GPR119 Agonists for the Potential Treatment of Type 2 Diabetes and Related Metabolic Disorders

GPCRs involved in metabolic diseases: pharmacotherapeutic development updates

G protein-coupled receptors (GPCRs) are expressed in a variety of cell types and tissues, and activation of GPCRs is involved in enormous metabolic pathways, including nutrient synthesis, transportation, storage or insulin sensitivity, etc. This review intends to summarize the regulation of metabolic homeostasis and mechanisms by a series of GPCRs, such as GPR91, GPR55, GPR119, GPR109a, GPR142, GPR40, GPR41, GPR43 and GPR120. With deep understanding of GPCR's structure and signaling pathways, it is attempting to uncover the role of GPCRs in major metabolic diseases, including metabolic syndrome, diabetes, dyslipidemia and nonalcoholic steatohepatitis, for which the global prevalence has risen during last two decades. An extensive list of agonists and antagonists with their chemical structures in a nature of small molecular compounds for above-mentioned GPCRs is provided as pharmacologic candidates, and their preliminary data of preclinical studies are discussed. Moreover, their beneficial effects in correcting abnormalities of metabolic syndrome, diabetes and dyslipidemia are summarized when clinical trials have been undertaken. Thus, accumulating data suggest that these agonists or antagonists might become as new pharmacotherapeutic candidates for the treatment of metabolic diseases.

Immunomodulation through Nutrition Should Be a Key Trend in Type 2 Diabetes Treatment

An organism's ability to function properly depends not solely on its diet but also on the intake of nutrients and non-nutritive bioactive compounds that exert immunomodulatory effects. This principle applies both to healthy individuals and, in particular, to those with concomitant chronic conditions, such as type 2 diabetes. However, the current food industry and the widespread use of highly processed foods often lead to nutritional deficiencies. Numerous studies have confirmed the occurrence of immune system dysfunction in patients with type 2 diabetes. This article elucidates the impact of specific nutrients on the immune system function, which maintains homeostasis of the organism, with a particular emphasis on type 2 diabetes. The role of macronutrients, micronutrients, vitamins, and selected substances, such as omega-3 fatty acids, coenzyme Q10, and alpha-lipoic acid, was taken into consideration, which outlined the minimum range of tests that ought to be performed on patients in order to either directly or indirectly determine the severity of malnutrition in this group of patients.

GPR119 agonists for type 2 diabetes: past failures and future hopes for preclinical and early phase candidates

INTRODUCTION

Type 2 diabetes (T2D) is metabolic disorder associated with a decrease in insulin activity and/or secretion from the β-cells of the pancreas, leading to elevated circulating glucose. Current management practices for T2D are complex with varying long-term effectiveness. Agonism of the G protein-coupled receptor GPR119 has received a lot of recent interest as a potential T2D therapeutic.

AREAS COVERED

This article reviews studies focused on GPR119 agonism in animal models of T2D and in patients with T2D.

EXPERT OPINION

GPR119 agonists in vitro and in vivo can potentially regulate incretin hormone release from the gut, then pancreatic insulin release which regulates blood glucose concentrations. However, the success in controlling glucose homeostasis in rodent models of T2D and obesity, failed to translate to early-stage clinical trials in patients with T2D. However, in more recent studies, acute and chronic dosing with the GPR119 agonist DS-8500a had increased efficacy, although this compound was discontinued for further development. New trials on GPR119 agonists are needed, however it may be that the future of GPR119 agonists lie in the development of combination therapy with other T2D therapeutics.

Structure of human GPR119-Gs complex binding APD597 and characterization of GPR119 binding agonists

The rhodopsin-like receptor GPR119 plays a crucial role in glucose homeostasis and is an emerging target for the treatment of type 2 diabetes mellitus. In this study, we analyzed the structure of GPR119 with the agonist APD597 bound and in complex with the downstream G protein trimer by single particle cryo-electron microscopy (cryo-EM). Structural comparison in combination with function assay revealed the conservative and specific effects of different kinds of GPR119 agonists. The activation mechanism of GPR119 was analyzed by comparing the conformational changes between the inactive and active states. The interaction between APD597 derivatives and synthetic agonists with GPR119 was analyzed by molecular docking technique, and the necessary structural framework was obtained. The above conclusions can provide structural and theoretical basis for the development of therapeutic drugs for type 2 diabetes mellitus.

First GPR119 PET Imaging Ligand: Synthesis, Radiochemistry, and Preliminary Evaluations

G-protein-coupled receptor 119 (GPR119) has emerged as a promising target for treating type 2 diabetes mellitus. Activating GPR119 improves glucose homeostasis, while suppressing appetite and weight gain. Measuring GPR119 levels in vivo could significantly advance GPR119-based drug development strategies including target engagement, occupancy, and distribution studies. To date, no positron emission tomography (PET) ligands are available to image GPR119. In this paper, we report the synthesis, radiolabeling, and preliminary biological evaluations of a novel PET radiotracer [18F]KSS3 to image GPR119. PET imaging will provide information on GPR119 changes with diabetic glycemic loads and the efficacy of GPR119 agonists as antidiabetic drugs. Our results demonstrate [18F]KSS3's high radiochemical purity, specific activity, cellular uptake, and in vivo and ex vivo uptake in pancreas, liver, and gut regions, with high GPR119 expression. Cell pretreatment with nonradioactive KSS3, rodent PET imaging, biodistribution, and autoradiography studies showed significant blocking in the pancreas showing [18F]KSS3's high specificity.

