Chronic treatment with novel GPR40 agonists improve whole-body glucose metabolism based on the glucose-dependent insulin secretion

Free-fatty acid receptor-1 (FFA1/GPR40) promotes papillary RCC proliferation and tumor growth via Src/PI3K/AKT/NF-κB but suppresses migration by inhibition of EGFR, ERK1/2, STAT3 and EMT

BACKGROUND

Papillary renal cell carcinoma (pRCC) is a highly metastatic genitourinary cancer and is generally irresponsive to common treatments used for the more prevalent clear-cell (ccRCC) subtype. The goal of this study was to examine the novel role of the free fatty-acid receptor-1 (FFA1/GPR40), a cell-surface expressed G protein-coupled receptor that is activated by medium-to-long chained dietary fats, in modulation of pRCC cell migration invasion, proliferation and tumor growth.

METHODS

We assessed the expression of FFA1 in human pRCC and ccRCC tumor tissues compared to patient-matched non-cancerous controls, as well as in RCC cell lines. Using the selective FFA1 agonist AS2034178 and the selective FFA1 antagonist GW1100, we examined the role of FFA1 in modulating cell migration, invasion, proliferation and tumor growth and assessed the FFA1-associated intracellular signaling mechanisms via immunoblotting.

RESULTS

We reveal for the first time that FFA1 is upregulated in pRCC tissue compared to patient-matched non-cancerous adjacent tissue and that its expression increases with pRCC cancer pathology, while the inverse is seen in ccRCC tissue. We also show that FFA1 is expressed in the pRCC cell line ACHN, but not in ccRCC cell lines, suggesting a unique role in pRCC pathology. Our results demonstrate that FFA1 agonism promotes tumor growth and cell proliferation via c-Src/PI3K/AKT/NF-κB and COX-2 signaling. At the same time, agonism of FFA1 strongly inhibits migration and invasion, which are mechanistically mediated via inhibition of EGFR, ERK1/2 and regulators of epithelial-mesenchymal transition.

CONCLUSIONS

Our data suggest that FFA1 plays oppositional growth and migratory roles in pRCC and identifies this receptor as a potential target for modulation of pathogenesis of this aggressive cancer.

Learn from failures and stay hopeful to GPR40, a GPCR target with robust efficacy, for therapy of metabolic disorders

GPR40 is a class A G-protein coupled receptor (GPCR) mainly expressed in pancreas, intestine, and brain. Its endogenous ligand is long-chain fatty acids, which activate GPR40 after meal ingestion to induce secretion of incretins in the gut, including GLP-1, GIP, and PYY, the latter control appetite and glucose metabolism. For its involvement in satiety regulation and metabolic homeostasis, partial and AgoPAM (Positive Allosteric Modulation agonist) GPR40 agonists had been developed for type 2 diabetes (T2D) by many pharmaceutical companies. The proof-of-concept of GPR40 for control of hyperglycemia was achieved by clinical trials of partial GPR40 agonist, TAK-875, demonstrating a robust decrease in HbA1c (-1.12%) after chronic treatment in T2D. The development of TAK-875, however, was terminated due to liver toxicity in 2.7% patients with more than 3-fold increase of ALT in phase II and III clinical trials. Different mechanisms had since been proposed to explain the drug-induced liver injury, including acyl glucuronidation, inhibition of mitochondrial respiration and hepatobiliary transporters, ROS generation, etc. In addition, activation of GPR40 by AgoPAM agonists in pancreas was also linked to β-cell damage in rats. Notwithstanding the multiple safety concerns on the development of small-molecule GPR40 agonists for T2D, some partial and AgoPAM GPR40 agonists are still under clinical development. Here we review the most recent progress of GPR40 agonists development and the possible mechanisms of the side effects in different organs, and discuss the possibility of developing novel strategies that retain the robust efficacy of GPR40 agonists for metabolic disorders while avoid toxicities caused by off-target and on-target mechanisms.

