Aug 7, 2025 at 5:51 PM#6
I want to bring in the clinical pharmacology perspective. Even if we achieve perfect Gs-biased agonism, we need to consider whether the clinical endpoints actually segregate along the Gs vs. β-arrestin axis.
Here's what we think each pathway contributes clinically:
Gs-dependent effects:
- Acute glucose-dependent insulin secretion
- Glucagon suppression
- Gastric emptying delay
- Central appetite suppression (likely — NTS/hypothalamic cAMP)
- Cardioprotection (endothelial NO, anti-inflammatory)
β-arrestin-dependent effects:
- β-cell proliferation/survival (ERK1/2 pathway)
- Receptor internalization/desensitization
- Possibly some anti-inflammatory effects via NFκB scaffolding
If the primary clinical goals are glycemic control + weight loss + cardiovascular protection, these are predominantly Gs-mediated. The β-cell preservation effect is important but operates on a longer timescale.
> "In a head-to-head comparison of Gs-biased versus balanced GLP-1R agonists in diabetic cynomolgus monkeys, the biased agonist achieved equivalent HbA1c reduction with 40% less nausea (as measured by kaolin consumption), suggesting that some GI side effects may be β-arrestin-mediated."
> — Griffith et al., *Diabetes*, 2019; 68(Supplement 1):Abstract 81-OR
Last edited: Aug 7, 2025 at 9:51 PM
37 7jim_asheville, matt_MKE, Dr.ReproEndo and 34 others
Reply Quote Save Share Report
Aug 7, 2025 at 6:21 PM#7
That NHP data is fascinating and suggests a possible separation of efficacy from tolerability — the holy grail of biased agonism.
One more structural insight worth mentioning: the GLP-1R is a Class B GPCR with a large extracellular domain (ECD) that acts as an "affinity trap." The initial binding event involves the C-terminus of the peptide ligand docking into the ECD, followed by the N-terminus engaging the transmembrane domain (TMD) core — the "two-domain model."
The bias-relevant interactions are primarily in the TMD engagement step. This means you could potentially modify the peptide N-terminus (residues 7-14) to tune bias while leaving the C-terminus and fatty acid linker (for PK) unchanged.
> "The two-domain binding model for Class B GPCRs suggests that ligand bias at GLP-1R is primarily determined by TMD interactions, with the ECD serving as an affinity anchor that is agnostic to signaling pathway selection."
> — Zhao et al., *Trends in Pharmacological Sciences*, 2020; 41(12):1007–1019
This is good news for drug design — it means PK optimization (via C-terminal modifications) and bias optimization (via N-terminal modifications) can potentially be performed independently.
Last edited: Aug 7, 2025 at 9:21 PM
36 6Dr.GutHealth, amsterdam_pete, LondonLisa and 33 others
Reply Quote Save Share Report
Aug 7, 2025 at 6:51 PM#8
To summarize where I think the field stands on biased agonism at GLP-1R:
What we know:
- Bias can be engineered into GLP-1 analogs through rational design
- Gs-biased agonists show less desensitization in vitro
- Preclinical data (including NHP) suggests potential for reduced GI side effects
- β-arrestin signaling contributes to β-cell trophic effects
What we don't know:
- Whether in vitro bias factors translate to in vivo tissue-level bias
- The optimal degree of bias for maximal clinical benefit
- Whether long-term β-cell preservation is clinically meaningful in patients already on GLP-1RAs (since they're continuously treated anyway)
- Whether CNS effects (appetite suppression) are differentially regulated by Gs vs. β-arrestin
What to watch for:
- Several biased GLP-1R agonists are in Phase 1 (most undisclosed structures)
- Novo Nordisk and Eli Lilly both have biased agonist programs
- The first clinical readouts should come in the next 2-3 years
This is one of the most scientifically exciting areas in incretin pharmacology right now.
35 5PeptideSynthNJ, Dr.KarenChen, Dr.NateNeph and 32 others
Reply Quote Save Share Report
Janoshik Analytical — Independent Testing
Trusted third-party HPLC & mass spectrometry analysis. Verify peptide purity with the lab the community relies on. Independent. Accurate. Transparent.
Verify Your PeptidesGL Biochem (Shanghai) Ltd. — Direct Manufacturer
Est. 1998. The synthesis house behind the vials you send for testing. ISO 9001 and cGMP certified, 1,500+ staff, batch-specific COA with every order.
Browse GL BiochemAug 7, 2025 at 7:21 PM#9
Great summary. One final thought — the dual/triple agonists (tirzepatide, retatrutide) add another layer of complexity. Tirzepatide is actually a biased agonist at GLP-1R (favoring cAMP over β-arrestin) in addition to being a GIP/GLP-1 dual agonist:
> "Tirzepatide exhibited imbalanced agonism at GLP-1R, showing reduced β-arrestin-2 recruitment (approximately 4-fold reduced Emax) relative to cAMP generation compared to native GLP-1, suggesting that its superior clinical efficacy may partly derive from biased GLP-1R signaling."
> — Willard et al., *Nature*, 2020; 587:560–564
So tirzepatide's advantage over semaglutide may not be JUST about GIP receptor co-agonism — it may also reflect a more favorable signaling profile at GLP-1R itself. Disentangling these contributions is going to keep pharmacologists busy for years.
34 4FranDenver, Dr.BariatricHTX, LindaRN_retired and 31 others
Reply Quote Save Share Report