Action of quinolones against Staphylococcus aureus topoisomerase IV: Basisfor DNA cleavage enhancement

Topoisomerase IV is the primary cellular target for most quinolones in Gram -positive bacteria; however, its interaction with these agents is pearly un derstood, Therefore, the effects of four clinically relevant antibacterial quinolones (ciprofloxacin, and three new generation quinolones: trovafloxac in, levofloxacin, and sparfloxacin) on the DNA cleavage/religation reaction of Staphylococcus aureus topoisomerase IV were characterized. These quinol ones stimulated enzyme-mediated DNA scission to a similar extent, but their potencies varied significantly. Drug order in the absence of ATP was trova floxacin > ciprofloxacin > levofloxacin > sparfloxacin, Potency was enhance d by ATP, but to a different extent for each drug. Under all conditions exa mined, trovafloxacin was the most potent quinolone and sparfloxacin was the least. The enhanced potency of trovafloxacin correlated with several prope rties. Trovafloxacin induced topoisomerase IV-mediated DNA scission more ra pidly than other quinolones and generated more cleavage at some sites. The most striking correlation, however, was between quinolone potency and inhib ition of enzyme-mediated DNA religation: the greater the potency, the stron ger the inhibition, Dose-response experiments with two topoisomerase IV mut ants that confer clinical resistance to quinolones (GrlA(Ser80Phe) and GrlA (Glu84Lys)) indicate that resistance is caused by a decrease in both drug a ffinity and efficacy. Trovafloxacin is more active against these enzymes th an ciprofloxacin because it partially overcomes the effect on affinity. Fin ally, comparative studies on DNA cleavage and decatenation suggest that the antibacterial properties of trovafloxacin result from increased S. aureus topoisomerase IV-mediated DNA cleavage rather than inhibition of enzyme cat alysis.