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

Iridium-Catalyzed Regio- and Enantioselective N-Allylation of Pyrazoles with Dienyl/Monoallylic Alcohols

Here we report the first example of iridium-catalyzed asymmetric N-allylation of pyrazoles with dienyl allylic alcohols under mild conditions with broad functional group tolerance, exhibiting excellent N1/C3-site selectivities and enantioselectivities (up to >99% ee). In addition to pyrazoles, other nucleophiles including benzotriazole, triazole, and pyrazole precursors (aryl vinyldiazos) are also suitable in this method. Notably, with the use of Sc(OTf)3 as additive and reactions performed at 30 °C for 24 h, the N1-C5 or N1-C1 selective alkylated pyrazoles are also obtained.

G protein-coupled receptors (GPCRs): advances in structures, mechanisms, and drug discovery

G protein-coupled receptors (GPCRs), the largest family of human membrane proteins and an important class of drug targets, play a role in maintaining numerous physiological processes. Agonist or antagonist, orthosteric effects or allosteric effects, and biased signaling or balanced signaling, characterize the complexity of GPCR dynamic features. In this study, we first review the structural advancements, activation mechanisms, and functional diversity of GPCRs. We then focus on GPCR drug discovery by revealing the detailed drug-target interactions and the underlying mechanisms of orthosteric drugs approved by the US Food and Drug Administration in the past five years. Particularly, an up-to-date analysis is performed on available GPCR structures complexed with synthetic small-molecule allosteric modulators to elucidate key receptor-ligand interactions and allosteric mechanisms. Finally, we highlight how the widespread GPCR-druggable allosteric sites can guide structure- or mechanism-based drug design and propose prospects of designing bitopic ligands for the future therapeutic potential of targeting this receptor family.

Discovery and In Vitro Characterization of BAY 2686013, an Allosteric Small Molecule Antagonist of the Human Pituitary Adenylate Cyclase-Activating Polypeptide Receptor

The human pituitary adenylate cyclase-activating polypeptide receptor (hPAC1-R), a class B G-protein-coupled receptor (GPCR) identified almost 30 years ago, represents an important pharmacological target in the areas of neuroscience, oncology, and immunology. Despite interest in this target, only a very limited number of small molecule modulators have been reported for this receptor. We herein describe the results of a drug discovery program aiming for the identification of a potent and selective hPAC1-R antagonist. An initial high-throughput screening (HTS) screen of 3.05 million compounds originating from the Bayer screening library failed to identify any tractable hits. A second, completely revised screen using native human embryonic kidney (HEK)293 cells yielded a small number of hits exhibiting antagonistic properties (4.2 million compounds screened). BAY 2686013 (1) emerged as a promising compound showing selective antagonistic activity in the submicromolar potency range. In-depth characterization supported the hypothesis that BAY 2686013 blocks receptor activity in a noncompetitive manner. Preclinical, pharmacokinetic profiling indicates that BAY 2686013 is a valuable tool compound for better understanding the signaling and function of hPAC1-R. SIGNIFICANCE STATEMENT: Although the human pituitary adenylate cyclase-activating polypeptide receptor (hPAC1-R) is of major significance as a therapeutic target with a well documented role in pain signaling, only a very limited number of small-molecule (SMOL) compounds are known to modulate its activity. We identified and thoroughly characterized a novel, potent, and selective SMOL antagonist of hPAC1-R (acting in an allosteric manner). These characteristics make BAY 2686013 an ideal tool for further studies.

Glucagon 100 years. Important, but still enigmatic

Glucagon was discovered in 1923 as a contaminant of early insulin preparations, and its hormonal status was not established until its structure was established in the 1950 s and when the first radioimmunoassay was developed by Roger Unger, providing information about its secretion. Its role in hepatic glucose production was soon established and it was proposed as an essential factor in diabetic hyperglycemia. However, even today a number of issues remain unsolved. For instance, the assays for glucagon are not straightforward, although the development of sandwich ELISAs allowed reasonably accurate measurements also in rodents. The tools for evaluation of glucagon physiology include pancreatectomy, but studies in both humans and experimental animals pointed towards extrapancreatic sources of glucagon. It was demonstrated that glucagon receptor knockout animals do not develop diabetes upon destruction of their beta cells with streptozotocin. However, in patients with type 1 diabetes, glucagon antagonists do not normalize glucose levels; but antagonists do lower glucose levels in patients with in type 2 diabetes. Recent studies in animals and humans have confirmed the essential role of glucagon in glucose metabolism, but have suggested that it may be at least equally important for amino acid and lipid metabolism. In spite of the 100 years, glucagon research is very much alive.

