How β3 -adrenoceptor-selective is mirabegron?

Project-Based Public-Private Collaborations

Project-based collaborations between a single academic group and a single pharmaceutical company arguably are the most frequent form of public-private partnership in preclinical research and development of new drugs. This chapter discusses the benefits of such collaborations for both sides and potential challenges that can arise before and during the conduct of a project. This is largely based on a survey of expectations and experience by 134 academic investigators with a history of engagement in a project-based collaboration with a pharmaceutical company as well as unstructured experience directly, and learned through discussions with colleagues, from the authors. Obviously, a key benefit for both sides is achieving goals that neither could easily achieve by itself. Scientific discovery, and publications, may be a shared benefit, while for academics, funding and access to compounds, and for industry, access to assay technology and reputational factors may be important. Major hurdles can be freedom to publish and assignment of intellectual property rights. On pragmatic grounds, reaching a contract can be cumbersome, which is largely attributable to the legal expectations and needs of both parties. However, overall satisfaction with project-based collaborations appears very high for academic investigators.

α1-adrenoceptor activity of β-adrenoceptor ligands - An expected drug property with limited clinical relevance

Many β-adrenoceptor agonists and antagonists including several clinically used drugs have been reported to also exhibit binding to α₁-adrenoceptors. Such promiscuity within the adrenoceptor family appears to occur more often than off-target effects of drugs in general. It should not be considered surprising based on the amino acid homology among the nine adrenoceptor subtypes including the counter-ions for binding the endogenous catecholamines. When β-adrenoceptor ligands also bind to α₁-adrenoceptors, they almost always act as antagonists, regardless of being agonists or antagonists at the β-adrenoceptor. The α₁-adrenoceptor affinity of β-adrenoceptor ligands in most cases is at least one, and often more log units lower than at their cognate receptor. Consistent evidence from multiple investigators indicates that β-adrenoceptor ligands relatively have the highest affinity for α_1A- and lowest for α_1B-adrenoceptors. While promiscuity among adrenoceptor subtypes causes misleading interpretation of experimental in vitro data, it is proposed based on the law of mass action that α₁-adrenoceptor binding of β-adrenoceptor ligands rarely contributes to the clinical profile of such drugs, particularly if they are agonists at the β-adrenoceptor.

Chronic mirabegron treatment increases human brown fat, HDL cholesterol, and insulin sensitivity

BACKGROUNDMirabegron is a β3-adrenergic receptor (β3-AR) agonist approved only for the treatment of overactive bladder. Encouraging preclinical results suggest that β3-AR agonists could also improve obesity-related metabolic disease by increasing brown adipose tissue (BAT) thermogenesis, white adipose tissue (WAT) lipolysis, and insulin sensitivity.METHODSWe treated 14 healthy women of diverse ethnicities (27.5 ± 1.1 years of age, BMI of 25.4 ± 1.2 kg/m2) with 100 mg mirabegron (Myrbetriq extended-release tablet, Astellas Pharma) for 4 weeks in an open-label study. The primary endpoint was the change in BAT metabolic activity as measured by [18F]-2-fluoro-d-2-deoxy-d-glucose (18F-FDG) PET/CT. Secondary endpoints included resting energy expenditure (REE), plasma metabolites, and glucose and insulin metabolism as assessed by a frequently sampled intravenous glucose tolerance test.RESULTSChronic mirabegron therapy increased BAT metabolic activity. Whole-body REE was higher, without changes in body weight or composition. Additionally, there were elevations in plasma levels of the beneficial lipoprotein biomarkers HDL and ApoA1, as well as total bile acids. Adiponectin, a WAT-derived hormone that has antidiabetic and antiinflammatory capabilities, increased with acute treatment and was 35% higher upon completion of the study. Finally, an intravenous glucose tolerance test revealed higher insulin sensitivity, glucose effectiveness, and insulin secretion.CONCLUSIONThese findings indicate that human BAT metabolic activity can be increased after chronic pharmacological stimulation with mirabegron and support the investigation of β3-AR agonists as a treatment for metabolic disease.TRIAL REGISTRATIONClinicaltrials.gov NCT03049462.FUNDINGThis work was supported by grants from the Intramural Research Program of the NIDDK, NIH (DK075112, DK075116, DK071013, and DK071014).

β3 -Adrenoceptors in the normal and diseased urinary bladder-What are the open questions?

β₃ -Adrenoceptor agonists are used in the treatment of overactive bladder syndrome. Although the relaxant response to adrenergic stimulation in human detrusor smooth muscle cells is mediated mainly via β₃ -adrenoceptors, the plasma concentrations of the therapeutic dose of mirabegron, the only clinically approved β₃ -adrenoceptor agonist, are considerably lower than the EC₅₀ for causing direct relaxation of human detrusor, suggesting a mechanism of action other than direct relaxation of detrusor smooth muscle. However, the site and mechanism of action of β₃ -adrenoceptor agonists in the bladder have not been firmly established. Postulated mechanisms include prejunctional suppression of ACh release from the parasympathetic nerves during the storage phase and inhibition of micro-contractions through β₃ -adrenoceptors on detrusor smooth muscle cells or suburothelial interstitial cells. Implications of possible desensitization of β₃ -adrenoceptors in the bladder upon prolonged agonist exposure and possible causes of rarely observed cardiovascular effects of mirabegron are also discussed. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Acute metabolic and cardiovascular effects of mirabegron in healthy individuals

AIMS

To quantify acute energy expenditure, supraclavicular skin temperature and cardiovascular responses to four doses of the β3-adrenoceptor agonist, mirabegron.

