Thiolato-Bridged Arene-Ruthenium Complexes: Synthesis, Molecular Structure, Reactivity, and Anticancer Activity of the Dinuclear Complexes [(arene)2Ru2(SR)2Cl2]

In vitro antibacterial activity of dinuclear thiolato-bridged ruthenium(II)-arene compounds

IMPORTANCE

The in vitro assessment of diruthenium(II)-arene compounds against Escherichia coli, Streptococcus pneumoniae, and Staphylococcus aureus showed a significant antibacterial activity of some compounds against S. pneumoniae, with minimum inhibitory concentration (MIC) values ranging from 1.3 to 2.6 µM, and a medium activity against E. coli, with MIC of 25 µM. The nature of the substituents anchored on the bridging thiols and the compounds molecular weight appear to significantly influence the antibacterial activity. Fluorescence microscopy showed that these ruthenium compounds enter the bacteria and do not accumulate in the cell wall of gram-positive bacteria. These diruthenium(II)-arene compounds exhibit promising activity against S. aureus and S. pneumoniae and deserve to be considered for further studies, especially the compounds bearing larger benzo-fused lactam substituents.

Synthesis and Antiparasitic Activity of New Trithiolato-Bridged Dinuclear Ruthenium(II)-arene-carbohydrate Conjugates

Eight novel carbohydrate-tethered trithiolato dinuclear ruthenium(II)-arene complexes were synthesized using CuAAC ‘click’ (Cu(I)-catalyzed azide-alkyne cycloaddition) reactions, and there in vitro activity against transgenic T. gondii tachyzoites constitutively expressing β-galactosidase (T. gondii β-gal) and in non-infected human foreskin fibroblasts, HFF, was determined at 0.1 and 1 µM. When evaluated at 1 µM, seven diruthenium-carbohydrate conjugates strongly impaired parasite proliferation by >90%, while HFF viability was retained at 50% or more, and they were further subjected to the half-maximal inhibitory concentration (IC50) measurement on T. gondii β-gal. Results revealed that the biological activity of the hybrids was influenced both by the nature of the carbohydrate (glucose vs. galactose) appended on ruthenium complex and the type/length of the linker between the two units. 23 and 26, two galactose-based diruthenium conjugates, exhibited low IC50 values and reduced effect on HFF viability when applied at 2.5 µM (23: IC50 = 0.032 µM/HFF viability 92% and 26: IC50 = 0.153 µM/HFF viability 97%). Remarkably, compounds 23 and 26 performed significantly better than the corresponding carbohydrate non-modified diruthenium complexes, showing that this type of conjugates are a promising approach for obtaining new antiparasitic compounds with reduced toxicity.

Effect of cysteine thiols on the catalytic and anticancer activity of Ru(II) sulfonyl-ethylenediamine complexes

We have synthesized a series of novel substituted sulfonyl ethylenediamine (en) Ru^II arene complexes 1-8 of [(η⁶-arene)Ru(R¹-SO₂-EnBz)X], where the arene is benzene, HO(CH₂)₂O-phenyl or biphenyl (biph), X = Cl or I, and R¹ is phenyl, 4-Me-phenyl, 4-NO₂-phenyl or dansyl. The 'piano-stool' structure of complex 3, [(η⁶-biph)Ru(4-Me-phenyl-SO₂-EnBz)I], was confirmed by X-ray crystallography. The values of their aqua adducts were determined to be high (9.1 to 9.7). Complexes 1-8 have antiproliferative activity against human A2780 ovarian, and A549 lung cancer cells with IC₅₀ values ranging from 4.1 to >50 μM, although, remarkably, complex 7 [(η⁶-biph)Ru(phenyl-SO₂-EnBz)Cl] was inactive towards A2780 cells, but as potent as the clinical drug cisplatin towards A549 cells. All these complexes also showed catalytic activity in transfer hydrogenation (TH) of NAD⁺ to NADH with sodium formate as hydride donor, with TOFs in the range of 2.5-9.7 h^-1. The complexes reacted rapidly with the thiols glutathione (GSH) and N-acetyl-L-cysteine (NAC), forming dinuclear bridged complexes [(η⁶-biph)₂Ru₂(GS)₃]^2- or [(η⁶-biph)₂Ru₂(NAC-H)₃]^2-, with the liberation of the diamine ligand which was detected by LC-MS. In addition, the switching on of fluorescence for complex 8 in aqueous solution confirmed release of the chelated DsEnBz ligand in reactions with these thiols. Reactions with GSH hampered the catalytic TH of NAD⁺ to NADH due to the decomposition of the complexes. Co-administration to cells of complex 2 [(η⁶-biph)Ru(4-Me-phenyl-SO₂-EnBz)Cl] with L-buthionine sulfoximine (L-BSO), an inhibitor of GSH synthesis, partially restored the anticancer activity towards A2780 ovarian cancer cells. Complex 2 caused a concentration-dependent G1 phase cell cycle arrest, and induced a significant level of reactive oxygen species (ROS) in A2780 human ovarian cancer cells. The amount of induced ROS decreased with increase in GSH concentration, perhaps due to the formation of the dinuclear Ru-SG complex.

