Evaluation of DNA binding, antioxidant and cytotoxic activity of mononuclear Co(III) complexes of 2-oxo-1,2-dihydrobenzoh]quinoline-3-carbaldehyde thiosemicarbazones

Four new 2-oxo-1,2-dihydrobenzoh]quinoline-3-carbaldehyde N-substituted thiosemicarbazone ligands (H-2-LR, where R = H, Me, Et or Ph) and their corresponding new cobalt(III) complexes have been synthesized and characterized. The structures of the complexes 2 and 3 were determined by single crystal X-ray diffraction analysis. The interactions of the new complexes with DNA were investigated by absorption, emission and viscosity studies which indicated that the complexes bind to DNA via intercalation. Antioxidant studies of the new complexes showed that the significant antioxidant activity against DPPH radical. In addition, the in vitro cytotoxicity of complexes 1-4 against A549 cell line was assayed which showed higher cytotoxic activity with lower IC50 values indicating their efficiency in killing the cancer cells even at very low concentrations. (C) 2012 Elsevier Masson SAS. All rights reserved.

Electrochemical, phosphate hydrolysis, DNA binding and DNA cleavage properties of new polyaza macrobicyclic dinickel(II) complexes

A new class of macrobicyclic dinickel(II) complexes Ni2L1,2 B](ClO4)(4) (1-6), where L-1,L-2 are polyaza macrobicyclic binucleating ligands, and B is a N,N-donor heterocyclic base (viz. 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen)) are synthesized and characterized. The redox, catalytic, DNA binding and DNA cleavage properties were studied. They exhibit two irreversible waves in the cathodic region around E-pc = -0.95 V and E-pa = -0.85 V vs. Ag/Ag+ in CH3CN-0.1 M TBAP, respectively. The first order rate constants for the hydrolysis of 4-nitrophenylphosphate to 4-nitrophenolate by the dinickel(II) complexes 1-6 are in the range from 3.36 x 10(-5) to 10.83 x 10(-5) Ms-1. The complexes 3 and 6 show good binding propensity to calf thymus DNA giving binding constant values (K-b) in the range from 3.08 x 10(5) to 5.37 x 10(5) M-1. The binding site sizes and viscosity data suggest the DNA intercalative and/or groove binding nature of the complexes. The complexes display significant hydrolytic cleavage of supercoiled pBR322DNA at pH 7.2 and 37 degrees C. The hydrolytic cleavage of DNA by the complexes is supported by the evidence from free radical quenching and T4 ligase ligation. The pseudo Michaelis-Menten kinetic parameters k(cat) = 5.44 x 10(-2) h(-1) and K-M = 6.23 x 10(-3) M for complex 3 were obtained. Complex 3 also shows an enormous enhancement of the cleavage rate, of 1.5 x 10(6), in comparison to the uncatalysed hydrolysis rate (k = 3.6 x 10(-8) h(-1)) of ds-DNA.

Recent Developments in the Chemistry and Biology of G-Quadruplexes with Reference to the DNA Groove Binders

DNA is the chemotherapeutic target for treating diseases of genetic origin. Besides well-known double-helical structures (A, B, Z, parallel stranded-DNA etc.), DNA is capable of forming several multi-stranded structures (triplex, tetraplex, i-motif etc.) which have unique biological significance. The G-rich 3'-ends of chromosomes, called telomeres, are synthesized by telomerase, a ribonucleoprotein, and over-expression of telomerase is associated with cancer. The activity of telomerase is suppressed if the G-rich region is folded into the four stranded structures, called G-quadruplexes (G4-DNAs) using small synthetic ligands. Thus design and synthesis of new G4-DNA ligands is an attractive strategy to combat cancer. G4-DNA forming sequences are also prevalent in other genomic regions of biological significance including promoter regions of several oncogenes. Effective gene regulation may be achieved by inducing a G4-DNA structure within the G-rich promoter sequences. To date, several G4-DNA stabilizing ligands are known. DNA groove binders interact with the duplex B-DNA through the grooves (major and minor groove) in a sequence-specific manner. Some of the groove binders are known to stabilize the G4-DNA. However, this is a relatively under explored field of research. In this review, we focus on the recent advances in the understanding of the G4-DNA structures, particularly made from the human telomeric DNA stretches. We summarize the results of various investigations of the interaction of various organic ligands with the G4-DNA while highlighting the importance of groove binder-G4-DNA interactions.

