Synthesis and structure of [(η(6)-p-cymene)Ru(2-anthracen-9-ylmethylene-N-ethylhydrazinecarbothioamide)Cl]Cl; biological evaluation, topoisomerase II inhibition and reaction with DNA and human serum albumin

Inhibition of Topoisomerases by Metal Thiosemicarbazone Complexes

Topoisomerases, common targets for anti-cancer therapeutics, are crucial enzymes for DNA replication, transcription, and many other aspects of DNA metabolism. The potential anti-cancer effects of thiosemicarbazones (TSC) and metal-TSC complexes have been demonstrated to target several biological processes, including DNA metabolism. Human topoisomerases were discovered among the molecular targets for TSCs, and metal-chelated TSCs specifically displayed significant inhibition of topoisomerase II. The processes by which metal-TSCs or TSCs inhibit topoisomerases are still being studied. In this brief review, we summarize the TSCs and metal-TSCs that inhibit various types of human topoisomerases, and we note some of the key unanswered questions regarding this interesting class of diverse compounds.

Interaction with bioligands and in vitro cytotoxicity of a new dinuclear dioxido vanadium(V) complex

One centrosymmetric bis(μ-oxido)-bridged vanadium(V) dimer with molecular formula [(V^VO₂)₂(pedf)₂] (1) has been synthesized from the reaction of VOSO₄·5H₂O with a Schiff base ligand (abbreviated with pedf^-) obtained from 2-acetylpyridine and 2-furoic hydrazide in methanol. Complex 1 was characterized by elemental analysis, UV-visible (UV-Vis), Fourier-transform infrared spectra (FT-IR), cyclic voltammetry (CV), electron paramagnetic resonance spectroscopy (EPR) and electrospray ionization-mass spectrometry (ESI-MS) techniques along with single crystal X-ray diffraction (SCXRD). The FT-IR spectral data of 1 indicated the involvement of oxygen and azomethine nitrogen in coordination to the central metal ion. The crystallographic studies revealed a dinuclear oxovanadium(V) complex with the Schiff base coordinated via the ONN donor set with formation of two five-membered chelate rings resulting in a distorted octahedral geometry. The interaction of 1 with calf thymus DNA (CT-DNA) was investigated by spectroscopic measurements and results suggested that the complex binds to CT-DNA via moderate intercalative mode with a binding constant (K_b) around 10³ M^-1. In addition, the in vitro protein binding behavior was studied by fluorescence spectrophotometric method using both bovine serum albumin (BSA) and human serum albumin (HSA) and a static quenching mechanism was observed for the interaction of the complex with both albumins that occurs with a K_b in the range (5-6) × 10³ M^-1. In vitro cytotoxicity of complex 1 on lung cancer cells (A549) and human skin carcinoma cell line (A431) demonstrated that the complex had a broad-spectrum of anti-proliferative activity with IC₅₀ value of 64.2 μM and 56.2 μM.

Research Progress on the Biological Activities of Metal Complexes Bearing Polycyclic Aromatic Hydrazones

Due to the abundant and promising biological activities of aromatic hydrazones, it is of great significance to study the biological activities of their metal complexes for the research and development of metal-based drugs. In this review, we focus on the metal complexes of polycyclic aromatic hydrazones, which still do not receive much attention, and summarize the studies related to their biological activities. Although the large number of metal complexes in phenylhydrazone prevent them all from being summarized, the significant value of polycyclic aromatic hydrocarbons themselves (such as naphthalene and anthracene) as pharmacophores are also considered. Therefore, the bioactivities of the metal complexes of naphthylhydrazone and anthrahydrazone are focused on, and the recent research progress on the metal complexes of anthrahydrazone by the authors is also included. In terms of biological activities, these complexes mainly show antibacterial and anticancer activities, along with less bioactivities. The present review demonstrates that the structural design and bioactivities of these complexes are fundamental, which also indicates a certain structure-activity relationship (SAR) in some substructural areas. However, a systematic and comprehensive conclusion of the SAR is still not available, which suggests that more attention should be paid to the bioactivities of the metal complexes of polycyclic aromatic hydrazones since their potential in structural design and biological activity remains to be explored. We hope that this review will attract more researchers to devote their interest and energy into this promising area.

