Nicotine: addictive and spreads cancer?

Nicotine: Addictive and spreads cancer?

Nicotine appears to be one of thosethings some people could die for--in more ways than one. One new study suggests it may promote the spread of cancer cells, while another indicates higher doses of nicotine replacements may be necessary to help smokers stop using tobacco.

At first, nicotine managed to keep clearof the fiery debate over whether tar and other tobacco constituents caused health problems. Then it was indicted in heart disease, and later found to cause a true physical addiction in many users (SN: 1/18/86, p.44). No longer the hidden ingredient, nicotine now is being studied in a broad range of research projects, including two reported last week in San Diego at the American Cancer Society's annual science writers' seminar.

At the University of South Alabama inMobile, Gesina L. Longenecker and her co-workers are assessing the interaction of tumor cells, nicotine and blood platelets. Other studies had shown that platelets (cell fragments essential in blood clotting) can be activated by tumor cells. These activated platelets attach to the cells, protect them from the immune system and apparently help them work their way through the blood vessel walls during metastasis, or spread, of the cancer.

The Alabama group found thatcultured cells from a human muscle cancer also produce significant amounts of prostacyclin, a substance released routinely from blood vessel walls that inhibits platelet activation and prevents unwanted clotting in the circulation. Thus these tumor cells, paradoxically, appear to release a negative signal that in effect slows the spread of cancer while at the same time promoting it.

But nicotine upsets this balancing act,says Longenecker, by inhibiting the production of prostacyclin by cancer cells, much as it inhibits prostacyclin produced by blood vessels. In addition, preliminary data suggest that nicotine increases the number of circulating tumor cells that stick to the sides of blood vessels. Longenecker explains that this would make nicotine not an initiator or promotor of cancer by itself, but perhaps a cofactor that aids metastasis.

Although the effect has been studied inonly one type of cancer, Longenecker says it could be important to varying degrees in numerous types of cancer. Does this mean that smoking could enhance the spread of many, if not all, types of cancer? And should cancer patients be told to stop tobacco use, given the pleasure they may receive from smoking or chewing tobacco?

The answers are complicated by thefact that only 20 percent of smokers are able to quit the habit "cold turkey.'

At last week's seminar, Jack E. Henningfield,from the National Institute of Drug Abuse (NIDA), said nicotine addiction "is a special sort of compulsive behavior,' similar to heroin and cocaine addiction in its behavioral and physical effects. Because a tolerance to nicotine builds over time, Henningfield says many tobacco users may require nicotine replacements like nicotine gum for a longer time and in larger doses than currently recommended by physicians. (Only half of the nicotine from the prescription chewing gum actually reaches the blood-stream.)

"The most desirable situation is nonicotine,' he says, "but it could be given much longer safely.' That would make it more likely to help the more than 60 percent of smokers who fail to stop, even after seven attempts, he says.

Despite the dangers of nicotine use,Henningfield feels that it is often a "trade-off' necessary to eliminate exposure to carcinogens in tobacco. Despite research on nicotine substitutes at NIDA's Addiction Research Center in Baltimore, nothing has been found to take its place for the addict, says Henningfield. NIDA studies are being done on smokeless cigarettes, suppositories and skin patches containing nicotine.