Alterations in the Binding of [Cl(NH3)5RuIII]2+ to DNA by Glutathione: Reduction, Autoxidation, Coordination, and Decomposition

Reactions of Ru(III)-drugs KP1019 and KP418 with guanine, 2'-deoxyguanosine and guanosine: a DFT study

Ruthenium (Ru)-based anticancer drugs are considered to be novel alternatives of platinum-based drugs. They exhibit potent cytotoxicity against the cancer cells and hence are useful for the treatment of cancer. Herein, the density functional theory calculations in the gas phase and aqueous media are carried out to study the reactions of two Ru(III)-based drugs such as KP1019 and KP418 with the N7 site of guanine (G), 2'-deoxyguanosine (dGua), and guanosine (Gua) to understand their reactivity against the DNA and RNA. All the reactions are found to be exothermic. The activation free energies and rate constants of these reactions indicate that KP1019 and KP418 would react with the dGua more readily than Gua. Hence, the binding of these drugs with the DNA would be more preferred as compared to RNA. It is further found that among these drugs, KP1019 would be more reactive than KP418 in agreement with the experimental observation. Thus, this study is expected to aid in the future development of potent anticancer drugs.

Pharmacological assessment of Ru(II) complex with GidA protein- A novel topoisomerase II inhibitor towards cancer therapeutics

The interactions of ruthenium(II) complex with Glucose inhibited division protein A (GidA protein) was studied through various spectroscopic techniques with the ultimate goal of preparing adducts with good selectivity for cancer cells. In all the cases, formation of a tight metal-protein conjugate was observed. The influence of pH, reducing agents and chelators on the formation of adduct was analysed by UV- visible spectroscopy. While there was no effect on the addition of sodium ascorbate, some alterations on some selected bands were seen on the UV-visible spectra on the addition of EDTA. The adduct was stable in the pH range of 5-8. Addition of ruthenium(II) complex effectively quenched the intrinsic fluorescence of GidA and it occurred through static quenching. The effect of ruthenium(II) complex on the conformation of GidA has been examined by analyzing CD spectrum. Though, there was some conformational changes observed in the presence of ruthenium(II) complex, α- helix in the secondary structure of GidA retained its identity. Molecular docking of ruthenium(II) complex with GidA also indicated that GidA docks through hydrophobic interaction. The stable semisynthetic complex (ruthenium(II) complex with GidA) was checked for topoisomerase II inhibition. Relaxation and decatenation assay proved topoisomerase II inhibition of semisynthetic complex.Communicated by Ramaswamy H. Sarma.

A Dinuclear Persulfide-Bridged Ruthenium Compound is a Hypoxia-Selective Hydrogen Sulfide (H2 S) Donor

Hydrogen sulfide (H2 S) is a gaseous molecule that has received attention for its role in biological processes and therapeutic potential in diseases, such as ischemic reperfusion injury. Despite its clinical relevance, delivery of H2 S to biological systems is hampered by its toxicity at high concentrations. Herein, we report the first metal-based H2 S donor that delivers this gas selectively to hypoxic cells. We further show that H2 S release from this compound protects H9c2 rat cardiomyoblasts from an in vitro model of ischemic reperfusion injury. These results validate the utility of redox-activated metal complexes as hypoxia-selective H2 S-releasing agents for use as tools to study the role of this gaseous molecule in complex biological systems.

Unveiling the Role of Hydrogen Bonding and g-Tensor in the Interaction of Ru-Bis-DMSO with Amino Acid Residue and Human Serum Albumin

Density functional theory calculations have been carried out to observe the role of hydrogen bonding in hydrolysis and the coordination mechanism of three amino acid residues (histidine, cysteine, and alanine) with Ru-bis-DMSO complex via which the complex tends to interact with the HSA protein receptor. The interaction mechanism shows that ruthenium complexes prefer to bind protein receptor through cysteine and histidine residues rather than through alanine, which has been confirmed by DFT evaluated H-bonding and g-tensor analysis. The number of H-bonds plays a major role in stabilizing the intermediates and transition states involved in the Ru-bis-DMSO and amino acid residue interactions. Our theoretical g-tensor values are in good agreement with the available experimental results. Further QM/MM calculation on the Ru-bis-DMSO-HSA adducts reveals that the adduct is more stable when Ru gets coordinated with histidine imidazole rather than cysteine. These investigations helped us in understanding the type of amino acid residue responsible for binding the metal complex Ru-bis-DMSO with the carrier protein HSA.

