Diversity in Guanine-Selective DNA Binding Modes for an Organometallic Ruthenium Arene Complex

Solution structure, oxidative DNA damage, biological activity and molecular docking of ternary copper(II) L-argininato complexes

Continuing our search for metal drugs with markedly higher toxicity to cancer cells than to normal cells, we evaluated the effect of 2,2'-bipyridine (bpy) as a co-ligand in the compounds [Cu(μ-O,O'-NO3)(l-Arg)(bpy)]NO3}n (1), [CuCl(l-Arg)(bpy)]Cl·3H2O (2) (l-Arg= l-arginine), on DNA interaction, cytotoxic and antiproliferative activity, compared to the effects induced by other co-ligands i.e. 1,10-phenanthroline (phen) and SCN- ions, in similar Cu(II) compounds we have studied previously. Potentiometric, EPR and UV-Vis experiments were first used to structurally characterise the complexes formed in solutions 1 and 2 and in model Cu(II)/bpy/l-Arg systems. Gel electrophoresis in the presence of H2O2 was used to identify DNA damage by 1 and 2. In addition, cyclic voltammetry of both compounds was performed to confirm the existence of Cu(II)/Cu(I) redox pairs involved in the free radical mechanism of this DNA damage. The DNA binding constants of 1 and 2 were determined spectrophotometrically. The selectivity of the cytotoxic and antiproliferative activity of compounds 1 and 2 was tested in vitro against human lung adenocarcinoma (A549), liver cancer (HepG2) and normal cells in comparison with those previously observed by us for compounds consisting of phen and SCN- ligands. Molecular docking calculations were performed for [Cu(l-Arg)(bpy)]2+ (present in solutions of 1 and 2) interacting with B-DNA (aureolin), metalloproteinase (S. aureus) and penicillin-binding protein (E. coli) to determine the nature of the complex-receptor interaction, potential binding modes and energies.

Immunostimulation with chemotherapy of a ruthenium-arene complex via blockading CD47 signal in chronic myelogenous leukemia cells

Combination of novel immunomodulation and traditional chemotherapy has become a new tendency in cancer treatment. Increasing evidence suggests that blocking the "don't eat me" signal transmitted by the CD47 can promote the phagocytic ability of macrophages to cancer cells, which might be promising for improved cancer chemoimmunotherapy. In this work, we conjugated CPI-alkyne modified by Devimistat (CPI-613) with ruthenium-arene azide precursor Ru-N₃ by copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction to construct Ru complex CPI-Ru. CPI-Ru exhibited satisfactory cytotoxicity towards the K562 cells while nearly non-toxic towards the normal HLF cells. CPI-Ru has been demonstrated to cause severe damage to mitochondria and DNA, ultimately inducing cancer cell death through the autophagic pathway. Moreover, CPI-Ru could significantly downregulate the expression of CD47 on the surface of K562 accompanied by the enhanced immune response by targeting the blockade of CD47. This work provides a new strategy for utilizing metal-based anticancer agents to block CD47 signal to achieve chemoimmunotherapy in chronic myeloid leukemia treatment.

Mononuclear half-sandwich nd7 metallo drug complexes based on bidentate N∩N dendritic scaffolds: DFT (B3LYP; BP86 and B3PW91) examination

Through an use of three functionals (B3PW91, B3LYP and BP86) associated to a generic basis set LanL2DZ for transition metals (as well as halogen atoms) and 6-311+G (d,p) for others atoms, an examination of the bonding properties of a series of mononuclear half-sandwich nd⁷ transition metal (anticancer) complexes based on N∩N dendritic scaffolds (L) has been done. Collectively, complexes studied have adopted the piano-stool environment. An examination of the performance of each functional has shown that for the most reliable geometrical analysis of Metal-Nitrogen and Metal-Halogen bonds, the B3LYP and B3PW91 functionalities are suitable respectively. Regardless of the halogen ligand adopted, the B3LYP metal-nitrogen bond lengths are the most widely overestimated. A correlation has been built between the retained charge on each divalent transition metal cation and its metal ion affinity (MIA). Topological examinations reveal the higher instability of metal-N bonds compared to metal-X ones (X = Cl and Br). By the mean of the energy decomposition analysis, a predominant electrostatic character of metal … halogen and [LCP]^- … [MX]⁺ interaction has been demonstrated. The transition metal atom … (hydrophobic) surface (Cp*) interaction is most pronounced for the chloride rhodium complexes of rhodium (combined with (E)-N-(pyridin-2-ylmethylene) Propan-1-amine and 2,2'- dipyridylketone ligands and iridium combined with 2,2'- dipyridylketone ligand. The charge decomposition analysis displays the weakening of the [Formula: see text] bonds in the studied complexes.

