Ruthenium metallopharmaceuticals

Recent advances of tryptanthrin and its derivatives as potential anticancer agents

Tryptanthrin is one of the well-known natural alkaloids with a broad spectrum of biological activities and can act as anti-inflammatory, anticancer, antibacterial, antifungal, antiviral, antitubercular, and other agents. Owing to its potent anticancer activity, tryptanthrin has been widely explored for the therapy of various cancers besides being effective against other diseases. Tryptanthrin with a pharmacological indoloquinazoline moiety can not only be modified by different functional groups to achieve various tryptanthrin derivatives, which may realize the improvement of anticancer activity, but also bind with different metal ions to obtain varied tryptanthrin metal complexes as potential anticancer agents, due to their higher anticancer activities in comparison with tryptanthrin (or its derivatives) and cisplatin. This review outlines the recent advances in the syntheses, structures, and anticancer activities of tryptanthrin derivatives and their metal complexes, trying to reveal their structure-activity relationships and to provide a helpful way for medicinal chemists in the development of new and effective tryptanthrin-based anticancer agents.

Advances in TRPV6 inhibitors for tumors by targeted therapies: Macromolecular proteins, synthetic small molecule compounds, and natural compounds

TRPV6, a Ca2+-selective member of the transient receptor potential vanilloid (TRPV) family, plays a key role in extracellular calcium transport, calcium ion reuptake, and maintenance of a local low calcium environment. An increasing number of studies have shown that TRPV6 is involved in the regulation of various diseases. Notably, overexpression of TRPV6 is closely related to the occurrence of various cancers. Research confirmed that knocking down TRPV6 could effectively reduce the proliferation and invasiveness of tumors by mainly mediating the calcium signaling pathway. Hence, TRPV6 has become a promising new drug target for numerous tumor treatments. However, the development of TRPV6 inhibitors is still in the early stage, and the existing TRPV6 inhibitors have poor selectivity and off-target effects. In this review, we focus on summarizing and describing the structure characters, and mechanisms of existing TRPV6 inhibitors to provide new ideas and directions for the development of novel TRPV6 inhibitors.

Molecular pharmacology of the onco-TRP channel TRPV6

TRPV6, a representative of the vanilloid subfamily of TRP channels, serves as the principal calcium uptake channel in the gut. Dysregulation of TRPV6 results in disturbed calcium homeostasis leading to a variety of human diseases, including many forms of cancer. Inhibitors of this oncochannel are therefore particularly needed. In this review, we provide an overview of recent advances in structural pharmacology that uncovered the molecular mechanisms of TRPV6 inhibition by a variety of small molecules, including synthetic and natural, plant-derived compounds as well as some prospective and clinically approved drugs.

Design and synthesis of ruthenium complexes and their studies on the inhibition of amyloid β (1-42) peptide aggregation

Misfolding and protein aggregation have been linked to numerous human neurodegenerative disorders such as Alzheimer's, prions, and Parkinson's. Due to their interesting photophysical properties, ruthenium (Ru) complexes have received considerable attention in studying protein aggregation. In this study, we synthesized the novel Ru complexes ([Ru(p-cymene)Cl(L-1)][PF₆](Ru-1), and [Ru(p-cymene)Cl(L-2)][PF₆](Ru-2)) and investigated their inhibitory activity against the bovine serum albumin (BSA) aggregation and the Aβ_1-42 peptides amyloid formation. Several spectroscopic methods were used to characterize the complexes, and the molecular structure was determined by X-ray crystallography. Amyloid aggregation and inhibition activity were examined using the Thioflavin-T (ThT) assay, and secondary structures were analyzed by circular dichroism (CD) spectroscopy and transmission electron microscopy (TEM). The cell viability assay was carried out on the neuroblastoma cell line, revealing that the Ru-2 complex showed better protective effects against Aβ_1-42 peptide toxicity on neuro-2a cells than the Ru-1 complex. Molecular docking studies elucidate binding sites and interactions between the Ru-complexes and the Aβ_1-42 fibrils. The experimental studies revealed that these complexes significantly inhibited BSA aggregation and Aβ_1-42 amyloid fibril formation at 1:3 and 1:1 equimolar concentrations, respectively. Antioxidant assays demonstrated that these complexes act as antioxidants, protecting from amyloid-induced oxidative stress. Molecular docking studies with the monomeric Aβ_1-42 (PDB: 1IYT) show hydrophobic interaction, and both complexes bind preferably in the central region of the peptide and coordinate with two binding sites of the peptide. Hence, we suggest that the Ru-based complexes could be applied as a potential agent in metallopharmaceutical research against Alzheimer's disease.

Biological Activities of Ruthenium NHC Complexes: An Update

Ruthenium N-heterocyclic carbene (NHC) complexes have unique physico-chemical properties as catalysts and a huge potential in medicinal chemistry and pharmacology, exhibiting a variety of notable biological activities. In this review, the most recent studies on ruthenium NHC complexes are summarized, focusing specifically on antimicrobial and antiproliferative activities. Ruthenium NHC complexes are generally active against Gram-positive bacteria, such as Bacillus subtilis, Staphylococcus aureus, Micrococcus luteus, Listeria monocytogenes and are seldom active against Gram-negative bacteria, including Salmonella typhimurium, Pseudomonas aeruginosa and Escherichia coli and fungal strains of Candida albicans. The antiproliferative activity was tested against cancer cell lines of human colon, breast, cervix, epidermis, liver and rat glioblastoma cell lines. Ruthenium NHC complexes generally demonstrated cytotoxicity higher than standard anticancer drugs. Further studies are needed to explore the mechanism of action of these interesting compounds.

