Jakob Kljun

Interaction of Zn(II) with quinolone drugs: Structure and biological evaluation

Zinc complexes with the third-generation quinolone antibacterial drugs levofloxacin and sparfloxacin have been synthesized and characterized. The deprotonated quinolones act as bidentate ligands coordinated to zinc ion through the pyridone and a carboxylato oxygen atom. The crystal structures of [bis(aqua)bis(levofloxacinato)zinc(II)], 1, and [bis(sparfloxacinato)(1,10-phenanthroline)zinc(II)], 3, have been determined by X-ray crystallography. The biological activity of the complexes has been evaluated by examining their ability to bind to calf-thymus DNA (CT DNA) by UV spectroscopy and viscosity measurements. UV studies of the interaction of the complexes with DNA have revealed that they can bind to CT DNA probably by the intercalative binding mode which has also been verified by DNA solution viscosity measurements. The DNA binding constants have been also calculated. A competitive study with ethidium bromide (EB) showed that the complexes exhibit the ability to displace the DNA-bound EB indicating that they bind to DNA in strong competition with EB for the intercalative binding site. The interaction of the complexes with human and bovine serum albumin proteins has been studied by fluorescence spectroscopy showing that the complexes exhibit good binding propensity to these proteins having relatively high binding constant values. The biological properties of the complexes have been evaluated in comparison to the previously reported Zn(II) complexes with the first- and second-generation quinolones oxolinic acid and enrofloxacin.

Physicochemical Studies and Anticancer Potency of Ruthenium η6-p-Cymene Complexes Containing Antibacterial Quinolones

With the aim of exploring the anticancer properties of organometallic compounds with bioactive ligands, Ru(arene) compounds of the antibacterial quinolones nalidixic acid (2) and cinoxacin (3) were synthesized, and their physicochemical properties were compared to those of chlorido(η6-p-cymene)(ofloxacinato-κ2O,O)ruthenium(II) (1). All compounds undergo a rapid ligand exchange reaction from chlorido to aqua species. 2 and 3 are significantly more stable than 1 and undergo minor conversion to an unreactive [(cym)Ru(μ-OH)3Ru(cym)]+ species (cym = η6-p-cymene). In the presence of human serum albumin 1−3 form adducts with this transport protein within 20 min of incubation. With guanosine 5′-monophosphate (5′-GMP; as a simple model for reactions with DNA) very rapid reactions yielding adducts via its N7 atom were observed, illustrating that DNA is a possible target for this compound class. A moderate capacity of inhibiting tumor cell proliferation in vitro was observed for 1 in CH1 ovarian cancer cells, whereas 2 and 3 turned out to be inactive.

New Uses for Old Drugs: Attempts to Convert Quinolone Antibacterials into Potential Anticancer Agents Containing Ruthenium

Continuing the study of the physicochemical and biological properties of ruthenium-quinolone adducts, four novel complexes with the general formula [Ru([9]aneS3)(dmso-κS)(quinolonato-κ(2)O,O)](PF6), containing the quinolones levofloxacin (1), nalidixic acid (2), oxolinic acid (3), and cinoxacin (4), were prepared and characterized in solid state as well as in solution. Contrary to their organoruthenium analogues, these complexes are generally relatively stable in aqueous solution as substitution of the dimethylsulfoxide (dmso) ligand is slow and not quantitative, and a minor release of the quinolonato ligand is observed only in the case of 4. The complexes bind to serum proteins displaying relatively high binding constants. DNA binding was studied using UV-vis spectroscopy, cyclic voltammetry, and performing viscosity measurements of CT DNA solutions in the presence of complexes 1-4. These experiments show that the ruthenium complexes interact with DNA via intercalation. Possible electrostatic interactions occur in the case of compound 4, which also shows the most pronounced rate of hydrolysis. Compounds 2 and 4 also exhibit a weak inhibition of cathepsins B and S, which are involved in the progression of a number of diseases, including cancer. Furthermore, complex 2 displayed moderate cytotoxicity when tested on the HeLa cell line.