Unlocking the potential of iridium and ruthenium arene complexes as anti-tumor and anti-metastasis chemotherapeutic agents

It is a major challenge to design novel multifunctional metal-based chemotherapeutic agents for anti-tumor and anti-metastasis applications. Two complexes (OA-Ir and OA-Ru) were synthesized via CuAAC (copper-catalyzed azide-alkyne cycloaddition) reaction from nontoxic Ir-N₃ or Ru-N₃ species and low toxic alkynyl precursor OA-Alkyne, and exhibited satisfactory anti-tumor and anti-metastasis pharmacological effects. Conjugation of Oleanolic acid (OA) and metal-arene species significantly enhanced the cytotoxicity in A2780 cells compared to the precursors through mitochondrial-induced autophagy pathway. Moreover, the two complexes could inhibit the cell metastasis and invasion through damage of actin dynamics and down-regulation of MMP2/MMP9 proteins. Combination of two precursors improved the lipophilicity and biocompatibility, simultaneously enhanced the cell uptake and the mitochondrial accumulation of metal-arene complexes, which caused mitochondrial membrane potential damage, oxidative phosphorylation, ATP depletion and autophagy. Besides, OA-Ir and OA-Ru displayed excellent activity to disintegrate the 3D multicellular tumor spheroids, showing potential for the treatment of solid tumors. This work provides a new way for developing novel metal-based complexes via CuAAC reaction for simultaneously inhibiting tumor proliferation and metastasis.

Development of novel ruthenium(II)-arene complexes displaying potent anticancer effects in glioblastoma cells

Glioblastomas (GBs) are highly aggressive and malignant brain tumors, which are highly resistant to conventional multimodal treatments, leading to their abysmal prognosis. Herein, we designed two organometallic half-sandwich Ru(ii)-η6-p-cymene complexes containing Schiff bases derived from 3-aminoquinoline and 2-hydroxy-benzaldehyde (L1) and 2-hydroxy-naphthaldehyde (L2), namely [Ru(η6-p-cymene)(L1)Cl] (1) and [Ru(η6-p-cymene)(L2)Cl] (2), respectively, and studied their activity on GB cells. Both complexes were structurally characterized using single-crystal X-ray diffraction, which exhibited their half-sandwich three-legged piano-stool geometry. Furthermore, we studied their physicochemical behavior, solution speciation, aquation kinetics, and photo-substitution reactions using various spectroscopic methods. The complexes exhibited a moderate binding affinity with calf-thymus (CT)-DNA (Kb ∼ 105 M-1). The complexes effectively interacted with human serum albumin (HSA) (K ∼ 105 M-1) with preferential tryptophan binding, as determined via synchronous fluorescence studies. The in vitro studies showed their significant antiproliferative activity against an aggressive human GB cell line, LN-229 (IC50 = 22.8 μM), with moderate selectivity relative to normal mouse fibroblast L929 cells. Notably, [Ru(η6-p-cymene)(L1)Cl] (1) exhibited a higher selectivity index (S.I.) than [Ru(η6-p-cymene)(L2)Cl] (2) and cisplatin. We evaluated the clonogenic potential of the GB cells using a colony formation assay in the presence of complex 1. Excitingly, it showed ∼75% inhibition of the clonogenic potential of GB cells at the IC50 concentration. Complex 1 also effectively lowered the migratory potential of the GB cells, as assessed by the wound healing assay. The studied compound led to the apoptosis of GB cells, as evidenced by nuclear condensation, blebbing, and enhanced caspase 3/7 activity, and thus has anticipated utility in the treatment of GBs using photochemotherapy.

Translational Theragnosis of Ovarian Cancer: where do we stand?

BACKGROUND

Ovarian cancer is the second most common gynecologic malignancy, accounting for approximately 220,000 deaths annually worldwide. Despite radical surgery and initial high response rates to platinum- and taxane-based chemotherapy, most patients experience a relapse, with a median progression-free survival of only 18 months. Overall survival is approximately 30% at 5 years from the diagnosis. In comparison, patients out from breast cancer are more than 80 % after ten years from the disease discovery. In spite of a large number of published fundamental and applied research, and clinical trials, novel therapies are urgently needed to improve outcomes of the ovarian cancer. The success of new drugs development in ovarian cancer will strongly depend on both fully genomic disease characterization and, then, availability of biomarkers able to identify women likely to benefit from a given new therapy.

METHODS

In this review, the focus is given to describe how complex is the diseases under the simple name of ovarian cancer, in terms of cell tumor types, histotypes, subtypes, and specific gene mutation or differently expressed in the tumor with respect the healthy ovary. The first- and second-line pharmacological treatment clinically used over the last fifty years are also described. Noteworthy achievements in vitro and in vivo tested new drugs are also summarized. Recent literature related to up to date ovarian cancer knowledge, its detection by biomarkers and chemotherapy was searched from several articles on Pubmed, Google Scholar, MEDLINE and various Governmental Agencies till April 2019.

RESULTS

The papers referenced by this review allow a deep analysis of status of the art in the classification of the several types of ovarian cancer, the present knowledge of diagnosis based on biomarkers and imaging techniques, and the therapies developed over the past five decades.

CONCLUSION

This review aims at stimulating more multi-disciplinary efforts to identify a panel of novel and more specific biomarkers to be used to screen patients for a very early diagnosis, to have prognosis and therapy efficacy indications. The desired final goal would be to have available tools allowing to reduce the recurrence rate, increase both the disease progression free interval and of course the overall survival at five years from the diagnosis that today is still very low.

