Gold(I) Complexes Derived from Alkynyloxy-Substituted Anthraquinones: Syntheses, Luminescence, Preliminary Cytotoxicity, and Cell Imaging Studies

Research progress of natural product-conjugated platinum and gold complexes as potential antitumor agents

Cancer is widely recognized as a serious disease that poses a significant threat to human life and health. The distinctive chemical properties and pronounced antiproliferative activity of platinum drugs are considered to be responsible for their remarkable efficacy in clinical applications. However, undesirable side effects and resistance have severely hampered the treatment of various types of cancer with platinum-based drugs. Natural products (NPs) exhibit extensive pharmacological activities and represent an important source for developing cancer therapeutics. Therefore, the combination of metals and NPs is an attractive strategy for the development of new anticancer agents. Several studies have indicated that combining metals with NPs has a synergistic enhancement effect in antitumor activity. For transition metals, there has been burgeoning research output investigating NP-conjugated platinum and gold complexes. The present article reviews the progress made over the past 5-10 years on the development of NP-conjugated platinum and gold complexes, including a brief introduction to their chemistry and mechanism of action, and a summary of their benefits.

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.

Ferrocene-appended anthraquinone and coumarin as redox-active cytotoxins

Appending of ferrocene (Fc) to biologically-active organic backbones can generate novel multi-functional species for targeting bacteria and cancer. In this work Fc was linked to coumarin and anthraquinone with the goal of harnessing the redox-active Fc centre to generate new compounds that exhibit cytoxicity through the generation of toxic reactive oxygen species (ROS). A Cu(I)-catalyzed azide-alkyne cycloaddition "click" reaction was used to connect the organic and Fc components via a triazole linker. Cyclic voltammetry shows that the Fc potentials are suitable for oxidation by biological hydrogen peroxide to give reactive ferrocenium (Fc⁺) species, which can then generate hydroxyl radicals. The ability of the compounds to generate hydroxyl radicals in the presence of hydrogen peroxide was shown directly using EPR spin-trapping experiments. Furthermore, in vitro studies in MCF-7 breast cancer cells show significant increases in ROS following incubation with the Fc-functionalized compounds. Screening for antibacterial activity produced negative results for all of the Fc compounds, consitent with low levels of hydrogen peroxide typically found in bacteria. By contrast, Fc-coumarin showed cytotoxicity against A549 lung cancer and SKOV3 ovarian cancer cell lines, whereas the parent compound was inactive. This is consistent both with the cytoxic potential of the Fc group and the elevated hydrogen peroxide levels found in many cancers. Interestingly, the anthraquinone compounds showed the opposite effect with the parent compounds showing modest activity against A549 cells, but the Fc compounds being inactive. This demonstrates other potential negative impacts of including Fc, such as significantly increased lipophilicity.

Impact of oppositely charged shell and cores on interaction of core-shell colloids with differently charged proteins as a route for tuning of the colloids cytotoxicity

The present work represents interactions between the core-shell nanoparticles and different proteins, exemplified by lysozyme (LSZ), pepsin, bovine serum albumin (BSA), thioredoxin (TRX) and yellow fluorescent protein (YFP). The core-shell morphology derives from the non-covalent deposition of polyethyleneimine (PEI) onto nanoprecipitated luminescent complex (AuCl)₂L (L is cyclic PNNP ligand). Analysis of the data obtained by DLS, CD spectroscopy, luminescence derived from both (AuCl)₂L and YFP reveal the electrostatically driven interaction of negatively charged proteins with the shell of PEI-(AuCl)₂L. The fluorescence of YFP enables to reveal the inclusion of the protein molecules into the shell. The lack of any luminescent response of PEI-(AuCl)₂L on TRX conforms its electrostatically driven interactions with the shell which, in turn, excludes a binding of the exposed thiol moieties with (AuCl)₂L. The negatively charged surface of pepsin provides the greatest recharging of the PEI-based shell versus the other proteins, which is followed by the enhanced luminescence of (AuCl)₂L. The significant effect of PEI-(AuCl)₂L on the CD spectra of LSZ followed by the decreased intensity of (AuCl)₂L-based luminescence points to specific interaction mode of PEI-(AuCl)₂L with LSZ. The flow cytometry and fluorescent microscopy measurements revealed efficient internalization of PEI-(AuCl)₂L into the Wi-38 cell samples resulting in the efficient staining of all cell organelles. The concentration dependent cytotoxicity of PEI-(AuCl)₂L is detectably enhanced by LSZ, which is correlated with its interaction mode with the nanoparticles.

