G Protein-coupled Receptors Antagonists Research Articles

Anti-Inflammatory Effects of GPR55 Agonists and Antagonists in LPS-Treated BV2 Microglial Cells.

Chronic inflammation is driven by proinflammatory cytokines such as interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and chemokines, such as c-c motif chemokine ligand 2 (CCL2), CCL3, C-X-C motif chemokine ligand 2 (CXCL2), and CXCL10. Inflammatory processes of the central nervous system (CNS) play an important role in the pathogenesis of various neurological and psychiatric disorders like Alzheimer's disease, Parkinson's disease, and depression. Therefore, identifying novel anti-inflammatory drugs may be beneficial for treating disorders with a neuroinflammatory background. The G-protein-coupled receptor 55 (GPR55) gained interest due to its role in inflammatory processes and possible involvement in different disorders. This study aims to identify the anti-inflammatory effects of the coumarin-based compound KIT C, acting as an antagonist with inverse agonistic activity at GPR55, in lipopolysaccharide (LPS)-stimulated BV2 microglial cells in comparison to the commercial GPR55 agonist O-1602 and antagonist ML-193. All compounds significantly suppressed IL-6, TNF-α, CCL2, CCL3, CXCL2, and CXCL10 expression and release in LPS-treated BV2 microglial cells. The anti-inflammatory effects of the compounds are partially explained by modulation of the phosphorylation of p38 mitogen-activated protein kinase (MAPK), p42/44 MAPK (ERK 1/2), protein kinase C (PKC) pathways, and the transcription factor nuclear factor (NF)-κB, respectively. Due to its potent anti-inflammatory properties, KIT C is a promising compound for further research and potential use in inflammatory-related disorders.

P055 GPR43 and GPR84 play a crucial role in supporting perianal fistula formation and disease progression in Crohn’s Disease

Abstract Background Fistula complication represents one of the most disabling manifestations of Crohn’s Disease and a risk factor for more aggressive disease progression and mucinous adenocarcinoma . However, molecular mechanisms behind this transformation are completely unknown. Growing evidence supported epithelial-to-mesenchymal transition (EMT) as a critical process to replace impaired intestinal fibroblasts in repairing mucosal membrane damage. However, EMT drivers during fistula formation and progression are still not completely known. Here, we investigated whether G-protein coupled receptors serve as new drivers of EMT and fistula disease progression. Methods Surgical specimens (N=9) collected from perianal fistula and non-involved areas of CD patients were analyzed by bulk RNA-sequencing and Lipidomics analysis. Gene set enrichment analysis (GSEA) was used to detect the levels of differentially expressed pathways. GPR43 and GPR84 analysis was performed on perianal fistula; adenocarcinoma; and mucinous adenocarcinoma-associated (MA) CD fistula FFPE tissue section. Caco-2 cell line was stimulated for 24 h with agonists and antagonists of GPRs. Genes associated to EMT were evaluated by RT-PCR and WB. Results Gene sets related to the signatures of epithelial-to-mesenchymal transition, G-protein coupled receptors (GPRs), immune response, lipid oxidation were significantly enriched in the fistula compared to non-involved tissue. Among differentially GPRs expressed genes FFAR2 encoding for GPR43, sensor for Small Chain Fatty Acids (SCFAs), and GPR84 sensor for Medium Chain Fatty Acids (MCFAs), predominantly expressed in immune cells, reported to be upregulated in the context of acute inflammation. Upregulation of GPRs expression correlated positively with enzymes associated to lipid oxidation gen set including PLA2G2D, ALOX5, NR4A3, PLA2G7, ACOXL and negatively with their lipids substrates. Caco2 cells stimulated with SCFAs and MCFAs upregulated not only the expression of GPR43 and GPR84, but also of EMT-transcription factor Twist1 and PLA2G2D, all effects reverted in the presence of their antagonists. An increase expression of GPR43 and GPR84 in association with Twist1 was found in MA-CD tissue section. Conclusion Our results highlighted GPR43 and GPR84 as new potential factors of fistula formation that support the EMT process through increased fatty acid oxidation, which in turn fuels the activation of GPRs. However, the increase expression of both receptors in the fistula oncogenic disease progression suggests that strategies regulating lipid metabolism or targeting GPRs could pave the way for novel therapeutic approaches to prevent fistula complication in CD patients.

The Structure-property Relationships of GPCR-targeted Drugs Approved between 2011 and 2021.

