by a final optimized hydride reduction. Both the open tetraamine intermediates and the cyclam derivatives successfully coordinated with AuCl₃ to give moderate to excellent yields (50-96%) of the corresponding novel tetra-coordinated N,N,N,N-Au(III) complexes with alternating five- and six-membered chelate rings. The testing of the catalytic ability of the cyclam-based N,N,N,N-Au(III) complexes demonstrated high catalytic activity of some complexes in selected test reactions (full conversion in 1-24 h, 62-97% product yields).

Mononuclear gold(iii) complexes with diazanaphthalenes: the influence of the position of nitrogen atoms in the aromatic rings on the complex crystalline properties

A series of mononuclear gold(iii) complexes of the general formula [AuCl3(diazanaphthalene)], where diazanaphthalene is quinazoline (qz, 1), phthalazine (phtz, 2), 1,5-naphthyridine (1,5-naph, 3), 1,6-naphthyridine (1,6-naph, 4) or 1,8-naphthyridine (1,8-naph, 5), were prepared and fully characterized. The complexes 1-5 consist of discrete monomeric species with the Au(iii) cation in a square planar coordination geometry surrounded by three chloride anions and one diazanaphthalene ligand. Crystallographic studies indicate the presence of an extended 4 + 1 or 4 + 2 geometry around the square planar [AuCl3(diazanaphthalene)] center due to Au⋯Cl and Au⋯N interactions. The crystal structures of these complexes are controlled by a variety of intermolecular interactions that utilize the amphiphilic properties of the coordinated chloride anions and involve C-H groups, π-electrons, and an uncoordinated nitrogen atom of the diazanaphthalene ligand. The usual offset π-stacking between the N-heteroaromatic ligands appears to be completely hindered between the 1,5-naph fragments and significantly weakened between the 1,6-naph and 1,8-naph in their respective complexes 3, 4 and 5, for which the average molecular polarizability (α) values are the lowest in the series. It is remarkable that the [AuCl3(benzodiazine)] complexes 1 and 2 form centrosymmetric crystals, but the [AuCl3(naphthyridine)] complexes 3-5 assemble into non-centrosymmetric aggregates, making them potential alternatives to the previously studied systems for application in various fields by taking advantage of their polarity.

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.

Gold(III) Complexes: An Overview on Their Kinetics, Interactions With DNA/BSA, Cytotoxic Activity, and Computational Calculations

In the last few years, metallodrugs play a key role in the development of medicinal chemistry. The choice of metal ion, its oxidation state and stability, and the choice of inert and labile ligands are just some of the very important facts which must be considered before starting the synthesis of complexes with utilization in medicinal purpose. As a result, a lot of compounds of different transition metal ions found application for diagnostic and therapeutic purpose. Beside all, gold compounds have attracted particular attention. It is well-known that gold compounds could be used for the treatment of cancer, HIV, rheumatoid arthritis (chrysotherapy), and other diseases. This metal ion has unoccupied d-sublevels and possibility to form compounds with different oxidation states, from -1 to +5. However, gold(I) and gold(III) complexes are dominant in chemistry and medicine. Especially, gold(III) complexes are of great interest due to their structural similarity with cisplatin. Accordingly, this review summarizes the chemistry of some mononuclear and polynuclear gold(III) complexes. Special attention is given to gold(III) complexes with nitrogen-donor inert ligands (aliphatic or aromatic that have a possibility to stabilize complex) and their kinetic behavior toward different biologically relevant nucleophiles, mechanism of interaction with DNA/bovine serum albumin (BSA), cytotoxic activity, as well as computational calculations.

