PeptidePlaza
The Free Peptide Reference

IGF-1 LR3

From PeptidePlaza, the free peptide reference · Entry #023 · Recovery · Hand-curated entry · Editorial standards

Research warning. Research chemical — not for human consumption. IGF-1 is a potent growth factor; unregulated use carries theoretical malignancy risk and hypoglycemia. Banned by WADA.

IGF-1 LR3 (also known as Long R3 IGF-1, LR3 IGF-1, Mecasermin analog) is a recovery research peptide. A modified recombinant IGF-1 with an arginine substitution and 13-residue N-terminal extension that reduces binding to IGF-binding proteins, increasing bioavailability. The FDA-approved drug mecasermin is the unmodified reference compound.

IGF-1 LR3 is a recombinant analog of insulin-like growth factor-1 engineered with an arginine at position 3 and an additional 13-amino-acid N-terminal extension (LR3 = Long Arginine-3). These modifications dramatically reduce its affinity for IGF-binding proteins (IGFBPs), increasing free IGF-1 bioavailability and half-life relative to native IGF-1. IGF-1 mediates many growth-promoting and anabolic effects of growth hormone. The unmodified peptide (mecasermin) is FDA-approved for severe primary IGF-1 deficiency; LR3 itself is an investigational research compound widely used in cell culture and animal models and is a doping-testing target.

1 Mechanism of action

Activates the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase, triggering PI3K-Akt and MAPK signaling cascades that promote protein synthesis, cell proliferation, and anti-apoptotic survival. Reduced IGFBP binding increases receptor exposure.

Primary targets: IGF-1R

2 Reported effects

Effects below are those reported in the published literature cited on this page. They are not claims of clinical benefit and not medical advice.

2.1 Reported benefits

  • Anabolic effects on skeletal muscle and protein synthesis in models
  • Longer half-life than native IGF-1 due to reduced IGFBP binding
  • Standard tool in cell culture and tissue-engineering research
  • Mediates many GH-dependent growth and repair functions

2.2 Side effects

  • Hypoglycemia (insulin-like activity)
  • Fluid retention and joint pain reported with IGF-1 class
  • Injection site reactions
  • Theoretical mitogenic / tumor-promotion risk

3 Chemical and physical properties

CAS number105817-59-6 (Long R3 IGF-1)
Molar mass9110.3 g/mol
Purity (typical)>98%
Half-life~20–30 hours (extended vs native IGF-1 ~10–12 min free)
Storage−20 °C, lyophilised powder, desiccated
SolubilitySterile water / bacteriostatic water
Receptors / targetsIGF-1R

3.1 Amino acid sequence

MFPAMPLSSLFNGPRGIVDECCFRSCDLRRLEMYCAPLKPTKSA (LR3 extension + IGF-1 core)

4 Research dosages

Cell culture: 10–100 ng/mL. Animal models: 50–150 μg/kg/day. No validated human research protocol; typical self-reported use 20–100 μg/day.

Dosages are reported from published protocols for reference only. Research chemicals are not for human consumption.

5 Research studies (6)

  1. Mecasermin.
    BioDrugs : clinical immunotherapeutics, biopharmaceuticals and gene therapy (2008) · Review
    Mecasermin (recombinant human insulin-like growth factor-I [IGF-I]) is approved in the US for the long-term treatment of growth failure in children with severe primary IGF-I deficiency or with growth hormone (GH)...
  2. Profile of mecasermin for the long-term treatment of growth failure in children and adolescents with severe primary IGF-1 deficiency.
    Therapeutics and clinical risk management (2009) · Review
    Growth hormone insensitivity syndrome (GHI) or insulin-like growth factor-1 (IGF-1) deficiency (IGFD) is characterized by deficit of IGF-1 production due to alteration of response of growth hormone (GH) receptor to GH.
  3. IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep.
    American journal of physiology. Endocrinology and metabolism (2025) · Review
    Insulin-like growth factor-1 (IGF-1) and insulin are important fetal anabolic hormones.
  4. Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris.
    Applied microbiology and biotechnology (2023) · Review
    Insulin-like growth factor-1 (IGF-1) is a pleiotropic protein hormone and has become an attractive therapeutic target because of its multiple roles in various physiological processes, including growth, development,...
  5. Mecasermin Tercica.
    Current opinion in investigational drugs (London, England : 2000) (2006) · Review
    Tercica, under license from Genentech, has developed and launched mecasermin, recombinant human insulin-like growth factor-1 (rhIGF-1), for the treatment of growth failure in children with primary IGF deficiency or...
  6. Mecasermin rinfabate: rhIGF-I/rhIGFBP-3 complex: iPLEX.
    Expert opinion on drug metabolism & toxicology (2008) · Review
    BACKGROUND: Mecasermin rinfabate (iPLEX), comprising rhIGF-I complexed to rhIGFBP-3, was developed in an attempt to prolong the half-life of IGF-I and potentially reduce side effects.

