Discovery of a strongly apoptotic ruthenium complex through combinatorial coordination chemistry

A Semi-Automated, High-Throughput Approach for the Synthesis and Identification of Highly Photo-Cytotoxic Iridium Complexes

The discovery of new compounds with pharmacological properties is usually a lengthy, laborious and expensive process. Thus, there is increasing interest in developing workflows that allow for the rapid synthesis and evaluation of libraries of compounds with the aim of identifying leads for further drug development. Herein, we apply combinatorial synthesis to build a library of 90 iridium(III) complexes (81 of which are new) over two synthesise-and-test cycles, with the aim of identifying potential agents for photodynamic therapy. We demonstrate the power of this approach by identifying highly active complexes that are well-tolerated in the dark but display very low nM phototoxicity against cancer cells. To build a detailed structure-activity relationship for this class of compounds we have used density functional theory (DFT) calculations to determine some key electronic parameters and study correlations with the experimental data. Finally, we present an optimised semi-automated synthesise-and-test protocol to obtain multiplex data within 72 hours.

Exploration of the Pharmacophore for Cytoskeletal Targeting Ruthenium Polypyridyl Complexes

Ruthenium(II) trisdiimine complexes of the formula, [Ru(dip)n (L-L)3-n ]2+ , where n=0-3; dip=4,7-diphenyl-1,10-phenanthroline; L-L=2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) were prepared and tested for cytotoxicity in two cell lines (H358, MCF7). Cellular uptake and subcellular localization were determined by harvesting treated cells and determining the ruthenium concentration in whole or fractionated cells (cytosolic, nuclear, mitochondrial/ ER/Golgi, and cytoskeletal proteins) by Ru ICP-MS. The logP values for the chloride salts of these complexes were measured and the data were analyzed to determine the role of lipophilicity versus structure in the various biological assays. Cellular uptake increased with lipophilicity but shows the biggest jump when the complex contains two or more dip ligands. Significantly, preferential cytoskeletal localization is also correlated with increased cytotoxicity. All of the RPCs promote tubulin polymerization in vitro, but [Ru(dip)2 phen]2+ and [Ru(dip)3 ]2+ show the strongest activity. Analysis of the pellet formed by centrifugation of MTs formed in the presence of [Ru(dip)2 phen]2+ establish a binding stoichiometry of one RPC per tubulin heterodimer. Complexes of the general formula [Ru(dip)2 (L-L)]2+ possess the necessary characteristics to target the cytoskeleton in live cells and increase cytotoxicity, however the nature of the L-L ligand does influence the extent of the effect.

Enantiomeric Complexes Based on Ruthenium(III) and 2,2'-Biimidazole: X-ray Structure and Magnetic Properties

We have prepared and characterized two Ru(III) compounds based on the 2,2'-biimidazole (H2biim) ligand, namely, a single complex of formula cis-[RuCl2(H2biim)2]Cl·4H2O (1) and a racemic mixture of formula {cis-[RuCl2(H2biim)2]Cl}2·4H2O (2), which contains 50% of Ru(III) complex 1. Both compounds crystallize in the monoclinic system with space groups C2 and P21 for 1 and 2, respectively. These complexes exhibit the metal ion bonded to four nitrogen atoms from two H2biim molecules and two chloride ions, which balance part of the positive charges in a distorted octahedral geometry. Significant differences are observed in their crystal packing, which leads to the observation of differences in their respective magnetic behaviors. Despite having imidazole rings in both compounds, π-π stacking interactions occur only in the crystal structure of 2, and the shortest intermolecular Ru···Ru separation in 2 is consequently shorter than that in 1. Variable-temperature dc magnetic susceptibility measurements performed on polycrystalline samples of 1 and 2 reveal different magnetic behaviors at low temperatures: while 1 behaves pretty much as a magnetically isolated mononuclear Ru(III) complex with S = 1/2, 2 exhibits the behavior of an antiferromagnetically coupled system with S = 0 and a maximum in the magnetic susceptibility curve at approximately 3.0 K.

