Deadly toxin turns into painkiller

British scientists say they are transforming one of the world's most toxic substances into a new non-addictive drug that could relieve chronic pain caused by cancer and other diseases.

Botulinum neurotoxin is released by a bacterium that can be found in contaminated food or infected wounds and which causes botulism, a rare but deadly illness.

The bacterium has been used in small, controlled doses for more than 10 years to treat patients with cerebral palsy, muscle spasms and other complaints caused by uncontrolled muscle contractions.

It has also gained popularity as a treatment for wrinkles under the name of Botox.

Scientists at the Centre for Applied Microbiology and Research, an arm of Britain's health ministry, are working on a new drug based on the toxin that will be an effective, safe and non-addictive pain reliever.

"The molecules we are developing are non-toxic," Dr Keith Foster, who is leading the project, told a science conference.

By understanding the structure of the toxin, Dr Foster and his colleagues have been able to devise a similar molecule with the beneficial properties of the natural bacterium's toxin but without its side-effects.

As well as providing a new pain reliever, Dr Foster and his team also hope to use the part of the toxin that targets nerve cells as a delivery system to take other therapeutic agents such as genes or enzymes into the nervous system. "We'll target only the cells that require treatment," he said.

Experimental results have shown there is potential to target the toxin to nerves that are responsible for pain and to block their function for many weeks.

"This opens up the possibility that we will be able to build on this research to develop novel pharmaceuticals for the treatment of chronic pain," Dr Foster told the British Association science conference.

Professor Michael Barnes of the University of Newcastle upon Tyne in northeast England said the natural toxin works by improving the function of muscles.

It has been particularly effective for muscle damage resulting from brain and spinal injury and strokes and for chronic back and neck pain. Injections of the toxin also relieve sweating, drooling and writer's cramp.

The new molecule is designed to treat conditions such as cancer where a muscle relaxant is not needed. Early laboratory and animal tests have shown promise but human trials are still a few years away.

"The primary targets of the natural neurotoxin are the nerves that control muscle function," Dr Foster said. "What we are hoping to do is to replace that targeting to other nerve cells so that we wouldn't get muscle relaxation and weakness as a side effect."

- REUTERS