Structural basis for GLP-1 receptor activation by LY3502970, an orally active nonpeptide agonist

Conserved class B GPCR activation by a biased intracellular agonist

Class B G-protein-coupled receptors (GPCRs), including glucagon-like peptide 1 receptor (GLP1R) and parathyroid hormone 1 receptor (PTH1R), are important drug targets1-5. Injectable peptide drugs targeting these receptors have been developed, but orally available small-molecule drugs remain under development6,7. Here we report the high-resolution structure of human PTH1R in complex with the stimulatory G protein (Gs) and a small-molecule agonist, PCO371, which reveals an unexpected binding mode of PCO371 at the cytoplasmic interface of PTH1R with Gs. The PCO371-binding site is totally different from all binding sites previously reported for small molecules or peptide ligands in GPCRs. The residues that make up the PCO371-binding pocket are conserved in class B GPCRs, and a single alteration in PTH2R and two residue alterations in GLP1R convert these receptors to respond to PCO371. Functional assays reveal that PCO371 is a G-protein-biased agonist that is defective in promoting PTH1R-mediated arrestin signalling. Together, these results uncover a distinct binding site for designing small-molecule agonists for PTH1R and possibly other members of the class B GPCRs and define a receptor conformation that is specific only for G-protein activation but not arrestin signalling. These insights should facilitate the design of distinct types of class B GPCR small-molecule agonist for various therapeutic indications.

Efficacy and safety of oral orforglipron in patients with type 2 diabetes: a multicentre, randomised, dose-response, phase 2 study

BACKGROUND

Orforglipron, an oral, non-peptide glucagon-like peptide-1 (GLP-1) receptor agonist, is in development for type 2 diabetes and obesity. We assessed the efficacy and safety of orforglipron versus placebo or dulaglutide in participants with type 2 diabetes.

METHODS

In this 26-week, phase 2, double-blind, randomised, multicentre study, participants were recruited from 45 centres (private clinics, hospitals, and research centers) in the USA, Hungary, Poland, and Slovakia. Adult participants aged 18 years or older with type 2 diabetes treated with diet and exercise, with or without metformin, and with a glycated haemoglobin (HbA1c) of 7·0-10·5%, and stable BMI of 23 kg/m2 or more, were randomly assigned (5:5:5:5:5:3:3:3:3) via an interactive web-response system to placebo, dulaglutide 1·5 mg once per week, or orforglipron 3 mg, 12 mg, 24 mg, 36 mg (group 1), 36 mg (group 2), 45 mg (group 1), or 45 mg (group 2) once per day with no food or water restrictions. Two different dose escalation regimens were evaluated for each of the 36 mg and 45 mg cohorts. Participants were masked to the study drug, dulaglutide, and placebo. The primary efficacy outcome The primary efficacy outcome was mean change in HbA1c from baseline with orforglipron versus placebo at week 26. Efficacy was analysed in all randomly assigned participants who received at least one dose of study drug and excluded data after the permanent discontinuation of study drug or initiation of rescue medication. Safety was analysed in all participants who received at least one dose of study treatment. This trial is registered at ClinicalTrials.gov (NCT05048719) and is completed.

FINDINGS

Between Sept 15, 2021, and Sept 30, 2022, 569 participants were screened and 383 were enrolled and randomly assigned to a group. 352 (92%) completed the study and 303 (79%) completed 26 weeks of treatment. At baseline, the mean age was 58·9 years, HbA1c was 8·1%, BMI was 35·2 kg/m2, 226 (59%) were men, and 157 (41%) were women. At week 26, mean change in HbA1c with orforglipron was up to -2·10% (-1·67% placebo adjusted), versus -0·43% with placebo and -1·10% with dulaglutide. HbA1c reduction was statistically superior with orforglipron versus placebo (estimated treatment difference -0·8% to -1·7%). Change in mean bodyweight at week 26 was up to -10·1 kg (95% CI -11·5 to -8·7; 7·9 kg placebo adjusted [-9·9 to -5·9]) with orforglipron versus -2·2 kg (-3·6 to -0·7) for placebo and -3·9 kg (-5·3 to -2·4) for dulaglutide. The incidence of treatment-emergent adverse events ranged from 61·8% to 88·9% in orforglipron-treated participants, compared with 61·8% with placebo and 56·0% with dulaglutide. The majority were gastrointestinal events (44·1% to 70·4% with orforglipron, 18·2% with placebo, and 34·0% with dulaglutide) of mild to moderate severity. Three participants receiving orforglipron and one participant receiving dulaglutide had clinically significant (<54 mg/dL [<3 mmol/L]) hypoglycaemia and no participants had severe hypoglycaemia. One death occurred in the placebo group and was not related to study treatment.

INTERPRETATION

In this phase 2 trial the novel, oral, non-peptide GLP-1 receptor agonist orforglipron at doses of 12 mg or greater showed significant reductions in HbA1c and bodyweight compared with placebo or dulaglutide. The adverse event profile was similar to other GLP-1 receptor agonists in similar stage of development. Orforglipron might provide an alternative to injectable GLP-1 receptor agonists and oral semaglutide, with the prospect of less burdensome administration to achieve treatment goals in people with type 2 diabetes.

FUNDING

Eli Lilly and Company.

Selective polypeptide ligand binding to the extracellular surface of the transmembrane domains of the class B GPCRs GLP-1R and GCGR

Crystal and cryo-EM structures of the glucagon-like peptide-1 receptor (GLP-1R) and glucagon receptor (GCGR) bound with their peptide ligands have been obtained with full-length constructs, indicating that the extracellular domain (ECD) is indispensable for specific ligand binding. This article complements these data with studies of ligand recognition of the two receptors in solution. Paramagnetic NMR relaxation enhancement measurements using dual labeling with fluorine-19 probes on the receptor and nitroxide spin labels on the peptide ligands provided new insights. The glucagon-like peptide-1 (GLP-1) was found to interact with GLP-1R by selective binding to the extracellular surface. The ligand selectivity toward the extracellular surface of the receptor was preserved in the transmembrane domain (TMD) devoid of the ECD. The dual labeling approach further provided evidence of cross-reactivity of GLP-1R and GCGR with glucagon and GLP-1, respectively, which is of interest in the context of medical treatments using combinations of the two polypeptides.

