Bioactivity of Isostructural Hydrogen Bonding Frameworks Built from Pipemidic Acid Metal Complexes.

We report herein three novel complexes whose design was based on the approach that consists of combining commercially available antibiotics with metals to attain different physicochemical properties and promote antimicrobial activity. Thus, new isostructural three-dimensional (3D) hydrogen bonding frameworks of pipemidic acid with manganese (II), zinc (II) and calcium (II) have been synthesised by mechanochemistry and are stable under shelf conditions. Notably, the antimicrobial activity of the compounds is maintained or even increased; in particular, the activity of the complexes is augmented against Escherichia coli, a representative of Gram-negative bacteria that have emerged as a major concern in drug resistance. Moreover, the synthesised compounds display similar general toxicity (Artemia salina model) levels to the original antibiotic, pipemidic acid. The increased antibacterial activity of the synthesised compounds, together with their appropriate toxicity levels, are promising outcomes.

A New Approach for Improving the Antibacterial and Tumor Cytotoxic Activities of Pipemidic Acid by Including It in Trimethyl-ß-cyclodextrin.

Pipemidic acid (HPPA) is a quinolone antibacterial agent used mostly to treat gram-negative infections of the urinary tract, but its therapeutic use is limited because of its low solubility. Thus, to improve drug solubility, natural cyclodextrins (CDs) are used for their ability of including guest molecules within their cavities. The aim of this work was to evaluate the antibacterial activity and the preliminary anticancer activity of HPPA included into Heptakis (2,3,6-tri-O-methyl)-ß-cyclodextrin (TRIMEB) as a possible approach for a new innovative formulation. The inclusion complex of HPPA with TRIMEB was prepared in solid state by the kneading method and confirmed by FT-IR and powered X-ray diffraction. The association in aqueous solutions of pipemidic acid with TRIMEB was investigated by UV-Vis spectroscopy. Job's plots have been drawn by UV-visible spectroscopy to confirm the 1:1 stoichiometry of the host⁻guest assembly. The antibacterial activity of HPPA, TRIMEB and of their complex was tested on Escherichia coli, Pseudomonas aeruginosa, and Staphilococcus aureus. The complex was able to increase 47.36% of the median antibacterial activity of the free HPPA against E. coli (IC50 = 249 µM vs. 473 µM). Furthermore, these samples were tested on HepG-2 and MCF-7. After 72 h, the median tumoral cytotoxicity exerted by the complex was increased by 78.08% and 94.27% for HepG-2 and MCF-7 respectively, showing a stronger bioactivity of the complex than the single HAPPA.

How to unravel the chemical structure and component localization of individual drug-loaded polymeric nanoparticles by using tapping AFM-IR.

AFM-IR is a photothermal technique that combines AFM and infrared (IR) spectroscopy to unambiguously identify the chemical composition of a sample with tens of nanometer spatial resolution. So far, it has been successfully used in contact mode in a variety of applications. However, the contact mode is unsuitable for soft or loosely adhesive samples such as polymeric nanoparticles (NPs) of less than 200 nm of wide interest for biomedical applications. We describe here the theoretical basis of the innovative tapping AFMIR mode that can address novel challenges in imaging and chemical mapping. The new method enables gaining information not only on NP morphology and composition, but also reveals drug location and core-shell structures. Whereas up to now the locations of NP components could only be hypothesized, tapping AFM-IR allows accurately visualizing both the location of the NPs' shells and that of the incorporated drug, pipemidic acid. The preferential accumulation of the drug in the NPs' top layers was proved, despite its low concentration (<1 wt%). These studies pave the way towards the use of tapping AFM-IR as a powerful tool to control the quality of NP formulations based on individual NP detection and component quantification.

Synthesis of novel tetrazole containing hybrid ciprofloxacin and pipemidic acid analogues and preliminary biological evaluation of their antibacterial and antiproliferative activity.

A series of 1-substituted-1H-tetrazole-5-thiol building blocks were synthesized and introduced to the N-4 piperazinyl group at C-7 position of the quinolone core, and these novel compounds (5a-g and 8a-g) were screened for their antibacterial and antiproliferative activities. Bioactive assay studies manifested that most of new compounds exhibited significant antibacterial activity against the tested strains, including multi-drug-resistant MRSA in comparison with reference drugs ciprofloxacin, streptomycin B and pipemidic acid. Among the synthesized compounds, only ciprofloxacin (5a-g) derivatives displayed significant activity ([Formula: see text]) compared to reference drugs. In addition, these compounds were evaluated for their in vitro inhibition of human cancer cell lines viz human cervical carcinoma cell line (SiHA), breast adenocarcinoma (MDA-MB-235) and human pancreas carcinoma (PANC-1) cell lines by using the SRB assay method. Most of the target compounds showed broad potent growth inhibition activity ([Formula: see text]) against all the tested cancer cell lines compared with reference drug. The most promising active compounds in this series were 5c, 5d, 8c, 8d and 8f endowed with excellent antiproliferative activity. A new class of compounds was designed rationally by introducing tetrazole building block on N-4 piperazinyl group at C-7 position of quinolones core. The titled compounds were evaluated for their preliminary antibacterial and antiproliferative activities.

