title: Hypoxic cell turnover in different solid tumor lines.
abstract: OBJECTIVE
  Most solid tumors contain hypoxic cells, and the amount of tumor hypoxia has been shown to have a negative impact on the outcome of radiotherapy. The efficacy of combined modality treatments depends both on the sequence and timing of the treatments. Hypoxic cell turnover in tumors may be important for optimal scheduling of combined modality treatments, especially when hypoxic cell targeting is involved.
  
  
  METHODS
  Previously we have shown that a double bioreductive hypoxic marker assay could be used to detect changes of tumor hypoxia in relation to the tumor vasculature after carbogen and hydralazine treatments. This assay was used in the current study to establish the turnover rate of hypoxic cells in three different tumor models. The first hypoxic marker, pimonidazole, was administered at variable times before tumor harvest, and the second hypoxic marker, CCI-103F, was injected at a fixed time before harvest. Hypoxic cell turnover was defined as loss of pimonidazole (first marker) relative to CCI-103F (second marker).
  
  
  RESULTS
  The half-life of hypoxic cell turnover was 17 h in the murine C38 colon carcinoma line, 23 h and 49 h in the human xenograft lines MEC82 and SCCNij3, respectively. Within 24 h, loss of pimonidazole-stained areas in C38 and MEC82 occurred concurrent with the appearance of pimonidazole positive cell debris in necrotic regions. In C38 and MEC82, most of the hypoxic cells had disappeared after 48 h, whereas in SCCNij3, viable cells that had been labeled with pimonidazole were still observed after 5 days.
  
  
  CONCLUSIONS
  The present study demonstrates that the double hypoxia marker assay can be used to study changes in both the proportion of hypoxic tumor cells and their lifespan at the same time. The present study shows that large differences in hypoxic cell turnover rates may exist among tumor lines, with half-lives ranging from 17-49 h.
authors.affiliation: Department of Radiation Oncology, Radboud University Medical Center Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands. a.ljungkvist@rther.umcn.nl
authors.forename: Anna S E
authors.initials: AS
authors.lastname: Ljungkvist
authors.forename: Johan
authors.initials: J
authors.lastname: Bussink
authors.forename: Johannes H A M
authors.initials: JH
authors.lastname: Kaanders
authors.forename: Paulus F J W
authors.initials: PF
authors.lastname: Rijken
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Begg
authors.forename: James A
authors.initials: JA
authors.lastname: Raleigh
authors.forename: Albert J
authors.initials: AJ
authors.lastname: van der Kogel
mesh_terms: D000818:Animals; D001562:Benzimidazoles / Q000008:administration & dosage / Q000032:analysis; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D002470:Cell Survival; D004396:Coloring Agents / Q000008:administration & dosage / Q000032:analysis*; D006207:Half-Life; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009369:Neoplasms / Q000098:blood supply / Q000473:pathology*; D009593:Nitroimidazoles / Q000008:administration & dosage / Q000032:analysis*; D013997:Time Factors; D005466:Fluorocarbons
chemical_list: D001562:Benzimidazoles; D004396:Coloring Agents; D009593:Nitroimidazoles; C049948:CCI 103F; D005466:Fluorocarbons; C033815:pimonidazole; C017807:bisbenzimide ethoxide trihydrochloride