Evaluation of the hepatotoxicity of the novel GPR40 (FFAR1) agonist CPL207280 in the rat and monkey

GPR40 (FFAR1) is a promising target for the managing type 2 diabetes (T2D). The most advanced GPR40 agonist TAK-875 exhibited satisfactory glucose-lowering effects in phase II and III studies. However, the phase III studies of TAK-875 revealed drug-induced liver injury (DILI). It is unknown whether DILI is a consequence of a specific GPR40 agonist or is an inherent feature of all GPR40 agonists. CPL207280 is a novel GPR40 agonist that improves diabetes in Zucker Diabetic Fatty (ZDF) rats, Goto Kakizaki (GK) rats and db/db mice. In this report, the DILI-related toxicity of CPL207280 was compared directly with that of TAK-875. In vitro studies evaluating hepatic biliary transporter inhibition, mitochondrial function, and metabolic profiling were performed in hepatocytes from different species. The long term toxicity of CPL207280 was studied in vivo in rats and monkeys. Activity of CPL207280 was one order of magnitude lesser than that of TAK-875 for the inhibition of bile acid transporters. CPL207280 had a negligible effect on the hepatic mitochondria. In contrast to TAK-875, which was metabolized through toxic glucuronidation, CPL207280 was metabolized mainly through oxidation. No deleterious hepatic effects were observed in chronically treated healthy and diabetic animals. The study presents promising data on the feasibility of creating a liver-safe GPR40 agonist. Additionally, it can be concluded that DILI is not a hallmark of GPR40 agonists; it is linked to the intrinsic properties of an individual agonist.

Type 2 diabetes mellitus: pathogenesis and genetic diagnosis

Type 2 diabetes mellitus (T2DM) is a heterogeneous condition that is related to both defective insulin secretion and peripheral insulin resistance. Beta cells are the major organ for secreting insulin hence, it is important to maintain an adequate beta-cell mass in response to various changes. Insulin resistance is a major cause of T2DM leads to elevated free fatty acid (FFA) levels which increases beta-cell mass and insulin secretion to compensate for insulin insensitivity. Chronic increase of plasma FFA levels results in disturbances in lipid metabolism, which contributes to decreased beta-cell function and lipotoxicity thus promoting T2DM. In the present review, we have discussed the process of beta-cell destruction, the role of genes in contributing to the fast increase in the progression of T2DM in detail. More than 130 variants in various T2DM susceptibility and candidate genes have been discovered to be associated with T2DM. Still, these variants elucidate only a small amount of total heritability of T2DM. Further, there is also an inventory of presently used therapeutic tools and a review of novel therapeutic approaches like incretin-based therapies or sodium-glucose transporter-2 inhibitors. Additionally, providing a concise but comprehensive update, this review will be essential to every clinician involved in the treatment of diabetes mellitus.

Role of GPR40 in pathogenesis and treatment of Alzheimer's disease and type 2 diabetic dementia

G-protein coupled receptor 40 (GPR40) is also known as free fatty acid receptor 1. It is a typical 7 transmembrane receptor and currently the natural receptor of the saturated or unsaturated long-chain fatty acids. It could trigger the intracellular signalling pathway when combined with the free long-chain fatty acids, thereby controlling cells physiological function. In this review, we summarised the relationships and the potential mechanisms between the promising target GPR40, and pathogenesis and treatment of Alzheimer's disease and type 2 diabetic dementia. It may provide a theoretical reference for the development of clinical drug targeting GPR40.

Free fatty acid receptor 1 as a novel therapeutic target for type 2 diabetes mellitus-current status

The incidence of type 2 diabetes mellitus (T2DM) has been on the increase in recent times. Although several oral treatments for T2DM are available, some of them have been found to elicit undesirable side effects. This therefore underscores the need for new treatment options with lesser side effects than the existing ones for people with T2DM. Free fatty acid receptor 1 (FFAR1), also known as GPR40, belongs to a class of G-protein coupled receptors that are encoded by FFAR1 genes in humans. It is expressed in the pancreatic β-cells and it is activated by medium- and long-chain saturated and unsaturated fatty acids. Thus it responds to endogenous medium and long chain unsaturated fatty acids, resulting in enhancement of insulin secretion during increased glucose levels. The glucose dependency of insulin secretion has made this receptor a very good target for developing therapies that could be efficacious with fewer side effects than the existing therapies for the treatment of T2DM. Given that tremendous efforts have been made in recent times in developing novel FFAR1 agonists with antidiabetic potentials, this article provides a current status of knowledge on the efforts made so far in developing novel FFAR1 agonists that would be of relevance in the management of T2DM.

