title: Does heterogeneity of pimonidazole labelling correspond to the heterogeneity of radiation-response of FaDu human squamous cell carcinoma?
abstract: OBJECTIVE
  Pimonidazole is a marker for hypoxic cells which are radioresistant and thereby important for the outcome of radiotherapy. The present study evaluates heterogeneity in pimonidazole binding within and between tumours and relates the results to the heterogeneity of radiation response in the same tumour cell line.
  
  
  METHODS
  FaDu, a poorly differentiated human squamous cell carcinoma line, was transplanted subcutaneously into the right hind-leg of NMRI nude mice. Tumours were irradiated with graded single doses either under ambient or clamped blood flow conditions and local tumour control was evaluated after 120 days. Complete dose-response curves for local tumour control were generated and the slope, a measure of heterogeneity of radiation response, was determined. In parallel, 12 unirradiated tumours were examined histologically. Seven serial 10 microm cross-sections per tumour were evaluated using fluorescence microscopy and computerised image analysis to determine the pimonidazole hypoxic fraction (pHF). Heterogeneity in pHF was quantified by its coefficient of variation (CV). Poisson-based model calculations considering the intertumoural heterogeneity of pHF were performed and the slopes of the predicted and the observed dose-response curves were compared.
  
  
  RESULTS
  The mean pHF was 11% [CV 50%] when one central section per tumour was evaluated. Measurements of multiple sections per tumour resulted in a mean pHF of 12% [CV 46%] (P=0.7). Intertumoural heterogeneity in pHF was more pronounced than heterogeneity in individual tumours by a factor of 2. Model calculations based on the variability in pHF resulted in similar slopes of the dose-response curve for local tumour control in comparison with the observed slope when the heterogeneity in an unknown and arbitrarily chosen additional radiobiologically relevant parameter, in this example clonogen density, was taken into account.
  
  
  CONCLUSIONS
  While the average pimonidazole hypoxic fraction in FaDu tumours corresponds well to the radiobiological hypoxic fraction, the variability of pHF in FaDu tumours was not sufficient to explain the heterogeneity of radiation response in the same tumour line. Information on at least one additional parameter is expected to substantially enhance the predictive power of histological markers of tumour hypoxia.
authors: Department of Radiation Oncology, Medical Faculty Carl Gustav Carus, University of Technology Dresden, Germany.
authors: Ala
authors: A
authors: Yaromina
authors: Tobias
authors: T
authors: Hölscher
authors: Wolfgang
authors: W
authors: Eicheler
authors: Andrea
authors: A
authors: Rosner
authors: Mechthild
authors: M
authors: Krause
authors: Franziska
authors: F
authors: Hessel
authors: Cordula
authors: C
authors: Petersen
authors: Howard D
authors: HD
authors: Thames
authors: Michael
authors: M
authors: Baumann
authors: Daniel
authors: D
authors: Zips
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000098:blood supply / Q000378:metabolism / Q000532:radiotherapy*; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009593:Nitroimidazoles; D011836:Radiation Tolerance
chemical_list: D009593:Nitroimidazoles; C033815:pimonidazole