IGF Analogue Research Profile

IGF-1 LR3

Long R3 Insulin-Like Growth Factor-I

IGF-1 LR3, more formally Long R3 IGF-I, is a synthetic analogue of insulin-like growth factor-I engineered to interact much less strongly with IGF-binding proteins than native IGF-I. It is widely used as a laboratory tool for investigating IGF receptor signalling, cell growth, survival, metabolism and the regulatory role of IGF-binding proteins.

83 Amino Acids Synthetic IGF-I Analogue IGF-1R Signalling Reduced IGFBP Binding Not Approved for Human Use

Compound Long R3 IGF-I

Common name IGF-1 LR3 / Long R3 IGF-I

Parent molecule Human IGF-I

Chain length 83 amino acids

Key substitution Arg at position 3

Additional feature 13-residue N-terminal extension

Research status Laboratory research / unapproved

Overview The Name LR3 vs IGF-1 Structure Research Interest Mechanisms IGF-Binding Proteins Research Applications Evidence Human Evidence Development Status Limitations Stability References

Scientific Overview

What is IGF-1 LR3?

IGF-1 LR3 is a recombinant synthetic analogue of insulin-like growth factor-I , or IGF-I.

Native human IGF-I is a 70-amino-acid peptide hormone whose biological activity is regulated by the IGF receptor system and a family of circulating IGF-binding proteins.

Long R3 IGF-I was deliberately engineered to alter this normal regulatory interaction.

The analogue contains a 13-amino-acid N-terminal extension and replaces the glutamic-acid residue at position 3 of native IGF-I with arginine.

These structural changes substantially reduce its affinity for IGF-binding proteins while preserving potent interaction with the type-1 IGF receptor.

The result is a useful experimental molecule that can produce stronger or more sustained IGF-like biological activity in some laboratory systems than native IGF-I.

Understanding the Name

What does IGF-1 LR3 mean?

IGF-I Insulin-Like Growth Factor-I

LONG 13-residue N-terminal extension

R3 Arginine substituted at position 3

The formal scientific name Long R3 IGF-I describes the two principal structural modifications made to native IGF-I.

Long refers to an additional 13 amino acids attached to the N-terminus of the IGF-I sequence.

R3 indicates that the amino acid at position 3 has been changed to arginine, represented by the one-letter code R.

Long N-Terminal Extension + [Arg3] IGF-I

The resulting molecule contains 83 residues compared with 70 residues in native human IGF-I.

The name “IGF-1 LR3” is widely used in research-product terminology, while Long R3 IGF-I is the more conventional scientific description.

Important Scientific Distinction

Long R3 IGF-I is not native human IGF-I

Long R3 IGF-I was deliberately engineered to behave differently from physiological IGF-I, particularly in its interaction with IGF-binding proteins.

NATURAL HUMAN HORMONE

IGF-I

Human IGF-I is a 70-amino-acid peptide involved in normal growth, development, metabolism and tissue signalling.

Most circulating IGF-I is associated with IGF-binding proteins, which strongly influence distribution, half-life and receptor availability.

MODIFIED INTO

SYNTHETIC ANALOGUE

Long R3 IGF-I

Long R3 IGF-I contains 83 residues, including an N-terminal extension and an Arg3 substitution.

These changes dramatically reduce binding to IGF-binding proteins while maintaining biological activity at IGF receptors.

Clinical IGF-I evidence cannot simply be transferred to LR3

Native recombinant human IGF-I has its own pharmaceutical and clinical literature. Long R3 IGF-I is a different molecule with altered binding-protein interactions and should not be treated as an equivalent approved form of IGF-I.

Molecular Information

How was Long R3 IGF-I engineered?

Long R3 IGF-I combines the IGF-I protein framework with two structural modifications designed to reduce interaction with IGF-binding proteins.

Structural architecture

13-residue N-terminal extension

[Arg3] IGF-I IGF-I core sequence with Glu3 replaced by Arg3

13-residue extension + 70-residue IGF-I core

Compound characteristics

Common name IGF-1 LR3

Scientific name Long R3 IGF-I

Residues 83

Parent sequence Human IGF-I

Key mutation Glu3 → Arg3

N-terminal extension 13 amino acids

Main design feature Reduced IGFBP affinity

Scientific Interest

Why do researchers use Long R3 IGF-I?

Its altered relationship with IGF-binding proteins makes Long R3 IGF-I particularly useful for studying receptor signalling independently from some of the normal extracellular regulation of native IGF-I.

IGF-1 Receptor Biology

Long R3 IGF-I is used to investigate activation of IGF-1R and downstream intracellular growth and survival pathways.

IGFBP Function

Its low affinity for IGF-binding proteins allows researchers to examine how IGFBPs normally regulate IGF availability.

Cell Growth & Survival

The analogue has been widely used in mammalian cell culture as a potent mitogenic and survival factor.

Metabolic Research

Animal studies have investigated effects on glucose regulation, insulin signalling, organ growth and endocrine feedback.

Mechanisms Under Investigation

How does Long R3 IGF-I signal?

