Publications by authors named "Stephen Rittenhouse"

27 Publications

  • Page 1 of 1

Efficacy of Human Exposures of Gepotidacin (GSK2140944) against in a Rat Pyelonephritis Model.

Antimicrob Agents Chemother 2019 07 24;63(7). Epub 2019 Jun 24.

GlaxoSmithKline, Collegeville, Pennsylvania, USA.

Gepotidacin is a first-in-class triazaacenaphthylene antibacterial that inhibits bacterial type II topoisomerases and has activity against a range of bacterial pathogens, including Urinary tract infections often progress to pyelonephritis and are a worldwide problem due to the prevalence of multidrug-resistant strains. This study evaluated the efficacy of gepotidacin against four strains of multidrug-resistant in a rat pyelonephritis model. Infected rats received controlled intravenous infusions of gepotidacin every 12 h for 4 days that recreated human systemic exposures from oral gepotidacin (800 or 1,500 mg twice daily for 4 days). Liquid chromatography-tandem mass spectrometry analysis of blood samples and kidney homogenates showed that gepotidacin levels were 6- to 7-fold higher in kidneys than in blood. Across experiments with 4-day gepotidacin treatments, bacterial CFU in kidneys were reduced by 2.9 to 4.9 log compared to pretreatment levels, and bladder CFU were reduced to the lower limit of detection (1.2 log). The efficacies of 800- and 1,500-mg gepotidacin exposures were statistically similar. A time-course experiment indicated that a period of more than 24 h of gepotidacin treatment was required for efficacy and that 4 days were needed for maximal response. Overall, these results demonstrate that the recreated human exposures of gepotidacin studied were effective in an animal model of pyelonephritis caused by multidrug-resistant and that further evaluation for clinical use is warranted.
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http://dx.doi.org/10.1128/AAC.00086-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6591613PMC
July 2019

Reducing Antibacterial Development Risk for GSK1322322 by Exploring Potential Human Dose Regimens in Nonclinical Efficacy Studies Using Immunocompetent Rats.

Antimicrob Agents Chemother 2017 11 24;61(11). Epub 2017 Oct 24.

GlaxoSmithKline, Collegeville, Pennsylvania, USA.

Directly testing proposed clinical dosing regimens in nonclinical studies can reduce the risk during the development of novel antibacterial agents. Optimal dosing regimens can be identified in animal models by testing recreated human pharmacokinetic profiles. An example of this approach using continuous intravenous infusions of GSK1322322 in immunocompetent rats to evaluate recreated human exposures from phase I trials in pneumonia models with and and an abscess model with is presented. GSK1322322 was administered via continuous intravenous infusion to recreate 1,000- or 1,500-mg oral doses every 12 h in humans. Significant reductions ( ≤ 0.05 for all comparisons) in bacterial numbers compared with those for the baseline controls were observed for and (mean log reductions, 1.6 to ≥2.7 and 1.8 to 3.3 CFU/lungs, respectively) with the recreated 1,000-mg oral dose. This profile was also efficacious against (mean log reduction, 1.9 to 2.4 CFU/abscess). There was a nonsignificant trend for improved efficacy against with the 1,500-mg oral dose (mean log reduction, 2.4 to 3.1 CFU/abscess). These results demonstrate that the human oral 1,000- or 1,500-mg exposure profiles of GSK1322322 recreated in rats were effective against representative community-associated pathogens and supported selection of the 1,500-mg oral dose given every 12 h for a phase II clinical skin infection study. Furthermore, this work exemplifies how the testing of recreated human pharmacokinetic profiles can be incorporated into the development process and serve as an aid for selecting optimal dosing regimens prior to conducting large-scale clinical studies.
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http://dx.doi.org/10.1128/AAC.00959-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5655044PMC
November 2017

Efficacy of Cefiderocol against Carbapenem-Resistant Gram-Negative Bacilli in Immunocompetent-Rat Respiratory Tract Infection Models Recreating Human Plasma Pharmacokinetics.

Antimicrob Agents Chemother 2017 09 24;61(9). Epub 2017 Aug 24.

Drug Discovery & Disease Research Laboratory, Shionogi & Co., Ltd., Toyonaka, Osaka, Japan.

