Influence of carboxylic acid functionalities in ruthenium (II) polypyridyl complexes on DNA binding, cytotoxicity and antioxidant activity: Synthesis, structure and in vitro anticancer activity

"Half-Sandwich" Ruthenium Complexes with Alizarin as Anticancer Agents: In Vitro and In Vivo Studies

Upon exploration of the chemistry of the combination of ruthenium/arene with anthraquinone alizarin (L), three new complexes with the general formulas [Ru(L)Cl(η⁶-p-cymene)] (C1), [Ru(L)(η⁶-p-cymene)(PPh₃)]PF₆ (C2), and [Ru(L)(η⁶-p-cymene)(PEt₃)]PF₆ (C3) were synthesized and characterized using spectroscopic techniques (mass, IR, and 1D and 2D NMR), molar conductivity, elemental analysis, and X-ray diffraction. Complex C1 exhibited fluorescence, such as free alizarin, while in C2 and C3, the emission was probably quenched by monophosphines and the crystallographic data showed that hydrophobic interactions are predominant in intermolecular contacts. The cytotoxicity of the complexes was evaluated in the MDA-MB-231 (triple-negative breast cancer), MCF-7 (breast cancer), and A549 (lung) tumor cell lines and MCF-10A (breast) and MRC-5 (lung) nontumor cell lines. Complexes C1 and C2 were more selective to the breast tumor cell lines, and C2 was the most cytotoxic (IC₅₀ = 6.5 μM for MDA-MB-231). In addition, compound C1 performs a covalent interaction with DNA, while C2 and C3 present only weak interactions; however, internalization studies by flow cytometry and confocal microscopy showed that complex C1 does not accumulate in viable MDA-MB-231 cells and is detected in the cytoplasm only after cell permeabilization. Investigations of the mechanism of action of the complexes indicate that C2 promotes cell cycle arrest in the Sub-G₁ phase in MDA-MB-231, inhibits its colony formation, and has a possible antimetastatic action, impeding cell migration in the wound-healing experiment (13% of wound healing in 24 h). The in vivo toxicological experiments with zebrafish indicate that C1 and C3 exhibit the most zebrafish embryo developmental toxicity (inhibition of spontaneous movements and heartbeats), while C2, the most promising anticancer drug in the in vitro preclinical tests, revealed the lowest toxicity in in vivo preclinical screening.

Mo(VI) Potential Metallodrugs: Explaining the Transport and Cytotoxicity by Chemical Transformations

The transport and cytotoxicity of molybdenum-based drugs have been explained with the concept of chemical transformation, a very important idea in inorganic medicinal chemistry that is often overlooked in the interpretation of the biological activity of metal-containing systems. Two monomeric, [MoO₂(L¹)(MeOH)] (1) and [MoO₂(L²)(EtOH)] (2), and two mixed-ligand dimeric Mo^VIO₂ species, [{MoO₂(L^1-2)}₂(μ-4,4'-bipy)] (3-4), were synthesized and characterized. The structures of the solid complexes were solved through SC-XRD, while their transformation in water was clarified by UV-vis, ESI-MS, and DFT. In aqueous solution, 1-4 lead to the penta-coordinated [MoO₂(L^1-2)] active species after the release of the solvent molecule (1 and 2) or removal of the 4,4'-bipy bridge (3 and 4). [MoO₂(L^1-2)] are stable in solution and react with neither serum bioligand nor cellular reductants. The binding affinity of 1-4 toward HSA and DNA were evaluated through analytical and computational methods and in both cases a non-covalent interaction is expected. Furthermore, the in vitro cytotoxicity of the complexes was also determined and flow cytometry analysis showed the apoptotic death of the cancer cells. Interestingly, μ-4,4'-bipy bridged complexes 3 and 4 were found to be more active than monomeric 1 and 2, due to the mixture of species generated, that is [MoO₂(L^1-2)] and the cytotoxic 4,4'-bipy released after their dissociation. Since in the cytosol neither the reduction of Mo^VI to Mo^V/IV takes place nor the production of reactive oxygen species (ROS) through Fenton-like reactions of 1-4 with H₂O₂ occurs, the mechanism of cytotoxicity should be attributable to the direct interaction with DNA that happens with a minor-groove binding which results in cell death through an apoptotic mechanism.

