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IGF-1 LR3

Long [Arg3] IGF-1 analog engineered to escape binding proteins for potent, long-acting IGF-1 receptor activation in research

Half-life

~20-30 hours in preclinical models (vs ~10-16 min for free native IGF-1)

Typical Dose

20-50mcg per day (subcutaneous, research)

Format

Injectable

Purity

≥98%

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Overview

IGF-1 LR3 (Long [Arg3] insulin-like growth factor-1) is an 83-amino-acid analog of the 70-residue native peptide, built by swapping glutamic acid for arginine at position 3 and adding a 13-residue N-terminal extension [1]. Those two edits cut affinity for the IGF-binding proteins by roughly a thousandfold while preserving IGF-1 receptor binding [1]. Because IGFBPs normally sequester the vast majority of circulating IGF-1, an analog that slips past them acts far longer and at lower molar amounts than the native hormone. That property is exactly why Long R3 IGF-1 became the standard IGF-1 supplement in serum-containing cell culture, where ordinary IGF-1 gets neutralized within minutes. The muscle-relevant biology comes from rodent work: localized IGF-I infusion drives measurable skeletal muscle hypertrophy [2], and about half of that growth traces to satellite cell activation with the remainder from protein synthesis in existing fibers [3]. No human performance or clinical trial has tested IGF-1 LR3 itself, so its research profile rests on native IGF-1 pharmacology plus in vitro potency data.

Mechanism

IGF-1 LR3 is a full agonist at the IGF-1 receptor, a receptor tyrosine kinase whose autophosphorylation recruits IRS-1 and fires the PI3K/Akt/mTOR pathway for protein synthesis alongside the Ras/MAPK pathway for proliferation [4]. The [Arg3] substitution and N-terminal extension lower IGFBP affinity so the analog stays free in solution rather than bound and inactive [1]. In muscle this translates to satellite cell recruitment plus increased synthesis in mature fibers [2,3]. The receptor also shares roughly 1% cross-reactivity with the insulin receptor, and both receptors converge on the same IRS/PI3K cascade [5], which is the mechanistic basis for the hypoglycemia risk that scales with the analog's long duration [6].

Researched benefits

  • Potent IGF-1 receptor activation that bypasses IGFBP sequestration [1]
  • Extended half-life versus the minutes-long native peptide
  • Satellite cell activation and myofiber protein synthesis in rodent muscle models [2,3]
  • Standard growth factor for serum-containing cell culture research
  • Anabolic and anti-catabolic signaling through the PI3K/Akt/mTOR axis [4]

Frequently asked

What makes IGF-1 LR3 different from native IGF-1?

Two structural edits: an arginine for glutamic acid swap at position 3 and a 13-amino-acid N-terminal extension [1]. Together they drop IGFBP affinity about a thousandfold while keeping IGF-1 receptor binding intact. Native IGF-1 circulates almost entirely bound to binding proteins and inactive; LR3 stays free, which is why it is more potent per microgram and lasts far longer.

What is the half-life of IGF-1 LR3?

Preclinical and cell-model estimates put it around 20-30 hours, compared with roughly 10-16 minutes for free native IGF-1. The gain comes from escaping the binding proteins and resisting aminopeptidase cleavage. There is no published human pharmacokinetic study on LR3 specifically, so treat the figure as an approximation carried over from analog and native-peptide data.

Is hypoglycemia a real risk with IGF-1 LR3?

Yes, and it is the effect to respect most. The IGF-1 receptor cross-reacts with the insulin receptor at roughly 1% affinity and feeds the same IRS/PI3K signaling cascade [5], so IGF-1 activity lowers blood glucose. That risk compounds with LR3's long duration and is worst in a fasted state. For context, recombinant native IGF-1 (mecasermin) produces hypoglycemia in about 14% of treated subjects and is dosed with food for that reason.

IGF-1 LR3 vs IGF-1 DES: what is the difference?

Both are binding-protein-evading analogs, but they trade duration for locality. LR3 uses an N-terminal extension plus the [Arg3] change for a long, systemic half-life measured in hours [1]. DES(1-3) IGF-1 simply removes the first three N-terminal residues, giving very low IGFBP binding but a short half-life, so researchers associate it with brief, localized activity. LR3 is the analog of choice when sustained receptor exposure is the goal; DES when a shorter pulse is.

What is the typical research dose and how is it reconstituted?

Research protocols commonly reference 20-50mcg per day subcutaneously, though no validated human dose-response data exist. Reconstitute a 1mg vial with 1mL bacteriostatic water for 1mg/mL, which puts 50mcg in 0.05mL. Swirl gently, refrigerate, and protect from light.

Are there human trials showing IGF-1 LR3 builds muscle?

No. There are zero human performance or clinical trials of IGF-1 LR3 itself. The muscle rationale comes from rodent studies where localized IGF-I drove hypertrophy through satellite cell activation and increased protein synthesis [2,3], plus in vitro potency data on the analog [1]. Elevated IGF-1 signaling also carries mitogenic concerns, which is why active malignancy is a hard contraindication in the underlying literature [6].

Scientific Literature

References

  1. [1]

    Francis GL, Ross M, Ballard FJ, et al. (1992). 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.

    Journal of Molecular Endocrinology · PubMed: 1378742

  2. [2]

    Adams GR, McCue SA. (1998). Localized infusion of IGF-I results in skeletal muscle hypertrophy in rats.

    Journal of Applied Physiology · PubMed: 9572822

  3. [3]

    Barton-Davis ER, Shoturma DI, Sweeney HL. (1999). Contribution of satellite cells to IGF-I induced hypertrophy of skeletal muscle.

    Acta Physiologica Scandinavica · PubMed: 10632630

  4. [4]

    Khan MZ, Zugaza JL, Torres Aleman I. (2025). The signaling landscape of insulin-like growth factor 1.

    Journal of Biological Chemistry · PubMed: 39638246

  5. [5]

    Siddle K. (2011). Signalling by insulin and IGF receptors: supporting acts and new players.

    Journal of Molecular Endocrinology · PubMed: 21498522

  6. [6]

    Clemmons D, Maile L, Xi G, et al. (2011). Igf-I signaling in response to hyperglycemia and the development of diabetic complications.

    Current Diabetes Reviews · PubMed: 21707534

Citations are provided for educational purposes. Always verify primary sources before drawing research conclusions.

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