PMC

The chemical structures of two pyrimidine-based GLP-1 receptor agonists, compound A (A) and compound B (B) are depicted.

Compound B increases glucose-dependent insulin secretion from SD rat islets. A: Insulin concentrations from static cultures of SD rat islets incubated in media containing low glucose (2.8 mmol/l) and either GLP-1 (100 nmol/l), compound B (3 μmol/l), or the sulfonylurea glibenclamide (5 μmol/l). B: Insulin concentrations from static cultures of SD rat islets incubated in media containing high glucose (11.2 mmol/l) and either GLP-1 (100 nmol/l) or various concentrations of compound B (0.3–10 μmol/l). All islet treatments were performed for 90 min. Results are expressed as mean ± SEM, *P < 0.05.

Compound B increases plasma insulin levels in the SD rat IVGTT model. Time course of plasma (A) glucose and (B) insulin concentrations in fasted, anesthetized animals treated with either vehicle (■), GLP-1 (×) (10 μg/kg), or compound B (○) (dosed at 10 mg/kg) immediately before intravenous administration of a glucose bolus (0.5 g/kg). Results are expressed as mean ± SEM. C: AUC of the insulin excursion curves for vehicle versus the GLP-1 or compound B treatment groups, *P < 0.05.

GLP-1 and compound B increase GLP-1 receptor signaling in an additive manner. A: Combination treatment of the GLP-1 peptide and compound B increases the intracellular concentration of cAMP in HEK293 cells expressing the human GLP-1 receptor. Treatment times for the cAMP assays were 20 min. B: Insulin concentrations from static cultures of SD rat islets incubated in media containing high glucose (11.2 mmol/l) and compound B plus increasing concentrations of GLP-1. Islet treatments were performed for 90 min. Results are expressed as mean ± SEM, *P < 0.05.

Compound B increases plasma insulin levels in the SD rat hyperglycemic clamp model. A: Intravenous dosing with vehicle (■) or 10 mg/kg compound B (○) occurred immediately before intravenous infusion of glucose. Glucose levels measured from venous blood every 5 min are shown. Results are expressed as mean ± SEM. B: Blood glucose concentrations of ∼250 mg/dl were maintained throughout the experiment by varying the glucose infusion rates. C: Time course of plasma insulin concentrations in fasted animals treated with either vehicle (■) or compound B (○). Results are expressed as mean ± SEM. D: AUC_{20–60 min} of the insulin secretion for vehicle (filled bar) versus compound B-treated (open bar) animals, *P < 0.05.

Compound B enhances insulin secretion in normal and diabetic human islets. A: Insulin concentrations from static cultures of normal human islets incubated in media containing high glucose (11.2 mmol/l) and either GLP-1 (100 nmol/l) or various concentrations of compound B (1–10 μmol/l). The treatments were performed for 90 min, and results are expressed as mean ± SEM, *P < 0.05. In perifusion experiments, insulin concentrations from reaction chambers containing 20 human islets from (B) normal or (C) diabetic individuals perifused with media containing either vehicle (■) or compound B (○) (3 or 10 μmol/l) in low glucose (3.3 mmol/l) for 40 min followed by high glucose (16.7 mmol/l) for an additional 35 min. AUC of the insulin excursion for vehicle versus compound B-treated (B) normal and (C) diabetic human islets, *P < 0.05.

Low molecular weight GLP-1 receptor agonists activate GLP-1 receptor signaling. A: Compound A and compound B induced GLP-1 receptor-mediated signaling in HEK293 cells coexpressing the human GLP-1 receptor and a 3x-cAMP response element-luciferase reporter, but were not active in cells lacking the GLP-1 receptor. In the human GLP-1 receptor HEK293 cells, the EC₅₀ values for compounds A and B were 1.6 μmol/l and 0.66 μmol/l, respectively; data are presented as percentages of stimulation of a maximum concentration of human GLP-1. B: The competitive GLP-1 receptor peptide antagonist exendin (9-39) blunted GLP-1 peptide activity but did not reduce compound B-induced signaling. C: Compound B was active in HEK293 cells expressing a modified form of the GLP-1 receptor lacking the NH₂-terminal ECD (Δ–ECD-GLP-1 receptor); the native GLP-1 peptide had no effect in cells expressing the Δ–ECD-GLP-1 receptor. D: Compound B was not active in HEK293 cells expressing the glucagon-like peptide-2 receptor (GLP-2R), glucose-dependent insulinotropic polypeptide receptor (GIP-R), glucagon receptor (GCG-R), or parathyroid hormone receptor (PTH-R).