360-Degree Perspectives on Obesity

Alarming statistics show that the number of people affected by excessive weight has surpassed 2 billion, representing approximately 30% of the world's population. The aim of this review is to provide a comprehensive overview of one of the most serious public health problems, considering that obesity requires an integrative approach that takes into account its complex etiology, including genetic, environmental, and lifestyle factors. Only an understanding of the connections between the many contributors to obesity and the synergy between treatment interventions can ensure satisfactory outcomes in reducing obesity. Mechanisms such as oxidative stress, chronic inflammation, and dysbiosis play a crucial role in the pathogenesis of obesity and its associated complications. Compounding factors such as the deleterious effects of stress, the novel challenge posed by the obesogenic digital (food) environment, and the stigma associated with obesity should not be overlooked. Preclinical research in animal models has been instrumental in elucidating these mechanisms, and translation into clinical practice has provided promising therapeutic options, including epigenetic approaches, pharmacotherapy, and bariatric surgery. However, more studies are necessary to discover new compounds that target key metabolic pathways, innovative ways to deliver the drugs, the optimal combinations of lifestyle interventions with allopathic treatments, and, last but not least, emerging biological markers for effective monitoring. With each passing day, the obesity crisis tightens its grip, threatening not only individual lives but also burdening healthcare systems and societies at large. It is high time we took action as we confront the urgent imperative to address this escalating global health challenge head-on.

Discovery of Novel 5,6-Dihydro-1,2,4-triazine Derivatives as Efficacious Glucagon-Like Peptide-1 Receptor Agonists

Danuglipron is the most representative small-molecule agonist of the glucagon-like peptide-1 receptor (GLP-1R) and has received considerable attention due to positive results in the treatment of type 2 diabetes mellitus (T2DM) and obesity in clinical trials. However, hERG inhibition, lower activity than endogenous GLP-1, and a short action time represent limitations in terms of feasible application. In this study, we report a new class of 5,6-dihydro-1,2,4-triazine derivatives that serve to eliminate potential hERG inhibition caused by the piperidine ring of danuglipron. Applying systematic in vitro to in vivo screening, we have identified compound 42 as a highly potent and selective GLP-1R agonist, which delivers improved (7-fold) efficacy in stimulating cAMP accumulation compared with danuglipron and which exhibits acceptable drug-like properties. Furthermore, 42 significantly reduces glucose excursion and inhibits food intake of hGLP-1R Knock-In mice. These effects are longer-lasting than that shown by danuglipron, demonstrating feasibility in the treatment of T2DM and obesity.

Conformational Dynamics of the Activated GLP-1 Receptor-Gs Complex Revealed by Cross-Linking Mass Spectrometry and Integrative Structure Modeling

Despite advances in characterizing the structures and functions of G protein-coupled receptors (GPCRs), our understanding of GPCR activation and signaling is still limited by the lack of information on conformational dynamics. It is particularly challenging to study the dynamics of GPCR complexes with their signaling partners because of their transient nature and low stability. Here, by combining cross-linking mass spectrometry (CLMS) with integrative structure modeling, we map the conformational ensemble of an activated GPCR-G protein complex at near-atomic resolution. The integrative structures describe heterogeneous conformations for a high number of potential alternative active states of the GLP-1 receptor-G_s complex. These structures show marked differences from the previously determined cryo-EM structure, especially at the receptor-G_s interface and in the interior of the G_s heterotrimer. Alanine-scanning mutagenesis coupled with pharmacological assays validates the functional significance of 24 interface residue contacts only observed in the integrative structures, yet absent in the cryo-EM structure. Through the integration of spatial connectivity data from CLMS with structure modeling, our study provides a new approach that is generalizable to characterizing the conformational dynamics of GPCR signaling complexes.

Affinity selection of double-click triazole libraries for rapid discovery of allosteric modulators for GLP-1 receptor

The recently developed double-click reaction sequence [G. Meng et al., Nature 574, 86-89 (2019)] is expected to vastly expand the number and diversity of synthetically accessible 1,2,3-triazole derivatives. However, it remains elusive how to rapidly navigate the extensive chemical space created by double-click chemistry for bioactive compound discovery. In this study, we selected a particularly challenging drug target, the glucagon-like-peptide-1 receptor (GLP-1R), to benchmark our new platform for the design, synthesis, and screening of double-click triazole libraries. First, we achieved a streamlined synthesis of customized triazole libraries on an unprecedented scale (composed of 38,400 new compounds). By interfacing affinity-selection mass spectrometry and functional assays, we identified a series of positive allosteric modulators (PAMs) with unreported scaffolds that can selectively and robustly enhance the signaling activity of the endogenous GLP-1(9-36) peptide. Intriguingly, we further revealed an unexpected binding mode of new PAMs which likely act as a molecular glue between the receptor and the peptide agonist. We anticipate the merger of double-click library synthesis with the hybrid screening platform allows for efficient and economic discovery of drug candidates or chemical probes for various therapeutic targets.

GLP-1R Signaling and Functional Molecules in Incretin Therapy

Glucagon-like peptide-1 receptor (GLP-1R) is a critical therapeutic target for type 2 diabetes mellitus (T2DM). The GLP-1R cellular signaling mechanism relevant to insulin secretion and blood glucose regulation has been extensively studied. Numerous drugs targeting GLP-1R have entered clinical treatment. However, novel functional molecules with reduced side effects and enhanced therapeutic efficacy are still in high demand. In this review, we summarize the basis of GLP-1R cellular signaling, and how it is involved in the treatment of T2DM. We review the functional molecules of incretin therapy in various stages of clinical trials. We also outline the current strategies and emerging techniques that are furthering the development of novel therapeutic drugs for T2DM and other metabolic diseases.

