July 8 (HealthDay News) -- Though researchers aren't ready to recommend that people start popping pills to live longer, they hope a drug used to prevent rejection of transplanted organs may turn out to extend lives, too.
Middle-age mice that were given the drug rapamycin (Sirolimus) lived as much as 38 percent longer than mice that didn't get the drug.
The findings, disclosed in a study released online Wednesday in the journal Nature, provides "a foundation for future research on retarding aging," said the study's lead author, David Harrison, a professor at the Jackson Laboratory in Bar Harbor, Maine.
The mice appeared to do well while taking the drug, but it is unclear if rapamycin would have a similar effect in humans. Also, the drug suppresses the immune system in people, leaving them open to the risk of infection.
"We don't know that the benefits in people at this point will be greater than the deleterious consequences," Harrison said.
Still, the findings appear to represent a step forward in efforts to develop a "longevity pill" that would allow people to live longer.
"It's a really big deal," said pathologist Matt Kaeberlein, who wrote a commentary accompanying the study. "This is the first demonstration of a compound that, when administered late in life, can increase life span in a mammal."
Previously, researchers have shown that greatly limiting food intake in rodents helps them live longer, but that's not a feasible option for many humans who like to eat.
Rapamycin is a compound discovered in the soil on Easter Island, a South Pacific island known for three giant monoliths that have survived for centuries. The name rapamycin is derived from the island's Polynesian name, Rapa Nui.
Today, rapamycin is used to prevent rejection of transplanted organs and to treat some kinds of cancer, said Kaeberlein, an assistant professor of pathology at the University of Washington in Seattle.
The study authors administered the drug to mice at the age of 600 days -- the equivalent of 60 years in humans -- and found that it boosted their life span by 28 to 38 percent.
The drug appears to work by preventing immune cells from reproducing, Kaeberlein said. This helps organ-transplant patients by preventing the immune system from thinking the body is being attacked by something foreign.
The researchers also noted an anti-cancer effect, saying cancer cells seem especially vulnerable to the drug. It "could be retarding a whole bunch of cancers," Harrison said.
Still, it would be premature to tout the compound as a cure-all for aging. Kaeberlein said the findings are "very exciting, but there's a lot that needs to be done so we know what the implications are for human aging."
Exactly how the drug extends life span in mice remains unclear. One possibility, Kaeberlein said, is that it delays the progress of diseases associated with age.
What it might cost if it were taken by humans for longevity is also unknown because researchers don't know what dose might work best.
SOURCES: David Harrison, Ph.D., professor, Jackson Laboratory, Bar Harbor, Maine; Matt Kaeberlein, Ph.D., assistant professor, pathology, University of Washington, Seattle; July 8, 2009, Nature