Tirzepatide 15mg

Tirzepatide (LY3298176, CAS 2023788-19-2) is a 39-amino acid linear peptide with a molecular formula of C₂₂₅H₃₄₈N₄₈O₆₈ and a molecular weight of approximately 4,813.45 Da. Engineered from a native glucose-dependent insulinotropic polypeptide (GIP) backbone, tirzepatide incorporates targeted structural modifications that enable simultaneous agonism at both the GIP receptor (GIPR) and glucagon-like peptide-1 receptor (GLP-1R).

Key structural modifications include: Position 2: Alpha-aminoisobutyric acid (Aib2) replacing alanine, conferring DPP-4 enzymatic resistance. Position 13: A second Aib substitution (Aib13) for enhanced stability. Position 20: Lysine conjugated to a C20 unsaturated fatty diacid moiety via a hydrophilic linker composed of L-gamma-glutamic acid and two 8-amino-3,6-dioxaoctanoic acid (OEG) spacers, enabling reversible serum albumin binding and extended circulating persistence. The C-terminus is amidated. Additional substitutions at positions 7 (Thr) and 18 (Ala) introduce GLP-1-like character into the GIP backbone.

Tirzepatide exhibits imbalanced and biased dual agonism as characterized in heterologous expression systems. At GIPR, it functions as a full agonist equipotent to native GIP in cAMP accumulation (EC₅₀ = 22.4 pM in low-receptor-density models), with full efficacy for beta-arrestin recruitment and receptor internalization. At GLP-1R, it displays approximately 5-fold lower binding affinity versus native GLP-1, approximately 13-20-fold reduced cAMP potency (EC₅₀ = 934 pM), pronounced cAMP-biased signaling over beta-arrestin recruitment (<10% E_max), and impaired receptor internalization (<40% E_max).

Cryo-electron microscopy structures of tirzepatide-bound receptor-G_s complexes have been resolved at 3.1 angstrom (GIPR) and 2.9 angstrom (GLP-1R) resolution. At GIPR, tirzepatide adopts a similar alpha-helical conformation to native GIP with deep N-terminal insertion into the transmembrane domain. At GLP-1R, weaker interactions with ECL2, loss of the Arg299(ECL2)-peptide contact, and an alternate Trp306 rotamer induced by the modified Tyr1 residue contribute to the reduced signaling efficacy at this receptor.

Supplied as a lyophilized powder for in vitro research applications only. Not for human or veterinary use.

In Vitro Research Applications: Tirzepatide is employed in dual incretin receptor pharmacology studies using HEK293 cells stably expressing human GIPR or GLP-1R. Standard assay platforms include cAMP accumulation assays (homogeneous time-resolved fluorescence or LANCE cAMP detection), beta-arrestin recruitment assays (PathHunter or NanoBiT complementation), ELISA-based receptor surface quantification for internalization kinetics, and GTP-gamma-S binding assays for G-protein activation profiling.

Signaling Pathway Studies: The imbalanced agonism profile makes tirzepatide a valuable pharmacological tool for dissecting biased signaling at class B1 GPCRs. Comparative studies quantify bias factors between cAMP and beta-arrestin pathways at each receptor, enabling structure-activity analysis of multi-receptor agonist design. Molecular dynamics simulations reveal differential intramolecular hydrogen bonding between the lipid chain and Gln24 at GIPR (~40% occupancy) versus GLP-1R (~18% occupancy), providing structural rationale for receptor-dependent pharmacology.

Molecular Characterization: Identity is confirmed by ESI-MS or MALDI-TOF mass spectrometry. Purity is determined by reversed-phase HPLC. Surface plasmon resonance (SPR) enables measurement of extracellular domain (ECD) binding kinetics (reported K_D values: GIPR ECD = 4.2 micromolar; GLP-1R ECD = 23 nM). DPP-4 resistance is quantifiable by incubation with recombinant enzyme and time-course chromatographic analysis.

References

1. Willard FS, et al. (2020) Tirzepatide is an imbalanced and biased dual GIP and GLP-1 receptor agonist. JCI Insight, 5(17):e140532. PMID: 33325008
2. Sun B, et al. (2022) Structural determinants of dual incretin receptor agonism by tirzepatide. Proc Natl Acad Sci USA, 119(13):e2116506119. PMID: 35333651