Antineoplastic activity of a novel ruthenium complex against human hepatocellular carcinoma (HepG2) and human cervical adenocarcinoma (HeLa) cells

Novel metal complexes have received much attention recently because of their potential anticancer activity. Notably, ruthenium-based complexes have emerged as good alternatives to the currently used platinum-based drugs for cancer therapy, with less toxicity and fewer side effects. The beneficial properties of Ru, which make it a highly promising therapeutic agent, include its variable oxidative states, low toxicity, and high selectivity for cancer cells. The present study evaluated the cytotoxic effects of a ruthenium complex, namely cis-[Ru(1,10-phenanthroline)2(imidazole)2]2+ (RuC), on human hepatocellular carcinoma (HepG2) and human cervical adenocarcinoma (HeLa) cells and analyzed metabolic parameters. RuC reduced HepG2 and HeLa cell viability at all tested concentrations (10, 50, and 100 nmol/L) at 48 h of incubation, based on the MTT, Crystal violet, and neutral red assays. The proliferation capacity of HepG2 cells did not recover, whereas HeLa cell proliferation partially recovered after RuC treatment. RuC also inhibited all states of cell respiration and increased the levels of the metabolites pyruvate and lactate in both cell lines. The cytotoxicity of RuC was higher than cisplatin (positive control) in both lineages. These results indicate that RuC affects metabolic functions that are related to the energy provision and viability of HepG2 and HeLa cells and is a promising candidate for further investigations that utilize models of human cervical adenocarcinoma and mainly hepatocellular carcinoma.

Kinetics and mechanism of formation of the complex [Ru(CN)5INH]3− through the ligand substitution reaction between the aquapentacyanoruthenate(II) anion and isoniazid

The formation kinetics of the complex, [Ru(CN)5INH]3−, formed through the ligand substitution reaction between isoniazid (INH) and aquapentacyanoruthenate(II) ([Ru(CN)5H2O]3−), have been investigated, under pseudo first-order conditions, as a function of concentrations of [INH] and [Ru(CN)5H2O]3−, ionic strength and temperature at pH = 4.0 ± 0.02 in 0.2 M NaClO4 spectrophotometrically at 502 nm ( λmax of intense yellow colour product [Ru(CN)5INH]3−) corresponding to metal-to-ligand charge-transfer transitions, in aqueous medium. The pseudo first-order condition was maintained by taking at least 10% excess of [INH] over [Ru(CN)5H2O]3−. The stoichiometry of the reaction product was found to be 1:1 which was further supported and characterized using elemental analysis, infrared, nuclear magnetic resonance and mass spectrometric techniques. Thermodynamic and kinetic parameters have also been computed, using the Eyring equation, and the values of ΔH≠, Ea, ΔG≠ and ΔS≠ were found to be 47.3 kJ mol−1, 49.8 kJ mol−1, −8.62 kJ mol−1 and 187.6 J K−1mol−1, respectively. The reaction was found to obey first-order kinetics with respect to [INH]. It exhibited a negative salt effect on the rate upon variation of ionic strength of the medium. A tentative mechanistic scheme was proposed on the basis of experimental findings.

Hypoxia-targeted drug delivery

Hypoxia is a state of low oxygen tension found in numerous solid tumours. It is typically associated with abnormal vasculature, which results in a reduced supply of oxygen and nutrients, as well as impaired delivery of drugs. The hypoxic nature of tumours often leads to the development of localized heterogeneous environments characterized by variable oxygen concentrations, relatively low pH, and increased levels of reactive oxygen species (ROS). The hypoxic heterogeneity promotes tumour invasiveness, metastasis, angiogenesis, and an increase in multidrug-resistant proteins. These factors decrease the therapeutic efficacy of anticancer drugs and can provide a barrier to advancing drug leads beyond the early stages of preclinical development. This review highlights various hypoxia-targeted and activated design strategies for the formulation of drugs or prodrugs and their mechanism of action for tumour diagnosis and treatment.