Selectively inhibiting malignant melanoma migration and invasion in an engineered skin model using actin-targeting dinuclear RuII-complexes

Due to the poor prognosis of metastatic cancers, there is a clinical need for agents with anti-metastatic activity. Here we report on the anti-metastatic effect of a previously reported Ru(ii) complex [{(phen)₂Ru}₂(tpphz)]⁴⁺, 1⁴⁺, that has recently been shown to disrupt actin fiber assembly. In this study, we investigated the anti-migratory effect of ⁺1⁴⁺ and a close structural analogue⁺, 2⁴⁺, on two highly invasive, metastatic human melanoma cell lines. Laser scanning confocal imaging was used to investigate the structure of actin filament and adhesion molecule vinculin and results show disassembly of central actin filaments and focal adhesions. The effect of both compounds on actin filaments was also found to be reversible. As these results revealed that the complexes were cytostatic and produced a significant inhibitory effect on the migration of both melanoma cell lines but not human dermal fibroblasts their effect on 3D-spheroids and a tissue-engineered living skin model were also investigated. These experiments demonstrated that the compounds inhibited the growth and invasiveness of the melanoma-based spheroidal tumor model and both complexes were found to penetrate the epidermis of the skin tissue model and inhibit the invasion of melanoma cells. Taken together, the cytostatic and antimigratory effects of the complexes results in an antimetastatic effect that totally prevent invasion of malignant melanoma into skin tissue.

Metal Complexes as Promising Matrix Metalloproteinases Regulators

Nowadays, cancers and dementia, such as Alzheimer's disease, are the most fatal causes of death. Many studies tried to understand the pathogenesis of those diseases clearly and develop a promising way to treat the diseases. Matrix metalloproteinases (MMPs) have been reported to be involved in the pathology of cancers and AD through tumor cell movement and amyloid degradation. Therefore, control of the levels and actions of MMPs, especially MMP-2 and MMP-9, is necessary to care for and/or cure cancer and AD. Various molecules have been examined for their potential application as regulators of MMPs expression and activity. Among the molecules, multiple metal complexes have shown advantages, including simple synthesis, less toxicity and specificity toward MMPs in cancer cells or in the brain. In this review, we summarize the recent studies and knowledge of metal complexes (e.g., Pt-, Ru-, Au-, Fe-, Cu-, Ni-, Zn-, and Sn-complexes) targeting MMPs and their potentials for treating and/or caring the most fatal human diseases, cancers and AD.

Insights of metal 8-hydroxylquinolinol complexes as the potential anticancer drugs

8-Hydroxyquinoline and its derivatives, which belong to a well-known class of quinoline based drugs with varied biological activities, have been extensively explored for the treatments of cancer, Alzheimer's disease, neurodegenerative diseases and other life-threatening diseases. In virtue of the existence of bicyclic heterocyclic scaffold, their bidentate chelators can further bind to metal ions via O- and N-donors from 8-hydroxylquinolinol skeletons to yield a variety of metal 8-hydroxylquinolinol complexes appealing as the anticancer drugs with low toxicity, due to their better biological effects and higher anticancer activities than free 8-hydroxylquinolinol ligands and cis-diammine-dichloro-platinum. The present review summarizes the recent developments in the syntheses, crystal structures, and anticancer activities of metal 8-hydroxylquinolinol complexes, attempting to discover a correlation between their structures and anticancer activities, and to provide an evidence for their potential application perspectives. It means to offer the helpful and meaningful guidance for the researchers in the future syntheses of new and highly efficient anticancer metal 8-hydroxylquinolinol complexes based drugs.

Synthesis, Crystallographic Structure, Theoretical Analysis, Molecular Docking Studies, and Biological Activity Evaluation of Binuclear Ru(II)-1-Naphthylhydrazine Complex

Ruthenium(II)-arene complexes have gained significant research interest due to their possible application in cancer therapy. In this contribution two new complexes are described, namely [{RuCl(η⁶-p-cymene)}₂(μ-Cl)(μ-1-N,N'-naphthyl)]X (X = Cl, 1; PF₆, 2), which were fully characterized by IR, NMR, and elemental microanalysis. Furthermore, the structure of 2 in the solid state was determined by a single crystal X-ray crystallographic study, confirming the composition of the crystals as 2·2MeOH. The Hirshfeld surface analysis was employed for the investigation of interactions that govern the crystal structure of 2·2MeOH. The structural data for 2 out of 2·2MeOH was used for the theoretical analysis of the cationic part [{RuCl(η⁶-p-cymene)}₂(μ-Cl)(μ-1-N,N'-naphthyl)]⁺ (2a) which is common to both 1 and 2. The density functional theory, at B3LYP/6-31+G(d,p) basis set for H, C, N, and Cl atoms and LanL2DZ for Ru ions, was used for the optimization of the 2a structure. The natural bond orbital and quantum theory of atoms in molecules analyses were employed to quantify the intramolecular interactions. The reproduction of experimental IR and NMR spectra proved the applicability of the chosen level of theory. The binding of 1 to bovine serum albumin was examined by spectrofluorimetry and molecular docking, with complementary results obtained. Compound 1 acted as a radical scavenger towards DPPH^• and HO^• radicals, along with high activity towards cancer prostate and colon cell lines.