Water-soluble trithiolato-bridged dinuclear ruthenium(II) and osmium(II) arene complexes with bisphosphonate functionalized ligands as anticancer organometallics

Trithiolato-bridged dinuclear ruthenium(II) complexes [Ru₂(p-cym)₂(SR)₃]Cl (p-cym = p-cymene, R = benzyl derivatives) are regarded as the most cytotoxically potent metal(II) arene antineoplastics, but are oftentimes limited by their poor solubility in aqueous media. Thus, we designed bisphosphonate-functionalized ligands for use in a modular two-step complexation process to synthesize six trithiolato-bridged dinuclear ruthenium(II) and osmium(II) arene complexes bearing one to three bisphosphonate-benzylmercaptane derived ligands. In addition to improved aqueous solubility the high affinity of bisphosphonates towards apatite structures found in bone and bone metastases may grant selective targeting properties to functionalized organometallics. The complex stabilities and hydroxyapatite binding behavior were determined by UV/Vis spectroscopy. The bisphosphonate functionalization decreases antiproliferative activity in vitro, which was correlated to lower cellular accumulation, due to the different lipophilic profiles of the drug candidates.

The quest of the best - A SAR study of trithiolato-bridged dinuclear Ruthenium(II)-Arene compounds presenting antiparasitic properties

A structure activity relationship (SAR) study of a library of 56 compounds (54 ruthenium and 2 osmium derivatives) based on the trithiolato-bridged dinuclear ruthenium(II)-arene scaffold (general formula [(η⁶-arene)₂Ru₂(μ₂-SR)₃]⁺, symmetric and [(η⁶-arene)₂Ru₂(μ₂-SR¹)₂(μ₂-SR²)]⁺, mixed, respectively) is reported. The 56 compounds (of which 34 are newly designed drug candidates) were synthesized by introducing chemical modifications at the level of bridge thiols, and they were grouped into eight families according to their structural features. The selected fittings were guided by previous results and focused on a fine-tuning of the physico-chemical and steric properties. Newly synthesized complexes were characterized by NMR spectroscopy, mass spectrometry and elemental analysis, and four single-crystal X-ray structures were obtained. The in vitro biological assessment of the compounds was realized by applying a three-step screening cascade: (i) evaluation of the activity against Toxoplasma gondii RH strain tachyzoites expressing β-galactosidase (T. gondii-β-gal) grown in human foreskin fibroblast monolayers (HFF) and assessment of toxicity in non-infected HFF host cells; (ii) dose-response assays using selected compound, and (iii) studies on the effects in murine splenocytes. A primary screening was performed at 1 and 0.1 μM, and resulted in the selection of 39 compounds that inhibited parasite proliferation at 1 μM by more than 95% and reduced the viability of HFF by less than 49%. In the secondary screening, dose-response assays showed that the selected compounds exhibited half maximal inhibitory concentration (IC₅₀) values for T. gondii-β-gal between 0.01 μM and 0.45 μM, with 30 compounds displaying an IC₅₀ lower than 0.1 μM. When applied to non-infected HFF monolayers at 2.5 μM, 8 compounds caused more than 90% and 31 compounds more than 30% viability impairment. The tertiary screening included 14 compounds that did not cause HFF viability loss higher than 50% at 2.5 μM. These derivatives were assessed for potential immunosuppressive activities. First, splenocyte viability was assessed after treatment of cells with concanavalin A (ConA) and lipopolysaccharide (LPS) with compounds applied at 0.1 and 0.5 μM. Subsequently, the 5 compounds exhibiting the lowest splenocyte toxicity were further evaluated for their potential to inhibit B and T cell proliferation. Overall, compound 55 [(η⁶-p-MeC₆H₄Prⁱ)₂Ru₂(μ₂-SC₆H₄-o-CF₃)₂(μ₂-SC₆H₄-p-OH)]Cl exhibited the most favorable features, and will be investigated as a scaffold for further optimization in terms of anti-parasitic efficacy and drug-like properties.

