Abstract
The preclinical pharmacological profile of 6-hydroxy-8-[(1R)-1-hydroxy-2-[[2-(4-methoxyphenyl)-1,1-dimethylethyl]amino]ethyl]-2H-1,4-benzoxazin-3(4H)-one monohydrochloride (olodaterol, previously known as BI 1744 CL), a novel, enantiomeric pure, inhaled human β2-adrenoceptor (hβ2-AR) agonist, was compared with marketed drugs, such as salmeterol and formoterol. In vitro, olodaterol showed a potent, nearly full agonistic response at the hβ2-AR (EC50 = 0.1 nM; intrinsic activity = 88% compared with isoprenaline) and a significant selectivity profile (241- and 2299-fold towards the hβ1- and hβ3-ARs, respectively). Likewise, olodaterol was able to potently reverse contraction induced by different stimuli in isolated human bronchi. In vivo, antagonistic effects of single doses of olodaterol and formoterol were measured against acetylcholine challenges in anesthetized guinea pigs and dogs for up to 24 h by using the Respimat Soft Mist inhaler. Heart rate and metabolic parameters (serum potassium, lactate, and glucose) were monitored to evaluate systemic pharmacodynamic effects in the dog model. In both models, olodaterol provided bronchoprotection over 24 h. Formoterol applied at an equally effective dose did not retain efficacy over 24 h. In both models olodaterol showed a rapid onset of action comparable with formoterol. Taken together, the preclinical behavior of olodaterol suggests that this novel β2-AR agonist has the profile for once-daily dosing in humans concomitant with a fast onset of action and a favorable systemic pharmacodynamic profile.
Asthma and chronic obstructive pulmonary disease (COPD) are conditions characterized by airway obstruction, which is variable and reversible in asthma but is progressive in COPD (Guerra, 2009). Both diseases are very common, and their incidence is increasing globally, placing a growing burden on patients and health services in industrialized and developing countries (Pauwels and Rabe, 2004; Braman, 2006). β2-Adrenoceptor (β2-AR) agonists are among the most potent and rapidly acting bronchodilators currently available for clinical use. In asthma, rapid-acting inhaled β2-AR agonists are the therapy of choice as a reliever therapy for episodes of dyspnea and the pretreatment of exercise-induced bronchoconstriction (Bateman et al., 2008). In asthma patients with persistent symptoms long-acting β-agonists (LABAs), such as salmeterol and formoterol, are administered as an add-on controller therapy when the first-line treatment of medium dose-inhaled corticosteroids alone fails to achieve control of asthma (Bateman et al., 2008). Recently, formoterol has gained some recognition as an as needed controller therapy because of its fast onset of action. In addition, inhaled β2-AR agonists provide major therapeutic benefits in the treatment of COPD, such as reduction in symptoms and exacerbations, increases in exercise capacity, and improvements of health-related quality of life (Gold, 2009).
β2-AR agonists exert a bronchodilatory effect through activation of β2-ARs expressed on airway smooth muscle cells. In addition, evidence exists that β2-AR mediated increases in cAMP have an anti-inflammatory effect in immune cells, e.g., neutrophils and mast cells, providing an additional rationale for the use of β2-AR agonists in chronic inflammatory diseases such as asthma and COPD.
However, the utility, convenience, and persistence of airflow improvement with short-acting β2-AR agonists, such as salbutamol, is limited by the need of repeated administration. Furthermore, there is an appreciable increase in efficacy in terms of patient-reported outcomes with long-acting bronchodilators (i.e., b.i.d. LABAs and q.d. anticholinergics) (Tashkin et al., 2008; Jenkins et al., 2009) and steroids and combinations (Jenkins et al., 2009).
Currently, two β2-AR agonists with a twice-daily dosing regimen are marketed, namely formoterol, a full agonist, and salmeterol, a partial agonist. The clinical significance of the different intrinsic activities between these two agonists is unclear. However, despite the decrease in dosing frequency with formoterol and salmeterol, patient compliance is an issue (Ying et al., 1999).
Thus, a once-a-day LABA may have several advantages compared with short-acting bronchodilators and twice-daily LABAs, including: 1) improved convenience and compliance (COPD and asthma), 2) improved airflow over a complete 24-h period (COPD and asthma), 3) a more convenient and stable once-a-day combination option with a long-acting muscarinic antagonist, such as tiotropium, for patients for whom more than one bronchodilator is indicated (COPD), and 4) a more convenient and sustained once-a-day free combination option with inhaled steroids (moderate to severe asthma). In addition, a higher therapeutic index would be desirable for the new generation of inhaled β2-AR agonists, because doubling the dose of currently marketed drugs, e.g., salmeterol and formoterol, causes a significant increase in the incidence of adverse effects, including headache, tremor, palpitations, muscle cramps, and a fall in serum potassium concentration (Sovani et al., 2004).
To achieve this, improving ligand selectivity for the hβ2-AR versus the other family subtypes, hβ1-AR (expressed prevalently on cardiac smooth muscle and responsible for inotropic effects) and hβ3-AR (on adipose tissue), is central.
