Optimization of (2,3-dihydro-1-benzofuran-3-yl)acetic acids: discovery of a non-free fatty acid-like, highly bioavailable G protein-coupled receptor 40/free fatty acid receptor 1 agonist as a glucose-dependent insulinotropic agent

CoH-catalyzed asymmetric remote hydroalkylation of heterocyclic alkenes: a rapid approach to chiral five-membered S- and O-heterocycles

Saturated heterocycles, which incorporate S and O heteroatoms, serve as fundamental frameworks in a diverse array of natural products, bioactive compounds, and pharmaceuticals. Herein, we describe a unique cobalt-catalyzed approach integrated with a desymmetrization strategy, facilitating precise and enantioselective remote hydroalkylation of unactivated heterocyclic alkenes. This method delivers hydroalkylation products with high yields and excellent stereoselectivity, representing good efficiency in constructing alkyl chiral centers at remote C3-positions within five-membered S/O-heterocycles. Notably, the broad scope and good functional group tolerance of this asymmetric C(sp3)-C(sp3) coupling enhance its applicability.

Discovery of orally effective and safe GPR40 agonists by incorporating a chiral, rigid and polar sulfoxide into β-position to the carboxylic acid

GPR40 is primarily expressed in pancreatic islet β-cells, and its activation by endogenous ligands of medium to long-chain free fatty acids or synthetic agonists is clinically proved to improve glycemic control by stimulating glucose-dependent insulin secretion. However, most of the reported agonists are highly lipophilic, which might cause lipotoxicity and the off-target effects in CNS. Particularly, the withdrawal of TAK-875 from clinical trials phase III due to liver toxicity concern threw doubt over the long-term safety of targeting GPR40. Improving the efficacy and the selectivity, thus enlarging the therapeutic window would provide an alternative to develop safe GPR40-targeted therapeutics. Herein, by employing an innovative "three-in-one" pharmacophore drug design strategy, the optimal structural features for GPR40 agonist was integrated into one functional group of sulfoxide, which was incorporated into the β-position of the propanoic acid core pharmacophore. As a result, the conformational constraint, polarity as well as chirality endowed by the sulfoxide significantly enhanced the efficacy, selectivity and ADMET properties of the novel (S)- 2-(phenylsulfinyl)acetic acid-based GPR40 agonists. The lead compounds (S)-4a and (S)-4s exhibited robust plasma glucose-lowering effects and insulinotropic action during an oral glucose tolerance test in C57/BL6 mice, excellent pharmacokinetic profile and little hepatobiliary transporter inhibition, marginal cell toxicities against human primary hepatocyte at 100 μM.

Highly Enantioselective Rhodium-Catalyzed Transfer Hydrogenation of Tetrasubstituted Olefins: Application toward the Synthesis of GPR40 Agonist MK-2305

A highly efficient enantioselective synthesis for the potent G-protein-coupled receptor 40 agonist MK-2305 was developed. The key tetrasubstituted olefin was prepared via a stereoselective Mukaiyama aldol reaction/elimination sequence. The highly enantioselective rhodium-catalyzed transfer hydrogenation of the tetrasubstituted olefin afforded the target compound MK-2305 in excellent optical and chemical purity. The key asymmetric transfer hydrogenation proceeds in excellent yields and enantioselectivities for a variety of substrates. The superior reactivity of the tethered catalysts was revealed by NMR studies.

Design, synthesis, and biological evaluation of novel dual FFA1 and PPARδ agonists possessing phenoxyacetic acid scaffold

The free fatty acid receptor 1 (FFA1/GPR40) and peroxisome proliferator-activated receptor δ (PPARδ) have been widely considered as promising targets for type 2 diabetes mellitus (T2DM) due to their respective roles in promoting insulin secretion and improving insulin sensitivity. Hence, the dual FFA1/PPARδ agonists may exert synergistic effects by simultaneously activating FFA1 and PPARδ. The present study performed systematic exploration around previously reported FFA1 agonist 2-(2-fluoro-4-((2'-methyl-4'-(3-(methylsulfonyl)propoxy)-[1,1'-biphenyl]-3-yl)methoxy)phenoxy)acetic acid (lead compound), leading to the identification of a novel dual FFA1/PPARδ agonist 2-(2-fluoro-4-((3-(6-methoxynaphthalen-2-yl)benzyl)oxy)phenoxy)acetic acid (the optimal compound), which displayed high selectivity over PPARα and PPARγ. In addition, the docking study provided us with detailed binding modes of the optimal compound in FFA1 and PPARδ. Furthermore, the optimal compound exhibited greater glucose-lowering effects than lead compound, which might attribute to its synergistic effects by simultaneously modulating insulin secretion and resistance. Moreover, the optimal compound has an acceptable safety profile in the acute toxicity study at a high dose of 500 mg/kg Therefore, our results provided a novel dual FFA1/PPARδ agonist with excellent glucose-lowering effects in vivo.