Zinc-Containing Metalloenzymes: Inhibition by Metal-Based Anticancer Agents

DNA is considered to be the primary target of platinum-based anticancer drugs which have gained great success in clinics, but DNA-targeted anticancer drugs cause serious side-effects and easily acquired drug resistance. This has stimulated the search for novel therapeutic targets. In the past few years, substantial research has demonstrated that zinc-containing metalloenzymes play a vital role in the occurrence and development of cancer, and they have been identified as alternative targets for metal-based anticancer agents. Metal complexes themselves have also exhibited a lot of appealing features for enzyme inhibition, such as: (i) the facile construction of 3D structures that can increase the enzyme-binding selectivity and affinity; (ii) the intriguing photophysical and photochemical properties, and redox activities of metal complexes can offer possibilities to design enzyme inhibitors with multiple modes of action. In this review, we discuss recent examples of zinc-containing metalloenzyme inhibition of metal-based anticancer agents, especially three zinc-containing metalloenzymes overexpressed in tumors, including histone deacetylases (HDACs), carbonic anhydrases (CAs), and matrix metalloproteinases (MMPs).

Imidazole and Benzimidazole Modified Half-Sandwich IridiumIII N-Heterocyclic Carbene Complexes: Synthesis, Anticancer Application, and Organelle Targeting

Herein, we report the synthesis, characterization and anticancer activity of a series of half-sandwich iridium^III imidazole and benzimidazole N-heterocyclic carbene (NHC) anticancer complexes, and the general formula of which can be expressed as [(η⁵-Cp^x)Ir(C^∧N)Cl]Cl (Cp^x: pentamethylcyclopentadienyl (Cp^*) or biphenyl derivatives (Cp^xbiph); C^∧N: imidazole and benzimidazole NHC chelating ligands). Compared with cis-platin, these complexes showed interesting antitumor activity against A549 cells. Complexes could bind to bovine serum albumin (BSA) by means of static quenching mode, catalyze the oxidation of nicotinamide adenine dinucleotide (NADH) and increase the levels of reactive oxygen species (ROS). Meanwhile, these complexes could arrest the cell cycles of A549 cells and influence the mitochondrial membrane potential significantly. Due to the inherent luminescence property, laser confocal test show that complexes could enter cells followed an energy-dependent mechanism and effectively accumulate in lysosome (the value of Pearson's co-localization coefficient is 0.70 after 1 h), further destroy lysosome integrity and induce apoptosis.

Synthesis, X-ray characterization and regium bonding interactions of a trichlorido(1-hexylcytosine)gold(iii) complex

Herein we report the synthesis and X-ray characterization of a gold(iii) complex of 1-hexylcytosine via N(3). The AuCl₃N complexes stack on top of each other by reciprocal [AuCl] regium bonding interactions. After the first example 35 years ago, this is the second available structure of a cytosine nucleobase model complexed to gold(iii).

Synthesis, characterization, and biological studies of multidentate gold(i) and gold(iii) NHC complexes

The synthesis and characterization of a novel macrocyclic Au(iii) N-heterocyclic carbene (NHC) imidazolyl complex, a novel macrocyclic tetra-NHC benzimidazole ligand, and the corresponding Ag(i) and Au(i) complexes are presented. Single-crystal X-ray diffraction analysis of the Au(i) benzimidazolyl complex 3 reveals an unusual structure, differing from the respective Au(i) imidazolyl complex 4. Both complexes have a Au₄L₂ composition; however, 3 has two C-Au(i)-C units acting as a connection between the two ligands with two Au(i) atoms being linearly coordinated inside the cavity of the macrocyclic ligand. In the case of complex 4, the structure shows a box-type coordination with all four Au(i) atoms being located between the two ligands. Stability studies in cell culture medium are performed for subsequent MTT assays and they show an unprecedented proton-to-deuterium exchange of the methylene bridge of the Au(iii) imidazolyl complex. In MTT assays, the tetranuclear acyclic Au(i) complex 5 displays the lowest IC₅₀ values in MCF-7, PC3, and A2780cisR cells with a selective cytotoxicity for MCF-7 and A2780cisR cells.

