Synthesis and Photobiological Activity of Ru(II) Dyads Derived from Pyrrole-2-carboxylate Thionoesters

Discovery and antitumor evaluation of a mitochondria-targeting ruthenium complex for effective cancer therapy

Ruthenium-based metallodrugs have garnered attention as a promising alternative for anticancer therapy, aiming to overcome chemoresistance and severe side effects linked to platinum-based drugs. However, ruthenium complexes tested in clinical trials to date have yielded unsatisfactory results. This study synthesized a positively charged ruthenium complex (Ru-2) that effectively penetrated cancer cells and exhibited superior cytotoxicity to cisplatin in vitro against cancer cell lines and organoids. Ru-2 selectively targeted mitochondria, disrupting their function by depolarizing mitochondrial membrane potential, elevating reactive oxygen species production, and impairing both oxidative phosphorylation and the tricarboxylic acid cycle. Furthermore, Ru-2 triggered endoplasmic reticulum (ER) stress and apoptosis. Integrative transcriptomic and proteomic analyses, performed using RNA sequencing and mass spectrometry, identified key molecular changes in cancer cells treated with Ru-2. For enhanced in vivo application, we developed a transferrin-based nanomedicine formulation, TF/Ru-2, incorporating Ru-2 into transferrin. In vivo studies demonstrated that both Ru-2 and TF/Ru-2 exhibited superior antitumor efficacy and improved biosafety compared to cisplatin. This study presents a novel ruthenium complex and a transferrin-based drug delivery platform with significant potential for future cancer therapies.

Ruthenium(II) complexes containing PEGylated N-heterocyclic carbene ligands for tunning biocompatibility in the fight against cancer

A synthetic procedure was designed for the preparation and characterization of Ag and Ru complexes containing NHC ligands functionalized with PEG fragments. Stability studies were conducted to gain insight of the species in water and other solvents like DMSO, or with reagents like imidazole as representative group for histidine amino acid. The presence of Cl atoms instead of H in the 4,5 positions of the N-heterocyclic carbene afforded higher water stability. The complexes containing PEG units must be considered inactive as anticancer agents. To enhance the anticancer activity of PEG-containing complexes, the balance between hydrophilicity and hydrophobicity was adjusted using a silane moiety, and an anionic carbosilane dendrimer as a lipophilic carrier.

Overcoming Resistance of Caco-2 Cells to 5-Fluorouracil through Diruthenium Complex Encapsulation in PMMA Nanoparticles

Drug resistance, one of the main drawbacks in cancer chemotherapy, can be tackled by employing a combination of drugs that target different biological processes in the cell, enhancing the therapeutic efficacy. Herein, we report the synthesis and characterization of a new paddlewheel diruthenium complex that includes 5-fluorouracil (5-FU), a commonly used anticancer drug. This drug was functionalized with a carboxylate group to take advantage of the previously demonstrated release capacity of carboxylate ligands from the diruthenium core. The resulting hydrophobic complex, [Ru2Cl(DPhF)3(5-FUA)] (Ru-5-FUA) (DPhF = N,N'-diphenylformamidinate; 5-FUA = 5-fluorouracil-1-acetate) was subsequently entrapped in poly(methyl methacrylate) (PMMA) nanoparticles (PMMA@Ru-5-FUA) via a reprecipitation method to be transported in biological media. The optimized encapsulation procedure yielded particles with an average size of 81.2 nm, a PDI of 0.11, and a zeta potential of 29.2 mV. The cytotoxicity of the particles was tested in vitro using the human colon carcinoma cell line Caco-2. The IC50 (half maximal inhibitory concentration) of PMMA@Ru-5-FUA (6.08 μM) was just slightly lower than that found for the drug 5-FU (7.64 μM). Most importantly, while cells seemed to have developed drug resistance against 5-FU, PMMA@Ru-5-FUA showed an almost complete lethality at ∼30 μM. Conversely, an analogous diruthenium complex devoid of the 5-FU moiety, [Ru2Cl(DPhF)3(O2CCH3)] (PMMA@RuA), displayed a reduced cytotoxicity at equivalent concentrations. These findings highlight the effect of combining the anticancer properties of 5-FU with those of diruthenium species. This suggests that the distinct modes of action of the two chemical species are crucial for overcoming drug resistance.

Naphthoyl benzhydrazine-decorated binuclear arene Ru(II) complexes as anticancer agents targeting human breast cancer cells

Breast cancer is the most dangerous type in women and its fatality rate has increased over the past decade. To develop more potent and target-specific breast cancer drugs, six arene ruthenium(II) complexes (1-6) containing naphthoyl benzhydrazine ligands (NL1-NL3) were synthesized and characterized by analytical and spectroscopic (infrared, UV-visible, NMR and HR-MS) methods. The SC-XRD analysis of 1 and 6 demonstrates the bis N^O bidentate binding nature of ligands to ruthenium ions and a pseudo-octahedral geometry around the Ru(II) ion. Solution stability studies using UV-Vis spectroscopy evidenced the instantaneous hydrolysis of the complexes to form monoaquated species in a solution of 1 : 9 (v/v) DMSO/phosphate buffer. All the complexes were screened for their in vitro antiproliferative activities against different human breast cancer cells, including MCF-7, SkBr3, MDA-MB-468, MDA-MB-231, and non-cancerous HEK-293 cells, by an MTT assay, and they displayed good cancer cell growth inhibitory capacity with low IC50 values. Notably, complexes 2 and 5 comprising methoxy and p-cymene groups exhibited excellent cytotoxicity towards SkBr3 cells compared to clinical drug cisplatin. AO-EB and HOECHST-33342 staining assays revealed apoptotic morphological changes in complex-treated cancer cells. Further, reactive oxygen species and mitochondrial membrane potential assays validated that the complexes induce apoptotic cell death via an intrinsic mitochondrial pathway with ROS production. In addition, the apoptotic induction and the quantification of late apoptosis were established with the aid of western blot and flow cytometry analysis, respectively.

