Novobiocin Enhances Polymyxin Activity by Stimulating Lipopolysaccharide Transport

Gram-negative bacteria are challenging to kill with antibiotics due to their impenetrableouter membrane containing lipopolysaccharide (LPS). The polymyxins, including colistin, are the drugsof last resortfor treating Gram-negative infections. These drugs bind LPS and disrupt the outer membrane; however, their toxicity limits their usefulness. Polymyxinhas been shown to synergize with many antibiotics including novobiocin, which inhibits DNA gyrase, by facilitating transport of these antibiotics across the outer membrane. Recently, we have shown that novobiocinnot only inhibits DNA gyrasebut also binds and stimulates LptB, the ATPase that powers LPS transport. Here, we report the synthesis of novobiocinderivatives that separate these two activities. One analog retains LptB-stimulatory activity but is unable to inhibit DNA gyrase. This analog, which is not toxic on its own, nevertheless enhances the lethality of polymyxinby binding LptB and stimulating LPS transport. Therefore, LPS transport agonism...