NEW ORLEANS — Medications in development would preserve muscle mass and augment fat loss when used in combination with glucagon-like peptide 1 (GLP-1) receptor agonists taken for weight loss.
As drugs such as semaglutide (Wegovy) and the dual agonist glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 tirzepatide (Zepbound) are producing unprecedented degrees of weight loss in increasing numbers of people, concern has arisen about the proportion of the lost weight, approximately 30%-50%, that is beneficial lean body mass vs fat mass. While some loss of muscle mass is expected with any rapid overall weight loss, it's not clear what long-term effect that may have on physical function, bone density, and longevity, particularly in older adults with sarcopenic obesity who are at risk for muscle atrophy and frailty.
Several drugs in various stages of development are aimed at preserving or building muscle mass and boosting fat loss when used in combination with one of these medications for weight loss. Trials now underway will need to show improved function — not just increased muscle — and also establish safety, experts told Medscape Medical News.
One such agent is Veru Inc.'s oral selective androgen receptor modulator (SARM) enobosarm, currently in a phase 2b clinical trial for use with semaglutide in people who are at risk for muscle atrophy and weakness.
Also in a phase 2b trial for use with semaglutide is the antimyostatin intravenous agent bimagrumab. In July 2023, Eli Lilly purchased Versanis, the company that was developing that drug. Previous phase 2 data on bimagrumab alone vs placebo in people with obesity and type 2 diabetes showed improvement in muscle mass with greater fat loss but also produced a signal for pancreatitis requiring further evaluation.
Scholar Rock's intravenous antimyostatin apitegromab is also now in a phase 2 trial and Biohaven Pharmaceuticals is expected to launch a phase 2 trial of its subcutaneous antimyostatin taldefgrobep alfa later this year.
Most of these and other similar agents have also been under investigation for use in one or more other muscle-losing conditions including spinal muscular atrophy, sarcopenia, and cancer.
"Wouldn't it be nice if there was a drug that built up muscle mass?"
Data presented in two late-breaking posters at the annual meeting of the American Association of Clinical Endocrinology meeting held on May 9-11, 2024, laid the groundwork for the subsequent phase 2 studies of enobosarm in combination with a GLP-1 RA. One showed increases in total lean mass and decreases in total fat mass with 3 mg enobosarm for 14 days compared with placebo in both healthy young men and older men (≥ 60 years), with the greatest benefit seen in the older men who had lower lean mass and higher fat mass at baseline.
The other was a post hoc analysis of a phase 3 clinical trial of 3 mg/d oral enobosarm for the treatment of muscle wasting in advanced lung cancer. Here, a subset of participants who were aged ≥ 60 years and had obesity also showed reductions in fat mass and preservation of lean body mass with the drug compared with placebo, leading to "high-quality weight loss."
Endocrinologist Adrian Dobs, MD, professor of medicine and oncology at Johns Hopkins University Medical School, Baltimore, an investigator on both of the Veru-sponsored studies, told Medscape Medical News,"The wishful thinking about these drugs has been around for quite a while, particularly in the cancer population or…in a frail population. The hope was, wouldn't it be nice if there was a drug that built up muscle mass? Certainly, we know that going into the gym does that but looking for some medication had been the goal. The thought was this class of medication would have a muscle-building effect, an anabolic effect without an androgenic effect causing masculinization."
The problem with those studies in terms of regulatory approval, Dobs said, was defining the endpoints. "The [US Food and Drug Administration] is very interested in functional status. You can show that there is an increase in muscle mass. But to take that leap and show that a person can walk upstairs, carry groceries, and be more functionally able is hard to prove."
And she noted that bringing frail elderly people into clinical trials isn't easy. But now, "this is an interesting new avenue of scientific pursuit, looking at this particular population that is losing weight due to GLP-1 [agonists]. Now we're dealing with high numbers of patients who are easy to identify because they're taking those medications."
"We have to also focus on 'first, do no harm'"
Asked to comment, Angela Fitch, MD, associate director of the Massachusetts General Hospital Weight Center, Boston, expressed caution. "We have to remember that it is not all about muscle mass. Maintaining muscle mass with weight loss is obviously important, but even today, with 30% of the weight loss coming from lean mass, which is not the same as muscle, there are huge benefits from fat loss, including cardiovascular and cancer risk reduction, increased life increased life expectancy, and diabetes remission."
Moreover, Fitch pointed out, SARMs have been linked to increased cardiovascular events and blood clots.
"So, we have to also focus on 'first, do no harm'. A lot of these muscle-promoting medications have been associated with increased risk of other things. So, it is going to take a lot of time and testing to be sure they are safe. While I am supportive of research to look into these risks vs benefits, we have to be mindful of the risks and recognize that in most cases of weight loss in people with obesity losing some lean mass is acceptable and the benefits of fat loss outweigh the risks of lean loss, especially if people are doing resistance exercise and maintaining strength."
"Wherever the GLP-1s go, we go"
In an investor call held on May 8, 2024, Veru's Chairman, CEO, and President Mitchell Steiner, MD, said that the current phase 2b study of enobosarm with semaglutide is only examining people aged ≥ 60 years to maximize the functional outcome benefit. But Phase 3, he anticipates, will be "all comers, for sure. And then we'll embed special populations." The thinking, he said, is "Wherever the GLP-1s go, we go."
Fitch has participated on advisory boards for Jenny Craig, Novo Nordisk, Eli Lily, Sidekick Health, and Vivus. Dobs had no disclosures beyond conducting research for Veru.
Miriam E. Tucker is a freelance journalist based in the Washington DC area. She is a regular contributor to Medscape Medical News, with other work appearing in the Washington Post, NPR's Shots blog, and Diatribe. She is on X @MiriamETucker.
