Tracheal relaxing effects and beta 2-selectivity of TA-2005, a newly developed bronchodilating agent, in isolated guinea pig tissues

Asthma and COPD: A Focus on β-Agonists - Past, Present and Future

Asthma has been recognised as a respiratory disorder for millennia and the focus of targeted drug development for the last 120 years. Asthma is one of the most common chronic non-communicable diseases worldwide. Chronic obstructive pulmonary disease (COPD), a leading cause of morbidity and mortality worldwide, is caused by exposure to tobacco smoke and other noxious particles and exerts a substantial economic and social burden. This chapter reviews the development of the treatments of asthma and COPD particularly focussing on the β-agonists, from the isolation of adrenaline, through the development of generations of short- and long-acting β-agonists. It reviews asthma death epidemics, considers the intrinsic efficacy of clinical compounds, and charts the improvement in selectivity and duration of action that has led to our current medications. Important β2-agonist compounds no longer used are considered, including some with additional properties, and how the different pharmacological properties of current β2-agonists underpin their different places in treatment guidelines. Finally, it concludes with a look forward to future developments that could improve the β-agonists still further, including extending their availability to areas of the world with less readily accessible healthcare.

Misuse, consequences and phototoxic skin-related effects of Rutaceae: a comprehensive literature review

Ruta is a common plant growing in Italy and in the Mediterranean area. It has been used in popular tradition with different aims, ranging from therapeutic to esoteric purposes. However, the plant is still used as a common remedy in some of present-day rural and urban communities and it can be found in gardens all over Europe. Ruta's photosensitizing effect has been described in the literature and seems to be mediated by furanocoumarins. We collected data from the 18 case-reports for a total of 32 patients that we included in our analysis, assessing demographic variables, clinical findings, diagnosis, time of onset of lesions, time of resolution and therapy. The main aim of this work was to outline the clinical presentation, therapeutic management and demography of phytophototoxic reactions from contact with Ruta in order to suggest the correct diagnostic approach and disease recognition, as well as its possible prevention.

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.

Ultra Long-Acting β-Agonists in Chronic Obstructive Pulmonary Disease

INTRODUCTION

Inhaled β-agonists have been foundational medications for maintenance COPD management for decades. Through activation of cyclic adenosine monophosphate pathways, these agents relax airway smooth muscle and improve expiratory airflow by relieving bronchospasm and alleviating air trapping and dynamic hyperinflation improving breathlessness, exertional capabilities, and quality of life. β-agonist drug development has discovered drugs with increasing longer durations of action: short acting (SABA) (4-6 h), long acting (LABA) (6-12 h), and ultra-long acting (ULABA) (24 h). Three ULABAs, indacaterol, olodaterol, and vilanterol, are approved for clinical treatment of COPD.

PURPOSE

This article reviews both clinically approved ULABAs and ULABAs in development.

CONCLUSION

Indacaterol and olodaterol were originally approved for clinical use as monotherapies for COPD. Vilanterol is the first ULABA to be approved only in combination with other respiratory medications. Although there are many other ULABA's in various stages of development, most clinical testing of these novel agents is suspended or proceeding slowly. The three approved ULABAs are being combined with antimuscarinic agents and corticosteroids as dual and triple agent treatments that are being tested for clinical use and efficacy. Increasingly, these clinical trials are using specific COPD clinical characteristics to define study populations and to begin to develop therapies that are trait-specific.

Design, synthesis and biological evaluation of 5-(2-amino-1-hydroxyethyl)-8-hydroxyquinolin-2(1H)-one derivatives as potent β2-adrenoceptor agonists

A series of novel β₂-adrenoceptor agonists with a 5-(2-amino-1-hydroxyethyl)-8-hydroxyquinolin-2(1H)-one moiety was designed, synthesized and evaluated for biological activity in human embryonic kidney 293 cells and isolated guinea pig trachea. Compounds 9g and (R)-18c exhibited the most excellent β₂-adrenoceptor agonistic effects and high β₂/β₁-selectivity with EC₅₀ values of 36 pM for 9g and 21 pM for (R)-18c. They produced potent airway smooth muscle relaxant effects with fast onset of action and long duration of action in an in vitro guinea pig trachea model of bronchodilation. These results support further development of the two compounds into drug candidates.

Sports doping: emerging designer and therapeutic β2-agonists

Beta2-adrenergic agonists, or β2-agonists, are considered essential bronchodilator drugs in the treatment of bronchial asthma, both as symptom-relievers and, in combination with inhaled corticosteroids, as disease-controllers. The use of β2-agonists is prohibited in sports by the World Anti-Doping Agency (WADA) due to claimed anabolic effects, and also, is prohibited as growth promoters in cattle fattening in the European Union. This paper reviews the last seven-year (2006-2012) literature concerning the development of novel β2-agonists molecules either by modifying the molecule of known β2-agonists or by introducing moieties producing indole-, adamantyl- or phenyl urea derivatives. New emerging β2-agonists molecules for future therapeutic use are also presented, intending to emphasize their potential use for doping purposes or as growth promoters in the near future.

