Preparation of new half sandwich ruthenium arene complexes with aminophosphines as potential chemotherapeutics

Synthesis and Investigations of the Antitumor Effects of First-Row Transition Metal(II) Complexes Supported by Two Fluorinated and Non-Fluorinated β-Diketonates

The 3d transition metal (Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)) complexes, supported by anions of sterically demanding β-diketones, 1,3-dimesitylpropane-1,3-dione (HLMes) and 1,3-bis(3,5-bis(trifluoromethyl)phenyl)-3-hydroxyprop-2-en-1-one (HLCF3), were synthesized and evaluated for their antitumor activity. To assess the biological effects of substituents on phenyl moieties, we also synthesized and investigated the analogous metal(II) complexes of the anion of the less bulky 1,3-diphenylpropane-1,3-dione (HLPh) ligand. The compounds [Cu(LCF3)2], [Cu(LMes)2] and ([Zn(LMes)2]) were characterized by X-ray crystallography. The [Cu(LCF3)2] crystallizes with an apical molecule of solvent (THF) and features a rare square pyramidal geometry at the Cu(II) center. The copper(II) and zinc(II) complexes of diketonate ligands, derived from the deprotonated 1,3-dimesitylpropane-1,3-dione (HLMes), adopt a square planar or a tetrahedral geometry at the metal, respectively. We evaluated the antitumor properties of the newly synthesized (Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)) complexes against a series of human tumor cell lines derived from different solid tumors. Except for iron derivatives, cellular studies revealed noteworthy antitumor properties, even towards cancer cells endowed with poor sensitivity to the reference drug cisplatin.

Synthesis and cytotoxicity studies of Cu(I) and Ag(I) complexes based on sterically hindered β-diketonates with different degrees of fluorination

Design, synthesis, and in vitro antitumor properties of Cu(I) and Ag(I) phosphane complexes supported by the anions of sterically hindered β-diketone ligands, 1,3-dimesitylpropane-1,3-dione (HLMes) and 1,3-bis(3,5-bis(trifluoromethyl)phenyl)-3-hydroxyprop-2-en-1-one (HLCF3) featuring trifluoromethyl or methyl groups on the phenyl moieties have been reported. In order to compare the biological effects of substituents on the phenyl moieties, the analogous copper(I) and silver(I) complexes of the anion of the parent 1,3-diphenylpropane-1,3-dione (HLPh) ligand were also synthesized and included in the study. In the syntheses of the Cu(I) and Ag(I) complexes, the phosphane coligands triphenylphosphine (PPh3) and 1,3,5-triaza-7-phosphaadamantane (PTA) were used to stabilize silver and copper in the +1 oxidation state, preventing the metal ion reduction to Ag(0) or oxidation to Cu(II), respectively. X-ray crystal structures of HLCF3 and the metal adducts [Cu(LCF3)(PPh3)2] and [Ag(LPh)(PPh3)2] are also presented. The antitumor properties of both classes of metal complexes were evaluated against a series of human tumor cell lines derived from different solid tumors, by means of both 2D and 3D cell viability studies. They display noteworthy antitumor properties and are more potent than cisplatin in inhibiting cancer cell growth.

Synthesis, characterization, solution chemistry and anticancer activity of [NiCl2(Ph2P-N(R)-PPh2)] (R = 2-CH2Py, CH2Ph and p-tol) complexes

In this work three Ni²⁺ complexes with general formula [NiCl₂(Ph₂P-N(R)-PPh₂)], R = 2-CH₂Py (Py = pyridine) - 1, CH₂Ph (Ph = phenyl) - 2 and p-tol (p-tol = p-tolyl) - 3, were synthesized and characterized. These complexes were obtained in high yield by the reaction of NiCl₂.6H₂O and the corresponding diphenylphosphinoamine ligand (Ph₂P-N(R)-PPh₂) in CH₂Cl₂/MeOH (1:1) solution, at room temperature (∼25 °C), and characterized by ¹H and ³¹P {¹H} NMR, vibrational spectroscopy in the infrared region, electronic spectroscopy in the UV-Vis regions, elemental analysis (%C, %H, %N) and single-crystal X-ray diffraction. The solution chemistry was studied in CDCl₃/dmso-d⁶ (dimethylsulfoxide) or neat dmso-d⁶ using complex 2 as a model. The complexes were evaluated as cytotoxic agents against two cancer cells lines, A549 (lung cancer cells), B16F10 (melanoma cells) and the health cells HaCaT (human epithelial keratinocytes).