A review on 1,1-bis(diphenylphosphino)methane bridged homo- and heterobimetallic complexes for anticancer applications: Synthesis, structure, and cytotoxicity

Herein, we review developments in synthesis, structure, and biological (anti-cancer) activities of 1,1-bis(diphenylphosphino)methane (dppm) bridged homo- and heterobimetallic systems of the type L_mM(μ₂-dppm)M'L_n (M and M' are transition metals which may be different or the same and L_n,m are co-ligands) since the first such reported bimetallic system in 1987 until the present time (2020). As the simplest diphosphine, dppm enables facile formation of bimetallic complexes, where, given the short spacer between the PPh₂ groups, close spatial proximity of the metal centres is ensured. We concentrate on complexes bearing no M-M interaction and contrast biological activities of these complexes with mononuclear counterparts and positive control agents such as cisplatin, in an attempt to elucidate patterns in the biological activities of these complexes.

DNA-Binding and Anticancer Activity of Binuclear Gold(I) Alkynyl Complexes with a Phenanthrenyl Bridging Ligand

3,6-Diethynyl-9,10-diethoxyphenanthrene (4) was synthesized from phenanthrene and employed in the synthesis of the binuclear gold(I) alkynyl complexes (R3P)Au(C≡C-3-[C14H6-9,10-diethoxy]-6-C≡C)Au(PR3) (R = Ph (5a), Cy (5b)). The diyne 4 and complexes 5a and 5b were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. UV-Vis spectroscopy studies of the metal complexes and precursor diyne show strong p à p* transitions in the near UV region that red shift by ca. 50 nm upon coordination at the gold centers. The emission spectrum of 4 shows an intense fluorescence band centered at 420 nm which red shifts, slightly upon coordination of 4 to gold. Binding studies of 4, 5a, and 5b against calf thymus DNA were carried out, revealing that 4, 5a, and 5b have >40% stronger binding affinities than the commonly used intercalating agent ethidium bromide. The molecular docking scores of 4, 5a, and 5b with B-DNA suggest a similar trend in behavior to that observed in the DNA-binding study. Unlike the ligand 4, promising anticancer properties for 5a and 5b were observed against several cell lines; the DNA binding capability of the precursor alkyne was maintained, and its anticancer efficacy enhanced by the gold centers. Such phenanthrenyl complexes could be promising candidates in certain biological applications because the two components (phenanthrenyl bridge and metal centers) can be altered independently to improve the targeting of the complex, as well as the biological and physicochemical properties.

Heterobimetallic propargyl gold complexes with π-bound copper or silver with enhanced anticancer activity

Heterometallic propargyl gold species in which copper or silver is bound to the triple bond were prepared. The bimetallic complexes had improved activities compared to the mononuclear gold complexes, suggesting a possible synergy between the two metal centres within the cell.

Alkynyl Gold(I) complexes derived from 3-hydroxyflavones as multi-targeted drugs against colon cancer

The design of multi-targeted drugs has gained considerable interest in the last decade thanks to their advantages in the treatment of different diseases, including cancer. The simultaneous inhibition of selected targets from cancerous cells to induce their death represents an attractive objective for the medicinal chemist in order to enhance the efficiency of chemotherapy. In the present work, several alkynyl gold(I) phosphane complexes derived from 3-hydroxyflavones active against three human cancer cell lines, colorectal adenocarcinoma Caco-2/TC7, breast adenocarcinoma MCF-7 and hepatocellular carcinoma HepG2, have been synthesized and characterized. Moreover, these compounds display high selective index values towards differentiated Caco-2 cells, which are considered as a model of non-cancerous cells. The antiproliferative effect of the most active complexes [Au(L2b)PPh₃] (3b) and [Au(L2c)PTA] (4c) on Caco-2 cells, seems to be mediated by the inhibition of the enzyme cyclooxygenase-1/2 and alteration of the activities of the redox enzymes thioredoxin reductase and glutathione reductase. Both complexes triggered cell death by apoptosis, alterations in cell cycle progression and increased of ROS production. These results provide support for the suggestion that multi-targeting approach involving the interaction with cyclooxygenase-1/2 and the redox enzymes that increases ROS production, enhances cell death in vitro. All these results indicate that complexes [Au(L2b)PPh₃] and [Au(L2c)PTA] are promising antiproliferative agents for further anticancer drug development.

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.