Cefiderocol (S-649266), a novel siderophore cephalosporin, shows potent activity against carbapenem-resistant Gram-negative bacilli. In this study, we evaluated the efficacy of cefiderocol against carbapenem-resistant Gram-negative bacilli (, , and ) in immunocompetent-rat respiratory tract infection models recreating plasma pharmacokinetics (PK) profiles in healthy human subjects. A total of 6 clinical isolates (1 cephalosporin-susceptible isolate, 1 multidrug-resistant isolate, 2 multidrug-resistant isolates, and 2 carbapenem-resistant isolates) were evaluated. Four-day treatment with a human exposure of 1 g ceftazidime every 8 h as a 0.5-h infusion showed potent efficacy only against a ceftazidime-susceptible isolate, not against five ceftazidime-resistant isolates harboring carbapenemase. With cefiderocol, a human exposure of 2 g every 8 h as a 3-h infusion for 4 days produced a >3 log reduction in the number of viable cells of these carbapenem-resistant isolates in the lungs. When the infusion time was 1 h, bactericidal activity was also observed against all isolates tested, although for 2 of 5 carbapenem-resistant isolates, a 3 log reduction was not achieved. The difference in efficacy achieved by changing the infusion period from 1 h to 3 h was considered to be due to the higher percentage of the dosing interval during which free-drug concentrations were above the MIC (%), as observed for β-lactam antibiotics. These results suggest the potential utility of cefiderocol for the treatment of lung infections caused by carbapenem-resistant , , and strains.
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http://dx.doi.org/10.1128/AAC.00700-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5571323PMC
September 2017

A Robust Pneumonia Model in Immunocompetent Rodents to Evaluate Antibacterial Efficacy against S. pneumoniae, H. influenzae, K. pneumoniae, P. aeruginosa or A. baumannii.

J Vis Exp 2017 01 2(119). Epub 2017 Jan 2.

Antibacterial Discovery Performance Unit, GlaxoSmithKline.

Efficacy of candidate antibacterial treatments must be demonstrated in animal models of infection as part of the discovery and development process, preferably in models which mimic the intended clinical indication. A method for inducing robust lung infections in immunocompetent rats and mice is described which allows for the assessment of treatments in a model of serious pneumonia caused by S. pneumoniae, H. influenzae, P. aeruginosa, K. pneumoniae or A. baumannii. Animals are anesthetized, and an agar-based inoculum is deposited deep into the lung via nonsurgical intratracheal intubation. The resulting infection is consistent, reproducible, and stable for at least 48 h and up to 96 h for most isolates. Studies with marketed antibacterials have demonstrated good correlation between in vivo efficacy and in vitro susceptibility, and concordance between pharmacokinetic/pharmacodynamic targets determined in this model and clinically accepted targets has been observed. Although there is an initial time investment when learning the technique, it can be performed quickly and efficiently once proficiency is achieved. Benefits of the model include elimination of the neutropenic requirement, increased robustness and reproducibility, ability to study more pathogens and isolates, improved flexibility in study design and establishment of a challenging infection in an immunocompetent host.
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http://dx.doi.org/10.3791/55068DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5408714PMC
January 2017

In vitro antimicrobial activity of S-649266, a catechol-substituted siderophore cephalosporin, when tested against non-fermenting Gram-negative bacteria.

J Antimicrob Chemother 2016 Mar 7;71(3):670-7. Epub 2015 Dec 7.

Discovery Research Laboratory for Core Therapeutic Areas, Shionogi & Co., Ltd, Toyonaka, Osaka, Japan.

Objectives: S-649266 is a parenteral siderophore cephalosporin antibiotic with a catechol moiety on its side chain. The in vitro antimicrobial activity of S-649266 against non-fermenting Gram-negative bacteria was evaluated and compared with the activities of meropenem, levofloxacin, cefepime, ceftazidime and piperacillin/tazobactam.

Methods: MIC values of S-649266 were determined in Mueller-Hinton broth or Iso-Sensitest broth supplemented with apo-transferrin.

Results: S-649266 showed potent in vitro activity against the non-fermenting Gram-negative bacteria Acinetobacter baumannii, Pseudomonas aeruginosa and Stenotrophomonas maltophilia, including MDR strains such as carbapenem-resistant A. baumannii and metallo-β-lactamase-producing P. aeruginosa. MIC90s of S-649266 for A. baumannii, P. aeruginosa and S. maltophilia were 2, 1 and 0.5 mg/L, respectively, whereas MIC90s of meropenem were >16 mg/L. S-649266 showed potent in vitro activities against A. baumannii producing carbapenemases such as OXA-type β-lactamases, and P. aeruginosa producing metallo-β-lactamases such as IMP type and VIM type. MIC90 values for these A. baumannii strains and P. aeruginosa strains were 8 and 4 mg/L, respectively.

Conclusions: S-649266 is a novel antibiotic with potent in vitro activity against a range of non-fermenting Gram-negative bacteria, including MDR strains.
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http://dx.doi.org/10.1093/jac/dkv402DOI Listing
March 2016

In Vitro Antimicrobial Activity of a Siderophore Cephalosporin, S-649266, against Enterobacteriaceae Clinical Isolates, Including Carbapenem-Resistant Strains.

Antimicrob Agents Chemother 2016 Feb 16;60(2):729-34. Epub 2015 Nov 16.