Discovery and development of CPL207280 as new GPR40/FFA1 agonist

Due to a unique mechanism that limits the possibility of hypoglycemia, the free fatty acid receptor (FFA1) is an attractive target for the treatment of type 2 diabetes. So far, however, none of the promising agonists have been able to enter the market. The most advanced clinical candidate, TAK-875, was withdrawn from phase III clinical trials due to liver safety issues. In this article, we describe the key aspects leading to the discovery of CPL207280 (13), the design of which focused on long-term safety. The introduction of small, nature-inspired acyclic structural fragments resulted in compounds with retained high potency and a satisfactory pharmacokinetic profile. Optimized synthesis and upscaling provided a stable, solid form of CPL207280-51 (45) with the properties required for the toxicology studies and ongoing clinical trials.

Recent Updates on Free Fatty Acid Receptor 1 (GPR-40) Agonists for the Treatment of Type 2 Diabetes Mellitus

BACKGROUND

The global incidence of type 2 diabetes mellitus (T2DM) has enthused the development of new antidiabetic targets with low toxicity and long-term stability. In this respect, free fatty acid receptor 1 (FFAR1), which is also recognized as a G protein-coupled receptor 40 (GPR40), is a novel target for the treatment of T2DM. FFAR1/GPR40 has a high level of expression in β-cells of the pancreas, and the requirement of glucose for stimulating insulin release results in immense stimulation to utilise this target in the medication of T2DM.

METHODS

The data used for this review is based on the search of several scienctific databases as well as various patent databases. The main search terms used were free fatty acid receptor 1, FFAR1, FFAR1 agonists, diabetes mellitus, G protein-coupled receptor 40 (GPR40), GPR40 agonists, GPR40 ligands, type 2 diabetes mellitus and T2DM.

RESULTS

The present review article gives a brief overview of FFAR1, its role in T2DM, recent developments in small molecule FFAR1 (GPR40) agonists reported till now, compounds of natural/plant origin, recent patents published in the last few years, mechanism of FFAR1 activation by the agonists, and clinical status of the FFAR1/GPR40 agonists.

CONCLUSION

The agonists of FFAR1/GRP40 showed considerable potential for the therapeutic control of T2DM. Most of the small molecule FFAR1/GPR40 agonists developed were aryl alkanoic acid derivatives (such as phenylpropionic acids, phenylacetic acids, phenoxyacetic acids, and benzofuran acetic acid derivatives) and thiazolidinediones. Some natural/plant-derived compounds, including fatty acids, sesquiterpenes, phenolic compounds, anthocyanins, isoquinoline, and indole alkaloids, were also reported as potent FFAR1 agonists. The clinical investigations of the FFAR1 agonists demonstrated their probable role in the improvement of glucose control. Though, there are some problems still to be resolved in this field as some FFAR1 agonists terminated in the late phase of clinical studies due to "hepatotoxicity." Currently, PBI-4050 is under clinical investigation by Prometic. Further investigation of pharmacophore scaffolds for FFAR1 full agonists as well as multitargeted modulators and corresponding clinical investigations will be anticipated, which can open up new directions in this area.

Iridium-Catalyzed Enantioselective Hydrogenation of Indole and Benzofuran Derivatives

Enantioselective hydrogenation of a broad spectrum of N-, O-, and S-containing aromatic benzoheterocycles or nonaromatic unsaturated heterocycles has been realized by using an Ir/SpinPHOX (SpinPHOX=spiro[4,4]-1,6-nonadiene-based phosphine-oxazoline) complex as the catalyst, affording an array of the corresponding chiral benzoheterocycles (30 examples) with excellent enantioselectivities (>99 % ee in most cases) and turnover numbers up to 500.