Synthesis, Characterization, and Cytotoxicity Studies of N-(4-Methoxybenzyl) Thiosemicarbazone Derivatives and Their Ruthenium(II)-p-cymene Complexes

The reaction of [Ru₂Cl₂(μ-Cl)₂(η⁶-p-cymene)₂] with two thiosemicarbazones obtained by the condensation of N-(4-methoxybenzyl) thiosemicarbazide and 1,4-hydroxy-3-methoxyphenyl)ethan-1-one (HL¹) or 2-fluoro-4-hydroxybenzaldehyde (HL²) was studied. The cationic complexes of formula [RuCl(η⁶-p-cymene)(HL)]⁺ were isolated as solid chloride and trifluoromethylsulfate (TfO) salts. A study of the solid state and NMR spectra suggests the presence in the material of two isomers that differ in the configuration in the iminic bond, C2=N3, of the coordinated thiosemicarbazone in the triflate salts and only the E isomer in the chloride. An X-ray study of single crystals of the complexes supports this hypothesis. The thiosemicarbazone ligand coordinates with the ruthenium center through the iminic and sulfur atoms to form a five-membered chelate ring. Furthermore, the isolation of single crystals containing the thiosemicarbazonate complex [Ru₂(μ-L²)₂(η⁶-p-cymene)₂]²⁺ suggests the easy labilization of the coordinated chloride in the complex. The redox behavior of the ligands and complexes was evaluated by cyclic voltammetry. It seems to be more difficult to oxidize the complex derived from HL¹ than HL². The ability of the complexes to inhibit cell growth against the NCI-H460, A549 and MDA-MB-231 lines was evaluated. The complexes did not show greater potency than cisplatin, although they did have greater efficacy, especially for the complex derived from HL¹.

Binding of RuCp complexes with human apo-transferrin: fluorescence spectroscopy and molecular docking methods

The interaction between human serum transferrin (hTf) and three promising organometallic Ru (II)- (η⁵-C₅H₅) derived complexes, that have already shown strong in vitro cytotoxicity towards human cancer cell lines, has been investigated using fluorescence spectroscopic techniques. The results suggested that the formation of Ru-hTf systems involves a dynamic collision. The binding process occurs spontaneously (ΔG < 0), mainly driven by hydrophobic interactions. Additional docking studies show that all complexes bind preferably to a specific hydrophobic pocket in the C2-subdomain as already observed for other metal-cyclopentadienyl (MCp) complexes and are in agreement with the experimental results. With these studies we hope to contribute to the understanding of the mechanism of action of these promising cytotoxic agents, thus providing clues for a more rational design.

A comprehensive review of topoisomerase inhibitors as anticancer agents in the past decade

The topoisomerase enzymes play an important role in DNA metabolism, and searching for enzyme inhibitors is an important target in the search for new anticancer drugs. Discovery of new anticancer chemotherapeutical capable of inhibiting topoisomerase enzymes is highlighted in anticancer research. Therefore, biologists, organic chemists and medicinal chemists all around the world have been identifying, designing, synthesizing and evaluating a variety of novel bioactive molecules targeting topoisomerase. This review summarizes types of topoisomerase inhibitors in the past decade, and divides them into nine classes by structural characteristics, including N-heterocycles compounds, quinone derivatives, flavonoids derivatives, coumarin derivatives, lignan derivatives, polyphenol derivatives, diterpenes derivatives, fatty acids derivatives, and metal complexes. Then we discussed the application prospect and development of these anticancer compounds, as well as concluded parts of their structural-activity relationships. We believe this review would be invaluable in helping to further search potential topoisomerase inhibition as antitumor agent in clinical usage.

Cyclometallated ruthenium(ii) complexes with 3-acetyl-2[H]-chromene-2-one derived CNS chelating ligand systems: synthesis, X-ray characterization and biological evaluation

The presented work focuses on the synthesis and biological evaluation of 3-acetylcoumarin Schiff bases and their cyclometallated ruthenium(ii) metallates.

An investigation on 3-acetyl-7-methoxy-coumarin Schiff bases and their Ru(ii) metallates with potent antiproliferative activity and enhanced LDH and NO release

New cyclometallated ruthenium(ii) complexes of 3-acetyl-7-methoxycoumarin-4N-substituted thiosemicarbazones were synthesized and characterized by analytical and spectral techniques.

