Guanine Residues Research Articles

Oxidative-stress-driven mutagenesis in the small intestine of the gpt delta mouse induced by oral administration of potassium bromate

Tumorigenesis induced by oxidative stress is thought to be initiated by mutagenesis, but via an indirect mechanism. The dose-response curves for agents that act by this route usually show a threshold, for unknown reasons. To gain insight into these phenomena, we have analyzed the dose response for mutagenesis induced by the oral administration of potassium bromate, a typical oxidative-stress-generating agent, to gpt delta mice. The agent was given orally for 90 d to either Nrf2+ or Nrf2-knockout (KO) mice and mutants induced in the small intestine were analyzed. In Nrf2+mice, the mutant frequency was significantly greater than in the vehicle controls at a dose of 0.6 g/L but not at 0.2 g/L, indicating that a practical threshold for mutagenesis lies between these doses. At 0.6 g/L, the frequencies of G-to-T transversions (landmark mutations for oxidative stress) and G-to-A transitions were significantly elevated. In Nrf2-KO mice, too, the total mutant frequency was increased only at 0.6 g/L. G-to-T transversions are likely to have driven tumorigenesis in the small intestine. A site-specific G-to-T transversion at guanine (nucleotide 406) in a 5′-TGAA-3′ sequence in gpt, and our primer extension reaction showed that formation of the oxidative DNA base modification 8-oxo-deoxyguanosine (8-oxo-dG) at nucleotide 406 was significantly increased at doses of 0.6 and 2 g/L in the gpt delta mice. In the Apc oncogene, guanine residues in the same or similar sequences (TGAA or AGAA) are highly substituted by thymine (G-to-T transversions) in potassium bromate-induced tumors. We propose that formation of 8-oxo-dG in the T(A)GAA sequence is an initiating event in tumor formation in the small intestine in response to oxidative stress.

Quantum chemical investigation on the interaction of cysteine and DNA purine bases with aquated ruthenium(III) anticancer drug (ImH)[trans-RuCl4(Im)2

Keppler type water-soluble ((ImH)[trans-RuCl4(Im)2], Im = imidazole), ICR (or KP418) exhibits promising anticancer activity against colorectal cancer. Interaction of aquated ICR complexes; i.e., [trans-RuCl3(H2O)(Im)2] (monoaqua ICR) and [trans-RuCl2(H2O)2(Im)2]+ (diaqua ICR) with cysteine (Cys), guanine (G), and adenine (A) residues have been investigated in details by DFT method and CPCM solvation model. Activation free energy for the substitution of aqua ligand from diaquated ICR by Cys is found to be apparently lower (13.28 kcal/mol) in aqueous phase and corresponding rate constant value is calculated to be kCys = 1.52 × 103 s−1. Calculated activation free energy values suggest that substitution of aqua ligand from diaqua ICR is observed to be more favourable by Cys, G or A in comparison to monoaqua ICR. Surprisingly, intermolecular hydrogen bondings play a significant role in stabilizing entire geometry. Furthermore, calculated net atomic charges based on natural population analysis show charge redistribution on interaction with Cys, G and A.

Antibody-Drug Conjugates with Indolinobenzodiazepine Dimer Payloads: DNA-Binding Mechanism of Indolinobenzodiazepine Dimer Catabolites in Target Cancer Cells.

