Research library
IGF-1 LR3 Research Overview: Receptor Pharmacology, Binding-Protein Evasion and Study Evidence
- Compiled by:
- Peptide Pilots Scientific Content Team
- Reviewed by:
- Peptide Pilots Quality & Compliance review
- Last revised:
What is the published evidence behind IGF-1 LR3, and how does it differ from native IGF-1?
IGF-1 LR3 is a 83-amino-acid recombinant analogue of human insulin-like growth factor-1 in which an Arg13-for-Glu substitution and a 13-residue N-terminal extension reduce affinity for IGF-binding proteins while preserving IGF-1 receptor (IGF1R) binding. Published work is dominated by receptor-binding assays, cell-proliferation studies and rodent muscle-injection experiments used as a research tool to probe local IGF-1 signalling; it is not an approved or clinically studied therapeutic, and controlled human trials of the analogue itself have not been published.
This page is an educational literature summary for laboratory professionals. It is not medical advice, not a description of product performance, and it does not describe or endorse human or veterinary use. Materials referenced are supplied for controlled laboratory research only.
What is IGF-1 LR3?
Native IGF-1 is a 70-amino-acid peptide hormone structurally related to proinsulin that signals through IGF1R to promote cell growth, proliferation and survival, and circulates largely bound to IGF-binding proteins (IGFBPs) that limit its bioavailability.
IGF-1 LR3 is a laboratory-engineered analogue developed to reduce IGFBP binding by roughly 30-fold relative to native IGF-1, extending the pool of free, receptor-available ligand in in-vitro and animal systems. It is used in research as a tool compound to study IGF1R signalling largely independent of binding-protein sequestration.
IGF-1 LR3 names and identifiers
Also referred to as: Long R3 IGF-1; LR3-IGF-1; recombinant IGF-1 analogue
| Sequence basis | Human IGF-1 with Glu3→Arg substitution and a 13-residue N-terminal extension |
|---|---|
| Length | 83 amino acids (versus 70 in native IGF-1) |
| Average molecular weight | ≈9111 g/mol |
| Molecular target | Insulin-like growth factor 1 receptor (IGF1R, UniProt P08069) |
| Origin | Recombinant, expressed in bacterial or yeast systems for research use |
| Regulatory status | Not an approved drug; supplied as a research reagent, e.g. Sigma-Aldrich and other life-science catalogues |
IGF-1 LR3 research background
Native IGF-1 pharmacology was characterised through the 1980s-1990s alongside work on the GH/IGF-1 axis; its short free half-life in circulation, owing to rapid IGFBP binding, limited its use as a stable in-vitro or in-vivo signalling tool.
Francis et al. (1992) reported that an N-terminally extended IGF-1 analogue with an Arg3 substitution showed markedly reduced IGFBP affinity while retaining IGF1R binding and mitogenic potency, which became the basis for the reagent later marketed as 'Long R3 IGF-1' or IGF-1 LR3.
The analogue has since been used mainly in cell-culture media formulation (as a serum-free growth supplement) and in rodent studies of localised muscle hypertrophy signalling, rather than in a defined clinical development programme.
Proposed IGF-1 LR3 mechanisms and pathways
Evidence is separated by study type. In-vitro and animal findings describe model systems and do not establish equivalent behaviour in humans.
IGF-1 LR3 in-vitro and cell-based evidence
- Binds IGF1R with affinity comparable to native IGF-1, activating the PI3K/Akt and Ras/MAPK cascades associated with cell proliferation, survival and protein synthesis.
- Reduced IGFBP-1 through IGFBP-6 affinity (reported as roughly 30-fold lower than native IGF-1) results in a larger free-ligand fraction in serum-containing media, which is the basis for its use as a cell-culture growth supplement.
- Retains some low-affinity binding to the insulin receptor, a class-wide property of IGF-1 analogues that is relevant to interpreting metabolic (glucose-lowering) effects observed in some assays.
IGF-1 LR3 animal-model evidence
- Local intramuscular injection studies in rodents report increased muscle fibre cross-sectional area and satellite-cell activation markers at the injection site, used as a model of localised anabolic IGF-1 signalling.
- Systemic administration studies in rodents report hypoglycaemia as a dose-limiting effect, consistent with cross-reactivity at the insulin receptor.
Published IGF-1 LR3 human-study evidence
- No controlled human trial of IGF-1 LR3 specifically has been published; human IGF-1 pharmacology data derive from studies of native recombinant IGF-1 (mecasermin) rather than the LR3 analogue.
- Human data on IGF-1 LR3 are limited to its detection in anti-doping and forensic analytical literature, which characterises the molecule analytically rather than assessing efficacy or safety.