Conjugates Containing Two and Three Trithiolato-Bridged Dinuclear Ruthenium(II)-Arene Units as In Vitro Antiparasitic and Anticancer Agents

The synthesis, characterization, and in vitro antiparasitic and anticancer activity evaluation of new conjugates containing two and three dinuclear trithiolato-bridged ruthenium(II)-arene units are presented. Antiparasitic activity was evaluated using transgenic Toxoplasmagondii tachyzoites constitutively expressing β-galactosidase grown in human foreskin fibroblasts (HFF). The compounds inhibited T.gondii proliferation with IC50 values ranging from 90 to 539 nM, and seven derivatives displayed IC50 values lower than the reference compound pyrimethamine, which is currently used for treatment of toxoplasmosis. Overall, compound flexibility and size impacted on the anti-Toxoplasma activity. The anticancer activity of 14 compounds was assessed against cancer cell lines A2780, A2780cisR (human ovarian cisplatin sensitive and resistant), A24, (D-)A24cisPt8.0 (human lung adenocarcinoma cells wild type and cisPt resistant subline). The compounds displayed IC50 values ranging from 23 to 650 nM. In A2780cisR, A24 and (D-)A24cisPt8.0 cells, all compounds were considerably more cytotoxic than cisplatin, with IC50 values lower by two orders of magnitude. Irrespective of the nature of the connectors (alkyl/aryl) or the numbers of the di-ruthenium units (two/three), ester conjugates 6-10 and 20 exhibited similar antiproliferative profiles, and were more cytotoxic than amide analogues 11-14, 23, and 24. Polynuclear conjugates with multiple trithiolato-bridged di-ruthenium(II)-arene moieties deserve further investigation.

Targeting of the mitochondrion by dinuclear thiolato-bridged arene ruthenium complexes in cancer cells and in the apicomplexan parasite Neospora caninum

A library of 18 dinuclear-thiolato bridged arene ruthenium complexes, some of which with demonstrated activity against cancer cells, was screened for activity against a transgenic Neospora caninum strain that constitutively expresses beta-galactosidase. Initial assessments were done at concentrations of 2500, 250, 25 and 2.5 nM, and 5 compounds were further evaluated with regard to their half maximal proliferation-inhibiting concentration (IC50). Among those, [(η6-p-MeC6H4Pri)2Ru2(μ2-SC6H4-p-CH3)3]Cl (1), [(η6-p-MeC6H4Pri)2Ru2(μ2-SC6H4-p-But)3]Cl (2) and [(η6-p-MeC6H4Pri)2Ru2(μ2-SCH2C6H4-p-But)2(μ2-SC6H4-p-OH)]BF4 (9) inhibited N. caninum proliferation with low C50 values of 15, 5 and 1 nM, respectively, while [(η6-p-MeC6H4Pri)2Ru2(μ2-SC6H4-p-OH)3]Cl (3) and [(η6-p-MeC6H4Pri)2Ru2(μ2-SC6H4-p-mco)3]Cl (5, mco = 4-methylcoumarinyl) were less active (IC50 = 280 and 108 nM, respectively). These compounds did not affect human foreskin fibroblast (HFF) host cells at dosages of 5 μM and above, but impaired proliferation of the human ovarian carcinoma cell line A2780 (IC50 values of 130 nM (1), 30 nM (2), 530 nM (3), 7730 nM (5), 130 nM (9)). A2780 cancer cells were treated with complexes 1, 2, and 5, and biodistribution analysis using inductively coupled plasma mass spectrometry (ICP-MS) showed that most of the drugs accumulated in the mitochondrial fractions. Transmission electron microscopy showed that the parasite mitochondrion is the primary target also in N. caninum tachyzoites, but these compounds, when applied at 200 nM for 15 days in vitro, did not act parasiticidal. Complexes 1, 2 and 9 applied orally at 2 and 10 mg kg-1 day-1 during 5 days in a neosporosis mouse model did not reduce parasite load and did not limit parasite dissemination to the central nervous system. In accordance with these results, ICP-MS carried out on different organs of mice orally administrated with complexes 1 and 9, demonstrated that the drugs were readily absorbed, and after 3 and 48 h, were mainly detected in liver and kidney, but were largely absent from the brain. Thus, dinuclear thiolato-bridged arene ruthenium complexes exhibit interesting activities against N. caninum in vitro, but further modifications of these promising molecules are required to improve their bioavailability and pharmacokinetic properties in order to exert a pronounced and selective effect against N. caninum in vivo.