Novel targets for potential therapeutic use in Diabetes mellitus

Future targets are a promising prospect to overcome the limitation of conventional and current approaches by providing secure and effective treatment without compromising patient compliance. Diabetes mellitus is a fast-growing problem that has been raised worldwide, from 4% to 6.4% (around 285 million people) in past 30 years. This number may increase to 430 million people in the coming years if there is no better treatment or cure is available. Ageing, obesity and sedentary lifestyle are the key reasons for the worsening of this disease. It always had been a vital challenge, to explore new treatment which could safely and effectively manage diabetes mellitus without compromising patient compliance. Researchers are regularly trying to find out the permanent treatment of this chronic and life threatening disease. In this journey, there are various treatments available in market to manage diabetes mellitus such as insulin, GLP-1 agonist, biguanides, sulphonyl ureas, glinides, thiazolidinediones targeting the receptors which are discovered decade before. PPAR, GIP, FFA1, melatonin are the recent targets that already in the focus for developing new therapies in the treatment of diabetes. Inspite of numerous preclinical studies very few clinical data available due to which this process is in its initial phase. The review also focuses on the receptors like GPCR 119, GPER, Vaspin, Metrnl, Fetuin-A that have role in insulin regulation and have potential to become future targets in treatment for diabetes that may be effective and safer as compared to the conventional and current treatment approaches.

DA-1241, a Novel GPR119 Agonist, Improves Hyperglycaemia by Inhibiting Hepatic Gluconeogenesis and Enhancing Insulin Secretion in Diabetic Mice

BACKGROUND

We investigated the antidiabetic effects of DA-1241, a novel G protein-coupled receptor (GPR) 119 agonist, in vitro and in vivo.

METHODS

DA-1241 was administrated to high-fat diet (HFD)-fed C57BL/6J mice for 12 weeks after hyperglycaemia developed. Oral/intraperitoneal glucose tolerance test and insulin tolerance test were performed. Serum insulin and glucagon-like peptide-1 (GLP-1) levels were measured during oral glucose tolerance test. Insulinoma cell line (INS-1E) cells and mouse islets were used to find whether DA-1241 directly stimulate insulin secretion in beta cell. HepG2 cells were used to evaluate the gluconeogenesis and autophagic process. Autophagic flux was evaluated by transfecting microtubule-associated protein 1 light chain 3-fused to green fluorescent protein and monomeric red fluorescent (mRFP-GFP-LC3) expression vector to HepG2 cells.

RESULTS

Although DA-1241 treatment did not affect body weight gain and amount of food intake, fasting blood glucose level decreased along with increase in GLP-1 level. DA-1241 improved only oral glucose tolerance test and showed no effect in intraperitoneal glucose tolerance test. No significant effect was observed in insulin tolerance test. DA-1241 did not increase insulin secretion in INS-1E cell and mouse islets. DA-1241 reduced triglyceride content in the liver thereby improved fatty liver. Additionally, DA-1241 reduced gluconeogenic enzyme expression in HepG2 cells and mouse liver. DA-1241 reduced autophagic flow in HepG2 cells.

CONCLUSION

These findings suggested that DA-1241 augmented glucose-dependent insulin release via stimulation of GLP-1 secretion, and reduced hepatic gluconeogenesis, which might be associated with autophagic blockage, leading to improved glycaemic control.

Therapeutics for type-2 diabetes mellitus: a glance at the recent inclusions and novel agents under development for use in clinical practice

Diabetes mellitus (DM) is a chronic, progressive, and multifaceted illness resulting in significant physical and psychological detriment to patients. As of 2019, 463 million people are estimated to be living with DM worldwide, out of which 90% have type-2 diabetes mellitus (T2DM). Over the years, significant progress has been made in identifying the risk factors for developing T2DM, understanding its pathophysiology and uncovering various metabolic pathways implicated in the disease process. This has culminated in the implementation of robust prevention programmes and the development of effective pharmacological agents, which have had a favourable impact on the management of T2DM in recent times. Despite these advances, the incidence and prevalence of T2DM continue to rise. Continuing research in improving efficacy, potency, delivery and reducing the adverse effect profile of currently available formulations is required to keep pace with this growing health challenge. Moreover, new metabolic pathways need to be targeted to produce novel pharmacotherapy to restore glucose homeostasis and address metabolic sequelae in patients with T2DM. We searched PubMed, MEDLINE, and Google Scholar databases for recently included agents and novel medication under development for treatment of T2DM. We discuss the pathophysiology of T2DM and review how the emerging anti-diabetic agents target the metabolic pathways involved. We also look at some of the limiting factors to developing new medication and the introduction of unique methods, including facilitating drug delivery to bypass some of these obstacles. However, despite the advances in the therapeutic options for the treatment of T2DM in recent years, the industry still lacks a curative agent.