G-protein-coupled receptors (GPCRs) are the largest family of membrane receptors and the most intensively studied drug targets. Given the physiological importance of signal transduction by GPCRs and the recent progress in the structure determination of membrane proteins, the development of GPCR antagonists and agonists is expected to continue to be a major area of medicinal chemistry research. The structure-property relationship illustrates how the modification of the chemical structure influences the absorption, distribution, metabolism, excretion, and other related properties of drug compounds. Understanding the structure-property relationships of clinically approved GPCR-targeted drugs and their analogues could provide useful information on the lead-to-candidate optimization strategies. Among more than 50 GPCR antagonists and agonists approved in the last decade, the structure-property relationships of 17 drugs are compiled from medicinal chemistry literature, in which detailed pharmacokinetic and toxicological properties are disclosed not only for the final drug candidate but also for key analogues generated during the lead optimization campaign. The structure-property relationships hereby summarized demonstrate how in vitro and in vivo properties of the membrane protein-targeted ligands could be effectively optimized, in many cases, without requiring a significant change in the molecular size. This information is expected to provide valuable insights to expedite new GPCR-targeted drug development.

Altered G-Protein Transduction Protein Gene Expression in the Testis of Infertile Patients with Nonobstructive Azoospermia.

Recent studies have shown that several members of the G-protein-coupled receptors (GPCR) superfamily play crucial roles in the maintenance of ion-water homeostasis of the sperm and Sertoli cells, development of the germ cells, formation of the blood barrier, and maturation of sperm. The GPCR, guanyl-nucleotide exchange factor, membrane traffic protein, and small GTPase genes were analyzed by microarray and bioinformatics (3513 sperm and Sertoli cell genes). In the microarray analyses of three human cases with different nonobstructive azoospermia sperm, the expression of GOLGA8IP, OR2AT4, PHKA1, A2M, OR56A1, SEMA3G, LRRC17, APP, ARHGAP33, RABGEF1, NPY2R, GHRHR, LTB4R2, GRIK5, OR6K6, NAPG, OR6C65, VPS35, FPR3, and ARL4A was upregulated, while expression of MARS, SIRPG, OGFR, GPR150, LRRK1, and NGEF was downregulated. There was an increase in GBP3, GBP3, TNF, TGFB3, and CLTC expression in the Sertoli cells of three human cases with NOA, whereas expression of PAQR4, RRAGD, RAC2, SERPINB8, IRPB1, MRGPRF, RASA2, SIRPG, RGS2, RAP2A, RAB2B, ARL17, SERINC4, XIAP, DENND4C, ANKRA2, CSTA, STX18, and SNAP23 were downregulated. A combined analysis of Enrich Shiny Gene Ontology (GO), STRING, and Cytoscape was used to predict proteins' molecular interactions and then to recognize master pathways. Functional enrichment analysis showed that the biological process (BP), regulation of protein metabolic process, regulation of small GTPase-mediated signal transduction were significantly expressed in up-/downregulated differentially expressed genes (DEGs) in sperm. In molecular function (MF) experiments of DEGs that were up-/downregulated, it was found that GPCR activity, guanyl ribonucleotide binding, GTPase activity and nucleoside-triphosphatase activity were overexpressed. An analysis of GO enrichment findings of Sertoli cells showed BP and MF to be common DEGs. When these gene mutations have been validated, they can be used to create new GPCR antagonists or agonists that are receptor-selective.

Lysophosphatidylglucoside/GPR55 signaling promotes foam cell formation in human M2c macrophages

Atherosclerosis is a major cause of cerebral and cardiovascular diseases. Intravascular plaques, a well-known pathological finding of atherosclerosis, have a necrotic core composed of macrophages and dead cells. Intraplaque macrophages, which are classified into various subtypes, play key roles in maintenance of normal cellular microenvironment. Excessive uptake of oxidized low-density lipoprotein causes conversion of macrophages to foam cells, and consequent progression/exacerbation of atherosclerosis. G-protein-coupled receptor 55 (GPR55) signaling has been reported to associate with atherosclerosis progression. We demonstrated recently that lysophosphatidylglucoside (lysoPtdGlc) is a specific ligand of GPR55, although in general physiological ligands of GPR55 are poorly understood. Phosphatidylglucoside is expressed on human monocytes and can be converted to lysoPtdGlc. In the present study, we examined possible involvement of lysoPtdGlc/GPR55 signaling in foam cell formation. In monocyte-derived M2c macrophages, lysoPtdGlc/GPR55 signaling inhibited translocation of ATP binding cassette subfamily A member 1 to plasma membrane, and cholesterol efflux. Such inhibitory effect was reversed by GPR55 antagonist ML193. LysoPtdGlc/GPR55 signaling in M2c macrophages was involved in excessive lipid accumulation, thereby promoting foam cell formation. Our findings suggest that lysoPtdGlc/GPR55 signaling is a potential therapeutic target for inhibition of atherosclerosis progression.