Pharmacology and therapeutics of bronchodilators

Bronchodilators are central in the treatment of of airways disorders. They are the mainstay of the current management of chronic obstructive pulmonary disease (COPD) and are critical in the symptomatic management of asthma, although controversies around the use of these drugs remain. Bronchodilators work through their direct relaxation effect on airway smooth muscle cells. at present, three major classes of bronchodilators, β(2)-adrenoceptor (AR) agonists, muscarinic receptor antagonists, and xanthines are available and can be used individually or in combination. The use of the inhaled route is currently preferred to minimize systemic effects. Fast- and short-acting agents are best used for rescue of symptoms, whereas long-acting agents are best used for maintenance therapy. It has proven difficult to discover novel classes of bronchodilator drugs, although potential new targets are emerging. Consequently, the logical approach has been to improve the existing bronchodilators, although several novel broncholytic classes are under development. An important step in simplifying asthma and COPD management and improving adherence with prescribed therapy is to reduce the dose frequency to the minimum necessary to maintain disease control. Therefore, the incorporation of once-daily dose administration is an important strategy to improve adherence. Several once-daily β(2)-AR agonists or ultra-long-acting β(2)-AR-agonists (LABAs), such as indacaterol, olodaterol, and vilanterol, are already in the market or under development for the treatment of COPD and asthma, but current recommendations suggest the use of LABAs only in combination with an inhaled corticosteroid. In addition, some new potentially long-acting antimuscarinic agents, such as glycopyrronium bromide (NVA-237), aclidinium bromide, and umeclidinium bromide (GSK573719), are under development, as well as combinations of several classes of long-acting bronchodilator drugs, in an attempt to simplify treatment regimens as much as possible. This review will describe the pharmacology and therapeutics of old, new, and emerging classes of bronchodilator.

Third-generation long-acting β₂-adrenoceptor agonists: medicinal chemistry strategies employed in the identification of once-daily inhaled β₂-adrenoceptor agonists

Inhaled long-acting β(2)-adrenoceptor agonists (LABAs) are highly effective bronchodilators in the treatment of asthma and chronic obstructive pulmonary disease. There is significant interest in the development of third-generation compounds that improve upon the marketed twice-daily LABAs salmeterol and formoterol. A principal advantage sought from the next generation is duration of action that supports once-daily dosing, although improved efficacy, faster onset, and increased therapeutic index are also frequently cited as objectives. Recent publications detailing medicinal chemistry programs directed at the discovery of third-generation LABAs illustrate a wide variety of strategies that have been successfully employed towards these goals. Some recent scientific advances in the understanding of inhaled bronchodilators are discussed and the reported medicinal chemistry strategies are reviewed in the context of these advances.

Therapeutic potential for novel ultra long-acting β2-agonists in the management of COPD: biological and pharmacological aspects

Chronic obstructive pulmonary disease (COPD) is characterised by progressive airflow limitation. In moderate-to-severe COPD, long-acting bronchodilators are the basis of therapy. Inhaled long-acting β(2)-agonists (LABAs) are used for the treatment of COPD. LABAs have been in use since the 1990s enabling persistent bronchodilation for 12 hours; however, sustained bronchodilation is desirable. Compared with twice-daily LABAs, new LABAs with ultra-long duration (ultra-LABAs) could provide improvements in efficacy and compliance with fast onset of action, 24-hour bronchodilation and a good safety profile. Several novel ultra-LABAs showing once-daily delivery profiles are in development. In this article, we discuss these novel agents' properties and clinical trials of their efficacy and safety, including the only licensed ultra-LABA, indacaterol.

β(2) -adrenoceptor agonists: current and future direction

Despite the passionate debate over the use of β(2) -adrenoceptor agonists in the treatment of airway disorders, these agents are still central in the symptomatic management of asthma and COPD. A variety of β(2) -adrenoceptor agonists with long half-lives, also called ultra long-acting β(2) -adrenoceptor agonists (ultra-LABAs; indacaterol, olodaterol, vilanterol, carmoterol, LAS100977 and PF-610355) are currently under development with the hopes of achieving once-daily dosing. It is likely that the once-daily dosing of a bronchodilator would be a significant convenience and probably a compliance-enhancing advantage, leading to improved overall clinical outcomes. As combination therapy with an inhaled corticosteroid (ICS) and a LABA is important for treating patients suffering from asthma, and a combination with an inhaled long-acting antimuscarinic agent (LAMA) is important for treating COPD patients whose conditions are not sufficiently controlled by monotherapy with a β(2) -adrenoceptor agonist, some novel once-daily combinations of LABAs and ICSs or LAMAs are under development.

Efficacy is a contributing factor to the clinical onset of bronchodilation of inhaled beta(2)-adrenoceptor agonists

Inhaled beta(2) adrenoceptor (beta(2) AR) agonists are widely used as bronchodilator therapies for asthma and COPD. Different agonists have varying rates of onset of action, e.g. indacaterol and salbutamol are effective bronchodilators within 5 min whereas salmeterol takes 15 min to achieve significant bronchodilation over baseline (Brookman et al., Curr Med Res Opin 23:3113-3122, 2007). This has been attributed to differences in the lipophilicity of the agonists such that hydrophobic ligands take longer to diffuse into tissue and may even access the receptor via the membrane compartment (Anderson et al., Eur Respir J 7:569-578, 1994). While this holds true for salmeterol and salbutamol, the relatively high lipophilicity of indacaterol should result in a slower onset of action. Here we have explored the possibility that the efficacy of these ligands may also contribute to their onset of action. We have characterised efficacy and rate of cyclic adenosine monophosphate (cAMP) accumulation in primary human bronchial smooth muscle cells using a competition assay (AlphaScreen, Perkin Elmer) and in HEK 293-GloSensor cells endogenously expressing the beta(2) AR using a luminescence readout. For all agonists tested, cAMP was generated in a concentration-dependent manner. For both assay formats, the relative efficacies were unchanged, with isoprenaline > formoterol > indacaterol > salbutamol > salmeterol. The rate of cAMP generation varied for each agonist and correlated well with intrinsic efficacy in that the high-efficacy agonists promoted the most rapid rise in cAMP levels. We have demonstrated that the rate of cAMP accumulation is influenced by agonist efficacy and that this, in combination with lipophilicity, may explain why beta(2) AR agonists demonstrate differences in their onset of action.

