LK 204-545, a highly selective beta1-adrenoceptor antagonist at human beta-adrenoceptors

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.

A Photoswitchable Ligand Targeting the β 1 ‐Adrenoceptor Enables Light‐Control of the Cardiac Rhythm**

Catecholamine‐triggered β‐adrenoceptor (β‐AR) signaling is essential for the correct functioning of the heart. Although both β₁‐ and β₂‐AR subtypes are expressed in cardiomyocytes, drugs selectively targeting β₁‐AR have proven this receptor as the main target for the therapeutic effects of beta blockers in the heart. Here, we report a new strategy for the light‐control of β₁‐AR activation by means of photoswitchable drugs with a high level of β₁‐/β₂‐AR selectivity. All reported molecules allow for an efficient real‐time optical control of receptor function in vitro. Moreover, using confocal microscopy we demonstrate that the binding of our best hit, pAzo‐2, can be reversibly photocontrolled. Strikingly, pAzo‐2 also enables a dynamic cardiac rhythm management on living zebrafish larvae using light, thus highlighting the therapeutic and research potential of the developed photoswitches. Overall, this work provides the first proof of precise control of the therapeutic target β₁‐AR in native environments using light.

Linked biaromatic compounds as cardioprotective agents

Cardiovascular diseases (CVDs) are widespread in the modern world, and their number is constantly growing. For a long time, CVDs have been the leading cause of morbidity and mortality worldwide. Drugs for the treatment of CVD have been developed almost since the beginning of the 20th century, and a large number of effective cardioprotective agents of various classes have been created. Nevertheless, the need for the design and development of new safe drugs for the treatment of CVD remains. Literature data indicate that a huge number of cardioprotective agents of various generations and mechanisms correspond to a single generalized pharmacophore model containing two aromatic nuclei linked by a linear linker. In this regard, we put forward a concept for the design of a new generation of cardioprotective agents with a multitarget mechanism of action within the indicated pharmacophore model. This review is devoted to a generalization of the currently known compounds with cardioprotective properties and corresponding to the pharmacophore model of biaromatic compounds linked by a linear linker. Particular attention is paid to the history of the creation of these drugs, approaches to their design, and analysis of the structure-action relationship within each class.

Beneficial and harmful effects of CB1 and CB2 receptor antagonists on chronotropic and inotropic effects related to atrial β-adrenoceptor activation in humans and in rats with primary hypertension

We have previously shown that cannabinoid CB₁ and CB₂ receptor antagonists, AM251 and AM630, respectively, modulate cardiostimulatory effects of isoprenaline in atria of Wistar rats. The aim of the present study was to examine whether such modulatory effects can also be observed (a) in the human atrium and (b) in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). Inotropic effects of isoprenaline and/or CGP12177 (that activate the high- and low-affinity site of β₁ -adrenoceptors, respectively) were examined in paced human atrial trabeculae and rat left atria; chronotropic effects were studied in spontaneously beating right rat atria. AM251 modified cardiostimulatory effects more strongly than AM630. Therefore, AM251 (1 μM) enhanced the chronotropic effect of isoprenaline in WKY and SHR as well as inotropic action of isoprenaline in WKY and in human atria. It also increased the inotropic influence of CGP12177 in SHR. AM630 (1 μM) decreased the inotropic effect of isoprenaline and CGP12177 in WKY, but enhanced the isoprenaline-induced inotropic effect in SHR and human atria. Furthermore, AM251 (0.1 and 3 μM) and AM630 (0.1 μM) reduced the inotropic action of isoprenaline in human atria. In conclusion, cannabinoid receptor antagonists have potentially harmful and beneficial effects through their amplificatory effects on β-adrenoceptor-mediated positive chronotropic and inotropic actions, respectively.

