DNA cleavage, binding and intercalation studies of drug-based oxovanadium(IV) complexes

The complexes of oxovanadium(IV) with ciprofloxacin and various uni-negative bidentate ligands have been prepared and their structure investigated using spectral, physicochemical and elemental analyses. The viscosity measurement suggest that the complexes bind to DNA by intercalation. The DNA binding efficacy was determined using absorption titration to obtain the binding constant (K(b)). The DNA cleavage efficacy was determined using gel electrophoresis. The DNA binding and cleavage efficacy were increased in the complexes relative to the parental ligands and metal salts. Antibacterial activity has been assayed against two Gram((- ve)) i.e. Escherichia coli, Pseudomonas aeruginosa and three Gram((+ ve)) Staphylococcus aureus, Bacillus subtilis, Serratia marcescens microorganisms using the doubling dilution technique. The results show a significant increase in antibacterial activity in the complexes compared with parental ligands and metal salts.     

DNA cleavage,binding and intercalation studies of drug-based oxovanadium(IV) complexes

The complexes of oxovanadium(IV) with ciprofloxacin and various uni-negative bidentate ligands have been prepared and their structure investigated using spectral, physicochemical and elemental analyses. The viscosity measurement suggest that the complexes bind to DNA by intercalation. The DNA binding efficacy was determined using absorption titration to obtain the binding constant (K_b). The DNA cleavage efficacy was determined using gel electrophoresis. The DNA binding and cleavage efficacy were increased in the complexes relative to the parental ligands and metal salts. Antibacterial activity has been assayed against two Gram^{( ? ve)} i.e. Escherichia coli, Pseudomonas aeruginosa and three Gram^{( + ve)} Staphylococcus aureus, Bacillus subtilis, Serratia marcescens microorganisms using the doubling dilution technique. The results show a significant increase in antibacterial activity in the complexes compared with parental ligands and metal salts.     

Synthesis, structure, DNA binding and DNA cleavage activity of oxovanadium(IV) N-salicylidene-S-methyldithiocarbazate complexes of phenanthroline bases

Ternary oxovanadium(IV) complexes [VO(salmdtc)(B)] (1-3), where salmdtc is dianionic N-salicylidene-S-methyldithiocarbazate and B is N,N-donor phenanthroline bases like 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3), are prepared, characterized and their DNA binding and DNA cleavage activity studied. Complex 3 is structurally characterized by single-crystal X-ray crystallography. The molecular structure shows the presence of a vanadyl group in six-coordinate VN₃O₂S coordination geometry. The S-methyldithiocarbazate Schiff base acts as a tridentate NSO-donor ligand in a meridional binding mode. The N,N-donor heterocyclic base displays a chelating mode of binding with an N-donor site trans to the vanadyl oxo-group. The complexes show a d-d band in the range of 675-707 nm in DMF. They exhibit an irreversible oxidative cyclic voltammetric response near 0.9 V due to the V(V)/V(IV) couple and a quasi-reversible reductive V(IV)/V(III) redox couple near −1.0 V vs. SCE in DMF-0.1 M TBAP. The complexes show good binding propensity to calf thymus DNA giving binding constant values in the range of 7.4 × 10⁴-2.3 × 10⁵ M⁻¹. The thermal denaturation and viscosity binding data suggest DNA surface and/or groove binding nature of the complexes. The complexes show poor chemical nuclease activity in dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide. The dpq and dppz complexes show efficient DNA cleavage activity in UV-A light of 365 nm via a type-II mechanistic pathway involving formation of singlet oxygen (¹O₂) as the reactive species.     

