Radiotherapy for cancer can also damage healthy cells
A drug which may protect the body against damage from radiation has been developed by US scientists.
It is hoped it could make radiotherapy safer for people with cancer and could also be used in the event of a "dirty bomb" or nuclear disaster.
Known as CBLB502, and so far tested in animals, it switches on a biological mechanism that helps healthy cells survive blasts of radiation.
The findings published in Science are set to be tested in clinical trials.
Radiation kills cells by causing damage which encourages cell suicide, or apoptosis.
But healthy cells may be killed alongside tumour cells in the process which is why radiologists need to target the tumour as specifically as possible.
Researchers developed the drug after looking at how some resistant cancer cells are able to withstand radiotherapy.
It works by inhibiting the protein that initiates the cell suicide programme.
Studies in animals suggest CBLB502 protects healthy cells in the bone marrow and digestive tract against radiation but does not seem to protect tumour cells which remain vulnerable to treatment.
Mice and monkeys injected with the drug between 45 minutes and 24 hours before being subjected to normally lethal radiation were more likely to survive or live longer than untreated animals, the researchers found.
One risk of preventing cell death is that defective cells may be allowed to survive which could then turn cancerous.
However, the researchers found no sign of this happening in the laboratory tests on mice.
Also, there were no apparent side effects.
Protecting healthy cells against the effects of radiation may allow cancer patients to receive higher doses of radiotherapy, or longer courses of treatment.
The drug may also be useful in protecting against fall out from a nuclear disaster, such as Chernobyl, or the effects of a terrorist "dirty bomb".
Dr Andrei Gudkov from the Lerner Research Institute in Cleveland, Ohio, said they had set out to enable healthy cells to imitate the ability of tumour cells to avoid cell death.
But they had to develop a way of making this effect temporary and reversible.
"We demonstrated the drug is efficacious when injected before radiation and after radiation.
"In summary, CBLB502 reduces radiation toxicity without diminishing the therapeutic anti-tumour effect of radiation and without promoting radiation-induced carcinogenicity."
Dr Joanna Owens, science information officer at Cancer Research UK, said: "These are interesting results and we look forward to following the progress of CBLB502 through planned clinical trials.
"If the protective properties seen in this laboratory study can be reproduced in people with cancer, this could be an important step towards reducing side effects for people having radiotherapy."