Eurcqman Journal of Plmrmacoh~.W Moh,cular PharmacohJgy Sectitm. 227 ( 19921403-4tl9 403 a:, 1992 Elsevier Science Publishers i~.V. All righls reserved 11922-41116/92/$(15.0(1 EJPMOL 911376 Atypical molecular pharmacology of a new long-acting/32-adrenoceptor agonist, TA 2005 Hans-Petcr Voss ", David Donnell ~' and Aalt Bast ~' " Departmem ~l" Pharmacochemisto'. l'~*culo' of Chemistry. Vrijc Unit cr.~iteit. Amsterdam. Netherlamls. and l. Medical l)¢7~urtmcnt. 3M th'alth ()m' kt~L. I.oto.,hhorot~.~h. UK Received 211 M~!y 1992, revised MS received !5 July IO'42. accepted I I August 1992 The molecular pharmacology of a new putative long-acting bronchodilator TA 211115 (8-hydmxy-5-[( 1R)- l-hydroxy-2-[N-[( 1R)- 2-(p-methoxy-phenyl)-l-methylethyl]amino]ethyl]carbostyril hydmehloride) has been compared with lhat of lhe reference com- pounds isoprenaline ~;nd salbutamol in bolh mcthacholine (3 × ill " M) precontracted guinea pig lracheal smooth muscle relaxation and in bovine mlpezium muscle binding e×r~eriments. TA 2005 appeared very potent compared will1 isoprenalinc and salbutamol (pD 2 values of ~).20 vs. 7.65 and 7.111 respectively). For isoprenaline and salbutamol a shallow displacement curve was observed and addition of the non-hydrolysablc GTP analogue guanylyl-imidudiphosphatc (GppNHp) gave a rightward shift (pKd.hig h and pKd,I. ~ values of 7.3 and 6.1 vs. 7.(1 and 5.4 rcspcctivcly}. F~r TA 2005 a slecp displacement curve was found wilh only one binding slate even wilhot:! GppNHp (PKd.higl, value of 8.2). The long duration of action of TA 2005 might be explained by tight binding of lifts compound to the /3:-adrcnoccptor. Thc e.'-:tenl of tight binding for TA 2()(}5 was extremely large, The molecular basis of the tight agonist binding phenomenon f~r TA 2~1a5 seems t:; be of difl~rem origin than for isoprcnalinc. It is l~ypolhesizcd Ihal a different mechanism of activation of the ~2-adrenoceptor may be involved for TA 2(1115. : cm~ceplor agonists (hmg acting); Ternary complex; Tight agonist binding; Tracheal smoolh muscle relaxation 1, Introduction /32-Adrenoceptor agonists form an important class of therapeutic agents in asthma. The drug of interest in this study, TA 20115 (Tanabe Seiyaku Co., Osaka, Japan), is chemically related to both procatero! and formoterol, two potent and long-acting /3,-adrenocep- tor stimulants. The bronchodilating activity of TA 2005 is stronger than observed for these two compounds (H. Kikkawa et al., 1991a, b), The chemical name of TA 211{15 is 8-hydroxy-5-[(l R)-l-hydrow-2-[N-[(1R)-2-(p- methoxy-phcnyl)-I -methylethyl]amino]ethyl]carbostyri! hydrochloride. Its structure is displayed in fig. 1. The molecular mechanism of action of TA 211115was studied to help elucidate the reasons for its long dura- tion of action. Isoprenalinc, a short-acting non-selec- tive /3-adrenoeeptor agonis|, was used as a reference compound. For reasons of comparison salbulamol, a /3-adrenoccptor agonist with higher selectivity for the ('orrt.'spt~llderlc¢ hi: llarls-Peler V(lss, I)epartnl~.qt[ ()f Pharmaco- cllemislry. Faculty ~lf ('hcmisll~", Vrij¢ tlniversi|eil, tie Boclcktan 11!83. 1(181 IIV Amslcrdam. Ncthcrklnds. Tel. 31-20-548.29SS; Fa× 3 f -2114~46. ] 479. /3:-adrenoceptor, was also incorporated in some experi- ments. Some hypothese,'; on the long duratk,n of action of the compound TA 211115 were considered. Firstly. this property might reside in the interactkm of the com- pound with tile t3-adrenoceptor. Secondly. tile com- pound might possess a phosphodiesterase inhibiting activity in addition to ~-adrenoccptor activation. A third possibility might be in the metabolism of the compound. The main objective of this study was Io investigate the drug-receptor interaction, including the coupling of tile drug-reccptor complex to the GTP- binding protein (G-protein), as an aid to test the firs1 hypothesis. om~ A .~ .-'~ OH Fig. 1. The slJucturc of TA 2111}5,