In vivo pharmacokinetic study and oral glucose tolerance test of sulfoxide analogs of GPR40 agonist TAK-875

TAK-875 (compound 1) was the only GPR40 agonist with promising oral glucose-lowering effect, which entered phase III clinical trials. In previous studies, we successfully synthesized the TAK-875 sulfoxide analog 2, which was further separated to optically pure compounds 3 (S, S, 100.0% de) and 4 (R, S, 100.0% de). In vitro biological evaluation revealed that the sulfoxide analogs 3 and 4 possessed comparable GPR40 agonist activity to TAK-875. Herein, in order to further evaluate the druglikeness of TAK-875 sulfoxide analogs, the pharmacokinetic properties of compounds 2, 3, and 4 in rats were investigated and compared with that of TAK-875. The results showed that sulfoxide (2, 3, and 4) and sulfone (TAK-875) could be converted into each other in different degrees in vivo. Interestingly, compound 3 showed higher drug exposure calculated by the AUC sum of sulfoxide and sulfone in plasma than TAK-875, 2 and 4. In order to further investigate the in vivo glucose-lowering potency of sulfoxide analogs, asymmetric synthesis was carried out and led to two sulfoxides with moderate de values, 5 (S, S, 66.4% de) and 6 (R, S, 71.0% de). The following oral glucose tolerance test (OGTT) in rats showed that 5 (S, S, 66.4% de) had stronger glucose-lowering effect in vivo than 6 (R, S, 71.0% de) and TAK-875, which could be partly rationalized by the superior pharmacokinetic property of sulfoxide 3 (the main component of 5) relative to sulfoxide 4 (the main component of 6) and TAK-875.

Discovery of novel potent GPR40 agonists containing imidazo[1,2-a]pyridine core as antidiabetic agents

Free fatty acid receptor 1 (FFA1 or GPR40) has been studied for many years as a target for the treatment of type 2 diabetes mellitus. In order to increase potency and reduce hepatotoxicity, a series of novel compounds containing imidazo[1,2-a]pyridine scaffold as GPR40 agonist were synthesized. Compound I-14 was identified as an effective agonist as shown by the conspicuous drop in blood glucose in normal and diabetic mice. It had no risk of hepatotoxicity compared with TAK-875. Moreover, good pharmacokinetic (PK) properties of I-14 were observed (CL = 27.26 ml/h/kg, t_1/2 = 5.93 h). The results indicate that I-14 could serve as a possible candidate to treat diabetes.

Design, synthesis and biological evaluation of novel FFA1/GPR40 agonists: New breakthrough in an old scaffold

Based on an old phenoxyacetic acid scaffold, CPU014 (compound 14) has been identified as a superior agonist by comprehensive exploration of structure-activity relationship. In vitro toxicity study suggested that CPU014 has lower risk of hepatotoxicity than TAK-875. During acute toxicity study (5-500 mg/kg), a favorable therapeutic window of CPU014 was observed by evaluation of plasma profiles and liver slices. Moreover, CPU014 promotes insulin secretion in a glucose-dependent manner, while no GLP-1 secretion has been enhanced. Other than good pharmacokinetic properties, CPU014 significantly improved glucose tolerance both in normal and diabetic models without the risk of hypoglycemia. These subversive findings provided a safer candidate CPU014, which is currently in preclinical study to assess its potential for the treatment of diabetes.

Synthesis and biological evaluation of novel potent FFA1 agonists containing 2,3-dihydrobenzo[b][1,4]dioxine

FFA1 (free fatty acid receptor 1) has emerged as an attractive antidiabetic target due to its role in mediating the enhancement of glucose-stimulated insulin secretion in pancreatic β cells with a low risk of hypoglycemia. Many reported FFA1 agonists possessed somewhat pharmacokinetic and/or safety issues. Herein, we describe the identification of 2,3-dihydrobenzo[b][1,4]dioxine as a novel scaffold for FFA1 agonists. Comprehensive structure-activity relationship study based on this scaffold led to the discovery of (S)-3-(4-(((S)-7-(4-methoxyphenyl)-2,3-dihydrobenzo [b][1,4]dioxin-2-yl)methoxy) phenyl)hex-4-ynoic acid (26k), which displayed a potent FFA1 agonistic activity and good pharmacokinetic profiles. Subsequent in vivo studies demonstrated that compound 26k significantly improved the glucose tolerance in ICR mice. In summary, compound 26k is a promising drug candidate for further investigation.

