An Overview of the Potential Medicinal and Pharmaceutical Properties of Ru(II)/(III) Complexes

This review examines the existing knowledge about Ru(II)/(III) ion complexes with a potential application in medicine or pharmacy, which may offer greater potential in cancer chemotherapy than Pt(II) complexes, which are known to cause many side effects. Hence, much attention has been paid to research on cancer cell lines and clinical trials have been undertaken on ruthenium complexes. In addition to their antitumor activity, ruthenium complexes are under evaluation for other diseases, such as type 2 diabetes, Alzheimer's disease and HIV. Attempts are also being made to evaluate ruthenium complexes as potential photosensitizers with polypyridine ligands for use in cancer chemotherapy. The review also briefly examines theoretical approaches to studying the interactions of Ru(II)/Ru(III) complexes with biological receptors, which can facilitate the rational design of ruthenium-based drugs.

Reactivity of a nitrosyl ruthenium complex and its potential impact on the fate of DNA - An in vitro investigation

The role of metal complexes on facing DNA has been a topic of major interest. However, metallonitrosyl compounds have been poorly investigated regarding their reactivities and interaction with DNA. A nitrosyl compound, cis-[Ru(bpy)₂(SO₃)(NO)](PF₆)(A), showed a variety of promising biological activities catching our attention. Here, we carried out a series of studies involving the interaction and damage of DNA mediated by the metal complex A and its final product after NO release, cis-[Ru(bpy)₂(SO₃)(H₂O](B). The fate of DNA with these metal complexes was investigated upon light or chemical stimuli using electrophoresis, electronic absorption spectroscopy, circular dichroism, size-exclusion resin, mass spectrometry, electron spin resonance (ESR) and viscometry. Since many biological disorders involve the production of oxidizing species, it is important to evaluate the reactivity of these compounds under such conditions as well. Indeed, the metal complex B exhibited important reactivity with H₂O₂ enabling DNA degradation, with detection of an unusual oxygenated intermediate. ESR spectroscopy detected mainly the DMPO-OOH adduct, which only emerges if H₂O₂ and O₂ are present together. This result indicated HOO^• as a key radical likely involved in DNA damage as supported by agarose gel electrophoresis. Notably, the nitrosyl ruthenium complex did not show evidence of direct DNA damage. However, its aqua product should be carefully considered as potentially harmful to DNA deserving further in vivo studies to better address any genotoxicity.

Ruthenium-based antitumor drugs and delivery systems from monotherapy to combination therapy

Ruthenium complex is an important compound group for antitumor drug research and development. NAMI-A, KP1019, TLD1433 and other ruthenium complexes have entered clinical research. In recent years, the research on ruthenium antitumor drugs has not been limited to single chemotherapy drugs; other applications of ruthenium complexes have emerged such as in combination therapy. During the development of ruthenium complexes, drug delivery forms of ruthenium antitumor drugs have also evolved from single-molecule drugs to nanodrug delivery systems. The review summarizes the following aspects: (1) ruthenium complexes from monotherapy to combination therapy, including the development of single-molecule compounds, carrier nanomedicine, and self-assembly of carrier-free nanomedicine; (2) ruthenium complexes in the process of ADME in terms of absorption, distribution, metabolism and excretion; (3) the applications of ruthenium complexes in combination therapy, including photodynamic therapy (PDT), photothermal therapy (PTT), photoactivated chemotherapy (PACT), immunotherapy, and their combined application; (4) the future prospects of ruthenium-based antitumor drugs.

Anticancer water-soluble organoruthenium complexes: synthesis and preclinical evaluation

The synthesis, characterisation, and evaluation of the in vitro cytotoxicity of five maleonitriledithiolate‐based ruthenium metal complexes bearing various phosphine ligands towards two ovarian cancer cell lines (A2780 and A2780cisR), one non‐small‐cell lung cancer cell line (H460) and one normal prostate cell line (PNT2) are presented herein. These 18‐electron complexes were designed with four water‐soluble phosphine ligands to increase the water‐solubility character of the corresponding electron‐deficient ruthenium complex which showed great in vitro promises, and triphenylphosphine for comparison. The complexes with triphenylphosphine‐3,3′,3′′‐trisulfonic acid and triphenylphosphine present similar cytotoxicity compared to the 16‐electron precursor, with equal cytotoxicity to both A2780 and A2780cisR. Hints at the mechanism of action suggest an apoptotic pathway based on reactive oxygen species (ROS) production. No toxicity was observed in preliminary in vivo pilot studies for these two complexes in subcutaneous A2780 and A2780cisR xenograft models, with some evidence of tumour growth delay.

