Summary
IGF-1 LR3 is an engineered form of insulin-like growth factor 1 that binds poorly to IGF-binding proteins, so more of it stays free to act on the IGF-1 receptor. It was designed for, and is mainly used in, cell culture, where it is several times more potent than native IGF-1.
Structure
Human IGF-1 with an Arg substitution at position 3 and a 13-residue N-terminal extension, for 83 residues in total.
How it works
IGF-binding proteins normally hold most circulating IGF-1 inactive. The LR3 modifications reduce that binding, extending half-life and increasing potency at the IGF-1 receptor.
Research use cases
Areas where IGF-1 LR3 has been studied. Inclusion here does not mean it works for that purpose.
- Mammalian cell culture media
- Muscle cell proliferation assays
- IGF-1 receptor signalling research
What the research found
Binding-protein escape
Recombinant fusion analogs of IGF-1, including the long R3 form, showed that reduced IGF-binding-protein affinity rather than receptor affinity explained their greater biological potency.1
Safety and open questions
No human clinical data. Systemic IGF-1 activity carries risk of hypoglycaemia, and the IGF-1 pathway is implicated in tumour growth.
Regulatory status
Not approved for human use. Widely used as a cell-culture supplement.
Status was accurate when this page was last reviewed on October 26, 2026. Regulations change; check with the relevant authority before relying on it.
IGF-1 LR3: common questions
How is IGF-1 LR3 different from mecasermin?
Mecasermin is recombinant native IGF-1, FDA-approved for severe primary IGF-1 deficiency. IGF-1 LR3 is a modified analog not approved for any human use.
Is IGF-1 LR3 approved for human use?
Not approved for human use. Widely used as a cell-culture supplement.
References
- Francis GL, Ross M, Ballard FJ, et al. (1992). Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. Journal of Molecular Endocrinology.
Links open a PubMed search for the exact title, or the original source where one is given.