B29-06 β2 Adrenergic Receptor Allosteric Modulator Augments β-agonists-induced Pka Signaling and Inhibition of Airway Smooth Muscle Proliferation

Abstract Rationale Airway remodeling, characterized by airway smooth muscle (ASM) hyperplasia, is a major pathological feature of chronic asthma that contributes to fixed airflow limitation and disease severity. Current asthma therapies, including β2-adrenergic receptor (β2AR) agonists, are not effective in mitigating features of airway remodeling. The beneficial functional effects of the β-agonists in ASM cells are mediated via cyclic AMP (cAMP)-dependent protein kinase A (PKA) signaling. Therefore, promoting β2AR-mediated cAMP-PKA signaling is therapeutically advantageous. We recently identified a class of Gs-biased allosteric modulators (AMs) of β2AR that preferentially enhance β2AR-Gs-cAMP-PKA signaling in ASM cells. Here, we hypothesize that PAM37, a biased positive AM (PAM) of β2AR, enhances β2AR-PKA signaling in ASM cells, thereby promoting the anti-mitogenic effect of β-agonists. Methods Human ASM (HASM) cells were stimulated with different β-agonists, isoproterenol (ISO), formoterol (FORM), epinephrine (EPI), norepinephrine (NE), albuterol (ALB), salmeterol (SALM), terbutaline (TERB), and fenoterol (FENO) in the presence/absence of PAM37 for different time periods. We assessed cell proliferation and phosphorylation of PKA targets cAMP response element binding (CREB) and Vasodilator-Stimulated Phosphoprotein (VASP) using the CyQUANT NF assay and western blotting, respectively. cAMP Response Element activity was measured using a luciferase assay in cells stably expressing CRE-luc upon treatment with β-agonists ± PAM 37. Results β-agonist stimulation induced phosphorylation of VASP and CREB at 10 and 30 minutes, indicating PKA activation. Importantly, co-treatment with PAM37 potentiated VASP and CREB phosphorylation in response to ISO, FORM, TERB, EPI, NE, and ALB, but not FENO or SAL, treatment. Time kinetics analysis revealed that β-agonist-induced PKA activation was prolonged by PAM37. Consistent with these results, CRE-luciferase activity was elevated by the same subset of β-agonists and further increased by PAM37 co-treatment, while FENO and SAL responses remained unchanged. Treatment with PAM37 in combination with β-agonists significantly inhibited ASM proliferation induced by PDGF or FBS. These results indicate that PAM37 amplifies β-agonist-mediated β2AR-PKA signaling and promotes suppression of ASM proliferation. Conclusion PAM 37 enhances the magnitude and duration of β-agonist-induced PKA and CRE-dependent signaling, thereby potentiating the anti-mitogenic effect of β-agonists. The lack of effect of PAM37 on FENO or SAL suggests differential conformation changes induced by different β-agonists such that accessibility for the AMs to their binding site on β2AR is different in the presence of different β-agonists. These findings highlight the potential use of PAM37 in mitigating the features of airway remodeling, in addition to enhancing the bronchodilatory effect of β-agonists in asthma. This abstract is funded by: NIH NHLBI R01HL173113, R01HL146645, P01HL180318