Mechanistic Aspects of Ligand Substitution on the Cis-Diaqua-Chloro-Tris(Dimethyl Sulfoxide)Ruthenium(II) Complex by Some Sulfur-Containing Bioactive Ligands in Aqueous Medium

The synthesis and interactions of the cis-diaqua-chloro-tris(dimethyl sulfoxide)ruthenium(II) complex with selected sulfur-containing ligands such as 2-thiouracil, glutathione and L-cysteine have been studied by UV-Vis spectrophotometry in aqueous medium at pH 4.5. From experimental data it is clear that all three reactions proceed via two steps: the first one being a rate-limiting ligand-dependent replacement of one water molecule, followed by a ligand-independent ring closure step with the expulsion of the second water molecule. The substituted products have been characterised by Job's method, FTIR spectroscopy and electrospray ionisation mass spectrometry. Activation parameters (Δ H≠ and Δ S≠) and thermodynamic parameters (Δ H0 and Δ S0, from the temperature dependence of the outer-sphere association equilibrium constant) are presented. Consistent with the experimental findings, an associative interchange mechanism is proposed.

Aerobic reactions of antitumor active dirhodium(II) tetraacetate Rh2(CH3COO)4 with glutathione

The aerobic reaction between glutathione (H3A) and dirhodium(II) tetraacetate, Rh2(AcO)4 (AcO- = CH3COO-), in aqueous solution (pH 7.4) breaks up the direct RhII-RhII bond and its carboxylate framework, as evidenced by UV-Vis spectroscopy. After purifying the reaction product using size exclusion chromatography, electrospray ionization mass spectrometry (ESI-MS) of the solution showed binuclear [Formula: see text] and [Formula: see text] ions. Evaporation yielded a solid compound, [Formula: see text], for which Rh K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy revealed ~ 2 Rh-O (2.08 ± 0.02 Å) and ~ 4 Rh-S (2.33 ± 0.02 Å) bond distances around each RhIII center, and the RhIII··RhIII distance 3.11 ± 0.02 Å, close to that in dirhodium(III) complexes with three bridging thiolates connecting [Formula: see text] units. The 13C CPMAS NMR spectrum of the RhIII-glutathione complex showed a change ∆δ C > 6 ppm in the chemical shift of the COO- signal, indicating some carboxylate coordination to the Rh(III) ions. This study shows that under aerobic conditions glutathione enables oxidation of Rh2(AcO)4 and thus reduces its antitumor efficiency. The reaction of Rh2(AcO)4 with glutathione was investigated by ESI-MS, UV-Vis, 13C NMR and X-ray absorption spectroscopy, revealing that glutathione breaks down the carboxylate framework enabling oxidization of the [Formula: see text] core to Rh(III) dimeric units, bridged by three thiolates.

Ruthenium complex exerts antineoplastic effects that are mediated by oxidative stress without inducing toxicity in Walker-256 tumor-bearing rats

The present study evaluated the in vivo antitumor effects and toxicity of a new Ru(II) compound, cis-(Ru[phen]₂[ImH]₂)²⁺ (also called RuphenImH [RuC]), against Walker-256 carcinosarcoma in rats. After subcutaneous inoculation of Walker-256 cells in the right pelvic limb, male Wistar rats received 5 or 10mgkg^-1 RuC orally or intraperitoneally (i.p.) every 3 days for 13 days. A positive control group (2mgkg^-1 cisplatin) and negative control group (vehicle) were also used. Tumor progression was checked daily. After treatment, tumor weight, plasma biochemistry, hematology, oxidative stress, histology, and tumor cell respiration were evaluated. RuC was effective against tumors when administered i.p. but not orally. The highest i.p. dose of RuC (10mgkg^-1) significantly reduced tumor volume and weight, induced oxidative stress in tumor tissue, reduced the respiration of tumor cells, and induced necrosis but did not induce apoptosis in the tumor. No clinical signs of toxicity or death were observed in tumor-bearing or healthy rats that were treated with RuC. These results suggest that RuC has antitumor activity through the modulation of oxidative stress and impairment of oxidative phosphorylation, thus promoting Walker-256 cell death without causing systemic toxicity. These effects make RuC a promising anticancer drug for clinical evaluation.

Mechanisms of reactions of Ru(iii)-based drug NAMI-A and its aquated products with DNA purine bases: a DFT study

The mechanism of reaction of NAMI-A with guanine has been investigated theoretically using density functional theory.

