Science Spyglass
GLP-1 receptor assay: drug discovery in the metabolic disorders field
Metabolic disorders, particularly type 2 diabetes and obesity, represent a major global health burden. In the United States alone, over 30 million people live with type 2 diabetes, and one-third of the population is affected by obesity. These conditions are closely linked to increased cardiovascular risk and long-term health complications. As their prevalence continues to rise, there is an urgent need for effective and innovative pharmacological interventions to manage and treat these chronic diseases.
In this article, we explore how metabolism is regulated, highlight the key cellular players, and introduce the tools developed by Axxam to study these mechanisms, focusing in particular on the GLP-1 (glucagon-like peptide-1) receptor assay.
Hormonal regulation of metabolism:
the role of enteroendocrine cells and incretins
Metabolic regulation is tightly controlled by a complex network of hormones, many of which are secreted by enteroendocrine cells (EECs), specialized sensory cells that make up about 1% of the gut epithelium. These cells detect the presence of nutrients in the intestinal lumen via chemosensory G protein-coupled receptors (GPCRs) and taste receptors, and in response, release hormones that influence digestion, appetite, and glucose metabolism. Besides nutrient availability, this process is regulated also by other stimuli, including mechanical stretch, and neural signals.
Key hormones released by EECs include GLP-1, GIP, cholecystokinin (CCK), ghrelin, and peptide YY (PYY). Among them, GLP-1 and GIP (gastric inhibitory polypeptide) are known as incretins, gut-derived hormones that enhance glucose-dependent insulin secretion, playing a pivotal role in maintaining glucose homeostasis and serve as important therapeutic targets for type 2 diabetes and obesity.
The GLP-1 receptor: a key target in glucose and appetite regulation
The glucagon-like peptide-1 receptor (GLP-1R) is a GPCR found primarily in pancreatic β-cells, brain, heart, kidney, and the gastrointestinal tract. It plays a key role in regulating blood sugar by enhancing insulin secretion in response to glucose and reducing glucagon secretion, which helps lower blood glucose levels. GLP-1R is activated by the hormone GLP-1, released from EECs after eating. Activation of this receptor also slows gastric emptying, promotes satiety, and reduces food intake, contributing to weight management and appetite control.
From a therapeutic perspective, GLP-1 receptor agonists — drugs that mimic the endogenous hormone GLP-1 — are used to treat type 2 diabetes and obesity by improving insulin secretion, lowering blood sugar, and supporting weight reduction. While peptide-based GLP-1 receptor agonists such as Exenatide, Liraglutide, Dulaglutide, and Semaglutide have demonstrated strong efficacy, there remains significant interest in developing next-generation therapies. One key challenge is that these biologics typically require injection, which can limit patient compliance and convenience.
To address this, researchers are exploring alternative routes of administration, including oral, transdermal, and inhalable formulations. In parallel, there is growing focus on small molecule GLP-1R agonists, which have the potential to be administered orally, produced more cost-effectively, and offer improved stability and pharmacokinetic profiles. These advancements aim to expand therapeutic options, enhance accessibility, and improve long-term adherence in the management of metabolic disorders.
Finally, beyond their role in controlling metabolic processes, GLP-1 receptor agonists also show promising potential benefits in treating cardiovascular and neurodegenerative diseases.
Axxam’s GLP-1 receptor assay: a tool for metabolic drug discovery
At Axxam, we have developed and optimized a GLP-1 recombinant assay using a CHO (Chinese Hamster Ovary) cell line. This GLP-1 receptor assay is ideal for studying receptor activation mediated by small molecules.
The GLP-1 receptor pathway involves GLP-1 binding to its receptor (GLP-1R), which activates G-proteins, leading to increased cyclic adenosine monophosphate (cAMP) levels and subsequent activation of protein kinase A (PKA). This pathway primarily influences insulin secretion and glucagon inhibition in pancreatic beta and alpha cells, respectively.
In our assay, we employ the HTRF® cAMP Gs HiRange detection kit from Revvity as the readout for the measurement of the cAMP levels produced upon GLP1 receptor activation.
The cAMP kit operates on a competitive format involving a specific antibody labeled with cryptate (donor) and cAMP coupled to d2 (acceptor). This setup enables direct characterization of all types of compounds acting on Gs-coupled receptors in either adherent or suspension cells. Native cAMP produced by the cells competes with the d2-labeled cAMP for binding to monoclonal anti-cAMP Eu3+ cryptate.