New Acridine Thiourea Gold(I) Anticancer Agents: Targeting the Nucleus and Inhibiting Vasculogenic Mimicry

Two new 1-acridin-9-yl-3-methylthiourea Au(I) DNA intercalators [Au(ACRTU)₂]Cl (2) and [Au(ACRTU) (PPh₃)]PF₆ (3) have been prepared. Both complexes were highly active in the human ovarian carcinoma cisplatin-sensitive A2780 cell line, exhibiting IC₅₀ values in the submicromolar range. Compounds 2 and 3 are also cytotoxic toward different phenotypes of breast cancer cell lines MDA-MB-231 (triple negative), SK-BR-3 (HER2+, ERα-, and ERβ-), and MCF-7 (ER+). Both complexes induce apoptosis through activation of caspase-3 in vitro. While inhibition of some proteins (thiol-containing enzymes) seems to be the main mechanism of action for cytotoxic gold complexes, 2 and 3 present a DNA-dependent mechanism of action. They locate in the cell nucleus according to confocal microscopy and transmission electronic microscopy. The binding to DNA resulted to be via intercalation as shown by spectroscopic methods and viscometry, exhibiting a dose-dependent response on topoisomerase I mediated DNA unwinding. In addition, 2 and 3 exhibit potent antiangiogenic effects and are also able to inhibit vasculogenic mimicry of highly invasive MDA-MB-231 cells.

One new azido bridged dinuclear copper(ii) thiosemicarbazide complex: synthesis, DNA/protein binding, molecular docking study and cytotoxicity activity

Biological potential of a copper(ii) complex found to exhibit in vitro antiproliferative activity towards two cell lines, AGS and A549 cancer cells.

Coordination chemistry of pyrazine derivatives analogues of PZA: design, synthesis, characterization and biological activity

A novel Ru(iii) complexes were synthesized and characterized. Their stabilities were discussed in terms of aqueous and MeCN solutions. Antimicrobial properties of complexes studied were characterized against reference strains of bacteria and yeast.

DNA-binding, topoisomerases I and II inhibition and in vitro cytotoxicity of ruthenium(II) polypyridyl complexes: [Ru(dppz)2L](2+) (L=dppz-11-CO2Me and dppz)

Two ruthenium(II) polypyridyl complexes, [Ru(dppz)2dppz-11-CO2Me](ClO4)2 (Ru1) and [Ru(dppz)3](ClO4)2 (Ru2), have been synthesized and characterized. The spectral characteristics of Ru1 and Ru2 were investigated by fluorescence spectroscopy and revealed that both complexes were sensitive to solvent polarity. The binding properties of the two complexes towards calf-thymus DNA (CT-DNA) have been investigated by different spectrophotometric methods and viscosity measurements, indicating that both complexes bind to CT-DNA by means of intercalation, but with different binding affinities. Topoisomerase inhibition and DNA strand passage assay demonstrates that the two complexes are dual inhibitors of topoisomerases I and IIa. On the other hand, the cytotoxicity of both complexes has been evaluated by MTT assays and Giemsa staining experiments. The main results reveal that the ester functional group has a significant effect on the DNA-binding affinities and topoisomerases inhibition effects of Ru1 and Ru2, and further advance our knowledge on the DNA-binding and topoisomerase inhibition by Ru(II) complexes.

Understanding the interaction of an antitumoral platinum(II) 7-azaindolate complex with proteins and DNA

