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Two new ligand PTTP (2-phenoxy-1,4,8,9-tetraazatriphenylene) and FTTP (2-(3-fluoronaphthalen-2-yloxy)-1,4,8,9-tetraazatriphenylene) and their six ruthenium(II) polypyridyl complexes [Ru(N-N)₂(PTTP)](ClO₄)₂ and [Ru(N-N)₂(FTTP)](ClO₄)₂ (N-N=dmb: 4,4'-dimethyl-2,2'-bipiridine; dmp: 2,9-dimethyl-1,10-phenanthroline; ttbpy: 4,4'-ditertiarybutyl-2,2'-bipyridine) were synthesized and characterized. The cytotoxic activity of the complexes against cancer cells HeLa, BEL-7402, A549, HepG-2, HOS and normal cell LO2 was evaluated by MTT method. The IC₅₀ values range from 1.5±0.1 to 55.9±7.5μM. Complex 3 shows the highest cytotoxic activity toward BEL-7402 cells (IC₅₀=1.5±0.1μM). Complex 5 displays most effective inhibition of the cell growth in A549 and HOS cells with low IC₅₀ values of 2.5±0.6 and 2.6±0.1μM, respectively. The apoptosis, reactive oxygen species, mitochondrial membrane potential, DNA damage, autophagy and anti-metastasis assay were investigated under a fluorescent microscope. The cell cycle arrest was assayed by flow cytometry, and the expression of caspases and Bcl-2 family proteins was studied by western blot. The results obtained show that the complexes induce apoptosis in BEL-7402 cells through a ROS-mediated mitochondrial dysfunction pathway. Show less

CHS-828 (N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N″-4-pyridyl guanidine) is an anticancer agent with low bioavailability and high systemic toxicity. Here we present an approach to improve the therapeutic profile of the drug using photolabile ruthenium complexes to generate light-activated prodrugs of CHS-828. Both prodrug complexes are stable in the dark but release CHS-828 when irradiated with visible light. The complexes are water-soluble and accumulate in tumour cells in very high concentrations, predominantly in the mitochondria. Both prodrug complexes are significantly less cyototoxic than free CHS-828 in the dark but their toxicity increases up to 10-fold in combination with visible light. The cellular responses to light treatment are consistent with release of the cytotoxic CHS-828 ligand. Show less

A library of new bis-picolinamide ruthenium(III) dihalide complexes of the type [RuX₂ L₂ ] (X=Cl or I, L=picolinamide) have been synthesised and characterised. The complexes exhibit different picolinamide ligand binding modes, whereby one ligand is bound (N,N) and the other bound (N,O). Structural studies revealed a mixture of cis and trans isomers for the [RuCl₂ L₂ ] complexes but upon a halide exchange reaction to yield [RuI₂ L₂ ], only single trans isomers were detected. High cytotoxic activity against human cancer cell lines was observed, with the potencies of some complexes similar to or better than cisplatin. The conversion to [RuI₂ L₂ ] substantially increased the activity towards cancer cell lines by more than twelvefold. The [RuI₂ L₂ ] complexes displayed potent activity against the A2780cis (cisplatin-resistant human ovarian cancer) cell line, with a more than fourfold higher potency than cisplatin. Equitoxic activity was observed against normoxic and hypoxic cancer cells, which indicates the potential to eradicate both the hypoxic and aerobic fractions of solid tumours with similar efficiency. The activity of selected complexes against non-cancer ARPE-19 cells was also tested. The [RuI₂ L₂ ] complexes were found to be more potent than the [RuCl₂ L₂ ] analogues and also more selective towards cancer cells with a selectivity factor in excess of sevenfold. Show less