Novel bronchodilators in asthma

PURPOSE OF REVIEW

Because of the central role of bronchodilators in the treatment of asthma, in recent years there has been a renewed interest in the field and now once-daily bronchodilators are in development in an attempt to simplify their use.

RECENT FINDINGS

A variety of beta2-agonists with long half-lives, also called ultra long-acting beta2-agonists (ultra-LABAs; indacaterol, carmoterol, milveterol, GSK-642444, BI-1744-CL, LAS-100977, and PF-00610355) are currently under development with the hopes of achieving once-daily dosing. Between them, indacaterol, GSK-642444, and carmoterol are at a more advanced stage of development. Also several novel inhaled long-acting antimuscarinic agents are currently being developed, but their role in the treatment of asthma is limited. As combination therapy with an inhaled corticosteroid (ICS) and a LABA is considered the first-line approach for treating patients suffering from asthma, some novel once-daily combinations of LABAs and ICSs are under development.

SUMMARY

Bronchodilators are central in the symptomatic management of asthma. It is likely that the once-daily dosing of a bronchodilator would be a significant convenience and probably a compliance-enhancing advantage, leading to improved overall clinical outcomes in patients with asthma. In any case, as a LABA in combination with an ICS continues to be the most effective asthma treatment, once-daily combinations of ultra-LABAs and ICSs will be central in the treatment of asthmatic patients in the next years.

Pharmacological strategies for improving the efficacy and therapeutic ratio of glucocorticoids in inflammatory lung diseases

Glucocorticoids are widely used to treat various inflammatory lung diseases. Acting via the glucocorticoid receptor (GR), they exert clinical effects predominantly by modulating gene transcription. This may be to either induce (transactivate) or repress (transrepress) gene transcription. However, certain individuals, including those who smoke, have certain asthma phenotypes, chronic obstructive pulmonary disease (COPD) or some interstitial diseases may respond poorly to the beneficial effects of glucocorticoids. In these cases, high dose, often oral or parental, glucocorticoids are typically prescribed. This generally leads to adverse effects that compromise clinical utility. There is, therefore, a need to enhance the clinical efficacy of glucocorticoids while minimizing adverse effects. In this context, a long-acting beta(2)-adrenoceptor agonist (LABA) can enhance the clinical efficacy of an inhaled corticosteroid (ICS) in asthma and COPD. Furthermore, LABAs can augment glucocorticoid-dependent gene expression and this action may account for some of the benefits of LABA/ICS combination therapies when compared to ICS given as a monotherapy. In addition to metabolic genes and other adverse effects that are induced by glucocorticoids, there are many other glucocorticoid-inducible genes that have significant anti-inflammatory potential. We therefore advocate a move away from the search for ligands of GR that dissociate transactivation from transrepression. Instead, we submit that ligands should be functionally screened by virtue of their ability to induce or repress biologically-relevant genes in target tissues. In this review, we discuss pharmacological methods by which selective GR modulators and "add-on" therapies may be exploited to improve the clinical efficacy of glucocorticoids while reducing potential adverse effects.

Homology modeling and flex-ligand docking studies on the guinea pig beta(2) adrenoceptor: structural and experimental similarities/ differences with the human beta(2)

The trachea of a guinea pig is widely used in drug development assays focused on the treatment of pulmonary diseases. Some of these drugs relax the airways by binding to the guinea pig beta(2)-adrenoceptor (Gbeta(2)AR). In this work, the amino acid sequence of the Gbeta(2)AR was searched to carry out homology modeling, using the Swiss-Model server, with the human beta(2)AR as the parent template. The Gbeta(2)AR 3-D structure was structurally and energetically optimized in vacuo using NAMD 2.6 program. The refined 3-D model obtained was used for further study. Molecular docking simulations were performed by testing a set of well-known beta(2)AR ligands using the AutoDock 3.0.5 program. The results show that the homology model of Gbeta(2)AR has a 3-D structure very similar to the crystal structure of recently studied human beta(2)AR. This was also corroborated by identity (94.23%), Ramachandran map, and docking results. The theoretical simulation showed that the ligands bind at sites that are similar to those reported for the human beta(2)AR. The R-enantiomer ligands showed correlation with in vitro data. We have obtained a Gbeta(2)AR 3-D model which can be used to carry out computational screening as a complementary tool during the drug design and experimental tests under guinea pig models.

Novel long-acting bronchodilators for COPD and asthma

An important step in simplifying asthma and chronic obstructive pulmonary disease (COPD) management and improving adherence with prescribed therapy is to reduce the dose frequency to the minimum necessary to maintain disease control. Therefore, the incorporation of once-daily dose administration is an important strategy to improve adherence and is a regimen preferred by most patients, which may also lead to enhancement of compliance, and may have advantages leading to improved overall clinical outcomes. Once-daily beta2-agonists or ultra long-acting beta2-agonists (LABAs) such as carmoterol, indacaterol, GSK-159797, GSK-597901, GSK-159802, GSK-642444 and GSK-678007 are under development for the treatment of asthma and COPD. Also some new long-acting antimuscarinic agents (LAMAs) such as aclidinium, LAS-35201, GSK656398, GSK233705, NVA-237 (glycopyrrolate) and OrM3 are under development. In any case, the current opinion is that it will be advantageous to develop inhalers containing combination of several classes of long-acting bronchodilator drugs in an attempt to simplify treatment regimens as much as possible. Consequently, several options for once-daily dual-action ultra LABA+LAMA combination products are currently being evaluated. A different approach is to have a dimer molecule in which both pharmacologies are present (these molecules are known as M3 antagonist-beta2 agonist (MABA) bronchodilators). The advent of a successful MABA product will revolutionize the field and open the door for a new range of combination products.

ultra-long-acting beta2-adrenoceptor agonists: an emerging therapeutic option for asthma and COPD?