Synthesis, characterization, and evaluation of the antimicrobial potential of copper(II) coordination complexes with quinolone and p-xylenyl-linked quinolone ligands.

The antimicrobial properties of copper have been known to mankind since the ancient times. In a coordination chemistry approach to develop novel antimicrobial agents, the quinolone antimicrobial agents ciprofloxacin (Hcipro) and pipemidic acid (Hpia), as well as dimers thereof (piperazinyl-linked with a p-xylenyl moiety) were complexed with copper(II). The synthesis and antimicrobial evaluation of bis(ciprofloxacino)copper(II) [Cu(cipro)2], bis(pipemido)copper(II) [Cu(pia)2], and the corresponding dimer complexes, [Cu2(ciproXcipro)2] and [Cu2(piaXpia)2], are reported. No combinational or synergistic effect between copper(II) and the respective quinolone ligands was observed in vitro.

Optimization of a pipemidic acid autotaxin inhibitor.

Autotaxin (ATX, NPP2) has recently been shown to be the lysophospholipase D responsible for synthesis of the bioactive lipid lysophosphatidic acid (LPA). LPA has a well-established role in cancer, and the production of LPA is consistent with the cancer-promoting actions of ATX. Increased ATX and LPA receptor expression have been found in numerous cancer cell types. The current study has combined ligand-based computational approaches (binary quantitative structure-activity relationship), medicinal chemistry, and experimental enzymatic assays to optimize a previously identified small molecule ATX inhibitor, H2L 7905958 (1). Seventy prospective analogs were analyzed via computational screening, from which 30 promising compounds were synthesized and screened to assess efficacy, potency, and mechanism of inhibition. This approach has identified four analogs as potent as or more potent than the lead. The most potent analog displayed an IC(50) of 900 nM with respect to ATX-mediated FS-3 hydrolysis with a K(i) of 700 nM, making this compound approximately 3-fold more potent than the previously described lead.

[Determination of DNA using Eu-PPA as fluorescence probe by time-resolved fluorescence].

In the Tris-HCl buffer solution, europium ion combined with pipemidic acid (PPA) to form a Eu-PPA complex. The fluorescence intensity was dramatically enhanced when herring sperm DNA was added in the Eu-PPA system. Furthermore, the fluorescence intensity was increased linearly with the concentrations of added DNA within a proper range. Based on this, a simple new method for the determination of herring sperm DNA was developed. Time-resolved fluorescence excitation and emission spectra and the fluorescence lifetime of the system were studied in detail and compared with that from conventional fluorescence method. The experimental results indicated that the time-resolved fluorescence method was superior over the conventional fluorescence method. The reaction conditions, measurement parameters and the adding order of reactants were optimized. The best concentration of both europium ion standard solution and PPA standard solution was 1.00 x 10(-5) mol x L(-1) in the Tris-HCl buffer solution of 0.005 mol x L(-1) with the optimal pH value of 7.2. A detection limit (3 s) of 0.03 mg x L(-1) was obtained with a RSD of 0.3% (4.0 mg x L(-1), n = 11). The linear relationship between deltaI = 89.58c (mg x L(-1)) +0.920 5 and the regression factor of 0.999 6 was obtained in the range of 0.1-6 mg x L(-1). This method was applied to the determination of DNA in synthetic samples. The results and recoveries of spiked standard solution in the sample were satisfied.

Enhanced permeability of the urinary bladder wall: the role of polymer charge.

