New beta-alanine derivatives are orally available glucagon receptor antagonists

Synthesis and anti-diabetic activity of novel biphenylsulfonamides as glucagon receptor antagonists

Type 2 diabetes is characterized by chronic hyperglycemia. Insulin, a hormone secreted from pancreatic β-cells, decreases blood glucose levels, and glucagon, a hormone secreted from pancreatic α-cells, increases blood glucose levels by counterregulation of insulin through stimulation of hepatic glucose production. In diabetic patients, dysregulation of glucagon secretion contributes to hyperglycemia. Thus, inhibition of the glucagon receptor is one strategy for the treatment of hyperglycemia in type 2 diabetes. In this paper, we report a series of biphenylsulfonamide derivatives that were designed, synthesized, and then evaluated by cAMP and hepatic glucose production assays as glucagon receptor antagonists. Of these, compound 7aB-3 decreased glucagon-induced cAMP production and glucagon-induced glucose production in the in vitro assays. Glucagon challenge tests and glucose tolerance tests showed that compound 7aB-3 significantly inhibited glucagon-induced glucose increases and improved glucose tolerance. These results suggest that compound 7aB-3 has therapeutic potential for the treatment of type 2 diabetes.

Glucagon delivery - An overview of current and future devices

Glucagon is crucial in the treatment of Type 1 diabetes mellitus due to the prevalence of hypoglycemia in patients with this disorder. Hypoglycemia can be life-threatening, leading to loss of consciousness, and requiring emergency glucagon to reverse the effects. Emergency kits are difficult to use, requiring reconstitution of glucagon, which itself is not stable for lengthy periods. Approaches have aimed to improve stability which has allowed for use in pens or pumps. Glucagon can now also be delivered intranasally. This review discusses the history of glucagon, its current delivery methods as well as some modern approaches being introduced.

Structure-based discovery of potent and selective small-molecule inhibitors targeting signal transducer and activator of transcription 3 (STAT3)

STAT3 has been validated as an attractive anticancer target due to its important roles in cancer initiation and progression. However, discovery of potent and selective STAT3 small-molecule inhibitors with druglike properties is still challenging. In this study, two series of substituted 2-phenylquinolines and 2-arylimidazo[1,2-a]pyridines were designed through structure-based drug discovery approach by condensing the privileged structures of STX-119 and SH4-54. Our study has resulted in the discovery of a number of highly potent and selective STAT3 inhibitors, exemplified by compound 39 with the privileged structure of 2-phenylimidazo[1,2-a]pyridine, which selectively inhibits phosphorylation of STAT3 and suppresses subsequent signaling pathway. Moreover, 39 inhibits cell growth, migration and invasion of human triple negative breast cancer (TNBC) cells lines. Consistently, it achieves significant and dose-dependent tumor growth inhibition in both cell line-derived and patient-derived xenograft tumor models in mice. These results clearly indicate that 39 is a highly potent and selective STAT3 inhibitor.

Glucagon's Metabolic Action in Health and Disease

Discovered almost simultaneously with insulin, glucagon is a pleiotropic hormone with metabolic action that goes far beyond its classical role to increase blood glucose. Albeit best known for its ability to directly act on the liver to increase de novo glucose production and to inhibit glycogen breakdown, glucagon lowers body weight by decreasing food intake and by increasing metabolic rate. Glucagon further promotes lipolysis and lipid oxidation and has positive chronotropic and inotropic effects in the heart. Interestingly, recent decades have witnessed a remarkable renaissance of glucagon's biology with the acknowledgment that glucagon has pharmacological value beyond its classical use as rescue medication to treat severe hypoglycemia. In this article, we summarize the multifaceted nature of glucagon with a special focus on its hepatic action and discuss the pharmacological potential of either agonizing or antagonizing the glucagon receptor for health and disease. © 2021 American Physiological Society. Compr Physiol 11:1759-1783, 2021.