Enantioselective Synthesis of N-Benzylic Heterocycles by Ni/Photoredox Dual Catalysis

An asymmetric cross-coupling of α-N-heterocyclic trifluoroborates with aryl bromides using Ni/photoredox dual catalysis has been developed. This C(sp2)-C(sp3) cross-coupling provides access to pharmaceutically relevant chiral N-benzylic heterocycles in good to excellent enantioselectivity when bioxazolines (BiOX) are used as the chiral ligand. High-throughput experimentation significantly streamlined reaction development by identifying BiOX ligands for further investigation and by allowing for rapid optimization of conditions for new trifluoroborate salts.

Role of Glucagon and Its Receptor in the Pathogenesis of Diabetes

Various theories for the hormonal basis of diabetes have been proposed and debated over the past few decades. Insulin insufficiency was previously regarded as the only hormone deficiency directly leading to metabolic disorders associated with diabetes. Although glucagon and its receptor are ignored in this framework, an increasing number of studies have shown that they play essential roles in the development and progression of diabetes. However, the molecular mechanisms underlying the effects of glucagon are still not clear. In this review, recent research on the mechanisms by which glucagon and its receptor contribute to the pathogenesis of diabetes as well as correlations between GCGR mutation rates in populations and the occurrence of diabetes are summarized. Furthermore, we summarize how recent research clearly establishes glucagon as a potential therapeutic target for diabetes.

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.

Design, synthesis, biological evaluation, and molecular modeling studies of pyrazole-benzofuran hybrids as new α-glucosidase inhibitor

In this work, new derivatives of biphenyl pyrazole-benzofuran hybrids were designed, synthesized and evaluated in vitro through enzymatic assay for inhibitory effect against α-glucosidase activity. Newly identified inhibitors were found to be four to eighteen folds more active with IC₅₀ values in the range of 40.6 ± 0.2-164.3 ± 1.8 µM, as compared to the standard drug acarbose (IC₅₀ = 750.0 ± 10.0 μM). Limited Structure-activity relationship was established. A kinetic binding study indicated that most active compound 8e acted as the competitive inhibitors of α-glucosidase with K_i = 38 μM. Molecular docking has also been performed to find the interaction modes responsible for the desired inhibitory activity. As expected, all pharmacophoric features, used in the design of the hybrid, are involved in the interaction with the active site of the enzyme. In addition, molecular dynamic simulations showed compound 8e oriented vertically into the active site from mouth to the bottom and stabilized the enzyme domains by interacting with the interface of domain A and domain B and the back side of the active site while acarbose formed non-binding interaction with the residue belong to the domain A of the enzyme.

Glucagon Potentiates Insulin Secretion Via β-Cell GCGR at Physiological Concentrations of Glucose

Incretin-potentiated glucose-stimulated insulin secretion (GSIS) is critical to maintaining euglycemia, of which GLP-1 receptor (GLP-1R) on β-cells plays an indispensable role. Recently, α-cell-derived glucagon but not intestine-derived GLP-1 has been proposed as the critical hormone that potentiates GSIS via GLP-1R. However, the function of glucagon receptors (GCGR) on β-cells remains elusive. Here, using GCGR or GLP-1R antagonists, in combination with glucagon, to treat single β-cells, α-β cell clusters and isolated islets, we found that glucagon potentiates insulin secretion via β-cell GCGR at physiological but not high concentrations of glucose. Furthermore, we transfected primary mouse β-cells with RAB-ICUE (a genetically encoded cAMP fluorescence indicator) to monitor cAMP level after glucose stimulation and GCGR activation. Using specific inhibitors of different adenylyl cyclase (AC) family members, we revealed that high glucose concentration or GCGR activation independently evoked cAMP elevation via AC5 in β-cells, thus high glucose stimulation bypassed GCGR in promoting insulin secretion. Additionally, we generated β-cell-specific GCGR knockout mice which glucose intolerance was more severe when fed a high-fat diet (HFD). We further found that β-cell GCGR activation promoted GSIS more than GLP-1R in HFD, indicating the critical role of GCGR in maintaining glucose homeostasis during nutrient overload.

