IGF-1 LR3

Chemical identity

IGF-1 LR3 is recombinant human IGF-1 carrying two deliberate modifications: an arginine substituted for glutamic acid at position 3, and a thirteen-residue extension added to the N-terminus. At 83 residues it is a small protein rather than a peptide, and it is produced by expression rather than solid-phase synthesis.

Both modifications serve one purpose — reducing affinity for the IGF binding proteins. In normal serum and in most culture media, the great majority of IGF-1 is bound to IGFBPs and unavailable to the receptor. LR3 largely escapes that sequestration, which is what makes it useful.

Mechanism in research models

LR3 binds IGF-1R, a receptor tyrosine kinase, and triggers autophosphorylation followed by recruitment of IRS-1 and Shc. The two principal downstream arms are PI3K/Akt/mTOR, associated with protein synthesis and survival signalling, and Ras/MAPK, associated with proliferation.

The relevant pharmacological point is potency in context. LR3's intrinsic receptor affinity is somewhat lower than native IGF-1, but because it is not sequestered by binding proteins its free concentration is far higher — producing markedly greater effect in systems where IGFBPs are present. In a binding-protein-free assay that advantage disappears.

It retains measurable affinity for the insulin receptor. In systems expressing both, effects attributed to IGF-1R signalling should be confirmed with a selective inhibitor rather than assumed.

What the literature establishes

LR3 is a standard reagent in cell-culture work, widely used as a serum-free medium supplement in mammalian cell production. The industrial literature on this application is substantial and consistent.

The IGF-1 axis is also central to cancer biology, where sustained IGF-1R signalling supports proliferation and resists apoptosis. Any protocol using LR3 in a proliferative system should treat that as a designed variable, not a side effect.

Note the ceiling on translation: results obtained with LR3 do not transfer cleanly to native IGF-1 physiology precisely because the binding-protein interaction — a major regulatory layer in vivo — has been engineered out.

Handling, reconstitution and storage

Lyophilised material is typically held at −20 °C; the validated condition is the one on the lot documentation. As a folded protein rather than a linear peptide, LR3 carries tertiary structure that can be lost irreversibly; a denatured preparation will not recover on cooling.

Reconstitute in dilute acetic acid or a buffer at the pH stated on the certificate, then dilute into medium. Adding lyophilised protein directly to neutral buffer frequently produces incomplete dissolution and aggregation.

Carrier protein — typically 0.1% BSA — is standard for dilute working solutions. Without it, protein adsorbs to tube and pipette surfaces and the effective concentration drops in ways that will not appear in your calculations. Never vortex, and never re-freeze a thawed aliquot.

Analytical documentation

Expect SDS-PAGE, RP-HPLC purity, endotoxin level and a bioassay-derived activity figure. For a recombinant protein, purity by chromatography is not sufficient — an ELISA or cell-based potency result is what distinguishes correctly folded material from a correct mass that has lost its structure.

Endotoxin matters in cell culture even at low concentrations. Ask for the figure in EU/mg, and treat its absence from a certificate as a reason to look elsewhere.

References and authoritative sources

Chemical identity, regulatory status and anti-doping classification should be confirmed against primary sources rather than against this page. The records below are the ones to check first.

1. PubChem compound record (US National Library of Medicine)
2. PubMed indexed literature
3. UniProt protein record

These are database and regulatory sources. Citations to specific primary papers are being added to this page as part of ongoing scientific review; until they appear, treat the mechanism and literature sections above as a summary to verify rather than a citation of record.