Molecular profile
- Entry type
- Peptide research profile
IGF-1 LR3
IGF-1 LR3, properly Long [Arg3] IGF-I, is an 83-residue analogue of human insulin-like growth factor 1 made at the University of Adelaide.
Dosing & scaling, explained
Amounts reported for IGF-1 LR3 are listed under Reported protocols, each with its source and study kind. No amount ladder is inferred from them. This is educational source context, not a protocol or recommendation.
No source-supported amount ladder is shown
Enter a target amount only from your own reviewed source. The calculator can convert it into concentration, volume and device markings, but it will not infer an amount from product availability or another compound.
Only mcg or mg amounts are retained. The calculator derives mL, syringe units or pen clicks from the current vial strength, water volume and device.
No independently verified schedule
Clinical context
Human study rows are described per source under Reported protocols; they belong to their trial populations and are not a general amount.
Storage, handling and interpretation
Product identity
Verify the exact compound, formulation and amount against the product label or certificate before calculation.
Storage & handling
Follow the product label, certificate and validated laboratory SOP; no universal storage assumption is applied here.
Prepared solutions
Label concentration and preparation date, use sterile technique where applicable, and follow a validated stability protocol.
Reported protocols for IGF-1 LR3
What published studies and recent community write-ups report about amounts, timing and course length. 2 clinical, 4 preclinical and 3 community-reported rows, each linked to its source. These are descriptions of what others report, not instructions, and nothing here is medical advice.
| Context | Dose | Frequency | Route | Course | Source |
|---|---|---|---|---|---|
| Clinical2 rows | |||||
| Mecasermin, the approved IGF-1 product, for contrastChildren and adolescents with severe primary IGF-1 deficiency | 0.04-0.08 mg/kg twice daily to start, to a maximum of 0.12 mg/kg twice daily | Twice daily | Subcutaneous injection, with sites rotated | Long-term treatment until the epiphyses closeNot applicable | DailyMed, National Library of Medicine2026 |
| This is what a real human IGF-1 dose looks like, and it is for the native hormone, not the LR3 analogue. The Increlex label requires dosing shortly before or after a meal because of insulin-like hypoglycaemic effects, and carries warnings for severe hypoglycaemia with seizures, anaphylaxis, intracranial hypertension, tonsillar and adenoidal hypertrophy, slipped capital femoral epiphysis, scoliosis progression and malignant neoplasia, with closed epiphyses and malignancy as contraindications. These figures cannot be transferred to IGF-1 LR3, whose reduced binding-protein capture would give it a different free fraction, distribution and clearance. | |||||
| Real-world registry of recombinant human IGF-1 treatment102 patients in the Global Increlex Growth Forum Database who reached near-adult height | Mecasermin as labelled, with a median treatment duration of 3.9 years | As per the approved label | Subcutaneous | Median 3.9 years, with some patients followed much longerNot applicable | Journal of Clinical Endocrinology and Metabolism (PubMed Central)2026 |
| Mean age at starting treatment was 11.8 years and mean height standard deviation score gain to near-adult height was 0.9, rising to 1.4 in treatment-naive prepubertal patients. In Laron syndrome only 10.5% reached a near-adult height within the normal range. Safety data aligned with previous reports. This is the depth of human evidence that exists for native recombinant IGF-1 and does not exist for the LR3 analogue in any form. | |||||
| Preclinical4 rows | |||||
| Original characterisation of the Arg3 substitutionRat L6 myoblasts, with binding assays against bovine IGF binding protein 2 and the type 1 receptor | Not stated in the abstract; potency compared with native IGF-I across 3 endpoints | Culture exposure | Cell culture | Per assayNot applicable | Journal of Molecular Endocrinology (PubMed)1992 |
| This 1992 paper describes the Escherichia coli expression system behind the molecule: a fusion protein whose N-terminal extension is the first 46 amino acids of methionyl porcine growth hormone plus Val-Asn, cleaved at the Asn-Gly bond to release the IGF-I peptide. The same system produced the Glu3 to Arg and Glu3 to Gly variants. Both analogues were more potent than native IGF-I at stimulating protein and DNA synthesis and at blocking protein breakdown in myoblasts, bound bovine IGFBP-2 very poorly, and bound the type 1 receptor slightly less well than IGF-I. The authors conclude the extra potency comes from reduced binding-protein capture rather than better receptor binding. | |||||
| The Long analogue series, where the LR3 name comes fromRat L6 myoblasts, H35 hepatoma cells and chicken embryo fibroblasts | Matched molar concentrations of 3 Long analogues against native IGF-I and des(1-3)IGF-I | Culture exposure | Cell culture | Per assayNot applicable | Journal of Molecular Endocrinology (PubMed)1992 |
