Synthesis and Structure−Activity Relationships of Long-acting β2 Adrenergic Receptor Agonists Incorporating Metabolic Inactivation: An Antedrug Approach

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.

New bronchodilators

Bronchodilators are central in the treatment of airway diseases including chronic obstructive pulmonary disease (COPD). Bronchodilators in COPD aim to improve lung function, reduce symptoms, prevent exacerbation, and enhance quality of life. The majority of programs in development for novel bronchodilators are focused on enhancing existing targets to once daily dosing and improving their safety profiles. However, just as important are other programs that aim to discover novel pharmacologic targets such as EP4 receptor agonists, bitter taste receptors, and selective PDE inhibitors. Furthermore, existing and novel bronchodilators have become vital components of multiple combination therapies targeting COPD. This review will discuss emerging bronchodilators highlighting preclinical data and available clinical trials.

Dual-pharmacology muscarinic antagonist and β₂ agonist molecules for the treatment of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death in the world today. Bronchodilators, particularly muscarinic antagonists and β(2) agonists, are recommended for patients with moderate to severe COPD. Dual-pharmacology muscarinic antagonist- β(2) agonist (MABA) molecules present an exciting new approach to the treatment of COPD by combining muscarinic antagonism and β(2) agonism in a single entity. They have the potential to demonstrate additive or synergistic bronchodilation over either pharmacology alone. Due to this enticing prospect, several companies have now reported MABA discovery efforts through a conjugated/linked strategy with one candidate (GSK-961081) demonstrating clinical proof of concept. Several MABA crystal forms have been identified, satisfying the requirements for inhaled dosing devices. There are significant challenges in designing MABAs, but the potential to achieve enhanced bronchoprotection in patients and facilitate 'triple therapy' makes this an extremely important and exciting area of pharmaceutical research.

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.

Efficacy and safety of 4 weeks' treatment with combined fluticasone furoate/vilanterol in a single inhaler given once daily in COPD: a placebo-controlled randomised trial

Background Fluticasone furoate/vilanterol (FF/VI) is a novel once-daily (OD) inhaled corticosteroid/long-acting β(2) agonist combination in development for chronic obstructive pulmonary disease (COPD) and asthma. Trial design A multicentre, randomised, double-blind, parallel-group, placebo-controlled study. Methods Participants were patients with moderate-to-severe COPD treated with placebo or FF/VI 400/25 μg OD for 4 weeks. Study objectives were to assess the safety and efficacy of FF/VI 400/25 μg OD administered for 4 weeks via a novel dry powder inhaler. Co-primary end points were change from baseline in weighted mean (wm) heart rate 0-4 h postdose at day 28 and the incidence of adverse events (AEs). Secondary end points included change from baseline in trough forced expiratory volume in one second (FEV(1)) (23-24 h postdose; day 29) and wm FEV(1) (0-4 h postdose; day 28). Patients were randomised to receive FF/VI 400/25 μg or placebo in a 2:1 ratio; all patients and investigators were blinded to active or placebo treatment. Results 60 patients (mean age 64 years) were randomised (FF/VI: n=40; placebo: n=20), and all contributed data to the analysis. Mean screening post-bronchodilator FEV(1) per cent predicted was comparable between groups (FF/VI: 58.5%; placebo: 60.1%). The wm heart rate 0-4 h postdose was similar between groups (difference: 0.6 beats per minute; 95% CI -3.9 to 5.1). More on-treatment AEs were reported in the FF/VI group (68%) compared with the placebo group (50%). The most common drug-related AEs in the FF/VI group were oral candidiasis (8%) and dysphonia (5%). There were no clinically relevant effects on laboratory values, including glucose and potassium, or on vital signs or ECGs/Holters. The FF/VI group had statistically greater improvements compared with placebo in trough FEV(1) (mean difference 183 ml) and 0-4 h postdose wm FEV(1) (mean difference 236 ml). Conclusion FF/VI has a good safety and tolerability profile and improves lung function compared with placebo in patients with COPD. Trial registration number clinical trials.gov-NCT00731822.

