Retatrutide

Retatrutide (LY3437943) is a synthetic lipidated peptide triagonist of GLP-1R (glucagon-like peptide-1 receptor), GIPR (glucose-dependent insulinotropic polypeptide receptor), and GCGR (glucagon receptor) — the first characterised triple incretin/glucagon receptor co-agonist in clinical development. Based on a glucagon backbone with modifications for GLP-1R and GIPR co-activation, Retatrutide produced the largest weight reduction of any pharmacological agent in published Phase 2 clinical trials (Jastreboff et al., NEJM 2023) — approximately 24% body weight reduction at 48 weeks — surpassing both GLP-1R monoagonists (Semaglutide, approximately 15% at 68 weeks) and dual GLP-1R/GIPR agonists (Tirzepatide, approximately 21% at 72 weeks).

The structural design of Retatrutide uses a glucagon backbone modified to achieve tri-agonism: glucagon itself activates GCGR and has some GIPR agonist activity but minimal GLP-1R activity. Through systematic amino acid substitutions, Retatrutide balances activity across all three receptors. A C18 fatty acid moiety attached via a linker to an internal lysine residue provides albumin binding through non-covalent hydrophobic interaction (similar to Semaglutide's albumin binding strategy), extending the half-life to approximately 6 days and enabling once-weekly dosing.

GLP-1R activation (Gs coupling, cAMP/PKA) drives glucose-dependent insulin secretion from pancreatic beta cells and suppresses appetite through hypothalamic and vagal GLP-1R circuits — the well-established mechanism shared with Semaglutide. GIPR activation (also Gs coupling) provides additional incretin effect, GIP-specific insulinotropic responses in beta cells, and effects on adipose tissue lipolysis and brown adipose tissue thermogenesis. GCGR activation (Gs coupling in hepatocytes) drives glycogenolysis, gluconeogenesis, and fatty acid oxidation — the classically defined glucagon actions.

The apparent paradox of including a hyperglycaemic (GCGR) agonist in a metabolic compound is resolved by metabolic context: in the presence of robust GLP-1R/GIPR-mediated glucose-dependent insulin secretion, hepatic GCGR-driven glucose output is compensated by increased insulin, preventing net hyperglycaemia. GCGR activation contributes thermogenic (increased metabolic rate through futile cycling), lipolytic (fatty acid mobilisation from adipose), and fatty acid oxidation-promoting effects not provided by GLP-1R/GIPR combination alone — explaining the incremental weight reduction beyond Tirzepatide.

For laboratory research, Retatrutide serves as the reference triple agonist in comparative studies using Semaglutide (GLP-1R monoagonist), Tirzepatide (GLP-1R/GIPR dual agonist), and Retatrutide (GLP-1R/GIPR/GCGR triple agonist) as a graduated receptor activation toolkit. Using receptor-selective antagonists (Exendin(9-39) for GLP-1R, specific anti-GIPR antibodies for GIPR, GCGR-selective antagonists) with each compound allows systematic receptor contribution attribution.

Research endpoints: cAMP accumulation in GLP-1R-, GIPR-, and GCGR-expressing cell lines (HTRF assay); beta-arrestin recruitment for biased agonism characterisation; hepatocyte glycogenolysis (glucose output assay); adipocyte lipolysis (glycerol and NEFA release); and pancreatic beta cell insulin secretion (GSIS assay at 2mM and 20mM glucose to confirm glucose dependency).

MW: approximately 4.8 kDa. CAS: 2381272-44-0. Reconstitute in bacteriostatic water at 1mg/mL. Store lyophilised at -20°C. For laboratory and analytical research purposes only.

For triple receptor attribution research: pre-treat GLP-1R-GIPR-GCGR-expressing cell models with Exendin(9-39) (GLP-1R antagonist, 1uM), specific anti-GIPR antibody (1ug/mL), or glucagon receptor antagonist (LY2409021, 1uM) individually and in combinations, then measure cAMP response to Retatrutide. The Bliss independence model applied to antagonist combination data allows quantification of each receptor's proportional contribution to total Retatrutide cAMP signal. For hepatocyte GCGR research: primary rat hepatocytes or HepG2 cells express endogenous GCGR; treat with Retatrutide (0.1-100nM) and measure glucose output (glucose oxidase assay), glycogen content (periodic acid-Schiff staining), and phospho-CREB (Ser133, PKA substrate) as downstream GCGR endpoints. MW: approximately 4.8 kDa. CAS: 2381272-44-0. Reconstitute in bacteriostatic water at 1mg/mL. Store lyophilised at -20°C. For laboratory and analytical research purposes only.