Study on the Multimodal Anticancer Mechanism of Ru(II)/Ir(III) Complexes Bearing a Poly(ADP-ribose) Polymerase 1 Inhibitor

A series of novel ruthenium(II) and iridium(III) complexes (Ru1-Ru3 and Ir1-Ir3) with different ancillary ligands and a PARP-1-inhibitory chelating ligand 2-(2,3-dibromo-4,5-dimethoxybenzylidene)hydrazine-1-carbothioamide (L1) were designed and prepared. The target complexes were structurally characterized by NMR and ESI-MS techniques. Among them, the crystal and molecular structures of Ir1 and Ir2 were also determined by X-ray crystallography. These complexes retained the PARP-1 enzyme inhibitory effect of L1 and showed potent antiproliferative activity on the tested cancer cell lines. The ruthenium(II) complexes Ru1-Ru3 were found to be more cytotoxic than the iridium(III) complexes Ir1-Ir3. Further investigations revealed that the most active complex Ru3 induced apoptosis in MCF-7 cells by multiple modes, inclusive of inducing DNA damage, suppressing DNA damage repair, disturbing cell cycle distribution, decreasing the mitochondrial membrane potential, and increasing the intracellular reactive oxygen species levels.

Synthesis, characterization, molecular docking, RNA-sequence and anticancer efficacy evaluation in vitro of ruthenium(II) complexes on B16 cells

In recent years, the studies of the ruthenium(II) complexes on anticancer activity have been paid great attention, many Ru(II) complexes possess high anticancer efficiency. In this paper, three ligands CPIP (2-(4-chlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), DCPIP (2-(3,4-dichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), TCPIP (2-(2,3,5-trichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) and their three ruthenium (II) complexes [Ru(dip)2(CPIP)](PF6)2 (1, dip = 4,7-diphenyl-1,10-phenanthroline), [Ru(dip)2(DCPIP)](PF6)2 (2) and [Ru(dip)2(TCPIP)](PF6)2 (3) were synthesized and characterized. 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) assay was used to investigate in vitro cytotoxicity of complexes against various cancer cells. The results showed that complexes 1-3 exhibited pronounced cytotoxic effect on B16 cells with low IC50 values of 7.2 ± 0.1, 11.7 ± 0.6 and 1.2 ± 0.2 μM, respectively. The 3D model demonstrated that the complexes can validly prevent the cell proliferation. Apoptosis determined using Annexin V-FITC/PI double staining revealed that complexes 1-3 can effectively induce apoptosis in B16 cells. The intracellular localization of 1-3 in the mitochondria, the levels of intracellular reactive oxygen species (ROS), the opening of mitochondrial permeability transition pore as well as the decline of mitochondrial membrane potential were investigated, which demonstrated that the complexes 1-3 led to apoptosis via a ROS-mediated mitochondrial dysfunction pathway. The RNA-sequence indicated that the complexes upregulate the expression of 74 genes and downregulate the expression of 81 genes. The molecular docking showed that the complexes interact with the proteins through hydrogen bond, π-cation and π-π interaction. The results show that ruthenium(II) complexes 1, 2 and 3 can block tumor cell growth and induce cell death through autophagy and ROS-mediated mitochondrial dysfunction pathways.

CuAAC "Click"-Derived Luminescent 2-(2-(4-(4-(Pyridin-2-yl)-1H-1,2,3-triazol-1-yl)butoxy)phenyl)benzo[d]thiazole-Based Ru(II)/Ir(III)/Re(I) Complexes as Anticancer Agents

To enhance the cytoselective behavior of the complexes, we intended to develop a CuAAC "click"-derived synthetic protocol for the preparation of 2-(2-(4-(4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl)butoxy)phenyl)benzo[d]thiazole-based Ru(II)/Ir(III)/Re(I) complexes, and their cytotoxicity against three different cancer cell lines (MCF-7, HeLa, and U87MG) in consort with one normal cell line (HEK-293) was evaluated. In our detailed investigations, the significant cytotoxic nature of the Ru(II) complex 7a compared to Ir(III) and Re(I) complexes (7b and 7c, respectively) was observed. Complex 7a was capable of MCF-7 cell apoptosis via the inhibition of both S- and G2/M-phase cell cycle arrest in association with a substantial quantity of ROS production and DNA intercalation.

Significant increase of anticancer efficacy in vitro and in vivo of liposome entrapped ruthenium(II) polypyridyl complexes

Two polypyridyl ruthenium(II) complexes [Ru(DIP)₂(BIP)](PF₆)₂ (DIP = 4,7-diphenyl-1,10-phenanthrolie, BIP = 2-(1,1'-biphenyl-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, Ru1) and [Ru(DIP)₂(CBIP)](PF₆)₂ (CBIP = 2-(4'-chloro-1,1'-biphenyl-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, Ru2) were synthesized. The cytotoxic activities in vitro of Ru1, Ru2 toward B16, A549, HepG2, SGC-7901, HeLa, BEL-7402, non-cancer LO2 were investigated using MTT method (3-(4,5-dimethylthiazole)-2,5-diphenltetraazolium bromide). Unexpectedly, Ru1, Ru2 can't prevent these cancer cells proliferation. To improve the anti-cancer effect, we used liposomes to entrap the complexes Ru1, Ru2 to form Ru1lipo, Ru2lipo. As expectation, Ru1lipo and Ru2lipo exhibit high anti-cancer efficacy, especially, Ru1lipo (IC₅₀ 3.4 ± 0.1 μM), Ru2lipo (IC₅₀ 3.5 ± 0.1 μM) display strong ability to block the cell proliferation in SGC-7901. The cell colony, wound healing, and cell cycle distribution show that the complexes can validly inhibit the cell growth at G2/M phase. Apoptotic studied with Annex V/PI doubling method showed that Ru1lipo and Ru2lipo can effectively induce apoptosis. Reactive oxygen species (ROS), malondialdehyde, glutathione and GPX4 demonstrate that Ru1lipo and Ru2lipo improve ROS and malondialdehyde levels, inhibit generation of glutathione, and finally result in a ferroptosis. Ru1lipo and Ru2lipo interact on the lysosomes and mitochondria and damage mitochondrial dysfunction. Additionally, Ru1lipo and Ru2lipo increase intracellular Ca²⁺ concentration and induce autophagy. The RNA-sequence and molecular docking were performed, the expression of Bcl-2 family was investigated by Western blot analysis. Antitumor in vivo experiments confirm that 1.23 mg/kg, 2.46 mg/kg of Ru1lipo possesses a high inhibitory rate of 53.53% and 72.90% to prevent tumor growth, hematoxylin-eosin (H&E) results show that Ru1lipo doesn't cause chronic organ damage and strongly promotes the necrosis of solid tumor. Taken together, we conclude that Ru1lipo and Ru2lipo cause cell death through the following pathways: autophagy, ferroptosis, ROS-regulated mitochondrial dysfunction, and blocking the PI3K/AKT/mTOR.

