title: Induction of lethal bystander effects in human breast cancer cell cultures by DNA-incorporated Iodine-125 depends on phenotype.
abstract: OBJECTIVE
  This study uses a three-dimensional cell culture model to investigate lethal bystander effects in human breast cancer cell cultures (MCF-7, MDA-MB-231) treated with (125)I-labeled 5-iodo-2 -deoxyuridine ((125)IdU). These breast cancer cell lines respectively form metastatic xenografts in nude mice in an estrogen-dependent and independent manner.
  
  
  METHODS
  In the present study, these cells were cultured in loosely-packed three-dimensional architecture in a Cytomatrix™ carbon scaffold. Cultures were pulse-labeled for 3 h with (125)IdU to selectively irradiate a minor fraction of cells, and simultaneously co-pulse-labeled with 0.04 mM 5-ethynyl-2'-deoxyuridine (EdU) to identify the radiolabeled cells using Click-iT(®) EdU and flow cytometry. The cultures were then washed and incubated for 48 h. The cells were then harvested, serially diluted, and seeded for colony formation. Aliquots of cells were subjected to flow cytometry to determine the percentage of cells labeled with (125)IdU/EdU. Additional aliquots were used to determine the mean (125)I activity per labeled cell. The percentage of labeled cells was about 15% and 10% for MCF-7 and MDA cells, respectively. This created irradiation conditions wherein the cross-dose to unlabeled cells was small relative to the self-dose to labeled cells. The surviving fraction relative to EdU-treated controls was measured.
  
  
  RESULTS
  Survival curves indicated significant lethal bystander effect in MCF-7 cells, however, no significant lethal bystander effect was observed in MDA-MB-231 cells.
  
  
  CONCLUSIONS
  These studies demonstrate the capacity of (125)IdU to induce lethal bystander effects in human breast cancer cells and suggest that the response depends on phenotype.
authors.affiliation: Division of Radiation Research, Department of Radiology, New Jersey Medical School Cancer Center, University of Medicine & Dentistry of New Jersey, Newark, New Jersey 07103, USA. jakudugu@sun.ac.za
authors.forename: John M
authors.initials: JM
authors.lastname: Akudugu
authors.forename: Edouard I
authors.initials: EI
authors.lastname: Azzam
authors.forename: Roger W
authors.initials: RW
authors.lastname: Howell
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000473:pathology*; D024201:Bystander Effect / Q000528:radiation effects*; D016923:Cell Death / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D004247:DNA / Q000378:metabolism*; D003857:Deoxyuridine / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D007065:Idoxuridine / Q000378:metabolism; D007457:Iodine Radioisotopes / Q000378:metabolism; D061986:MCF-7 Cells; D051379:Mice; D010641:Phenotype
chemical_list: D007457:Iodine Radioisotopes; D004247:DNA; C031086:5-ethynyl-2'-deoxyuridine; D007065:Idoxuridine; D003857:Deoxyuridine