The Anti-Methicillin-Resistant Staphylococcus aureus Quinolone WCK 771 Has Potent Activity against Sequentially Selected Mutants, Has a Narrow Mutant Selection Window against Quinolone-Resistant Staphylococcus aureus , and Preferentially Targets DNA Gyrase

Abstract

WCK 771 is a broad-spectrum fluoroquinolone with enhanced activity against quinolone-resistant staphylococci. To understand the impact of the target-level interactions of WCK 771 on its antistaphylococcal pharmacodynamic properties, we determined the MICs for genetically defined mutants and studied the mutant prevention concentrations (MPCs), the frequency of mutation, and the cidality against the wild type and double mutants. There was a twofold increase in the MICs of WCK 771 for single gyrA mutants, indicating that DNA gyrase is its primary target. All first-and second-step mutants selected by WCK 771 revealed gyrA and grlA mutations, respectively. The MICs of WCK 771 and clinafloxacin were found to be superior to those of other quinolones against strains with double and triple mutations. WCK 771 was also cidal for high-density double mutants at low concentrations. WCK 771 and clinafloxacin showed narrow mutant selection windows compared to those of the other quinolones. Against a panel of 50 high-level quinolone-resistant clinical isolates of staphylococci (ciprofloxacin MIC > 16 g/ml), the WCK 771 MPCs were <2 g/ml for 68% of the strains and <4 g/ml for 28% of the strains. Our results demonstrate that gyrA is the primary target of WCK 771 and that it has pharmacodynamic properties remarkably different from those of quinolones with dual targets (garenoxacin and moxifloxacin) and topoisomerase IV-specific quinolones (trovafloxacin). WCK 771 displayed an activity profile comparable to that of clinafloxacin, a dual-acting quinolone with a high affinity to DNA gyrase. Overall, the findings signify the key role of DNA gyrase in determining the optimal antistaphylococcal features of quinolones.Multidrug-resistant gram-positive bacteria are a growing problem in both hospitals and the community. Methicillinresistant Staphylococcus aureus (MRSA) was first reported sporadically in Europe beginning in 1961 and over the span of the last 15 years has emerged as a major multidrug-resistant pathogen worldwide (17).Quinolones interact with type II topoisomerases, DNA gyrase, and topoisomerase IV (topo IV) to execute their bactericidal activity. In S. aureus, quinolone resistance occurs stepwise by mutations in the two target topoisomerase enzymes, with the first mutation usually occurring in topo IV, followed by a mutation in DNA gyrase, due to the preferential affinities of the currently used quinolones to topo IV (31). With the increasing use of older quinolones, resistance in staphylococci has emerged rather quickly, and therefore, it is desirable that new quinolones be optimized against staphylococci carrying multiple resistance mechanisms, particularly the ones manifested through mutations in both the target genes. A higher affinity toward mutated targets results in higher potency and a lower frequency of mutation (FM). From a pharmacodynamic (PD) angle, one of the parameters of quinolone optimization would be lower, therapeutically attainable mutant prevention concentrations (MPCs) for quinolone-resistant strains that...

Antistaphylococcal Activities of the New Fluoroquinolone JNJ-Q2

“…New fluoroquinolone agents active against ciprofloxacin-resistant MRSA would likely display equipotent activities against staphylococcal DNA gyrase and DNA topoisomerase IV and not serve as a substrate for efflux pumps. Several investigational fluoroquinolones have demonstrated in vitro activity against MRSA and are reported to be the subject of clinical studies to evaluate their efficacy in the treatment of ABSSSI, including infections caused by MRSA (2,4,20,22 Herein we report the activities of JNJ-Q2 and comparator fluoroquinolone agents against methicillin-susceptible S. aureus (MSSA) and MRSA carrying defined target mutations and upregulated efflux, as well as the inhibition of S. aureus wildtype and mutant DNA gyrase and topoisomerase IV enzymes.…”

In Vitro Activity of the Quinolone WCK 771 against Recent U.S. Hospital and Community-Acquired Staphylococcus aureus Pathogens with Various Resistance Types

“…WCK 771 is a broad-spectrum intravenous quinolone active against MRSA and quinolone-resistant S. aureus and is currently being studied in phase 2 clinical trials (2,8,14). Its oral form is under development in phase 1 clinical studies.…”

“…Unlike other quinolones such as levofloxacin and moxifloxacin, WCK 771 demonstrates distinctive antistaphylococcal properties, such as preferential action toward DNA gyrase, unaltered activity against strains exhibiting quinolone efflux, low most probably counts, and induction of growth-defective, noninfectious, small colony variants, resulting in superior pharmacodynamic features against quinoloneresistant strains (2,8,14) (Wockhardt Research Center, unpublished data). During phase 1 clinical trials in India, WCK 771 administered as an intravenous infusion at 800 mg, twice a day, attained mean 24-h total areas under the concentrationtime curves (AUCs) of 390 g · h/ml, with 58.5 g · h/ml being unbound (9).…”

“…Vancomycin MICs were read after a full 24-h incubation. Genomic DNA isolation, PCR amplification (of the quinolone resistance-determining region [QRDR]) of vancomycin-susceptible MRSA, VISA, and VRSA, and sequencing were performed as described previously (2,4,6). 50 and MIC 90 values of 0.03 g/ml and 1 g/ml, respectively.…”

Surmounting antimicrobial resistance in the Millennium Superbug: Staphylococcus aureus

“…The potency of WCK-771 is four to eight fold higher than other fluoroquinolones in combating VISA and VRSA. The Nor A efflux pump did not have any activity against WCK-771 [86]. This arginine salt of S-(−)-nadifloxacin is under phase II clinical trials.…”