Synthesis and characterisation of fluorescent aminophosphines and their coordination to gold(i)

Three novel fluorescent aminophosphine ligands have been synthesised that incorporate napthyl (L1), pyrenyl (L2) and anthraquinone (L3) chromophores into their structures. The ligands react with [AuCl(tht)] (tht = tetrahydrothiophene) to give neutral complexes of the form [AuCl(L1-3)]. Solid state, X-ray crystallographic data was obtained for the anthraquinone derivative, [AuCl(L3)], and showed a distorted linear coordination geometry at Au(i). The packing structure also revealed a number of intermolecular π-π interactions that involve the anthraquinone and phenyl units of the aminophosphine ligand. 31P NMR spectroscopic data revealed δP values of +42.2 (L1), +42.1 (L2) and +26.1 (L3) ppm, which shifted downfield upon coordination to Au(i) to +64.6, +64.7, and +55.8 ppm, respectively. Supporting TD-DFT studies were able to reproduce the structure and 31P NMR chemical shifts of [AuCl(L3)] as well as rationalise the HOMO-LUMO compositions. Photophysical studies showed that the appended fluorophore dominates the absorption and emission properties for the ligands and complexes, with the anthraquinone derivatives showing visible emission at ca. 570 nm which was attributed to the intramolecular charge transfer character of the phosphinoaminoanthraquinone fragment.

Near-unity thermally activated delayed fluorescence efficiency in three- and four-coordinate Au(i) complexes with diphosphine ligands

The synthesis and photoluminescence properties of three-coordinate Au(i) complexes with rigid diphosphine ligands LMe {1,2-bis[bis(2-methylphenyl)phosphino]benzene}, LEt {1,2-bis[bis(2-ethylphenyl)phosphino]benzene}, and LiPr {1,2-bis[bis(2-isopropylphenyl)phosphino]benzene} are investigated. The LMe and LEt ligands afford two types of complexes: dinuclear complexes [μ-LMe(AuCl)2] (1d) and [μ-LEt(AuCl)2] (2d) with an Au(i)-Au(i) bond and mononuclear three-coordinate Au(i) complexes LMeAuCl (1) and LEtAuCl (2). On the other hand, the bulkiest ligand, LiPr, affords three-coordinate Au(i) complexes, LiPrAuCl (3) and LiPrAuI (4), but no dinuclear complexes. X-ray analysis suggests that both 3 and 4 possess a highly distorted trigonal planar geometry. Moreover, luminescence data reveal that at room temperature, 3 and 4 exhibit yellow-green thermally activated delayed fluorescence in the crystalline state with maximum emission wavelengths at 558 and 549 nm, respectively. The emission yields are close to unity. Quantum chemical calculations suggest that the emission of 4 originates from the (σ + X) → π* excited state that possesses strong intraligand charge-transfer character. The luminescent properties of four-coordinate Au(i) complex (5) possessing a tetrahedral geometry are discussed on the basis of the emission spectra and decay times measured in a temperature range of 309-77 K.

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.

Synthesis, cytotoxicity and anti-cancer activity of new alkynyl-gold(i) complexes

Alkynyl(triphenylphosphine)gold(i) complexes carrying variously substituted propargylic amines have been synthesized and fully characterized in solution and solid state.

Near-IR luminescent lanthanide complexes with 1,8-diaminoanthraquinone-based chromophoric ligands

1,8-Anthraquinone derivatives can act as low energy, visible light sensitizers for near-IR emitting lanthanides.

Development of trackable metal-based drugs: new generation of therapeutic agents

Today, it is not sufficient to conceive an efficient drug, its mechanism of action have to be understood. To tackle this issue, trackable therapeutic agents are an interesting solution.

Anticancer and Antibacterial Activity Studies of Gold(I)-Alkynyl Chromones

Three gold(I) complexes of alkynyl chromones were synthesized and characterized. The single-crystal X-ray structure analysis of a dinuclear compound and of a flavone derivative exhibit a typical d10 gold(I)-alkynyl linear arrangement. All complexes were evaluated as anticancer and antibacterial agents against four human cancer cell lines and four pathogenic bacterial strains. All compounds show antiproliferative activity at lower micromolar range concentrations. Complex 4 showed a broad activity profile, being more active than the reference drug auranofin against HepG2, MCF-7 and CCRF-CEM cancer cells. The cellular uptake into MCF-7 cells of the investigated complexes was measured by atomic absorption spectroscopy (AAS). These measurements showed a positive correlation between an increased cellular gold content and the incubation time of the complexes. Unexpectedly an opposite effect was observed for the most active compound. Biological assays revealed various molecular mechanisms for these compounds, comprising: (i) thioredoxin reductase (TrxR) inhibition, (ii) caspases-9 and -3 activation; (iii) DNA damaging activity and (iv) cell cycle disturbance. The gold(I) complexes were also bactericidal against Gram-positive methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) bacterial strains, while showing no activity against the Gram-negative Escherichia coli bacterial strain.

