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Activation of muscarinic subtype 3 (M3) muscarinic cholinergic receptors (mAChRs) increases airway tone, whereas its blockade improves lung function and quality of life in patients with pulmonary diseases. The present study evaluated the pharmacological properties of a novel mAChR antagonist, GSK573719 (4-[hydroxy(diphenyl)methyl]-1-{2-[(phenylmethyl)oxy]ethyl}-1-azoniabicyclo[2.2.2]octane; umeclidinium). The affinity (Ki) of GSK573719 for the cloned human M1-M5 mAChRs ranged from 0.05 to 0.16 nM. Dissociation of [(3)H]GSK573719 from the M3 mAChR was slower than that for the M2 mAChR [half-life (t1/2) values: 82 and 9 minutes, respectively]. In Chinese hamster ovary cells transfected with recombinant human M3 mAChRs, GSK573719 demonstrated picomolar potency (-log pA2 = 23.9 pM) in an acetylcholine (Ach)-mediated Ca(2+) mobilization assay. Concentration-response curves indicate competitive antagonism with partial reversibility after drug washout. Using isolated human bronchial strips, GSK573719 was also potent and showed competitive antagonism (-log pA2 = 316 pM) versus carbachol, and was slowly reversible in a concentration-dependent manner (1-100 nM). The time to 50% restoration of contraction at 10 nM was about 381 minutes (versus 413 minutes for tiotropium bromide). In mice, the ED50 value was 0.02 μg/mouse intranasally. In conscious guinea pigs, intratracheal administration of GSK573719 dose dependently blocked Ach-induced bronchoconstriction with long duration of action, and was comparable to tiotropium; 2.5 μg elicited 50% bronchoprotection for >24 hours. Thus, GSK573719 is a potent anticholinergic agent that demonstrates slow functional reversibility at the human M3 mAChR and long duration of action in animal models. This pharmacological profile translated into a 24-hour duration of bronchodilation in vivo, which suggested umeclidinium will be a once-daily inhaled treatment of pulmonary diseases.

The purpose of the present study was to examine the tissue selectivity of several [Arg1-D-Phe7]-substituted analogs of bradykinin. Unlike D-Arg-[Hyp3-D-Phe7]-bradykinin (NPC567), which antagonizes bradykinin-induced contractions both in rat isolated uterus and guinea pig ileum, [D-Nal1-Thi5,8-D-Phe7]-bradykinin (NPC573) was active only in uterine smooth muscle. Binding studies revealed that, unlike several [D-Phe7]-substituted analogs, including NPC567, NPC573 competed with radiolabeled bradykinin neither at receptors in uterus nor ileum. Moreover, no [Arg1-D-Phe7]-substituted analog competed with bradykinin binding in guinea pig ileum, suggesting that these agents, which inhibit uterine but not ileal contractions to bradykinin, may not be bradykinin receptor antagonists. NPC573 inhibited [Arg8]-vasopressin-induced contraction of the uterus more potently than it did bradykinin, although NPC573 (and other [Arg1-D-Phe7]-substituted analogs tested) did not inhibit binding of a vasopressin antagonist either in uterus or liver membranes. We therefore suggest that [Arg1-D-Phe7]-substituted analogs of bradykinin inhibit contractions of uterine smooth muscle by a mechanism other than receptor antagonism. In addition, the tissue selectivity of these agents suggests that the mechanisms underlying bradykinin's contractile effect in uterus are different than in intestinal smooth muscle.