Dihydroxyquingdainone Induces Apoptosis in Leukaemia and Lymphoma Cells via the Mitochondrial Pathway in a Bcl-2- and Caspase-3-Dependent Manner and Overcomes Resistance to Cytostatic Drugs In Vitro

Isatis tinctoria and its indigo dyes have already provided highly active anti-leukaemic lead compounds, with the focus mainly being on indirubin, whereas indigo itself is inactive. There are many more indigoids to find in this plant extract, for example, quingdainone, an indigoid derived from tryptanthrin. We present here a new synthesis of hitherto neglected substituted quingdainones, which is very necessary due to their poor solubility behaviour, and a structure-dependent anti-leukaemic activity study of a number of compounds. Substituted α-phenylaminoacrylic acid was synthesised by hydrogen sulfide extrusion from an analogue mercaptoacetic acid, available from the condensation of rhodanin and a substituted tryptanthrin. It is shown that just improving water solubility does not increase anti-leukaemic activity, since a quingdainone carboxylic acid is inactive compared to dihydroxyquingdainone. The most effective compound, dihydroxyquingdainone with an AC₅₀ of 7.5 µmole, is further characterised, revealing its ability to overcome multidrug resistance in leukaemia cells (Nalm-6/BeKa) with p-glycoprotein expression.

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.

Novel Papaverine Metal Complexes with Potential Anticancer Activities

Cancer is one of the leading causes of death worldwide. Although several potential therapeutic agents have been developed to efficiently treat cancer, some side effects can occur simultaneously. Papaverine, a non-narcotic opium alkaloid, is a potential anticancer drug that showed selective antitumor activity in various tumor cells. Recent studies have demonstrated that metal complexes improve the biological activity of the parent bioactive ligands. Based on those facts, herein we describe the synthesis of novel papaverine–vanadium(III), ruthenium(III) and gold(III) metal complexes aiming at enhancing the biological activity of papaverine drug. The structures of the synthesized complexes were characterized by various spectroscopic methods (IR, UV–Vis, NMR, TGA, XRD, SEM). The anticancer activity of synthesized metal complexes was evaluated in vitro against two types of cancer cell lines: human breast cancer MCF-7 cells and hepatocellular carcinoma HepG-2 cells. The results revealed that papaverine-Au(III) complex, among the synthesized complexes, possess potential antimicrobial and anticancer activities. Interestingly, the anticancer activity of papaverine–Au(III) complex against the examined cancer cell lines was higher than that of the papaverine alone, which indicates that Au-metal complexation improved the anticancer activity of the parent drug. Additionally, the Au complex showed anticancer activity against the breast cancer MCF-7 cells better than that of cisplatin. The biocompatibility experiments showed that Au complex is less toxic than the papaverine drug alone with IC₅₀ ≈ 111µg/mL. These results indicate that papaverine–Au(III) complex is a promising anticancer complex-drug which would make it a suitable candidate for further in vivo investigations.

Synthesis, Characterisation and In Vitro Anticancer Activity of Catalytically Active Indole-Based Half-Sandwich Complexes

The synthesis, characterisation and evaluation of the in vitro cytotoxicity of four indole-based half-sandwich metal complexes towards two ovarian cancer cell lines (A2780 and A2780cisR) and one normal prostate cell line (PNT2) are presented herein. Although capable of inducing catalytic oxidation of NADH and able to reduce NAD+ with high turnover frequencies, in cells and in the presence of sodium formate, these complexes also strongly interact with biomolecules such as glutathione. This work highlights that efficient out-of-cells catalytic activity might lead to higher reactivity towards biomolecules, thus inhibiting the in-cells catalytic processes.

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.

