Bottom line
IGF-1 LR3 (Long R3 IGF-1) is a recombinant analog of human IGF-1 with two modifications: (1) a Glu3→Arg substitution, and (2) a 13-amino-acid N-terminal extension derived from methionyl porcine growth hormone. These modifications reduce binding to IGF-binding proteins (IGFBPs) by >1000-fold, creating a research tool for cell culture where IGFBP interference is unwanted. It is marketed in the research chemical space as a "longer-acting IGF-1," but it has never been studied in human clinical trials and is not approved for any human use. It is a distinct compound from the approved drug mecasermin.
Identity and composition
| Field | Verified information |
|---|---|
| Preferred name | Long R3 IGF-1 |
| Key aliases | IGF-1 LR3, LR3 IGF-1, Long Arg3 IGF-1 |
| Molecular/sequence identity | Recombinant 83-amino-acid protein = 13-aa N-terminal extension (derived from porcine GH) + full-length human IGF-1 (70 aa) sequence with Arg substituting Glu at position 3 of the mature sequence |
| Modifications/form | N-terminal 13-aa extension + Glu3→Arg substitution; reduced IGFBP affinity |
| Stable identifiers | MW ~9.1 kDa; Sigma-Aldrich I1146/I1271; R&D Systems 8335D-GMP |
| Identity caveats | IG is NOT the same as mecasermin (Increlex), which is full-length unmodified rhIGF-1. The "R3" refers to the arginine substitution at position 3. The term "Long" refers to the N-terminal extension. Vendor marketing often misrepresents this cell-culture reagent as a "research peptide" with implied human applications. |
Development and approval status
| Jurisdiction | Status and indication | Product/source | As of |
|---|---|---|---|
| US (FDA) | No human clinical use; sold as cell culture reagent / research chemical | — | 2026-08-06 |
| Registers reviewed | No FDA-approved product or EMA-authorized medicine identified; status elsewhere requires a current national-register check | — | 2026-08-06 |
- UNITED STATES
- US (FDA): No human clinical use; sold as cell culture reagent / research chemical
- EU/EEA
- No EU/EEA row is present in the source status table
- UNITED KINGDOM
- No UNITED KINGDOM row is present in the source status table
- OTHER DOCUMENTED
- Registers reviewed: No FDA-approved product or EMA-authorized medicine identified; status elsewhere requires a current national-register check
Sport status: IGF-1 LR3 falls within WADA S2 prohibition (IGF-1 and its analogs). The approved drug mecasermin is the only IGF-1 medicine; modified analogues are unapproved.
Mechanism and pharmacology
IGF-1 LR3 binds the IGF-1 receptor with affinity comparable to native IGF-1 but has dramatically reduced affinity for IGFBPs (Kd >1 µM vs nM for native IGF-1). This results in greater free peptide availability at the receptor. The modifications also confer enhanced proteolytic stability. In cell culture, the reported The time for the amount of a substance in the body to fall by half. Quelle der Definition: Neutral gloss; usage context: Routes, devices, and absorption primer · Glossar of free IGF-1 LR3 is longer than native IGF-1, but in vivo How a substance is absorbed, distributed, metabolized, and eliminated by the body; atlas pages report pharmacokinetic data such as half-life, metabolism, and clearance. Quelle der Definition: Neutral gloss; usage context: Routes, devices, and absorption primer · Glossar in humans have not been studied.
Evidence by claim
| Claim/indication | Stage | Grade | Best human evidence | Main result | Important limitations |
|---|---|---|---|---|---|
| Cell culture growth supplement | Reagent | ? | Extensive in vitro use | Maintains IGF-1R activation in serum-supplemented media | Cell culture only; no human relevance |
| Muscle growth (IGF-1R activation) | Evidence from in vitro or animal studies with no adequate human efficacy evidence — the atlas Grade D lane. Quelle der Definition: Evidence grading methodology · Glossar | D | Rodent studies from 1990s | Anabolic effects in several rodent models | Animal data only; not translatable to humans without human studies |
| Anabolic/body composition | Marketing | E | No controlled human studies | No adequate evidence | No human data of any kind |
| Human therapeutic use | None | X | No clinical trials | Never studied in humans | No safety or efficacy data in humans |
- AKlasse A: Für eine bestimmte gekennzeichnete Anwendung nachgewiesen
- BKlasse B: Mäßige Humanstudien
- CKlasse C: Vorläufige Humanstudien
- DKlasse D: Nur präklinisch
- EKlasse E: Anekdotisch/Vermarktungsbehauptung
- XKlasse X: Die Evidenz widerspricht der Behauptung oder stützt sie nicht
Text alternative for the claim-evidence diagram. Each grade is defined below:
- A — Established for a specific labeled use
- 0 claims
- B — Moderate human evidence
- 0 claims
- C — Preliminary human evidence
- 0 claims
- D — Preclinical only
- 1 claim: Muscle growth (IGF-1R activation)
- E — Anecdotal/marketing claim
- 1 claim: Anabolic/body composition
- X — Evidence contradicts or does not support the claim
- 1 claim: Human therapeutic use
Key studies
| Study | Design/population | Exposure studied | Endpoints and result | Limitations |
|---|---|---|---|---|
| Tomas et al., J Endocrinol 1993 | Rat pharmacology | Administered into the tissue layer under the skin. Quelle der Definition: Neutral gloss; usage context: Routes, devices, and absorption primer · Glossar IGF-1 LR3 | Anabolic effect; reduced IGFBP binding | Rodent; no human |
| Francis et al., J Mol Endocrinol 1992 | Structure-activity | In vitro | Reduced IGFBP binding characterized | In vitro only |
| Voorhamme & Yandell, Mol Biotechnol 2006 | Reagent characterization | In vitro | >100-fold reduced IGFBP affinity vs wild-type | Technical reagent paper |
Dose and administration evidence
Approved labeled regimen
Not applicable.