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.

Synthesis, RNA-sequence and evaluation of anticancer efficacy of ruthenium(II) polypyridyl complexes toward HepG2 cells

In this article, four new Ru(II) complexes [Ru(dmbpy)₂(TFBIP)](PF₆)₂ (dmbpy = 4,4'-dimethyl-2,2'-bipyridine, TFPIP = 2-(4'-trifluoromethyl)-[1,1'-biphenyl]-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) (Ru1), [Ru(bpy)₂(TFBIP)](PF₆)₂ (bpy = 2,2'-bipyridine) (Ru2), [Ru(phen)₂(TFBIP)](PF₆)₂ (phen = 1,10-phenanthroline) (Ru3) and [Ru(dmp)₂(TFBIP)](PF₆)₂ (dmp = 2,9-dimethyl-1,10-phenanthroline) (Ru4) were synthesized and characterized by elemental analysis, HRMS, IR, ¹H NMR, ¹³C NMR and ¹⁹F NMR. The in vitro anticancer effect of the complexes on HepG2, A549, B16, HeLa, BEL-7402 and non-cancer LO2 cells was screened using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method. The results illustrate that the complexes display moderate anticancer activity. Apoptotic assay with Annexin V/PI double staining method indicated that complexes induce apoptosis in HepG2 cells. Also, the complexes interfere with the mitochondrial functions, accompanied by the production of intracellular ROS as well as a reduction of mitochondrial membrane potential. The results obtained from the western blot demonstrated that the complexes upregulate pro-apoptotic Bax and downregulate anti-apoptotic Bcl-2, which further activates caspase 3 and promotes the cleavage of PARP. RNA-sequence showed that the complexes upregulate the expression of 40 genes and downregulate 66 genes. Antitumour in vivo demonstrated that Ru1 inhibits the tumor growth with a high inhibitory rate of 51.19%. Taken together, these results revealed that complexes Ru1, Ru2, Ru3 and Ru4 induce cell death in HepG2 cells via autophagy and a ROS-mediated mitochondrial apoptotic pathway.

N-Heterocyclic Carbene-Iridium Complexes as Photosensitizers for In Vitro Photodynamic Therapy to Trigger Non-Apoptotic Cell Death in Cancer Cells

A series of seven novel iridium complexes were synthetized and characterized as potential photosensitizers for photodynamic therapy (PDT) applications. Among them, four complexes were evaluated in vitro for their anti-proliferative activity with and without irradiation on a panel of five cancer cell lines, namely PC-3 (prostate cancer), T24 (bladder cancer), MCF7 (breast cancer), A549 (lung cancer) and HeLa (cervix cancer), and two non-cancerous cell models (NIH-3T3 fibroblasts and MC3T3 osteoblasts). After irradiation at 458 nm, all tested complexes showed a strong selectivity against cancer cells, with a selectivity index (SI) ranging from 8 to 34 compared with non-cancerous cells. The cytotoxic effect of all these complexes was found to be independent of the anti-apoptotic protein Bcl-xL. The compound exhibiting the best selectivity, complex 4a, was selected for further investigations. Complex 4a was mainly localized in the mitochondria. We found that the loss of cell viability and the decrease in ATP and GSH content induced by complex 4a were independent of both Bcl-xL and caspase activation, leading to a non-apoptotic cell death. By counteracting the intrinsic or acquired resistance to apoptosis associated with cancer, complex 4a could be an interesting therapeutic alternative to be studied in preclinical models.

Quaternary Ru(II) complexes of terpyridines, saccharin and 1,2-azoles: effect of substituents on molecular structure, speciation, photoactivity, and photocytotoxicity

Six photoactive ruthenium quaternary complexes (a four-component system consisting of three different N-donor ligands and Ru(II)): trans-[Ru(R-tpy)(pyz/ind)(sac)₂] (1-6) containing substituted terpyridine (R-tpy), saccharin (sac), and monodentate N-donor heterocycles were designed. Here, R-tpy = 4'-(2-furyl (1, 2); thienyl (3, 4); pyridyl (5, 6))-2,2':6',2'' terpyridines, pyz = 1H-pyrazole for 1, 3 and 5 and ind = 1H-indazole for 2, 4 and 6. The azoles are present in a large number of FDA-approved clinical drugs and bioactive molecules. The saccharin acting as a carbonic anhydrase inhibitor (CA-IX) could potentially target aggressive hypoxic tumors that overexpress CA-IX. Such multi-functional ligands bound to a Ru(II)-photocage provide ample scope to tune the electronic structures, photochemistry, and synergistic effect of the photolabile ligands in photoactivated chemotherapy (PACT). The complexes were characterized using various spectroscopic studies, and the molecular structures were determined from X-ray crystallography. They exhibit a distorted octahedral {RuN₆} geometry with equatorial sites coordinated to the tridentate N₃-donor R-tpy and N-donor pyz/ind, while two transoidal axial sites bound to the N-donor saccharinate (sac) ligands. The solvolysis kinetics showed these complexes undergo facile ligand-exchange reactions in equilibrium with varying rates reflecting the possible electronic effect of the R-groups in R-tpy. The photoreactivity of the complexes in green (λ_ex = 530 nm) LED light indicates that the complexes undergo photodissociation of the monodentate N-donors (i.e., sac/pyz/ind) and showed an efficient generation of singlet oxygen (Φ_1O2 = 0.29-0.47), signifying the potential of these complexes in PACT and/or PDT. All the complexes show good binding affinity with CT-DNA with possible intercalation from extended planar polypyridyl ligands with duplex DNA and BSA. The synchronous fluorescence study with BSA suggested preferential interaction at the tryptophan residue in the protein microenvironment. The confocal microscopy studies showed adequate permeability and localization in the cytosol and nucleus of cervical cancer (HeLa) and breast cancer (MCF7) cells. The dose-dependent cytotoxicity of the complexes for both HeLa and MCF7 cells increases upon low-energy (365 nm) photoirradiation. The mechanistic studies revealed that the complexes induce apoptosis and generate reactive oxygen species (ROS) upon green light (λ_ex = 530 nm) irradiation. Overall, these quaternary Ru(II) complexes equipped with three different types of ligands with distinct roles could pave the way for designing multi-targeted chemotherapeutic metallodrugs with synergistic roles for each bioactive ligand.

