IGF-1 LR3
IGF-1 LR3 is a modified IGF-1 analogue with Arg at native position 3 and a 13-amino-acid N-terminal extension. It was engineered to reduce binding-protein restraint in experimental systems. The cited evidence includes no direct human administration, pharmacokinetic, efficacy, or safety study.
long R3 insulin-like growth factor I analogue
- 13-residue N-terminal extension MFPAMPLSSLFVN
- Arg replaces Glu at native IGF-1 position 3
- Reduced IGF-binding-protein interaction in vitro
- No registered human trial in the cited records
How is IGF-1 LR3 different from native IGF-1?
It adds MFPAMPLSSLFVN to the N-terminus and replaces native Glu3 with Arg. Those changes reduce binding-protein interaction and alter potency and exposure. It is not mecasermin or ordinary recombinant IGF-1.
Correct folding and three disulfide bonds are part of the active identity. Purity percentage or nominal mass alone cannot show the right conformation and potency.
Primary paper · modified analogue in cells
Protein-engineering and cell study
Francis GL et al. Journal of Molecular Endocrinology, 1992.
Long R3 IGF-I was engineered with a 13-amino-acid N-terminal extension and Arg replacing Glu at native position 3. It was more potent than IGF-I in cells that secreted IGF-binding proteins, but less potent in cells without them. The work was in vitro and did not administer the analogue to people.
- Participants / model
- Cultured cell systems with different IGF-binding-protein conditions
- Treatment
- Long R3 IGF-I and native IGF-I
- Study design
- Protein-engineering and comparative cell-bioactivity study
Protein chemistry · disulfide folding
Protein chemistry study
Milner SJ et al. Biotechnology and Bioengineering, 1998.
The study examined production and disulfide folding of recombinant Long R3 IGF-I. It supports the importance of manufacturing and conformational control but supplies no human efficacy or safety result.
- Participants / model
- Recombinant production and analytical systems
- Treatment
- Long R3 IGF-I folding and purification
- Study design
- Protein-process study
Has IGF-1 LR3 built muscle or improved recovery in people?
The cited records include no direct administered-human trial. Cell potency, animal growth studies, and clinical experience with native recombinant IGF-1 do not establish efficacy, pharmacokinetics, or safety for LR3.
Can mecasermin’s label be used for LR3?
No. Mecasermin is recombinant human IGF-1. LR3 has 14 sequence changes or additions designed to alter binding-protein control, so exposure and risk cannot be assumed equivalent.
Primary paper · modified analogue in cells
Protein-engineering and cell study
Francis GL et al. Journal of Molecular Endocrinology, 1992.
Long R3 IGF-I was engineered with a 13-amino-acid N-terminal extension and Arg replacing Glu at native position 3. It was more potent than IGF-I in cells that secreted IGF-binding proteins, but less potent in cells without them. The work was in vitro and did not administer the analogue to people.
- Participants / model
- Cultured cell systems with different IGF-binding-protein conditions
- Treatment
- Long R3 IGF-I and native IGF-I
- Study design
- Protein-engineering and comparative cell-bioactivity study
PubMed and registry · no direct human trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, and LR3.
The cited records include no relevant registered human intervention trial or administered-human publication for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, LR3, or the extension sequence.
Read the original sourcePrimary paper · modified analogue in cells
Protein-engineering and cell study
Francis GL et al. Journal of Molecular Endocrinology, 1992.
Long R3 IGF-I was engineered with a 13-amino-acid N-terminal extension and Arg replacing Glu at native position 3. It was more potent than IGF-I in cells that secreted IGF-binding proteins, but less potent in cells without them. The work was in vitro and did not administer the analogue to people.
- Participants / model
- Cultured cell systems with different IGF-binding-protein conditions
- Treatment
- Long R3 IGF-I and native IGF-I
- Study design
- Protein-engineering and comparative cell-bioactivity study
Animal study · growth and nitrogen effects
Animal study
Experimental IGF-I analogue research.
Long R3 IGF-I altered growth or nitrogen-related measures in an animal model. Species exposure and growth readouts do not establish human muscle benefit or safety.
- Participants / model
- Experimental animals
- Treatment
- Long R3 IGF-I
- Study design
- Controlled animal study
What does LR3 do in experiments?
LR3 can be more potent than native IGF-1 in cell systems that secrete IGF-binding proteins, while being less potent in systems without them. Animal studies show growth and metabolic activity. The cited experiments do not support a universal multiplier such as ‘three times stronger.’
Primary paper · modified analogue in cells
Protein-engineering and cell study
Francis GL et al. Journal of Molecular Endocrinology, 1992.
Long R3 IGF-I was engineered with a 13-amino-acid N-terminal extension and Arg replacing Glu at native position 3. It was more potent than IGF-I in cells that secreted IGF-binding proteins, but less potent in cells without them. The work was in vitro and did not administer the analogue to people.
- Participants / model
- Cultured cell systems with different IGF-binding-protein conditions
- Treatment
- Long R3 IGF-I and native IGF-I
- Study design
- Protein-engineering and comparative cell-bioactivity study
Animal study · growth and nitrogen effects
Animal study
Experimental IGF-I analogue research.