Using bio-orthogonally catalyzed lethality strategy to generate mitochondria-targeting anti-tumor metallodrugs in vitro and in vivo

Synthetic lethality was proposed nearly a century ago by geneticists and recently applied to develop precision anti-cancer therapies. To exploit the synthetic lethality concept in the design of chemical anti-cancer agents, we developed a bio-orthogonally catalyzed lethality (BCL) strategy to generate targeting anti-tumor metallodrugs both in vitro and in vivo. Metallodrug Ru-rhein was generated from two non-toxic species Ru-N₃ and rhein-alkyne via exclusive endogenous copper-catalyzed azide alkyne cycloaddition (CuAAC) reaction without the need of an external copper catalyst. The non-toxic species Ru-arene complex Ru-N₃ and rhein-alkyne were designed to perform this strategy, and the mitochondrial targeting product Ru-rhein was generated in high yield (>83%) and showed high anti-tumor efficacy in vitro. This BCL strategy achieved a remarkable tumor suppression effect on the tumor-bearing mice models. It is interesting that the combination of metal-arene complexes with rhein via CuAAC reaction could transform two non-toxic species into a targeting anti-cancer metallodrug both in vitro and in vivo, while the product Ru-rhein was non-toxic towards normal cells. This is the first example that exclusive endogenous copper was used to generate metal-based anti-cancer drugs for cancer treatment. The anti-cancer mechanism of Ru-rhein was studied and autophagy was induced by increased reactive oxygen species and mitochondrial damage. The generality of this BCL strategy was also studied and it could be extended to other metal complexes such as Os-arene and Ir-arene complexes. Compared with the traditional methods for cancer treatment, this work presented a new approach to generating targeting metallodrugs in vivo via the BCL strategy from non-toxic species in metal-based chemotherapy.

Experimental and theoretical characterization of the strong effects on DNA stability caused by half-sandwich Ru(II) and Ir(III) bearing thiabendazole complexes

The synthesis and characterization of two half-sandwich complexes of Ru(II) and Ir(III) with thiabendazole as ancillary ligand and their DNA binding ability were investigated using experimental and computational methods. ¹H NMR and acid-base studies have shown that aquo-complexes are the reactive species. Kinetic studies show that both complexes bind covalently to DNA through the metal site and non covalently through the ancillary ligand. Thermal stability studies, viscosity, circular dichroism measurements and quantum chemical calculations have shown that the covalent binding causes breaking of the H-bonding between base pairs, bringing about DNA denaturation and compaction. Additionally, molecular dynamics (MD) simulations and quantum mechanics/molecular mechanics (QM/MM) calculations shed light into the binding features of the Ru(II) and Ir(III) complexes and their respective enantiomers toward double-helical DNA, highlighting the important role played by the NˆN ancillary ligand once the complexes are covalently linked to DNA. Moreover, metal quantification in the nucleus of SW480 colon adenocarcinoma cells were carried out by inductively coupled plasma-mass spectrometry (ICP-MS), both complexes are more internalized than cisplatin after 4 h of exposition. However, in spite of the dramatic changes in the helicity of the DNA secondary structure induced by these complexes and their nuclear localization, antiproliferative studies have revealed that both, Ru(II) and Ir(III) complexes, cannot be considered cytotoxic. This unexpected behavior can be justified by the fast formation of aquo-complexes, which may react with components of the cell culture medium or the cytoplasm compartment in such a way that they may become deactivated before reaching DNA.

Metallation-Induced Heterogeneous Dynamics of DNA Revealed by Single-Molecule FRET

The metallation of nucleic acids is key to wide-ranging applications, from anticancer medicine to nanomaterials, yet there is a lack of understanding of the molecular-level effects of metallation. Here, we apply single-molecule fluorescence methods to study the reaction of an organo-osmium anticancer complex and DNA. Individual metallated DNA hairpins are characterised using Förster resonance energy transfer (FRET). Although ensemble measurements suggest a simple two-state system, single-molecule experiments reveal an underlying heterogeneity in the oligonucleotide dynamics, attributable to different degrees of metallation of the GC-rich hairpin stem. Metallated hairpins display fast two-state transitions with a two-fold increase in the opening rate to ≈2 s^-1 , relative to the unmodified hairpin, and relatively static conformations with long-lived open (and closed) states of 5 to ≥50 s. These studies show that a single-molecule approach can provide new insight into metallation-induced changes in DNA structure and dynamics.