DNA-targeting indolinobenzodiazepine dimer (IGN) payloads are used in several clinical-stage antibody-drug conjugates. IGN drugs alkylate DNA through the single imine moiety present in the dimer in contrast to the pyrrolobenzodiazepine dimer drugs, such as talirine and tesirine, which contain two imine moieties per dimer and cross-link DNA. This study explored the mechanism of binding of IGN to DNA in cells and to synthetic duplex and hairpin oligonucleotides. New, highly sensitive IGN-DNA binding enzyme-linked immunosorbent assay methods were developed using biotinylated IGN analogues (monoimine, diimine, and diamine IGNs) and digoxigenin-labeled duplex oligonucleotides, which allowed the measurement of drug-DNA adducts in viable cells at concentrations below IC50. Furthermore, the release of free drug from the IGN-DNA adduct upon treatment with nuclease ex vivo was tested under physiological conditions. The monoimine IGN drug formed a highly stable adduct with DNA in cells, with stability similar to that of the diimine drug analogue. Both monoimine and diimine IGN-DNA adducts released free drugs upon DNA cleavage by nuclease at 37 °C, although more free drug was released from the monoimine compared to the diimine adduct, which presumably was partly cross-linked. The strong binding of the monoimine IGN drug to duplex DNA results from both the noncovalent IGN-DNA interaction and the covalent bond formation between the 2-amino group of a guanine residue and the imine moiety in IGN.

Interaction of Human Telomeric i-Motif DNA with Single-Walled Carbon Nanotubes: Insights from Molecular Dynamics Simulations.

This work deals with molecular dynamics simulations of human telomeric i-motif DNA interacting with functionalized single-walled carbon nanotubes. We study two kinds of i-motifs differing by the protonation state of cytosines, i.e., unprotonated ones representative to neutral pH and with half of the cytosines protonated and representative to acidic conditions. These i-motifs interact with two kinds of carbon nanotubes differing mainly in chirality (diameter), i.e., (10, 0) and (20, 0). Additionally, these nanotubes were on-tip functionalized by amino groups or by guanine- containing residues. We found that protonated i-motif adsorbs strongly, although not specifically, on the nanotube surfaces with its 3' and 5' ends directed toward the surface and that adsorption does not affect the i-motif shape and hydrogen bonds existing between C:C+ pairs. The functional groups on the nanotube tips have minimal effect either on position of i-motif or on its binding strength. Unprotonated i-motif, in turn, deteriorates significantly during interaction with the nanotubes and its binding strength is rather high as well. We found that (10, 0) nanotubes destroy the i-motif shape faster than (20, 0). Moreover the i-motif either tries to wrap the nanotube or migrates to its tip and becomes immobilized due to interaction with guanine residue localized on the nanotube tip and attempts to incorporate its 3' end into the nanotube interior. No hydrogen bonds exist within the unprotonated i-motif prior to and after adsorption on the nanotube. Thus, carbon nanotubes do not improve the stability of unprotonated i-motif due to simple adsorption or just physical interactions. We hypothesize that the stabilizing effect of carbon nanotubes reported in the literature is due to proton transfer from the functional group in the nanotube to cytosines and subsequent formation of C:C+ pairs.

Artificial small RNA-mediated growth inhibition in Escherichia coli and Salmonella enterica serovar Typhimurium

We developed a synthetic RNA approach to identify growth inhibition sequences by cloning random 24-nucleotide (nt) sequences into an arabinose-inducible expression vector. This vector expressed a small RNA (sRNA) of ∼140 nt containing a 24 nt random sequence insert. After transforming Escherichia coli with the vector, 10 out of 954 transformants showed strong growth defect phenotypes and two clones caused cell lysis. We then examined growth inhibition phenotypes in the Salmonella Typhimurium LT2 strain using the twelve sRNAs that exerted an inhibitory effect on E. coli growth. Three of these clones showed strong growth inhibition phenotypes in S. Typhimurium LT2. The most effective sRNA contained the same insert (N1) in both bacteria. The 24 nt random sequence insert of N1 was abundant in guanine residues (ten out of 24 nt), and other random sequences causing growth defects were also highly enriched for guanine (G) nucleotides. We, therefore, generated clones that express sRNAs containing a stretch of 16 to 24 continuous guanine sequences (poly-G16, -G18, -G20, -G22, and -G24). All of these clones induced growth inhibition in both liquid and agar plate media and the poly-G20 clone showed the strongest effect in E. coli. These results demonstrate that our sRNA expression system can be used to identify nucleotide sequences that are potential candidates for oligonucleotide antimicrobial drugs.

Molecular Structure of Binary Chromium(III)-DNA Adducts.

