A novel β2-AR agonist, Higenamine, induces β-arrestin-biased signaling

Structural insight into the dual-antagonistic mechanism of AB928 on adenosine A2 receptors

The adenosine subfamily G protein-coupled receptors A2AR and A2BR have been identified as promising cancer immunotherapy candidates. One of the A2AR/A2BR dual antagonists, AB928, has progressed to a phase II clinical trial to treat rectal cancer. However, the precise mechanism underlying its dual-antagonistic properties remains elusive. Herein, we report crystal structures of the A2AR complexed with AB928 and a selective A2AR antagonist 2-118. The structures revealed a common binding mode on A2AR, wherein the ligands established extensive interactions with residues from the orthosteric and secondary pockets. In contrast, the cAMP assay and A2AR and A2BR molecular dynamics simulations indicated that the ligands adopted distinct binding modes on A2BR. Detailed analysis of their chemical structures suggested that AB928 readily adapted to the A2BR pocket, while 2-118 did not due to intrinsic differences. This disparity potentially accounted for the difference in inhibitory efficacy between A2BR and A2AR. This study serves as a valuable structural template for the future development of selective or dual inhibitors targeting A2AR/A2BR for cancer therapy.

Higenamine inhibits acute and chronic inflammatory pain through modulation of TRPV4 channels

Pain is the cardinal symptom of many debilitating diseases and results in heavy health and economic burdens worldwide. Asarum (Asarum sieboldii Miq.) is a commonly used analgesic in Chinese medicine. However, the analgesic components and mechanisms of asarum in acute and chronic pain mice model remain unknown. In this study, we first generated asarum water extract and confirmed strong analgesic properties in mice in both the acute thermal and mechanical pain models, as well as in the complete Freund's adjuvant (CFA) induced chronic inflammatory pain model. Second, we identified higenamine as a major component of asarum and found that higenamine significantly inhibited thermal and mechanical induced acute pain and CFA induced chronic inflammatory pain. Then, using Trpv4-/- mice, we found that TRPV4 is necessary for CFA induced thermal and mechanical allodynia, and demonstrated that higenamine analgesia in the CFA model is partly through TRPV4 channel inhibition. Finally, we found that GSK1016790A, a TRPV4 agonist, induced calcium response was significantly inhibited by higenamine in both cultured DRG neurons and TRPV4 transfected HEK293 cells. Consistent with calcium imaging results, higenamine pretreatment also dose-dependently inhibited GSK1016790A induced acute pain. Taken together, our behavior and calcium imaging results demonstrate that the asarum component higenamine inhibits acute and chronic inflammatory pain by modulation of TRPV4 channels.

β2 -Adrenoceptor agonist profiling reveals biased signalling phenotypes for the β2 -adrenoceptor with possible implications for the treatment of asthma

BACKGROUND AND PURPOSE

β-Adrenoceptor agonists relieve airflow obstruction by activating β2 -adrenoceptors, which are G protein-coupled receptors (GPCRs) expressed on human airway smooth muscle (HASM) cells. The currently available β-adrenoceptor agonists are balanced agonists, however, and signal through both the stimulatory G protein (Gs )- and β-arrestin-mediated pathways. While Gs signalling is beneficial and promotes HASM relaxation, β-arrestin activation is associated with reduced Gs efficacy. In this context, biased ligands that selectively promote β2 -adrenoceptor coupling to Gs signalling represent a promising strategy to treat asthma. Here, we examined several β-adrenoceptor agonists to identify Gs -biased ligands devoid of β-arrestin-mediated effects.

EXPERIMENTAL APPROACH

Gs -biased ligands for the β2 -adrenoceptor were identified by high-throughput screening and then evaluated for Gs interaction, Gi interaction, cAMP production, β-arrestin interaction, GPCR kinase (GRK) phosphorylation of the receptor, receptor trafficking, ERK activation, and functional desensitization of the β2 -adrenoceptor.

KEY RESULTS

We identified ractopamine, dobutamine, and higenamine as Gs -biased agonists that activate the Gs /cAMP pathway upon β2 -adrenoceptor stimulation while showing minimal Gi or β-arrestin interaction. Furthermore, these compounds did not induce any receptor trafficking and had reduced GRK5-mediated phosphorylation of the β2 -adrenoceptor. Finally, we observed minimal physiological desensitization of the β2 -adrenoceptor in primary HASM cells upon treatment with biased agonists.

CONCLUSION AND IMPLICATIONS

Our work demonstrates that Gs -biased signalling through the β2 -adrenoceptor may prove to be an effective strategy to promote HASM relaxation in the treatment of asthma. Such biased compounds may also be useful in identifying the molecular mechanisms that determine biased signalling and in design of safer drugs.

Pharmacological effects of higenamine based on signalling pathways and mechanism of action

Higenamine (HG) is a chemical compound found in various plants, such as aconite. Recent pharmacological studies have demonstrated its effectiveness in the management of many diseases. Several mechanisms of action of HG have been proposed; however, they have not yet been classified. This review summarises the signalling pathways and pharmacological targets of HG, focusing on its potential as a naturally extracted drug. Articles related to the pharmacological effects, signalling pathways and pharmacological targets of HG were selected by searching the keyword "Higenamine" in the PubMed, Web of Science and Google Scholar databases without limiting the search by publication years. HG possesses anti-oxidant, anti-apoptotic, anti-inflammatory, electrophysiology regulatory, anti-fibrotic and lipid-lowering activities. It is a structural analogue of catecholamines and possesses characteristics similar to those of adrenergic receptor ligands. It can modulate multiple targets, including anti-inflammation- and anti-apoptosis-related targets and some transcription factors, which directly or indirectly influence the disease course. Other naturally occurring compounds, such as cucurbitacin B (Cu B) and 6-gingerol (6-GR), can be combined with HG to enhance its anti-apoptotic activity. Although significant research progress has been made, follow-up pharmacological studies are required to determine the exact mechanism of action, new signalling pathways and targets of HG and the effects of using it in combination with other drugs.