Recent progress in the development of β2 adrenergic receptor agonists: a patent review (2015-2020)

INTRODUCTION

The β₂ adrenergic receptor (β₂AR) is a member of G protein-coupled receptors (GPCRs) that mediate the majority of cellular responses to external stimuli. The agonists can cause smooth muscle relaxation; therefore, many β₂AR agonists have been developed especially for the treatment of pulmonary disorders such as asthma and chronic obstructive pulmonary disease (COPD). Many new natural and synthetic compounds have been discovered and developed as novel β₂AR agonists over the past 5 years.

AREAS COVERED

This review offers an update for the development of β₂AR agonists in the patents published from 2015 to 2020, including new natural and synthetic compounds for the treatment of asthma and COPD. In particular, the latest patents about compounds possessing both muscarinic receptor antagonist and β₂ adrenergic receptor agonist activity are reviewed.

EXPERT OPINION

β₂AR agonists have been developed extensively for the treatment of asthma and COPD. In the past 5 years, novel agonists from both natural sources and synthetic methods were intensively developed. Compounds possessing both muscarinic receptor antagonist and β₂AR agonist activity represent a new trend in this area because they are possibly able to act together in a synergistic fashion, therefore, relieve the symptoms of patients through two distinct mechanisms.

PDK1/Akt/PDE4D axis identified as a target for asthma remedy synergistic with β2 AR agonists by a natural agent arctigenin

BACKGROUND

Asthma is a heterogenetic disorder characterized by chronic inflammation with variable airflow obstruction and airway hyper-responsiveness. As the most potent and popular bronchodilators, β2 adrenergic receptor (β2 AR) agonists bind to the β2 ARs that are coupled via a stimulatory G protein to adenylyl cyclase, thereby improving cAMP accumulation and resulting in airway smooth muscle relaxation. We previously demonstrated arctigenin had a synergistic function with the β2 AR agonist, but the target for this remained elusive.

METHOD

Chemical proteomics capturing was used to enrich and uncover the target of arctigenin in human bronchial smooth muscle cells, and reverse docking and molecular dynamic stimulation were performed to evaluate the binding of arctigenin and its target. In vitro enzyme activities and protein levels were demonstrated with special kits and Western blotting. Finally, guinea pig tracheal muscle segregation and ex vivo function were analysed.

RESULTS

Arctigenin bound to PDK1 with an ideal binding free energy -25.45 kcal/mol and inhibited PDK1 kinase activity without changing its protein level. Additionally, arctigenin reduced PKB/Akt-induced phosphorylation of PDE4D, which was first identified in this study. Attenuation of PDE4D resulted in cAMP accumulation in human bronchial smooth muscle. The inhibition of PDK1 showed a synergistic function with β2 AR agonists and relaxed the constriction of segregated guinea pig tracheal muscle.

CONCLUSIONS

The PDK1/Akt/PDE4D axis serves as a novel asthma target, which may benefit airflow obstruction.