| This companion paper names the molecules: the analogues carry the first 11 amino acids of methionyl porcine growth hormone plus Val-Asn, and are called Long IGF-I, Long [Gly3]-IGF-I and Long [Arg3]-IGF-I depending on the substitution. In cell lines that secrete IGF binding proteins, the potency order ran Long [Arg3]-IGF-I ahead of Long [Gly3]-IGF-I, ahead of Long IGF-I, ahead of native IGF-I. In chicken embryo fibroblasts, which secrete no detectable binding proteins, Long [Arg3]-IGF-I was less potent than native IGF-I. That reversal is the whole mechanism in one experiment: the advantage exists only where binding proteins do. | |||||
| Systemic infusion in suckling ratsNeonatal rats infused from day 6 or day 12 after birth | 0, 2, 5 or 12.5 mcg per gram of body weight per day | Continuous delivery by mini osmotic pump | Systemic infusion | 6.5 daysNot applicable | American Journal of Physiology (PubMed)1997 |
| The clearest in vivo comparison. Both peptides raised kidney and spleen weight by up to 85% and 76%, and IGF-I raised gut weight and length by up to 60% and 32%, with Long [Arg3] IGF-I more potent than native IGF-I for every growth measure at both ages. Notably, infusing the analogue did not raise measured plasma IGF-I levels, because the assay reads the native hormone. These are rat pup doses in micrograms per gram of body weight, which do not translate to a person. | |||||
| Clearance and tissue delivery after an intravenous bolus in ratsPreweaning rats at day 19 and adult rats, 5 to 6 per group | 2.6 mcg/kg, spiked with iodine-125 labelled peptide | Single bolus | Intravenous | Blood and tissue sampled at 5 and 10 minutesNot applicable | Endocrinology (PubMed)2003 |
| At both ages, less labelled Long [Arg3] IGF-I remained in blood than labelled native IGF-I, consistent with faster clearance when the binding proteins are not holding the peptide in circulation, while gastrointestinal tissue levels per gram were 37% to 50% higher. The ratio of analogue to native peptide in gut tissue was about 2 to 1 at both ages, so the authors conclude selective delivery does not explain the analogue's much greater potency in the immature gut. This is the only pharmacokinetic comparison of the two molecules on this page, and it is in rats. | |||||
| Community-reported3 rows | |||||
| Cell-culture working concentrations, the actual commercial use | 50-100 ng/mL standard; 10-20 ng/mL for sensitive cell types, up to 200 ng/mL specialised | Added at each media change, typically every 2 to 3 days | Added to culture media | The duration of the culture experimentNot applicable | Community resource2026 |
| This reference page is explicit that no human dosing protocol exists because no clinical trial has been run, and that its figures apply only to cell culture and bioprocessing, where the analogue is routinely added to serum-free media for CHO, HEK293 and hybridoma lines. It reports a half-maximal effect at roughly 5 to 30 ng/mL depending on cell type, with little further gain above 100 ng/mL, and places the analogue at 2 to 3 times the potency of native IGF-1 in serum-containing media but equal potency in serum-free media. It also notes the separate 20-80 mcg daily figure that circulates in community protocols, which has no trial behind it. | |||||
| Community injection band | 20-100 mcg a day, with 20-40 mcg the most commonly cited start | Once daily | Subcutaneous or intramuscular from a reconstituted vial | Not validated by any trialNot validated by any trial | Community resource2026 |
| A community source, and one that says so. It states that no formal human clinical trial has ever evaluated IGF-1 LR3 for any therapeutic or performance endpoint, that ClinicalTrials.gov lists no IGF-1 LR3 efficacy or safety study, and that the 20-100 mcg band is extrapolated from preclinical work, the Increlex record and community reporting rather than measured. The nearest safety dataset it can point to is the Increlex programme in children with severe primary IGF-1 deficiency, a different molecule in a different population. | |||||
| Research-chemical vendor listing | 1 mg lyophilised vial, measured at 1.06 mg and 99.61% pure | Not stated by the vendor | Supplied as a freeze-dried powder for reconstitution | Not stated by the vendorNot stated by the vendor | Community resource2026 |
| A vendor claim. The page states the product is not for human, veterinary or food use, gives no amount or schedule, and is unusually frank that this analogue has repeatedly tested in the low-90% range across runs and that a single purity figure may not represent the batch. One correction worth recording: the listing publishes CAS 946870-92-4 for IGF-1 LR3, and that CAS resolves in PubChem to an unrelated ionisable lipid, not to any IGF-1 analogue, so the identifier on the page is wrong. The 5 papers it cites are genuine Long R3 IGF-I studies, all in animals or cell culture. | |||||
Sources for this section (11)
- 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
- 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
- Solution structure and backbone dynamics of long-[Arg(3)]insulin-like growth factor-I
- Systemic infusion of IGF-I or LR(3)IGF-I stimulates visceral organ growth and proliferation of gut tissues in suckling rats
- Preferential intestinal delivery of long[Arg3] insulin-like growth factor (LR3IGF-I) over IGF-I in preweaning and adult rats
- INCRELEX (mecasermin) injection, prescribing information
- Near-Adult Height Outcomes in Patients Treated With rhIGF-1 for Severe Growth Failure: Real-World IGFD Registry Data
- IGF-I abuse in sport
Plus 3 community resources (dosing guides, forum threads and vendor write-ups), reported above but not linked.
