G-quadruplex forming region within WT1 promoter is selectively targeted by daunorubicin and mitoxantrone: A possible mechanism for anti-leukemic effect of drugs.

Wilms tumor 1 (WT1) has long been overexpressed in acute myeloid leukemia and has a prognostic value in its diagnosis. Lately, the formation of G-quadruplexes in oncogenic promoters like (WT1) has been widely investigated since stabilization of these structures leads to transcriptional inhibition of the oncogene. Daunorubicin and mitoxantrone considered as crucial components of almost all standard acute myeloid leukemia induction regimens. Herein we have proposed a probable molecular mechanism of action through which the drugs may stabilize (WT1) promoter G-quadruplexes. Differential pulse voltammetry, circular dichroism, and polyacrylamide gel electrophoresis, electrophoretic mobility shifts assay, polymerase chain reaction (PCR) stop assays, and quantitative RT-PCR were performed in order to better understanding the nature of interactions between the drugs and G-quadruplexes. Data revealed that both drugs had potential to stabilize G-quadruplexes and down-regulate WT1 transcription but daunorubicin exposed more silencing impact. The results illustrated the therapeutic association of these two commercial FDA-approved drugs in (WT1) transcriptional down-regulation. Since (WT1) has known as a transcriptional regulator of at least 137 target genes, so the new data are significant for the development of new approaches to regulating WT1 and other target genes by employing special drugs in cancer treatment.

An impedimetric biosensor for DNA damage detection and study of the protective effect of deferoxamine against DNA damage.

The detection and inhibition of DNA damage are of great importance in the prevention and treatment of diseases. Developing a simple and sensitive tool for this purpose would be a chance to monitor the DNA damage and could be helpful in introducing some drugs which can prevent this phenomenon. Here, we report a novel and sensitive electrochemical biosensor based on DNA/Au nanoparticles (AuNPs) modified screen printed gold electrode (DNA/AuNPs/SPGE) to investigate the DNA damage process and also to study the protective behavior of deferoxamine (DFO). The proposed biosensor was fabricated by electrodeposition of AuNPs onto SPGE, followed by chemical immobilisation of thiol-terminated DNA. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) have been used to characterise this biosensor. Hydroxyl radical (OH), which is generated during the Fenton reaction, is responsible for the induced damage to DNA. EIS technique was applied to monitor the DNA damage, and the increase in charge transfer resistance (Rct) following the DNA damage, was considered as an indicator. Furthermore, the ability of the electrochemical screening system was proved by the investigation of the antioxidant effect of DFO in prohibiting the DNA damage.

SiO2 nanoparticles modified CPE as a biosensor for determination of i-motif DNA/Tamoxifen interaction.

Cytosine-rich DNA sequences can form a highly ordered structure known as i-motif in slightly acidic solutions. The stability of the folded i-motif structure is a good strategy to inhibit the telomerase reaction in cancer cells. The electrochemical biosensor was prepared by modifying carbon paste electrode with SiO2 nanoparticles to investigate drugs which can stabilize this structure. Tamoxifen (Tam), an antiestrogen hormonal agent for treatment of breast cancer, was chosen as the model ligand and its interaction with i-motif structure was examined. The interaction between i-motif DNA and Tam was studied in PBS buffer and [Fe(CN)6](3-) through the cyclic voltammetry and square wave voltammetry methods. The oxidation peak of Tam, due to the i-motif DNA/Tam interaction, was observed after i-motif immobilized on the surface of the electrode. The i-motif formation was investigated by circular dichroism spectroscopy and the results showed that this structure can certainly be made with pH around 4.5, but its stability reduced by going to the more alkaline pH. The selectivity which was studied in the presence of complementary strand demonstrated that i-motif structure could be stabilized in acidic pH even in the presence of its complementary strand.

Diazonium-based impedimetric aptasensor for the rapid label-free detection of Salmonella typhimurium in food sample.

