Low-dose ionizing radiation decreases the frequency of neoplastic transformation to a level below the spontaneous rate in C3H 10T 1/2 cells

Journal Article · Tue Oct 01 04:00:00 EDT 1996 · Radiation Research

DOI:https://doi.org/10.2307/3579298· OSTI ID:405359

Azzam, E I; Toledo, S.M. de; Mitchel, R E.J. ^[1]; Raaphorst, G P ^[2]

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1. Chalk River Labs., Ontario (Canada)
2. Ottawa Regional Cancer Center, Ontario (Canada)

We have previously shown that chronic exposure of plateau-phase C3H 10T 1/2 cells to {sup 60}Co {gamma} 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{degree}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. 21 refs., 2 tabs.

• Sponsoring Organization: USDOE
• OSTI ID: 405359
• Journal Information: Radiation Research, Journal Name: Radiation Research Journal Issue: 4 Vol. 146; ISSN 0033-7587; ISSN RAREAE
• Country of Publication: United States
• Language: English

Related Subjects

56 BIOLOGY AND MEDICINE
APPLIED STUDIES
ANIMAL CELLS
BIOLOGICAL RADIATION EFFECTS
CELL CULTURES
CHRONIC EXPOSURE
COBALT 60
GAMMA RADIATION
NEOPLASMS
OCCUPATIONAL EXPOSURE