Dual incretin agonist (revision 13)
Old revision·08:37, 18 Dec 2024·TrialsTabitha
| Dual incretin agonistDrug class | |
|---|---|
One peptide, two class B receptors, one fixed intramolecular potency ratio. | |
| Also called | Unimolecular dual agonist, twincretin |
| Usual receptor pair | GIP receptor and GLP-1 receptor |
| Marketed example | Tirzepatide (2022) |
| Topic infobox · conventions | |
A dual incretin agonist is a single engineered peptide that activates two receptors of the glucagon-secretin family — most often the receptor for Glucose-dependent insulinotropic polypeptide and the GLP-1 receptor — in a ratio fixed by its chemistry rather than by a prescriber's choice of two drugs.[1]
The approach differs fundamentally from co-administration of two agents. A single molecule delivers both activities to the same tissues with identical pharmacokinetics, so the ratio at the receptor does not drift with differential clearance. The price is that the ratio cannot be adjusted: it is a property of the molecule, and changing it means changing the drug.[2]
Tirzepatide is the only member marketed to date. Why dual agonism outperforms GLP-1 monotherapy is not settled, and the leading explanations — adipose-tissue GIP action, central GIP effects that improve tolerability, and restoration of beta-cell GIP responsiveness under ambient GLP-1 signalling — have not been separated by any published trial.[3]
Design problem
[edit]The receptors of this family share a common architecture — a large extracellular domain capturing the C-terminal helix of the ligand, and a transmembrane bundle engaged by the ligand N-terminus — and roughly 40–50% sequence identity in the transmembrane region. That relatedness is what makes a single ligand for two of them possible.[1]
The design proceeds by choosing a backbone, then substituting residues that confer activity at the second receptor while retaining activity at the first. In practice a GIP backbone has proved more tolerant of the substitutions needed for GLP-1 activity than the reverse, which is why tirzepatide is built from GIP rather than from GLP-1.[2]
Reported potency ratios are assay-dependent — cell line, readout, incubation time and receptor expression level all move them — and cross-publication comparison of ratios is unreliable. A ratio quoted without its assay system is not a meaningful number.
Why dual agonism might work
[edit]Three explanations circulate, and they are not mutually exclusive.
- Adipose GIP action. GIP receptors are expressed on adipocytes, where GIP promotes triglyceride storage. Whether the clinical benefit arises from agonism or from functional antagonism through receptor desensitisation is genuinely disputed, and — awkwardly for the field — GIP-receptor antagonists have also produced weight loss in early studies.
- Improved tolerability. If GIP-receptor agonism in the area postrema reduces nausea, a dual agonist can be escalated to a total exposure that a GLP-1 agonist alone could not reach. On this account the benefit is not a new mechanism but a higher tolerable dose.
- Restored beta-cell responsiveness. Beta-cell responsiveness to GIP is impaired in type 2 diabetes but is partly restored when glycaemia improves, so a dual agonist may create the conditions for its own GIP component to work.
See also
References
- ^ a b Finan B, Ma T, Ottaway N, et al. "Unimolecular dual incretins maximize metabolic benefits in rodents, monkeys, and humans." Science Translational Medicine 5(209):209ra151 (2013). DOI:10.1126/scitranslmed.3007218. PMID 24174327.
- ^ a b Coskun T, Sloop KW, Loghin C, et al. "LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus." Molecular Metabolism 18:3–14 (2018). PMID 30473097.
- ^ Frías JP, Davies MJ, Rosenstock J, et al. "Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes." New England Journal of Medicine 385(6):503–515 (2021). PMID 34170647.