HM500197: Hanmi's Myostatin Peptide, Read Carefully
A viral post says Hanmi's new peptide matched Lilly's muscle drug and is built to pair with GLP-1s. Hanmi's own poster shows something narrower: promising, selective, and so far tested only in cells and obese mice.
Myostatin, and Why Hanmi Built a Peptide
Myostatin (GDF-8) was identified in 1997 as a negative regulator of skeletal muscle growth: mice lacking the gene had individual muscles weighing 2-3 times those of normal mice (PMID 9139826). Blocking it is the idea behind every drug in this class.
Most drugs in this class are antibodies. Per Hanmi's poster, HM500197 is a de novo-designed peptide conjugated to a fatty-acid chain that binds serum albumin to extend its half-life. Hanmi says that design targets once-weekly dosing and co-formulation with incretin drugs; in the mouse studies it was dosed every two days.
Bimagrumab blocks the activin type II receptors, which carry signals from both myostatin and activin A (PMID 38218536). In Hanmi's cell reporter assay, HM500197 matched bimagrumab's myostatin inhibition (106.8% relative activity) but showed under 0.01% of its activity against activin A and B and 0.02% against BMP9. Hanmi argues that selectivity could mean fewer off-target effects; that is untested in people.
GLP-1 weight loss is not all fat. In obese mice, semaglutide reduced both muscle and fat mass, and adding an ActRII antibody preserved lean mass while increasing fat loss (PMID 38218536). A 2026 review notes GLP-1 drugs and tirzepatide preferentially reduce fat, but significant lean-mass loss has been described in people with pronounced weight reduction (PMID 41954678).
What the Data Shows
Key Takeaways
- Hanmi's ADA 2026 poster reports HM500197 inhibited myostatin about as potently as bimagrumab in a cell assay, with under 0.01% activity against activin A and B and 0.02% against BMP9.
- In diet-induced obese mice over 28 days, HM500197 raised lean mass by up to 6.7% and cut fat mass by up to 17.0%; bimagrumab gave 11.0% and 21.0%.
- Hanmi reports skeletal-muscle gains comparable to bimagrumab, without increases in liver or heart weight.
- Added to tirzepatide in obese mice, HM500197 preserved lean mass without changing overall body-weight loss; the drop in fat mass was a non-significant trend.
- In humans, adding the selective myostatin antibody apitegromab to tirzepatide meant 1.9 kg less lean-mass loss than placebo at 24 weeks (n=102).
- Whether HM500197 works or is safe in humans: Hanmi's June 2026 materials report only cell and mouse data and give no clinical timeline.
- Whether the once-weekly dosing Hanmi designed for holds in people; the mice were dosed every two days.
- Whether myostatin-only blockade beats broader ActRII blockade in people; the mouse comparison cuts both ways (less total lean mass, similar skeletal muscle).
- Whether preserved lean mass on a GLP-1 drug translates into better strength or function in humans.
- Independent replication: the HM500197 data is a company poster, not a peer-reviewed paper.
Frequently Asked Questions
What is HM500197?
HM500197 is Hanmi Pharmaceutical's investigational, long-acting peptide designed to block myostatin, a protein that limits muscle growth. Hanmi unveiled it at the American Diabetes Association's 2026 Scientific Sessions as a candidate to preserve muscle during GLP-1 and incretin weight loss. All published data so far come from cell assays and obese mice.
Did HM500197 really match Lilly's bimagrumab?
Only partly. In Hanmi's cell assay its myostatin inhibition was comparable to bimagrumab's. In obese mice it raised lean mass by up to 6.7% versus 11.0% with bimagrumab, and cut fat mass by up to 17.0% versus 21.0%. Hanmi reports similar skeletal-muscle gains without increases in liver or heart weight. These are company poster results in mice, not a human head-to-head.
Has HM500197 been tested in humans?
No human results have been reported. Hanmi's June 2026 press release and ADA poster describe in vitro and mouse studies only and give no clinical-trial timeline. Hanmi's other muscle-focused obesity candidate, HM17321, is the one it describes as being in a US Phase 1 trial.
How does HM500197 compare with apitegromab and bimagrumab?
Both are antibodies with human data. Bimagrumab blocks activin type II receptors; in the phase 2 BELIEVE trial (n=507, 48 weeks), bimagrumab 30 mg/kg plus semaglutide 2.4 mg produced a mean 17.8 kg weight loss at week 48 versus 14.2 kg with semaglutide alone and 3.3 kg with placebo (PMID 41772149). Apitegromab selectively blocks myostatin activation and reduced lean-mass loss on tirzepatide by 1.9 kg versus placebo at 24 weeks (PMID 42260100). HM500197 is a selective peptide with mouse data only.
Is HM500197 available to buy?
No. HM500197 is an unapproved preclinical compound in development at Hanmi, and Hanmi has not reported dosing it in people. For muscle preservation on a GLP-1 drug today, the evidence-backed basics remain adequate protein and resistance training, discussed with your prescriber.
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Peer-Reviewed References
Educational purposes only. Not medical advice.
HM500197 data on this page come from Hanmi Pharmaceutical's ADA 2026 poster 3073-LB and June 16, 2026 press release (company-reported, not peer-reviewed). HM500197 is not approved for any use.