Anti-smoking campaigners say quitting is still best

US researchers believe they could be used to stop the smoking-related damage which causes 99% of the most lethal type of lung cancer.

However, anti-smoking campaigners stressed the healthiest option was never to start smoking in the first place.

The research centres on the Sonic Hedgehog (Shh) gene, named after the cartoon character.

The guaranteed way to extend your lifespan is not to smoke Amanda Sandford, ASH

It has a range of roles, one of which is to help embryos sprout properly branched lungs.

Scientists at the Johns Hopkins Medical Institutions in Baltimore, Maryland, found it helps repair damaged lung tissue in adults.

The researchers suggest the severe lung damage caused by smoking causes this repair message to be constantly switched on, making too many new cells and ultimately resulting in cancer.

Drugs to switch the repair message off would therefore prevent the damage, they say.

Promise

Researchers analysed tissue samples and tumour cell lines from patients with small cell lung cancer and non-small cell lung cancer.

Small cell is the most dangerous form of lung cancer and usually cannot be treated with surgery.

It usually responds initially to chemotherapy, but most patients relapse.

Of 10 small-cell samples studied, five showed activation of the Shh pathway and increased expression of a related gene called Gli1.

In laboratory tests, five out of seven cell lines showed similar results.

Tests on the non-small cell samples showed limited activation of the pathway.

The team are now testing drugs that might block the Hedgehog pathway in mice. One which has shown promise is called cyclopamine.

It could be three to four years before the drugs can be tested on humans. But if trials were successful, they could lead to a treatment that halts the most harmful effect of smoking.

'Too many cells'

Dr Neil Watkins, from the Kimmel Cancer Centre at Johns Hopkins, who led the research, said: "We believe chronic injury to the lungs by cigarette smoking re-activates genes in the Hedgehog pathway to repair cell damage in the lining of the lungs.

"The ongoing and regular assault to the lungs by cigarettes causes the usually dormant pathway to be stuck in activation mode making too many new cells, ultimately resulting in cancer."

He added: "As cigarette smoking persists among young people, we expect to be dealing with this disease for years to come.

"As a result, the search for potential new therapies are key to controlling this disease."

But UK anti-smoking campaigners said new cancer treatments were no alternative to non smoking.

Amanda Sandford, spokeswoman for Action on Smoking and Health (ASH) said: "Obviously it's important that research continues into identifying the causes of cancer and finding ways to treat it.

"But when it comes to smoking, quite simply the message is still don't start, and if you are a smoker, quit."

She added: "Therapies like this are always going to be a secondary tier of treatment. The guaranteed way to extend your lifespan is not to smoke."