Inhibitory effects of quinolones on pro- and eucaryotic DNA topoisomerases I and II

As a means of gaining information on the selectivity of quinolone antibacterial agents, we examined their effect on four topoisomerases, topoisomerases I and II purified from Escherichia coli and calf thymus. The inhibition of supercoiling and relaxation activities was monitored by using the classical gel electrophoresis assay. Eight quinolones were assayed by using the four enzymes. Gyrase was much more sensitive to quinolones than the other topoisomerases which can therefore be inhibited by moderate concentrations of certain quinolones. No good correlation was observed between the activity on gyrase and on the other enzymes, since the ratio varied from 15 to more than 8,500. On the contrary, there was a good correlation between early inhibition of DNA synthesis, inhibition of gyrase, and MICs.