Long R3 — the 13-residue N-terminal extension (Long) and arginine substituted for glutamic acid at position 3 (R3). Both changes reduce its affinity for IGF binding proteins.

Why is IGF-1 LR3 used in cell culture?

Because binding proteins present in culture media interfere with measuring what IGF-1 does to cells. An analogue that binds them a thousandfold less weakly gives a cleaner readout, which is the reason it was engineered.

Is IGF-1 LR3 the same as the IGF-1 used clinically?

No. Clinical IGF-1 is recombinant human IGF-1, used in severe primary IGF-1 deficiency. LR3 is a modified analogue designed for laboratory use, and the clinical evidence does not carry across to it.

Has IGF-1 LR3 been tested in humans?

No published randomised trial exists for any indication. The characterisation literature is in vitro and in rodents, and was written to answer questions about reagent potency.

Is IGF-1 LR3 approved as a medicine?

No, in any jurisdiction. It is supplied here as a laboratory reagent for in-vitro research and not for human or veterinary use.

Research guides

IGF-1 LR3 (Long R3 IGF-1): what the research says

An analogue engineered to evade the binding proteins that regulate natural IGF-1 — which is exactly why it is a cell-culture reagent, and why that matters.

Available in the catalogue

Supplied as research material. Sizes and pricing are on the product page. Availability is not a statement about what a compound does.

IGF-1 LR3
Growth Hormone

IGF-1 LR3 is the one compound in this group that is not a secretagogue. It sits at the far end of the axis the others act on, and it was engineered to defeat a regulatory mechanism rather than to work with one.

What the molecule is

A recombinant analogue of insulin-like growth factor 1, carrying a 13-residue extension at the N-terminus and arginine substituted for glutamic acid at position 3. Both modifications serve one purpose.

The binding proteins are the point

Natural IGF-1 circulates almost entirely bound to a family of binding proteins that control how much of it is free to reach a receptor at any moment. The two modifications in this analogue cut its affinity for those proteins by roughly a thousandfold, so far more of it stays unbound.

In cell culture that is a genuine advantage and is why the reagent exists: binding protein interference is a well-documented confounder when measuring what IGF-1 does to cells, and an analogue that evades it produces cleaner experiments. The founding characterisation work established exactly this — that binding-protein affinity, not receptor affinity, was doing most of the work in the potency differences between analogues.

Why the same property is the caution

Binding proteins are not an obstacle the body accidentally evolved. They are the regulatory system for a growth factor whose signalling is implicated in cell proliferation. A molecule designed to bypass that system does not have a mechanism for the body to moderate it in the way it moderates its own IGF-1, and no published work establishes what that means outside a culture dish.

The human clinical literature on IGF-1 concerns recombinant human IGF-1 in severe primary IGF-1 deficiency — a different molecule, a rare condition, and a supervised medical context. It is not evidence about this analogue.

What studies reported

Each entry states what a study examined and the model it used. Nothing below describes an outcome for a person.

Everything below is drawn from published research, and each entry names the model the study used. Approval status varies by compound and by country, and nothing described here is supplied as a medicine or for use in a person.

Francis et al. (1992)Journal of Molecular Endocrinology · 8(3):213–23
Compared recombinant fusion protein analogues of IGF-1 to establish the relative contribution of binding-protein affinity and receptor affinity to biological potency, reporting that reduced binding-protein affinity accounted for most of the enhanced potency.
in vitro, recombinant analogues Source
King et al. (1992)Journal of Molecular Endocrinology · 8(1):29–41
Production and characterisation of IGF-1 and of potent analogues carrying glycine or arginine in place of glutamic acid at position 3 — the substitution this compound is built on.
in vitro, recombinant analogues Source
Tomas et al. (1992)Biochemical Journal · 282(Pt 1):91–7
Reported that IGF-1 variants with reduced binding-protein affinity were anabolic in a catabolic rat model, and more so than unmodified IGF-1.
rat, dexamethasone-treated Source

Adverse and null findings reported

No dedicated safety study has been published for this compound. That is not a finding that none exists — it means the question has not been asked in print, and the gaps below say so.

What the research does not establish

An absence cannot be cited, so these are stated plainly. They are the part of the picture that silence would otherwise hide.

The `adverse` list is empty because no safety study of this analogue in humans has been published — not because it was studied and found safe. That distinction matters more here than for most compounds in the catalogue.
No randomised controlled trial of IGF-1 LR3 has been published for any indication, and it holds no marketing authorisation anywhere.
The human IGF-1 clinical literature concerns recombinant human IGF-1 in severe primary IGF-1 deficiency, which is a different molecule in a different context. None of it is evidence about this analogue.
The molecule was engineered to evade the binding proteins that regulate IGF-1 availability. What escaping that regulatory system does over time has not been studied in any whole-organism model at length.
IGF-1 signalling is implicated in cell proliferation, and the question of what a binding-protein-evading analogue means in the presence of existing pathology is an obvious one that the published work does not address.
The characterisation literature is thirty years old and was written to answer a reagent-design question, not a safety question.

Common questions

What does LR3 mean?: Long R3 — the 13-residue N-terminal extension (Long) and arginine substituted for glutamic acid at position 3 (R3). Both changes reduce its affinity for IGF binding proteins.
Why is IGF-1 LR3 used in cell culture?: Because binding proteins present in culture media interfere with measuring what IGF-1 does to cells. An analogue that binds them a thousandfold less weakly gives a cleaner readout, which is the reason it was engineered.
Is IGF-1 LR3 the same as the IGF-1 used clinically?: No. Clinical IGF-1 is recombinant human IGF-1, used in severe primary IGF-1 deficiency. LR3 is a modified analogue designed for laboratory use, and the clinical evidence does not carry across to it.
Has IGF-1 LR3 been tested in humans?: No published randomised trial exists for any indication. The characterisation literature is in vitro and in rodents, and was written to answer questions about reagent potency.
Is IGF-1 LR3 approved as a medicine?: No, in any jurisdiction. It is supplied here as a laboratory reagent for in-vitro research and not for human or veterinary use.

Compounds covered

The reference page for each compound this article discusses.

IGF-1 LR3

Tesamorelin (Egrifta): what the research says
An approved medicine in the US with one of the largest trial programmes here. Every efficacy trial was in HIV-associated visceral fat, and that limits it.
CJC-1295 (Mod GRF 1-29): what the research says
The best-known CJC-1295 human trial studied the DAC form, not the no-DAC form sold as Mod GRF 1-29. Why the two have very different pharmacokinetics.
How to reconstitute lyophilised peptides
How to reconstitute a lyophilised peptide with bacteriostatic water without damaging it: why you run the liquid down the vial wall and never shake it.

About this article

Everything reported here comes from published research, and each finding names the model the study used — cell culture, rat, or human. Findings in one model do not transfer to another, most of the work described is preclinical, and none of it is a claim that a compound is safe or effective for any purpose. Nothing on this page describes doses, routes of administration, or use in a person.

Approval status varies by compound and by country. A few of the substances described are the active ingredient of medicines authorised in the EU; most have no marketing authorisation anywhere and have never been assessed by a regulator. Neither is supplied as a medicine here. All material supplied by ASSAY is sold for in-vitro laboratory research only, and is not a drug, food, cosmetic or medical device, and not for human or veterinary use.

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