Microbeams found to have unexpected results on cancer cells

LONDON - Scientists testing the effects of microbeams have discovered that targeting just a few cells can cause massive destruction to other diseased cells.

Scientists at Cancer Research UK have dubbed it the "bystander effect" because the cancer cells zapped by the microbeams not only die but send out suicide signals to other abnormal cells, telling them to self-destruct.

"We used to assume that the only way to kill cancer cells with radiotherapy was to hit every one of the cells in the tumour with a fatal dose of radiation," said Dr Kevin Prise, of the charity's Gray Cancer Institute in southern England.

"Now we're finding that it's possible to hit just a handful of cells with much lower doses and let the cells' natural suicide machinery do the rest."

The findings could have important implications for improving the effectiveness of radiotherapy for cancer sufferers because hitting just one cell with the microbeam, which launches streams of helium ions a thousandth of a millimetre wide, has an effect on so many other cells.

Prise and his colleagues, who reported their findings in the journal Cancer Research, tested microbeams in the laboratory on brain-cancer cells that were highly resistant to conventional radiotherapy. Although they targeted the beam at a single cell, it had an impact and triggered a significant proportion of other cells to commit suicide in a process known as apoptosis.

Cancer develops when abnormal cells do not self-destruct but continue dividing and form tumours.

"If we could enhance the bystander effect within tumours, we could develop much more effective systems of radiotherapy, perhaps using lower doses to reduce side effects," Prise said.

"But of course it also means that even very low doses of radiation may be doing more damage to normal cells than we'd thought, so we'll have to look for ways of protecting healthy tissue more effectively."

An estimated 50 per cent of patients diagnosed with cancer would benefit from radiotherapy, which kills cancerous cells with tight beams of radiation.

The scientists said the bystander effect is linked to a molecule called nitric oxide which plays a role in cell suicide. Nitric oxide seems to be important in sending out suicide signals in cells when they are hit by radiation.

"Making sure that there are high amounts of the molecule produced within tumours may be essential to optimise the bystander effect and improve treatments," Prise said.

"We also think the mechanisms involved in the bystander effect might be different in healthy and cancerous tissue, so it might be possible to develop drugs that protect normal tissue from radiotherapy while leaving cancer cells more vulnerable."

- NZPA