Ru(II)/amino acid complexes inhibit the progression of breast cancer cells through multiple mechanism-induced apoptosis

For some cancer subtypes, such as triple-negative breast cancer, there are no specific therapies, which leads to a poor prognosis associated with invasion and metastases. Ruthenium complexes have been developed to act in all steps of tumor growth and its progression. In this study, we investigated the effects of Ruthenium (II) complexes coupled to the amino acids methionine (RuMet) and tryptophan (RuTrp) on the induction of cell death, clonogenic survival ability, inhibition of angiogenesis, and migration of MDA-MB-231 cells (human triple-negative breast cancer). The study also demonstrated that the RuMet and RuTrp complexes induce cell cycle blockage and apoptosis of MDA-MB-231 cells, as evidenced by an increase in the number of Annexin V-positive cells, p53 phosphorylation, caspase 3 activation, and poly(ADP-ribose) polymerase cleavage. Moreover, morphological changes and loss of mitochondrial membrane potential were detected. The RuMet and RuTrp complexes induced DNA damage probably due to reactive oxygen species production related to mitochondrial membrane depolarization. Therefore, the RuMet and RuTrp complexes acted directly on breast tumor cells, leading to cell death and inhibiting their metastatic potential; this reveals the potential therapeutic action of these drugs.

Experimental and theoretical studies of Palladium-hydrazide complexes' interaction with DNA and BSA, in vitro cytotoxicity activity and plasmid cleavage ability

New palladium complexes with general formula trans-[Pd(L)₂(OAc)₂] (1,2), (L = Benzhydrazide and 2-Furoic hydrazide) have been synthesized and characterized with various methods including elemental analysis, FT-IR, ¹HNMR and mass spectroscopy. Afterward their interactions with bovine serum albumin and calf thymus deoxyribonucleic acid have been investigated by UV-vis absorption, fluorescence emission and circular dichroism spectroscopy. Also, site-selective replacement experiments with site probes have been carried out. Analysis of fluorescence spectrum indicated static quenching mechanism. Spectroscopic measurements for DNA binding showed the groove binding to DNA for both complexes. Furthermore, cytotoxicity studies of complexes and cis-platin have been done against colon carcinoma (CT26) and breast cancer (4T1) cell lines. Evaluation of complexes (1) and (2) on induction of apoptosis in CT26 cells has been done. Finally, plasmid cleavage ability of (1) and (2) was investigated by gel electrophoresis that indicate the more activity of (1) than (2).

Functionalization and cancer-targeting design of ruthenium complexes for precise cancer therapy

The successful clinical application of the three generation platinum anticancer drugs, cisplatin, carboplatin and oxaliplatin, has promoted research interest in metallodrugs; however, the problems of drug resistance and adverse effects have hindered their further application and effects. Thus, scientists are searching for new anticancer metallodrugs with lower toxicity and higher efficacy. The ruthenium complexes have emerged as the most promising alternatives to platinum-based anticancer agents because of their unique multifunctional biochemical properties. In this review, we first focus on the anticancer applications of various ruthenium complexes in different signaling pathways, including the mitochondria-mediated pathway, the DNA damage-mediated pathway, and the death receptor-mediated pathway. We then discuss the functionalization and cancer-targeting designs of different ruthenium complexes in conjunction with other therapies such as photodynamic therapy, photothermal therapy, radiosensitization, targeted therapy and nanotechnology for precise cancer therapy. This review will help in designing and accelerating the research progress regarding new anticancer ruthenium complexes.