6 Safety and risk profile

6.1 Regulatory status

IGF-1 LR3 is currently classified as Not approved. It has no approved human indication in the United States; availability elsewhere does not imply demonstrated safety or efficacy.

Safety score: 35/100 — high concern. Derived from clinical data volume, known risks and regulatory status.

6.2 Contraindications

Conditions and populations in which use is contraindicated:

  • Active or suspected malignancy
  • Pregnancy or lactation
  • Hypoglycemia-prone conditions

6.3 Drug interactions

Drug or classInteractionRisk
Insulin / sulfonylureasAdditive hypoglycemia risk — monitor glucose closely.High
GH secretagogues (GHRP-6, ipamorelin, CJC-1295)Synergistic IGF-1 elevation may amplify growth signaling.Moderate

6.4 Long-term risks

  • Malignancy promotion (theoretical, growth-factor mediated)
  • Hypoglycemia with repeated dosing
  • Unknown effects of chronic IGF-1R stimulation

6.5 Research best practices

  • Store lyophilized at −20 °C, desiccated
  • Reconstitute with 0.1% acetic acid or provided diluent; do not use plain water (precipitation risk)
  • Aliquot to avoid repeated freeze-thaw
  • Monitor glucose in any metabolic study
Safety data disclaimer. Safety assessments are based on published literature and are for educational reference only. Clinical evidence varies significantly between peptides. Always consult primary research and current regulatory guidance.

7 Frequently asked questions

Why is IGF-1 LR3 "long"?
The LR3 analog has an N-terminal 13-amino-acid extension and an arginine at position 3, which together reduce binding to IGF-binding proteins — so more peptide remains free to activate the IGF-1 receptor.
Is IGF-1 LR3 the same as mecasermin?
Mecasermin (Increlex) is native-sequence recombinant IGF-1 and is FDA-approved for severe primary IGF-1 deficiency. LR3 is the research analog with altered pharmacokinetics; it is not an approved drug.
What are the main safety concerns?
IGF-1 is a growth factor: unregulated signaling can promote cell proliferation, so malignancy is the dominant theoretical concern. Hypoglycemia is also a risk because IGF-1 has insulin-like effects.

8 References

  1. Mecasermin. PubMed (2008). Keating GM, et al.. View source
  2. Profile of mecasermin for the long-term treatment of growth failure in children and adolescents with severe primary IGF-1 deficiency. PubMed (2009). Fintini D, et al.. View source
  3. IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep. PubMed (2025). White A, et al.. View source
  4. Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris. PubMed (2023). Lu Z, et al.. View source

Related compounds

Entries that share a target, a mechanism, or a research area with IGF-1 LR3.

Teduglutideapproved

Shares triggering and igf-1 pharmacology

A single amino acid substitution turns GLP-2 from a 7-minute hormone into a drug that regrows intestinal villi. The only approved peptide that makes the gut physically bigger.

ARA-290recovery

Shares activates and triggering pharmacology

A non-erythropoietic peptide derived from erythropoietin (EPO) that activates the innate repair receptor. Studied in Phase 2 clinical trials for neuropathy, inflammation, and tissue protection without EPO’s red-cell effects.

Follistatin-344recovery

Shares cell and proliferation pharmacology

A glycoprotein that binds and neutralises myostatin — the brake on muscle growth. Knock out the brake in animals and muscle mass increases dramatically.

Dihexanootropic

Shares tyrosine and kinase pharmacology

An angiotensin IV derivative reported to be orders of magnitude more potent than BDNF at driving synaptogenesis. Its mechanism runs through c-Met — the same receptor that drives many cancers.

Thymosin Alpha-1recovery

Shares cell and activates pharmacology

A 28-amino acid thymic peptide that modulates T-cell function and cytokine balance. Studied clinically for chronic hepatitis B, sepsis, and vaccine response augmentation for over 30 years.

GHK-Cuanti-aging

Shares activates and synthesis pharmacology

A naturally occurring tripeptide-copper complex found in human plasma, saliva, and urine. Plasma levels decline sharply with age. Extensively studied for collagen induction, skin remodeling, and gene expression regulation.

9 See also

For research reference only. Not medical advice. Peptides may be regulated or restricted in your jurisdiction. Entry validated by the PeptidePlaza Biomedical Research Desk; see editorial standards.