title: Tissue pO2 of orthotopic 9L and C6 gliomas and tumor-specific response to radiotherapy and hyperoxygenation.
abstract: OBJECTIVE
  Tumor hypoxia is a well-known therapeutic problem; however, a lack of methods for repeated measurements of glioma partial pressure of oxygen (pO(2)) limits the ability to optimize the therapeutic approaches. We report the effects of 9.3 Gy of radiation and carbogen inhalation on orthotopic 9L and C6 gliomas and on the contralateral brain pO(2) in rats using a new and potentially widely useful method, multisite in vivo electron paramagnetic resonance oximetry.
  
  
  METHODS
  Intracerebral 9L and C6 tumors were established in the left hemisphere of syngeneic rats, and electron paramagnetic resonance oximetry was successfully used for repeated tissue pO(2) measurements after 9.3 Gy of radiation and during carbogen breathing for 5 consecutive days.
  
  
  RESULTS
  Intracerebral 9L gliomas had a pO(2) of 30-32 mm Hg and C6 gliomas were relatively hypoxic, with a pO(2) of 12-14 mm Hg (p < 0.05). The tissue pO(2) of the contralateral brain was 40-45 mm Hg in rats with either 9L or C6 gliomas. Irradiation resulted in a significant increase in pO(2) of the 9L gliomas only. A significant increase in the pO(2) of the 9L and C6 gliomas was observed in rats breathing carbogen, but this effect decreased during 5 days of repeated experiments in the 9L gliomas.
  
  
  CONCLUSIONS
  These results highlight the tumor-specific effect of radiation (9.3.Gy) on tissue pO(2) and the different responses to carbogen inhalation. The ability of electron paramagnetic resonance oximetry to provide direct repeated measurements of tissue pO(2) could have a vital role in understanding the dynamics of hypoxia during therapy that could then be optimized by scheduling doses at times of improved tumor oxygenation.
authors.affiliation: EPR Center for Viable Systems, Dartmouth Medical School, Hanover, NH 03755, USA. Nadeem.khan@dartmouth.edu
authors.forename: Nadeem
authors.initials: N
authors.lastname: Khan
authors.forename: Hongbin
authors.initials: H
authors.lastname: Li
authors.forename: Huagang
authors.initials: H
authors.lastname: Hou
authors.forename: Jean P
authors.initials: JP
authors.lastname: Lariviere
authors.forename: David J
authors.initials: DJ
authors.lastname: Gladstone
authors.forename: Eugene
authors.initials: E
authors.lastname: Demidenko
authors.forename: Harold M
authors.initials: HM
authors.lastname: Swartz
mesh_terms: D000818:Animals; D001932:Brain Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D002245:Carbon Dioxide / Q000008:administration & dosage*; D015687:Cell Hypoxia; D016009:Chi-Square Distribution; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005910:Glioma / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D010092:Oximetry / Q000379:methods; D010100:Oxygen / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism*; D010101:Oxygen Consumption; D010313:Partial Pressure; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage*; D011879:Radiotherapy Dosage; D051381:Rats; D011916:Rats, Inbred F344; D017208:Rats, Wistar; D047368:Tumor Burden
chemical_list: D011838:Radiation-Sensitizing Agents; D002245:Carbon Dioxide; C011700:carbogen; D010100:Oxygen