Medicinal organometallic chemistry: designing metal arene complexes as anticancer agents

Functionalization of Ruthenium(II)(η6 -p-cymene)(3-hydroxy-2-pyridone) Complexes with (Thio)Morpholine: Synthesis and Bioanalytical Studies

Hydroxypyr(id)ones constitute an emerging platform for the design of drug molecules, owing to their favorable biocompatibility and toxicity profiles. Herein, [Ru^II (η⁶ -p-cymene)] complexes with 3-hydroxy-2-pyridinone functionalized with morpholine and thiomorpholine, as a means often used in medicinal chemistry to alter the physicochemical properties of drug compounds, are reported. The compounds underwent hydrolysis of the Ru-Cl bond and the aqua species were stable for up to 48 h in aqueous solution, as observed by ¹ H NMR spectroscopy and ESI-MS. The compounds formed adducts with amino acids and proteins through cleavage of the pyridinone ligand. Binding experiments to the nucleosome core particle by means of X-ray crystallography revealed similar reactivity and exclusive binding to histidine moieties of the histone proteins. Preliminary cyclin-dependent kinase 2 (CDK2)/cyclin A kinase inhibitory studies revealed promising activity similar to that of structurally related organometallic compounds.

Anticancer osmium complex inhibitors of the HIF-1α and p300 protein-protein interaction

The hypoxia inducible factor (HIF) pathway has been considered to be an attractive anti-cancer target. One strategy to inhibit HIF activity is through the disruption of the HIF-1α–p300 protein-protein interaction. We report herein the identification of an osmium(II) complex as the first metal-based inhibitor of the HIF-1α–p300 interaction. We evaluated the effect of complex 1 on HIF-1α signaling pathway in vitro and in cellulo by using the dual luciferase reporter assay, co-immunoprecipitation assay, and immunoblot assay. Complex 1 exhibited a dose-dependent inhibition of HRE-driven luciferase activity, with an IC₅₀ value of 1.22 μM. Complex 1 interfered with the HIF-1α–p300 interaction as revealed by a dose-dependent reduction of p300 co-precipitated with HIF-1α as the concentration of complex 1 was increased. Complex 1 repressed the phosphorylation of SRC, AKT and STAT3, and had no discernible effect on the activity of NF-κB. We anticipate that complex 1 could be utilized as a promising scaffold for the further development of more potent HIF-1α inhibitors for anti-cancer treatment.

Ruthenium(II) piano stool coordination compounds with aminomethylphosphanes: Synthesis, characterisation and preliminary biological study in vitro

Reaction of {[Ru(η⁶-p-cymene)Cl]₂(μ-Cl)₂} (1) with aminomethylphosphane derived from morpholine (P{CH₂N(CH₂CH₂)₂O}₃ (A), PPh₂{CH₂N(CH₂CH₂)₂O} (B)) or piperazine (P{CH₂N(CH₂CH₂)₂NCH₂CH₃}₃ (C), PPh₂{CH₂N(CH₂CH₂)₂NCH₂CH₃} (D)) results in four new piano stool ruthenium(II) coordination compounds: [Ru(η⁶-p-cymene)Cl₂(A)] (2A), [Ru(η⁶-p-cymene)Cl₂(B)] (2B), [Ru(η⁶-p-cymene)Cl₂(C)] (2C) and [Ru(η⁶-p-cymene)Cl₂(D)] (2D). Every complex was fully characterized using spectroscopic methods (¹H, ¹³C{¹H}, ³¹P{¹H} NMR and ESI-MS), elemental analysis, X-ray single crystal diffraction and DFT calculations. Preliminary studies of in vitro cytotoxicity on the A549 (human lung adenocarcinoma) and MCF7 (human breast adenocarcinoma) cell lines revealed 2A-2D activity in the same order of magnitude as in the case of cisplatin. Additionally, the study confirmed the ability of 2A-2D to interact with DNA helix and transferrin.

Synthesis of Ru(ii)–benzene complexes containing aroylthiourea ligands, and their binding with biomolecules and in vitro cytotoxicity through apoptosis

Ru(ii)(η⁶-benzene) complexes containing sulfur donor monodentate aroylthiourea ligands have been synthesized and evaluated for their biological applications.