Experimental research in rats on the reactivity of new corneal blood vessels to adrenaline

Aim: The purpose of this experimental study was to evaluate the existence of adrenergic receptors in ketamine-induced corneal blood vessels in rat pups. Methods: The study of corneal neovascularization motricity was performed on 45-day-old Wistar rats in which, starting from the 15th day of life, corneal blood vessels were obtained by injecting intraperitoneal ketamine at a dose of 150 mg/ kg body weight, a total of 5 successive doses. The examination of the neovascularization was done with the help of a Nikon stereomicroscope connected to a video camera and a computer, the total magnification being 400X. The reactivity of the new corneal blood vessels to the administration in conjunctival instillations of a 1.5 mmol/L adrenaline solution was tested. The parameters followed were represented by variations in the caliber of corneal blood vessels. The data were analyzed using Microsoft Office Excel. Results: Administration of distilled water did not produce statistically significant changes in corneal blood vessels, while adrenaline produced a statistically significant constriction of vascular diameter (p=0.01 at T9, p=0.004 at T10, p=0.019 at time T11 of examinations). Conclusions: The results showed that adrenaline produces vasoconstriction in the new corneal blood vessels, which allows us to assume that they contain α-adrenergic receptors. However, we cannot say that corneal pathological vessels do not contain β2-type adrenergic receptors, because the effect of adrenaline may be an algebraic sum between vasoconstriction produced by stimulating α-adrenergic receptors and vasodilation produced by stimulating β2-adrenergic receptors, but in which the vasodilating effect may be masked by the vasoconstrictor effect given by a higher density of α-adrenergic receptors. Abbreviations: A= adrenaline, DNM = non-measurable diameter, NA= noradrenaline, Std.Er.= Standard error.

Cardiovascular Effects of Micromeria graeca (L.) Benth. ex Rchb in Normotensive and Hypertensive Rats

AIMS

The present study was performed in order to analyze the antihypertensive activity of Micromeria graeca (L.) Benth. ex Rchb.

BACKGROUND

Micromeria graeca (L.) Benth. ex Rchb is an aromatic and medicinal plant belonging to the Lamiaceae family. This herb is used to treat various pathologies such as cardiovascular disorders. Meanwhile, its pharmacological effects on the cardiovascular system have not been studied.

OBJECTIVE

The present study aimed to evaluate the effect of aqueous extract of aerial parts of Micromeria graeca (AEMG) on the cardiovascular system in normotensive and hypertensive rats.

METHODS

In this study, the cardiovascular effect of AEMG was evaluated using in vivo and in vitro investigations. In order to assess the acute effect of AEMG on the cardiovascular system, anesthetized L-NAME-hypertensive and normotensive rats received AEMG (100 mg/kg) orally and arterial blood pressure parameters were monitored during six hours. In the sub-chronic study, rats were orally treated for one week, followed by blood pressure assessment during one week of treatment. Blood pressure was measured using a tail-cuff and a computer-assisted monitoring device. In the second experiment, isolated rat aortic ring pre-contracted with Epinephrine (EP) or KCl was used to assess the vasorelaxant effect of AEMG.

RESULTS

Oral administration of AEMG (100 mg/kg) provoked a decrease of arterial blood pressure parameters in hypertensive rats. In addition, AEMG induced a vasorelaxant effect in thoracic aortic rings pre-contracted with EP (10 μM) or KCl (80 mM). This effect was attenuated in the presence of propranolol and methylene blue. While in the presence of glibenclamide, L-NAME, nifedipine or Indomethacin, the vasorelaxant effect was not affected.

CONCLUSION

This study showed that Micromeria graeca possesses a potent antihypertensive effect and relaxes the vascular smooth muscle through β-adrenergic and cGMP pathways.