A Lock‐and‐Kill Anticancer Photoactivated Chemotherapy Agent †

Photosubstitutionally active ruthenium complexes show high potential as prodrugs for the photoactivated chemotherapy (PACT) treatment of tumors. One of the problems in PACT is that the localization of the ruthenium compound is hard to trace. Here, a ruthenium PACT prodrug, [Ru(3)(biq)(STF-31)](PF₆ )₂ (where 3 = 3-(([2,2':6',2″-ter- pyridin]-4'-yloxy)propyl-4-(pyren-1-yl)butanoate) and biq = 2,2'-biquinoline), has been prepared, in which a pyrene tracker is attached via an ester bond. The proximity between the fluorophore and the ruthenium center leads to fluorescence quenching. Upon intracellular hydrolysis of the ester linkage, however, the fluorescence of the pyrene moiety is recovered, thus demonstrating prodrug cellular uptake. Further light irradiation of this molecule liberates by photosubstitution STF-31, a known cytotoxic nicotinamide phosphoribosyltransferase (NAMPT) inhibitor, as well as singlet oxygen via excitation of the free pyrene chromophore. The dark and light cytotoxicity of the prodrug, embedded in liposomes, as well as the appearance of blue emission upon uptake, were evaluated in A375 human skin melanoma cells. The cytotoxicity of the liposome-embedded prodrug was indeed increased by light irradiation. This work realizes an in vitro proof-of-concept of the lock-and-kill principle, which may ultimately be used to design strategies aimed at knowing where and when light irradiation should be realized in vivo.

Ru(II) CONTAINING PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY: A CRITIQUE ON REPORTING AND AN ATTEMPT TO COMPARE EFFICACY

Ruthenium(II)-based coordination complexes have emerged as photosensitizers (PSs) for photodynamic therapy (PDT) in oncology as well as antimicrobial indications and have great potential. Their modular architectures that integrate multiple ligands can be exploited to tune cellular uptake and subcellular targeting, solubility, light absorption, and other photophysical properties. A wide range of Ru(II) containing compounds have been reported as PSs for PDT or as photochemotherapy (PCT) agents. Many studies employ a common scaffold that is subject to systematic variation in one or two ligands to elucidate the impact of these modifications on the photophysical and photobiological performance. Studies that probe the excited state energies and dynamics within these molecules are of fundamental interest and are used to design next-generation systems. However, a comparison of the PDT efficacy between Ru(II) containing PSs and 1st or 2nd generation PSs, already in clinical use or preclinical/clinical studies, is rare. Even comparisons between Ru(II) containing molecular structures are difficult, given the wide range of excitation wavelengths, power densities, and cell lines utilized. Despite this gap, PDT dose metrics quantifying a PS's efficacy are available to perform qualitative comparisons. Such models are independent of excitation wavelength and are based on common outcome parameters, such as the photon density absorbed by the Ru(II) compound to cause 50% cell kill (LD50) based on the previously established threshold model. In this focused photophysical review, we identified all published studies on Ru(II) containing PSs since 2005 that reported the required photophysical, light treatment, and in vitro outcome data to permit the application of the Photodynamic Threshold Model to quantify their potential efficacy. The resulting LD50 values range from less than 1013 to above 1020 [hν cm-3], indicating a wide range in PDT efficacy and required optical energy density for ultimate clinical translation.

In-vitro anticancer profile of recent ruthenium complexes against liver cancer

Ruthenium complexes are considered as the most favorable alternatives to traditional platinum-based cancer drugs owing to their acceptable toxicity level, selectivity, variant oxidation states and ability to treat platinum-resistant cancer cells. They have similar ligand exchange kinetics as platinum drugs but can be tailored according to our desire by ligands influence. In the current study, we illustrate the in-vitro anticancer profile of some ruthenium complexes (2016–2021) against human hepatocellular carcinoma (HepG2). The anticancer activity of ruthenium complexes is determined by comparing their IC50 values with one another and positive controls. Fortunately, some ruthenium complexes including 3, 4, 6, 14, 15, 20, 42, and 48 exhibit surpassed in-vitro anticancer profile than that of positive controls promising as potential candidates against liver cancer. We also explored the structure-activity relationship (SAR) which is a key factor in the rational designing and synthesis of new ruthenium drugs. It covers the factors affecting anticancer activity including lipophilicity, planarity, area and bulkiness, the steric influence of different ligands, and electronic effects induced by ligands, stability, aqueous solubility and bioavailability to the target sites. The data reported here will provide strong support in the plausible design and synthesis of ruthenium anticancer drugs in the upcoming days.

Binuclear Heteroleptic Ru(III) Dithiocarbamate Complexes: A Step towards Tunable Antiproliferative Agents

Binuclear dithiocarbamate complexes of Ru(III) are promising candidates in the search for outstanding metal-based anticancer agents. While different dithiocarbamates have shown ligand-dependent cytotoxicity in homoleptic binuclear Ru(III) complexes, the properties of heteroleptic analogues with different dithiocarbamate (DTC) ligands have yet to be explored. We herein propose the introduction of heteroleptic ligands as tunable features for the development of improved ruthenium-based antiproliferative agents and report a synthetic strategy for their synthesis as well as the evaluation of the cytotoxic activity of a selection of binuclear heteroleptic Ru(III) compounds towards MDA-MB-231 and PC3 cells.

