Most research peptides started out as drug candidates. IGF-1 LR3 started out as a laboratory tool. It was engineered in Australia in the early 1990s to do one job better than natural IGF-1: keep cells growing in a dish. It remains a standard supplement in industrial cell culture, which makes it unusual among the compounds on research-peptide shelves.
This guide explains what IGF-1 does, how LR3 was built, why it slips past the proteins that normally neutralize IGF-1, what it is actually used for, and what to check before ordering it.
The short answer
- IGF-1 LR3 (Long R3 IGF-I) is an 83-amino-acid analogue of insulin-like growth factor 1: the full 70-amino-acid IGF-1 sequence with arginine swapped in at position 3 and a 13-amino-acid extension added to the front.
- Those two changes sharply reduce binding to IGF binding proteins (IGFBPs) while keeping activity at the IGF-1 receptor, so more of the molecule stays available to act.
- It was developed by GroPep in Adelaide and described in 1992, specifically for mammalian cell culture, and it is still sold as a culture supplement, including as an insulin alternative for production cell lines such as CHO cells.
- It is not an approved drug anywhere, and IGF-1 and its analogues are prohibited in sport. The approved IGF-1 medicine, mecasermin, is a different, native-sequence product.
- Research-grade IGF-1 LR3 is a laboratory reagent, not for human or veterinary use.
IGF-1 LR3
Long R3 IGF-I · LR3-IGF-1 · Long Arg3 IGF-1
- Length
- 83 amino acids (native IGF-1 has 70)
- Mass
- About 9.1 kDa
- Changes
- Glutamic acid 3 replaced by arginine (“R3”); 13-amino-acid N-terminal extension (“Long”)
- Target
- The IGF-1 receptor, a tyrosine kinase
- Developed
- GroPep, Adelaide, Australia (Francis et al., 1992)
- Status
- No approved medical use; prohibited in sport
Where the evidence stands
- Cell studies
- Animal studies
- Human studies
- Controlled clinical trials
Native IGF-1 (mecasermin) is an approved drug, but no human trials of IGF-1 LR3 itself have been published.
What IGF-1 does
Insulin-like growth factor 1 is a 70-amino-acid protein held together by three disulfide bonds and structurally related to insulin. The liver releases most circulating IGF-1 in response to growth hormone, and IGF-1 carries out many of growth hormone’s effects on growth and tissue maintenance by activating the IGF-1 receptor on target cells. Our growth hormone peptides map shows where it sits in that axis.
IGF-1 rarely travels alone. Six IGF binding proteins hold most of it in the blood, much of it in a large complex with IGFBP-3 and a third protein called the acid-labile subunit. Binding proteins extend IGF-1’s lifespan but also keep it away from its receptor, so only a small free fraction is active at any moment. Many cultured cells also secrete their own IGFBPs, which soak up IGF-1 added to the dish.
How LR3 was built
Researchers at GroPep in Adelaide set out to make an IGF-1 that binding proteins would ignore. Two changes did it. Replacing glutamic acid at position 3 with arginine disrupts a key contact in the binding-protein interface, and adding a 13-amino-acid extension to the N-terminus interferes further. Receptor binding is largely preserved, so the result is a molecule that reaches the receptor far more easily than native IGF-1. The work was published in 1992, and the reagent is still marketed for cell culture today, including by Repligen as LONG R3 IGF-I.
What it is used for in research
- Serum-free cell culture and biomanufacturing. Manufacturers market LR3 as a growth-factor supplement for mammalian cell lines, including Chinese hamster ovary (CHO) cells used to produce biologic drugs, often as an alternative to insulin.
- IGF-1 receptor signalling studies. It is used to switch on the receptor’s downstream pathways, such as PI3K–Akt and MAPK, without binding-protein interference.
- Muscle and other cell models. Myoblast proliferation and differentiation studies use IGF-1 analogues to probe growth signalling.
- Early animal studies. In the 1990s, the Adelaide group compared LR3 with native IGF-1 in rats and reported greater growth-promoting potency for the analogues that escape binding proteins.
Research-grade IGF-1 LR3 with a batch-matched COA.
View IGF-1 LR3What IGF-1 LR3 is not
It is not mecasermin. The approved IGF-1 medicine is recombinant native-sequence IGF-1, authorized in the US and Europe for severe primary IGF-1 deficiency in children. Its labelling warns about low blood sugar, a reminder that IGF-1 has insulin-like effects.
