Coopman, K., Huang, Y., Johnston, N., Bradley, S. J. , Wilkinson, G. F. and Willars, G. B. (2010) Comparative effects of the endogenous agonist glucagon-like peptide-1 (GLP-1)-(7-36) amide and the small-molecule ago-allosteric agent "compound 2" at the GLP-1 receptor. Journal of Pharmacology and Experimental Therapeutics, 334(3), pp. 795-808. (doi: 10.1124/jpet.110.166009) (PMID:20507928) (PMCID:PMC2939672)
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Abstract
Glucagon-like peptide-1 (GLP-1) mediates antidiabetogenic effects through the GLP-1 receptor (GLP-1R), which is targeted for the treatment of type 2 diabetes. Small-molecule GLP-1R agonists have been sought due to difficulties with peptide therapeutics. Recently, 6,7-dichloro-2-methylsulfonyl-3-N-tert-butylaminoquinoxaline (compound 2) has been described as a GLP-1R allosteric modulator and agonist. Using human embryonic kidney-293 cells expressing human GLP-1Rs, we extended this work to consider the impact of compound 2 on G protein activation, Ca2+ signaling and receptor internalization and particularly to compare compound 2 and GLP-1 across a range of functional assays in intact cells. GLP-1 and compound 2 activated Gαs in cell membranes and increased cellular cAMP in intact cells, with compound 2 being a partial and almost full agonist, respectively. GLP-1 increased intracellular [Ca2+] by release from intracellular stores, which was mimicked by compound 2, with slower kinetics. In either intact cells or membranes, the orthosteric antagonist exendin-(9-39), inhibited GLP-1 cAMP generation but increased the efficacy of compound 2. GLP-1 internalized enhanced green fluorescent protein-tagged GLP-1Rs, but the speed and magnitude evoked by compound 2 were less. Exendin-(9-39) inhibited internalization by GLP-1 and also surprisingly that by compound 2. Compound 2 displays GLP-1R agonism consistent with action at an allosteric site, although an orthosteric antagonist increased its efficacy on cAMP and blocked compound 2-mediated receptor internalization. Full assessment of the properties of compound 2 was potentially hampered by damaging effects that were particularly manifest in either longer term assays with intact cells or in acute assays with membranes.
| Item Type: | Articles |
|---|---|
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Bradley, Dr Sophie |
| Authors: | Coopman, K., Huang, Y., Johnston, N., Bradley, S. J., Wilkinson, G. F., and Willars, G. B. |
| College/School: | College of Medical Veterinary and Life Sciences > School of Molecular Biosciences |
| Journal Name: | Journal of Pharmacology and Experimental Therapeutics |
| Publisher: | American Society for Pharmacology and Experimental Therapeutics (ASPET) |
| ISSN: | 0022-3565 |
| ISSN (Online): | 1521-0103 |
| Published Online: | 19 August 2010 |
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