Synthesis and Anticancer Activity of Gold Porphyrin Linked to Malonate Diamine Platinum Complexes

Recently, gold(III) porphyrins have gained great interest as anticancer drugs not only for the stability of gold(III) but also for the functionalization of the porphyrin to allow bridging with another metal such as platinum(II). We report here, for the first time, the synthesis of three new bimetal compounds containing a gold(III) porphyrin conjugated to a platinum diamine moiety through malonate bridging to obtain enhanced cytotoxicity from both metals combined with the phototoxicity of the porphyrin. The three complexes differ in the type of diamine ligand around platinum(II): ammonia (NH₃), cyclohexanediamine (CyDA), and pyridylmethylamine (Py). The synthesis was carried out using the complexation of activated malonic acid derivatives with aquadiaminoplatinum(II) complexes, and the products were characterized by IR, NMR, mass spectra, and elementary analysis. The cytotoxic activity of the conjugates was screened in both healthy cell lines and cancer cell lines, human fibroblast cells (FS-68) and human breast cancer cells (MCF-7), and was compared to that of the corresponding platinum(II) complexes. The cyclohexyldiamine (CyDA) derivative exhibited the greatest cytotoxic effect among the series. The results showed that Au(III)/Pt(II) conjugates are more potent by 2-5.6-fold than the corresponding platinum complexes. Moreover, the dyad AuP-PtCyDA is 18% more potent and also more selective toward cancer cells than the parent gold porphyrin substituted with malonic acid. On the other hand, the IC₅₀ of the dyad AuP-PtCyDA is 43% lower than that of AuTPP but is more selective toward healthy cells. Singlet oxygen measurements indicated that gold(III) porphyrin derivatives are poor oxygen sensitizers and cell death occurred potentially due to generation of other reactive oxygen species (ROS) upon reductive quenching of the gold porphyrin excited state. In addition, the increase in cancer cell death obtained after light irradiation is totally absent in healthy cells, demonstrating the specificity of this PDT treatment on cancer cells. Our findings imply that the incorporation of two different cytotoxic metals in the same molecule represents a remarkable cytotoxic effect in comparison to traditional homometallic Pt(II) drugs.

Electrochemical Sensors Containing Schiff Bases and their Transition Metal Complexes to Detect Analytes of Forensic, Pharmaceutical and Environmental Interest. A Review

Schiff bases and their transition metal complexes are inexpensive and easy to synthesize. These compounds display several structural and electronic features that allow their application in numerous research fields. Over the last three decades, electroanalytical scientists of various areas have developed electrochemical sensors from many compounds. The present review discusses the applicability of Schiff bases, their transition metal complexes and new materials containing these compounds as electrode modifiers in sensors to detect analytes of forensic, pharmaceutical and environmental interest. In forensic sciences, Schiff bases are mainly used to analyze illicit drugs: chemical reactions involving Schiff bases can help to elucidate illicit drug production and to determine analytes in seized samples. In the environmental area, given that most methodologies provide Limit of Detection (LOD) values below the values recommended by regulatory agencies, Schiff bases constitute a promising strategy. As for pharmaceutical applications, Schiff bases represent an approach for analysis of complex biological samples containing low levels of the target analytes in the presence of a large quantity of interfering compounds. This review will show that new highly specific materials can be synthesized based on Schiff bases and applied in the pharmaceutical industry, toxicological studies, electrocatalysis and biosensors. Most literature papers have reported on Schiff bases combined with carbon paste to give a chemically modified electrode that is easy and inexpensive to produce and which displays specific and selective sensing capacity for different applications.

Stimuli-Responsive Near-Infrared Emissive Os(II)-Terpyridine Complexes with a Sense of Logic

Two bis-tridentate Os(II) compounds based on a heteroditopic terpyridine-bipyridine-type ligand were synthesized, and their photophysical properties were thoroughly studied. The compounds exhibit strong spin-allowed ¹MLCT bands in the visible domain (489-521 nm) as well as weak ¹GS to ³MLCT bands within the 668-815 nm domain. The compounds display strong luminescence from the ³MLCT state in the near-infrared domain (728-780 nm) at room temperature having lifetimes in the range of 20.0-171.0 ns. After coordination of [Os(tpy-PhCH₃/H₂pbbzim)₂]²⁺ unit to the terpyridine site of tpy-Hbzim-dipy, the complexes offer vacant pyridine-imidazole motifs for interacting with cationic and anionic guests. Consequently, photophysical properties of the compounds were tuned to a great extent upon interaction with selected cations, anions, pH, as well as protons. Anion-induced alteration of the ground- and excited-state properties of the compound lead to recognition of specific anions in solution. Significant change in the optical spectral behaviors as well as switching of emission spectral properties of the compounds was done in the NIR region upon treating with anions, cations, protons, and solvents (dichloromethane, acetonitrile, methanol, dimethylsulfoxide, and water). Moreover, the optical outputs in response to external stimuli were used to demonstrate binary functions of two-input IMPLICATION, NOR, and XNOR logic gates.