New Ru(II) complexes with lawsone (law) characterized as trans-[Ru(law)(PPh₃)₂(N-N)]PF₆, where PPh₃ means triphenylphosphine and N-N is 2,2'-bipyridine (1), 4,4'-dimethyl-2,2'-bipyridine (2), 4,4'-dimethoxy-2,2'-bipyridine (3), 1,10-phenanthroline (4) or 4,7-diphenyl-1,10-phenanthroline (5), induce apoptosis in tumor cells. Cytotoxicity of the complexes against the tumor cell lines DU-145 (prostate cancer cells), MCF-7 (breast cancer cells), A549 (lung cancer cells) and lung non-tumor cell line MRC-5 demonstrated promising IC₅₀ values, lower than those found for the cisplatin, a drug used as a reference. Due to the high cytotoxic activity and selectivity against A549 cells line, complex (5) was selected for detailed assays. The complex (5) inhibits cells migration in concentrations in a nanomolar range, inducing tumor cell death by apoptosis, as confirmed by flow cytometry experiments. Furthermore, the antiproliferative activity of complex (5) on A549 tumor cells is attributed to a cell cycle arrest at the Sub G1 phase, followed by a decrease in the number of cells at the S phase. In addition, the interaction of the complexes (1-5) with CT-DNA was evaluated by circular dichroism, in which no changes in the secondary structure of DNA were observed, suggesting a weak interaction of the complexes with the biomolecule. On the other hand, complexes (1-5) showed a higher interaction with human serum albumin (HSA) by non-covalent van der Waals forces and hydrogen bonding, resulting in static quenching. Show less

Herein, we report a simple and rational approach to the design of a targeted therapy (i.e., complex1) whose mechanism of action involves targeting a single cancer relevant pathwayviatwo independent mechanisms. Show less

Light-activated compounds are powerful tools and potential agents for medical applications, as biological effects can be controlled in space and time. Ruthenium polypyridyl complexes can induce cytotoxic effects through multiple mechanisms, including acting as photosensitizers for singlet oxygen (¹O₂) production, generating other reactive oxygen species (ROS), releasing biologically active ligands, and creating reactive intermediates that form covalent bonds to biological molecules. A structure-activity relationship (SAR) study was performed on a series of Ru(II) complexes containing isomeric tetramethyl-substituted bipyridyl-type ligands. Three of the ligand systems studied contained strain-inducing methyl groups and created photolabile metal complexes, which can form covalent bonds to biomolecules upon light activation, while the fourth was unstrained and resulted in photostable complexes, which can generate ¹O₂. The compounds studied included both bis-heteroleptic complexes containing two bipyridine ligands and a third, substituted ligand and tris-homoleptic complexes containing only the substituted ligand. The photophysics, electrochemistry, photochemistry, and photobiology were assessed. Strained heteroleptic complexes were found to be more photoactive and cytotoxic then tris-homoleptic complexes, and bipyridine ligands were superior to bipyrimidine. However, the homoleptic complexes exhibited an enhanced ability to inhibit protein production in live cells. Specific methylation patterns were associated with improved activation with red light, and photolabile complexes were generally more potent cytotoxic agents than the photostable ¹O₂-generating compounds. Show less

Although cisplatin and its analogues have been widely utilized as anticancer metallodrugs in clinics, their serious side effects and damage to normal tissues cannot be avoided because cisplatin kills cancer cells by attacking genomic DNA. Thus the design of metallodrugs possessing different actions of anti-cancer mechanism is promising. G-quadruplex nucleic acid, which is formed by self-assembly of guanine-rich nucleic acid sequences, has recently been considered as an attractive target for anticancer drug design. The basic unit of a G-quadruplex is a G-quartet, a planar motif generated from four guanine residues pairing together through Hoogsteen like hydrogen bonds. DNA G-quadruplex (G4) structures exist in the chromosomal telomeric sequences and the promoter regions of numerous genes, including oncogenetic promoters. Formation of G4 structures within the 3′-overhang of telomeric DNA can inhibit the telomerase activity, which is silent in normal cells but up-regulated in most cancer cells, thus significantly shortening telomeres and preventing cancer cell proliferation and immortalization. Intramolecular G4 structures formed within the oncogene promoter regions can effectively inhibit oncogenen transcription and expression. Thus rational design of small molecular ligands to selectively interact, stabilize or cleave G4 structures is a promising strategy for developing potent anti-cancer drugs with selective toxicity towards cancer cells over normal ones. This review will highlight the recent development of G4-interacting metal complexes, termed G4-ligands, discussing their binding modes with G-quadruplex DNA and their potential to serve as anticancer drugs in the medical field. Introduction to the international collaboration The collaboration between Prof. Zong-Wan Mao from Sun Yat-Sen University, P. R. China and Prof. Roland K. O. Sigel from the University of Zurich, Switzerland officially began in January, 2014. The international collaborative research project titled “Chemical Biology Research of New Metallodrugs for Cancer Therapy” is supported by the Science and Technology Program of Guangdong Provincial Government [20130501c]. With the rapid development of tumor molecular pharmacology, molecular targeted anti-tumor drugs have become a hot spot in the research of cancer therapy. This international collaborative research project combines the computer simulation and in vitro drug screening platform to design a series of metallodrugs that are systematic and have structural diversity, which can target specific nucleic acid structures (e.g. G-quadruplexes), key proteins (DNA topoisomerase, telomerase, CDK kinase) associated with the occurrence and development of tumor. With the advantages of both laboratories, the structural–functional relationship, interaction modes, co-crystallization, and mechanisms of action of these newly designed metallodrugs are intensively studied, and their in vitro and in vivo anti-tumor activities are comprehensively evaluated. Show less

