GF-1 LR3, short for Long R3 Insulin-like Growth Factor-1, commonly known as LR3 or Long R3, is a modified version of endogenous IGF-1. Human IGF-1 originally has 70 peptides (7.6 kDa). It has 13 amino acids (MFPAMPLSSLFVN…) hard-attached at the N-terminus, and the third glutamate (Glu) has been replaced with Arg, resulting in an 83-peptide, 9117.5 Da, CAS 946870-92-4.
Native IGF-1 is immediately bound by six IGFBP (binding proteins), with less than 1% in the free state and a plasma half-life of only 15 minutes, making it extremely difficult to perform long-acting signaling assays. This modification to LR3 drastically reduced its affinity for IGFBP by approximately 1000 times, maximizing the proportion of free peptides and extending the half-life to 20–30 hours, while maintaining the same affinity for the receptor (IGF-1R) as the original, essentially making it an "unbound IGF-1".
Binding IGF-1R (tyrosine kinase) → triggers two pathways: PI3K/Akt/mTOR and MAPK/ERK. This leads to ribosomal S6K and 4E-BP1 phosphorylation, full protein translation, and suppression of FoxO, resulting in protein breakdown and synthesis. This promotes the proliferation and differentiation of myoblasts/C2C12, chondrocytes, CHO cells, and MSCs.
Core Research Value (Don't misread as "muscle growth with a single injection"):
Long-acting IGF-1R probe: Stable receptor occupancy in serum/IGFBP-containing systems, significantly cleaner than the original IGF-1 in terms of signal duration, receptor downregulation, and mTOR kinetics.
Serum-free/low-serum culture gold partner: Repligen's LONG R3 IGF-I is an industrial-grade supplement, inhibiting apoptosis and increasing CHO/MSC density, offering greater stability and lower cost than insulin.
Approximately 3 times the in vitro potency of the original IGF-1, requiring less dosage; however, high concentrations (>200 ng/mL) can actually downregulate receptor endocytosis and promote platelet proliferation; higher concentrations are not always better.
A word of caution: This is not a clinical drug; it hasn't been approved by the FDA, and WADA classifies it in the gray area for peptides. The "50-100 μg subcutaneous ablation" regimen used in the fitness community is a community dose, not a research protocol. Furthermore, IGF-1R itself is associated with tumor proliferation, and long-term misuse carries significant theoretical risks.
Storage (Reagent lyophilized powder, 9 kDa protein is not a small peptide)
Unreconstituted lyophilized powder: Store at -20℃, sealed, protected from light, and with desiccant for 1-3 years. Archiving at -80℃ is most stable. Do not store at 4℃ long-term, and do not store at room temperature.
Reconstituted stock solution: Most brands recommend initial reconstitution with sterile 0.1% acetic acid (pH 3.5–4.5) (direct dissolution with neutral water will cause aggregation!), concentration 0.1–2 mg/mL; shelf life is only 2–7 days at 2–8℃. For long-term storage, it must be aliquoted with loading media (0.1% BSA / 5% HSA / 5% trehalose / 10% FBS). A single serving at -80℃ can last 3–12 months.
Working solution: Dilute with PBS or complete culture medium containing 0.1% BSA. Briefly store in a cell culture room at 4℃. Avoid repeated freeze-thaw cycles.
Precautions:
Center at 8000–12000 g for 30 seconds before opening. For 9 kDa protein lyophilization, adhere the bottle to the wall and cap. Do not add water directly without centrifugation; the "invisible powder" at the bottom of the bottle is money.
For initial dissolution, use 0.1% acetic acid to slowly churn along the cell wall, avoiding vortexing. Each vortex will distort the conformation by half. Mix slowly by rotating/inverting the tube until clear and colorless. Discard any solution that is foggy or flocculent, as aggregated LR3 receptors will have zero binding affinity.
Low concentrations cause excessive adsorption to the tube wall: When the working concentration is 1–100 ng/mL, do not use 0.1% BSA as a carrier or low-adsorption tubes. The actual amount added to the wells will only be 30–50% of the nominal concentration, resulting in alarming intracellular volumetric emissions (CVs).
pH sensitivity: Do not directly add acetic acid stock solution to cells (pH shock kills cells). Pre-dilute at least 1:100 to a neutral buffer containing BSA before adding to the culture system.
CoA monitoring: HPLC ≥98%, MS confirmation 9117.5 Da, endotoxin <0.01–1 EU/μg (stricter requirements for cell therapy-grade MSCs); oxidized Met or its truncated form are latent antagonists. RUO label: The label reads "Research Use Only, not for human use," indicating it's not a legally approved drug for human injection; it's for internal use within the IACUC system. Don't mistake peptide suppliers for pharmacies.
For proliferation experiments, three controls are essential: blank homologous serum control + original IGF-1 equimolar control + IGF-1R inhibitor (picropodophyllin/OSI-906). Otherwise, it's unclear whether LR3 is the active ingredient or other factors in the serum are contributing.
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