New barium, strontium and strontium-doped barium squarates: synthesis, crystal structures and DNA/BSA binding, antioxidant and in vitro cytotoxicity studies

A new set of differently hydrated barium and strontium squarates, namely poly[[triaqua(μ-1,2-dioxocyclobut-3-ene-1,2-diolato)barium] monohydrate], {[Ba(C₄O₄)(H₂O)₃]·H₂O}_n (1), poly[[diaqua(μ-1,2-dioxocyclobut-3-ene-1,2-diolato)strontium] monohydrate], {[Sr(C₄O₄)(H₂O)₂]·H₂O}_n (2), and poly[[triaqua(μ-1,2-dioxocyclobut-3-ene-1,2-diolato)barium/strontium(0.85/0.15)] monohydrate], {[Ba_0.85Sr_0.15(C₄O₄)(H₂O)₃]·H₂O}_n (3), is reported. The study of their crystal structures indicates that all the complexes crystallize in the triclinic space group P-1. Complexes 1 and 3 have a rare combination of squarate units coordinated through monodentate O atoms to two different metal atoms and through two bidentate O atoms to three different metal atoms. Furthermore, they have three coordinated water molecules to give a coordination number of nine. The squarate ligands in complex 2 exhibit two different coordination modes: (i) monodentate O atoms coordinated to four different Sr atoms and (ii) two monodentate O atoms coordinated to two different metal atoms with the other two O atoms bidentate to four different Sr atoms. All the compounds decompose to give the respective carbonates when heated to 800 °C, as evidenced by thermogravimetry/differential thermal analysis (TG-DTA), which are clusters of nanoparticles. Complexes 1 and 3 show additional endothermic peaks at 811 and 820 °C, respectively, indicating the phase transition of BaCO₃ from an orthorhombic (α-Pmcn) to a trigonal phase (β-R3m). All three complexes have significant DNA-binding constants, ranging from 2.45 × 10⁴ to 9.41 × 10⁴ M^-1 against EB-CT (ethidium bromide-calf thymus) DNA and protein binding constants ranging from 1.1 × 10⁵ to 8.6 × 10⁵ with bovine serum albumin. The in vitro cytotoxicity of the complexes is indicated by the IC₅₀ values, which range from 128.8 to 261.3 µg ml^-1. Complex 3 shows better BSA binding, antioxidant activity against the DPPH radical and cytotoxicity than complexes 1 and 2.

Anti-cancer organoruthenium(ii) complexes and their interactions with cysteine and its analogues. A mass-spectrometric study

The ruthenium complexes [Ru(CYM)(p-Cl-dkt)(Cl)] (1), [Ru(CYM)(pta)(p-Cl-dkt)]PF₆ (2), and [Ru(CYM)(pta)Cl₂] (3, RAPTA-C) (CYM = para-cymene, p-Cl-dkt = 1-(4-chlorophenyl)-4,4,4-trifluorobutane-1,3-dione, pta = 1,3,5-triaza-7-phosphaadamantane) are biologically active and show anti-cancer activities, albeit with different mechanisms. To further understand these mechanisms, we compared their speciation in aqueous solutions with an amino acid (cysteine), with an amino acid derivative (N-acetylcysteine) and with a tripeptide (glutathione) by Mass Spectrometry (MS). Here, we show that all ruthenium complexes have high selectivity for cysteine and cysteine-derived molecules. On one hand, [Ru(CYM)(p-Cl-dkt)(Cl)] undergoes solvolysis in water and forms [Ru₂(CYM)₂(OH)₃]⁺. Subsequently, all hydroxyl anions are exchanged by deprotonated cysteine. Infrared Photodissociation Spectroscopy (IRPD) showed that cysteine binds to the ruthenium atoms via the deprotonated thiol group and that sulfur bridges the ruthenium centers. On the other hand, the pta-bearing complexes remain monometallic and undergo only slow Cl or p-Cl-dkt exchange by deprotonated cysteine. Therefore, the pta ligand protects the ruthenium complexes from ligand exchange with water and from the formation of biruthenium clusters, possibly explaining why the mechanism of pta-bearing ruthenium complexes is not based on ROS production but on their reactivity as monometallic complexes.

ESI-MS study of ruthenium complexes shows their high selectivity toward thiol containing molecules and formation of larger thiolate-bound clusters in absence of a protecting ligand such as pta.

Esterification of the free carboxylic group from the lutidinic acid ligand as a tool to improve the cytotoxicity of Ru(ii) complexes

The esterification of the free carboxyl group in ruthenium complexes improves the complex interactions with biomolecules, lipophilicity, and cellular uptake, making them more selective against tumor cells than cisplatin.

Ru(II) Compounds: Next-Generation Anticancer Metallotherapeutics?

