J Biol Chem, Vol. 274, Issue 50, 35927-35932, December 10, 1999

Quinolones Inhibit DNA Religation Mediated by Staphylococcus aureus Topoisomerase IV
CHANGES IN DRUG MECHANISM ACROSS EVOLUTIONARY BOUNDARIES^*

Virginia E. Anderson^§, Richard P. Zaniewski^¶, Frank S. Kaczmarek^¶, Thomas D. Gootz^¶, and Neil Osheroff^**

From the Departments of  Biochemistry and  Medicine (Hematology/Oncology), Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146 and the ^¶ Department of Cancer, Immunology, and Infectious Diseases, Pfizer Central Research, Pfizer, Inc., Groton, Connecticut 06340

Quinolones are the most active oral antibacterials in clinical use and act by increasing DNA cleavage mediated by prokaryotic type II topoisomerases. Although topoisomerase IV appears to be the primary cytotoxic target for most quinolones in Gram-positive bacteria, interactions between the enzyme and these drugs are poorly understood. Therefore, the effects of ciprofloxacin on the DNA cleavage and religation reactions of Staphylococcus aureus topoisomerase IV were characterized. Ciprofloxacin doubled DNA scission at 150 nM drug and increased cleavage ~9-fold at 5 µM. Furthermore, it dramatically inhibited rates of DNA religation mediated by S. aureus topoisomerase IV. This inhibition of religation is in marked contrast to the effects of antineoplastic quinolones on eukaryotic topoisomerase II, and suggests that the mechanistic basis for quinolone action against type II topoisomerases has not been maintained across evolutionary boundaries. The apparent change in quinolone mechanism was not caused by an overt difference in the drug interaction domain on topoisomerase IV. Therefore, we propose that the mechanistic basis for quinolone action is regulated by subtle changes in drug orientation within the enzyme·drug·DNA ternary complex rather than gross differences in the site of drug binding.