Antiproliferative Activity of Gold(I) Alkyne Complexes Containing Water-Soluble Phosphane Ligands

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.

Insights into the κ-P,N Coordination of 1,3,5-Triaza-7-phosphaadamantane and Derivatives: κ-P,N-Heterometallic Complexes and a 15N Nuclear Magnetic Resonance Survey

Complexes {[(PTA)₂CpRu-μ-CN-1κC:2κ²N-RuCp(PTA)₂-ZnCl₃]}·2DMSO (13) {[ZnCl₂(H₂O)]-(PTA-1κP:2κ²N)(PTA)CpRu-μ-CN-1κC:2κ²N-RuCp(PTA)(PTA-1κP:2κ²N)-[ZnCl₂(H₂O)]}Cl (14), [RuCp(HdmoPTA)(PPh₃)(PTA)](CF₃SO₃)₂ (20), [RuCp(HdmoPTA)(HPTA)(PPh₃)](CF₃SO₃)₃ (21), and [RuCp(dmoPTA)(PPh₃)(PTA)](CF₃SO₃) (22) were obtained and characterized, and their crystal structure together with that of the previously published complex 18 is reported. The behavior of the 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane (PTA) and 3,7-dimethyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (dmoPTA) ligands against protonation and κN-coordination is discussed, on the basis of ¹⁵N nuclear magnetic resonance data collected on 22 different compounds, including PTA (1), HdmoPTA (7H), and some common derivatives as free ligands (2–6 and 8), along with mono- and polymetallic complexes containing PTA and/or HdmoPTA (9–22). ¹⁵N detection via ¹H–¹⁵N heteronuclear multiple bond correlation allowed the construction of a small library of ¹⁵N chemical shifts that shed light on important features regarding κN-coordination in PTA and its derivatives.

To shed light on the behavior of the triazaphosphines 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane (PTA) and 3,7-dimethyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (dmoPTA) upon κN coordination and N protonation, the ¹⁵N chemical shifts of 22 compounds, including PTA and a representative variety of its derivatives, piano-stool complexes, were collected by ¹H−¹⁵N heteronuclear multiple bond correlation nuclear magnetic resonance. New heterometallic complexes containing PTA were also synthesized and fully characterized.

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.

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.

A Combination of Rosa Canina Extracts and Gold Complex Favors Apoptosis of Caco-2 Cells by Increasing Oxidative Stress and Mitochondrial Dysfunction

Given the alarming increase in colorectal cancer (CRC) worldwide, novel therapies are urgently needed. Plant-derived extracts have gained considerable interest in the last years due to their strong anticancer effect mediated by their unique bioactive compounds. Specifically, rosehips from Rosa canina have been successfully tested against several cancer models, including colon cancer. Moreover, gold derivatives are a promising alternative to the current platinum-based drugs commonly used in CRC chemotherapy due to their lack of affinity for DNA. Herein we have investigated the antitumor potential of a drug combination made of acidic polyphenols extracted from R. canina and the gold complex (Au(C≡C-2-NC₅H₄) (PTA)) in Caco-2 cell line as a model of CRC. The combination triggered strong apoptosis mediated by a blockage of the autophagic flux, which might be a consequence of a reactive oxygen species (ROS) increase and mitochondrial dysfunctionality. Our results suggest that the clinical application of plant polyphenols might enhance the anticancer effect of metallodrugs and reduce drug exposure time and therefore its side effects.

An Erlotinib gold(I) conjugate for combating triple-negative breast cancer

An Erlotinib triphenylphosphane gold(I) conjugate has been prepared from AuCl(PPh₃) and its crystal structure has been established by X-ray diffraction, showing a metallo-helicate formation. IC₅₀ values of the new gold conjugate were calculated towards a panel of human tumor cell lines representative of breast (MCF-7, MDA-MB-231) and colon (HT-29) cancer cells. Overall, the gold conjugate exhibited higher cytotoxic activity than that of Erlotinib against the cancer cells studied. Particularly, the antiproliferative effect of the conjugate demonstrated to be 68-fold higher than Erlotinib in highly metastatic and triple negative MDA-MB-231 cell line. The gold conjugate caused DNA damage, reactive oxygen species (ROS) increase and induced apoptosis. Flow cytometry analysis showed that the conjugate induces significant arrest in S and G₂/M phases primarily, whereas Erlotinib, as an inhibitor of epidermal growth factor receptor (EGFR), blocks G₁/S transition and increases G₁ cell population.