Systematic Study on the Cytotoxic Potency of Commonly Used Dimeric Metal Precursors in Human Cancer Cell Lines

The cytotoxicities of seven dimeric metal species of the general formula [M(arene)Cl₂]₂, commonly used as precursors for complex synthesis and deemed biologically inactive, are investigated in seven commonly employed human cancer cell lines. Four of these complexes featured a ruthenium(II) core, where p‐cymene, toluene, benzene and indane were used as arenes. Furthermore, the osmium(II) p‐cymene dimer, as well as the Cp* dimers of rhodium(III) and its heavier analogue iridium(III) were included in this work (Cp*=1,2,3,4,5‐pentamethylcyclopentadienide). While the cytotoxic potencies of the ruthenium(II) and osmium(II) dimers are very low (or not even detectable at applicable concentrations), surprising activity, especially in cells from ovarian malignancies (with one or two‐digit micromolar IC₅₀ values), have been found for the rhodium(III) and iridium(III) representatives. This publication is aimed at all researchers using synthetic procedures based on functionalization of these dimeric starting materials to rationalize changes in biological properties, especially cytotoxicity in cancer cells.

The Polysite Pharmacology of TREK K2P Channels

K_2P (KCNK) potassium channels form "background" or "leak" currents that have critical roles in cell excitability control in the brain, cardiovascular system, and somatosensory neurons. Similar to many ion channel families, studies of K_2Ps have been limited by poor pharmacology. Of six K_2P subfamilies, the thermo- and mechanosensitive TREK subfamily comprising K_2P2.1 (TREK-1), K_2P4.1 (TRAAK), and K_2P10.1 (TREK-2) are the first to have structures determined for each subfamily member. These structural studies have revealed key architectural features that underlie K_2P function and have uncovered sites residing at every level of the channel structure with respect to the membrane where small molecules or lipids can control channel function. This polysite pharmacology within a relatively small (~70 kDa) ion channel comprises four structurally defined modulator binding sites that occur above (Keystone inhibitor site), at the level of (K_2P modulator pocket), and below (Fenestration and Modulatory lipid sites) the C-type selectivity filter gate that is at the heart of K_2P function. Uncovering this rich structural landscape provides the framework for understanding and developing subtype-selective modulators to probe K_2P function that may provide leads for drugs for anesthesia, pain, arrhythmia, ischemia, and migraine.

DNA binding, antitubercular, antibacterial and anticancer studies of newly designed piano-stool ruthenium(ii) complexes

The chemotherapeutic potential of ruthenium(ii) complexes as DNA binding, antitubercular, antibacterial, and anticancer agents.

Ru(II)-Based Acetylacetonate Complexes Induce Apoptosis Selectively in Cancer Cells

The synthesis, chemical and biological characterization of seven Ru(II) polypyridyl complexes containing acetylacetonate (acac) ligands are reported. Electronic absorption spectra were determined and electrochemical potentials consistent with Ru(III/II) couples ranging from +0.60 to +0.73 V vs Ag/AgCl were measured. A series of complexes were screened against MDA-MB-231, DU-145, and MCF-10A cell lines to evaluate their cytotoxicities in cancer and normal cell lines. Although most complexes were either nontoxic or equipotent in cancer cells and normal cell lines, compound 1, [Ru(dpqy)(acac)(py)](PF6), where dqpy is 2,6-di(quinolin-2-yl)pyridine, showed up to 2.5:1.0 selectivity for cancer as compared to normal cells, along with nanomolar EC50 values in MDA-MB-231 cells. Lipophilicity, determined as the octanol/water partition coefficient, log Po/w, ranged from -0.33 (0.06) to 1.15 (0.10) for the complexes. Although cytotoxicity was not correlated with electrochemical potentials, a moderate linear correlation between lipophilicity and toxicities was observed. Cell death mechanism studies indicated that several of the Ru-acac compounds, including 1, induce apoptosis in MDA-MB-231 cells.

Synthesis, characterisation and biological activity of the ruthenium(II) complexes of the N4-tetradentate (N4-TL), 1,6-di(2'-pyridyl)-2,5-dibenzyl-2,5-diazahexane (picenBz2)

A series of complexes of the type rac-cis-β-[Ru(N₄-T_L)(N₂-bidentates)]²⁺ (where N₄-T_L = 1,6-di(2'-pyridyl)-2,5-dibenzyl-2,5-diazahexane (picenBz₂, N₄-T_L-2) and N₂-bidentates = 1,10-phenanthroline (phen, Ru-2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, Ru-3), 7,8-dimethyl-dipyrido[3,2-a:2',3'-c] phenazine (dppzMe_2,Ru-4), 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (phenpyrBz, Ru-5), 2-(p-tolyl)-1H-imidazo[4,5-f][1,10]phenanthroline (phenpyrBzMe, Ru-6), 2-(4-nitrophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (phenpyrBzNO_2,Ru-7), were synthesised and characterised and X-ray crystallography of Ru-5 obtained. The in vitro cytotoxicity assays revealed that Ru-6 was 5, 2 and 19-fold more potent than oxaliplatin, cisplatin, and carboplatin, respectively displaying an average GI₅₀ value of ≈ 0.76 μM against a panel of 11 cancer cell lines.