6-Hydroxy-8-[(1R)-1-hydroxy-2-[[2-(4-methoxyphenyl)-1,1-dimethylethyl]amino]ethyl]-2H-1,4-benzoxazin-3(4H)-one monohydrochloride (olodaterol, previously known as BI 1744 CL) is a novel, enantiopure inhaled β2-AR agonist that was discovered in a program to identify compounds with a duration of action compatible with once-daily dosing in humans, a fast onset of action, and an increased therapeutic index compared with the available inhaled β2-AR agonists. Here, we describe the preclinical pharmacological profile of olodaterol compared with the marketed drugs formoterol and salmeterol. To understand the behavior of olodaterol at the molecular level, interaction with the different β-AR subtypes was analyzed in binding and functional assays. Efficacy and duration of bronchoprotection were tested in pharmacological models of acetylcholine (ACh)-induced bronchoconstriction in anesthetized guinea pigs and dogs over a time period of 24 h. We report that olodaterol has an optimized profile of an inhaled LABA combining high β2-selectivity, rapid onset of action, and at least a 24-h duration of action after a single once-daily administration with minimal systemic pharmacodynamic effects.
Materials and Methods
Compounds.
Olodaterol hydrochloride, (R,R)/(S,S)-salmeterol xinafoate, and (R,R)/(S,S)-formoterol fumarate were synthesized by the Department of Chemical Research, Boehringer Ingelheim Pharma GmbH and Co. KG, Biberach, Germany. Acetylcholine (Acetylcholine ophthalmicum Dispers) was from Dispersa GmbH (Germering, Germany). Propofol (propofol-Lipuro 2%) was obtained from B Braun Melsungen AG, (Melsungen, Germany). Propranolol hydrochloride (Obsidan) was from Alpharma-Isis GmbH and Co. KG (Langenfeld, Germany).
Cell Culture Techniques.
Chinese hamster ovary (CHO) cells transfected with the cDNAs encoding the human β1-, β2-, or β3-ARs were purchased from PerkinElmer Life and Analytical Sciences (Waltham, MA). CHO cells were grown in Ham's F12 without glycine, hypoxanthine, and thymidine, 10% dialyzed fetal bovine serum, 100 U/ml penicillin, and 100 μg/ml streptomycin. Because of their high level of receptor expression (see Table 1), these cells were used for performing the affinity binding studies. A second set of CHO cells stably transfected with human β1-, β2-, and β3-ARs was generated in-house, and clones harboring low receptor expression were further selected and used in the functional assays to avoid high receptor spare numbers and potential overestimation of agonist potency and intrinsic activity (IA). This second set of cells, referred to as CHO-hβ1–3LOW (see Table 1), was grown in Dulbecco's modified Eagle's medium supplemented with 1× nonessential amino acids and 10% fetal calf serum in the presence of the selection agent Geneticin (G418 sulfate) (500 μg/ml). Cells were maintained at 37°C in humidified air containing 5% CO2.
Pharmacological characterization of the different CHO cell lines stably expressing the human β1–3 adrenoceptors
Levels of receptor expression (expressed in pmol/mg of protein content in membrane preparations) were determined in saturation binding assays, as described under Materials and Methods. The average of at least three independent experiments performed in triplicate is shown.
Equilibrium Binding Experiments.
Membrane isolation and purification from CHO cells stably expressing the hβ1–3-ARs (high expressing clones) was performed as described previously (Casarosa et al., 2005). In all radioligand experiments the binding buffer consisted of 50 mM Tris-HCl, 2 mM MgCl2, and 1 mM EGTA, pH 7.3. After the indicated incubation period, bound and free [3H]-CGP 12177 [4-(3-tertiarybutylamino-2-hydroxypropoxy)-benzimidazole-2-on hydrochloride] were separated by vacuum filtration using a Brandel Inc. (Gaithersburg, MD) Harvester on GF/B filters presoaked in 0.5% polyethyleneimine and washed three times with ice-cold binding buffer. Filter disks were added to 3 ml of scintillation fluid (Ultima Gold from PerkinElmer Life and Analytical Sciences) in pony vials, and radioactivity was quantified by using liquid scintillation spectrometry on a Tri-Carb 2900TR Liquid Scintillation Analyzer (PerkinElmer Life and Analytical Sciences). In all experiments, total binding did not reach 10% of the amount added, limiting complications associated with depletion of the free radioligand concentration. Saturation binding experiments were performed by incubating membranes (usually 5 to 20 μg/sample, adjusted according to the Bmax of the individual cell line) with a range of concentrations of [3H]-CGP 12177 in a total volume of 4 ml, to avoid significant ligand depletion at the lower concentrations. Samples were incubated at room temperature for at least 2 h under gentle agitation before filtration. To obtain affinity estimates of unlabeled agonists, heterologous competition experiments against [3H]-CGP 12177 were performed at equilibrium. Membranes were incubated in the presence of [3H]-CGP 12177 (final concentration approximately 0.2 nM) and 10 μM 5′-guanylyl-imidodiphosphate to ensure an homogeneous receptor population and different concentrations of agonists at room temperature with gentle agitation for at least 2 h before filtration. Competition displacement binding data were fitted to the Hill equation, and IC50 values obtained from the inhibition curves were converted to Ki values (Cheng and Prusoff, 1973).
cAMP Assay.
To determine the functional potency of the different agonists against the different hβ-ARs, changes in intracellular cAMP levels were determined with CHO-hβ1–3 LOW cells in suspension (15,000 cells/well) by using Alphascreen technology (PerkinElmer Life and Analytical Sciences) and a 384-well plate format (Optiplate; PerkinElmer Life and Analytical Sciences), according to the manufacturer's protocol. In brief, cells were stimulated with the respective agonists at different concentrations in Hanks' buffered saline solution supplemented with 5 mM HEPES, 0.1% bovine serum albumin, and 500 mM 3-isobutyl-1-methylxanthine for 30 min at room temperature. Cells were lysed by using Alphascreen reagents. After 2 h, plates were read on an Envision plate reader (PerkinElmer Life and Analytical Sciences). The concentration of cAMP in the samples was calculated from a standard curve.