Discovery Research Laboratory for Core Therapeutic Areas, Shionogi & Co., Ltd., Toyonaka, Osaka, Japan.

S-649266 is a novel siderophore cephalosporin antibiotic with a catechol moiety on the 3-position side chain. Two sets of clinical isolate collections were used to evaluate the antimicrobial activity of S-649266 against Enterobacteriaceae. These sets included 617 global isolates collected between 2009 and 2011 and 233 β-lactamase-identified isolates, including 47 KPC-, 49 NDM-, 12 VIM-, and 8 IMP-producers. The MIC90 values of S-649266 against the first set of Escherichia coli, Klebsiella pneumoniae, Serratia marcescens, Citrobacter freundii, Enterobacter aerogenes, and Enterobacter cloacae isolates were all ≤1 μg/ml, and there were only 8 isolates (1.3%) among these 617 clinical isolates with MIC values of ≥8 μg/ml. In the second set, the MIC values of S-649266 were ≤4 μg/ml against 109 strains among 116 KPC-producing and class B (metallo) carbapenemase-producing strains. In addition, S-649266 showed MIC values of ≤2 μg/ml against each of the 13 strains that produced other types of carbapenemases such as SME, NMC, and OXA-48. The mechanisms of the decreased susceptibility of 7 class B carbapenemase-producing strains with MIC values of ≥16 μg/ml are uncertain. This is the first report to demonstrate that S-649266, a novel siderophore cephalosporin, has significant antimicrobial activity against Enterobacteriaceae, including strains that produce carbapenemases such as KPC and NDM-1.
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http://dx.doi.org/10.1128/AAC.01695-15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4750680PMC
February 2016

Pharmacokinetics/Pharmacodynamics of Peptide Deformylase Inhibitor GSK1322322 against Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus in Rodent Models of Infection.

Antimicrob Agents Chemother 2016 01 19;60(1):180-9. Epub 2015 Oct 19.

Antibacterial Discovery Performance Unit, Infectious Disease Therapeutic Area, GlaxoSmithKline, Collegeville, Pennsylvania, USA.

GSK1322322 is a novel inhibitor of peptide deformylase (PDF) with good in vitro activity against bacteria associated with community-acquired pneumonia and skin infections. We have characterized the in vivo pharmacodynamics (PD) of GSK1322322 in immunocompetent animal models of infection with Streptococcus pneumoniae and Haemophilus influenzae (mouse lung model) and with Staphylococcus aureus (rat abscess model) and determined the pharmacokinetic (PK)/PD index that best correlates with efficacy and its magnitude. Oral PK studies with both models showed slightly higher-than-dose-proportional exposure, with 3-fold increases in area under the concentration-time curve (AUC) with doubling doses. GSK1322322 exhibited dose-dependent in vivo efficacy against multiple isolates of S. pneumoniae, H. influenzae, and S. aureus. Dose fractionation studies with two S. pneumoniae and S. aureus isolates showed that therapeutic outcome correlated best with the free AUC/MIC (fAUC/MIC) index in S. pneumoniae (R(2), 0.83), whereas fAUC/MIC and free maximum drug concentration (fCmax)/MIC were the best efficacy predictors for S. aureus (R(2), 0.9 and 0.91, respectively). Median daily fAUC/MIC values required for stasis and for a 1-log10 reduction in bacterial burden were 8.1 and 14.4 for 11 S. pneumoniae isolates (R(2), 0.62) and 7.2 and 13.0 for five H. influenzae isolates (R(2), 0.93). The data showed that for eight S. aureus isolates, fAUC correlated better with efficacy than fAUC/MIC (R(2), 0.91 and 0.76, respectively), as efficacious AUCs were similar for all isolates, independent of their GSK1322322 MIC (range, 0.5 to 4 μg/ml). Median fAUCs of 2.1 and 6.3 μg · h/ml were associated with stasis and 1-log10 reductions, respectively, for S. aureus.
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http://dx.doi.org/10.1128/AAC.01842-15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704172PMC
January 2016

Bacterial resistance to leucyl-tRNA synthetase inhibitor GSK2251052 develops during treatment of complicated urinary tract infections.

Antimicrob Agents Chemother 2015 Jan 27;59(1):289-98. Epub 2014 Oct 27.