Glucagon and Glucagon-like Peptide-1 Receptors: Promising Therapeutic Targets for an Effective Management of Diabetes Mellitus

G-protein-coupled receptors (GPCRs) are membrane-bound proteins, which are responsible for the detection of extracellular stimuli and the origination of intracellular responses. Both glucagon and glucagon-like peptide-1 (GLP-1) receptors belong to G protein-coupled receptor (GPCR) superfamily. Along with insulin, glucagon and GLP-1 are critical hormones for maintaining normal serum glucose within the human body. Glucagon generally plays its role in the liver through cyclic adenosine monophosphate (cAMP), where it compensates for the action of insulin. GLP-1 is secreted by the L-cells of the small intestine to stimulate insulin secretion and inhibit glucagon action. Despite extensive research efforts and the multiple approaches adopted, the glycemic control in the case of type-2 diabetes mellitus remains a major challenge. Therefore, a deep understanding of the structure-function relationship of these receptors will have great implications for future therapies in order to maintain a normal glucose level for an extended period of time. The antagonists of glucagon receptors that can effectively block the hepatic glucose production, as a result of glucagon action, are highly desirable for the tuning of the hyperglycemic state in type 2 diabetes mellitus. In the same manner, GLP-1R agonists act as important treatment modalities, thanks to their multiple anti-diabetic actions to attain normal glucose levels. In this review article, the structural diversity of glucagon and GLP-1 receptors along with their signaling pathways, site-directed mutations and significance in drug discovery against type-2 diabetes are illustrated. Moreover, the promising non-peptide antagonists of glucagon receptor and agonists of GLP-1 receptor, for the management of diabetes are presented with elaboration on the structure-activity relationship (SAR).

Structural Basis for Allosteric Modulation of Class B G Protein-Coupled Receptors

Recent advances in our understanding of the structure and function of class B G protein-coupled receptors (GPCRs) provide multiple opportunities for targeted development of allosteric modulators. Given the pleiotropic signaling patterns emanating from these receptors in response to a variety of natural agonist ligands, modulators have the potential to sculpt the responses to meet distinct needs of different groups of patients. In this review, we provide insights into how this family of GPCRs differs from the rest of the superfamily, how orthosteric agonists bind and activate these receptors, the potential for allosteric modulators to interact with various regions of these targets, and the allosteric influence of endogenous proteins on the pharmacology of these receptors, all of which are important considerations when developing new therapies.

Problem or solution: The strange story of glucagon

Globally, 13% of the world's adult population is obese, and more than 400 million people suffer from diabetes. These conditions are both associated with significant morbidity, mortality and financial cost. Therefore, finding new pharmacological treatments is an imperative. Relative hyperglucagonaemia is seen in all types of diabetes, and has been implicated in its pathogenesis. Consequently, clinical trials are underway using drugs which block glucagon activity to treat type 2 diabetes. Conversely, exogenous glucagon can increase energy expenditure. Therefore, researchers are designing peptides that combine activation of the glucagon receptor with further incretin properties, which will treat obesity while mitigating the hyperglycaemic effects of glucagon. This review will discuss these conflicting physiological properties of glucagon, and the attempts to harness these effects pharmacologically.

Extending the Structural View of Class B GPCRs

The secretin-like class B family of G protein-coupled receptors (GPCRs) are key players in hormonal homeostasis. Recent structures of various receptors in complex with a variety of orthosteric and allosteric ligands provide fundamental new insights into the function and mechanism of class B GPCRs, including: (i) ligand-induced changes in the relative orientation of the extracellular and transmembrane receptor domains; (ii) intramolecular interaction networks that stabilize conformational changes to accommodate intracellular G protein binding; and (iii) allosteric modulation of receptor activation. This review provides a comprehensive analysis of the structural, biochemical, and pharmacological data on class B GPCRs for understanding ligand-receptor interaction and modulation mechanisms and assessing the potential implications for drug discovery for the secretin-like GPCR family.

Landmark studies on the glucagon subfamily of GPCRs: from small molecule modulators to a crystal structure

The glucagon subfamily of class B G protein-coupled receptors (GPCRs) has been proposed to be a crucial drug target for the tretmaent of type 2 diabetes. The challenges associated with determining the crystal structures of class B GPCRs relate to their large amino termini and the lack of available small molecule ligands to stabilize the receptor proteins. Following our discovery of non-peptidic agonists for glucagon-like peptide-1 receptor (GLP-1R) that have therapeutic effects, we initiated collaborative efforts in structural biology and recently solved the three-dimensional (3D) structure of the human glucagon receptor (GCGR) 7-transmembrane domain, providing in-depth information about the underlying signaling mechanisms. In this review, some key milestones in this endeavor are highlighted, including discoveries of small molecule ligands, their roles in receptor crystallization, conformational changes in transmembrane domains (TMDs) upon activation and structure-activity relationship analyses.