Photocytotoxicity and near-IR light DNA cleavage activity of oxovanadium(IV) Schiff base complexes having phenanthroline bases

Oxovanadium(IV) complexes [VO(L)(B)] (1-3), where H₂L is a Schiff base ligand 2-(2-hydroxybenzylideneamino)phenol and B is 1,10-phenanthroline (phen for 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq for 2) or dipyrido[3,2-a:2′,3′-c]phenazine (dppz for 3), have been prepared, characterized and their DNA binding property and photo-induced DNA cleavage activity studied. Complex 3 which is structurally characterized by X-ray crystallography shows the presence of an oxovanadium(IV) moiety in a six coordinate VO₃N₃ coordination geometry. The complexes show a d-d band within 800-850 nm in DMF. The complexes display an oxidative response near 0.7 V versus SCE for V(V)-V(IV) and a reductive response within −1.1 to −1.3 V due to V(IV)-V(III) couple in DMF-0.1 M TBAP. The complexes are avid binders to calf thymus DNA giving binding constant values of 4.2 × 10⁴ to 1.2 × 10⁵ M⁻¹. The complexes do not show any “chemical nuclease” activity in dark. The dpq and dppz complexes are photocleavers of plasmid DNA in UV-A light of 365 nm via ¹O₂ pathway and in near-IR light (752.5 to 799.3 nm IR optics) by HO^• pathway. Complex 3 exhibits significant photocytotoxicity in visible light in HeLa cells giving IC₅₀ value of 13 μM, while it is less toxic in dark (IC₅₀ = 97 μM).     

Effective DNA cleavage by bleomycin-vanadium(IV) complex plus hydrogen peroxide

It has been firstly found that the bleomycin-vanadyl(IV) complex is effectively capable of cleaving DNA in the presence of hydrogen peroxide. The 1:1 bleomycin-VO(IV) complex has been characterized by ESR and electronic absorption spectra, and its ESR parameters (go = 1.982 and Ao = 93.5 G) are indicative of VO(N5) coordination type for the metal-binding environment. The mode of nucleotide sequence cleavage induced by the present bleomycin-VO(IV)-H2O2 complex system was appreciably different from the corresponding Fe(III) complex system. Of special interest is the fact that the bleomycin-vanadium complex system more preferentially attacked G-A(5'----3') sequences than the bleomycin-iron complex system.     

Characterization of new oxovanadium(IV) complexes of saccharides

Oxovanadium(IV) complexes of the monosaccharides D- and L-arabinose, D-galactose, D-mannose, D-lyxose, D-xylose and the disaccharide maltose were obtained in aqueous solutions at pH 13. Their sodium salts were precipitated with absolute ethanol and characterized by UV-vis spectroscopy (absorption and reflectance), thermo-analytical (TG and DTA) data, magnetic susceptibility measurements and IR-spectroscopy. All the complexes were found to be mononuclear, possessing the VO2+ moiety. The IR spectra were analyzed and discussed in detail allowing one to determine the characteristics of the metal-to-ligand interactions.     

DNA modification by oxovanadium(IV) complexes of salen derivatives

Oxovanadium(IV) complexes of hydroxysalen derivatives have been prepared and tested as DNA reactive agents. The nuclease activity has been investigated under oxidative or reducing conditions, on the basis of the various oxidation states of vanadium: V^III, V^IV and V^V. In the absence of an activating agent, none of the compounds tested was able to induce cleavage of DNA, whereas in the presence of mercaptopropionic acid (MPA) or Oxone the four complexes induced DNA modifications. Under both conditions, the para-hydroxy complex was found to be the most active compound. Reaction of these salen complexes with DNA occurs essentially at guanine residues and is more efficient in the presence of Oxone than under reducing conditions. The extent of Oxone-mediated DNA oxidation by the four vanadyl complexes was clearly superior to VOSO₄ and was observed without piperidine treatment. EPR studies provided information on the reactive metal-oxo species involved under each conditions and a mechanism of reaction with DNA is discussed.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00775-004-0529-0Abbreviations BPE buffer bis-phosphate EDTA buffer - DMPO 5,5-dimethylpyrroline N-oxide - DMS dimethyl sulfate - HFS hyperfine structure - Lin linear - MPA 3-mercaptopropionic acid - Nck nicked - salen (salicylidene)ethylenediamine - Sc supercoiled - TBE buffer tris-borate EDTA buffer - Tris tris(hydroxymethyl)aminomethane     