There has been a real interest recently in developing once-daily beta(2)-adrenoceptor agonists (ultra-long-acting beta(2)-adrenoceptor agonists [ultra-LABAs]) for treating asthma and chronic obstructive pulmonary disease (COPD) in an attempt to simplify their management, although an increasing amount of convincing data show an association of LABAs with a rise in asthma-related deaths and life-threatening experiences. This paper reviews the effects of different ultra-LABAs that are at varying stages of development. Arformoterol, carmoterol, indacaterol and GSK-159797 are ultra-LABAs that are likely to be introduced into the market before 2010. It is plausible that once-daily dose administration of an LABA will lead to increased convenience for patients, which may also lead to enhancement of adherence, and may have advantages leading to improved overall clinical outcomes in patients with asthma and COPD.

Ultra long-acting beta 2-agonists in development for asthma and chronic obstructive pulmonary disease

After the discovery of formoterol and salmeterol, new candidates for long-acting beta2-adrenoceptor agonists (LABAs) have emerged from various companies. In particular, once-daily beta2-adrenoceptor agonists such as arformoterol, carmoterol, indacaterol, GSK-159797, GSK-597901, 159802, 642444 and 678007 are under development for the treatment of asthma and chronic obstructive pulmonary disease. The majority of these compounds are (R,R)-isomers in order to control desensitisation and accumulation. Several options for combination products are currently being evaluated in parallel with the development of these ultra LABAs. Once-daily dosing of an ultra LABA would be a significant convenience and probably a compliance-enhancing advantage leading to improved overall clinical outcomes in patients with asthma and chronic obstructive pulmonary disease. The only limits set for the development of a LABA with a new product profile are medical needs and marketing opportunities.

Positive interaction of the novel beta2-agonist carmoterol and tiotropium bromide in the control of airway changes induced by different challenges in guinea-pigs

This study evaluated the bronchodilating activity of the beta(2)-agonist carmoterol and the muscarinic M(3)-antagonist tiotropium, given intratracheally alone or in combination in anaesthetized artificially ventilated normal and actively sensitized guinea-pigs. Carmoterol (0.3-100pmol) and tiotropium (10-1000pmol) were superfused (0.01ml/min) for 5min before challenges with acetylcholine (20mug/kg i.v.), histamine (10mug/kg i.v.) or ovalbumin (5mg/kg i.v.). Both compounds given alone were markedly active against all the challenges. Tiotropium resulted more effective towards cholinergic challenge and carmoterol was very potent against histamine and ovalbumin-induced reaction, being effective already at 1pmol. In the presence of tiotropium, the bronchodilating activity of carmoterol was significantly augmented. The ED(50) value of carmoterol on the acetylcholine challenge was reduced by about 10 and 28 times (0.1 and 0.3pmol of tiotropium), that on the histamine one by 4.5 and 13 times (1 and 3pmol of tiotropium) and that on the ovalbumin-induced one by 8 and 25 times (10 and 30pmol of tiotropium). A positive interaction was also evident when other parameters were evaluated. The histamine-induced release of thromboxane B(2) was markedly reduced (56%, P<0.001) by combining completely ineffective doses of the two drugs (0.3 and 3pmol for carmoterol and tiotropium, respectively). In ovalbumin-challenged animals the time to death, amounting in control animals to 7.2+/-0.9min, was dose-dependently prolonged up to achieve complete protection from death with combination of 1 and 30pmol of carmoterol and tiotropium, respectively. The favorable interaction between carmoterol and tiotropium can represent a good option in the control of bronchopulmonary diseases marked by an increase of airway resistances.

Positive interaction of the beta2-agonist CHF 4226.01 with budesonide in the control of bronchoconstriction induced by acetaldehyde in the guinea-pigs

Pretreatment of anaesthetized guinea-pigs with either CHF 4226.01 (8-hydroxy-5-[(1R)-1-hydroxy-2-[N-[(1R)-2-(p-methoxyphenyl)-1-methylethyl]amino]ethyl] carbostyril hydrochloride), formoterol or budesonide reduced acetaldehyde (AcCHO)-evoked responses in the lungs with a rank order of potency CHF 4226.01 (ED(50) values, from 1.88 to 3.31 pmol) > formoterol (ED(50) values, from 3.03 to 5.51 pmol) >> budesonide (ED(50) values, from 335 to 458 nmol). The duration of action of CHF 4226.01 in antagonizing the airway obstruction elicited by AcCHO was also substantially longer than formoterol (area under the curve) at 10 pmol, 763+/-58 and 480+/-34, respectively; P<0.01). Continuous infusion of a subthreshold dose of AcCHO enhanced the intratracheal pressure (ITP) increases caused by subsequent challenges with substance P (from 9.7+/-0.8 to 27.5+/-1.6 cm H(2)O as a peak, P<0.001). Pretreatment with either CHF 4226.01 or formoterol prevented the sensitizing effect of AcCHO on substance P responses (ED(50) values, 2.85 and 6.11 pmol, respectively; P<0.01). The ED(50) value of budesonide (396 nmol) in preventing AcCHO-evoked ITP increase was reduced when this glucocorticoid was combined with 0.1 pmol CHF 4226.01 (ED(50) 76 nmol; P<0.001). CHF 4226.01/budesonide was two-fold more effective (P<0.01) than the formoterol/budesonide combination. These results suggest that CHF 4226.01/budesonide, by optimizing each other's beneficial potential in the control of pulmonary changes caused by AcCHO in the guinea-pigs, may represent a new fixed combination in asthma.

