A 4-week study assessing the pharmacokinetics, pharmacodynamics, safety, and tolerability of the glucagon receptor antagonist PF-06291874 administered as monotherapy in subjects with type 2 diabetes mellitus

Hepatic PKA Mediates Liver and Pancreatic α-Cell Cross Talk

Glucagon stimulates hepatic glucose production, in part by promoting the uptake and catabolism of amino acids. Inhibition of the liver glucagon receptor (GCGR) results in elevated plasma amino acids, which triggers the proliferation of pancreatic α-cells, forming a liver-α-cell loop. This study aims to delineate hepatic signaling molecules downstream of GCGR that mediate the liver-α-cell loop. We knocked down liver GCGR, its G-coupled protein GNAS, and two GNAS downstream effectors, PKA and EPAC2 (RAPGEF4). Mice with GCGR, GNAS, and PKA knockdown had similar suppression of hepatic amino acid catabolism genes, hyperaminoacidemia, and α-cell hyperplasia, but those with EPAC2 knockdown did not. We then demonstrated that activating liver PKA was sufficient to reverse hyperaminoacidemia and α-cell hyperplasia caused by GCGR blockade. These results suggest that liver GCGR signals through PKA to control amino acid metabolism and that hepatic PKA plays a critical role in the liver-α-cell loop.

ARTICLE HIGHLIGHTS

A liver-α-cell loop exists, where inhibition of the liver glucagon receptor (GCGR) causes hyperaminoacidemia and pancreatic α-cell hyperplasia, but the GCGR downstream factors responsible for these effects are not clear. We silenced GCGR, its G-coupled protein GNAS, and two GNAS downstream effectors, PKA and EPAC2, to assess their effects on the liver-α-cell loop. Inhibition of the GCGR-GNAS-PKA pathway suppresses amino acid catabolism and causes α-cell hyperplasia, whereas PKA activation promotes amino acid catabolism and reduces alpha cell mass even when GCGR is blocked. Our study establishes hepatic PKA as the critical regulator of the liver-α-cell loop.

Non-canonical hepatic androgen receptor mediates glucagon sensitivity in female mice through the PGC1α/ERRα/mitochondria axis

Glucagon has recently been found to modulate liver fat content, in addition to its role in regulating gluconeogenesis. However, the precise mechanisms by which glucagon signaling synchronizes glucose and lipid metabolism in the liver remain poorly understood. By employing chemical and genetic approaches, we demonstrate that inhibiting the androgen receptor (AR) impairs the ability of glucagon to stimulate gluconeogenesis and lipid catabolism in primary hepatocytes and female mice. Notably, AR expression in the liver of female mice is up to three times higher than that in their male littermates, accounting for the more pronounced response to glucagon in females. Mechanistically, hepatic AR promotes energy metabolism and enhances lipid breakdown for liver glucose production in response to glucagon treatment through the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α)/estrogen-related receptor alpha (ERRα)-mitochondria axis. Overall, our findings highlight the crucial role of hepatic AR in mediating glucagon signaling and the sexual dimorphism in hepatic glucagon sensitivity.

Glucagon-based therapy for people with diabetes and obesity: What is the sweet spot?

People with obesity and type 2 diabetes have a high prevalence of metabolic-associated steatotic liver disease, hyperlipidemia and cardiovascular disease. Glucagon increases hepatic glucose production; it also decreases hepatic fat accumulation, improves lipidemia and increases energy expenditure. Pharmaceutical strategies to antagonize the glucagon receptor improve glycemic outcomes in people with diabetes and obesity, but they increase hepatic steatosis and worsen dyslipidemia. Co-agonism of the glucagon and glucagon-like peptide-1 (GLP-1) receptors has emerged as a promising strategy to improve glycemia in people with diabetes and obesity. Addition of glucagon receptor agonism enhances weight loss, reduces liver fat and ameliorates dyslipidemia. Prior to clinical use, however, further studies are needed to investigate the safety and efficacy of glucagon and GLP-1 receptor co-agonists in people with diabetes and obesity and related conditions, with specific concerns regarding a higher prevalence of gastrointestinal side effects, loss of muscle mass and increases in heart rate. Furthermore, co-agonists with differing ratios of glucagon:GLP-1 receptor activity vary in their clinical effect; the optimum balance is yet to be identified.

