A supplement made from grape seeds can destroy leukaemia cells, say scientists.

In laboratory experiments, commercially-available grapeseed extract forced the cancer cells to commit suicide.

Within 24 hours, 76% of leukaemia cells exposed to the extract died through a process of natural self-destruction called apoptosis. Healthy cells were unharmed.

The US researchers believe the discovery could open the door to promising new treatments.

But they warn it is too early to justify recommending that people eat grapes or take grapeseed extract to stave off cancer.

Grape seeds contain a number of antioxidant plant chemicals including resveratrol, which is known to have anti-cancer properties.

Previous research has shown that grapeseed extract has an effect on skin, breast, bowel, lung, stomach and prostate cancer cells in the laboratory.

It can also reduce the size of breast tumours in rats and skin tumours in mice.

It has never before been tested on a blood cancer.

Professor Xianglin Shi, from the University of Kentucky in Philadelphia, who led the research, said: "These results could have implications for the incorporation of agents such as grapeseed extract into prevention or treatment of haematological (blood) malignancies and possibly other cancers.

"What everyone seeks is an agent that has an effect on cancer cells but leaves normal cells alone, and this shows that grapeseed extract fits into this category."

Prof Shi exposed leukaemia cells to grape extract in a range of different doses. One of the higher doses produced a marked effect, causing large numbers of the cells to commit suicide.

Programmed cell suicide, or apoptosis, is a natural method of getting rid of damaged and potentially dangerous cells. When the mechanism behind apoptosis breaks down, cancerous cells can survive and multiply.

The Kentucky scientists found that grapeseed extract strongly activates a protein called JNK which helps to regulate apoptosis.

When the scientists exposed the leukaemia cells to an agent that inhibits JNK, the grapeseed extract effect was cancelled out.

Silencing the gene that makes JNK also blocked the extract's ability to kill cancer cells.

"This is a natural compound that appears to have relatively important properties," said Prof Shi.

The findings appear in the January 1 edition of the journal Clinical Cancer Research.