Unlocking the Potential of Ru(II) Dual-action Compounds with the Power of the Heavy-atom Effect

We report the synthesis, photochemical and biological characterization of two new Ru(II) photoactivated complexes based on [Ru(tpy)(Me₂ bpy)(L)]²⁺ (tpy = 2,2':6',2''-terpyridine, Me₂ bpy = 6,6'-dimethyl-2,2'-bipyridine), where L = pyridyl-BODIPY (pyBOD). Two pyBOD ligands were prepared bearing flanking hydrogen or iodine atoms. Ru(II)-bound BODIPY dyes show a red-shift of absorption maxima relative to the free dyes and undergo photodissociation of BODIPY ligands with green light irradiation. Addition of iodine into the BODIPY ligand facilitates intersystem crossing, which leads to efficient singlet oxygen production in the free dye, but also enhances quantum yield of release of the BODIPY ligand from Ru(II). This represents the first report of a strategy to enhance photodissociation quantum yields through the heavy-atom effect in Ru(II) complexes. Furthermore, Ru(II)-bound BODIPY dyes display fluorescence turn-on once released, with a lead analog showing nanomolar EC₅₀ values against triple negative breast cancer cells, >100-fold phototherapeutic indexes under green light irradiation, and higher selectivity toward cancer cells as compared to normal cells than the corresponding free BODIPY photosensitizer. Conventional Ru(II) photoactivated complexes require nonbiorthogonal blue light for activation and rarely show submicromolar potency to achieve cell death. Our study represents an avenue for the improved photochemistry and potency of future Ru(II) complexes.

Role of the (pseudo)halido ligand in ruthenium(II) p-cymene α-amino acid complexes in speciation, protein reactivity and cytotoxicity

The reactions of the dimeric complexes [RuX2(η6-p-cymene)]2 (X = Br, I, SCN) with L-proline (ProH) and trans-4-hydroxy-L-proline (HypH), in methanol in the presence of NaOH, afforded [RuX(κ2N,O-Pro)(η6-p-cymene)] (X = Br, 1b; I, 1c; SCN, 1d) and [RuX(κ2N,O-Hyp)(η6-p-cymene)] (X = Br, 2b; I, 2c; SCN, 2d), respectively. Alternatively, the one-pot, sequential addition of the appropriate α-amino carboxylate and X- salt to [RuCl2(η6-p-cymene)]2 led to [RuX(κ2N,O-Pro)(η6-p-cymene)] (X = N3, 1e; NO2, 1f; CN 1g) and [Ru(N3)(κ2N,O-Hyp)(η6-p-cymene)] (2e). Complexes [Ru(κ3N,O,O'-O2CCH(NH2)(R)O)(η6-p-cymene)] (R = CH2, 3h; R = CHMe, 4h; R = CH2CH2, 5h) were prepared from the reaction of [RuCl2(η6-p-cymene)]2 with the appropriate α-amino acid and NaOH in refluxing isopropanol. Treatment of the L-serine (SerH2) derivative [RuCl(κ2N,O-SerH)(η6-p-cymene)] (3a) with 1,3,5-triaza-7-phosphaadamantane (PTA) in water at reflux produced [Ru(κ2N,O-Ser)(κP-PTA)(η6-p-cymene)]Cl ([3i]Cl). The products were isolated in good to excellent yields, and were characterized by elemental analysis, IR and multinuclear NMR spectroscopy. The structures of 1f and 2b-e were ascertained by X-ray diffraction studies. The behaviour of the complexes in water and cell culture medium was investigated by multinuclear NMR and UV-Vis spectroscopy, revealing a considerable influence of the monodentate ligand on the aqueous chemistry. Complexes 1d-e, 2d-e, 3h, 4h and [3i]Cl, showing substantial inertness in aqueous media, were assessed for their cytotoxicity towards A2780 and A2780cisR cancer cell lines and the noncancerous HEK 293T cell line. A selection of compounds was also investigated for Ru uptake in A2780 cells and interactions with cytochrome c as a model protein. Combined, these studies provide insights into the previously debated role of the 'leaving' ligand on the biological activity of Ru(II) arene α-amino acid complexes.

Past, present and future-sample environments for materials research studies in scattering and spectroscopy; a UK perspective

Small angle x-ray scattering and x-ray absorption fine structure are two techniques that have been employed at synchrotron sources ever since their inception. Over the course of the development of the techniques, the introduction of sample environments for added value experiments has grown dramatically. This article reviews past successes, current developments and an exploration of future possibilities for these two x-ray techniques with an emphasis on the developments in the United Kingdom between 1980-2020.