Mitochondria-Targeting Anticancer Metal Complexes

Background:

Since the serendipitous discovery of the antitumor activity of cisplatin there has been a continuous surge in studies aimed at the development of new cytotoxic metal complexes. While the majority of these complexes have been designed to interact with nuclear DNA, other targets for anticancer metallodrugs attract increasing interest. In cancer cells the mitochondrial metabolism is deregulated. Impaired apoptosis, insensitivity to antigrowth signals and unlimited proliferation have been linked to mitochondrial dysfunction. It is therefore not surprising that mitochondria have emerged as a major target for cancer therapy. Mitochondria-targeting agents are able to bypass resistance mechanisms and to (re-) activate cell-death programs.

Methods:

Web-based literature searching tools such as SciFinder were used to search for reports on cytotoxic metal complexes that are taken up by the mitochondria and interact with mitochondrial DNA or mitochondrial proteins, disrupt the mitochondrial membrane potential, facilitate mitochondrial membrane permeabilization or activate mitochondria-dependent celldeath signaling by unbalancing the cellular redox state. Included in the search were publications investigating strategies to selectively accumulate metallodrugs in the mitochondria.

Results:

This review includes 241 references on antimitochondrial metal complexes, the use of mitochondria-targeting carrier ligands and the formation of lipophilic cationic complexes.

Conclusion:

Recent developments in the design, cytotoxic potency, and mechanistic understanding of antimitochondrial metal complexes, in particular of cyclometalated Au, Ru, Ir and Pt complexes, Ru polypyridine complexes and Au-N-heterocyclic carbene and phosphine complexes are summarized and discussed.

Combinatorial Synthesis to Identify a Potent, Necrosis-Inducing Rhenium Anticancer Agent

Combinatorial synthesis can be applied for developing a library of compounds that can be rapidly screened for biological activity. Here, we report the application of microwave-assisted combinatorial chemistry for the synthesis of 80 rhenium(I) tricarbonyl complexes bearing diimine ligands. This library was evaluated for anticancer activity in three different cancer cell lines, enabling the identification of three lead compounds with cancer cell growth-inhibitory activities of less than 10 μM. These three lead structures, Re-9B, Re-9C, and Re-9D, were synthesized independently and fully characterized by NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray crystallography. The most potent of these three complexes, Re-9D, was further explored to understand its mechanism of action. Complex Re-9D is equally effective in both wild-type and cisplatin-resistant A2780 ovarian cancer cells, indicating that it circumvents cisplatin resistance. This compound was also shown to possess promising activity against ovarian cancer tumor spheroids. Additionally, flow cytometry showed that Re-9D does not induce cell cycle arrest or flipping of phosphatidylserine to the outer cell membrane. Analysis of the morphological changes of cancer cells treated with Re-9D revealed that this compound gives rise to rapid plasma membrane rupture. Collectively, these data suggest that Re-9D induces necrosis in cancer cells. To assess the in vivo biodistribution and stability of this compound, a radioactive ^99mTc analogue of Re-9D, ^99mTc-9D(H₂O), was synthesized and administered to naı̈ve BALB/c mice. Results of these studies indicate that ^99mTc-9D(H₂O) exhibits high metabolic stability and a distinct biodistribution profile. This research demonstrates that combinatorial synthesis is an effective approach for the development of new rhenium anticancer agents with advantageous biological properties.

Ruthenium(II)-Polypyridyl Compounds with π-Extended Nitrogen Donor Ligands Induce Apoptosis in Human Lung Adenocarcinoma (A549) Cells by Triggering Caspase-3/7 Pathway

