Activation of FFA1 (GPR40), a member of G protein-coupling receptor family A, is mediated by medium-and long-chain fatty acids and leads to amplification of glucose-stimulated insulin secretion, suggesting a potential role for free fatty acid 1 (FFA1) as a target for type 2 diabetes. It was assumed previously that there is a single binding site for fatty acids and synthetic FFA1 agonists. However, using members of two chemical series of partial and full agonists that have been identified, radioligand binding interaction studies revealed that the full agonists do not bind to the same site as the partial agonists but exhibit positive heterotropic cooperativity. Analysis of functional data reveals positive functional cooperativity between the full agonists and partial agonists in various functional assays (in vitro and ex vivo) and also in vivo. Furthermore, the endogenous fatty acid docosahexaenoic acid (DHA) shows negative or neutral cooperativity with members of both series of agonists in binding assays but displays positive cooperativity in functional assays. Another synthetic agonist is allosteric with members of both agonist series, but apparently competitive with DHA. Therefore, there appear to be three allosterically linked binding sites on FFA1 with agonists specific for each of these sites. Activation of free fatty acid 1 receptor (FFAR1) by each of these agonists is differentially affected by mutations of two arginine residues, previously found to be important for FFAR1 binding and activation. These ligands with their high potencies and strong positive functional cooperativity with endogenous fatty acids, demonstrated in vitro and in vivo, have the potential to deliver therapeutic benefits.

Type 2 diabetes is characterized by impaired glucose homeostasis due to defects in insulin secretion, insulin resistance and the incretin response. GPR40 (FFAR1 or FFA1) is a G-protein-coupled receptor (GPCR), primarily expressed in insulin-producing pancreatic β-cells and incretin-producing enteroendocrine cells of the small intestine. Several GPR40 agonists, including AMG 837 and TAK-875, have been disclosed, but no GPR40 synthetic agonists have been reported that engage both the insulinogenic and incretinogenic axes. In this report we provide a molecular explanation and describe the discovery of a unique and potent class of GPR40 full agonists that engages the enteroinsular axis to promote dramatic improvement in glucose control in rodents. GPR40 full agonists AM-1638 and AM-6226 stimulate GLP-1 and GIP secretion from intestinal enteroendocrine cells and increase GSIS from pancreatic islets, leading to enhanced glucose control in the high fat fed, streptozotocin treated and NONcNZO10/LtJ mouse models of type 2 diabetes. The improvement in hyperglycemia by AM-1638 was reduced in the presence of the GLP-1 receptor antagonist Ex(9–39)NH2.

GPR40 (FFA1) is a G-protein-coupled receptor, primarily expressed in pancreatic islets, the activation of which elicits increased insulin secretion only in the presence of elevated glucose levels. A potent, orally bioavailable small molecule GPR40 agonist is hypothesized to be an effective antidiabetic posing little or no risk of hypoglycemia. We recently reported the discovery of AMG 837 (1), a potent partial agonist of GPR40. Herein, we present the optimization from the GPR40 partial agonist 1 to the structurally and pharmacologically distinct GPR40 full agonist AM-1638 (21). Moreover, we demonstrate the improved in vivo efficacy that GPR40 full agonist 21 exhibits in BDF/DIO mice as compared to partial agonist 1. KEYWORDS: GPR40, full agonist, AM-1638, AMG 837, insulin secretagogue, FFA1 T ype II diabetics lose their ability to maintain glucose homeostasis due to defects in both insulin secretion and action.1 GPR40 (FFA1) is a G-protein-coupled receptor, primarily expressed in pancreatic islets.2 When activated by medium to long chain fatty acids, GPR40 elicits increased insulin secretion only in the presence of elevated glucose levels. 3This alluring mechanism to treat type II diabetes presents the potential of little or no risk of hypoglycemia and has been investigated by multiple groups, leading to the discovery of several clinical candidates.4−7 We previously described the discovery of AMG 837 (1), 8−10 a small molecule partial agonist of GPR40 that displays oral efficacy in a variety of rodent diabetic models without exhibiting hypoglycemia. Because of the robust antidiabetic activity and favorable pharmacokinetic properties, 1 was selected for clinical evaluation. Because the ability of partial agonist 1 to maintain glycemic control was being tested in a clinical setting, we became interested in interrogating GPR40 with full agonists. We hypothesized that a GPR40 full agonist should have a greater ability to induce insulin secretion and thus provide greater glycemic control. In this letter, we describe in detail the structure−activity relationship (SAR) studies that started from the GPR40 partial agonist 1 and culminate with the identification of GPR40 full agonist AM-1638 (21) and provide further evidence that GPR40 full agonists demonstrate superior efficacy over partial agonists when evaluated in vivo.To provide a greater dynamic range with which to assess improvements in intrinsic efficacy, we chose to reevaluate compounds previously synthesized toward discovery of partial agonist 1 in CHO cells transfected with lower levels of GPR40 expression plasmid [from 5.0 ( Figure 1A) to 0.05 μg ( Figure 1B)].9 Under the original 5.0 μg plasmid conditions, partial agonist 1 demonstrates 75% of the response (E max ) shown by the natural free fatty acid ligand docosahexaenoic acid (DHA) ( Figure 1A). In contrast, reducing the expression plasmid to 0.05 μg affords an assay with the appropriate dynamic range to distinguish GPR40 partial and full agonists. As depicted in Figure 1B, partial agonist 1 dis...

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GPR40 (FFAR1 or FFA1) is a target of high interest being pursued to treat type II diabetes due to its unique mechanism leading to little risk of hypoglycemia. We recently reported the discovery of AM-1638 (2), a potent full agonist of GPR40. In this report, we present the discovery of GPR40 full agonists containing conformationally constrained tricyclic spirocycles and their structure-activity relationships leading to more potent agonists such as AM-5262 (26) with improved rat PK profile and general selectivity profile. AM-5262 enhanced glucose stimulated insulin secretion (mouse and human islets) and improved glucose homeostasis in vivo (OGTT in HF/STZ mice) when compared to AM-1638.

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GPR40 (FFA1 and FFAR1) has gained significant interest as a target for the treatment of type 2 diabetes. TAK-875 (1), a GPR40 agonist, lowered hemoglobin A1c (HbA1c) and lowered both postprandial and fasting blood glucose levels in type 2 diabetic patients in phase II clinical trials. We optimized phenylpropanoic acid derivatives as GPR40 agonists and identified AMG 837 (2) as a clinical candidate. Here we report our efforts in searching for structurally distinct back-ups for AMG 837. These efforts led to the identification of more polar GPR40 agonists, such as AM-4668 (10), that have improved potency, excellent pharmacokinetic properties across species, and minimum central nervous system (CNS) penetration.

We recently reported the discovery of a potent GPR40 full agonist AM-1638 (1). Herein, we describe our efforts in improving the drug-like properties of the full agonists through the systematic introduction of polar groups in the C-, D-, and A-rings. This led to the discovery of new GPR40 full agonists with significantly improved pharmacokinetic propeties. Compound 8 and 20 also showed potent in vivo efficacy in oral glucose tolerance tests in mice in addition to the improvement in properties.