Improved Split TEV GPCR β-arrestin-2 Recruitment Assays via Systematic Analysis of Signal Peptide and β-arrestin Binding Motif Variants

G protein-coupled receptors (GPCRs) are major disease-relevant drug targets; robust monitoring of their activities upon drug treatment is key to drug discovery. The split TEV cell-based assay technique monitors the interaction of an activated GPCR with β-arrestin-2 through TEV protein fragment complementation using a luminescent signal as the readout. In this work, split TEV GPCR β-arrestin-2 recruitment assays were optimized to monitor the endogenous ligand-induced activities of six GPCRs (DRD1, DRD2, HTR2A, GCGR, AVPR2, and GLP1R). Each GPCR was tested in four forms; i.e., its wildtype form, a variant with a signal peptide (SP) to facilitate receptor expression, a variant containing the C-terminal tail from the V2 vasopressin receptor (V2R tail) to promote β-arrestin-2 recruitment, and a variant containing both the SP and V2R tail. These 24 GPCR variants were systematically tested for assay performance in four cell lines (HEK-293, PC12 Tet-Off, U-2 OS, and HeLa). We found that the assay performance differed significantly for each GPCR variant and was dependent on the cell line. We found that V2R improved the DRD2 split TEV assays and that HEK-293 cells were the preferred cell line across the GPCRs tested. When taking these considerations into account, the defined selection of assay modifications and conditions may improve the performance of drug development campaigns that apply the split TEV technique as a screening tool.

New insights into the structure and function of class B1 GPCRs

G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors. Class B1 GPCRs constitute a subfamily of 15 receptors that characteristically contain large extracellular domains (ECDs) and respond to long polypeptide hormones. Class B1 GPCRs are critical regulators of homeostasis, and as such, many are important drug targets. While most transmembrane proteins, including GPCRs, are recalcitrant to crystallization, recent advances in electron cryo-microscopy (cryo-EM) have facilitated a rapid expansion of the structural understanding of membrane proteins. As a testament to this success, structures for all the class B1 receptors bound to G proteins have been determined by cryo-EM in the past five years. Further advances in cryo-EM have uncovered dynamics of these receptors, ligands, and signalling partners. Here, we examine the recent structural underpinnings of the class B1 GPCRs with an emphasis on structure-function relationships.

Current Advances in the Management of Diabetes Mellitus

Diabetes mellitus (DM) underscores a rising epidemic orchestrating critical socio-economic burden on countries globally. Different treatment options for the management of DM are evolving rapidly because the usual methods of treatment have not completely tackled the primary causes of the disease and are laden with critical adverse effects. Thus, this narrative review explores different treatment regimens in DM management and the associated challenges. A literature search for published articles on recent advances in DM management was completed with search engines including Web of Science, Pubmed/Medline, Scopus, using keywords such as DM, management of DM, and gene therapy. Our findings indicate that substantial progress has been made in DM management with promising results using different treatment regimens, including nanotechnology, gene therapy, stem cell, medical nutrition therapy, and lifestyle modification. However, a lot of challenges have been encountered using these techniques, including their optimization to ensure optimal glycemic, lipid, and blood pressure modulation to minimize complications, improvement of patients' compliance to lifestyle and pharmacologic interventions, safety, ethical issues, as well as an effective delivery system among others. In conclusion, lifestyle management alongside pharmacological approaches and the optimization of these techniques is critical for an effective and safe clinical treatment plan.

Membranes under the Magnetic Lens: A Dive into the Diverse World of Membrane Protein Structures Using Cryo-EM

Membrane proteins are highly diverse in both structure and function and can, therefore, present different challenges for structure determination. They are biologically important for cells and organisms as gatekeepers for information and molecule transfer across membranes, but each class of membrane proteins can present unique obstacles to structure determination. Historically, many membrane protein structures have been investigated using highly engineered constructs or using larger fusion proteins to improve solubility and/or increase particle size. Other strategies included the deconstruction of the full-length protein to target smaller soluble domains. These manipulations were often required for crystal formation to support X-ray crystallography or to circumvent lower resolution due to high noise and dynamic motions of protein subdomains. However, recent revolutions in membrane protein biochemistry and cryo-electron microscopy now provide an opportunity to solve high resolution structures of both large, >1 megadalton (MDa), and small, <100 kDa (kDa), drug targets in near-native conditions, routinely reaching resolutions around or below 3 Å. This review provides insights into how the recent advances in membrane biology and biochemistry, as well as technical advances in cryo-electron microscopy, help us to solve structures of a large variety of membrane protein groups, from small receptors to large transporters and more complex machineries.

Biased Agonism and Polymorphic Variation at the GLP-1 Receptor: Implications for the Development of Personalised Therapeutics

Glucagon-like peptide-1 receptor (GLP-1R) is a well-studied incretin hormone receptor and target of several therapeutic drugs for type 2 diabetes (T2D), obesity and, more recently, cardiovascular disease. Some signalling pathways downstream of GLP-1R may be responsible for drug adverse effects such as nausea, while others mediate therapeutic outcomes of incretin-based T2D therapeutics. Understanding the interplay between different factors that alter signalling, trafficking, and receptor activity, including biased agonism, single nucleotide polymorphisms and structural modifications is key to develop the next-generation of personalised GLP-1R agonists. However, these interactions remain poorly described, especially for novel therapeutics such as dual and tri-agonists that target more than one incretin receptor. Comparison of GLP-1R structures in complex with G proteins and different peptide and non-peptide agonists has revealed novel insights into important agonist-residue interactions and networks crucial for receptor activation, recruitment of G proteins and engagement of specific signalling pathways. Here, we review the latest knowledge on GLP-1R structure and activation, providing structural evidence for biased agonism and delineating important networks associated with this phenomenon. We survey current biased agonists and multi-agonists at different stages of development, highlighting possible challenges in their translational potential. Lastly, we discuss findings related to non-synonymous genomic variants of GLP1R and the functional importance of specific residues involved in GLP-1R function. We propose that studies of GLP-1R polymorphisms, and specifically their effect on receptor dynamics and pharmacology in response to biased agonists, could have a significant impact in delineating precision medicine approaches and development of novel therapeutics.

Actions of Parathyroid Hormone Ligand Analogues in Humanized PTH1R Knockin Mice

Rodent models are commonly used to evaluate parathyroid hormone (PTH) and PTH-related protein (PTHrP) ligands and analogues for their pharmacologic activities and potential therapeutic utility toward diseases of bone and mineral ion metabolism. Divergence, however, in the amino acid sequences of rodent and human PTH receptors (rat and mouse PTH1Rs are 91% identical to the human PTH1R) can lead to differences in receptor-binding and signaling potencies for such ligands when assessed on rodent vs human PTH1Rs, as shown by cell-based assays in vitro. This introduces an element of uncertainty in the accuracy of rodent models for performing such preclinical evaluations. To overcome this potential uncertainty, we used a homologous recombination-based knockin (KI) approach to generate a mouse (in-host strain C57Bl/6N) in which complementary DNA encoding the human PTH1R replaces a segment (exon 4) of the murine PTH1R gene so that the human and not the mouse PTH1R protein is expressed. Expression is directed by the endogenous mouse promoter and hence occurs in all biologically relevant cells and tissues and at appropriate levels. The resulting homozygous hPTH1R-KI (humanized) mice were healthy over at least 10 generations and showed functional responses to injected PTH analog peptides that are consistent with a fully functional human PTH1R in target bone and kidney cells. The initial evaluation of these mice and their potential utility for predicting behavior of PTH analogues in humans is reported here.