Three-dimensional pharmacology, a subject ranging from ignorance to overstatements

Stereoselectivity has been known to play a role in drug action for 100 years or more. Nevertheless, chiral drugs have been developed and used as racemates, neglecting the fact that they comprise mixtures of two or more compounds which may have quite different pharmacological properties. A very limited access to pure enantiomers in the past has been responsible for this unsatisfactory state of affairs. During the last 20 years, significant achievements have made it possible to perform stereoselective synthesis and analysis. Today, novel chiral drugs are as a rule developed as single enantiomers. Yet, studies of old racaemic drugs are still designed, performed and published without mention of the fact that two or more compounds are involved. In recent years, a number of old racaemic drugs have been re-evaluated and re-introduced into the clinical area as the pure, active enantiomer (the eutomer). While in principle correct, the clinical benefit of this shift from a well established racaemate to a pure enantiomer often seems to be limited and sometimes exaggerated. Racaemic drugs with a deleterious enantiomer that does not contribute to the therapeutic effect (the distomer), may have been sorted out in the safety evaluation process. However, in the future any pharmacological study of racaemic drugs must include the pure enantiomers. This will generate new, valuable information on stereoselectivity in drug action and interaction.

Three-dimensional models for beta-adrenergic receptor complexes with agonists and antagonists

Molecular modeling methods have been used to construct three-dimensional models for agonist and antagonist complexes with beta-adrenergic receptors. The recent rhodopsin crystal structure was used as a template in standard homology modeling methods. The rhodopsin-based homology models were assessed for agreement with experimental results for beta-adrenergic receptors, and compared with receptor models developed using de novo modeling techniques. While the de novo and homology-derived receptor models are generally quite similar, there are some localized structural differences that impact the putative ligand-binding site significantly. The de novo receptor models appear to provide much better agreement with experimental data, particularly for receptor complexes with agonist ligands. The de novo receptor models also yield some interesting and testable hypotheses for the structural basis of beta-adrenergic receptor subtype ligand selectivity.

Trachea relaxing effects and beta2-selectivity of SPFF, a newly developed bronchodilating agent, in guinea pigs and rabbits

In this paper we evaluated the bronchodilator effects of SPFF [2-(4-amino-3-chloro-5-trifluomethyl-phenyl)-2-tert-butylamino-ethanol chloride], a newly synthesized beta(2) adrenergic agonist in guinea pigs and rabbits, in comparison with other beta(2) adrenergic agonists, isoprenaline or salbutamol. We studied in vitro the bronchodilator effects of SPFF and isoprenaline on isolated guinea pig trachea strips with or without the precontraction of bronchocontractors (acetylcholine and histamie). The positive chronotropic effects of SPFF and isoprenaline on isolated guinea pig left atria were also tested in vitro. Potency values (pD(2), pA(2) or ED(50)) were determined from the cumulative concentration-response curves. The results showed that SPFF and isoprenaline dose-dependently relaxed the isolated guinea pig trachea strips and the pD(2) values of both drugs were 7.66+/-0.68 and 8.79+/-0.19, respectively. Moreover, we confirmed that the bronchodilator effect of SPFF was due to the activation of beta(2) adrenoceptor because this effect was easily antagonized by ICI-118551 (pA(2) 8.90+/-0.01), a specific beta(2) adrenoceptor antagonist. SPFF also dose-dependently relaxed the isolated guinea pig trachea strip precontraction with acetylcholine or histamine with ED(50) values of 10.2+/-0.7 microM and 550+/-38.2 nM, respectively. Furthermore, the positive chronotropic effect of SPFF on isolated guinea pig left atria (pD(2) 5.41+/-0.38) was much weaker than that of isoprenaline (pD(2) 8.75+/-0.24), which implied that SPFF was more selective to airway beta(2) adrenoceptor than isoprenaline; the beta(1)/beta(2) selectivity assay also showed that SPFF was about 162 times more selective to beta(2) adrenoceptor than isoprenaline. A radioligand binding experiment using guinea pig lung and cardiac ventricle as beta(2) and beta(1) adrenoceptor sources, respectively, also demonstrated that SPFF possesses high affinity (27.3 nM) and selectivity (4.6 fold) to beta(2) adrenoceptors. The protective effects of SPFF and salbutamol on bronchospasm induced by bronchoconstrictor aerosol in guinea pigs in vivo were investigated, and the Konzett and Rössler experiment in rabbits in vivo was also carried out. SPFF significantly prolonged the latency time of histamine and acetylcholine induced asphyxiation collapse in guinea pigs: the ED(50) value of SPFF i.g. was 0.32+/-0.05 mg.kg(-1) in this experiment. Meanwhile, the ED(50) values of salbutamol was 2.37+/-0.22, which meant that the bronchorelaxation effect of salbutamol was about 6 times less potent than that of SPFF. The Konzett and Rössler experiment performed in anesthetized rabbit showed that intraduodenal administration of SPFF exerted action of longer duration than salbutamol. From the results above we suggested that SPFF was a potent, long-acting bronchodilator with relatively higher beta(2) adrenoceptor selectivity.