In Vitro Human Bronchial Tissue Assays.
Human bronchial tissue sampling and tissue preparation were done as described before (Naline et al., 1994). The use of human lung tissue for in vitro experiments was approved by the Regional Ethics Committee. Lung tissue was obtained from 15 patients (12 men, 3 women, mean age = 66 ± 2 years) undergoing surgery for lung carcinoma. None of the patients had a history of asthma. After the resection a piece of macroscopically normal tissue obtained at a distance of at least 20 mm from the malignancy was supplied by the hospital pathologist. Subsegmental bronchi were dissected free from adhering lung parenchyma and connective tissue, cut in rings, suspended in parallel on tissue hooks in 10 ml of organ baths under an initial load of 3 g, and equilibrated for 60 to 90 min with changes in PSS (118 mM NaCl, 4.7 mM KCl, 2.5 mM CaCl2, 0.6 mM MgSO4, 1.1 mM KH2PO4, 25.0 mM NaHCO3, 11.7 mM glucose) every 15 to 20 min before any pharmacological intervention. At the end of the equilibration period, the resting load was stable at 2 to 4 g. Under these conditions, responses were optimal and reproducible (Naline et al., 1994). The total number of rings used was 157.
Potency and Efficacy.
A total of 82 rings obtained from 13 patients was used, and one concentration-response curve was recorded with a single ring for each compound. Concentration-response curves for olodaterol and formoterol were produced by cumulative addition of the compounds at intervals of 5 to 10 min to bronchi at resting tone (to obtain a relaxation plateau) and bronchi precontracted with either histamine (10 μM, representing 51% of the maximal contraction induced by 3 mM ACh) or ACh (0.1 mM, representing 80% of ACh max). After the end of the experiment, 3 mM theophylline was added to determine the maximal relaxation.
Electrical Field Stimulation.
Experiments were performed as described previously (Naline et al., 2007). A total of 96 rings obtained from six patients was used for these experiments. Only one compound and one concentration were studied in each ring. Each organ bath was fitted with two platinum plate electrodes (1 cm2) placed alongside the tissue (10 mm apart) to cause neural release of ACh by transmural electric field stimulation (EFS) (biphasic pulse width 1 ms, constant current of 320 mA for 10 s at 5 Hz). To obtain the plateau of maximal contraction, a control response was determined for all bronchi preparations by adding 3 mM ACh first. After washing, bronchi were allowed to equilibrate for 60 min with a change of the medium every 15 min. For the subsequent duration of the experiment, 1 μM montelukast and 1 μM indomethacin were present in the buffer to avoid the influence of leukotrienes and prostaglandins on the neuronal responses, respectively. After tension had returned to the baseline tone, the preparation was stimulated every 10 min at 5 Hz, pulse width 1 ms, and 320 mA current for 10 s by using a stimulator (EMKA Technologies, Mitry Mory, France) where the voltage output was adjusted to give a constant current and biphasic rectangular pulse of alternating polarity. These contractions represent 20 to 50% of the maximal contraction induced by 3 mM ACh. Compounds (tested at one dose for each ring) or vehicle were added to the bath for 1 h to reach the relaxation plateau. Magnitude of the relaxation was expressed as percentage of inhibition of EFS-induced contraction recorded before drug administration to the organ bath. To determine their respective potency in preventing EFS-induced contraction (−logIC50), olodaterol and formoterol were tested at different concentrations (3 × 10−11 to 3 × 10−8 M).
Animal Studies.
All animal studies were performed with approval from the Veterinary Authorities in Regierungspräsidum Tübingen, Germany. For inhaled administration olodaterol and formoterol were dissolved in a mixture of distilled water and ethanol (40:60, v/v) at concentrations permitting the administration of the desired dose with three actuations of the Respimat Soft Mist inhaler (Boehringer-Ingelheim International GmbH, Ingelheim, Germany) connected to the endotracheal tube. For intraduodenal administration the compounds were dissolved in 1% Natrosol and applied at a volume of 1 ml/kg.
Bronchoprotection in Guinea Pigs.
Male Dunkin-Harley guinea pigs (350–400 g, obtained from Harlan, Winkelmann, Germany) fasted overnight were used. Anesthesia was induced by intraperitoneal injection of 50 mg/kg pentobarbital followed by intravenous infusion of pentobarbital (15 mg/kg/h) via the jugular vein. A tracheal cannula was introduced after tracheotomy for artificial ventilation, and the internal jugular vein was cannulated for ACh injection. The animals were ventilated (starling ventilator; Hugo Sachs Elektronik-Harvard Apparatus GmbH, March-Hugstetten, Germany) at a stroke volume of 10 ml/1 kg at a rate of 60 strokes per minute. A branch of the tracheal cannula was connected to a pressure transducer (bronchospasm transducer 7020; Ugo Basile, Comerio, Italy). Bronchospasm (cm of H2O) was recorded by using a modified version of the method of Konzett-Roessler (Walland et al., 1997). Blood pressure and heart rate were monitored from a carotid artery. All signals were amplified and measured by using a lung and cardiovascular function recording system (Notocord-hem, Notocord, France). After three stable ACh-induced bronchospasms, compounds were administered via the tracheal tube by using a Respimat Soft Mist inhaler. To address the efficacy and duration of action of the compounds over 5 h, ACh (10 μg/kg i.v.) was injected every 10 min for the entire study period. To address the onset of action of the compounds, bronchoconstrictions were induced by ACh (10 μg/kg i.v.) 1, 3, 5, 7 and 20 min after drug inhalation. To address the duration of action, increasing doses of ACh (2–20 μg/kg i.v.) were injected 6 or 24 h after drug inhalation.
