title: Effects of exposure to low-dose-rate (60)co gamma rays on human tumor cells in vitro.
abstract: Cells of three asynchronously growing human tumor cell lines, PC3 (human prostate carcinoma), T98G and A7 (human glioblastomas), which have been shown previously to demonstrate low-dose hyper-radiosensitivity to low acute single doses, were irradiated with (60)Co gamma rays at low dose rates (2 cGy-1 Gy h(-1)). Instead of a dose-rate sparing response, these cell lines demonstrated an inverse dose-rate effect on cell survival at dose rates below 1 Gy h(-1), whereby a decrease in dose rate resulted in an increase in cell killing per unit dose. A hyper-radiosensitivity-negative cell line, U373MG, did not demonstrate an inverse dose-rate effect. Analysis of the cell cycle indicated that this inverse dose-rate effect was not due to accumulation of cells in G(2)/M phase or to other cell cycle perturbations. T98G cells in reversible G(1)-phase arrest also showed an inverse dose-rate effect at dose rates below 30 cGy h(-1) but a sparing effect as the dose rate was reduced from 60 to 30 cGy h(-1). We conclude that this inverse dose-rate effect in continuous exposures reflects the hyper-radiosensitivity seen in the same cell lines in response to very small acute single doses.
authors.affiliation: Gray Cancer Institute, Mount Vernon Hospital, Northwood, United Kingdom.
authors.forename: Catherine R
authors.initials: CR
authors.lastname: Mitchell
authors.forename: Melvyn
authors.initials: M
authors.lastname: Folkard
authors.forename: Michael C
authors.initials: MC
authors.lastname: Joiner
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology; D001932:Brain Neoplasms / Q000473:pathology; D002453:Cell Cycle / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D003037:Cobalt Radioisotopes; D004260:DNA Repair; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D005909:Glioblastoma / Q000473:pathology; D006801:Humans; D008297:Male; D008954:Models, Biological; D011471:Prostatic Neoplasms / Q000473:pathology; D011836:Radiation Tolerance; D014407:Tumor Cells, Cultured / Q000528:radiation effects*
chemical_list: D003037:Cobalt Radioisotopes