Development of covalent antagonists for β1- and β2-adrenergic receptors

The selective covalent tethering of ligands to a specific GPCR binding site has attracted considerable interest in structural biology, molecular pharmacology and drug design. We recently reported on a covalently binding noradrenaline analog (FAUC37) facilitating crystallization of the β₂-adrenergic receptor (β₂AR^H2.64C) in an active state. We herein present the stereospecific synthesis of covalently binding disulfide ligands based on the pharmacophores of adrenergic β₁- and β₂ receptor antagonists. Radioligand depletion experiments revealed that the disulfide-functionalized ligands were able to rapidly form a covalent bond with a specific cysteine residue of the receptor mutants β₁AR^I2.64C and β₂AR^H2.64C. The propranolol derivative (S)-1a induced nearly complete irreversible blockage of the β₂AR^H2.64C within 30 min incubation. The CGP20712A-based ligand (S)-4 showed efficient covalent blocking of the β₂AR^H2.64C at very low concentrations. The analog (S)-5a revealed extraordinary covalent cross-linking at the β₁AR^I2.64C and β₂AR^H2.64C mutant while retaining a 41-fold selectivity for the β₁AR wild type over β₂AR. These compounds may serve as valuable molecular tools for studying β₁/β₂ subtype selectivity or investigations on GPCR trafficking and dimerization.

Search for β2 adrenergic receptor ligands by virtual screening via grid computing and investigation of binding modes by docking and molecular dynamics simulations

We designed a program called MolGridCal that can be used to screen small molecule database in grid computing on basis of JPPF grid environment. Based on MolGridCal program, we proposed an integrated strategy for virtual screening and binding mode investigation by combining molecular docking, molecular dynamics (MD) simulations and free energy calculations. To test the effectiveness of MolGridCal, we screened potential ligands for β2 adrenergic receptor (β2AR) from a database containing 50,000 small molecules. MolGridCal can not only send tasks to the grid server automatically, but also can distribute tasks using the screensaver function. As for the results of virtual screening, the known agonist BI-167107 of β2AR is ranked among the top 2% of the screened candidates, indicating MolGridCal program can give reasonable results. To further study the binding mode and refine the results of MolGridCal, more accurate docking and scoring methods are used to estimate the binding affinity for the top three molecules (agonist BI-167107, neutral antagonist alprenolol and inverse agonist ICI 118,551). The results indicate agonist BI-167107 has the best binding affinity. MD simulation and free energy calculation are employed to investigate the dynamic interaction mechanism between the ligands and β2AR. The results show that the agonist BI-167107 also has the lowest binding free energy. This study can provide a new way to perform virtual screening effectively through integrating molecular docking based on grid computing, MD simulations and free energy calculations. The source codes of MolGridCal are freely available at http://molgridcal.codeplex.com.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Synthesis and in vitro and in vivo characterization of highly β1-selective β-adrenoceptor partial agonists

β-Adrenoceptor antagonists boast a 50-year use for symptomatic control in numerous cardiovascular diseases. One might expect highly selective antagonists are available for the human β-adrenoceptor subtype involved in these diseases, yet few truly β₁-selective molecules exist. To address this clinical need, we re-evaluated LK 204-545 (1),1 a selective β₁-adrenoceptor antagonist, and discovered it possessed significant partial agonism. Removal of 1’s aromatic nitrile afforded 19, a ligand with similar β₁-adrenoceptor selectivity and partial agonism (log K_D of −7.75 and −5.15 as an antagonist of functional β₁- and β₂-mediated responses, respectively, and 34% of the maximal response of isoprenaline (β₁)). In vitro β-adrenoceptor selectivity and partial agonism of 19 were mirrored in vivo. We designed analogues of 19 to improve affinity, selectivity, and partial agonism. Although partial agonism could not be fully attenuated, SAR suggests that an extended alkoxyalkoxy side chain, alongside substituents at the meta- or para-positions of the phenylurea, increases ligand affinity and β₁-selectivity.

Effect of altered AGP plasma binding on heart rate changes by S(-)-propranolol in rats using mechanism-based estimations of in vivo receptor affinity (K(B,vivo))

