Vitamin A derivative could restore smokers' health
of a key protein, which has been damaged by cigarettes in the lungs
of former smokers, and protects the cells against lung cancer,
according to new findings published this week.
Use of a Vitamin A derivative could protect against lung cancer development in former smokers by restoring production of a crucial protein, claim researchers in the US.
The scientists at the University of Texas M. D. Anderson Cancer Center carried out a trial on 9-cis retinoic acid (9-cis-RA), a chemical cousin of vitamin A.
While they failed to find clear evidence that the three-month therapy using the chemical restored health to cells that were already precancerous, they said the work demonstrates that 'chemoprevention' of future lung cancer may be feasible.
"The drug we used acts to reverse a genetic abnormality associated with development of lung cancer," said Dr Jonathan Kurie, an associate professor of medicine in the thoracic/head and neck medical oncology department.
"The work is a proof of concept, suggesting that compounds like this may prove to have a protective effect against development of precancerous lesions."
The findings, to be published in the 5 February issue of the Journal of the National Cancer Institute, are important because they are the first to study chemoprevention in former smokers, according to Kurie.
People who quit smoking reduce their risk of developing lung cancer, but genetic damage caused by smoking does not immediately disappear. Half of all newly-diagnosed lung cancer occurs in former smokers - a way to stop the genetic damage from turning into cancer is of key importance.
"This work shows that we can restore the gatekeeper in those who have quit smoking," said co-author Dr Waun Ki Hong, head of the Division of Cancer Medicine. "It may be possible to reverse some of the genetic damage that has accumulated."
Hong, recognised for his study of chemoprevention, has previously shown that a different vitamin A derivative known as 13-cis-retionic acid (13-cis-RA) can prevent development of head and neck cancer.
Retinoids are natural and synthetic compounds related to vitamin A (retinol). Retinoic acid (RA) is needed for normal function of the epithelial cells that line the lung. Retinoic acid activates retinoic acid receptors (RARs) that regulate cell growth, differentiation, and death.
Heavy smoking, however, is known to reduce levels of a key receptor, retinoic acid receptor beta (RAR-b). Because loss of this receptor has been linked to development of pre-cancerous lesions in the lung - and thus is considered a biomarker of 'preneoplasia' - the researchers looked at whether retinoid therapy could restore expression of the protective protein receptor.
They randomised 226 patients who had stopped smoking for at least one year to one of three groups. One group received a placebo daily and the second group was given supplements of 9-cis-RA, which had been shown in laboratory work to bind to a number of different RARs, and so might be highly effective. The supplement has also been found to prevent development of breast cancer in lab animals. The third patient group received 13-cis-RA, the drug that has worked well in head and neck cancer, and it was combined with alpha-tocopherol (a synthetic form of vitamin E), in order to reduce toxicity known to be associated with 13-cis-RA therapy. All took the oral treatment daily for a period of three months.
The researchers took lung biopsies from six predetermined sites in each patient before treatment, after the three-month treatment period, and three months after treatment ended. Kurie's team then analysed the biopsies for histological abnormalities and for RAR-b expression in the 177 patients who completed three months of therapy.
The results show that RAR-b gene expression had increased in patients who received 9-cis-RA; the percentage of biopsies with RAR-b protein expression increased from 69 per cent to 76 per cent, a statistically significant difference compared to the other two groups. Gene expression dropped from 75 per cent to 69 per cent in placebo-treated patients, and there was no substantial change in RAR-b expression in patients taking 13-cis-RA.
The researchers also found a statistically significant reduction in the number of biopsies with potentially precancerous lesions known as metaplasia in the 9-cis-RA group (from 8 per cent to 4.7 per cent) compared to patients treated with 13-cis-RA (from 5.8 per cent to 3.6 per cent). But, compared to placebo (9.2 percent to 7.8 per cent), neither retinoic treatment had a statistically significant effect on development of metaplasia in this study.
"There was a decrease in precancerous lesions in the 9-cis-RA group, but it was not statistically significant compared to the patients who didn't receive a retinoic treatment," Kurie said.
Kurie warned however that despite promising results, this form of vitamin A may not be the best drug for lung cancer prevention because of side effects such as headaches, skin rashes, and fatigue. A related form, LGD1069, is in clinical trials in the United States, and Kurie is testing celecoxib, one of the so-called 'super-aspirin' drugs, to determine if it might help repair lung damage from cigarette smoking.
Celecoxib is a non-steroidal anti-inflammatory drug (NSAID) known as a COX-2 inhibitor, which works to ease inflammation without causing stomach ulcers and other side effects of similar drugs. Celecoxib has already been shown to reduce the number of precancerous intestinal polyps in patients with a rare colon cancer.
The study was supported by the National Cancer Institute and by the Rippel Foundation, the American Cancer Society, the National Foundation for Cancer Research, and by M. D. Anderson Cancer Center.