A NIR phosphorescent osmium(ii) complex as a lysosome tracking reagent and photodynamic therapeutic agent

In comparison to a ruthenium(ii) complex, an osmium(ii) complex has great advantages of NIR phosphorescence imaging and NIR photodynamic therapy.

Novel mitochondria targeted copper(ii) complexes of ferrocenyl terpyridine and anticancer active 8-hydroxyquinolines showing remarkable cytotoxicity, DNA and protein binding affinity

Mixed-ligand ferrocenyl copper(ii) complexes target the mitochondria of cancer cells showing remarkable cytotoxicity against HeLa and MCF-7 cancer cells while being much less toxic to MCF-10A normal cells.

Ruthenation of Non-stacked Guanines in DNA G-Quadruplex Structures: Enhancement of c-MYC Expression

Guanine quadruplexes (GQs) are compact four-stranded DNA structures that play a key role in the control of a variety of biological processes, including gene transcription. Bulky ruthenium complexes featuring a bipyridine, a terpyridine, and one exchangeable ligand ([Ru(terpy)(bpy)X]n+ ) are able to metalate exposed guanines present in the GQ of the c-MYC promoter region that are not involved in quadruplex base pairing. qRT-PCR and western-blot experiments indicated that the complexes promote a remarkable increase in the expression of this oncogene. We also show that exchangeable thioether ligands (X=RSR', Met) allow regulation of the metalating activity of the complex with visible light.

Impact of cyclometalated ruthenium(II) complexes on lactate dehydrogenase activity and cytotoxicity in gastric and colon cancer cells

Lactate dehydrogenase (LDH) is a redox enzyme often overexpressed in cancer cells allowing their survival in stressful metabolic tumor environment. Ruthenium(II) complexes have been shown to impact on the activity of purified horseradish peroxidase and glucose oxidase but the physiological relevance remains unclear. In this study we investigated how ruthenium complexes impact on the activity of LDH in vitro and in cancer cells and performed a comparative study using polypyridine ruthenium(II) complex [Ru(bpy)₃]²⁺ (1) and its structurally related cyclometalated 2-phenylpyridinato counterpart [Ru(phpy)(bpy)₂]⁺ (2) (bpy=2,2'-bipyridine, phpyH=2-phenylpyridine). We show that the cytotoxicity in gastric and colon cancer cells induced by 2 is significantly higher compared to 1. The kinetic inhibition mechanisms on purified LDH and the corresponding inhibition constants K_i or i_0.5 values were calculated. Though complexes 1 and 2 are structurally very similar (one Ru-C bond in 2 replaces one Ru-N bond in 1), their inhibition modes are different. Cyclometalated complex 2 behaves exclusively as a non-competitive inhibitor of LDH from rabbit muscle (LDH_rm), strongly suggesting that 2 does not interact with LDH in the vicinities of either lactate/pyruvate or NAD⁺/NADH binding sites. Sites of interaction of 1 and 2 with LDH_rm were revealed theoretically through computational molecular docking. Inhibition of LDH activity by 2 was confirmed in cancer cells. Altogether, these results revealed an inhibition of LDH activity by ruthenium complex through a direct interaction structurally tuned by a Ru-C bond.

Chloroquine-containing organoruthenium complexes are fast-acting multistage antimalarial agents

We report the pharmacological activity of organoruthenium complexes containing chloroquine (CQ) as a chelating ligand. The complexes displayed intraerythrocytic activity against CQ-sensitive 3D7 and CQ-resistant W2 strains of Plasmodium falciparum, with potency and selectivity indexes similar to those of CQ. Complexes displayed activity against all intraerythrocytic stages, but moderate activity against Plasmodium berghei liver stages. However, unlike CQ, organoruthenium complexes impaired gametocyte viability and exhibited fast parasiticidal activity against trophozoites for P. falciparum. This functional property results from the ability of complexes to quickly induce oxidative stress. The parasitaemia of P. berghei-infected mice was reduced by treatment with the complex. Our findings demonstrated that using chloroquine for the synthesis of organoruthenium complexes retains potency and selectivity while leading to an increase in the spectrum of action and parasite killing rate relative to CQ.

