Stamulumab (MYO-029)
Stamulumab (MYO-029) was the first anti-myostatin monoclonal antibody tested in humans, a recombinant human IgG1 designed to neutralise circulating myostatin in adults with muscular dystrophy. A Phase 1/2 safety trial found it well tolerated but showed no significant improvement in muscle strength or function, and development was discontinued.
01 Overview
Stamulumab targets myostatin directly rather than trapping it at the receptor. In a randomised, placebo-controlled Phase 1/2 study across several adult muscular dystrophies (FSHD, Becker, limb-girdle), the antibody demonstrated an acceptable safety profile, with hypersensitivity being the main concern at higher doses.
Crucially, the trial did not show meaningful gains in muscle strength or size, tempering early enthusiasm that simply blocking myostatin would translate to functional benefit in humans. The negative result is historically important: it established that myostatin blockade is achievable and reasonably safe, but not automatically effective for muscle disease.
02 Mechanism
A neutralising IgG1 monoclonal antibody that binds mature myostatin (GDF-8) in the circulation, preventing it from engaging activin type II receptors and relieving myostatin's suppression of muscle growth.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Trial dosing | 1–30 mg/kg/wk | IV | Dose-escalation range studied in the Phase 1/2 muscular dystrophy trial; not marketed. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Muscle strength improvementThe trial did not demonstrate statistically significant gains in strength or function despite target engagement. | None significant | Clinical | |
| Trend toward increased muscle massSome measures suggested minor increases in muscle size that did not reach significance. | Small, non-significant | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Immunogenicity (anti-drug antibodies)Development of antibodies against the drug can reduce efficacy over time. | Mild | Uncommon | Clinical | |
| Hypersensitivity reactionsCutaneous hypersensitivity was seen mainly at the two highest dose levels. | Moderate | Uncommon | Clinical |