Preclinical Anticancer Activity of an Electron-Deficient Organoruthenium(II) Complex

Ruthenium compounds have been shown to be promising alternatives to platinum(II) drugs. However, their clinical success depends on achieving mechanisms of action that overcome Pt-resistance mechanisms. Electron-deficient organoruthenium complexes are an understudied class of compounds that exhibit unusual reactivity in solution and might offer novel anticancer mechanisms of action. Here, we evaluate the in vitro and in vivo anticancer properties of the electron-deficient organoruthenium complex [(p-cymene)Ru(maleonitriledithiolate)]. This compound is found to be highly cytotoxic: 5 to 60 times more potent than cisplatin towards ovarian (A2780 and A2780cisR), colon (HCT116 p53+/+ and HCT116 p53-/-), and non-small cell lung H460 cancer cell lines. It shows no cross-resistance and is equally cytotoxic to both A2780 and A2780cisR cell lines. Furthermore, unlike cisplatin, the remarkable in vitro antiproliferative activity of this compound appears to be p53-independent. In vivo evaluation in the hollow-fibre assay across a panel of cancer cell types and subcutaneous H460 non-small cell lung cancer xenograft model hints at the activity of the complex. Although the impressive in vitro data are not fully corroborated by the in vivo follow-up, this work is the first preclinical study of electron-deficient half-sandwich complexes and highlights their promise as anticancer drug candidates.

Synthesis, Modification, and Biological Evaluation of a Library of Novel Water-Soluble Thiopyridone-Based Organometallic Complexes and Their Unexpected (Biological) Behavior

A series of 16 dinuclear thiopyridone-based organometallics with excellent water solubility, increased stability and remarkable cytotoxicity were synthesized and characterized. The complexes of this work formed dimeric species featuring a double positive charge in polar protic solvents, accounting for their outstanding solubility in aqueous solution. Most of them displayed higher antiproliferative activity than their parental thiomaltol complex, with unexpected cytotoxicity trends depending on the employed metal center, ligand modification, and cell line. Insights into their behavior in biological systems were gathered by means of amino-acid interaction studies, cytotoxicity tests in 3D spheroid models, laser ablation, cellular accumulation measurements, as well as cell cycle experiments.

Dinuclear thiolato-bridged arene ruthenium complexes: from reaction conditions and mechanism to synthesis of new complexes

Several dinuclear thiophenolato-bridged arene ruthenium complexes [(η⁶-p-MeC₆H₄Prⁱ)₂Ru₂(μ₂-SC₆H₄-R)₃]⁺ (R = H, NO₂, F) could so far only be obtained in fair yields using the synthetic route established in the early 2000s. With much less reactive aliphatic thiols or with bulky thiols, the reactions become even less efficient and the desired complexes are obtained with low yields or not at all. We employed density functional theory (DFT) calculations to gain a fundamental understanding of the reaction mechanisms leading to the formation of dithiolato and trithiolato complexes starting from the dichloro(p-cymene)ruthenium(ii) dimer [(η⁶-p-MeC₆H₄Prⁱ)Ru(μ₂-Cl)Cl]₂. The results of the DFT study enabled us to rationalise the experimental results and allowed us, via a modified synthetic route, to synthesise previously unreported and hitherto considered as unrealistic complexes. Our study opens up possibilities for the synthesis of so far inaccessible thiolato-bridged dinuclear arene ruthenium(ii) complexes but more generally, also the synthesis of other thiolato-bridged dinuclear group 8 and 9 metal complexes could be reexamined.

