title: Cleavable-complex formation by wild-type and quinolone-resistant Streptococcus pneumoniae type II topoisomerases mediated by gemifloxacin and other fluoroquinolones.
abstract: Gemifloxacin is a recently developed fluoroquinolone with potent activity against Streptococcus pneumoniae. We show that the drug is more active than moxifloxacin, gatifloxacin, levofloxacin, and ciprofloxacin against S. pneumoniae strain 7785 (MICs, 0.03 to 0.06 microg/ml versus 0.25, 0.25, 1, and 1 to 2 microg/ml, respectively) and against isogenic quinolone-resistant gyrA-parC mutants (MICs, 0.5 to 1 microg/ml versus 2 to 4, 2 to 4, 16 to 32, and 64 microg/ml, respectively). Gemifloxacin was also the most potent agent against purified S. pneumoniae DNA gyrase and topoisomerase IV in both catalytic inhibition and DNA cleavage assays. The drug concentrations that inhibited DNA supercoiling or DNA decatenation by 50% (IC(50)s) were 5 to 10 and 2.5 to 5.0 microM, respectively. Ciprofloxacin and levofloxacin were some four- to eightfold less active against either enzyme; moxifloxacin and gatifloxacin showed intermediate activities. In assays of drug-mediated DNA cleavage by gyrase and topoisomerase IV, the same order of potency was seen: gemifloxacin > moxifloxacin > gatifloxacin > levofloxacin approximately ciprofloxacin. For gemifloxacin, the drug concentrations that caused 25% linearization of the input DNA by gyrase and topoisomerase IV were 2.5 and 0.1 to 0.3 microM, respectively; these values were 4-fold and 8- to 25-fold lower than those for moxifloxacin, respectively. Each drug induced DNA cleavage by gyrase at the same spectrum of sites but with different patterns of intensity. Finally, for enzymes reconstituted with quinolone-resistant GyrA S81F or ParC S79F subunits, although cleavable-complex formation was reduced by at least 8- to 16-fold for all the quinolones tested, gemifloxacin was the most effective; e.g., it was 4- to 16-fold more active than the other drugs against toposiomerase IV with the ParC S79F mutation. It appears that the greater potency of gemifloxacin against both wild-type and quinolone-resistant S. pneumoniae strains arises from enhanced stabilization of gyrase and topoisomerase IV complexes on DNA.
authors.affiliation: Molecular Genetics Group, Department of Biochemistry and Immunology, St. George's Hospital Medical School, University of London, London SW17 0RE, United Kingdom.
authors.forename: Genoveva
authors.initials: G
authors.lastname: Yague
authors.forename: Julia E
authors.initials: JE
authors.lastname: Morris
authors.forename: Xiao-Su
authors.initials: XS
authors.lastname: Pan
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Gould
authors.forename: L Mark
authors.initials: LM
authors.lastname: Fisher
mesh_terms: D019943:Amino Acid Substitution; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002384:Catalysis; D027081:DNA Gyrase / Q000235:genetics / Q000378:metabolism; D027101:DNA Topoisomerase IV / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004269:DNA, Bacterial / Q000187:drug effects / Q000378:metabolism; D024881:Drug Resistance, Bacterial / Q000502:physiology; D004795:Enzyme Stability; D024841:Fluoroquinolones; D000077735:Gemifloxacin; D008826:Microbial Sensitivity Tests; D009287:Naphthyridines / Q000494:pharmacology*; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D059005:Topoisomerase II Inhibitors
chemical_list: D000890:Anti-Infective Agents; D004269:DNA, Bacterial; D024841:Fluoroquinolones; D009287:Naphthyridines; D059005:Topoisomerase II Inhibitors; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II; D000077735:Gemifloxacin