IGF-1 LR3

Research · IGF-1 LR3

Overview

IGF-1 LR3 (Long R3 IGF-I) is an 83-amino-acid recombinant analog of human insulin-like growth factor 1. It differs from the native 70-residue sequence by substitution of arginine for glutamic acid at position 3 and by a 13-residue N-terminal extension. These modifications sharply reduce affinity for IGF-binding proteins while preserving activity at the type 1 IGF receptor. Originally developed by Australian researchers in the early 1990s, it is widely used as a cell culture supplement and as a research tool in IGF receptor pharmacology.

Mechanism of action

Activates the type 1 IGF receptor (IGF-1R), a receptor tyrosine kinase expressed in skeletal muscle, bone, liver, and many cultured cell lines. Ligand binding triggers receptor autophosphorylation and recruitment of insulin receptor substrate proteins, activating the PI3K/Akt/mTOR pathway that regulates protein synthesis and cell survival, and the Ras/MAPK pathway that regulates proliferation and differentiation. Because native IGF-1 is largely sequestered by IGF-binding proteins in serum and conditioned media, the reduced binding-protein affinity of the LR3 analog increases the free, receptor-available fraction and extends its effective activity in experimental systems.

Key research findings

1. 01

   Comparative in vitro studies of recombinant fusion analogs established that reduced IGF-binding protein affinity, rather than altered receptor affinity, accounts for the enhanced biological potency of the Long R3 variant.

2. 02

   Preclinical rodent studies characterized anabolic endpoints, including nitrogen balance and organ growth, in dexamethasone-treated models, with IGF-1 variants producing larger responses than native IGF-1.

3. 03

   Myoblast culture studies use the analog to characterize IGF-driven proliferation and differentiation in the presence and absence of exogenous binding proteins.

4. 04

   Infusion studies in pigs and guinea pigs documented reduced endogenous IGF-1, IGFBP-3, and growth hormone concentrations, consistent with feedback suppression of the somatotropic axis.

Published references

• 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

  Francis GL et al. — J Mol Endocrinol, 1992 · PMID: 1378742

• Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats

  Tomas FM et al. — Biochem J, 1992 · PMID: 1371669

The information above is derived from published preclinical and clinical research. It is provided for educational purposes only and does not constitute medical advice, diagnosis, or treatment recommendations.