The interactions of the ruthenium(II)-cymene complexes with lysozyme and cytochrome c

The reactions of four cymene-capped ruthenium(II) compounds with pro-apoptotic protein, cytochrome c (Cyt), and anti-proliferative protein lysozyme (Ly) in carbonate buffer were investigated by ESI-MS, UV-vis absorption, and CD spectroscopy. The complexes with two chloride ligands (C2 and C3) were more reactive toward proteins than those with only one (C1 and C4), and the complex with S,N-chelating ligand (C4) was less reactive than one with O,N-chelating ligand (C1). Dehalogenated complexes are most likely species, initially coordinating proteins for all tested complexes. During the time, protein adducts vividly exchanged non-arene organic ligand L with CO₃^2- and OH^-, while cymene moiety was retained. In water, only dehalogenated adducts were identified suggesting that in vivo, in the presence of various anions, dynamic ligand exchange could generate different intermediate protein species. Although all complexes reduced Cyt, the reduction was not dependent on their reactivity to protein, implying that initially noncovalent binding to Cyt occurs, causing its reduction, followed by coordination to protein. Cyt reduction was accompanied with rupture of ferro-Met 80 and occupation of this hem coordination site by a histidine His-33/26. Therefore, in Cyt with C2 and C3, less intensive reduction of hem iron leaves more unoccupied target residues for Ru coordination, leading to more efficient formation of covalent adducts, in comparison to C1 and C4. This study contributes to development of new protein-targeted Ru(II) cymene complexes, and to the design of new cancer therapies based on targeted delivery of Ru(II) arene complexes bound on pro-apoptotic/anti-proliferative proteins as vehicles.

DNA/lysozyme binding propensity and nuclease properties of benzimidazole/2,2'-bipyridine based binuclear ternary transition metal complexes

In the present contribution, new binuclear ternary complexes; [M2(bpy)4L](ClO4)4 (M = Co(ii) (1) and Ni(ii) (2); bpy = 2,2'-bipyridine; L = 1,1'-(hexane-1,6-diyl)bis[2-(pyridin-2-yl)1H-benzimidazole] and [Cu2(bpy)2(OH2)2L](BF4)4 (3) were synthesized, characterized and screened for their antimicrobial activity and cytotoxicity against human liver carcinoma cells (HepG-2) as well as non-malignant human embryonic kidney cells (HEK-293). The structural studies were complemented by density functional theory (DFT) calculations. DNA binding of 1-3 was spectrophotometrically studied. The DNA cleavage ability of 1-3 towards the supercoiled plasmid DNA (pBR322 DNA) was examined through gel electrophoresis. Compound 3 has the highest cytotoxic activity (IC50 = 3.5 μg mL-1) against HepG-2 among the investigated complexes and is non cytotoxic to noncancerous HEK-293. Complexes (1 and 2) exhibited toxicity to HEK-293 with IC50 values of 30.3 and 23.5 μg mL-1 in that order. While compound 1 showed antifungal activity against Cryptococcus neoformans, complex 2 exhibited its toxicity against Candida albicans.

Toward Multi-Targeted Platinum and Ruthenium Drugs-A New Paradigm in Cancer Drug Treatment Regimens?

While medicinal inorganic chemistry has been practised for over 5000 years, it was not until the late 1800s when Alfred Werner published his ground-breaking research on coordination chemistry that we began to truly understand the nature of the coordination bond and the structures and stereochemistries of metal complexes. We can now readily manipulate and fine-tune their properties. This had led to a multitude of complexes with wide-ranging biomedical applications. This review will focus on the use and potential of metal complexes as important therapeutic agents for the treatment of cancer. With major advances in technologies and a deeper understanding of the human genome, we are now in a strong position to more fully understand carcinogenesis at a molecular level. We can now also rationally design and develop drug molecules that can either selectively enhance or disrupt key biological processes and, in doing so, optimize their therapeutic potential. This has heralded a new era in drug design in which we are moving from a single- toward a multitargeted approach. This approach lies at the very heart of medicinal inorganic chemistry. In this review, we have endeavored to showcase how a "multitargeted" approach to drug design has led to new families of metallodrugs which may not only reduce systemic toxicities associated with modern day chemotherapeutics but also address resistance issues that are plaguing many chemotherapeutic regimens. We have focused our attention on metallodrugs incorporating platinum and ruthenium ions given that complexes containing these metal ions are already in clinical use or have advanced to clinical trials as anticancer agents. The "multitargeted" complexes described herein not only target DNA but also contain either vectors to enable them to target cancer cells selectively and/or moieties that target enzymes, peptides, and intracellular proteins. Multitargeted complexes which have been designed to target the mitochondria or complexes inspired by natural product activity are also described. A summary of advances in this field over the past decade or so will be provided.

Intracellular Catalysis with Selected Metal Complexes and Metallic Nanoparticles: Advances toward the Development of Catalytic Metallodrugs

