A novel small-molecule secretagogue, MDC134, amplifies glucose-dependent insulin secretion in pancreatic β-cells

Insulin secretion from pancreatic β-cells is controlled by multiple mechanisms, including metabolic, electrophysiological, and second-messenger pathways. To identify insulinotropic small molecules, we performed in silico similarity screening using zatebradine, an HCN-channel ligand, as a structural query and functionally evaluated 26 hit compounds. Compound 2 showed the strongest insulinotropic activity and was used to synthesize the novel compound MDC134. MDC134 enhanced insulin secretion in MIN6-K8 cells and isolated mouse islets under stimulatory glucose conditions. MDC134 enhanced insulin secretion in isolated mouse islets and showed a tendency to increase insulin secretion in isolated non-diabetic human islets. Under high-glucose conditions, MDC134 increased intracellular Ca²⁺ levels, and nifedipine abolished its insulinotropic effect, indicating the involvement of voltage-dependent L-type Ca²⁺ channel-mediated Ca²⁺ influx. MDC134 also increased cellular cAMP content, although less potently than GLP-1. MDC134 treatment did not clearly affect glucose tolerance in C57BL/6J or ob/ob mice but significantly suppressed glucose elevation in β-cell-specific Kcnj11 knockout mice. These findings identify MDC134 as a novel glucose-dependent insulinotropic small molecule that enhances β-cell insulin secretion through Ca²⁺ influx and cAMP-associated amplification, and suggest that it may be useful for therapeutic strategies for diabetes characterized by impaired insulin secretion.