Distinct mechanisms of DNA repair in mycobacteria and their implications in attenuation of the pathogen growth

About a third of the human population is estimated to be infected with Mycobacterium tuberculosis. Emergence of drug resistant strains and the protracted treatment strategies have compelled the scientific community to identify newer drug targets, and to develop newer vaccines. In the host macrophages, the bacterium survives within an environment rich in reactive nitrogen and oxygen species capable of damaging its genome. Therefore, for its successful persistence in the host, the pathogen must need robust DNA repair mechanisms. Analysis of M. tuberculosis genome sequence revealed that it lacks mismatch repair pathway suggesting a greater role for other DNA repair pathways such as the nucleotide excision repair, and base excision repair pathways. In this article, we summarize the outcome of research involving these two repair pathways in mycobacteria focusing primarily on our own efforts. Our findings, using Mycobacterium smegmatis model, suggest that deficiency of various DNA repair functions in single or in combinations severely compromises their DNA repair capacity and attenuates their growth under conditions typically encountered in macrophages. (C) 2011 Elsevier Ireland Ltd. All rights reserved.

A Novel Property of DNA - As a Bioflotation Reagent in Mineral Processing

Environmental concerns regarding the use of certain chemicals in the froth flotation of minerals have led investigators to explore biological entities as potential substitutes for the reagents in vogue. Despite the fact that several microorganisms have been used for the separation of a variety of mineral systems, a detailed characterization of the biochemical molecules involved therein has not been reported so far. In this investigation, the selective flotation of sphalerite from a sphalerite-galena mineral mixture has been achieved using the cellular components of Bacillus species. The key constituent primarily responsible for the flotation of sphalerite has been identified as DNA, which functions as a bio-collector. Furthermore, using reconstitution studies, the obligatory need for the presence of non-DNA components as bio-depressants for galena has been demonstrated. A probable model involving these entities in the selective flotation of sphalerite from the mineral mixture has been discussed.

Sm(III)nitrate-catalyzed one-pot synthesis of furano3,2c]-1,2,3,4-tetrahydroquinolines and DNA photocleavage studies

The synthesis and DNA photocleavage studies of furano3,2-c]-1,2,3,4-tetrahydroquinolines have been reported. Sm(III)nitrate was found to be an efficient for the Diels-Alder reaction of aryl amines with 2,3-dihydrofuran to offer the corresponding furano3,2-c]-1,2,3,4-tetrahydroquinolines derivatives as a mixture of cis/trans stereoisomers in moderate yields. The aqueous solubility of acid catalyst can be recycled without significant loss of activity. The DNA photocleavage studies shows that, the cis/trans stereoisomers are good DNA cleavage mimic in terms of molecular structure. (C) 2012 Elsevier B.V. All rights reserved.

Designing carboxymethyl cellulose based layer-by-layer capsules as a carrier for protein delivery

Stable hollow microcapsules composed of sodium carboxymethyl cellulose (CMC) and poly (allylamine hydrochloride) (PAH) were produced by layer-by-layer adsorption of polyelectrolytes onto CaCO 3 microparticles. Subsequently the core was removed by addition of chelating agents for calcium ions. Zeta potential studies showed charge reversal with deposition of successive polyelectrolyte layers, indicating that the alternate electrostatic adsorption of polyelectrolytes of opposite charge was successfully achieved. The size and surface morphology of the capsules was characterized by various microscopy techniques. The pH responsive loading behavior was elucidated by confocal laser scanning microscopy (CLSM) studies using fluorescence labeled dextran (FITC-dextran) and labeled BSA (FITC-BSA). CLSM images confirmed the open (pH ≤ 6) and closed state (pH ≥ 7) of the capsules. A model drug bovine serum albumin (BSA) was spontaneously loaded below its isoelectric point into hollow microcapsules, where BSA is positively charged. The loading of the BSA into the microcapsules was found to be dependent on the feeding concentration and pH of the medium. 65 of the loaded BSA was released over 7h of which about 34 was released in the first hour. These findings demonstrate that (CMC/PAH) 2 hollow capsules can be further exploited as a potential drug delivery system.