Beta-adrenoceptor agonists and asthma--100 years of development

Inhaled beta(2)-adrenoceptor agonists are by far the most effective and safe bronchodilators currently available. They have not been surpassed by any other bronchodilating principle. The way to this position has been long and started with the first successful treatment of acute, severe asthma with s.c. injections of adrenaline 100 years ago. Over the years, synthetic congeners of adrenaline have been produced and tested for their pharmacological properties. During the first decades, little attention was given airway smooth muscle. The discovery of isoprenaline in 1940 was the first major step towards selective bronchodilation. This compound became a key tool for the classification of adrenoceptors into alpha and beta. Salbutamol and terbutaline were the first to show a significant attenuation of the cardiostimulant effect and confirmed the subdivision of beta-adrenoceptors into beta(1) and beta(2). Much effort was made to eliminate the next dose-limiting side effect, skeletal muscle tremor but in vain. Prolonged duration of action was achieved in three ways: with bambuterol, an orally active carbamate ester prodrug of terbutaline, salmeterol, an inhaled beta(2)-adrenoceptor agonist emerging from a purposeful research project, and formoterol which was found, accidentally, to have a long duration of action when inhaled. Throughout the 20th century, beta-adrenoceptor agonists have been developed and marketed as racemates. The pharmacological activity usually resides in the (R)-enantiomer. Despite claims for the opposite, there is so far no compelling evidence that the presence of the less active (S)-enantiomer is of any harm to the patient. One hundred years of experience of structural modifications of adrenaline has shown that the possibilities to modify the properties of this endogenous prototype appear to be unlimited.

Tracheal relaxing effects and beta2 adrenoceptor selectivity of S1319, a novel sponge-derived bronchodilator agent, in isolated guinea-pig tissues

1. S1319 (4-hydroxy-7-[1-(1-hydroxy-2-methylamino)ethyl]-1, 3-benzothiazol-2(3H)-one acetate), a novel non-catecholamine beta-adrenoceptor agonist, has been compared with isoprenaline, salbutamol and formoterol for activity in vitro on a range of beta-adrenoceptor containing preparations from guinea-pig. 2. S1319, like isoprenaline, salbutamol and formoterol, relaxed preparations of guinea-pig trachea (contracted by histamine) in a concentration-dependent manner. The relaxing activity of S1319 appeared to be more potent than that of isoprenaline and salbutamol, and similar to that of formoterol (pD2 values of 10.58+/-0.03 vs 7. 60+/-0.01, 7.50+/-0.01 and 10.52+/-0.04, respectively), and was blocked by the beta2-adrenoceptor selective antagonist (ICI 118,551). The intrinsic activity of S1319 was close to 1.0. 3. In the beta1-adrenoceptor containing preparations, guinea-pig right and left atria, a monophasic inotropic response of S1319 was observed. The pD2 value of S1319 for left atrial and right atrial inotropism was 6.70+/-0.15 and 7.81+/-0.01, respectively. 4. The selectivity ratio (trachea/left atrial inotropism) of S1319, formoterol, salbutamol and isoprenaline was 8523, 284, 4.8 and 0.45, respectively. The relative selectivity ratio of S1319 was 18743, 1858 and 30 times greater than that of isoprenaline, salbutamol and formoterol, respectively. 5. Relaxant responses of guinea-pig trachea to S1319 declined rapidly when the agonist was washed from the tissues, with complete recovery within 30 min. The duration of action of S1319 was similar to that of isoprenaline and less than that of salbutamol and formoterol. 6. In summary, S1319, a sponge-derived beta-adrenoceptor agonist, is a potent and selective beta2-adrenoceptor agonist with a short-duration of action in isolated guinea-pig tracheas.

Pharmacological evidence for β2-adrenoceptor in right atria from stressed female rats

The purpose of the present study was to demonstrate a physiological response to TA2005, a potent β2-adrenoceptor (β2-AR) selective agonist, in right atria isolated from stressed female rats under the influence of the estrous cycle. We obtained concentration-response curves to the agonist in the presence and in the absence of selective antagonists in right atria isolated from female rats submitted to three daily foot-shock sessions (30 min duration, 120 pulses of 1.0 mA, 1.0 s, applied at random intervals of 5-25 s) and sacrificed at estrus or diestrus. Our results showed that the pD2 values of TA2005 were not influenced by estrous cycle phase or foot-shock stress. However, in right atria from stressed rats sacrificed during diestrus, the concentration-response curve to TA2005 was biphasic, with a response being obtained at concentrations of 0.1 nM, whereas during estrus no response was observed at doses lower than 3 nM. ICI118,551, a β2-AR antagonist, abolished the response to nanomolar concentrations of TA2005 in right atria from stressed rats at diestrus, with no changes in agonist pD2 values in right atria from control rats (7.47 ± 0.09, p > 0.05) but a 3-fold decrease in pD2 values of TA2005 in right atria from foot shock stressed rats (7.90 ± 0.07, p [Formula: see text] 0.05). Concentration-response curves to TA2005 in the presence of ICI118,551 were best fitted by a one-site model equation. The β1-AR antagonist, CGP20712A, shifted to the right only the second part of the concentration-response curves to the agonist, unmasking the putative β2-AR-mediated response to the agonist in tissues isolated from stressed rats at diestrus. Under this condition, concentration-response curves to the agonist were best fitted by a two-site model equation. pD2 and maximum response of TA2005 interaction with β1- and putative β2-adrenoceptor components were calculated. Schild analyses gave a pKB value for CGP20712A that was typical for the interaction with β1-AR in each experimental group. pKB values for ICI118,551 could not be obtained in stressed rats sacrificed at diestrus since Schild plot slopes were lower than 1.0. In right atria from control rats, ICI118,551 pKB values were similar to reported values for the interaction of the antagonist with β1-AR. These results confirm that a heterogenous β-AR population mediating the chronotropic response to catecholamines can be demonstrated in right atria from foot shock stressed female rats sacrificed at diestrus. The stress-induced response seems to be mediated by the β2-AR subtype. Right atria from rats sacrificed during estrus are protected against stress-induced alterations on the homogeneity of β-AR population.Key words: foot-shock stress, TA2005, ICI118,551, CGP20712A, estrus, diestrus.