Evaluation of Drug Responses to Human β2AR Using Native Mass Spectrometry.

We aimed to develop a platform to rapidly investigate the responses of agonists and antagonists to G-protein-coupled receptors (GPCRs) using native mass spectrometry (MS). We successfully observed the ligand-bound human β2 adrenergic receptor (hβ2AR); however, it was challenging to quantitatively discuss drug efficacy from MS data alone. Since ligand-bound GPCRs are stabilized by the Gα subunit of G proteins on the membrane, mini-Gs and nanobody80 (Nb80) that can mimic the Gα interface of the GPCR were utilized. Ternary complexes of hβ2AR, ligand, and mini-Gs or Nb80 were prepared and subjected to native MS. We found a strong correlation between the hβ2AR-mini-Gs or -Nb80 complex ratio observed in the mass spectra and agonist/antagonist efficacy obtained using a cell-based assay. This method does not require radioisotope labeling and would be applicable to the analysis of other GPCRs, facilitating the characterization of candidate compounds as GPCR agonists and antagonists.

Role of G-protein coupled receptors in cardiovascular diseases.

Cardiovascular diseases (CVDs) are the leading cause of death globally, with CVDs accounting for nearly 30% of deaths worldwide each year. G-protein-coupled receptors (GPCRs) are the most prominent family of receptors on the cell surface, and play an essential regulating cellular physiology and pathology. Some GPCR antagonists, such as β-blockers, are standard therapy for the treatment of CVDs. In addition, nearly one-third of the drugs used to treat CVDs target GPCRs. All the evidence demonstrates the crucial role of GPCRs in CVDs. Over the past decades, studies on the structure and function of GPCRs have identified many targets for the treatment of CVDs. In this review, we summarize and discuss the role of GPCRs in the function of the cardiovascular system from both vascular and heart perspectives, then analyze the complex ways in which multiple GPCRs exert regulatory functions in vascular and heart diseases. We hope to provide new ideas for the treatment of CVDs and the development of novel drugs.

Therapeutic antagonism of the neurokinin 1 receptor in endosomes provides sustained pain relief

The hypothesis that sustained G protein-coupled receptor (GPCR) signaling from endosomes mediates pain is based on studies with endocytosis inhibitors and lipid-conjugated or nanoparticle-encapsulated antagonists targeted to endosomes. GPCR antagonists that reverse sustained endosomal signaling and nociception are needed. However, the criteria for rational design of such compounds are ill-defined. Moreover, the role of natural GPCR variants, which exhibit aberrant signaling and endosomal trafficking, in maintaining pain is unknown. Herein, substance P (SP) was found to evoke clathrin-mediated assembly of endosomal signaling complexes comprising neurokinin 1 receptor (NK1R), Gαq/i, and βarrestin-2. Whereas the FDA-approved NK1R antagonist aprepitant induced a transient disruption of endosomal signals, analogs of netupitant designed to penetrate membranes and persist in acidic endosomes through altered lipophilicity and pKa caused sustained inhibition of endosomal signals. When injected intrathecally to target spinal NK1R+ve neurons in knockin mice expressing human NK1R, aprepitant transiently inhibited nociceptive responses to intraplantar injection of capsaicin. Conversely, netupitant analogs had more potent, efficacious, and sustained antinociceptive effects. Mice expressing C-terminally truncated human NK1R, corresponding to a natural variant with aberrant signaling and trafficking, displayed attenuated SP-evoked excitation of spinal neurons and blunted nociceptive responses to SP. Thus, sustained antagonism of the NK1R in endosomes correlates with long-lasting antinociception, and domains within the C-terminus of the NK1R are necessary for the full pronociceptive actions of SP. The results support the hypothesis that endosomal signaling of GPCRs mediates nociception and provides insight into strategies for antagonizing GPCRs in intracellular locations for the treatment of diverse diseases.

GPCR Signaling Measurement and Drug Profiling with an Automated Live-Cell Microscopy System.