Computational Biology, Quantitative Sciences, GlaxoSmithKline R&D, Collegeville, Pennsylvania, USA

GSK2251052, a novel leucyl-tRNA synthetase (LeuRS) inhibitor, was in development for the treatment of infections caused by multidrug-resistant Gram-negative pathogens. In a phase II study (study LRS114688) evaluating the efficacy of GSK2251052 in complicated urinary tract infections, resistance developed very rapidly in 3 of 14 subjects enrolled, with ≥32-fold increases in the GSK2251052 MIC of the infecting pathogen being detected. A fourth subject did not exhibit the development of resistance in the baseline pathogen but posttherapy did present with a different pathogen resistant to GSK2251052. Whole-genome DNA sequencing of Escherichia coli isolates collected longitudinally from two study LRS114688 subjects confirmed that GSK2251052 resistance was due to specific mutations, selected on the first day of therapy, in the LeuRS editing domain. Phylogenetic analysis strongly suggested that resistant Escherichia coli isolates resulted from clonal expansion of baseline susceptible strains. This resistance development likely resulted from the confluence of multiple factors, of which only some can be assessed preclinically. Our study shows the challenges of developing antibiotics and the importance of clinical studies to evaluate their effect on disease pathogenesis. (These studies have been registered at ClinicalTrials.gov under registration no. NCT01381549 for the study of complicated urinary tract infections and registration no. NCT01381562 for the study of complicated intra-abdominal infections.).
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http://dx.doi.org/10.1128/AAC.03774-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4291364PMC
January 2015

Novel amino-piperidines as potent antibacterials targeting bacterial type IIA topoisomerases.

Bioorg Med Chem Lett 2011 Dec 10;21(24):7489-95. Epub 2011 Oct 10.

Diseases of the Developing World CEDD, GlaxoSmithKline, Calle Severo Ochoa 2, 28760, Tres Cantos, Madrid, Spain.

We have identified a series of amino-piperidine antibacterials with a good broad spectrum potency. We report the investigation of various subunits in this series and advanced studies on compound 8. Compound 8 possesses good pharmacokinetics, broad spectrum antibacterial activity and demonstrates oral efficacy in a rat lung infection model.
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http://dx.doi.org/10.1016/j.bmcl.2011.09.117DOI Listing
December 2011

Novel cyclohexyl-amides as potent antibacterials targeting bacterial type IIA topoisomerases.

Bioorg Med Chem Lett 2011 Dec 10;21(24):7483-8. Epub 2011 Oct 10.

Diseases of the Developing World CEDD, GlaxoSmithKline, Calle Severo Ochoa, 2, 28760, Tres Cantos, Madrid, Spain.

As part of our wider efforts to exploit novel mode of action antibacterials, we have discovered a series of cyclohexyl-amide compounds that has good Gram positive and Gram negative potency. The mechanism of action is via inhibition of bacterial topoisomerases II and IV. We have investigated various subunits in this series and report advanced studies on compound 7 which demonstrates good PK and in vivo efficacy properties.
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http://dx.doi.org/10.1016/j.bmcl.2011.09.114DOI Listing
December 2011

Challenges of antibacterial discovery revisited.

Ann N Y Acad Sci 2010 Dec 8;1213:5-19. Epub 2010 Nov 8.

Antibacterial Discovery Performance Unit, Infectious Diseases Center of Excellence for Drug Discovery, GlaxoSmithKline, Collegeville, Pennsylvania, USA.

The discovery of novel antibiotic classes has not kept pace with the growing threat of bacterial resistance. Antibiotic candidates that act at new targets or via distinct mechanisms have the greatest potential to overcome resistance; however, novel approaches are also associated with higher attrition and longer timelines. This uncertainty has contributed to the withdrawal from antibiotic programs by many pharmaceutical companies. Genomic approaches have not yielded satisfactory results, in part due to nascent knowledge about unprecedented molecular targets, the challenge of achieving antibacterial activity by lead optimization of enzyme inhibitors, and the limitations of compound screening libraries for antibacterial discovery. Enhanced diversity of compound screening banks, entry into new chemical space, and new screening technologies are currently being exploited to improve hit rates for antibacterial discovery. Antibacterial compound lead optimization faces hurdles associated with the high plasma exposures required for efficacy. Lead optimization would be enhanced by the identification of new antibiotic classes with improved tractability and by expanding the predictability of in vitro safety assays. Implementing multiple screening and target identification strategies is recommended for improving the likelihood of discovering new antibacterial compounds that address unmet needs.
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http://dx.doi.org/10.1111/j.1749-6632.2010.05828.xDOI Listing
December 2010

A rapid microtiter plate assay for measuring the effect of compounds on Staphylococcus aureus membrane potential.

J Microbiol Methods 2010 Nov 27;83(2):254-6. Epub 2010 Aug 27.

Antibacterial Discovery Performance Unit, Infectious Diseases Center of Excellence in Drug Discovery, GlaxoSmithKline Pharmaceuticals, Collegeville, PA 19426, United States.

