Design of vanadium mixed-ligand complexes as potential anti-protozoa agents

In the search for new therapeutic tools against Chagas’ disease (American Trypanosomiasis) four novel mixed-ligand vanadyl complexes, [V^IVO(L²-2H)(L¹)], including a bidentate polypyridyl DNA intercalator (L¹) and a tridentate salycylaldehyde semicarbazone derivative (L²) as ligands were synthesized, characterized by a combination of techniques, and in vitro evaluated. EPR suggest a distorted octahedral geometry with the tridentate semicarbazone occupying three equatorial positions and the polypyridyl ligand coordinated in an equatorial/axial mode. Both complexes including dipyrido[3,2-a: 2′,3′-c]phenazine (dppz) as polypyridyl coligand showed IC₅₀ values in the μM range against Dm28c strain (epimastigotes) of Trypanosoma cruzi, causative agent of the disease, being as active as the anti-trypanosomal reference drug Nifurtimox. To get an insight into the trypanocidal mechanism of action of these compounds, DNA was evaluated as a potential parasite target and EPR, and ⁵¹V NMR experiments were also carried out upon aging aerated solutions of the complexes. Data obtained by electrophoretic analysis suggest that the mechanism of action of these complexes could include DNA interactions.     

Vanadium polypyridyl compounds as potential antiparasitic and antitumoral agents: new achievements

In the search for new therapeutic tools against diseases produced by kinetoplastid parasites five vanadyl complexes, [V^IVO(L-2H)(phen)], including 1,10-phenanthroline (phen) and tridentate salicylaldehyde semicarbazone derivatives as ligands have been synthesized and characterized in the solid state and in solution by using different techniques. EPR suggested a distorted octahedral geometry with the tridentate semicarbazone occupying three equatorial positions and phen coordinated in an equatorial/axial mode. The compounds were evaluated in vitro on epimastigotes of Trypanosoma cruzi, causative agent of Chagas disease, Leishmania panamensis and Leishmania chagasi and on tumor cells. The complexes showed higher in vitro anti-trypanosomal activities than the reference drug Nifurtimox (IC₅₀ values in the range 1.6-3.8 μM) and increased activities in respect to the free semicarbazone ligands. In vitro activity on promastigote and amastigote forms of Leishmania showed interesting results. The compounds [VO(L1-2H)(phen)] and [VO(L3-2H)(phen)], where L1 = 2-hydroxybenzaldehyde semicarbazone and L3 = 2-hydroxy-3-methoxybenzaldehyde semicarbazone, resulted active (IC₅₀ 2.74 and 2.75 μM, respectively, on promastigotes of L. panamensis; IC₅₀ 19.52 and 20.75 μM, respectively, on intracellular amastigotes of L. panamensis) and showed low toxicity on THP-1 mammalian cells (IC₅₀ 188.55 and 88.13 μM, respectively). In addition, the complexes showed cytotoxicity on human promyelocytic leukemia HL-60 cells with IC₅₀ values of the same order of magnitude as cisplatin. The interaction of the complexes with DNA was demonstrated by different techniques, suggesting that this biomolecule could be a potential target either in the parasites or in tumor cells.     

A new salicylic acid-derivatized kojic acid vanadyl complex: synthesis, characterization and anti-diabetic therapeutic potential

The molecular mechanisms of vanadium toxicity suggest that incorporation of antioxidant groups in the structure of vanadium complexes could be a preferable strategy in designing novel hypoglycemic vanadium complexes with proper efficacy and safety. By conjugating a pyrone skeleton to provide a coordination group and antioxidative motifs, we synthesized a novel complex of bis ((5-hydroxy-4-oxo-4 H-pyran-2-yl) methyl 2-hydroxy- benzoatato) oxovanadium (IV) (BSOV). Evaluation of the anti-diabetic effects of BSOV using streptozotocin (STZ)-induced diabetic rats with bis (maltolato) oxovanadium (BMOV) as a positive control showed that BSOV effectively lowered blood glucose level, ameliorated damages of hepatic and renal function in diabetic rats and improved lipid metabolism. The signs of potential alteration of renal function caused by BSOV and BMOV were observed and are discussed. Overall, the experimental results suggest BSOV as a potent hypoglycemic agent and further studies using this strategy for anti-diabetic agents.     