Deciphering the conformational landscape of few selected aromatic noncoded amino acids (NCAAs) for applications in rational design of peptide therapeutics

Amino acids are the essential building blocks of both synthetic and natural peptides, which are crucial for biological functions and also important as biological probes for mapping the complex protein-protein interactions (PPIs) in both prokaryotic and eukaryotic systems. Mapping the PPIs through the chemical biology approach provides pharmacologically relevant peptides, which can have agonistic or antagonistic effects on the targeted biological systems. It is evidenced that ≥ 60 peptide-based drugs have been approved by the US-FDA so far, and the number will improve further in the foreseeable future, as ≥ 140 peptides are currently in clinical trials. However, natural peptides often require fine-tuning of their pharmacological properties by strategically replacing the α_L-amino acids of the peptides with non-coded amino acids (NCAA), for which codons are absent in the genetic code for biosynthesis of proteins, prior to their applications as therapeutics. Considering the diverse repertoire of the NCAAs, the conformational space of many NCAAs is yet to be explored systematically in the context of the rational design of therapeutic peptides. The current study deciphers the conformational landscape of a few such Cα-substituted aromatic NCAAs (Ing: 2-indanyl-L-Glycine; Bpa: 4-benzoyl-L-phenylalanine; Aic: 2-aminoindane-2-carboxylic acid) both in the context of tripeptides and model synthetic peptide sequences, using alanine (Ala) and proline (Pro) as the reference. The combined data obtained from the computational and biophysical studies indicate the general success of this approach, which can be exploited further to rationally design optimized peptide sequences of unusual architecture with potent antimicrobial, antiviral, gluco-regulatory, immunomodulatory, and anti-inflammatory activities.

Investigating Potential GLP-1 Receptor Agonists in Cyclopeptides from Pseudostellaria heterophylla, Linum usitatissimum, and Drymaria diandra, and Peptides Derived from Heterophyllin B for the Treatment of Type 2 Diabetes: An In Silico Study

GLP-1 receptor agonists stimulate GLP-1R to promote insulin secretion, whereas DPP4 inhibitors slow GLP-1 degradation. Both approaches are incretin-based therapies for T2D. In addition to GLP-1 analogs, small nonpeptide GLP-1RAs such as LY3502970, TT-OAD2, and PF-06882961 have been considered as possible therapeutic alternatives. Pseudostellaria heterophylla, Linum usitatissimum, and Drymaria diandra are plants rich in cyclopeptides with hypoglycemic effects. Our previous study demonstrated the potential of their cyclopeptides for DPP4 inhibition. Reports of cyclic setmelanotide as an MC4R (GPCR) agonist and cyclic α-conotoxin chimeras as GLP-1RAs led to docking studies of these cyclopeptides with GLP-1R. Heterophyllin B, Pseudostellarin B, Cyclolinopeptide B, Cyclolinopeptide C, Drymarin A, and Diandrine C are abundant in these plants, with binding affinities of −9.5, −10.4, −10.3, −10.6, −11.2, and −11.9 kcal/mol, respectively. The configuration they demonstrated established multiple hydrogen bonds with the transmembrane region of GLP-1R. DdC:(cyclo)-GGPYWP showed the most promising docking score. The results suggest that, in addition to DPP4, GLP-1R may be a hypoglycemic target of these cyclopeptides. This may bring about more discussion of plant cyclopeptides as GLP-1RAs. Moreover, peptides derived from the HB precursor (IFGGLPPP), including IFGGWPPP, IFPGWPPP, IFGGYWPPP, and IFGYGWPPPP, exhibited diverse interactions with GLP-1R and displayed backbones available for further research.

Anti-Obesity Medications and Investigational Agents: An Obesity Medicine Association (OMA) Clinical Practice Statement (CPS) 2022

Background

This "Anti-Obesity Medications and Investigational Agents: An Obesity Medicine Association Clinical Practice Statement 2022" is intended to provide clinicians an overview of Food and Drug Administration (FDA) approved anti-obesity medications and investigational anti-obesity agents in development.

Methods

The scientific information for this Clinical Practice Statement (CPS) is based upon published scientific citations, clinical perspectives of OMA authors, and peer review by the Obesity Medicine Association leadership.

Results

This CPS describes pharmacokinetic principles applicable to those with obesity, and discusses the efficacy and safety of anti-obesity medications [e.g., phentermine, semaglutide, liraglutide, phentermine/topiramate, naltrexone/bupropion, and orlistat, as well as non-systemic superabsorbent oral hydrogel particles (which is technically classified as a medical device)]. Other medications discussed include setmelanotide, metreleptin, and lisdexamfetamine dimesylate. Data regarding the use of combination anti-obesity pharmacotherapy, as well as use of anti-obesity pharmacotherapy after bariatric surgery are limited; however, published data support such approaches. Finally, this CPS discusses investigational anti-obesity medications, with an emphasis on the mechanisms of action and summary of available clinical trial data regarding tirzepatide.

Conclusion

This "Anti-Obesity Medications and Investigational Agents: An Obesity Medicine Association Clinical Practice Statement 2022" is one of a series of OMA CPSs designed to assist clinicians in the care of patients with pre-obesity/obesity.

A Small-Molecule Oral Agonist of the Human Glucagon-like Peptide-1 Receptor

Peptide agonists of the glucagon-like peptide-1 receptor (GLP-1R) have revolutionized diabetes therapy, but their use has been limited because they require injection. Herein, we describe the discovery of the orally bioavailable, small-molecule, GLP-1R agonist PF-06882961 (danuglipron). A sensitized high-throughput screen was used to identify 5-fluoropyrimidine-based GLP-1R agonists that were optimized to promote endogenous GLP-1R signaling with nanomolar potency. Incorporation of a carboxylic acid moiety provided considerable GLP-1R potency gains with improved off-target pharmacology and reduced metabolic clearance, ultimately resulting in the identification of danuglipron. Danuglipron increased insulin levels in primates but not rodents, which was explained by receptor mutagensis studies and a cryogenic electron microscope structure that revealed a binding pocket requiring a primate-specific tryptophan 33 residue. Oral administration of danuglipron to healthy humans produced dose-proportional increases in systemic exposure (NCT03309241). This opens an opportunity for oral small-molecule therapies that target the well-validated GLP-1R for metabolic health.