Overview
IGF-1 LR3, properly Long [Arg3] IGF-I, is an 83-residue analogue of human insulin-like growth factor 1 made at the University of Adelaide and CSIRO in the early 1990s: arginine replaces glutamate at position 3, and a 13-residue extension is added to the N-terminus, the first 11 amino acids of methionyl porcine growth hormone followed by the dipeptide Val-Asn. Those two changes cut its affinity for the IGF binding proteins that normally hold IGF-1 inactive, which makes it more potent in culture and is why it is sold commercially as a cell-culture and bioprocessing supplement under the trade name LONG R3 IGF-I rather than as a medicine. PubChem holds no compound record for it under any of its names, so this page shows no formula, molar mass or structure; it has never been tested in a human trial, and the only IGF-1 product with real human dosing is mecasermin, the recombinant native hormone sold as Increlex with an FDA-approved label.
What researchers are exploring
These themes describe recurring questions in published research. They are not claims of effectiveness or recommendations for use.
- 1
Growth hormone signaling
GH-axis, secretagogue and growth-factor research.
- 2
Muscle & performance
Androgen receptor modulators, myostatin pathways and exercise-mimetic research.
- 3
Original characterisation of the Arg3 substitution
This 1992 paper describes the Escherichia coli expression system behind the molecule: a fusion protein whose N-terminal extension is the first 46 amino acids of methionyl porcine growth hormone plus Val-Asn, cleaved at.
- 4
The Long analogue series, where the LR3 name comes from
This companion paper names the molecules: the analogues carry the first 11 amino acids of methionyl porcine growth hormone plus Val-Asn, and are called Long IGF-I, Long [Gly3]-IGF-I and Long [Arg3]-IGF-I depending on.
- 5
Systemic infusion in suckling rats
The clearest in vivo comparison. Both peptides raised kidney and spleen weight by up to 85% and 76%, and IGF-I raised gut weight and length by up to 60% and 32%, with Long [Arg3] IGF-I more potent than native IGF-I for.
- 6
Clearance and tissue delivery after an intravenous bolus in rats
At both ages, less labelled Long [Arg3] IGF-I remained in blood than labelled native IGF-I, consistent with faster clearance when the binding proteins are not holding the peptide in circulation, while gastrointestinal.
What the current evidence can support
Study models remain visible so laboratory and animal findings are not mistaken for established human outcomes.
- Human
Human studies and registrations
2 protocol rows on this page come from human trials, trial registrations, regulator labels or reviews of human data. Approval status and populations are stated per row.
- Animal
Preclinical models
4 protocol rows describe animal, cell or toxicology work. Amounts from these rows do not translate to people.
- Not graded
Community-reported use
3 rows record what blogs, vendor write-ups or forums describe for IGF-1 LR3. None has been verified against primary literature.
Identity, limitations and unknowns
Important limitations
- Every amount on this page is a report of what a source describes, not a protocol to follow.
- Preclinical and community rows do not establish a human amount, schedule or route.
- Formulation, purity and presentation vary by supplier and are not covered by the dossier.
Sources
8 curated references, each with its journal, year and study model, plus 3 community resources reported but not linked.
- 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
- 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
- Solution structure and backbone dynamics of long-[Arg(3)]insulin-like growth factor-I
- Systemic infusion of IGF-I or LR(3)IGF-I stimulates visceral organ growth and proliferation of gut tissues in suckling rats
- Preferential intestinal delivery of long[Arg3] insulin-like growth factor (LR3IGF-I) over IGF-I in preweaning and adult rats
- INCRELEX (mecasermin) injection, prescribing information
- Near-Adult Height Outcomes in Patients Treated With rhIGF-1 for Severe Growth Failure: Real-World IGFD Registry Data
- IGF-I abuse in sport