The past, present, and future physiology and pharmacology of glucagon

The evolution of glucagon has seen the transition from an impurity in the preparation of insulin to the development of glucagon receptor agonists for use in type 1 diabetes. In type 2 diabetes, glucagon receptor antagonists have been explored to reduce glycemia thought to be induced by hyperglucagonemia. However, the catabolic actions of glucagon are currently being leveraged to target the rise in obesity that paralleled that of diabetes, bringing the pharmacology of glucagon full circle. During this evolution, the physiological importance of glucagon advanced beyond the control of hepatic glucose production, incorporating critical roles for glucagon to regulate both lipid and amino acid metabolism. Thus, it is unsurprising that the study of glucagon has left several paradoxes that make it difficult to distill this hormone down to a simplified action. Here, we describe the history of glucagon from the past to the present and suggest some direction to the future of this field.

Regulation of Hepatic Lipid and Glucose Metabolism by INSP3R1

With the rising epidemics of obesity and nonalcoholic fatty liver disease (NAFLD) and its downstream consequences including steatohepatitis, cirrhosis, and type 2 diabetes in the U.S. and worldwide, new therapeutic approaches are urgently needed to treat these devastating conditions. Glucagon, known for a century to be a glucose-raising hormone and clearly demonstrated to contribute to fasting and postprandial hyperglycemia in both type 1 and type 2 diabetes, represents an unlikely target to improve health in those with metabolic syndrome. However, recent work from our group and others' identifies an unexpected role for glucagon as a potential means of treating NAFLD, improving insulin sensitivity, and improving the lipid profile. We propose a unifying, calcium-dependent mechanism for glucagon's effects both to stimulate hepatic gluconeogenesis and to enhance hepatic mitochondrial oxidation: signaling through the inositol 1,4,5-trisphosphate receptor type 1 (INSP3R1), glucagon activates phospholipase C (PKC)/protein kinase A (PKA) signaling to enhance adipose triglyceride lipase (ATGL)-dependent intrahepatic lipolysis and, in turn, increase cytosolic gluconeogenesis by allosteric activation of pyruvate carboxylase. Simultaneously in the mitochondria, calcium transferred through mitochondria-associated membranes activates several dehydrogenases in the tricarboxylic acid cycle, correlated with an increase in mitochondrial energy expenditure and reduction in ectopic lipid. This model suggests that short-term, cyclic treatment with glucagon or other INSP3R1 antagonists could hold promise as a means to reset lipid homeostasis in patients with NAFLD.

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'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-based therapy: Past, present and future

Diabesity and its related cardio-hepato-renal complications are of absolute concern globally. Last decade has witnessed a growing interest in the scientific community in investigating novel pharmaco-therapies employing the pancreatic hormone, glucagon. Canonically, this polypeptide hormone is known for its use in rescue treatment for hypoglycaemic shocks owing to its involvement in the counter-regulatory feedback mechanism. However, substantial studies in the recent past elucidated the pleiotropic effects of glucagon in diabesity and related complications like non-alcoholic steatohepatitis (NASH) and non-alcoholic fatty liver disease (NAFLD). Thus, the dual nature of this peptide has sparked the search for drugs that can modify glucagon signalling to combat hypoglycaemia or diabesity. Thus far, researchers have explored various pharmacological approaches to utilise this peptide in imminent modern therapies. The research endeavours in this segment led to explorations of stable glucagon formulations/analogues, glucagon receptor antagonism, glucagon receptor agonism, and incretin poly-agonism as new strategies for the management of hypoglycaemia or diabesity. This 'three-dimensional' research on glucagon resulted in the discovery of various drug candidates that proficiently modify glucagon signalling. Currently, several emerging glucagon-based therapies are under pre-clinical and clinical development. We sought to summarise the recent progress to comprehend glucagon-mediated pleiotropic effects, provide an overview of drug candidates currently being developed and future perspectives in this research domain.

Antagonistic Glucagon Receptor Antibody Promotes α-Cell Proliferation and Increases β-Cell Mass in Diabetic Mice

Under extreme conditions or by genetic modification, pancreatic α-cells can regenerate and be converted into β-cells. This regeneration holds substantial promise for cell replacement therapy in diabetic patients. The discovery of clinical therapeutic strategies to promote β-cell regeneration is crucial for translating these findings into clinical applications. In this study, we reported that treatment with REMD 2.59, a human glucagon receptor (GCGR) monoclonal antibody (mAb), lowered blood glucose without inducing hypoglycemia in normoglycemic, streptozotocin-induced type 1 diabetic (T1D) and non-obesity diabetic mice. Moreover, GCGR mAb treatment increased the plasma glucagon and active glucagon-like peptide-1 levels, induced pancreatic ductal ontogenic α-cell neogenesis, and promoted α-cell proliferation. Strikingly, the treatment also increased the β-cell mass in these two T1D models. Using α-cell lineage-tracing mice, we found that the neogenic β-cells were likely derived from α-cell conversion. Therefore, GCGR mAb-induced α- to β-cell conversion might represent a pre-clinical approach for improving diabetes therapy.