A novel series of indazole-/indole-based glucagon receptor antagonists

A novel, potent series of glucagon receptor antagonists (GRAs) was discovered. These indazole- and indole-based compounds were designed on an earlier pyrazole-based GRA lead MK-0893. Structure-activity relationship (SAR) studies were focused on the C3 and C6 positions of the indazole core, as well as the benzylic position on the N-1 of indazole. Multiple potent GRAs were identified with excellent in vitro profiles and good pharmacokinetics in rat. Among them, GRA 16d was found to be orally active in blunting glucagon induced glucose excursion in an acute glucagon challenge model in glucagon receptor humanized (hGCGR) mice at 1, 3 and 10mg/kg (mpk), and significantly lowered acute glucose levels in hGCGR ob/ob mice at 3 mpk dose.

Conformational states of the full-length glucagon receptor

Class B G protein-coupled receptors are composed of an extracellular domain (ECD) and a seven-transmembrane (7TM) domain, and their signalling is regulated by peptide hormones. Using a hybrid structural biology approach together with the ECD and 7TM domain crystal structures of the glucagon receptor (GCGR), we examine the relationship between full-length receptor conformation and peptide ligand binding. Molecular dynamics (MD) and disulfide crosslinking studies suggest that apo-GCGR can adopt both an open and closed conformation associated with extensive contacts between the ECD and 7TM domain. The electron microscopy (EM) map of the full-length GCGR shows how a monoclonal antibody stabilizes the ECD and 7TM domain in an elongated conformation. Hydrogen/deuterium exchange (HDX) studies and MD simulations indicate that an open conformation is also stabilized by peptide ligand binding. The combined studies reveal the open/closed states of GCGR and suggest that glucagon binds to GCGR by a conformational selection mechanism.

Interaction of Glucagon G-Protein Coupled Receptor with Known Natural Antidiabetic Compounds: Multiscoring In Silico Approach

Glucagon receptor (GCGR) is a secretin-like (class B) family of G-protein coupled receptors (GPCRs) in humans that plays an important role in elevating the glucose concentration in blood and has thus become one of the promising therapeutic targets for treatment of type 2 diabetes mellitus. GCGR based inhibitors for the treatment of type 2 diabetes are either glucagon neutralizers or small molecular antagonists. Management of diabetes without any side effects is still a challenge to the medical system, and the search for a new and effective natural GCGR antagonist is an important area for the treatment of type 2 diabetes. In the present study, a number of natural compounds containing antidiabetic properties were selected from the literature and their binding potential against GCGR was determined using molecular docking and other in silico approaches. Among all selected natural compounds, curcumin was found to be the most effective compound against GCGR followed by amorfrutin 1 and 4-hydroxyderricin. These compounds were rescored to confirm the accuracy of binding using another scoring function (x-score). The final conclusions were drawn based on the results obtained from the GOLD and x-score. Further experiments were conducted to identify the atomic level interactions of selected compounds with GCGR.

Recent Progress in the Use of Glucagon and Glucagon Receptor Antago-nists in the Treatment of Diabetes Mellitus

Glucagon is an important pancreatic hormone, released into blood circulation by alpha cells of the islet of Langerhans. Glucagon induces gluconeogenesis and glycogenolysis in hepatocytes, leading to an increase in hepatic glucose production and subsequently hyperglycemia in susceptible individuals. Hyperglucagonemia is a constant feature in patients with T2DM. A number of bioactive agents that can block glucagon receptor have been identified. These glucagon receptor antagonists can reduce the hyperglycemia associated with exogenous glucagon administration in normal as well as diabetic subjects. Glucagon receptor antagonists include isoserine and beta-alanine derivatives, bicyclic 19-residue peptide BI-32169, Des-His1-[Glu9] glucagon amide and related compounds, 5-hydroxyalkyl-4-phenylpyridines, N-[3-cano-6- (1,1 dimethylpropyl)-4,5,6,7-tetrahydro-1-benzothien-2-yl]-2-ethylbutamide, Skyrin and NNC 250926. The absorption, dosage, catabolism, excretion and medicinal chemistry of these agents are the subject of this review. It emphasizes the role of glucagon in glucose homeostasis and how it could be applied as a novel tool for the management of diabetes mellitus by blocking its receptors with either monoclonal antibodies, peptide and non-peptide antagonists or gene knockout techniques.