We developed a homogenous microtiter based assay using the cationic dye 3, 3'-Diethyloxacarbocyanine iodide, DiOC2(3), to measure the effect of compounds on membrane potential in Staphylococcus aureus. In a screen of 372 compounds from a synthetic compound collection with anti-Escherichia coli activity due to unknown modes of action at least 17% demonstrated potent membrane activity, enabling rapid discrimination of nuisance compounds.
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http://dx.doi.org/10.1016/j.mimet.2010.08.012DOI Listing
November 2010

Genetic characterization of Vga ABC proteins conferring reduced susceptibility to pleuromutilins in Staphylococcus aureus.

Antimicrob Agents Chemother 2008 Dec 6;52(12):4507-9. Epub 2008 Oct 6.

Department of Microbiology, ID-CEDD, GlaxoSmithKline, Collegeville, Pennsylvania 19426, USA.

Retapamulin MICs of > or =2 microg/ml were noted for 6 of 5,676 S. aureus recent clinical isolates evaluated. The ABC proteins VgaAv and VgaA were found to be responsible for the reduced susceptibility to pleuromutilins exhibited by these six isolates.
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http://dx.doi.org/10.1128/AAC.00915-08DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2592886PMC
December 2008

Stepwise exposure of Staphylococcus aureus to pleuromutilins is associated with stepwise acquisition of mutations in rplC and minimally affects susceptibility to retapamulin.

Antimicrob Agents Chemother 2007 Jun 2;51(6):2048-52. Epub 2007 Apr 2.

UP1345, GlaxoSmithKline, 1250 S. Collegeville Road, Collegeville, PA 19426, USA.

To assess their effects on susceptibility to retapamulin in Staphylococcus aureus, first-, second-, and third-step mutants with elevated MICs to tiamulin and other investigational pleuromutilin compounds were isolated and characterized through exposure to high drug concentrations. All first- and second-step mutations were in rplC, encoding ribosomal protein L3. Most third-step mutants acquired a third mutation in rplC. While first- and second-step mutations did cause an elevation in tiamulin and retapamulin MICs, a significant decrease in activity was not seen until a third mutation was acquired. All third-step mutants exhibited severe growth defects, and faster-growing variants arose at a high frequency from most isolates. These faster-growing variants were found to be more susceptible to pleuromutilins. In the case of a mutant with three alterations in rplC, the fast-growing variants acquired an additional mutation in rplC. In the case of fast-growing variants of isolates with two mutations in rplC and at least one mutation at an unmapped locus, one of the two rplC mutations reverted to wild type. These data indicate that mutations in rplC that lead to pleuromutilin resistance have a direct, negative effect on fitness. While reduction in activity of retapamulin against S. aureus can be seen through mutations in rplC, it is likely that target-specific resistance to retapamulin will be slow to emerge due to the need for three mutations for a significant effect on activity and the fitness cost of each mutational step.
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http://dx.doi.org/10.1128/AAC.01066-06DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1891380PMC
June 2007

Use of the surgical wound infection model to determine the efficacious dosing regimen of retapamulin, a novel topical antibiotic.

Antimicrob Agents Chemother 2006 Nov;50(11):3886-8

Department of Microbiology Research, MMPD CEDD, GlaxoSmithKline Pharmaceuticals, 1250 S. Collegeville Rd, Collegeville, PA 19426-0989, USA.

The effect of topically applied retapamulin ointment was evaluated using various dosing regimens in the Staphylococcus aureus and Streptococcus pyogenes wound infection model. Retapamulin (1%, wt/wt) was efficacious using twice-daily (b.i.d.) applications for 4 or 5 days. These data underpinned the decision to evaluate 1% retapamulin b.i.d. in clinical trials.
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http://dx.doi.org/10.1128/AAC.00183-06DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1635196PMC
November 2006

Selection of retapamulin, a novel pleuromutilin for topical use.

Antimicrob Agents Chemother 2006 Nov;50(11):3882-5

Department of Microbiology Research, MMPD CEDD, GlaxoSmithKline Pharmaceuticals, 1250 S. Collegeville Rd, Collegeville, PA 19426-0989, USA.

The in vitro activity of retapamulin was determined and compared to that of topical and community antibiotics. The MIC(90)s of retapamulin against Staphylococcus aureus and Streptococcus pyogenes were 0.12 microg/ml and 0.016 microg/ml, respectively. Retapamulin has a low propensity to select resistance and produces an in vitro postantibiotic effect.
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http://dx.doi.org/10.1128/AAC.00178-06DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1635201PMC
November 2006

Definition of the heterocyclic pharmacophore of bacterial methionyl tRNA synthetase inhibitors: potent antibacterially active non-quinolone analogues.

Bioorg Med Chem Lett 2004 Aug;14(15):3937-41

GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK.