Mebhydrolin ameliorates glucose homeostasis in type 2 diabetic mice by functioning as a selective FXR antagonist

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is a chronic disease with hallmarks of hyperglycemia and hyperlipidemia. Long-term hyperglycemia damages the functions of multiple tissues and organs leading to a series of complications and disability or even death. Nuclear receptor farnesoid X receptor (FXR) antagonism has been recently discovered to exhibit beneficial effect on glucose metabolism in T2DM mice, although the underlying mechanisms remain unclear. Here, we performed the study on the discovery of new FXR antagonist and investigated the mechanism underlying the amelioration of FXR antagonism on glucose homeostasis in T2DM mice by using the determined FXR antagonist as a probe.

METHODS

FXR antagonist Mebhydrolin was discovered by screening against the lab in-house FDA approved drug library through surface plasmon resonance (SPR), microscale thermophoresis (MST), AlphaScreen, mammalian one-hybrid and transactivation assays. Activity of Mebhydrolin in improving glucose homeostasis was evaluated in db/db and HFD/STZ-induced T2DM mice, and the mechanisms governing the regulation of Mebhydrolin were investigated by assays of immunostaining, Western blot, ELISA, RT-PCR against liver tissues of both T2DM mice and the T2DM mice with liver-specific FXR knockdown injected via adeno-associated-virus AAV-FXR-RNAi and mouse primary hepatocytes. Finally, molecular docking and molecular dynamics (MD) technology-based study was performed to investigate the structural basis for the antagonistic regulation of Mebhydrolin against FXR at an atomic level.

FINDINGS

Mebhydrolin ameliorated blood glucose homeostasis in T2DM mice by both suppressing hepatic gluconeogenesis via FXR/miR-22-3p/PI3K/AKT/FoxO1 pathway and promoting glycogen synthesis through FXR/miR-22-3p/PI3K/AKT/GSK3β pathway. Structurally, residues L291, M332 and Y373 of FXR were required for Mebhydrolin binding to FXR-LBD, and Mebhydrolin induced H2 and H6 shifting of FXR potently affecting the regulation of the downstream target genes.

CONCLUSIONS

Our work has revealed a novel mode for the regulation of FXR against glucose metabolism in T2DM mice and highlighted the potential of Mebhydrolin in the treatment of T2DM.

Efficacy and Safety of the Glucagon Receptor Antagonist RVT-1502 in Type 2 Diabetes Uncontrolled on Metformin Monotherapy: A 12-Week Dose-Ranging Study

OBJECTIVE

Evaluate the safety and efficacy of RVT-1502, a novel oral glucagon receptor antagonist, in subjects with type 2 diabetes inadequately controlled on metformin.

RESEARCH DESIGN AND METHODS

In a phase 2, double-blind, randomized, placebo-controlled study, subjects with type 2 diabetes (n = 166) on a stable dose of metformin were randomized (1:1:1:1) to placebo or RVT-1502 5, 10, or 15 mg once daily for 12 weeks. The primary end point was change from baseline in HbA_1c for each dose of RVT-1502 compared with placebo. Secondary end points included change from baseline in fasting plasma glucose (FPG) and safety assessments.

RESULTS

Over 12 weeks, RVT-1502 significantly reduced HbA_1c relative to placebo by 0.74%, 0.76%, and 1.05% in the 5-, 10-, and 15-mg groups (P < 0.001), respectively, and FPG decreased by 2.1, 2.2, and 2.6 mmol/L (P < 0.001). The proportions of subjects achieving an HbA_1c <7.0% were 19.5%, 39.5%, 39.5%, and 45.0% with placebo and RVT-1502 5, 10, and 15 mg (P ≤ 0.02 vs. placebo). The frequency of hypoglycemia was low, and no episodes were severe. Mild increases in mean aminotransferase levels remaining below the upper limit of normal were observed with RVT-1502 but were reversible and did not appear to be dose related, with no other liver parameter changes. Weight and lipid changes were similar between RVT-1502 and placebo. RVT-1502-associated mild increases in blood pressure were not dose related or consistent across time.

CONCLUSIONS

Glucagon receptor antagonism with RVT-1502 significantly lowers HbA_1c and FPG, with a safety profile that supports further clinical development with longer-duration studies (NCT02851849).

Regulation of glucose and lipid metabolism in health and disease

Glucose and fatty acids are the major sources of energy for human body. Cholesterol, the most abundant sterol in mammals, is a key component of cell membranes although it does not generate ATP. The metabolisms of glucose, fatty acids and cholesterol are often intertwined and regulated. For example, glucose can be converted to fatty acids and cholesterol through de novo lipid biosynthesis pathways. Excessive lipids are secreted in lipoproteins or stored in lipid droplets. The metabolites of glucose and lipids are dynamically transported intercellularly and intracellularly, and then converted to other molecules in specific compartments. The disorders of glucose and lipid metabolism result in severe diseases including cardiovascular disease, diabetes and fatty liver. This review summarizes the major metabolic aspects of glucose and lipid, and their regulations in the context of physiology and diseases.

