What is IGF-1 LR3?
IGF-1 LR3 (also written IGF1 LR3, Long R3 IGF-I or LR3IGF-I) is a recombinant analog of human insulin-like growth factor I, built in Escherichia coli as a fusion peptide: the IGF-I sequence carries a 13-residue N-terminal extension, the first 11 amino acids of methionyl porcine growth hormone plus the dipeptide Val-Asn, and arginine replaces glutamate at position 3.
The authors named the family Long IGF-I, Long [Gly3]-IGF-I and Long [Arg3]-IGF-I by the IGF-I sequence present, so LR3 means the long extension plus the Arg3 substitution (King et al., 1992; Francis et al., 1992). The literature is rodent, livestock and cell-culture work, much of it from one Australian group in the 1990s, plus later analytical chemistry. Disguised Alpha supplies IGF-1 LR3 as a lyophilized powder for laboratory research use only. Nothing on this page is guidance for use in people.
Analogs of this type were never approved for use in people, as stated by the anti-doping laboratory that validated a detection method for them while noting that they circulate as unregulated products (Mongongu et al., 2021; Dominikowski et al., 2026). Our material is research-grade powder, not a drug product, and not for people.
IGF-1 LR3 reference data
| Property | Value |
|---|---|
| Name | IGF-1 LR3 (catalog listing: IGF1-LR3) |
| Aliases | Long R3 IGF-I, LR3IGF-I, LONG R3IGF-I, Long [Arg3]-IGF-I, long-Arg3-IGF-I |
| Construct | Human IGF-I with a 13-residue N-terminal extension, [Met1]-pGH(1-11)-Val-Asn, and Arg substituted for Glu at IGF-I position 3 (King et al., 1992; Francis et al., 1992) |
| Peptide class | N-terminally extended recombinant IGF-I analog (growth factor analog) |
| Molecular formula | Not listed in the Compound Information section of the product page |
| Molecular weight | Not listed in the Compound Information section of the product page; no PubChem record corresponds to this construct, so no verified figure is published here |
| CAS number | Not listed in the Compound Information section of the product page |
| Form | Lyophilized powder |
| Testing | Third-party tested, certificate published on the product page and in the COA portal |
The product page's Compound Information section lists storage requirements but no molecular profile, and PubChem holds no record matching the LR3 construct, so identity figures are left blank above rather than carried over from third-party listings. The certificate panel on the product page records the label mass, printed identity and measured content for each lot. Take identity and content for quantitative work from that certificate.
What the research covers
Published work on Long R3 IGF-I falls into six areas. Each summary below states the model used.
Construction and design rationale
Two 1992 papers describe the expression system. Fusion protein was isolated from inclusion bodies, cleaved at an Asn-Gly bond, refolded and purified, with identity checked by HPLC and N-terminal sequencing. In L6 rat myoblasts, [Gly3]-IGF-I and [Arg3]-IGF-I were more potent than IGF-I at stimulating protein and DNA synthesis and at inhibiting protein breakdown, yet both bound slightly less well to the type 1 receptor, which the authors attributed to weaker binding-protein association rather than stronger receptor binding (King et al., 1992).
The hydrophobic extension also improved folding yields, and in chicken embryo fibroblasts, a line that secretes no detectable binding proteins, Long [Arg3]-IGF-I was less potent than IGF-I (Francis et al., 1992).
Binding protein affinity
IGF-I has roughly 1000-fold higher affinity than LR3IGF-I for IGFBP-3, IGFBP-4, total rat plasma binding proteins and L6 myoblast binding protein, which tracked with a 5 to 10-fold greater potency for the analog in L6 myoblast culture (Ballard et al., 1993). A five-species survey found binding differed markedly between rat, sheep, human, pig and chicken plasma, so one species does not predict another (Lord et al., 1994).
Clearance and distribution in rodents
In virgin and pregnant rats given labeled tracer, the metabolic clearance rate was 9.19 and 9.84 milliliters per minute per kilogram for LR3IGF-I against 2.88 and 0.90 for IGF-I. Most analog tracer was free peptide rather than bound in the 150 kDa complex, and tissue distribution differed between the two (Bastian et al., 1993).
