Low doses of radiation equivalent to three CT scans, which are considered
safe, give cancer-capable cells a competitive advantage over normal cells in
healthy tissue, scientists have discovered. Researchers at the Wellcome Sanger
Institute and the University of Cambridge studied the effects of low doses of
radiation in the esophagus of mice.
The team found that low doses of radiation increase the number of cells
with mutations in p53, a well-known genetic change associated with cancer.
However, giving the mice an antioxidant before radiation promoted the growth of
healthy cells, which outcompeted and replaced the p53 mutant cells.
The results, published today (18 July) in Cell Stem Cell show
that low doses of radiation promote the spread of cancer-capable cells in
healthy tissue. Researchers recommend that this risk should be considered in
assessing radiation safety. The study also offers the possibility of developing
non-toxic preventative measures to cut the risk of developing cancer by
bolstering our healthy cells to outcompete and eradicate cancer-capable cells.
Every day we are exposed to various sources of ionising radiation,
including natural radiation in soil and rock, and important medical procedures
like CT scans and x-rays.
Low doses of radiation, such as the exposure from medical imaging, are
considered safe as they cause little DNA damage and apparently minimal effect
on long-term health. Until now, other effects of exposure to low levels of
radiation have remained hidden, meaning understanding the true risk associated
with low doses of radiation has been difficult.
Researchers have previously shown that our normal tissues, like skin, are
battlefields where mutant cells compete for space against healthy cells. We all
have cancer-capable mutant cells in healthy tissues, including those with p53
mutations, which increase in number as we age, yet very few eventually go on to
form cancer.
In this new study, researchers show that low doses of radiation weigh the
odds in favour of cancer-capable mutant cells in the esophagus. The Sanger
Institute researchers and their collaborators gave mice a 50 milligray dose of
radiation, equivalent to three or four CT scans. As a result, the p53 mutant
cells spread and outcompeted healthy cells.
Dr David Fernandez-Antoran, first author from the Wellcome Sanger Institute,
said: “Our bodies are the set of ‘Game of Clones’ — a continuous battle for
space between normal and mutant cells. We show that even low doses of
radiation, similar to three CT scans’ worth, can weigh the odds in favour of
cancer-capable mutant cells. We’ve uncovered an additional potential cancer
risk as a result of radiation that needs to be recognised.”
Researchers then gave the mice an over-the-counter antioxidant — N-Acetyl
Cysteine (NAC) — before exposure to the same level of radiation. The team
discovered that the antioxidant gave normal cells the boost needed to
outcompete and eradicate the p53 mutant cells.
However, the antioxidant alone without exposure to radiation did not help
normal cells battle the mutant clones.
Dr Kasumi Murai, an author from the Wellcome Sanger Institute, said:
“Giving mice an antioxidant before exposing them to low doses of radiation gave
healthy cells the extra boost needed to fight against the mutant cells in the
esophagus and make them disappear. However, we don’t know the effect this
therapy would have in other tissues — it could help cancer-capable cells
elsewhere become stronger. What we do know is that long term use of
antioxidants alone is not effective in preventing cancer in people, according
to other studies.”
Professor Phil Jones, lead author from the Wellcome Sanger Institute and
MRC Cancer Unit, University of Cambridge, said: “Medical imaging procedures
using radiation, such as CT scans and x-rays, have a very low level of risk —
so low that it’s hard to measure. This research is helping us understand more
about the effects of low doses of radiation and the risks it may carry. More
research is needed to understand the effects in people.”
The team suggests this research also highlights the possibility of
developing therapies to prevent cancer. By making healthy cells fitter they
naturally push out cancer-capable cells, without any toxic side effects for the
patient.
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