LY3298176 Research

LY3298176 is a single synthetic peptide that activates two receptors, the GIP receptor and the GLP-1 receptor. Both are class B1 G protein-coupled receptors in the secretin family, and the molecule was first characterized in a 2018 discovery and pharmacology paper [1].

What LY3298176 is

LY3298176 is a 39-residue synthetic peptide with a C-terminal amide.

• CAS 2023788-19-2
• UNII OYN3CCI6QE
• PubChem CID 166567236, one of several records carrying this CAS
• Molecular formula C225H348N48O68
• Molecular weight 4813.5 g/mol

More than one database record carrying a single CAS is a common situation rather than evidence of two different molecules. CID 166567236 is one whose drawn structure matches the sequence and side chain below. Research-grade material such as Pure-TRZ-2 is characterized by its own analytical data.

How the chain is built

The full 39-residue sequence runs:

Y-Aib-E-G-T-F-T-S-D-Y-S-I-Aib-L-D-K-I-A-Q-K*-A-F-V-Q-W-L-I-A-G-G-P-S-S-G-A-P-P-P-S-NH2

Four features separate this chain from a native incretin peptide. Two of its residues are non-coded, with Aib at position 2 and Aib at position 13 [1]. Aib, alpha-aminoisobutyric acid, carries two methyl groups on its alpha carbon.

The third feature is the side chain on lysine 20, written K* above. It carries two AEEA spacer units, then gamma-glutamic acid, then a C20 fatty diacid, eicosanedioic acid. The discovery paper describes this acylation as what enables albumin binding [1]. The fourth feature is the C-terminal amide, which removes the free carboxylate at the end of the chain [1].

The discovery paper describes the molecule as GIP-based, so its backbone follows the GIP peptide family rather than the GLP-1 family [1].

Receptor pharmacology in the laboratory

Receptor activity measured in cell assays

The first pharmacology came from HEK293 cells engineered to express the human GIP receptor or the human GLP-1 receptor, where binding and cAMP accumulation were measured [1]. The peptide produced responses at both receptors, which is what makes it a dual agonist peptide. That same study also used two systems carrying the receptors natively, a human pancreatic beta-cell line expressing both and cultured human adipocytes expressing only the GIP receptor [1]. The peptide showed minimal activity at the closely related glucagon receptor [1]. The recombinant assays measure receptor engagement in an engineered system, not an effect in an organism.

Signaling bias and imbalanced agonism

A 2020 signaling study characterized the molecule as an imbalanced and biased dual agonist [2]. Imbalanced means the two receptor activities are not matched. In the signaling assays the peptide mimicked the actions of native GIP at the GIP receptor [2]. At the GLP-1 receptor it favored cAMP generation over beta-arrestin recruitment, and it drove receptor internalization less strongly than GLP-1 did [2]. That split between two downstream readouts is what biased means here.

The same study also measured insulin secretion by perifusion in pancreatic islets from wild-type mice and from a line lacking beta-arrestin1 in its beta cells [2]. Removing beta-arrestin1 limited the insulin response to GLP-1, but not the response to GIP or to this peptide [2]. Those are isolated mouse islets, so the readout belongs to that preparation.

Structural studies at the incretin receptors

Two structural studies paired cryo-electron microscopy with molecular dynamics simulations to resolve the peptide bound to the GIP receptor and the GLP-1 receptor [3] [4]. The peptide forms a helix whose N-terminus reaches deep into the transmembrane core of both receptors [3].

Comparing the poses across receptors is how structural work accounts for the imbalance seen in the signaling assays [3] [4]. In one study, the N-terminal tyrosine made only a weak contact with the GLP-1 receptor [3]. Simulations showed its lipid side chain forming hydrogen bonds more often at the GIP receptor than at the GLP-1 receptor, consistent with a more compact complex [3]. The authors conclude that the fatty-acid modification, together with the sequence, determines how the peptide acts [3]. That study reports that the difference in GLP-1 receptor activation results in less agonist-induced receptor desensitization [3]. A structure is still a picture of a purified, stabilized complex, and the simulations only partly offset that.

Cell studies in cultured human adipocytes

Adipocytes carry the GIP receptor, and a 2024 study looked there directly [5]. Its human cells were adipocytes grown in the laboratory from one donor's precursor cells. That is laboratory work on human cells, not a study in people.

In those cells the peptide acted on glucose metabolism much like native GIP, both on its own and together with insulin [5]. With insulin present, it increased insulin-stimulated glucose uptake, and GIP receptor agonism also raised insulin signaling and the conversion of glucose to glycerol [5]. Without insulin, the same agonism raised lipolysis, the breakdown of stored lipid, instead [5].

The authors propose that a long-acting GIP receptor agonist works with insulin to clear glucose and lipid after meals, and promotes lipid release when insulin is low [5].

Animal models

In a diet-induced obese mouse model in the discovery and pharmacology paper, researchers measured body weight, food intake and energy expenditure [1]. Chronic administration in mice was compared against a selective GLP-1 receptor agonist as the reference arm [1]. Glucose tolerance was tested separately in normal mice and in mice lacking either the GIP or the GLP-1 receptor [1]. None of these animal readouts transfers to people.

The 2024 adipocyte study's mouse lipid experiments used a separate agonist selective for the GIP receptor, not LY3298176 [5]. Its authors chose it because GLP-1 receptor activity slows stomach emptying, which would confound an oral lipid test [5].

Degradation and clearance

Three of the modifications above bear on how the molecule is broken down. Dipeptidyl peptidase-4 cleaves the native incretins after position 2, so a non-coded residue there resists that cleavage. The C-terminal amide caps the other end of the chain, and the C20 diacid binds the peptide to albumin [1]. The discovery paper states that pharmacokinetic studies in mice and rats showed a long-acting profile, but it does not publish those data [1]. No laboratory-species persistence figure for LY3298176 appears in these references.

Human research

Human clinical studies of LY3298176 have been published. This article does not summarize them. It covers what laboratory research has measured about the molecule itself: its structure, its receptor activity, and what cell, tissue and animal studies report.

Research directions and limits

Two limits stand out. First, much of the laboratory record comes from the developer's own scientists, which concentrates methods and assumptions [1] [2] [3] [5]. The structural record is the clearest counterweight, because one of the two structural sets comes from a separate group [4]. Second, the bias finding was characterized in recombinant cell assays and tested functionally in isolated mouse islets [2]. No test of the bias finding in primary human cells appears in this reference set.

Open questions include whether the islet result holds in human islets, and whether the adipocyte results hold in cells from more than one donor [5].

Conclusion

LY3298176 is a 39-residue, lipid-modified peptide built on the GIP sequence. Laboratory work describes imbalanced dual receptor activity with signaling bias at the GLP-1 receptor, and structural work gives a physical basis for that profile. Cell assays, isolated mouse islets, cultured human adipocytes and mouse models make up the rest of the preclinical record. Each finding holds for the system that produced it.

References

1. 1

   Coskun T, Sloop KW, Loghin C, et al. Mol Metab. 2018;18:3-14. PMID 30473097
2. 2

   Willard FS, Douros JD, Gabe MB, et al. JCI Insight. 2020;5(17):e140532. PMID 32730231
3. 3

   Sun B, Willard FS, Feng D, et al. Proc Natl Acad Sci U S A. 2022;119(13):e2116506119. PMID 35333651
4. 4

   Zhao F, Zhou Q, Cong Z, et al. Nat Commun. 2022;13(1):1057. PMID 35217653
5. 5

   Regmi A, Aihara E, Christe ME, et al. Cell Metab. 2024;36(7):1534-1549.e7. PMID 38878772