Luminescent ruthenium complexes for theranostic applications

The water-soluble and visible luminescent complexes cis-[Ru(L-L)2(L)2](2+) where L-L = 2,2-bipyridine and 1,10-phenanthroline and L= imidazole, 1-methylimidazole, and histamine have been synthesized and characterized by spectroscopic techniques. Spectroscopic (circular dichroism, saturation transfer difference NMR, and diffusion ordered spectroscopy NMR) and isothermal titration calorimetry studies indicate binding of cis-[Ru(phen)2(ImH)2](2+) and human serum albumin occurs via noncovalent interactions with K(b) = 9.8 × 10(4) mol(-1) L, ΔH = -11.5 ± 0.1 kcal mol(-1), and TΔS = -4.46 ± 0.3 kcal mol(-1). High uptake of the complex into HCT116 cells was detected by luminescent confocal microscopy. Cytotoxicity of cis-[Ru(phen)2(ImH)2](2+) against proliferation of HCT116p53(+/+) and HCT116p53(-/-) shows IC50 values of 0.1 and 0.7 μmol L(-1). Flow cytometry and western blot indicate RuphenImH mediates cell cycle arrest in the G1 phase in both cells and is more prominent in p53(+/+). The complex activates proapoptotic PARP in p53(-/-), but not in p53(+/+). A cytostatic mechanism based on quantification of the number of cells during the time period of incubation is suggested.

Interactions of the aquated forms of ruthenium(iii) anticancer drugs with protein: a detailed molecular docking and QM/MM investigation

The interaction of monoaqua and diaqua ruthenium complexes which are formed after intracellular aquation of their respective complexes with human serum albumin (HSA) has been computationally investigated by molecular docking and two layer QM/MM hybrid methods.

Oxidation of glutathione by hexachloroiridate(IV), dicyanobis(bipyridine)iron(III), and tetracyano(bipyridine)iron(III)

The aqueous oxidations of glutathione (GSH) by [IrCl(6)](2-), [Fe(bpy)(2)(CN)(2)](+), and [Fe(bpy)(CN)(4)](-) are described. All three reactions are highly susceptible to catalysis by traces of copper ions, but this catalysis can be fully suppressed with suitable chelating agents. The direct oxidation by [IrCl(6)](2-) yields [IrCl(6)](3-) and GSO(3)(-); some GSSG is also obtained in the presence of O(2). The two Fe(III) oxidants are reduced to their corresponding Fe(II) complexes with nearly quantitative formation of GSSG. The kinetics of these reactions have been studied at 25 °C and μ = 0.1 M between pH 1 and 11. All three reactions have rate laws that are first order in [M(ox)] and [GSH](t) and show a general increase in rate with increasing pH. Detailed studies of the pH dependence enable the rate law to be elaborated with terms for reaction of the individual protonation states of GSH. These pH-resolved rate constants are interpreted with a mechanism having rate-limiting outer-sphere electron-transfer from the various thiolate forms of GSH.

Kinetics and Mechanism of the Interaction of Glycyl-L-Leucine with [(H2O)(Tap)2Ruoru(Tap)2(H2O)]2+ Ion at Physiological Ph

The interaction of glycyl-L-leucine (L-I/H) with [(H2O) (tap)2RuORu(tap)2(H2O)]2+ (tap=2-(m-tolylazo) pyridine) has been studied spectrophotometrically in aqueous medium as a function of [(H2O) (tap)2RuORu(tap)2(H2O)2+], [glycyl-L-leucine], pH and temperature. The reaction was monitored at 600 nm where the spectral difference between the reactant and product is a maximum. At pH 7.4, the interaction with glycyl-L-leucine shows two parallel steps, i.e. it shows a non-linear dependence on the concentration of glycyl-L-leucine; both processes are ligand dependent. The rate constants for the processes are: kl 10−3 s 1 and K2∼10−5 s−1. The activation parameters calculated from Eyring plots are: Δ H#1 = 15.8∓0.6kJ mol−1, A Sf = −232 + 2J K 1 mol−1, AH2# =31.7∓3.5kJmol−1, AS* = −216∓ 10J K−1 mol−1. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. from the temperature dependence of the outer sphere association equilibrium constant, the thermodynamic parameters were also calculated, which gave a negative AG° value for both the steps at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex. The product of the reaction has been characterized from IR and ESI-mass spectroscopic analysis.

