IGF-1 LR3, also known as Long-Arginine-3-IGF-1, is an analogue of human IGF-1 that has been modified to include a 13 amino acid N-terminus extension and the substitution of Arginine for Glutamic Acid at position 3. As a result of these modifications, IGF-1 LR3 is approximately three times more potent than IGF-1 and possesses an increased half-life due to lowered affinity for binding to the Insulin-Like Growth Factor-Binding Proteins (IGFBPs). IGF-1 LR3 retains the ability to bind agonistically to the IGF-1 receptor with improved metabolic stability, relative to IGF-1. The supplementation of mammalian cell cultures with Long R3 IGF-1 at a much lower concentration results in more highly elevated productivity than with standard concentrations of insulin and/or standard IGF-1. IGF-1 LR3 is more able to stimulate the type 1 IGF receptor and thus induce a higher level of activation of intracellular signaling, which is responsible for promoting cell proliferation and the inhibition of apoptosis.
Long arginine 3-IGF-1, abbreviated as IGF-1 LR3 or LR3-IGF-1, is a synthetic protein and lengthened analogue of human insulin-like growth factor 1 (IGF-1). It differs from native IGF-1 in that it possesses an arginine instead of a glutamic acid at the third position in its amino acid sequence ("arginine 3"), and also has an additional 13 amino acids at its N-terminus (MFPAMPLLSLFVN) ("long"), for a total of 83 amino acids (relative to the 70 of IGF-1). The consequences of these modifications are that IGF-1 LR3 retains the pharmacological activity of IGF-1 as an agonist of the IGF-1 receptor, has very low affinity for the insulin-like growth factor-binding proteins (IGFBPs), and has improved metabolic stability. As a result, it is approximately three times more potent than IGF-1, and possesses a significantly longer half-life of about 20–30 hours (relative to IGF-1's half-life of about 12–15 hours).