Specific targeting of pancreatic β‐cells by simultaneous binding of GLP‐1 and α2‐adrenergic receptors with a multivalent ligand

Abstract

Diabetes Mellitus is characterized by a decline in β‐cell mass and function. The lack of specificity of β‐cell targeting agents poses a challenge to observe changes in β‐cell mass and thus monitor disease progression. We propose β‐cell specificity can be enhanced by using multivalent ligands that simultaneously bind to multiple unique surface receptors that, as a combination, identify a cell type of interest. We synthesized a ligand composed of Yohimbine (Yhb) (α2 adrenergic receptor (α2AR) antagonist) linked to Glucagon‐like Peptide 1(GLP‐1). Receptors to both ligands are expressed on βTC3 cells at a ratio of ~ 1.5:1 (GLP‐1R/α2AR). Microscopy of a fluorophore tagged ligand indicated that binding was rapid with removal of ligand from the cell surface seen within 2–3 min. From population based competition assays, the binding affinity for monovalent GLP‐1 was ~10 nM, whereas GLP‐1/Yhb exhibited 2 distinct binding sites. The high affinity binding (9 pM) is correlated to MVL crosslinking the complementary receptors causing a decrease in ligand off rate, resulting in a 1000X increase in apparent affinity. The low affinity binding (225 nM) is consistent with weak binding of the GLP‐1 moiety in the MVL to the spare GLP‐1 receptors in βTC3 cells. Our findings suggest that GLP‐1/Yhb acts as a specific targeting agent to β‐cells as it exhibits enhanced binding to and retention in β‐cells compared to other cells in the imaging field.Supported by: Juvenile Diabetes Research Foundation, and the Arizona Biomedical Research Commission