Rapamycin has been called a potential miracle drug, capable of slowing the effects of aging — everything from greying hair to age-related diseases like Alzheimer’s. And even though the bacteria that produces rapamycin was discovered about six decades ago, the drug still isn’t used or prescribed often. In the early phases of testing, experts discovered many side effects.

“We’re the dog that caught the car — nobody seems to know what to do,” says Arlan Richardson, a biochemist at the University of Oklahoma Health Sciences Center.

The Discovery of Rapamycin

A Canadian team first discovered rapamycin, also known as sirolimus, in 1964 on Easter Island while on an expedition to gather isolated microbes. The researchers, who arrived by ship, gathered soil samples, and brought them back to Canada.

In Montreal, Suren Sehgal isolated the bacteria species Streptomyces hydroscopicus from the soil. He discovered that the bacteria produced a molecule with antifungal properties, and named the molecule rapamycin after Rapa Nui, the local name for the island.

“There was a great deal of excitement because it’s difficult to find a bacterium that knocks out fungi,” Richardson says.

But despite the initial excitement, the lab closed, and further research halted until the late 1980s.

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What Can Rapamycin Be Used For?

In the 1990s, Richardson says researchers had discovered that the molecule can shut down the general process of protein synthesis. This essentially meant that it could slow down cell growth, which had promising applications for limiting tumor growth and cancer cells.

While there haven’t been too many studies on this topic, some research has found that the drug can help the immune system against tumors and help inhibit some cancer growth.

“Results from clinical trials indicate that the [rapamycin analogs] may be useful for the treatment of subsets of certain types of cancer,” wrote the authors of a review published in Oncogene in 2006.

In 1999, the U.S. Food and Drug Administration (FDA) first approved the drug for its use as an immunosuppressant. Rapamycin, in combination with other chemicals, can relax parts of the immune system to help a new body tolerate a transplanted kidney.

When used however, rapamycin caused various possible side effects that included pneumonitis — lung inflammation — and high cholesterol. As a result, it hasn’t been used for transplants over the years, though it remains approved by the FDA.

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Does Rapamycin Slow Aging?

Studies of the applications of rapamycin have increased over the years. A study published in 2009 in Nature revealed that when fed to mice, rapamycin increased the lifespan of elderly females by 14 percent and males by 9 percent.

“This was the first time that one pharmacological intervention slowed the aging of a mammalian species,” Richardson says.

To increase the lifespan of mice, Richardson says they don’t have to start giving rapamycin to the mice at a young age. The drug still improves their lifespan at around 18 months — the equivalent of a 60-year-old human, he says.

It doesn’t only increase lifespan, Richardson says. Despite being used as an immunosuppressant, the drug may help improve the immune system and health of the elderly, some research has found.

“The large amount of data in mice shows that rapamycin has a major impact on cancer, cardiac diseases and function, and normal brain aging including brain vascular aging and neurodegenerative-like processes in neurodegenerative diseases,” Richardson and his coauthors wrote.

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The Side Effects of Rapamycin

Rapamycin has its issues, however. Richardson believes that some of the early side effects attributed to the drug during kidney transplants may have come from some of the other compounds used with rapamycin. But side effects still appear in mice, and in non-clinical use.

The studies on mice continue to show lung problems as an occasional side effect, as well as potential issues with diabetes, Richardson says.

“Anytime you are taking something, there is a potential for side effects,” he says.

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