Fast and accurate detection of microorganisms is of key importance in clinical analysis and in food and water quality monitoring. Salmonella typhimurium is responsible for about a third of all cases of foodborne diseases and consequently, its fast detection is of great importance for ensuring the safety of foodstuffs. We report the development of a label-free impedimetric aptamer-based biosensor for S. typhimurium detection. The aptamer biosensor was fabricated by grafting a diazonium-supporting layer onto screen-printed carbon electrodes (SPEs), via electrochemical or chemical approaches, followed by chemical immobilisation of aminated-aptamer. FTIR-ATR, contact angle and electrochemical measurements were used to monitor the fabrication process. Results showed that electrochemical immobilisation of the diazonium-grafting layer allowed the formation of a denser aptamer layer, which resulted in higher sensitivity. The developed aptamer-biosensor responded linearly, on a logarithm scale, over the concentration range 1 × 10(1) to 1 × 10(8)CFU mL(-1), with a limit of quantification (LOQ) of 1 × 10(1) CFU mL(-1) and a limit of detection (LOD) of 6 CFU mL(-1). Selectivity studies showed that the aptamer biosensor could discriminate S. typhimurium from 6 other model bacteria strains. Finally, recovery studies demonstrated its suitability for the detection of S. typhimurium in spiked (1 × 10(2), 1 × 10(4) and 1 × 10(6) CFU mL(-1)) apple juice samples.

Voltammetric characterization of human telomeric G-quadruplex: A label free method for anticancer drug detection.

Human telomeric DNA typically consists of many tandem repeats of the guanine-rich sequences d (TTAGGG) termed an intermolecular Gquadruplex structure. This structure plays an important role in the protection, stabilization and replication of chromosome ends and so is an active target for therapeutic purposes. Recently ligands that are able to stabilize Gquadruplex structure, have received great attention because quadruplex-binding ligands have potential applications in cancer therapy. The screen-printed graphite electrode (SPE) was modified with synthesized SBA-N-propylpipyrazine-N-(2-mercaptopropane-1-one) (SBA-NPPNSH) mesoporous structure to investigate the Gquadruplex DNA (G4DNA) formation and stabilization. Differential pulse voltammetry was used to examine the stability and formation of G4DNA in various K(+) concentrations, under different pH conditions and also in the presence of positive and negative G4DNA-binding ligands. The stability effect of TMPyP4 as a positive G4DNA-binding ligand was examined in the presence of complementary G4DNA strands. This studying revealed that after adding K(+) or positive G4DNA-binding ligand a new peak observed in higher potential due to oxidation of guanine residuals in the Gquadruplex structure.

Preparation of a new nanobiosensor for the determination of some biogenic polyamines and investigation of their interaction with DNA.

Biogenic polyamines are small organic polycations involving in a variety of biological processes. They form high affinity complexes with DNA. Here, we have followed two different novel approaches, either fabrication of an electrochemical nanobiosensor for determination of three of the most important biogenic polyamines; spermine (SPM), spermidine (SPD) and putrescine (PUT), or electrochemical investigation of their interaction with DNA. Strong binding of polyamines to DNA makes the DNA a suitable recognition element for construction of a sensitive biosensor. The fabricated biosensor responded to SPM, SPD and PUT over an extended dynamic range of 0.04-100 µM, 0.01-24 µM, and 0.08-100 µM respectively, with low detection limits of a few nM. We also studied the interaction of polyamines with three different DNA sequences with base composition of 100% AT, 80% AT and 100% GC in the presence of [Ru(NH3)6]3(+) as a redox probe. The highest kb values were obtained in the interaction of polyamines with 80% AT (mixed) DNA sequence. The kb values were 5.24 × 10(5), 4.17 × 10(5) and 1.46 × 10(5)M(-1) for SPM, SPD and PUT, respectively, which correlated well with their increasing number of amino groups. In addition, competition study showed the impotence of SPD to replace with histone H1 in histone H1-DNA complex, which indicates the more potent interaction of histone H1 with DNA. In this proof-of-principle study, we have proposed an approach for simple, cost-effective, miniaturizable, and direct-readout detection of polyamines, as well as the understanding of the modes of interaction between polyamines and DNA.

A switchable Gquadruplex device with the potential of a nanomachine for anticancer drug detection.

The unique ability of living systems to translate biochemical reactions into mechanical work has inspired the design of synthetic DNA motors which generate nanoscale motion via controllable conformational change. It is believable that G-quadruplex structures in certain regions of the genome may play a role in the poor maintenance of genomic stability, which is a characteristic of many types of cancers. In this regards, formation and stabilization of the quadruplex structures at the telomeric repeats is an effective way to hamper the telomere extension and blocking the elongation step. Here, we report a DNA machine for selective Gquadruplex-binding ligand recognition, based on a conformational change; the forces exerted by the precise DNA machine for Gquadruplex conformational change were probed via an electrical signal transducer electrochemically by differential pulse voltammetry and cyclic voltammetry. The proposed machine was prepared by modifying the screen-printed graphite electrode (SPE) with the synthesized SBA-N-propylpipyrazine-N-(2-mercaptopropane-1-one) (SBA@NPPNSH) mesoporous structures and Au nanoparticles (AuNPs). The thiolated functionalized groups of SBA@NPPNSH structures can help for preconcentration of the synthesize AuNPs on the surface. Then SH-G4DNA was linked to the modified electrode by an AuNPsS bond. The morphology of constructed machine was characterized by the Field emission scanning electron microscope (FESEM).