The synthesis and characterization of Pt(II) (1 and 2) and Ru(II) arene (3 and 4) or polypyridine (5 and 6) complexes is described. With the aim of having a functional group to form bioconjugates, one uncoordinated carboxyl group has been introduced in all complexes. Some of the complexes were selected for their potential in photodynamic therapy (PDT). The molecular structures of complexes 2 and 5, as well as that of the sodium salt of the 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine ligand (cptpy), were determined by X-ray diffraction. Different techniques were used to evaluate the binding capacity to model DNA molecules, and MTT cytotoxicity assays were performed against four cell lines. Compounds 3, 4, and 5 showed little tendency to bind to DNA and exhibited poor biological activity. Compound 2 behaves as bonded to DNA probably through a covalent interaction, although its cytotoxicity was very low. Compound 1 and possibly 6, both of which contain a cptpy ligand, were able to intercalate with DNA, but toxicity was not observed for 6. However, compound 1 was active in all cell lines tested. Clonogenic assays and apoptosis induction studies were also performed on the PC-3 line for 1. The photodynamic behavior for complexes 1, 5, and 6 indicated that their nuclease activity was enhanced after irradiation at λ = 447 nm. The cell viability was significantly reduced only in the case of 5. The different behavior in the absence or presence of light makes complex 5 a potential prodrug of interest in PDT. Molecular docking studies followed by molecular dynamics simulations for 1 and the counterpart without the carboxyl group confirmed the experimental data that pointed to an intercalation mechanism. The cytotoxicity of 1 and the potential of 5 in PDT make them good candidates for subsequent conjugation, through the carboxyl group, to "selected peptides" which could facilitate the selective vectorization of the complex toward receptors that are overexpressed in neoplastic cell lines. Show less

Following the identification of a ruthenium(II)-arene complex with an ethacrynic acid-modified imidazole ligand, which inhibits glutathione transferase (GST) and is cytotoxic to chemo-resistant cancer cells, a series of structurally related ruthenium(II)- and osmium(II)-p-cymene compounds have been prepared. In these complexes the ethacrynic acid is linked to the metals via appropriately modified pyridine ligands. The influence of the metal center and the metal:ethacrynic acid ratio on the cytotoxicity of the compounds was evaluated with the derivatives with one metal center and two ethacrynic acid moieties being the most potent against chemo-resistant A2780cisR cells (human ovarian cancer cells with acquired resistance to cisplatin). Moreover, compared to a complex with an ethacrynic acid-modified imidazole ligand (RAIMID-EA, Figure 2), these complexes display a significant degree of cancer cell specificity. Show less

