Structural insight into a quinolone-topoisomerase II-DNA complex. Further evidence for a 2:2 quinobenzoxazine-mg2+ self-assembly model formed in the presence of topoisomerase ii.
(17/2071)
Quinobenzoxazine A-62176, developed from the antibacterial fluoroquinolones, is active in vitro and in vivo against murine and human tumors. It has been previously claimed that A-62176 is a catalytic inhibitor of mammalian topoisomerase II that does not stabilize the cleaved complex. However, at low drug concentrations and pH 6-7, we have found that A-62176 can enhance the formation of the cleaved complex at certain sites. Using a photocleavage assay, mismatched sequences, and competition experiments between psorospermin and A-62176, we pinpointed the drug binding site on the DNA base pairs between positions +1 and +2 relative to the cleaved phosphodiester bonds. A 2:2 quinobenzoxazine-Mg2+ self-assembly model was previously proposed, in which one drug molecule intercalates into the DNA helix and the second drug molecule is externally bound, held to the first molecule and DNA by two Mg2+ bridges. The results of competition experiments between psorospermin and A-62176, as well as between psorospermin and A-62176 and norfloxacin, are consistent with this model and provide the first evidence that this 2:2 quinobenzoxazine-Mg2+ complex is assembled in the presence of topoisomerase II. These results also have parallel implications for the mode of binding of the quinolone antibiotics to the bacterial gyrase-DNA complex. (+info)
Characterization of the membrane quinoprotein glucose dehydrogenase from Escherichia coli and characterization of a site-directed mutant in which histidine-262 has been changed to tyrosine.
(18/2071)
The requirements for substrate binding in the quinoprotein glucose dehydrogenase (GDH) in the membranes of Escherichia coli are described, together with the changes in activity in a site-directed mutant in which His262 has been altered to a tyrosine residue (H262Y-GDH). The differences in catalytic efficiency between substrates are mainly related to differences in their affinity for the enzyme. Remarkably, it appears that, if a hexose is able to bind in the active site, then it is also oxidized, whereas some pentoses are able to bind (and act as competitive inhibitors), but are not substrates. The activation energies for the oxidation of hexoses and pentoses are almost identical. In a previously published model of the enzyme, His262 is at the entrance to the active site and appears to be important in holding the prosthetic group pyrroloquinoline quinone (PQQ) in place, and it has been suggested that it might play a role in electron transfer from the reduced PQQ to the ubiquinone in the membrane. The H262Y-GDH has a greatly diminished catalytic efficiency for all substrates, which is mainly due to a marked decrease in their affinities for the enzyme, but the rate of electron transfer to oxygen is unaffected. During the processing of the PQQ into the apoenzyme to give active enzyme, its affinity is markedly dependent on the pH, four groups with pK values between pH7 and pH8 being involved. Identical results were obtained with H262Y-GDH, showing that His262 it is not directly involved in this process. (+info)
In-vitro activity of 29 antimicrobial agents against penicillin-resistant and -intermediate isolates of Streptococcus pneumoniae.
(19/2071)
Antibiotic resistance among isolates of Streptococcus pneumoniae is increasing worldwide. Optimal therapy, though unknown, should be guided by in-vitro susceptibility testing. Currently, vancomycin is the only approved antibiotic that is universally active against multiresistant S. pneumoniae. In-vitro activities were determined for 29 antimicrobial agents against 22 penicillin-intermediate S. pneumoniae (PISP) and 16 penicillin-resistant S. pneumoniae (PRSP) isolates. MICs were determined in cation-adjusted Mueller-Hinton broth with 3% lysed horse blood in microtitre trays. Antimicrobial classes tested included cephalosporins, penicillin, aminopenicillins, macrolides, quinolones, carbapenems and other antimicrobial agents. Among the classes of antimicrobial agents tested, wide differences in susceptibility were demonstrated for both PISP and PRSP. Of the cephalosporins, ceftriaxone and cefotaxime demonstrated the best in-vitro activity for both PISP and PRSP. Of the quinolones, clinafloxacin and trovafloxacin showed the greatest in-vitro activity. Rifampicin and teicoplanin demonstrated excellent in-vitro activity. Promising in-vitro results of newer agents, such as quinupristin/dalfopristin, ramoplanin, teicoplanin and linezolid may justify further evaluation of these agents in clinical trials. (+info)
Quinolone accumulation by Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli.
(20/2071)
The accumulation of nalidixic acid and 14 fluoroquinolones over a range of external drug concentrations (10-100 mg/L; c. 25-231 microM) into intact cells of Escherichia coli KL-16, Staphylococcus aureus NCTC 8532, Pseudomonas aeruginosa NCTC 10662 and spheroplasts of E. coli was investigated. The effect of 100 microM carbonyl cyanide m-chlorophenyl hydrazone (CCCP) upon the concentration of quinolone accumulated by intact cells and spheroplasts of E. coli was also determined. Except for pefloxacin, there was an increase in the concentration of the six quinolones examined accumulated by E. coli, despite a reduction in fluorescence at alkaline pH. For ciprofloxacin the partition coefficient (P(app)) was constant despite an increase in the pH; however, the P(app) for nalidixic acid decreased significantly with an increase in pH. The concentration of nalidixic acid, ciprofloxacin and enrofloxacin accumulated by E. coli and S. aureus increased with an increase in temperature up to 40 degrees C and 50 degrees C, respectively. Above these temperatures the cell viability decreased. With an increase in drug concentration there was, for intact E. coli and 12/15 agents, and for S. aureus and 10/15 agents, a linear increase in the concentration of drug accumulated. However, for P. aeruginosa and 13/15 agents there was apparent saturation of an accumulation pathway. Assuming 100% accumulation into intact cells of E. coli, for 10/14 fluoroquinolones < or = 40% was accumulated by spheroplasts. CCCP increased the concentration of quinolone accumulated but the increase varied with the agent and the bacterial species. The variation in the effect of CCCP upon accumulation of the different quinolones into E. coli could result from chemical interactions or from different affinities of the proposed efflux transporter for each quinolone. Overall, these data suggest that accumulation of most quinolones into E. coli and S. aureus proceeds by simple diffusion, but that P. aeruginosa behaves differently. (+info)
CNQX but not NBQX prevents expression of amphetamine-induced place preference conditioning: a role for the glycine site of the NMDA receptor, but not AMPA receptors.