Potent inhibitors of bacterial methionyl tRNA synthetase (MRS) have previously been reported. Through SAR of the quinolone moiety, the right hand side pharmacophore for MRS inhibition has now been defined as an NH-C-NH functionality in the context of a bicyclic heteroaromatic system. Potent antibacterial fused-pyrimidone and fused-imidazole analogues have been obtained and enantioselective activity demonstrated. Compound 46 demonstrated very good antibacterial activity against panels of antibiotic-resistant staphylococci and enterococci.
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http://dx.doi.org/10.1016/j.bmcl.2004.05.070DOI Listing
August 2004

New benzylidenethiazolidinediones as antibacterial agents.

Bioorg Med Chem Lett 2003 Nov;13(21):3771-3

Medicinal Chemistry Department, Microbial, Musculoskeletal and Proliferative Diseases, GlaxoSmithKline Pharmaceuticals, 1250 S. Collegeville Road, Collegeville, PA 19426, USA.

A novel benzylidenethiazolidinedione has been discovered with antimicrobial activity. Here, we present the results of a structure-activity study on this compound with respect to its antimicrobial activity.
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http://dx.doi.org/10.1016/j.bmcl.2003.07.010DOI Listing
November 2003

Variable sensitivity to bacterial methionyl-tRNA synthetase inhibitors reveals subpopulations of Streptococcus pneumoniae with two distinct methionyl-tRNA synthetase genes.

Antimicrob Agents Chemother 2003 Jun;47(6):1784-9

Department of Microbiology, Microbial, Musculoskeletal, and Proliferative Diseases Center of Excellence for Drug Discovery, GlaxoSmithKline, Collegeville, Pennsylvania 19426, USA.

As reported previously (J. R. Jarvest et al., J. Med. Chem. 45:1952-1962, 2002), potent inhibitors (at nanomolar concentrations) of Staphylococcus aureus methionyl-tRNA synthetase (MetS; encoded by metS1) have been derived from a high-throughput screening assay hit. Optimized compounds showed excellent activities against staphylococcal and enterococcal pathogens. We report on the bimodal susceptibilities of S. pneumoniae strains, a significant fraction of which was found to be resistant (MIC, > or =8 mg/liter) to these inhibitors. Using molecular genetic techniques, we have found that the mechanism of resistance is the presence of a second, distantly related MetS enzyme, MetS2, encoded by metS2. We present evidence that the metS2 gene is necessary and sufficient for resistance to MetS inhibitors. PCR analysis for the presence of metS2 among a large sample (n = 315) of S. pneumoniae isolates revealed that it is widespread geographically and chronologically, occurring at a frequency of about 46%. All isolates tested also contained the metS1 gene. Searches of public sequence databases revealed that S. pneumoniae MetS2 was most similar to MetS in Bacillus anthracis, followed by MetS in various non-gram-positive bacterial, archaeal, and eukaryotic species, with streptococcal MetS being considerably less similar. We propose that the presence of metS2 in specific strains of S. pneumoniae is the result of horizontal gene transfer which has been driven by selection for resistance to some unknown class of naturally occurring antibiotics with similarities to recently reported synthetic MetS inhibitors.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC155832PMC
http://dx.doi.org/10.1128/aac.47.6.1784-1789.2003DOI Listing
June 2003

Indole naphthyridinones as inhibitors of bacterial enoyl-ACP reductases FabI and FabK.

J Med Chem 2003 Apr;46(9):1627-35

GlaxoSmithKline Pharmaceuticals, 1250 South Collegeville Road, P.O. Box 5089, Collegeville, Pennsylvania 19426, USA.

Bacterial enoyl-ACP reductase (FabI) is responsible for catalyzing the final step of bacterial fatty acid biosynthesis and is an attractive target for the development of novel antibacterial agents. Previously we reported the development of FabI inhibitor 4 with narrow spectrum antimicrobial activity and in vivo efficacy against Staphylococcus aureus via intraperitoneal (ip) administration. Through iterative medicinal chemistry aided by X-ray crystal structure analysis, a new series of inhibitors has been developed with greatly increased potency against FabI-containing organisms. Several of these new inhibitors have potent antibacterial activity against multidrug resistant strains of S. aureus, and compound 30 demonstrates exceptional oral (po) in vivo efficacy in a S. aureus infection model in rats. While optimizing FabI inhibitory activity, compounds 29 and 30 were identified as having low micromolar FabK inhibitory activity, thereby increasing the antimicrobial spectrum of these compounds to include the FabK-containing pathogens Streptococcus pneumoniae and Enterococcus faecalis. The results described herein support the hypothesis that bacterial enoyl-ACP reductases are valid targets for antibacterial agents.
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http://dx.doi.org/10.1021/jm0204035DOI Listing
April 2003

Conformational restriction of methionyl tRNA synthetase inhibitors leading to analogues with potent inhibition and excellent gram-positive antibacterial activity.

Bioorg Med Chem Lett 2003 Apr;13(7):1265-8

GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex, UK.