A new candidate for insulinomimetic vanadium complex: synergism of oxovanadium(IV)porphyrin and sodium ascorbate

Vanadyl-meso-tetrakis(1-methylpyridinium-4-yl)porphyrin, VOTMpyP with the VO(N(4)) coordination mode, was found to have a potent insulinomimetic activity on the basis of in vitro and in vivo experiments. When the complex was given simultaneously with sodium ascorbate, the high blood glucose levels of type 1 diabetic model STZ-rats were lowered by synergistic effect, probably sustaining the vanadyl state by means of ascorbate distributed in the organs and tissues of animals. This is the first finding on not only the insulinomimetic vanadyl-porphyrin complex but also the occurrence of a synergistic effect of VOTMpyP and sodium ascorbate to lower the high blood glucose levels in diabetic animals.     

Hydrolysis of DNA by Ce(IV)/EDTA complexes--the mechanism of DNA cleavage and design of artificial restriction enzymes.

Homogeneous Ce(IV) complex of EDTA promptly hydrolyzes oligonucleotides under physiological conditions. Moreover, the activity of Ce(IV)/EDTA for DNA hydrolysis is promoted by the addition of amines. When [Ce(IV)/EDTA] = 5 mumol dm3 and [ethylenediamine] = 100 mmol dm3, the catalytic activity is about 50 times as large as that of Ce(IV)/EDTA. The combination of Ce(IV)/EDTA and amines is eminent tools for the future molecular biology and biotechnology.     

Crystal structure of Ce(IV)/dipicolinate complex as catalyst for DNA hydrolysis

The structures of Ce⁴⁺ complexes that are active for DNA hydrolysis were determined for the first time by X-ray crystallography. The crystals were prepared from a 1:2 mixture of Ce(NH₄)₂(NO₃)₆ and dipicolinic acid (2,6-pyridinedicarboxylic acid). Depending on the recrystallization conditions, three types of crystals were obtained. Some of the Ce⁴⁺ ions in these complexes have enough coordinated water molecules that can directly and indirectly participate in the catalysis. The distances between the Ce⁴⁺ and the dipicolinate ligand are considerably shorter than those in the corresponding La³⁺ and Ce³⁺ complexes. On the other hand, the distances between the Ce⁴⁺ and its coordinated water are similar to those for the La³⁺ and Ce³⁺ complexes. In a proposed mechanism of DNA hydrolysis, the scissile phosphodiester linkage is notably activated by coordination to Ce⁴⁺ and attacked by the Ce⁴⁺-bound hydroxide. The process is further assisted by acid catalysis of Ce⁴⁺-bound water. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

DNA cleavage by a Chromium(III) complex

A new Cr(III) complex with the empirical formula [Cr(Schiff base) (H(2)O)(2)]ClO(4), where the Schiff base is 2, 3-bis?[(2-hydroxy-4-diethylamino) (phenyl) (methylene)]amino?2-butenedinitrile has been synthesized and characterized spectroscopically. Binding of this complex to DNA has been studied using UV-visible spectroscopy. The complex has been found to bind to the major groove of DNA with a binding constant, K = (1.3 +/- 0.2) x 10(3) M(-1). The induced CD spectrum of the complex in the presence of DNA is also indicative of major groove binding. Gel electrophoresis of plasmid DNA in the presence of the complex shows that the complex brings about nicking of the DNA.     

