Retatrutide receptor targets: GIPR, GLP-1R and GCGR

The three receptors

All three are class B1 (secretin-family) G-protein-coupled receptors coupling principally to Gs.

Why the glucagon receptor is the distinguishing target

Selective GLP-1 receptor agonists engage one of these receptors and dual incretin agonists engage two. The tri-agonist class is defined by the addition of glucagon receptor agonism, and GCGR expression is concentrated in a different tissue — the liver — than the islet-weighted GIPR and GLP-1R populations. Comparative work between agonist classes is therefore as much about which tissue model is used as about potency.

Profiling activity, receptor by receptor

• Use monoreceptor cell lines. A system expressing more than one of the three cannot attribute a cAMP response to a single receptor.
• Include the native agonist for each receptor — GIP, GLP-1(7-36)amide and glucagon respectively — as the in-run reference, and report potency relative to it.
• Report the readout, cell background, incubation time and reference agonist with every potency value; cross-study EC50 comparison between different systems is unreliable.
• Where signalling bias is the question, pair cAMP accumulation with a β-arrestin recruitment assay at the same receptor. Bias is a relationship between two readouts, not a property of one.
• Confirm the identity and content of the lot in use before interpreting a potency shift — an under-filled or partially degraded vial reads as reduced potency at every receptor at once.

Reading the published potency data

The characterisation literature reports that LY3437943 is not equipotent across the three receptors; the balance between them is the engineered property under study. When citing a potency figure, cite the receptor, the assay and the reference agonist together with the number — a bare EC50 for a tri-agonist is not interpretable.

Research use

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