A triazole-based small molecule with a second chiral center achieved nanomolar binding affinity at the ghrelin receptor and partial inverse agonist activity — mimicking peptide analogs with a simpler, drug-like molecule.
Nanomolar affinity with partial inverse agonist activityA small synthetic molecule achieved peptide-level binding to the ghrelin (hunger) receptor and actively suppressed its baseline signaling — a pharmacological profile ideal for appetite suppression
What the researchers found
By introducing a second chiral center to a previously described 1,2,4-triazole scaffold, the researchers expanded the chemical diversity of their ghrelin receptor ligand library and extended the molecule's 'C-terminal part' to mimic substance P analog inverse agonists.
Several compounds achieved nanomolar binding affinities at the ghrelin receptor (GHS-R1a) with potent biological activities. One compound demonstrated partial inverse agonist behavior — meaning it not only blocked ghrelin from activating the receptor but actively reduced the receptor's constitutive (basal) signaling. This is pharmacologically significant because the ghrelin receptor has high constitutive activity, which contributes to baseline appetite drive.
Why it matters
The ghrelin receptor is one of the most attractive drug targets for obesity, but developing effective drugs has been challenging. Ghrelin receptor inverse agonists are particularly interesting because the receptor is constitutively active — it signals even without ghrelin binding, maintaining a baseline appetite drive. A drug that suppresses this basal signaling could reduce appetite more effectively than simply blocking ghrelin. Achieving this with a small molecule (rather than a peptide) would enable oral drug delivery, dramatically improving patient convenience and reducing cost.
How the study worked
Chemical synthesis of 1,2,4-triazole derivatives incorporating a second chiral center, inspired by the structure of substance P analogs known to act as ghrelin receptor inverse agonists. Binding affinity was determined by competitive radioligand displacement assays. Biological activity was assessed using functional assays measuring receptor activation (agonism), inhibition (antagonism), and inverse agonism (suppression of constitutive activity).
What this study cannot tell us
The abstract describes only in vitro binding and functional data — no in vivo experiments were performed to assess effects on food intake, body weight, or metabolic parameters. Selectivity over other receptors was not detailed. The pharmacokinetic properties (oral bioavailability, half-life, brain penetration) that would determine clinical utility were not assessed. Only binding affinities and functional activities at the ghrelin receptor were reported; off-target effects are unknown.
How to read the evidence
This is a medicinal chemistry study reporting in vitro binding and functional data. The structure-activity relationship work is well-executed, but the absence of in vivo data and selectivity profiling limits the evidence for therapeutic potential.
When this study was published
Published in 2016, this study is about a decade old. Ghrelin receptor drug development has continued, though no approved ghrelin-targeting obesity drug has emerged, partly due to the complexity of the ghrelin system and the dominance of GLP-1-based approaches.
The bigger picture
The ghrelin system has been a target of interest for obesity drug development for over 20 years, but no ghrelin receptor drug has yet been approved for weight management. Early approaches used peptide-like molecules (growth hormone secretagogue mimetics), but the field has shifted toward small molecules that could be given orally. This study represents progress in that direction by using the triazole scaffold to create drug-like molecules with peptide-level potency. The inverse agonist concept is particularly relevant because GHS-R1a's constitutive activity has been linked to body weight regulation independent of circulating ghrelin levels.
Questions still open
- Do these triazole-based ghrelin receptor inverse agonists reduce food intake and body weight when administered to obese mice?
- Can the partial inverse agonist be optimized for full inverse agonist activity while maintaining selectivity?
- Would oral bioavailability and brain penetration of these small molecules be sufficient for clinical appetite suppression?
Common questions
What is ghrelin and why is it relevant to obesity?
Why make a small molecule instead of using ghrelin peptide blockers?
Read the original research
New ligands of the ghrelin receptor based on the 1,2,4-triazole scaffold by introduction of a second chiral center.
Bioorganic & medicinal chemistry letters, 26(10), 2408-2412
Citation
Maingot, Mathieu; Blayo, Anne-Laure; Denoyelle, Séverine; M'Kadmi, Céline; Damian, Marjorie; Mary, Sophie; Gagne, Didier; Sanchez, Pierre; Aicher, Babette; Schmidt, Peter; Müller, Gilbert; Teifel, Michael; Günther, Eckhard; Marie, Jacky; Banères, Jean-Louis; Martinez, Jean; Fehrentz, Jean-Alain. (2016). New ligands of the ghrelin receptor based on the 1,2,4-triazole scaffold by introduction of a second chiral center.. Bioorganic & medicinal chemistry letters, 26(10), 2408-2412. https://doi.org/10.1016/j.bmcl.2016.04.003