IGF-1 LR3, also called Long R3 IGF-1, is a modified analog of insulin-like growth factor 1 (IGF-1) engineered to be far less affected by the binding proteins that normally restrict IGF-1 activity. It is widely used as a cell culture supplement and as a research tool for studying IGF-1 receptor signaling. This guide covers what IGF-1 LR3 is, how it works at the molecular level, how it is handled in the lab and how to check batch quality.
What is IGF-1 LR3?
Native IGF-1 is a 70-amino-acid peptide hormone that is structurally related to insulin. It plays a central role in growth signaling, and much of its activity in the body is regulated by a family of IGF binding proteins (IGFBPs) that bind IGF-1 and control how much of it is free to reach its receptor.
IGF-1 LR3 differs from native IGF-1 in two ways:
- The R3 substitution: the glutamic acid at position 3 is replaced with arginine. This change sharply reduces the peptide's affinity for IGF binding proteins.
- The long extension: a 13-amino-acid extension peptide is added to the N-terminus, which further affects binding protein interactions and aids recombinant production.
The result is an 83-amino-acid analog that remains able to activate the IGF-1 receptor but is much less sequestered by binding proteins. In experimental systems this generally means more of the peptide stays available to cells and its activity persists longer than native IGF-1.
IGF-1 LR3 is a research compound. It is not an approved medicine in the United States, and PRIME supplies it for laboratory research use only.
How IGF-1 LR3 works: mechanism studied in research
IGF-1 LR3 acts through the same receptor as native IGF-1, so its mechanism is best understood through IGF-1 receptor biology.
IGF-1 receptor activation
The IGF-1 receptor (IGF-1R) is a receptor tyrosine kinase. When a ligand binds, the receptor autophosphorylates and recruits adapter proteins such as the insulin receptor substrate (IRS) proteins and Shc.
Downstream signaling
Two major pathways are studied downstream of IGF-1R activation:
- PI3K-Akt-mTOR: associated with cell survival, protein synthesis and metabolic signaling.
- Ras-MAPK (ERK): associated with cell proliferation and differentiation.
Researchers use IGF-1 LR3 to activate these pathways in cell models and to study how they control growth, survival and differentiation.
Why reduced binding protein affinity matters
In serum-containing cultures and in animal models, IGF binding proteins can bind most native IGF-1. Because IGF-1 LR3 largely escapes this binding, it has been used to separate receptor-driven effects from binding protein regulation and to deliver more consistent receptor stimulation in culture.
Areas of research
IGF-1 LR3 is used in both applied and basic research. Common themes include:
- Cell culture media supplementation, including biomanufacturing cell lines
- Cell proliferation and survival signaling
- Myoblast proliferation and differentiation in muscle cell models
- IGF-1 receptor pharmacology and downstream kinase signaling
- IGF binding protein biology and how binding proteins regulate IGF activity
- Growth and metabolism in animal models
- Comparison with native IGF-1 and other growth factor analogs
These describe research uses and experimental findings. They are not evidence of any effect of the research material in people.
Choosing between IGF-1 LR3 and native IGF-1
Which form a lab uses depends on the research question. Native IGF-1 is the better choice when the aim is to study normal physiology, including how binding proteins shape IGF activity. IGF-1 LR3 is often preferred when the goal is steady, receptor-driven stimulation in culture, or when binding proteins in serum would otherwise mask receptor effects. Researchers comparing results across studies should note which form was used, since the two are not interchangeable in experimental outcomes.
Key facts table
| Property | IGF-1 LR3 |
|---|---|
| Class | Growth factor analog (modified IGF-1) |
| Structure | 83-amino-acid analog: human IGF-1 with Glu3 to Arg substitution plus a 13-residue N-terminal extension |
| Other names | Long R3 IGF-1, LR3 IGF-1 |
| Target | IGF-1 receptor (receptor tyrosine kinase) |
| Key design feature | Greatly reduced binding to IGF binding proteins |
| Form supplied | Lyophilized powder in a sealed vial |
| Research status | Research compound; not an approved medicine in the US |
| Storage | Cold, dry and protected from light; refrigerate after reconstitution |
Handling and storage in the lab
IGF-1 LR3 is a larger, folded protein compared with short peptides, so it benefits from careful handling.
- Before reconstitution: keep vials sealed, cold, dry and away from light. For longer storage, freezer conditions are commonly used.
- Reconstitution: labs often use bacteriostatic water or a sterile diluent suited to their protocol; some cell culture protocols call for a mildly acidic diluent. Add diluent slowly and swirl gently. Do not shake, since agitation can denature folded proteins.
- After reconstitution: keep the solution refrigerated and protected from light, labeled with date, lot number and concentration.
- Adsorption: dilute protein solutions can stick to plastic and glass surfaces, so many labs use low-binding tubes or add carrier protein according to their protocol.
- Stability: prepare single-use aliquots to avoid repeated freeze-thaw cycles.
These are general laboratory handling notes only and are not guidance for personal use.
Quality and lab results
For a modified growth factor, confirming the correct sequence and purity is central to reproducible cell signaling experiments. Every PRIME batch is independently tested, and the certificate of analysis for each lot is available on the lab results page. Match the lot number on your vial to its report before use. Research material is available on the IGF-1 LR3 product page.
Related research
IGF-1 LR3 is often studied alongside compounds that act on the growth hormone axis upstream of IGF-1. See the CJC-1295 and Ipamorelin blend guide, the tesamorelin research guide, and the Ipamorelin vs tesamorelin comparison for background on growth hormone secretagogues.
FAQ
What is IGF-1 LR3?
IGF-1 LR3 is an 83-amino-acid analog of IGF-1 with an arginine substitution at position 3 and a 13-residue N-terminal extension. These changes reduce its binding to IGF binding proteins while keeping IGF-1 receptor activity.
What does LR3 stand for?
The L refers to the long N-terminal extension, and R3 refers to the arginine that replaces glutamic acid at position 3 of the IGF-1 sequence.
How is IGF-1 LR3 different from native IGF-1?
Both activate the IGF-1 receptor, but IGF-1 LR3 is far less bound by IGF binding proteins. In experimental systems this leaves more of it free to reach the receptor, and its activity persists longer.
Is IGF-1 LR3 FDA approved?
No. IGF-1 LR3 is a research compound and is not an approved medicine in the United States. PRIME supplies it for laboratory research use only.
Why is IGF-1 LR3 used in cell culture?
Because it largely avoids IGF binding proteins, IGF-1 LR3 provides more consistent IGF-1 receptor stimulation in culture, which supports cell growth and survival in many cell lines used in research and biomanufacturing.
For laboratory research use only. Not for human consumption. Not a drug, food or cosmetic.