(RxWiki News) They put you to sleep and relieve pain. They're vital drugs for cancer patients. And yet these very medications may be having a potentially negative side-effect.
Powerful pain relievers known as opioid drugs and anesthesia used for cancer surgery may be promoting tumor growth and metastasis (spread), according to two newly published laboratory research studies.
"Find out what types of pain relievers you're being given."
Lab studies at the University of Chicago Medicine and a genetic study from the University of North Carolina Medical Center find that opioid receptors in the brain (which regulate responses to opioids) already in the body play a role in the development, growth, spread and outcome of lung and breast cancers.
Co-author, Jonathan Moss, M.D., Ph.D., professor of anesthesiology and critical care at University of Chicago Medicine, said "Epidemiologic findings suggest that the type of anesthesia we do for cancer surgery influences recurrence rate, and laboratory studies demonstrate that opioids influence tumor progression and metastasis,"
Opioids such as morphine have been used for over two centuries to relieve pain.
One of the studies, led by Patrick Singleton, Ph.D., assistant professor of medicine at the University of Chicago Medicine, discovered that some types of lung cancer cells have 10 times as many opioid receptors as normal cells.
Human cancer cells engineered with additional opioid receptors were transplanted into mice. These cancer cells grew twice as fast as the cells without the extra receptors. Even evidence showed that the padded cancer cells were 20 times more likely to spread to distant sites.
When opioid receptor blocking medications were given, the growth and spread slowed.
The upshot of these findings, according to Singleton, is that the mu opioid receptor may be a target for new therapeutic drugs.
The research led by Andrey Bortsov, M.D., Ph.D., assistant professor of anesthesiology and colleagues at the University of North Carolina, used human data in a retrospective study.
The team studied data on 2,000 breast cancer patients. Those women who had genetic mutations that resulted in their being less sensitive to opioids lived longer. And the more copies of the mutation, the more likely they were to be alive 10 years after treatment for invasive breast cancer.
Dr. Bortsoy says, "If opioid systems influence tumor growth, then this could open up new opportunities for treating cancer using relatively non-toxic treatments.”
In an accompanying editorial, researchers say that morphine-like medications and the body's own opioids, such as endorphins, appear to have an impact on the proliferation of cancer cells.
As a result, agents that block the mu opioid receptors may help to discourage cancer growth and spread.
Still, they caution that "there are no clinical trials in humans demonstrating a direct effect."
Both studies were published in the March, 2012 issue of Anesthesiology, the academic journal of the American Society of Anesthesiologists.
Funding for the studies was provided by the National Cancer Institute, the University of North Carolina and the University of Chicago. One of the authors, Moss, developed and receives royalties from one of the developers of methylnaltrexone, a drug that blocks the side effects of opioids and is a paid consultant for its distributor, Salix Pharmaceuticals Inc.