Fine Tuning of Cholinesterase and Glutathione-S-Transferase Activities by Organoruthenium(II) Complexes

Cholinesterases (ChEs) show increased activities in patients with Alzheimer’s disease, and remain one of the main therapeutic targets for treatment of this neurodegenerative disorder. A library of organoruthenium(II) complexes was prepared to investigate the influence of their structural elements on inhibition of ChEs, and on another pharmacologically important group of enzymes, glutathione S-transferases (GSTs). Two groups of organoruthenium(II) compounds were considered: (i) organoruthenium(II) complexes with p-cymene as an arene ligand, and (ii) organoruthenium(II) carbonyl complexes as CO-releasing molecules. Eight organoruthenium complexes were screened for inhibitory activities against ChEs and GSTs of human and animal origins. Some compounds inhibited all of these enzymes at low micromolar concentrations, while others selectively inhibited either ChEs or GSTs. This study demonstrates the importance of the different structural elements of organoruthenium complexes for their inhibitory activities against ChEs and GSTs, and also proposes some interesting compounds for further preclinical testing as ChE or GST inhibitory drugs.

Half-Sandwich Ru(p-cymene) Compounds with Diphosphanes: In Vitro and In Vivo Evaluation As Potential Anticancer Metallodrugs

Ruthenium(II) complexes are currently considered attractive alternatives to the widely used platinum-based drugs. We present herein the synthesis and characterization of half-sandwich ruthenium compounds formulated as [Ru(p-cymene)(L)Cl][CF₃SO₃] (L = 1,1-bis(methylenediphenylphosphano)ethylene, 1; L = 1,1-bis(diphenylphosphano)ethylene, 2), which were characterized by elemental analysis, mass spectrometry, ¹H and ³¹P{¹H} NMR, UV-vis and IR spectroscopy, conductivity measurements and cyclic voltammetry. The molecular structures for both complexes were determined by single-crystal X-ray diffraction. Their cytotoxic activity was evaluated using the MTT assay against human tumor cells, namely ovarian (A2780) and breast (MCF7 and MDA-MB-231). Both complexes were active against breast adenocarcinoma cells, with complex 1 exhibiting a quite remarkable cytotoxicity in the submicromolar range. Interestingly, at concentrations equivalent to the IC₅₀ values in the MCF7 cancer cells, complexes 1 and 2 presented lower cytotoxicity in normal human primary fibroblasts. The antiproliferative effects of 1 and 2 in MCF7 cells might be associated with the induction of reactive oxygen species (ROS), leading to a combined cell death mechanism via apoptosis and autophagy. Despite the fact that in vitro a partial intercalation between complexes and DNA was observed, no MCF7 cell cycle delay or arrest was observed, indicating that DNA might not be a direct target. Complexes 1 and 2 both exhibited a moderate to strong interaction with human serum albumin, suggesting that protein targets may be involved in their mode of action. Their acute toxicity was evaluated in the zebrafish model. Complex 1 (the most toxic of the two) exhibited a lethal toxicity LC₅₀ value about 1 order of magnitude higher than any IC₅₀ concentrations found for the cancer cell models used, highlighting its therapeutic relevance as a drug candidate in cancer chemotherapy.

Ruthenium arene complexes in the treatment of 3D models of head and neck squamous cell carcinomas

Current chemotherapy for head and neck squamous cell carcinomas (HNSCCs) are based on cisplatin, which is usually associated to severe side effects. In general, the exploration for metal-based alternatives to cisplatin has resulted in the development of a series of ruthenium complexes that are able to produce a safe therapeutic action against some neoplasms, among which are lung and ovarian cancers. Here, we evaluate the efficacy of well defined, easily available and robust ruthenium(II) η⁶-arene compounds on 3D models of HNSCCs with or without human papillomavirus (HPV) infection and compare their effects to the state-of-the-art RAPTA-C, a promising ruthenium compound with known anti-cancer activity. One of the compounds induces a significant therapeutic action especially on HPV negative carcinoma. Besides viability and repopulation evaluations, we performed quantitative analysis of the internalized Ru compounds to further validate our findings and elucidate the possible mechanisms of action. These results show that Ru arene compounds represent a promising alternative for the treatment of HNSCCs and pave the way for the composition of innovative (co)therapies.