Bronchoprotection in Dogs.
The bronchoprotective effect of olodaterol and formoterol were investigated in a model of ACh-induced bronchoconstriction in anesthetized, ventilated beagle dogs over 3 and 24 h, respectively. The model was essentially performed as described before (Casarosa et al., 2009). In the 3-h setting bronchoprotection, cardiovascular, and metabolic parameters were evaluated immediately before and 5, 10, 30, 60, 90, 120, 150, and 180 min after administration of the compounds. To address the duration of action and the systemic pharmacodynamic effect profile over 24 h, cardiovascular, metabolic parameters, and bronchospasms were recorded 5 min, 30 min, 6 h, 12 h, and 24 h after administration of the compounds. In this setting dogs were anesthetized 30 min before ACh challenge (10 μg/kg i.v.) and regained consciousness 1 h later. Concentrations of potassium, glucose, and lactate in heparinized venous blood samples were determined with an ABL 605 analyzer (Radiometer, Copenhagen, Denmark).
Data were analyzed by using commercially available software (Prism, version 5.02; GraphPad Software Inc., San Diego, CA). All results are expressed as mean ± S.E.M. For the duration of action studies, a two-way analysis of variance with repeated measures was calculated followed by a Bonferroni multiple comparison test versus the time-matched vehicle control.
Intraduodenal Administration.
Beagle dogs of both genders were used (3–5 animals per dose). Animals were anesthetized with pentobarbital (30 mg/kg i.v. bolus) for intubation followed by a pancuronium bolus (0.5 mg) for muscle relaxation. Maintenance of anesthesia was done by intravenous infusion of pentobarbital (10 mg/kg/h) and pancuronium (0.03 mg/kg/h) into the saphenous vein. While placing the devices, piritramid (10 mg i.v.) and fentanyl (0.05 mg i.v.) boli were applied. Artificial respiration was maintained with a gas mixture of 70% nitrous oxide and 30% oxygen by using a Vivolec respirator (MEGAMED AG, Cham, Switzerland). The respiratory parameters were monitored continuously by using a POET (model II, CSI-Europe, Bad Homburg, Germany).
After the instrumentation was complete, animals were allowed to stabilize for 20 to 30 min before the start of the experiments. Compound administration was done via a catheter placed beforehand into the duodenum. Blood pressure was measured with a catheter in the femoral artery, and heart rate was derived from blood pressure. Blood pressure and heart rate were continuously recorded on a computer system after A/D conversion for further analysis by using Notocord-hem and Excel (Microsoft, Redmond, WA) software. At the end of 10-min periods, mean values were calculated from data over 1 min. Data were expressed as mean ± S.E.M and normalized to the time point just before compound administration (time 0) for graphical presentation.
Results
In Vitro Characterization of Olodaterol (BI 1744 CL).
The in vitro pharmacology of olodaterol (Fig. 1) was determined in CHO-K1 cell lines selectively and stably expressing either of the human β1-, β2-, or β3-ARs to ensure that measurements were made at a single receptor subtype. Different clones bearing high or low levels of receptors were selected (Table 1) and used in binding and functional assays, respectively.
Chemical structures of salmeterol (A), formoterol (B), and olodaterol (C).
The agonists' affinities for the different β-adrenoceptor subtypes were determined in heterologous competitive binding experiments against [3H]CGP 12177 in the presence of 5′-guanylyl-imidodiphosphate, a nonhydrolyzable analog of GTP, to ensure monophasic binding curves. Results are summarized in Table 2. Olodaterol had a subnanomolar affinity for the β2-AR (pKi of 9.14) and was selective for this receptor in comparison with the β1-AR and β3-AR subtypes.
Binding affinities of different β2-AR agonists against the three human β-adrenoceptor subtypes
The equilibrium dissociation constants (pKi) of the different ligands were determined in heterologous competition experiments against [3H]CGP 12177 in the presence of a GTP analog. The pKi values (± S.E.M.) shown are the average of at least three independent experiments performed in triplicate.
Given the Gαs coupling of β-ARs, the agonist-induced accumulation of cAMP was used as a functional readout (Fig. 2). CHO cell lines stably expressing low levels of β-ARs were selected (Table 1) to avoid high receptor spare numbers and potential overestimation of agonist potency and IA. The agonists' potencies (pEC50) and intrinsic activities (reported as percentage of the maximal effect of isoprenaline) are summarized in Table 3. In line with the binding data, olodaterol shows the highest potency for the hβ2-AR among the tested drugs (EC50 = 0.1 nM) and the profile of an almost full agonist with an IA of 88%, not statistically different from the reference full agonists isoprenaline and formoterol. However, in contrast to formoterol, olodaterol is only a partial agonist for the hβ1-AR (IAs at hβ1-AR are 52 and 91% for olodaterol and formoterol, respectively) and shows an increased functional selectivity versus the β1 and β3 adrenoceptors (Table 3).
Functional selectivity of β2-AR agonists against the different β-AR subtypes. CHO cells selectively expressing hβ1-AR (A), hβ2-AR (B), or hβ3-AR (C) were stimulated with increasing concentrations of agonists, and cAMP levels were quantified. Data are presented as percentage of maximal isoprenaline-induced cAMP accumulation, and the mean of three independent experiments (± S.E.M.) is shown.
