title: Biological actions of formoterol isomers.
abstract: Racemic beta(2) agonists, composed of equal amounts of (R)- and (S)-isomers, can display anomalous actions that compromise their effectiveness as asthma therapies. Loss of efficacy during regular use is characteristic of isoprenaline, albuterol and terbutaline and has in part been attributed to the biological effects of the (S)-isomer. This hypothesis was applied to the (R,R)- and (S,S)-isomers of formoterol. (R,R)-formoterol had 1000-times greater affinity (2.9 nm) to the human beta(2) adrenoceptor than (S,S)-formoterol (3100 nm), with receptor binding modulating intracellular cAMP levels. The minimum lethal intravenous (IV) dose was determined to be 100 mg/kg for (R,R)- and 50 mg/kg for (S,S)-formoterol, suggesting that the toxicity of (S,S)-formoterol may not be related to the binding of beta(2) adrenoceptors. In tissues pretreated with (S,S)-formoterol but not with (R,R)- or racemic formoterol contractions to high concentrations of carbachol were exaggerated. In vivo experiments with sensitized guinea pigs demonstrated that (R,R)-formoterol inhibited both histamine and antigen-induced bronchoconstriction with greater potency than (R,R/S,S)-formoterol while (S,S)-formoterol was ineffective. Metabolic radiolabeling experiments of (R,R)-, (S,S)- or (R,R/S,S)-formoterol with crude human liver phenolsulfotransferase (PST) determined the V(max)/K(m) values to be (0.151), (0.74) and (0.143), respectively. The reciprocal plot illustrates a 2-fold reduction in sulfation rate when (R,R)-formoterol is present as a single isomer. The data presented here suggest that (R,R)-formoterol binds to the beta(2) adrenoceptor and inhibits the contraction of bronchial tissues by spasmogens. However, (S,S)-formoterol exhibits properties inconsistent as an asthma therapeutic and may antagonize the actions of (R,R)-formoterol.
authors.affiliation: Sepracor Inc., 111 Locke Drive, Marlborough, MA 01752, USA. dhandley@sprecor.com
authors.forename: Dean A
authors.initials: DA
authors.lastname: Handley
authors.forename: Chris H
authors.initials: CH
authors.lastname: Senanayake
authors.forename: William
authors.initials: W
authors.lastname: Dutczak
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Benovic
authors.forename: Thomas
authors.initials: T
authors.lastname: Walle
authors.forename: Raymond B
authors.initials: RB
authors.lastname: Penn
authors.forename: H Scott
authors.initials: HS
authors.lastname: Wilkinson
authors.forename: Gerald J
authors.initials: GJ
authors.lastname: Tanoury
authors.forename: Rolf G G
authors.initials: RG
authors.lastname: Andersson
authors.forename: Fredrik
authors.initials: F
authors.lastname: Johansson
authors.forename: John
authors.initials: J
authors.lastname: Morley
mesh_terms: D000318:Adrenergic beta-Agonists / Q000378:metabolism / Q000633:toxicity*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004983:Ethanolamines / Q000378:metabolism / Q000633:toxicity*; D005260:Female; D000068759:Formoterol Fumarate; D006168:Guinea Pigs; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014132:Trachea / Q000187:drug effects
chemical_list: D000318:Adrenergic beta-Agonists; D004983:Ethanolamines; D011943:Receptors, Adrenergic, beta; D000068759:Formoterol Fumarate