Design, synthesis, and evaluation of a series of novel phenylpropanoic acid derivatives agonists for the FFA1

Free fatty acid 1 (FFA1/GPR40) has attracted extensive attention as a novel target for the treatment of type 2 diabetes for its role in the enhancement of insulin secretion with glucose dependency. Aiming to develop novel potent FFA1 agonists, a new series of phenylpropionic acid derivatives were designed and synthesized on the basis of the modification of chemical cement of TAK-875, AMG-837, and LY2881835. Among them, most promising compounds 7, 14, and 15 were obtained with EC₅₀ values of 82, 79, and 88 nM, exhibiting a powerful agonistic activity compared to TAK-875 (95.1 nM). During Oral glucose tolerance test in normal mice, compound 7, 14, and 15 had significant glucose-lowering effect at the dose of 50 mg/kg. Furthermore, compound 15 (50 mg/kg) also significantly improved in glucose tolerance in type 2 diabetic mice. Herein, we reported the discovery and optimization of a series of potent FFA1 agonists. The discovery supported further exploration surrounding this scaffold.

A high molar activity 18F-labeled TAK-875 derivative for PET imaging of pancreatic β-cells

Background

Results

Conclusions

Improving metabolic stability with deuterium: The discovery of HWL-066, a potent and long-acting free fatty acid receptor 1 agonists

The free fatty acid receptor 1 (FFA1) is a potential target due to its function in enhancing of glucose-stimulated insulin secretion. The FFA1 agonist GW9508 has great potential for the treatment of type 2 diabetes mellitus, but it has been suffering from high plasma clearance probably because the phenylpropanoic acid is vulnerable to β-oxidation. To identify orally available analog without influence on the unique pharmacological mechanism of GW9508, we tried to interdict the metabolically labile group by incorporating two deuterium atoms at the α-position of phenylpropionic acid affording compound 4 (HWL-066). As expected, HWL-066 revealed a lower clearance (CL = 0.23 L^-1  hr^-1  kg^-1 ), higher maximum concentration (C_max  = 5907.47 μg/L), and longer half-life (T_1/2  = 3.50 hr), resulting in a 2.8-fold higher exposure than GW9508. Moreover, the glucose-lowering effect of HWL-066 was far better than that of GW9508 and comparable with TAK-875. Different from glibenclamide, no side-effect of hypoglycemia was observed in mice after oral administrating HWL-066 (80 mg/kg).

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

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

Design, Synthesis and in Combo Antidiabetic Bioevaluation of Multitarget Phenylpropanoic Acids

We have synthesized a small series of five 3-[4-arylmethoxy)phenyl]propanoic acids employing an easy and short synthetic pathway. The compounds were tested in vitro against a set of four protein targets identified as key elements in diabetes: G protein-coupled receptor 40 (GPR40), aldose reductase (AKR1B1), peroxisome proliferator-activated receptor gama (PPARγ) and solute carrier family 2 (facilitated glucose transporter), member 4 (GLUT-4). Compound 1 displayed an EC₅₀ value of 0.075 μM against GPR40 and was an AKR1B1 inhibitor, showing IC₅₀ = 7.4 μM. Compounds 2 and 3 act as slightly AKR1B1 inhibitors, potent GPR40 agonists and showed an increase of 2 to 4-times in the mRNA expression of PPARγ, as well as the GLUT-4 levels. Docking studies were conducted in order to explain the polypharmacological mode of action and the interaction binding mode of the most active molecules on these targets, showing several coincidences with co-crystal ligands. Compounds 1–3 were tested in vivo at an explorative 100 mg/kg dose, being 2 and 3 orally actives, reducing glucose levels in a non-insulin-dependent diabetes mice model. Compounds 2 and 3 displayed robust in vitro potency and in vivo efficacy, and could be considered as promising multitarget antidiabetic candidates. This is the first report of a single molecule with these four polypharmacological target action.

