Analysis of the cytotoxic effects of ruthenium–ketoconazole and ruthenium–clotrimazole complexes on cancer cells

Ruthenium-based compounds have intriguing anti-cancer properties, and some of these novel compounds are currently in clinical trials. To continue the development of new metal-based drug combinations, we coupled ruthenium (Ru) with the azole compounds ketoconazole (KTZ) and clotrimazole (CTZ), which are well-known antifungal agents that also display anticancer properties. We report the activity of a series of 12 Ru–KTZ and Ru–CTZ compounds against three prostate tumor cell lines with different androgen sensitivity, as well as cervical cancer and lymphoblastic lymphoma cell lines. In addition, human cell lines were used to evaluate the toxicity against non-transformed cells and to establish selectivity indexes. Our results indicate that the combination of ruthenium and KTZ/CTZ in a single molecule results in complexes that are more cytotoxic than the individual components alone, displaying in some cases low micromolar CC₅₀ values and high selectivity indexes. Additionally, all compounds are more cytotoxic against prostate cell lines with lower cytotoxicity against non-transformed epidermal cell lines. Some of the compounds were found to primarily induce cell death via apoptosis yet weakly interact with DNA. Our studies also demonstrate that the cytotoxicity induced by our Ru-based compounds is not directly related to their ability to interact with DNA.     

Is photoisomerization required for NO photorelease in ruthenium nitrosyl complexes?

The factors that explain the competition between intramolecular NO linkage photoisomerization and NO photorelease in five ruthenium nitrosyl complexes were investigated. By applying DFT-based methods, it was possible to characterize the ground states and lowest triplet potential energy surfaces of these species, and to establish that both photoisomerization and photorelease processes can occur in the lowest triplet state of each species. This work highlights the crucial role of the sideways-bonded isomer, a metastable state also known as the MS2 isomer, in the photochemical loss of NO, while the results obtained also indicate that the population of the triplet state of this isomer is compulsory for both processes and show how photoisomerization and photorelease interfere.

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Graphical Abstract Illustration of the crucial role of the ³MS2 state in the photoreactivities of ruthenium nitrosyl complexes

     

Redox potentials of trinuclear μ-oxo ruthenium acetate clusters with N-heterocyclic ligands

The trinuclear clusters of general composition [Ru₃O(OOCCH₃)₆(N-Het)₃], where N-Het=pyridine and pyrazine derivatives, exhibit a series of reversible waves in the range of −1.8 to 2.4 V versus SHE, in acetonitrile, ascribed to the successive [cluster]^{−2/−1/0/+1/+2/+3} redox couples. The redox potentials decrease with the pK_a of the N-heterocyclic ligands according to the equations E°(+3/+2)= 2.24−0.023 pK_a; E°(+2/+1)=1.34−0.029 pK_a; E°(+1/0)=0.36−0.039 pK_a and E°(0/−1)=−0.68− 0.074 pK_a. The dependence is greater at lower oxidation states, reflecting the role of π-backbonding in the complexes.     

Structure of anticancer ruthenium half-sandwich complex bound to glycogen synthase kinase 3β

The 3.15-Å-resolution crystal structure of the R enantiomer of the highly bioactive and antiproliferative half-sandwich ruthenium complex DW12 bound to the ATP binding site of glycogen synthase kinase 3β (GSK-3β) is reported and the binding is compared with the GSK-3β binding of staurosporine and other organic inhibitors. The structure reveals a close packing of the organometallic inhibitor in the ATP binding site of GSK-3β via an induced-fit mechanism. The molecular structure of (R)-DW12 with the CO ligand oriented perpendicular to the pyridocarbazole heterocycle allows the complex to stretch the whole distance sandwiched between the faces of the N- and C-terminal lobes and to interact tightly with the flexible glycine-rich loop, which is uncommon for the interaction of GSK-3β with organic inhibitors.     

Metallopolymers from ruthenium and iron pyrrole-containing π-extended complexes as model components for solid state solar cells

New metallopolymers were generated efficiently on Pt and ITO (indium-tin oxide) glass slides by repeated scan oxidation of Ru and Fe complexes containing pyrrolostyryl bipyridine ligands. The UV-Vis spectrum and voltammogram of Ru-based polymer films showed blue-shifts of the MLCT absorption bands and increased oxidation potentials indicating conjugation cut in the π-extended system. In contrast, formation of polypyrrole occurred in Fe-based polymers due to oxidation of pyrrole groups by the initially oxidised metal centres. The coated ITO electrodes displayed promising wide absorption domains for use in light conversion devices.     

