Specific modulation of β‐cell signaling using a heterobivalent GLP1/glibenclamide ligand

Changes in pancreatic β‐cell signaling and function underlie development of Diabetes Mellitus. We synthesized a ligand composed of two different receptor binding moieties Glucagon‐like Peptide 1 (GLP1) and Glibenclamide (Gbc, Sulfonylurea ligand, SUR1) with the goal of developing a β‐cell specific imaging agent. The receptors for both ligands are expressed in the βTC3 cell line while INS‐1 cells express only SUR1. The divalent GLP1/Gbc binds βTC3 cells with a K m of ~10 nM, but does not bind INS‐1 cells below 10 nM (Km ≥ 300 nM). The high specificity of binding to cells that express only the complimentary receptor pair is likely due to receptor cross‐linking. GLP1 elevates cAMP, while Gbc increases Ca 2+ , in β‐cells. The GLP1/Gbc ligand elicits a half maximal Ca 2+ response at ~10 nM reflecting its K m , however the magnitude of the Ca 2+ response was at least 10X less than for monomeric Gbc. Similarly, cAMP elevation was attenuated when compared to monomeric GLP1. The decreased response is likely a property of GLP1/Gbc binding and efficacy, since both the sensitivity and magnitude of the Ca 2+ response was depressed in cells expressing only the SUR1. Thus, despite the higher affinity and specificity of the GLP1/Gbc for binding to β‐cells, the activity of the ligand is depressed, and may act as a partial antagonist. Our findings indicate that multivalent ligands may provide cell type specific agents with modified signaling behavior. Supported by: Juvenile Diabetes Research Foundation, Arizona Biomedical Research Commission, and the ARCS Foundation