title: In vitro biological evaluation of novel broad-spectrum isothiazolone inhibitors of bacterial type II topoisomerases.
abstract: To evaluate the in vitro biological properties of a novel class of isothiazolone inhibitors of the bacterial type II topoisomerases.
  
  
  
  Inhibition of DNA gyrase and topoisomerase IV activity was assessed using DNA supercoiling and decatenation assays. MIC and MBC were determined according to CLSI guidelines. Antibacterial combinations were assessed using a two-dimensional chequerboard MIC method. Spontaneous frequency of resistance was measured at various multiples of the MIC. Resistant mutants were generated by serial passage at subinhibitory concentrations of antibacterials and genetic mutations were determined through whole genome sequencing. Mammalian cytotoxicity was evaluated using the HepG2 cell line.
  
  
  
  Representative isothiazolone compound REDX04957 and its enantiomers (REDX05967 and REDX05990) showed broad-spectrum bactericidal activity against the ESKAPE organisms, with the exception of Enterococcus spp., as well as against a variety of other human bacterial pathogens. Compounds retained activity against quinolone-resistant strains harbouring GyrA S83L and D87G mutations (MIC ≤4 mg/L). Compounds inhibited the supercoiling activity of wild-type DNA gyrase and the decatenation function of topoisomerase IV. Frequency of resistance of REDX04957 at 4× MIC was <9.1 × 10(-9). Against a panel of recent MDR isolates, REDX05967 demonstrated activity against Acinetobacter baumannii with MIC50 and MIC90 of 16 and 64 mg/L, respectively. Compounds showed a lack of cytotoxicity against HepG2 cells at 128 mg/L.
  
  
  
  Isothiazolone compounds show potent activity against Gram-positive and -negative pathogens with a dual targeting mechanism-of-action and a low potential for resistance development, meriting their continued investigation as broad-spectrum antibacterial agents.
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK c.charrier@redxpharma.com.
authors.forename: Cédric
authors.initials: C
authors.lastname: Charrier
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Salisbury
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Savage
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Moyo
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Henry
authors.initials: H
authors.lastname: Forward
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Nicola
authors.initials: N
authors.lastname: Ooi
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Cheung
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Metzger
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: David
authors.initials: D
authors.lastname: McGarry
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Rolf
authors.initials: R
authors.lastname: Walker
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Ian R
authors.initials: IR
authors.lastname: Cooper
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Ratcliffe
authors.affiliation: Redx Pharma, Alderley Park, Cheshire SK10 4TG, UK.
authors.forename: Neil R
authors.initials: NR
authors.lastname: Stokes
mesh_terms: D040981:Acinetobacter baumannii / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015373:Bacterial Typing Techniques; D027081:DNA Gyrase / Q000378:metabolism; D027101:DNA Topoisomerase IV / Q000037:antagonists & inhibitors; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism; D016983:Enterococcus / Q000187:drug effects / Q000201:enzymology; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000201:enzymology; D006094:Gram-Positive Bacteria / Q000187:drug effects* / Q000201:enzymology; D056945:Hep G2 Cells; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation; D013844:Thiazoles / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D059005:Topoisomerase II Inhibitors / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D013844:Thiazoles; D059005:Topoisomerase II Inhibitors; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II