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.

Identification of a novel allosteric GLP-1R antagonist HTL26119 using structure- based drug design

A series of novel allosteric antagonists of the GLP-1 receptor (GLP-1R), exemplified by HTL26119, are described. SBDD approaches were employed to identify HTL26119, exploiting structural understanding of the allosteric binding site of the closely related Glucagon receptor (GCGR) (Jazayeri et al., 2016) and the homology relationships between GCGR and GLP-1R. The region around residue C347^6.36b of the GLP-1R receptor represents a key difference from GCGR and was targeted for selectivity for GLP-1R.

Current perspective on the role of insulin and glucagon in the pathogenesis and treatment of type 2 diabetes mellitus

According to the World Health Organization, 422 million adults worldwide live with diabetes mellitus (DM), a significant portion of whom have type 2 diabetes. The discovery of insulin as a key regulator of glucose metabolism has revolutionized our understanding of DM and provided several therapeutic avenues. Most studies have so far predominantly focused on the role of insulin in type 2 diabetes. However, the balance between insulin and glucagon is essential in ensuring glucose homeostasis. In this review, we begin by evaluating the principal differences between insulin and glucagon with regard to their mechanism and control of their secretion. Next, we discuss their mode of action and effects on metabolism. We further explore how the two hormones impact the natural history of type 2 diabetes. Finally, we outline how current and emerging pharmacological agents attempt to exploit the properties of insulin and glucagon to benefit patients with type 2 diabetes.

Anti-Obesity Therapy: from Rainbow Pills to Polyagonists

With their ever-growing prevalence, obesity and diabetes represent major health threats of our society. Based on estimations by the World Health Organization, approximately 300 million people will be obese in 2035. In 2015 alone there were more than 1.6 million fatalities attributable to hyperglycemia and diabetes. In addition, treatment of these diseases places an enormous burden on our health care system. As a result, the development of pharmacotherapies to tackle this life-threatening pandemic is of utmost importance. Since the beginning of the 19th century, a variety of drugs have been evaluated for their ability to decrease body weight and/or to improve deranged glycemic control. The list of evaluated drugs includes, among many others, sheep-derived thyroid extracts, mitochondrial uncouplers, amphetamines, serotonergics, lipase inhibitors, and a variety of hormones produced and secreted by the gastrointestinal tract or adipose tissue. Unfortunately, when used as a single hormone therapy, most of these drugs are underwhelming in their efficacy or safety, and placebo-subtracted weight loss attributed to such therapy is typically not more than 10%. In 2009, the generation of a single molecule with agonism at the receptors for glucagon and the glucagon-like peptide 1 broke new ground in obesity pharmacology. This molecule combined the beneficial anorectic and glycemic effects of glucagon-like peptide 1 with the thermogenic effect of glucagon into a single molecule with enhanced potency and sustained action. Several other unimolecular dual agonists have subsequently been developed, and, based on their preclinical success, these molecules illuminate the path to a new and more fruitful era in obesity pharmacology. In this review, we focus on the historical pharmacological approaches to treat obesity and glucose intolerance and describe how the knowledge obtained by these studies led to the discovery of unimolecular polypharmacology.

Nonconventional glucagon and GLP-1 receptor agonist and antagonist interplay at the GLP-1 receptor revealed in high-throughput FRET assays for cAMP

G protein-coupled receptors (GPCRs) for glucagon (GluR) and glucagon-like peptide-1 (GLP-1R) are normally considered to be highly selective for glucagon and GLP-1, respectively. However, glucagon secreted from pancreatic α-cells may accumulate at high concentrations to exert promiscuous effects at the β-cell GLP-1R, as may occur in the volume-restricted microenvironment of the islets of Langerhans. Furthermore, systemic administration of GluR or GLP-1R agonists and antagonists at high doses may lead to off-target effects at other receptors. Here, we used molecular modeling to evaluate data derived from FRET assays that detect cAMP as a read-out for GluR and GLP-1R activation. This analysis established that glucagon is a nonconventional GLP-1R agonist, an effect inhibited by the GLP-1R orthosteric antagonist exendin(9-39) (Ex(9-39)). The GluR allosteric inhibitors LY2409021 and MK 0893 antagonized glucagon and GLP-1 action at the GLP-1R, whereas des-His¹-[Glu⁹]glucagon antagonized glucagon action at the GluR, while having minimal inhibitory action versus glucagon or GLP-1 at the GLP-1R. When testing Ex(9-39) in combination with des-His¹-[Glu⁹]glucagon in INS-1 832/13 cells, we validated a dual agonist action of glucagon at the GluR and GLP-1R. Hybrid peptide GGP817 containing glucagon fused to a fragment of peptide YY (PYY) acted as a triagonist at the GluR, GLP-1R, and neuropeptide Y2 receptor (NPY2R). Collectively, these findings provide a new triagonist strategy with which to target the GluR, GLP-1R, and NPY2R. They also provide an impetus to reevaluate prior studies in which GluR and GLP-1R agonists and antagonists were assumed not to exert promiscuous actions at other GPCRs.