Preferential hydrolysis of gap and bulge sites in DNA by Ce(IV)/EDTA complex

A new strategy for site-selective DNA hydrolysis, which takes advantage of the difference in reactivity between the phosphodiester linkages at the target site and the others, is presented. As the molecular scissors, homogeneous Ce(IV)/ethylenediamine-N,N,N′,N′-tetraacetate (EDTA) complex is used without being bound to any sequence-recognizing moiety. When a gap structure is formed at the target site by using two short oligonucleotides and the composite is treated with the Ce(IV)/EDTA complex at pH 7.0 and 37°C, the gap site in the substrate DNA is preferentially hydrolyzed over the double-stranded portion of the DNA. Site-selective DNA scission is also achieved by forming a bulge structure at the target site with the use of the appropriate oligonucleotide. These site-selective scissions are based on the following two factors: (i) the phosphodiester linkages in a single-stranded DNA are far more susceptible to the hydrolysis by the Ce(IV) complex than are the linkages in double-stranded DNA, and (ii) the phosphodiester linkages in the bulge sites are still more reactive than those in single-stranded DNA. In both cases, the addition of spermine significantly accelerates the scission.     

Oligoamine-acridine conjugates for promotion of gap-selective DNA hydrolysis by Ce(IV)/EDTA complex

Oligoamines (spermidine, dipropylenetriamine and propylenediamine) were covalently attached to acridine via a hexamethylene linker. These oligoamine–acridine conjugates were efficiently bound to gap sites in substrate DNA, and promoted the DNA hydrolysis by a homogeneous Ce(IV)/ethylenediamine-N,N,N′,N′-tetraacetate (EDTA) complex at these sites. In contrast, the hydrolysis of the double-stranded portion in the DNA was little affected by these conjugates, although they were strongly bound thereto by the intercalation of their acridine moieties. As a result, the gap site was selectively and efficiently hydrolyzed by combining the Ce(IV)/EDTA complex with the oligoamine– acridine conjugate. Either the oligoamine or the acridine was only poorly active for the purpose, substantiating the essential role of cooperation between them. The promotion of gap-selective DNA hydrolysis by the conjugates has been ascribed to electrostatic stabilization of a negatively charged transition state by their positive charges.     

Radioprotection of plasmid and cellular DNA and Swiss mice by silibinin

The radioprotective effect of a non-toxic bioactive component in plant milk thistle, silibinin against genotoxicity induced by γ-irradiation was investigated in vivo/in vitro. Under in vitro conditions of irradiation, silibinin protected plasmid pBR322 DNA against γ-radiation-induced strand breaks in a concentration dependent manner (0–200 μM). Under cellular conditions of radiation exposure (3 Gy), silibinin offered protection to lymphocyte DNA as evidenced from reduction in DNA damage and micronuclei formation, which showed correlation to the extent of intracellular reactive oxygen species reduction. Our extended animal studies suggest that oral administration of silibinin (70 mg/kg for 3 days) to mice prior to whole-body γ-exposure (7.5 Gy) resulted in significant protection to radiation-induced mortality and DNA damage in blood leukocytes. However, silibinin treatment after irradiation was not as effective as pre-administration. In conclusion, present study indicated that silibinin has a strong potential to prevent radiation-induced DNA damage under both in vitro and in vivo.     

Oxidative DNA cleavage mediated by a new copper (II) terpyridine complex: crystal structure and DNA binding studies

The copper (II) complex [Cu(Itpy)(2)](ClO(4))(2) (1), (Itpy=imidazole terpyridine) has been synthesized and structurally characterized. Crystal structure of the complex shows the complex to be a monomeric copper (II) species with two Itpy ligands coordinated to the metal ion to give a six coordinate complex. The complex has a distorted octahedral geometry with axial elongation. Variable temperature crystal structure data shows dynamic nature of the Jahn-Teller distortion. The complex is an avid DNA binder with a binding constant of 4.26+/-0.20x10(3)M(-1). Observed changes in the viscosity and circular dichroic spectrum of calf thymus DNA solution in the presence of complex 1 suggests intercalative binding of complex 1 to DNA. The complex cleaves supercoiled pBR322 DNA oxidatively in the presence of hydrogen peroxide.     