Synthesis, Biomacromolecular Interactions, Photodynamic NO Releasing and Cellular Imaging of Two [RuCl(qn)(Lbpy)(NO)]X Complexes

Two light-activated NO donors [RuCl(qn)(Lbpy)(NO)]X with 8-hydroxyquinoline (qn) and 2,2′-bipyridine derivatives (Lbpy) as co-ligands were synthesized (Lbpy₁ = 4,4′-dicarboxyl-2,2′-dipyridine, X = Cl⁻ and Lbpy₂ = 4,4′-dimethoxycarbonyl-2,2′-dipyridine, X = NO₃⁻), and characterized using ultraviolet–visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (¹H NMR), elemental analysis and electrospray ionization mass spectrometry (ESI-MS) spectra. The [RuCl(qn)(Lbpy₂)(NO)]NO₃ complex was crystallized and exhibited distorted octahedral geometry, in which the Ru–N(O) bond length was 1.752(6) Å and the Ru–N–O angle was 177.6(6)°. Time-resolved FT-IR and electron paramagnetic resonance (EPR) spectra were used to confirm the photoactivated NO release of the complexes. The binding constant (K_b) of two complexes with human serum albumin (HSA) and DNA were quantitatively evaluated using fluorescence spectroscopy, Ru-Lbpy₁ (K_b~10⁶ with HSA and ~10⁴ with DNA) had higher affinity than Ru-Lbpy₂. The interactions between the complexes and HSA were investigated using matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) and EPR spectra. HSA can be used as a carrier to facilitate the release of NO from the complexes upon photoirradiation. The confocal imaging of photo-induced NO release in living cells was successfully observed with a fluorescent NO probe. Moreover, the photocleavage of pBR322 DNA for the complexes and the effect of different Lbpy substituted groups in the complexes on their reactivity were analyzed.

Polymeric Encapsulation of a Ru(II)-Based Photosensitizer for Folate-Targeted Photodynamic Therapy of Drug Resistant Cancers

The currently used photodynamic therapy (PDT) photosensitizers (PSs) are generally associated with a poor cancer cell selectivity, which is responsible for some undesirable side effects. To overcome these problems, there is an urgent need for a selective drug delivery system for PDT PSs. Herein, the encapsulation of a promising Ru(II) polypyridine complex in a polymer with terminal folate groups to form nanoparticles is presented. While the Ru(II) complex itself has a cytotoxic effect in the dark, the encapsulation is able to overcome this drawback. Upon light exposure, the nanoparticles were found to be highly phototoxic in 2D monolayer cells as well as 3D multicellular tumor spheroids upon 480 or 595 nm irradiation. Importantly, the nanoparticles demonstrated a high selectivity for cancerous cells over noncancerous cells and were found to be active in drug resistant cancer cells lines, indicating that they are able to overcome drug resistances.

RAPTA-Decorated Polyacrylamide Nanoparticles: Exploring their Synthesis, Physical Properties and Effect on Cell Viability

In this study, we report the first successful immobilisation of a known cytoactive [Ru(η⁶ -arene)(C₂ O₄ )PTA] (RAPTA) complex to a biologically inert polyacrylamide nanoparticle support. The nanoparticles have been characterised by zetasizer analysis, UV/Vis, ATR-FTIR, TGA and ICP-MS to qualitatively and quantitatively confirm the presence of the metallodrug on the surface of the carrier. The native RAPTA complex required a concentration of 50 μM to produce a cell viability of 47.1±2.1 % when incubated with human Caucasian colorectal adenocarcinoma cells for 72 h. Under similar conditions a cell viability of 45.1±1.9 % was obtained with 0.5 μM of RAPTA complex in its immobilised form. Therefore, conjugation of the RAPTA metallodrug to our nanoparticle carriers resulted in a significant 100-fold decrease in effective concentration of ruthenium required for a near identical biological effect on cell viability.

Cytotoxic (cis,cis-1,3,5-triaminocyclohexane)ruthenium(II)-diphosphine complexes; evidence for covalent binding and intercalation with DNA

We report cytotoxic ruthenium(ii) complexes of the general formula [RuCl(cis-tach)(diphosphine)]+ (cis-tach = cis-cis-1,3,5-triaminocyclohexane) that have been characterised by 1H, 13C and 31P{1H} NMR spectroscopy, mass spectrometry, X-ray crystallography and elemental analysis. The kinetics of aquation and stability of the active species have been studied, showing that the chlorido ligand is substituted by water at 298 K with first order rate constants of 10-2-10-3 s-1, ideal for potential clinical use as anti-tumour agents. Strong interactions with biologically relevant duplex and quadruplex DNA models correlate with the activity observed with A549, A2780 and 293T cell lines, and the degree of activity was found to be sensitive to the chelating diphosphine ligand. A label-free ptychographic cell imaging technique recorded cell death processes over 4 days. The Ru(ii) cis-tach diphosphine complexes exhibit anti-proliferative effects, in some cases outperforming cisplatin and other cytotoxic ruthenium complexes.

