The Isoleucine at Position 118 in Transmembrane 2 Is Responsible for the Selectivity of Xamoterol, Nebivolol, and ICI89406 for the Human β 1-Adrenoceptor

• Published in: Molecular pharmacology 2023-02, Vol.103 (2), p.89
• Main Authors: Lim, Victor Jun Yu, Proudman, Richard G W, Monteleone, Stefania, Kolb, Peter, Baker, Jillian G
• Format: Article
• Language: English
• Subjects: Adrenergic beta-Agonists; Adrenergic beta-Antagonists - metabolism; Animals; Betaxolol; Bisoprolol; CHO Cells; Cricetinae; Cricetulus; Humans; Isoleucine; Ligands; Nebivolol - pharmacology; Receptors, Adrenergic; Receptors, Adrenergic, beta-1 - chemistry; Receptors, Adrenergic, beta-2 - metabolism; Xamoterol
• ISSN: 1521-0111
• DOI: 10.1124/molpharm.122.000583

Known off-target interactions frequently cause predictable drug side-effects (e.g., 1-antagonists used for heart disease, risk 2-mediated bronchospasm). Computer-aided drug design would improve if the structural basis of existing drug selectivity was understood. A mutagenesis approach determined the ligand-amino acid interactions required for 1-selective affinity of xamoterol and nebivolol, followed by computer-based modeling to provide possible structural explanations. H-CGP12177 whole cell binding was conducted in Chinese hamster ovary cells stably expressing human 1, 2, and chimeric 1/ 2-adrenoceptors (ARs). Single point mutations were investigated in transiently transfected cells. Modeling studies involved docking ligands into three-dimensional receptor structures and performing molecular dynamics simulations, comparing interaction frequencies between and structures of 1 and 2-ARs. From these observations, an ICI89406 derivative was investigated that gave further insights into selectivity. Stable cell line studies determined that transmembrane 2 was crucial for the 1-selective affinity of xamoterol and nebivolol. Single point mutations determined that the 1-AR isoleucine (I118) rather than the 2 histidine (H93) explained selectivity. Studies of other 1-ligands found I118 was important for ICI89406 selective affinity but not that for betaxolol, bisoprolol, or esmolol. Modeling studies suggested that the interaction energies and solvation of 1-I118 and 2-H93 are factors determining selectivity of xamoterol and ICI89406. ICI89406 without its phenyl group loses its high 1-AR affinity, resulting in the same affinity as for the 2-AR. The human 1-AR residue I118 is crucial for the 1-selective affinity of xamoterol, nebivolol, and ICI89406 but not all 1-selective compounds. SIGNIFICANCE STATEMENT: Some ligands have selective binding affinity for the human β1 versus the β2-adrenoceptor; however, the molecular/structural reason for this is not known. The transmembrane 2 residue isoleucine I118 is responsible for the selective β1-binding of xamoterol, nebivolol, and ICI89406 but does not explain the selective β1-binding of betaxolol, bisoprolol, or esmolol. Understanding the structural basis of selectivity is important to improve computer-aided ligand design, and targeting I118 in β1-adrenoceptors is likely to increase β1-selectivity of drugs.