IGF-1 LR3: Long-Acting IGF-1 Analog — Research Overview

IGF-1 LR3 is an engineered, long-acting analog of a well-characterized growth factor, studied for its prolonged activity in cell and tissue models. This overview is for laboratory and educational reference only.

What is IGF-1 LR3?

IGF-1 LR3 (Long R3 Insulin-like Growth Factor 1) is a recombinant 83-amino-acid analog of native IGF-1. It differs from the parent molecule in two engineered ways: an arginine-for-glutamate substitution at position 3 (the "R3") and a 13-residue N-terminal extension (the "Long").¹ Together, these modifications reduce the analog's affinity for the insulin-like growth factor binding proteins (IGFBPs) that normally sequester circulating IGF-1.¹

Key reference identifiers used in the literature and on catalog documentation include CAS 946870-92-4 and a molecular weight of approximately 9117.5 Da. Because IGF-1 LR3 is a single-chain polypeptide of 83 residues, it is produced by recombinant expression rather than solid-phase synthesis, and its full-length structure is characterized by mass spectrometry rather than the shorter-sequence methods used for tripeptides.

Native IGF-1 is a 70-amino-acid single-chain polypeptide. The two engineering changes in IGF-1 LR3 are additive: the position-3 arginine substitution alters a residue implicated in binding-protein contact, while the N-terminal extension lengthens the chain by 13 residues.¹ Neither change is intended to alter the receptor-binding face itself, which is why research characterizes the analog as retaining IGF-1R engagement while shifting its binding-protein behavior.¹ Solution-structure work using multidimensional NMR has since mapped the analog's backbone and confirmed that its core fold mirrors that of native IGF-1, with the N-terminal extension appearing as a largely unstructured addition rather than a refolding of the receptor-binding domain.²³

Mechanism

Native IGF-1 signals through the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase that activates downstream pathways associated with growth, proliferation, and anabolic signaling.⁴ In research models, IGF-1 LR3 also acts at IGF-1R.¹⁴

The functional distinction is pharmacokinetic. Circulating IGF-1 is largely bound to a family of six high-affinity IGF-binding proteins, which act as a reservoir and limit how much ligand is free to engage the receptor at any moment.⁵ The Arg3 substitution and N-terminal extension lower IGFBP affinity, so a greater proportion of the analog remains unbound in laboratory systems.¹⁵ In cultured cells that secrete IGFBPs, this reduced sequestration is the reported basis for the analog's enhanced biological potency relative to native IGF-1 — the change is driven by binding-protein interactions rather than by tighter receptor binding.¹ This is also the structural rationale for the prolonged activity reported for IGF-1 LR3, with a half-life on the order of 20–30 hours described in research characterizations — substantially longer than the minutes-scale clearance of native IGF-1.

Research models

Preclinical and laboratory studies involving IGF-1 LR3 and closely related low-IGFBP-affinity variants have examined:

• Cell growth — proliferation assays in cultured cell lines, where reduced IGFBP sequestration increases the free ligand available to IGF-1R.¹
• Proliferation and differentiation — models probing IGF-1R-driven signaling pathways.⁴
• Anabolic signaling — tissue and cell models of protein-synthesis-associated signaling. In one comparative animal study, IGF-1 variants that bind IGFBPs poorly (including the LR3 variant) were reported to be substantially more potent than native IGF-1 in a catabolic model.⁶

These are strictly laboratory and preclinical research contexts, not established or approved uses. The prolonged activity profile reported for the analog is one reason it appears frequently in time-course experiments, where the longer window between clearance and receptor engagement is a variable of interest. Study of the analog in any of these models does not imply a validated outcome, and results in cell or animal systems do not translate to any human or animal application.

What the research does not establish

The evidence base for IGF-1 LR3 is preclinical and limited — recombinant-protein characterization, structural NMR studies, cultured-cell potency assays, and animal models of anabolism. Much of the primary literature dates from the analog's development as a research and cell-culture reagent, and the strongest claims that can be supported are comparative (LR3 versus native IGF-1 in defined laboratory systems), not clinical. There are no controlled human trials establishing safety or efficacy for any use, and Renova makes no human-use, performance, or therapeutic claims. The citations below are provided so researchers can consult the primary literature directly and judge the evidence for themselves.

How it's supplied

Renova supplies IGF-1 LR3 as a lyophilized powder. For laboratory work it is reconstituted with bacteriostatic water, then kept refrigerated at 2–8°C. Every unit ships with a per-batch third-party COA.

See Understanding Peptide Reconstitution and How to Store Research Peptides for general handling references, and the reconstitution calculator for working out concentrations for any vial size.

Purity & verification

Renova material is third-party tested, with identity and purity documented on a per-batch certificate of analysis. For growth-factor analogs like IGF-1 LR3, the COA is the primary reference for confirming that a given lot matches its stated identity, mass, and purity — typically via HPLC for purity and mass spectrometry for the intact-mass identity check that a full-length 83-residue polypeptide requires. See How to Read a Peptide COA, understand why peptide purity matters, and confirm any lot with Verify Your Vial.

Researchers comparing signaling approaches may also review Sermorelin, which is studied for stimulating endogenous growth-hormone secretion at the pituitary rather than acting directly at IGF-1R.

Explore IGF-1 LR3 →

References

1. 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. PMID: 1378742. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

2. Laajoki LG, Le Breton E, Shooter GK, et al. Secondary structure determination of 15N-labelled human Long-[Arg-3]-insulin-like growth factor 1 by multidimensional NMR spectroscopy. FEBS Lett. 1997;420(1):97–102. PMID: 9450557. ↩

3. Laajoki LG, Francis GL, Wallace JC, Carver JA, Keniry MA. Solution structure and backbone dynamics of long-[Arg(3)]insulin-like growth factor-I. J Biol Chem. 2000;275(14):10009–10015. PMID: 10744677. ↩

4. Denley A, Cosgrove LJ, Booker GW, Wallace JC, Forbes BE. Molecular interactions of the IGF system. Cytokine Growth Factor Rev. 2005;16(4-5):421–439. PMID: 15936977. ↩ ↩² ↩³

5. Firth SM, Baxter RC. Cellular actions of the insulin-like growth factor binding proteins. Endocr Rev. 2002;23(6):824–854. PMID: 12466191. ↩ ↩²

6. Tomas FM, Knowles SE, Owens PC, et al. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochem J. 1992;282(Pt 1):91–97. PMID: 1371669. ↩