A major limitation of time-lapse microscopy combined with fluorescent biosensors, a powerful tool for quantifying spatiotemporal dynamics of signaling in single living cells, is low-experimental throughput. To overcome this limitation, we created a highly customizable, MATLAB-based platform: flexible automated liquid-handling combined microscope (FALCOscope) that coordinates an OpenTrons liquid handler and a fluorescence microscope to automate drug treatments, fluorescence imaging, and single-cell analysis. To test the feasibility of the FALCOscope, we quantified G protein-coupled receptor (GPCR)-stimulated Protein Kinase A activity and cAMP responses to GPCR agonists and antagonists. We also characterized cAMP dynamics induced by GPR68/OGR1, a proton-sensing GPCR, in response to variable extracellular pH values. GPR68-induced cAMP responses were more transient in acidic than neutral pH values, suggesting a pH-dependence for signal attenuation. Ogerin, a GPR68 positive allosteric modulator, enhanced cAMP response most strongly at pH 7.0 and sustained cAMP response for acidic pH values, thereby demonstrating the capability of the FALCOscope to capture allosteric modulation. At a high concentration, ogerin increased cAMP signaling independent of GPR68, likely via phosphodiesterase inhibition. The FALCOscope system thus enables enhanced throughput single-cell dynamic measurements and is a versatile system for interrogating spatiotemporal regulation of signaling molecules in living cells and for drug profiling and screening.

Small Molecule Tools to Study Cellular Target Engagement for the Intracellular Allosteric Binding Site of GPCRs.

A conserved intracellular allosteric binding site (IABS) has recently been identified at several G protein-coupled receptors (GPCRs). Ligands targeting the IABS, so-called intracellular allosteric antagonists, are highly promising compounds for pharmaceutical intervention and currently evaluated in several clinical trials. Beside co-crystal structures that laid the foundation for the structure-based development of intracellular allosteric GPCR antagonists, small molecule tools that enable an unambiguous identification and characterization of intracellular allosteric GPCR ligands are of utmost importance for drug discovery campaigns in this field. Herein, we discuss recent approaches that leverage cellular target engagement studies for the IABS and thus play a critical role in the evaluation of IABS-targeted ligands as potential therapeutic agents.

GPR55 activation prevents amphetamine-induced conditioned place preference and decrease the amphetamine-stimulated inflammatory response in the ventral hippocampus in male rats

Inflammatory response in the Central Nervous System (CNS) induced by psychostimulants seems to be a crucial factor in the development and maintenance of drug addiction. The ventral hippocampus (vHp) is part of the reward system involved in substance addiction and expresses abundant G protein-coupled receptor 55 (GPR55). This receptor modulates the inflammatory response in vitro and in vivo, but there is no information regarding its anti-inflammatory effects and its impact on psychostimulant consumption. The aim of the present study was to investigate whether vHp GPR55 activation prevents both the inflammatory response induced by amphetamine (AMPH) in the vHp and the AMPH-induced conditioned place preference (A-CPP). Wistar adult male rats with a bilateral cannula into the vHp or intact males were subjected to A-CPP (5 mg/kg). Upon the completion of A-CPP, the vHp was dissected to evaluate IL-1β and IL-6 expression through RT-PCR, Western blot and immunofluorescence. Our results reveal that AMPH induces both A-CPP and an increase of IL-1β and IL-6 in the vHp. The GPR55 agonist lysophosphatidylinositol (LPI, 10 μM) infused into the vHp prevented A-CPP and the AMPH-induced IL-1β increase. CID 16020046 (CID, 10 μM), a selective GPR55 antagonist, abolished LPI effects. To evaluate the effect of the inflammatory response, lipopolysaccharide (LPS, 5 μg/μl) was infused bilaterally into the vHp during A-CPP acquisition. LPS strengthened A-CPP and increased IL-1β/IL-6 mRNA and protein levels in the vHp. LPS also increased CD68, Iba1, GFAP and vimentin expression. All LPS-induced effects were blocked by LPI. Our results suggest that GPR55 activation in the vHp prevents A-CPP while decreasing the local neuro-inflammatory response. These findings indicate that vHp GPR55 is a crucial factor in preventing the rewarding effects of AMPH due to its capacity to interfere with proinflammatory responses in the vHp.

