IGF-1 LR3 (Long R3 IGF-1) is an 83-residue recombinant analogue of human insulin-like growth factor 1 carrying an arginine substitution at position 3 and a 13-residue N-terminal extension. The two changes cut its affinity for the IGF-binding proteins while leaving IGF-1 receptor binding largely intact, which is why it is the standard IGF-1 analogue used as a mitogen in serum-free cell culture media and in IGF-1 receptor signalling assays. NuVion supplies IGF-1 LR3 as a laboratory chemical for in vitro research use only.
Key facts
| Type | Recombinant IGF-1 analogue, IGF-1 receptor agonist |
| Amino acid count | 83 (13-residue extension plus the 70 residues of IGF-1) |
| Modifications | Glu3 to Arg substitution; N-terminal extension MFPAMPLSSLFVN; three disulfide bonds |
| Molecular weight | Approximately 9.1 kDa |
| CAS number | 946870-92-4 |
| Synonyms | Long R3 IGF-1, LR3-IGF-I, Long Arg3 IGF-1, LR3IGF-1 |
| Supplied form | Lyophilised powder in a sealed vial |
IGF-1 LR3
$159 AUD
View productResearch use only. Not for human or veterinary use.
Structure and chemistry
Human IGF-1 is a 70-residue single-chain polypeptide of about 7.6 kDa with B, C, A and D domains, homologous to proinsulin, and held together by three disulfide bonds (Cys6-Cys48, Cys18-Cys61 and Cys47-Cys52). IGF-1 LR3 keeps that fold and its cysteine pairing. The first change is the substitution of glutamate 3 in the B domain with arginine. Glu3 sits in the epitope that the IGF-binding proteins (IGFBP-1 to IGFBP-6) recognise, and replacing an acidic residue with a basic one disrupts that contact. The second change is the extension Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn fused to the N-terminus, a remnant of the fusion leader used for expression in E. coli that was retained once it was found to reduce IGFBP binding further.
Together the two modifications lower IGFBP affinity by orders of magnitude while reducing IGF-1 receptor affinity only modestly, by a few fold. In practice that makes the analogue more active than native IGF-1 in cell culture, because IGF-1 added to medium is largely sequestered by IGFBPs secreted by the cells or carried in with serum, whereas IGF-1 LR3 stays free to reach the receptor. The molecule is basic, with an isoelectric point above 8, and is most soluble in mildly acidic solution. Handling considerations follow from the structure: the disulfides make it sensitive to reducing agents, the methionine residues (including two in the extension) are susceptible to oxidation, and at low concentrations the protein adsorbs to plastic and glass unless a carrier protein is present.
Mechanism of action
IGF-1 LR3 acts through the type 1 IGF receptor (IGF-1R), a disulfide-linked alpha2beta2 receptor tyrosine kinase closely related to the insulin receptor. Ligand binding to the extracellular alpha subunits brings the two intracellular beta-subunit kinase domains together, and they transphosphorylate each other on activation-loop tyrosines (Tyr1131, Tyr1135 and Tyr1136 in the human receptor). The phosphorylated receptor recruits the adaptor proteins IRS-1, IRS-2 and Shc. IRS proteins engage the p85 subunit of PI3K, generating PIP3, activating PDK1 and Akt, and feeding into mTORC1 through TSC2, into protein synthesis through S6K1 and 4E-BP1, and into survival signalling through inhibition of FoxO transcription factors and GSK3beta. Shc engages Grb2 and SOS, activating Ras, Raf, MEK and ERK1/2, which drives cyclin D1 expression and progression through G1 of the cell cycle. IGF-1 LR3 also binds the insulin receptor and IGF-1R/IR hybrid receptors with lower affinity, so assays that need a clean IGF-1R readout use IGF-1R-selective inhibitors or knockdown as controls.
The IGFBPs are the second half of the mechanism. Six binding proteins are present in serum and are secreted by most cultured cells, binding native IGF-1 with affinities as high as the receptor and controlling how much free ligand is available. Because IGF-1 LR3 escapes this buffering, its concentration-response curves in cell assays are shifted to lower concentrations and are less variable between cell lines and serum lots than those of native IGF-1. The same property means IGF-1 LR3 is a poor probe for IGFBP biology itself and is used instead as the low-IGFBP-affinity comparator in ligand blot and surface plasmon resonance studies of binding protein interactions.
Research applications
- Mitogenic additive in serum-free and chemically defined culture media, where it replaces insulin at nanogram-per-millilitre concentrations for CHO, hybridoma and other production cell lines.