Structural mechanisms of TRPV6 inhibition by ruthenium red and econazole

TRPV6 is a calcium-selective ion channel implicated in epithelial Ca²⁺ uptake. TRPV6 inhibitors are needed for the treatment of a broad range of diseases associated with disturbed calcium homeostasis, including cancers. Here we combine cryo-EM, calcium imaging, and mutagenesis to explore molecular bases of human TRPV6 inhibition by the antifungal drug econazole and the universal ion channel blocker ruthenium red (RR). Econazole binds to an allosteric site at the channel’s periphery, where it replaces a lipid. In contrast, RR inhibits TRPV6 by binding in the middle of the ion channel’s selectivity filter and plugging its pore like a bottle cork. Despite different binding site locations, both inhibitors induce similar conformational changes in the channel resulting in closure of the gate formed by S6 helices bundle crossing. The uncovered molecular mechanisms of TRPV6 inhibition can guide the design of a new generation of clinically useful inhibitors.

TRPV6 is a calcium-selective ion channel that is involved in numerous calcium-dependent physiological processes and it is of interest as a potential drug target. Here, the authors present the cryo-EM structures of human TRPV6 with the bound inhibitors ruthenium red and the antifungal drug econazole and discuss their inhibition mechanisms.

Anticancer Activity of Half-Sandwich Ru, Rh and Ir Complexes with Chrysin Derived Ligands: Strong Effect of the Side Chain in the Ligand and Influence of the Metal

An important challenge in the field of anticancer chemotherapy is the search for new species to overcome the resistance of standard drugs. An interesting approach is to link bioactive ligands to metal fragments. In this work, we have synthesized a set of p-cymene-Ru or cyclopentadienyl-M (M = Rh, Ir) complexes with four chrysin-derived pro-ligands with different -OR substituents at position 7 of ring A. The introduction of a piperidine ring on chrysin led to the highly cytotoxic pro-ligand HL4 and its metal complexes L4-M (SW480 and A549 cell lines, cytotoxic order: L4-Ir > L4-Ru ≈ L4-Rh). HL4 and its complexes induce apoptosis and can overcome cis-platinum resistance. However, HL4 turns out to be more cytotoxic in healthy than in tumor cells in contrast to its metal complexes which displayed higher selectivity than cisplatin towards cancer cells. All L4-M complexes interact with double stranded DNA. Nonetheless, the influence of the metal is clear because only complex L4-Ir causes DNA cleavage, through the generation of highly reactive oxygen species (1O2). This result supports the hypothesis of a potential dual mechanism consisting of two different chemical pathways: DNA binding and ROS generation. This behavior provides this complex with a great effectivity in terms of cytotoxicity.

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.

Ruthenium(II) and Platinum(II) Complexes with Biologically Active Aminoflavone Ligands Exhibit In Vitro Anticancer Activity

Continuing our studies on the mechanisms underlying the cytotoxicity of potential drugs, we have described several aspects of the in vitro anticancer activity of ruthenium(II) and platinum(II) complexes with bioactive, synthetic aminoflavone ligands. We examined the mechanism of proapoptotic activity of cis-dichlorobis(3-imino-2-methoxyflavanone)ruthenium(II), cis-dichlorobis(3-imino-2-ethoxyflavanone)ruthenium(II), and trans-dichlorobis(3-aminoflavone)platinum(II). Cisplatin was used as a reference compound. The cytotoxicity was investigated by MTT assay. The mechanism of proapoptotic activity of the tested compounds was investigated by evaluation of caspase-8 activity, cytometric analysis of annexin-V positive cells, and mitochondrial potential loss measurement. The results showed that ruthenium compounds break partially or completely the cisplatin resistance by activating the caspase 8-dependent apoptosis pathway and loss of mitochondrial membrane potential. Platinum compounds also have a cytostatic effect, but their action requires more exposure time. Potential mechanisms underlying drug resistance in the two pairs of cancer cell lines were investigated: total glutathione content, P-glycoprotein activity, and differences in the activity of DNA repair induced by nucleotide excision. Results showed that cisplatin-resistant cells have elevated glutathione levels relative to sensitive cells. Moreover, they indicated the mechanisms enabling cells to avoid apoptosis caused by DNA damage. Pg-P activity has no effect on the development of cisplatin resistance in the cell lines described.

Organometallic dendrimers based on Ruthenium(II) N-heterocyclic carbenes and their implication as delivery systems of anticancer small interfering RNA

With the purpose of obtaining a new dendritic system against cancer, this paper is focused on the synthesis of spherical carbosilane metallodendrimers of different generations holding Ru(II) N-heterocyclic carbene (NHC) on the periphery from the imidazolium precursors. Both imidazolium salt dendrimers and their metallodendrimers counterparts showed promising anticancer activity, similar to cisplatin, mainly at high generations. In addition, both families of second and third generations were able to form dendriplexes with anticancer small interfering RNA (siRNA), protecting the cargo against RNAse and being able to internalize it in HEPG2 (human liver cancer) tumour cells. The characterization and effectiveness of the dendriplexes were evaluated by various analytical techniques such as zeta potential, electrophoresis and circular dichroism, the stability of the system and the protective nature of the dendrimer estimated using RNAse and the internalization of dendriplexes by confocal microscopy. The major advantage observed with the ruthenium metallodendrimers with respect to the imidazolium salts precursors was in cellular uptake, where the internalization of Mcl-1-FITC siRNA (myeloid cell leukaemia-1 fluorescein labelled siRNA) proceeded more efficiently. Therefore, we propose here that both imidazolium and Ru metallodendrimers are interesting candidates in cancer due to their double action, as anticancer per se and as carrier for anticancer siRNA, providing in this way a combined action.