Preparation and Antitumoral Activity of Au-Based Inorganic-Organometallic Nanocomposites

The synergy between gelator molecules and nanostructured materials is currently a novel matter of study. The possibility to carefully design the skeleton of the molecular entity as well as the nanostructure's morphological and chemical features offers the possibility to prepare a huge variety of nanocomposites with properties potentially different than just the sum of those of the individual building blocks. Here we describe the synthesis and characterization of nanocomposites made by the unconventional combination of phosphine-Au(I)-alkynyl-based organometallic gelating molecules and plasmonic Au nanoparticles. Our results indicate that the interaction between the two moieties leads to a significant degree of aggregation in both hydrophilic and hydrophobic media, either when using DAPTA or PTA-based organometallic molecules, with the formation of a sponge-like hybrid powder upon solvent evaporation. The biological activity of the nanocomposites was assessed, suggesting the existence of a synergetic effect evidenced by the higher cytotoxicity of the hybrid systems with respect to that of any of their isolated counterparts. These results represent a preliminary proof-of-concept for the exploitation of these novel nanocomposites in the biomedical field.

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.

Supramolecular tripodal Au(i) assemblies in water. Interactions with a pyrene fluorescent probe

The synthesis of three gold(i) tripodal complexes derived from tripropargylamine and containing the water soluble phosphines PTA (1,3,5-triaza-7-phosphaadamantane), DAPTA (3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) and TPPTS (triphenylphosfine-3,3′,3′′-trisulfonic acid trisodium salt) is described here.

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.

Polarized Supramolecular Aggregates Based on Luminescent Perhalogenated Gold Derivatives

The reaction of [Au(C₆F₅)(tht)] (tht = tetrahydrothiophene) with 1,3,5-triaza-7-phosphaadamantane (PTA) and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) leads to the formation of [Au(C₆F₅)(phosph)] (phosph = PTA, 1; phosph = DAPTA, 2). The compounds are slightly soluble in water and aggregate at higher concentrations, giving rise to the formation of needle- and rodlike structures (1) and well-organized spherical aggregates (2). Compounds 1 and 2 were reacted with AgPF₆, giving rise to the formation in all cases of luminescent water-soluble 1:1 Au···Ag heterometallic complexes, as evidenced by X-ray crystal structure determination. The use of different silver salts that differ on the counterion induces changes in the resulting luminescence and aggregation morphology.

Alkynyl gold(I) complex triggers necroptosis via ROS generation in colorectal carcinoma cells

Given the rise of apoptosis-resistant tumors, there exist a growing interest in developing new drugs capable of inducing different types of cell death to reduce colorectal cancer-related death rates. As apoptosis and necroptosis do not share cellular machinery, necroptosis induction may have a great therapeutic potential on those apoptosis-resistant cancers, despite the inflammatory effects associated with it. We have synthesized an alkynyl gold(I) complex [Au(CC-2-NC₅H₄)(PTA)] whose anticancer effect was tested on the colorectal adenocarcinoma Caco-2 cell line. With regard to its mechanism of action, this gold complex enters the mitochondria and disrupts its normal function, leading to an increase in ROS production, which triggers necroptosis. Necroptosis induction has been found dependent of TNF-α (Tumor necrosisfactor α) and TNFR1(Tumor necrosisfactor receptor 1) binding, RIP1(Receptor-Interacting Protein 1) activation and NF-κB (Nuclear Factor Kappa-Light-Chain-Enhancer of Activated B Cells) signaling. Moreover, the antitumor potential of [Au(CC-2-NC₅H₄)(PTA)] has also been confirmed on the 3D cancer model spheroid. Overall, the obtained data show firstly that gold complexes might have the ability of inducing necroptosis, and secondarily that our compound [Au(CC-2-NC₅H₄)(PTA)] is an interesting alternative to current chemotherapy drugs in cases of apoptosis resistance.

The anticancer effect related to disturbances in redox balance on Caco-2 cells caused by an alkynyl gold(I) complex

The alkynyl gold(I) derivative [Au(C≡CPh)(PTA)] (PTA=1,3,5-triaza-7-phosphaadamantane) induces apoptosis in colorectal carcinoma tumour cells (Caco-2) without affecting to normal enterocytes. [Au(C≡CPh)(PTA)] is a slight lipophilic drug, stable in PBS (Phosphate Buffered Saline) and able to bind BSA (Bovin Serum Albumin) by hydrophobic interactions. Once inside the cell, [Au(C≡CPh)(PTA)] targets seleno proteins such as Thioredoxin Reductase 1, increasing ROS (Reactive Oxygen Species) levels, reducing cell viability and proliferation and inducing mitochondrial apoptotic pathway, pro-apoptotic and anti-apoptotic protein imbalance, loss of mitochondrial membrane potential, cytochrome c release and activation of caspases 9 and 3. Moreover, unlike other metal-based drugs such as cisplatin, [Au(C≡CPh)(PTA)] does not target nucleic acid, reducing the risk of side mutation in the DNA. In consequence, our results predict a promising future for [Au(C≡CPh)(PTA)] as a chemotherapeutic agent for colorectal carcinoma.