DNA as molecular target of analogous palladium and platinum anti-Trypanosoma cruzi compounds: a comparative study

In the search for drugs with anti-trypanosome activity, we had previously synthesized two series of platinum and palladium analogous compounds of the formula [M^IICl₂(HL)], where HL were bioactive 5-nitrofuryl or 5-nitroacroleine thiosemicarbazone derivatives. In this work, we thoroughly characterized [M^IICl₂(HL)] complexes interaction with DNA by using different techniques: gel electrophoresis, DNA viscosity measurements, circular dichroism (CD) and atomic force microscopy (AFM). Electrophoresis results showed that all complexes induced a withdrawal of DNA superhelicity demonstrated by a decrease in electrophoretic mobility of supercoiled DNA form. This effect on migration was dependent on dose but also on the nature of both the metal and the ligand. In general, the effect produced by palladium complexes was significantly more intense than that observed for the corresponding platinum analogs. Differences between palladium and platinum complexes were also observed in CD experiments. While palladium complexes induce evident calf thymus (CT)-DNA profile changes compatible with B-DNA to Z-DNA conformational transition, no clear effect was observed for platinum ones. Additionally, AFM studies showed that changes in the shape of plasmid DNA, like supercoiling, kinks and thickness increase resulted more intense for the former. In addition, either Pd or Pt complexes increased the viscosity of CT DNA solutions in a concentration dependent manner. Although the nature of DNA interaction of both series of analogous palladium and platinum complexes seemed to be similar, an explanation for the observed differential intensity of the effect could be related to the known kinetic stability differences between palladium and platinum compounds.     

Zebularine: a novel DNA methylation inhibitor that forms a covalent complex with DNA methyltransferases

Mechanism-based inhibitors of enzymes, which mimic reactive intermediates in the reaction pathway, have been deployed extensively in the analysis of metabolic pathways and as candidate drugs. The inhibition of cytosine-[C5]-specific DNA methyltransferases (C5 MTases) by oligodeoxynucleotides containing 5-azadeoxycytidine (AzadC) and 5-fluorodeoxycytidine (FdC) provides a well-documented example of mechanism-based inhibition of enzymes central to nucleic acid metabolism. Here, we describe the interaction between the C5 MTase from Haemophilus haemolyticus (M.HhaI) and an oligodeoxynucleotide duplex containing 2-H pyrimidinone, an analogue often referred to as zebularine and known to give rise to high-affinity complexes with MTases. X-ray crystallography has demonstrated the formation of a covalent bond between M.HhaI and the 2-H pyrimidinone-containing oligodeoxynucleotide. This observation enables a comparison between the mechanisms of action of 2-H pyrimidinone with other mechanism-based inhibitors such as FdC. This novel complex provides a molecular explanation for the mechanism of action of the anti-cancer drug zebularine.     

DNA binding behaviors and cleavage properties of a Ru(II) polypyridyl complex

A novel complex, [Ru(phen)₂pzip]²⁺1 (phen = 1,10-phenanthroline; pzip = 2-(pyrazine-2-yl)imidazo-[4,5-f][1,10]phenanthroline]), has been synthesized and characterized by elemental analysis, ES-MS, ¹H NMR. The DNA-binding behaviors of this complex were studied by spectroscopic methods and viscosity measurements. The results indicate that the complex can bind to CT-DNA in an intercalative mode. When irradiated at 365 nm, complex 1 can promote the cleavage of plasmid pBR322DNA. Furthermore, Zn²⁺ can trigger the DNA cleavage of complex 1 without irradiation. The mechanism studies revealed that the DNA cleavage by complex 1 in the presence of Zn²⁺ is likely to proceed via a hydrolytic cleavage process.     