Targeting the GPR119/incretin axis: a promising new therapy for metabolic-associated fatty liver disease

In the past decade, G protein-coupled receptors have emerged as drug targets, and their physiological and pathological effects have been extensively studied. Among these receptors, GPR119 is expressed in multiple organs, including the liver. It can be activated by a variety of endogenous and exogenous ligands. After GPR119 is activated, the cell secretes a variety of incretins, including glucagon-like peptide-1 and glucagon-like peptide-2, which may attenuate the metabolic dysfunction associated with fatty liver disease, including improving glucose and lipid metabolism, inhibiting inflammation, reducing appetite, and regulating the intestinal microbial system. GPR119 has been a potential therapeutic target for diabetes mellitus type 2 for many years, but its role in metabolic dysfunction associated fatty liver disease deserves further attention. In this review, we discuss relevant research and current progress in the physiology and pharmacology of the GPR119/incretin axis and speculate on the potential therapeutic role of this axis in metabolic dysfunction associated with fatty liver disease, which provides guidance for transforming experimental research into clinical applications.

Discovery of a novel series of GPR119 agonists: Design, synthesis, and biological evaluation of N-(Piperidin-4-yl)-N-(trifluoromethyl)pyrimidin-4-amine derivatives

We undertook an optimization effort involving propan-2-yl 4-({6-[5-(methanesulfonyl)-2,3-dihydro-1H-indol-1-yl]pyrimidin-4-yl}oxy)piperidine-1-carboxylate 1, which we had previously discovered as a novel G protein-coupled receptor 119 (GPR119) agonist. To occupy a presumed hydrophobic space between the pyrimidine and piperidine rings in interaction with GPR119, we replaced the linker oxygen with nitrogen. Subsequently, the introduction of a substituent at the bridging nitrogen atom was explored. We found that the installation of N-trifluoromethyl group 10 not only enhanced GPR119 agonist activity but also considerably improved the human ether-à-go-go-related gene (hERG) inhibition profile. These improvements were not observed for non-fluorinated substituents, such as ethyl analog 8b. The next optimization effort focused on the exploration of a new surrogate structure for the indoline ring and the isosteric replacements of the piperidine N-Boc group to improve solubility, metabolic stability, and oral bioavailability. As a result, N-{1-[3-(2-fluoropropan-2-yl)-1,2,4-oxadiazol-5-yl]piperidin-4-yl}-6-{[1-(methanesulfonyl)piperidin-4-yl]oxy}-N-(trifluoromethyl)pyrimidin-4-amine (27) was identified as a potent and orally bioavailable GPR119 agonist. This compound augmented insulin secretion and effectively lowered plasma glucose excursion in a diabetic animal model after oral administration. In this study, we discuss the designs, syntheses, and biological activities of a novel series of N-(piperidin-4-yl)-N-(trifluoromethyl)pyrimidin-4-amine derivatives as GPR119 agonists, and to determine the distinctive effect of the N-trifluoromethyl group on hERG inhibition, we also discuss the conformational preference of representative compounds.

GPR119 agonists: Novel therapeutic agents for type 2 diabetes mellitus

Diabetes mellitus type 2 (T2D) is a group of genetically heterogeneous metabolic disorders whose frequency has gradually risen worldwide. Diabetes mellitus Type 2 (T2D) has started to achieve a pandemic level, and it is estimated that within the next decade, cases of diabetes might get double due to increase in aging population. Diabetes is rightly called the 'silent killer' because it has emerged to be one of the major causes, leading to renal failure, loss of vision; besides cardiac arrest in India. Thus, a clinical requirement for the oral drug molecules monitoring glucose homeostasis appears to be unmet. GPR119 agonist, a family of G-protein coupled receptors, usually noticed in β-cells of pancreatic as well as intestinal L cells, drew considerable interest for type 2 diabetes mellitus (T2D). GPR119 monitors physiological mechanisms that enhance homeostasis of glucose, such as glucose-like peptide-1, gastrointestinal incretin hormone levels, pancreatic beta cell-dependent insulin secretion and glucose-dependent insulinotropic peptide (GIP). In this manuscript, we have reviewed the work done in the last five years (2015-2020) which gives an approach to design, synthesize, evaluate and study the structural activity relationship of novel GPR119 agonist-based lead compounds. Our article would help the researchers and guide their endeavours in the direction of strategy and development of innovative, effective GPR119 agonist-based compounds for the management of diabetes mellitus type 2.

GPR119 agonists for the treatment of type 2 diabetes: an updated patent review (2014-present)

Introduction: Type 2 diabetes is a rapid-growing complex chronic metabolic disease characterized by hyperglycemia due to lessened insulin secretion, insulin resistance and hepatic glucose overproduction. GPR119 is a class A of G protein-coupled receptor, expressed on certain enteroendocrine L and K cells in the small intestine and by β-cells within the islets of Langerhans of the pancreas. Activation of GPR119 stimulates the secretion of glucagon-like peptide-1 (GLP-1) in the intestinal tract and glucose-dependent release of insulin in pancreatic β-cells.Area covered: This review summarized the reported patents on GPR119 agonists from 2014 to present. The authors described the structural features of these novel synthetic molecules and compared their biological activities (including in vitro and in vivo) as potent GPR119 agonists for the treatment of diabetes.Expert opinion: GPR119 agonists remain the advantage of stimulating both insulin and incretin release in a glucose-dependent manner over other hypoglycemic agents, although some GPR119 agonist clinical candidates have been discontinued in Phase І or Phase II. GPR119 agonists will succeed to be developed as anti-diabetic drugs after accumulated scaffolds of agonists are discovered and the crystallographic structure of GPR119 is elucidated. The synergic effect of GPR119 agonist and DPP-4 inhibitor will also elicit a benefit for the new therapeutic of diabetes.