Functional properties of different β2-AR agonists against the three human β-adrenoceptor subtypes
Potency (pEC50 values) and IA (expressed as percentage of isoprenaline-induced maximal response) of the different β2-adrenoceptor agonists were determined in CHO cell lines selectively expressing the β-AR subtype of interest, with the cAMP accumulation assay. Values shown are the average (± S.E.M.) of at least three independent experiments, with each point determined in triplicate. The statistical significance of differences in intrinsic activity among the agonists for each receptor subtype were determined by using one-way analysis of variance with Dunnett's post test for multiple comparisons. Statistical significance is denoted compared with the reference agonist isoprenaline (*, P < 0.05).
In Vitro Pharmacological Profile of Olodaterol on Human Bronchi: Potency and Efficacy.
The pharmacological behavior of olodaterol, in comparison with formoterol, was next assessed in human bronchial strips in the presence of different contractile agents (Table 4). On basal tone preparations, olodaterol and formoterol potently relaxed the bronchi with nonsignificant differences in potency and efficacy (Table 4 and Fig. 3A) (two-tailed t test). Likewise, the potency and efficacy of olodaterol and formoterol were not statistically different when histamine was used as a contractile agent (Table 4 and Fig. 3B). To mimic the cholinergic tone typical of COPD, ACh and EFS (to induce neural-mediated release of ACh) were used. EFS-induced contractions were potently inhibited in a concentration-dependent manner by olodaterol (pIC50 = 9.49) and formoterol (pIC50 = 9.73) (Table 4 and Fig. 3D), with formoterol causing a slightly higher maximal inhibition of EFS-induced contraction (97%) compared with BI 1744 CL (86%).
Potency and maximal efficacy (Emax) of olodaterol and formoterol on human isolated bronchi at resting tone or after a precontraction with 10 μM histamine or 0.1 mM acetylcholine
Potency values (pEC50, mean ± S.E.M.) represent the average of n independent experiments. Maximal efficacy (Emax, mean ± S.E.M.) is reported as percentage of the maximal effect of theophilline. The maximal efficacies obtained with either olodaterol or formoterol in the presence of the different stimuli were analyzed by using one-way analysis of variance followed by Dunnet's multiple-comparison test. Statistical significance is denoted compared versus resting tone (*, P < 0.05).
Effect of olodaterol and formoterol on isolated human bronchi at resting tone (A) and on bronchi precontracted with 10 μM histamine (51% ACh maximum) (B) and 0.1 mM ACh (80% ACh maximum) (C), and electrical field stimulation (D). Data are shown as percentage of theophylline-induced relaxation and are expressed as mean + S.E.M of a number of experiments indicated in Table 4 for each condition.
Conversely, precontraction with ACh (100 μM) decreased the potencies and maximal relaxant effects of BI 1744 CL and formoterol (p < 0.05) with no significant difference between the two β2-AR agonists (Table 4 and Fig. 3D).
In Vivo Profile of Olodaterol.
The in vivo efficacy and systemic pharmacodynamic profile of olodaterol and formoterol were determined in bronchoconstriction models in guinea pigs and dogs. In these models, the compounds were applied intratracheally to anesthetized animals by using the Respimat Soft Mist inhaler, and bronchoconstriction was induced by intravenous application of acetylcholine at various time points after administration of the compounds.
Dose Response in Guinea Pigs.
After administration of different doses of each compound, bronchoprotection, heart rate, and blood pressure were recorded over 5 h. As shown in Fig. 4A, olodaterol induced a dose-dependent bronchoprotection when applied at doses from 0.1 to 3 μg/kg. A full bronchoprotection of 100% was achieved at the dose of 3 μg/kg. Olodaterol demonstrated at all efficacious doses a bronchoprotection lasting over the entire study period of 5 h. For formoterol the maximal bronchoprotection of 100% was achieved at doses of 1 and 3 μg/kg (Fig. 4B). In contrast to olodaterol, formoterol demonstrated an increased duration of action with increased doses. A decline in bronchoprotection was observed after 30 and 150 min at doses of 0.3 and 1 μg/kg, respectively. Formoterol retained a full bronchoprotection over 5 h at a dose of 3 μg/kg (Fig. 4B). Both compounds did not show increases in heart rate and blood pressure over the entire study period at all doses tested (data not shown).
Bronchoprotective efficacy of olodaterol and formoterol in guinea pigs. The bronchoprotection of olodaterol (A) and formoterol (B) was determined in a model of ACh-induced bronchoconstriction in anesthetized guinea pigs. Submaximal bronchospasms were induced by intravenous injections of ACh (10–12 μg/kg) every 10 min. Bronchoprotection is expressed as the percentage of inhibition of the increase in pulmonary resistance induced by ACh. Both compounds were administered with the Respimat Soft Mist inhaler. The time course of the bronchoprotection was recorded for 5 h (n = two animals per dose).
Duration of Action in Guinea Pigs.
To address the duration of action of olodaterol and formoterol, both compounds were applied via intratracheal instillation to guinea pigs, and bronchoconstrictions were induced by increasing ACh doses from 2 to 20 μg/kg after 6 or 24 h, respectively. Olodaterol and formoterol were applied at a dose that achieved equivalent bronchoprotective efficacy over 5 h (3 μg/kg). In addition, two lower doses of olodaterol (1 and 0.1 μg/kg) were tested in this setting. As shown in Fig. 5A, olodaterol and formoterol administered at a dose of 3 μg/kg retained a strong efficacy after 6 h. However, only olodaterol still protected the animals against ACh-induced bronchospasms when administered at a dose of 3 μg/kg and a lower dose (1 μg/kg) after 24 h. In contrast, formoterol applied at the initially equal effective dose retained no activity after 24 h (Fig. 5B).