Anticancer activity of Ru- and Os(arene) compounds of a maleimide-functionalized bioactive pyridinecarbothioamide ligand

With the aim of increasing the accumulation of Ru anticancer agents in the tumor, a targeted delivery strategy based on a maleimide anchor for the biological vector human serum albumin (HSA) was developed. A group of piano stool Ru- and Os(η⁶-arene) complexes carrying a maleimide-functionalized N-phenyl-2-pyridinecarbothioamide (PCA) ligand was designed allowing for covalent conjugation to biological thiols. The complexes were characterized by NMR spectroscopy, ESI-MS, elemental analysis and single-crystal X-ray diffraction analysis. The compounds were shown to undergo halido/aqua ligand exchange reactions in aqueous solution, depending mainly on the metal center and the nature of the halide. In vitro cytotoxicity studies revealed low potency which is explained by the observed high reactivity of the maleimide to the thiol of l-cysteine (Cys), while the metal center itself shows little affinity to amino acids of the model protein lysozyme.

The water soluble ruthenium(II) organometallic compound [Ru(p-cymene)(bis(3,5 dimethylpyrazol-1-yl)methane)Cl]Cl suppresses triple negative breast cancer growth by inhibiting tumor infiltration of regulatory T cells

Ruthenium compounds have become promising alternatives to platinum drugs by displaying specific activities against different cancers and favorable toxicity and clearance properties. Here, we show that the ruthenium(II) complex [Ru(p-cymene)(bis(3,5-dimethylpyrazol-1-yl)methane)Cl]Cl (UNICAM-1) exhibits potent in vivo antitumor effects. When administered as four-dose course, by repeating a single dose (52.4mgkg-1) every three days, UNICAM-1 significantly reduces the growth of A17 triple negative breast cancer cells transplanted into FVB syngeneic mice. Pharmacokinetic studies indicate that UNICAM-1 is rapidly eliminated from kidney, liver and bloodstream thanks to its high hydrosolubility, exerting excellent therapeutic activity with minimal side effects. Immunohistological analysis revealed that the efficacy of UNICAM-1, mainly relies on its capacity to reverse tumor-associated immune suppression by significantly reducing the number of tumor-infiltrating regulatory T cells. Therefore, UNICAM-1 appears very promising for the treatment of TNBC.

DNA binding properties, histidine interaction and cytotoxicity studies of water soluble ruthenium(ii) terpyridine complexes

In this study, two representatives of previously synthesized ruthenium(ii) terpyridine complexes, i.e., [Ru(Cl-tpy)(en)Cl][Cl] (1) and [Ru(Cl-tpy)(dach)Cl][Cl] (2), were chosen and a detailed study of the kinetic parameters of their reactivity toward l-histidine (l-His), using the UV-Vis and (1)H NMR techniques, was developed. The inner molecular rearrangement from N3-coordinated l-His to the N1 bound isomer, observable in the NMR data, was corroborated by DFT calculations favoring N1 coordination by nearly 4 kcal mol(-1). These two ruthenium(ii) terpyridine complexes were investigated for their interactions with DNA employing UV-Vis spectroscopy, DNA viscosity measurements and fluorescence quenching measurements. The high binding constants obtained in the DNA binding studies (Kb = 10(4)-10(5) M(-1)) suggest a strong binding of the complexes to calf thymus (CT) DNA. Competitive studies with ethidium bromide (EB) showed that the complexes can displace DNA-bound EB, suggesting strong competition with EB (Ksv = 1.5-2.5 × 10(4) M(-1)). In fact, the results indicate that these complexes can bind to DNA covalently and non-covalently. In order to gain insight of the behavior of a neutral compound, besides the four previously synthesized cationic complexes [Ru(Cl-tpy)(en)Cl][Cl] (1), [Ru(Cl-tpy)(dach)Cl][Cl] (2), [Ru(Cl-tpy)(bpy)Cl][Cl] (3) and [Ru(tpy)Cl3] (P2), a new complex, [Ru(Cl-tpy)(pic)Cl] (4), was used in the biological studies. Their cytotoxicity was investigated against three different tumor cell lines, i.e., A549 (human lung carcinoma cell line), HCT116 (human colon carcinoma cell line), and CT26 (mouse colon carcinoma cell line), by the MTT assay. Complexes 1 and 2 showed higher activity than complexes 3, 4 and P2 against all the selected cell lines. The results on in vitro anticancer activity confirmed that only compounds that hydrolyze the monodentate ligand at a reasonable rate show moderate activity, provided that the chelate ligand is a hydrogen bond donor.