Platinum-containing drugs (e.g., cisplatin) are among the most frequently used chemotherapeutic agents. Their tremendous success has spurred research and development of other metal-based drugs, with notable achievements. Generally, the vast majority of metal-based drug candidates in clinical and developmental stages are stoichiometric agents, i.e., each metal complex reacts only once with their biological target. Additionally, many of these metal complexes are involved in side reactions, which not only reduce the effective amount of the drug but may also cause toxicity. On a separate note, transition metal complexes and nanoparticles have a well-established history of being potent catalysts for selective molecular transformations, with examples such as the Mo- and Ru-based catalysts for metathesis reactions (Nobel Prize in 2005) or palladium catalysts for C-C bond forming reactions such as Heck, Negishi, or Suzuki reactions (Nobel Prize in 2010). Also, notably, no direct biological equivalent of these transformations exists in a biological environment such as bacteria or mammalian cells. It is, therefore, only logical that recent interest has focused on developing transition-metal based catalytic systems that are capable of performing transformations inside cells, with the aim of inducing medicinally relevant cellular changes. Because unlike in stoichiometric reactions, a catalytically active compound may turn over many substrate molecules, only very small amounts of such a catalytic metallodrug are required to achieve a desired pharmacologic effect, and therefore, toxicity and side reactions are reduced. Furthermore, performing catalytic reactions in biological systems also opens the door for new methodologies to study the behavior of biomolecules in their natural state, e.g., via in situ labeling or by increasing/depleting their concentration at will. There is, of course, an art to the choice of catalysts and reactions which have to be compatible with biological conditions, namely an aqueous, oxygen-containing environment. In this review, we aim to describe new developments that bring together the far-distant worlds of transition-metal based catalysis and metal-based drugs, in what is termed "catalytic metallodrugs". Here we will focus on transformations that have been performed on small biomolecules (such as shifting equilibria like in the NAD⁺/NADH or GSH/GSSG couples), on non-natural molecules such as dyes for imaging purposes, or on biomacromolecules such as proteins. Neither reactions involving release (e.g., CO) or transformation of small molecules (e.g., ¹O₂ production), degradation of biomolecules such as proteins, RNA or DNA nor light-induced medicinal chemistry (e.g., photodynamic therapy) are covered, even if metal complexes are centrally involved in those. In each section, we describe the (inorganic) chemistry involved, as well as selected examples of biological applications in the hope that this snapshot of a new but quickly developing field will indeed inspire novel research and unprecedented interactions across disciplinary boundaries.

Selective binding of an organoruthenium complex to G-rich human telomeric sequence by tandem mass spectrometry

RATIONALE

Human telomeric DNA is reported to be a potential target for anticancer organometallic ruthenium(II) complexes, however, the interaction sites were not clearly discriminated and identified.

METHODS

In the current study, tandem mass spectrometry (MS/MS) using collision-induced dissociation (CID) was firstly introduced to identify the interaction sites of an organometallic ruthenium(II) complex [(η⁶ -biphenyl)Ru(en)Cl][PF₆ ] (1; en = ethylenediamine) with 5'-T₁ T₂ A₃ G₄ G₅ G₆ -3' (I), the repeating unit of human telomeric DNA, in both positive- and negative-ion mode at a low reaction molar ratio (1/I = 0.2) which was applied to preserve the site selectivity.

RESULTS

Mass spectrometric results showed that mono-ruthenated I was the main product under the conditions. In positive-ion mode, MS/MS results indicated that ruthenium complex 1 binds to T₂ or G₆ in strand I. However, in negative-ion mode, no efficient information was obtained for exact identification of ruthenation sites which may be attributed to losses of fragment ions due to charge neutralization by the coordination of the positively charged ruthenium complex to the short MS/MS fragments.

CONCLUSIONS

This is the first report of using top-down MS to characterize the interactions of organometallic ruthenium(II) complexes and human telomeric DNA. Thymine can be thermodynamically competitive with guanine for binding to ruthenium complexes even at low reaction molar ratio, which inspired us to explore in greater depth the significance of thymine binding.

Rigid dinuclear ruthenium-arene complexes showing strong DNA interactions

Six novel dinuclear Ru(II)-arene complexes [Ru₂(η⁶-p-cymene)₂(1,3-bib)₂Cl₂]×₂·Solvent (X = Cl^- (1), I^- (2), NO₃^- (3), BF₄^- (4), PF₆^- (5), CF₃SO₃^- (6); 1,3-bib = 1,3-di(1H-imidazol-1-yl) benzene) were synthesized and fully characterized by FT-IR, ¹H NMR, ESI-MS, Elemental Analysis (EA) and Powder X-ray Diffraction (PXRD). Single crystal X-ray diffractions studies showed that 3 and 4 have rigid bowl-like structures, where one counter-anion (NO₃^- for 3 and BF₄^- for 4) was trapped inside the cavity to balance the charge, respectively. Even complexes 1-6 showed only moderate or little anti-proliferative activity toward cancer cells, strong interactions with DNA molecules through intercalation, however, were confirmed by UV-Vis, CD and fluorescence spectroscopy. Apoptosis and cell cycle arrest studies for complex 2 with cancer A549 cells indicated concentration-dependent late apoptosis and the G1/G0 phase arrest. Interactions with the tripeptide glutathione (γ-L-Glu-L-Cys-Gly, GSH) might explain the relatively low antiproliferative potency of these complexes. This class of rigid dinuclear cations hold potential as DNA-targeting anticancer agents if their uptake and delivery could be under controlled.