Cobaltoceniumethynyl gold(I) as an unusual heterodinuclear bioorganometallic fragment to study the biological properties of alkynyl gold complexes

A cobaltoceniumethynyl gold(i) complex with a triphenylphosphane ligand triggered efficient cytotoxic effects in cancer cells in contrast to a derivative with two cobaltocenium moieties. The complex effectively inhibited the enzyme thioredoxin reductase (TrxR) suggesting this enzyme as a possible biological target. The cellular uptake of both metal fragments of the active complex was studied by atomic absorption spectroscopy and indicated a high biological stability of the complex.

Facile synthesis of a peptidic Au(I)-metalloamphiphile and its self-assembly into luminescent micelles in water

We report a short synthetic route for the preparation of a peptidic Au(I)-metalloamphiphile which, in buffered environments of physiological ionic strength, self-assembles into luminescent micellar nanostructures of 14 nm in diameter.

Effect of solvent polarity on the spectroscopic properties of an alkynyl gold(i) gelator. The particular case of water

The spectroscopic properties of an aurophilic hydrogelator depend on solvent polarity and concentration.

Tuning supramolecular aurophilic structures: the effect of counterion, positive charge and solvent

The synthesis of different cationic gold(i) complexes gave rise to the formation of unexpected supramolecular assemblies in water going from rod-like structures to vesicles and square-like structures.

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.

Au(i) N-heterocyclic carbenes from bis-imidazolium amphiphiles: synthesis, cytotoxicity and incorporation onto gold nanoparticles

Bis-imidazolium amphiphiles capable of forming Au(i) N-heterocyclic carbenes and gold nanoparticles for potential cancer therapy.

Fluorescence probes for prokaryotic and eukaryotic cells using Re(CO)3+complexes with an electron withdrawing ancillary ligand

Re(CO)₃⁺complexes with an ancillary ligand present an electron withdrawing effect suitable for cell imaging.

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.

In vitro and in vivo evaluation of organometallic gold(I) derivatives as anticancer agents

Alkyne gold(I) derivatives with the water soluble phosphanes PTA (1,3,5-triaza-7-phosphaadamantane) and DAPTA (3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) were described and their anticancer potential against the colon cancer cell line Caco-2 (PD7 and TC7 clones) was studied. Strong antiproliferative effects are found, for all the new complexes, to be even more pronounced than for the reference drug cisplatin, and similar to auranofin. The interaction of these derivatives with bovine serum albumin (BSA) was studied by fluorescence spectroscopy. The types of quenching and binding constants were determined by a fluorescence quenching method. Moderate values of the binding constants are calculated for the tested derivatives indicating that these complexes can be stored and carried easily by this protein in the body. The study of the thermodynamic parameters in the case of [Au(C[triple bond, length as m-dash]CCH2Spyridine)(PTA)] points out to the presence of van der Waals interactions or hydrogen bonding between the metallic complex and the protein. In addition, the complex [Au(C[triple bond, length as m-dash]CCH2Spyridine)(PTA)] has shown inhibition in colon cancer proliferation of HTC-116-luc2 cell lines via the apoptotic pathway and S-phase arrest of the cell cycle. Intraperitoneal injection of this derivative in athymic nude mice inoculated with HTC-116-luc2 cells prolonged their survival and displayed moderate inhibition of the tumour growth with no subsequent organ (kidney and liver) damage after treatment.

Dinuclear organogold(i) complexes bearing uracil moieties: chirality of Au(i)–Au(i) axis and self-assembly

Dinuclear organogold(i) complexes bearing uracil moieties were designed, wherein the chirality of the Au(i)–Au(i) axis was induced by coordination regulation of the axially chiral bidentate diphosphine ligand, and intermolecular hydrogen-bonded assemblies were formed between the uracil moieties.

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.

A coumarin based gold(i)-alkynyl complex: a new class of supramolecular hydrogelators

A phosphine-gold(i)-alkynyl-coumarin complex, [Au{7-(prop-2-ine-1-yloxy)-1-benzopyran-2-one}(DAPTA)] (1), was synthesized and the formation of long luminescent fibers in solution was characterized via fluorescence microscopy and dynamic light scattering.