Computational identification of novel natural inhibitors of glucagon receptor for checking type II diabetes mellitus

BACKGROUND

Interaction of the small peptide hormone glucagon with glucagon receptor (GCGR) stimulates the release of glucose from the hepatic cells during fasting; hence GCGR performs a significant function in glucose homeostasis. Inhibiting the interaction between glucagon and its receptor has been reported to control hepatic glucose overproduction and thus GCGR has evolved as an attractive therapeutic target for the treatment of type II diabetes mellitus.

RESULTS

In the present study, a large library of natural compounds was screened against 7 transmembrane domain of GCGR to identify novel therapeutic molecules that can inhibit the binding of glucagon with GCGR. Molecular dynamics simulations were performed to study the dynamic behaviour of the docked complexes and the molecular interactions between the screened compounds and the ligand binding residues of GCGR were analysed in detail. The top scoring compounds were also compared with already documented GCGR inhibitors- MK-0893 and LY2409021 for their binding affinity and other ADME properties. Finally, we have reported two natural drug like compounds PIB and CAA which showed good binding affinity for GCGR and are potent inhibitor of its functional activity.

CONCLUSION

This study contributes evidence for application of these compounds as prospective small ligand molecules against type II diabetes. Novel natural drug like inhibitors against the 7 transmembrane domain of GCGR have been identified which showed high binding affinity and potent inhibition of GCGR.

Effects of short-term chemical ablation of glucagon signalling by peptide-based glucagon receptor antagonists on insulin secretion and glucose homeostasis in mice

Glucagon is a hormone with important effects on blood glucose regulation. This study has utilized the stable glucagon receptor antagonists, desHis1Pro4Glu9-glucagon and desHis1Pro4Glu9(Lys12PAL)-glucagon, to evaluate the effects of sustained inhibition of glucagon receptor signalling in normal mice. Twice-daily injection of either analogue for 10 days had no effect on food intake, body weight and non-fasting plasma glucose concentrations. However, insulin levels were significantly raised (p<0.05 to p<0.01) from day 3 onwards in desHis1Pro4Glu9-glucagon mice. After 10 days, glucose tolerance was improved (p<0.05) in desHis1Pro4Glu9-glucagon treated mice. Glucose-mediated insulin secretion and circulating cholesterol levels were significantly (p<0.05 to p<0.01) decreased in both treatment groups. Importantly, the effects of glucagon to increase blood glucose and insulin concentrations were still annulled on day 10. Insulin sensitivity was almost identical in all groups of mice at the end of the study. In addition, no changes in pancreatic insulin and glucagon content or islet morphology were observed in either treatment group. Finally, acute injection of desHis1Pro4Glu9-glucagon followed by a 24-h fast in treatment naïve mice was not associated with any hypoglycaemic episodes. These data indicate that peptide-based glucagon receptor antagonists represent safe and effective treatment options for type 2 diabetes.

Characterisation of structurally modified analogues of glucagon as potential glucagon receptor antagonists

Acute in vitro and in vivo biological activities of four novel structural analogues of glucagon were tested. desHis(1)Pro(4)-glucagon, desHis(1)Pro(4)Glu(9)-glucagon, desHis(1)Pro(4)Glu(9)Lys(12)FA-glucagon and desHis(1)Pro(4)Glu(9)Lys(30)FA-glucagon were stable to DPP-4 degradation and dose-dependently inhibited glucagon-mediated cAMP production (p<0.05 to p<0.001). None stimulated insulin secretion in vitro above basal levels, but all inhibited glucagon-induced insulin secretion (p<0.01 to p<0.001). In normal mice all analogues antagonised acute glucagon-mediated elevations of blood glucose (p<0.05 to p<0.001) and blocked corresponding insulinotropic responses. In high-fat fed mice, glucagon-induced increases in plasma insulin (p<0.05 to p<0.001) and glucagon-induced hyperglycaemia were blocked (p<0.05 to p<0.01) by three analogues. In obese diabetic (ob/ob) mice only desHis(1)Pro(4)Glu(9)-glucagon effectively (p<0.05 to p<0.01) inhibited both glucagon-mediated glycaemic and insulinotropic responses. desHis(1)Pro(4)-glucagon and desHis(1)Pro(4)Glu(9)-glucagon were biologically ineffective when administered 8h prior to glucagon, whereas desHis(1)Pro(4)Glu(9)Lys(12)FA-glucagon retained efficacy (p<0.01) for up to 24h. Such peptide-derived glucagon receptor antagonists have potential for type 2 diabetes therapy.