Photocytotoxic Oxidovanadium(IV) Complexes of Polypyridyl Ligands Showing DNA-Cleavage Activity in Near-IR Light

Oxidovanadium(IV) complexes VO(pyphen)(L)]Cl2 (1, 2) and VO(pydppz)(L)]Cl2 (3, 4), where L is 1,10-phenanthroline (phen in 1 and 3) and dipyrido3,2-a:2',3'-c]phenazine (dppz in 2 and 4) are prepared and characterized. The crystal structure of VO(pyphen)(phen)](ClO4)2 (1a) shows a six-coordinate VN5O geometry with a VO2+ moiety in which the polypyridyl ligand binds in a meridional fashion and the phen ligand displays a chelating binding mode with an N-donor site trans to the oxidovanadyl group. The complexes show a dd band within 720-750 nm in DMF. The one-electron paramagnetic complexes are 1:2 electrolytes in DMF. The complexes exhibit an irreversible VIV/VIII redox response near -0.85 V vs. SCE in DMF/0.1 M TBAP. The complexes bind to calf thymus (ct) DNA giving Kb values within 7.5 x 104 to 1.1 x 106 M1. The complexes show poor chemical nuclease activity in the dark and exhibit significant DNA-photocleaving activity in near-IR light of 705 and 785 nm forming .OH radicals. Complexes 2-4 show remarkable photocytotoxicity in HeLa cancer cells. FACS analysis of the HeLa cells treated with complex 4 shows cell death as highlighted by the sub G1 peak. Propidium iodide staining data indicate apoptosis as the primary mode of cell death.

Novel tetranuclear distorted open-cubane copper complex containing oximate bridges: Synthesis, crystal structure, DNA binding and cleavage activity

The synthesis, molecular structure, DNA binding and nuclease activity of Cu4O4 open-cubane tetranuclear copper(II) complex with 3-2-(ethyl amino)ethyl]imino]-2-butanoneoxime (HL) are reported for the first time. The neutral tetranuclear Cu4L4(ClO4)(4)] complex crystallizes in tetragonal space group P (4) over bar2(1)c with the unit cell parameters; a = 13.798(4) angstrom, b = 13.798(4) angstrom, c = 14.119(6) angstrom, V = 2688(16) angstrom(3), Z = 8, R = 0.0636. Symmetrically equivalent copper atoms exhibit a CuN3O3 elongated distorted octahedral coordination environment, with three nitrogen atoms of the L ligand and one oxime-oxygen atom of second L ligand at equatorial positions, one oxime-oxygen atom of the third L ligand and perchlorate oxygen at axial positions. The complex shows quasireversible cyclic voltammetric response at 0.805 V (Delta E-p = 277 mV) at 100 mV s (1) in DMF for the Cu(II)/Cu(I) redox couple. The binding study of the complex with calf-thymus DNA has been investigated using absorption spectrophotometry. The complex shows strong nuclease activity on stranded pBR 322 plasmid DNA in the presence of hydrogen peroxide and marginal nuclease activity in the presence of reducing agent (dithiothreitol). (C) 2012 Elsevier B. V. All rights reserved.

An efficient one-pot synthesis and photoinduced DNA cleavage studies of 2-chloro-3-(5-aryl-4,5-dihydroisoxazol-3-yl)quinolines

4,5-Dihydroisoxazoles continue to attract considerable interest due to their wide spread biological activities. Here, we identify an efficient protocol for the preparation of 4,5-dihydroisoxazoles (2-isaxazolines) (4a-g) from quinolinyl chalcones. The nucleolytic activities of synthesized compounds were investigated by agarose gel electrophoresis. All these compounds were showed the remarkable DNA cleavage activity (concentration dependent) with pUC19 DNA at 365 nm UV light. The DNA cleavage activity was significantly enhanced by the presence of iminyl and carboxy radicals of DIQ. (C) 2012 Elsevier Ltd. All rights reserved.

Under-representation of intrinsic terminators across bacterial genomic islands: Rho as a principal regulator of xenogenic DNA expression

Two transcription termination mechanisms - intrinsic and Rho-dependent - have evolved in bacteria. The Rho factor occurs in most bacterial lineages, and has been hypothesized to play a global regulatory role. Genome-wide studies using microarray, 2D-gel electrophoresis and ChIP-chip provided evidence that Rho serves to silence transcription from horizontally acquired genes and prophages in Escherichia coli K-12, implicating the factor to be a part of the ``cellular immune mechanism'' protecting against deleterious phages and aberrant gene expression from acquired xenogenic DNA. We have investigated this model by adopting an alternate in silico approach and have extended the study to other species. Our analysis shows that several genomic islands across diverse phyla have under-representation of intrinsic terminators, similar to that experimentally observed in E. coli K-12. This implies that Rho-dependent termination is the predominant process operational in these islands and that silencing of foreign DNA is a conserved function of Rho. From the present analysis, it is evident that horizontally acquired islands have lost intrinsic terminators to facilitate Rho-dependent termination. These results underscore the importance of Rho as a conserved, genome-wide sentinel that regulates potentially toxic xenogenic DNA. (C) 2012 Elsevier B.V. All rights reserved.