The neuroprotective effects of GPR55 against hippocampal neuroinflammation and impaired adult neurogenesis in CSDS mice

Depression is one of the most prevalent mental illnesses in the world today, and the onset of depression is usually accompanied by neuroinflammation and impaired adult neurogenesis. As a new potential member of the endocannabinoid (eCB) system, G protein coupled receptor 55 (GPR55) has been associated with mood regulation. However, the role of GPR55 in the pathophysiology of depression remains poorly understood. Thus, a 10-day chronic social defeat stress (CSDS) paradigm was utilized as an animal model of depression to explore the potential role of GPR55 in depression. After CSDS, the protein level of GPR55 decreased significantly, but the mRNA expression did not change significantly, highlighting that although the GPR55 protein was involved in the progression of the depression- and anxiety-like phenotypes, its mRNA was not. Additionally, depression- and anxiety-like behaviors were also accompanied by neuroinflammation and impaired adult neurogenesis in the hippocampus. Interestingly, O-1602, a GPR55 agonist, remarkably prevented the development of depression- and anxiety-like behaviors as well as hippocampal neuroinflammation and neurogenesis deficits induced by CSDS. However, after electroacupuncture (EA) alleviated depression- and anxiety-like behaviors induced by CSDS, treatment with a GPR55 antagonist (CID16020046) reversed this effect. Our research demonstrated that downregulation of GPR55 expression in the hippocampus might mediate CSDS-induced depression- and anxiety-like phenotypes, and activation and upregulation of GPR55, which might be correlated with its anti-inflammatory and subsequent neuroprotective effects, could be a potential treatment for depression.

CID16020046, a GPR55 antagonist, attenuates sepsis‑induced acute kidney injury.

Acute kidney injury (AKI) is the most common and serious complication of sepsis, and it is also the main cause of mortality in patients with sepsis. The G protein-coupled receptor 55 (GPR55) inhibitor CID16020046 was found to suppress the inflammatory response in sepsis models in mice. The aim of the present study was to investigate the effect of CID16020046 on AKI in sepsis mouse models and elucidate the possible underlying mechanisms. A sepsis model in mice was established by cecal ligation/perforation (CLP). The expression levels of GPR55 in the serum of patients with sepsis and the renal tissues of septic mice were determined via reverse transcription-quantitative PCR and western blot analyses, respectively. The pathological injury of renal tissue was evaluated using H&E and periodic acid-Schiff staining. ELISA was performed to detect the levels of renal injury-related factors, including blood urea nitrogen (BUN), creatinine (Cre), kidney injury molecule 1 (KIM1) and neutrophil gelatinase-associated lipocalin (NGAL) in septic mice. Moreover, the levels of pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β) were detected via ELISA and western blotting. Apoptosis was determined using TUNEL staining and western blotting. The expression levels of Rho-associated protein kinase (ROCK) pathway-related proteins (Ras homolog family member A, ROCK1 and ROCK2) was measured via western blotting. Finally, H&E staining was used to evaluate the effect of CID16020046 on various organs in mice. Compared with the control subjects, the expression level of GPR55 in the serum of patients with sepsis was significantly increased. Compared with the sham group, CID16020046 (20 mg/kg) significantly decreased the levels of BUN and Cre in the serum, as well as the contents of KIM1 and NGAL in the urine. Furthermore, CID16020046 significantly decreased the contents of TNF-α, IL-6 and IL-1β in the serum and renal tissue of septic mice, and reduced cell apoptosis. In addition, CID16020046 effectively suppressed the expression levels of ROCK pathway-related proteins, and H&E staining revealed that CID16020046 (20 mg/kg) had no toxic effect on the heart, liver, spleen or lung in normal mice. In conclusion, CID16020046 may prove useful for the development of drugs for the treatment of sepsis-induced AKI.

Identification of G protein-coupled receptor 55 (GPR55) as a target of curcumin

The identification of molecular targets of bioactive food components is important to understand the mechanistic aspect of their physiological functions. Here, we have developed a screening system that enables us to determine the activation of G protein-coupled receptors (GPCRs) by food components and have identified GPR55 as a target for curcumin. Curcumin activated GPR55 and induced serum-response element- and serum-response factor-mediated transcription, which were inhibited by Rho kinase and GPR55 antagonists. Both the methoxy group and the heptadienone moiety of curcumin were required for GPR55 activation. The F1905.47 residue of GPR55 was important for the interaction with curcumin. The curcumin-induced secretion of glucagon-like peptide-1 in GLUTag cells was inhibited by a GPR55 antagonist. These results indicate that expression screening is a useful system to identify GPCRs as targets of food components and strongly suggest that curcumin activates GPR55 as an agonist, which is involved in the physiological function of curcumin.