Human monoclonal antibodies against glucagon receptor improve glucose homeostasis by suppression of hepatic glucose output in diet-induced obese mice

Aim

Glucagon is an essential regulator of hepatic glucose production (HGP), which provides an alternative therapeutic target for managing type 2 diabetes with glucagon antagonists. We studied the effect of a novel human monoclonal antibody against glucagon receptor (GCGR), NPB112, on glucose homeostasis in diet-induced obese (DIO) mice.

Methods

The glucose-lowering efficacy and safety of NPB112 were investigated in DIO mice with human GCGR for 11 weeks, and a hyperinsulinemic-euglycemic clamp study was conducted to measure HGP.

Results

Single intraperitoneal injection of NPB112 with 5 mg/kg effectively decreased blood glucose levels in DIO mice for 5 days. A significant reduction in blood glucose was observed in DIO mice treated with NPB112 at a dose ≥5 mg/kg for 6 weeks, and its glucose-lowering effect was dose-dependent. Long-term administration of NPB112 also caused a mild 29% elevation in glucagon level, which was returned to the normal range after discontinuation of treatment. The clamp study showed that DIO mice injected with NPB112 at 5 mg/kg were more insulin sensitive than control mice, indicating amelioration of insulin resistance by treatment with NPB112. DIO mice treated with NPB112 showed a significant improvement in the ability of insulin to suppress HGP, showing a 33% suppression (from 8.3 mg/kg/min to 5.6 mg/kg/min) compared to the 2% suppression (from 9.8 mg/kg/min to 9.6 mg/kg/min) in control mice. In addition, no hypoglycemia or adverse effect was observed during the treatment.

Conclusions

A novel human monoclonal GCGR antibody, NPB112, effectively lowered the glucose level in diabetic animal models with mild and reversible hyperglucagonemia. Suppression of excess HGP with NPB112 may be a promising therapeutic modality for the treatment of type 2 diabetes.

Discovery of a novel glucagon receptor antagonist N-[(4-{(1S)-1-[3-(3, 5-dichlorophenyl)-5-(6-methoxynaphthalen-2-yl)-1H-pyrazol-1-yl]ethyl}phenyl)carbonyl]-β-alanine (MK-0893) for the treatment of type II diabetes

A potent, selective glucagon receptor antagonist 9m, N-[(4-{(1S)-1-[3-(3,5-dichlorophenyl)-5-(6-methoxynaphthalen-2-yl)-1H-pyrazol-1-yl]ethyl}phenyl)carbonyl]-β-alanine, was discovered by optimization of a previously identified lead. Compound 9m is a reversible and competitive antagonist with high binding affinity (IC(50) of 6.6 nM) and functional cAMP activity (IC(50) of 15.7 nM). It is selective for glucagon receptor relative to other family B GPCRs, showing IC(50) values of 1020 nM for GIPR, 9200 nM for PAC1, and >10000 nM for GLP-1R, VPAC1, and VPAC2. Compound 9m blunted glucagon-induced glucose elevation in hGCGR mice and rhesus monkeys. It also lowered ambient glucose levels in both acute and chronic mouse models: in hGCGR ob/ob mice it reduced glucose (AUC 0-6 h) by 32% and 39% at 3 and 10 mpk single doses, respectively. In hGCGR mice on a high fat diet, compound 9m at 3, and 10 mpk po in feed lowered blood glucose levels by 89% and 94% at day 10, respectively, relative to the difference between the vehicle control and lean hGCGR mice. On the basis of its favorable biological and DMPK properties, compound 9m (MK-0893) was selected for further preclinical and clinical evaluations.

A genome-wide siRNA screen to identify modulators of insulin sensitivity and gluconeogenesis

Background

Hepatic insulin resistance impairs insulin’s ability to suppress hepatic glucose production (HGP) and contributes to the development of type 2 diabetes (T2D). Although the interests to discover novel genes that modulate insulin sensitivity and HGP are high, it remains challenging to have a human cell based system to identify novel genes.