Microwave-Assisted Synthesis of Ruthenium(II) Complexes with Trimethylsilylacetylene as Inhibitors against the Migration of Breast Cancer Cells

In the present study, two novel chiral ruthenium(ii) complexes with trimethylsilylacetylene (TMSA), Λ- and Δ-[Ru(bpy)2(p-TEPIP)](ClO4)2 (bpy = 2,2-bipyridine; p-TEPIP = 5-(2-(p-trimethylsilyl propargyl)-1H-imidazo[4,5-f][1,10] phenanthroline) (Λ-1 and Δ-1) were prepared using Sonogashira coupling reaction under microwave irradiation. We found that both Λ-1 and Δ-1 could inhibit the growth of highly metastatic human breast cancer cells (MDA-MB-231) with half-maximal inhibitory concentration (IC50) of 32.1 and 36.9 µM, respectively. Wound healing assay demonstrated that both isomers inhibited the migration of MDA-MB-231 cells. Both Λ-1 and Δ-1 compounds were found throughout the cell and were particularly enriched in the nucleus. Furthermore, we observed fragmentation of the nucleus leading to apoptosis. To conclude, it is clear that this type of chiral ruthenium(ii) complex with TMSA can induce apoptosis and thus inhibit the growth and migration of tumour cells.

Fluorescence sensing systems for gold and silver species

Here, we provide an overview of the reported fluorescent detection systems for gold and silver species, and discuss their sensing properties with promising features.

A golden future in medicinal inorganic chemistry: the promise of anticancer gold organometallic compounds

From wedding rings on fingers to stained glass windows, by way of Olympic medals, gold has been highly prized for millennia. Nowadays, organometallic gold compounds occupy an important place in the field of medicinal inorganic chemistry due to their unique chemical properties with respect to gold coordination compounds. In fact, several studies have proved that they can be used to develop highly efficient metal-based drugs with possible applications in the treatment of cancer. This Perspective summarizes the results obtained for different families of bioactive organometallic gold compounds including cyclometallated gold(iii) complexes with C,N-donor ligands, gold(I) and gold(I/III) N-heterocyclic (NHC) carbene complexes, as well as gold(I) alkynyl complexes, with promising anticancer effects. Most importantly, we will focus on recent developments in the field and discuss the potential of this class of organometallic compounds in relation to their versatile chemistry and innovative mechanisms of action.

Modulation of the organelle specificity in Re(i) tetrazolato complexes leads to labeling of lipid droplets

Neutral Re(i) tetrazolato complexes exhibit labeling of lipid droplets with high specificity.

Combined spectral experiment and theoretical calculation to study the interaction of 1,4-dihydroxyanthraquinone for metal ions in solution

The interaction between 1,4-dihydroxyanthraquinone (1,4-DHA) and metal ions was studied by UV-Visible and fluorescence spectroscopies in solution. Time-dependent density functional theory calculations confirmed complex structures. The investigation results showed 1,4-DHA can selectively respond some metal ions and can be monitored by UV-Vis, fluorescence spectra and naked-eye. So 1,4-DHA has a potential application in the design of metal ions probe. More, as typical metal ions, Hg(2+) and Er(3+), their reaction abilities for 1,4-DHA were studied in detailed. Experimental results showed they have better response for 1,4-DHA. And theoretical calculation concluded that Er(3+) easily reacts with 1,4-DHA over Hg(2+) attributed to the low reaction energy of Er(3+)-1,4-DHA than Hg(2+)-1,4-DHA.

The influence of R substituents in triphenylphosphinegold(I) carbonimidothioates, Ph3PAu[SC(OR)=NPh] (R=Me, Et and iPr), upon in vitro cytotoxicity against the HT-29 colon cancer cell line and upon apoptotic pathways

The Ph3PAu[SC(OR)=NPh], R=Me (1), Et (2) and iPr (3), compounds are significantly cytotoxic to the HT-29 cancer cell line with 1 being the most active. Based on human apoptosis PCR-array analysis, caspase activities, DNA fragmentation, cell apoptotic assays, intracellular reactive oxygen species (ROS) measurements and human topoisomerase I inhibition, induction of apoptosis is demonstrated and both the extrinsic and intrinsic pathways of apoptosis have been shown to occur. Compound 1 activates the p73 gene, whereas each of 2 and 3 activates the p53 gene. An additional apoptotic mechanism is exhibited by 2, that is, via the JNK/MAP pathway.