Exercise Mimetics: Fitness in a Pill?
Physical activity builds muscle and fitness, helps keeps bones strong, sharpens thinking and memory, guards against depression, and helps discourage a slew of health concerns from weight gain and high blood pressure to diabetes and heart disease. Muscle becomes more dense, more powerful and may even burn more calories, said Dr. Burris. The problem: That pesky part about actually moving. Fewer than half of American adults get recommended amounts of aerobic exercise and fewer than a quarter fit in strength training, according to the Centers for Disease Control and Prevention.
Enter the exercise mimetics. Unlike CR mimetics, exercise mimetics affect mitochondria — the tiny power plants in muscle and every other cell in the body. They switch on genes that encourage the growth of more mitochondria and encourage them to burn fatty acids, not just glucose, for fuel.
In mice, this can keep them from gaining weight, increase insulin sensitivity, and boost exercise endurance. “We can use a drug to activate the same networks that are activated by physical activity,” said Ronald Evans, PhD, professor and director of the Gene Expression Laboratory at the Salk Institute for Biological Studies in La Jolla, California.
Among notable mimetics moving into human studies is ASP0367, a drug in a class called PPAR delta modulators first developed in Evans’ lab. ASP0367 was licensed to the pharmaceutical company Mitobridge, later acquired by Astellas. Astellas is currently running a phase 2/3 human trial of the investigational drug in people with the rare genetic disorder primary mitochondrial myopathy.
At the University of Florida, Dr. Burris and team hope to soon move the exercise mimetic SLU-PP-332 into human studies. “It targets a receptor called ERR that I’ve been working on since the 1980s,” Dr. Burris said. “We knew from genetic studies that ERR has a role in exercise’s effects on mitochondrial function in muscle.” The calorie mimetics he’s studying also activate genes for making more mitochondria and driving them to burn fatty acids. “This generates a lot of energy,” he said. In a January 2024 study in Circulation, Dr. Burris found the drug restores heart function in mice experiencing heart failure. “Very little heart function was lost,” he said. It’s had no serious side effects.
The Future of Exercise and CR Pills
The field has hit some bumps. Some feel inevitable — such as otherwise healthy people misusing the drugs. GW1516, an early experimental exercise mimetic studied by Dr. Evans and abandoned because it triggered tumor growth in lab studies, is used illegally by elite athletes as a performance-enhancing drug despite warnings from the US Anti-Doping Agency. Dr. Burris worries that future CR mimetics could be misused the same way.
But he and others see plenty of benefits in future, FDA-approved drugs. Exercise mimetics like SLU-PP-332 might one day be given to people alongside weight-loss drugs, such as Mounjaro (tirzepatide) or Ozempic (semaglutide) to prevent muscle loss. “SLU-PP-332 doesn’t affect hunger or food intake the way those drugs do,” he said. “It changes muscle.”
Mimetics may one day help older adults and people with muscle disorders rebuild muscle even when they cannot exercise and to delay a range of age-related diseases without onerous dieting. “The chance to intervene and provide a longer healthspan and lifespan — that’s been the moon shot,” Dr. Roth said.
Dr. Guarente noted that CR mimetics may work best for people who aren’t carrying extra pounds but want the health benefits of slashing calories without sacrificing meals and snacks. “Fat is still going to be a problem for joints, cholesterol, inflammation,” he said. “Calorie mimetics are not a panacea for obesity but could help preserve overall health and vitality.”
And what about the billion-dollar question: What happens when these drugs become available to a general public that has issues with actual exercise and healthy diet?
Evans sees only positives. “Our environment is designed to keep people sitting down and consuming high-calorie foods,” he said. “In the absence of people getting motivated to exercise — and there’s no evidence the country is moving in that direction on its own — a pill is an important option to have.”
A version of this article appeared on Medscape.com.