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

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

Ni(II) curcumin complexes for cellular imaging and photo-triggered in vitro anticancer activity

Nickel(II) complexes [Ni(cur)(L)₂](OAc) (1-3) where L is N,N-donor heterocyclic bases namely 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 2), dipyrido[3,2-a:2',3'-c]phenazine (dppz in 3) and Hcur is curcumin were prepared, fully characterized and light-induced in vitro anticancer activity studied. Three nickel(II) complexes containing acetylacetonato (Hacac) ligand, viz.[Ni(acac)(L)₂](OAc) (4-6) where L is phen (in 4), dpq (in 5), dppz (in 6) were prepared and used as controls. Complex 4 was structurally characterized by single crystal X-ray diffraction technique, which revealed an octahedral NiN₄O₂ geometry around the metal centre. Complexes 1-3 showed an intense curcumin-based band at ∼440 nm in DMSO-Tris-HCl buffer (pH = 7.2) (1:4 v/v) which masks the nickel based d-d band. The curcumin comlexes (1-3) were redox inactive at the nickel centre, whereas the acetylacetonato complexes (4-6) displayed an irreversible voltammetric response at ∼1.00 V vs. Ag/AgCl reference electrode in DMF. The complexes bind to calf thymus DNA (ct-DNA) with considerable affinity and interacted with human serum albumin (HSA) with moderate affinity. The Ni(II) curcumin complexes display significant in vitro light-induced cytotoxicity in HeLa (human cervical carcinoma) and A549 (lung cancer cells) involving reactive oxygen species (ROS), with very low dark toxicity. The complexes were found to be much less toxic to immortalized lung epithelial normal cells (HPL1D). Confocal microscopic images using complex 2 and 3 showed that they primarily localize in the cytosol of A549 cells. The mechanism of cell death is mainly apoptosis in nature showing arrest of sub-G1 phase of cell cycle progression in A549 cells under visible light exposure and involves significant loss of mitochondrial membrane potential as observed from JC-1 assay.

A Multi-action and Multi-target RuII -PtIV Conjugate Combining Cancer-Activated Chemotherapy and Photodynamic Therapy to Overcome Drug Resistant Cancers

Pt^II complexes are commonly used to treat cancer. To reduce their side effects and improve their pharmacological properties, Pt^IV complexes are being developed as prodrug candidates that are activated by reduction in cancer cells. Concomitantly, Ru^II polypyridine complexes have gained much attention as photosensitizers for use in photodynamic therapy due to their attractive characteristics. In this article, a novel Pt^IV -Ru^II conjugate, which combines cancer activated chemotherapy with PDT, is presented. Upon entering the cancer cell, the Pt^IV centre is reduced to Pt^II and the axial ligands including the Ru^II complex and phenylbutyrate are released. As each component has its individual targets, the conjugate exerts a multi-target and multi-action effect with (photo-)cytotoxicity values upon irradiation up to 595 nm in the low nanomolar range in various (drug resistant) 2D monolayer cancer cells and 3D multicellular tumour spheroids.

Recent progress in the development of organometallics for the treatment of cancer

From their early successes in medicine, organometallic compounds continue to attract interest as potential chemotherapeutics to treat a range of diseases. Here, we show from recent literature selected largely from the last two years that organometallics offer unique opportunities in medicine and, increasingly, a mechanistic-based approach is applied to their development, which has not always been the case.

Polymeric Bis(dipyrrinato) Zinc(II) Nanoparticles as Selective Imaging Probes for Lysosomes of Cancer Cells

Fluorescence imaging is a powerful tool in biomedical research. It has been frequently used to uncover or better understand physiological mechanisms in disease-related processes such as cancer. The majority of chromophores used for imaging are based on a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) scaffold. However, their applications are limited due to their poor water solubility as well as poor cancer cell selectivity. To circumvent these drawbacks, we present herein the use of bis(dipyrrinato)zinc(II) complexes. As this class of compounds is associated with a quenching effect of the excited state in water, the lead compound of this study (3) was encapsulated in a polymer matrix with biotin as a targeting moiety (3-NP). This encapsulation improved the water solubility, overcame the quenching effects in water, as well as allowed selective accumulation in the lysosomes with a bright fluorescence signal in monolayer cells as well as 3D multicellular tumor spheroids (MCTS). As a benefit from the biotin targeting moiety, the nanoparticles were majorly taken up by the sodium dependent multivitamin transporter (SMVT) which is overexpressed in various cancers cells and selectively accumulated in cancerous cells over noncancerous cells.