Structure-affinity profile of 8-hydroxycarbostyril-based agonists that dissociate slowly from the β2-adrenoceptor

Abstract

Several carbostyril-based beta-agonists have been shown to bind tightly to and slowly dissociate from the beta2-adrenoceptor (beta2AR). In the present study, the structural features of 8-hydroxy-5-[2-[(1-phenyl-2-methylprop-2-yl)amino]-1-hydroxyethyl] -carbostyril (11a) which contribute to its binding properties at the beta2AR were investigated using a series of synthesized analogs. The k(off), estimated by the rate of cAMP decline in DDT1 MF-2 (DDT) cells with a reduced receptor density, Ki and ligand-induced receptor reductions were determined. All of the derivatives stimulated cAMP accumulation in DDT cells in the sub to mid nanomolar range and elicited the same maximal stimulation as (-)isoproterenol. Derivatives of 11a with side chain N-substitutions comprising 2-methylbutyl, phenylethyl and isopropyl had higher k(off)-values and lower affinities as compared to 11a. Increasing the number of methylenes between the side chain tertiary alpha carbon and phenyl from 1 in 11a to 3 or reducing the number to 0 also resulted in derivatives with higher k(off)- and Ki-values. In addition, replacement of the 8-hydroxycarbostyril nucleus of 11a with catechol reduced the affinity of the compound for the beta2AR by 48-fold and increased its k(off). Only those derivatives with the lowest k(off)-values induced a decrease in the receptor density of DDT cell membranes following a preincubation and extensive washing. The data show that the 8-hydroxycarbostyril nucleus in conjunction with substitutions on the tertiary alpha carbon of the side chain and positioning of the phenyl group are important characteristics determining the high affinity and slow dissociation of 11a from the beta2AR.

Slow receptor dissociation is not a key factor in the duration of action of inhaled long‐acting β2‐adrenoceptor agonists

“…These studies were designed to more closely mimic in vivo conditions, allowing better extrapolation to the clinical situation. Indirect isoprenaline k off measurements have been made previously in HBSS using the rate of cAMP decline following the addition of a high concentration of propranolol, as a measure of k off (Deyrup et al ., 1999). The value of 5.5 min −1 was in agreement with the reported k off (4 min −1 ) for isoprenaline based on recovery of a chemo attractant‐mediated cellular response inhibited by β 2 ‐adrenoceptor activation in neutrophils (Mueller et al ., 1988).…”

“…Using this method, isoprenaline and adrenaline produced off‐rates of 4.68 min −1 and 7.20 min −1 , respectively, following displacement by alprenolol (Devanathan et al ., 2004). These values, as well as the values obtained for isoprenaline in functional studies (Mueller et al ., 1988; Deyrup et al ., 1999), agree closely with the value of 3.06 min −1 for isoprenaline and 5.12 min −1 for adrenaline obtained in our competition kinetic studies.…”

“…It has been demonstrated that slow dissociation kinetics plays an important role in the duration of drug action of inhaled muscarinic antagonists (Disse et al ., 1999). In the case of β‐adrenoceptors, several slowly dissociating antagonists from this receptor have been described (Lucas et al ., 1979; De Blasi et al ., 1988; Pauwels et al ., 1988; Keith et al ., 1989; Doggrell, 1990; Deyrup et al ., 1999). In keeping with their slow dissociation, several of these antagonists, including bornaprolol (FM 24) and ICI 147,798, have been shown to have a relatively long duration of action in vivo that is independent of their plasma levels (Le Fur et al ., 1980; Keith et al ., 1989).…”

Lead Generation Approaches Delivering Inhaled β 2 ‐Adrenoreceptor Agonist Drug Candidates

“…• High agonist intrinsic activity (IA), resulting from high receptor occupancy leading to maintenance of the pharmacological effect [11]. • Receptor kinetics, in which slow receptor off-rates have been proposed to lead to enhanced duration of action in both inhaled β 2 AR agonists and inhaled muscarinic M 3 receptor antagonists [12].…”

Photocytotoxicity of the Fluorescent Nonsteroidal Androgen Receptor Ligand TDPQ†

“…Another quinoline derivative showing close resemblance to TDPQ is carbostyril 151 (C151, Scheme 1). Carbostyrils (also referred to as 1‐aza coumarins) are a class of compounds showing a wide range of interesting biological and pharmacological activities (5), including beta‐adrenergic (6–12) and neuronal mediation (13). Although the biological properties of carbostyrils may manifest themselves in a different manner from TDPQ, C151 is a fluorescent molecule with an identical aromatic core and –CF 3 moiety at the same position (see formulas in Scheme 1).…”