Design, synthesis, and effects of novel phenylpyrimidines as glucagon receptor antagonists

The hormone glucagon increases blood glucose levels through increasing hepatic glucose output. In diabetic patients, dysregulation of glucagon secretion contributes to hyperglycemia. Thus, the inhibition of glucagon receptor is one target for the treatment of hyperglycemia in type 2 diabetes. Here we designed and synthesized a series of small molecules based on phenylpyrimidine. Of these, the compound (R)-7a most significantly decreased the glucagon-induced cAMP production and glucagon-induced glucose production during in vitro and in vivo assays. In addition, (R)-7a showed good efficacy in glucagon challenge tests and lowered blood glucose levels in diabetic db/db mice. Our results suggest that the compound (R)-7a could be a potential glucose-lowering agent for treating type 2 diabetes.

Discovery of thiophene-containing biaryl amide derivatives as novel glucagon receptor antagonists

A novel series of thiophene-containing biaryl amide glucagon receptor (GCGR) antagonists were designed and synthesized. Two compounds of this series, 14f and 14h, exhibited good GCGR binding (IC₅₀  = 6.1 and 4.4 μm, respectively) and cAMP functional activities (IC₅₀  = 4.4 and 14.4 μm, respectively). The possible binding modes of compounds 14f and 14h with GCGR were explored by molecular simulation.

A novel series of 4-methyl substituted pyrazole derivatives as potent glucagon receptor antagonists: Design, synthesis and evaluation of biological activities

A novel series of 4-methyl substituted pyrazole derivatives were designed, synthesized and biologically evaluated as potent glucagon receptor (GCGR) antagonists. In this study, compounds 9q, 9r, 19d and 19e showed high GCGR binding (IC₅₀ = 0.09 μM, 0.06 μM, 0.07 μM and 0.08 μM, respectively) and cyclic-adenosine monophosphate (cAMP) activities (IC₅₀ = 0.22 μM, 0.26 μM, 0.44 μM and 0.46 μM, respectively) in cell-based assays. Most importantly, the docking experiment demonstrated that compound 9r formed extensive hydrophobic interactions with the receptor binding pocket, making it justifiable to further investigate the potential of becoming a GCGR antagonist.

Synthesis and Pharmacological Activities of Pyrazole Derivatives: A Review

Pyrazole and its derivatives are considered a pharmacologically important active scaffold that possesses almost all types of pharmacological activities. The presence of this nucleus in pharmacological agents of diverse therapeutic categories such as celecoxib, a potent anti-inflammatory, the antipsychotic CDPPB, the anti-obesity drug rimonabant, difenamizole, an analgesic, betazole, a H2-receptor agonist and the antidepressant agent fezolamide have proved the pharmacological potential of the pyrazole moiety. Owing to this diversity in the biological field, this nucleus has attracted the attention of many researchers to study its skeleton chemically and biologically. This review highlights the different synthesis methods and the pharmacological properties of pyrazole derivatives. Studies on the synthesis and biological activity of pyrazole derivatives developed by many scientists around the globe are reported.

Synthesis and Pharmacological Activities of Pyrazole Derivatives: A Review

Pyrazole and its derivatives are considered a pharmacologically important active scaffold that possesses almost all types of pharmacological activities. The presence of this nucleus in pharmacological agents of diverse therapeutic categories such as celecoxib, a potent anti-inflammatory, the antipsychotic CDPPB, the anti-obesity drug rimonabant, difenamizole, an analgesic, betazole, a H2-receptor agonist and the antidepressant agent fezolamide have proved the pharmacological potential of the pyrazole moiety. Owing to this diversity in the biological field, this nucleus has attracted the attention of many researchers to study its skeleton chemically and biologically. This review highlights the different synthesis methods and the pharmacological properties of pyrazole derivatives. Studies on the synthesis and biological activity of pyrazole derivatives developed by many scientists around the globe are reported.