Chromium(VI) is a carcinogen and mutagen, and its mechanisms of action are proposed to involve binding of its reduction product, chromium(III), to DNA. The manner in which chromium(III) binds DNA has not been established, particularly at a molecular level. Analysis of oligonucleotide duplex DNAs by NMR, EPR, and IR spectroscopies in the presence of chromium(III) allows the elucidation of the Cr binding site. The metal centers were found to interact exclusively with guanine N7 positions. No evidence of chromium interactions with other bases or backbone phosphates nor of Cr forming intra-strand crosslinks between neighboring guanine residues was observed.

Dynamical ensemble of the active state and transition state mimic for the RNA-cleaving 8-17 DNAzyme in solution.

We perform molecular dynamics simulations, based on recent crystallographic data, on the 8–17 DNAzyme at four states along the reaction pathway to determine the dynamical ensemble for the active state and transition state mimic in solution. A striking finding is the diverse roles played by Na+ and Pb2+ ions in the electrostatically strained active site that impact all four fundamental catalytic strategies, and share commonality with some features recently inferred for naturally occurring hammerhead and pistol ribozymes. The active site Pb2+ ion helps to stabilize in-line nucleophilic attack, provides direct electrostatic transition state stabilization, and facilitates leaving group departure. A conserved guanine residue is positioned to act as the general base, and is assisted by a bridging Na+ ion that tunes the pKa and facilitates in-line fitness. The present work provides insight into how DNA molecules are able to solve the RNA-cleavage problem, and establishes functional relationships between the mechanism of these engineered DNA enzymes with their naturally evolved RNA counterparts. This adds valuable information to our growing body of knowledge on general mechanisms of phosphoryl transfer reactions catalyzed by RNA, proteins and DNA.

Electric-Field-Driven Molecular Recognition Reactions of Guanine with 1,2-Dipalmitoyl-sn-glycero-3-cytidine Monolayers Deposited on Gold Electrodes

Monolayers of 1,2-dipalmitoyl-sn-glycero-3-cytidine were incubated with guanine in a 0.1 M NaF electrolyte at the surface of a Langmuir trough and transferred to gold (111) electrodes using the Langmuir-Schaefer technique. Chronocoulometry and photon polarization modulation infrared reflection absorption spectroscopy were employed to investigate the influence of the static electric field on the orientation and conformation of the cytidine nucleolipid molecules on the metal surface in the presence of guanine and to monitor the molecular recognition of guanine with the cytosine moiety. When the monolayer is exposed to guanine solutions, the cytosine moiety binds to the guanine residue in either a Watson-Crick complex at positively charged electrode surfaces or a noncomplexed state at negative surface charges. The positive electrostatic field causes the cytosine moiety and the cytosine-guanine complex to adopt a nearly parallel orientation with respect to the plane of the monolayer with a measured tilt angle of ∼10°. The parallel orientation is stabilized by the interactions between the permanent dipole of the cytosine moiety or the Watson-Crick complex and the static electric field. At negative charge densities, the tilt of the cytosine moiety increases by ∼15-20°, destabilizing the complex. Our results demonstrate that the static electric field has an influence on the molecular recognition reactions between nucleoside base pairs at the metal-solution interface and can be controlled by altering the surface charge at the metal.

RETRACTED: CDX2/mir-145-5p/SENP1 Pathways Affect LNCaP Cells Invasion and Migration