Analysis of Ion Pairing in Solid State and Solution in p-Cymene Ruthenium Complexes

The importance of ion pairing in different fields of chemistry is widely recognized. In this work, we have synthesized a set of cationic p-cymene ruthenium complexes of general formula [(p-cym)Ru(L')(κ²-O^N-L)]X (p-cym = p-cymene; L' = N-methylimidazole (MeIm), N-ethylpiperidylimidazole (EpipIm), 1,3,5-triaza-7-phosphaadamantane (PTA); L = 2-(1H-benzimidazol-2-yl)phenolato (L1), 2-(1,3-benzothiazol-2-yl)phenolato (L2); X = Cl^-, BF₄^-, OTf^-, BPh₄^-). X-ray diffraction studies on selected complexes revealed relatively strong anion-cation interactions in the solid state mainly based on N-H···X (X = Cl, F, O) and C-H···π interactions, also observed in the DFT-modeled complexes in the gas phase. Moreover, NMR studies showed that they exist as intimate ion pairs in solution and, remarkably, as head-to-tail quadruples in the particular case of the cation [(p-cym)Ru(MeIm)(κ²- O^N-L1)]⁺ ([1]⁺) with Cl^- and BPh₄^- as counteranions. Furthermore, a value of ΔG = -2.9 kcal mol^-1 at 299 K has been estimated for the equilibrium {[1]BPh₄···[1]BPh₄} ⇆ 2{[1]⁺···BPh₄^-} in concentrated CDCl₃ solutions. In addition, preliminary studies concerning the cytotoxic properties against HeLa cell lines of the derivatives suggested a positive effect derived from the presence of the lipophilic BPh₄^- anion and also from the NH group of the benzimidazolyl fragment.

Effect of N,N Coordination and RuII Halide Bond in Enhancing Selective Toxicity of a Tyramine-Based RuII (p-Cymene) Complex

Ruthenium compounds are promising anticancer candidates owing to their lower side-effects and encouraging activities against resistant tumors. Half-sandwich piano-stool type Ru^II compounds of general formula [(L)Ru^II(η⁶-arene)(X)]⁺ (L = chelating bidentate ligand, X = halide) have exhibited significant therapeutic potential against cisplatin-resistant tumor cell lines. In Ru^II (p-cymene) based complexes, the change of the halide leaving group has led to several interesting features, viz., hydrolytic stability, resistance toward thiols, and alteration in pathways of action. Tyramine is a naturally occurring monoamine which acts as a catecholamine precursor in humans. We synthesized a family of N,N and N,O coordinated Ru^II (p-cymene) complexes, [(L)Ru^II(η⁶-arene)(X)]⁺ (1-4), with tyramine and varied the halide (X = Cl, I) to investigate the difference in reactivity. Our studies showed that complex 2 bearing N,N coordination with an iodido leaving group shows selective in vitro cytotoxicity against the pancreatic cancer cell line MIA PaCa-2 (IC₅₀ ca. 5 μM) but is less toxic to triple-negative breast cancer (MDA-MB-231), hepatocellular carcinoma (Hep G2), and the normal human foreskin fibroblasts (HFF-1). Complex 2 displays stability toward hydrolysis and does not bind with glutathione, as confirmed by ¹H NMR and ESI-HRMS experiments. The inert nature of 2 leads to enhancement of cytotoxicity (IC₅₀ = 5.3 ± 1 μM) upon increasing the cellular treatment time from 48 to 72 h.

Antiproliferative activity of ruthenium(ii) arene complexes with mono- and bidentate pyridine-based ligands

A series of Ru(II) arene complexes of mono- and bidentate N-donor ligands with carboxyl or ester groups and chlorido ancillary ligands were synthesised and structurally characterised. The complexes have a distorted tetrahedral piano-stool geometry. The binding interaction was studied with calf thymus DNA (CT-DNA) by absorption titration, viscosity measurement, thermal melting, circular dichroism, ethidium bromide displacement assay and DNA cleavage of plasmid DNA (pBR322), investigated by gel electrophoresis. The dichlorido complexes bind covalently to DNA in the dark, similar to cisplatin, while the monochlorido complexes bind covalently on irradiation, similar to cisplatin analogues. The compounds are selectively cytotoxic against several tumour cell lines and show specific nonlinear correlation between dose and activity. This phenomenon is closely related to their potential to act preferentially as inhibitors of cell division.