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.

Bichromophoric ruthenium(II) bis-terpyridine-BODIPY based photosensitizers for cellular imaging and photodynamic therapy

Two multichromophoric homoleptic ruthenium(II) complexes [Ru(tpy-BODIPY)₂]Cl₂ (complexes 1 and 2, tpy = 4-phenyl-2,2:6,2-terpyridine, BODIPY = boron-dipyrromethene) were prepared, characterized and their phototherapeutic activity and bioimaging properties were studied. The complexes having structural similarity differ only by a phenylethynyl linker, and its overall influence on their physicochemical and photobiological behavior was evaluated. The terpyridine-BODIPY ligand L¹ was structurally characterized by X-ray crystallography. The complexes showed intense absorption near 500 nm (ε: ∼1.5 × 10⁵ M^-1 cm^-1 in DMSO), have a high singlet oxygen quantum yield (Φ_Δ: ∼0.6 in DMSO), and displayed low photobleaching thus making them suitable for PDT applications. The complexes showed high DNA binding affinity and induced DNA damage on light activation via multiple types of ROS production. Confocal laser scanning microscopy experiments revealed their incorporation in the cancer cells and complex 1 predominantly accumulated in lysosomes. The complexes displayed a significant PDT effect in cancerous cells with visible light activation with a high photocytotoxicity index (PI) value in HeLa cells. Both type-I and type-II photosensitization processes were involved in the PDT effect. The photodynamic action of complex 2 initiated cellular apoptosis. Finally, their diagnostic potential was evaluated against clinically relevant 3D multicellular tumor spheroids (MCTs).

A single-molecular ruthenium(II) complex-based NIR-II fluorophore for enhanced chemo-photothermal therapy

Novel NIR-II Ru(II) polypyridyl fluorophore Ru-1 dots for synergistic chemo-photothermal therapy against 4T1 tumors were designed and synthesized. Guided by in vivo NIR-II fluorescence imaging, the synergistic therapeutic efficacy, intracellular delivery, and biodistribution of the Ru-1 dots were precisely tracked in real-time.

[Ru(η6-p-cymene)(N^O 8-hydroxyquinoline)(PTA)] complexes as rising stars in medicinal chemistry: synthesis, properties, biomolecular interactions, in vitro anti-tumor activity toward human brain carcinomas, and in vivo biodistribution and toxicity in a zebrafish model

Herein, we have introduced a class of half-sandwich [Ru(η⁶-p-cymene)(N^O 8-hydroxyquinoline)(PTA)] complexes for brain cancer therapy. Among all the complexes, [RuL3PTA] and [RuL4PTA] exhibited excellent cytotoxicity profiles against T98G, LN229, and U87MG cancer cells. Notably, the antiproliferative activities of the relevant complexes were also supported by neurosphere, DNA intercalation, agarose gel electrophoresis, and time-dependent ROS detection assay studies. Detailed molecular assays were obtained via real-time reverse transcription (RT)-polymerase chain reaction (PCR) experiments. Moreover, the in vivo biodistribution of the [RuL4PTA] complex in different organs and the morphological patterns of zebrafish embryos due to toxic effects have been evaluated.

Ruthenium(ii)-arene complexes as anti-metastatic agents, and related techniques

With the discovery of cisplatin, a vast area of applications of metallodrugs in cancer treatment was opened but due to the side effects caused by the cisplatin complexes, researchers began to look for alternatives with similar anticancer properties but fewer side effects. Ruthenium was found to be a promising candidate, considering its significant anticancer properties and low side effects. Several ruthenium complexes, viz. NAMI-A, KP1019, KP1339, and TLD1433, have entered clinical trials. Some other arene ruthenium complexes such as RM175 and RAPTA-C have also entered clinical trials but very few of them have shown anti-metastatic properties. Herein, we provide information and probable mechanistic pathways for ruthenium(ii)-arene complexes that have been studied, so far, for their anti-metastatic activities. Also, we discuss the techniques and their significance for determining the anti-metastatic effects of the complexes.

In vitro studies on the selective cytotoxic effect of luminescent Ru(ii)-p-cymene complexes of imidazo-pyridine and imidazo quinoline ligands

In recent years, Ru(ii) complexes have gained high importance in medicinal chemistry due to their significant anti-cancer activities, which are directly related to their DNA binding ability.

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.

Cyclometalated Ru(II)-isoquinoline complexes overcome cisplatin resistance of A549/DDP cells by downregulation of Nrf2 via Akt/GSK-3β/Fyn pathway

Both ruthenium (Ru) and isoquinoline (IQ) compounds are regarded as potential anticancer drug candidates. Here, we report the synthesis and characterization of three novel cyclometalated Ru(II)-isoquinoline complexes: RuIQ-3, RuIQ-4, and RuIQ-5, and evaluation of their in vitro cytotoxicities against a panel of cell lines including A549/DDP, a cisplatin-resistant human lung cancer cell line. A549/DDP 3D multicellular tumor spheroids (MCTSs) were also used to detect the drug resistance reversal effect of Ru(II)-IQ complexes. Our results indicated that the cytotoxic activities against cancer cells of Ru(II)-IQ complexes, especially RuIQ-5, were superior compared with cisplatin. In addition, RuIQ-5 exhibited low toxicity towards both normal HBE cells in vitro and zebrafish embryos in vivo. Further investigation on cellular mechanism of action indicated that after absorption by A549/DDP cells, RuIQ-5 was mainly distributed in the nucleus, which is different from cisplatin. Besides, RuIQ-5 could induce apoptosis through mitochondrial dysfunction, reactive oxygen species (ROS) accumulation, ROS-mediated DNA damage, and cycle arrest at both S and G2/M phases. Moreover, RuIQ-5 could inhibit the overexpression of Nrf2 through regulation of Akt/GSK-3β/Fyn signaling pathway and hindering the nuclear translocation of Nrf2. Based on these findings, we firmly believe that the studied Ru(II)-IQ complexes hold great promise as anticancer therapeutics with high effectiveness and low toxicity.