Accelerating GPCR Drug Discovery With Conformation-Stabilizing VHHs

The human genome encodes 850 G protein-coupled receptors (GPCRs), half of which are considered potential drug targets. GPCRs transduce extracellular stimuli into a plethora of vital physiological processes. Consequently, GPCRs are an attractive drug target class. This is underlined by the fact that approximately 40% of marketed drugs modulate GPCRs. Intriguingly 60% of non-olfactory GPCRs have no drugs or candidates in clinical development, highlighting the continued potential of GPCRs as drug targets. The discovery of small molecules targeting these GPCRs by conventional high throughput screening (HTS) campaigns is challenging. Although the definition of success varies per company, the success rate of HTS for GPCRs is low compared to other target families (Fujioka and Omori, 2012; Dragovich et al., 2022). Beyond this, GPCR structure determination can be difficult, which often precludes the application of structure-based drug design approaches to arising HTS hits. GPCR structural studies entail the resource-demanding purification of native receptors, which can be challenging as they are inherently unstable when extracted from the lipid matrix. Moreover, GPCRs are flexible molecules that adopt distinct conformations, some of which need to be stabilized if they are to be structurally resolved. The complexity of targeting distinct therapeutically relevant GPCR conformations during the early discovery stages contributes to the high attrition rates for GPCR drug discovery programs. Multiple strategies have been explored in an attempt to stabilize GPCRs in distinct conformations to better understand their pharmacology. This review will focus on the use of camelid-derived immunoglobulin single variable domains (VHHs) that stabilize disease-relevant pharmacological states (termed ConfoBodies by the authors) of GPCRs, as well as GPCR:signal transducer complexes, to accelerate drug discovery. These VHHs are powerful tools for supporting in vitro screening, deconvolution of complex GPCR pharmacology, and structural biology purposes. In order to demonstrate the potential impact of ConfoBodies on translational research, examples are presented of their role in active state screening campaigns and structure-informed rational design to identify de novo chemical space and, subsequently, how such matter can be elaborated into more potent and selective drug candidates with intended pharmacology.

Structural basis of peptidomimetic agonism revealed by small- molecule GLP-1R agonists Boc5 and WB4-24

Glucagon-like peptide-1 receptor (GLP-1R) agonists are efficacious in the treatment of type 2 diabetes and obesity. While most clinically used agents require subcutaneous injection, Boc5, as the first orthosteric nonpeptidic agonist of GLP-1R, suffers from poor oral bioavailability that hinders its therapeutic development. The cryoelectron microscopy structures of Boc5 and its closely related analog WB4-24 presented here reveal a binding pocket located deeper in the transmembrane domain for nonpeptidic GLP-1R agonists. Molecular interaction with this site may facilitate a broad spectrum of in vivo agonistic activities, in addition to that with the upper helical bundles presumably responsible for biased signaling. These findings deepen our understanding of peptidomimetic agonism at GLP-1R and may help design better drug leads against this important target.

Glucagon-like peptide-1 receptor (GLP-1R) agonists are effective in treating type 2 diabetes and obesity with proven cardiovascular benefits. However, most of these agonists are peptides and require subcutaneous injection except for orally available semaglutide. Boc5 was identified as the first orthosteric nonpeptidic agonist of GLP-1R that mimics a broad spectrum of bioactivities of GLP-1 in vitro and in vivo. Here, we report the cryoelectron microscopy structures of Boc5 and its analog WB4-24 in complex with the human GLP-1R and G_s protein. Bound to the extracellular domain, extracellular loop 2, and transmembrane (TM) helices 1, 2, 3, and 7, one arm of both compounds was inserted deeply into the bottom of the orthosteric binding pocket that is usually accessible by peptidic agonists, thereby partially overlapping with the residues A8 to D15 in GLP-1. The other three arms, meanwhile, extended to the TM1-TM7, TM1-TM2, and TM2-TM3 clefts, showing an interaction feature substantially similar to the previously known small-molecule agonist LY3502970. Such a unique binding mode creates a distinct conformation that confers both peptidomimetic agonism and biased signaling induced by nonpeptidic modulators at GLP-1R. Further, the conformational difference between Boc5 and WB4-24, two closed related compounds, provides a structural framework for fine-tuning of pharmacological efficacy in the development of future small-molecule therapeutics targeting GLP-1R.

Cardiovascular effects of GLP-1 receptor agonism

Glucagon-like peptide-1 (GLP-1) receptor agonists are extensively used in type 2 diabetic patients for the effective control of hyperglycemia. It is now clear from outcomes trials that this class of drugs offers important additional benefits to these patients due to reducing the risk of developing major adverse cardiac events (MACE). This risk reduction is, in part, due to effective glycemic control in patients; however, the various outcomes trials, further validated by subsequent meta-analysis of the outcomes trials, suggest that the risk reduction in MACE is also dependent on glycemic-independent mechanisms operant in cardiovascular tissues. These glycemic-independent mechanisms are likely mediated by GLP-1 receptors found throughout the cardiovascular system and by the complex signaling cascades triggered by the binding of agonists to the G-protein coupled receptors. This heterogeneity of signaling pathways underlying different downstream effects of GLP-1 agonists, and the discovery of biased agonists favoring specific signaling pathways, may have import in the future treatment of MACE in these patients. We review the evidence supporting the glycemic-independent evidence for risk reduction of MACE by the GLP-1 receptor agonists and highlight the putative mechanisms underlying these benefits. We also comment on the different signaling pathways which appear important for mediating these effects.

