title: Repair of potentially lethal radiation damage in human squamous carcinoma cells after chronic hypoxia.
abstract: OBJECTIVE
  To examine the repair of radiation induced potentially lethal damage in A431 and CaSki cells after chronic hypoxia.
  
  
  METHODS
  Cells in exponential phase are subjected to hypoxia (< 10 ppm oxygen) for up to 12 h and then are allowed to re-oxygenate in air for up to 4 h. Cells are then irradiated with gamma rays. Cell survivals are measured by clonogenic assay immediately and at different times after irradiation.
  
  
  RESULTS
  Compared to aerobic controls, an increase in the level of potentially lethal damage repair (PLDR) is demonstrated in A431 cells reoxygenated for 10 min after > 4 h of hypoxia. The repair returned to aerobic control level by 3 h of reoxygenation. PLDR of A431 cells reached maximum at about 9 h after irradiation in cells reoxygenated for 10 min after hypoxia. However, the repair is maximum at 6 h in cells reoxygenated for 3 h after hypoxia and in aerobic cells not previously exposed to hypoxia. Reoxygenation after chronic hypoxia did not affect the PLDR capacity and repair kinetics of CaSki cells.
  
  
  CONCLUSIONS
  The results suggest that radiosensitization by reoxygenation after chronic hypoxia is not related to inhibition of PLDR.
authors.affiliation: Department of Cell and Molecular Biology, SRI International, Menlo Park, CA.
authors.forename: T T
authors.initials: TT
authors.lastname: Kwok
authors.forename: R M
authors.initials: RM
authors.lastname: Sutherland
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D015687:Cell Hypoxia; D002470:Cell Survival / Q000528:radiation effects*; D006801:Humans; D011836:Radiation Tolerance; D014407:Tumor Cells, Cultured