Inhibitory Activities of Gatifloxacin (AM-1155), a Newly Developed Fluoroquinolone, against Bacterial and Mammalian Type II Topoisomerases

We determined the inhibitory activities of gatifloxacin againstStaphylococcus aureus topoisomerase IV,Escherichia coli DNA gyrase, and HeLa cell topoisomerase II and compared them with those of several quinolones. The inhibitory activities of quinolones against these type II topoisomerases significantly correlated with their antibacterial activities or cytotoxicities (correlation coefficient [r ] = 0.926 forS. aureus ,r = 0.972 forE. coli , andr = 0.648 for HeLa cells). Gatifloxacin possessed potent inhibitory activities against bacterial type II topoisomerases (50% inhibitory concentration [IC50 ] = 13.8 μg/ml forS. aureus topoisomerase IV; IC50 = 0.109 μg/ml forE. coli DNA gyrase) but the lowest activity against HeLa cell topoisomerase II (IC50 = 265 μg/ml) among the quinolones tested. There was also a significant correlation between the inhibitory activities of quinolones againstS. aureus topoisomerase IV and those againstE. coli DNA gyrase (r = 0.969). However, the inhibitory activity against HeLa cell topoisomerase II did not correlate with that against either bacterial enzyme. The IC50 of gatifloxacin for HeLa cell topoisomerase II was 19 and was more than 2,400 times higher than that forS. aureus topoisomerase IV and that forE. coli DNA gyrase. These ratios were higher than those for other quinolones, indicating that gatifloxacin possesses a higher selectivity for bacterial type II topoisomerases.