Ruthenium(ii) arene complexes containing benzhydrazone ligands: synthesis, structure and antiproliferative activity

Six new Ru(ii) arene anthracene benzhydrazone complexes have been synthesized and show excellent cytotoxicity against human cancer cell lines. The results of apoptosis assays demonstrated that complexes4and6are able to induce apoptosis in human cancer cells.

Mitochondrial selectivity and remarkable photocytotoxicity of a ferrocenyl neodymium(iii) complex of terpyridine and curcumin in cancer cells

A mixed-ligand neodymium(iii) complex of ferrocene appended terpyridine and curcumin targets the mitochondria and shows remarkable visible-light induced cytotoxicity in HeLa and MCF-7 cancer cells while being much less toxic in dark and to MCF-10A normal cells.

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

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

Synthesis, structures, and DNA and protein binding of ruthenium(ii)-p-cymene complexes of substituted pyridylimidazo[1,5-a]pyridine: enhanced cytotoxicity of complexes of ligands appended with a carbazole moiety

The cytotoxicity of ruthenium-arene complexes appended with carbazole moiety correlates with their DNA binding ability.

Cytotoxicity and preliminary mode of action studies of novel 2-aryl-4-thiopyrone-based organometallics

Organometallic 2-aryl-4-thiopyrone-based Ru(ii) and Rh(iii) complexes have been established and their potential as anticancer metallodrugs was investigated.

Development of trackable metal-based drugs: new generation of therapeutic agents

Today, it is not sufficient to conceive an efficient drug, its mechanism of action have to be understood. To tackle this issue, trackable therapeutic agents are an interesting solution.

Heteroleptic arene Ru(ii) dipyrrinato complexes: DNA, protein binding and anti-cancer activity against the ACHN cancer cell line

The in vitro cytotoxicities of heteroleptic Ru(ii) complexes were studied in ACHN cell lines by MTT assay, DNA cleavage, (AO/EtBr) and FACS analysis.

Arene ruthenium(ii) complexes with chalcone, aminoantipyrine and aminopyrimidine based ligands: synthesis, structure and preliminary evaluation of anti-leukemia activity

A series of arene ruthenium(ii) complexes with N-monodentate (AAP) and N,O- and N,N-bidentate chelating ligands (AAPS, ADABS, AAPPA and P2P) have been synthesized and evaluated for preliminary antileukemia activity against K562 (Human chronic myeloid leukemia cell line).

Development of ruthenium-based complexes as anticancer agents: toward a rational design of alternative receptor targets

In the search for novel anticancer agents, the development of metal-based complexes that could serve as alternatives to cisplatin and its derivatives has received considerable attention in recent years. This becomes necessary because, at present, cisplatin and its derivatives are the only coordination complexes being used as anticancer agents in spite of inherent serious side effects and their limitation against metastasized platinum-resistant cancer cells. Although many metal ions have been considered as possible alternatives to cisplatin, the most promising are ruthenium (Ru) complexes and two Ru compounds, KP1019 and NAMI-A, which are currently in phase II clinical trials. The major obstacle against the rational design of these compounds is the fact that their mode of action in relation to their therapeutic activities and selectivity is not fully understood. There is an urgent need to develop novel metal-based anticancer agents, especially Ru-based compounds, with known mechanism of actions, probable targets, and pharmacodynamic activity. In this paper, we review the current efforts in developing metal-based anticancer agents based on promising Ru complexes and the development of compounds targeting receptors and then examine the future prospects.