In situ methanolic solvent synthesis, spectroscopic and thermogravimetric characterizations of three new transition metal complexes of trimethoprim drug

Trimethoprim drug (TMP) complexes of copper (II), cobalt (II), and nickel (II) were prepared and discussed by using elemental analysis (C, H, N analysis), magnetic, molar conductance, FTIR, Raman spectroscopy, electron spin resonance (ESR) and UV-vis spectroscopy analyses. TMP drug coordinated as a tridentate ligand towards the respected three metal ions through two nitrogen atoms of amino groups and nitrogen atom of pyrimidine ring which flanked between –NH2 groups, these assignments confirmed by spectroscopic, magnetic, ESR and thermogravimetric analyses with formulas [Cu(TMP)(H2O)3]Cl2, [Co(TMP)(H2O)3]Cl2 and [Ni(TMP) (H2O)]Cl2. Copper (II) and cobalt (II) complexes have an octahedral geometrical structure included one TMP molecule, three coordinated water molecules and two uncoordinated chlorine atoms while, nickel(II)–TMP complex has a tetrahedral geometric configuration that involved one TMP molecule, one coordinated water molecule and two uncoordinated chlorine atoms. The activation energies and other kinetic thermodynamic parameters were estimated based on the employed of the Coats-Redfern and Horowitz-Metzger equations. The nano–structured form of the synthesized TMP complexes was confirmed dependent on the transmission electron microscopy (TEM).

Ruthenium-based Photoactive Metalloantibiotics†

Antibiotic resistance is one of the world's most urgent public health problems. Antimicrobial photodynamic therapy (aPDT) is a promising therapy to combat the growing threat of antibiotic resistance. The aPDT combines a photosensitizer and light to generate reactive oxygen species to induce bacterial inactivation. Ruthenium polypyridyl complexes are significant because they possess unique photophysical properties that allow them to produce reactive oxygen species upon photoirradiation, which leads to cytotoxicity. These antimicrobial agents cause bacterial cell death by DNA and cytoplasmic membrane damage. This article presents a comprehensive review of photoactive antimicrobial properties of kinetically inert and labile ruthenium complexes, nanoparticles coupled photoactive ruthenium complexes, and photoactive ruthenium nanoparticles. Additionally, limitations of current ruthenium-based photoactive antimicrobial agents and future directions for the development of antibiotic-resistant photoactive antimicrobial agents are discussed. It is important to raise awareness for the ruthenium-based aPDT agents in order to develop a new class of photoactive metalloantibiotics capable of combating antibiotic resistance.

Structural Insights into the Mechanisms and Pharmacology of K2P Potassium Channels

Leak currents, defined as voltage and time independent flows of ions across cell membranes, are central to cellular electrical excitability control. The K_2P (KCNK) potassium channel class comprises an ion channel family that produces potassium leak currents that oppose excitation and stabilize the resting membrane potential in cells in the brain, cardiovascular system, immune system, and sensory organs. Due to their widespread tissue distribution, K_2Ps contribute to many physiological and pathophysiological processes including anesthesia, pain, arrythmias, ischemia, hypertension, migraine, intraocular pressure regulation, and lung injury responses. Structural studies of six homomeric K_2Ps have established the basic architecture of this channel family, revealed key moving parts involved in K_2P function, uncovered the importance of asymmetric pinching and dilation motions in the K_2P selectivity filter (SF) C-type gate, and defined two K_2P structural classes based on the absence or presence of an intracellular gate. Further, a series of structures characterizing K_2P:modulator interactions have revealed a striking polysite pharmacology housed within a relatively modestly sized (~70 kDa) channel. Binding sites for small molecules or lipids that control channel function are found at every layer of the channel structure, starting from its extracellular side through the portion that interacts with the membrane bilayer inner leaflet. This framework provides the basis for understanding how gating cues sensed by different channel parts control function and how small molecules and lipids modulate K_2P activity. Such knowledge should catalyze development of new K_2P modulators to probe function and treat a wide range of disorders.

Ruthenium (II)/allopurinol complex inhibits breast cancer progression via multiple targets

Metal complexes based on ruthenium have established excellent activity with less toxicity and great selectivity for tumor cells. This study aims to assess the anticancer potential of ruthenium(II)/allopurinol complexes called [RuCl₂(allo)₂(PPh₃)₂] (1) and [RuCl₂(allo)₂(dppb)] (2), where allo means allopurinol, PPh₃ is triphenylphosphine and dppb, 1,4-bis(diphenylphosphino)butane. The complexes were synthesized and characterized by elemental analysis, IR, UV-Vis and NMR spectroscopies, cyclic voltammetry, molar conductance measurements, as well as the X-ray crystallographic analysis of complex 2. The antitumor effects of compounds were determined by cytotoxic activity and cellular and molecular responses to cell death mechanisms. Complex 2 showed good antitumor profile prospects because in addition to its cytotoxicity, it causes cell cycle arrest, induction of DNA damage, morphological and biochemical alterations in the cells. Moreover, complex 2 induces cell death by p53-mediated apoptosis, caspase activation, increased Beclin-1 levels and decreased ROS levels. Therefore, complex 2 can be considered a suitable compound in antitumor treatment due to its cytotoxic mechanism.