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GCGR mAb induced α-cell expansion by neogenesis and cell proliferation

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GCGR mAb increased the β-cell mass in type 1 diabetic mice

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GCGR mAb might promote α- to β-cell conversion in type 1 diabetic mice

Single and multiple ascending-dose study of glucagon-receptor antagonist RN909 in type 2 diabetes: a phase 1, randomized, double-blind, placebo-controlled trial

PURPOSE

This first-in-human study assessed safety, immunogenicity, pharmacokinetics, and pharmacodynamics of RN909, a monoclonal antibody antagonist of the glucagon receptor, in type 2 diabetes (T2DM) subjects.

METHODS

This study enrolled 84 T2DM subjects receiving stable metformin regimens. Forty-four subjects were randomized to receive single escalating doses of RN909 (0.3 to 6 mg/kg subcutaneously (SC), or 1 mg/kg intravenously (IV)), or placebo; 40 subjects were randomized to receive multiple escalating doses (50 to 150 mg SC) or placebo every 4 weeks for 12 weeks.

RESULTS

RN909 was well tolerated; treatment-related elevated liver function tests (LFTs) were observed in 4/33 (12.1%) and 5/32 (15.6%) subjects treated with single and multiple doses, respectively, versus 1/10 (10%) and 0 in the respective placebo groups. RN909 dose-normalized AUC_inf increased more than dose-proportionally following single SC doses, and after multiple doses, accumulation ratios ranged from 1.3 to 3.4. The incidence of antidrug antibodies (ADA) was 33% after single doses and 50% after multiple doses. RN909 produced dose-dependent, durable fasting plasma glucose (FPG)-lowering at day 29 (mean change -20.6 to -97.5 mg/dL) and day 85 (mean change; -27.2 to -43.5 mg/dL) after single and multiple doses, respectively. HbA1c also was reduced after single (mean change -0.30% to -1.44%), and multiple doses (-0.83% to -1.56%).

CONCLUSION

RN909 was well tolerated after single and multiple doses in T2DM subjects, with diarrhea and elevated LFTs the most frequent adverse events. The appearance of ADA did not affect pharmacokinetics or efficacy. Robust lowering of FPG and HbA1c was observed.

Efficacy and safety of the glucagon receptor antagonist PF-06291874: A 12-week, randomized, dose-response study in patients with type 2 diabetes mellitus on background metformin therapy

AIMS

To conduct a dose-response assessment of the efficacy and safety of the glucagon receptor antagonist PF-06291874 in adults with type 2 diabetes (T2DM) using stable doses of metformin.

MATERIALS AND METHODS

This randomized, double-blind, statin-stratified, placebo-controlled, 4-arm, parallel-group study was conducted in patients with T2DM who were receiving background metformin. After an 8-week, non-metformin oral antidiabetic agent washout period, 206 patients were randomized to placebo or PF-06291874 (30, 60 or 100 mg once daily) for 12 weeks. Glycosylated haemoglobin (HbA1c), fasting plasma glucose (FPG) and safety endpoints were assessed at baseline and post baseline.

RESULTS

Dose-dependent mean reductions from baseline in HbA1c for PF-06291874 ranged from -0.67% (-7.29 mmol/mol) to -0.93% (-10.13 mmol/mol), and for FPG from -16.6 to -33.3 mg/dL after 12 weeks of dosing. The incidence of hypoglycaemia was low and was similar between groups receiving PF-06291874 and placebo. Small, non-dose-dependent increases in LDL cholesterol (<10%) and blood pressure (BP) (systolic BP > 2 mm Hg; diastolic BP > 1 mm Hg) were observed with PF-06291874. Modest non-dose-dependent median increases were observed across PF-06291874 groups at 12 weeks for alanine aminotransferase (range, 37.6-48.7 U/L vs placebo) and aspartate aminotransferase (range, 33.3-36.6 U/L vs placebo); these were not associated with bilirubin changes. Small increases were observed in body weight (< 0.5 kg) in each PF-06291874 group vs placebo.

CONCLUSIONS

In patients with T2DM, PF-06291874 significantly lowered HbA1c and glucose, was well tolerated and carried a low risk of hypoglycaemia. Small, non-dose-related increases in BP, lipids and hepatic transaminases were observed.