Scope of organometallic compounds based on transition metal-arene systems as anticancer agents: starting from the classical paradigm to targeting multiple strategies

The advent of the clinically approved drug cisplatin started a new era in the design of metallodrugs for cancer chemotherapy. However, to date, there has not been much success in this field due to the persistence of some side effects and multi-drug resistance of cancer cells. In recent years, there has been increasing interest in the design of metal chemotherapeutics using organometallic complexes due to their good stability and unique properties in comparison to normal coordination complexes. Their intermediate properties between that of traditional inorganic and organic materials provide researchers with a new platform for the development of more promising cancer therapeutics. Classical metal-based drugs exert their therapeutic potential by targeting only DNA, but in the case of organometallic complexes, their molecular target is quite distinct to avoid drug resistance by cancer cells. Some organometallic drugs act by targeting a protein or inhibition of enzymes such as thioredoxin reductase (TrRx), while some target mitochondria and endoplasmic reticulum. In this review, we mainly discuss organometallic complexes of Ru, Ti, Au, Fe and Os and their mechanisms of action and how new approaches improve their therapeutic potential towards various cancer phenotypes. Herein, we discuss the role of structure-reactivity relationships in enhancing the anticancer potential of drugs for the benefit of humans both in vitro and in vivo. Besides, we also include in vivo tumor models that mimic human physiology to accelerate the development of more efficient clinical organometallic chemotherapeutics.

Bioactive and luminescent indole and isatin based gold(i) derivatives

Combination of bioactive indole and isatin derivatives with Au(i) affords highly cytotoxic metallic species even for cisplatin resistant leukemia cells (Jurkat-shBak).

Mitochondrial toxicity induced by a thiourea gold(i) complex: mitochondrial permeability transition and respiratory deficit

Gold(i) complexes have been widely used as antibacterial and antitumor agents because of their excellent biological activities. However, there are few reports on the study of gold(i) complexes at the subcellular level. Herein, we investigated the toxicity of a gold(i) complex (N,N'-disubstituted cyclic thiourea ligand) - AuTuCl - to isolated mitochondria via various methods. The results showed that AuTuCl induced mitochondrial swelling, elevated ROS generation and triggered collapse of the membrane potential, which indicated the induction of mitochondrial permeability transition (MPT). It also enhanced the permeability of H+ and K+ of the inner membrane and declined membrane fluidity, which might be the result of MPT. Moreover, AuTuCl impaired the mitochondrial respiratory chain and suppressed the activities of complexes II and IV in the respiratory chain. It also triggered the deficiency of ATP and the effusion of Cyt c, which were strictly related to respiration and apoptosis. These results indicated that AuTuCl severely affected the structure and function of mitochondria. It was proposed that MPT and impairment of the respiratory chain were responsible for the mitotoxicity of AuTuCl, thus causing energy deficiency and even apoptosis. This conceivable mechanism can serve as a clue for better understanding of the toxicology of AuTuCl.

The Next Generation of Anticancer Metallopharmaceuticals: Cancer Stem Cell-Active Inorganics

Cancer stem cells (CSCs) are heavily linked to fatal incidences of cancer relapse and metastasis. Conventional cancer therapies such as surgery, chemotherapy and radiation are largely futile against CSCs. Therefore, highly original approaches are needed to overcome CSCs and to provide durable, long-term clinical outcomes. Many academia- and pharmaceutical-led studies aimed at developing chemical or biological anti-CSC agents are ongoing; however, the application of inorganic compounds is rare. In this minireview, we discuss how the chemical diversity and versatility offered by metals has been harnessed to develop an unprecedented, emerging class of metallopharmaceuticals: CSC-active inorganics. A detailed account of their mechanism(s) of action is provided, and possible future directions for exploration are also put forward.