The rapid and modular synthesis of the aminophosphine core has been exploited as a tool for rapid development of antitumoral metallodrug candidates. Starting with a series of structurally diverse aminophosphines, all obtained in a single step from commercial amines, a family of Ru(ii)-cymene complexes have been generated and tested in vitro for anti-tumoral activity in a series of cell lines, including the platinum-resistant A2780R. Through this approach, Ru(ii)-aminophosphine complexes have been identified with the IC₅₀ value range as low as 10-0.8 μM. Several biological assays were carried out to gain insight into the mechanism of action. Cell death by apoptosis and pH-independent action has been demonstrated. In addition, a selective cytotoxicity profile for tumoral cells over non-tumoral cells has been identified. Importantly, for the key candidates no loss of activity was observed when applied to the Pt-resistant A2780R, which highlights the potential utility of the bis-phospinoamine scaffold as an easily-tunable auxiliary ligand core in both drug discovery and subsequently a logical design of new anticancer metal-containing drugs. The complexes are characterised by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction. Show less

Ruthenium complexes capable of light-triggered cytotoxicity are appealing potential prodrugs for photodynamic therapy (PDT) and photoactivated chemotherapy (PACT). Two groups of Ru(II) polypyridyl complexes with 2-(2-pyridyl)-benzazole ligands were synthesized and investigated for their photochemical properties and anticancer activity to compare strained and unstrained systems that are likely to have different biological mechanisms of action. The structure-activity relationship was focused on the benzazole core bioisosterism and replacement of coligands in Ru(II) complexes. Strained compounds rapidly ejected the 2-(2-pyridyl)-benzazole ligand after light irradiation, and possessed strong toxicity in the HL-60 cell line both under dark and light conditions. In contrast, unstrained Ru(II) complexes were non-toxic in the absence of light, induced cytotoxicity at nanomolar concentrations after light irradiation, and are capable of light-induced DNA damage. The 90-220-fold difference in light and dark IC₅₀ values provides a large potential therapeutic window to allow for selective targeting of cells by exposure to light. Show less

A photochemically dissociating ligand in Ru(bpy)₂(dmphen)Cl₂ [bpy = 2,2'-bipyridine; dmphen = 2,9-dimethyl-1,10-phenanthroline] was found to be more cytotoxic on the ML-2 Acute Myeloid Leukemia cell line than Ru(bpy)₂(H₂O)₂²⁺ and prototypical cisplatin. Our findings illustrate the potential potency of diimine ligands in photoactivatable Ru(ii) complexes. Show less

Piplartine (piperlongumine) is a plant-derived molecule that has been receiving intense interest due to its anticancer characteristics that target the oxidative stress. In the present paper, two novel piplartine-containing ruthenium complexes [Ru(piplartine)(dppf)(bipy)](PF₆)₂ (1) and [Ru(piplartine)(dppb)(bipy)](PF₆)₂ (2) were synthesized and investigated for their cellular and molecular responses on cancer cell lines. We found that both complexes are more potent than metal-free piplartine in a panel of cancer cell lines on monolayer cultures, as well in 3D model of cancer multicellular spheroids formed from human colon carcinoma HCT116 cells. Mechanistic studies uncovered that the complexes reduced the cell growth and caused phosphatidylserine externalization, internucleosomal DNA fragmentation, caspase-3 activation and loss of the mitochondrial transmembrane potential on HCT116 cells. Moreover, the pre-treatment with Z-VAD(OMe)-FMK, a pan-caspase inhibitor, reduced the complexes-induced apoptosis, indicating cell death by apoptosis through caspase-dependent and mitochondrial intrinsic pathways. Treatment with the complexes also caused a marked increase in the production of reactive oxygen species (ROS), including hydrogen peroxide, superoxide anion and nitric oxide, and decreased reduced glutathione levels. Application of N-acetyl-cysteine, an antioxidant, reduced the ROS levels and apoptosis induced by the complexes, indicating activation of ROS-mediated apoptosis pathway. RNA transcripts of several genes, including gene related to the cell cycle, apoptosis and oxidative stress, were regulated under treatment. However, the complexes failed to induce DNA intercalation. In conclusion, the complexes are more potent than piplartine against different cancer cell lines and are able to induce caspase-dependent and mitochondrial intrinsic apoptosis on HCT116 cells by ROS-mediated pathway. Show less

Background

The RAPTA-EA1 complex [ruthenium(II)-arene 1,3,5-triaza-7-phosphaadamantane (pta) complex with an arene-tethered ethacrynic acid ligand] has been reported to overcome drug resistance that developed due to the current use of platinum-based treatments. However, the exact mechanism of action of RAPTA-EA1 remains largely unexplored and unknown.