Methodology/Principal Findings

To identify genes that modulate hepatic insulin signaling and HGP, we generated a human cell line stably expressing beta-lactamase under the control of the human glucose-6-phosphatase (G6PC) promoter (AH-G6PC cells). Both beta-lactamase activity and endogenous G6PC mRNA were increased in AH-G6PC cells by a combination of dexamethasone and pCPT-cAMP, and reduced by insulin. A 4-gene High-Throughput-Genomics assay was developed to concomitantly measure G6PC and pyruvate-dehydrogenase-kinase-4 (PDK4) mRNA levels. Using this assay, we screened an siRNA library containing pooled siRNA targeting 6650 druggable genes and identified 614 hits that lowered G6PC expression without increasing PDK4 mRNA levels. Pathway analysis indicated that siRNA-mediated knockdown (KD) of genes known to positively or negatively affect insulin signaling increased or decreased G6PC mRNA expression, respectively, thus validating our screening platform. A subset of 270 primary screen hits was selected and 149 hits were confirmed by target gene KD by pooled siRNA and 7 single siRNA for each gene to reduce G6PC expression in 4-gene HTG assay. Subsequently, pooled siRNA KD of 113 genes decreased PEPCK and/or PGC1alpha mRNA expression thereby demonstrating their role in regulating key gluconeogenic genes in addition to G6PC. Last, KD of 61 of the above 113 genes potentiated insulin-stimulated Akt phosphorylation, suggesting that they suppress gluconeogenic gene by enhancing insulin signaling.

Conclusions/Significance

These results support the proposition that the proteins encoded by the genes identified in our cell-based druggable genome siRNA screen hold the potential to serve as novel pharmacological targets for the treatment of T2D.

Small molecule drug discovery at the glucagon-like peptide-1 receptor

The therapeutic success of peptide glucagon-like peptide-1 (GLP-1) receptor agonists for the treatment of type 2 diabetes mellitus has inspired discovery efforts aimed at developing orally available small molecule GLP-1 receptor agonists. Although the GLP-1 receptor is a member of the structurally complex class B1 family of GPCRs, in recent years, a diverse array of orthosteric and allosteric nonpeptide ligands has been reported. These compounds include antagonists, agonists, and positive allosteric modulators with intrinsic efficacy. In this paper, a comprehensive review of currently disclosed small molecule GLP-1 receptor ligands is presented. In addition, examples of "ligand bias" and "probe dependency" for the GLP-1 receptor are discussed; these emerging concepts may influence further optimization of known molecules or persuade designs of expanded screening strategies to identify novel chemical starting points for GLP-1 receptor drug discovery.

The alpha-cell as target for type 2 diabetes therapy

Glucagon is the main secretory product of the pancreatic alpha-cells. The main function of this peptide hormone is to provide sustained glucose supply to the brain and other vital organs during fasting conditions. This is exerted by stimulation of hepatic glucose production via specific G protein-coupled receptors in the hepatocytes. Type 2 diabetic patients are characterized by elevated glucagon levels contributing decisively to hyperglycemia in these patients. Accumulating evidence demonstrates that targeting the pancreatic alpha-cell and its main secretory product glucagon is a possible treatment for type 2 diabetes. Several lines of preclinical evidence have paved the way for the development of drugs, which suppress glucagon secretion or antagonize the glucagon receptor. In this review, the physiological actions of glucagon and the role of glucagon in type 2 diabetic pathophysiology are outlined. Furthermore, potential advantages and limitations of antagonizing the glucagon receptor or suppressing glucagon secretion in the treatment of type 2 diabetes are discussed with a focus on already marketed drugs and drugs in clinical development. It is concluded that the development of novel glucagon receptor antagonists are confronted with several safety issues. At present, available pharmacological agents based on the glucose-dependent glucagonostatic effects of GLP-1 represent the most favorable way to apply constraints to the alpha-cell in type 2 diabetes.

Glucagon antagonism as a potential therapeutic target in type 2 diabetes

Glucagon is a hormone secreted from the alpha cells of the pancreatic islets. Through its effect on hepatic glucose production (HGP), glucagon plays a central role in the regulation of glucose homeostasis. In patients with type 2 diabetes mellitus (T2DM), abnormal regulation of glucagon secretion has been implicated in the development of fasting and postprandial hyperglycaemia. Therefore, new therapeutic agents based on antagonizing glucagon action, and hence blockade of glucagon-induced HGP, could be effective in lowering both fasting and postprandial hyperglycaemia in patients with T2DM. This review focuses on the mechanism of action, safety and efficacy of glucagon antagonists in the treatment of T2DM and discusses the challenges associated with this new potential antidiabetic treatment modality.