Pharmacomodulation on Gold-NHC complexes for anticancer applications - is lipophilicity the key point?

A series of four new mononuclear cationic gold(I) complexes containing nitrogen functionalized N-heterocyclic carbenes (NHCs) was synthesized and fully characterized by spectroscopic methods. The X-ray structures of three complexes are presented. These lipophilic gold(I) complexes originate from a pharmacomodulation of previously described gold(I)-NHC complexes, by replacing an aliphatic spacer with an aromatic one. The Log P values of the resulting complexes increased by 0.7-1.5, depending on the substituents in comparison to the aliphatic-linker systems. The new series of complexes has been investigated in vitro for their anti-cancer activities in PC-3 (prostate cancer) and T24 (bladder cancer) cell lines and in the non-cancerous MC3T3 (osteoblast) cell line. All tested complexes show high activities against the cancer cell lines with GI₅₀ values lower than 500 nM. One complex (11) has been selected for further investigations. It has been tested in vitro in six cancer cell lines from different origins (prostate, bladder, lung, bone, liver and breast) and two non-cancerous cell lines (osteoblasts, fibroblasts). Moreover, cellular uptake measurements were indicative of a good bioavailability. By various biochemical assays, this complex was found to effectively inhibit the thioredoxin reductase (TrxR) and its cytotoxicity towards prostate PC-3, bladder T24 and liver HepG2 cells was found to be ROS-dependent.

Oncosis-inducing cyclometalated iridium(iii) complexes

Oncosis is a non-apoptotic form of programmed cell death (PCD), which differs from apoptosis in both morphological changes and inner pathways, and might hold the key to defeating a major obstacle in cancer therapy - drug-resistance, which is often a result of the intrinsic apoptosis resistance of tumours. However, despite the fact that the term "oncosis" was coined and used much earlier than apoptosis, little effort has been made to discover new drugs which can initiate this form of cell death, in comparison to drugs inducing apoptosis or any other type of PCD. So herein, we present the synthesis of a series of mitochondria-targeting cyclometalated Ir(iii) complexes, which activated the oncosis-specific protein porimin and calpain in cisplatin-resistant cell line A549R, and determined their cytotoxicity against a wide range of drug-resistant cancer types. To the best of our knowledge, these complexes are the very first metallo-components to induce oncosis in drug-resistant cancer cells.

Cationic and Neutral N-Heterocyclic Carbene Gold(I) Complexes: Cytotoxicity, NCI-60 Screening, Cellular Uptake, Inhibition of Mammalian Thioredoxin Reductase, and Reactive Oxygen Species Formation

A structurally diverse library of 14 gold(I) cationic bis(NHC) and neutral mono(NHC) complexes (NHC: N-heterocyclic carbene) was synthesized and characterized in this work. Four of them were new cationic gold(I) complexes containing functionalized NHCs, and their X-ray crystal structures are presented herein. All of the complexes were investigated for their anticancer activities in four cancer cell lines, including a cisplatin-resistant variant, and a noncancerous cell line. Seven of the cationic gold(I) complexes were found to display high and specific cytotoxic activities toward cancer cells. Two of them were even able to overcome cisplatin resistance. Two highly potent cationic complexes (11 and 15) were also submitted to the NCI-60 cancer panel for further cytotoxicity evaluation. Complex 15 showed a surprisingly high potency toward leukemia among the nine examined cancer subtypes, particularly toward the CCRF-CEM leukemia cell line with a concentration for 50 % inhibition of growth down to 79.4 nm. In addition, cationic complex 13, which demonstrated a remarkable cytotoxicity against hepatocellular carcinoma, was selected to obtain insight into the mechanistic aspects in HepG2 cells. Cellular uptake measurements were indicative of good bioavailability. By various biochemical assays, this complex was found to effectively inhibit thioredoxin reductase and its cytotoxicity toward HepG2 cells was found to be reactive oxygen species dependent.