Long R3 IGF-I broadly retains IGF-I-like receptor pharmacology while its reduced IGFBP binding changes how much peptide remains available for receptor interaction.

IGF-1R Activation

Long R3 IGF-I activates the type-1 IGF receptor, a receptor tyrosine kinase that controls multiple growth and survival pathways.

PI3K–AKT Signalling

IGF-1R activation can stimulate the PI3K–AKT pathway involved in cellular survival, metabolism and protein regulation.

MAPK Signalling

IGF receptor activation can also engage MAPK-related pathways associated with proliferation and gene-expression responses.

Reduced IGFBP Regulation

Lower affinity for IGF-binding proteins means LR3 is less constrained by an important regulatory system controlling native IGF-I.

Native IGF-I Circulating IGF-I normally binds strongly to members of the IGF binding-protein family.

IGFBPs regulate exposure Binding proteins influence transport, half-life, tissue distribution and receptor access.

LR3 binds poorly Long R3 IGF-I was engineered to exhibit substantially lower affinity for these proteins.

Greater apparent potency In some experimental systems, reduced sequestration can increase biological potency relative to native IGF-I.

Central Design Feature

Why does reduced IGFBP binding matter?

IGF-binding proteins are not simply passive carriers. They are a major regulatory part of the IGF system.

Native IGF-I binds strongly to several IGFBPs, which can either limit or facilitate access to IGF receptors depending on tissue and physiological context.

Long R3 IGF-I was engineered specifically to have much lower affinity for IGF-binding proteins .

This can increase the fraction of peptide available to interact directly with cellular receptors in experimental environments.

That property makes LR3 extremely useful for experimental biology, but it also means that results obtained with LR3 should not automatically be assumed to represent the physiology of natural IGF-I.

Research Applications

What is Long R3 IGF-I used to investigate?

LR3 has primarily functioned as a research reagent rather than a therapeutic drug-development candidate.

01 / CELL BIOLOGY

Cell Growth & Survival

Long R3 IGF-I has been used extensively in mammalian cell culture to investigate proliferation, survival and receptor signalling.

02 / IGF REGULATION

IGF-Binding Protein Research

Because LR3 binds poorly to IGFBPs, it is a valuable experimental comparator for determining how binding proteins modify normal IGF-I action.

03 / METABOLISM

Metabolic Physiology

Animal research has investigated glucose lowering, endocrine feedback, insulin biology and changes in circulating IGF systems after LR3 exposure.

04 / BIOTECHNOLOGY

Biopharmaceutical Cell Culture

Long R3 IGF-I has been specifically used as a potent growth and survival factor in serum-free mammalian cell culture, including HEK293 and CHO systems.

Research potency should not be interpreted as clinical benefit

Increased signalling activity in cultured cells or animals does not establish that Long R3 IGF-I is safe or beneficial for muscle growth, recovery, body composition, ageing or any other human use.

Evidence Assessment

How strong is the evidence?

Long R3 IGF-I has a substantial experimental literature, but that literature is overwhelmingly laboratory and animal based rather than human therapeutic research.

Molecular Evidence

The structural modifications, IGFBP affinity and IGF-receptor activity are well characterized.

Cell-Culture Evidence

Extensive in-vitro research demonstrates strong mitogenic and survival-factor activity.

Animal Evidence

Multiple animal studies have investigated growth, metabolism, glucose lowering and endocrine effects.

Human Therapeutic Evidence

Controlled therapeutic evidence in humans is not established.

Human Evidence

Has IGF-1 LR3 been clinically developed in humans?

HUMAN THERAPEUTIC EVIDENCE Not Established

Long R3 IGF-I should not be confused with recombinant human IGF-I medicines or clinical studies of native IGF-I.

Long R3 IGF-I has not developed the conventional human therapeutic evidence base seen with approved pharmaceutical products.

The majority of peer-reviewed LR3 research involves cell cultures, rats, pigs, guinea pigs and other experimental systems .

Native recombinant human IGF-I has been investigated and developed clinically for specific endocrine disorders, but this evidence cannot simply be assigned to Long R3 IGF-I.

LR3 was deliberately engineered to alter IGF-binding-protein interactions. Consequently, its distribution, biological availability and metabolic effects can differ from those of native IGF-I.

Anti-doping scientific literature specifically describes LongR3-IGF-I, R3-IGF-I and Des(1-3)-IGF-I as synthetic IGF analogues that have never been approved for use in humans.

Detection methods have nevertheless been developed because these compounds may appear in non-approved performance- enhancement contexts.

Development Status

Where is Long R3 IGF-I in the development process?

Long R3 IGF-I is best understood as an established experimental research analogue rather than a conventional clinical drug candidate.

Molecular Engineering Well characterized

Cell-Culture Research Extensive

Animal & Laboratory Research Extensive experimental use

Established Human Therapeutic Programme Not established

Regulatory Approval Not reached

CURRENT SCIENTIFIC STATUS

Experimental IGF-I analogue

Long R3 IGF-I remains useful as a laboratory reagent for studying IGF biology but is not an approved therapeutic form of IGF-I.