A multivalent approach to the discovery of long-acting β(2)-adrenoceptor agonists for the treatment of asthma and COPD

A multivalent approach was applied to the design of long-acting inhaled β(2)-adrenoceptor agonists. A series of dimeric arylethanolamines based on the short acting β(2)-adrenoceptor agonist albuterol were prepared, varying the nature and length of the linker between the basic nitrogens. None of the C(2)-symmetric dimers demonstrated increased potency, however dimer 5j, derived from 4-phenethylamine, was found to have increased binding potency in vitro relative to the parent monomer. Optimization of this structure led to the identification of 22 (milveterol) which demonstrates high potency in vitro and long duration of action in a guinea pig model of bronchoprotection.

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.

A perspective on synthetic and solid-form enablement of inhalation candidates

The administration of compounds by a dry-powder inhaler presents significant challenges to the development and discovery chemist, owing to the stringent requirements placed upon the physical characteristics of the active pharmaceutical ingredient and the high complexity of the molecules concerned. The current state of synthetic chemistry technology is such that commercial syntheses of these compounds are demanding but achievable. While synthetic chemistry will remain a major component of the development of inhaled therapies, the main challenge facing practitioners in this area is the early identification of a suitable solid form. Further advances in the prediction of solid-form properties would significantly enable this field and may allow triage of molecules to be carried out at the design stage of projects.

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.

Long-acting beta-agonists in the management of chronic obstructive pulmonary disease: current and future agents

Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation and debilitating symptoms. For patients with moderate-to-severe COPD, long-acting bronchodilators are the mainstay of therapy; as symptoms progress, guidelines recommend combining bronchodilators from different classes to improve efficacy. Inhaled long-acting β2-agonists (LABAs) have been licensed for the treatment of COPD since the late 1990s and include formoterol and salmeterol. They improve lung function, symptoms of breathlessness and exercise limitation, health-related quality of life, and may reduce the rate of exacerbations, although not all patients achieve clinically meaningful improvements in symptoms or health related quality of life. In addition, LABAs have an acceptable safety profile, and are not associated with an increased risk of respiratory mortality, although adverse effects such as palpitations and tremor may limit the dose that can be tolerated. Formoterol and salmeterol have 12-hour durations of action; however, sustained bronchodilation is desirable in COPD. A LABA with a 24-hour duration of action could provide improvements in efficacy, compared with twice-daily LABAs, and the once-daily dosing regimen could help improve compliance. It is also desirable that a new LABA should demonstrate fast onset of action, and a safety profile at least comparable to existing LABAs.A number of novel LABAs with once-daily profiles are in development which may be judged against these criteria. Indacaterol, a LABA with a 24-hour duration of bronchodilation and fast onset of action, is the most advanced of these. Preliminary results from large clinical trials suggest indacaterol improves lung function compared with placebo and other long-acting bronchodilators. Other LABAs with a 24-hour duration of bronchodilation include carmoterol, vilanterol trifenatate and oldaterol, with early results indicating potential for once-daily dosing in humans.The introduction of once-daily LABAs also provides the opportunity to develop combination inhalers of two or more classes of once-daily long-acting bronchodilators, which may be advantageous for COPD patients through simplification of treatment regimens as well as improvements in efficacy. Once-daily LABAs used both alone and in combination with long-acting muscarinic antagonists represent a promising advance in the treatment of COPD, and are likely to further improve outcomes for patients.

Inhalation by design: novel ultra-long-acting β(2)-adrenoreceptor agonists for inhaled once-daily treatment of asthma and chronic obstructive pulmonary disease that utilize a sulfonamide agonist headgroup

A novel series of potent and selective sulfonamide derived β(2)-adrenoreceptor agonists are described that exhibit potential as inhaled ultra-long-acting bronchodilators for the treatment of asthma and chronic obstructive pulmonary disease. Analogues from this series mediate very long-lasting smooth muscle relaxation in guinea pig tracheal strips. The sulfonamide agonist headgroup confers high levels of intrinsic crystallinity that could relate to the acidic sulfonamide motif supporting a zwitterionic form in the solid state. Optimization of pharmacokinetic properties was achieved through targeted introduction of a phenolic moiety to support rapid phase II clearance, thereby minimizing systemic exposure following inhalation and reducing systemically mediated adverse events. Compound 38 (PF-610355) is identified as a clinical candidate from this series, with in vivo duration of action studies confirming its potential for once-daily use in humans. Compound 38 is currently in advanced phase II clinical studies.