An Orally Active Allosteric GLP-1 Receptor Agonist Is Neuroprotective in Cellular and Rodent Models of Stroke

Abstract

Diabetes is a major risk factor for the development of stroke. Glucagon-like peptide-1 receptor (GLP-1R) agonists have been in clinical use for the treatment of diabetes and also been reported to be neuroprotective in ischemic stroke. The quinoxaline 6,7-dichloro-2-methylsulfonyl-3-N-tert- butylaminoquinoxaline (DMB) is an agonist and allosteric modulator of the GLP-1R with the potential to increase the affinity of GLP-1 for its receptor. The aim of this study was to evaluate the neuroprotective effects of DMB on transient focal cerebral ischemia. In cultured cortical neurons, DMB activated the GLP-1R, leading to increased intracellular cAMP levels with an EC50 value about 100 fold that of exendin-4. Pretreatment of neurons with DMB protected against necrotic and apoptotic cell death was induced by oxygen-glucose deprivation (OGD). The neuroprotective effects of DMB were blocked by GLP-1R knockdown with shRNA but not by GLP-1R antagonism. In C57BL/6 mice, DMB was orally administered 30 min prior to middle cerebral artery occlusion (MCAO) surgery. DMB markedly reduced the cerebral infarct size and neurological deficits caused by MCAO and reperfusion. The neuroprotective effects were mediated by activation of the GLP-1R through the cAMP-PKA-CREB signaling pathway. DMB exhibited anti-apoptotic effects by modulating Bcl-2 family members. These results provide evidence that DMB, a small molecular GLP-1R agonist, attenuates transient focal cerebral ischemia injury and inhibits neuronal apoptosis induced by MCAO. Taken together, these data suggest that DMB is a potential neuroprotective agent against cerebral ischemia.

An Overview, Advantages and Therapeutic Potential of Nonpeptide Positive Allosteric Modulators of Glucagon‐Like Peptide‐1 Receptor

“…Compound 25 induces cAMP signaling by activating GLP‐1R and increases the glucose‐dependent secretion of insulin in islets from wild type, but not from GLP‐1R knockout, mice; thus confirming its GLP‐1R‐mediated action . Furthermore, compound 25 activates GLP‐1R‐dependent pathways and decreases transient focal cerebral ischemia and neuronal apoptosis in vitro and in vivo, which indicates its possible therapeutic indication as a neuroprotective agent …”

“…GLP‐1R might represent a potential target for the treatment of disorders of the nervous system, due to reported neuroprotective effects after GLP‐1R activation. Agonists of GLP‐1R exhibit antiapoptotic effects by altering the expression of proteins of the Bcl‐2 family, and reduce inflammatory response and oxidative stress in the nervous system . Additionally, agonists of GLP‐1R regulate the expression of inflammatory mediators in pancreatic islets, inhibit apoptosis, improve lipid metabolism, and histological indicators of inflammation in the liver, as well as suppress infiltration of immune cells and fibrotic signaling in the lung…”

“…[12] The development of DPP-4 inhibitors has been followed by the development of peptide agonists of GLP-1Rt hat are resistantt o DPP-4 inactivation, such as exenatide, liraglutide, lixisenatide, albiglutide, dulaglutide, and taspoglutide. These peptides, however,r equire parenteral administration due to inherent in-stabilityi nt he proteolytic milieu of the gastrointestinal tract, [8,9,13] and adherence to an injectable medication might be the limiting factor in life-long therapy.U nfortunately,t argeting the GLP-1Ro rthosteric binding site with direct small-molecule drugs would requiret heir interference with protein-protein interactions, whichs eldom leads to successful drug-discovery campaigns; [14] this opens aw indow for the development of orally available small-molecule GLP-1R allostericm odulators. [3] Allosteric modulation of GLP-1Re nables fine-tuning of native GLP-1 action that might improve current therapies of type 2 diabetes mellitus.…”

“…Agonists of GLP-1Re xhibit antiapoptotic effects by alteringt he expression of proteins of the Bcl-2 family,a nd reduce inflammatory response and oxidative stress in the nervous system. [13,17] Additionally,a gonists of GLP-1Rr egulate the expression of inflammatory mediators in pancreatic islets, inhibit apoptosis, improve lipid metabolism, and histological indicators of inflammation in the liver,a sw ell as suppress infiltrationo fi mmune cells and fibrotic signaling in the lung. [17] From at herapeutic perspective,l igands that act allosterically have severala dvantageso ver orthosteric ligands, including enhanced receptor subtype selectivity,t he ability to interactw ith the receptor simultaneously with the endogenous ligand,t he induction of novel receptor conformations, as well as potential for oral administration, and the same is true for GLP-1R PAMs.…”

“…[26] Furthermore, compound 25 activates GLP-1R-dependentp athways and decreases transientf ocal cerebral ischemia andn euronal apoptosis in vitro and in vivo, which indicates its possiblet herapeutic indication as an europrotective agent. [13] The structure-activity relationship of quinoxalines indicated 6,7-dichloroquinoxalines with as ulfone/alkyls ulfonyl group and as econdary alkyl amino group at the C2 and C3 positions, respectively (compounds 26 and 27), as the most effective PAMs. Chlorides ubstituents at positions C6 and C7 are essential and required for potent activity;6 ,7-dichloroquinoxaline is optimal.…”