New Class of Half-Sandwich Ruthenium(II) Arene Complexes Bearing the Water-Soluble CAP Ligand as an in Vitro Anticancer Agent

Ruthenium(II) arene complexes of 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP) were obtained. Cytotoxicity studies against cancer cell lines reveal higher activity than the corresponding PTA analogues and, in comparison to the effects on noncancerous cells, the complexes are endowed with a reasonable degree of cancer cell selectivity.

Interstrand DNA covalent binding of two dinuclear Ru(ii) complexes. Influence of the extra ring of the bridging ligand on the DNA interaction and cytotoxic activity

The quinones naphthazarin and quinizarin intercalate into DNA whereas their p-cymene di-ruthenium(ii) complexes bind covalently via interstrand crosslinking.

Tuning the cytotoxicity of ruthenium(ii) para-cymene complexes by mono-substitution at a triphenylphosphine/phenoxydiphenylphosphine ligand

The cytotoxic activities of novel Ru(ii) arene complexes with variably mono-substituted phosphine ligands have been assessed towards MDA-MB-231 and A2780 cancer cell lines.

Ruthenium arene complexes with triphenylphosphane ligands: cytotoxicity towards pancreatic cancer cells, interaction with model proteins, and effect of ethacrynic acid substitution

The anticancer behaviour of Ru arene complexes can be tuned by an appropriate choice of the site and linkage of the bioactive group to the phosphane ligand.

Structure-Related Mode-of-Action Differences of Anticancer Organoruthenium Complexes with β-Diketonates

A series of organoruthenium(II) chlorido complexes with fluorinated O,O-ligands [(η(6)-p-cymene)Ru(F3C-acac-Ar)Cl] (1a-6a) and their respective 1,3,5-triaza-7-phosphaadamantane (pta) derivatives [(η(6)-p-cymene)Ru(F3C-acac-Ar)pta]PF6 (1b-6b) were synthesized and fully characterized in both solution and solid state. All complexes were inactive against nonmalignant keratinocytes but displayed variable activity against cancer cell models (ovarian, osteosarcoma). Compounds with a ligand containing the 4-chlorophenyl substituent (6a and 6b) exhibited the strongest anticancer effects. Despite a marginally lower cellular Ru accumulation compared to the chlorido complexes, pta analogues showed higher activity especially in the osteosarcoma model. Reduction of glutathione levels by buthionine sulfoximine (BSO) significantly enhanced the activity of all compounds with the most pronounced effects being observed for the pta series resulting in IC50 values down to the nanomolar range. While all chlorido complexes potently induce reactive oxygen species, DNA damage, and apoptosis, the respective pta compounds widely lacked ROS production but blocked cell cycle progression in G0/G1 phase.

Derivation of structure-activity relationships from the anticancer properties of ruthenium(II) arene complexes with 2-aryldiazole ligands

The ligands 2-pyridin-2-yl-1H-benzimidazole (HL(1)), 1-methyl-2-pyridin-2-ylbenzimidazole (HL(2)), and 2-(1H-imidazol-2-yl)pyridine (HL(3)) and the proligand 2-phenyl-1H-benzimidazole (HL(4)) have been used to prepare five different types of new ruthenium(II) arene compounds: (i) monocationic complexes with the general formula [(η(6)-arene)RuCl(κ(2)-N,N-HL)]Y [HL = HL(1), HL(2), or HL(3); Y = Cl or BF4; arene = 2-phenoxyethanol (phoxet), benzene (bz), or p-cymene (p-cym)]; (ii) dicationic aqua complexes of the formula [(η(6)-arene)Ru(OH2)(κ(2)-N,N-HL(1))](Y)2 (Y = Cl or TfO; arene = phoxet, bz, or p-cym); (iii) the nucleobase derivative [(η(6)-arene)Ru(9-MeG)(κ(2)-N,N-HL(1))](PF6)2 (9-MeG = 9-methylguanine); (iv) neutral complexes consistent with the formulation [(η(6)-arene)RuCl(κ(2)-N,N-L(1))] (arene = bz or p-cym); (v) the neutral cyclometalated complex [(η(6)-p-cym)RuCl(κ(2)-N,C-L(4))]. The cytototoxic activity of the new ruthenium(II) arene compounds has been evaluated in several cell lines (MCR-5, MCF-7, A2780, and A2780cis) in order to establish structure-activity relationships. Three of the compounds with the general formula [(η(6)-arene)RuCl(κ(2)-N,N-HL(1))]Cl differing in the arene moiety have been studied in depth in terms of thermodynamic dissociation constants, aquation kinetic constants, and DNA binding measurements. The biologically most active compound is the p-cym derivative, which strongly destabilizes the DNA double helix, whereas those with bz and phoxet have only a small effect on the stability of the DNA double helix. Moreover, the inhibitory activity of several compounds toward CDK1 has also been evaluated. The DNA binding ability of some of the studied compounds and their CDK1 inhibitory effect suggest a multitarget mechanism for their biological activity.