Structure-based discovery of allosteric modulators of two related class B G-protein-coupled receptors

Despite the availability of X-ray crystal structure data for several members of the G-protein-coupled receptor (GPCR) superfamily, structure-based discovery of GPCR ligands has been exclusively restricted to class A (rhodopsin-like) receptors. Herein we report the identification, by a docking-based virtual screening approach, of noncompetitive ligands for two related class B (secretin-like) GPCRs: the glucagon receptor (GLR) and the glucagon-like peptide 1 receptor (GLP-1R). Starting from a knowledge-based three-dimensional model of the GLR, a database of 1.9 million commercially available drug-like compounds was screened for chemical similarity to existing GLR noncompetitive antagonists and docked to the transmembrane cavity of the GLR; 23 compounds were then selected based on protein-ligand interaction fingerprints, and were then purchased and evaluated for in vitro binding to GLR and modulation of glucagon-induced cAMP release. Two of the 23 compounds inhibited the effect of glucagon in a dose-dependent manner, with one inhibitor exhibiting the same potency as L-168 049, a reference noncompetitive GLR antagonist, in a whole-cell-based functional assay. Interestingly, one virtual hit that was inactive at the GLR was shown to bind to GLP-1R and potentiate the response to the endogenous GLP-1 ligand.

Chronic treatment with a glucagon receptor antagonist lowers glucose and moderately raises circulating glucagon and glucagon-like peptide 1 without severe alpha cell hypertrophy in diet-induced obese mice

AIMS/HYPOTHESIS

Antagonism of the glucagon receptor (GCGR) represents a potential approach for treating diabetes. Cpd-A, a potent and selective GCGR antagonist (GRA) was studied in preclinical models to assess its effects on alpha cells.

METHODS

Studies were conducted with Cpd-A to examine the effects on glucose-lowering efficacy, its effects in combination with a dipeptidyl peptidase-4 (DPP-4) inhibitor, and the extent and reversibility of alpha cell hypertrophy associated with GCGR antagonism in mouse models.

RESULTS

Chronic treatment with Cpd-A resulted in effective and sustained glucose lowering in mouse models in which endogenous murine Gcgr was replaced with human GCGR (hGCGR). Treatment with Cpd-A also led to stable, moderate elevations in both glucagon and glucagon-like peptide 1 (GLP-1) levels, which were completely reversible and not associated with a hyperglycaemic overshoot following termination of treatment. When combined with a DPP-4 inhibitor, Cpd-A led to additional improvement of glycaemic control correlated with elevated active GLP-1 levels after glucose challenge. In contrast to Gcgr-knockout mice in which alpha cell hypertrophy was detected, chronic treatment with Cpd-A in obese hGCGR mice did not result in gross morphological changes in pancreatic tissue.

CONCLUSIONS/INTERPRETATION

A GRA lowered glucose effectively in diabetic models without significant alpha cell hypertrophy during or following chronic treatment. Treatment with a GRA may represent an effective approach for glycaemic control in patients with type 2 diabetes, which could be further enhanced when combined with DPP-4 inhibitors.

Discovery of novel, potent, selective, and orally active human glucagon receptor antagonists containing a pyrazole core

A novel class of 1,3,5-pyrazoles has been discovered as potent human glucagon receptor antagonists. Notably, compound 26 is orally bioavailable in several preclinical species and shows selectivity towards cardiac ion channels, other family B receptors such hGIP and hGLP1, and a large panel of enzymes and additional receptors. When dosed orally, compound 26 is efficacious in suppressing glucagon induced plasma glucose excursion in rhesus monkey and transgenic murine pharmacodynamic models at 1 and 10 mpk, respectively.

Structure-activity relationships of antitubercular nitroimidazoles. 2. Determinants of aerobic activity and quantitative structure-activity relationships

The (S)-2-nitro-6-substituted 6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazines have been extensively explored for their potential use as new antituberculars based on their excellent bactericidal properties on aerobic whole cells of Mycobacterium tuberculosis. An oxygen atom at the 2-position of the imidazole ring is required for aerobic activity. Here, we show that substitution of this oxygen by either nitrogen or sulfur yielded equipotent analogues. Acylating the amino series, oxidizing the thioether, or replacing the ether oxygen with carbon significantly reduced the potency of the compounds. Replacement of the benzylic oxygen at the 6-position by nitrogen slightly improved potency and facilitated exploration of the SAR in the more soluble 6-amino series. Significant improvements in potency were realized by extending the linker region between the 6-(S) position and the terminal hydrophobic aromatic substituent. A simple four-feature QSAR model was derived to rationalize MIC results in this series of bicyclic nitroimidazoles.