Metal–metal interactions in linear tri-, penta-, hepta-, and nona-nuclear ruthenium string complexes

Density functional theory (DFT) methodology was used to examine the structural properties of linear metal string complexes: [Ru(3)(dpa)(4)X(2)] (X = Cl(-), CN(-), NCS(-), dpa = dipyridylamine(-)), [Ru(5)(tpda)(4)Cl(2)], and hypothetical, not yet synthesized complexes [Ru(7)(tpta)(4)Cl(2)] and [Ru(9)(ppta)(4)Cl(2)] (tpda = tri-α-pyridyldiamine(2-), tpta = tetra-α-pyridyltriamine(3-), ppta = penta-α-pyridyltetraamine(4-)). Our specific focus was on the two longest structures and on comparison of the string complexes and unsupported ruthenium backboned chain complexes, which have weaker ruthenium-ruthenium interactions. The electronic structures were studied with the aid of visualized frontier molecular orbitals, and Bader's quantum theory of atoms in molecules (QTAIM) was used to study the interactions between ruthenium atoms. The electron density was found to be highest and distributed most evenly between the ruthenium atoms in the hypothetical [Ru(7)(tpta)(4)Cl(2)] and [Ru(9)(ppta)(4)Cl(2)] string complexes.     

Synthesis of new chiral (η6-arene)(η4-diene)ruthenium(O) complexes

New Ru(η⁶-arene)(η⁴-diene) complexes, containing chiral substituents on the aromatic ring, have been prepared and characterized. The ¹H NMR inequivalence of the ortho and meta protons of the phenyl ring is discussed.     

A dimeric tris(2,2′-bipyridine)ruthenium(II) system: Emission spectrum and cyclic voltammogram

A dimeric ruthenium(II) compound in which two Ru(bpy)₃ groups are linked by an amide bonding has been prepared as a model compound to study an energy transfer between Ru(bpy)₃ chelates. The nature of the solution luminescence spectrum varied with concentration: the emission maximum appeared at 650 nm for dilute solutions and at 670 nm for concentrated solutions. This concentration dependence has been interpreted in terms of excimers that are formed due to an energy transfer between two Ru(bpy)₃ groups in a dimer molecule. The cyclic voltammogram for the Ru³⁺/Ru²⁺ reaction is quasireversible: the reaction is governed by a sluggish electron transfer which may be due to an intradimer electronic interaction.     

Dinuclear ruthenium(II) catecholato and 2,3-naphthalenediolato complexes featuring κ-diaryloxo/η-arene coordination mode

A new dinuclear ruthenium(II) catecholato complex [Cp*Ru(κ²:η⁶-μ₂-1,2-O₂C₆H₄)RuCp*] (3; Cp* = η⁵-C₅Me₅) has been prepared by the reaction of [Cp*RuCl]₄ with 2 equiv. of disodium catecholate in THF. Complex 3 has a dinuclear structure, in which one of the Cp*Ru fragments is κ²-bonded to the two oxygen atoms and the other is η⁶-bonded to the aromatic ring. Similar treatment of [Cp*RuCl]₄ with disodium 2,3-naphthalenediolate affords an analogous κ²:η⁶-bonded dinuclear complex [Cp*Ru(κ²:η⁶-μ₂-2,3-O₂C₁₀H₆)RuCp*] (4) with selective π-complexation at the oxygen-substituted naphthalene ring. The molecular structure of 4 has been determined by X-ray crystallography. The oxygen-bound ruthenium atoms in complexes 3 and 4 are coordinatively unsaturated and readily uptake 1 equiv. of carbon monoxide to give the corresponding carbonyl adducts [Cp*Ru(CO)(κ²:η⁶-μ₂-1,2-O₂C₆H₄)RuCp*] (5) and [Cp*Ru(CO)(κ²:η⁶-μ₂-2,3-O₂C₁₀H₆)RuCp*] (6), respectively.     

