Mazdutide: Mechanism of Action

Introduction

Mazdutide (IBI362 / LY3305677) is a synthetic peptide dual agonist of the glucagon-like peptide-1 receptor (GLP-1R) and the glucagon receptor (GCGR). Both target receptors belong to the class B1 subfamily of G protein-coupled receptors (GPCRs). The dual-receptor pharmacological architecture distinguishes mazdutide from selective GLP-1R agonists and has been the subject of growing structural and molecular characterization across multiple publication venues. The clinical context for these molecular findings is summarized in the mazdutide published research article. This article summarizes the reported molecular interactions and downstream signaling effects of mazdutide at these two receptor systems, drawing on published primary literature.

Receptor Targets and Binding Profile

GLP-1R and GCGR are structurally related class B1 GPCRs expressed in multiple tissues including the pancreas, liver, brain, and gastrointestinal tract. Their endogenous ligands — glucagon-like peptide-1 and glucagon — are both derived from the proglucagon precursor gene and differ in post-translational processing and tissue of origin.

Mazdutide was engineered as a synthetic analog of oxyntomodulin (OXM), an endogenous peptide co-secreted with GLP-1 from intestinal L cells that was characterized in earlier research as a dual GLP-1R/GCGR agonist with a very short plasma half-life [1]. Structural modifications incorporated into mazdutide — including sequence alterations and fatty acid conjugation via a linker — extend plasma half-life through reversible albumin binding while preserving activity at both receptors.

Ji and colleagues (2021) reported that mazdutide engages human and murine GCGR with Ki values of approximately 17.7 nM and 15.9 nM, respectively, and human and murine GLP-1R with Ki values of approximately 28.6 nM and 25.1 nM, respectively [2]. In isolated mouse islet preparations, mazdutide was reported to stimulate insulin secretion with an EC50 of approximately 5.2 nM [2]. This nanomolar-range, balanced binding profile at both receptor subtypes contrasts with compounds that display substantially preferential engagement of one receptor over the other.

Findings from research models do not establish safety or efficacy in humans. SpartaLabs makes no claims about the use of this compound.

Reported Molecular Interactions

Both GLP-1R and GCGR primarily couple to stimulatory Gs proteins upon agonist binding, leading to activation of adenylate cyclase and intracellular accumulation of cyclic adenosine monophosphate (cAMP). Downstream cAMP signaling activates protein kinase A (PKA) and exchange proteins directly activated by cAMP (Epac), initiating receptor-specific transcriptional and post-translational cascades.

A 2023 cryo-electron microscopy study published in the Proceedings of the National Academy of Sciences resolved structures of GLP-1R and GCGR in complex with Gs protein and several GLP-1R/GCGR dual agonist peptides, providing structural context for dual receptor engagement at the molecular level [3]. The study demonstrated that subtle differences in peptide N-terminal residue conformations determine receptor selectivity profiles among dual agonists in this class, and that the middle region of these peptides interacts with extracellular loops ECL1 and ECL2 of each receptor, inducing conformational changes that propagate to the transmembrane domain.

A 2025 preprint by Zhang and colleagues reported cryo-EM structures of GLP-1R and GCGR in complex specifically with mazdutide and Gs protein, providing direct structural characterization of mazdutide's receptor engagement geometry at both target GPCRs [4]. This structural work awaited peer-reviewed publication at the time this article was prepared.

Downstream Effects Reported in Published Literature

At GLP-1R, cAMP/PKA signaling in pancreatic beta cells potentiates glucose-dependent insulin secretion — the incretin effect — without inducing insulin release in the absence of elevated glucose. GLP-1R signaling additionally modulates gastric emptying and acts in the central nervous system at satiety-regulating circuits, effects reported across the GLP-1 receptor agonist pharmacological class and reviewed extensively by Holst (2007) [5]. Related class B1 GPCR signaling mechanisms in other dual agonists are examined in the tirzepatide mechanism of action article.