Binding of Organometallic Ruthenium Anticancer Complexes to DNA: Thermodynamic Base and Sequence Selectivity

Organometallic ruthenium(II) complexes [(η⁶-arene)Ru(en)Cl][PF₆] (arene = benzene (1), p-cymene (2), indane (3), and biphenyl (4); en = ethylenediamine) are promising anticancer drug candidates both in vitro and in vivo. In this paper, the interactions between ruthenium(II) complexes and 15-mer single- and double-stranded oligodeoxynucleotides (ODNs) were thermodynamically investigated using high performance liquid chromatography (HPLC) and electrospray ionization mass spectroscopy (ESI-MS). All of the complexes bind preferentially to G₈ on the single strand 5'-CTCTCTT₇G₈T₉CTTCTC-3' (I), with complex 4 containing the most hydrophobic ligand as the most reactive one. To the analogs of I (changing T₇ and/or T₉ to A and/or C), complex 4 shows a decreasing affinity to the G₈ site in the following order: -AG₈T- (K: 5.74 × 10⁴ M^-1) > -CG₈C- > -TG₈A- > -AG₈A- > -AG₈C- > -TG₈T- (I) ≈ -CG₈A- (K: 2.81 × 10⁴ M^-1). In the complementary strand of I, the G bases in the middle region are favored for ruthenation over guanine (G) bases in the end of oligodeoxynucleotides (ODNs). These results indicate that both the flanking bases (or base sequences) and the arene ligands play important roles in determining the binding preference, and the base- and sequence-selectivity, of ruthenium complex in binding to the ODNs.

"Head-to-head" double-hamburger-like structure of di-ruthenated d(GpG) adducts of mono-functional Ru-arene anticancer complexes

Guanine bases in DNA are targets for some Ru-arene anticancer complexes. We have investigated the structure of the novel di-ruthenated d(GpG) adduct Ru₂-GpG (where Ru = {(η⁶-biphenyl)-Ru(en)}²⁺ (1')) in aqueous solution. 2D NMR results indicate that there are two conformers, supported by modeling studies. The major conformer I is a novel double-hamburger-like structure with a "head-to-head" (HH) base arrangement involving hydrophobic interactions between neighboring arene rings, the first example of a HH d(GpG) adduct constructed by weak interactions. Hence there are significant differences compared to Pt-d(GpG) adducts formed by cisplatin. There is no obviously rigid bending for the major conformer I. The minor conformer II of Ru₂-GpG has a back-to-back structure, with two ruthenated guanine bases flipped away from each other. 19-23 base-pair oligodeoxyribonucleotides containing central TGGT sequences di-ruthenated by 1 show no directional bending, only slightly distorted di-ruthenated duplexes, consistent with the NMR data for conformer I. The structural differences and similarities of d(GpG) residues which are di-ruthenated or cross-linked by platination are discussed in the context of the biological activity of these metal complexes.

Lysozyme and DNA binding affinity of Pd(ii) and Pt(ii) complexes bearing charged N,N-pyridylbenzimidazole bidentate ligands

The 2-pyridylbenzimidazole Pt(ii) complex functionalized with triphenylphosphonium interacts covalently with lysozyme via the loss of labile ligands and the departure of the TPP⁺ part.

Ruthenium complex exerts antineoplastic effects that are mediated by oxidative stress without inducing toxicity in Walker-256 tumor-bearing rats

The present study evaluated the in vivo antitumor effects and toxicity of a new Ru(II) compound, cis-(Ru[phen]₂[ImH]₂)²⁺ (also called RuphenImH [RuC]), against Walker-256 carcinosarcoma in rats. After subcutaneous inoculation of Walker-256 cells in the right pelvic limb, male Wistar rats received 5 or 10mgkg^-1 RuC orally or intraperitoneally (i.p.) every 3 days for 13 days. A positive control group (2mgkg^-1 cisplatin) and negative control group (vehicle) were also used. Tumor progression was checked daily. After treatment, tumor weight, plasma biochemistry, hematology, oxidative stress, histology, and tumor cell respiration were evaluated. RuC was effective against tumors when administered i.p. but not orally. The highest i.p. dose of RuC (10mgkg^-1) significantly reduced tumor volume and weight, induced oxidative stress in tumor tissue, reduced the respiration of tumor cells, and induced necrosis but did not induce apoptosis in the tumor. No clinical signs of toxicity or death were observed in tumor-bearing or healthy rats that were treated with RuC. These results suggest that RuC has antitumor activity through the modulation of oxidative stress and impairment of oxidative phosphorylation, thus promoting Walker-256 cell death without causing systemic toxicity. These effects make RuC a promising anticancer drug for clinical evaluation.

A novel strategy to construct Janus metallamacrocycles with both a Ru–arene face and an imidazolium face

We report a novel strategy to synthesize Janus metallocyclic Ru–arene complexes with both a Ru–arene face and a didentate imidazolium face, which possess unusual structures and properties.