(21/2071)
We investigated the role of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor in the induction and expression of an amphetamine-induced conditioned place preference (CPP) in mice. The selective AMPA-receptor antagonist 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX) failed to prevent the induction of a CPP, except at a dose (30 mg/kg) that also produced a conditioned place aversion. NBQX also failed to affect the expression of a CPP at a dose high enough to reduce activity levels. In contrast, the less selective AMPA receptor antagonist 6-cyano-7-nitroquinoxalone-2,3-dione (CNQX) prevented the expression of a CPP at doses (1-10 mg/kg) that had no effect on activity levels. We therefore tested the possibility that CNQX exerted its effects due to antagonism at the glycine site of the N-methyl-D-aspartate receptor. The glycine-site antagonist 7-chloro-4-hydroxy-3-(2-phenoxy)phenyl-2(1H)-quinolone also prevented the expression of a CPP at doses that had no effect on activity levels (0.1-0.3 mg/kg). These results suggest that neither the induction nor the expression of an amphetamine-induced CPP requires AMPA receptor-mediated transmission and that effects found in previous studies using the less selective AMPA receptor antagonists may be due to the effects of these compounds at the glycine site of the N-methyl-D-aspartate receptor. (+info)
Efflux transport of a new quinolone antibacterial agent, HSR-903, across the blood-brain barrier.
(22/2071)
The distribution of HSR-903, a new quinolone antibacterial agent, to the brain after i.v. administration to rats was low compared with that to other tissues. The blood-brain barrier permeability to HSR-903 determined by the brain perfusion method was low, and increased nonlinearly with increasing concentration of HSR-903 in the perfusate. When the brain-to-plasma concentration ratio (Kp, brain) was measured in mdr1a gene-knockout mice, the value was 8 times higher than that in normal mice. The uptake of [14C]HSR-903 by multidrug-resistant K562/ADM cells, which express P-glycoprotein (P-gp), was significantly lower than that by the drug-sensitive parent K562 cells. In addition, the uptake of [14C]HSR-903 by K562/ADM cells was significantly increased in the presence of cyclosporin A and ATP-depleting agents. These observations support the idea that P-gp participates in HSR-903 efflux from the brain. The steady-state uptake of HSR-903 by a monolayer of primary cultured bovine brain capillary endothelial cells was increased in the presence of several quinolone antibacterial agents or anionic compounds, such as 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, and in bicarbonate ion-free medium, as well as by P-gp inhibitors (cyclosporin A and quinidine). These results suggested that the efflux of HSR-903 proceeds at least partly via an anion-sensitive efflux transport mechanism as well as via P-gp. In conclusion, the low brain distribution of the new quinolone antibacterial agent HSR-903 can be ascribed to multiple efflux mechanisms including P-gp and an unidentified anion-sensitive transporter operating in the brain capillary endothelial cells that constitute the blood-brain barrier. (+info)
Fluoroquinolone phototoxicity: a comparison of moxifloxacin and lomefloxacin in normal volunteers.
(23/2071)
Moxifloxacin, a broad-spectrum fluoroquinolone with the methoxy group at position 8 of the quinolone structure that is believed to confer reduced phototoxicity, was investigated in 32 healthy human male volunteers by a randomized double-blind placebo and positive control (lomefloxacin) phototest technique. A comparison of pre- and on-drug photosensitivity levels tested with an irradiation monochromator using relevant sunlight wavelengths, failed to demonstrate phototoxicity after administration of either placebo or moxifloxacin (200 mg or 400 mg/day) for 7 days. As expected, lomefloxacin (400 mg/day) phototoxicity was revealed at the UVA wavebands 335 +/- 30 nm and 365 +/- 30 nm (maximal at 24 h), with a phototoxic index of 3-4. The susceptibility to this effect rapidly normalized within 48 h of stopping the drug. No special protection from UVA wavelengths is necessary for those taking moxifloxacin. (+info)
Mechanisms of resistance to ampicillin, chloramphenicol and quinolones in multiresistant Salmonella typhimurium strains isolated from fish.
(24/2071)
Mechanisms of antibiotic resistance and epidemiological relationships were investigated for five multiresistant strains of Salmonella typhimurium isolated from fish in India. Four strains showed resistance to nalidixic acid, chloramphenicol, tetracycline, co-trimoxazole, gentamicin and beta-lactam antibiotics. The remaining strain was susceptible to all beta-lactam antibiotics tested and to co-trimoxazole but resistant to the other antibiotics tested. Epidemiological analysis performed by REP-PCR showed that the five isolates belonged to the same clone. Resistance to nalidixic acid was related to a single mutation in the gyrA gene. Chloramphenicol resistance was related to the production of chloramphenicol acetyl-transferase. An OXA-1 beta-lactamase, located in an integron, was responsible for resistance to ampicillin. These results indicate the health hazard posed by the fact that S. typhimurium may acquire or develop several mechanisms of resistance to a variety of antibiotics, including quinolones, and can thus cause disease in humans which may be difficult to treat. (+info)