title: Intrinsic radiosensitivity and repair of sublethal radiation-induced damage in canine osteosarcoma cell lines.
abstract: OBJECTIVE
  To characterize the radiosensitivity and capacity for sublethal damage repair (SLDR) of radiation-induced injury in 4 canine osteosarcoma cell lines.
  
  
  METHODS
  4 canine osteosarcoma cell lines (HMPOS, POS, COS 31, and D17).
  
  
  METHODS
  A clonogenic colony-forming assay was used to evaluate the cell lines' intrinsic radiosensitivities and SLDR capacities. Dose-response curves for the cell lines were generated by fitting the surviving fractions after radiation doses of 0 (control cells), 1, 2, 3, 6, and 9 Gy to a linear quadratic model. To evaluate SLDR, cell lines were exposed to 2 doses of 3 Gy (split-dose experiments) at an interval of 0 (single 6-Gy dose), 2, 4, 6, or 24 hours, after which the surviving fractions were assessed.
  
  
  RESULTS
  Mean surviving fraction did not differ significantly among the 4 cell lines at the radiation doses tested. Mean surviving fraction at 2 Gy was high (0.62), and the alpha/beta ratios (predictor of tissue sensitivity to radiation therapy) for the cell lines were low (mean ratio, 3.47). The split-dose experiments revealed a 2.8- to 3.9-fold increase in cell survival when the radiation doses were applied at an interval of 24 hours, compared with cell survival after radiation doses were applied consecutively (0-hour interval).
  
  
  CONCLUSIONS
  Results indicated that these canine osteosarcoma cell lines are fairly radioresistant; alpha/beta ratios were similar to those of nonneoplastic, late-responding tissues. Future clinical investigations should involve increasing the fraction size in a manner that maximizes tumor killing without adverse effects on the nonneoplastic surrounding tissues.
authors.affiliation: Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Courtney L
authors.initials: CL
authors.lastname: Fitzpatrick
authors.forename: James P
authors.initials: JP
authors.lastname: Farese
authors.forename: Rowan J
authors.initials: RJ
authors.lastname: Milner
authors.forename: Marc E
authors.initials: ME
authors.lastname: Salute
authors.forename: Didier A
authors.initials: DA
authors.lastname: Rajon
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Morris
authors.forename: Francis J
authors.initials: FJ
authors.lastname: Bova
authors.forename: David M
authors.initials: DM
authors.lastname: Lurie
authors.forename: Dietmar W
authors.initials: DW
authors.lastname: Siemann