IGF-1 LR3

IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is an engineered analog of human IGF-1 designed to resist capture by IGF binding proteins, and it is most commonly encountered as a laboratory cell-culture reagent rather than an approved medicine. The molecule keeps the full insulin-like growth factor-1 sequence but adds a 13-amino-acid extension at one end and swaps a single residue near the start. Those two changes blunt the molecule’s affinity for the binding proteins that normally sequester IGF-1 in the body, leaving more of it free to engage its receptor in a culture dish. This page is an informational reference only. It is not medical advice, does not endorse any vendor, and does not provide human dosing.

What is IGF-1 LR3?

Native insulin-like growth factor-1 (IGF-1) is a 70-amino-acid protein, structurally related to insulin, that plays a central role in cell growth, survival and metabolism. IGF-1 LR3 is a recombinant analog of that protein, 83 amino acids long, produced in E. coli and supplied as a lyophilized (freeze-dried) powder. Its name encodes its two defining modifications: “R3” refers to a substitution of arginine for glutamic acid at position 3 (Glu3-to-Arg3), and “Long” refers to an extra 13-residue peptide stretch added to the N-terminus.

Reported chemical descriptors include CAS number 946870-92-4, the molecular formula C400H625N111O115S9, and a molecular weight near 9,111 Da (sources cite roughly 9,111-9,117 Da depending on calculation method). The compound was originally developed as a more potent, more stable growth-factor supplement for serum-free and low-serum cell culture, and that is the context in which suppliers such as Sigma-Aldrich (Merck) catalog it. It is a research reagent, not a drug approved for human use.

How IGF-1 LR3 is studied to work

In laboratory systems, IGF-1 LR3 acts on the same machinery as native IGF-1, but the structural edits change how much of it stays available. The proposed mechanism, drawn from IGF-1 biology, can be summarized as follows:

• IGF-1 receptor (IGF-1R) engagement. Like native IGF-1, the analog binds and activates IGF-1R, a receptor tyrosine kinase, triggering receptor autophosphorylation.
• Reduced IGFBP binding. The Arg3 substitution and N-terminal extension together disrupt the surface that IGF binding proteins (IGFBP-1 through -6) recognize, lowering IGFBP affinity by roughly two-to-three orders of magnitude in reported assays.
• Greater free fraction and longer functional half-life. Because less of the molecule is captured by binding proteins, more remains free to act, and it persists longer in research models.
• Downstream PI3K/Akt and MAPK signaling. Activated IGF-1R recruits IRS-1 and Shc adaptor proteins, feeding the PI3K/Akt pathway (cell survival and protein synthesis) and the Ras/MAPK (ERK) pathway (proliferation).

Reported effects in the research literature

Most of what is described for IGF-1 LR3 comes from in-vitro cell culture and animal studies, where its enhanced potency is the main point of interest:

• Increased proliferation and viability of cultured cells in serum-free or low-serum media.
• Higher recombinant-protein yields when used as a growth-factor supplement in bioprocessing cell lines.
• Potency in vitro reported as greater than that of native IGF-1 or insulin in some assays, attributed to reduced IGFBP capture.
• Activation of growth and survival signaling consistent with general IGF-1R biology.

What this does not mean: these observations are from controlled laboratory and animal settings, not from rigorous human trials of IGF-1 LR3. In-vitro potency does not translate directly into a safe or predictable effect in a living person, and the very property that makes the analog useful in a dish, more free growth-factor activity, is also a source of safety concern in whole organisms.

What the human evidence shows

There is no body of controlled human clinical-trial evidence supporting IGF-1 LR3 as a therapy, and it is not an approved drug anywhere as a human medicine. The structurally related, FDA-approved product is mecasermin (Increlex), which is recombinant human IGF-1 (not the LR3 analog), indicated narrowly for growth failure in children with severe primary IGF-1 deficiency. Mecasermin’s labeling is instructive about the hazards of pushing IGF-1 activity in people.

Documented concerns for IGF-1 therapy include hypoglycemia (low blood sugar, sometimes severe), which is why mecasermin must be dosed with food, along with hypersensitivity reactions, fluid retention, intracranial hypertension and tonsillar/adenoid hypertrophy. Because IGF-1 LR3 produces even more sustained, less-regulated IGF-1R signaling, extrapolating its effects to humans is not supported and is potentially riskier than the approved native-sequence drug. Anyone with a genuine medical condition should speak with a licensed clinician; this page does not substitute for medical care.

Handling, storage and reconstitution (research context)

The notes below describe general laboratory handling of a lyophilized peptide reagent and are not instructions for any human use.

• Storage of powder: keep the sealed, lyophilized vial desiccated and cold, commonly at -20C, away from light and moisture until use.
• Reconstitution: peptides of this type are typically dissolved in a small volume of dilute acetic acid or sterile water per the supplier’s datasheet, then diluted into culture medium or buffer.
• Working solution: reconstituted material is generally held briefly at 2-8C or aliquoted and frozen to limit degradation.
• Freeze-thaw: repeated freeze-thaw cycles degrade peptides, so single-use aliquots are preferred.
• Sterility: aseptic technique and clean labware matter, especially for cell-culture applications. See our guides on how to reconstitute peptides and sterile technique.

Cautions and considerations

• Growth-factor / cancer-signaling caution. IGF-1R signaling drives proliferation and survival pathways heavily implicated in tumor biology; sustained, unregulated IGF-1 activity is a recognized safety concern.
• Metabolic effects. IGF-1 activity overlaps with insulin signaling and can lower blood glucose, a hazard well documented for the approved IGF-1 drug.
• Not approved for human use. IGF-1 LR3 is a research reagent; quality, identity and purity of materials sold outside regulated supply chains are not assured.
• Sport status. IGF-1 and its analogs are prohibited in sport by anti-doping rules.
• Informational only, 21+. This content is educational, is not medical advice, and does not recommend, sell or endorse any product or protocol.

Frequently asked questions

Is IGF-1 LR3 the same as IGF-1?

No. IGF-1 LR3 is an engineered analog of native IGF-1. It retains the IGF-1 sequence but adds an arginine-3 substitution and a 13-amino-acid N-terminal extension, which reduce its binding to IGF binding proteins and increase its potency and persistence in laboratory models.

Why is IGF-1 LR3 described as longer-acting?

In the body, native IGF-1 is largely bound by IGFBPs, limiting how much is free and active. The structural changes in IGF-1 LR3 sharply lower IGFBP binding, so more remains free; in animal studies this corresponds to a longer functional half-life. Exact values vary by model.

Is IGF-1 LR3 an approved drug?

No. It is sold as a research reagent and cell-culture supplement, not an approved human medicine. The related FDA-approved product is mecasermin (recombinant human IGF-1), used narrowly in pediatric primary IGF-1 deficiency, not IGF-1 LR3.

What are the main safety concerns?

Based on IGF-1 biology and the labeling of approved IGF-1 therapy, the principal concerns are hypoglycemia and the broad role of IGF-1R signaling in cell proliferation and cancer biology. There is no controlled human trial evidence establishing safe use of IGF-1 LR3 in people.

Related compounds and further reading

• How to reconstitute peptides
• Sterile technique
• Browse the peptide library
• Reconstitution calculator

For informational use only. Not medical advice; consult a qualified healthcare professional. 21+.