Current anti-diabetic agents and their molecular targets: A review

Diabetes mellitus is a medical condition characterized by the body's loss of control over blood sugar. The frequency of diagnosed cases and consequential increases in medical costs makes it a rapidly growing chronic disease that threatens human health worldwide. In addition, its unnerving statistical projections are perilous to both the economy of the nation and man's life expectancy. Type-I and type-II diabetes are the two clinical forms of diabetes mellitus. Type-II diabetes mellitus (T2DM) is illustrated by the abnormality of glucose homeostasis in the body, resulting in hyperglycemia. Although significant research attention has been devoted to the development of diabetes regimens, which demonstrates success in lowering blood glucose levels, their efficacies are unsustainable due to undesirable side effects such as weight gain and hypoglycemia. Over the years, heterocyclic scaffolds have been the basis of anti-diabetic chemotherapies; hence, in this review we consolidate the use of bioactive scaffolds, which have been evaluated for their biological response as inhibitors against their respective anti-diabetic molecular targets over the past five years (2012-2017). Our investigation reveals a diverse target set which includes; protein tyrosine phosphatase 1 B (PTP1B), dipeptidly peptidase-4 (DPP-4), free fatty acid receptors 1 (FFAR1), G protein-coupled receptors (GPCR), peroxisome proliferator activated receptor-γ (PPARγ), sodium glucose co-transporter-2 (SGLT2), α-glucosidase, aldose reductase, glycogen phosphorylase (GP), fructose-1,6-bisphosphatase (FBPase), glucagon receptor (GCGr) and phosphoenolpyruvate carboxykinase (PEPCK). This review offers a medium on which future drug design and development toward diabetes management may be modelled (i.e. optimization via structural derivatization), as many of the drug candidates highlighted show promise as an effective anti-diabetic chemotherapy.

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.

Alpha cell dysfunction in type 1 diabetes

Type 1 diabetes is characterized by selective loss of beta cells and insulin secretion, which significantly impact glucose homeostasis. However, this progressive disease is also associated with dysfunction of the alpha cell component of the islet, which can exacerbate hyperglycemia due to paradoxical hyperglucagonemia or lead to severe hypoglycemia as a result of failed counterregulation. In this review, the physiology of alpha cell secretion and the potential mechanisms underlying alpha cell dysfunction in type 1 diabetes will be explored. Because type 1 diabetes is a progressive disease, a synthesized timeline of aberrant alpha cell function will be presented as an attempt to delineate the natural history of type 1 diabetes with respect to the alpha cell.

The Role of Glucagon in the Pathophysiology and Treatment of Type 2 Diabetes

Type 2 diabetes is a disease involving both inadequate insulin levels and increased glucagon levels. While glucagon and insulin work together to achieve optimal plasma glucose concentrations in healthy individuals, the usual regulatory balance between these 2 critical pancreatic hormones is awry in patients with diabetes. Although clinical discussion often focuses on the role of insulin, glucagon is equally important in understanding type 2 diabetes. Furthermore, an awareness of the role of glucagon is essential to appreciate differences in the mechanisms of action of various classes of glucose-lowering therapies. Newer drug classes such as dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 receptor agonists improve glycemic control, in part, by affecting glucagon levels. This review provides an overview of the effect of glucose-lowering therapies on glucagon on the basis of an extensive PubMed literature search to identify clinical studies of glucose-lowering therapies in type 2 diabetes that included assessment of glucagon. Clinical practice currently benefits from available therapies that impact the glucagon regulatory pathway. As clinicians look to the future, improved treatment strategies are likely to emerge that will either use currently available therapies whose mechanisms of action complement each other or take advantage of new therapies based on an improved understanding of glucagon pathophysiology.

Investigational glucagon receptor antagonists in Phase I and II clinical trials for diabetes

INTRODUCTION

Despite type 2 diabetes (T2D) being recognized as a bihormonal pancreatic disease, current therapies are mainly focusing on insulin, while targeting glucagon has been long dismissed. However, glucagon receptor (GCGr) antagonists are currently investigated in clinical trials. Area covered: Following a brief description of the rationale for antagonizing GCGr in T2D, lessons from GCGr knock-out mice and pharmacological means to antagonize GCGr, a detailed description of the main results obtained with GCGr antagonists in Phase I-II clinical trials is provided. The development of several small molecules has been discontinued, while new ones are currently considered as well as innovative approaches such as monoclonal antibodies or antisense oligonucleotides inhibiting GCGr gene expression. Their potential benefits but also limitations are discussed. Expert opinion: The proof-of-concept that antagonizing GCGr improves glucose control in T2D has been confirmed in humans. Nevertheless, some adverse events led to stopping the development of some of these GCGr antagonists. New approaches seem to have a better benefit/risk balance, although none has progressed to Phase III clinical trials so far. Pharmacotherapy of T2D is becoming a highly competitive field so that GCGr antagonists should provide clear advantages over numerous existing glucose-lowering medications before eventually reaching clinical practice.