Expression and function of the bile acid receptor TGR5 in Kupffer cells

Kupffer cells are resident macrophages in the liver and play a central role in the hepatic response to injury. Bile acids can impair macrophage function leading to decreased cytokine release. TGR5 is a novel, membrane-bound bile acid receptor, and it has been suggested that the immunosuppressive effect of bile acids can be mediated by TGR5. However, the function of TGR5 in Kupffer cells has not been studied and a direct link between TGR5 and cytokine production in macrophages has not been established. The present study demonstrates that TGR5 is localized in the plasma membrane of isolated Kupffer cells and is responsive to bile acids. Furthermore, bile acids inhibited LPS-induced cytokine expression in Kupffer cells via TGR5-cAMP dependent pathways. TGR5-immunoreactivity in Kupffer cells was increased in rat livers following bile-duct ligation, suggesting that TGR5 may play a protective role in obstructive cholestasis preventing excessive cytokine production thereby reducing liver injury.     

Synthesis and SAR of potent and selective tetrahydropyrazinoisoquinolinone 5-HT2C receptor agonists

The 5-HT_2C receptor has been implicated as a critical regulator of appetite. Small molecule activation of the 5-HT_2C receptor has been shown to affect food intake and regulate body weight gain in rodent models and more recently in human clinical trials. Therefore, 5-HT_2C is a well validated target for anti-obesity therapy. The synthesis and structure–activity relationships of a series of novel tetrahydropyrazinoisoquinolinone 5-HT_2C receptor agonists are presented. Several members of this series were identified as potent 5-HT_2C receptor agonists with high functional selectivity against the 5-HT_2A and 5-HT_2B receptors and reduced food intake in an acute rat feeding model upon oral dosing.     

The G protein-coupled bile acid receptor, TGR5, stimulates gallbladder filling

TGR5 is a G protein-coupled bile acid receptor present in brown adipose tissue and intestine, where its agonism increases energy expenditure and lowers blood glucose. Thus, it is an attractive drug target for treating human metabolic disease. However, TGR5 is also highly expressed in gallbladder, where its functions are less well characterized. Here, we demonstrate that TGR5 stimulates the filling of the gallbladder with bile. Gallbladder volume was increased in wild-type but not Tgr5(-/-) mice by administration of either the naturally occurring TGR5 agonist, lithocholic acid, or the synthetic TGR5 agonist, INT-777. These effects were independent of fibroblast growth factor 15, an enteric hormone previously shown to stimulate gallbladder filling. Ex vivo analyses using gallbladder tissue showed that TGR5 activation increased cAMP concentrations and caused smooth muscle relaxation in a TGR5-dependent manner. These data reveal a novel, gallbladder-intrinsic mechanism for regulating gallbladder contractility. They further suggest that TGR5 agonists should be assessed for effects on human gallbladder as they are developed for treating metabolic disease.     

Synthesis and SAR of heterocyclic carboxylic acid isosteres based on 2-biarylethylimidazole as bombesin receptor subtype-3 (BRS-3) agonists for the treatment of obesity

SAR around non-peptidic potent bombesin receptor subtype-3 (BRS-3) agonist lead 2 is presented. Attempts to replace the carboxylic acid with heterocyclic isosteres to improve oral bioavailability and brain penetration are described.     

Discovery of novel pyrimidine and malonamide derivatives as TGR5 agonists

Takeda G-protein-coupled receptor 5 (TGR5) is a promising molecular target for metabolic diseases. A series of 4-(2,5-dichlorophenoxy)pyrimidine and cyclopropylmalonamide derivatives were synthesized as potent agonists of TGR5 based on a bioisosteric replacement strategy. Several compounds exhibited improved potency, compared to a reference compound with a pyridine scaffold. The pharmacokinetic profile of the representative compound 18 was considered moderate.     

Synthesis and SAR studies of 3-phenoxypropyl piperidine analogues as ORL1 (NOP) receptor agonists

A series of 3-phenoxypropyl piperidine analogues have been discovered as novel ORL1 receptor agonists. Structure-activity relationships have been explored around the 3-phenoxypropyl region with several potent and selective analogues identified.     

Synthesis and SAR of derivatives based on 2-biarylethylimidazole as bombesin receptor subtype-3 (BRS-3) agonists for the treatment of obesity

This Letter describes a series of potent and selective BRS-3 agonists containing a biarylethylimidazole pharmacophore. Extensive SAR studies were carried out with different aryl substitutions. This work led to the identification of a compound 2-{2-[4-(pyridin-2-yl)phenyl]ethyl}-5-(2,2-dimethylbutyl)-1H-imidazole 9 with excellent binding affinity (IC₅₀ = 18 nM, hBRS-3) and functional agonist activity (EC₅₀ = 47 nM, 99% activation). After oral administration, compound 9 had sufficient exposure in diet induced obese mice to demonstrate efficacy in lowering food intake and body weight via BRS-3 activation.     