We used DFT calculations to understand the reaction mechanisms leading to the formation of dinuclear thiophenolato-bridged arene ruthenium complexes. DFT prompted us to modify the usual synthetic route, which enabled the synthesis of new complexes.

Encapsulation of the Dinuclear Trithiolato-Bridged Arene Ruthenium Complex Diruthenium-1 in an Apoferritin Nanocage: Structure and Cytotoxicity

The effects of encapsulating the cytotoxic dinuclear trithiolato-bridged arene ruthenium complex [(η⁶ -p-MeC₆ H₄ iPr)₂ Ru₂ (μ₂ -S-p-C₆ H₄ tBu)₃ ]Cl (DiRu-1) within the apoferritin (AFt) nanocage were investigated. The DiRu-1-AFt nanocarrier was characterized by UV/Vis spectroscopy, ICP-MS, CD and X-ray crystallography. In contrast to previously reported Au- and Pt-based drug-loaded AFt carriers, we found no evidence of direct interactions between DiRu-1 and AFt. DiRu-1-AFt is cytotoxic toward immortalized murine BALB/c-3T3 fibroblasts transformed with SV40 virus (SVT2) and human epidermoid carcinoma A431 malignant cells, and exhibits moderate selectivity for these cancer cells over normal BALB/c-3T3 cells. DiRu-1-AFt triggers the production of reactive oxygen species, depolarization of mitochondrial membrane potential, and induces cell death via p53-mediated apoptosis. Comparison between our data and previous results suggests that the presence of specific interactions between a metal-based drug and AFt within the protein cage is not essential for drug encapsulation.

Intracellular Catalysis with Selected Metal Complexes and Metallic Nanoparticles: Advances toward the Development of Catalytic Metallodrugs

Platinum-containing drugs (e.g., cisplatin) are among the most frequently used chemotherapeutic agents. Their tremendous success has spurred research and development of other metal-based drugs, with notable achievements. Generally, the vast majority of metal-based drug candidates in clinical and developmental stages are stoichiometric agents, i.e., each metal complex reacts only once with their biological target. Additionally, many of these metal complexes are involved in side reactions, which not only reduce the effective amount of the drug but may also cause toxicity. On a separate note, transition metal complexes and nanoparticles have a well-established history of being potent catalysts for selective molecular transformations, with examples such as the Mo- and Ru-based catalysts for metathesis reactions (Nobel Prize in 2005) or palladium catalysts for C-C bond forming reactions such as Heck, Negishi, or Suzuki reactions (Nobel Prize in 2010). Also, notably, no direct biological equivalent of these transformations exists in a biological environment such as bacteria or mammalian cells. It is, therefore, only logical that recent interest has focused on developing transition-metal based catalytic systems that are capable of performing transformations inside cells, with the aim of inducing medicinally relevant cellular changes. Because unlike in stoichiometric reactions, a catalytically active compound may turn over many substrate molecules, only very small amounts of such a catalytic metallodrug are required to achieve a desired pharmacologic effect, and therefore, toxicity and side reactions are reduced. Furthermore, performing catalytic reactions in biological systems also opens the door for new methodologies to study the behavior of biomolecules in their natural state, e.g., via in situ labeling or by increasing/depleting their concentration at will. There is, of course, an art to the choice of catalysts and reactions which have to be compatible with biological conditions, namely an aqueous, oxygen-containing environment. In this review, we aim to describe new developments that bring together the far-distant worlds of transition-metal based catalysis and metal-based drugs, in what is termed "catalytic metallodrugs". Here we will focus on transformations that have been performed on small biomolecules (such as shifting equilibria like in the NAD⁺/NADH or GSH/GSSG couples), on non-natural molecules such as dyes for imaging purposes, or on biomacromolecules such as proteins. Neither reactions involving release (e.g., CO) or transformation of small molecules (e.g., ¹O₂ production), degradation of biomolecules such as proteins, RNA or DNA nor light-induced medicinal chemistry (e.g., photodynamic therapy) are covered, even if metal complexes are centrally involved in those. In each section, we describe the (inorganic) chemistry involved, as well as selected examples of biological applications in the hope that this snapshot of a new but quickly developing field will indeed inspire novel research and unprecedented interactions across disciplinary boundaries.