DNA binding and bending by dinuclear complexes comprising ruthenium polypyridyl centres linked by a bis(pyridylimine) ligand

The interaction of enantiomerically pure dinuclear complexes of the form [Ru₂(L-L)₄L¹]⁴⁺ (where L-L = 2,2^′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L¹ = bis(pyridylimine) ligand ((C₅H₄N)CN(C₆H₄))₂CH₂)) with ct-DNA have been investigated by absorbance, circular dichroism, fluorescence displacement assays, thermal analysis, linear dichroism and gel electrophoresis. The complexes all bind more strongly to DNA than ethidium bromide, stabilise DNA and have a significant bending effect on DNA. The data for Δ,Δ-[Ru₂(bpy)₄L¹]⁴⁺ are consistent with it binding to DNA outside the grooves wrapping the DNA about it. By way of contrast the other complexes are groove-binders. The phen complexes provide a chemically and enantiomerically stable alternative to the DNA-coiling di-iron triple-helical cylinder previously studied. In contrast to the di-iron helicates, the phen complexes show DNA sequence effects with Δ,Δ-[Ru₂(phen)₄L¹]⁴⁺ binding preferentially to GC and Λ,Λ-[Ru₂(phen)₄L¹]⁴⁺ to AT.     

A new naphthalene derivative with anti-amyloidogenic activity as potential therapeutic agent for Alzheimer's disease

The aggregation of β-amyloid peptides is associated to neurodegeneration in Alzheimer’s disease (AD) patients. Consequently, the inhibition of both oligomerization and fibrillation of β-amyloid peptides is considered a plausible therapeutic approach for AD. Herein, the synthesis of new naphthalene derivatives and their evaluation as anti-β-amyloidogenic agents are presented. Molecular dynamic simulations predicted the formation of thermodynamically stable complexes between the compounds, the Aβ_1-42 peptide and fibrils. In human microglia cells, these compounds inhibited the aggregation of Aβ_1-42 peptide. The lead compound 8 showed a high affinity to amyloid plaques in mice brain ex vivo assays and an adequate log P_oct/PBS value. Compound 8 also improved the cognitive function and decreased hippocampal β-amyloid burden in the brain of 3xTg-AD female mice. Altogether, our results suggest that 8 could be a novel therapeutic agent for AD.     

Synthesis and photophysical properties of zinc myoglobin appending an ethidium ion as a DNA intercalator

In order to elucidate the intramolecular photoinduced electron-transfer or energy-transfer mechanisms of the zinc myoglobin (ZnMb) dyad and to construct a photoreaction system within a Mb–DNA complex, we newly prepared ZnMb appending an ethidium ion (Et⁺). The steady-state fluorescence of ZnMb–Et⁺ at 600 nm and its lifetime (2.2 ns) indicate that the excited singlet state of ¹(ZnMb)* is not quenched by the Et⁺ moiety, whereas the lifetime of the excited triplet state of ³(ZnMb)*–Et⁺ was shorter (τ = 4.3 ms) than those of ZnMb and the intermolecular (ZnMb + ethidium) system. Upon photoirradiation of Et⁺, fluorescence studies indicated the intramolecular quenching reactions from the excited singlet state, ¹(Et⁺)*, to ZnMb, the process of which is likely the photoinduced energy-transfer reaction via a through-space mechanism. We also demonstrate the photophysical and spectroscopic properties of ZnMb–Et⁺ in the presence of calf thymus (CT) DNA. The changes in the absorption and fluorescence spectra of ZnMb–Et⁺ on the addition of CT-DNA up to 15 equiv were very small, indicating that there are no major changes in the heme pocket. However, we observed a longer lifetime of ³(ZnMb)*–Et⁺ in the presence of CT-DNA (τ = 5.3 ms) by single flash photolysis. This was induced by noncovalent interactions between Et⁺ and CT-DNA, followed by a conformational change of Et⁺ at the surface of ZnMb, where the donor–acceptor distance was probably elongated by CT-DNA. The synthetic manipulation at the Mb surface, by using a DNA intercalator coupled with photoinduced reaction, may provide a sensitive transient signal for DNA and valuable information to construct new Mb–DNA complex. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Interaction of DNA with a novel photoactive platinum diimine complex

Interaction of DNA with a novel photoactive platinum diimine compound has been studied by electronic absorption spectra, fluorescence spectra and viscosity measurements. The red light-induced DNA cleavage activity of the platinum compound has also been studied by agarose gel electrophoresis. The results suggest that the platinum compound may interact with DNA by intercalation mode. When irradiated with red light, the platinum compound can generate singlet oxygen, resulting in cleavage of DNA.     

