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Minireview: Signal bias, allosterism, and polymorphic variation at the GLP-1R: implications for drug discovery.

ABSTRACT: The glucagon-like peptide-1 receptor (GLP-1R) controls the physiological responses to the incretin hormone glucagon-like peptide-1 and is a major therapeutic target for the treatment of type 2 diabetes, owing to the broad range of effects that are mediated upon its activation. These include the promotion of glucose-dependent insulin secretion, increased insulin biosynthesis, preservation of ?-cell mass, improved peripheral insulin action, and promotion of weight loss. Regulation of GLP-1R function is complex, with multiple endogenous and exogenous peptides that interact with the receptor that result in the activation of numerous downstream signaling cascades. The current understanding of GLP-1R signaling and regulation is limited, with the desired spectrum of signaling required for the ideal therapeutic outcome still to be determined. In addition, there are several single-nucleotide polymorphisms (used in this review as defining a natural change of single nucleotide in the receptor sequence; clinically, this is viewed as a single-nucleotide polymorphism only if the frequency of the mutation occurs in 1% or more of the population) distributed within the coding sequence of the receptor protein that have the potential to produce differential responses for distinct ligands. In this review, we discuss the current understanding of GLP-1R function, in particular highlighting recent advances in the field on ligand-directed signal bias, allosteric modulation, and probe dependence and the implications of these behaviors for drug discovery and development.

SUBMITTER: Koole C

PROVIDER: S-EPMC3725346 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Minireview: Signal bias, allosterism, and polymorphic variation at the GLP-1R: implications for drug discovery.

Koole Cassandra C Savage Emilia E EE Christopoulos Arthur A Miller Laurence J LJ Sexton Patrick M PM Wootten Denise D

Molecular endocrinology (Baltimore, Md.) 20130717 8

The glucagon-like peptide-1 receptor (GLP-1R) controls the physiological responses to the incretin hormone glucagon-like peptide-1 and is a major therapeutic target for the treatment of type 2 diabetes, owing to the broad range of effects that are mediated upon its activation. These include the promotion of glucose-dependent insulin secretion, increased insulin biosynthesis, preservation of β-cell mass, improved peripheral insulin action, and promotion of weight loss. Regulation of GLP-1R functi ...[more]

PMID: 23864649

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Project description:AimElevated kidney uptake in insulinoma patients remains a major limitation of radiometallated exendin-derived ligands of the glucagon-like peptide 1 receptor (GLP-1R). Based on the previously published potent GLP-1R-activating undecapeptide 1, short-chained GLP-1R ligands were developed to investigate whether kidney uptake can be reduced by means of direct 18F-labeling (nuclide-based accelerated renal excretion) or the reduction of the overall ligand charge (ligand-based reduced kidney uptake).Materials & methodsGLP-1R ligands were prepared according to optimized standard protocols via solid-phase peptide synthesis (SPPS) or, when not practicable, via fragment coupling in solution. Synthesis of (2'-Et, 4'-OMe)4, 4'-L-biphenylalanine ((2'-Et, 4'-OMe)BIP), required for the preparation of 1, was accomplished by Suzuki-Miyaura cross-coupling. In vitro experiments were performed using stably transfected GLP-1R+ HEK293-hGLP-1R cells.ResultsIn contrast to the three reference ligands glucagon-like peptide 1 (GLP-1, IC50 = 23.2 ± 12.2 nM), [Nle14, Tyr(3-I)40]exendin-4 (IC50 = 7.63 ± 2.78 nM) and [Nle14, Tyr40]exendin-4 (IC50 = 9.87 ± 1.82 nM), the investigated GLP-1R-targeting small peptides (9-15 amino acids), including lead peptide 1, exhibited only medium to low affinities (IC50 > 189 nM). Only SiFA-tagged undecapeptide 5 (IC50 = 189 ± 35 nM) revealed a higher affinity than 1 (IC50 = 669 ± 242 nM).ConclusionThe investigated small peptides, including lead peptide 1, could not compete with favorable in vitro characteristics of glucagon-like peptide 1 (GLP-1), [Nle14, Tyr(3-I)40]exendin-4 and [Nle14, Tyr40]exendin-4. The auspicious EC50 values of 1 provided by the literature could not be transferred to competitive binding experiments. Therefore, the use of 1 as a basic scaffold for the design of further GLP-1R-targeting radioligands cannot be recommended. Further investigations might include the scaffold of 5, although substantial optimizations concerning affinity and lipophilicity would be required. In sum, GLP-1R-targeting radioligands with reduced kidney uptake could not be obtained in this work, which emphasizes the need for further ligands addressing this particular issue.

Project description:There is increasing concern about the development of pancreatitis in patients with diabetes mellitus who received long-term glucagon-like peptide-1 (GLP-1) analog treatment. Its pathogenesis is unknown. The effects of GLP-1 agonists on pancreatic endocrine cells are well studied; however, there is little information on effects on other pancreatic tissues that might be involved in inflammatory processes. Pancreatic stellate cells (PSCs) can have an important role in pancreatitis, secreting various inflammatory cytokines/chemokines, as well as collagen. In this study, we investigated GLP-1R occurrence in normal pancreas, acute pancreatitis (AP)/chronic pancreatitis (CP), and the effects of GLP-1 analog on normal PSCs, their ability to stimulate inflammatory mediator secretion or proliferation. GLP-1 receptor (GLP-1R) expression/localization in normal pancreas and pancreatitis (AP/CP) tissues were evaluated with histological/immunohistochemical analysis. PSCs were isolated from male Wistar rats. GLP-1R expression and effects of GLP-1 analog on activated PSCs was examined with real-time PCR, MTS assays and western blotting. In normal pancreas, pancreatic ? cells expressed GLP-1R, with only low expression in acinar cells, whereas in AP or CP, acinar cells, ductal cells and activated PSCs expressed GLP-1R. With activation of normal PSCs, GLP-1R is markedly increased, as is multiple other incretin-related receptors. The GLP-1 analog, liraglutide, did not induce inflammatory genes expression in activated PSCs, but induced proliferation. Liraglutide activated multiple signaling cascades in PSCs, and the extracellular signal-regulated kinase pathway mediated the PSCs proliferation. GLP-1Rs are expressed in normal pancreas and there is marked enhanced expression in AP/CP. GLP-1-agonist induced cell proliferation of activated PSCs without increasing release of inflammatory mediators. These results suggest chronic treatment with GLP-1R agonists could lead to proliferation/chronic activation of PSCs, which may lead to important effects in the pancreas.

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Minireview: Signal bias, allosterism, and polymorphic variation at the GLP-1R: implications for drug discovery.

Publications

Minireview: Signal bias, allosterism, and polymorphic variation at the GLP-1R: implications for drug discovery.

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