The gut-brain axis: Identifying new therapeutic approaches for type 2 diabetes, obesity, and related disorders

BACKGROUND

The gut-brain axis, which mediates bidirectional communication between the gastrointestinal system and central nervous system (CNS), plays a fundamental role in multiple areas of physiology including regulating appetite, metabolism, and gastrointestinal function. The biology of the gut-brain axis is central to the efficacy of glucagon-like peptide-1 (GLP-1)-based therapies, which are now leading treatments for type 2 diabetes (T2DM) and obesity. This success and research to suggest a much broader role of gut-brain circuits in physiology and disease has led to increasing interest in targeting such circuits to discover new therapeutics. However, our current knowledge of this biology is limited, largely because the scientific tools have not been available to enable a detailed mechanistic understanding of gut-brain communication.

SCOPE OF REVIEW

In this review, we provide an overview of the current understanding of how sensory information from the gastrointestinal system is communicated to the central nervous system, with an emphasis on circuits involved in regulating feeding and metabolism. We then describe how recent technologies are enabling a better understanding of this system at a molecular level and how this information is leading to novel insights into gut-brain communication. We also discuss current therapeutic approaches that leverage the gut-brain axis to treat diabetes, obesity, and related disorders and describe potential novel approaches that have been enabled by recent advances in the field.

MAJOR CONCLUSIONS

The gut-brain axis is intimately involved in regulating glucose homeostasis and appetite, and this system plays a key role in mediating the efficacy of therapeutics that have had a major impact on treating T2DM and obesity. Research into the gut-brain axis has historically largely focused on studying individual components in this system, but new technologies are now enabling a better understanding of how signals from these components are orchestrated to regulate metabolism. While this work reveals a complexity of signaling even greater than previously appreciated, new insights are already being leveraged to explore fundamentally new approaches to treating metabolic diseases.

Discovery of a novel series of indolinylpyrimidine-based GPR119 agonists: Elimination of ether-a-go-go-related gene liability using a hydrogen bond acceptor-focused approach

We previously identified a novel series of indolinylpyrimidine derivatives exemplified by 2 in Figure 1, which is an indoline based derivative, as potent GPR119 agonists. Despite the attractive potency of 2, this compound inhibited the human ether-a-go-go-related gene (hERG) K⁺ channel. We elucidated crucial roles of the methylsulfonyl group of 2 in its interaction with the hERG channel and the GPR119 receptor, presumably as a hydrogen bond acceptor (HBA). To remove the undesirable hERG inhibitory activity, a strategy was implemented to arrange an HBA on a less conformationally flexible framework at the indoline 5-position instead of the methylsulfonyl group. This successfully led to the discovery of a piperidinone ring as a desirable motif at the indoline 5-position, which could minimize hERG liability as shown by 24b. Further optimization focused on the reduction of lipophilicity in terms of more favorable drug-like properties. Consequently, the introduction of a hydroxy group at the 3-position of the piperidinone ring effectively reduced lipophilicity without compromising GPR119 potency, resulting in the identification of (3S)-3-hydroxy-1-{1-[6-({1-[3-(propan-2-yl)-1,2,4-oxadiazol-5-yl]piperidin-4-yl}oxy)pyrimidin-4-yl]- 2,3-dihydro-1H-indol-5-yl}piperidin-2-one ((S)-29) as a novel, potent, and orally bioavailable GPR119 agonist with a well-balanced profile. The pharmacological effects of this compound were also confirmed after single and chronic oral administration in diabetic animal models.

Identification of Novel, Structurally Diverse, Small Molecule Modulators of GPR119

GPR119 drug discovery efforts in the pharmaceutical industry for the treatment of type 2 diabetes mellitus (T2DM) and obesity, were initiated based on its restricted distribution in pancreas and GI tract, and its possible role in glucose homeostasis. While a number of lead series have emerged, the pharmacological endpoints they provide have not been clear. In particular, many lead series have demonstrated loss of efficacy and significant toxic side effects. Thus, we sought to identify novel, potent, positive modulators of GPR119. In this study, we have successfully developed and optimized a high-throughput screening strategy to identify GPR119 modulators using a live cell assay format that utilizes a cyclic nucleotide-gated channel as a biosensor for cAMP production. Our high-throughput screening (HTS) approach is unique to that of previous HTS approaches targeting this receptor, as changes in cAMP were measured both in the presence and absence of an EC₁₀ of the endogenous ligand, oleoylethanolamide, enabling detection of both agonists and potential allosteric modulators in a single assay. From these efforts, we have identified positive modulators of GPR119 with similar as well as unique scaffolds compared to existing compounds and similar as well as unique signaling properties. Our compounds will not only serve as novel molecular probes to better understand GPR119 pleiotropic signaling and the underlying physiological consequences of receptor activation, but are also well-suited for translation as potential therapeutic agents.