Anticancer Activity and Catalytic Potential of Ruthenium(II)-Arene Complexes with N,O-Donor Ligands

The special ability of organometallic complexes to catalyze various transformations might offer new effective mechanisms for the treatment of cancer. Studies that report both the biological properties and the ability of metallic complexes to promote therapeutically relevant catalytic reactions are limited. Herein, we report the anticancer activity and catalytic potential of some ruthenium(II)-arene complexes bearing bidentate Schiff base ligands (2a and 2b) and their reduced analogues (5a and 5b, respectively). In comparison to their Schiff base counterparts 2a and 2b, we demonstrate that amine complexes 5a and 5b display (i) a higher in vitro antiproliferative activity on different human cancer cell lines, (ii) a lower rate of hydrolysis, and (iii) an improved initial catalytic rate for the reduction of NAD⁺ to NADH. In contrast to their imine analogues 2a and 2b, we also show that amine complexes 5a and 5b induce the generation of intracellular reactive oxygen species (ROS) in MCF-7 breast cancer cells. Our results highlight the impact that a simple ligand modification such as the reduction of an imine moiety can have on both the catalytic and biological activities of metal complexes. Moreover, the ruthenium complexes reported here display some antiproliferative activity against T47D breast cancer cells, known for their cis-platin resistance.

Synthesis and structure of new binuclear ruthenium(ii) arene benzil bis(benzoylhydrazone) complexes: investigation on antiproliferative activity and apoptosis induction

New binuclear Ru(ii) arene benzil bis(benzoylhydrazone) complexes show excellent cytotoxicity against human cancer cell lines. The results of biochemical assays demonstrated that complexes are able to induce apoptosis.

Characterization of the Activities of Dinuclear Thiolato-Bridged Arene Ruthenium Complexes against Toxoplasma gondii

The in vitro effects of 18 dinuclear thiolato-bridged arene ruthenium complexes (1 monohiolato compound, 4 dithiolato compounds, and 13 trithiolato compounds), originally designed as anticancer agents, on the apicomplexan parasite Toxoplasma gondii grown in human foreskin fibroblast (HFF) host cells were studied. Some trithiolato compounds exhibited antiparasitic efficacy at concentrations of 250 nM and below. Among those, complex 1 and complex 2 inhibited T. gondii proliferation with 50% inhibitory concentrations (IC₅₀s) of 34 and 62 nM, respectively, and they did not affect HFFs at dosages of 200 μM or above, resulting in selectivity indices of >23,000. The IC₅₀s of complex 9 were 1.2 nM for T. gondii and above 5 μM for HFFs. Transmission electron microscopy detected ultrastructural alterations in the matrix of the parasite mitochondria at the early stages of treatment, followed by a more pronounced destruction of tachyzoites. However, none of the three compounds applied at 250 nM for 15 days was parasiticidal. By affinity chromatography using complex 9 coupled to epoxy-activated Sepharose followed by mass spectrometry, T. gondii translation elongation factor 1α and two ribosomal proteins, RPS18 and RPL27, were identified to be potential binding proteins. In conclusion, organometallic ruthenium complexes exhibit promising activities against Toxoplasma, and the potential mechanisms of action of these compounds as well as their prospective applications for the treatment of toxoplasmosis are discussed.

Chlorambucil conjugates of dinuclear p-cymene ruthenium trithiolato complexes: synthesis, characterization and cytotoxicity study in vitro and in vivo

Four diruthenium trithiolato chlorambucil conjugates have been prepared via Steglich esterification from chlorambucil and the corresponding trithiolato precursors. All conjugates are highly cytotoxic towards human ovarian A2780 and A2780cisR cancer cell lines with IC50 values in the nanomolar range. The conjugates exhibit selectivity towards A2780 cells as compared to non-cancerous HEK293 cells, while being only slightly selective for RF24 and A2780cisR cells. In vivo, the conjugate [10]BF4 suppressed the growth of a solid Ehrlich tumor in immunocompetent NMRI mice but did not prolong their overall survival. The reactivity of the chlorambucil conjugates with glutathione, a potential target of the dinuclear ruthenium motive, and with the 2-deoxyguanosine 5'-monophosphate (dGMP-a model target of chlorambucil) was studied by mass spectrometry and NMR spectroscopy. The conjugates did not show catalytic activity for the oxidation of glutathione nor binding to nucleotides, indicating that glutathione oxidation and DNA alkylation are not key mechanisms of action. Four highly cytotoxic diruthenium trithiolato chlorambucil conjugates have been prepared. All conjugates exhibit selectivity towards A2780 cells as compared to HEK293 cells, while being only slightly active in RF24 and A2780cisR cells. In vivo, the best candidate suppressed the growth of a solid Ehrlich tumor in immunocompetent NMRI mice but did not prolong their overall survival.