Identification and preliminary structure-activity relationship studies of novel pyridyl sulfonamides as potential Chagas disease therapeutic agents

Chagas disease is a neglected pathology responsible for about 12,000 deaths every year across Latin America. Although six million people are infected by the Trypanosoma cruzi, current therapeutic options are limited, highlighting the need for new drugs. Here we report the preliminary structure activity relationships of a small library of 17 novel pyridyl sulfonamide derivatives. Analogues 4 and 15 displayed significant potency against intracellular amastigotes with EC₅₀ of 5.4?µM and 8.6?µM. In cytotoxicity assays using mice fibroblast L929 cell lines, both compounds indicated low toxicity with decent selectivity indices (SI) >36 and?>23 respectively. Hence these compounds represent good starting points for further lead optimization.     

A novel binuclear palladium complex with benzothiazole-2-thiolate: synthesis, crystal structure and interaction with DNA

The novel Pd(II) complex, [Pd(2)(micro-bzta)(4)].1.5DMSO (where bzta=benzothiazole-2-thiolate) has been synthesized and structurally characterized by element analysis, IR and single-crystal X-ray diffractometry. In the binuclear complex, two palladium(II) are bridged by four deprotonated benzothiazole-2-thialate in a head to tail disposition and the distance of the two Pd(II) is 2.747 A. Three-dimensional structure of the complex was constructed though S...S (3.339 A) weak interaction and pi...pi stack. The binding of the title complex with fish sperm DNA (FS-DNA) has been investigated by absorption and fluorescence spectra. The results indicate that the complex bind to FS-DNA in an intercalative mode and the intrinsic binding constant K of the title complex with FS-DNA is about 1.2 x 10(4)M(-1). Gel electrophoresis assay demonstrates the ability of the complex to cleave the pUC19 plasmid DNA.     

RNAi-based screening identifies the Mms22L-Nfkbil2 complex as a novel regulator of DNA replication in human cells

Cullin 4 (Cul4)-based ubiquitin ligases emerged as critical regulators of DNA replication and repair. Over 50 Cul4-specific adaptors (DNA damage-binding 1 (Ddb1)-Cul4-associated factors; DCAFs) have been identified and are thought to assemble functionally distinct Cul4 complexes. Using a live-cell imaging-based RNAi screen, we analysed the function of DCAFs and Cul4-linked proteins, and identified specific subsets required for progression through G1 and S phase. We discovered C6orf167/Mms22-like protein (Mms22L) as a putative human orthologue of budding yeast Mms22, which, together with cullin Rtt101, regulates genome stability by promoting DNA replication through natural pause sites and damaged templates. Loss of Mms22L function in human cells results in S phase-dependent genomic instability characterised by spontaneous double-strand breaks and DNA damage checkpoint activation. Unlike yeast Mms22, human Mms22L does not stably bind to Cul4, but is degraded in a Cul4-dependent manner and upon replication stress. Mms22L physically and functionally interacts with the scaffold-like protein Nfkbil2 that co-purifies with histones, several chromatin remodelling and DNA replication/repair factors. Together, our results strongly suggest that the Mms22L-Nfkbil2 complex contributes to genome stability by regulating the chromatin state at stalled replication forks.     

Preparation and biodistribution of a 99mTc tricarbonyl complex with deoxyglucose dithiocarbamate as a tumor imaging agent for SPECT

The deoxyglucose dithiocarbamate (DGDTC) was successfully labeled with the ^99mTc(CO)₃ core to provide the corresponding ^99mTc(CO)₃–DGDTC complex in good yields. The radiochemical purity of the ^99mTc(CO)₃–DGDTC complex was over 90%, as measured by high performance liquid chromatography (HPLC). The complex possessed good stability in saline at room temperature and in mouse plasma at 37 °C. Its partition coefficient result indicated that it was a hydrophilic complex. The electrophoresis results showed the complex was neutral. The biodistribution of ^99mTc(CO)₃–DGDTC in mice bearing S 180 tumor showed that the complex clearly accumulated in tumor, exhibiting high tumor/blood and tumor/muscle ratios and good tumor retention. Single photon emission computed tomography (SPECT) image studies showed there was a visible uptake in tumor sites, suggesting ^99mTc(CO)₃–DGDTC could be considered as a potential tumor imaging agent.     