Modulation of the Oxidative Stress and Lipid Peroxidation by Endocannabinoids and Their Lipid Analogues

Growing evidence supports the pivotal role played by oxidative stress in tissue injury development, thus resulting in several pathologies including cardiovascular, renal, neuropsychiatric, and neurodegenerative disorders, all characterized by an altered oxidative status. Reactive oxygen and nitrogen species and lipid peroxidation-derived reactive aldehydes including acrolein, malondialdehyde, and 4-hydroxy-2-nonenal, among others, are the main responsible for cellular and tissue damages occurring in redox-dependent processes. In this scenario, a link between the endocannabinoid system (ECS) and redox homeostasis impairment appears to be crucial. Anandamide and 2-arachidonoylglycerol, the best characterized endocannabinoids, are able to modulate the activity of several antioxidant enzymes through targeting the cannabinoid receptors type 1 and 2 as well as additional receptors such as the transient receptor potential vanilloid 1, the peroxisome proliferator-activated receptor alpha, and the orphan G protein-coupled receptors 18 and 55. Moreover, the endocannabinoids lipid analogues N-acylethanolamines showed to protect cell damage and death from reactive aldehydes-induced oxidative stress by restoring the intracellular oxidants-antioxidants balance. In this review, we will provide a better understanding of the main mechanisms triggered by the cross-talk between the oxidative stress and the ECS, focusing also on the enzymatic and non-enzymatic antioxidants as scavengers of reactive aldehydes and their toxic bioactive adducts.

Discovery of MK-8282 as a Potent G-Protein-Coupled Receptor 119 Agonist for the Treatment of Type 2 Diabetes

The ever-growing prevalence of type 2 diabetes in the world has necessitated an urgent need for multiple orally effective agents that can regulate glucose homeostasis with a concurrent reduction in body weight. G-Protein coupled receptor 119 (GPR119) is a GPCR target at which agonists have demonstrated glucose-dependent insulin secretion and shows beneficial effects on glycemic control. Herein, we describe our efforts leading to the identification of a potent, oral GPR-119 agonist, MK-8282, which shows improved glucose tolerance in multiple animal models and has excellent off-target profile. The key design elements in the compounds involved a combination of a fluoro-pyrimidine and a conformationally constrained bridged piperidine to impart good potency and efficacy.

Structure and biological activity of endogenous and synthetic agonists of GPR119

A G-protein-coupled receptor, GPR119, is a promising pharmacological target for a new class of hypoglycaemic drugs with an original mechanism of action, namely, increase in the glucose-dependent incretin and insulin secretion. In 2005, the first ligands were found and in the subsequent years, a large number of GPR119 agonists were synthesized in laboratories in various countries; the safest and most promising agonists have entered phase I and II clinical trials as agents for the treatment of type 2 diabetes mellitus and obesity. The review describes the major endogenous GPR119 agonists and the main trends in the design and modification of synthetic structures for increasing the hypoglycaemic activity. The data on synthetic agonists are arranged according to the type of the central core of the molecules.

The bibliography includes 104 references.

Therapeutic application of GPR119 ligands in metabolic disorders

GPR119 belongs to the G protein-coupled receptor family and exhibits dual modes of action upon ligand-dependent activation: pancreatic secretion of insulin in a glucose-dependent manner and intestinal secretion of incretins. Hence, GPR119 has emerged as a promising target for treating type 2 diabetes mellitus without causing hypoglycaemia. However, despite continuous efforts by many major pharmaceutical companies, no synthetic GPR119 ligand has been approved as a new class of anti-diabetic agents thus far, nor has any passed beyond phase II clinical studies. Herein, we summarize recent advances in research concerning the physiological/pharmacological effects of GPR119 and its synthetic ligands on the regulation of energy metabolism, and we speculate on future applications of GPR119 ligands for the treatment of metabolic diseases, focusing on non-alcoholic fatty liver disease.

Gut hormone pharmacology of a novel GPR119 agonist (GSK1292263), metformin, and sitagliptin in type 2 diabetes mellitus: results from two randomized studies

GPR119 receptor agonists improve glucose metabolism and alter gut hormone profiles in animal models and healthy subjects. We therefore investigated the pharmacology of GSK1292263 (GSK263), a selective GPR119 agonist, in two randomized, placebo-controlled studies that enrolled subjects with type 2 diabetes. Study 1 had drug-naive subjects or subjects who had stopped their diabetic medications, and Study 2 had subjects taking metformin. GSK263 was administered as single (25–800 mg; n = 45) or multiple doses (100–600 mg/day for 14 days; n = 96). Placebo and sitagliptin 100 mg/day were administered as comparators. In Study 1, sitagliptin was co-administered with GSK263 or placebo on Day 14 of dosing. Oral glucose and meal challenges were used to assess the effects on plasma glucose, insulin, C-peptide, glucagon, peptide tyrosine-tyrosine (PYY), glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). After 13 days of dosing, GSK263 significantly increased plasma total PYY levels by ∼five-fold compared with placebo, reaching peak concentrations of ∼50 pM after each of the three standardized meals with the 300 mg BID dose. Co-dosing of GSK263 and metformin augmented peak concentrations to ∼100 pM at lunchtime. GSK263 had no effect on active or total GLP-1 or GIP, but co-dosing with metformin increased post-prandial total GLP-1, with little effect on active GLP-1. Sitagliptin increased active GLP-1, but caused a profound suppression of total PYY, GLP-1, and GIP when dosed alone or with GSK263. This suppression of peptides was reduced when sitagliptin was co-dosed with metformin. GSK263 had no significant effect on circulating glucose, insulin, C-peptide or glucagon levels. We conclude that GSK263 did not improve glucose control in type 2 diabetics, but it had profound effects on circulating PYY. The gut hormone effects of this GPR119 agonist were modulated when co-dosed with metformin and sitagliptin. Metformin may modulate negative feedback loops controlling the secretion of enteroendocrine peptides.