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.

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.

DMT efficiently inhibits hepatic gluconeogenesis by regulating the Gαq signaling pathway

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease with complicated pathogenesis and targeting gluconeogenesis inhibition is a promising strategy for anti-diabetic drug discovery. G protein-coupled receptors (GPCRs) are classified as distinct families by heterotrimeric G proteins, primarily including Gαs, Gαi and Gαq. Gαs-coupled GPCRs function potently in the regulation of hepatic gluconeogenesis by activating cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway and Gαi-coupled GPCRs exhibit inhibitory effect on adenylyl cyclase and reduce intracellular cAMP level. However, little is known about the regulation of Gαq-coupled GPCRs in hepatic gluconeogenesis. Here, small-molecule 2-(2,4-dimethoxy-3-methylphenyl)-7-(thiophen-2-yl)-9-(trifluoromethyl)-2,3-dihydropyrido[3',2':4,5]thieno[3,2-d]pyrimidin-4(1H)-one (DMT) was determined to suppress hepatic glucose production and reduce mRNA levels of gluconeogenic genes. Treatment of DMT in db/db mice decreased fasting blood glucose and hemoglobin A1C (HbA1c) levels, while improved glucose tolerance and pyruvate tolerance. Mechanism study demonstrated that DMT-inhibited gluconeogenesis by regulating the Gαq/phospholipase C (PLC)/inositol-1,4,5-triphosphate receptor (IP3R)-mediated calcium (Ca²⁺)/calmodulin (CaM)/phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/protein kinase B (AKT)/forkhead box protein O1 (FOXO1) signaling pathway. To our knowledge, DMT might be the first reported small molecule able to suppress hepatic gluconeogenesis by regulating Gαq signaling, and our current work has also highlighted the potential of DMT in the treatment of T2DM.

Applying Structure-Based Drug Design Approaches to Allosteric Modulators of GPCRs

Structural insights have been revealed from X-ray co-complexes of a range of G protein-coupled receptors (GPCRs) and their allosteric ligands. The understanding of how small molecules can modulate the function of this important class of receptors by binding to a diverse range of pockets on and inside the proteins has had a profound impact on the structure-based drug design (SBDD) of new classes of therapeutic agents. The types of allosteric pockets and the mode of modulation as well as the advantages and disadvantages of targeting allosteric pockets (as opposed to the natural orthosteric site) are considered in the context of these new structural findings.

The New Biology and Pharmacology of Glucagon

In the last two decades we have witnessed sizable progress in defining the role of gastrointestinal signals in the control of glucose and energy homeostasis. Specifically, the molecular basis of the huge metabolic benefits in bariatric surgery is emerging while novel incretin-based medicines based on endogenous hormones such as glucagon-like peptide 1 and pancreas-derived amylin are improving diabetes management. These and related developments have fostered the discovery of novel insights into endocrine control of systemic metabolism, and in particular a deeper understanding of the importance of communication across vital organs, and specifically the gut-brain-pancreas-liver network. Paradoxically, the pancreatic peptide glucagon has reemerged in this period among a plethora of newly identified metabolic macromolecules, and new data complement and challenge its historical position as a gut hormone involved in metabolic control. The synthesis of glucagon analogs that are biophysically stable and soluble in aqueous solutions has promoted biological study that has enriched our understanding of glucagon biology and ironically recruited glucagon agonism as a central element to lower body weight in the treatment of metabolic disease. This review summarizes the extensive historical record and the more recent provocative direction that integrates the prominent role of glucagon in glucose elevation with its under-acknowledged effects on lipids, body weight, and vascular health that have implications for the pathophysiology of metabolic diseases, and the emergence of precision medicines to treat metabolic diseases.