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.

Anticancer activity and DNA binding of a bifunctional Ru(II) arene aqua-complex with the 2,4-diamino-6-(2-pyridyl)-1,3,5-triazine ligand

The synthesis and full characterization of the new aqua-complex [(η(6)-p-cymene)Ru(OH2)(κ(2)-N,N-2-pydaT)](BF4)2, [2](BF4)2, and the nucleobase derivative [(η(6)-p-cymene)Ru(9-MeG)(κ(2)-N,N-2-pydaT)](BF4)2, [4](PF6)2, where 2-pydaT = 2,4-diamino-6-(2-pyridyl)-1,3,5-triazine and 9-MeG = 9-methylguanine, are reported here. The crystal structures of both [4](PF6)2 and the chloro complex [(η(6)-p-cymene)RuCl(κ(2)-N,N-2-pydaT)](PF6), [1](PF6), have been elucidated by X-ray diffraction. The former provided relevant information regarding the interaction of the metallic fragment [(η(6)-p-cymene)Ru(κ(2)-N,N-2-pydaT)](2+) and a simple model of DNA. NMR and kinetic absorbance studies have proven that the aqua-complex [2](BF4)2 binds to the N7 site of guanine in nucleobases, nucleotides, or DNA. A stable bifunctional interaction (covalent and partially intercalated) between the [(η(6)-p-cymene)Ru(κ(2)-N,N-2-pydaT)](2+) fragment and CT-DNA has been corroborated by kinetic, circular dichroism, viscometry, and thermal denaturation experiments. The reaction mechanism entails the very fast formation of the Ru-O-(PO3) linkage prior to the fast intercalation of the 2-pydaT fragment. Then, a Ru-N7-(G) covalent bond is formed at the expense of the Ru-O-(PO3) bond, yielding a bifunctional complex. The dissociation rate of the intercalated fragment is slow, and this confers additional interest to [2](BF4)2 in view of the likely correlation between slow dissociation and biological activity, on the assumption that DNA is the only biotarget. Furthermore, [2](BF4)2 displays notable pH-dependent cytotoxic activity in human ovarian carcinoma cells (A2780, IC50 = 11.0 μM at pH = 7.4; IC50 = 6.58 μM at pH = 6.5). What is more, complex [2](BF4)2 is not cross-resistant with cisplatin, exhibiting a resistance factor, RF(A2780cis), of 0.28, and it shows moderate selectivity toward the cancer cell lines, in particular, A2780cis (IC50 = 3.0 5 ± 0.08 μM), relative to human lung fibroblast cells (MRC-5; IC50 = 24 μM), the model for healthy cells.

Ruthenium-Arene-β-Carboline Complexes as Potent Inhibitors of Cyclin-Dependent Kinase 1: Synthesis, Characterization and Anticancer Mechanism Studies

A series of Ru(II)-arene complexes (1-6) of the general formula [(η(6)-arene)Ru(L)Cl]PF6 (arene=benzene or p-cymene; L=bidentate β-carboline derivative, an indole alkaloid with potential cyclin-dependent kinases (CDKs) inhibitory activities) is reported. All the complexes were fully characterized by classical analytical methods, and three were characterized by X-ray crystallography. Hydrolytic studies show that β-carboline ligands play a vital role in their aqueous behaviour. These complexes are highly active in vitro, with the most active complex 6 displaying a 3- to 12-fold higher anticancer activity than cisplatin against several cancer cell lines. Interestingly, the complexes are able to overcome cross-resistance to cisplatin, and show much lower cytotoxicity against normal cells. Complexes 1-6 may directly target CDK1, because they can block cells in the G2M phase, down-regulate the expression of CDK1 and cyclin B1, and inhibit CDK1/cyclin B in vitro. Further mechanism studies show that the complexes can effectively induce apoptosis through mitochondrial-related pathways and intracellular reactive oxygen species (ROS) elevation.