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Off-Target Biology: The Critical Comparison Point
ACE-031’s broader ligand sequestration introduces off-target effects that Follistatin largely avoids. BMP9 and BMP10, which signal through ActRIIB and are sequestered by ACE-031, play important roles in vascular endothelial homeostasis — BMP9/ActRIIB-ALK1 sign
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- ACE-031’s broader ligand sequestration introduces off-target effects that Follistatin largely avoids. BMP9 and BMP10, which signal through ActRIIB and are sequestered by ACE-031, play important roles in vascular endothelial homeostasis — BMP9/ActRIIB-ALK1 signalling maintains endothelial quiescence and prevents abnormal vascular remodelling. ACE-031 sequestration of BMP9/10 in clinical trial participants produced telangiectasias (dilated small vessels visible on the skin surface) in 24% of subjects, and epistaxis (nosebleeds) in 11%, leading to early trial discontinuation for DMD and healthy volunteer studies.
- In rodent models, ACE-031 at hypertrophy-relevant doses (10mg/kg 2×/week) produces measurable increases in pulmonary vascular density by µCT (8.4→10.2 vessel density index, P<0.05) and von Willebrand factor plasma elevation (+22-28% by ELISA) — consistent with vascular endothelial activation. FST-315 at equivalent doses shows neither effect (pulmonary vessel density NS, vWF NS), consistent with its lack of BMP9/10 binding.
- For research designs where vascular endpoints are not under study, ACE-031’s vascular biology introduces a potential confounder — particularly in tumour models where vascular density is itself an endpoint, or in cardiovascular models where vWF is a thrombotic risk marker. Researchers should include vascular histology (CD31+, α-SMA, von Willebrand factor IHC) in any ACE-031 study design to monitor and document this off-target effect.
- FST-315 does sequester BMP family members at high concentrations, but its primary research-relevant affinities are for activin A (Kd ~0.1nM), activin B (~0.3nM) and myostatin (~0.5-1nM), with substantially weaker affinity for BMP9/10 (Kd ~50-100nM, requiring concentrations well above those achieved at standard research doses). For vascular-safe myostatin/activin inhibition in muscle research, FST-315 provides the better safety profile with mechanistically cleaner interpretation.
- 🔗 Related Reading: For context on ActRIIB biology in the broader muscle research landscape, see our ACE-031 Pillar Guide.