Ru(ii), Ir(iii), Re(i) and Rh(iii) based complexes as next generation anticancer metallopharmaceuticals

Several anticancer drugs such as cisplatin, and its analogues, epirubicin, and doxorubicin are well known for their anticancer activity but the therapeutic value of these drugs comes with certain side effects and they cannot distinguish between normal and cancer cells. Thus, a major challenge for researchers around the world is to develop an anticancer drug with the least toxicity and more target specificity. With the successful reporting of NAMI-A and KP1019, a new path has emerged in the anticancer field. Recently, several Ru(ii) complexes have been reported for their anticancer activity due to their enhanced cellular uptake and selectivity towards cancer cells. Apart from the Ru(ii) complexes, a large amount of research has been carried out with Ir(iii), Re(i), and Rh(iii) based complexes, which exhibited promising anticancer activity. The present review reports various Ru(ii), Ir(iii), Re(i), and Rh(iii) based complexes for their anticancer activity based on their cytotoxicity profiles, biological targets and mechanism of action.

GSH-resistant and highly cytoselective ruthenium(II)-p-cymene-(imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol complexes as potential anticancer agents

To avoid the side effects of the current popular platinum-based anticancer drugs, researchers have made tireless attempts to design appropriate GSH-resistant Ru(ii)-arene complexes. In this regard, luminescent ruthenium(ii)-p-cymene-imidazophenanthroline complexes were developed as promising highly cytoselective cancer theraputic agents for HeLa and Caco-2 cells.

Synthesis, Characterization, and Cytotoxicity of Morpholine-Containing Ruthenium(II) p-Cymene Complexes

Morpholine motif is an important pharmacophore and, depending on the molecular design, may localize in cellular acidic vesicles. To understand the importance of the presence of pendant morpholine in a metal complex, six bidentate N,O-donor ligands with or without a pendant morpholine unit and their corresponding ruthenium(II) p-cymene complexes (1-6) are synthesized, purified, and structurally characterized by various analytical methods including X-ray diffraction. Complexes 2-4 crystallized in the P2₁/c space group, whereas 5 and 6 crystallized in the P1̅ space group. The solution stability studies using ¹H NMR support instantaneous hydrolysis of the native complexes to form monoaquated species in a solution of 3:7 (v/v) dimethyl sulfoxide-d₆ and 20 mM phosphate buffer (pH* 7.4, containing 4 mM NaCl). The monoaquated complexes are stable for at least up to 24 h. The complexes display excellent in vitro antiproliferative activity (IC₅₀ ca. 1-14 μM) in various cancer cell lines, viz., MDA-MB-231, MiaPaCa2, and Hep-G2. The presence of the pendant morpholine does not improve the dose efficacy, but rather, with 2-[[(2,6-dimethylphenyl)imino]methyl]phenol (HL1) and its pendant morpholine analogue (HL3) giving complexes 1 and 3, respectively, the antiproliferative activity was poorer with 3. MDA-MB-231 cells treated with the complexes show that the acidic vesicles remain acidic, but the population of acidic vesicles increases or decreases with time of exposure, as observed from the dispersed red puncta, depending on the complex used. The presence of the 2,6-disubstituted aniline and the naphthyl group seems to improve the antiproliferative dose. The complex treated MDA-MB-231 cells show that cathepsin D, which is otherwise present in the cytosolic lysosomes, translocates to the nucleus as a result of exposure to the complexes. Irrespective of the presence of a morpholine motif, the complexes do not activate caspase-3 to induce apoptosis and seem to favor the necrotic pathway of cell killing.

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.

Investigation into antiproliferative activity and apoptosis mechanism of new arene Ru(ii) carbazole-based hydrazone complexes

Ruthenium complexes with bioactive ligands are becoming promising substitutes for platinum complexes due to their precise action against various cancers. In the present study, the synthesis of three new arene Ru(ii) complexes containing new carbazole-based hydrazone ligands of general formula [(η6-benzene)Ru(L)Cl] (1-3; L = carbazolone benzhydrazone ligands), and their anticancer properties are described. The structural characterization of the ligands and their ruthenium complexes has been realized with the aid of elemental analysis, IR, UV-vis, NMR and HR-MS techniques. The molecular structures of all three complexes have been elucidated by single crystal X-ray crystallography and reveal the existence of pseudo-octahedral geometry around the ruthenium. The in vitro cancer cell growth inhibition property of the complexes against A549 (lung carcinoma), A2780 (ovarian adenocarcinoma) and non-cancerous 16HBE (human lung bronchial epithelium) cells were examined by MTT assay. All the complexes display good cytotoxicity towards both of these types of cancer cell compared to the standard drug cisplatin, with low IC50 values. Remarkably, complex 3, which contains an electron-donating substituent, induces a significant reduction of viability in A2780 cells. The inhibition capacity of the complexes towards A2780 cells proliferation was further confirmed using 5-ethynyl-2-deoxyuridine (EdU) assay via minimal DNA synthesis. The result of the acridine orange-ethidium bromide (AO-EB) fluorescent staining assay establishes that the cytotoxicity of the complexes was mediated by apoptosis in cancer cells. Furthermore, flow cytometry using Annexin V-FITC/propidium iodide (PI) double staining determines the quantitative discrimination of early apoptosis by the externalization of phosphatidylserine. In addition, cell cycle distribution indicates that the complexes block the cell cycle progression in the S-phase. The outcome of our investigation shows the promising scope and potency of tailored arene ruthenium complexes for precise cancer chemotherapy beyond platinum drugs.

Piano-Stool Ruthenium(II) Complexes with Delayed Cytotoxic Activity: Origin of the Lag Time