Metal based therapeutics are a precious class of drugs in oncology research that include examples of theranostic drugs, which are active in both diagnostic, specifically imaging, and therapeutics applications. Ruthenium compounds have shown selective bioactivity and the ability to overcome the resistance that platinum-based therapeutics face, making them effective oncotherapeutic competitors in rational drug invention approaches. The development of antineoplastic ruthenium therapeutics is of particular interest because ruthenium containing complexes NAMI-A, KP1019, and KP1339 entered clinical trials and DW1/2 is in preclinical levels. The very robust, conformationally rigid organometallic Ru(II) compound DW1/2 is a protein kinase inhibitor and presents new Ru(II) compound designs as anticancer agents. Over the recent years, numerous strategies have been used to encapsulate Ru(II) derived compounds in a nanomaterial system, improving their targeting and delivery into neoplastic cells. A new photodynamic therapy based Ru(II) therapeutic, TLD-1433, has also entered clinical trials. Ru(II)-based compounds can also be photosensitizers for photodynamic therapy, which has proven to be an effective new, alternative, and noninvasive oncotherapy modality.

cis-[RuCl(BzCN)(bipy)(dppe)]PF6 induces anti-angiogenesis and apoptosis by a mechanism of caspase-dependent involving DNA damage, PARP activation, and Tp53 induction in Ehrlich tumor cells

Antimetastatic activities, low toxicity to normal cells and high selectivity for tumor cells make of the ruthenium complexes promising candidates in the search for develop new chemotherapeutic agents for the treatment of cancer. This study aimed to determine the cytotoxic, genotoxic and to elucidate the signaling pathway involved in the death cell process induced by cis-[RuCl(BzCN)(bipy)(dppb)]PF₆(1) and cis-[RuCl(BzCN)(bipy)(dppe)]PF₆(2) in Ehrlich ascites carcinoma (EAC) in vitro. Moreover, we report for the first time the anti-angiogenic potential on chick embryo chorioallantoic membrane (CAM) model. Peripheral blood mononuclear cells (PBMC) were isolated from healthy controls with an age range of 20-30 years and used to calculate the selectivity index (SI). The complex 2 (IC₅₀ = 8.5 ± 0.4/SI = 6.3) showed high cytotoxic and selectivity index against EAC cells than complex 1 (IC₅₀ = 14.9 ± 0.2/SI = 0.2) using the MTT assay. Complex 2 induced DNA damage on Ehrlich tumor cells at concentrations and time periods evalueted. In consequence, it was observed an increase of Tp53 gene expression, G0/G1-arrest cells, and increased levels of cleaved PARP protein. Beside that, the treatment of EAC with complex 2 led to an increase in Annexin V-positive cells and apoptosis induction by Caspase-7. Additionally, the complex 2 inhibited the angiogenesis caused by Ehrlich tumor cells in CAM model. This complex is active and selective for Ehrlich tumor cells, inducing DNA damage, cell cycle arrest and cell death by caspase-dependent apoptosis involving PARP activation (PARP1), and Tp53 induction.

A Review on Platelet Activating Factor Inhibitors: Could a New Class of Potent Metal-Based Anti-Inflammatory Drugs Induce Anticancer Properties?

In this minireview, we refer to recent results as far as the Platelet Activating Factor (PAF) inhibitors are concerned. At first, results of organic compounds (natural and synthetic ones and specific and nonspecific) as inhibitors of PAF are reported. Emphasis is given on recent results about a new class of the so-called metal-based inhibitors of PAF. A small library of 30 metal complexes has been thus created; their anti-inflammatory activity has been further evaluated owing to their inhibitory effect against PAF in washed rabbit platelets (WRPs). In addition, emphasis has also been placed on the identification of preliminary structure-activity relationships for the different classes of metal-based inhibitors.

The effect of incorporating carboxylic acid functionalities into 2,2′-bipyridine on the biological activity of the complexes formed: synthesis, structure, DNA/protein interaction, antioxidant activity and cytotoxicity

Incorporation of carboxylic acid group in the bipyridine moiety has resulted in showing differences in DNA/protein binding affinity, efficiency in antioxidant activity and cytotoxicity.