Rodent growth and gut models
In rats made catabolic with dexamethasone, the analog was about 2.5-fold more potent than IGF-I at restoring body weight and nitrogen retention over 7 days, with coordinate changes in muscle protein turnover markers and gut weight increases of up to 45 percent (Tomas et al., 1992).
In normal female rats treated for 14 days through osmotic minipumps, gut weight, small intestinal weight and intestinal length rose with concentration, with more crypt cells and cells per villus column while the crypt growth fraction stayed unchanged (Steeb et al., 1994). A separate 14-day rat study put the analog about 6-fold above IGF-I on growth measures (Ballard et al., 1993).
Species where results reversed
In finisher pigs, a four-day infusion decreased average daily gain, food intake and plasma IGFBP-3, IGF-I and insulin, and lowered mean plasma growth hormone by 23 percent, so the analog inhibited rather than stimulated growth in that species (Dunaiski et al., 1997). In pigs and marmoset monkeys, variants that bind binding proteins poorly lowered plasma glucose 2 to 3-fold more than IGF-I and for longer (Tomas et al., 1997). In growth-restricted fetal sheep, one week of treatment did not raise fetal weight and circulating amino acids fell (White et al., 2025).
Cell-culture use and analytical detection
The analog is widely used as a serum-free culture supplement. In two recombinant protein-expressing Chinese hamster ovary lines it sustained viability under production conditions better than insulin (Morris and Schmid, 2000), and in HEK293 cells it was a more potent growth and survival factor than insulin or native IGF-I, supporting CHO cells at concentrations at least 200-fold below those needed for insulin (Voorhamme and Yandell, 2006).
On the analytical side, an immunopurification and high-resolution mass spectrometry method detected LongR3-IGF-I and related analogs in serum, identified new N-terminal degradation products, and reported abundant oxidized forms in unregulated market products (Mongongu et al., 2021). An earlier case report identified His-tagged Long-R3-IGF-I, a form normally made for biochemical studies, in a confiscated vial (Kohler et al., 2010).
Key studies
- King R, et al. "Production and characterization of recombinant insulin-like growth factor-I (IGF-I) and potent analogues of IGF-I, with Gly or Arg substituted for Glu3, following their expression in Escherichia coli as fusion proteins." J Mol Endocrinol. 1992. PMID 1311930. DOI 10.1677/jme.0.0080029. Expression system, L6 rat myoblast assays and binding comparisons.
- Francis GL, et al. "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." J Mol Endocrinol. 1992. PMID 1378742. DOI 10.1677/jme.0.0080213. Cell culture: L6 myoblasts, H35 hepatoma cells and chicken embryo fibroblasts.
- Tomas FM, et al. "Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats." Biochem J. 1992. PMID 1371669. DOI 10.1042/bj2820091. Rat catabolic model, 7 days: weight, nitrogen retention, protein turnover.
- Ballard FJ, et al. "Effects of interactions between IGFBPs and IGFs on the plasma clearance and in vivo biological activities of IGFs and IGF analogs." Growth Regul. 1993. PMID 7683526. IGFBP affinity, L6 myoblast potency and a 14-day rat growth study.
- Bastian SE, et al. "Plasma clearance and tissue distribution of labelled insulin-like growth factor-I (IGF-I) and an analogue LR3IGF-I in pregnant rats." J Endocrinol. 1993. PMID 7693845. DOI 10.1677/joe.0.1380327. Clearance and tissue distribution in virgin and pregnant rats.
- Steeb CB, et al. "Prolonged administration of IGF peptides enhances growth of gastrointestinal tissues in normal rats." Am J Physiol. 1994. PMID 7912894. DOI 10.1152/ajpgi.1994.266.6.G1090. Normal rats, 14 days: gut weight and crypt/villus morphometry.