We have recently reported a series of piano-stool ruthenium(II) complexes of the general formula [RuCl₂(η⁶-arene)(P(1-pyrenyl)R²R³)] showing excellent cytotoxic activities (particularly when R² = R³ = methyl). In the present study, new members of this family of compounds have been prepared with the objective to investigate the effect of the steric hindrance of a bulky phosphane ligand, namely diisopropyl(1-pyrenyl)phosphane (L), on exchange reactions involving the coordinated halides (X = Cl, I). Two η⁶-arene rings were used, i.e. η⁶-methyl benzoate (mba) and η⁶-p-cymene (p-cym), and four complexes were synthesized, namely [RuCl₂(mba)(L)] (1_Cl2^iPr), [RuI₂(mba)(L)] (1_I2^iPr), [RuCl₂(p-cym)(L)] (2_Cl2^iPr), and [RuI₂(p-cym)(L)] (2_I2^iPr). Unexpectedly, all of the complexes exhibited poor cytotoxic activities after 24 h of incubation with cells, in contrast to the related compounds previously reported. However, it was observed that aged DMSO solutions of 2_I2^iPr (from 2 to 7 days) exhibited better activities in comparison to freshly prepared solutions and that the activity improved over “aging” time. Thorough studies were therefore performed to uncover the origin of this lag time in the cytotoxicity efficiency. The data achieved clearly demonstrated that compounds 2_I2^iPr and 2_Cl2^iPr were undergoing a series of transformation reactions in DMSO (with higher rates for the iodido complex 2_I2^iPr), ultimately generating cyclometalated species through a mechanism involving DMSO as a coordinated proton abstractor. The cyclometalated complexes detected in solution were subsequently prepared; hence, pure [RuCl(p-cym)(κ²C-diisopropyl(1-pyrenyl)phosphane)] (3_Cl^iPr), [RuI(p-cym)(κ²C-diisopropyl(1-pyrenyl)phosphane)] (3_I^iPr), and [Ru(p-cym)(κS-dmso)(κ²C-diisopropyl(1-pyrenyl)phosphane)]PF₆ (3_dmso^iPr) were synthesized and fully characterized. Remarkably, 3_Cl^iPr, 3_I^iPr, and 3_dmso^iPr are all very efficient cytotoxic agents, exhibiting slightly better activities in comparison to the chlorido noncyclometalated complexes [RuCl₂(η⁶-arene)(P(1-pyrenyl)R²R³)] described in an earlier report. For comparison purposes, the iodido compounds [RuI₂(mba)(dimethyl(1-pyrenyl)phosphane)] (1_I2^Me) and [RuI₂(p-cym)(dimethyl(1-pyrenyl)phosphane)] (2_I2^Me), bearing the less hindered dimethyl(1-pyrenyl)phosphane ligand, have also been prepared. The cytotoxic and chemical behaviors of 1_I2^Me and 1_I2^Me were comparable to those of their chlorido counterparts reported previously.

DMSO gradually converts half-sandwich, 1-pyrenyl-containing ruthenium(II) complexes into cyclometalated species showing notable cytotoxic properties.

DNA targeting half sandwich Ru(II)-p-cymene-N^N complexes as cancer cell imaging and terminating agents: influence of regioisomers in cytotoxicity

For diagnosing and annihilating cancer in the human body, herein, we have adopted a one pot convenient synthetic protocol to synthesize a library of half sandwich Ru(ii)-p-cymene-N^N complexes under continuous sonication and isolated their regioisomers by preparative thin layer chromatography followed by justification of stability using DFT. The present work has resulted in a library of ruthenium arene complexes and their isolated regioisomers following environmentally benign green processes and their screening of anticancer activity in terms of cytotoxicity and selectivity against cancer cell lines where [(η6-p-cymene)RuCl{2-(5,6-dichloro-1H-benzo[d]imidazole-2-yl)quinolone}] (11j) has been elicited to be significantly more potent as well as selective in Caco-2 and HeLa cell lines than the normal HEK-293 cell line compared to cisplatin and it has even shown marked cytotoxicity against the more aggressive HT-29 colorectal cancer cell line being capable of producing oxidative stress or arresting the cell cycle. Moreover, these types of Ru(ii)-arene complexes exhibited excellent binding efficacy with DNA and the compounds [(η6-p-cymene)RuCl{5-chloro-2-(6-(4-chlorophenyl)pyridin-2-yl)benzo[d]thiazole}]PF6 (8l4), [(η6-p-cymene)Ru-2-(6-(benzofuran-2-yl)pyridin-2-yl)-5-chlorobenzo[d]thiazole (8l9) and [(η6-p-cymene)RuCl{2-(6-nitro-1H-benzo[d]imidazol-2-yl)quinolone}]Cl (11f') and might be applied for cancer theranostic treatment due to their good fluorescence properties and remarkable potency.

Kinetically labile ruthenium(II) complexes of terpyridines and saccharin: effect of substituents on photoactivity, solvation kinetics, and photocytotoxicity

Herein, we designed six kinetically labile ruthenium(ii) complexes containing saccharin (sac) and 4'-substituted-2,2':6',2''-terpyridines (R-tpy), viz. trans-[Ru(sac)2(H2O)3(dmso-S)] (1) and [RuII(R-tpy)(sac)2(X)] [X = solvent molecule] (2-6). We intentionally kept the labile hydrolysable Ru-X bonds that were potentially activated via solvent-exchange reactions. This strategy generates a coordinative vacancy that allows further binding with potential biological targets. To gain insight into the electronic effects of ancillary ligands on Ru-X ligand-exchange kinetics or photoreactions, we have used a series of substituted terpyridines (R-tpy) and studied their solvation kinetics. The ternary complexes were also studied for their potential utility in Ru-assisted photoactivated chemotherapy (PACT) synergized with release of saccharin as a highly selective carbonic anhydrase IX (CA-IX) inhibitor, over-expressed in hypoxic tumors. The ternary complexes exhibit distorted octahedral geometry around Ru(ii) from two monodentate transoidal saccharin in the axial position, and tridentate terpyridines and labile solvent molecules at the basal plane (2-6). We studied their speciation, solvation kinetics, and photoreactivity in the presence of green LED light (λirr = 530 nm). All the complexes are relatively labile and undergo solvation in coordinating solvents (e.g. DMSO/DMF). The complexes undergo the ligand-substitution reaction, and their speciation and kinetics were studied by UV-Vis, ESI-MS, 1H-NMR, and structural analysis. We also attempted to assess the effect of various substituents on the ancillary terpyridine ligand (R-tpy) in photo-reactivity and ligand-exchange reactions. The photo-induced absorption and emission measurements suggested dissociation of the saccharin from the Ru-center supporting PACT pathways. The complexes display a significant binding affinity with CT-DNA (Kb ∼ 104-105 M-1) and bovine serum albumin (BSA) (KBSA ∼ 105 M-1). Cytotoxicity was studied in the dark and the presence of low energy UV-A light (365 nm) in cervical cancer cells (HeLa) and breast cancer cells (MCF7). Photoirradiation of the complexes induces the generation of reactive oxygen species (ROS) assessed using 1,3-diphenylisobenzofuran (DPBF) and intracellular DCFDA assays. The complexes are sufficiently internalized in cancer cells throughout the cytoplasm and nucleus and induce apoptosis as studied by staining with dual dyes using confocal microscopy.

