Following a lipophilicity-based hypothesis, an 8-hydroxyquinolinone 2-aminoindan derived series of beta(2)-adrenoceptor agonists have been prepared and evaluated for their potential as inhaled ultralong-acting bronchodilators. Determination of their activities at the human beta(2)-adrenoceptor receptor showed symmetrical substitution of the 2-aminoindan moiety at the 5- and 6-positions delivered the targeted intermediate potency and intrinsic-efficacy profiles relative to a series of clinical reference beta(2)-adrenoceptor agonists. Further assessment with an in vitro superfused electrically stimulated guinea-pig tracheal-strip assay established the onset and duration of action time courses, which could be rationalized by considering the lipophilicity, potency, and intrinsic efficacy of the compounds. From these studies the 5,6-diethylindan analogue indacaterol 1c was shown to possess a unique profile of combining a rapid onset of action with a long duration of action. Further in vivo profiling of 1c supported the long duration of action and a wide therapeutic index following administration to the lung, which led to the compound being selected as a development candidate.

Here we describe the pharmacologic properties of a series of clinically relevant chemoattractant receptor-homologous molecules expressed on T-helper type 2 (CRTh2) receptor antagonists, including fevipiprant (NVP-QAW039 or QAW039), which is currently in development for the treatment of allergic diseases. min 21 and 0.048 minute 21 , respectively. Importantly, the k off of QAW039 (half-life 5 14.4 minutes) was .7-fold slower than the slowest reference compound tested, AZD-1981. In functional studies, QAW039 behaved as an insurmountable antagonist of PGD 2 -stimulated [35 S]-GTPgS activation, and its effects were not fully reversed by increasing concentrations of PGD 2 after an initial 15-minute incubation period. This behavior is consistent with its relatively slow dissociation from the human CRTh2 receptor.In contrast for the other ligands tested this time-dependent effect on maximal stimulation was fully reversed by the 15-minute time point, whereas QAW039's effects persisted for .180 minutes. All CRTh2 antagonists tested inhibited PGD 2 -stimulated human eosinophil shape change, but importantly QAW039 retained its potency in the whole-blood shape-change assay relative to the isolated shape change assay, potentially reflective of its relatively slower off rate from the CRTh2 receptor. QAW039 was also a potent inhibitor of PGD 2 -induced cytokine release in human Th2 cells. Slow CRTh2 antagonist dissociation could provide increased receptor coverage in the face of pathologic PGD 2 concentrations, which may be clinically relevant.

BACKGROUND AND PURPOSEThe molecular mechanism underlying the clinical efficacy of FTY720-P is thought to involve persistent internalization and enhanced degradation of the S1P1 receptor subtype (S1P1R). We have investigated whether receptor binding kinetics and β-arrestin recruitment could play a role in the persistent internalization of the S1P1R by FTY720-P. release. CHO-S1P1/3R numbers were determined, following FTY720-P treatment using flow cytometry. EXPERIMENTAL APPROACH KEY RESULTSThe kinetic off-rate of [ 3 H]-FTY720-P from the S1P1R was sixfold slower than from the S1P3R, and comparable to [ 33 P]-S1P dissociation from S1P1/3Rs. S1P and FTY720-P stimulated [ 35 S]-GTPγS incorporation to similar degrees, but FTY720-P was over 30-fold less potent at S1P3Rs. FTY720-P stimulated a higher level of β-arrestin recruitment at S1P1Rs, 132% of the total recruited by S1P. In contrast, FTY720-P was a weak partial agonist at S1P3R, stimulating just 29% of the total β-arrestin recruited by S1P. Internalization experiments confirmed that cell surface expression of the S1P1R but not the S1P3R was reduced following a pulse exposure to FTY720-P, which is metabolically stable unlike S1P. CONCLUSIONS AND IMPLICATIONSFTY720-P and S1P activation of the S1P1R results in receptor internalization as a consequence of an efficient recruitment of β-arrestin. The combination of slow off-rate, efficacious β-arrestin recruitment and metabolic stability all contribute to FTY720-P's ability to promote prolonged S1P1R internalization and may be critical factors in its efficacy in the clinic. AbbreviationsFTY720-P, 2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol phosphate; MEM, minimal essential medium; NSB, non-specific binding; S1P, sphingosine 1-phosphate; SPA, scintillation proximity assay BJP British Journal of Pharmacology