Fluoroquinolone interactions withMycobacterium tuberculosisgyrase: Enhancing drug activity against wild-type and resistant gyrase

Abstract

Mycobacterium tuberculosisis a significant source of global morbidity and mortality. Moxifloxacin and other fluoroquinolones are important therapeutic agents for the treatment of tuberculosis, particularly multidrug-resistant infections. To guide the development of new quinolone-based agents, it is critical to understand the basis of drug action againstM. tuberculosisgyrase and how mutations in the enzyme cause resistance. Therefore, we characterized interactions of fluoroquinolones and related drugs with WT gyrase and enzymes carrying mutations at GyrAA90and GyrAD94.M. tuberculosisgyrase lacks a conserved serine that anchors a water–metal ion bridge that is critical for quinolone interactions with other bacterial type II topoisomerases. Despite the fact that the serine is replaced by an alanine (i.e., GyrAA90) inM. tuberculosisgyrase, the bridge still forms and plays a functional role in mediating quinolone–gyrase interactions. Clinically relevant mutations at GyrAA90and GyrAD94cause quinolone resistance by disrupting the bridge–enzyme interaction, thereby decreasing drug affinity. Fluoroquinolone activity against WT and resistant enzymes is enhanced by the introduction of specific groups at the C7 and C8 positions. By dissecting fluoroquinolone–enzyme interactions, we determined that an 8-methyl-moxifloxacin derivative induces high levels of stable cleavage complexes with WT gyrase and two common resistant enzymes, GyrAA90Vand GyrAD94G. 8-Methyl-moxifloxacin was more potent than moxifloxacin against WTM. tuberculosisgyrase and displayed higher activity against the mutant enzymes than moxifloxacin did against WT gyrase. This chemical biology approach to defining drug–enzyme interactions has the potential to identify novel drugs with improved activity against tuberculosis.