IGF-1 LR3
Long Arginine-3 Insulin-like Growth Factor-1
Half-life: ~20–30 hours (extended vs native IGF-1 ~10–12 min free)
Research Profile
Relative research assessments — educational reference only.
Target Receptors
Critical Research Warning
Research chemical — not for human consumption. IGF-1 is a potent growth factor; unregulated use carries theoretical malignancy risk and hypoglycemia. Banned by WADA.
"A modified recombinant IGF-1 with an arginine substitution and 13-residue N-terminal extension that reduces binding to IGF-binding proteins, increasing bioavailability. The FDA-approved drug mecasermin is the unmodified reference compound."
Full Description
IGF-1 LR3 is a recombinant analog of insulin-like growth factor-1 engineered with an arginine at position 3 and an additional 13-amino-acid N-terminal extension (LR3 = Long Arginine-3). These modifications dramatically reduce its affinity for IGF-binding proteins (IGFBPs), increasing free IGF-1 bioavailability and half-life relative to native IGF-1. IGF-1 mediates many growth-promoting and anabolic effects of growth hormone. The unmodified peptide (mecasermin) is FDA-approved for severe primary IGF-1 deficiency; LR3 itself is an investigational research compound widely used in cell culture and animal models and is a doping-testing target.
Mechanism of Action
Activates the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase, triggering PI3K-Akt and MAPK signaling cascades that promote protein synthesis, cell proliferation, and anti-apoptotic survival. Reduced IGFBP binding increases receptor exposure.
Reported Benefits
- • Anabolic effects on skeletal muscle and protein synthesis in models
- • Longer half-life than native IGF-1 due to reduced IGFBP binding
- • Standard tool in cell culture and tissue-engineering research
- • Mediates many GH-dependent growth and repair functions
Potential Side Effects
- • Hypoglycemia (insulin-like activity)
- • Fluid retention and joint pain reported with IGF-1 class
- • Injection site reactions
- • Theoretical mitogenic / tumor-promotion risk
Frequently Asked Questions
Why is IGF-1 LR3 "long"?▼
Is IGF-1 LR3 the same as mecasermin?▼
What are the main safety concerns?▼
For Research Reference Only
Not medical advice. Peptides may be regulated or restricted in your jurisdiction.
References
- 1.Mecasermin.. PubMed (2008). Keating GM, et al.. pubmed.ncbi.nlm.nih.gov/18481900/ ↑
- 2.Profile of mecasermin for the long-term treatment of growth failure in children and adolescents with severe primary IGF-1 deficiency.. PubMed (2009). Fintini D, et al.. pubmed.ncbi.nlm.nih.gov/19707272/ ↑
- 3.IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep.. PubMed (2025). White A, et al.. pubmed.ncbi.nlm.nih.gov/39679943/ ↑
- 4.Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris.. PubMed (2023). Lu Z, et al.. pubmed.ncbi.nlm.nih.gov/37261455/ ↑
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