Trial Registration:

Clinicaltrials.gov NCT01119846 Clinicaltrials.gov NCT01128621

Intercellular Lipid Mediators and GPCR Drug Discovery

G-protein-coupled receptors (GPCR) are the largest superfamily of receptors responsible for signaling between cells and tissues, and because they play important physiological roles in homeostasis, they are major drug targets. New technologies have been developed for the identification of new ligands, new GPCR functions, and for drug discovery purposes. In particular, intercellular lipid mediators, such as, lysophosphatidic acid and sphingosine 1-phosphate have attracted much attention for drug discovery and this has resulted in the development of fingolimod (FTY-720) and AM095. The discovery of new intercellular lipid mediators and their GPCRs are discussed from the perspective of drug development. Lipid GPCRs for lysophospholipids, including lysophosphatidylserine, lysophosphatidylinositol, lysophosphatidylcholine, free fatty acids, fatty acid derivatives, and other lipid mediators are reviewed.

A categorical structure-activity relationship analysis of GPR119 ligands

The categorical structure-activity relationship (cat-SAR) expert system has been successfully used in the analysis of chemical compounds that cause toxicity. Herein we describe the use of this fragment-based approach to model ligands for the G protein-coupled receptor 119 (GPR119). Using compounds that are known GPR119 agonists and compounds that we have confirmed experimentally that are not GPR119 agonists, four distinct cat-SAR models were developed. Using a leave-one-out validation routine, the best GPR119 model had an overall concordance of 99%, a sensitivity of 99%, and a specificity of 100%. Our findings from the in-depth fragment analysis of several known GPR119 agonists were consistent with previously reported GPR119 structure-activity relationship (SAR) analyses. Overall, while our results indicate that we have developed a highly predictive cat-SAR model that can be potentially used to rapidly screen for prospective GPR119 ligands, the applicability domain must be taken into consideration. Moreover, our study demonstrates for the first time that the cat-SAR expert system can be used to model G protein-coupled receptor ligands, many of which are important therapeutic agents.

Structure-activity relationships of fatty acid amide ligands in activating and desensitizing G protein-coupled receptor 119

The purpose of the current study was to apply a high throughput assay to investigate the structure-activity relationships of fatty acid amides for activating and desensitizing G protein-coupled receptor 119, a promising therapeutic target for both type 2 diabetes and obesity. A cell-based, homogenous time resolved fluorescence (HTRF) method for measuring G protein-coupled receptor 119-mediated increase of cyclic adenosine monophosphate (cAMP) levels was validated and applied in this study. Using novel fatty acid amides and detailed potency and efficacy analyses, we have demonstrated that degree of saturation in acyl chain and charged head groups of fatty acid amides have profound effects on the ability of these compounds to activate G protein-coupled receptor 119. In addition, we have demonstrated for the first time that pretreatments with G protein-coupled receptor 119 agonists desensitize the receptor and the degrees of desensitization caused by fatty acid amides correlate well with their structure-activity relationships in activating the receptor.

GPR119 agonists: a promising approach for T2DM treatment? A SWOT analysis of GPR119

Ever since its advent as a promising therapeutic target for type 2 diabetes mellitus (T2DM), G-protein-coupled receptor 119 (GPR119) has received much interest from the pharmaceutical industry. This interest peaked in June 2010, when Sanofi-Aventis agreed to pay Metabolex (Cymabay Therapeutics) US$375 million for MBX-2982, which was a representative orally active GPR119 agonist. However, Sanofi-Aventis opted to terminate the deal in May 2011 and another leading GPR119 agonist, GSK1292263, had a loss of efficacy during its clinical trial. In this review, I discuss the pros and cons of GPR119 through a strengths, weaknesses, opportunities, and threats (SWOT) analysis and propose development strategies for the eventual success of a GPR119 agonist development program.

International Union of Basic and Clinical Pharmacology. LXXXVIII. G protein-coupled receptor list: recommendations for new pairings with cognate ligands

In 2005, the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) published a catalog of all of the human gene sequences known or predicted to encode G protein-coupled receptors (GPCRs), excluding sensory receptors. This review updates the list of orphan GPCRs and describes the criteria used by NC-IUPHAR to recommend the pairing of an orphan receptor with its cognate ligand(s). The following recommendations are made for new receptor names based on 11 pairings for class A GPCRs: hydroxycarboxylic acid receptors [HCA₁ (GPR81) with lactate, HCA₂ (GPR109A) with 3-hydroxybutyric acid, HCA₃ (GPR109B) with 3-hydroxyoctanoic acid]; lysophosphatidic acid receptors [LPA₄ (GPR23), LPA₅ (GPR92), LPA₆ (P2Y5)]; free fatty acid receptors [FFA4 (GPR120) with omega-3 fatty acids]; chemerin receptor (CMKLR1; ChemR23) with chemerin; CXCR7 (CMKOR1) with chemokines CXCL12 (SDF-1) and CXCL11 (ITAC); succinate receptor (SUCNR1) with succinate; and oxoglutarate receptor [OXGR1 with 2-oxoglutarate]. Pairings are highlighted for an additional 30 receptors in class A where further input is needed from the scientific community to validate these findings. Fifty-seven human class A receptors (excluding pseudogenes) are still considered orphans; information has been provided where there is a significant phenotype in genetically modified animals. In class B, six pairings have been reported by a single publication, with 28 (excluding pseudogenes) still classified as orphans. Seven orphan receptors remain in class C, with one pairing described by a single paper. The objective is to stimulate research into confirming pairings of orphan receptors where there is currently limited information and to identify cognate ligands for the remaining GPCRs. Further information can be found on the IUPHAR Database website (http://www.iuphar-db.org).