Activation of the bile acid receptor TGR5 enhances LPS-induced inflammatory responses in a human monocytic cell line

Abstract

Introduction: Bile acids are recognized as signaling molecules, mediating their effects both through the cell surface receptor TGR5 and the nuclear receptor FXR. After a meal, approximately 95% of the bile acids are transported from terminal ileum and back to the liver via the portal vein, resulting in postprandial elevations of bile acids in blood. During the digestion of fat, components from the microbiota, including LPS, are thought to reach the circulation where it may lead to inflammatory responses after binding TLR4 immune cells. Both LPS and bile acids are present in blood after a high-fat meal; we therefore wanted to study consequences of a possible interplay between TGR5 and TLR4 in human monocytes. Methods: The monocytic cell line U937 stably transfected with the NF-κB reporter plasmid 3x-κB-luc was used as a model system to study the effects of TGR5 and TLR4. Activation of MAP kinases was studied to reveal functional consequences of triggering TGR5 in U937 cells. Effects of TGR5 and TLR4 activation were monitored using NF-κB luciferase assay and by quantification of the pro-inflammatory cytokines IL-6 and IL-8 using ELISA. Results: In this study, results show that triggering TGR5 with the specific agonist betulinic acid (BA), and the bile acids CDCA or DCA, activated both the main MAP kinases ERK1/2, p38 and JNK, and the NF-κB signaling pathway. We further demonstrated that co-triggering of TLR4 and TGR5 enhanced the activation of NF-κB and the release of inflammatory cytokines in a synergistic manner compared to triggering of TLR4 alone. Conclusions: Thus, two different and simultaneous events associated with the digestive process coordinately affect the function of human monocytes and contribute to enhanced inflammation. Because elevated levels of circulatory LPS may contribute to the development of insulin resistance, the results from this study suggest that bile acids through the activation of TGR5 may have a role in the development of insulin resistance as well.     

Synthesis and SAR of 5-aryl-furan-2-carboxamide derivatives as potent urotensin-II receptor antagonists

The synthesis and biological evaluation as potential urotensin-II receptor antagonists of a series of 5-arylfuran-2-carboxamide derivatives 1, bearing a 4-(3-chloro-4-(piperidin-4-yloxy)benzyl)piperazin-1-yl group, are described. The results of a systematic SAR investigation of furan-2-carboxamides with C-5 aryl groups possessing a variety of aryl ring substituents led to identification of the 3,4-difluorophenyl analog 1y as a highly potent UT antagonist with an IC₅₀ value of 6?nM. In addition, this substance was found to display high metabolic stability, and low hERG inhibition and cytotoxicity, and to have an acceptable PK profile.     

Discovery of 3-aryl-5-acylpiperazinyl-pyrazoles as antagonists to the NK3 receptor

A series of 3-aryl-5-acylpiperazinyl-pyrazoles (e.g., 3a-b) initially identified through a high-throughput screening campaign using the aequorin Ca²⁺ bioluminescence assay as novel, potent small molecule antagonists of the G protein-coupled human tachykinin NK₃ receptor (hNK3-R) is described. Preliminary profiling revealed poor plasma and metabolic stability for these structures in rodents. Further optimization efforts resulted in analogs with improved potency, stability, and pharmacokinetic properties as well as good brain permeability, for example, compounds 26 and 42. Unexpected cytotoxicity was observed in such N-Me pyrazole structures as compounds 41-42.     

SAR studies of 6-aryl-1,3-dihydrobenzimidazol-2-ones as progesterone receptor antagonists

We have previously reported that the aryl substituted benzimidazolones, benzoxazinones, and oxindoles (e.g., 1-3) are progesterone receptor (PR) antagonists and have recently disclosed that the nature of 5- and 6-aryl moieties played a critical role in PR functional activity in the oxindole and benzoxazinone templates. For example, replacing the phenyl group of PR antagonists 2 and 3 with a 5'-cyanopyrrol-2'-yl moiety switched their functional activity to PR agonist activity (2a and 3a). These findings prompted us to examine if there is a similar effect of the 6-aryl moieties on the PR functional activity for the benzimidazolone template. Numerous analogs, such as 5, showed potent PR antagonist activity with about a 10-fold increase in potency as compared to those reported earlier in the same series. More interestingly, pyrrole-containing benzimidazolones 24-27 remained as PR antagonists in contrast to the PR agonist activity switch for oxindole and benzoxazinone scaffolds when a 5'-cyanopyrrol-2'-yl group was installed as a pendant aryl group.     

C3'-cis-Substituted carboxycyclopropyl glycines as metabotropic glutamate 2/3 receptor agonists: synthesis and SAR studies

The synthesis of a series of C3'-cis-substituted carboxycyclopropyl glycines bearing a wide variety of functional groups is described, and the structure-activity relationship for this series as agonists of group II metabotropic glutamate receptors is reported.     