Objective

Here we have further studied the effect of RAPTA-EA1 on BRCA1-defective HCC1937 breast cancer cells and compared its effects on BRCA1-competent MCF-7 breast cancer cells.

Method

HCC1937 and MCF-7 breast cancer cells were treated with the RAPTA-EA1 complex. The cytotoxicity of ruthenium-induced cells was evaluated by a MTT assay. Cellular uptake of ruthenium was determined by ICP-MS. Cell cycle and apoptosis were assessed using a flow cytometer. Expression of BRCA1 mRNA and its encoded protein was quantitated by a real-time RT-PCR and Western blotting.

Results

Differences in cytotoxicity were correlated with the differential accumulations of ruthenium and the induction of apoptosis. The ruthenium complex caused dramatically more damage to the BRCA1 gene in the BRCA1-defective HCC1937 cells than to the BRCA1-competent MCF-7 cells. It decreased the expression of BRCA1 mRNA in the BRCA1-competent cells, while in contrast, its expression increased in the BRCA1-defective cells. However, the expression of the BRCA1 protein was significantly reduced in both types of breast cancer cells.

Conclusion

The results presented here have demonstrated a differential cellular response for the BRCA1-defective and BRCA1-competent breast cancer cells to RAPTA-EA1. These findings have provided more insight into the actions and development of the ruthenium-based compounds for use for the treatment of breast cancer. Show less

Abstract The aim of this research is to evaluate for the first time the in vitro leishmanicidal activity and inhibition of α‐glucosidase and β‐glucuronidase of new gold(I) and gold(III) complexes involving N‐heterocyclic carbene (NHC) ligands, with the general formula [Au(X) n (NHC)R 2 ][BF 4 ] (X=Cl, OAc, R=various aromatic and aliphatic substituents). The Au(III) complexes were shown to have a significant antileishmanial activity, and were also found to be more potent inhibitors of α‐glucosidase and β‐glucuronidase enzymes than the standard drugs. Some complexes were also identified as potent anti‐inflammatory agents with activity comparable to that of tested standard drugs, allopurinol and ibuprofen. These gold complexes were also evaluated for their in vitro cytotoxic activity against HeLa (cervical cancer), MCF‐3 (breast cancer), and 3T3 (mouse fibroblast) cell lines. Show less

Ru(II)-arene complexes are attracting increasing attention due to their considerable antitumoral activity. However, it is difficult to clearly establish a direct relationship between their structure and antiproliferative activity, as substantial structural changes might not only affect their anticancer activity but also tightly control their activation site(s) and/or their biological target(s). Herein, we describe the synthesis and characterization of four ruthenium(II) arene complexes bearing bidentate N,O-donor Schiff-base ligands ([Ru(η⁶-benzene)(N-O)Cl]) that display a significantly distinct antiproliferative activity against cancer cells, despite their close structural similarity. Furthermore, we suggest there is a link between their respective antiproliferative activity and their lipophilicity, as the latter affects their ability to accumulate into cancer cells. This lipophilicity-cytotoxicity relationship was exploited to design another structurally related ruthenium complex with a much higher antiproliferative activity (IC₅₀ > 25.0 μM) against three different human cancer cell lines. Whereas this complex shows a slightly lower activity than that of clinically approved cis-platin against the same human cancer cell lines, it displays a lower toxicity in zebrafish (Danio rerio) embryos at concentrations up to 20 μM. Show less