Development of micro-shock wave assisted dry particle and fluid jet delivery system

Small quantity of energetic material coated on the inner wall of a polymer tube is proposed as a new method to generate micro-shock waves in the laboratory. These micro-shock waves have been harnessed to develop a novel method of delivering dry particle and liquid jet into the target. We have generated micro-shock waves with the help of reactive explosive compound high melting explosive (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and traces of aluminium] coated polymer tube, utilising 9 J of energy. The detonation process is initiated electrically from one end of the tube, while the micro-shock wave followed by the products of detonation escape from the open end of the polymer tube. The energy available at the open end of the polymer tube is used to accelerate tungsten micro-particles coated on the other side of the diaphragm or force a liquid jet out of a small cavity filled with the liquid. The micro-particles deposited on a thin metal diaphragm (typically 100-mu m thick) were accelerated to high velocity using micro-shock waves to penetrate the target. Tungsten particles of 0.7 mu m diameter have been successfully delivered into agarose gel targets of various strengths (0.6-1.0 %). The device has been tested by delivering micro-particles into potato tuber and Arachis hypogaea Linnaeus (ground nut) stem tissue. Along similar lines, liquid jets of diameter 200-250 mu m (methylene blue, water and oils) have been successfully delivered into agarose gel targets of various strengths. Successful vaccination against murine salmonellosis was demonstrated as a biological application of this device. The penetration depths achieved in the experimental targets are very encouraging to develop a future device for biological and biomedical applications.

The zinc finger proteins Mxr1p and repressor of phosphoenolpyruvate carboxykinase (ROP) have the same DNA binding specificity but regulate Methanol Metabolism antagonistically in pichia pastoris

The methanol-inducible alcohol oxidase I (AOXI) promoter of the methylotrophic yeast, Pichia pastoris, is used widely for the production of recombinant proteins. AOXI transcription is regulated by the zinc finger protein Mxr1p (methanol expression regulator 1). ROP (repressor of phosphoenolpyruvate carboxykinase, PEPCK) is a methanol- and biotin starvation-inducible zinc finger protein that acts as a negative regulator of PEPCK in P. pastoris cultured in biotin-deficient, glucose-ammonium medium. The function of ROP during methanol metabolism is not known. In this study, we demonstrate that ROP represses methanol-inducible expression of AOXI when P. pastoris is cultured in a nutrient-rich medium containing yeast extract, peptone, and methanol (YPM). Deletion of the gene encoding ROP results in enhanced expression of AOXI and growth promotion whereas overexpression of ROP results in repression of AOXI and growth retardation of P. pastoris cultured in YPM medium. Surprisingly, deletion or overexpression of ROP has no effect on AOXI gene expression and growth of P. pastoris cultured in a minimal medium containing yeast nitrogen base and methanol (YNBM). Subcellular localization studies indicate that ROP translocates from cytosol to nucleus of cells cultured in YPM but not YNBM. In vitro DNA binding studies indicate that AOXI promoter sequences containing 5' CYCCNY 3' motifs serve as binding sites for Mxr1p as well as ROP. Thus, Mxr1p and ROP exhibit the same DNA binding specificity but regulate methanol metabolism antagonistically in P. pastoris. This is the first report on the identification of a transcriptional repressor of methanol metabolism in any yeast species.

Co-evolution of content popularity and delivery in mobile P2P networks

Mobile P2P technology provides a scalable approach for content delivery to a large number of users on their mobile devices. In this work, we study the dissemination of a single item of content (e. g., an item of news, a song or a video clip) among a population of mobile nodes. Each node in the population is either a destination (interested in the content) or a potential relay (not yet interested in the content). There is an interest evolution process by which nodes not yet interested in the content (i.e., relays) can become interested (i.e., become destinations) on learning about the popularity of the content (i.e., the number of already interested nodes). In our work, the interest in the content evolves under the linear threshold model. The content is copied between nodes when they make random contact. For this we employ a controlled epidemic spread model. We model the joint evolution of the copying process and the interest evolution process, and derive joint fluid limit ordinary differential equations. We then study the selection of parameters under the content provider's control, for the optimization of various objective functions that aim at maximizing content popularity and efficient content delivery.