A new orally active antidiabetic vanadyl complex--bis(alpha-furancarboxylato)oxovanadium(IV)

Bis(alpha-furancarboxylato)oxovanadium(IV)--a new orally active antidiabetic vanadyl complex has been synthesized, characterized, and tested for bioactivity as insulin-enhancing agents. The complex was administered intragastrically to both normal and STZ-diabetic rats for 4 weeks. The results show that the complex at a dose of 10.0 and 20.0 mg V kg(-1), could significantly lower the blood glucose level rats and ameliorated impaired glucose tolerance in STZ-diabetic, but not in normal rats. It was suggested that the complex exerted an antidiabetic effect in STZ-diabetic rats, which maybe was related to increasing the sensitivity to insulin.     

Antioxidant effects of the VO(IV) hesperidin complex and its role in cancer chemoprevention

Vanadium compounds are known for a variety of pharmacological properties. Many of them display antitumoral and osteogenic effects in several cell lines. Free radicals induce the development of tumoral processes. Natural polyphenols such as flavonoids have antioxidant properties since they scavenge different free radicals. For these reasons it is interesting to investigate the effects of a new complex generated between the vanadyl(IV) cation and the flavonoid hesperidin. The complex has been synthesized and characterized by physicochemical methods. Spectroscopic analysis revealed a 1:1 stoichiometry of ligand:VO and coordination by deprotonated cis-hydroxyl groups to the disaccharide moiety of the ligand. The complex improves the superoxide dismutase (SOD)-like activity of the ligand, but the scavenging of other radicals tested does not change upon complexation. When tested on two tumoral cell lines in culture (one of them derived from a rat osteosarcoma UMR106 and the other from human colon adenocarcinoma Caco-2), the complex enhanced the antiproliferative effects of the free ligand, and this effect correlated with the morphological alterations toward apoptosis. Also, on the osteoblastic cell line the complex stimulated cell proliferation and collagen type I production at low concentrations. At higher doses the complex behaved as a cytotoxic compound for the osteoblasts.     

A new halogenated antidiabetic vanadyl complex, bis(5-iodopicolinato)oxovanadium(IV): in vitro and in vivo insulinomimetic evaluations and metallokinetic analysis

A new vanadyl complex, bis(5-iodopicolinato)oxovanadium(IV), VO(IPA)2, with a VO(N2O2) coordination mode, was prepared by mixing 5-iodopicolinic acid and VOSO4 at pH 5, with the structure characterized by electronic absorption, IR, and EPR spectra. Introduction of the halogen atom on to the ligand enhanced the in vitro insulinomimetic activity (IC50 = 0.45 mM) compared with that of bis(picolinato)oxovanadium(IV) (IC50 = 0.59 mM). The hyperglycemia of streptozotocin-induced insulin-dependent diabetic rats was normalized when VO(IPA)2 was given by daily intraperitoneal injection. The normoglycemic effect continued for more than 14 days after the end of treatment. To understand the insulinomimetic action of VO(IPA)2, the organ distribution of vanadium and the blood disposition of vanadyl species were investigated. In diabetic rats treated with VO(IPA)2, vanadium was distributed in almost all tissues examined, especially in bone, indicating that the action of vanadium is not peripheral. Vanadyl concentrations in the blood of normal rats given VO(IPA)2 remain significantly higher and longer than those given other complexes because of its slower clearance rate. VO(IPA)2 binds with the membrane of erythrocytes, probably owing to its high hydrophobicity in addition to its binding with serum albumin. The longer residence of vanadyl species shows the higher normoglyceric effects of VO(IPA)2 among three complexes with the VO(N2O2) coordination mode. On the basis of these results, VO(IPA)2 is indicated to be a preferred agent to treat insulin-dependent diabetes mellitus in experimental animals.     

Cerium(IV)/Lanthanide(III)/Dextran Ternary Solutions for Efficient and Homogeneous DNA Hydrolysis

Abstract

Homogeneous and neutral solutions are prepared by mixing Ce(NH₄)₂(NO₃)₆ and dextrans at pH 7. These homogeneous solutions are active for DNA hydrolysis. Still more importantly, the activities of the binary solutions are greatly promoted by the addition of various lanthanide(III) ions.