Free fatty acid receptor 1 agonist, MR1704, lowers blood glucose levels in rats unresponsive to the sulfonylurea, glibenclamide

Preclinical Research & Development MR1704 is a selective G protein-coupled receptor 40/free fatty acid receptor 1 agonist, which exhibited favorable pharmacokinetic profiles and glucose-lowering effects in animal models. We studied the effects of MR1704 in a sulfonylurea-desensitized Sprague-Dawley rat model and evaluated the risk of pancreatic β-cell exhaustion compared to that of glibenclamide in Zucker fatty rats. Rats fed ad libitum a diet containing 0.03% glibenclamide exhibited lower non-fasting blood glucose levels compared to those in rats fed a control diet during the first 6 days. However, the response to glibenclamide disappeared on day 9. In a rat oral glucose tolerance test (OGTT), MR1704 reduced the plasma glucose excursion, whereas glibenclamide did not show this effect. In Zucker fatty rats, oral administration of MR1704 reduced glucose excursion during the OGTT, and the effects of MR1704 were maintained after 2-week treatment. In contrast, the glucose-lowering effects of glibenclamide were diminished, and glucose tolerance was aggravated after 2-week treatment. These results indicated that MR1704 provided more sustainable effects compared to those of the sulfonylurea, glibenclamide suggesting that MR1704 may be an attractive therapeutic option for diabetic patients who are unresponsive to sulfonylurea treatment.

A novel free fatty acid receptor 1 (GPR40/FFAR1) agonist, MR1704, enhances glucose-dependent insulin secretion and improves glucose homeostasis in rats

Activation of G protein‐coupled receptor 40/Free fatty acid receptor 1 (GPR40/FFAR1), which is highly expressed in pancreatic β cells, is considered an important pharmacologic target for the treatment of type 2 diabetes mellitus. The aim of this study was to determine the effect of MR1704, a novel GPR40/FFAR1 agonist, on glucose homeostasis in rats. MR1704 is a highly potent and selective, orally bioavailable agonist with similar in vitro potencies among humans, mice, and rats. Treatment of rat islets with MR1704 increased glucose‐dependent insulin secretion. Augmentation of glucose‐dependent insulin secretion was abolished by adding a GPR40/FFAR1 antagonist. In mouse, insulinoma MIN6 cells, palmitic acid induced the activity of caspase 3/7 after a 72‐h exposure, while pharmacologically active concentrations of MR1704 did not. In an oral glucose tolerance test in normal Sprague‐Dawley rats, orally administered MR1704 (1–10 mg·kg⁻¹) reduced plasma glucose excursion and enhanced insulin secretion, but MR1704 did not induce hypoglycemia, even at 300 mg·kg⁻¹, in fasted Sprague‐Dawley rats. In addition, orally administered MR1704 reduced plasma glucose excursion and enhanced insulin secretion in diabetic Goto‐Kakizaki rats. Oral administration of MR1704 once daily to Goto‐Kakizaki rats reduced their blood glucose levels during a 5‐week treatment period without reducing pancreatic insulin content; as a result, hemoglobin A1C levels significantly decreased. These results suggest that MR1704 improves glucose homeostasis through glucose‐dependent insulin secretion with a low risk of hypoglycemia and pancreatic toxicity. MR1704 shows promise as a new, glucose‐lowering drug to treat type 2 diabetes mellitus.