Ru(II)-polypyridyl complexes exhibit antitumor properties that can be systematically tailored by means of adjusting the ligand environment. In this work, the effect of incorporating π-extended moieties into anionic N^∧O^- based chelating ligands on the cytotoxic properties of Ru compounds is explored. Four new Ru(II) complexes, [Ru(bpy)₂(dphol)][PF₆] (1; bpy = 2,2'-bipyridine, dphol = dibenzo[ a, c]phenazin-10-olate), [Ru(phen)₂(dphol)][PF₆] (2; phen = 1,10-phenanthroline), [Ru(bpy)₂(hbtz)][PF₆] (3; hbtz = 2-(benzo[ d]thiazol-2-yl)phenolate), and [Ru(phen)₂(hbtz)][PF₆] (4) were synthesized and thoroughly characterized. In vitro cytotoxicity was investigated in human lung adenocarcinoma (A549) cells, which revealed that 4 is the most cytotoxic compound (IC₅₀ = 0.8 μM) in the series including a control compound [Ru(bpy)₂(quo)][PF₆] (5; quo = 8-hydroxyquinolinate) and is nearly 8-fold more cytotoxic than cisplatin. An investigation of the mechanism of cell death led to the finding that compounds 1-4 disrupt the mitochondrial transmembrane potential (ΔΨ_m) in a concentration-dependent fashion, which is an event associated with the intrinsic pathway of apoptosis. Moreover, compound 4 triggers the activity of caspase-3/7, which eventually induces the apoptotic cellular death of A549 cells. Thus, increasing the overall lipophilicity of the Ru compounds by introducing π-extended moieties in the anionic N^∧O^- ligand is a successful strategy for realizing a new family of pro-apoptotic compounds with a [Ru^IIN₅O]⁺ coordination environment.

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.

Four monomeric copper(ii) complexes of non-steroidal anti-inflammatory drug Ibuprofen and N-donor ligands: syntheses, characterization, crystal structures and cytotoxicity studies

The cytotoxic effects of four new Ibuprofen–Cu(ii) complexes were tested finding significant cytotoxicity on human melanoma cell line HT-144.

Monomeric and dimeric coordinatively saturated and substitutionally inert Ru(ii) polypyridyl complexes as anticancer drug candidates

Monomeric and dimeric coordinatively saturated and substitutionally inert Ru(ii) polypyridyl complexes with anticancer properties are reviewed.

Study of apoptosis-related interactions in colorectal cancer

Abnormalities in apoptotic functions contribute to the pathogenesis of colorectal cancer. In this study, molecular interactions behind the apoptotic regulation have been explored. For this purpose, enrichment analysis was performed considering microRNAs (miRNAs) that putatively target TP53 and altered during colon cancer. This revealed gene associated with both TP53 and miRNAs. Further analysis showed that a significant molecular interaction between the shortlisted candidates (TP53, miR-143, KRAS, BCL2, and PLK1) exists. Mutation study was conducted to confirm the clinical relevance of candidates. It showed that the mutation extent does not significantly alter survival in patients thus making these candidates suitable as drug targets. Overall, we showed the importance of interactions between TP53, miR-143, KRAS, BCL2, and PLK1 with respect to colorectal cancer using bioinformatics approach.

Solid-phase synthesis as a platform for the discovery of new ruthenium complexes for efficient release of photocaged ligands with visible light

Ruthenium-based photocaging groups have important applications as biological tools and show great potential as therapeutics. A method was developed to rapidly synthesize, screen, and identify ruthenium-based caging groups that release nitriles upon irradiation with visible light. A diverse library of tetra- and pentadentate ligands was synthesized on polystyrene resin. Ruthenium complexes of the general formula [Ru(L)(MeCN)n](m+) (n = 1-3, m = 1-2) were generated from these ligands on solid phase and then cleaved from resin for photochemical analysis. Data indicate a wide range of spectral tuning and reactivity with visible light. Three complexes that showed strong absorbance in the visible range were synthesized by solution phase for comparison. Photochemical behavior of solution- and solid-phase complexes was in good agreement, confirming that the library approach is useful in identifying candidates with desired photoreactivity in short order, avoiding time-consuming chromatography and compound purification.