Antagonism of G protein-coupled receptor 55 prevents lipopolysaccharide-induced damages in human dental pulp cells.

Pulpitis is a common oral inflammatory disease in dental pulp commonly associated with bacterial infection. G protein-coupled receptor 55 (GPR55) is a member of the G protein-coupled receptors family that has been found to regulate inflammatory response. However, its roles in dental pulp inflammation have not been investigated. In this study, we used lipopolysaccharide (LPS) to induce inflammation in human dental pulp cells (hDPCs) to simulate an in vitro model of pulpitis. We found that LPS markedly induced the GPR55 expression in hDPCs. Treatment with the GPR55 antagonist ML-193 ameliorated the LPS-caused decrease in cell viability and increase in lactate dehydrogenase release. The upregulated inflammatory cytokines, interleukin-6 (IL-6) and tumour necrosis factor α, in LPS-challenged hDPCs were also attenuated by ML-193. Treatment with ML-193 ameliorated LPS-induced production of the inflammatory mediators cyclooxygenase-2/prostaglandin E2 (COX-2/PGE2), and inducible nitric oxide synthase/nitric oxide (iNOS/NO) in hDPCs. ML-193 also inhibited the activation of Toll-like receptor 4-myeloid differentiation primary response 88-nuclear factor-κB (TLR4-Myd88-NF-κB) signaling in LPS-induced hDPCs via decreased expressions of TLR4, Myd88, and p-NF-κB 65. Our study provides evidence that the GPR55 antagonist ML-193 exhibited anti-inflammatory activity in LPS-stimulated hDPCs through inhibiting TLR4-Myd88-NF-κB signaling. The results imply that ML-193 might be a novel agent for pulpitis.

Distinct classes of potassium channels fused to GPCRs as electrical signaling biosensors

SummaryLigand-gated ion channels (LGICs) are natural biosensors generating electrical signals in response to the binding of specific ligands. Creating de novo LGICs for biosensing applications is technically challenging. We have previously designed modified LGICs by linking G protein-coupled receptors (GPCRs) to the Kir6.2 channel. In this article, we extrapolate these design concepts to other channels with different structures and oligomeric states, namely a tetrameric viral Kcv channel and the dimeric mouse TREK-1 channel. After precise engineering of the linker regions, the two ion channels were successfully regulated by a GPCR fused to their N-terminal domain. Two-electrode voltage-clamp recordings showed that Kcv and mTREK-1 fusions were inhibited and activated by GPCR agonists, respectively, and antagonists abolished both effects. Thus, dissimilar ion channels can be allosterically regulated through their N-terminal domains, suggesting that this is a generalizable approach for ion channel engineering.

Therapeutic Potential of G Protein-Coupled Receptors Against Nonalcoholic Steatohepatitis.

Nonalcoholic steatohepatitis (NASH), the advanced stage of nonalcoholic fatty liver disease (NAFLD), affects approximately 6% of the population worldwide and is strongly associated with cardiometabolic disorders, placing subjects at a sharply increased risk of end-stage hepatic diseases and extrahepatic symptoms. Despite the importance of NASH, no NASH-specific drugs have been approved by the FDA. G protein-coupled receptors (GPCRs), which represent the largest group of druggable targets in the human genome, strongly regulate pathophysiological events. Recent structural and molecular studies have further expanded upon the classic pharmacological applications of GPCRs and enabled the use of emerging GPCR agonists or antagonists for the treatment of metabolic diseases. These advances have encouraged new insights regarding the development of GPCR-targeted NASH therapies. In this review, we analyze up-to-date reports of GPCRs in NASH and discuss trends in the use of GPCRs as targets for NASH treatment.