Kinetics and Mechanism of the Reaction of Dichlorotetraaquaruthenium(III) and Thiols

The formation of an intermediate ruthenium(iii) thiolate complex by the interaction of thiols, RSH (R = glutathione and l-cysteine) and dichlorotetraaquaruthenium(iii), [RuIIICl2(H2O)4]+, is reported in the temperature range 25–40°C. The kinetics and mechanism of formation of the intermediate complex were studied as a function of [RuIIICl2(H2O)4]+, [RSH], pH, ionic strength and temperature. Reduction of the intermediate complex takes place slowly and results in the corresponding disulfides RSSR and [RuIICl2(H2O)4]+. The results are interpreted in terms of a mechanism involving a rate-determining inner-sphere one-electron transfer from RSH to the oxidant used in the present investigation and a comparison of rate and equilibrium constants is presented with activation parameters.

Anticancer activity of metal complexes: involvement of redox processes

Cells require tight regulation of the intracellular redox balance and consequently of reactive oxygen species for proper redox signaling and maintenance of metal (e.g., of iron and copper) homeostasis. In several diseases, including cancer, this balance is disturbed. Therefore, anticancer drugs targeting the redox systems, for example, glutathione and thioredoxin, have entered focus of interest. Anticancer metal complexes (platinum, gold, arsenic, ruthenium, rhodium, copper, vanadium, cobalt, manganese, gadolinium, and molybdenum) have been shown to strongly interact with or even disturb cellular redox homeostasis. In this context, especially the hypothesis of "activation by reduction" as well as the "hard and soft acids and bases" theory with respect to coordination of metal ions to cellular ligands represent important concepts to understand the molecular modes of action of anticancer metal drugs. The aim of this review is to highlight specific interactions of metal-based anticancer drugs with the cellular redox homeostasis and to explain this behavior by considering chemical properties of the respective anticancer metal complexes currently either in (pre)clinical development or in daily clinical routine in oncology.

The ruthenium complex cis-(dichloro)tetraammineruthenium(III) chloride presents selective cytotoxicity against murine B cell lymphoma (A-20), murine ascitic sarcoma 180 (S-180), human breast adenocarcinoma (SK-BR-3), and human T cell leukemia (Jurkat) tumor cell lines

The aim of present study was to verify the in vitro antitumor activity of a ruthenium complex, cis-(dichloro)tetraammineruthenium(III) chloride (cis-[RuCl(2)(NH(3))(4)]Cl) toward different tumor cell lines. The antitumor studies showed that ruthenium(III) complex presents a relevant cytotoxic activity against murine B cell lymphoma (A-20), murine ascitic sarcoma 180 (S-180), human breast adenocarcinoma (SK-BR-3), and human T cell leukemia (Jurkat) cell lines and a very low cytotoxicity toward human peripheral blood mononuclear cells. The ruthenium(III) complex decreased the fraction of tumor cells in G0/G1 and/or G2-M phases, indicating that this compound may act on resting/early entering G0/G1 cells and/or precycling G2-M cells. The cytotoxic activity of a high concentration (2 mg mL(-1)) of cis-[RuCl(2)(NH(3))(4)]Cl toward Jurkat cells correlated with an increased number of annexin V-positive cells and also the presence of DNA fragmentation, suggesting that this compound induces apoptosis in tumor cells. The development of new antineoplastic medications demands adequate knowledge in order to avoid inefficient or toxic treatments. Thus, a mechanistic understanding of how metal complexes achieve their activities is crucial to their clinical success and to the rational design of new compounds with improved potency.

Is vanadate reduced by thiols under biological conditions? Changing the redox potential of V(V)/V(IV) by complexation in aqueous solution

Although dogma states that vanadate is readily reduced by glutathione, cysteine, and other thiols, there are several examples documenting that vanadium(V)-sulfur complexes can form and be observed. This conundrum has impacted life scientists for more than two decades. Investigation of this problem requires an understanding of both the complexes that form from vanadium(IV) and (V) and a representative thiol in aqueous solution. The reactions of vanadate and hydrated vanadyl cation with 2-mercaptoethanol have been investigated using multinuclear NMR, electron paramagnetic resonance (EPR), and UV-vis spectroscopy. Vanadate forms a stable complex of 2:2 stoichiometry with 2-mercaptoethanol at neutral and alkaline pH. In contrast, vanadate can oxidize 2-mercaptoethanol; this process is favored at low pH and high solute concentrations. The complex that forms between aqueous vanadium(IV) and 2-mercaptoethanol has a 1:2 stoichiometry and can be observed at high pH and high 2-mercaptoethanol concentration. The solution structures have been deduced based on coordination induced chemical shifts and speciation diagrams prepared. This work demonstrates that both vanadium(IV) and (V)-thiol complexes form and that redox chemistry also takes place. Whether reduction of vanadate takes place is governed by a combination of parameters: pH, solute- and vanadate-concentrations and the presence of other complexing ligands. On the basis of these results it is now possible to understand the distribution of vanadium in oxidation states (IV) and (V) in the presence of glutathione, cysteine, and other thiols and begin to evaluate the forms of the vanadium compounds that exert a particular biological effect including the insulin-enhancing agents, antiamoebic agents, and interactions with vanadium binding proteins.

