What Is FLGR242?
FLGR242 is a recombinant follistatin-albumin fusion protein engineered to selectively inhibit myostatin (GDF-8) and related TGF-β superfamily ligands, while minimizing activin binding and extending circulation time via albumin fusion technology. Unlike native Follistatin-344 — which binds both myostatin and activin, raising endocrine safety concerns — FLGR242 is a fragmented, modified construct designed to preserve high-affinity myostatin antagonism while eliminating or greatly reducing activin binding. The albumin-binding fusion segment dramatically extends circulatory half-life compared to native follistatin, enabling weekly or biweekly dosing. As of 2026, FLGR242 remains strictly research-use only (RUO) with no regulatory approvals and no formal Phase II/III human trials.
Quick Reference
Member reference tables summarize the compound's research parameters.
Key Benefits
- Selective myostatin antagonism via ligand-trap mechanism — increases satellite-cell activation, protein synthesis, and fiber hypertrophy in preclinical models
- Designed to spare activin binding, potentially reducing off-target endocrine and gonadal effects compared to native FST-344
- Extended circulatory half-life through albumin-binding fusion, enabling once-weekly or biweekly dosing rather than daily injections
- Dual research tracks: primary muscle/hypertrophy biology and a secondary fibroblast-matrix signaling track for extracellular matrix and tissue remodeling studies
- Conceptualized as a muscle-preserving adjunct in GLP-1-driven weight loss contexts to counteract lean mass reduction
Mechanism of Action
FLGR242 functions as a ligand trap: it binds myostatin and other ActRIIB ligands, preventing receptor interaction and lifting the inhibitory "brake" on muscle satellite-cell activation, fiber hypertrophy, and metabolic signaling. Downstream effects include suppression of Smad2/3 phosphorylation in muscle and metabolic tissues, modulation of TGF-β pathway balance affecting fibrosis and tissue remodeling, and reduced ActRIIB receptor activity. The albumin-binding peptide linker allows FLGR242 to bind circulating serum albumin, substantially extending its functional half-life to an estimated 5–15 days — a design adapted from albumin-fusion and Fc-fusion biologics. A separate research framing characterizes FLGR242 as a sequence-defined peptide analog modeling fibroblast-regulatory motifs involved in extracellular matrix assembly, representing a non-muscle research track distinct from the myostatin-inhibition application.
Research Indications
Research Protocols
As reported in cited literature and research-community logs (see Research Citations below), not a personal dosing recommendation.
This member section describes parameters reported in the research literature.
Peptide Interactions
This member section summarizes reported compound interactions and evidence limitations.
Safety Notes
Included for harm-reduction awareness only, in the event this compound is encountered outside its labeled research use. Inclusion here does not imply RUO Codes endorses, recommends, or instructs human use.
This member section discusses research safety considerations and uncertainties.
Quality Indicators
Reported Research Time Points
This member section summarizes reported research time points.
Research Citations
- Lee SJ, McPherron AC. Regulation of myostatin activity and muscle growth. Proc Natl Acad Sci USA. 2001.
- Amthor H et al. The expression and action of myostatin-inhibitor follistatin isoforms during mouse embryogenesis. Dev Biol. 2002.
- Whittemore LA et al. Inhibition of myostatin in adult mice increases skeletal muscle mass and strength. Biochem Biophys Res Commun. 2003.
- Pearsall RS et al. A soluble activin type IIA receptor induces bone formation and improves skeletal integrity. PNAS. 2008.
- Note: No formal human pharmacokinetic or efficacy trials for FLGR242 are publicly available as of 2026. The above citations reflect foundational follistatin and myostatin biology underpinning FLGR242 research. All FLGR242-specific applications remain research-use only (RUO).