What does the 'LR3' in LR3 IGF-1 mean?

'LR3' encodes the two engineering modifications relative to native IGF-1. 'L' stands for 'Long,' referring to the 13-residue N-terminal extension (sequence MFPAMPLSSLFVN) appended to the native sequence; this extension is a remnant of a methionyl-protein-A fusion construct used in the original recombinant production. 'R3' refers to the arginine substitution at position 3 in place of the native glutamate. Together these two changes reduce the molecule's affinity for IGF-binding proteins (IGFBPs) while preserving IGF-1R binding.

Why was LR3 IGF-1 designed?

LR3 IGF-1 was designed in the late 1980s as a cell-culture growth supplement. Native IGF-1 added to serum-containing or IGFBP-secreting cell-culture systems is largely sequestered by IGFBPs and therefore has limited biological potency in vitro. The combination of the R3 substitution and the N-terminal extension produces a variant that escapes IGFBP binding and therefore acts as a more potent IGF-1R agonist in IGFBP-rich systems — particularly useful in CHO cell-culture for biopharmaceutical production and in primary cell culture.

Is LR3 IGF-1 the same as native IGF-1?

No. Native human IGF-1 is a 70-residue polypeptide; LR3 IGF-1 is an 83-residue engineered variant with an N-terminal extension and an E3R substitution. The two molecules engage the IGF-1 receptor with similar affinity, but their behavior in IGFBP-rich systems differs substantially because LR3 largely escapes IGFBP sequestration while native IGF-1 is largely IGFBP-bound. The FDA-approved native human IGF-1 product (mecasermin/Increlex) is the native molecule, not LR3.

How does LR3 IGF-1 differ from MGF?

LR3 IGF-1 is an engineered analog of mature IGF-1 with reduced IGFBP affinity. MGF (mechano growth factor) is the IGF-1Eb splice variant — a different mRNA from the IGF1 gene that, after processing, generates a 24-residue C-terminal E-peptide (the 'MGF peptide') with biological activity distinct from mature IGF-1. Mature IGF-1 from the IGF-1Eb transcript is identical to mature IGF-1 from the IGF-1Ea transcript; the difference between MGF and IGF-1 is the E-domain peptide, not the mature IGF-1 sequence. LR3 modifies the mature sequence; MGF involves the E-peptide.

What are IGFBPs and why do they matter?

IGFBPs (IGF-binding proteins 1–6) are a family of high-affinity binding proteins that sequester IGF-1 and IGF-2 in serum and extracellular fluid. They extend the circulating half-life of IGF-1 in protein-bound form and restrain free IGF-1 access to IGF-1R. In serum, IGFBP-3 dominates and forms a ternary complex with the acid-labile subunit. In tissues, locally secreted IGFBP-2, -4, -5, and -6 modulate local IGF-1 access. The IGFBP system is the principal extracellular regulator of IGF-1 bioavailability and is a major determinant of how potent added IGF-1 is in any given cell-culture system.

What receptor does LR3 IGF-1 activate?

LR3 IGF-1 activates the IGF-1 receptor (IGF-1R), a heterotetrameric transmembrane tyrosine kinase receptor closely related to the insulin receptor. Ligand binding triggers β-subunit transphosphorylation, IRS recruitment, and activation of PI3K-AKT-mTOR and Ras-Raf-MEK-ERK signaling cascades. LR3 IGF-1 also binds to a small extent to the insulin receptor and to insulin/IGF-1 hybrid receptors, with much lower affinity than to IGF-1R.

Why is LR3 IGF-1 used in CHO cell culture?

CHO (Chinese hamster ovary) cell lines used in biopharmaceutical production benefit from IGF-1R-mediated proliferation and survival signaling in serum-free or low-serum fed-batch culture. LR3 IGF-1 is the canonical IGF-1 analog used in this application because its reduced IGFBP affinity provides reliable, dose-dependent IGF-1R stimulation in the IGFBP-secreting CHO culture system. Major bioscience reagent suppliers document LR3 IGF-1 as a cell-culture growth supplement for this purpose.

Has LR3 IGF-1 been studied as a medicine?

No major clinical-research program has developed LR3 IGF-1 as a therapy in any jurisdiction. The molecule was designed for cell-culture and laboratory use, and its altered IGFBP pharmacology raises distinct considerations for in-vivo use that are different from those for native IGF-1. The native molecule (mecasermin) was developed for clinical use, with FDA approval in 2005 for severe primary IGF-1 deficiency. LR3 IGF-1 is a research and cell-culture reagent, not an approved medicine.

How is LR3 IGF-1 reconstituted and stored?

Lyophilized LR3 IGF-1 is typically reconstituted in dilute acetic acid (e.g., 0.1 M) or sterile aqueous buffer at acidic pH, in which the molecule is more stable than at neutral pH. After reconstitution, working solutions are diluted into the desired culture medium. The lyophilized material is stable at -20 °C or below for extended periods; reconstituted solutions should be stored at 4 °C for short-term use or aliquoted and frozen for longer-term storage. Repeated freeze-thaw cycles should be avoided.

Does LR3 IGF-1 cross-react with insulin receptor?

LR3 IGF-1 binds insulin receptor with much lower affinity than IGF-1R, but in cells expressing both receptors, some cross-talk through insulin/IGF-1 hybrid receptors occurs. This is a feature of the broader IGF-1 / insulin receptor family and is not unique to LR3 IGF-1; native IGF-1 has the same cross-reactivity pattern. In most cell-culture applications, IGF-1R is the dominant target.

What is the half-life of LR3 IGF-1?

Published pharmacokinetic data on LR3 IGF-1 are limited because the molecule has not been extensively studied in vivo. The combination of reduced IGFBP affinity and small protein size suggests a relatively short circulating half-life — likely tens of minutes rather than the many hours characteristic of native IGFBP-bound IGF-1 — but specific values depend on species, route, and assay. Cell-culture applications, the principal use, do not depend on in-vivo pharmacokinetics.

Is LR3 IGF-1 produced in bacteria or mammalian cells?

Research-grade LR3 IGF-1 is typically produced recombinantly in bacterial (E. coli) expression systems. The protein is expressed in inclusion bodies, solubilized, refolded under controlled redox conditions to form the three intrachain disulfide bonds in the correct arrangement, and purified by chromatographic methods. The lack of N-glycosylation in IGF-1 makes bacterial production feasible, in contrast to glycosylated proteins like follistatin that require mammalian expression.

IGF-1 LR3 (with Bacteriostatic Water) lyophilized vial with bacteriostatic water for research

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IGF-1 LR3 (with Bacteriostatic Water)

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IGF-1 LR3 (Long R3 IGF-1) is a synthetic analog of human insulin-like growth factor-1 (IGF-1) that has been modified to extend its half-life and increase stability in research models. It is widely studied in cellular biology, metabolic research, and growth signaling pathways due to its enhanced receptor binding activity and prolonged biological action compared to native IGF-1.

IGF-1 LR3Long R3 IGF-1Growth Factor ResearchCellular SignallingLyophilized

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