Design, Synthesis And Biological Evaluation Of GPR120 Agonists

Since the first discovery in 1979, over 800 GPCRs have been reported. G protein-coupled receptor is a membrane receptor having seven transmembrane structure and conserved transmembrane signal transduction, and regulating of a variety of enzymes and ion channels. GPR120 (FFA4) receptor functions as a receptor for ω-3 fatty acid, thus involving in regulating the secretion of gastrointestinal peptide hormone, adipogenesis, adipogenic differentiation and anti-inflammatory process. In view that the dysfunction of GPR120 receptor is closely correlated with metabolic disorders, GPR120 can act as a novel potential therapeutic target for the treatment of obesity, insulin resistance, type II diabetes and so on.Diabetes is a kind of metabolic diseases in which body does not produce enough insulin due to pancreatic β-cell loss (type I diabetes) or insulin resistance in metabolic tissues (type II diabetes). Adipocytes play major role in obesity-induced insulin resistance. There are two main pathway of the insulin signaling:the phosphatidylinositol 3-kinase (PI3K)-AKT pathway and the Ras-extracellular signal-related kinase (ERK) pathway. If insulin signaling is restricted at any point in this signaling cascade, insulin resistance will offen occur. Incretins are a group of gastrointestinal hormones stimulating a decrease glucose level in blood. The three main candidates of incretins are glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Both secretion of GLP-1 and GIP are indirectly regulated by FFAs through GPR120, and increasing of these incretins can result into enhancing insulin sensitivity.Oh and his colleagues revealed that the GPR120 functions as an co-3 FAs sensor. Broad anti-inflammatory effects in monocytic RAW64.7 cells and in primary intraperitoneal macrophages can be caused after ω-3 FAs or agonists by stimulating GPR120. They proposed a mechanism of signaling pathway that GPR120 couples to β-arrestin2, inhibitory both the TLR and TNF-a proinflammatory signaling pathways. In view of those evidences, GPR120 may serve as an important control point in the integration of anti-inflammatory and insulin sensitizing responses, which may prove useful in the future development of new therapeutic methods for the treatment of insulin resistance diseases.Some long-chainω-3 polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA, C20:5n-3 Δ5,8,11-14,17) and docosahexaenoic acid (DHA, C22:6n-3 Δ4,7,10-13,16,19), have been found as ligands for the GPR120 for leading anti-inflammmatory properties. Hirasawa and his coworkers tested over 1000 chemical compounds on HEK 293 cells stably expressing GPR120-EGFP to identify endogenous ligands for GPR120. Furthermore, they used HEK 293 cells stably expressing the mouse GPR120-Ga16 fusion protein to examine the dose-response of compounds on the concentration of intracellular Ca2+. These two experiments both verified that long-chain saturated FFAs, especially with a chain as long as C14 to C18, are specific ligand for GPR120.Since then, the synthetized small molecule agonists have also been found, for example, GW9508, NCG21 and TUG-891 that demonstrate similarity effectiveness with endogenous GPR120 ligands long-chain fatty acids in activation of release of intracellular Ca2+, phosphorylation of ERK and secretion of GLP-1. Sun et al. calculated the hydrogen bonding energies between the candidates and GPR120 homology model derived from the crystal structure of bovine rhodopsin. As a result, compound NCG21 not only presented the lowest energy, but the most potent ERK activation, intracellular calcium responses in a cloned GPR120 system and GLP-1 secretion in STC-1 cells. Moreover, NCG21 was also examined in vivo effect that directly increased the plasma GLP-1 level in the mouse after administration.The discovery of NCG-21 displays the feasibility of computer-aided design GPR120 agonists.In the current thesis, by using pharmacophore modeling and virtual screening methods, twelve compounds were provided with equivalent similar or improved potency on GPR120 receptor, compared with GW9508. Among these active molecules, some demonstrate appealing β-arr2-biased. For example, compound 25 and 50 present as micromolar β-arr2-biased agonists. In addition to P-arr2-biased ligands, we also identified that compound 40 presents up to nanomolar agonism in both Gq and β-arrestin pathways. It should be underlined that all above-mentioned molecules would become the important pharmacological tools to investigate the biological functions of signaling pathway through FFA4 receptor. To the best of our knowledge, these compounds are the very first characterized biased agonists for FFA4 receptor, which could be used by the medicinal chemist to sculpt a preferred functional response from the FFA4 through the design of small molecules, as well as the manifestation of their biological functions and therapeutic advantages on the basis of the different signaling pathways. A relationship intriguing β-arr2-biased activity and ligand structure properties could be appreciated by further research. Furthermore we purchased 19 aromatic acid derivatives based on lead compound 41, and preliminary structure-activity relationships was summarized by BRET, which provides the theoretical guidance for next structural optimization. Based on compound 18 as a lead compound, this research also designed and synthesized of 25 compounds, which need further biological evaluation.