The reactivity of the [Pt(dmba)(aza-N1)(dmso)] complex 1, (a potential antitumoral drug with lower IC50 than cisplatin in several tumoral cell lines) with different proteins and oligonucleotides is investigated by means of mass spectrometry (ESI-TOF MS). The results obtained show a particular binding behaviour of this platinum(II) complex. The interaction of 1 with the assayed proteins apparently takes place by Pt-binding to the most accessible coordinating amino acids, presumably at the surface of the protein -this avoiding protein denaturation or degradation- with the subsequent release of one or two ligands of 1. The specific reactivity of 1 with distinct proteins allows to conclude that the substituted initial ligand (dmso or azaindolate) is indicative of the nature of the protein donor atom finally bound to the platinum(II) centre, i.e. N- or S-donor amino acid. Molecular modeling calculations suggest that the release of the azaindolate ligand is promoted by a proton transfer to the non-coordinating N present in the azaindolate ring, while the release of the dmso ligand is mainly favoured by the binding of a deprotonated Cys. The interaction of complex 1 with DNA takes always place through the release of the azaindolate ligand. Interestingly, the interaction of 1 with DNA only proceeds when the oligonucleotides are annealed forming a double strand. Complex 1 is also capable to displace ethidium bromide from DNA and it also weakly binds to DNA at the minor groove, as shown by Hoechst 33258 displacement experiments. Furthermore, complex 1 is also a good inhibitor of cathepsin B (an enzyme implicated in a number of cancer related events). Therefore, although compound 1 is definitely able to bind proteins that can hamper its arrival to the nuclear target, it should be taken into consideration as a putative anticancer drug due to its strong interaction with oligonucleotides and its effective inhibition of cat B.

Exploring the effect of the ligand design on the interactions between [Ru(η(5)-C5H5)(PPh3)(N,O)][CF3SO3] complexes and human serum albumin

Ruthenium complexes hold a great potential in chemotherapy as an alternative to the classical platinum based drugs. The organometallic compounds studied in the present work were previously found to exhibit important anticancer activities. Here we have investigated the binding of three ruthenium compounds, namely [Ru(η(5)-C5H5)(PPh3)(bopy)][CF3SO3] 1, [Ru(η(5)-C5H5)(PPh3)(2-ap)][CF3SO3] 2, and [Ru(η(5)-C5H5)(PPh3)(isoquinpk)][CF3SO3] 3 (bopy=2-benzoylpyridine; 2-ap=2-acetylpyridine; isoquinpk=1-isoquinolinyl phenyl ketone) to fatty acid human serum albumin (HSA) and fatty acid-free human serum albumin (HSA(faf)) at physiological pH7.4. The influence of the substituent groups on the heteroaromatic (N,O) coordinated ligand was also studied by fluorescence spectroscopy to get information about this binding. The Stern-Volmer quenching constants (KSV) were calculated at 293, 298 and 310K, with the corresponding thermodynamic parameters ∆G, ∆H and ∆S as well. The fluorescence quenching method was used to determine the number of binding sites (n) and association constants (Ka) at the same temperatures. The binding site to HSA was confirmed by competitive studies of the ruthenium compounds with warfarin.

Solution equilibria of anticancer ruthenium(II)-(η(6)-p-cymene)-hydroxy(thio)pyr(id)one complexes: impact of sulfur vs. oxygen donor systems on the speciation and bioactivity

Stoichiometry and stability of antitumor ruthenium(II)-η(6)-p-cymene complexes of bidentate (O,O) hydroxypyrone and (O,S) hydroxythiopyr(id)one type ligands were determined by pH-potentiometry, (1)H NMR spectroscopy and UV-Vis spectrophotometry in aqueous solution and in dependence of chloride ion concentration. Formation of mono-ligand complexes with moderate stability was found in the case of the hydroxypyrone ligands (ethyl maltol and allomaltol) predominating at the physiological pH range. These complexes decompose to the dinuclear tri-hydroxido bridged species [{Ru(II)(η(6)-p-cymene)}2(OH)3](+) and to the metal-free ligand at basic pH values. In addition, formation of a hydroxido [Ru(II)(η(6)-p-cymene)(L)(OH)] species was found. The hydroxythiopyr(id)one ligands (thiomaltol, thioallomaltol, 3-hydroxy-1,2-dimethyl-thiopyridone) form complexes of significantly higher stability compared with the hydroxypyrones; their complexes are biologically more active, the simultaneous bi- and monodentate coordination of the ligands in the bis complexes (ML2 and ML2H) was also demonstrated. In the case of thiomaltol, formation of tris complexes is also likely at high pH. The replacement of the chlorido by the aqua ligand in the [Ru(II)(η(6)-p-cymene)(L)(Cl)] species was monitored, which is an important activation step in the course of the mode of action of the complexes, facilitating binding to biological targets.