Discovery of a dual-targeting organometallic ruthenium complex with high activity inducing early stage apoptosis of cancer cells

Ruthenium based complexes are promising antitumour candidates due to their lower toxicity and better water-solubility compared to the platinum antitumour complexes. An epidermal growth factor receptor (EGFR) has been found to be overexpressed in a large set of tumour cells. In this work, a series of organoruthenium complexes containing EGFR-inhibiting 4-anilinoquinazoline pharmacophores were synthesised and characterised. These complexes exhibited excellent inhibitory activity against EGFR and high affinity to interact with DNA via minor groove binding, featuring dual-targeting properties. In vitro screening demonstrated that the as-prepared ruthenium complexes are anti-proliferating towards a series of cancer cell lines, in particular the non-small-cell lung cancer cell line A549. Fluorescence-activated cell sorting analysis and fluorescence microscopy revealed that the most active complex 3 induced much more early-stage cell apoptosis than its cytotoxic arene ruthenium analogue and the EGFR-inhibiting 4-anilinoquinazolines, verifying the synergetic effect of the two mono-functional pharmacophores.

A comparative study on the interactions of human copper chaperone Cox17 with anticancer organoruthenium(II) complexes and cisplatin by mass spectrometry

Herein we report investigation of the interactions between anticancer organoruthenium complexes, [(η(6)-arene)Ru(en)(Cl)]PF6 (en=ethylenediamine, arene=p-cymene (1) or biphenyl (2)), and the human copper chaperone protein Cox17 by mass spectrometry with cisplatin as a reference. The electrospray ionization mass spectrometry (ESI-MS) results indicate much weaker binding of the ruthenium complexes than that of cisplatin to apo-Cox172s-s, the functional state of Cox17. Up to tetra-platinated Cox17 adducts were identified while only mono-ruthenated and a little amount of di-ruthenated Cox17 adducts were detected even for the reactions with 10-fold excess of the Ru complexes. However, ESI-MS analysis coupled with liquid chromatography of tryptic digests of metalated proteins identified only three platination sites as Met4, Cys27 and His47 residues, possibly due to the lower abundance or facile dissociation of Pt bindings at other sites. Complexes 1 and 2 were found to bind to the same three residues with Met4 as the major site. Inductively coupled plasma mass spectrometry results revealed that ~7mol Pt binding to 1mol apo-Cox172s-s molecules, compared to only 0.17 (1) and 0.10 (2) mol Ru to 1mol apo-Cox172s-s. This is in line with the circular dichroism results that much larger unfolding extent of α-helix of apo-Cox172s-s was observed upon cisplatin binding than that upon organoruthenium bindings. These results collectively indicate that Cox17 might not participate in the action of these anticancer organoruthenium complexes, and further verify the distinct anticancer mechanism of the organoruthenium(II) complexes from cisplatin.

Dual-targeting organometallic ruthenium(II) anticancer complexes bearing EGFR-inhibiting 4-anilinoquinazoline ligands

We have recently demonstrated that complexation with (η(6)-arene)Ru(II) fragments confers 4-anilinoquinazoline pharmacophores a higher potential for inducing cellular apoptosis while preserving the highly inhibitory activity of 4-anilinoquinazolines against EGFR and the reactivity of the ruthenium centre to 9-ethylguanine (Chem. Commun., 2013, 49, 10224-10226). Reported herein are the synthesis, characterisation and evaluation of the biological activity of a new series of ruthenium(ii) complexes of the type [(η(6)-arene)Ru(N,N-L)Cl]PF6 (arene = p-cymene, benzene, 2-phenylethanol or indane, L = 4-anilinoquinazolines). These organometallic ruthenium complexes undergo fast hydrolysis in aqueous solution. Intriguingly, the ligation of (arene)Ru(II) fragments with 4-anilinoquinazolines not only makes the target complexes excellent EGFR inhibitors, but also confers the complexes high affinity to bind to DNA minor grooves while maintaining their reactivity towards DNA bases, characterising them with dual-targeting properties. Molecular modelling studies reveal that the hydrolysis of these complexes is a favourable process which increases the affinity of the target complexes to bind to EGFR and DNA. In vitro biological activity assays show that most of this group of ruthenium complexes are selectively active inhibiting the EGF-stimulated growth of the HeLa cervical cancer cell line, and the most active complex [(η(6)-arene)Ru(N,N-L13)Cl]PF6 (, IC50 = 1.36 μM, = 4-(3'-chloro-4'-fluoroanilino)-6-(2-(2-aminoethyl)aminoethoxy)-7-methoxyquinazoline) is 29-fold more active than its analogue, [(η(6)-arene)Ru(N,N-ethylenediamine)Cl]PF6, and 21-fold more active than gefitinib, a well-known EGFR inhibitor in use clinically. These results highlight the strong promise to develop highly active ruthenium anticancer complexes by ligation of cytotoxic ruthenium pharmacophores with bioactive organic molecules.