Understanding of [RuL(ONO)]n+ acting as nitric oxide precursor, a theoretical study of ruthenium complexes of 1,4,8,11-tetraazacyclo- tetradecane having different substituents: How spin multiplicity influences bond angle and bond lengths (Ru-O-NO) in releasing of NO

Generation of nitric oxide has been a great interest in cell biology as it involves a wide range of physiological functions including the blood pressure control; thus the exploitation of ruthenium chemistry has been motivated in biochemical and clinical points of view. Herein, the structural and electronic properties of ruthenium(II) complexes of 1,4,8,11-tetraazacyclotetradecane containing pyridyl, imidazole and benzimidazole (L¹, L², L³) were analyzed theoretically in the context of how spin multiplicity plays a crucial role influencing the NO release from the LRu-ONO moiety. The results show that β-cleavage of nitrito in the complex motivates the release of NO as it depends highly on total spin multiplicity of metal ion altering significantly the geometrical parameters; particularly, a decrease of bond length of Ru-ONO is highly associated with an increase of RuO-NO bond distance that correlates with the decrease of the Ru-O-NO bond angle ultimately leading to the release of NO; apparently, the bending nature of Ru-O-NO defines its release from the complex. This is consistent with orbital energy (d_x²-_y²) where the stabilization of axial Ru-O bond in the complex was observed, and proved by molecular orbital studies. In the excitation of the complex (singlet to triplet or singlet to quintet), the NO release has been facilitated, agreeing with the Gibbs free energy data where a lower energy for NO release was obtained compared to other types of excitations. In the calculated electronic spectra, a visible broad band with relatively high intensity for [RuL¹ONO]⁺ was observed, agreeing approximately with reported experimental results.

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.

Electronic structure and mechanism for the uptake of nitric oxide by the Ru(iii) antitumor complex NAMI-A

Nitric oxide (NO) has well known vasodilation effects in living organisms and its participation in the metastasis of cancer cells through the angiogenesis process has been demonstrated experimentally. Therefore, the uptake of NO has become one focus of investigation to produce anti-metastatic drugs. In this article we have investigated the uptake of NO by the ruthenium based metallodrug trans-tetrachloride(dimethylsulfoxide)imidazole ruthenate(iii) [Im]trans-[RuCl4(Im)(DMSO)], known as New Anti-tumor Metastasis Inhibitor-A (NAMI-A). Electronic structure calculations using Density Functional Theory, DFT, and State-Averaged Complete Active Space Self Consistent Field, SA-CASSCF, with second order perturbation theory corrections, NEVPT2 were carried out to investigate the mechanism involved in the uptake of NO by the Ru-based anticancer metallodrug NAMI-A. The calculations revealed that the reaction takes place at the triplet potential energy surface, with the singlet surface being ∼15 kcal mol-1 shifted to higher energies, and there is a surface crossing to form the most stable singlet product after the reaction takes place at the triplet surface. The spin pairing and electron transfer from the nitric oxide to the metallic fragment takes place at the region of the minimum energy crossing point between the two surfaces. The Ru-NO bond in the {Ru-NO}6 product has ∼10% of the RuIII-NO0 character. The SA-CASSCF/NEVPT2 calculations revealed that the uptake of NO by NAMI-A has a small energy barrier of ∼8 kcal mol-1 and, therefore a rate constant of 11.3 × 106 s-1 at 300 K. In addition, the reaction is thermodynamically favorable, with a Gibbs free energy of ∼30 kcal mol-1. These results show that the uptake of nitric oxide by the NAMI-A complex is kinetically and thermodynamically feasible in biological medium and, therefore, gives support to the anti-angiogenesis theory associated to the mode of action of NAMI-A and other related compounds.

A New Piano-Stool Ruthenium(II) P-Cymene-Based Complex: Crystallographic, Hirshfeld Surface, DFT, and Luminescent Studies

A new complex (Ru(η6-p-cymene)(5-ASA)Cl2) (1) where 5-ASA is 5-aminosalicylic acid has been prepared by reacting the ruthenium arene precursors ((η6-arene)Ru(μ-Cl)Cl)2, with the 5-ASA ligands in a 1:1 ratio. Full characterization of complex 1 was accomplished by elemental analysis, IR, and TGA following the structure obtained from a single-crystal X-ray pattern. The structural analysis revealed that complex 1 shows a “piano-stool” geometry with Ru-C (2.160(5)- 2.208(5)Å), Ru-N (2.159(4) Å) distances, which is similar to equivalents sister complex. Density functional theory (DFT) was used to calculate the significant molecular orbital energy levels, binding energies, bond angles, bond lengths, and spectral data (FTIR, NMR, and UV–VIS) of complex 1, consistent with the experimental results. The IR and UV–VIS spectra of complex 1 were computed using all of the methods and choose the most appropriate way to discuss. Hirshfeld surface analysis was also executed to understand the role of weak interactions such as H⋯H, C⋯H, C-H⋯π, and vdW interactions, which play a significant role in the crystal environment’s stability. Moreover, the luminescence results at room temperature show that complex 1 gives a more intense emission band positioned at 465 nm upon excitation at 330 nm makes it a suitable candidate for the building of photoluminescent material.