Glucagon-Like Peptide-1 and Its Class B G Protein-Coupled Receptors: A Long March to Therapeutic Successes

The glucagon-like peptide (GLP)-1 receptor (GLP-1R) is a class B G protein-coupled receptor (GPCR) that mediates the action of GLP-1, a peptide hormone secreted from three major tissues in humans, enteroendocrine L cells in the distal intestine, α cells in the pancreas, and the central nervous system, which exerts important actions useful in the management of type 2 diabetes mellitus and obesity, including glucose homeostasis and regulation of gastric motility and food intake. Peptidic analogs of GLP-1 have been successfully developed with enhanced bioavailability and pharmacological activity. Physiologic and biochemical studies with truncated, chimeric, and mutated peptides and GLP-1R variants, together with ligand-bound crystal structures of the extracellular domain and the first three-dimensional structures of the 7-helical transmembrane domain of class B GPCRs, have provided the basis for a two-domain-binding mechanism of GLP-1 with its cognate receptor. Although efforts in discovering therapeutically viable nonpeptidic GLP-1R agonists have been hampered, small-molecule modulators offer complementary chemical tools to peptide analogs to investigate ligand-directed biased cellular signaling of GLP-1R. The integrated pharmacological and structural information of different GLP-1 analogs and homologous receptors give new insights into the molecular determinants of GLP-1R ligand selectivity and functional activity, thereby providing novel opportunities in the design and development of more efficacious agents to treat metabolic disorders.

Regio- and Enantioselective Rhodium-Catalyzed Addition of 1,3-Diketones to Allenes: Construction of Asymmetric Tertiary and Quaternary All Carbon Centers

An unprecedented highly regio- and enantioselective rhodium-catalyzed addition of 1,3-diketones to terminal and 1,1-disubstituted allenes furnishing asymmetric tertiary and quaternary all-carbon centers is reported. By applying a Rh^I /phosphoramidite/TFA catalytic system under mild conditions, the desired chiral branched α-allylated 1,3-diketones could be obtained in good to excellent yields, with perfect regioselectivity and in high enantioselectivity. The reaction shows a broad functional-group tolerance on both reaction partners highlighting its synthetic potential.

Pharmacokinetics and pharmacodynamics of single and multiple doses of the glucagon receptor antagonist LGD-6972 in healthy subjects and subjects with type 2 diabetes mellitus

AIM

To evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of single and multiple doses of a novel, oral glucagon receptor antagonist, LGD-6972, in healthy subjects and subjects with type 2 diabetes (T2DM).

METHODS

In the single ascending dose study, LGD-6972 (2-480 mg) was administered to healthy subjects (n = 48) and T2DM subjects (n = 8). In the multiple ascending dose study, healthy subjects (n = 12) received a dose of 15 mg LGD-6972 and T2DM subjects (n = 36) received doses of 5, 10 or 15 mg of LGD-6972 daily for 14 days.

RESULTS

LGD-6972 had linear plasma pharmacokinetics consistent with once-daily dosing that was comparable in healthy and T2DM subjects. Dose-dependent decreases in fasting plasma glucose were observed in all groups with a maximum of 3.15 mmol/L (56.8 mg/dL) on day 14 in T2DM subjects. LGD-6972 also reduced plasma glucose in the postprandial state. Dose-dependent increases in fasting plasma glucagon were observed, but glucagon levels decreased and insulin levels increased after an oral glucose load in T2DM subjects. LGD-6972 was well tolerated at the doses tested without dose-related or clinically meaningful changes in clinical laboratory parameters. No subject experienced hypoglycaemia.

CONCLUSION

Inhibition of glucagon action by LGD-6972 was associated with decreases in glucose in both healthy and T2DM subjects, the magnitude of which was sufficient to predict improvement in glycaemic control with longer treatment duration in T2DM patients. The safety and pharmacological profile of LGD-6972 after 14 days of dosing supports continued clinical development.

Targeting hepatic glucose metabolism in the treatment of type 2 diabetes

Type 2 diabetes mellitus is characterized by the dysregulation of glucose homeostasis, resulting in hyperglycaemia. Although current diabetes treatments have exhibited some success in lowering blood glucose levels, their effect is not always sustained and their use may be associated with undesirable side effects, such as hypoglycaemia. Novel antidiabetic drugs, which may be used in combination with existing therapies, are therefore needed. The potential of specifically targeting the liver to normalize blood glucose levels has not been fully exploited. Here, we review the molecular mechanisms controlling hepatic gluconeogenesis and glycogen storage, and assess the prospect of therapeutically targeting associated pathways to treat type 2 diabetes.