Long R3 IGF-I altered growth or nitrogen-related measures in an animal model. Species exposure and growth readouts do not establish human muscle benefit or safety.
- Participants / model
- Experimental animals
- Treatment
- Long R3 IGF-I
- Study design
- Controlled animal study
Animal study · analogue exposure
Animal study
Experimental IGF-I analogue research.
The analogue was administered in an animal metabolic or growth experiment. The result does not supply a human dose, glucose-risk estimate, or clinical outcome.
- Participants / model
- Experimental animals
- Treatment
- Long R3 IGF-I
- Study design
- Controlled animal study
What are the main safety concerns?
The cited records provide no direct human rates. Potent IGF-receptor signaling raises plausible concerns about hypoglycemia, edema, intracranial pressure, tissue overgrowth, cardiac effects, and tumor biology, but exact LR3 risks and frequencies cannot be quantified from native IGF-1 labels or epidemiology.
- Glucose: direct LR3 dose-response and interaction data with insulin or glucose-lowering drugs are absent.
- Growth signaling: endogenous IGF-1 associations do not quantify cancer risk from LR3 exposure.
- Product quality: sequence, fold, aggregates, endotoxin, sterility, concentration, and bioactivity all need product-specific control.
PubMed and registry · no direct human trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, and LR3.
The cited records include no relevant registered human intervention trial or administered-human publication for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, LR3, or the extension sequence.
Read the original sourcePrimary paper · modified analogue in cells
Protein-engineering and cell study
Francis GL et al. Journal of Molecular Endocrinology, 1992.
Long R3 IGF-I was engineered with a 13-amino-acid N-terminal extension and Arg replacing Glu at native position 3. It was more potent than IGF-I in cells that secreted IGF-binding proteins, but less potent in cells without them. The work was in vitro and did not administer the analogue to people.
- Participants / model
- Cultured cell systems with different IGF-binding-protein conditions
- Treatment
- Long R3 IGF-I and native IGF-I
- Study design
- Protein-engineering and comparative cell-bioactivity study
Is IGF-1 LR3 approved?
The cited FDA and clinical records include no approved IGF-1 LR3 drug, prescribing label, or registered human trial. WADA prohibits IGF-1 analogues for covered athletes.
PubMed and registry · no direct human trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, and LR3.
The cited records include no relevant registered human intervention trial or administered-human publication for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, LR3, or the extension sequence.
Read the original sourceWADA 2026 · IGF-1 and analogues
Sports rule
World Anti-Doping Agency, effective 1 January 2026.
IGF-1 and its analogues are prohibited under S2 for athletes covered by the Code.
- Study design
- Binding sport rule for covered athletes
Studies and sources
Primary paper · modified analogue in cells
Protein-engineering and cell study
Francis GL et al. Journal of Molecular Endocrinology, 1992.
Long R3 IGF-I was engineered with a 13-amino-acid N-terminal extension and Arg replacing Glu at native position 3. It was more potent than IGF-I in cells that secreted IGF-binding proteins, but less potent in cells without them. The work was in vitro and did not administer the analogue to people.
- Participants / model
- Cultured cell systems with different IGF-binding-protein conditions
- Treatment
- Long R3 IGF-I and native IGF-I
- Study design
- Protein-engineering and comparative cell-bioactivity study
Protein chemistry · disulfide folding
Protein chemistry study
Milner SJ et al. Biotechnology and Bioengineering, 1998.
The study examined production and disulfide folding of recombinant Long R3 IGF-I. It supports the importance of manufacturing and conformational control but supplies no human efficacy or safety result.
- Participants / model
- Recombinant production and analytical systems
- Treatment
- Long R3 IGF-I folding and purification
- Study design
- Protein-process study
Animal study · growth and nitrogen effects
Animal study
Experimental IGF-I analogue research.
Long R3 IGF-I altered growth or nitrogen-related measures in an animal model. Species exposure and growth readouts do not establish human muscle benefit or safety.
- Participants / model
- Experimental animals
- Treatment
- Long R3 IGF-I
- Study design
- Controlled animal study
Animal study · analogue exposure
Animal study
Experimental IGF-I analogue research.
The analogue was administered in an animal metabolic or growth experiment. The result does not supply a human dose, glucose-risk estimate, or clinical outcome.
- Participants / model
- Experimental animals
- Treatment
- Long R3 IGF-I
- Study design
- Controlled animal study
PubMed and registry · no direct human trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, and LR3.
The cited records include no relevant registered human intervention trial or administered-human publication for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, LR3, or the extension sequence.
Read the original sourceWADA 2026 · IGF-1 and analogues
Sports rule
World Anti-Doping Agency, effective 1 January 2026.
IGF-1 and its analogues are prohibited under S2 for athletes covered by the Code.
- Study design
- Binding sport rule for covered athletes
Why is IGF-1 LR3 in F tier?
F reflects potent growth-factor biology without a direct human product record. Mecasermin and native IGF-1 use different molecules and cannot supply LR3 pharmacokinetics, efficacy, or safety.