title: Residual gammaH2AX foci as an indication of lethal DNA lesions.
abstract: BACKGROUND
  Evidence suggests that tumor cells exposed to some DNA damaging agents are more likely to die if they retain microscopically visible gammaH2AX foci that are known to mark sites of double-strand breaks. This appears to be true even after exposure to the alkylating agent MNNG that does not cause direct double-strand breaks but does produce gammaH2AX foci when damaged DNA undergoes replication.
  
  
  METHODS
  To examine this predictive ability further, SiHa human cervical carcinoma cells were exposed to 8 DNA damaging drugs (camptothecin, cisplatin, doxorubicin, etoposide, hydrogen peroxide, MNNG, temozolomide, and tirapazamine) and the fraction of cells that retained gammaH2AX foci 24 hours after a 30 or 60 min treatment was compared with the fraction of cells that lost clonogenicity. To determine if cells with residual repair foci are the cells that die, SiHa cervical cancer cells were stably transfected with a RAD51-GFP construct and live cell analysis was used to follow the fate of irradiated cells with RAD51-GFP foci.
  
  
  RESULTS
  For all drugs regardless of their mechanism of interaction with DNA, close to a 1:1 correlation was observed between clonogenic surviving fraction and the fraction of cells that retained gammaH2AX foci 24 hours after treatment. Initial studies established that the fraction of cells that retained RAD51 foci after irradiation was similar to the fraction of cells that retained gammaH2AX foci and subsequently lost clonogenicity. Tracking individual irradiated live cells confirmed that SiHa cells with RAD51-GFP foci 24 hours after irradiation were more likely to die.
  
  
  CONCLUSIONS
  Retention of DNA damage-induced gammaH2AX foci appears to be indicative of lethal DNA damage so that it may be possible to predict tumor cell killing by a wide variety of DNA damaging agents simply by scoring the fraction of cells that retain gammaH2AX foci.
authors.affiliation: Medical Biophysics Department, BC Cancer Agency Research Centre, 675 W, 10th Ave, Vancouver, BC V5Z 1L3, Canada.
authors.forename: Judit P
authors.initials: JP
authors.lastname: Banáth
authors.forename: Dmitry
authors.initials: D
authors.lastname: Klokov
authors.forename: Susan H
authors.initials: SH
authors.lastname: MacPhail
authors.forename: C Adriana
authors.initials: CA
authors.lastname: Banuelos
authors.forename: Peggy L
authors.initials: PL
authors.lastname: Olive
mesh_terms: D000818:Animals; D016466:CHO Cells; D045744:Cell Line, Tumor; D020552:Comet Assay; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D005260:Female; D005434:Flow Cytometry / Q000379:methods; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006657:Histones / Q000378:metabolism*; D006801:Humans; D051135:Rad51 Recombinase / Q000378:metabolism; D013997:Time Factors; D002583:Uterine Cervical Neoplasms / Q000235:genetics
chemical_list: C468783:H2AX protein, human; D006657:Histones; D049452:Green Fluorescent Proteins; C495153:RAD51 protein, human; D051135:Rad51 Recombinase