title: Effect of phenazine compounds XR11576 and XR5944 on DNA topoisomerases.
abstract: OBJECTIVE
  Previous in vitro cleavage data showed that XR11576 and XR5944 stabilised topoisomerase I and topoisomerase II complexes on DNA in a dose-dependent fashion. However, some studies indicated a possible topoisomerase-independent mechanism of action for these drugs.
  
  
  METHODS
  Three methods, the TARDIS assay, immunoband depletion and the K(+)/SDS assay have been used to assess topoisomerase complex formation induced by XR11576 or XR5944 in human leukaemic K562 cells.
  
  
  RESULTS
  TARDIS and immunoband depletion assays demonstrated that XR11576 and XR5944 induced complex formation for both topoisomerase I and topoisomerase II (alpha and beta) in a dose- and time-dependent manner, following exposure times of 24 and 48 h at concentrations of 1 or 10 microM. The K(+)/SDS assay showed the formation of protein/DNA complexes after a 1 h exposure to 1 or 10 muM XR11576.
  
  
  CONCLUSIONS
  Our data confirm that XR11576 or XR5944 can form topoisomerase complexes, after long periods of exposure.
authors.affiliation: Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Newcastle Upon Tyne, NE2 4HH, UK.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Jobson
authors.forename: Elaine
authors.initials: E
authors.lastname: Willmore
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Tilby
authors.forename: Prakash
authors.initials: P
authors.lastname: Mistry
authors.forename: Peter
authors.initials: P
authors.lastname: Charlton
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Austin
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D016466:CHO Cells; D002478:Cells, Cultured; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000737:chemistry / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007118:Immunoassay; D020014:K562 Cells; D010619:Phenazines / Q000494:pharmacology*; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors
chemical_list: C446952:4-methoxybenzo(a)phenazine-11-carboxylic acid (2-(dimethylamino)-1-methylethyl)amide; C468783:H2AX protein, human; D006657:Histones; D010619:Phenazines; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; C434883:XR5944; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II