Ruthenium Complexes as Anticancer Agents: A Brief History and Perspectives

Platinum (Pt)-based anticancer drugs such as cisplatin have been used to treat various cancers. However, they have some limitations including poor selectivity and toxicity towards normal cells and increasing chemoresistance. Therefore, there is a need for novel metallo-anticancers, which has not been met for decades. Since the initial introduction of ruthenium (Ru) polypyridyl complex, a number of attempts at structural evolution have been conducted to improve efficacy. Among them, half-sandwich Ru-arene complexes have been the most prominent as an anticancer platform. Such complexes have clearly shown superior anticancer profiles such as increased selectivity toward cancer cells and ameliorating toxicity against normal cells compared to existing Pt-based anticancers. Currently, several Ru complexes are under human clinical trials. For improvement in selectivity and toxicity associated with chemotherapy, Ru complexes as photodynamic therapy (PDT), and photoactivated chemotherapy (PACT), which can selectively activate prodrug moieties in a specific region, have also been investigated. With all these studies on these interesting entities, new metallo-anticancer drugs to at least partially replace existing Pt-based anticancers are anticipated. This review covers a brief description of Ru-based anticancer complexes and perspectives.

Bis[pyrrolyl Ru(ii)] triads: a new class of photosensitizers for metal-organic photodynamic therapy

A new family of ten dinuclear Ru(ii) complexes based on the bis[pyrrolyl Ru(ii)] triad scaffold, where two Ru(bpy)2 centers are separated by a variety of organic linkers, was prepared to evaluate the influence of the organic chromophore on the spectroscopic and in vitro photodynamic therapy (PDT) properties of the compounds. The bis[pyrrolyl Ru(ii)] triads absorbed strongly throughout the visible region, with several members having molar extinction coefficients (ε) ≥ 104 at 600-620 nm and longer. Phosphorescence quantum yields (Φ p) were generally less than 0.1% and in some cases undetectable. The singlet oxygen quantum yields (Φ Δ) ranged from 5% to 77% and generally correlated with their photocytotoxicities toward human leukemia (HL-60) cells regardless of the wavelength of light used. Dark cytotoxicities varied ten-fold, with EC50 values in the range of 10-100 μM and phototherapeutic indices (PIs) as large as 5400 and 260 with broadband visible (28 J cm-2, 7.8 mW cm-2) and 625 nm red (100 J cm-2, 42 mW cm-2) light, respectively. The bis[pyrrolyl Ru(ii)] triad with a pyrenyl linker (5h) was especially potent, with an EC50 value of 1 nM and PI > 27 000 with visible light and subnanomolar activity with 625 nm light (100 J cm-2, 28 mW cm-2). The lead compound 5h was also tested in a tumor spheroid assay using the HL60 cell line and exhibited greater photocytotoxicity in this more resistant model (EC50 = 60 nM and PI > 1200 with 625 nm light) despite a lower dark cytotoxicity. The in vitro PDT effects of 5h extended to bacteria, where submicromolar EC50 values and PIs >300 against S. mutans and S. aureus were obtained with visible light. This activity was attenuated with 625 nm red light, but PIs were still near 50. The ligand-localized 3ππ* state contributed by the pyrenyl linker of 5h likely plays a key role in its phototoxic effects toward cancer cells and bacteria.

Mitochondria-Targeting Click-Derived Pyridinyltriazolylmethylquinoxaline-Based Y-Shaped Binuclear Luminescent Ruthenium(II) and Iridium(III) Complexes as Cancer Theranostic Agents

Due to several negative issues, market available drugs have been gradually losing their importance in the treatment of cancer. With a view to discover suitable drugs capable of diagnosing as well as inhibiting the growth of cancer cells, we have aspired to develop a group of theranostic metal complexes which will be (i) target specific, (ii) cytoselective, thus rendering the normal cell unaffected, (iii) water-soluble, (iv) cancer cell permeable, and (v) luminescent, being beneficial for healing the cancer eternally. Therefore, to reach our goal, we have prepared novel Ru(II)- and Ir(III)-based bimetallic and hetero bimetallic scaffolds using click-derived pyridinyltriazolylmethylquinoxaline ligands followed by metal coordination. Most of the compounds have displayed significant cytoselectivity against colorectal adenocarcinoma (Caco-2) and epithiloid cervical carcinoma (HeLa) cells with respect to normal human embryonic kidney cells (HEK-293) compared to cisplatin [cis-diamminedichloroplatinum(II)] along with excellent binding efficacy with DNA as well as serum albumin. Complex [(η⁶-p-cymene)(η⁵-Cp*)Ru^IIIr^IIICl₂(K²-N,N-L)](PF₆)₂ [RuIrL] exhibited the best cytoselectivity against all the human cancer cells and was identified as the most significant cancer theranostic agent in terms of potency, selectivity, and fluorescence quantum yield. Investigation of the localization of complex [Ir₂L] and [RuIrL] in the more aggressive colorectal adenocarcinoma cell HT-29 indicates that mitochondria are the key cellular target for destroying cancer cells. Mitochondrial dysfunction and G2/M phase cell cycle arrest in HT-29 cell were found to be involved in the apoptotic cell death pathway induced by the test complexes [Ir₂L] and [RuIrL]. These results validate the concept that these types of complexes will be reasonably able to exert great potential for tumor diagnosis as well as therapy in the near future.

