Scientists are developing a treatment for a form of lung disease which is one of the UK's biggest killers.
COPD is very common
A team from Imperial College London has discovered why chronic obstructive pulmonary disease (COPD) is resistant to steroid therapy.
They have found a way to combat the problem and have started clinical trials of a potential therapy.
Details were presented at a British Endocrine Societies meeting.
COPD is an umbrella term covering a range of lung diseases, including chronic bronchitis and emphysema.
It is estimated to affect 6% of the UK population, and it is the fourth most common cause of death in the country.
Steroids would normally be effective at treating inflammatory diseases such as COPD.
However, COPD patients do not respond to steroid therapy.
Inflammation is caused by specific genes triggering the production of certain key chemicals.
It is possible to block inflammation by switching off these genes, using an enzyme called Histone Deacetylase 2 (HDAC2).
Steroids usually aid this process by mopping up HDAC2, and targeting the appropriate genes.
However, the Imperial team found HDAC2 levels are very low in COPD patients, so steroids have little chance to have any effect.
Working on lung cells, they found they could raise levels of HDAC2 - and allow steroids to do their work - by administering low doses of a cheap and widely available drug, theophylline.
Lead researcher Professor Peter Barnes said: "COPD kills tens of thousands of people in the UK every year and currently we can only treat the symptoms not the underlying problem of inflammation of the lungs.
"Our work has finally provided an explanation for steroid resistance in COPD and has allowed us to identify ways to combat this.
"We hope that the clinical trials of theophylline will be successful so that we can finally offer an effective therapy to COPD sufferers."
Dame Helena Shovelton, chief executive of the British Lung Foundation, said: "COPD is the only major cause of death which is increasing in the UK with 900,000 people living with the condition.
"Worryingly it is estimated that a further 2.5m people have COPD and are either undiagnosed or misdiagnosed.
"We will follow the progress of this research very closely and hope that it will result in improving the quality of life for people with COPD."
Dr Steve Connellan, of the British Thoracic Society COPD Consortium, said smoking appeared to reduce the effect of steroid therapy, both for COPD patients and people with asthma.
Whether or not the latest research led to real benefits for patients, smokers at risk of lung problems should be encouraged to give up their habit, he said.