Doctors may one day be able to use powerful electric fields to help destroy cancer cells from outside.

US researchers say they can use energy pulses - which last a tiny fraction of a second - to attack the cell without harming its healthy neighbors.

The pulses do not physically destroy the cell, but appear to start a process which makes them "commit suicide".

The technique, reported in New Scientist magazine, could also be used to tackle obesity, say experts.

Currently, surgery, chemotherapy or radiotherapy are used to destroy cancer cells.

The "nanopulse" system is closest to radiotherapy, but may perhaps offer a gentler alternative to radiation.

Non-invasive

The electric field could in theory be focused on a tumor sited deep inside the body using antennas placed around the body.

By fine-tuning the frequency of the field, it may be possible to target only particular cell types, and hopefully spare healthy tissue around the tumor.

The short duration of the pulses - measured in hundreds of microseconds - are designed to prevent the outer membrane of the cell "charging up" fully and acting as a shield for its contents.

Researchers at the University of Southern California at Los Angeles, and Old Dominion University in Norfolk, Virginia, have shown that, in a laboratory dish at least, "nonpluses" can kill tumour cells.

The Virginian team has also slowed the growth of tumors in mice using the technique.

'Reaching in'

Professor Tom Vernier, from the Los Angeles team, said: "The effects of these pulses are fairly dramatic.

"We see it as reaching into the cell and manipulating internal structures."

The only detectable physiological change within the cell is a release of calcium from a structure called the endoplasmic reticulum.

Although this would not seem to be able to have any direct impact on whether a cancer cell lives or dies, it is taken as evidence of the power of the pulse to influence the make-up of the cell.

The Virginia team has also found that they can use the same method to trigger suicide in cells which can become fat cells - perhaps offering a technique to help control obesity, they believe.

In the UK, a team at Imperial College London and Loughborough University is pursuing the same goal.

Dr Michael Kong, from Loughborough, said that the use of electric fields in this way was a "hot area".

"There are only about three or four groups in the world working on this, but I would expect others to start when they see the potential.

"It's an exciting new field - no-one knows exactly how this effect happens."