A novel electrochemical biosensor for selective determination of mercury ions based on DNA hybridization.

An electrochemical biosensor was developed for Hg(2+) determination based on DNA hybridization. In the presence of Hg(2+), the target and probe DNAs with thymine-thymine (T-T) mismatches could hybridize by forming T-Hg(2+)-T complex. This induced DNA hybridization led to the decrease in reduction peak currents of ethyl green (EG) as electroactive label, which could be used for determination of Hg(2+). The difference in the value of the peak currents of EG before and after DNA hybridization (ΔI) was linear with the concentration of Hg(2+) in the range of 9.0 × 10(-11)-1.0 × 10(-9) M. The detection limit was 3.08 × 10(-11) M.

A human telomeric G-quadruplex-based electronic nanoswitch for the detection of anticancer drugs.

An electronic nanoswitch is described based on the conformational change of the DNA sequence in the presence of stabilizing ligands. The new electrochemical biosensor was prepared by modifying a screen-printed graphite electrode (SPE) with functionalized SiO2 nanoparticles [(SiO2-N-propylpiperazine-N-(2-mercaptopropane-1-one) (SiO2@NPPNSH)] and Au nanoparticles (AuNPs). These nanoparticles are able to immobilize thiolated G-quadruplex DNA structures (SH-G4DNA). The SH groups on the SiO2@NPPNSH nanoparticles provide a good platform for stabilizing AuNPs on the surface of the electrode. This is due to the fact that AuNPs are able to bind to the organic SH groups on the SiO2@NPPNSH. The SH-G4DNA binds to the modified electrode by a AuNPs-S bond. The structure of SiO2@NPPNSH was characterized by scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA) and infrared (IR) spectroscopy. The morphology of the modified electrode was characterized by SEM. The interaction between G4DNA and the anticancer drug, Tamoxifen (Tam), was studied in Tris-HCl buffer and [Fe(CN)6](3-) using cyclic (CV) and square wave voltammetry (SWV). The G-quadruplex formation and the interaction mechanism were identified by circular dichroism (CD) measurements. The CV current was seen to decrease with increasing concentration of Tam due to interaction between G4DNA and Tam. This biosensor is a simple and useful tool for selecting G-quadruplex-binding ligands.

Development of a new biosensor based on functionalized SBA-15 modified screen-printed graphite electrode as a nano-reactor for Gquadruplex recognition.

Gquadruplex is an active target for therapeutic purposes because of the evidence which suggest that G-rich region of the human genome may form Gquadruplex structure. The electrochemical biosensor was prepared by modifying screen-printed graphite electrode (SPE) with synthesized SBA-N-propylpipyrazine-N-(2-mercaptopropane-1-one) (SBA@NPPNSH) mesoporous structure to investigate the Gquadruplex DNA structure (G4DNA). Ascorbic acid (AA) is known as an antioxidant agent that induces reductive properties. It is also important for some therapeutic purposes. In this study, AA was used as the model ligand and its ability to interact with Gquadruplex structure was examined. The pore of SBA@NPPNSH structure can act as a nano-reactor and the interaction of G4DNA/AA is accomplished inside these channels. The structure of SBA@NPPNSH was characterized by transmission electron microscope (TEM), X-ray powder diffraction (XRD), thermo gravimetric analysis (TGA) methods and atomic force microscopy (AFM). The interaction of AA with G4DNA was studied in Tris-HCl buffer and also in the presence of [Fe(CN)6](3-) as a redox label using the CV method. CV current decreases with the increasing concentrations of AA due to the interaction of G4DNA/AA. Circular dichroism (CD) spectroscopy was used to examine the ability of AA to form Gquadruplexes from short and long complementary G4DNA strands. Studying the selectivity using different dsDNA sequences revealed that AA could stabilize G4DNA. Thus, the proposed biosensor can distinguish G4DNA structure from other dsDNA structures.