Background/Aims: Recently, rapidly accumulating evidence has shown that microRNAs (miRNAs) are involved in human tumorigenesis, and the dysregulation of miRNAs has been observed in many cancers, including prostate cancer. miR-145-5p, an miRNA with reduced expression in prostate cancer cells, has been shown to have a tumor suppressive role in a variety of tumors. However, its underlying mechanism requires further elucidation.Methods: A lentiviral expression vector for miR-145-5p was constructed and used to establish a stable cell line (LNCaP) expressing miR-145-5p. The cells were cultured normally and divided into the control group (control), negative control group (negative control), and test group (miR-145-5p). Inhibition of proliferation was measured by a WST-8 assay. The early apoptosis rate of cells was detected by flow cytometry. Clone formation ability was detected by a clone formation inhibition test. Cell invasion and migration capacity was detected by a Transwell assay. The relative expression levels of proteins were detected by western blotting. We constructed a nude mouse model of prostate cancer to observe the effect of miR-145-5p on the growth of transplanted tumors. TargetScan bioinformatics software was used to predict target genes regulated by miR-14-5p. ChIPBase was used to predict transcription factors with binding sites in the upstream promoter region of miR-145-5p. Quantitative reverse transcription PCR was used to detect the relative expression level of genes. A bifluorescence-reporter gene vector was constructed to confirm the regulation of target genes by miR-145-5p. We used 5′ rapid amplification of cDNA ends to confirm the transcription start site of miR-145-5p.Chromatin immunoprecipitation technology was used to detect the effect of transcription factors binding to miR-145-5p.Results: The overexpression of miR-145-5p not only inhibited the proliferation, invasion, and migration of LNCaP cells but also promoted their early apoptosis. After overexpressing miR-145-5p, the expression of small ubiquitin-like modifier protein-specific protease 1 (SENP1), and caudal-related homeobox 2 (CDX2) protein was decreased in LNCaP cells. The transcription factor CDX2 bound to the miR-145-5p promoter region and inhibited its transcription. The transcription start site of miR-145-5p was located at a guanine residue 1,408 bp upstream of the stem-loop sequence. Upon overexpression, miR-145-5p could bind to the 3′-untranslated region of SENP1 to inhibit its translation.Conclusion: These results suggested that CDX2 inhibits the expression of miR-145-5p, thereby relieving the inhibitory effect of miR-145-5p on the translation of SENP1 and affecting the invasion and migration of prostate cancer cells.

RNA ligands activate the Machupo virus polymerase and guide promoter usage

Segmented negative-sense (SNS) RNA viruses initiate infection by delivering into cells a suite of genomic RNA segments, each sheathed by the viral nucleocapsid protein and bound by the RNA-dependent RNA-polymerase (RdRP). For the orthomyxovirus influenza and the bunyavirus La Crosse, the 5' end of the genomic RNA binds as a hook-like structure proximal to the active site of the RdRP. Using an in vitro assay for the RNA-dependent RNA-polymerase (RdRP) of the arenavirus Machupo (MACV), we demonstrate that the 5' genomic and antigenomic RNAs of both small and large genome segments stimulate activity in a promoter-specific manner. Functional probing of the activating RNAs identifies intramolecular base-pairing between positions +1 and +7 and a pseudotemplated 5' terminal guanine residue as key for activation. Binding of structured 5' RNAs is a conserved feature of all SNS RNA virus polymerases, implying that promoter-specific RdRP activation extends beyond the arenaviruses. The 5' RNAs and the RNA binding pocket itself represent targets for therapeutic intervention.

Towards Understanding of Polymorphism of the G-rich Region of Human Papillomavirus Type 52.

The potential to affect gene expression via G-quadruplex stabilization has been extended to all domains of life, including viruses. Here, we investigate the polymorphism and structures of G-quadruplexes of the human papillomavirus type 52 with UV, CD and NMR spectroscopy and gel electrophoresis. We show that oligonucleotide with five G-tracts folds into several structures and that naturally occurring single nucleotide polymorphisms (SNPs) have profound effects on the structural polymorphism in the context of G-quadruplex forming propensity, conformational heterogeneity and folding stability. With help of SNP analysis, we were able to select one of the predominant forms, formed by G-rich sequence d(G3TAG3CAG4ACACAG3T). This oligonucleotide termed HPV52(1–4) adopts a three G-quartet snap back (3 + 1) type scaffold with four syn guanine residues, two edgewise loops spanning the same groove, a no-residue V loop and a propeller type loop. The first guanine residue is incorporated in the central G-quartet and all four-guanine residues from G4 stretch are included in the three quartet G-quadruplex core. Modification studies identified several structural elements that are important for stabilization of the described G-quadruplex fold. Our results expand set of G-rich targets in viral genomes and address the fundamental questions regarding folding of G-rich sequences.