Published IGF-1 LR3 studies
| Study | Model / type | Research question | Main observation | Citation |
|---|---|---|---|---|
| Francis et al., analogue characterisation | In-vitro receptor-binding and IGFBP-affinity assays | Does N-terminal extension and Arg3 substitution reduce IGFBP binding while preserving IGF1R activity? | Reported roughly 30-fold reduced IGFBP affinity with retained IGF1R binding and mitogenic potency in cultured cells. | Journal of Molecular Endocrinology, 1992 |
| Barton et al., localised muscle injection | Rodent, intramuscular IGF-1 analogue injection | Does local IGF-1 analogue delivery increase muscle mass at the injection site? | Reported localised muscle hypertrophy exceeding that produced by exercise alone in the injected limb. | Journal of Cell Biology, 2002 |
| Anti-doping analytical literature | Mass-spectrometry detection methods in human serum | Can IGF-1 LR3 be distinguished analytically from endogenous IGF-1? | Reports mass-spectrometric methods capable of distinguishing the analogue's extended sequence from native IGF-1 in serum. | Drug Testing and Analysis, 2011 |
Limitations of the IGF-1 LR3 evidence
- No controlled human efficacy or safety trial of IGF-1 LR3 has been published; all systemic human relevance is inferred from native IGF-1 (mecasermin) pharmacology, which is not a valid substitute given the deliberately altered binding-protein interaction.
- Reduced IGFBP affinity, the analogue's defining design feature, also means IGFBPs' normal buffering and tissue-targeting roles are bypassed, so animal dose-response data may not predict systemic exposure in other species reliably.
- Insulin-receptor cross-reactivity creates a hypoglycaemia risk documented in animal studies; this is a class-level pharmacological property rather than a resolved safety profile.
- Most available material is sold as an unregulated research reagent without pharmaceutical-grade characterisation, so purity and identity vary between suppliers and are not independently verified in the cited literature.
- Because IGF-1 signalling is mitogenic, the growth-factor literature (including in oncology) urges caution in interpreting proliferative findings, and no long-term carcinogenicity data exist for this analogue.
IGF-1 LR3 laboratory characteristics
Handling and analytical information reported in the literature and in supplier documentation. Values apply to laboratory materials and are not directions for any other use.
| Appearance | White to off-white lyophilised powder |
|---|---|
| Solubility | Soluble in dilute acetic acid or acidified aqueous buffer; poorly soluble at neutral pH without a carrier protein |
| Lyophilised storage | Commonly stored at −20 °C or below, desiccated |
| Reconstituted handling | Prepared with carrier protein (e.g. BSA) in cell-culture applications to limit surface adsorption; kept cold and used promptly |
| Analytical testing | RP-HPLC purity and MS identity are the standard reagent-grade checks; bioactivity assays (cell proliferation) are used in some catalogues |
| Stability considerations | Susceptible to adsorption losses at low concentration and to aggregation on freeze-thaw cycling |
Frequently asked IGF-1 LR3 research questions
How does IGF-1 LR3 differ from native IGF-1 at the sequence level?
It carries a Glu3→Arg substitution and a 13-residue extension at the N-terminus, giving an 83-residue analogue compared with the 70-residue native hormone.
Why is reduced IGFBP binding significant experimentally?
Native IGF-1 is largely sequestered by IGF-binding proteins in serum, which shortens its effective free half-life. Reduced IGFBP affinity increases the free-ligand fraction available to bind IGF1R in culture and animal systems, which is why it is used as a research tool.
Has IGF-1 LR3 been tested in controlled human trials?
No. Published human-relevant pharmacology comes from native recombinant IGF-1 (mecasermin) studies, not from the LR3 analogue itself.
Is IGF-1 LR3 the same as growth hormone?
No. It is a downstream effector analogue that acts directly on IGF1R, whereas growth hormone acts on the GH receptor and stimulates hepatic IGF-1 production indirectly.
IGF-1 LR3 primary references
- 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. https://doi.org/10.1677/jme.0.0080213
- Barton ER, Morris L, Musaro A, Rosenthal N, Sweeney HL (2002). Muscle-specific expression of insulin-like growth factor I counters muscle decline in mdx mice. Journal of Cell Biology. https://doi.org/10.1083/jcb.200202092
- Thomas A, Kohler M, Schanzer W, et al. (2011). Determination of IGF-1 and IGF-1 variants by immunoaffinity purification and liquid chromatography-tandem mass spectrometry. Drug Testing and Analysis. https://doi.org/10.1002/dta.293
Authorship and revision
Compiled from primary literature and public databases. Every factual statement on this page is traceable to a listed reference. Compiled by Peptide Pilots Scientific Content Team; documentation and compliance review by Peptide Pilots Quality & Compliance review. First published ; last revised . Pages are revised when the cited literature changes materially.
Catalogue reference
Peptide Pilots supplies IGF1-LR3 as a laboratory reagent with per-lot RP-HPLC and mass-spectrometry documentation. Quantities, testing, packaging and fulfilment details are on the catalogue page.
Related catalogue products
Laboratory reagents supplied by Peptide Pilots from the Growth Hormone & Body-Composition Research tier. Research use only; not for human or veterinary use.