Exploring metallodrug–protein interactions by mass spectrometry: comparisons between platinum coordination complexes and an organometallic ruthenium compound

Electrospray ionisation mass spectrometry was used to analyse the reactions of metal compounds with mixtures of selected proteins. Three representative medicinally relevant compounds, cisplatin, transplatin and the organometallic ruthenium compound RAPTA-C, were reacted with a pool of three proteins, ubiquitin, cytochrome c and superoxide dismutase, and the reaction products were analysed using high-resolution mass spectrometry. Highly informative electrospray ionisation mass spectra were acquired following careful optimisation of the experimental conditions. The formation of metal–protein adducts was clearly observed for the three proteins. In addition, valuable information was obtained on the nature of the protein-bound metallofragments, on their distribution among the three different proteins and on the binding kinetics. The platinum compounds were less reactive and considerably less selective in protein binding than RAPTA-C, which showed a high affinity towards ubiquitin and cytochrome c, but not superoxide dismutase. In addition, competition studies between cisplatin and RAPTA-C showed that the two metallodrugs have affinities for the same amino acid residues on protein binding. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Formation of novel ene-yne substituted β-diketonato ruthenium(III) complexes by the Heck-like reactions on coordinated ligand

Two new ene-yne substituted 2,4-pentanedionatoruthenium(III) complexes formed by the Heck-like reactions in the course of the Sonogashira reactions. The two complexes are structural isomers; one is [Ru(E-1,4-mBSima)(dpm)₂] and another is [Ru(E-2,4-mBSima)(dpm)₂], where E-1,4-mBSima is E-3-(1,4-bis(trimethylsilyl)-1-butene-3-ynyl)-2,4-pentanedionate, E-2,4-mBSima is E-3-(2,4-bis(trimethylsilyl)-1-butene-3-ynyl)-2,4-pentanedionate, and dpm is dipivaloylmethanate (2,2,6,6-tetramethylheptan-3,5-dionate). Both of complexes have been characterized by ¹H NMR and infrared spectroscopies, mass spectrometry, and electrochemistry. [Ru(E-1,4-mBSima)(dpm)₂] has also been characterized by X-ray crystallography. The ruthenium(III) is coordinated in an octahedral arrangement by the oxygen atoms of three β-diketonate ligands. The dihedral angle between the 2,4-pentanedionato chelate ring and the ene-yne plane on the E-1,4-mBSima ligand is 91°. The ene-yne group in [Ru(E-1,4-mBSima)(dpm)₂] is fixed either in the solution state suggested by the ¹H NMR spectrum with no symmetry.     

A ruthenium(II) β-carboline complex induced p53-mediated apoptosis in cancer cells

A ruthenium(II) β-carboline complex [Ru(tpy)(Nh)₃]²⁺ (tpy = 2,2′:6′,2″-terpyridine, Nh = Norharman, Ru1) has been synthesized and characterized. This complex induced apoptosis against various cancer cell lines and had high selectivity between tumor cells and normal cells. In vivo examination indicated Ru1 decreased mouse MCF-7 and HepG2 tumor growth. Signaling pathways analysis demonstrated that this complex induced apoptosis via the mitochondrial pathway, as evidenced by the loss of mitochondrial membrane potential (MMP, ΔΨ_m) and the release of cytochrome c. The resulting accumulation of p53 proteins from phosphorylation at Ser-15 and Ser-392 correlated with an increase in p21 and caspase activation. Taken together, these findings suggest that Ru1 exhibits high and selective cytotoxicity induced p53-mediated apoptosis and may contribute to the future development of improved chemotherapeutics against human cancers.     

Evaluation of (ɳ6-p-cymene) ruthenium diclofenac complex as anticancer chemotherapeutic agent: interaction with biomolecules,cytotoxicity assays

abstract

The designing of metal-based anticancer therapeutic agents can be optimized in a better and rapid way if the ligands utilized have standalone properties. Therefore, even when the organometallic/coordination complex (i.e., metallodrug) gets dissociated in extreme conditions, the ligand can endorse its biological properties. Herein, we have synthesized and characterized ?⁶-p-cymene ruthenium diclofenac complex. Furthermore, the ruthenium complex interactions with human serum albumin (HSA) and ct-DNA have been studied using various spectroscopic studies viz., UV, fluorescence, and circular dichroism and exhibited a significant binding propensity. Furthermore, in vitro cytotoxicity assays were carried out against human breast cancer “MCF-7” cell line. The ?⁶-p-cymene ruthenium diclofenac complex registered significant cytotoxicity with an IC₅₀ value of ～25.0?µM which is comparable to the standard drugs. The ?⁶-p-cymene ruthenium diclofenac complex was able to decrease the MCF-7 cell proliferation and induced significant levels of apoptosis with relatively low toxicity.     

