Dataset Information

The Quinazolinone Allosteric Inhibitor of PBP 2a Synergizes with Piperacillin and Tazobactam against Methicillin-Resistant Staphylococcus aureus.

ABSTRACT: The quinazolinones are a new class of antibacterials with in vivo efficacy against methicillin-resistant Staphylococcus aureus (MRSA). The quinazolinones target cell wall biosynthesis and have a unique mechanism of action by binding to the allosteric site of penicillin-binding protein 2a (PBP 2a). We investigated the potential for synergism of a lead quinazolinone with several antibiotics of different classes using checkerboard and time-kill assays. The quinazolinone synergized with ?-lactam antibiotics. The combination of the quinazolinone with commercial piperacillin-tazobactam showed bactericidal synergy at sub-MICs of all three drugs. We demonstrated the efficacy of the triple-drug combination in a mouse MRSA neutropenic thigh infection model. The proposed mechanism for the synergistic activity in MRSA involves inhibition of the ?-lactamase by tazobactam, which protects piperacillin from hydrolysis, which can then inhibit its target, PBP 2. Furthermore, the quinazolinone binds to the allosteric site of PBP 2a, triggering the allosteric response. This leads to the opening of the active site, which, in turn, binds another molecule of piperacillin. In other words, PBP 2a, which is not normally inhibited by piperacillin, becomes vulnerable to inhibition in the presence of the quinazolinone. The collective effect is the impairment of cell wall biosynthesis, with bactericidal consequence. Two crystal structures for complexes of the antibiotics with PBP 2a provide support for the proposed mechanism of action.

SUBMITTER: Janardhanan J

PROVIDER: S-EPMC6496080 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

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The Quinazolinone Allosteric Inhibitor of PBP 2a Synergizes with Piperacillin and Tazobactam against Methicillin-Resistant Staphylococcus aureus.

Janardhanan Jeshina J Bouley Renee R Martínez-Caballero Siseth S Peng Zhihong Z Batuecas-Mordillo Mayte M Meisel Jayda E JE Ding Derong D Schroeder Valerie A VA Wolter William R WR Mahasenan Kiran V KV Hermoso Juan A JA Mobashery Shahriar S Chang Mayland M

Antimicrobial agents and chemotherapy 20190425 5

The quinazolinones are a new class of antibacterials with <i>in vivo</i> efficacy against methicillin-resistant <i>Staphylococcus aureus</i> (MRSA). The quinazolinones target cell wall biosynthesis and have a unique mechanism of action by binding to the allosteric site of penicillin-binding protein 2a (PBP 2a). We investigated the potential for synergism of a lead quinazolinone with several antibiotics of different classes using checkerboard and time-kill assays. The quinazolinone synergized wit ...[more]

PMID: 30858202

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Project description:Our objective was to examine whether empirical antimicrobial therapy (EAT) against methicillin-susceptible Staphylococcus aureus bacteremia (MS-SAB) with piperacillin-tazobactam (TZP), cefuroxime or combination therapy with one of these was differentially associated with 7-, 30-, and 90- day all-cause mortality or MS-SAB relapse. A multicenter retrospective cohort study of adults with MS-SAB from 2009 through 2018 was used, and 7-, 30-, 90-day mortality and relapse within 90 days were assessed and expressed as hazard ratio (HR) with a 95% confidence interval (95% CI) using Cox proportional hazard regression analysis. Matching of the two monotherapy groups was performed using propensity score matching. In total, 1158 MS-SAB cases were included and received one of three EAT regimens: TZP (n = 429), cefuroxime (n = 337), or TZP or cefuroxime with one or more additional effective antimicrobial (n = 392). The overall 30-day mortality was 28.0% (25.5 to 30.3%). After adjustment and matching, there was no significant difference in 7-, 30-, or 90-day mortality between the therapy groups. The matched HR of death was 0.81 (95% CI, 0.38 to 1.76) at 7 days, 0.82 (95% CI, 0.47 to 1.46) at 30 days, and 0.81 (95% CI, 0.50 to 1.32) at 90 days for TZP compared with cefuroxime. Adjusted HR of 90-day relapse was insignificant between the three therapy groups: TZP: 1.55 (95% CI, 0.54 to 4.43); combination therapy: 1.73 (95% CI, 0.62 to 4.80) compared to cefuroxime. There was no significant difference in 7-, 30-, or 90-day mortality or relapse between MS-SAB patients treated with empirical TZP or cefuroxime after adjustment and matching of covariables. IMPORTANCE This multicenter retrospective matched cohort study evaluated the effect of empirical antimicrobial therapy on the clinical outcome of methicillin-susceptible Staphylococcus aureus bacteremia (MS-SAB) in >1100 adult patients. To the best of our knowledge, this is the largest study to date evaluating the effect of empirical treatment on the MS-SAB outcome. Importantly, the study found no significant difference in either short- or long-term mortality nor relapse between patients with MS-SAB receiving empirical treatment with cefuroxime or piperacillin-tazobactam. As such, this study provides crucial contemporary data supporting the widespread clinical practice of initiating empirical antimicrobial therapy of sepsis with β-lactam-β-lactamase-inhibitor.

Project description:The mechanism of the β-lactam antibacterials is the functionally irreversible acylation of the enzymes that catalyze the cross-linking steps in the biosynthesis of their peptidoglycan cell wall. The Gram-positive pathogen Staphylococcus aureus uses one primary resistance mechanism. An enzyme, called penicillin-binding protein 2a (PBP2a), is brought into this biosynthetic pathway to complete the cross-linking. PBP2a effectively discriminates against the β-lactam antibiotics as potential inhibitors, and in favor of the peptidoglycan substrate. The basis for this discrimination is an allosteric site, distal from the active site, that when properly occupied concomitantly opens the gatekeeper residues within the active site and realigns the conformation of key residues to permit catalysis. We address the molecular basis of this regulation using crystallographic studies augmented by computational analyses. The crystal structures of three β-lactams (oxacillin, cefepime, ceftazidime) complexes with PBP2a-each with the β-lactam in the allosteric site-defined (with preceding PBP2a structures) as the "open" or "partially open" PBP2a states. A particular loop motion adjacent to the active site is identified as the driving force for the active-site conformational change that accompanies active-site opening. Correlation of this loop motion to effector binding at the allosteric site, in order to identify the signaling pathway, was accomplished computationally in reference to the known "closed" apo-PBP2a X-ray crystal structure state. This correlation enabled the computational simulation of the structures coinciding with initial peptidoglycan substrate binding to PBP2a, acyl enzyme formation, and acyl transfer to a second peptidoglycan substrate to attain cross-linking. These studies offer important insights into the structural bases for allosteric site-to-active site communication and for β-lactam mimicry of the peptidoglycan substrates, as foundational to the mechanistic understanding of emerging PBP2a resistance mutations.

Dataset Information

The Quinazolinone Allosteric Inhibitor of PBP 2a Synergizes with Piperacillin and Tazobactam against Methicillin-Resistant Staphylococcus aureus.

Publications

The Quinazolinone Allosteric Inhibitor of PBP 2a Synergizes with Piperacillin and Tazobactam against Methicillin-Resistant Staphylococcus aureus.

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