Synthesis, characterization, and reaction pathways for the formation of a GMP adduct of a cytotoxic thiocyanato ruthenium arene complex

The organoruthenium complex [(eta(6)-hmb)Ru(en)(Cl)][PF6] (hmb is hexamethylbenzene, en is ethylenediamine) undergoes facile aquation and then reacts with KSCN in unbuffered solution to give the S-coordinated thiocyanato product [(eta(6)-hmb)Ru(en)(S-SCN)]+ which slowly converts to the thermodynamically favored N-bound complex [(eta(6)-hmb)Ru(en)(N-NCS)]+ (1+). Complex 1 was synthesized and characterized by X-ray crystallography and mass spectrometry. Despite its lack of hydrolysis over 24 h, complex 1 exhibits moderate cytotoxicity (IC(50) 24 microM) towards the human ovarian cancer cell line A2780, comparable with that of the chlorido analogue which is thought to be activated (towards potential target DNA) via a rapid aquation (Wang et. al. in Proc Natl Acad Sci USA 102:18269-18274, 2005). Detailed kinetic studies suggest that complex 1 binds to guanosine 5'-monophosphate (GMP) through direct N7 substitution of the N-bound SCN ligand. In the presence of a high concentration of chloride (104 mM), however, complex 1 may bind partly to GMP via Cl substitution.

An electrochemical sensing strategy for ultrasensitive detection of glutathione by using two gold electrodes and two complementary oligonucleotides

We herein report an ultrasensitive electrochemical sensing strategy for picomole determination of glutathione by using two gold electrodes and two complementary thiolated oligonucleotides. When one gold electrode whose surface has been immobilized with one of the two oligonucleotides is immersed in a glutathione solution for detection, due to the ligand release effect, the oligonucleotides will be replaced by glutathione. Consequently, the released oligonucleotide molecules will exist in the solution, and therefore, if the other gold electrode is immersed in this solution, the released oligonucleotide molecules will be immobilized onto this electrode surface. Meanwhile, since the complementary oligonucleotide molecules have been previously modified on the surface of gold nanoparticles, the nanoparticles can be thus immobilized onto this electrode surface through hybridization, and large numbers of [Ru(NH(3))(6)](3+) molecules as electrochemical species can be localized onto the electrode surface via the electrostatic interaction between the electrochemical species and oligonucleotide molecules. And, since the nanoparticles can amplify the detection signal, ultrasensitive detection of glutathione can be achieved in the range of 1 x 10(-12) to 1 x 10(-10)M, with a detection limit as low as 4 x 10(-13)M. Moreover, this method has shown fairly good utility in the detection of glutathione in fetal calf serum.

KP1019, a new redox-active anticancer agent--preclinical development and results of a clinical phase I study in tumor patients

The promising drug candidate indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019) is the second Ru-based anticancer agent to enter clinical trials. In this review, which is an update of a paper from 2006 (Hartinger et al., J. Inorg. Biochem. 2006, 100, 891-904), the experimental evidence for the proposed mode of action of this coordination compound is discussed, including transport into the cell via the transferrin cycle and activation by reduction. The results of the early clinical development of KP1019 are summarized in which five out of six evaluated patients experienced disease stabilization with no severe side effects.