Structural determinants of dual incretin receptor agonism by tirzepatide

Tirzepatide is a dual agonist of the glucose-dependent insulinotropic polypeptide receptor (GIPR) and the glucagon-like peptide-1 receptor (GLP-1R), which are incretin receptors that regulate carbohydrate metabolism. This investigational agent has proven superior to selective GLP-1R agonists in clinical trials in subjects with type 2 diabetes mellitus. Intriguingly, although tirzepatide closely resembles native GIP in how it activates the GIPR, it differs markedly from GLP-1 in its activation of the GLP-1R, resulting in less agonist-induced receptor desensitization. We report how cryogenic electron microscopy and molecular dynamics simulations inform the structural basis for the unique pharmacology of tirzepatide. These studies reveal the extent to which fatty acid modification, combined with amino acid sequence, determines the mode of action of a multireceptor agonist.

Tirzepatide (LY3298176) is a fatty-acid-modified, dual incretin receptor agonist that exhibits pharmacology similar to native GIP at the glucose-dependent insulinotropic polypeptide receptor (GIPR) but shows bias toward cyclic adenosine monophosphate signaling at the glucagon-like peptide-1 receptor (GLP-1R). In addition to GIPR signaling, the pathway bias at the GLP-1R may contribute to the efficacy of tirzepatide at improving glucose control and body weight regulation in type 2 diabetes mellitus. To investigate the structural basis for the differential signaling of tirzepatide, mechanistic pharmacology studies were allied with cryogenic electron microscopy. Here, we report high-resolution structures of tirzepatide in complex with the GIPR and GLP-1R. Similar to the native ligands, tirzepatide adopts an α-helical conformation with the N terminus reaching deep within the transmembrane core of both receptors. Analyses of the N-terminal tyrosine (Tyr1^Tzp) of tirzepatide revealed a weak interaction with the GLP-1R. Molecular dynamics simulations indicated a greater propensity of intermittent hydrogen bonding between the lipid moiety of tirzepatide and the GIPR versus the GLP-1R, consistent with a more compact tirzepatide–GIPR complex. Informed by these analyses, tirzepatide was deconstructed, revealing a peptide structure–activity relationship that is influenced by acylation-dependent signal transduction. For the GIPR, Tyr1^Tzp and other residues making strong interactions within the receptor core allow tirzepatide to tolerate fatty acid modification, yielding an affinity equaling that of GIP. Conversely, high-affinity binding with the extracellular domain of the GLP-1R, coupled with decreased stability from the Tyr1^Tzp and the lipid moiety, foster biased signaling and reduced receptor desensitization. Together, these studies inform the structural determinants underlying the function of tirzepatide.

Non-peptide agonists and positive allosteric modulators of glucagon-like peptide-1 receptors: Alternative approaches for treatment of Type 2 diabetes

Glucagon-like peptide-1 (GLP-1) receptors belong to the pharmaceutically important Class B family of GPCRs and are involved in many biologically significant signalling pathways. Its incretin peptide ligand GLP-1 analogues are effective treatments for Type 2 diabetes. Although developing non-peptide low MW drugs targeting GLP-1 receptors remains elusive, considerable progress has been made in discovering non-peptide agonists and positive allosteric modulators (PAMs) of GLP-1 receptors with demonstrated efficacy. Many of these compounds induce biased signalling in GLP-1 receptor-mediated functional pathways. High-quality structures of GLP-1 receptors in both inactive and active states have been reported, revealing detailed molecular interactions between GLP-1 receptors and non-peptide agonists or PAMs. These progresses raise the exciting possibility of developing non-peptide drugs of GLP-1 receptors as alternative treatments for Type 2 diabetes. The insight into the interactions between the receptor and the non-peptide ligand is also useful for developing non-peptide ligands targeting other Class B GPCRs. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

The therapeutic potential of GLP-1 receptor biased agonism

Glucagon-like peptide-1 (GLP-1) receptor agonists are effective treatments for type 2 diabetes as they stimulate insulin release and promote weight loss through appetite suppression. Their main side effect is nausea. All approved GLP-1 agonists are full agonists across multiple signalling pathways. However, selective engagement with specific intracellular effectors, or biased agonism, has been touted as a means to improve GLP-1 agonists therapeutic efficacy. In this review, I critically examine how GLP-1 receptor-mediated intracellular signalling is linked to physiological responses and discuss the implications of recent studies investigating the metabolic effects of biased GLP-1 agonists. Overall, there is little conclusive evidence that beneficial and adverse effects of GLP-1 agonists are attributable to distinct, nonoverlapping signalling pathways. Instead, G protein-biased GLP-1 agonists appear to achieve enhanced anti-hyperglycaemic efficacy by avoiding GLP-1 receptor desensitisation and downregulation, partly via reduced β-arrestin recruitment. This effect seemingly applies more to insulin release than to appetite regulation and nausea, possible reasons for which are discussed. At present, most evidence derives from cellular and animal studies, and more human data are required to determine whether this approach represents a genuine therapeutic advance. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

Applications of Cryo-EM in small molecule and biologics drug design

Electron cryo-microscopy (cryo-EM) is a powerful technique for the structural characterization of biological macromolecules, enabling high-resolution analysis of targets once inaccessible to structural interrogation. In recent years, pharmaceutical companies have begun to utilize cryo-EM for structure-based drug design. Structural analysis of integral membrane proteins, which comprise a large proportion of druggable targets and pose particular challenges for X-ray crystallography, by cryo-EM has enabled insights into important drug target families such as G protein-coupled receptors (GPCRs), ion channels, and solute carrier (SLCs) proteins. Structural characterization of biologics, such as vaccines, viral vectors, and gene therapy agents, has also become significantly more tractable. As a result, cryo-EM has begun to make major impacts in bringing critical therapeutics to market. In this review, we discuss recent instructive examples of impacts from cryo-EM in therapeutics design, focusing largely on its implementation at Pfizer. We also discuss the opportunities afforded by emerging technological advances in cryo-EM, and the prospects for future development of the technique.

The rapidly evolving role of cryo-EM in drug design

Since the early 2010s, cryo-electron microscopy (cryo-EM) has evolved to a mainstream structural biology method in what has been dubbed the "resolution revolution". Pharma companies also began to use cryo-EM in drug discovery, evidenced by a growing number of industry publications. Hitherto limited in resolution, throughput and attainable molecular weight, cryo-EM is rapidly overcoming its main limitations for more widespread use through a new wave of technological advances. This review discusses how cryo-EM has already impacted drug discovery, and how the state-of-the-art is poised to further revolutionize its application to previously intractable proteins as well as new use cases.