The Role and Future of FFA1 as a Therapeutic Target

Of the 415 million people suffering from diabetes worldwide, 90% have type 2 diabetes. Type 2 diabetes is characterized by hyperglycemia and occurs in obese individuals as a result of insulin resistance and inadequate insulin levels. Accordingly, diabetes drugs are tailored to enhance glucose disposal or target the pancreatic islet β cell to increase insulin secretion. The majority of the present-day insulin secretagogues, however, increase the risk of iatrogenic hypoglycemia, and hence alternatives are actively sought. The long-chain fatty acid, G protein-coupled receptor FFA1/Gpr40, is expressed in β cells, and its activation potentiates insulin secretion in a glucose-dependent manner. Preclinical data indicate that FFA1 agonism is an effective treatment to restore glucose homeostasis in rodent models of diabetes. This initial success prompted clinical trials in type 2 diabetes patients, the results of which were promising; however, the field suffered a significant setback when the lead compound TAK-875/fasiglifam was withdrawn from clinical development due to liver safety concerns. Nevertheless, recent developments have brought to light a surprising complexity of FFA1 agonist action, signaling diversity, and biological outcomes, raising hopes that with a greater understanding of the mechanisms at play the second round will be more successful.

A selective GPR40 (FFAR1) agonist LY2881835 provides immediate and durable glucose control in rodent models of type 2 diabetes

LY2881835 is a selective, potent, and efficacious GPR40 agonist. The objective of the studies described here was to examine the pharmacological properties of LY2881835 in preclinical models of T2D. Significant increases in insulin secretion were detected when LY2881835 was tested in primary islets from WT mice but not in islets from GPR40 KO mice. Furthermore, LY2881835 potentiated glucose stimulated insulin secretion in normal lean mice. Acute administration of LY2881835 lowered glucose during OGTTs in WT mice but not in GPR40 KO mice. These findings demonstrate that LY2881835 induces GPR40‐mediated activity ex vivo and in vivo. LY2881835 was administered orally at 10 mg/kg to diet‐induced obese (DIO) mice (an early model of T2D due to insulin resistance) for 14 days. Statistically significant reductions in glucose were seen during OGTTs performed on days 1 and 15. When a study was done for 3 weeks in Zucker fa/fa rats, a rat model of insulin resistance, normalization of blood glucose levels equivalent to those seen in lean rats was observed. A similar study was performed in streptozotocin (STZ)‐treated DIO mice to explore glucose control in a late model of T2D. In this model, pancreatic insulin content was reduced ~80% due to STZ‐treatment plus the mice were insulin resistant due to their high fat diet. Glucose AUCs were significantly reduced during OGTTs done on days 1, 7, and 14 compared to control mice. In conclusion, these results demonstrate that LY2881835 functions as a GPR40‐specific insulin secretagogue mediating immediate and durable glucose control in rodent models of early‐ and late‐stage T2D.

Free fatty acid receptor agonists for the treatment of type 2 diabetes: drugs in preclinical to phase II clinical development

INTRODUCTION

The alarming prevalence of type 2 diabetes mellitus (T2DM) stimulated the exploitation of new antidiabetic drugs with extended durability and enhanced safety. In this regard, the free fatty acid receptor 1 (FFA1) and FFA4 have emerged as attractive targets in the last decade. FFA1 has prominent advantages in promoting insulin and incretin secretion while FFA4 shows great potential in incretin secretion, insulin sensitization and anti-inflammatory effects.

AREA COVERED

Herein, the authors focus specifically on FFA1 and FFA4 agonists in clinical trials and preclinical development. LY2922470, P11187 and SHR0534 are currently active in clinical trials while the CNX-011-67, SAR1, DS-1558 and BMS-986118 are in preclinical phase. The information for this review is retrieved from Integrity, Scifinder, Espacenet and clinicaltrials.gov databases.

EXPERT OPINION

Current proof-of-concept in clinical trials suggests that FFA1 agonists have a significant improvement for T2DM without the risk of hypoglycemia. However, there are still several challenging problems including the mechanism of the receptor and the efficacy and safety of the ligands.