Duration of action of olodaterol and formoterol in guinea pigs. The bronchoprotective efficacy of olodaterol and formoterol was determined 6 h (A) and 24 h (B) after intratracheal instillation. Bronchospasms were induced by increasing ACh doses from 2 to 20 μg/kg with a progression of 2 μg/kg per intravenous injection. n = five to six animals per dose. Data are shown as mean ± S.E.M. Significance, p < 0.05, indicated by * is against the respective control values.
Onset of Action in Guinea Pigs.
The onset of action of olodaterol in comparison with formoterol was determined in the guinea pig model described above. Both compounds were administered at three different doses by using the Respimat Soft Mist inhaler, and bronchospasms were induced by ACh 1, 3, 5, 7, and 20 min after drug inhalation. As shown in Fig. 6, both compounds exerted a rapid onset of action and achieved a full bronchoprotection within 3 to 6 min after inhalation.
Onset of action of olodaterol and formoterol in guinea pigs. Olodaterol (A) or formoterol (B) were administered with the Respimat Soft Mist inhaler at three different doses. Bronchospasms were induced by ACh (10 μg/kg) 1, 3, 5, 7 and 20 min after drug inhalation. Bronchoprotection is expressed as the percentage of inhibition of the increase in pulmonary resistance induced by ACh. n = six animals per dose.
Dose Response and Systemic Pharmacodynamic Effect Profile in Dogs.
The efficacy and duration of bronchoprotection induced by olodaterol was investigated in a second species, namely anesthetized ventilated beagle dogs. Again, test compounds were administered by inhalation using the Respimat Soft Mist inhaler, and bronchoconstriction was induced by repeated intravenous injections of acetylcholine at different time points after compound administration. This model was also used to study the systemic pharmacodynamic effects of the compounds in further detail, because beagle dogs are very sensitive to the cardiovascular (e.g., heart rate increase) and metabolic (e.g., increase in serum potassium, glucose and lactate) effects mediated by systemic stimulation of β-adrenoceptors (Greaves, 1998).
Olodaterol inhibited the ACh-induced bronchoconstriction in dogs in a dose-dependent manner (Fig. 7A). A maximal bronchoprotective effect of approximately 60% was reached after 10 min at a dose of 0.3 μg/kg olodaterol. At this dose, bronchoprotection was approximately 20% after 3 h. At the inhaled dose of 0.6 μg/kg olodaterol exerted the same maximal efficacy but maintained a bronchoprotection of approximately 40% after 3 h. At the highest dose tested (1.2 μg/kg), a profile comparable with the 0.6 μg/kg dose was observed (data not shown). However, at this dose cardiovascular effects (e.g., increase in heart rate above 50%; see Fig. 7B) were observed. Administration of olodaterol did not result in changes in serum potassium (Fig. 7C), serum lactate (Fig. 7D), and serum glucose (data not shown) at any dose tested. From this experiment, the maximum effective dose of olodaterol in the dog was determined as 0.6 μg/kg. The maximum effective dose of formoterol was determined as 0.6 μg/kg (see Fig. 7A). At this dose, formoterol showed, compared with olodaterol, a more pronounced and longer-lasting tachycardia (Fig. 7B). In addition and in contrast to olodaterol, a long-lasting decrease in serum potassium levels (Fig. 7C) and a significant increase in serum lactate (Fig. 7D) were observed for formoterol at both doses used. Formoterol was devoid of effects on serum glucose (data not shown).
Bronchoprotective efficacy and systemic pharmacodynamic effects of olodaterol and formoterol in dogs over 3 h. Both compounds were administered to anesthetized ventilated dogs at doses of 0.15, 0.3, 0.6, and 1.2 μg/kg using the Respimat Soft Mist inhaler. Bronchospasms were induced by injection of ACh (10 μg/kg i.v.) after 10, 30, 60, 120, and 180 min. A, bronchoprotection is expressed as the percentage of inhibition of the increase in pulmonary resistance induced by ACh. B–D, systemic pharmacodynamic effects including heart rate (B), serum potassium (C), and serum lactate (D) were recorded at the same time points. n = six animals per dose.
Duration of Action in Dogs.
The bronchoprotection of olodaterol and formoterol was determined 0.1, 0.5, 6, 12, and 24 h after inhalation of a single dose of each compound. Both compounds were administered at the maximum effective dose (0.6 μg/kg). Olodaterol was also used at a 2-fold lower dose. As shown in Fig. 8, olodaterol (0.6 μg/kg) induced a maximal bronchoprotection of approximately 60% after 0.5 h, consistent with the 3-h study described above. Twenty-four hours after administration, animals treated with 0.6 μg/kg olodaterol retained a bronchoprotection of approximately 20%. In contrast, formoterol tested at its maximum effective dose was completely inactive after 12 h (Fig. 8). When administered at a 2-fold lower dose olodaterol exerted no bronchoprotection after 12 h. The two doses of olodaterol tested were devoid of heart rate effects and metabolic effects (data not shown).
Bronchoprotective efficacy and duration of action of olodaterol and formoterol in dogs over 24 h. Both compounds were administered by using the Respimat Soft Mist inhaler. Olodaterol and formoterol were applied at a dose that achieved equivalent bronchoprotective efficacy over 5 h (0.6 μg/kg) and a lower dose of olodaterol (0.3 μg/kg). Bronchospasms were induced by intravenous injection of ACh (10 μg/kg) 0.5, 1, 6, 12 and 24 h after administration of the compounds. n = six animals per dose. Data are shown as mean ± S.E.M. Significance, p < 0.05, indicated by *, is against the respective control values.