The assay has been validated with both GLP-1 (7-36), the endogenous physiological full agonist secreted by intestinal L-cells, and its metabolite GLP1 (9-36) which is a weaker partial agonist. The EC50 of GLP1 (7-36) is in the expected 2 digits pM range (25-60pM), while its metabolite shows a potency which is 4 logs lower and falls into the low µM range.
We also tested the effect of the known covalent allosteric modulator BETP, which – as expected – significantly potentiated the activity of GLP-1 (9-36) on the GLP-1 receptor.
This GLP-1 receptor assay is suitable for compound profiling studies as well as high throughput screening campaigns with proven high sensitivity to the GLP-1 (7-36) reference ligand and robustness. The GLP-1 receptor assay is also suitable for testing natural compounds and extracts, supporting the development of nutraceuticals and functional food products aimed at improving metabolic health.
Axxam’s GLP-1 secretion assay: metabolic drug discovery from a different perspective
Studies have shown that fatty acids and other endogenous ligands may engage with relevant GPCRs, including GPR40, GPR120, GPR119 and TGR5, to promote GLP-1 secretion. Taking into account the above-mentioned considerations on cost and safety aspects, oral small molecule agonists stimulating endogenous GLP-1 secretion by intestinal L-cells may offer a promising alternative for developing new treatments for Type 2 diabetes and obesity.
As a novel method for identifying compounds that promote the release of the physiological agonist GLP-1, we have developed and optimized a GLP-1 secretion assay. We employ NCI-H716 * and STC-1 cell lines, well-characterized models respectively for human and murine intestinal L-cells. To detect GLP-1 secretion from enteroendocrine cell supernatants, we exploit a reporter cell line that expresses the recombinant GLP-1 receptor in combination with the chAMPion reporter system in a CHO background. This cell line expresses a Ca2+ sensitive photoprotein and a cAMP gated channel. The activation of GLP-1R by a specific agonist induces an increase in intracellular cAMP levels, which leads to channel opening. This allows for the influx of external Ca2+, ultimately stimulating light emission through the activity of the Ca2+ sensitive photoprotein.
This GLP-1 secretion assay, suitable for compound profiling studies, has been functionally validated using carbohydrate stimuli. It shows the expected pharmacological response for Fructose (≈ 5 mM) and exhibits good sensitivity to the GLP-1 (7-36) control (50-100 pM). Furthermore, validation has been achieved with small molecules such as GSK137647A, which activates the Free Fatty Acid Receptor 4 (FFAR4, also known as GPR120), and with Sinigrin, an agonist of the Bitter Taste Receptor 38 (TAS2R38). This confirms the critical roles of these GPCRs in stimulating GLP-1 release from STC-1 and NCI-H716 cells, respectively.
In summary, our secretion assay is a robust tool for identifying and pharmacologically profiling novel GLP-1 stimulators, highlighting its potential for developing innovative therapeutic strategies for the treatment of diabetes and obesity.
* Axxam hereby acknowledges that the NCI-H716 cell line (ATCC Ref. No. CCL-251), as described in R. Phelps et al. Journal of Cellular Biochemistry Supplement (1996) 24:32-91 (HHS Ref. No. E-112-2007-0), has been developed in the laboratories of Drs. Gazdar and Minna at the National Cancer Institute.
Axxam’s metabolic platform assays
Enteroendocrine cells act as nutrient sensors in the gut, detecting dietary components through receptors located on their luminal surface. These include GPCRs such as GPR40, GPR120, and various taste receptors, which respond to the presence of nutrients and trigger the secretion of hormones involved in metabolism.
To support drug discovery in this field, Axxam has developed a comprehensive metabolic assay platform. Besides the GLP-1 receptor assay, the platform includes validated assays targeting key receptors such as CCK1R, and Y2R. Transporter assays for SGLT1 (Sodium-GLUcose Transporter 1) and GLUT2 (Glucose Transporter 2) are also available. In addition, Axxam offers a fully cloned panel of taste receptors with ready-to-use assays and provides the flexibility to rapidly develop custom cell-based assays tailored to specific project needs.
This platform enables the functional screening and profiling of compounds that modulate gut hormone secretion and nutrient sensing, accelerating innovation in the treatment of metabolic disorders.
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