Studied regimens (not recommendations)
No established or recommended human dose. No human study has established a dose for this compound.
What is not established
No human How a substance is absorbed, distributed, metabolized, and eliminated by the body; atlas pages report pharmacokinetic data such as half-life, metabolism, and clearance. Quelle der Definition: Neutral gloss; usage context: Routes, devices, and absorption primer · Glossar
No human safety data
No human efficacy data
The marketed in vivo "dosing protocols" are community practice without clinical support
The time for the amount of a substance in the body to fall by half. Quelle der Definition: Neutral gloss; usage context: Routes, devices, and absorption primer · Glossar in humans is unknown
Safety
No human safety data exist. Theoretical risks from IGF-1 receptor activation include hypoglycemia (IGF-1 has weak insulin-like activity), mitogenic effects promoting neoplasia, and acromegalic effects if systemic levels are elevated. Research-grade material from unregulated suppliers may have degradation products with unknown bioactivity.
Unknowns and product-quality risks
All safety parameters in humans are unknown. The compound is a cell culture reagent being sold for unapproved human use. Identity and purity of gray-market material are not regulated. PEGylation or other claims of extended The time for the amount of a substance in the body to fall by half. Quelle der Definition: Neutral gloss; usage context: Routes, devices, and absorption primer · Glossar beyond the intrinsic modification are often unsubstantiated.
Interactions and special populations
No data exist.
Regulatory, compounding, and sport notes
IGF-1 LR3 falls within The World Anti-Doping Agency; its Prohibited List classifies many peptides as prohibited substances in sport. Quelle der Definition: WADA and sport regulation brief · Glossar WADA Prohibited List class S2 (peptide hormones, growth factors, related substances and mimetics): prohibited at all times, with subsections of materially different scope. Quelle der Definition: WADA and sport regulation brief · Glossar prohibition (IGF-1 and its analogs). The approved drug mecasermin is the only IGF-1 medicine; modified analogues are unapproved.
Evidence gaps
No human study of any kind
No How a substance is absorbed, distributed, metabolized, and eliminated by the body; atlas pages report pharmacokinetic data such as half-life, metabolism, and clearance. Quelle der Definition: Neutral gloss; usage context: Routes, devices, and absorption primer · Glossar data in humans
No toxicology data
No efficacy data in humans
No data on tissue distribution or IGFBP interaction in vivo in humans
Search notes
Databases and registries: PubMed, PubChem, Sigma-Aldrich, FDA Drugs@FDA
Search terms: "IGF-1 LR3", "Long R3 IGF-1", "LR3 IGF-1", "Long Arg3 IGF-1"
Last searched: 2026-08-06
Inclusion emphasis: Primary peer-reviewed data; manufacturer specifications for cell culture use
Sources
Tomas FM et al. The anabolic effects of insulin-like growth factor-I (IGF-I) and long R3 IGF-I in rats. J Endocrinol. 1993;137(3):413-421. PMID 8371075. https://pubmed.ncbi.nlm.nih.gov/8371075/
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;8(3):213-223. PMID 1371669. https://pubmed.ncbi.nlm.nih.gov/1371669/
Voorhamme D, Yandell CA. LONG R3 IGF-I as a more potent alternative to insulin in serum-free culture of HEK293 cells. Mol Biotechnol. 2006;34(2):201-204. PMID 17172665. https://pubmed.ncbi.nlm.nih.gov/17172665/
Repligen. LONG R3 IGF-I Cell Culture Supplement. https://www.repligen.com/products/cell-culture-supplements/long-r3-igf-i
WADA Prohibited List 2026. https://www.wada-ama.org/en/prohibited-list