The urothelium is usually impermeable to substances present in the urine. In the current work the possibility of using different absorption enhancers in the development of intravesical drug delivery systems was explored. To establish the role of the polymer charge on its ability to improve bladder wall permeability, cationic poly-L-arginine, anionic NaCMC and alginate as well as nonionic HPC and HPMC were tested. The permeability experiments were performed on isolated pig urinary bladders. We established that the charge of the polymer affects its ability to enhance the permeability of the urinary bladder wall, but to a limited extent. Positively charged polymers were the most promising absorption enhancers for the urinary bladder wall. In order to significantly enhance the permeability of the bladder wall, higher concentrations of poly-L-arginine were needed compared to chitosan. Moreover, chitosan reached the plateau of its absorption enhancement effect after 60 min, while poly-L-arginine increased the permeability continuously over 90 min. In contrast to polycarbophil, two other anionic polymers, NaCMC and alginate, did not significantly enhance the permeation of pipemidic acid into the tissue. Interactions between the polymers and the drug might prevail over the potential effect of NaCMC and alginate on tissue permeability. Furthermore, for the nonionic polymers HPMC and HPC an insignificant influence on bladder wall permeability was determined. Therefore, the selection of absorption enhancers for intravesical drug delivery systems is limited and cannot be done only on the basis of polymer charge.

Structure and medium effects on the photochemical behavior of nonfluorinated quinolone antibiotics.

The photophysical behavior of the quinolone antibiotics, oxolinic (OX), cinoxacin (CNX) and pipemidic (PM) acids was studied as a function of pH and solvent properties. The ground state of these compounds exhibits different protonated forms, which also exist in the first excited states. Theoretical calculations of the Fukui indexes allowed to assigning the different protonation equilibria. The pK values indicate that the acidity of the 3-carboxylic and 4-carbonyl groups increases with the N-atom at position 2 in CNX. It has been found that fluorescence properties are strongly affected by pH, the more fluorescent species is that with protonated carboxylic acid, protonated species at the carbonyl group and the totally deprotonated form present very low fluorescence. The fluorescence behavior also depends on the chemical structure of the quinolone and on the solvent properties. The analysis of the solvent effect on the maximum and the width of the fluorescence band of OX, using the linear solvent-energy relation solvatochromic equation, indicates that the polarizability and hydrogen bond donor ability are the parameters that condition the spectral changes. The hydrogen bond acceptor ability of the solvents also contributes to the spectral shifts of CNX. The compound bearing the piperazinyl group at the position 7, PM only is fluorescent in high protic solvents. These results are discussed in terms of the competition between the intra- and intermolecular hydrogen bonds. The irradiation of OX, CNX and PM using 300 nm UV light led to a very low photodecomposition rate. Under the same conditions the nalidixic acid (NA), a structurally related quinolone, photodecomposes two orders of magnitude faster.

T cell-mediated hypersensitivity to quinolones: mechanisms and cross-reactivity.

BACKGROUND: Quinolones are widely used, broad spectrum antibiotics that can induce immediate- and delayed-type hypersensitivity reactions, presumably either IgE or T cell mediated, in about 2-3% of treated patients. OBJECTIVE: To better understand how T cells interact with quinolones, we analysed six patients with delayed hypersensitivity reactions to ciprofloxacin (CPFX), norfloxacin (NRFX) or moxifloxacin (MXFX). METHODS: We confirmed the involvement of T cells in vivo by patch test and in vitro by means of the lymphocyte proliferation test (LTT). The nature of the drug-T cell interaction as well as the cross-reactivity with other quinolones were investigated through the generation and analysis (flow cytometry and proliferation assays) of quinolone-specific T cell clones (TCC). RESULTS: The LTT confirmed the involvement of T cells because peripheral blood mononuclear cells (PBMC) mounted an enhanced in vitro proliferative response to CPFX and/or NRFX or MXFX in all patients. Patch tests were positive after 24 and 48 h in three out of the six patients. From two patients, CPFX- and MXFX-specific CD4(+)/CD8(+) T cell receptor (TCR) alphabeta(+) TCC were generated to investigate the nature of the drug-T cell interaction as well as the cross-reactivity with other quinolones. The use of eight different quinolones as antigens (Ag) revealed three patterns of cross-reactivity: clones exclusively reacting with the eliciting drug, clones with a limited cross-reactivity and clones showing a broad cross-reactivity. The TCC recognized quinolones directly without need of processing and without covalent association with the major histocompatability complex (MHC)-peptide complex, as glutaraldehyde-fixed Ag-presenting cells (APC) could present the drug and washing quinolone-pulsed APC removed the drug, abrogating the reactivity of quinolone-specific TCC. CONCLUSION: Our data show that T cells are involved in delayed immune reactions to quinolones and that cross-reactivity among the different quinolones is frequent.

Synthesis and spectroscopic study of copper(II) and manganese(II) complexes with pipemidic acid.