Stimulation of proglucagon gene expression by human GPR119 in enteroendocrine L-cell line GLUTag

GPR119 is a G protein-coupled receptor expressed on enteroendocrine L-cells that synthesize and secrete the incretin hormone glucagon-like peptide-1 (GLP-1). Although GPR119 agonists stimulate L-cell GLP-1 secretion, there is uncertainty concerning whether GLP-1 biosynthesis is under the control of GPR119. Here we report that GPR119 is functionally coupled to increased proglucagon (PG) gene expression that constitutes an essential first step in GLP-1 biosynthesis. Using a mouse L-cell line (GLUTag) that expresses endogenous GPR119, we demonstrate that PG gene promoter activity is stimulated by GPR119 agonist AS1269574. Surprisingly, transfection of GLUTag cells with recombinant human GPR119 (hGPR119) results in a constitutive and apparently ligand-independent increase of PG gene promoter activity and PG mRNA content. These constitutive actions of hGPR119 are mediated by cAMP-dependent protein kinase (PKA) but not cAMP sensor Epac2. Thus, the constitutive action of hGPR119 to stimulate PG gene promoter activity is diminished by: 1) a dominant-negative Gαs protein, 2) a dominant-negative PKA regulatory subunit, and 3) a dominant-negative A-CREB. Interestingly, PG gene promoter activity is stimulated by 6-Bn-cAMP-AM, a cAMP analog that selectively activates α and β isoforms of type II, but not type I PKA regulatory subunits expressed in GLUTag cells. Finally, our analysis reveals that a specific inhibitor of Epac2 activation (ESI-05) fails to block the stimulatory action of 6-Bn-cAMP-AM at the PG gene promoter, nor is PG gene promoter activity stimulated by: 1) a constitutively active Epac2, or 2) cAMP analogs that selectively activate Epac proteins. Such findings are discussed within the context of ongoing controversies concerning the relative contributions of PKA and Epac2 to the control of PG gene expression.

Endogenous metabolites as ligands for G protein-coupled receptors modulating risk factors for metabolic and cardiovascular disease

During the last decade, several G protein-coupled receptors activated by endogenous metabolites have been described. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Receptors of endogenous metabolites are expressed in taste cells, the gastrointestinal tract, adipose tissue, endocrine glands, immune cells, or the kidney and are therefore in a position to sense food intake in the gastrointestinal tract or to link metabolite levels to the appropriate responses of metabolic organs. Some of the receptors appear to provide a link between metabolic and neuronal or immune functions. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

Bowels control brain: gut hormones and obesity

Peptide hormones are released from the gastrointestinal tract in response to nutrients and communicate information regarding the current state of energy balance to the brain. These hormones regulate appetite, energy expenditure and glucose homeostasis. They can act either via the circulation at target peripheral tissues, by activation of the vagus nerve or by acting on key brain regions implicated in energy homeostasis such as the hypothalamus and brainstem. This review gives an overview of the main gut hormones implicated in the regulation of food intake and how some of these are being targeted to develop anti obesity treatments.

The cytoprotective effects of oleoylethanolamide in insulin-secreting cells do not require activation of GPR119

BACKGROUND AND PURPOSE

β-cells express a range of fatty acid-responsive G protein-coupled receptors, including GPR119, which regulates insulin secretion and is seen as a potential therapeutic target in type 2 diabetes. The long-chain unsaturated fatty acid derivative oleoylethanolamide (OEA) is an endogenous agonist of GPR119 and, under certain conditions, some long-chain unsaturated fatty acids can promote β-cell cytoprotection. It is not known, however, if OEA is cytoprotective in β-cells. The present study has examined this and determined whether GPR119 is involved.

METHODS

Clonal rat insulin-secreting cell lines, BRIN-BD11 or INS-1E, were exposed to fatty acids complexed with BSA. cAMP levels, insulin release and cell viability were measured. Protein expression was studied by Western blotting and receptor expression by RT-PCR.

KEY RESULTS

GPR119 was expressed in both BRIN-BD11 and INS-1E cells and OEA was cytoprotective in these cells. However, cytoprotection was not reproduced by any of a range of selective, synthetic ligands of GPR119. The cytoprotective response to OEA was lost during exposure to inhibitors of fatty acid amide hydrolase (FAAH) suggesting that OEA per se is not the cytoprotective species but that release of free oleate is required. Similar data were obtained with anandamide, which was cytoprotective only under conditions favouring release of free arachidonate.

CONCLUSIONS AND IMPLICATIONS

Activation of GPR119 is not required to mediate the cytoprotective actions of OEA in BRIN-BD11 or INS-1E cells. Rather, OEA is internalised and subjected to hydrolysis by FAAH to release free oleate, which then mediates the cytoprotection.