G Protein-coupled Receptor 40 (GPR40) and Peroxisome Proliferator-activated Receptor γ (PPARγ): AN INTEGRATED TWO-RECEPTOR SIGNALING PATHWAY

Peroxisome proliferator-activated receptor γ (PPARγ) ligands have been widely used to treat type 2 diabetes mellitus. However, knowledge of PPARγ signaling remains incomplete. In addition to PPARγ, these drugs also activate G protein-coupled receptor 40 (GPR40), a Gαq-coupled free fatty acid receptor linked to MAPK networks and glucose homeostasis. Notably, p38 MAPK activation has been implicated in PPARγ signaling. Here, rosiglitazone (RGZ) activation of GPR40 and p38 MAPK was found to boost PPARγ-induced gene transcription in human endothelium. Inhibition or knockdown of p38 MAPK or expression of a dominant negative (DN) p38 MAPK mutant blunted RGZ-induced PPARγ DNA binding and reporter activity in EA.hy926 human endothelial cells. GPR40 inhibition or knockdown, or expression of a DN-Gαq mutant likewise blocked activation of both p38 MAPK and PPARγ reporters. Importantly, RGZ induction of PPARγ target genes in primary human pulmonary artery endothelial cells (PAECs) was suppressed by knockdown of either p38 MAPK or GPR40. GPR40/PPARγ signal transduction was dependent on p38 MAPK activation and induction of PPARγ co-activator-1 (PGC1α). Silencing of p38 MAPK or GPR40 abolished the ability of RGZ to induce phosphorylation and expression of PGC1α in PAECs. Knockdown of PGC1α, its essential activator SIRT1, or its binding partner/co-activator EP300 inhibited RGZ induction of PPARγ-regulated genes in PAECs. RGZ/GPR40/p38 MAPK signaling also led to EP300 phosphorylation, an event that enhances PPARγ target gene transcription. Thus, GPR40 and PPARγ can function as an integrated two-receptor signal transduction pathway, a finding with implications for rational drug development.

Characterizing pharmacological ligands to study the long-chain fatty acid receptors GPR40/FFA1 and GPR120/FFA4

The free fatty acid receptors (FFA) 1 (previously designated GPR40) and FFA4 (previously GPR120) are two GPCRs activated by saturated and unsaturated longer-chain free fatty acids. With expression patterns and functions anticipated to directly or indirectly promote insulin secretion, provide homeostatic control of blood glucose and improve tissue insulin sensitivity, both receptors are being studied as potential therapeutic targets for the control of type 2 diabetes. Furthermore, genetic and systems biology studies in both humans and mouse models link FFA4 receptors to diabetes and obesity. Although activated by the same group of free fatty acids, FFA1 and FFA4 receptors are not closely related and, while the basis of recognition of fatty acids by FFA1 receptors is similar to that of the short-chain fatty acid receptors FFA2 and FFA3, the amino acid residues involved in endogenous ligand recognition by FFA4 receptors are more akin to those of the sphingosine 1 phosphate receptor S1P1 . Screening and subsequent medicinal chemistry programmes have developed a number of FFA1 receptor selective agonists that are effective in promoting insulin secretion in a glucose concentration-dependent manner, and in lowering blood glucose levels. However, the recent termination of Phase III clinical trials employing TAK-875/fasiglifam has caused a setback and raises important questions over the exact nature and mechanistic causes of the problems. Progress in the identification and development of highly FFA4 receptor-selective pharmacological tools has been less rapid and several issues remain to be clarified to fully validate this receptor as a therapeutic target. Despite this, the ongoing development of a range of novel ligands offers great opportunities to further unravel the contributions of these receptors.

Free fatty acid receptors as therapeutic targets for the treatment of diabetes

Nutrition regulates energy balance; however, dysfunction of energy balance can cause metabolic disorders, such as obesity and diabetes. Fatty acids are an essential energy source and signaling molecules that regulate various cellular processes and physiological functions. Recently, several orphan G protein-coupled receptors were identified as free fatty acid receptors (FFARs). GPR40/FFAR1 and GPR120/FFAR4 are activated by medium- and/or long-chain fatty acids, whereas GPR41/FFAR3 and GPR43/FFAR2 are activated by short-chain fatty acids. FFARs are regarded as targets for novel drugs to treat metabolic disorders, such as obesity and type 2 diabetes, because recent studies have showed that these receptors are involved in the energy metabolism in various tissues, including adipose, intestinal, and immune tissue. In this review, we summarize physiological roles of the FFARs, provide a comprehensive overview of energy regulation by FFARs, and discuss new prospects for treatment of metabolic disorders.

