24 Jul 2006

Nicotine patch may spur lung cancer

While the nicotine in tobacco and in nicotine-replacement patches and gums doesn't cause lung cancer, it may help it along, a new study finds.

"Nicotine can promote the growth of new blood vessels and new cells - two things that are correlated with the progression of cancer - and our study shows how this actually happens," said study co-author Srikumar P. Chellappan, an associate professor in the Drug Discovery Program with the H. Lee Moffitt Cancer Centre and Research Institute at the University of South Florida, in Tampa.

The finding raises questions about the use by lung cancer patients of nicotine-containing interventions aimed at helping smokers quit, such as popular patches and gums.

Nicotine spurs cancer cells
Chellappan's team identified a key binding process taking place between nicotine and receptors found on cells lining the lung's air passages, and in lung cancer cells themselves. The bond between nicotine and these receptors provokes further lung cancer cell proliferation, the researchers report in the August issue of the Journal of Clinical Investigation.

The Florida group conducted their lab work on cancer cells taken from patients afflicted with non-small cell lung cancer (NSCLS).

According to the American Cancer Society, lung cancer accounts for 13 percent of all new cancers and is the leading cancer killer of American men and women.

But while tobacco smoke is the direct cause of eight out of 10 lung malignancies, nicotine - the addictive chemical in tobacco - does not have cancer-causing properties. The role, if any, of nicotine in lung cancer has long been the subject of debate.

May undermine chemotherapy
In previous work, Chellapan found that nicotine exposure among lung cancer patients did appear to undermine chemotherapy's effectiveness in killing off cancer cells. Because so many patients use nicotine patches or gums to help them quit, this raise the troubling notion that these interventions might actually help encourage the disease.

In this study, Chellappan's focused on NSCLS cells and adjacent cells from the lung's air passages also known as bronchial cells. They exposed both cell types to nicotine in the test tube. The amount of nicotine used was the equivalent to what would typically be present in the bloodstream of a patient who smokes one pack of cigarettes a day.

In addition to binding with what are known as nicotinic acetylcholine receptors, the nicotine appeared to help create signalling pathways that promoted the cancer cell growth cycle. This growth activated and recruited other cell machinery known to stimulate tumour growth.

Promotes tumour progression
The researchers concluded that, in the test-tube setting, nicotine appears to go beyond simply protecting cancer cells as had been previously observed. Instead, it appears to promote cancer-cell proliferation and tumour progression.

"We found that a normal amount of nicotine that is typically present in the blood of smokers can really induce a proliferation of cancer cells, and we have identified some proteins in the cell that facilitate this proliferation," said Chellappan.

"So, smokers should be staying away from all products that contain nicotine," he cautioned. "Not just cigarettes - anything. I cannot say that this is just about smoking. This is about exposure to any nicotine. Even a patch to help quit smoking may not be the best idea."

Nevertheless, one expert is still on the fence when it comes to the risks and benefits for lung cancer patients in using nicotine-replacement therapies.

"You can't necessarily say whether nicotine-replacement therapy is a good or bad idea," said Dr Norman H. Edelman, chief medical officer with the American Lung Association.

Still better to quit
"My guess is that it's a good idea to engage in smoking cessation," he said. "Smoking cessation is a much healthier way to go rather than avoiding the nicotine in smoking-cessation therapies based on the theoretical risk shown in test tubes that nicotine can promote tumours."

Edelman emphasised, however, that the current study is "an important biologic finding" that will need to be followed up with research in animals and ultimately humans.

Two other major groups agreed. The US National Cancer Institute's Web site states that "any potential risks of short-term use of nicotine-replacement therapy to stop smoking are far outweighed by the significant and known benefits that accrue to patients who stop smoking."

And the American Cancer Society's Web site notes that "numerous studies have shown that these products are safe and effective in helping smokers quit." Society experts also point out that the use of nicotine-replacement products, alongside in-person and phone counselling, can double a smoker's chances of successfully quitting. – (HealthDayNews)