Low-Dose Ionizing Radiation Decreases the Frequency of Neoplastic Transformation to a Level below the Spontaneous Rate in C3H 10T1/2 Cells

• Published in: Radiation research 1996-10, Vol.146 (4), p.369-373
• Main Authors: Azzam, E. I., de Toledo, S. M., Raaphorst, G. P., Mitchel, R. E. J.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cell Line; Cell Transformation, Neoplastic - radiation effects; Dosage; Dose-Response Relationship, Radiation; Embryonic cells; Flasks; Fundamental and applied biological sciences. Psychology; Gamma Rays; Humans; Interphase; Ionizing radiation; Irradiation; Lymphocytes; Mice; Molecular and cellular biology; Molecular genetics; Mutagenesis. Repair; Neoplasms, Radiation-Induced - etiology; Neoplasms, Radiation-Induced - prevention & control; Radiation dosage; Radiation protection; Radiation Tolerance; Radiobiology; Radiotherapy; Rapid Communications; Risk Factors
• ISSN: 0033-7587; 1938-5404
• DOI: 10.2307/3579298

We have previously shown that chronic exposure of plateau-phase C3H 10T1/2 cells to 60 Co γ radiation at doses as low as 10 cGy protected the cells against neoplastic transformation by a subsequent large acute radiation exposure. We have also shown that this induced resistance to neoplastic transformation correlated with an increased ability to repair radiation-induced chromosome breaks. We now show that a single exposure of quiescent cells to doses as low as 0.1 cGy also reduces the risk of neoplastic transformation, from the spontaneous level to a rate three- to fourfold below that level. Higher doses, up to 10 cGy at the same dose rate (0.24 cGy/min), did not reduce the neoplastic transformation frequency further. This protective effect was seen only in irradiated cells that were allowed to incubate at 37°C before release from contact inhibition. Cells released into low-density subcultures immediately after irradiation had unchanged neoplastic transformation frequencies. These results demonstrate that low or chronic exposure to radiation can induce processes which protect the cell against naturally occurring as well as radiation-induced alterations that lead to cell transformation. If similar processes are induced in human cells, the results also suggest that a single low dose, at background or occupational exposure levels, may in some circumstances reduce rather than increase cancer risk, a conclusion inconsistent with the linear no-threshold model of cancer risk from radiation.