Systemic Pharmacodynamic Effects of Olodaterol after Intraduodenal Administration.
In humans a significant proportion of the dose inhaled via the Respimat Soft Mist inhaler is swallowed (Dalby et al., 2004). In the animal experiments described above, swallowing did not occur, because the compounds were applied either by intratracheal administration or the Respimat Soft Mist inhaler connected to the endotracheal tube. To mimic the systemic pharmacodynamic effects after complete swallowing of the entire dose, olodaterol was applied intraduodenally to anesthetized dogs at 1.2 and 2.4 μg/kg corresponding to doses 2- and 4-fold above its maximum effective dose. Cardiovascular and metabolic parameters were recorded over 3 h. For comparison, formoterol was applied in the same experimental setting at its maximum effective dose (0.6 μg/kg) and 2-fold above (1.2 μg/kg). As shown in Fig. 9, intraduodenal administration of olodaterol induced only a small increase in heart rate of maximally 10 and 20% when given 2- and 4-fold above the maximum effective dose, respectively. Systolic and diastolic blood pressure were decreased by maximally 10% up to 40 min after olodaterol administration and returned to normal (data not shown). Formoterol administered intraduodenally at its maximum effective dose and 2-fold above induced, compared with olodaterol, more pronounced and stronger dose-dependent effects on heart rate (Fig. 9) and systolic blood pressure (data not shown). Blood pressure was initially decreased up to 25% with the 2-fold fully effective dose. This decrease persisted for diastolic blood pressure, whereas systolic blood pressure increased by approximately 10% starting at approximately 40 min after administration.
Effect of olodaterol and formoterol on heart rate after intraduodenal administration to anesthetized beagle dogs. Olodaterol was applied at 1.2 and 2.4 μg/kg intraduodenally, and formoterol was applied intraduodenally at 0.6 and 1.2 μg/kg. Heart rate is expressed as a percentage of heart rate at time 0 (beats/min) recorded 1 min before intraduodenal drug application as means ± S.E.M. n = three to five animals per dose.
Discussion
With chronic diseases, such as COPD and asthma, patient adherence to medication plans is a major obstacle to successful management (Bender, 2002). One factor contributing to poor adherence is a complicated or a multiple treatment regimen, and simplified dosing regimens are known to improve compliance (Bender, 2002). Therefore, long duration of action (preferably 24 h) is an important feature of drugs intended to treat chronic diseases, enabling both prolonged efficacy and a simple, once-daily dosing regime that improves patient compliance (Tamura and Ohta, 2007). This strategy, which has proven successful with the long-acting muscarinic antagonist tiotropium (Spiriva) (Tashkin et al., 2008), is currently being pursued within a second class of bronchodilators, namely the β2-AR agonists (Cazzola and Matera, 2008).
Here, we describe a comprehensive preclinical characterization of olodaterol (previously known as BI 1744 CL), which was identified as part of a program aimed at the discovery of selective β2-AR agonists with potential for once-daily administration. In vitro data indicate that olodaterol possesses a high, subnanomolar affinity for the hβ2-AR and an excellent selectivity against the other adrenoceptor subtypes. In line with the binding data, olodaterol was the most potent agonist for the β2-AR-mediated stimulation of cAMP and exerted an excellent selectivity profile. In the evaluation of new β2-AR agonists under development, their intrinsic activity needs to be taken into consideration, as partial agonists may act as a β2-antagonist in the presence of a full β-agonist (Lipworth and Grove, 1997). In fact, a partial β-AR agonist exhibits opposite agonist and antagonist activity depending on the prevailing degree of adrenergic tone or the presence of a β-AR agonist with higher intrinsic activity (e.g., rescue therapies). To this end, we took particular care in testing the functional response of olodaterol in a cell line with moderate levels of β2-AR expression (Table 1), similar to airway smooth muscle cells (expression levels reported to be 100 fmol/mg; Mak et al., 1994) to avoid an overestimation of the agonist efficacy, as it is known for systems with high receptor spare numbers (Kenakin, 2004). In this setting, olodaterol offered the profile of an almost full agonist, with an intrinsic activity of 88%. These results were further translated into a more physiologically relevant model, i.e., human lung parenchyma. Here, olodaterol dose-dependently reversed the constriction induced by different stimuli, such as histamine, ACh, and EFS, with an efficacy not statistically different from the full agonist formoterol under all conditions. Taken together, the in vitro data indicate that olodaterol, similarly to formoterol and salmeterol, shows high selectivity for the hβ2-AR in terms of affinity and potency. However, unlike the currently marketed β2-AR agonists, olodaterol has a differential efficacy profile toward the different β-ARs, with a full agonist-like profile on the hβ2-AR and a partial agonism against the hβ1-AR, whereas formoterol and salmeterol exert either a full-agonistic or a partial agonistic profile for all β-ARs, respectively. This profile could translate in an efficacious bronchodilatory effect with reduced cardiovascular side effects.
To obtain information regarding the functional in vivo bronchoprotective profile, taking into account both pharmacodynamic and pharmacokinetic properties, olodaterol was tested in pharmacological models of ACh-induced bronchoconstriction in anesthetized guinea pigs and dogs. ACh-induced bronchoconstriction models are widely used to test the in vivo efficacy, potency, and duration of action of bronchodilators, such as β-agonists and anticholinergics, and are a good predictor for the efficacy of compounds in human airway diseases such as COPD, because an increase in the vagal cholinergic tone is discussed as the major reversible component in COPD (Barnes, 2004).