Discovery and investigation of anticancer ruthenium-arene Schiff-base complexes via water-promoted combinatorial three-component assembly

The structural diversity of metal scaffolds makes them a viable alternative to traditional organic scaffolds for drug design. Combinatorial chemistry and multicomponent reactions, coupled with high-throughput screening, are useful techniques in drug discovery, but they are rarely used in metal-based drug design. We report the optimization and validation of a new combinatorial, metal-based, three-component assembly reaction for the synthesis of a library of 442 Ru-arene Schiff-base (RAS) complexes. These RAS complexes were synthesized in a one-pot, on-a-plate format using commercially available starting materials under aqueous conditions. The library was screened for their anticancer activity, and several cytotoxic lead compounds were identified. In particular, [(η6-1,3,5-triisopropylbenzene)RuCl(4-methoxy-N-(2-quinolinylmethylene)aniline)]Cl (4) displayed low micromolar IC50 values in ovarian cancers (A2780, A2780cisR), breast cancer (MCF7), and colorectal cancer (HCT116, SW480). The absence of p53 activation or changes in IC50 value between p53+/+ and p53-/- cells suggests that 4 and possibly the other lead compounds may act independently of the p53 tumor suppressor gene frequently mutated in cancer.

Ruthenium(II) polypyridyl complexes: cellular uptake, cell image and apoptosis of HeLa cancer cells induced by double targets

Studies have shown that ruthenium complexes have relatively strong anticancer activity, cell uptake of drugs have a crucial impact on the pharmacological activity, using autofluorescence of ruthenium complexes could effectively track cancer cells and drug distribution, transport accurately in real time. In this work, we present the synthesis and detailed characterization of two novel Ru(II) complexes with hydrophobic ancillary ligands, namely [Ru(bpy)2(5-idip)](2+) (RBD) and [Ru(phen)2(5-idip)](2+) (RPD) (5-idip = 2-indole-[4,5-f][1,10]phenanthroline). We have shown that RPD can enter the HeLa cells efficiently through non-endocytotic, but energy-dependent mechanism and first accumulated in lysosomes, and then escape from the lysosomes and localize within the nuclei, efficiently lead to the inhibition of DNA transcription and translation and induced cell apoptosis. Further studies on the mechanism of apoptosis in HeLa cells demonstrate that RPD is able to induce mitochondria-mediated apoptosis in HeLa cells through activation of initiator caspase-9 and down-stream effector caspase-3 and -7 and cleavage of PARP. We have also demonstrated that RPD bind to telomeric G-quadruplex DNA effectively and selectively, together with increased p21 and p16 expression. Our findings suggest that RPD induces HeLa cell apoptosis through mitochondria-mediated pathway and inhibition of telomerase activity. RPD may be a candidate for further evaluation as a chemotherapeutic agent for human cancers.

Mitochondria are the primary target in the induction of apoptosis by chiral ruthenium(II) polypyridyl complexes in cancer cells

A series of novel chiral ruthenium(II) polypyridyl complexes (Δ-Ru1, Λ-Ru1, Δ-Ru2, Λ-Ru2, Δ-Ru3, Λ-Ru3) were synthesized and evaluated to determine their antiproliferative activities. Colocalization, inductively coupled plasma mass spectrometry, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay studies showed that these ruthenium(II) complexes accumulated preferentially in the mitochondria and exhibited cytotoxicity against various cancer cells in vitro. The complex Δ-Ru1 is of particular interest because it was found to have half-maximal inhibitory concentrations comparable to those of cisplatin and better activity than cisplatin against a cisplatin-resistant cell line, A549-CP/R. Δ-Ru1 induced alterations in the mitochondrial membrane potential and triggered intrinsic mitochondria-mediated apoptosis in HeLa cells, which involved the regulation of Bcl-2 family members and the activation of caspases. Taken together, these data suggest that Δ-Ru1 may be a novel mitochondria-targeting anticancer agent.