Hydrolytic behaviour of mono- and dithiolato-bridged dinuclear arene ruthenium complexes and their interactions with biological ligands

Compared to the inert and highly cytotoxic dinuclear p-cymene ruthenium trithiolato complexes, the less cytotoxic mono- and dithiolato complexes readily hydrolyse in aqueous solution and form adducts with cysteine, but do not interact with DNA.

Crystal structure of bis-[μ-(4-meth-oxy-phen-yl)methane-thiol-ato-κ(2) S:S]bis-[chlorido-(η(6)-1-isopropyl-4-methyl-benzene)-ruthenium(II)] chloro-form disolvate

The mol-ecular structure of the title complex, [Ru2(C8H9OS)2Cl2(C10H14)2]·2CHCl3 or (p-MeC6H4Pr (i) )2Ru2(SCH2-p-C6H5-OCH3)2Cl2·2CHCl3, shows inversion symmetry. The two symmetry-related Ru(II) atoms are bridged by two 4-meth-oxy-α-toluene-thiol-ato [(4-meth-oxy-phen-yl)methane-thiol-ato] units. One chlorido ligand and the p-cymene ligand complete the typical piano-stool coordination environment of the Ru(II) atom. In the crystal, the CH moiety of the chloro-form mol-ecule inter-acts with the chlorido ligand of the dinuclear complex, while one Cl atom of the solvent inter-acts more weakly with the methyl group of the bridging 4-meth-oxy-α-toluene-thiol-ato unit. This assembly leads to the formation of supra-molecular chains extending parallel to [021].

Crystal structure of (μ-4-hy-droxy-benzene-thiol-ato-κ(2) S:S)bis-(μ-phenyl-methane-thiol-ato-κ(2) S:S)bis-[(η(6)-1-isopropyl-4-methyl-benzene)-ruthenium(II)] tetra-fluorido-borate

The crystal structure of the dinuclear arene ruthenium title complex, [Ru2(C6H5OS)(C7H7S)2(C10H14)2]BF4, shows the two Ru(II) atoms to be bridged by two benzyl-thio-pheno-late units and one 4-hy-droxy-thio-pheno-late unit, with the remaining three coordination sites of each Ru(II) atom being occupied by p-cymene ligands, completing the typical piano-stool coordination geometry. The BF4 (-) counter-anion is surrounded by four cationic dinuclear complexes, showing an O-H⋯F hydrogen bond and several weak C-H⋯F inter-actions. This is the first example of an X-ray analysis of a mixed dinuclear tri-thiol-ate arene ruthenium(II) complex.

Approaches to the design of catalytic metallodrugs

Metal ions are known to act as catalytic centres in metallo-enzymes. On the other hand, low-molecular-weight metal complexes are widely used as catalysts in chemical systems. However, small catalysts do not have a large protein ligand to provide substrate selectivity and minimize catalyst poisoning. Despite the challenges that the lack of a protein ligand might pose, some success in the use of metal catalysts for biochemical transformations has been reported. Here, we present a brief overview of such reports, especially involving catalytic reactions in cells. Examples include C-C bond formation, deprotection and functional group modification, degradation of biomolecules, and redox modulation. We discuss four classes of catalytic redox modulators: photosensitizers, superoxide dismutase mimics, thiol oxidants, and transfer hydrogenation catalysts. Catalytic metallodrugs offer the prospect of low-dose therapy and a challenging new design strategy for future exploration.

Cytotoxic peptide conjugates of dinuclear arene ruthenium trithiolato complexes

Novel dinuclear arene ruthenium trithiolato complexes containing a water-soluble peptide moiety in one of the three thiolato bridges were designed and evaluated against A2780 human ovarian cancer cells and against their cisplatin-resistant mutant A2780cisR.