Specific Photocleavage Activity of N‐Methylmesoporphyrin IX on G‐Quadruplex DNA Structures

G‐rich regions, at which G‐quadruplexes (G4) are proposed to form, are associated with promoter regions within proto‐oncogenes and may play a role in cell proliferation and carcinogenesis. The ability to identify the formation of G4 structures in these regions, including the temporal aspects of G‐quadruplex formation, is essential to establish the role of these structures in transcriptional regulation. We have focused on identifying highly selective G4 photocleavage agents as molecular probes for establishing the location and timing of G4 formation. N‐methylmesoporphyrin IX (NMM) has long been known as a G4 ligand; however, there has been little investigation into its DNA photocleavage activity. Here we report the ability of NMM to act as a highly selective photocleavage agent for specific G4 structures. We first studied the interaction of NMM with the G4 structures formed by DNA oligonucleotides containing the c‐MYC promoter or human telomeric (hTel) sequences formed in the presence of either Na+ or K+‐containing buffers using a FRET‐based Tm assay and CD spectroscopy. We employed a fluorescence‐based solution assay for G4 cleavage to establish that NMM effects photocleavage (420 nm) of c‐MYC more efficiently than the hTel G4 under both Na+ and K+ conditions, and effects photocleavage of c‐MYC G4 even under white light irradiation. Using denaturing polyacrylamide gel electrophoresis (PAGE), we confirmed this selective photocleavage and demonstrate that cleavage occurs at specific guanine residues of the c‐MYC G4. In order to determine if the photocleavage proceeds through the generation of reactive oxygen species like singlet oxygen, we carried out photocleavage reactions in the presence of H2O and D2O, and employed a turn‐on fluorescent singlet oxygen sensor to detect 1O2 generation. We find that NMM acts to destabilize specific G4 topologies, but oligonucleotides annealed in the presence of NMM form alternative topologies that are thermally stabilized. NMM photocleavage is highly selective for G4 DNA versus duplex DNA, and the K+‐stabilized c‐MYC G4 is preferentially cleaved compared to the Na+‐stabilized structure and the hTel G4 in either Na+ or K+. PAGE analysis indicates that NMM photocleavage of c‐MYC G4 occurs preferentially at the 3′ G‐tetrad residues. This photocleavage does not appear to be due to 1O2. These results indicate that NMM may be a useful tool for elucidating the role of promoter G‐quadruplex structures.Support or Funding InformationSupport for this work by the Cancer Prevention and Research Institute of Texas (RP160852) and Texas State University is gratefully acknowledged.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Theoretical modeling of DNA electron hole transport through polypyrimidine sequences: a QM/MM study.

The phenomenon of DNA hole transport (HT) has attracted of scientists for several decades, mainly due to its potential application in molecular electronics. As electron holes mostly localize on purine bases in DNA, the majority of scientific effort has been invested into chemically modifying the structures of adenine and guanine in order to increase their HT-mediating properties. In this work we examine an alternative, never yet explored, way of affecting the HT efficiency by forcing electron holes to localize on pyrimidine bases and move between them. Using an enhanced and revised version of our previously developed QM/MM model, we perform simulations of HT through polyadenine, polycytosine, polyguanine, and polythymine stacks according to a multistep hopping mechanism. From these simulations, kinetic parameters for HT are obtained. The results indicate a particularly high efficiency of cytosine→cytosine hopping, which is about ten times higher than the G → G hopping. We also discuss possible improvement of cytosine HT by modifying the oxidoreductive properties of complementary guanine residues.

Guanine residues of precursor microRNA’s terminal loop as a potential target for cancer therapy and prevention

MicroRNAs (miRNAs) are small endogenous RNA molecules with diverse biological functions that have been implicated in various human diseases, including cancer. Global downregulation of miRNA expression in different human cancer types, after exposure to cigarette-smoke, or to the hormone estrogen, have been shown to be associated with guanine (G) enrichment in the terminal loops (TLs) of their precursors. Here, we describe the role of G content of TLs in the regulation of miRNA expression, and highlight its potential as a target in cancer prevention and treatment.