Conformationally restricted analogues of the central linker unit of bacterial methionyl tRNA synthetase (MRS) inhibitors have been prepared. The (1S,2R)-cyclopentylmethyl moiety was identified as the preferred cyclic linker, with significant diastereo- and enantioselectivity of activity. Combination of this linker with an optimal substituted aryl right-hand side has resulted in a compound with exceptionally good antibacterial activity against staphylococci and enterococci, including antibiotic resistant strains.
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http://dx.doi.org/10.1016/s0960-894x(03)00093-3DOI Listing
April 2003

Optimisation of aryl substitution leading to potent methionyl tRNA synthetase inhibitors with excellent gram-positive antibacterial activity.

Bioorg Med Chem Lett 2003 Feb;13(4):665-8

GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK.

Optimisation of the left-hand-side aryl moiety of a file compound screening hit against Staphylococcus aureus methionyl tRNA synthetase led to the identification of a series of potent nanomolar inhibitors. The best compounds showed excellent antibacterial activity against staphylococcal and enterococcal pathogens, including strains resistant to clinical antibiotics.
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http://dx.doi.org/10.1016/s0960-894x(02)01027-2DOI Listing
February 2003

Defining and combating the mechanisms of triclosan resistance in clinical isolates of Staphylococcus aureus.

Antimicrob Agents Chemother 2002 Nov;46(11):3343-7

Microbial, Musculoskeletal and Proliferative Diseases CEDD. Computational and Structural Sciences, GlaxoSmithKline Pharmaceuticals, Collegeville, Pennsylvania 19426, USA.

The MICs of triclosan for 31 clinical isolates of Staphylococcus aureus were 0.016 micro g/ml (24 strains), 1 to 2 micro g/ml (6 strains), and 0.25 micro g/ml (1 strain). All the strains for which triclosan MICs were elevated (>0.016 micro g/ml) showed three- to fivefold increases in their levels of enoyl-acyl carrier protein (ACP) reductase (FabI) production. Furthermore, strains for which triclosan MICs were 1 to 2 micro g/ml overexpressed FabI with an F204C alteration. Binding studies with radiolabeled NAD(+) demonstrated that this change prevents the formation of the stable triclosan-NAD(+)-FabI complex, and both this alteration and its overexpression contributed to achieving MICs of 1 to 2 micro g/ml for these strains. Three novel, potent inhibitors of FabI (50% inhibitory concentrations, < or =64 nM) demonstrated up to 1,000-fold better activity than triclosan against the strains for which triclosan MICs were elevated. None of the compounds tested from this series formed a stable complex with NAD(+)-FabI. Consequently, although the overexpression of wild-type FabI gave rise to an increase in the MICs, as expected, overexpression of FabI with an F204C alteration did not cause an additional increase in resistance. Therefore, this work identifies the mechanisms of triclosan resistance in S. aureus, and we present three compounds from a novel chemical series of FabI inhibitors which have excellent activities against both triclosan-resistant and -sensitive clinical isolates of S. aureus.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC128739PMC
http://dx.doi.org/10.1128/aac.46.11.3343-3347.2002DOI Listing
November 2002

Discovery of a novel and potent class of FabI-directed antibacterial agents.

Antimicrob Agents Chemother 2002 10;46(10):3118-24

Microbial, Musculoskeletal and Proliferative Diseases Center of Excellence in Drug Discovery, GlaxoSmithKline Pharmaceuticals, Collegeville, Pennsylvania 19426, USA.

Bacterial enoyl-acyl carrier protein (ACP) reductase (FabI) catalyzes the final step in each elongation cycle of bacterial fatty acid biosynthesis and is an attractive target for the development of new antibacterial agents. High-throughput screening of the Staphylococcus aureus FabI enzyme identified a novel, weak inhibitor with no detectable antibacterial activity against S. aureus. Iterative medicinal chemistry and X-ray crystal structure-based design led to the identification of compound 4 [(E)-N-methyl-N-(2-methyl-1H-indol-3-ylmethyl)-3-(7-oxo-5,6,7,8-tetrahydro-1,8-naphthyridin-3-yl)acrylamide], which is 350-fold more potent than the original lead compound obtained by high-throughput screening in the FabI inhibition assay. Compound 4 has exquisite antistaphylococci activity, achieving MICs at which 90% of isolates are inhibited more than 500 times lower than those of nine currently available antibiotics against a panel of multidrug-resistant strains of S. aureus and Staphylococcus epidermidis. Furthermore, compound 4 exhibits excellent in vivo efficacy in an S. aureus infection model in rats. Biochemical and genetic approaches have confirmed that the mode of antibacterial action of compound 4 and related compounds is via inhibition of FabI. Compound 4 also exhibits weak FabK inhibitory activity, which may explain its antibacterial activity against Streptococcus pneumoniae and Enterococcus faecalis, which depend on FabK and both FabK and FabI, respectively, for their enoyl-ACP reductase function. These results show that compound 4 is representative of a new, totally synthetic series of antibacterial agents that has the potential to provide novel alternatives for the treatment of S. aureus infections that are resistant to our present armory of antibiotics.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC128775PMC
http://dx.doi.org/10.1128/aac.46.10.3118-3124.2002DOI Listing
October 2002

Discovery of aminopyridine-based inhibitors of bacterial enoyl-ACP reductase (FabI).