At GCGR, activation in hepatocytes drives cAMP/PKA-mediated effects that include modulation of fatty acid oxidation pathways, mitochondrial energy substrate utilization, and hepatic lipid turnover. Shi and colleagues (2024) reported in a phase 2 publication in Diabetes Care that mazdutide administration in Chinese patients with type 2 diabetes was associated with reductions in liver enzyme markers (ALT, AST) and favorable lipid parameters alongside glycemic outcomes [6]. The authors attributed these hepatic observations in part to the GCGR-mediated component of mazdutide's pharmacological profile, consistent with preclinical mechanistic characterization of GCGR agonism and hepatic lipid metabolism.

A 2025 multi-omics study published in eBioMedicine investigated mazdutide's effects in a db/db mouse model of diabetic cognitive dysfunction, identifying molecular pathway changes associated with neuroinflammation, synaptic plasticity, and energy metabolism [7]. The study reported that mazdutide-treated animals showed changes in expression of glutamate transporter VGluT2 and GABA receptor subunits compared to dulaglutide-treated controls; multi-omics analyses identified pathways involving neuroprotection and synaptic excitatory-inhibitory balance. These preclinical observations in animal models represent an active area of mechanistic inquiry; their relevance to human pharmacology is under investigation.

Areas of Ongoing Mechanistic Investigation

The precise contribution of GLP-1R versus GCGR engagement to the compound's observed metabolic profile in human clinical trials has not been definitively apportioned in published studies — an area the research community is actively investigating. The potency balance between the two receptors may also differ between in vitro binding assays and the in vivo pharmacological milieu, a question amenable to future mechanistic dissection.

Direct structural characterization of mazdutide's receptor engagement geometry through cryo-EM — as distinct from inference from structurally related dual agonists [3] — represents an active research frontier, with the 2025 preprint by Zhang and colleagues [4] advancing this work pending peer-reviewed publication. Long-term receptor desensitization and biased signaling profiles at each receptor target, characterized for other members of the GLP-1R agonist class, await systematic published study for mazdutide specifically. Researchers sourcing material for mechanistic investigation can review purity and identity specifications on the Mazdutide product page.

References

1. Wynne K, Park AJ, Small CJ, Patterson M, Ellis SM, Murphy KG, et al. Subcutaneous oxyntomodulin reduces body weight in overweight and obese subjects: a double-blind, randomized, controlled trial. Diabetes. 2005;54(8):2390-2395. PMID: 16046306. DOI: 10.2337/diabetes.54.8.2390

2. Ji L, Jiang H, Shi W, Wang H, Cheng Z, Pan T, et al. IBI362 (LY3305677), a weekly-dose GLP-1 and glucagon receptor dual agonist, in Chinese adults with overweight or obesity: a randomised, placebo-controlled, multiple ascending dose phase 1b study. eClinicalMedicine. 2021;40:101088. PMCID: PMC8374649. DOI: 10.1016/j.eclinm.2021.101088

3. Zhou F, Zhang H, Cong Z, Zhao F, Zhao L, Cai X, et al. Structural analysis of the dual agonism at GLP-1R and GCGR. Proc Natl Acad Sci USA. 2023;120(35):e2303696120. PMCID: PMC10438375. DOI: 10.1073/pnas.2303696120

4. Zhang J, Li R, et al. Structural insights into multiplexed pharmacological actions of mazdutide at the GLP-1 or glucagon receptors. SSRN preprint. 2025. Available at: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5376321 [Preprint — not peer-reviewed at time of writing]

5. Holst JJ. The physiology of glucagon-like peptide 1. Physiol Rev. 2007;87(4):1409-1439. PMID: 17928588. DOI: 10.1152/physrev.00034.2006

6. Shi W, Zhou X, Zhang D, Zou Y, Liu Y, Li X, et al. Efficacy and safety of mazdutide in Chinese patients with type 2 diabetes: a randomized, double-blind, placebo-controlled phase 2 trial. Diabetes Care. 2024;47(1):160-168. DOI: 10.2337/dc23-1287

7. Peng J, Li M, Zhao Z, Wang R, Huang Y, Zhang H, et al. Mazdutide, a dual agonist targeting GLP-1R and GCGR, mitigates diabetes-associated cognitive dysfunction: mechanistic insights from multi-omics analysis. eBioMedicine. 2025;107:105791. PMID: 40479843. DOI: 10.1016/j.ebiom.2025.105791