Mechanisms of DNA damage induced by morin, an inhibitor of amyloid β-peptide aggregation

Morin is a potential inhibitor of amyloid β-peptide aggregation. This aggregation is involved in the pathogenesis of Alzheimer’s disease. Meanwhile, morin has been found to be mutagenic and exhibits peroxidation of membrane lipids concurrent with DNA strand breaks in the presence of metal ions. To clarify a molecular mechanism of morin-induced DNA damage, we examined the DNA damage and its site specificity on 32P-5′-end-labeled human DNA fragments treated with morin plus Cu(II). The formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), an indicator of oxidative DNA damage, was also determined in calf thymus DNA treated with morin plus Cu(II). Morin-induced DNA strand breaks and base modification in the presence of Cu(II) were dose dependent. Morin plus Cu(II) caused piperidine-labile lesions preferentially at thymine and guanine residues. The DNA damage was inhibited by methional, catalase and Cu(I)-chelator bathocuproine. The typical •OH scavengers ethanol, mannitol and sodium formate showed no inhibitory effect on DNA damage induced by morin plus Cu(II). When superoxide dismutase was added to the solution, DNA damage was not inhibited. In addition, morin plus Cu(II) increased 8-oxodG formation in calf thymus DNA fragments. We conclude that morin undergoes autoxidation in the presence of Cu(II) via a Cu(I)/Cu(II) redox cycle and H2O2 generation to produce Cu(I)-hydroperoxide, which causes oxidative DNA damage.

Preparation and Purification of Oligodeoxynucleotide Duplexes Containing a Site-Specific, Reduced, Chemically Stable Covalent Interstrand Cross-Link Between a Guanine Residue and an Abasic Site.

Methods for the preparation of DNA duplexes containing interstrand covalent cross-links may facilitate research in the fields of biochemistry, molecular biology, nanotechnology, and materials science. Here we report methods for the synthesis and isolation of DNA duplexes containing a site-specific, chemically stable, reduced covalent interstrand cross-link between a guanine residue and an abasic site. The method uses experimental techniques and equipment that are common in most biochemical laboratories and inexpensive, commercially available oligonucleotides and reagents.

Binding of platinum derivative, oxaliplatin to deoxyribonucleic acid: structural insight into antitumor action

Platinum-derived chemodrugs constitute an active class in cancer therapeutics. Besides being potent against various solid tumors, oxaliplatin has been recognized as the first platinum compound to be approved for the treatment of colorectal cancer. Structurally, oxaliplatin consists of a platinum metal complexed to oxalate and diaminocyclohexane (DACH) and exert its anticancer action by inhibiting DNA replication and transcription. The present study highlights the binding properties of oxaliplatin with calf thymus DNA using spectroscopic methods to comprehend its binding mechanism at molecular level to overcome associated cellular resistance and side effects. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic outcomes confirm that oxaliplatin is a covalent binding agent and also provide sequence specificity in DNA molecule. Infrared spectral results further indicate that oxaliplatin alkylates purine nitrogenous bases majorly guanine residues (G) in the major groove via formation of either interstrand or intrastrand guanine–guanine d(GpG) and guanine–adenine d(GpA) (N7 position) crosslinks accompanied with a slight external binding to sugar–phosphate backbone. Again, circular dichroism (CD) spectroscopic results suggest subtle conformational changes in DNA molecule due to its complexation with oxaliplatin and duplex attains an intermediate conformational state, having characteristics of both B- and C-forms. Further, a moderate binding strength of 4.12 ± 0.2 × 104 M−1 for the interaction has been estimated via ultraviolet–visible spectroscopy. The inferences obtained from these investigations are encouraging and can form the basis for further exploration in the field of rational drug development based on platinum compounds possessing preferential binding for nucleic acid with improved competence.Communicated by Ramaswamy H. Sarma

