IGF-1 LR3

This is an analogue, and the native IGF-1 literature does not transfer to it. The molecule was created in 1992 as an Escherichia coli expression construct: the glutamate at position 3 of human IGF-1 is replaced by arginine, and a 13-residue N-terminal extension is fused on, made of the first 11 amino acids of methionyl porcine growth hormone plus a Val-Asn dipeptide. Native IGF-1 is 70 residues, so this construct is 83. The 1992 papers measured protein synthesis, DNA synthesis and protein breakdown in rat L6 myoblasts along with binding-protein and receptor binding, concluding that the analogue's greater in-vitro potency comes from REDUCED binding to the IGF binding proteins rather than from increased receptor binding. In-vivo work exists but is in animals. A 2010 study at the German Sport University identified a histidine-tagged form in a seized injection vial and described it as a substance usually produced for biochemical studies.

What is not established

There is no human data on this analogue at all. The 2010 paper states it plainly: the effects of the histidine-tagged form in humans have not been elucidated or described. Nothing about its safety, pharmacokinetics, immunogenicity or biological effect in humans is established, and the extensive clinical record behind mecasermin says nothing about it.

What distinguishes IGF-1 LR3

IGF-1 LR3 is the only compound in this range whose near-namesake is an approved medicine while it is not. Mecasermin, the native 70-residue IGF-1, holds a US biologics licence and a European authorisation from 2007, and the two are routinely conflated. They are not the same molecule. The documented consequence of the substitution and the N-terminal extension is loss of binding-protein affinity, which is precisely the property that makes native-protein pharmacology non-transferable. It is also the only one here placed in WADA S2.3 rather than S2.2, and its provenance is a laboratory expression construct designed as a research reagent rather than a discontinued drug candidate.

Sources

1. Francis GL et al. Novel recombinant fusion protein analogues of IGF-I. J Mol Endocrinol. 1992;8(3):213-23
2. King R et al. Production and characterization of recombinant IGF-I and potent analogues with Gly or Arg substituted for Glu3. J Mol Endocrinol. 1992;8(1):29-41
3. Kohler M et al. Detection of His-tagged Long-R3-IGF-I in a black market product. Growth Horm IGF Res. 2010;20(5):386-90
4. European Medicines Agency. Increlex, EPAR, mecasermin, the native protein and not this compound
5. World Anti-Doping Agency. 2026 Prohibited List, section S2.3

This page describes a compound as a material and summarises published research about it. It is for general and procurement information only. It is not medical advice, not a treatment recommendation, and not guidance on use. Supplied for laboratory and research use, not for human consumption.