Swim stress differentially affects limbic contents of 2-arachidonoylglycerol and 2-oleoylglycerol

Restraint stress exposures evoke progressively larger increases in 2-arachidonoylglycerol (2-AG) in limbic brain regions as the number of repetitions increases. The Porsolt swim test usually involves two swim exposures separated by 24 h, and we asked whether the 2-AG response differed between the first and second exposures.

METHODS

Four groups of male C57/Bl6N mice were studied: control; exposed to a single 6 min swim and killed immediately; exposed to a single 6 min swim and killed 24 h later; and exposed to two swims, separated by 24 h, and killed after the second swim. Outcomes were swim behavior, serum corticosterone, and 2-AG and 2-oleoylglycerol (2-OG) contents in amygdala, hippocampus, and prefrontal cortex.

RESULTS

Mean 2-AG contents were not significantly different among the four treatment groups in any brain region and did not correlate with immobility in either forced swim exposure. However, 2-AG contents in all three brain regions only of the mice exposed to two swims were significantly, positively correlated with serum corticosterone concentrations measured at the same time. 2-OG is present in brain and exhibits a striking regional heterogeneity in control mice. 2-OG concentrations in prefrontal cortex were significantly reduced in the mice killed on the second day compared with the mice killed on the first day. As the target of 2-OG in brain is not known, the significance of these observations await further studies.

CONCLUSIONS

Although prior exposure to swim stress does not alter brain 2-AG contents upon re-exposure, 2-AG concentrations in brain become significantly correlated with the hypothalamic-pituitary-adrenal (HPA) axis response to stress when prior exposure to the stress has occurred. These data suggest that even a single exposure to a short period of intense stress sensitizes the 2-AG response to re-exposure to that situation and are consistent with a role for endocannabinoid signaling in modulating stress responses.

The role of the gut/brain axis in modulating food intake

Peptide hormones released from the gastrointestinal tract communicate information about the current state of energy balance to the brain. These hormones regulate appetite and energy expenditure via the vagus nerve or by acting on key brain regions implicated in energy homeostasis such as the hypothalamus and brainstem. This review gives an overview of the main gut hormones implicated in the regulation of food intake. Research in this area has provided novel targets for the pharmacological treatment of obesity. This article is part of a Special Issue entitled 'Central Control Food Intake'

The future of incretin-based therapy: novel avenues--novel targets

Incretin-based therapy for type 2 diabetes is based on the antidiabetic effects of glucagon-like peptide-1 (GLP-1) and instituted by GLP-1 receptor agonists and dipeptidyl peptidase-4 inhibitors targeting the key islet defects of the disease. The treatment is clinically efficient and safe, and associated with a low risk of adverse events. It can be used both in early and late stages of the disease and both as monotherapy and add-on to other therapies. Current research on the future of incretin-based therapy focuses on optimizing its place in diabetes treatment and examines its potential in type 1 diabetes, in subjects with obesity without type 2 diabetes and in cardiovascular and neurodegenerative disorders. Other studies aim at prolonging the duration of action of the GLP-1 receptor agonists to allow weekly administration, and to develop orally GLP-1 receptor agonists. Furthermore, other investigators focus on stimulation of GLP-1 secretion by activating GLP-1-producing L-cells or using gene therapy. Finally, also other gastro-entero-pancreatic bioactive peptides are potential targets for drug development as are synthetic peptides engineered as co-agonists stimulating more than one receptor. We can therefore expect a dynamic development within this field in the coming years.

Molecular physiology of glucagon-like peptide-1 insulin secretagogue action in pancreatic β cells

Insulin secretion from pancreatic β cells is stimulated by glucagon-like peptide-1 (GLP-1), a blood glucose-lowering hormone that is released from enteroendocrine L cells of the distal intestine after the ingestion of a meal. GLP-1 mimetics (e.g., Byetta) and GLP-1 analogs (e.g., Victoza) activate the β cell GLP-1 receptor (GLP-1R), and these compounds stimulate insulin secretion while also lowering levels of blood glucose in patients diagnosed with type 2 diabetes mellitus (T2DM). An additional option for the treatment of T2DM involves the administration of dipeptidyl peptidase-IV (DPP-IV) inhibitors (e.g., Januvia, Galvus). These compounds slow metabolic degradation of intestinally released GLP-1, thereby raising post-prandial levels of circulating GLP-1 substantially. Investigational compounds that stimulate GLP-1 secretion also exist, and in this regard a noteworthy advance is the demonstration that small molecule GPR119 agonists (e.g., AR231453) stimulate L cell GLP-1 secretion while also directly stimulating β cell insulin release. In this review, we summarize what is currently known concerning the signal transduction properties of the β cell GLP-1R as they relate to insulin secretion. Emphasized are the cyclic AMP, protein kinase A, and Epac2-mediated actions of GLP-1 to regulate ATP-sensitive K⁺ channels, voltage-dependent K⁺ channels, TRPM2 cation channels, intracellular Ca⁺ release channels, and Ca⁺-dependent exocytosis. We also discuss new evidence that provides a conceptual framework with which to understand why GLP-1R agonists are less likely to induce hypoglycemia when they are administered for the treatment of T2DM.