Enantiomers of bronchodilating beta2-adrenoceptor agonists: is there a cause for concern?

All bronchodilating beta2-adrenoceptor agonists in current clinical use are derivatives of adrenaline and are available as racemates. Whereas the vast majority of the pharmacologic and clinical documentation has been made with the racemates, there are a few studies with the individual enantiomers. It thus appears that all established pharmacologic effects of racemic beta2-agonists reside in the (R)-enantiomer, with the (S)-enantiomer being virtually inactive. In recent years the suspicion has been raised that the (S)-enantiomer of the beta2-agonists is responsible for induction of airway hyperreactivity. This suspicion is based primarily on results obtained in guinea pigs exposed to (S)-enantiomers of beta2-agonists. A number of experiments in vitro have been undertaken to find a mechanism of action for these observations in vivo. Most of the results obtained are equivocal. However, the observation that (S)-salbutamol may cause mobilization of intracellular Ca2+, apparently by means of a cholinergic mechanism, deserves further investigation. The clinical studies are focused on the enantiomers of salbutamol. They confirm the preclinical findings that the pulmonary, as well as the extrapulmonary, effects of salbutamol reside in the (R)-enantiomer. The studies available so far do not convincingly show clinically significant airway hyperreactivity after exposure to the (S)-enantiomer. Further studies are needed to settle this issue.

Enzyme-linked immunosorbent assay for TA-2005-glucuronide in human plasma

A sensitive enzyme-linked immunosorbent assay (ELISA) for TA-2005-glucuronide, a main metabolite of new adrenergic beta-receptor agonist TA-2005, has been investigated without prior deconjugation. Coupling of the hapten with bovine serum albumin (BSA) or beta-D-galactosidase was carried out by the N-hydroxysuccinimide ester method. An anti-TA-2005-glucuronide antiserum was obtained from guinea pig immunized with the hapten-BSA conjugate. The ELISA was based upon a competitive assay in which the separation of bound from free fraction was performed by the double antibody technique using rabbit anti guinea pig immunoglobulin antibody adsorbed to microtiter plates. A satisfactory standard curve for the ELISA of TA-2005-glucuronide was observed in the range of 30 pg-3 ng ml-1 using 25 microliters of human plasma. Inter-day and intra-assay variations were 7.0-17.5% and 1.0-11.7% respectively. The recoveries of TA-2005-glucuronide spiked to plasma samples were 95.5-120% (inter-assay) and 96.0-123.3% (intra-assay). The cross-reactivities of the prepared antiserum with the related compound of TA-2005-glucuronide were quite low though there was a considerable cross-reaction with TA-2005. However, TA-2005-glucuronide could be easily separated from TA-2005 by a simple pretreatment of the plasma sample with a C18 cartridge column. This method was applied to the determination of TA-2005-glucuronide in human plasma samples for the evaluation of the pharmacokinetics of TA-2005. From the results, it was demonstrated that the ELISA developed was useful for the determination of TA-2005-glucuronide in human plasma and that the method was applicable to pharmacokinetic studies in humans.

The role of the seventh transmembrane region in high affinity binding of a beta 2-selective agonist TA-2005

To determine the structural basis for binding subtype selective agonists in the beta-adrenergic receptor (beta AR), we examined the interaction of the mutant beta 2AR and chimeric beta 1/beta 2AR with a selective beta 2AR agonist, TA-2005 (8-hydroxy-5-[(1R)-1-hydroxy-2-[N-[(1R)-2-(p-methoxyphenyl)-1-methyle thy l] amino]ethyl] carbostyril hydrochloride). The beta 2AR mutant with Ala substituted for Ser204 (S204A) significantly decreased the affinities for TA-2005, des-8-hydroxy-TA-2005 derivative (compound I), and isoproterenol. In contrast, a S207A mutation slightly decreased the affinities for TA-2005 and compound I, although the affinity for isoproterenol was decreased dramatically. The EC50 values of TA-2005 to activate adenylyl cyclase were not changed in either the S204A- or S207A-beta 2AR. In contrast with TA-2005, the EC50 values of compound I were reduced in the S204A-beta 2AR but not in the S207A-beta 2AR. These results suggest that Ser204 is important for high affinity binding but not necessary to activate adenylyl cyclase. Although TA-2005 was highly selective at the beta 2AR, the compounds lacking p-methoxyphenyl-ethyl (compound II) or p-methoxyphenyl-methylethyl groups (compound III) on the amine portion of TA-2005 lost beta 2AR subtype selectivity. When the second and seventh transmembrane (TM) region but not the TM1 region of the beta 2AR were replaced with the corresponding regions of the beta 1AR, the affinities of the chimeras for TA-2005 decreased compared with those of the wild type beta 2AR. Furthermore, substitution of the TM7 region of the beta 1AR with the corresponding region of the beta 2AR significantly increased the affinities for TA-2005. The affinities for isoproterenol and compounds II and III were not affected in the chimeras. These data suggest that the TM7 region of the beta 2AR plays an important role in beta 2-selective agonist binding. To determine the specific amino acid which confers this high affinity binding of TA-2005 to the beta 2AR, an alanine-scanning mutagenesis approach was employed. All amino acids that were different from those of the beta 1AR were individually changed to alanine. One mutant receptor (Y308A-beta 2AR) out of 10 point-mutated beta 2ARs showed a dramatically reduced affinity for TA-2005. These results indicate that Tyr308 is an essential amino acid for high affinity binding of the beta 2-selective agonist TA-2005.