Reactions of ketones with coordinated nitriles on β-diketonato ruthenium complexes leading to formation of compounds with new carbon-carbon bonds

The reactions of [Ru(acac)₂(CH₃CN)₂] with four ketones (acetone, ethyl methyl ketone, acetylacetone and monochloroacetone), and the reactions of [Ru(acac)₂(C₆H₅CN)₂] with two ketones (acetone and ethyl methyl ketone) yielded six novel compounds of β-ketiminato ruthenium complexes: [Ru(acac)₂(mhmk)], [Ru(acac)₂(ehmk)], [Ru(acac)₂(mAmk)], [Ru(acac)₂(mClmk)], Ru(acac)₂(mhbk)], and [Ru(acac)₂(ehbk)] (mhmk = 4-iminopentane-2-one mono anion, ehmk = 5-iminohexane-3-one mono anion, mAmk = 3-(1-iminoethyl)-2,4-pentanedione mono anion, mClmk = 3-chloro-4-imino-pentane-2-one mono anion, mhbk = 1-phenyl-1-iminobutane-3-one mono anion, ehbk = 1-phenyl-1-iminopentane-3-one mono anion). All the new complexes have been characterized by elemental analyses, ¹H NMR, MS and electronic spectral data. Crystal and molecular structures for the six β-ketimine complexes have been solved by single crystal X-ray diffraction studies. A mechanism involving the attack of ketones on the coordinated nitrile has been proposed. The electrochemical redox behavior of the β-ketimine complexes has been elucidated.     

Synthesis,electrochemistry and spectroscopy of novel ruthenium and rhodium complexes bound to 2,2′-Bi-1,3-dithiol (TTF)

The (TTF)₂MCl₃ (M = Ru(II) and Rh(I), TTF (tetrathiafulvalene) = 2,2′-bi-1,3-dithiol) complexes have been prepared by direct reaction of TTF and the MCI₃ salt. Ultraviolet-visible spectra of the complexes are reported and indicate formation of a TTF⁺ cation with a reduced metal center. The presence of the oxidized TTF⁺ is further confirmed by resonance raman peaks near 1416 cm⁻¹. Electrochemistry indicates oxidation/reduction of the complexes is localized on the TTF ligand rather than from the metal.     

Protein recognition of hetero-/homoleptic ruthenium(II) tris(bipyridine)s for α-chymotrypsin and cytochrome c

We examined the relationship between the structures of hetero-/homoleptic ruthenium(II) tris(bipyridine) metal complexes (Ru(II)(bpy)(3)) and their binding properties for α-chymotrypsin (ChT) and cytochrome c (cyt c). Heteroleptic compound 1a binds to both ChT and cyt c in 1:1 ratio, whereas homoleptic 2 forms 1:2 protein complex with ChT but 1:1 complex with cyt c. These results suggest that the structure of the recognition cavity in Ru(II)(bpy)(3) can be designed for shape complementarity to the targeted proteins. In addition, Ru(II)(bpy)(3) complexes were found to be potent inhibitors of cyt c reduction and to permeate A549 cells.     

The mechanism of antimalarial action of the ruthenium(II)–chloroquine complex [RuCl2(CQ)]2