Osmium(III) analogues of KP1019: electrochemical and chemical synthesis, spectroscopic characterization, X-ray crystallography, hydrolytic stability, and antiproliferative activity

A one-electron reduction of osmium(IV) complexes trans-[Os(IV)Cl4(Hazole)2], where Hazole = 1H-pyrazole ([1](0)), 2H-indazole ([2](0)), 1H-imidazole ([3](0)), and 1H-benzimidazole ([4](0)), afforded a series of eight new complexes as osmium analogues of KP1019, a lead anticancer drug in clinical trials, with the general formula (cation)[trans-Os(III)Cl4(Hazole)2], where cation = H2pz(+) (H2pz[1]), H2ind(+) (H2ind[2]), H2im(+) (H2im[3]), Ph4P(+) (Ph4P[3]), nBu4N(+) (nBu4N[3]), H2bzim(+) (H2bzim[4]), Ph4P(+) (Ph4P[4]), and nBu4N(+) (nBu4N[4]). All complexes were characterized by elemental analysis, (1)H NMR spectroscopy, electrospray ionization mass spectrometry, UV-vis spectroscopy, cyclic voltammetry, while H2pz[1], H2ind[2], and nBu4[3], in addition, by X-ray diffraction. The reduced species [1](-) and [4](-) are stable in aqueous media in the absence of air oxygen and do not react with small biomolecules such as amino acids and the nucleotide 5'-dGMP. Cell culture experiments in five different human cancer cell lines (HeLa, A549, FemX, MDA-MB-453, and LS-174) and one noncancerous cell line (MRC-5) were performed, and the results were discussed and compared to those for KP1019 and cisplatin. Benzannulation in complexes with similar structure enhances antitumor activity by several orders of magnitude, implicating different mechanisms of action of the tested compounds. In particular, complexes H2ind[2] and H2bzim[4] exhibited significant antiproliferative activity in vitro when compared to H2pz[1] and H2im[3].

Competition between glutathione and DNA oligonucleotides for ruthenium(II) arene anticancer complexes

The organometallic anticancer complex [(η(6)-bip)Ru(en)Cl](+) (1; bip = biphenyl, en = ethylenediamine) selectively binds to N7 of guanine bases of oligonucleotides and native DNA. However, under physiologically relevant conditions (micromolar Ru concentrations, pH 7, 22 mM NaCl, 310 K), the tripeptide glutathione (γ-L-Glu-L-Cys-Gly; GSH) is kinetically competitive with guanine (as guanosine 3',5'-cyclic monophosphate, cGMP) for coordination with complex 1, and gives rise to a ruthenium thiolato adduct. This thiolato adduct can subsequently undergo oxidation to a sulfenate intermediate, providing a facile route for the formation of a final cGMP adduct via the displacement of S-bound glutathione by G N7 (F. Y. Wang, J. J. Xu, A. Habtemariam, J. Bella and P. J. Sadler, J. Am. Chem. Soc., 2005, 127, 17734). In this work, the competition between GSH and the single-stranded 14-mer oligonucleotide 5'-TATGTACCATGTAT-3' (I) and duplex III (III = I + II, II = 5'-ATACATGGTACATA) for complex 1 and its analogue [(η(6)-tha)Ru(en)Cl](+) (2, tha = tetrahydroanthracene) under physiologically relevant conditions was investigated using conventional ESI-MS and high resolution ESI-FTICR-MS coupled to conventional HPLC and nanoscale HPLC, respectively. The results indicate that whether there was high excess of GSH or not in the reaction mixtures, the reaction of complex 1 or 2 with single-stranded oligonucleotide I always gave rise to mono-ruthenated oligonucleotide, and the reaction of complex 1 or 2 with duplex III gave rise to the mono-ruthenated duplex oligonucleotide. Furthermore, the ruthenation of duplex III by complex 1 showed no significant discrimination between the complementary strands I and II, but complex 2 appeared to bind preferentially to strand II compared to strand I as revealed by the high resolution FTICR-MS analysis. GSH is highly abundant in cells at millimolar concentrations and is well known to be involved in the deactivation of the clinical drug cisplatin and in platinum resistance. Our findings reveal a potentially contrasting role for GSH in the mechanism of action of these ruthenium anticancer complexes that may contribute to the lack of cross-resistance with platinum drugs.