Enantioselective binding of S- and R-ofloxacin to various synthetic polynucleotides

Separation of ofloxacin enantiomers by CE with fluorescence detection using DNA oligonucleotides as chiral selectors

This study used CE with fluorescence detection- and partial-filling mode-based method for chiral separation of ofloxacin. The DNA oligonucleotides with different base sequences were studied as potential chiral selectors including DNA tetrahedron, G-quadruplex, and G-riched double-strand DNA. Under the optimized conditions, all the DNA chiral selectors exhibited excellent chiral separation capabilities with a resolution higher than 1.5. The electrophoretic behavior of the ofloxacin enantiomer might result from the intermediate conjugate with different stabilities between chiral selectors and analytes by a combination of the hydrogen bond and spatial recognition structure. Moreover, satisfactory repeatability regarding run-to-run and interday repeatability was obtained, and all the RSD values of migration times and resolutions were below 4% (n = 6). Conclusively, both spatial structure and arrangement of the G bases potentiated the chiral separation capability of DNA for ofloxacin enantiomer. This work offered a stepping stone for enantioseparation using DNA as chiral selectors. This article is protected by copyright. All rights reserved.

Study on orally delivered paclitaxel nanocrystals: modification, characterization and activity in the gastrointestinal tract

Drug nanocrystals (NCs) can improve the solubility and bioavailability of insoluble drugs for oral administration. However, the biocompatibility and mechanisms of transmittance of drug NCs through the intestinal epithelial tissue are still not well understood. In this work, the physico-chemical properties and interactions with biomolecules in oral delivery pathways, as well as the transmittance through mimical intestinal epithelial cells, of NCs of paclitaxel (PTX) are investigated. PTX was previously demonstrated to be an effective anti-cancer drug. It is found that maximum 1% (w/v) poly(styrenesulfonate) is sufficient to keep PTX NCs monodisperse in varied biological environments and presents no significant interaction with extracellular biomolecules for at least 24 h. The concentration of PTX NCs is kept carefully controlled to avoid serious toxicity to cells (10 µg ml^-1 in our experiments but this also depends on NC size). The transmittance of PTX NCs through mimical intestinal epithelial reached 25% in 6 h, demonstrating its comparatively high oral bioavailability in the human body. This work demonstrates the great potential of PTX NC treated in oral delivery.

Chiral resolution capabilities of DNA oligonucleotides

Herein, we studied the chiral resolution properties of a repertoire of arbitrarily chosen DNA oligonucleotides (ON). Ten oligonucleotidic sequences characterized by diverse base compositions, sizes, and structural features, ranging from secondary structure-free homo-oligonucleotides to duplex, hairpin, and three-way junction architectures, were investigated as potential chiral selectors. Their enantioselective features were assessed by using ONs as running buffer additives in partial-filling capillary electrophoresis. It was shown that all the screened sequences displayed enantiodiscrimination capabilities toward small aromatic compounds. Under (sub)millimolar DNA concentration conditions, the combination of only three oligonucleotidic sequences provided the chiral resolution of around 20 racemates, including drugs, illegal drugs, amino-acids, and nucleosides. This work represents the first demonstration of such analyte selectivity spectrum for nucleic acid-based chiral separation tools.

Enantioselective recognition mechanism of ofloxacin via Cu(II)-modulated DNA

The specific interactions of Cu(2+) with self-complementary DNA sequences involving d[G4C4(GC)2G4C4], d[(GC)10], and d[(AT)10], as well as the chiral recognition mechanism of ofloxacin enantiomers via the Cu(II)-modulated DNAs, were investigated using characterizations of circular dichroism, gel electrophoresis, FT-IR spectroscopy, UV melting measurement, electron paramagnetic resonance, and HPLC. The Cu(II)-coordinated GC-rich DNAs exhibit amplified enantioselectivity toward the S-enantiomer of ofloxacin. Especially in the case of d[G4C4(GC)2G4C4], ofloxacin enantiomers intercalate into the two adjacent guanine bases through the minor groove mediated by Cu(2+), which leads to a more favorable binding between S-ofloxacin and DNA. The highest ee value of ofloxacin enantiomers in the permeate after being adsorbed by the Cu(II)-DNA complex is obtained as 49.2% in the R-enantiomer at the [Cu(2+)]/[base] molar ratio of 0.25, while at the [Cu(2+)]/[base] molar ratio of 0.05 the highest ee value of ofloxacin enantiomers in the retentate reaches 26.3% in the S-enantiomer. This work illustrates a novel promising route to construct DNA-based chiral selectors toward certain drug enantiomers through the programmable enantioselective recognition on the basis of DNA chirality and the specific binding of transition metal ions.

Interaction studies of an anticancer alkaloid, (+)-(13aS)-deoxytylophorinine, with calf thymus DNA and four repeated double-helical DNAs

BACKGROUND

Phenanthroindolizidine alkaloids are a family of plant-derived compounds with significant antineoplastic activity. The specific biomolecular targets of these alkaloids have not yet been clearly identified. (+)-(13aS)-deoxytylophorinine is a new phenanthroindolizidine alkaloid originally extracted from the roots of Tylophora atrofolliculata and Tylophora ovata in our institute. (+)-(13aS)-deoxytylophorinine exerts both in vitro and in vivoanticancer activities.

METHODS

The in vivo anticancer effects and toxicity of this compound were investigated in mice, and interactions between this compound and double-helical DNA sequences were studied in detail with circular dichroic spectroscopy and fluorescence spectroscopy. Viscosity measurements were applied to check the interactive mode between this compound and DNA.

RESULTS

Potent anticancer effects were observed in vivo. Also, concentration-dependent interactions were observed and this compound seemed to interact in a sequence-specific manner with AT-repeated sequences of double-helical DNA. Such interactions were proved to be intercalating by viscosity measurements.