The interactions of novel mononuclear platinum-based complexes with DNA

BackgroundCisplatin has been widely used for the treatment of cancer and its antitumour activity is attributed to its capacity to form DNA adducts, predominantly at guanine residues, which impede cellular processes such as DNA replication and transcription. However, there are associated toxicity and drug resistance issues which plague its use. This has prompted the development and screening of a range of chemotherapeutic drug analogues towards improved efficacy. The biological properties of three novel platinum-based compounds consisting of varying cis-configured ligand groups, as well as a commercially supplied compound, were characterised in this study to determine their potential as anticancer agents.MethodsThe linear amplification reaction was employed, in conjunction with capillary electrophoresis, to quantify the sequence specificity of DNA adducts induced by these compounds using a DNA template containing telomeric repeat sequences. Additionally, the DNA interstrand cross-linking and unwinding efficiency of these compounds were assessed through the application of denaturing and native agarose gel electrophoresis techniques, respectively. Their cytotoxicity was determined in HeLa cells using a colorimetric cell viability assay.ResultsAll three novel platinum-based compounds were found to induce DNA adduct formation at the tandem telomeric repeat sequences. The sequence specificity profile at these sites was characterised and these were distinct from that of cisplatin. Two of these compounds with the enantiomeric 1,2-diaminocyclopentane ligand (SS and RR-DACP) were found to induce a greater degree of DNA unwinding than cisplatin, but exhibited marginally lower DNA cross-linking efficiencies. Furthermore, the RR-isomer was more cytotoxic in HeLa cells than cisplatin.ConclusionsThe biological characteristics of these compounds were assessed relative to cisplatin, and a variation in the sequence specificity and a greater capacity to induce DNA unwinding was observed. These compounds warrant further investigations towards developing more efficient chemotherapeutic drugs.

Development of Polarization Force Field for Guanine and Amino Acid Residues Systems

Development of Polarization Force Field for Guanine and Amino Acid Residues Systems

A Label-Free Electrochemical Biosensor for Kanamycin Determination Based on Single-Stranded DNA Immobilized on Graphene-Cds-Chitosan Modified Electrode

Background: Overuse of antibiotics has become a serious ecological problem worldwide. It is necessary to monitor and control the pollution of antibiotics. Kanamycin is a representative antibiotic and has widely been used to treat a wide variety of infections. Although different methods have been established for kanamycin detection, it is still of great significance to develop new sensing approach to kanamycin monitoring. Methods: Graphene and Cadmium Sulphide (GR-CdS) nanocomposites were dispersed in 0.035% chitosan (CHIT) aqueous solution containing 0.52% acetic acid. Then, Glass Carbon Electrode (GCE) surface was coated with 5 µL of 1 mg·mL-1 GR-CdS suspension. The GR-CdS-CHIT modified electrode was immersed in 0.5 mg mL-1 single-stranded DNA (ssDNA) solution and 0.5 V potential was applied for 200 s to immobilize ssDNA on the electrode surface. Results: GR-CdS-CHIT dramatically promoted the electrochemical oxidation response of guanine residue in DNA. ssDNA exhibited higher oxidation peak current than double-stranded DNA (dsDNA). Under optimal conditions, ssDNA/GR-CdS-CHIT/GCE was prepared and used as the sensor to determine kanamycin, which showed a linear response to kanamycin in the concentration range of 0.10 to 1.0 mg mL-1. The proposed sensor was successfully applied to monitoring photodegradation of kanamycin. Conclusion: ssDNA was effectively immobilized on GR-CdS-CHIT modified electrode and exhibited high electrochemical oxidation response. When kanamycin was present in the solution, the electrochemical oxidation peak current of ssDNA on the modified electrode declined due to the interaction between kanamycin and DNA. Thus, a novel electrochemical DNA biosensor for kanamycin was successfully developed. Keywords: CdS, differential pulse voltammetry, graphene, kanamycin, photodegradation, single-stranded DNA.