Binding of Antitumor Ruthenium Complexes to DNA and Proteins: A Theoretical Approach

The thermodynamics of the binding of the antitumor ammine, amine, and immine complexes of ruthenium(II) and ruthenium(III) to DNA and peptides was studied computationally using model molecules. We performed density functional calculations on several monofunctional ruthenium complexes of the formula [Ru(NH3)5B]z+, where B is an adenine, guanine, or cytosine nucleobase or an 4-methylimidazole, a dimethylthioether, or a dimethylphosphate anion and z = 2 and 3. The pentammineruthenium fragment has been intensively studied and also constitutes a good model for a wide class of antitumor ammine, amine, and imine complexes of Ru(II) and Ru(III), while the considered bases/ligands have been chosen as models for the main binding sites of DNA, nucleobases, and phosphate backbone and proteins, histidyl, and sulfur-containing residue such as methionine or cysteine. Bond dissociation enthalpies and free energies have been calculated for all the considered metal binding sites both in the gas phase and in solution and allow building a binding affinity order for the considered nucleic acid or protein binding sites. The binding of guanine to some bifunctional complexes, [Ru(NH3)(4)Cl2], [cis-RuCl(2)(bpy)2], and [cis-RuCl(2)(azpy)2], has also been considered to evaluate the effect of a second labile chloro or aquo ligand and more realistic polypyridyl and arylazopyridine ligands.

The hydrolysis process of the anticancer complex [ImH][trans-RuCl4(Im)2]: a theoretical study

A hydrolysis process of the anticancer drug [ImH][trans-RuCl4(Im)2] (ICR, Im=imidazole) has been investigated using density functional theory (DFT), and the aqueous solution effect has been considered and calculated by the conductor-like polarizable calculation model (CPCM). The stationary points on the potential energy surfaces for the first and second hydrolysis steps (including two different paths) were fully optimized and characterized. The results show that the computed values of free energy barriers DeltaG degrees (aq) and rate constants (k) in aqueous solution, in particular for the first hydrolysis step, are in excellent agreement with the experimental results. The analysis of electronic characteristics of species in the hydrolysis process suggests that the nucleophilic attack abilities (A) of hydrolysis products by biomolecular targets is in the sequence of A()<A()<A() (, and express the hydrolysis products of the first hydrolysis step, and of the second hydrolysis step through path 1 and path 2, respectively). On the basis of our present limited work, the following can reasonably be suggested: path 1 in the second hydrolysis step has thermodynamic preference over path 2, and thus the cis-diaqua species may dominate. The theoretical results provide the structural properties as well as the detailed energy profiles for the hydrolysis process of ICR, so such results may contribute to understanding the reaction mechanism of this drug with the biomolecular target.

Competition between glutathione and guanine for a ruthenium(II) arene anticancer complex: detection of a sulfenato intermediate

The organometallic anticancer complex [(eta6-bip)Ru(en)Cl]+ (1; bip = biphenyl, en = ethylenediamine) selectively binds to guanine (N7) bases of DNA (Novakova, O.; Chen, H.; Vrana, O.; Rodger, A.; Sadler, P. J.; Brabec, V. Biochemistry 2003, 42, 11544-11554). In this work, competition between the tripeptide glutathione (gamma-L-Glu-L-Cys-Gly; GSH) and guanine (as guanosine 3',5'-cyclic monophosphate, cGMP) for complex 1 was investigated using HPLC, LC-MS and 1H,15N NMR spectroscopy. In unbuffered solution (pH ca. 3), the reaction of 1 with GSH gave rise to three intermediates: an S-bound thiolato adduct [(eta6-bip)Ru(en)(GS-S)] (4) and two carboxylate-bound glutathione products [(eta6-bip)Ru(en)(GSH-O)]+ (5, 6) during the early stages (<6 h), followed by en displacement and formation of a tri-GS-bridged dinuclear Ru(II) complex [((eta6-bip)Ru)2(GS-mu-S)3]2- (7). Under physiologically relevant conditions (micromolar Ru concentrations, pH 7, 22 mM NaCl, 310 K), the thiolato complex 4 was unexpectedly readily oxidized by dioxygen to the sulfenato complex [(eta6-bip)Ru(en)(GS(O)-S)] (8) instead of forming the dinuclear complex 7. Under these conditions, competitive reaction of complex 1 with GSH and cGMP gave rise to the cGMP adduct [(eta6-bip)Ru(en)(cGMP-N7)]+ (10) as the major product, accounting for ca. 62% of total Ru after 72 h, even in the presence of a 250-fold molar excess of GSH. The oxidation of coordinated glutathione in the thiolato complex 4 to the sulfenate in 8 appears to provide a facile route for displacement of S-bound glutathione by G N7. Redox reactions of cysteinyl adducts of these Ru(II) arene anticancer complexes could therefore play a significant role in their biological activity.