Biological activity and binding properties of [Ru(II)(dcbpy)2Cl2] complex to bovine serum albumin, phospholipase A2 and glutathione

Ruthenium compounds are highly regarded as metallo-drug candidates. Many studies have focused their attention on the interaction between ruthenium complexes with their possible biological targets. The interaction of ruthenium complexes with transport proteins, enzymes and peptides is of great importance for understanding their biodistribution and mechanism of action, therefore, the development of an anti-cancer therapy involving ruthenium complexes has recently shifted from DNA targeting towards protein targeting. With the aim of gaining insight into possible interactions between ruthenium complexes with biologically relevant proteins, we have studied the interaction of cis-dichlorobis(2,2'-bipyridyl-4,4'-dicarboxylic acid)ruthenium(II) complex [Ru(II)(dcbpy)2Cl2], which previously showed good potency in photo-dynamic chemotherapy, with bovine serum albumin (BSA), phospholipase A2 (PLA2) and glutathione (GSH). Binding constants and possible number of binding sites to mentioned proteins and peptide are investigated by ultraviolet-visible spectroscopy and Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI TOF MS). The complex binding affinities were in the following order: PLA2 > BSA > GSH. Moreover, genotoxic profile of the complex, tested on peripheral blood lymphocytes as a model system, was also promising.

Studies on some metal complexes of quinoxaline based unsymmetric ligand: Synthesis, spectral characterization, in vitro biological and molecular modeling studies

Mononuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes of an unsymmetric Schiff base ligand, 3-(-(3-(-3,5-dichloro-2-hydroxybenzylideneamino)propylimino)methyl)quinoxalin-2(1H) -one (L) were synthesized and characterized by various analytical and spectral techniques. The molar conductance values of metal complexes indicate non-electrolytic behavior of the metal complexes. The Schiff base act as tetra dentate ONNO donor ligand in Co(II), Ni(II), Zn(II) complexes and tridentate NNO donor in Cu(II) complex. Thermal stabilities of the newly synthesized compounds were determined by thermal analysis. Crystallinity, average grain size and unit cell parameters were determined from powder X-ray diffraction study. Electrochemical behaviors of the compounds were examined by cyclic voltammetry technique. The Schiff base and its complexes have been screened for their in vitro antimicrobial activities against some bacterial and fungal strains by disc diffusion method. The interaction of the compounds with calf thymus DNA (CT DNA) has been investigated by electronic absorption spectral titration and viscosity measurement (hydrodynamic) methods. Furthermore, the pUC18 DNA cleavage activities of the complexes have been explored. The compounds were also subjected to in vitro antioxidant, anticancer activity screening, druglikeness and bioactivity predictions using Molinspiration software. Molecular docking studies of the present compounds were carried out against B-DNA dodecamer d(CGCGAATTCGCG)2 and vascular endothelial growth factor receptor (VEGFR-2) kinase. Quantum chemical calculations were done with DFT method to determine the optimum geometry of the ligand and its metal complexes. From the quantum chemical parameters, the reactivity parameters of the compounds were established.

Anticancer Activities of Mononuclear Ruthenium(II) Coordination Complexes

Ruthenium compounds are highly regarded as potential drug candidates. The compounds offer the potential of reduced toxicity and can be tolerated in vivo. The various oxidation states, different mechanism of action, and the ligand substitution kinetics of ruthenium compounds give them advantages over platinum-based complexes, thereby making them suitable for use in biological applications. Several studies have focused attention on the interaction between active ruthenium complexes and their possible biological targets. In this paper, we review several ruthenium compounds which reportedly possess promising cytotoxic profiles: from the discovery of highly active compounds imidazolium [trans-tetrachloro(dmso)(imidazole)ruthenate(III)] (NAMI-A), indazolium [trans-tetrachlorobis(1H-indazole)ruthenate(III)](KP1019), and sodium trans-[tetrachloridobis(1H-indazole)ruthenate(III)] (NKP-1339) to the recent work based on both inorganic and organometallic ruthenium(II) compounds. Half-sandwich organometallic ruthenium complexes offer the opportunity of derivatization at the arene moiety, while the three remaining coordination sites on the metal centre can be functionalised with various coordination groups of various monoligands. It is clear from the review that these mononuclear ruthenium(II) compounds represent a strongly emerging field of research that will soon culminate into several ruthenium based antitumor agents.

