Capillary electrophoresis for studying drug–DNA interactions

Fabrication of an ultra-sensitive electrochemical DNA biosensor based on CT-DNA/NiFe2O4NPs/Au/CPE for detecting rizatriptan benzoate

A novel and first electrochemical biosensor based on Deoxyribonucleic acid (DNA) as a biological component to measure an antimigraine drug, rizatriptan benzoate (RZB) for patients under treatment in biological samples was developed. A carbon paste electrode (CPE) was modified by calf thymus (CT) double-stranded (ds)-DNA, nickel ferrite magnetic nanoparticles (NiFe2O4NPs), and gold nanoparticles (AuNPs). The morphology of the CT-DNA/NiFe2O4NPs/AuNPs/CPE was characterized by Field emission scanning electron microscope (FESEM). The presence of NiFe2O4NPs and AuNPs was confirmed by energy-dispersive X-ray spectroscopy (EDS) image of the NiFe2O4NPs/AuNPs/CPE surface. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to determine the structure and electrochemical characteristics of the CT-DNA/NiFe2O4NPs/AuNPs/CPE. Differential pulse voltammetry (DPV) was used to investigate the electrochemical behavior of RZB. Chronoamperometry (CA) was applied to study the effect of CT-DNA immobilization time on the peak oxidation current of RZB accumulated on the surface of the CT-DNA/NiFe2O4NPs/AuNPs/CPE. The results showed that, under optimum conditions, the prepared electrode responded linearly to RZB concentrations between 0.01 and 2.0 μM, with a 0.0033 μM detection limit (LOD) and 0.01 μM limit of quantification (LOQ). The parameters influencing the biosensor performance (temperature, CT-DNA immobilization time, and RZB/CT-DNA accumulation time) were optimized. DPV showed the displacement of the peak potential towards positive values and the reduction of its current, indicating that the drug could intercalate between the guanine base pairs of CT-DNA. Our biosensor was successfully applied for RZB measurement in human urine, blood serum, plasma samples, and tablets. The presented biosensor was fast response, sensitive, selective, cost-effective, and easy-to-use for RZB determination in pharmaceutical formulations and biological samples.

Comparative studies on the interaction of anticancer drug irinotecan with dsDNA and ssDNA

The binding mode and thermodynamic characteristics of the anticancer drug irinotecan (Irino) with dsDNA were investigated. The interaction of Irino with dsDNA indicated its intercalation into the base stacking domain of dsDNA double helix.

Novel application of fluorescence coupled capillary electrophoresis to resolve the interaction between the G-quadruplex aptamer and thrombin

The dynamic binding status between the thrombin and its G-quadruplex aptamers and the stability of its interaction partners were probed using our previously established fluorescence-coupled capillary electrophoresis method. A 29-nucleic acid thrombin binding aptamer was chosen as a model to study its binding affinity with the thrombin ligand. First, the effects of the cations on the formation of G-quadruplex from unstructured 29-nucleic acid thrombin binding aptamer were examined. Second, the rapid binding kinetics between the thrombin and 6-carboxyfluorescein labeled G-quadruplex aptamer was measured. Third, the stability of G-quadruplex aptamer-thrombin complex was also examined in the presence of the interfering species. Remarkably, it was found that the complementary strand of 29-nucleic acid thrombin binding aptamer could compete with G-quadruplex aptamer and thus disassociated the G-quadruplex structure into an unstructured aptamer. These data suggest that our in-house established fluorescence-coupled capillary electrophoresis assay could be applied to binding studies of the G-quadruplex aptamers, thrombin, and their ligands, while overcoming the complicated and costly approaches currently available.

A novel diazoresin/poly(N-vinyl aminobutyric acid) covalent capillary coating for the analysis of proteins by capillary electrophoresis

A novel method for the preparation of covalently linked capillary coatings of poly(N-vinyl aminobutyric acid) (PVAA) obtained from hydrolyzed polyvinylpyrrolidone was demonstrated using photosensitive diazoresin (DR) as a coupling agent. A layer-by-layer self-assembled film of DR and PVAA based on ionic bonding was first fabricated on the inner wall of capillary, then ionic bonding was converted into covalent bonding after treatment with UV light through a unique photochemical reaction of DR. The covalently bonded coatings suppressed protein adsorption on the inner surface of the capillary, and thus a baseline separation of lysozyme, cytochrome c, BSA, amyloglucosidase, and myoglobin was achieved using CE. Compared with bare capillary or noncovalently bonded DR/PVAA coatings, the covalently linked DR/PVAA capillary coatings not only improved the CE separation performance for proteins, but also exhibited good stability and repeatability. Due to the replacement of the highly toxic and moisture-sensitive silane coupling agent by DR in the covalent coating preparation, this method may provide a green and easy way to make covalently coated capillaries for CE.

Synthesis of novel Eu(III) luminescent probe based on 9- acridinecarboxylic acid skelton for sensing of ds-DNA

Eu(III)-9-acridinecarboxylate (9-ACA) complex was synthesized and characterized by elemental analysis, conductivity measurement, IR spectroscopy, thermal analysis, mass spectroscopy, (1)H-NMR, fluorescence and ultraviolet spectra. The results indicated that the composition of this complex is [Eu(III)-(9-ACA)(2)(NCS)(C(2)H(5)OH)(2)] 2.5 H(2)O and the oxygen of the carbonyl group coordinated to Eu(III). The interaction between the complex with nucleotides guanosine 5'- monophosphate (5'-GMP), adenosine 5'-diphosphates (5'-ADP), inosine (5'-IMP) and CT-DNA was studied by fluorescence spectroscopy. The fluorescence intensity of Eu(III)-9-acridinecarboxylate complex was enhanced with the addition of CT-DNA. The effect of pH values on the fluorescence intensity of Eu(III) complex was investigated. Under experimental conditions, the linear range was 9-50 ng mL(-1) for calf thymus DNA (CT- DNA) and the corresponding detection limit was 5 ng mL(-1). The results showed that Eu(III)-(9-ACA)(2) complex binds to CT-DNA with stability constant of 2.41 × 10(4) M.

Quantification of binding data using capillary electrophoresis

The design of new DNA-targeted molecules, primarily for use in the therapy of diseases such as cancer, relies on the assessment of both affinity for DNA and selectivity of binding to chosen base pair sequences. Capillary electrophoresis, with a polymer added to the running buffer, is very well suited to the separation of oligonucleotides in the range 12-20 base pairs, with the separation based on length rather than base pair sequence. In this way, it is possible to conduct competition experiments using mixtures of up to four oligonucleotides and giving a direct measure of the relative affinity of high-affinity ligands, specifically those binding in the minor groove with slow on-off rates. The relative affinities can be securely quantified, even where the affinities are very high. Working from first principles, it is shown that the measurement of absolute affinities presents various problems, not least that the concentration of DNA and ligand used in the experiment will affect the magnitude of K(d), which is not constant.