It is not approved anywhere. IGF-1 LR3 has never been authorized as a medicine in Canada or elsewhere, and its human safety has not been studied in published trials. IGF-1 signalling is also studied in cancer biology, where higher circulating IGF-1 has been associated with the risk of some cancers in observational studies, one of several reasons growth-factor analogues receive careful scrutiny.
It is prohibited in sport. The World Anti-Doping Agency lists insulin-like growth factor 1 and its analogues under class S2, prohibited at all times.
What’s established and what isn’t
Reasonably well established
- LR3 binds IGF binding proteins far more weakly than native IGF-1 while still activating the IGF-1 receptor.
- It is more potent than native IGF-1 in cell culture, the purpose it was designed for.
- It is used as a growth-factor supplement in industrial cell culture.
Open questions
- Any data in people; no human trials have been published.
- Long-term effects of growth-factor signalling that bypasses the binding-protein system.
- How results in cultured cells, with their own binding proteins, translate to whole tissues.
Verifying IGF-1 LR3
At 83 residues with three disulfide bonds, IGF-1 LR3 is closer to a small protein than a typical research peptide, and that changes what a COA should show:
- A deconvoluted mass near 9.1 kDa. It appears as a ladder of multiply charged ions; see how to read a peptide mass spectrum.
- HPLC that resolves misfolded forms. Mispaired disulfide bonds give inactive isomers with exactly the same mass, so only chromatography can reveal them. See our HPLC testing guide.
- The production method. Proteins of this size are usually made recombinantly, often in bacteria, which makes endotoxin worth checking for any cell-culture work.
- A lot number matching your vial. See our COA guide.
IGF-1 LR383-residue IGF-1 analogueView product and COA
SermorelinUpstream in the GH axisView product and COA
TesamorelinStabilized GHRH analogueView product and COA
CJC-1295 + ipamorelinGHRH analogue with a ghrelin mimeticView product and COA
Research use only. IGF-1 LR3 from Pure Peptides Canada is a laboratory reagent for in-vitro research. It is not mecasermin or any approved drug, it is not for human or veterinary use, and nothing in this article is dosing or medical guidance.
Frequently asked questions
What is IGF-1 LR3?
IGF-1 LR3 is an 83-amino-acid analogue of insulin-like growth factor 1, made by swapping arginine in at position 3 and adding a 13-amino-acid extension to the front. It was developed in Australia in the early 1990s as a cell-culture supplement.
How is IGF-1 LR3 different from IGF-1?
Native IGF-1 has 70 amino acids and is mostly held by IGF binding proteins. IGF-1 LR3’s two changes make it bind those proteins only weakly while still activating the IGF-1 receptor, so more of it is available to act.
What is IGF-1 LR3 used for in research?
Mainly as a growth-factor supplement in mammalian cell culture, including production cell lines such as CHO cells, and as a tool for studying IGF-1 receptor signalling in cell models.
Is IGF-1 LR3 the same as mecasermin?
No. Mecasermin is recombinant native-sequence IGF-1, approved in the US and Europe for severe primary IGF-1 deficiency. IGF-1 LR3 is a different, modified molecule that has never been approved as a medicine.
Is IGF-1 LR3 approved in Canada?
No. It is not authorized as a drug in Canada or anywhere else. Research-grade IGF-1 LR3 is a laboratory reagent and is not for human use.
Is IGF-1 LR3 banned in sport?
Yes. The World Anti-Doping Agency prohibits insulin-like growth factor 1 and its analogues, including IGF-1 LR3, under class S2 at all times.
IGF-1 LR3 for laboratory research
Research-grade IGF-1 LR3 with an independent, batch-matched COA, tracked delivery from inside Canada and pricing in Canadian dollars.
References
- Francis GL, Ross M, Ballard FJ, et al. 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. J Mol Endocrinol. 1992;8(3):213–223.
- Firth SM, Baxter RC. Cellular actions of the insulin-like growth factor binding proteins. Endocr Rev. 2002;23(6):824–854.
- Repligen. LONG R3 IGF-I cell culture supplement: product information. Repligen
- World Anti-Doping Agency. The Prohibited List. WADA
For laboratory research use only. Not for human or veterinary use. This article summarizes published research for educational purposes and is not medical advice. Nothing here is intended to diagnose, treat, cure or prevent any disease.