The Black Vault - Scientists find enzyme to trigger cancer cell 'suicide'

Radiotherapy attacks cancer by kick-starting a natural tumour control process as well as destroying cells directly, says new research.

The discovery may help doctors prepare tumours for treatment, allowing the radiation dose to be reduced.

Experiments with mice identified a "cell suicide" enzyme that is activated when struck by radiation.

The enzyme, acid sphingomyelinase, causes cells which normally form tumour-nourishing blood vessels to die.

Tumours cannot survive without being fed oxygen and nutrients in the blood.

Dr Richard Kolesnick, who led the research at the Memorial Sloan-Kettering Cancer Centre in New York City said: "People assumed that damage to the DNA in the nuclei of tumour cells was the only way that radiation killed tumour cells."

But the new research showed the endothelium - the cells which line organs and the gut - was also targeted through the action of acid sphingomyelinase.

"Our work shows that there is another radiation-induced pathway initiated when radiation strikes endothelial cells," said Dr Kolesnick.

"We found that acid sphingomyelinase is necessary for programmed cell death, or 'apoptosis' of endothelial cells. When the endothelium contained the enzyme, the tumour was radiosensitive. In contrast, when the endothelium lacked the enzyme, tumours became radioresistant."

The findings are reported in the journal Science.

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