An update on pharmacologic management of chronic obstructive pulmonary disease

Second M3 muscarinic receptor binding site contributes to bronchoprotection by tiotropium

BACKGROUND AND PURPOSE

The bronchodilator tiotropium binds not only to its main binding site on the M₃ muscarinic receptor but also to an allosteric site. Here, we have investigated the functional relevance of this allosteric binding and the potential contribution of this behaviour to interactions with long-acting β-adrenoceptor agonists, as combination therapy with anticholinergic agents and β-adrenoceptor agonists improves lung function in chronic obstructive pulmonary disease.

EXPERIMENTAL APPROACH

ACh, tiotropium, and atropine binding to M₃ receptors were modelled using molecular dynamics simulations. Contractions of bovine and human tracheal smooth muscle strips were studied.

KEY RESULTS

Molecular dynamics simulation revealed extracellular vestibule binding of tiotropium, and not atropine, to M₃ receptors as a secondary low affinity binding site, preventing ACh entry into the orthosteric binding pocket. This resulted in a low (allosteric binding) and high (orthosteric binding) functional affinity of tiotropium in protecting against methacholine-induced contractions of airway smooth muscle, which was not observed for atropine and glycopyrrolate. Moreover, antagonism by tiotropium was insurmountable in nature. This behaviour facilitated functional interactions of tiotropium with the β-agonist olodaterol, which synergistically enhanced bronchoprotective effects of tiotropium. This was not seen for glycopyrrolate and olodaterol or indacaterol but was mimicked by the interaction of tiotropium and forskolin, indicating no direct β-adrenoceptor-M₃ receptor crosstalk in this effect.

CONCLUSIONS AND IMPLICATIONS

We propose that tiotropium has two binding sites at the M₃ receptor that prevent ACh action, which, together with slow dissociation kinetics, may contribute to insurmountable antagonism and enhanced functional interactions with β-adrenoceptor agonists.

Evaluation of the preference, satisfaction and correct use of Breezhaler® and Respimat® inhalers in patients with chronic obstructive pulmonary disease - INHALATOR study

The INHALATOR study was a randomized, multicentre, open label, two-period of 7 days each, crossover study, with 7 days of washout in-between, aiming to evaluate the correct use, satisfaction and preference between Breezhaler^® and Respimat^® devices in patients under daily use of open Spiriva^® or open Onbrize^®, as monotherapy for treatment of mild or moderate COPD. Patients aged ≥40 years with a smoking history of at least 10 pack-year were included in the study. Primary endpoint was the rate of correct use of each device at the first day of treatment after reading the drug leaflet information and was evaluated under the supervision of a trained evaluator. At the end of each treatment phase, the inhaler use was re-evaluated and a satisfaction questionnaire was completed. The patients' preference for the inhaler devices was assessed at the end of the study. After exclusions due to screening failures, 140 patients were randomized: 136 received at least one dose of Breezhaler^® and 135 of Respimat^®. At treatment start, the rate of correct inhaler use was 40.4% (95%CI: 32.2%-48.7%) for Breezhaler^® and 36.3% (95%CI: 28.2%-44.4%) for Respimat^® (p = 0.451). After 7 days, the rates were 68.9% (95%CI: 61.1%-76.7%) and 60.4% (95%CI: 52.2%-68.7%), respectively (p = 0.077). According to the Feeling of Satisfaction with Inhaler Questionnaire - FSI 10 patients were more satisfied using Breezhaler^® than Respimat^® and 57.1% preferred using Breezhaler^® (p = 0.001) while 30.1% preferred Respimat^® (p < 0.001).