MATERIALS AND METHODS

A total of 17 individuals (11 men, six women) participated in this ascending-dose study, receiving single 50-, 100-, 150- and 200-mg doses of mirabegron on four separate days with 3 to 14 days wash-out between each dose. All variables were measured each visit from baseline to 180 minutes post mirabegron treatment. To determine brown adipose tissue (BAT) thermogenic efficacy at each dose, energy expenditure and supraclavicular skin temperature were compared from baseline to 180 minutes post mirabegron treatment. To examine safety, changes in cardiovascular variables at 100, 150 and 200 mg were compared with the standard clinical dose of 50 mg.

RESULTS

Energy expenditure significantly increased after the 100- (35.6 ± 5.4 kJ/h) and 200-mg (35.6 ± 13.1 kJ/h) doses (P ≤ 0.05), and trended towards an increase after 150 mg (24.1 ± 13.6 kJ/h). Supraclavicular skin temperature increased after 50- (0.22 ± 0.1°C), 100- (0.30 ± 0.1°C) and 150-mg mirabegron doses (0.29 ± 0.1°C; P ≤ 0.05). The change in systolic blood pressure was greater after 150- (7.1 ± 1.3 mm Hg) and 200-mg doses (9.3 ± 1.9 mm Hg) than after the 50-mg dose (2.2 ± 1.3 mm Hg; P ≤ 0.05). The change in heart rate was greater after 200 mg (9.0 ± 2.2 bpm) compared with 50 mg (2.9 ± 1.4 bpm; P ≤ 0.05).

CONCLUSIONS

A 100-mg dose of mirabegron increases energy expenditure and supraclavicular skin temperature in a β3-adrenoceptor-specific manner, without the off-target elevations in blood pressure or heart rate observed at higher doses.

Beta-3 Adrenoceptor Signaling Pathways in Urothelial and Smooth Muscle Cells in the Presence of Succinate

Succinate, an intermediate metabolite of the Krebs cycle, can alter the metabolomics response to certain drugs and controls an array of molecular responses in the urothelium through activation of its receptor, G-protein coupled receptor 91 (GPR91). Mirabegron, a β3-adrenergic receptor (β3-AR) agonist used to treat overactive bladder syndrome (OAB), increases intracellular cAMP in the detrusor smooth muscle cells (SMC), leading to relaxation. We have previously shown that succinate inhibits forskolin-stimulated cAMP production in urothelium. To determine whether succinate interferes with mirabegron-mediated bladder relaxation, we examined their individual and synergistic effect in urothelial-cell and SMC signaling. We first confirmed β3-AR involvement in the mirabegron response by quantifying receptor abundance by immunoblotting in cultured urothelial cells and SMC and cellular localization by immunohistochemistry in rat bladder tissue. Mirabegron increased cAMP levels in SMC but not in urothelial cells, an increase that was inhibited by succinate, suggesting that it impairs cAMP-mediated bladder relaxation by mirabegron. Succinate and mirabegron increased inducible nitric oxide synthesis and nitric oxide secretion only in urothelial cells, suggesting that its release can indirectly induces SMC relaxation. Succinate exposure decreased the expression of β3-AR protein in whole bladder in vivo and in SMC in vitro, indicating that this metabolite may lead to impaired pharmacodynamics of the bladder. Together, our results demonstrate that increased levels of succinate in settings of metabolic stress (e.g., the metabolic syndrome) may lead to impaired mirabegron and β3-AR interaction, inhibition of cAMP production, and ultimately requiring mirabegron dose adjustment for its treatment of OAB related to these conditions.

Mirabegron: potential off target effects and uses beyond the bladder

The β₃ -adrenoceptor was initially an attractive target for several pharmaceutical companies due to its high expression in rodent adipose tissue, where its activation resulted in decreased adiposity and improved metabolic outputs (such as glucose handling) in animal models of obesity and Type 2 diabetes. However, several drugs acting at the β₃ -adrenoceptor failed in clinical trials. This was thought to be due to their lack of efficacy at the human receptor. Recently, mirabegron, a β₃ -adrenoceptor agonist with human efficacy, was approved in North America, Europe, Japan and Australia for the treatment of overactive bladder syndrome. There are indications that mirabegron may act at other receptors/targets, but whether they have any clinical relevance is relatively unknown. Besides overactive bladder syndrome, mirabegron may have other uses such as in the treatment of heart failure or metabolic disease. This review gives an overview of the off-target effects of mirabegron and its potential use in the treatment of other diseases.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

On the Site and Mechanism of Action of β3-Adrenoceptor Agonists in the Bladder

The clinical success of mirabegron as the first β₃-adrenoceptor (AR) agonist for treatment of the overactive bladder (OAB) syndrome, has resulted in substantial interest in its site and mechanism of action. Even if the adrenergic innervation of the bladder and urethra has been well studied, the location(s) of β₃-ARs in different structures within the bladder wall and urethra, and the mode(s) of action of β₃-AR stimulation have still not been established. The recent demonstration of β₃-ARs on cholinergic nerve terminals with no immunoreactivity in urothelium or detrusor smooth muscle, is not in agreement with previous morphological studies, and functional data strongly suggest that β₃-ARs can be found these structures. However, recent studies suggest that the β₃-ARs on detrusor smooth muscle may not be the functionally most relevant. The assumption that β₃-AR activation during bladder filling inhibits acetylcholine release from parasympathetic neurons by a prejunctional mechanism and that this decreases bladder micromotions that generate afferent activity, is an attractive hypothesis. It does not exclude that other mechanisms may be contributing, and supports combined approaches to reduce afferent activity for treatment of the OAB syndrome.