Topoisomerase Inhibitors: Fluoroquinolone Mechanisms of Action and Resistance

Abstract

Quinolone antimicrobials are widely used in clinical medicine and are the only current class of agents that directly inhibit bacterial DNA synthesis. Quinolones dually target DNA gyrase and topoisomerase IV binding to specific domains and conformations so as to block DNA strand passage catalysis and stabilize DNA-enzyme complexes that block the DNA replication apparatus and generate double breaks in DNA that underlie their bactericidal activity. Resistance has emerged with clinical use of these agents and is common in some bacterial pathogens. Mechanisms of resistance include mutational alterations in drug target affinity and efflux pump expression and acquisition of resistance-conferring genes. Resistance mutations in one or both of the two drug target enzymes are commonly in a localized domain of the GyrA and ParC subunits of gyrase and topoisomerase IV, respectively, and reduce drug binding to the enzyme-DNA complex. Other resistance mutations occur in regulatory genes that control the expression of native efflux pumps localized in the bacterial membrane(s). These pumps have broad substrate profiles that include other antimicrobials as well as quinolones. Mutations of both types can accumulate with selection pressure and produce highly resistant strains. Resistance genes acquired on plasmids confer low-level resistance that promotes the selection of mutational high-level resistance. Plasmid-encoded resistance is because of Qnr proteins that protect the target enzymes from quinolone action, a mutant aminoglycoside-modifying enzyme that also modifies certain quinolones, and mobile efflux pumps. Plasmids with these mechanisms often encode additional antimicrobial resistances and can transfer multidrug resistance that includes quinolones.

Antibiotic usage promotes the evolution of resistance against gepotidacin, a novel multi-targeting drug

“…mutS displays around 100-fold increase in mutation rate, and as being a hypermutator, it adapts especially rapidly to various antibiotic stresses. In line with previous clinical and laboratory studies 33,53 , ciprofloxacin resistance was seen to emerge quickly in our experiments ( Figure 7). Despite the short time-frame, all E. coli and K. pneumoniae populations reached ciprofloxacin-resistance levels equal to or above the EUCAST clinical breakpoint 54 (Figure 7).…”

“…Thus, we hypothesized that prolonged use of other antibiotics might select for mutations that serve as stepping-stones towards gepotidacinresistance. The best candidate antibiotic family is fluoroquinolones, as they are widely employed in clinical practice, and similarly to gepotidacin, they target the gyrase/topoisomerase protein complexes, albeit with a notably different molecular mechanism 18,33 . Moreover, the putative binding sites of gepotidacin and fluoroquinolones on the GyrA protein are adjacent to each other, separated by a single amino acid only (see figure 1B, and [34][35][36] ).…”

Separation of newly replicated bacterial chromosomes: the role ofEscherichia coliTopoisomerase IV

“…The group of antibiotics termed fluoroquinolones is known to bind and inhibit Gyrase and TopoIV by forming a ternary complex with these enzymes and DNA. Upon drug interaction Gyrase/TopoIV remains as a “frozen” adduct on DNA after the cleavage step, and is unable to reseal the double-strand ends after strand passage 27 . We decided to use the fluoroquinolone Ciprofloxacin to shed more light on the positioning of TopoIV during replication.…”

Identifying Small Molecules That Promote Quasipalindrome-Associated Template-Switch Mutations inEscherichia coli

“…5-azaC requires a higher dosage to induce template switching than the 80 mM limit of our collection. Fluoroquinolones are derived from Nal, the first antibacterial quinolone utilized clinically (Lesher et al 1962;Hooper and Jacoby 2016). Fluoroquinolones differ from quinolones by the addition of fluorine at position 6, which significantly increases the antimicrobial potency of the compound (Ito et al 1980;Koga et al 1980;Eliopoulos et al 1984).…”