- IGF-1R signalling studies: receptor autophosphorylation, IRS-1 recruitment, and phospho-Akt, phospho-S6K1 and phospho-ERK1/2 readouts by western blot or in-cell assays.
- Proliferation and cell cycle assays (BrdU or EdU incorporation, cell counting) in fibroblast, epithelial and neuronal cell lines, and myotube formation assays in C2C12 myoblasts.
- Survival signalling assays after serum withdrawal, following caspase activation, FoxO phosphorylation and Bcl-2 family expression.
- Receptor binding studies as a competitor for labelled IGF-1, and IGFBP binding studies as the low-affinity control ligand.
- RP-HPLC, size-exclusion and LC-MS method development for disulfide-rich proteins, including oxidation and aggregation monitoring.
IGF-1 LR3 sits in NuVion’s Growth Hormones category with the GH secretagogue and GHRH-analogue peptides.
Handling in the laboratory
IGF-1 LR3 is supplied lyophilised and is reconstituted with bacteriostatic water added slowly down the wall of the vial and swirled, never vortexed, until dissolved. The reconstitution calculator converts vial content and diluent volume into a stock concentration, using a molecular weight of about 9,100 g/mol if molar units are needed. Where the assay is sensitive to benzyl alcohol, or where the stock will be diluted only a few fold into medium, sterile water or 10 mM acetic acid is an alternative diluent; the protein is more soluble at acidic pH. Working dilutions are made in buffer or medium containing at least 0.1% bovine serum albumin to limit adsorption to labware.
Unopened vials are kept sealed, dry, away from light and refrigerated as stated on the product documentation. Reconstituted stock is refrigerated and used within the period given on the documentation, or divided into single-use aliquots and frozen; repeated freeze-thaw cycles cause aggregation and loss of activity in disulfide-bonded proteins. Reducing agents such as DTT or 2-mercaptoethanol are kept out of stock solutions. The compound is characterised by RP-HPLC for purity and by mass spectrometry for identity, with the intact mass confirming both the extension and the correct disulfide-bonded state.
Testing and supply from NuVion
NuVion’s IGF-1 LR3 is manufactured at a GMP-audited facility and independently tested by Janoshik Analytical, with purity determined by RP-HPLC and identity confirmed by mass spectrometry. Most batches are tested, and the Certificate of Analysis for a tested batch is published on the product page and in the COA library. The product is supplied lyophilised in sealed vials and dispatched from within Australia.
Related compounds
Upstream of IGF-1 in the same category are HGH, the 191-residue recombinant growth hormone that drives IGF-1 expression through GH receptor and JAK2-STAT5 signalling, and sermorelin, the GRF(1-29) amide that acts at the GHRH receptor in pituitary cell models. The N-terminally truncated analogue IGF-1 DES reaches the same low binding protein affinity by deletion instead of extension, and the E domain peptide of the IGF-1Ec splice variant is covered in MGF.
Frequently asked questions
What is IGF-1 LR3 used for in research?
Its main use is as a mitogen in cell culture, particularly in serum-free media where it substitutes for insulin and gives reproducible IGF-1 receptor stimulation without interference from binding proteins. It is also the standard ligand for IGF-1R signalling experiments and the low-IGFBP-affinity comparator in binding protein studies.
How does IGF-1 LR3 differ from IGF-1?
IGF-1 LR3 has 83 residues against 70 for IGF-1: a 13-residue N-terminal extension and an arginine in place of glutamate at position 3. Those changes reduce binding to IGFBP-1 to IGFBP-6 by orders of magnitude while reducing IGF-1R affinity only a few fold, so more of the added analogue is available to the receptor in culture. The disulfide pattern and receptor pharmacology are otherwise the same.
Is IGF-1 LR3 a therapeutic good in Australia?
No. NuVion’s IGF-1 LR3 is a laboratory chemical for in vitro research. It is not included in the Australian Register of Therapeutic Goods, has not been assessed by the Therapeutic Goods Administration, and is not for human or veterinary use.
How should IGF-1 LR3 be stored?
Lyophilised vials are kept sealed, dry, protected from light and refrigerated per the product documentation. Reconstituted stock is refrigerated for short-term use or aliquoted and frozen, with dilute working solutions made fresh in carrier-containing buffer. Freeze-thaw cycles and reducing agents are avoided.
Research use only. This product is a laboratory chemical supplied for in vitro research. It is not included in the Australian Register of Therapeutic Goods and has not been assessed by the Therapeutic Goods Administration for quality, safety or efficacy. It is not for human or veterinary use, and nothing on this page is a representation about therapeutic use.
