Bypassing Fluoroquinolone Resistance with Quinazolinediones: Studies of Drug−Gyrase−DNA Complexes Having Implications for Drug Design

*S Supporting Information ABSTRACT: Widespread fluoroquinolone resistance has drawn attention to quinazolinediones (diones), fluoroquino-lone-like topoisomerase poisons that are unaffected by common quinolone-resistance mutations. To better under-stand differences between quinolones and diones, we examined their impact on the formation of cleaved complexes (drug−topoisomerase−DNA complexes in which the DNA moiety is broken) with gyrase, one of two bacterial targets of the drugs. Formation of cleaved complexes, measured by linearization of a circular DNA substrate, required lower concentrations of quinolone than dione. The reverse reaction, detected as resealing of DNA breaks in cleaved complexes, required higher temperatures and EDTA concentrations for quinolones than diones. The greater stability of quinolone-containing complexes was attributed to the unique ability of the quinolone C3/C4 keto acid to complex with magnesium an