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

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

New Tailored RNA-Targeted Organometallic Drug Candidates against Huh7 (Liver) and Du145 (Prostate) Cancer Cell Lines

New organometallic drug candidates [Ph2Sn(HL)], 1, and [Ru(η6--p-cymene)(HL)Cl], 2, were designed and synthesized by in situ reaction of a Schiff base ligand (HL) and diphenyltin dichloride and [RuCl2(p-cymene)]2, respectively. The drug candidates 1 and 2 have been characterized by spectroscopic methods (Fourier-transform infrared spectroscopy, UV-vis, and 1H/13C NMR), elemental analysis, and single X-ray crystallographic studies (in case of 1). The ground-state geometry optimization of 1 and 2 was performed by density functional theory calculations. The interaction of 1 and 2 with tRNA was assessed by absorption spectroscopy, cyclic voltammetry, circular dichroism, and ethidium bromide displacement assay using fluorescence emission spectroscopy to determine their potential to act as antitumor agents. The cytotoxicity of 1 and 2 was screened against human liver carcinoma (Huh7), prostate cancer (Du145), and the normal prostate cell line (PNT 2). The results implicated a dose-dependent growth inhibition of the two cancer cells at concentrations (2.5-15 μM) of 1 and 2 with the treatment after 48 h. Interestingly, 1 revealed good selective activity toward the liver cancer cell line (Huh7). Furthermore, both the drug candidates 1 and 2 were found to be nontoxic toward the PNT 2 normal cell line. These studies lay a paradigm for rational efficacious drug design for chemotherapeutic intervention in cancers using new tailored organometallic drug entities; organotin(IV) and organoruthenium(II) have been demonstrated to be viable for the safe administration and specific targeted drug uptake by the resistant cancerous cell lines at low intracellular concentrations.

Polynuclear Ruthenium Amines Inhibit K2P Channels via a "Finger in the Dam" Mechanism

The trinuclear ruthenium amine ruthenium red (RuR) inhibits diverse ion channels, including K2P potassium channels, TRPs, the calcium uniporter, CALHMs, ryanodine receptors, and Piezos. Despite this extraordinary array, there is limited information for how RuR engages targets. Here, using X-ray crystallographic and electrophysiological studies of an RuR-sensitive K2P, K2P2.1 (TREK-1) I110D, we show that RuR acts by binding an acidic residue pair comprising the "Keystone inhibitor site" under the K2P CAP domain archway above the channel pore. We further establish that Ru360, a dinuclear ruthenium amine not known to affect K2Ps, inhibits RuR-sensitive K2Ps using the same mechanism. Structural knowledge enabled a generalizable design strategy for creating K2P RuR "super-responders" having nanomolar sensitivity. Together, the data define a "finger in the dam" inhibition mechanism acting at a novel K2P inhibitor binding site. These findings highlight the polysite nature of K2P pharmacology and provide a new framework for K2P inhibitor development.

Tracking the role of trans-ligands in ruthenium–NO bond lability: computational insight

Ruthenium–NO tetraamine structures control the nitric oxide bioavailability. The ligand trans to NO modulates the Ru–NO bond stability.

Antiproliferative and proapoptotic activity of molecular copper(II) complex of N-1-tosylcytosine

In an attempt to enhance the previously observed antiproliferative capacity of 1-(p-toluenesulfonyl)cytosine (N-1-tosylcytosine, ligand 1), its copper(II) complex (Cu(1-TsC-N3)₂Cl₂, complex 2) was prepared and tested in vitro on various carcinoma and leukemia cells. The comparative in vitro studies using the ligand 1, the complex 2, CuCl₂x2H₂O salt (salt 3) and the 1:2 mixture of the salt 3 and ligand 1 (mixture 4) were performed on normal (WI38), human carcinoma (HeLa, CaCo2, MiaPaCa2, SW620), lymphoma (Raji) and leukemia (K562) cell lines. Significantly elevated concentration of the intracellular copper after treatment of K562 cells and HeLa cells during 2h with complex 2 (7.83 vs. 5.4 times) was detected by atomic absorption spectroscopy. Cytotoxicity was analyzed by MTT assay. We found that antiproliferative capacity of the tested compounds varies (IC₅₀ after 72h of exposure: 0.6×10^-6M to>100×10^-6M). Leukemia and lymphoma cells were found the most sensitive to complex 2 which showed more than 100 times higher in vitro activity against K562 cells than ligand 1. Apoptotic morphological changes, an externalization of phosphatydilserine, and changes in the mitochondrial membrane potential of treated cells were found. The caspase-3 activity in HeLa and K562 cells was measured by caspase-3 colorimetric assay kit. Caspase-3 was not activated in the treated K562 cells while salt 3 and the mixture 4 in the HeLa cells significantly increased tested enzyme activity. These findings suggest that copper(II) in the molecular complex 2 by improving entry of the N-1-tosylcytosine 1 into cells increases its antiproliferative capacity. In summary, the present study demonstrated that complex 2 possesses an antileukemic effect on K562 cells, and its anticancer activity was attributed with induction of apoptosis. The exact mechanism of apoptosis induction by complex 2 must be further investigated.