Metabolic phenotyping guidelines: assessing glucose homeostasis in rodent models

The pathophysiology of diabetes as a disease is characterised by an inability to maintain normal glucose homeostasis. In type 1 diabetes, this is due to autoimmune destruction of the pancreatic β-cells and subsequent lack of insulin production, and in type 2 diabetes it is due to a combination of both insulin resistance and an inability of the β-cells to compensate adequately with increased insulin release. Animal models, in particular genetically modified mice, are increasingly being used to elucidate the mechanisms underlying both type 1 and type 2 diabetes, and as such the ability to study glucose homeostasis in vivo has become an essential tool. Several techniques exist for measuring different aspects of glucose tolerance and each of these methods has distinct advantages and disadvantages. Thus the appropriate methodology may vary from study to study depending on the desired end-points, the animal model, and other practical considerations. This review outlines the most commonly used techniques for assessing glucose tolerance in rodents and details the factors that should be taken into account in their use. Representative scenarios illustrating some of the practical considerations of designing in vivo experiments for the measurement of glucose homeostasis are also discussed.

Recent developments in the discovery of FFA1 receptor agonists as novel oral treatment for type 2 diabetes mellitus

Despite the availability of established medication for treatment of type 2 diabetes mellitus (T2DM) there still remains a significant unmet need for new effective, oral antidiabetic agents that improve glycemic control while maintaining an excellent safety profile. In this regard the FFA1 receptor has emerged as an attractive target in recent years. Activation of the FFA1 receptor has been shown to not only amplify glucose induced insulin secretion from pancreatic beta cells but also to stimulate incretin secretion from intestinal endocrine cells. The current review highlights on the latest developments and clinical data from evolving research on the potential of FFA1 agonists as effective treatment for T2DM.

Risk factors contributing to type 2 diabetes and recent advances in the treatment and prevention

Type 2 diabetes is a serious and common chronic disease resulting from a complex inheritance-environment interaction along with other risk factors such as obesity and sedentary lifestyle. Type 2 diabetes and its complications constitute a major worldwide public health problem, affecting almost all populations in both developed and developing countries with high rates of diabetes-related morbidity and mortality. The prevalence of type 2 diabetes has been increasing exponentially, and a high prevalence rate has been observed in developing countries and in populations undergoing "westernization" or modernization. Multiple risk factors of diabetes, delayed diagnosis until micro- and macro-vascular complications arise, life-threatening complications, failure of the current therapies, and financial costs for the treatment of this disease, make it necessary to develop new efficient therapy strategies and appropriate prevention measures for the control of type 2 diabetes. Herein, we summarize our current understanding about the epidemiology of type 2 diabetes, the roles of genes, lifestyle and other factors contributing to rapid increase in the incidence of type 2 diabetes. The core aims are to bring forward the new therapy strategies and cost-effective intervention trials of type 2 diabetes.

Treatment of type 2 diabetes by free Fatty Acid receptor agonists

Dietary free fatty acids (FFAs), such as ω-3 fatty acids, regulate metabolic and anti-inflammatory processes, with many of these effects attributed to FFAs interacting with a family of G protein-coupled receptors. Selective synthetic ligands for free fatty acid receptors (FFA1-4) have consequently been developed as potential treatments for type 2 diabetes (T2D). In particular, clinical studies show that Fasiglifam, an agonist of the long-chain FFA receptor, FFA1, improved glycemic control and reduced HbA1c levels in T2D patients, with a reduced risk of hypoglycemia. However, this ligand was removed from clinical trials due to potential liver toxicity and determining if this is a target or a ligand-specific feature is now of major importance. Pre-clinical studies also show that FFA4 agonism increases insulin sensitivity, induces weight loss, and reduces inflammation and the metabolic and anti-inflammatory effects of short chain fatty acids (SCFAs) are linked with FFA2 and FFA3 activation. In this review, we therefore show that FFA receptor agonism is a potential clinical target for T2D treatment and discuss ongoing drug development programs within industry and academia aimed at improving the safety and effectiveness of these potential treatments.