Molecular and cellular characterization of the biological effects of ruthenium(II) complexes incorporating 2-pyridyl-2-pyrimidine-4-carboxylic acid

A great majority of the Ru complexes currently studied in anticancer research exert their antiproliferative activity, at least partially, through ligand exchange. In recent years, however, coordinatively saturated and substitutionally inert polypyridyl Ru(II) compounds have emerged as potential anticancer drug candidates. In this work, we present the synthesis and detailed characterization of two novel inert Ru(II) complexes, namely, [Ru(bipy)(2)(Cpp-NH-Hex-COOH)](2+) (2) and [Ru(dppz)(2)(CppH)](2+) (3) (bipy = 2,2'-bipyridine; CppH = 2-(2'-pyridyl)pyrimidine-4-carboxylic acid; Cpp-NH-Hex-COOH = 6-(2-(pyridin-2-yl)pyrimidine-4-carboxamido)hexanoic acid; dppz = dipyrido[3,2-a:2',3'-c]phenazine). 3 is of particular interest as it was found to have IC(50) values comparable to cisplatin, a benchmark standard in the field, on three cancer cell lines and a better activity on one cisplatin-resistant cell line than cisplatin itself. The mechanism of action of 3 was then investigated in detail and it could be demonstrated that, although 3 binds to calf-thymus DNA by intercalation, the biological effects that it induces did not involve a nuclear DNA related mode of action. On the contrary, confocal microscopy colocalization studies in HeLa cells showed that 3 specifically targeted mitochondria. This was further correlated by ruthenium quantification using High-resolution atomic absorption spectrometry. Furthermore, as determined by two independent assays, 3 induced apoptosis at a relatively late stage of treatment. The generation of reactive oxygen species could be excluded as the cause of the observed cytotoxicity. It was demonstrated that the mitochondrial membrane potential in HeLa was impaired by 3 as early as 2 h after its introduction and even more with increasing time.

Bioactive cyclometalated phthalimides: design, synthesis and kinase inhibition

The regioselective cyclometalation of 4-(pyridin-2-yl)phthalimide was exploited for the economical design of organometallic protein kinase inhibitors. 4-(Pyridin-2-yl)phthalimide can be prepared from inexpensive 4-bromophthalimide in just three steps including one Pd-catalyzed Stille cross-coupling. The versatility of this new ligand was demonstrated with the synthesis of ruthenium(II) half-sandwich as well as octahedral ruthenium(II) and iridium(III) complexes. The regioselectivity of the C-H activation in the course of the cyclometalation can be influenced by the reaction conditions and the steric demand of the introduced metal complex fragment. The biological activity of this new class of metalated phthalimides was evaluated by profiling two representative members against a large panel of human protein kinases. A cocrystal structure of one metallo-phthalimide with the protein kinase Pim1 confirmed an ATP-competitive binding with the intended hydrogen bonding between the phthalimide moiety and the hinge region of the ATP-binding site.

Cytotoxicity and cellular impact of dinuclear organoiridium DNA intercalators and nucleases with long rigid bridging ligands