Allosteric Modulators Enhancing GLP-1 Binding to GLP-1R via a Transmembrane Site

The glucagon-like peptide-1 receptor (GLP-1R) is a well-established drug target for the treatment of type II diabetes. The development of small-molecule positive allosteric modulators (PAMs) of GLP-1R is a promising therapeutic strategy. Here, we report the discovery and characterization of PAMs with distinct chemotypes, binding to a cryptic pocket formed by the cytoplasmic half of TM3, TM5, and TM6. Molecular dynamic simulations and mutagenesis studies indicate that the PAM enlarges the orthosteric pocket to facilitate GLP-1 binding. Further signaling assays characterized their probe-dependent signaling profiles. Our findings provide mechanistic insights into fine-tuning GLP-1R via this allosteric pocket and open up new avenues to design small-molecule drugs for class B G-protein-coupled receptors.

Identification of novel positive allosteric modulators of GLP1R that stimulate its interaction with ligands and Gα subunits

Glucagon-like peptide-1 (GLP-1) is a major incretin hormone that enhances the release of insulin from pancreatic β-cells by activating the glucagon-like peptide-1 receptor (GLP1R), which belongs to secretin-like class B of G protein-coupled receptors (GPCRs). Owing to the absence of small molecule agonist drugs to GLP1R, focus has been placed on chemical modulators that bind to the allosteric site of GLP1R. In this study, we identified novel small-molecule positive allosteric modulators of GLP1R from a chemical library consisting of commercial drug compounds using an assay system that measures the direct interaction between a purified GLP1R and its ligand, exendin-4. Two newly identified compounds, benzethonium and tamoxifen, significantly enhanced the affinity of peptide ligands for GLP1R although they lacked agonist activity by themselves. In addition, benzethonium augmented the ligand-induced accumulation of cAMP in GLP1R-transfected HEK293T cells. These compounds significantly increased the affinity of GLP1R to the alpha-subunit of G proteins, suggesting that they stabilize GLP1R in a conformation with a higher affinity to peptide ligand as well as G proteins. These compounds may lead to the design of an orally active positive allosteric modulator for GLP1R.

Treatment of type 2 diabetes: challenges, hopes, and anticipated successes

Despite the successful development of new therapies for the treatment of type 2 diabetes, such as glucagon-like peptide-1 (GLP-1) receptor agonists and sodium-glucose cotransporter-2 inhibitors, the search for novel treatment options that can provide better glycaemic control and at reduce complications is a continuous effort. The present Review aims to present an overview of novel targets and mechanisms and focuses on glucose-lowering effects guiding this search and developments. We discuss not only novel developments of insulin therapy (eg, so-called smart insulin preparation with a glucose-dependent mode of action), but also a group of drug classes for which extensive research efforts have not been rewarded with obvious clinical impact. We discuss the potential clinical use of the salutary adipokine adiponectin and the hepatokine fibroblast growth factor (FGF) 21, among others. A GLP-1 peptide receptor agonist (semaglutide) is now available for oral absorption, and small molecules activating GLP-1 receptors appear on the horizon. Bariatric surgery and its accompanying changes in the gut hormonal milieu offer a background for unimolecular peptides interacting with two or more receptors (for GLP-1, glucose-dependent insulinotropic polypeptide, glucagon, and peptide YY) and provide more substantial glycaemic control and bodyweight reduction compared with selective GLP-1 receptor agonists. These and additional approaches will help expand the toolbox of effective medications needed for optimising the treatment of well delineated subgroups of type 2 diabetes or help develop personalised approaches for glucose-lowering drugs based on individual characteristics of our patients.

Molecular insights into ago-allosteric modulation of the human glucagon-like peptide-1 receptor

The glucagon-like peptide-1 (GLP-1) receptor is a validated drug target for metabolic disorders. Ago-allosteric modulators are capable of acting both as agonists on their own and as efficacy enhancers of orthosteric ligands. However, the molecular details of ago-allosterism remain elusive. Here, we report three cryo-electron microscopy structures of GLP-1R bound to (i) compound 2 (an ago-allosteric modulator); (ii) compound 2 and GLP-1; and (iii) compound 2 and LY3502970 (a small molecule agonist), all in complex with heterotrimeric G_s. The structures reveal that compound 2 is covalently bonded to C347 at the cytoplasmic end of TM6 and triggers its outward movement in cooperation with the ECD whose N terminus penetrates into the GLP-1 binding site. This allows compound 2 to execute positive allosteric modulation through enhancement of both agonist binding and G protein coupling. Our findings offer insights into the structural basis of ago-allosterism at GLP-1R and may aid the design of better therapeutics.

The glucagon-like peptide-1 (GLP-1) receptor is a key regulator of glucose homeostasis and a drug target for type 2 diabetes but available GLP-1R agonists are suboptimal due to several side-effects. Here authors report the cryo-EM structure of GLP-1R bound to an ago-allosteric modulator in complex with heterotrimeric G_s which offers insights into the molecular details of ago-allosterism.

Systemic GLP-1R agonist treatment reverses mouse glial and neurovascular cell transcriptomic aging signatures in a genome-wide manner

Pharmacological reversal of brain aging is a long-sought yet challenging strategy for the prevention and treatment of age-related neurodegeneration, due to the diverse cell types and complex cellular pathways impacted by the aging process. Here, we report the genome-wide reversal of transcriptomic aging signatures in multiple major brain cell types, including glial and mural cells, by systemic glucagon-like peptide-1 receptor (GLP-1R) agonist (GLP-1RA) treatment. The age-related expression changes reversed by GLP-1RA encompass both shared and cell type-specific functional pathways that are implicated in aging and neurodegeneration. Concomitantly, Alzheimer's disease (AD)-associated transcriptomic signature in microglia that arises from aging is reduced. These results show the feasibility of reversing brain aging by pharmacological means, provide mechanistic insights into the neurological benefits of GLP-1RAs, and imply that GLP-1R agonism may be a generally applicable pharmacological intervention for patients at risk of age-related neurodegeneration.

