Mice with colon cancer waste away. In a new study, a small peptide that their own cells already make held onto some of their muscle, even as the animals kept losing weight everywhere else.
The peptide is MOTS-c ↗, sixteen amino acids long, encoded not in the cell nucleus where most proteins come from but inside the mitochondria, the tiny compartments that turn food into usable energy. The body makes it on its own. Levels climb with exercise and fall with age. A team led by Andrea Bonetto's lab gave it twice a day to mice carrying Colon-26 tumors, a standard model of the wasting that comes with cancer, and reported the results in Frontiers in Medicine ↗.
The wasting has a name. Cancer cachexia is the progressive loss of muscle and weight that hollows out patients in the late stages of many cancers. It is not simple starvation and it does not reverse with more food. The tumor reprograms the body's metabolism so that muscle is broken down faster than it can be rebuilt, and the authors note that this wasting tracks with worse outcomes and higher mortality. There is no approved drug that stops it.
This is a different problem from the muscle loss the section tracked this week in weight-loss drugs ↗. There, the muscle comes off because patients eat far less while the drug works. In cachexia, the muscle is actively dismantled by the disease itself, whether or not the patient is eating.
The mice on MOTS-c still lost about 9 percent of their body weight, and they lost fat. The peptide did not save the whole animal. What it saved was muscle. Quadriceps weight came in about 12 percent higher than in untreated tumor-bearing mice (a statistically significant gap), with a weaker trend toward sparing a second leg muscle and its grip-style force.
The interesting part is how. Wasting muscle runs a specific demolition program: a pair of genes, Atrogin-1 and MuRF1, that tag muscle proteins for destruction. In the tumor-bearing mice those two genes were running hot, up roughly 8.6-fold and 16-fold over normal. MOTS-c turned the volume back down on both. It did so by acting on FOXO, the switch that flips that demolition program on. The peptide pushed FOXO into its inactive, parked state (one form of it up 80 percent in the parked configuration, another down 39 percent in its active one) and at the same time restored a master regulator of mitochondrial building called PGC-1alpha to more than double its suppressed level. In isolated muscle cells, MOTS-c roughly doubled the activity of AMPK, the energy sensor that sits upstream of all of this.
Read plainly, the peptide does two things at once. It eases off the genes that take muscle apart, and it helps the muscle rebuild the energy machinery the tumor was degrading. That fits what MOTS-c is. It belongs to a small family of mitochondrial-derived peptides ↗, short signals the mitochondria themselves encode, that includes Humanin ↗. The family's whole job is metabolic housekeeping, and exercise is its natural trigger. A drug that mimics part of the exercise signal is exactly the kind of thing a wasting muscle might respond to.
The caveats are the honest ones for work at this stage. This is mice and cultured cells, not people. The protection was partial, not a rescue. The dose was high and given by injection twice a day. The authors say plainly that human studies in cancer cachexia are still needed, and none exist yet. MOTS-c is an experimental peptide, not an approved drug.
Still, the result names a target worth chasing. Most cachexia research has gone after appetite or after single muscle pathways like myostatin. A peptide the body already makes, that works by quieting the muscle-destruction genes rather than by forcing food in, is a different line of attack on a syndrome that has resisted every line tried so far.