Mitchell Catherine R, Folkard Melvyn, Joiner Michael C
Gray Cancer Institute, Mount Vernon Hospital, Northwood, United Kingdom.
Radiat Res. 2002 Sep;158(3):311-8. doi: 10.1667/0033-7587(2002)158[0311:eoetld]2.0.co;2.
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.
三种异步生长的人类肿瘤细胞系，即PC3（人类前列腺癌）、T98G和A7（人类胶质母细胞瘤）的细胞，先前已被证明对低急性单剂量表现出低剂量超放射敏感性，用（60）Coγ射线以低剂量率（2 cGy - 1 Gy h(-1)）进行照射。这些细胞系并未表现出剂量率节省效应，而是在低于1 Gy h(-1)的剂量率下对细胞存活呈现出剂量率反比效应，即剂量率降低导致单位剂量的细胞杀伤增加。一种超放射敏感性阴性细胞系U373MG未表现出剂量率反比效应。细胞周期分析表明，这种剂量率反比效应并非由于细胞在G(2)/M期积累或其他细胞周期扰动所致。处于可逆性G(1)期停滞的T98G细胞在低于30 cGy h(-1)的剂量率下也表现出剂量率反比效应，但当剂量率从60 cGy h(-1)降至30 cGy h(-1)时则表现出节省效应。我们得出结论，连续照射中的这种剂量率反比效应反映了同一细胞系对非常小的急性单剂量所表现出的超放射敏感性。