Zinc(II) complexes with the quinolone antibacterial drug flumequine: structure, DNA- and albumin-binding

The interaction of Zn(II) with the quinolone antibacterial drug flumequine (Hflmq) in the presence or absence of an N,N′-donor heterocyclic ligand, 2,2′-bipyridine (bipy), is being investigated. Interaction of equimolar quantities of ZnCl2 with flumequine and 2,2′-bipyridine results in the formation of a structurally characterized [Zn(flmq)(bipy)Cl] (2) complex, while excess of flumequine leads to a structurally characterized [Zn(flmq)2(bipy)] (3) compound. The reaction of ZnCl2 with flumequine in the absence of 2,2′-bipyridine leads to formation of complex [Zn(flmq)2(H2O)2] (1). In all these complexes, the deprotonated bidentate flumequinato ligands are coordinated to zinc ions through pyridone and carboxylato oxygens. The complexes exhibit good binding propensity to human or bovine serum albumin protein having relatively high binding constant values. UV study of interaction of the complexes with calf-thymus DNA (CT DNA) has shown that they bind to CT DNA and [Zn(flmq)(bipy)Cl] exhibits the highest binding constant. A competitive study with ethidium bromide (EB) has shown that the complexes can displace DNA-bound EB, indicating that they bind to DNA in strong competition with EB. The complexes bind to CT DNA in an intercalative binding mode which has also been verified by DNA solution viscosity measurements. DNA electrophoretic mobility experiments showed that all complexes bind to pDNA possibly in an intercalative manner resulting in catenanes formation as well as in double-stranded cleavage reflecting (or ending) in the formation of linear DNA.

Interactions of Metal Ions with DNA, Its Constituents and Derivatives, which may be Relevant for Anticancer Research

In this review several types of interactions between metal ions and DNA are given, starting from basic binding to the use of metal complexes in cancer treatment and diagnostics. Metal cations help to neutralize the negative charge of DNA and thus enable the normal functions of DNA but many other interactions are also possible and are discussed in this paper. Various consequences of such interactions can be reversible (e. g. conformational changes) or irreversible (e. g. cleavage). It is known that some metal ions can also damage DNA which can provoke mutations and in some cases leads to cancer. It is clear that we know a lot about metal-DNA interactions but much more information is needed to understand the role of metal ions completely and to use this knowledge successfully.

Structure-Related Mode-of-Action Differences of Anticancer Organoruthenium Complexes with β-Diketonates.

A series of organoruthenium(II) chlorido complexes with fluorinated O,O-ligands [(η(6)-p-cymene)Ru(F3C-acac-Ar)Cl] (1a-6a) and their respective 1,3,5-triaza-7-phosphaadamantane (pta) derivatives [(η(6)-p-cymene)Ru(F3C-acac-Ar)pta]PF6 (1b-6b) were synthesized and fully characterized in both solution and solid state. All complexes were inactive against nonmalignant keratinocytes but displayed variable activity against cancer cell models (ovarian, osteosarcoma). Compounds with a ligand containing the 4-chlorophenyl substituent (6a and 6b) exhibited the strongest anticancer effects. Despite a marginally lower cellular Ru accumulation compared to the chlorido complexes, pta analogues showed higher activity especially in the osteosarcoma model. Reduction of glutathione levels by buthionine sulfoximine (BSO) significantly enhanced the activity of all compounds with the most pronounced effects being observed for the pta series resulting in IC50 values down to the nanomolar range. While all chlorido complexes potently induce reactive oxygen species, DNA damage, and apoptosis, the respective pta compounds widely lacked ROS production but blocked cell cycle progression in G0/G1 phase.

Cobalt(II) complexes with the quinolone antimicrobial drug oxolinic acid: structure and biological perspectives