Differential contribution of two serine residues of wild type and constitutively active beta2-adrenoceptors to the interaction with beta2-selective agonists

1. We have studied the difference in receptor binding activity between partial and full beta2-adrenoceptor agonists and the abilities of the agonists to interact with Ser204 and Ser207 in the fifth transmembrane region of the beta2-adrenoceptor, amino acid residues that are important for activation of the beta2-adrenoceptor. 2. In the binding study with [125I]-iodocyanopindolol, the Ki values of (+/-)-salbutamol, (+/-)-salmeterol, TA-2005 and (-)-isoprenaline for the beta2-adrenoceptor expressed in COS-7 cell membranes were 3340, 21.0, 12.0 and 904 nM, respectively. The beta1/beta2 selectivity of these agonists was in the order of (+/-)-salmeterol (332 fold) > TA-2005 (52.8) > (+/-)-salbutamol (6.8) > (-)-isoprenaline (1.1), and the beta3-/beta2-adrenoceptor selectivity of these agonists was in the order of TA-2005 (150 fold) > (+/-)-salmeterol (88.6) > (+/-)-salbutamol (10.4) > (-)-isoprenaline (3.2). 3. The maximal activation of adenylyl cyclase by stimulation of the beta1-, beta2- and beta3-adrenoceptors by TA-2005 was 32, 100 and 100% of that by (-)-isoprenaline, respectively, indicating that TA-2005 is a full agonist at the beta2- and beta3-adrenoceptors and a partial agonist at the beta1-adrenoceptor. (+/-)-Salbutamol and (+/-)-salmeterol were partial agonists at both beta1- (8% and 9% of (-)-isoprenaline) and beta2- (83% and 74% of (-)-isoprenaline) adrenoceptors. 4. The affinities of full agonists, TA-2005 and (-)-isoprenaline, were markedly decreased by substitution of Ala for Ser204 (S204A) of the beta2-adrenoceptor, whereas this substitution slightly reduced the affinities of partial agonists, (+/-)-salbutamol and (+/-)-salmeterol. Although the affinities of full agonists for the S207A-beta2-adrenoceptor were decreased, those of partial agonists for the S207A-beta2-adrenoceptor were essentially the same as for the wild type receptor. 5. The constitutively active mutant (L266S, L272A) of the beta2-adrenoceptor had an increased affinity for all four agonists. The affinities of full agonists were decreased by substitution of Ser204 of the constitutively active mutant, whereas the degree of decrease was smaller than that caused by the substitution of the wild type receptor. Although the affinities of (+/-)-salbutamol and (+/-)-salmeterol for the S207A-beta2-adrenoceptor were essentially the same as those for the wild type beta2-adrenoceptor, the affinities of (+/-)-salbutamol and (+/-)-salmeterol for the constitutively active beta2-adrenoceptor were decreased by substitution of Ser207. 6. These results suggest that Ser204 and Ser207 of the wild type and constitutively active beta2-adrenoceptors differentially interacted with beta2-selective agonists.

Some pharmacodynamic aspects on long-acting beta-adrenoceptor agonists

1. Formoterol and salmeterol are the first members of a new generation of long-acting beta(2)-adrenoceptor agonists for inhalation. The discovery of the long effect duration of formoterol was made by chance, while the development of salmeterol appeared to follow a purposeful research strategy. 2. Preclinical evaluation predictive of the clinical duration of effect of long-acting bronchodilators is not straightforward. Experiments in vitro may give false positive results, while experiments in vivo may show false negative results. 3. Once the principle of a long duration of effect was established, a number of novel long-acting beta(2)-adrenoceptor agonists of various chemical structure have emerged. 4. There are two alternative models for the explanation of the long duration of effect: the exosite binding explaining the mode of action of salmeterol, and the more general diffusion microkinetic model applicable for both formoterol and salmeterol. 5. Long-acting beta-adrenoceptor agonists with a relatively low efficacy like salmeterol may, under certain circumstances, inhibit competitively the relaxing effect of agonists with higher efficacy like formoterol and salbutamol. 6. Like all other beta(2)-adrenoceptor agonists in current clinical use, formoterol and salmeterol comprise racemic mixtures. Only the RR- and R-enantiomers are pharmacologically active. The experimental compounds TA-2005 and picumeterol have been developed as pure RR- and R-enantiomers, respectively.

Atypical molecular pharmacology of a new long-acting β2-adrenoceptor agonist, TA 2005

The molecular pharmacology of a new putative long-acting bronchodilator TA 2005 (8-hydroxy-5-[(1R)-1-hydroxy-2-[N-[(1R)-2-(p-methoxy-phenyl)- 1-methylethyl]amino]ethyl]carbostyril hydrochloride) has been compared with that of the reference compounds isoprenaline and salbutamol in both methacholine (3 x 10(-6) M) precontracted guinea pig tracheal smooth muscle relaxation and in bovine trapezium muscle binding experiments. TA 2005 appeared very potent compared with isoprenaline and salbutamol (pD2 values of 9.29 vs. 7.65 and 7.10 respectively). For isoprenaline and salbutamol a shallow displacement curve was observed and addition of the non-hydrolysable GTP analogue guanylyl-imidodiphosphate (GppNHp) gave a rightward shift (pKd,high and pKd,low values of 7.3 and 6.1 vs. 7.0 and 5.4 respectively). For TA 2005 a steep displacement curve was found with only one binding state even without GppNHp (pKd,high value of 8.2). The long duration of action of TA 2005 might be explained by tight binding of this compound to the beta 2-adrenoceptor. The extent of tight binding for TA 2005 was extremely large. The molecular basis of the tight agonist binding phenomenon for TA 2005 seems to be of different origin than for isoprenaline. It is hypothesized that a different mechanism of activation of the beta 2-adrenoceptor may be involved for TA 2005.