CONCLUSIONS

Anticancer alkaloid (+)-(13aS)-deoxytylophorinine can have sequence-specific interactions with DNA in an intercalating manner.

Anticancer effect and neurotoxicity of S-(+)-deoxytylophorinidine, a new phenanthroindolizidine alkaloid that interacts with nucleic acids

Phenanthroindolizidine alkaloids are a family of plant-derived compounds with significant antineoplastic activity as well as other effects like antiamebicidal, antiviral, and anti-inflammatory activities. The specific biomolecular targets of these compounds have not yet been clearly identified. S-(+)-Deoxytylophorinidine (CAT) is a new phenanthroindolizidine alkaloid, originally extracted from the roots of Tylophora atrofolliculata and Tylophora ovata. Potent anticancer activity was observed in vitro and in vivo. Neurotoxicity of CAT was also studied and it was far less serious than that of vinblastine. Interactions between this compound and DNA had been studied in detail in our laboratory previously, and we further studied its interactions with RNA.

Enantioselective binding of L,D-phenylalanine to ct DNA

The enantioselective binding of L,D-phenylalanine to calf thymus DNA was studied by absorption, circular dichroism, fluorescence quenching, viscosity, salt effect and emission experiments. The results obtained from absorption, circular dichroism, fluorescence quenching and viscosity experiments excluded the intercalative binding and salt effect experiments did not support electrostatic binding. So the binding of l,d-phenylalanine to ct DNA should be groove binding. Furthermore, the emission spectra revealed that the binding is enantioselective.

Surface plasmon resonance biosensor for enrofloxacin based on deoxyribonucleic acid

A DNA-based surface plasmon resonance biosensor for enrofloxacin was developed. Heating denatured DNA immobilized on the gold-coated glass surface was exploited. The immobilization was performed by a layer-by-layer co-deposition with a cationic polymer. The sensor performance was tested with real biological probes. Direct and simple determination of enrofloxacin in milk samples was demonstrated. The sensor response obeys Langmuir binding isotherm being almost linear until about 20 microg mL(-1). The detection limit in milk samples was estimated to be 3 microg mL(-1).

Detection of antibiotics in food: Extraction of fluoroquinolones by DNA

The ability of DNA to extract fluoroquinolones from model solutions and real probes of food was demonstrated and investigated quantitatively. The interaction between fluoroquinolones and different types of DNA was studied by equilibrium dialysis. The first application of this direct approach allowed us to determine binding constants and binding stoichiometries in different conditions. The binding of enrofloxacin to heat-denatured DNA (d-DNA) from herring sperm is pH- and magnesium-dependent; the highest fraction of bound drugs was found at pH 7 and a magnesium concentration of 0.5-1 mM. Results for three types of DNA: d-DNA, double-stranded DNA and single-stranded DNA were compared. The unwound DNA showed almost doubled binding constants and stoichiometries, thus indicating preferable interaction of enrofloxacin with single-strand regions of DNA. The binding of other fluoroquinolones (lomefloxacin, ciprofloxacin, norfloxacin, danofloxacin and sarafloxacin) with d-DNA is very similar to that of enrofloxacin: the binding constants are in the range from 0.94x10(5) to 2.40x10(5) M-1, and the stoichiometries range from 4.1 to 6.9 fluoroquinolone molecules per 100 DNA bases. The binding properties were quantitatively the same for extraction of fluoroquinolones from model aqueous solutions and from liquid food (milk). The results indicate the efficiency of DNA for selective extraction of fluoroquinolones from real samples for further analysis. This selective binding also allows us to consider DNA as a natural receptor for development of analytical techniques for fluoroquinolones.

Vibrational spectra study on quinolones antibiotics

In order to be able to fully understand and easily identify the quilonoles, we collected IR and Raman spectra of six quinolones, and attempted to assign the attribution of the observed frequencies and their association with specific modes of vibration. According to the structure, the compounds were divided into the groups, and the similarities and differences were further studied by comparing. The result of the study shows that the frequency and intensity are comparable to the corresponding structure. The spectra not only have the commonness but also the individualities.

X-Ray crystallographic, NMR and antimicrobial activity studies of magnesium complexes of fluoroquinolones - racemic ofloxacin and its S-form, levofloxacin

The magnesium complexes of racemic ofloxacin (oflo) and its pure S-form levofloxacin (S-oflo) have been studied by X-ray crystallography and NMR spectroscopy. Two compounds, [Mg(R-oflo)(S-oflo)(H(2)O)(2)].2H(2)O (1) and [Mg(S-oflo)(2)(H(2)O)(2)].2H(2)O (2), respectively, have been prepared by hydrothermal reactions and their crystal structures have been determined. In both structures the anionic fluoroquinolone ligands are coordinated through the keto and carboxylate oxygens forming 1:2 Mg:oflo complexes. The two structures are practically identical except for the orientation of one of the oxazine methyl groups at the chiral center of 2 which was found in equatorial position, the other oxazine methyl groups in 1 and 2 being axial. This difference affects the stacking pattern of quinolone molecules in the cell. (1)H NMR chemical shift data and Mn(II) paramagnetic line broadening measurements on the free ofloxacin suggest that the coordination of the ligands in solution involves the keto and carboxylate oxygens. However, it is not possible to decide whether the complexes in aqueous solution have 1:1 or 1:2 stoichiometry. The methylated piperazine nitrogen does not interact with the metal ion. Magnesium-quinolone interaction is discussed in relation to the biological activity of quinolones. The antimicrobial activity of the complexes against various microorganisms was tested and it was established that their activity is similar to that of free quinolone drugs.