Conjugates of desferrioxamine B (DFOB) with derivatives of adamantane or with orally available chelators as potential agents for treating iron overload

Desferrioxamine B (DFOB) conjugates with adamantane-1-carboxylic acid, 3-hydroxyadamantane-1-carboxylic acid, 3,5-dimethyladamantane-1-carboxylic acid, adamantane-1-acetic acid, 4-methylphenoxyacetic acid, 3-hydroxy-2-methyl-4-oxo-1-pyridineacetic acid (N-acetic acid derivative of deferiprone), or 4-[3,5-bis(2-hydroxyphenyl)-1,2,4-triazol-1-yl]benzoic acid (deferasirox) were prepared and the integrity of Fe(III) binding of the compounds was established from electrospray ionization mass spectrometry and RP-HPLC measurements. The extent of intracellular (59)Fe mobilized by the DFOB-3,5-dimethyladamantane-1-carboxylic acid adduct was 3-fold greater than DFOB alone, and the IC(50) value of this adduct was 6- or 15-fold greater than DFOB in two different cell types. The relationship between logP and (59)Fe mobilization for the DFOB conjugates showed that maximal mobilization of intracellular (59)Fe occurred at a logP value approximately 2.3. This parameter, rather than the affinity for Fe(III), appears to influence the extent of intracellular (59)Fe mobilization. The low toxicity-high Fe mobilization efficacy of selected adamantane-based DFOB conjugates underscores the potential of these compounds to treat iron overload disease in patients with transfusional-dependent disorders such as beta-thalassemia.

Benefits and limitations of reducing glucagon action for the treatment of type 2 diabetes

Glucagon is secreted from the alpha-cells of the pancreatic islets and regulates glucose homeostasis through modulation of hepatic glucose production. As elevated glucagon levels contribute to the pathophysiology of hyperglycemia in subjects with type 2 diabetes, reduction of glucagon receptor gene (Gcgr) activity represents a potential target for the treatment of T2DM. Herein, we review current concepts of glucagon action in hepatic and extrahepatic tissues and evaluate the therapeutic potential, mechanisms of action, and safety of reducing Gcgr signaling for the treatment of T2DM.

Discovery of potent, orally active benzimidazole glucagon receptor antagonists

The discovery and optimization of potent and selective aminobenzimidazole glucagon receptor antagonists are described. One compound possessing moderate pharmacokinetic properties in multiple preclinical species was orally efficacious at inhibiting glucagon-mediated glucose excursion in transgenic mice expressing the human glucagon receptor, and in rhesus monkeys. The compound also significantly lowered glucose levels in a murine model of diabetes.

Bullwhip neurons in the retina regulate the size and shape of the eye

Bullwhip and mini-bullwhip cells are unconventional types of retinal neurons that utilize the neuropeptides glucagon, glucagon-like peptide 1 (GLP1) and substance P. These cells have been implicated in regulating the proliferation of neural progenitors in the circumferential marginal zone (CMZ) of the chicken retina. The purpose of this study was to investigate the roles of the bullwhip cells in regulating ocular size and shape. We found that intravitreal delivery of colchicine at postnatal day 7 destroys the vast majority (approximately 98%) of the bullwhip and mini-bullwhip cells and their peptidergic terminals that are concentrated in the CMZ near the equator of the eye. Interestingly, colchicine-treatment resulted in excessive ocular growth that involved the expansion of equatorial diameter, but not axial length. Intraocular injections of glucagon completely prevented the equatorial expansion that occurs with colchicine-treatment. In eyes with undamaged retinas, exogenous glucagon suppressed equatorial eye growth, whereas glucagon receptor antagonists caused excessive equatorial growth. Furthermore, visual stimuli that increase or decrease rates of ocular growth caused a down- or up-regulation, respectively, of the immediate early gene Egr1 in the bullwhip cells; indicating that the activity of the bullwhip cells is regulated by growth-guiding visual cues. We found that the glucagon receptor was expressed by cells in the fibrous and cartilaginous sclera in equatorial regions of the eye. Taken together, these findings suggest that glucagon peptide released from the terminals of the bullwhip and mini-bullwhip cells regulates the growth of the equatorial sclera in a vision-dependent manner. Although the bullwhip and mini-bullwhip cells are not abundant, less than 1000 cells per retina, their influence on the development of the eye is substantial and includes vision-guided ocular growth.