Although morphine has been the gold-standard treatment for postoperative and chronic cancer pain for two centuries, a growing body of evidence is showing that opiate-based painkillers can stimulate the growth and spread of cancer cells. Two new studies advance that argument and demonstrate how shielding lung cancer cells from opiates reduces cell proliferation, invasion and migration in both cell-culture and mouse models.
The reports--to be presented November 18, 2009, at "Molecular Targets and Cancer Therapeutics," a joint meeting in Boston of the American Association for Cancer Research, the National Cancer Institute, and the European Organization for Research and Treatment of Cancer--highlight the mu opiate receptor, where morphine works, as a potential therapeutic target.
"If confirmed clinically, this could change how we do surgical anesthesia for our cancer patients," said Patrick A. Singleton, PhD, assistant professor of medicine at the University of Chicago Medical Center and principal author of both studies. "It also suggests potential new applications for this novel class of drugs which should be explored."
The proposition that opiates influence cancer recurrence, prompted by several unrelated clinical and laboratory studies, has gradually gained support. It started with a 2002 palliative-care trial in which patients who received spinal rather than systemic pain relief survived longer. Soon after that, Singleton's colleague, anesthesiologist Jonathan Moss, noticed that several cancer patients receiving a selective opiate blocker in a compassionate-use protocol lived longer than expected. Two recent retrospective studies found that breast and prostate cancer patients who received regional rather than general anesthesia had fewer recurrences. In February, 2009, the Anesthesia Patient Safety Foundation highlighted the issue.
Moss's palliative-care patients were taking methylnaltrexone (MNTX), developed in the 1980s for opiate-induced constipation by the late University of Chicago pharmacologist Leon Goldberg. Goldberg modified an established drug that blocks morphine so that it could no longer cross the protective barrier that surrounds the brain. So MNTX blocks morphine's peripheral side effects but does not interfere with its effect on pain, which is centered in the brain. It won FDA approval in 2008.
"These were patients with advanced cancer and a life expectancy of one to two months," Moss recalled, "yet several lived for another five or six. It made us wonder whether this was just a consequence of better GI function or could there possibly be an effect on the tumors."