Ligand-Receptor Interactions and Machine Learning in GCGR and GLP-1R Drug Discovery

The large amount of data that has been collected so far for G protein-coupled receptors requires machine learning (ML) approaches to fully exploit its potential. Our previous ML model based on gradient boosting used for prediction of drug affinity and selectivity for a receptor subtype was compared with explicit information on ligand-receptor interactions from induced-fit docking. Both methods have proved their usefulness in drug response predictions. Yet, their successful combination still requires allosteric/orthosteric assignment of ligands from datasets. Our ligand datasets included activities of two members of the secretin receptor family: GCGR and GLP-1R. Simultaneous activation of two or three receptors of this family by dual or triple agonists is not a typical kind of information included in compound databases. A precise allosteric/orthosteric ligand assignment requires a continuous update based on new structural and biological data. This data incompleteness remains the main obstacle for current ML methods applied to class B GPCR drug discovery. Even so, for these two class B receptors, our ligand-based ML model demonstrated high accuracy (5-fold cross-validation Q² > 0.63 and Q² > 0.67 for GLP-1R and GCGR, respectively). In addition, we performed a ligand annotation using recent cryogenic-electron microscopy (cryo-EM) and X-ray crystallographic data on small-molecule complexes of GCGR and GLP-1R. As a result, we assigned GLP-1R and GCGR actives deposited in ChEMBL to four small-molecule binding sites occupied by positive and negative allosteric modulators and a full agonist. Annotated compounds were added to our recently released repository of GPCR data.

Discovery of an Orally Efficacious Positive Allosteric Modulator of the Glucagon-like Peptide-1 Receptor

The identification of LSN3318839, a positive allosteric modulator of the glucagon-like peptide-1 receptor (GLP-1R), is described. LSN3318839 increases the potency and efficacy of the weak metabolite GLP-1(9-36)NH2 to become a full agonist at the GLP-1R and modestly potentiates the activity of the highly potent full-length ligand, GLP-1(7-36)NH2. LSN3318839 preferentially enhances G protein-coupled signaling by the GLP-1R over β-arrestin recruitment. Ex vivo experiments show that the combination of GLP-1(9-36)NH2 and LSN3318839 produces glucose-dependent insulin secretion similar to that of GLP-1(7-36)NH2. Under nutrient-stimulated conditions that release GLP-1, LSN3318839 demonstrates robust glucose lowering in animal models alone or in treatment combination with sitagliptin. From a therapeutic perspective, the biological properties of LSN3318839 support the concept that GLP-1R potentiation is sufficient for reducing hyperglycemia.

Peptidyl and Non-Peptidyl Oral Glucagon-Like Peptide-1 Receptor Agonists

Glucagon-like peptide-1 (GLP-1) receptor agonists are efficacious glucose-lowering medications with salient benefits for body weight and cardiovascular events. This class of medications is now recommended as the top priority for patients with established cardiovascular disease or indicators of high risk. Until the advent of oral semaglutide, however, GLP-1 receptor agonists were available only in the form of subcutaneous injections. Aversion to needles, discomfort with self-injection, or skin problems at the injection site are commonly voiced problems in people with diabetes, and thus, attempts for non-invasive delivery strategies have continued. Herein, we review the evolution of GLP-1 therapy from its discovery and the development of currently approved drugs to the unprecedented endeavor to administer GLP-1 receptor agonists via the oral route. We focus on the pharmacokinetic and pharmacodynamic properties of the recently approved oral GLP-1 receptor agonist, oral semaglutide. Small molecule oral GLP-1 receptor agonists are currently in development, and we introduce how these chemicals have addressed the challenge posed by interactions with the large extracellular ligand binding domain of the GLP-1 receptor. We specifically discuss the structure and pharmacological properties of TT-OAD2, LY3502970, and PF-06882961, and envision an era where more patients could benefit from oral GLP-1 receptor agonist therapy.

GLP-1 Val8: A Biased GLP-1R Agonist with Altered Binding Kinetics and Impaired Release of Pancreatic Hormones in Rats

Biased ligands that selectively confer activity in one pathway over another are pharmacologically important because biased signaling may reduce on-target side effects and improve drug efficacy. Here, we describe an N-terminal modification in the incretin hormone glucagon-like peptide (GLP-1) that alters the signaling capabilities of the GLP-1 receptor (GLP-1R) by making it G protein biased over internalization but was originally designed to confer DPP-4 resistance and thereby prolong the half-life of GLP-1. Despite similar binding affinity, cAMP production, and calcium mobilization, substitution of a single amino acid (Ala8 to Val8) in the N-terminus of GLP-1(7-36)NH₂ (GLP-1 Val8) severely impaired its ability to internalize GLP-1R compared to endogenous GLP-1. In-depth binding kinetics analyses revealed shorter residence time for GLP-1 Val8 as well as a slower observed association rate. Molecular dynamics (MD) displayed weaker and less interactions of GLP-1 Val8 with GLP-1R, as well as distinct conformational changes in the receptor compared to GLP-1. In vitro validation of the MD, by receptor alanine substitutions, confirmed stronger impairments of GLP-1 Val8-mediated signaling compared to GLP-1. In a perfused rat pancreas, acute stimulation with GLP-1 Val8 resulted in a lower insulin and somatostatin secretion compared to GLP-1. Our study illustrates that profound differences in molecular pharmacological properties, which are essential for the therapeutic targeting of the GLP-1 system, can be induced by subtle changes in the N-terminus of GLP-1. This information could facilitate the development of optimized GLP-1R agonists.

GLP-1 Receptor Agonists: Beyond Their Pancreatic Effects

Glucagon like peptide-1 (GLP-1) is an incretin secretory molecule. GLP-1 receptor agonists (GLP-1RAs) are widely used in the treatment of type 2 diabetes (T2DM) due to their attributes such as body weight loss, protection of islet β cells, promotion of islet β cell proliferation and minimal side effects. Studies have found that GLP-1R is widely distributed on pancreatic and other tissues and has multiple biological effects, such as reducing neuroinflammation, promoting nerve growth, improving heart function, suppressing appetite, delaying gastric emptying, regulating blood lipid metabolism and reducing fat deposition. Moreover, GLP-1RAs have neuroprotective, anti-infectious, cardiovascular protective, and metabolic regulatory effects, exhibiting good application prospects. Growing attention has been paid to the relationship between GLP-1RAs and tumorigenesis, development and prognosis in patient with T2DM. Here, we reviewed the therapeutic effects and possible mechanisms of action of GLP-1RAs in the nervous, cardiovascular, and endocrine systems and their correlation with metabolism, tumours and other diseases.