- Dunaiski V, et al. "Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs." J Endocrinol. 1997. PMID 9488001. DOI 10.1677/joe.0.1550559. Finisher pigs, four days: growth performance and plasma hormones.
- Morris AE, Schmid J. "Effects of insulin and LongR(3) on serum-free Chinese hamster ovary cell cultures expressing two recombinant proteins." Biotechnol Prog. 2000. PMID 11027158. DOI 10.1021/bp0000914. Serum-free CHO culture: growth, viability and productivity.
- Mongongu C, et al. "Detection of LongR3-IGF-I, Des(1-3)-IGF-I, and R3-IGF-I using immunopurification and high resolution mass spectrometry for antidoping purposes." Drug Test Anal. 2021. PMID 33587816. DOI 10.1002/dta.3016. Method validation in human serum, with degradation products identified.
Handling and storage of lyophilized IGF-1 LR3
General laboratory practice for this material:
- Store the lyophilized powder at -20°C, protected from light, until use (storage guidance on the product page).
- Let the sealed vial reach room temperature before opening so moisture does not condense on the powder.
- This is a small protein rather than a short peptide, so handle it as one: reconstitute gently without vortexing or shaking, and avoid foaming at the air interface.
- The construct begins with a methionine, and methionine side chains oxidize readily: one anti-doping method monitors native and mono-oxidized species because oxidized forms were abundant in market material (Mongongu et al., 2021). Limit exposure to air, light and oxidizers.
- After reconstitution, keep solutions at 2 to 8°C and protected from light, and split stock into single-use aliquots to avoid freeze/thaw cycles.
- Record the lot number and keep its certificate with your notes. Because no CAS number, formula or molecular weight is published for this construct, base identity and quantitative calculations on the certificate.
Frequently asked questions
What is IGF-1 LR3?
A recombinant IGF-I analog with a 13-residue N-terminal extension and arginine in place of glutamate at position 3, originally produced as a bacterial fusion protein (King et al., 1992). It is used as a reagent for IGF-I receptor signaling work and as a serum-free culture supplement.
What does the name Long R3 mean?
Long refers to the N-terminal extension from methionyl porcine growth hormone plus a Val-Asn linker, and R3 to the arginine substituted for glutamate at position 3. The convention comes from the original papers on Long IGF-I, Long [Gly3]-IGF-I and Long [Arg3]-IGF-I (Francis et al., 1992).
How does IGF-1 LR3 differ from IGF-I and des(1-3)IGF-I?
All three bind the type 1 IGF receptor and differ mainly in how strongly they associate with IGF binding proteins, a roughly 1000-fold affinity gap for IGFBP-3 and IGFBP-4 that tracked with a 5 to 10-fold potency difference in L6 myoblast culture (Ballard et al., 1993). In a cell line that secretes no binding proteins the ranking reversed and the analog was less potent (Francis et al., 1992), so the difference is about binding protein interaction rather than intrinsic receptor activity.
Is IGF-1 LR3 approved anywhere?
No. The anti-doping laboratory that validated detection methods for these analogs states they were never approved for use in humans and are prohibited in sport (Mongongu et al., 2021). Our material is research-grade powder for laboratory use, not a drug product, and not for use in people.
How should IGF-1 LR3 powder be stored?
Keep the lyophilized powder at -20°C and protected from light. After reconstitution, store the solution at 2 to 8°C, protected from light, and avoid freeze/thaw cycles, as listed on the product page.
Where can researchers buy IGF-1 LR3?
Disguised Alpha sells it for laboratory research, third-party tested with the certificate published on the product page: IGF-1 LR3.
Related compounds and guides
- PEG-MGF and its research guide: a pegylated mechano growth factor peptide studied in the same signaling area
- AOD-9604 and its research guide
- Tesamorelin and its research guide
- Sermorelin Acetate, CJC-1295 No DAC and Ipamorelin
- MK677 (Ibutamoren) and ACE-031
- COA portal: every published certificate, by lot
This product is for research use only. It has not been evaluated for safety or effectiveness in humans. Not for human consumption. All products are intended for laboratory research purposes only.