A drug derived from vitamin A could help prevent former smokers from developing lung cancer, it has been claimed.

It may help restore the production of a protein which is believed to protect against the disease.

Researchers from the University of Texas say their findings are not conclusive, but could point the way to the development of "chemoprevention" drugs.

Stopping smoking reduces the risk of someone developing lung cancer, but the genetic damage it causes takes time to disappear - and half of all newly-diagnosed lung cancers occur in former smokers.

It may be possible to reverse some of the genetic damage that has accumulated Dr Waun Ki Hong, University of Texas

Scientists want to find a way to stop this genetic damage from turning into cancer.

Gene therapy

The Texas research focuses on retinoids, which are natural and synthetic compounds related to vitamin A (retinol).

Retinoic acid (RA) is needed for the epithelial cells that line the lung to function normally.

It activates retinoic acid receptors (RARs) which regulate cell growth and death.

Heavy smoking is known to reduce levels of a key receptor, RAR beta.

Loss of that receptor has already been linked to the development of precancerous lesions in the lung.

The Texas University team decided to look at whether genetic therapy could restore its production.

They studied 177 patients who had stopped smoking at least a year earlier.

Biopsies were taken from six sections of patients' lungs before treatment, after the three month trial, and three months after treatment stopped.

The samples were then studied for levels of the RAR beta gene.

Those given a vitamin A derivative called 9-cis retinoic acid (9-cis-RA), saw a 7% increase in expression of the gene, compared to a fall in patients taking a dummy pill.

There was no change in a third group taking a different type of vitamin A derivative.

Protective effect

Dr Waun Ki Hong, head of the Division of Cancer Medicine at the University of Texas, said: "This work shows that we can restore the gatekeeper in those who have quit smoking.

"It may be possible to reverse some of the genetic damage that has accumulated."

Dr Jonathan Kurie, who led the study, said it was important because it was the first to study chemoprevention in former smokers.

Vitamin A derivatives might have the potential to help repair cells damaged by smoking Dr Julie Sharp, Cancer Research UK

He added: "The work is a proof of concept, suggesting that compounds like this may prove to have a protective effect against development of precancerous lesions."

But researchers warn the therapy may not be the best drug for lung cancer prevention because it causes side effects such as headaches, skin rashes, and fatigue.

Other researchers are testing different drugs which they hope could act as chemoprevention drugs.

Dr Julie Sharp of Cancer Research UK said: "Tobacco smoking causes nine out of 10 lung cancers so the best way to prevent the disease is not to smoke.

"But many people are ex-smokers or continue to smoke and smoking can also put never-smokers at risk of lung cancer through passive smoking.

"For this reason it's essential to look for other ways of preventing the disease."

She added: "Professor Lotan and his colleagues are experts in chemoprevention, which uses drugs to prevent cancer before it has a chance to develop.

"Their work shows that Vitamin A derivatives might have the potential to help repair cells damaged by smoking. However, more research needs to be done before we can be sure of the clinical benefits."

The research is published in the Journal of the National Cancer Institute.