The interaction of cobalt(II) with the quinolone antimicrobial agent oxolinic acid (Hoxo) in the absence or presence of the Lewis bases 2,2′-bipyridine (bipy), 2,2′-bipyridylamine (bipyam), 1,10-phenanthroline (phen), pyridine (py) or 4-benzylpyridine (4bzpy) resulted in the formation of a series of mononuclear complexes which were characterized with physicochemical and spectroscopic techniques. The crystal structure of [Co(oxo)2(bipy)]·3MeOH was determined by X-ray crystallography. The interaction of the complexes with calf-thymus DNA (CT DNA) was investigated by UV spectroscopy, viscosity measurements and cyclic voltammetry in order to evaluate the possible DNA-binding mode and to calculate the corresponding DNA-binding constants. The binding of the complexes to human or bovine serum albumin was monitored by fluorescence emission spectroscopy and relatively high binding constant values were determined. The antimicrobial activity of the complexes was tested against four different microorganisms (Escherichia coli, Xanthomonas campestris, Staphylococcus aureus and Bacillus subtilis) and was found to be similar to that of free Hoxo. Molecular docking simulations on the crystal structure of CT DNA, HSA and BSA were employed in order to study in silico the ability of the resultant complexes to bind biomacromolecules. This is the first report for metal–quinolone complexes combining experimental data and molecular docking simulations of their interaction with DNA and serum albumins.

Ruthenium complexes as inhibitors of the aldo-keto reductases AKR1C1-1C3.

The human aldo-keto reductases (AKRs) from the 1C subfamily are important targets for the development of new drugs. In this study, we have investigated the possible interactions between the recombinant AKR1C enzymes AKR1C1-AKR1C3 and ruthenium(II) complexes; in particular, we were interested in the potential inhibitory actions. Five novel ruthenium complexes (1a, 1b, 2a, 2b, 2c), two precursor ruthenium compounds (P1, P2), and three ligands (a, b, c) were prepared and included in this study. Two different types of novel ruthenium(II) complexes were synthesized. First, bearing the sulphur macrocycle [9]aneS3, S-bonded dimethylsulphoxide (dmso-S), and an N,N-donor ligand, with the general formula of [Ru([9]aneS3)(dmso)(N,N-ligand)](PF6)2 (1a, 1b), and second, with the general formula of [(η(6)-p-cymene)RuCl(N,N-ligand)]Cl (2a, 2b, 2c). All of these synthesized compounds were characterized by high-resolution NMR spectroscopy, X-ray crystallography (compounds a, b, c, 1a, 1b) and other standard physicochemical methods. To evaluate the potential inhibitory actions of these compounds on the AKR1C enzymes, we followed enzymatically catalyzed oxidation of the substrate 1-acenaphthenol by NAD(+) in the absence and presence of various micromolar concentrations of the individual compounds. Among 10 compounds, one ruthenium complex (2b) and two precursor ruthenium compounds (P1, P2) inhibited all three AKR1C enzymes, and one ruthenium complex (2a) inhibited only AKR1C3. Ligands a, b and c revealed no inhibition of the AKR1C enzymes. All four of the active compounds showed multiple binding with the AKR1C enzymes that was characterized by an initial instantaneous inhibition followed by a slow quasi-irreversible step. To the best of our knowledge, this is the first study that has examined interactions between these AKR1C enzymes and ruthenium(II) complexes.

Clioquinol–ruthenium complex impairs tumour cell invasion by inhibiting cathepsin B activity

Over the past few years, the organometalled compounds, including ruthenium, gained a lot of attention as anticancer agents. We report on the clioquinol-ruthenium complex [Ru(η6-p-cymene)(Cq)Cl] as a potent inhibitor of cathepsin B, a lysosomal cysteine peptidase, involved in tumour cell invasion and metastasis. In the low micromolar concentration range, the clioquinol-ruthenium complex did not exhibit cytotoxic effects on MCF-10A neoT and U-87 MG cells; it did, however, significantly reduce their ability for extracellular matrix degradation and invasiveness in two independent cell-based models, measuring either electrical impedance in real time or the growth of multicellular tumour spheroids implanted in Matrigel, a model representing the extracellular matrix. These results establish ruthenium based organometallic compounds as promising candidates for further pre-clinical studies as anticancer therapeutics.

Synthesis and Characterization of Novel Ruthenium(III) Complexes with Histamine.

Novel ruthenium(III) complexes with histamine [RuCl4(dmso-S)(histamineH)] · H2O (1a) and [RuCl4(dmso-S)(histamineH)] (1b) have been prepared and characterized by X-ray structure analysis. Their crystal structures are similar and show a protonated amino group on the side chain of the ligand which is not very common for a simple heterocyclic derivative such as histamine. Biological assays to test the cytotoxicity of the compound 1b combined with electroporation were performed to determine its potential for future medical applications in cancer treatment.