Antioxidant, DNA binding and nuclease activities of heteroleptic copper(II) complexes derived from 2-((2-(piperazin-1-yl)ethylimino)methyl)-4-substituted phenols and diimines

A series of heteroleptic copper(II) complexes of the type [CuL(1-4)(diimine)](ClO4)2 (1-8) [L(1-4)=2-((2-(piperazin-1-yl)ethylimino)methyl)-4-substituted phenols, and diimine=2,2'-bipyridyl (bpy) or 1,10-phenanthroline (phen)], have been synthesized and characterized by spectroscopic methods. The IR spectra of complexes indicate the presence of uncoordinated perchlorate anions and the electronic spectra revealed the square pyramidal geometry with N4O coordination environment around copper(II) nuclei. Electrochemical studies of the mononuclear complexes evidenced one-electron irreversible reduction wave in the cathodic region. The EPR spectra of complexes with g|| (2.206-2.214) and A|| (154-172×10(-)(4)cm(-)(1)) values support the square-based CuN3O coordination chromophore and the presence of unpaired electron localized in [Formula: see text] ground state. Antioxidant studies against DPPH revealed effective radical scavenging properties of the synthesized complexes. Binding studies suggest that the heteroleptic copper(II) complexes interact with calf thymus DNA (CT-DNA) through minor-groove and electrostatic interaction, and all the complexes display pronounced nuclease activity against supercoiled pBR322 DNA.

Anticancer activity for targeting telomeric G-quadruplex and antiangiogenesis of a novel Ru(II)-Se complex

A new Ru(II)-Se complex, Ru(bpy)2L2Cl2 (bpy = 2,2'-bipyridine, L = 1,10-phenanthrolineselenazole) (Ru-Se) has been synthesized and characterized. The G-quadruplex DNA-binding properties of the complex and its selenium ligand (Phen-Se) were evaluated by thermal denaturation study, polymerase chain reaction (PCR) stop assay, and telomerase repeat amplification protocol (TRAP). The results showed that the obtained complex could induce and stabilize G-quadruplex structure as well as exhibit potent inhibitory activity against telomerase. In vitro cytotoxicity studies showed that complex Ru-Se inhibited the cancer cell growth through apoptosis. However, the presence of the ligand Phen-Se did not appear to have a significant effect either on G-quadruplex binding or on biological activity. Furthermore, the cell migration assay and the tube formation assay also demonstrated that the complex Ru-Se significantly inhibited human umbilical vascular endothelial cell (HUVEC) proliferation, migration, and tube formation. These findings indicate that the Ru-Se complex may be a potential telomerase inhibitor and a viable drug candidate in antiangiogenesis for anticancer therapies.

Targeting the endoplasmic reticulum with a membrane-interactive luminescent ruthenium(ii) polypyridyl complex†Electronic supplementary information (ESI) available: Experimental details, characterization of and Fig. S1-S6. See DOI: 10.1039/c3sc51725jClick here for additional data file

The characterization and bioactivity of the dinuclear ruthenium(ii) complex [(Ru(DIP)2)2(tpphz)]4+ (DIP = 4,7-diphenyl-1,10-phenanthroline and tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) is reported. This new complex is found to be luminescent in acetonitrile, where excitation into MLCT (metal-to-ligand charge-transfer) bands in the visible area of the spectrum (λex = 450 nm, ε = 45 000 M-1 cm-1) result in red emission (λem,max = 620 nm, ΦMLCT = 0.017). Aqueous in vitro binding studies indicate that this complex binds to duplex DNA with an affinity of 1.8 × 106 M-1 through a non-classical groove-binding interaction, however, unlike the parent complex [(Ru(phen)2)2(tpphz)]4+ (phen = 1,10-phenanthroline), it also displays an increase in MLCT luminescence on addition of liposomes. Confocal microscopy and TEM studies show that this lipophilic complex targets the endoplasmic reticulum of eukaryotic cells, where it functions as an imaging agent for this organelle, and cytotoxicity studies in human cancer cell lines indicate a comparable potency to the anti-cancer drug cisplatin.