IGF-1 LR3: Long R3 IGF-1 Analog Research Overview

IGF-1 (insulin-like growth factor 1) is a 70-amino acid polypeptide produced primarily in the liver in response to growth hormone stimulation. Endogenous IGF-1 circulates predominantly bound to a family of six IGF-binding proteins (IGFBPs), which regulate its bioavailability and half-life. Free IGF-1 binds the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase, and activates downstream PI3K/Akt and Ras/MAPK signaling.^[1]

IGF-1 LR3 was developed by Francis and colleagues in the early 1990s as a tool for studying IGF biology with reduced IGFBP interference. The Arg3 substitution dramatically reduces binding to IGFBPs while preserving IGF-1R binding, effectively making LR3 a 'free' IGF-1 analog in the bloodstream.^[2]

IGF-1 LR3 is studied as a research reference compound. It has not been approved by the FDA for any human therapeutic, diagnostic, or medical purpose.

IGF-1 LR3 has two engineered modifications relative to native IGF-1:

• N-terminal extension: 13 additional amino acids (MFPAMPLSSLFVN) added to the N-terminus of mature IGF-1

• Position 3 substitution: glutamate (Glu) replaced by arginine (Arg)

• Total length: 83 amino acids (vs 70 for native IGF-1)

• Molecular weight: approximately 9,200 Da

• Disulfide bonds: three (preserved from native IGF-1)

The IGFBPs bind IGF-1 in a region that includes the N-terminus and the early residues. The 13-amino acid extension and the Arg3 substitution disrupt this binding interface, reducing IGFBP affinity dramatically (estimates range from 100 to 1000-fold weaker binding).^[2][3]

Importantly, the IGF-1R binding interface is on a different face of the molecule. LR3's modifications target IGFBP binding selectively without disrupting receptor engagement, so the analog retains IGF-1R-binding affinity comparable to native IGF-1.

IGF-1 LR3's research-characterized activity is at the IGF-1 receptor.

IGF-1R is a receptor tyrosine kinase structurally related to the insulin receptor. Ligand binding induces receptor dimerization, autophosphorylation, and recruitment of IRS-1/IRS-2 signaling adapters that propagate to PI3K/Akt and MAPK pathways.^[4]

Because LR3 doesn't sequester to IGFBPs, the unbound (active) fraction is much higher than for native IGF-1 in identical preparation conditions. This makes LR3 useful for in vitro studies where IGFBP interference would complicate interpretation.^[3]

IGF-1 LR3 has been used across many preclinical research contexts.

Cell culture systems where IGFBPs in serum-containing media would otherwise sequester native IGF-1 are a primary application for LR3. Researchers use the analog to maintain bioavailable IGF-1 receptor signaling in serum-containing cultures.^[5]

Skeletal muscle cell differentiation and myotube formation assays use IGF-1R signaling as a research endpoint. LR3 is a tool for examining receptor-mediated effects on myogenic differentiation in vitro.^[6]

IGF-1R signaling is implicated in numerous cancer cell biology research questions. LR3 provides a research tool for studying receptor-mediated proliferation and survival pathways in cell lines without IGFBP confounders.^[4]

IGF-1 LR3 is a relatively large polypeptide with three disulfide bonds, requiring careful handling.

Lyophilized IGF-1 LR3 is stored at minus 20 degrees Celsius or colder. Repeated freeze-thaw cycles should be avoided. Reconstituted solution is sensitive to repeated freeze-thaw.

Acetic acid solutions (typically 0.1 percent acetic acid in water) are commonly used to reconstitute IGF-1 LR3, as the slightly acidic conditions help solubilize the peptide. Bacteriostatic water can also be used.

Quality verification includes HPLC for purity, mass spectrometry for identity confirmation matching the 83-amino acid modified sequence, and verification of correct disulfide bond formation by reduced/oxidized peptide mapping. Each batch of Instant Peptides IGF-1 LR3 ships with a full Certificate of Analysis.

Instant Peptides supplies IGF-1 LR3 as a synthetic lyophilized reference compound. Material is supplied to qualified research professionals. Not for human or animal consumption.

View the product page for current pricing and the Certificate of Analysis for the active batch.