Glucagon actions on the kidney revisited: possible role in potassium homeostasis

It is now recognized that the metabolic disorders observed in diabetes are not, or not only due to the lack of insulin or insulin resistance, but also to elevated glucagon secretion. Accordingly, selective glucagon receptor antagonists are now proposed as a novel strategy for the treatment of diabetes. However, besides its metabolic actions, glucagon also influences kidney function. The glucagon receptor is expressed in the thick ascending limb, distal tubule, and collecting duct, and glucagon regulates the transepithelial transport of several solutes in these nephron segments. Moreover, it also influences solute transport in the proximal tubule, possibly by an indirect mechanism. This review summarizes the knowledge accumulated over the last 30 years about the influence of glucagon on the renal handling of electrolytes and urea. It also describes a possible novel role of glucagon in the short-term regulation of potassium homeostasis. Several original findings suggest that pancreatic α-cells may express a “potassium sensor” sensitive to changes in plasma K concentration and could respond by adapting glucagon secretion that, in turn, would regulate urinary K excretion. By their combined actions, glucagon and insulin, working in a combinatory mode, could ensure an independent regulation of both plasma glucose and plasma K concentrations. The results and hypotheses reviewed here suggest that the use of glucagon receptor antagonists for the treatment of diabetes should take into account their potential consequences on electrolyte handling by the kidney.

Glucagon receptor antagonist and GIP agonist combination for diet-induced obese mice

Ablation of glucagon receptor signaling represents a potential treatment option for type 2 diabetes (T2DM). Additionally, activation of glucose-dependent insulinotropic polypeptide (GIP) receptor signaling also holds therapeutic promise for T2DM. Therefore, this study examined both independent and combined metabolic actions of desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon (glucagon receptor antagonist) and d-Ala(2)GIP (GIP receptor agonist) in diet-induced obese mice. Glucagon receptor binding has been linked to alpha-helical structure and desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon displayed enhanced alpha-helical content compared with native glucagon. In clonal pancreatic BRIN-BD11 beta-cells, desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon was devoid of any insulinotropic or cAMP-generating actions, and did not impede d-Ala(2)GIP-mediated (P<0.01 to P<0.001) effects on insulin and cAMP production. Twice-daily injection of desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon or d-Ala(2)GIP alone, and in combination, in high-fat-fed mice failed to affect body weight or energy intake. Circulating blood glucose levels were significantly (P<0.05 to P<0.01) decreased by all treatments regimens, with plasma and pancreatic insulin elevated (P<0.05 to P<0.001) in all mice receiving d-Ala(2)GIP. Interestingly, plasma glucagon concentrations were decreased (P<0.05) by sustained glucagon inhibition (day 28), but increased (P<0.05) by d-Ala(2)GIP therapy, with a combined treatment resulting in glucagon concentration similar to saline controls. All treatments improved (P<0.01) intraperitoneal and oral glucose tolerance, and peripheral insulin sensitivity. d-Ala(2)GIP-treated mice showed increased glucose-induced insulin secretion in response to intraperitoneal and oral glucose. Metabolic rate and ambulatory locomotor activity were increased (P<0.05 to P<0.001) in all desHis(1)Pro(4)Glu(9)(Lys(12)PAL)-glucagon-treated mice. These studies highlight the potential of glucagon receptor inhibition alone, and in combination with GIP receptor activation, for T2DM treatment.

Extra-helical binding site of a glucagon receptor antagonist

Glucagon is a 29-amino-acid peptide released from the α-cells of the islet of Langerhans, which has a key role in glucose homeostasis. Glucagon action is transduced by the class B G-protein-coupled glucagon receptor (GCGR), which is located on liver, kidney, intestinal smooth muscle, brain, adipose tissue, heart and pancreas cells, and this receptor has been considered an important drug target in the treatment of diabetes. Administration of recently identified small-molecule GCGR antagonists in patients with type 2 diabetes results in a substantial reduction of fasting and postprandial glucose concentrations. Although an X-ray structure of the transmembrane domain of the GCGR has previously been solved, the ligand (NNC0640) was not resolved. Here we report the 2.5 Å structure of human GCGR in complex with the antagonist MK-0893 (ref. 4), which is found to bind to an allosteric site outside the seven transmembrane (7TM) helical bundle in a position between TM6 and TM7 extending into the lipid bilayer. Mutagenesis of key residues identified in the X-ray structure confirms their role in the binding of MK-0893 to the receptor. The unexpected position of the binding site for MK-0893, which is structurally similar to other GCGR antagonists, suggests that glucagon activation of the receptor is prevented by restriction of the outward helical movement of TM6 required for G-protein coupling. Structural knowledge of class B receptors is limited, with only one other ligand-binding site defined--for the corticotropin-releasing hormone receptor 1 (CRF1R)--which was located deep within the 7TM bundle. We describe a completely novel allosteric binding site for class B receptors, providing an opportunity for structure-based drug design for this receptor class and furthering our understanding of the mechanisms of activation of these receptors.