SLU-PP-332: The Molecule That Mimics a Workout in Mice

What if a molecule could tell your muscles they had been for a run? That is the big idea behind SLU-PP-332.

In 2023, a team in St. Louis, Missouri, shared a striking result. Mice given SLU-PP-332 ran about 70% longer than untreated mice. Scientists call it an "exercise mimetic," a copycat of exercise.

What it is

SLU-PP-332 is not a peptide. A peptide is a short chain of amino acids, like a short bead bracelet. New to this? Start with what a peptide is.

SLU-PP-332 is a small, lab-made molecule, much smaller than most peptides. It belongs here because it works on the same cell parts many peptides do: the switches and power plants that run your energy.

Chemists at Saint Louis University were part of that team. The team reshaped an older molecule so it would grip its main target far better.

What it does in the body

SLU-PP-332 switches on proteins called ERRs. Think of each ERR as a master switch inside a cell. Flip it, and a whole set of genes gets to work.

Many of those genes help cells burn fat and build mitochondria. Mitochondria are the cell's power plants.

ERR stands for estrogen-related receptor. ERRs look a lot like the body's estrogen sensors, but estrogen does not bind to them.

ERRs are busy where the body needs lots of energy. That includes muscle, the heart, the brain, the liver and body fat.

When you train, your muscles change. They build more power plants and get better at going the distance. ERRs help drive that change. So scientists asked a bold question: could a molecule flip these switches without the workout?

There are three ERRs. SLU-PP-332 turns on all three, but it pulls hardest on one called ERR-alpha. Drugs that switch on ERR-alpha had been very hard to make.

What scientists have found

In cells: In mouse muscle cells in a dish, SLU-PP-332 made the power plants work harder. The cells built more of them, too.

In a 2025 study from Italy, researchers grew muscle cells taken from inactive older women during hip surgery. With SLU-PP-332, the cells showed fewer signs of stress and aging. They also formed plenty of new muscle fibers.

In animals: In the 2023 study, SLU-PP-332 gave mice more endurance fibers in their muscles. These fibers are built for long efforts. After about a week of it, the mice ran about 70% longer and 45% farther than untreated mice.

In mice whose muscles lacked ERR-alpha, the running boost was gone. So that one switch seems to be the key.

Next, the team tested mice that were obese from a high-fat diet. After 28 days, treated mice weighed about 12% less than untreated ones. Untreated mice gained about 5 grams of fat. Treated mice gained less than half a gram. Both groups ate about the same and moved about the same.

Related studies looked at the heart and kidneys. In mice with a failing heart, it helped the heart pump better, and more of the mice lived. In old mice, eight weeks of it turned back several signs of kidney aging.

In people: SLU-PP-332 has not been tested in people yet. No human studies have been published, and none are listed in the U.S. trial registry.

There is a clue from people, though. In that Italian study, muscle from 10 inactive women had less ERR-alpha than muscle from 10 active women.