The interaction of copper(II) and manganese(II) with pipemidic acid, Hpipem, afforded the complexes [Cu(pipem)(2)(H(2)O)] x 2H(2)O, 1 and [Mn(pipem)(2)(H(2)O)], 2. The new complexes have been characterised by elemental analyses, infrared, UV-vis and X-band EPR spectroscopy in the temperature range from 4 to 300 K. The monoanion, pipem, exhibits O,O ligation through the carbonyl and carboxylato oxygen atoms. Five coordinate square-pyramid configuration has been proposed for 1 and 2, and the fifth apical position is occupied by a coordinated water molecule.

Micellar electrokinetic chromatography for determination of drug partition in phospholipids.

The lipophilicity of pipemidic, nalidixic and oxolinic acids was determined by forming phospholipidic micelles directly in an electrophoretic capillary. Phosphatidylcholine derivatives, namely L-alpha-dilauroyl phosphatidylcholine (DLPC) or L-alpha-dimiristoyl phosphatidylcholine (DMPC), were added in the run buffer (50 mM phosphate buffer at pH 7.4). To obtain a mixed micelle, phospholipidic derivatives and sodium cholate were together added in the run buffer. Considering the increasing of migration time when phosphatidylcholine derivative is added in the run buffer, Ks can be determined and then quinolones lipophilicity.

Determination of pipemidic acid based on flow-injection chemiluminescence due to energy transfer from peroxynitrous acid synthesized on-line.

A flow-injection chemiluminescence (CL) method for the determination of pipemidic acid is described. It is based on energy transfer from excited state peroxynitrous acid to pipemidic acid, in which the excited state peroxynitrous acid is synthesized on-line by the mixing of acid hydrogen peroxide with nitrite in a flow system and the CL is from two excited states of pipemidic acid. The proposed method allows the measurement of pipemidic acid over the range of 2.0 x 10(-7)-2.0 x 10(-5) mol l(-1) . The detection limit is 6.3 x 10(-8) mol l(-1), and the relative standard deviation for 2.0 x 10(-6) mol l(-1) pipemidic acid (n = 9) is 0.9%. This method was evaluated by the analysis of pipemidic acid in pharmaceutical preparations.

[A study on europium sensitized chemiluminescence of pipemidic acid].

A flow injection chemiluminescence method for the determination of Pipemidic acid (PPA) was developed. It is based on luminescence produced with KMnO4-Na2S2O4 CL system sensitized by Eu3+-PPA. The familar excipients such as starch and dextrine do not cause interference. The several kinds of affect on chemiluminescence were studied. The linear range and detection limit for PPA are 7.00 x 10(-9)-9.00 x 10(-7) mol x L(-1) and 4.09 x 10(-9) mol x L(-1), respectively. This method have successfully been applied to the determination of PPA in tablet and urine. And the mechanism of chemiluminescence is proposed.

[Study of filter-paper-substrate delay fluorescence of three quinolones].

Paper-substrate delay fluorimetry (PS-DF) for three quinolones, i.e. Pefloxacin, Norfloxacin and Pepemidic acid, were given. Various factors affecting the PS-DF intensity of quinolones, including pH condition, drying time of sample etc., were studied in detail. The experiments showed that the PS-DF intensities of three quinolones in acidic solution were stronger than those in other conditions. The proper pH was 1.6. These quinolones have wide dynamic ranges, low limit of detection and relatively small standard deviations. The method was fast with, a small amount of sample and low cost. The recovery was 98.5%-104%. The determination results of the samples were satisfactory.

The influence of stirring rate on biopharmaceutical properties of Eudragit RS microspheres.

Eudragit RS microspheres containing pipemidic acid, as a model drug, were prepared by the solvent evaporation method using an acetone/liquid paraffin solvent system. The aim of the work was to evaluate the influence of stirring rate on the average particle size, particle morphology, drug content and release kinetics, as well as the influence of particle size on microsphere morphology, drug content and release kinetics. Stirring rate has been found to significantly influence the average diameter of microspheres. The average diameter decreases as the stirring rate increases. This can be explained by production of a finer dispersion of droplets when higher stirring rates are applied and, consequently, by the formation of smaller microspheres. With increasing stirring rate and increasing fraction particle size the drug content also increases. It is assumed that this dependence is a consequence of an uneven diffusion of the drug from the inner to the outer emulsion phase, and an uneven encapsulation of drug particles during the preparation. Drug release follows the Higuchi model. As seen from SEM photographs, larger microspheres are more porous and the microspheres produced at higher stirring rates are more porous than those produced at lower stirring rates. This explains the unexpected finding that the release rate increases as the fraction particle size and the stirring rate increase.