Structure-based optimization of free fatty acid receptor 1 agonists bearing thiazole scaffold

The free fatty acid receptor 1 (FFA1) plays an important role in amplifying insulin secretion in a glucose dependent manner. We have previously reported a series of FFA1 agonists with thiazole scaffold exemplified by compound 1, and identified a small hydrophobic subpocket partially occupied by the methyl group of compound 1. Herein, we describe further structure optimization to better fit the small hydrophobic subpocket by replacing the small methyl group with other hydrophobic substituents. All of these efforts resulted in the identification of compound 6, a potent FFA1 agonist (EC₅₀ = 39.7 nM) with desired ligand efficiency (0.24) and ligand lipophilicity efficiency (4.7). Moreover, lead compound 6 exhibited a greater potential for decreasing the hyperglycemia levels than compound 1 during an oral glucose tolerance test. In summary, compound 6 is a promising FFA1 agonist for further investigation, and the structure-based study promoted our understanding for the binding pocket of FFA1.

Probing the Hydrophobic Binding Pocket of G-Protein-Coupled Lysophosphatidylserine Receptor GPR34/LPS1 by Docking-Aided Structure-Activity Analysis

The ligands of certain G-protein-coupled receptors (GPCRs) have been identified as endogenous lipids, such as lysophosphatidylserine (LysoPS). Here, we analyzed the molecular basis of the structure-activity relationship of ligands of GPR34, one of the LysoPS receptor subtypes, focusing on recognition of the long-chain fatty acid moiety by the hydrophobic pocket. By introducing benzene ring(s) into the fatty acid moiety of 2-deoxy-LysoPS, we explored the binding site's preference for the hydrophobic shape. A tribenzene-containing fatty acid surrogate with modifications of the terminal aromatic moiety showed potent agonistic activity toward GPR34. Computational docking of these derivatives with a homology modeling/molecular dynamics-based virtual binding site of GPR34 indicated that a kink in the benzene-based lipid surrogates matches the L-shaped hydrophobic pocket of GPR34. A tetrabenzene-based lipid analogue bearing a bulky tert-butyl group at the 4-position of the terminal benzene ring exhibited potent GPR34 agonistic activity, validating the present hydrophobic binding pocket model.

GPR40 partial agonist MK-2305 lower fasting glucose in the Goto Kakizaki rat via suppression of endogenous glucose production

GPR40 (FFA1) is a fatty acid receptor whose activation results in potent glucose lowering and insulinotropic effects in vivo. Several reports illustrate that GPR40 agonists exert glucose lowering in diabetic humans. To assess the mechanisms by which GPR40 partial agonists improve glucose homeostasis, we evaluated the effects of MK-2305, a potent and selective partial GPR40 agonist, in diabetic Goto Kakizaki rats. MK-2305 decreased fasting glucose after acute and chronic treatment. MK-2305-mediated changes in glucose were coupled with increases in plasma insulin during hyperglycemia and glucose challenges but not during fasting, when glucose was normalized. To determine the mechanism(s) mediating these changes in glucose metabolism, we measured the absolute contribution of precursors to glucose production in the presence or absence of MK-2305. MK-2305 treatment resulted in decreased endogenous glucose production (EGP) driven primarily through changes in gluconeogenesis from substrates entering at the TCA cycle. The decrease in EGP was not likely due to a direct effect on the liver, as isolated perfused liver studies showed no effect of MK-2305 ex vivo and GPR40 is not expressed in the liver. Taken together, our results suggest MK-2305 treatment increases glucose stimulated insulin secretion (GSIS), resulting in changes to hepatic substrate handling that improve glucose homeostasis in the diabetic state. Importantly, these data extend our understanding of the underlying mechanisms by which GPR40 partial agonists reduce hyperglycemia.

Central Agonism of GPR120 Acutely Inhibits Food Intake and Food Reward and Chronically Suppresses Anxiety-Like Behavior in Mice

BACKGROUND

GPR120 (FFAR4) is a G-protein coupled receptor implicated in the development of obesity and the antiinflammatory and insulin-sensitizing effects of omega-3 (ω-3) polyunsaturated fatty acids. Increasing central ω-3 polyunsaturated fatty acid levels has been shown to have both anorectic and anxiolytic actions. Despite the strong clinical interest in GPR120, its role in the brain is largely unknown, and thus we sought to determine the impact of central GPR120 pharmacological activation on energy balance, food reward, and anxiety-like behavior.

METHODS

Male C57Bl/6 mice with intracerebroventricular cannulae received a single injection (0.1 or 1 µM) or continuous 2-week infusion (1 µM/d; mini-pump) of a GPR120 agonist or vehicle. Free-feeding intake, operant lever-pressing for palatable food, energy expenditure (indirect calorimetry), and body weight were measured. GPR120 mRNA expression was measured in pertinent brain areas. Anxiety-like behavior was assessed in the elevated-plus maze and open field test.