From bench to bedside--preclinical and early clinical development of the anticancer agent indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019 or FFC14A)

Indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019 or FFC14A) is just the second ruthenium-based anticancer agent after NAMI-A which was developed to the stage of clinical trials. Important steps in the mode of action of KP1019 are thought to be the binding to the serum protein transferrin and the transport into the cell via the transferrin pathway. Additionally, the selective activation by reduction in the tumor might contribute to the low side effects observed in in vivo studies. Apoptosis is induced at non-toxic levels via the mitochondrial pathway. These features distinguish it from the established platinum anticancer drugs and suggest that different types of cancer might be treatable with this drug. Indeed, promising activity against certain types of tumors, which are not successfully treatable with cisplatin, and only a very low incidence of acquired resistance has been observed in in vitro and in vivo studies. Recently, a clinical phase I trial was finished in which none of the treated patients experienced serious side effects, while disease stabilization in five of six evaluable patients was achieved. In this review, the preclinical and early clinical development of KP1019 - from bench to bedside - is recapitulated.

Redox behavior of tumor-inhibiting ruthenium(III) complexes and effects of physiological reductants on their binding to GMP

Biotransformation of ruthenium(III) anticancer complexes as hypothesized in the activation-by-reduction theory is the central topic of the present paper. The redox behavior of tetrachlorobis(azole)ruthenate(III)-type complexes was studied by NMR spectroscopy and square wave voltammetry. The influence of reducing agents on the binding behavior toward the DNA-modeling nucleotide GMP was determined by capillary electrophoresis, accompanied by identification of arising peaks by online coupling to electrospray ionization mass spectrometry. The determination of redox potentials revealed that the biologically relevant reductants ascorbic acid and glutathione are capable of reducing the studied Ru(III) complexes under physiological conditions. Characteristic differences in reduction kinetics dependent on the pH value can be explained by higher reduction strength of ascorbic acid and glutathione at higher pH compared to the pH-independent redox response of ruthenium(III) complexes. Binding behavior of (H2ind)[trans-RuCl4(Hind)2] (Hind = 1H-indazole) toward GMP was found to be increased upon addition of two equivalents of glutathione but not of ascorbic acid. In contrast, only a minor influence on the GMP-binding under reductive conditions was found for (H2im)[trans-RuCl4(Him)2] (KP418, Him = 1H-imidazole).

A Mass Spectrometric and Molecular Modelling Study of Cisplatin Binding to Transferrin

A combination of mass spectrometry, UV/Vis spectroscopy and molecular modelling techniques have been used to characterise the interaction of cisplatin with human serum transferrin (Tf). Mass spectrometry indicates that cisplatin binds to the hydroxy functional group of threonine 457, which is located in the iron(III)-binding site on the C-terminal lobe of the protein. UV/Vis spectroscopy confirms the stoichiometry of binding and shows that cisplatin and iron(III) binding are competitive. The binding of cisplatin has been modelled by using molecular dynamic simulations and the results suggest that cisplatin can occupy part of both the iron(III)- and carbonate-binding sites in the C-terminal lobe of the protein. Combined, the studies suggest that cisplatin binding sterically restricts iron(III) binding to the C-terminal lobe binding site, whereas the N-terminal lobe binding site appears to be unaffected by the cisplatin interaction, possibly allowing the iron(III)-induced conformational change necessary for binding to a Tf receptor.

Binding sites of [Ru(bpy)2(H2O)2](BF4)2 with sulfur- and histidine-containing peptides studied by electrospray ionization mass spectrometry and tandem mass spectrometry

The composition and binding sites of cis-[Ru(II)(bpy)2]2+-bound sulfur-containing peptides of Met-Arg-Phe-Ala, glutathione and oxidized glutathione, and also histidine-containing peptide of oxidized insulin B chain, were investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The composition of Ru(II)-containing peptides was precisely determined by ESI-MS, zoom scan and simulation of isotope distribution patterns. MS/MS analysis shows that, in sulfur-containing peptides, the Ru(II) complex prefers to anchor to a carboxyl group, although some other potential binding sites of thiol, thioether and N-terminal amino groups present in these peptides, and in oxidized insulin B chain, Ru(II) first anchors to His10, then either to the hydroxyl group of Thr27 or to the carboxyl group of Ala30. Its secondary structure and microenvironment surrounding the potential binding sites may affect the binding ability of cis-[Ru(II)(bpy)2]2+ to oxidized insulin B chain.