The bile acid membrane receptor TGR5: a novel pharmacological target in metabolic,inflammatory and neoplastic disorders

Abstract

TGR5 is the G-protein–coupled bile acid-activated receptor, found in many human and animal tissues. Considering different endocrine and paracrine functions of bile acids, the current review focuses on the role of TGR5 as a novel pharmacological target in the metabolic syndrome and related disorders, such as diabetes, obesity, atherosclerosis, liver diseases and cancer. TGR5 ligands improve insulin sensitivity and glucose homeostasis through the secretion of incretins. The bile acid/TGR5/cAMP signaling pathway increases energy expenditure in brown adipose tissue and skeletal muscle. Activation of TGR5 in macrophages inhibits production of proinflammatory cytokines and attenuates the development of atherosclerosis. This receptor has been detected in many cell types of the liver where it has anti-inflammatory effects, thus reducing liver steatosis and damage. TGR5 also modulates hepatic microcirculation and fluid secretion in the biliary tree. In cell culture models TGR5 has been linked to signaling pathways involved in metabolism, cell survival, proliferation and apoptosis, which suggest a possible role of TGR5 in cancer development. Despite the fact that TGR5 ligands may represent novel drugs for prevention and treatment of different aspects of the metabolic syndrome, clinical studies are awaited with the perspective that they will complete TGR5 biology and identify efficient and safe TGR5 agonists.     

Novel 5-aryl-1,3-dihydro-indole-2-thiones. potent,orally active progesterone receptor agonists

During the course of our studies on 3,3-disubstituted-5-aryloxindoles derived progesterone receptor (PR) antagonists we discovered that changing the amide funtionality to a thio-amide resulted in compounds displaying potent PR agonist activity. In this communication, the synthesis, structure activity relationships (SAR) and in vivo activity of various 5-arylthio-oxindoles will be discussed.     

3-Acyloxy-2-phenalkylpropyl amides and esters of homovanillic acid as novel vanilloid receptor agonists

A series of 3-acyloxy-2-phenalkylpropyl amides and esters of homovanillic acid were designed and synthesized as vanilloid receptor agonists containing the three principal pharmacophores of resiniferatoxin. Amide analogues 23, 5 and 11 were found to be potent agonists in vanilloid receptor assay both for ligand binding and for activation.     

Synthesis of 3'-acetamidoadenosine derivatives as potential A3 adenosine receptor agonists

On the basis of high binding affinity of 3'-aminoadenosine derivatives 2b at the human A3 adenosine receptor (AR), 3'-acetamidoadenosine derivatives 3a-e were synthesized from 1,2:5,6-di-O-isopropylidene-D-glucose via stereoselective hydroboration as a key step. Although all synthesized compounds were totally devoid of binding affinity at the human A3AR, our results revealed that 3'-position of adenosine can only be tolerated with small size of a hydrogen bonding donor like hydroxyl or amino group in the binding site of human A3AR.     

Synthesis and SAR of aminothiazole fused benzazepines as selective dopamine D2 partial agonists

Dopamine (D₂) partial agonists (D2PAs) have been regarded as a potential treatment for schizophrenia patients with expected better side effect profiles than currently marketed antipsychotics. Herein we report the synthesis and SAR of a series of aminothiazole fused benzazepines as selective D₂ partial agonists. These compounds have good selectivity, CNS drug-like properties and tunable D₂ partial agonism. One of the key compounds, 8h, has good in vitro/in vivo ADME characteristics, and is active in a rat amphetamine-induced locomotor activity model.     

Synthesis and SAR study of a novel series of dopamine receptor agonists

The synthesis of a novel series of dopamine receptor agonists are described as well as their in vitro potency and efficacy on dopamine D₁ and D₂ receptors. This series was designed from pergolide and (4aR,10aR)-1-propyl-1,2,3,4,4a,5,10,10a-octahydro-benzo[g]quinolin-6-ol (PHBQ) and resulted in the synthesis of (2R,4aR,10aR)-2-methylsulfanylmethyl-4-propyl-3,4,4a,5,10,10a-hexahydro-2H-naphtho[2,3-b][1,4]oxazin-9-ol (compound 27), which has a D₁ and D₂ receptor profile similar to that of the most recently approved drug for Parkinson’s disease, rotigotine.     

Synthesis and structure-activity relationships of a series of benzazepine derivatives as 5-HT2C receptor agonists

To identify potent and selective 5-HT(2C) receptor agonists, a series of novel benzazepine derivatives were synthesized, and their structure-activity relationships examined. The compounds were evaluated for their 5-HT(2C), 5-HT(2A), and 5-HT(2B) receptor binding affinity and intrinsic activity for the 5-HT(2C) and 5-HT(2A) receptors. Among these compounds, 6,7-dichloro-2,3,4,5-tetrahydro-1H-3-benzazepine (6) was effective in a rat penile erection model when administered po, which is a symptom of the serotonin syndrome reflecting 5-HT(2C) receptor activation. Moreover, compound 6 was characterized as a partial agonist of 5-HT(2A) receptors; therefore, it had little effect on the cardiovascular system.