Menin-mll inhibitor 21 is a selective, oral and irreversible Menin inhibitor. Menin-MLL inhibitor 21 promotes selective proliferation of beta cells and improvement of beta cell function in human islet cultures in vitro. Menin-MLL inhibitor 21 enhances glycemic control in animal models of diabetes. Menin-MLL inhibitor 21 induced a dose-dependent increase in insulin secretion that was augmented by a GLP-1 receptor agonist (RA).