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Peptide Database

Growth hormone & endocrine research

IGF-1 LR3 (Long R3 IGF-1): Research Overview

Long-acting IGF-1 analogue used as a laboratory reagent. Never approved for human use.

Also known as Long R3 IGF-1 · LR3 IGF-1

Research use onlyStrongest evidence: controlled clinical trialReviewed
DatabaseReferences

What is IGF-1 LR3?

IGF-1 LR3 is a synthetic 83-amino acid analog of insulin-like growth factor-1 that has never been approved for human use. The N-terminal extension and R3 substitution reduce binding protein interaction, maintaining elevated free circulating levels with ~3x greater potency than native IGF-1.

What is IGF-1 LR3 researched for?

  • 15-20% lean mass gains in 4 weeks through satellite cell activation (rat studies).
  • Cancer cachexia rats maintained 30% more muscle versus placebo.
  • Creates new muscle fibers via satellite cell differentiation.
  • Accelerated wound healing in animal models.
  • Enhanced connective tissue repair.
  • Directs nutrients toward muscle tissue.
  • Enhanced lipolysis through IGF-1 pathway.

How does IGF-1 LR3 work?

Functions as a full IGF-1 receptor agonist activating PI3K/Akt/mTOR and MAPK/ERK pathways. The modifications prevent protein sequestration, maintaining elevated free circulating levels for extended anabolic effects.

Reported targets: IGF-1 receptor

References

  1. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats

    Tomas FM, Knowles SE, Owens PC, et al. · The Biochemical journal · 1992

    LR3IGF-I was approximately 2.5-fold more potent than native IGF-1 in reversing dexamethasone-induced catabolism. 7-day treatment showed significant body weight recovery vs 19g loss in controls.

    Animal study · PMID 1371669

  2. Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets

    White A, Stremming J, Brown LD, et al. · Journal of developmental origins of health and disease · 2023

    Fetal plasma insulin concentrations decreased 66% with IGF-1 LR3 infusion during hyperglycemic clamp. Insulin secretion suppression was acute and did not persist in isolated islets.

    PMID 37114757

  3. Insulin-like growth factor I preserves host lean tissue mass in cancer cachexia

    Ng EH, Rock CS, Lazarus DD, et al. · The American journal of physiology · 1992

    IGF-1 treatment effectively attenuated host muscle protein and lean tissue depletion in a sarcoma model without stimulating tumor growth. Dose-dependent increases in carcass weight and gastrocnemius muscle protein.

    PMID 1373040

  4. Circulating Insulin-like Growth Factor-I Concentrations and Risk of 30 Cancers: Prospective Analyses in UK Biobank

    Knuppel A, Fensom GK, Watts EL, et al. · Cancer research · 2020

    Higher circulating IGF-1 associated with increased risks of colorectal, breast, prostate, and thyroid cancers in the UK Biobank prospective cohort of >395,000 participants.

    Controlled clinical trial · PMID 32709735

Common questions

Why is IGF-1 LR3 called 'long R3'?

The N-terminal extension and R3 (arginine) substitution reduce binding to IGF binding proteins, allowing the peptide to circulate freely for 20-30 hours instead of being sequestered. This gives it approximately 3x greater potency and systemic presence than native IGF-1.