The DNA binding modes and cleavage properties of novel dinuclear Ir(III) polypyridyl (pp) complexes [{(η(5)-C(5)Me(5))Ir(pp)}(2)(μ-B)](CF(3)SO(3))(4) depend on the lengths of their rigid bridging dipyridinyl ligands B. Mono-intercalation and strong DNA cleavage properties were observed for the dipyrido[2,3-a:2',3'-c]phenazine (dppz) complexes 1 (B = 4-[(E)-2-(4-pyridinyl)ethenyl]pyridine) and 3 (B = 4-(2-pyridin-4-ylethynyl)pyridine), whose intracationic Ir···Ir' distances are about 13.1 and 13.3 Å, respectively. In contrast, UV/Vis and CD spectra were in accordance with a stable intertwined bis-intercalation mode for pairs of cations of 5 (B = 1,4-di(2-pyridin-4-ylethynyl)benzene), whose much longer Ir···Ir' distance of 20.6 Å allows a stack of five aromatic chromophores to be sandwiched between its effectively parallel dppz ligands. Whereas both 1 and 3 cleaved DNA in the dark, complex 5 exhibited only photoinduced nuclease activity. A significantly higher antiproliferative activity towards MCF-7 breast carcinoma cells was observed for the nucleases 1 and 3, whose IC(50) values of 0.61 and 0.49 were much lower than that of 2.2 μM for bis-intercalator 5. Values of 3.8 μM, only slightly higher than that of 5, were recorded for the 5,6-dimethylphenanthroline complexes 4 and 6, whose bridging ligands are identical to those of 3 and 5, respectively. Marked antileukemic activity (IC(50) = 6-7 μM) associated with increased levels of reactive oxygen species and apoptosis induction was recorded for both 3 and 5 towards Jurkat cells at concentrations of 5 μM and above. Online studies with a sensor chip system indicated that 5 μM solutions of these complexes invoke a rapid and massive reduction in MCF-7 cell respiration.

Sixty Years Young: The Diverse Biological Activities of Metal Polypyridyl Complexes Pioneered by Francis P. Dwyer

Sixty years ago, the Australian chemist Francis P. Dwyer pioneered the use of ruthenium polypyridyl complexes as biologically active compounds. These chemically inert and configurationally stable complexes revealed an astonishing range of interesting biological activities, such as the inhibition of the enzyme acetylcholinesterase, anti-cancer activity in vivo, and bacteriostatic/bacteriocidal action. This review commemorates the sixtieth anniversary of Dwyer and co-workers’ landmark 1952 publication, summarises their broader achievements in biological inorganic chemistry, and discusses the contribution of this work to the development of modern biological and medicinal inorganic chemistry.

Cationic ruthenium(III) maltolato–imidazole complexes — Synthesis, characterization, and antiproliferatory activity*Adapted from the Ph.D. thesis of D.C. Kennedy (see the References section)

The cationic RuIII complexes, trans-[Ru(ma)2(L)2]CF3SO3, where Hma = maltol = 3-hydroxy-2-methyl-4-pyrone; L = imidazole (Im) (complex 2), 1(N)-methylimidazole (N-MeIm) (3), 2-methylimidazole (2-MeIm) (4), and 4-methylimidazole (4-MeIm) (5), were synthesized via the known L = EtOH (complex 1a), and characterized by elemental analysis, 1H NMR and IR spectroscopies, mass spectrometry, cyclic voltammetry, and (for 3 and 4) by X-ray crystallography. The trans-[Ru(ma)2(H2O)2]CF3SO3 complex (1b) was inadvertently isolated and characterized crystallographically, and the monomaltolato species [Ru(ma)(N-MeIm)4][CF3SO3]2 (6) was also isolated and characterized. In vitro antiproliferatory activity of complexes 2−6 against human breast cancer cells (MDA-MB-435S) was tested using an MTT assay: 4 and 5 exhibit the lowest IC50 values, ~5 and ~15 µmol/L, respectively, whereas cisplatin exhibits an IC50 value of ~35 µmol/L against this cell line.

Organometallic Pyridylnaphthalimide Complexes as Protein Kinase Inhibitors

A new metal-containing scaffold for the design of protein kinase inhibitors is introduced. Key feature is a 3-(2-pyridyl)-1,8-naphthalimide "pharmacophore chelate ligand" which is designed to form two hydrogen bonds with the hinge region of the ATP-binding site and is at the same time capable of serving as a stable bidentate ligand through C-H-activation at the 4-position of the electron-deficient naphthalene moiety. This C-H-activation leads to a reduced demand for coordinating heteroatoms and thus sets the basis for a very efficient three-step synthesis starting from 1,8-naphthalic anhydride. The versatility of this ligand is demonstrated with the discovery of a ruthenium complex that functions as a nanomolar inhibitor for myosin light-chain kinase (MYLK or MLCK).