[(η(6)-p-cymene)Ru(H2O)3](2+) binding capability of aminohydroxamates - A solution and solid state study

Complex forming capabilities of [(η(6)-p-cymene)Ru(H2O)3](2+) with aminohydroxamates (2-amino-N-hydroxyacetamide (α-alahaH), 3-amino-N-hydroxypropanamide (β-alahaH) and 4-amino-N-hydroxybutanamide (γ-abhaH)) having the primary amino group in different chelatable position to the hydroxamic function were studied by pH-potentiometry, NMR and MS methods. Formation of stable [O,O] and mixed [O,O][N,N] chelated mono- and dinuclear species is detected in partially slow with α-alahaH and β-alahaH or in fast processes with γ-abhaH and the formation constants of the complexes present in aqueous solution are reported. Synthesis, spectral (NMR, IR) and ESI mass spectrometric characterization of novel dinuclear α-alaninehydroximato complexes containing the half-sandwich type Ru(II) core is described. The crystal and molecular structure of [{(η(6)-p-cymene)Ru}2(μ(2)-α-alahaH-1)(H2O)Br]Br∙H2O (1) and [{(η(6)-p-cymene)Ru}2(μ(2)-α-alahaH-1)(H2O)Cl]BF4∙H2O (2) was determined by single crystal X-ray diffraction method. In the complexes one half-sandwich core is coordinated by a hydroxamate [O,O] chelate while the other one by [Namino,Nhydroxamate] fashion of the bridging ligand. In both cases the remaining coordination sites of one of the Ru cores are taken by a halide ion whiles the other one by a water molecule. Reaction of 2 with 9-methylguanine indicates the N7 coordination of this simple DNA model. Complexes 1 and 2 were tested for their in vitro cytotoxicity using human-derived cancer cell lines (A2780, MCF-7, SKOV-3, HCT-116, HeLa) and showed no anti-proliferative activity in the micromolar concentration range.

Kinetico-mechanistic studies of substitution reactions on cross-bridged cyclen Co(III) complexes with nucleosides and nucleotides

Kinetico-mechanistic studies on the substitution reactivity of the [Co{(μ-ET)cyclen}(H2O)2](3+) complex cation at pH values within the 6.0-7.0 range with biologically significant ligands have been carried out. The substitution processes have been found to occur exclusively on the mono-hydroxobridged [(Co{(μ-ET)cyclen}(H2O))2(μ-OH)](5+) species formed after equilibration of the cobalt complex in the relevant medium. The studies conducted on the substitution of the aqua/hydroxo ligands of this dinuclear species are indicative of a dominant role of outer-sphere complexation, involving hydrogen-bonding interactions. The values of the outer-sphere complex formation equilibrium constant are in line with the intervention of both the exiting aqua ligands and the NH groups at the encapsulating {(μ-ET)cyclen} ligand. These complexes result in the preferential formation of O- or N-bonded nucleotides depending on the structure of the base moiety of the ligand. Even the entry of the different donor bonded nucleotides is hampered by the hydrogen-bonding interaction with the dangling moiety of an already coordinated ligand. In general the overall substitution processes occur at a faster rate than those published for the fully alkylated encapsulating {(Me)2(μ-ET)cyclen} ligand derivative, as expected for the still available base-catalysing NH groups in the {(μ-ET)cyclen} ligand.

Speciation of precious metal anti-cancer complexes by NMR spectroscopy

Understanding the mechanism of action of anti-cancer agents is of paramount importance for drug development. NMR spectroscopy can provide insights into the kinetics and thermodynamics of the binding of metallodrugs to biomolecules. NMR is most sensitive for highly abundant I=1/2 nuclei with large magnetic moments. Polarization transfer can enhance NMR signals of insensitive nuclei at physiologically-relevant concentrations. This paper reviews NMR methods for speciation of precious metal anti-cancer complexes, including platinum-group and gold-based anti-cancer agents. Examples of NMR studies involving interactions with DNA and proteins in particular are highlighted.

Identification and discrimination of binding sites of an organoruthenium anticancer complex to single-stranded oligonucleotides by mass spectrometry

We here report the identification of the binding sites of an organometallic ruthenium anticancer complex [(η(6)-biphenyl)Ru(en)Cl](+) (1) to single-stranded oligodeoxynucleotides (ODNs) 5'-CCCA4G5C6CC-3' (I) and 5'-CCC3G4A5CCC-3' (II) by mass spectrometry. The MS analysis of exonuclease ladders demonstrated that the 5'-exonuclease bovine spleen phosphodiesterase digestion of I and II mono-ruthenated by complex 1 was arrested solely at A4 and partially at C3 and G4, respectively, and that the 3'-exonuclease snake venom phosphodiesterase digestion of the ruthenated ODNs was arrested solely at G5 and G4, respectively, due to the ruthenation. These results did not allow unambiguous identification of ruthenation sites on the metallated ODNs. In contrast, tandem mass spectrometry analysis with CID fragmentation of the mono-ruthenated ODNs provided sequential and complementary [a(i) - B]/wi fragments, leading to unambiguous identification of G5 in I and G4 in II as the ruthenation sites on the ODN adducts, which is in line with the high selectivity of the complex towards guanine base as reported previously. These findings suggest that caution should be raised with regard to the identification of the binding sites of metal complexes, in particular complexes with bulky ligands, like biphenyl in complex 1, to DNA by MS analysis of exonuclease ladders of the metallated adducts, because the bulky ligands may adopt such an orientation that they block the exonuclease cleavage of the 5'- or 3'-side phosphodiester bonds adjacent to the binding sites, leading to digestion stalling at the nucleotides before the binding sites.