Respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD) are commonly treated with β₂-adrenergic receptor agonists that activate intracellular signaling pathways to induce airway relaxation. However, current therapies are limited by progressive receptor desensitization, or tachyphylaxis, largely attributed to β-arrestin recruitment. This desensitization reduces therapeutic efficacy over time and complicates long-term disease management, resulting in suboptimal outcomes for patients who rely on bronchodilators for daily symptom control.
Our researchers have identified a novel agonist, denoted Compound A, which is 5-hydroxy-8-(1-hydroxy-2-(phenethylamino)ethyl)-2H-benzo[b][1,4] oxazin-3(4H)-one, shown in Fig1A, through in silico docking of a multimillion-member library and subsequent optimization of leads by synthesis of compounds with R group substitutions. Screening utilized CHO cells measuring cAMP and b-arrestin2 via transfected biosensors and human airway smooth muscle (HASM) cells measuring relaxation via magnetic twisting cytometry. Compound A activates the human β₂-adrenergic receptor with sub-nanomolar potency (cAMP, EC₅₀ = 0.25 nM) and is a full agonist when compared to ISO (Fig 1B). However, unlike conventional balanced agents such as ISO, Compound A selectively activates Gαs-mediated cAMP signaling with minimal β-arrestin2 recruitment (Fig 1B). In HASM cells, Compound A elicits sustained airway relaxation without evidence of tachyphylaxis (loss of responsiveness with continuous exposure to agonist), offering a promising next-generation bronchodilator with extended therapeutic efficacy over existing β₂-agonists.