In contrast to the impact of plasma protein binding on pharmacokinetics, no quantitative in vivo information is available on its impact on pharmacodynamics. The pharmacokinetic-pharmacodynamic relationship of the model drug S(-)-propranolol was evaluated using mechanism-based estimations of in vivo receptor affinity (K(B,vivo)), under conditions of altered plasma protein binding resulting from different levels of alpha-1-acid glycoprotein (AGP). Male Wistar Kyoto rats with isoprenaline-induced tachycardia received an intravenous infusion of S(-)-propranolol, on postsurgery day 2 (n = 7) and day 7 (n = 8) with elevated and normal plasma protein binding, respectively. Serial blood samples were taken in parallel to heart rate measurements. AGP concentrations at 2 and 7 days postsurgery were 708 +/- 274 and 176 +/- 111 microg/mL (mean +/- SE), respectively. Using nonlinear mixed effects modeling, AGP concentration was a covariate for intercompartmental clearance for the third compartment of the pharmacokinetic model of S(-)-propranolol. Individual values of AGP concentrations ranged between 110 and 1150 microg/mL, and were associated with K(B,vivo) values of S(-)-propranolol from 7.0 to 30 nM. Using the K(B,vivo) for S(-)-propranolol with correction for average values for normal and elevated plasma protein binding, nearly identical values were found. This confirms, strictly quantitative, earlier indications that plasma protein binding restricts the pharmacodynamics of S(-)-propranolol.

Influence of plasma protein binding on pharmacodynamics: Estimation of in vivo receptor affinities of beta blockers using a new mechanism-based PK-PD modelling approach

The objective of this investigation was to examine in a systematic manner the influence of plasma protein binding on in vivo pharmacodynamics. Comparative pharmacokinetic-pharmacodynamic studies with four beta blockers were performed in conscious rats, using heart rate under isoprenaline-induced tachycardia as a pharmacodynamic endpoint. A recently proposed mechanism-based agonist-antagonist interaction model was used to obtain in vivo estimates of receptor affinities (K(B,vivo)). These values were compared with in vitro affinities (K(B,vitro)) on the basis of both total and free drug concentrations. For the total drug concentrations, the K(B,vivo) estimates were 26, 13, 6.5 and 0.89 nM for S(-)-atenolol, S(-)-propranolol, S(-)-metoprolol and timolol. The K(B,vivo) estimates on the basis of the free concentrations were 25, 2.0, 5.2 and 0.56 nM, respectively. The K(B,vivo)-K(B,vitro) correlation for total drug concentrations clearly deviated from the line of identity, especially for the most highly bound drug S(-)-propranolol (ratio K(B,vivo)/K(B,vitro) approximately 6.8). For the free drug, the correlation approximated the line of identity. Using this model, for beta-blockers the free plasma concentration appears to be the best predictor of in vivo pharmacodynamics.

Binding affinities of ocular hypotensive beta-blockers levobetaxolol, levobunolol, and timolol at endogenous guinea pig beta-adrenoceptors

The current study determined the relative affinities and selectivities of numerous beta-adrenoceptor antagonists at the endogenous beta(1)- and beta(2)-adrenoceptors in guinea pig heart and lung, respectively, using [(3)H]-CGP12177. Specific binding of [(3)H]-CGP12177 comprised 80 +/- 0.2% (n = 11) and 94 +/- 0.2% (n = 16) of the total binding in washed heart and lung homogenates, respectively. Concentration-dependent displacement of [(3)H]-CGP12177 binding from beta-adrenoceptors in both preparations was observed with nine different beta-adrenoceptor antagonists. Levobetaxolol, betaxolol, CGP-20712A, levobunolol, and timolol yielded bi-phasic (two-site-fit) competition curves in the heart, while CGP-20712A, ICI-118551 and levobunolol produced bi-phasic curves in the lung preparation. The high-affinity component of [(3)H]-CGP12177 binding in the heart and lung reflected binding to beta(1)-receptors and beta(2)-receptors, respectively. The binding inhibition parameters (IC(50)s) for displacement of [(3)H]-CGP12177 from these predominantly high-affinity sites were: levobetaxolol (24.9 +/- 1.6 nM heart, 4810 +/- 367 nM lung), racemic betaxolol (37.9 +/- 8.7 mM heart; 8840 +/- 424 mM lung), CGP-20712A (4.6 +/- 0.9 nM heart; 171,000 +/- 109,000 nM lung), ICI-118551 (9230 +/- 3240 nM heart; 2.9 +/- 0.6 nM lung), levobunolol (42 +/- 15 nM heart, 0.3 +/- 0.2 nM lung), (l)-timolol (3.1 nM heart, 2.9 +/- 1.5 nM lung), ICI-215001 (5840 +/- 114 nM heart; 26100 +/- 3200 nM lung), BRL-37344 (83,300 +/- 2660 nM heart; 13,200 +/- 1250 lung). These data indicated that while levobetaxolol and betaxolol possessed a 193-233-fold selectivity for beta(1)-receptors, levobunolol exhibited a 140-fold beta(2)-receptor selectivity and (l)-timolol was essentially nonselective.