Tissue-Engineered “Metastases”: Treatment of Hepatic Colon Tumors with a Dual Action Autotaxin Inhibitor-Lysophosphatidic Acid Receptor Antagonist

Lysophosphatidic acid (LPA) acts via G protein coupled receptors (GPCRs) to regulate critical cellular functions and pathophysiological levels of LPA or its receptors are linked to cancer initiation, progression and metastasis. LPA is biosynthesized by the lysophospholipase D activity of autotaxin(ATX/lysoPLD), a known factor for tumorigenesis. By attenuating both LPA signaling and LPA production, we expected to observe synergistic anti-cancer therapeutic effects. In vitro, treatment of human colon cancer cells (HCT 116) with BrP-LPA, a potent dual action ATX inhibitor and pan-LPA GPCR antagonist, significantly reduced cell proliferation, migration and invasion. Next, a tissue-engineered xenograft model to mimic hepatic metastasis of colon cancer was used to evaluate BrP-LPA efficacy in vivo. HCT 116 cells were suspended in Extracel™, a synthetic extracellular matrix (sECM), and injected directly into the livers of nude mice (n = 8). After 1 week, BrP-LPA in saline buffer was administered for two weeks by intraperitoneal injection (10 mg/kg) twice per week. Controls were injected with saline buffer only. The BrP-LPA treated group showed reduced liver tumor weight (p < 0.05) and reduced tumor volume (p < 0.05) relative to controls. This study is the first demonstration of the effects of a dual action ATX inhibitor/LPA antagonist on colon cancer cells, and the first example of a tissue-engineered hepatic colon cancer “metastases” as a platform for anti-cancer drug evaluation. The results suggest that attenuation of signaling through the LPA pathway offers a promising therapeutic target for reducing colon cancer growth and metastasis.

G protein- and β-arrestin Signaling Profiles of Endothelin Derivatives at the Type A Endothelin Receptor.

Endothelin-1 (ET-1) is a potent vasoconstrictor in the cardiovascular system, an effect mediated through the type A endothelin receptor (ETAR), a G protein-coupled receptor (GPCR). Antagonists of the ETAR have shown promising results in randomized clinical trials. However, side effects limit widespread use. Biased agonists have been developed to mitigate the untoward effects of a number of GPCR antagonists. These agents block deleterious G-coupled pathways while stimulating protective β-arrestin pathways. The goal of this study was to test whether there was any significant ligand bias between endothelin derivatives, and whether this could have any physiologic effects in the cardiovascular system. A panel of endothelin derivatives were tested in assays of G protein signaling and β-arrestin 2 recruitment at the ETAR. We then tested the effects of ET-1 on the vasopressor response in wild-type and β-arrestin 1 and 2 KO mice. We found the endothelins activated a wide range of G proteins at the ETAR, but none of the endothelin derivatives demonstrated significant biased agonism. Endothelin derivatives did display structure-activity relationships with regards to their degrees of agonism. β-arrestin 1 and 2 knockout mice did not display any differences to wild-type mice in the acute pressor response to ET-1, and β-arrestin 2 knockout mice did not display any blood pressure differences to wild-type mice in the chronic responses to ET-1. Our findings are consistent with vasoconstriction being mediated by G proteins with a lack of significant desensitization by β-arrestins at the ETAR. These findings suggest that G protein- and β-arrestin-biased ETAR agonists could have distinct physiologic effects from balanced agonists, although the endothelin peptide scaffold does not appear suitable for designing such ligands.

GPCR-Based Bioactive Peptide Screening Using Phage-Displayed Peptides and an Insect Cell System for Insecticide Discovery.

The discovery of new insecticides improves integrated pest management (IPM), but is usually a long high-risk process with a low probability of success. For over two decades, insect neuropeptides (NPs) and their G-protein coupled receptors (GPCRs) have been considered as biological targets for insect pest control, because they are involved in almost all physiological processes associated with insect life stages. A key roadblock to success has been the question of how large volume chemical libraries can be efficiently screened for active compounds. New genomic and proteomic tools have advanced and facilitated the development of new approaches to insecticide discovery. In this study, we report a novel GPCR-based screening technology that uses millions of short peptides randomly generated by bacteriophages, and a method using an insect Sf9 cell expression system. The fire ant is a good model system, since bioactive peptides have been identified for a specific GPCR. The novel small peptides could interfere with the target GPCR-ligand functions. Therefore, we refer to this new mechanism as “receptor interference” (RECEPTORi). The GPCR-based bioactive peptide screening method offers multiple advantages. Libraries of phage-displayed peptides (~109 peptides) are inexpensive. An insect cell-based screening system rapidly leads to target specific GPCR agonists or antagonists in weeks. Delivery of bioactive peptides to target pests can be flexible, such as topical, ingestion, and plant-incorporated protectants. A variety of GPCR targets are available, thus minimizing the development of potential insecticide resistance. This report provides the first proof-of-concept for the development of novel arthropod pest management strategies using neuropeptides, and GPCRs.