J Med Chem 2002 Jul;45(15):3246-56

GlaxoSmithKline Pharmaceuticals, 1250 South Collegeville Road, P.O. Box 5089, Collegeville, PA 19426, USA.

Bacterial enoyl-ACP reductase (FabI) catalyzes the final step in each cycle of bacterial fatty acid biosynthesis and is an attractive target for the development of new antibacterial agents. Our efforts to identify potent, selective FabI inhibitors began with screening of the GlaxoSmithKline proprietary compound collection, which identified several small-molecule inhibitors of Staphylococcus aureus FabI. Through a combination of iterative medicinal chemistry and X-ray crystal structure based design, one of these leads was developed into the novel aminopyridine derivative 9, a low micromolar inhibitor of FabI from S. aureus (IC(50) = 2.4 microM) and Haemophilus influenzae (IC(50) = 4.2 microM). Compound 9 has good in vitro antibacterial activity against several organisms, including S. aureus (MIC = 0.5 microg/mL), and is effective in vivo in a S. aureus groin abscess infection model in rats. Through FabI overexpressor and macromolecular synthesis studies, the mode of action of 9 has been confirmed to be inhibition of fatty acid biosynthesis via inhibition of FabI. Taken together, these results support FabI as a valid antibacterial target and demonstrate the potential of small-molecule FabI inhibitors for the treatment of bacterial infections.
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http://dx.doi.org/10.1021/jm020050+DOI Listing
July 2002

Identification of a series of tricyclic natural products as potent broad-spectrum inhibitors of metallo-beta-lactamases.

Antimicrob Agents Chemother 2002 Jun;46(6):1880-6

Microbial, Musculoskeletal and Proliferative Diseases CEDD (UP1345), GlaxoSmithKline, Collegeville, Pennsylvania 19426-0989, USA.

This work describes the discovery and characterization of a novel series of tricyclic natural product-derived metallo-beta-lactamase inhibitors. Natural product screening of the Bacillus cereus II enzyme identified an extract from a strain of Chaetomium funicola with inhibitory activity against metallo-beta-lactamases. SB236050, SB238569, and SB236049 were successfully extracted and purified from this extract. The most active of these compounds was SB238569, which possessed K(i) values of 79, 17, and 3.4 microM for the Bacillus cereus II, Pseudomonas aeruginosa IMP-1, and Bacteroides fragilis CfiA metallo-beta-lactamases, respectively, yet none of the compounds exhibited any inhibitory activity against the Stenotrophomonas maltophilia L-1 metallo-beta-lactamase (50% inhibitory concentration > 1,000 microM). The lack of activity against angiotensin-converting enzyme and serine beta-lactamases demonstrated the selective nature of these compounds. The crystal structure of SB236050 complexed in the active site of CfiA has been obtained to a resolution of 2.5 A. SB236050 exhibits key polar interactions with Lys184, Asn193, and His162 and a stacking interaction with the indole ring of Trp49 in the flap, which is in the closed conformation over the active site groove. SB236050 and SB238569 also demonstrate good antibacterial synergy with meropenem. Eight micrograms of SB236050 per ml gave rise to an eightfold drop in the MIC of meropenem for two clinical isolates of B. fragilis producing CfiA, making these strains sensitive to meropenem (MIC < or = 4 microg/ml). Consequently, this series of metallo-beta-lactamase inhibitors exhibit the most promising antibacterial synergy activity so far observed against organisms producing metallo-beta-lactamases.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC127244PMC
http://dx.doi.org/10.1128/aac.46.6.1880-1886.2002DOI Listing
June 2002

Nanomolar inhibitors of Staphylococcus aureus methionyl tRNA synthetase with potent antibacterial activity against gram-positive pathogens.

J Med Chem 2002 May;45(10):1959-62

Potent nanomolar inhibitors of Staphylococcus aureus methionyl tRNA synthetase have been derived from a file compound high throughput screening hit. Optimized compounds show excellent antibacterial activity against staphylococcal and enterococcal pathogens, including strains resistant to clinical antibiotics. Compound 11 demonstrated in vivo efficacy in an S. aureus rat abscess infection model.
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http://dx.doi.org/10.1021/jm025502xDOI Listing
May 2002