RESULTS

GPR120 agonist injections substantially reduced chow intake during 4 hours postinjection, suppressed the rewarding effects of high-fat/-sugar food, and blunted approach-avoidance behavior in the open field. Conversely, prolonged central GPR120 agonist infusions reduced anxiety-like behavior in the elevated-plus maze and open field, yet failed to affect free-feeding intake, energy expenditure, and body weight on a high-fat diet.

CONCLUSION

Acute reductions in food intake and food reward suggest that GPR120 could mediate the effects of central ω-3 polyunsaturated fatty acids to inhibit appetite. The anxiolytic effect elicited by GPR120 agonist infusions favors the testing of compounds that can enter the brain to activate GPR120 for the mitigation of anxiety.

Synthesis and Characterization of a Promising Novel FFAR1/GPR40 Targeting Fluorescent Probe for β-Cell Imaging

Diabetes affects an increasing number of patients worldwide and is responsible for a significant rise in healthcare expenses. Imaging of β-cells bears the potential to contribute to an improved understanding, diagnosis, and development of new treatment options for diabetes. Here, we describe the first small molecule fluorescent probe targeting the free fatty acid receptor 1 (FFAR1/GPR40). This receptor is highly expressed on β-cells, and was up to now unexplored for imaging purposes. We designed a novel probe by facile modification of the selective and potent FFAR1 agonist TAK-875. Effective and specific binding of the probe was demonstrated using FFAR1 overexpressing cells. We also successfully labeled FFAR1 on MIN6 and INS1E cells, two widely used β-cell models, by applying an effective amplification protocol. Finally, we showed that the probe is capable of inducing insulin secretion in a glucose-dependent manner, thus demonstrating that functional activity of the probe was maintained. These results suggest that our probe represents a first important step to successful β-cell imaging by targeting FFAR1. The developed probe may prove to be particularly useful for in vitro and ex vivo studies of diabetic cellular and animal models to gain new insights into disease pathogenesis.

Complex Pharmacology of Free Fatty Acid Receptors

G protein-coupled receptors (GPCRs) are historically the most successful family of drug targets. In recent times it has become clear that the pharmacology of these receptors is far more complex than previously imagined. Understanding of the pharmacological regulation of GPCRs now extends beyond simple competitive agonism or antagonism by ligands interacting with the orthosteric binding site of the receptor to incorporate concepts of allosteric agonism, allosteric modulation, signaling bias, constitutive activity, and inverse agonism. Herein, we consider how evolving concepts of GPCR pharmacology have shaped understanding of the complex pharmacology of receptors that recognize and are activated by nonesterified or "free" fatty acids (FFAs). The FFA family of receptors is a recently deorphanized set of GPCRs, the members of which are now receiving substantial interest as novel targets for the treatment of metabolic and inflammatory diseases. Further understanding of the complex pharmacology of these receptors will be critical to unlocking their ultimate therapeutic potential.

Synthesis of GPR40 targeting 3 H- and 18 F-probes towards selective beta cell imaging

Diabetes affects an increasing number of patients worldwide and is responsible for a significant rise in healthcare expenses. Imaging of β-cells in vivo is expected to contribute to an improved understanding of the underlying pathophysiology, improved diagnosis, and development of new treatment options for diabetes. Here, we describe the first radiosyntheses of [³ H]-TAK875 and [¹⁸ F]-TAK875 derivatives to be used as β-cell imaging probes addressing the free fatty acid receptor 1 (FFAR1/GPR40). The fluorine-labeled derivative showed similar agonistic activity as TAK875 in a functional assay. The radiosynthesis of the ¹⁸ F-labelled tracer 2a was achieved with 16.7 ± 5.7% radiochemical yield in a total synthesis time of 60-70 min.

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.