Nanohybrids can in most cases kill cancer cells more efficiently as compared with free photosensitizers. In this work, we constructed nanohybrid Ru1@CDs composed of carbon nanodots (CDs) and a phosphorescent Ru(ii) complex (Ru1) for one- and two-photon photodynamic therapy of cancer. The photosensitizer and imaging agent Ru1 is decorated onto the nanocarrier CDs covalently. Ru1 and Ru1@CDs can penetrate into cancer cells through an energy-dependent mechanism and endocytosis, respectively. Both Ru1 and Ru1@CDs are capable of lysosome-targeted phosphorescence imaging and photodamage under either 450 nm (one-photon) or 810 nm (two-photon) excitation. Conjugation with CDs can increase the cellular uptake efficacy of Ru1. Mechanism investigations show that both Ru1 and Ru1@CDs can induce apoptosis through generation of reactive oxygen species and cathepsin-initiated apoptotic signaling pathways. Upon two-photon excitation, Ru1@CDs show better penetrability, as well as higher inhibitory effects on cancer cell growth in both 2D cell and 3D multicellular tumor spheroid models. Our work provides an effective strategy for the construction of multifunctional imaging and phototherapeutic nanohybrids for the treatment of cancer. Show less

Novel metal complexes have received great attention in the last decades due to their potential anticancer activity. Notably, ruthenium-based complexes have emerged as good alternative to the currently used platinum-based drugs for cancer therapy, providing less toxicity and side effects to patients. Glioblastoma is an aggressive and invasive type of brain tumor and despite of advances is the field of neurooncology there is no effective treatment until now. Therefore, we sought to investigate the potential antiproliferative activity of phosphine-ruthenium-based complexes on human glioblastoma cell lines. Due to its octahedral structure as opposed to the square-planar geometry of platinum(II) compounds, ruthenium(II) complexes exhibit different structure-function relationship probably acting through a different mechanism from that of cisplatin beyond their ability to bind DNA. To better improve the pharmacological activity of metal complexes we hypothesized that neutron activation of ruthenium in the complexes would allow to decrease the effective concentration of the compound needed to kill tumor cells. Herein we report on the effect of unmodified and neutron activated phosphine ruthenium II complexes on glioblastoma cell lines carrying wild-type and mutated p53 tumor suppressor gene. Induction of apoptosis/authophagy as well as generation of reactive oxygen species were determined. The phosphine ruthenium II complexes tested were highly active against glioblastoma cell lines inducing cell death both through apoptosis and autophagy in a p53 independent fashion. Neutron activation of ruthenium compounds rendered them more active than their original counterparts suggesting a new strategy to improve the antitumor activity of these compounds. Show less

Four mononuclear [(L-L)₂ Ru(tatpp)]²⁺ and two dinuclear [(L-L)₂ Ru(tatpp)Ru(L-L)₂ ]⁴⁺ ruthenium(II) polypyridyl complexes (RPCs) containing the 9,11,20,22-tetraazatetrapyrido[3,2-a:2',3'-c:3'',2''-l:2''',3'''-n]pentacene (tatpp) ligand were synthesized, in which L-L is a chelating diamine ligand such as 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 3,4,7,8-tetramethyl-1,10-phenanthroline (Me₄ phen) or 4,7-diphenyl-1,10-phenanthroline (Ph₂ phen). These Ru-tatpp analogues all undergo reduction reactions with modest reducing agents, such as glutathione (GSH), at pH 7. These, plus several structurally related but non-redox-active RPCs, were screened for DNA cleavage activity, cytotoxicity, acetylcholinesterase (AChE) inhibition, and acute mouse toxicity, and their activities were examined with respect to redox activity and lipophilicity. All of the redox-active RPCs show single-strand DNA cleavage in the presence of GSH, whereas none of the non-redox-active RPCs do. Low-micromolar cytotoxicity (IC₅₀ ) against malignant H358, CCL228, and MCF7 cultured cell lines was mainly restricted to the redox-active RPCs; however, they were substantially less toxic toward nonmalignant MCF10 cells. The IC₅₀ values for AChE inhibition in cell-free assays and the acute toxicity of RPCs in mice revealed that whereas most RPCs show potent inhibitory action against AChE (IC₅₀ values <15 μm), Ru-tatpp complexes as a class are surprisingly well tolerated in animals relative to other RPCs. Show less