Receptor activity Well characterized

Reduced IGFBP binding Established

Cell-culture use Extensive

Animal research Extensive

Human therapeutic efficacy Not established

Approved medicine No

Evidence Limitations

What don't we know?

Human safety is not established Extensive laboratory use does not provide the kind of human safety evidence required for an approved medicine.

Human efficacy is not established There is no validated therapeutic evidence showing that LR3 improves muscle, recovery, body composition or other health outcomes in humans.

Reduced IGFBP binding changes normal physiology LR3 does not reproduce the normal regulatory relationship between physiological IGF-I and circulating binding proteins.

Hypoglycaemic activity has been observed experimentally Animal studies show that IGF-I analogues with reduced IGFBP affinity can produce potent and prolonged glucose-lowering effects.

Growth effects are tissue and species dependent Animal studies have produced markedly different responses across species, demonstrating that simple extrapolation is unreliable.

No validated therapeutic regimen exists Experimental concentrations used in cell culture or animal research should not be interpreted as human dosing guidance.

Laboratory Stability

Factors affecting Long R3 IGF-I stability

Long R3 IGF-I is a folded protein analogue whose activity depends on maintaining correct molecular structure. Stability should therefore be based on analytical documentation for the exact recombinant material and formulation under investigation.

Temperature

Elevated temperatures can accelerate degradation and loss of biological activity.

pH & Buffer

Solution pH and buffer composition can influence folding, aggregation and chemical stability.

Protein Folding

Correct disulfide bonding and tertiary structure are important for IGF-receptor activity.

Material Specification

Recombinant source, purity, aggregation state and formulation should be defined in analytical documentation.

CURRENT STATUS

Experimental IGF-I analogue — not approved for human therapeutic use

Long R3 IGF-I is a synthetic 83-residue analogue designed primarily for experimental research into the IGF system and the role of IGF-binding proteins.

It has extensive laboratory and animal research history but has not become an approved therapeutic medicine.

Native recombinant IGF-I and Long R3 IGF-I should not be treated as equivalent compounds because LR3 was specifically engineered to alter normal IGF-binding protein interactions.

ASA Research Labs provides this information for scientific and educational purposes only. Nothing on this page should be interpreted as medical advice, dosing guidance or a recommendation for human use.

Scientific Literature

Selected scientific references

Selected literature covering the design of Long R3 IGF-I, IGF-binding proteins, receptor pharmacology, animal research, biotechnology applications and analytical detection.

1 Francis GL, et al. Novel recombinant fusion protein analogues of insulin-like growth factor-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. 1992. Foundational work describing Long IGF-I and Long [Arg3] IGF-I analogues and the structural basis of their altered biological activity.

2 Gajanandana O, Irvine K, Grant PA, Francis GL, et al. Measurement of an analog of insulin-like growth factor-I in blood plasma using a novel enzyme-linked immunosorbent assay. Journal of Endocrinology. 1998;156(3):407–414. Describes Long-Arg3-IGF-I as a synthetic IGF-I analogue with substantially reduced affinity for IGF-binding proteins.

3 Walton PE, et al. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in animal models. Experimental comparison of IGF-I, R3IGF-I, Long IGF-I, Long R3 IGF-I and related analogues.

4 Dunaiski V, Dunshea FR, Walton PE, Goddard C. Long R3 insulin-like growth factor-I reduces growth, plasma growth hormone, IGF-binding protein-3 and endogenous IGF-I concentrations in pigs. Journal of Endocrinology. 1997. Demonstrates complex endocrine feedback and species-specific biological responses.

5 Tomas FM, et al. Long R3 insulin-like growth factor-I infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF-binding protein concentrations in the guinea pig. Journal of Endocrinology. 1995.

6 Voorhamme D, Yandell CA. LONG R3IGF-I as a more potent alternative to insulin in serum-free culture of HEK293 cells. Molecular Biotechnology. 2006;34(2):201–204. Demonstrates the use of LR3 as a highly potent growth and survival factor in mammalian cell culture.

7 Thomas A, Walpurgis K, Delahaut P, Fichant E, Schänzer W, Thevis M. Determination of LongR3-IGF-I, R3-IGF-I, Des1-3 IGF-I and their metabolites in human plasma by LC-MS. Growth Hormone & IGF Research. 2017;35:33–39. Analytical and metabolism research supporting detection of synthetic IGF analogues.

8 Thomas A, et al. Detection of LongR3-IGF-I, Des(1-3)-IGF-I and R3-IGF-I using immunopurification and high resolution mass spectrometry for anti-doping purposes. Drug Testing and Analysis. 2021. Notes that these synthetic IGF-I analogues have never been approved for use in humans.

Scientific research information only

This profile is provided for scientific and educational information. Long R3 IGF-I is a synthetic experimental analogue of insulin-like growth factor-I and is not presented by ASA Research Labs as an approved treatment for growth, muscle development, recovery, body composition, metabolic disease, ageing or any other human condition. Laboratory and animal activity does not establish human safety or therapeutic efficacy. This page does not provide instructions for administration, dosing or human use.

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