To mimic the clinical situation further, the Respimat Soft Mist Inhaler was also used for the administration of olodaterol and for better comparison for formoterol. The Respimat inhaler is a novel device that creates a soft mist aerosol without the use of propellants. In our in vivo studies the drugs were provided in water/ethanol (40:60, v/v) solutions dissolved at concentrations permitting the administration of the desired dose with three actuations.
In both models, olodaterol provided bronchoprotection over 24 h, whereas formoterol applied at an equally effective dose did not retain efficacy over 24 h. It is noteworthy to mention that according to our observations the bronchoprotection mediated by β2-AR agonists in the ACh-induced bronchoconstriction model in dogs is significantly less efficacious than in guinea pigs. Whereas most β2-AR agonists studied during our research project easily exerted a 100% bronchoprotection in guinea pigs, we did not identify a β-adrenoceptor agonist capable of a 100% bronchoprotection in the dog model. We do not understand the reason behind this discrepancy, but the different sensitivities of the two models may explain why in the dog model, in contrast to guinea pigs, olodaterol showed only at its maximum effective dose a duration of action over 24 h.
Formoterol is known as a β2-AR agonist with a fast onset of action in humans and has gained recognition as an as needed controller therapy because of this fast onset of action. Most interestingly, in the two species studied, olodaterol also offered a quick onset of action, similar to formoterol. The maximal bronchoprotection after inhalation of a single dose of olodaterol or formoterol was reached in guinea pigs within 3 to 6 min and 10 min in dogs, suggesting that olodaterol may have an rapid onset of action in humans, too.
Because beagle dogs are very sensitive to the cardiovascular (e.g., heart rate increase) and metabolic (e.g., increase in serum potassium, glucose, and lactate) effects mediated by the systemic stimulation of β-adrenoceptors (Greaves, 2000), the systemic pharmacodynamic effects of olodaterol were studied in this species. In the first experimental setting we determined the systemic effects after inhaled (intratracheal) administration of the compound in the same animals used for the efficacy studies. In the second setting we applied the compounds by intraduodenal administration to mimic swallowing of the entire dose. Our preclinical data obtained in the two settings show that, for a given degree of bronchodilator activity, olodaterol has a greater cardiovascular (as assessed by heart rate) and metabolic (as assessed serum potassium, serum, glucose, and serum lactate) safety margin than formoterol. Furthermore, in the two preclinical species analyzed, olodaterol was devoid of systemic pharmacodynamic effects at doses achieving a duration of action of 24 h, suggesting a sufficient therapeutic window for its use in humans. Because the systemic effects of β-agonists on serum potassium, serum lactate, or serum glucose are caused by the activation of β2-ARs in skeletal muscle and liver, we speculate that the larger safety margin we observed for olodaterol in comparison to formoterol in the dog model reflects differences in the pharmacokinetic profile and thus the systemic exposure of the two compounds.
The preclinical data presented here were confirmed in clinical studies in patients with asthma (O'Byrne et al., 2009) and COPD. In all studies, olodaterol showed a 24-h duration of action after once-a-day dosing concomitant with a good safety profile. The 24-h bronchodilator efficacy of once-daily dosing with olodaterol in patients with COPD was confirmed in a 4-week study, with all doses of olodaterol showing statistically significant increases in the primary endpoint, trough FEV1 (forced expiratory volume in 1 second), compared with placebo after 28 days of treatment, again with an excellent safety profile (Van Noord et al., 2009). Furthermore, in the 4-week study no differences in the FEV1 profile after the first dose (day 1) and after 4 weeks of treatment (day 29) were observed, implying the absence of clinical desensitization noted in some clinical studies after regular use of β2-adrenoceptor agonists (Larj and Bleecker, 2002).
Therefore, a once-daily β2-AR agonist, such as olodaterol, offers, compared with short-acting bronchodilators and b.i.d. LABAs, an improved convenience and compliance for asthma and COPD patients and has the potential to be combined with either a once-daily anticholinergic, such as tiotropium (Tashkin et al., 2008; Casarosa et al., 2009) or upcoming new compounds within this class (Cazzola and Matera, 2008), once-daily corticosteroids, or both, presented to the patients either as free or fixed-dose combinations. Besides the improved convenience, these combinations may offer beneficial long-term outcomes for the patients.
In summary, our preclinical data demonstrate that olodaterol is an enantiomeric pure, selective, and potent agonist of the human β2-AR. This molecule combines a novel efficacy profile toward the different β-ARs by exerting almost full intrinsic activity at β2-AR and a weak partial agonism at β1-AR together with a long duration of action, allowing a once-daily administration in humans, a rapid onset of action, and an improved systemic pharmacodynamic effect profile.
Footnotes
- Received February 5, 2010.
- Accepted April 2, 2010.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.167007.
ABBREVIATIONS:
- olodaterol (BI 1744 CL)
- 6-hydroxy-8-[(1R)-1-hydroxy-2-[[2-(4-methoxyphenyl)-1,1-dimethylethyl]amino]ethyl]-2H-1,4-benzoxazin-3(4H)-one monohydrochloride
- β-AR
- β-adrenoceptor
- hβ-AR
- human β-AR
- ACh
- acetylcholine
- LABA
- long-acting β-agonist
- COPD
- chronic obstructive pulmonary disease
- CHO
- Chinese hamster ovary
- EFS
- electric field stimulation
- IA
- intrinsic activity
- CGP 12177
- 4-(3-tertiarybutylamino-2-hydroxypropoxy)-benzimidazole-2-on hydrochloride.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