Potentiation of Glucose-stimulated Insulin Secretion by the GPR40-PLC-TRPC Pathway in Pancreatic β-Cells

G protein-coupled receptors (GPCRs) are expressed in pancreatic beta-cells. G protein-coupled receptor 40 (GPR40) contributes to medium- or long-chain fatty acid-induced amplification of glucose-stimulated insulin secretion (GSIS), and GPR40 agonists are promising therapeutic targets in type 2 diabetes. Recently, we demonstrated that glucagon-like peptide 1, a ligand of pancreatic GPCR, activates a class of nonselective cation channels (NSCCs) and enhances GSIS. The aim of the current study was to determine whether the GPR40 signal interacts with NSCCs. A GPR40 agonist (fasiglifam) potentiated GSIS at 8.3 and 16.7 mM glucose but not 2.8 mM glucose. The NSCC current was activated by fasiglifam at 5.6 mM glucose with 100 μM tolbutamide (−70 mV), and this activation was prevented by the presence of pyrazole-3 (transient receptor potential canonical; a TRPC3 channel blocker). Inhibitors of phospholipase C or protein kinase C (PKC) inhibited the increases in GSIS and the NSCC current induced by GPR40 stimulation. The present study demonstrates a novel mechanism for the regulation of insulin secretion by GPR40 agonist in pancreatic beta-cells. The stimulation of the GPR40–PLC/PKC–TRPC3 channel pathway potentiates GSIS by the depolarization of the plasma membrane in pancreatic beta-cell.

Fasiglifam (TAK-875) has dual potentiating mechanisms via Gαq-GPR40/FFAR1 signaling branches on glucose-dependent insulin secretion

Fasiglifam (TAK‐875) is a free fatty acid receptor 1 (FFAR1)/G‐protein–coupled receptor 40 (GPR40) agonist that improves glycemic control in type 2 diabetes with minimum risk of hypoglycemia. Fasiglifam potentiates glucose‐stimulated insulin secretion (GSIS) from pancreatic β‐cells glucose dependently, although the precise mechanism underlying the glucose dependency still remains unknown. Here, we investigated key cross‐talk between the GSIS pathway and FFAR1 signaling, and Ca²⁺ dynamics using mouse insulinoma MIN6 cells. We demonstrated that the glucose‐dependent insulinotropic effect of fasiglifam required membrane depolarization and that fasiglifam induced a glucose‐dependent increase in intracellular Ca²⁺ level and amplification of Ca²⁺ oscillations. This differed from the sulfonylurea glimepiride that induced changes in Ca²⁺ dynamics glucose independently. Stimulation with cell‐permeable analogs of IP₃ or diacylglycerol (DAG), downstream second messengers of Gαq‐FFAR1, augmented GSIS similar to fasiglifam, indicating their individual roles in the potentiation of GSIS pathway. Intriguingly, the IP₃ analog triggered similar Ca²⁺ dynamics to fasiglifam, whereas the DAG analog had no effect. Despite the lack of an effect on Ca²⁺ dynamics, the DAG analog elicited synergistic effects on insulin secretion with Ca²⁺ influx evoked by an L‐type voltage‐dependent calcium channel opener that mimics glucose‐dependent Ca²⁺ dynamics. These results indicate that the Gαq signaling activated by fasiglifam enhances GSIS pathway via dual potentiating mechanisms in which IP₃ amplifies glucose‐induced Ca²⁺ oscillations and DAG/protein kinase C (PKC) augments downstream secretory mechanisms independent of Ca²⁺ oscillations.

2-(5-Methyl-1-benzofuran-3-yl)acetic acid

The asymmetric unit of the title compound, C11H10O3, contains two crystallographically independent molecules,AandB, with closely matching conformations (r.m.s. overlay fit = 0.105 Å). In each case, the OH group of the acetic acid residue occupies a position approximately antiperiplanar to the C atom of the heterocycle. A short intramolecular C—H...O contact occurs within each molecule. In the crystal, carboxylic acidA+Bdimers generateR22(8) loops.

G-protein coupled receptor 40 agonists as novel therapeutics for type 2 diabetes

With growing needs for new antidiabetic drugs which are safe and effective alone or in combination with existing drugs, G-protein coupled receptor 40 (GPR40) has drawn a considerable attention as a potential therapeutic target for type 2 diabetes. As GPR40 agonist may offer advantages to commonly used agents, by acting ambient glucose dependent manner which mechanistically leads to reduced risk of developing hypoglycemia. Since deorphanization in 2003, development of small molecule GPR40 agonists has been spurred by several research groups. There are a number of lead molecules targeting GPR40, and among these molecules TAK-875 (full agonist) and AMG 837 (partial agonist) advanced into clinical stage.

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.