IGF-1 LR3: Long-Acting Analogue of Insulin-Like Growth Factor-1
Recombinant IGF-1 with an extended N-terminus and Arg-for-Glu substitution. Long-acting, low IGFBP affinity. Used in cell culture; not approved for humans.
🐀 Animal
- Full name
- IGF-1 LR3 (Long R3 IGF-1)
- Class
- Modified IGF-1 analogue
- Half-life
- ~20–30 hours
- Route
- Research: subcutaneous / IM
- Developer
- Originally Gropep (AU) for cell culture
- Regulatory status
- Not approved as a medicine; used industrially in cell culture; WADA-banned
What it is
IGF-1 LR3 is a recombinant IGF-1 analogue with a 13-residue N-terminal extension and Arg substituted for Glu at position 3. These modifications block binding to IGFBPs, markedly extending half-life and free bioactivity compared with native IGF-1.
How it works
By escaping IGFBP sequestration, LR3 reaches IGF-1 receptors at higher effective concentrations and signals via the IGF-1R → PI3K/Akt and MAPK pathways — driving cell proliferation, hypertrophy, and metabolic effects similar to native IGF-1 but more potently in vivo.
The analogue is widely used in industrial cell culture to enhance cell line productivity. Its use in humans is unapproved and concerns include hypoglycaemia and unchecked growth signalling.
What the research shows
Evidence comes from cell-culture applications and rodent studies; human controlled trials do not exist.
Tomas FM et al. (1993) — rodent protein metabolism
Tomas F.M. et al., J Endocrinol 1993;137:413–421. 🐀 Animal
Rats receiving LR3 IGF-1 showed greater nitrogen retention and lean mass increases than those receiving equivalent native IGF-1.
Effects persisted at lower doses, consistent with the enhanced free bioactivity.
Limitations: Rodent; short duration.
Chen JW et al. (2005) — bioactivity characterisation
Chen J.W. et al., Growth Horm IGF Res 2005;15:77–84. 🐀 Animal
Side-by-side pharmacokinetic comparisons quantified the extended half-life and receptor binding of LR3.
Results inform cell-culture formulations and highlight the safety implications of unchecked IGF-1R signalling in vivo.
Limitations: Not a clinical trial.
Safety and limitations
In humans, anecdotal reports describe hypoglycaemia (IGF-1R and low-affinity insulin-receptor activation) and fluid retention. Chronic theoretical risks include tumour promotion and organomegaly. No quality-controlled human product exists.
Banned by WADA. Street products labelled IGF-1 LR3 have highly variable potency and purity.