Lapachol in the Design of a New Ruthenium(II)-Diphosphine Complex as a Promising Anticancer Metallodrug

The preparation of two new Ru(II)/diphosphine complexes containing Lapachol (Lap) and Lawsone (Law): (1) [Ru(Lap)(dppm)₂]PF₆ and (2) [Ru(Law)(dppm)₂]PF₆, where dppm = bis(diphenylphosphino)methane, is reported here. The complexes were synthetized and fully characterized by elemental analyses, molar conductivity, UV-Vis, IR, ³¹P{¹H}, ¹H and ¹³C NMR, and the crystal structure of the complex (1) was determined by X-ray diffraction. Complexes (1) and (2) showed high in vitro cytotoxicity against four cancer cells (MDA-MB-231, MCF-7, A549 and DU-145), with IC₅₀ values in the micromolar range (0.03 to 2.70 μM). Importantly, complexes (1) and (2) were more active than the cisplatin, the drug used as a reference in the cytotoxic assays. Moreover, complex (1) showed high selectivity to triple-negative breast cancer cells (MDA-MB-231). Studies of the mechanism of action in MDA-MB-231 cancer cells showed that complex (1) inhibits cell migration, colony formation, and induces cell cycle arrest and apoptosis by activation of the mitochondrial pathway through the loss of mitochondrial membrane potential (ΔΨm). Furthermore, complex (1) induces ROS (Reactive Oxygen Species) generation in MDA-MB-231 cells, which can cause DNA damage. Finally, complexes (1) and (2) interact with DNA by minor grooves and show a moderate interaction with BSA (Bovine Serum Albumin), with the involvement of hydrophobic interactions. Essentially, Ru(II)/diphosphine-naphthoquinone complexes have remarkable cytotoxic effects with high selectivity to triple-negative breast cancer (MDA-MB-231) and could be promising anticancer candidates for cancer treatment. SYNOPSIS: The naphthoquinones Lapachol and Lawsone can form new ruthenium compounds with promising anticancer properties.

Ru(II) Complexes Bearing O, O-Chelated Ligands Induced Apoptosis in A549 Cells through the Mitochondrial Apoptotic Pathway

Two new Ru(II) complexes containing O, O-chelated ligands, Ru(dip)₂(SA) (Ru-1) and Ru(dmp)₂(SA) (Ru-2) (dip = 4,7-diphenyl-1,10-phenanthroline; dmp = 2,9-dimethyl-1,10-phenanthroline; SA = salicylate) were synthesized to evaluate their cytotoxicity in vitro. These complexes were found to exhibit moderate antitumor activity to different types of human cancers, including A549 (human lung carcinoma), MCF-7 (breast cancer), HeLa (human cervical cancer), and HepG2 (human hepatocellular carcinoma) cell lines, but displayed low toxicity to human normal cell lines BEAS-2B (immortalized human bronchial epithelial cells) when compared with that of cisplatin. Further studies revealed that these complexes could induce apoptosis in A549 cells, including activating caspase family proteins and poly (ADP-ribose) polymerase (PARP), reducing Bcl-2/Bax and Bcl-xl/Bad ratio, enhancing cellular reactive oxygen species (ROS) accumulation, triggering DNA damage, decreasing mitochondrial membrane potential (MMP), and leading cytochrome c release from mitochondria. Notably, complex Ru-1 showed low toxicity to developing zebrafish embryos. The obtained results suggest that these new synthetic complexes have the potential to be developed as low-toxicity agents for lung cancer treatment.

Dual-Action Ru(II) Complexes with Bulky π-Expansive Ligands: Phototoxicity without DNA Intercalation

We report the synthesis and photochemical and biological characterization of Ru(II) complexes containing π-expansive ligands derived from dimethylbenzo[i]dipyrido[3,2-a:2',3'-c]phenazine (Me₂dppn) adorned with flanking aryl substituents. Late-stage Suzuki couplings produced Me₂dppn ligands substituted at the 10 and 15 positions with phenyl (5), 2,4-dimethylphenyl (6), and 2,4-dimethoxyphenyl (7) groups. Complexes of the general formula [Ru(tpy)(L)(py)](PF₆)₂ (8-10), where L = 4-7, were characterized and shown to have dual photochemotherapeutic (PCT) and photodynamic therapy (PDT) behavior. Quantum yields for photodissociation of monodentate pyridines from 8-10 were about 3 times higher than that of parent complex [Ru(tpy)(Me₂dppn)(py)](PF₆)₂ (1), whereas quantum yields for singlet oxygen (¹O₂) production were ∼10% lower than that of 1. Transient absorption spectroscopy indicates that 8-10 possess long excited state lifetimes (τ = 46-50 μs), consistent with efficient ¹O₂ production through population and subsequent decay of ligand-centered ³ππ* excited states. Complexes 8-10 displayed greater lipophilicity relative to 1 and association to DNA but do not intercalate between the duplex base pairs. Complexes 1 and 8-10 showed photoactivated toxicity in breast and prostate cancer cell lines with phototherapeutic indexes, PIs, as high as >56, where the majority of cell death was achieved 4 h after treatment with Ru(II) complexes and light. Flow cytometric data and rescue experiments were consistent with necrotic cell death mediated by the production of reactive oxygen species, especially ¹O₂. Collectively, this study confirms that DNA intercalation by Ru(II) complexes with π-expansive ligands is not required to achieve photoactivated cell death.

Hypoxia efficient and glutathione-resistant cytoselective ruthenium(ii)-p-cymene-arylimidazophenanthroline complexes: biomolecular interaction and live cell imaging

A series of ruthenium(ii)–arene-2-arylimidazophenanthroline based DNA targeting, cytoselective, hypoxia efficient and glutathione-resistant luminescent anticancer drugs have been developed which are also represented as HeLa cell imaging probes.

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.

Screening and Preliminary Biochemical and Biological Studies of [RuCl(p-cymene)(N,N-bis(diphenylphosphino)-isopropylamine)][BF4] in Breast Cancer Models

Breast cancer is the second leading cause of cancer death worldwide. Despite progress in drug discovery, identification of the correct population is the limiting factor to develop new compounds in the clinical setting. Therefore, the aim of this study is to evaluate the effects of a new metallodrug, [RuCl(p-cymene)(N,N-bis(diphenylphosphino)-isopropylamine)][BF₄] (pnpRu-14), as a lead pnp-Ru compound by screening and preliminary biochemical and biological studies in different breast cancer subtypes. The results show that complex pnpRu-14 is much more effective in promoting in vitro cytotoxic effects on HER2+ and RH+/HER2- breast cancer than the reference metallodrugs cisplatin, carboplatin, or RAPTA-C. It is important to highlight that pnpRu-14 shows an impressive cytotoxicity against BT474 cells. Caspase-dependent apoptosis is the mechanism of action for these compounds. In addition, treatment of SKBR3, BT474, T47D, and MCF7 cancer cells with pnpRu-14 caused an accumulation of cells in the G0/G1 phase cells. The human serum albumin, DNA, and H1 histones binding properties of the lead compound are reported. Pharmacokinetic and biodistribution studies show a quick absorption of pnpRu-14 in serum with no significant accumulation in any of the tested organs. This work provides evidence to support the preclinical and clinical development of pnpRu-14 in breast cancer.