The mechanism of antimalarial action of the ruthenium-chloroquine complex [RuCl(2)(CQ)](2) (1), previously shown by us to be active in vitro against CQ-resistant strains of Plasmodium falciparum and in vivo against P. berghei, has been investigated. The complex is rapidly hydrolyzed in aqueous solution to [RuCl(OH(2))(3)(CQ)](2)[Cl](2), which is probably the active species. This compound binds to hematin in solution and inhibits aggregation to beta-hematin at pH approximately 5 to a slightly lower extent than chloroquine diphosphate; more importantly, the heme aggregation inhibition activity of complex 1 is significantly higher than that of CQ when measured at the interface of n-octanol-aqueous acetate buffer mixtures under acidic conditions modeling the food vacuole of the parasite. Partition coefficient measurements confirmed that complex 1 is considerably more lipophilic than CQ in n-octanol-water mixtures at pH approximately 5. This suggests that the principal target of complex 1 is the heme aggregation process, which has recently been reported to be fast and spontaneous at or near water-lipid interfaces. The enhanced antimalarial activity of complex 1 is thus probably due to a higher effective concentration of the drug at or near the interface compared with that of CQ, which accumulates strongly in the aqueous regions of the vacuole under those conditions. Furthermore, the activity of complex 1 against CQ-resistant strains of P. falciparum is probably related to its greater lipophilicity, in line with previous reports indicating a lowered ability of the mutated transmembrane transporter PfCRT to promote the efflux of highly lipophilic drugs. The metal complex also interacts with DNA by intercalation, to a comparable extent and in a similar manner to uncomplexed CQ and therefore DNA binding does not appear to be an important part of the mechanism of antimalarial action in this case.     

Water soluble (η-arene) ruthenium(II) complexes incorporating marine derived bioligand: Synthesis, spectral and structural studies

A series of water soluble compounds of general formula [{(η⁶-arene)Ru(HMP)Cl}], [η⁶-arene = η⁶-cymene (1), η⁶-HMB (2), η⁶-C₆H₆ (3); HMP = 5-hydroxy-2-(hydroxymethyl)-4-pyrone] have been prepared by the reaction of [{(η⁶-arene) RuCl₂}₂] with HMP. The complexes 1 and 2 react with NaN₃ to give in excellent yield tetra-azido complexes [{(η⁶-arene)Ru(μN₃)N₃}₂] (arene = cymene 4, HMB = 5) but similar reaction of complex 3 with NaN₃ yielded di-azdo complex [{(η⁶-C₆H₆)Ru(μN₃)Cl}₂] (6). Reaction of [{(η⁶-arene)Ru(μN₃)Cl}₂] with HMP in the presence of NaOMe resulted in the formation of azido complex [{(η⁶-arene)Ru(HMP)N₃}]. Mono and dinuclear complexes [{(η⁶-arene)Ru(HMP)(L₁)}]⁺ and [{(η⁶-arene)Ru(HMP)}₂(μL₂)]²⁺ were also prepared by the reaction of complexes 1 and 2 with the appropriate ligand, L₁ or L₂ in the presence of AgBF₄ (L₁ = PyCN, DMAP; L₂ = 4,4′-bipy, pyrazine). The complexes are characterized on the basis of spectroscopic data and molecular structures of three representative compounds have been determined by single crystal X-ray diffraction study.     

The ruthenium(II)–arene compound RAPTA-C induces apoptosis in EAC cells through mitochondrial and p53–JNK pathways

An investigation of the molecular mechanism of the anticancer activity demonstrated by the ruthenium(II)–arene compound [Ru(η⁶-p-cymene)Cl₂(pta)] (pta is 1,3,5-triaza-7-phosphaadamantane), termed “RAPTA-C”, in Ehrlich ascites carcinoma (EAC) bearing mice is described. RAPTA-C exhibits effective cell growth inhibition by triggering G₂/M phase arrest and apoptosis in cancer cells. Cell cycle arrest is associated with increased levels of p21 and reduced amounts of cyclin E. RAPTA-C treatment also enhances the levels of p53, and its treatment triggers the mitochondrial apoptotic pathway, as shown by the change in Bax to Bcl-2 ratios, resulting in cytochrome c release and caspase-9 activation. c-Jun NH₂-terminal kinase (JNK) is a critical mediator in RAPTA-C-induced cell growth inhibition. Activation of JNK by RAPTA-C increases significantly during apoptosis. Overall, these results suggest a critical role for JNK and p53 in RAPTA-C-induced G₂/M arrest and apoptosis of EAC-bearing mice. Consequently, RAPTA-C treatment results in a significant inhibition in the progression of cancer in an animal model, which emulates the human disease, and does so with remarkably low general toxicity; hence, RAPTA-C has potential for clinical application.