A new oxo-vanadium complex employing an imidazole-rich tripodal ligand: A bioinspired bromide and hydrocarbon oxidation catalyst

A vanadyl complex with the ligand (bis(1-methylimidazol-2-yl)methyl)(2-(pyridyl-2-yl)ethyl)amine was synthesized and fully characterized by X-ray crystallography, elemental analyses, cyclic voltammetry and infrared, electronic and electron paramagnetic resonance spectroscopies. This compound was designed under the so called hybrid concept. It shows to be able to promiscuously use hydrogen peroxide to oxidize bromide and to catalyze the oxidation of benzene and cyclohexane with very good selectivities.     

Synthesis and biological evaluation of a novel 99mTc labeled 2-nitroimidazole derivative as a potential agent for imaging tumor hypoxia

Tumor hypoxia plays a major role in reducing the efficacy of therapeutic modalities like chemotherapy and radiation therapy in combating cancer. In order to target hypoxic tissues, a tripeptide ligand having a 2-nitroimidazole moiety, as a bioreductive species, was synthesized. The latter was radiolabeled with ^99mTc for imaging hypoxic regions of tumors and was characterized by means of its rhenium analogue. The biodistribution and scintigraphic image of the corresponding ^99mTc-complex showed accumulation in tumor and these results suggest that it could be a marker for imaging tumor hypoxia.     

Trinuclear Cu(II) complex with tetrazolyl-pyridine units as a bridging ligand: synthesis, characterization and X-ray structure

Reaction of 5-(2-pyridyl)tetrazole with 1,3-dibromopropane afforded three regioisomeric multidentate ligands L¹, L² and L³ containing two tetradentate pyridyl/tetrazolyl units linked by a flexible propylene spacer. These compounds were fully characterized by IR, ¹H and ¹³C NMR spectroscopy and elemental analysis. The crystal structure of L¹ was determined. With Cu(II), L¹ formed a trinuclear complex Cu₃(L¹)₂Cl₆. Its structure was determined crystallographically. In the complex, the three copper atoms are found to be in a strict linear arrangement, with the ligand bridging two adjacent copper atoms. The central copper ion is six-co-ordinated. The co-ordination spheres of the terminal copper atoms are distorted square pyramidal. Inter and intramolecular π,π-stacking interactions are observed in the free ligand and in complex 1.     

A potential rhodium cancer therapy: Studies of a cytotoxic organorhodium(I) complex that binds DNA

Described is a novel organorhodium(I) complex that is cytotoxic to the colon cancer cell line HCT116 and alters cell migration, DNA replication, and DNA condensation. Most importantly, the mechanism observed is not seen for the parent organorhodium dimer complex [{RhCl(COD)}₂], RhCl₃, or the free ligand/proligands (COD and 1-ⁿbutyl-3-methylimidazolium chloride). Thus, the activity of this organorhodium complex is attributable to its unique structure.     

DNA binding and oxidative DNA damage induced by a quercetin copper(II) complex: potential mechanism of its antitumor properties

The interaction of a quercetin copper(II) complex with DNA was investigated using UV–vis spectra, fluorescence measurement, viscosity measurement, agarose gel electrophoresis, and thiobarbituric acid reactive substances assay. The results indicate that the quercetin copper(II) complex can promote the cleavage of plasmid DNA, producing single and double DNA strand breaks, and intercalate into the stacked base pairs of DNA. Moreover, the complex can induce oxidative DNA damage involving generation of reactive oxygen species such as H₂O₂ and Cu(I)OOH. In addition, the cytotoxicity experiments carried out with A549 cells confirmed its apoptosis-inducing activity. And we also demonstrate that the levels of survivin protein expression in A549 cells decreased, and that relative activity of caspase-3 increased significantly after treatment with the complex. So our results suggest that the antitumor mechanism of the quercetin copper(II) complex involves not only its oxidative DNA damage with generation of reactive oxygen species but also its specific interaction with DNA. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.