title: Activation of type II NADH dehydrogenase by quinolinequinones mediates antitubercular cell death.
abstract: Quinolinequinones (QQ) have been shown to inhibit the growth of mycobacterial species, but their mode(s) of action and molecular target(s) remain unknown. To facilitate further development of QQ as antimycobacterial drugs, we investigated the molecular mechanism and target of QQ in mycobacteria.
  
  
  
  Cell viability of Mycobacterium tuberculosis and Mycobacterium bovis bacillus Calmette-Guérin was determined in the presence of QQ8c, a representative QQ compound, and isoniazid, a frontline antitubercular drug. The effect of QQ8c on mycobacterial energetics was studied using inverted membrane vesicles. NADH oxidation and formation of reactive oxygen species (ROS) were measured in the presence and absence of KCN. Generation of ROS was measured via oxygen consumption in an oxygen electrode. The effects of QQ8c were compared with the antimycobacterial drug clofazimine in side-by-side experiments.
  
  
  
  QQ8c challenge resulted in complete sterilization of cultures with no refractory resistant population observed. QQ8c stimulated NADH oxidation by type II NADH dehydrogenase (NDH-2) and oxygen consumption in inverted membrane vesicles. Large quantities of ROS were produced in the presence of QQ8. Even when oxygen consumption was blocked with KCN, activation of NDH-2 by QQ8c occurred suggesting QQ8c was redox cycling.
  
  
  
  QQ8c targets NDH-2 of the mycobacterial respiratory chain leading to activation of NADH oxidation and generating bactericidal levels of ROS in a manner similar to, but more effectively than, the antimycobacterial drug clofazimine. Our results validate respiratory-generated ROS as an avenue for antimycobacterial drug development.
authors.affiliation: Department of Microbiology and Immunology, University of Otago, Dunedin 9054, New Zealand Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland, Private Bag 92019, Auckland 1042, New Zealand adam.heikal@otago.ac.nz.
authors.forename: Adam
authors.initials: A
authors.lastname: Heikal
authors.affiliation: Department of Microbiology and Immunology, University of Otago, Dunedin 9054, New Zealand.
authors.forename: Kiel
authors.initials: K
authors.lastname: Hards
authors.affiliation: Department of Microbiology and Immunology, University of Otago, Dunedin 9054, New Zealand.
authors.forename: Chen-Yi
authors.initials: CY
authors.lastname: Cheung
authors.affiliation: Department of Microbiology and Immunology, University of Otago, Dunedin 9054, New Zealand.
authors.forename: Ayana
authors.initials: A
authors.lastname: Menorca
authors.affiliation: School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand.
authors.forename: Mattie S M
authors.initials: MS
authors.lastname: Timmer
authors.affiliation: School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand Malaghan Institute of Medical Research, PO Box 7060, Wellington, New Zealand.
authors.forename: Bridget L
authors.initials: BL
authors.lastname: Stocker
authors.affiliation: Department of Microbiology and Immunology, University of Otago, Dunedin 9054, New Zealand Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland, Private Bag 92019, Auckland 1042, New Zealand.
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Cook
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D002991:Clofazimine / Q000494:pharmacology; D055808:Drug Discovery; D004579:Electron Transport / Q000187:drug effects; D004789:Enzyme Activation; D050296:Microbial Viability / Q000187:drug effects; D009163:Mycobacterium bovis / Q000187:drug effects / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D009245:NADH Dehydrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D015363:Quinolones / Q000494:pharmacology*; D011809:Quinones / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: C000621703:7-chloro-6-(2-chloroethylamino)-5,8-quinolinequinone; D000995:Antitubercular Agents; D001426:Bacterial Proteins; D015363:Quinolones; D011809:Quinones; D017382:Reactive Oxygen Species; D002991:Clofazimine; C088908:NADH dehydrogenase II; D009245:NADH Dehydrogenase