title: Antistaphylococcal activity of DNA-interactive pyrrolobenzodiazepine (PBD) dimers and PBD-biaryl conjugates.
abstract: OBJECTIVE
  Pyrrolobenzodiazepine (PBD) dimers, tethered through inert propyldioxy or pentyldioxy linkers, possess potent bactericidal activity against a range of Gram-positive bacteria by virtue of their capacity to cross-link duplex DNA in sequence-selective fashion. Here we attempt to improve the antibacterial activity and cytotoxicity profile of PBD-containing conjugates by extension of dimer linkers and replacement of one PBD unit with phenyl-substituted or benzo-fused heterocycles that facilitate non-covalent interactions with duplex DNA.
  
  
  METHODS
  DNase I footprinting was used to identify high-affinity DNA binding sites. A staphylococcal gene microarray was used to assess epidemic methicillin-resistant Staphylococcus aureus 16 phenotypes induced by PBD conjugates. Molecular dynamics simulations were employed to investigate the accommodation of compounds within the DNA helix.
  
  
  RESULTS
  Increasing the length of the linker in PBD dimers led to a progressive reduction in antibacterial activity, but not in their cytotoxic capacity. Complex patterns of DNA binding were noted for extended PBD dimers. Modelling of DNA strand cross-linking by PBD dimers indicated distortion of the helix. A majority (26 of 43) of PBD-biaryl conjugates possessed potent antibacterial activity with little or no helical distortion and a more favourable cytotoxicity profile. Bactericidal activity of PBD-biaryl conjugates was determined by inability to excise covalently bound drug molecules from bacterial duplex DNA.
  
  
  CONCLUSIONS
  PBD-biaryl conjugates have a superior antibacterial profile compared with PBD dimers such as ELB-21. We have identified six PBD-biaryl conjugates as potential drug development candidates.
authors.affiliation: School of Pharmacy,  University College London, London WC1N 1AX,  UK.
authors.forename: Khondaker M
authors.initials: KM
authors.lastname: Rahman
authors.forename: Helena
authors.initials: H
authors.lastname: Rosado
authors.forename: Joao B
authors.initials: JB
authors.lastname: Moreira
authors.forename: Eva-Anne
authors.initials: EA
authors.lastname: Feuerbaum
authors.forename: Keith R
authors.initials: KR
authors.lastname: Fox
authors.forename: Eva
authors.initials: E
authors.lastname: Stecher
authors.forename: Philip W
authors.initials: PW
authors.lastname: Howard
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Gregson
authors.forename: Colin H
authors.initials: CH
authors.lastname: James
authors.forename: Maria
authors.initials: M
authors.lastname: de la Fuente
authors.forename: Denise E
authors.initials: DE
authors.lastname: Waldron
authors.forename: David E
authors.initials: DE
authors.lastname: Thurston
authors.forename: Peter W
authors.initials: PW
authors.lastname: Taylor
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D001569:Benzodiazepines / Q000378:metabolism / Q000494:pharmacology*; D001665:Binding Sites; D018983:DNA Footprinting; D004269:DNA, Bacterial / Q000378:metabolism; D020869:Gene Expression Profiling; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects*; D046228:Microarray Analysis; D050296:Microbial Viability / Q000187:drug effects; D056004:Molecular Dynamics Simulation; D011758:Pyrroles / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D011758:Pyrroles; C438462:pyrrolo(2,1-c)(1,4)benzodiazepine; D001569:Benzodiazepines