Synthesis, beta-adrenoceptor pharmacology and toxicology of S-(-)-1-(4-(2-ethoxyethoxy)phenoxy)-2-hydroxy-3-(2-(3,4-dimethoxyphenyl)ethylamino)propane hydrochloride, a short acting beta(1)-specific antagonist

The synthesis of S-(-)-1-(4-(2-ethoxyethoxy)phenoxy)-2-hydroxy-3-(2-(3,4-dimethoxyphenyl)ethylamino)propane hydrochloride (D140S.HCl 6), a novel short acting beta(1)-specific adrenoceptor antagonist, has been described. The antagonist potency for D140S.HCl 6 has been compared with esmolol, another short acting agent, and other well known beta-adrenoceptor antagonists in isolated rat tissue preparations. The pharmacokinetics of D140S.HCl 6 in 7 day continuous intravenous infusions and 4 weeks intravenous bolus injection studies in conscious rats and dogs have been examined in toxicology studies. The effect on the isoprenaline-induced heart rate increase and the pharmacodynamic half-life of D140S.HCl 6 has been compared with esmolol in a conscious rat model. In addition, the results of a range of toxicological studies are presented. The results indicate that D140S.HCl 6 is a highly specific beta(1)-adrenoceptor antagonist (pA(2) = 8.15+/-0.22, beta(1)/beta(2) selectivity > 4400). The in vitro studies suggest D140S.HCl is ca. ten times more potent and 60 times more beta(1)-specific than racemic esmolol. Pharmacokinetic non-linearity was seen when given as a 7 day intravenous infusion at toxicological doses above 10 mg kg(-1) h(-1) in the rat and 2.5 mg kg(-1) h(-1) in the dog. Both D140S.HCl 6 and esmolol have very short durations of action after intravenous infusion in the rat (pharmacodynamic half-life is < 15 min for D140S.HCl and 10 min for esmolol). The toxicological tests indicate that D140S.HCl 6 shows no unexpected toxicity and none of the tissue irritancy problems reported for esmolol formulations.

beta(1)- and beta(2)-Adrenoceptor antagonist activity of a series of para-substituted N-isopropylphenoxypropanolamines

To further explore the structure-activity relationships of beta-adrenoceptor (beta-AR) antagonists, a series of 25 para-substituted N-isopropylphenoxy-propanolamines were synthesised, nine of which are new compounds. All have been examined for their ability to antagonise beta(1)-ARs in rat atria and beta(2)-ARs in rat trachea. Substitution in the para-position of the phenyl ring is thought to confer beta(3)-specificity and the selectivity of these compounds for the beta(1)-AR ranges from 1.5-234. None of the compounds tested were selective for the beta(2)-AR. Of the 25 compounds studied, 22 had reasonable (pA(2) > 7) potencies for the rat beta(1)-AR. Only compound 1 displayed reasonable (pA(2) > 7) potency for the rat beta(2)-AR. Twenty two compounds were used as the training set for comparative molecular field analysis (CoMFA) of antagonist potency (pA(2)) at the rat beta(1)- and beta(2)-ARs. The inclusion of a number of additional physical characteristics improved the QSAR analysis over models derived solely using the CoMFA electrostatic and steric fields. The final models predicted the beta(1)- and beta(2)-AR potency of the compounds in the training set with high accuracy (r(2) = 0.93 and 0.86 respectively). The final beta(1)-AR model predicted the beta(1)-potencies of two out of the three test compounds, not included in the training set, with residual pA(2) values < -0.14, whereas the test compounds were not as well predicted by our final beta(2)-AR model (residual pA(2) values < -0.38).