Combinatorial Targeting of the Glucagon-Like Peptide-1 And Sulfonylurea-1 Receptors Using a Complimentary Multivalent Glucagon-Like Peptide-1/Glibenclamide Ligand for the Improvement of β-Cell Targeting Agents and Diabetic Treatment

Abstract

A scourge of Type I and Type II diabetes impacts the health of hundreds of millions worldwide. The number and prevalence of diabetics are expected to rise dramatically in the next two decades. Diabetes is defined by chronic hyperglycemia which can result in a number of detrimental and costly metabolic, renal, cardiovascular and neurological disorders. Identification of at risk individuals and effective blood glucose management are critical to improving diabetic outcomes and preventing hyperglycemic complications. Diabetes prevention and treatment is limited by the understanding of islet function and mass in the diabetogenic and diabetic state. The islets of Langerhans are dispersed throughout the pancreas and comprise <2% of the pancreatic mass. The reclusive nature of islet cells presents unique challenges understanding disease development. No agent capable of exclusively targeting pancreatic β-cells within the islet has been discovered and the lack of targeting agent specificity impedes efforts to: quantify β-cell mass and develop novel therapeutics. We propose β-cell targeting can be improved by targeting unique combinations of receptors simultaneously with multivalent ligands. A synthetic multivalent agent composed of two β-cell specific diabetic therapeutics, glucagon-like peptide-1 (GLP-1) and glibenclamide (Glb), targeted against the GLP-1R and the sulfonylurea-1 receptor (SUR1) is a lead compound for the development of specific bi-functional islet cell targeting agents for use in the in vivo detection and treatment of β -cells. Herein, we describe the synthesis and initial characterization of a heterobivalent ligand composed of GLP-1 coupled to Glb. The heterobivalent ligand binds to an unaltered β-cell line with increased specificity relative to a human pancreatic exocrine cell line. Additionally, receptor cross-linking modifies β-cell signaling. Exposure of β-cells to the heterobivalent ligand results in antagonism of SUR1-Ca²⁺ signaling and equipotent agonism of GLP-1R-cAMP signaling, in comparison to the cognate monomeric ligands (Glb and GLP-1). Perturbations in intracellular signaling modifies β-cell insulin secretion resulting in decreased basal insulin secretion and with maintained yet reduced ability to potentiate β-cell glucose stimulated insulin secretion. GLP-1/Glb β-cell specificity and functional modulation suggests combinatorial receptor targeting is an effective strategy for the development of bi-functional cell-specific targeting agents, warranting further investigation and optimization.