Two dimeric analogs of the muscarinic acetylcholine receptor (mAChR) agonist phenylpropargyloxy-1,2,5-thiadiazole-quinuclidine (NNC 11-1314) were synthesized and pharmacologically evaluated. In radioligand binding assays on Chinese hamster ovary (CHO) cell membranes expressing the individual human M1 to M5 mAChR subtypes, both dimers [(3S)-1,4-bis-(3-[(3-azabicyclo[2.2.2]octanyl)-1,2,5-thiadiazol-4-yloxy] -1-propyn-1-yl) benzene,2-L-(+)-tartrate (NNC 11-1607) and (3S)-1,3-bis-(3-[(3-azabicyclo[2.2.2]octanyl)-1,2,5-thiadiazol-4- yloxy]-1-propyn-1-yl)benzene,2-L-(+)-tartrate (NNC 11-1585)] exhibited higher binding affinities than the monomeric NNC 11-1314. Only NNC 11-1585, however, displayed significant selectivity for the M1 and M2 mAChRs relative to the other subtypes. Although binding studies in rat brain homogenates supported the selectivity profile of NNC 11-1585 observed in the CHO membranes, rat heart membrane experiments revealed complex binding behavior for all three agonists that most likely reflected differences in species and host cell environment between the heart and CHO cells. Subsequent functional assays with phosphatidylinositol hydrolysis revealed that all three novel ligands were partial agonists relative to the full agonist oxotremorine-M at the CHO M1, M3, and M5 mAChRs, with NNC 11-1607 displaying the highest functional selectivity. In the CHO M2 and M4 mAChR cells, agonist-mediated effects on forskolin-stimulated cAM P accumulation were characterized by bell-shaped concentration-response curves, with the exceptions of NNC 11-1607, which had no discernible effects at the M2 mAChR, and NNC 11-1585, which could only inhibit cAMP accumulation at the M4 mAChR. Thus, we identified NNC 11-1607 as a novel functionally selective M1/M4 mAChR agonist. Our data suggest that dimerization of mAChR agonists is a viable approach in designing more potent and functionally selective agonists, as well as in providing novel tools with which to probe the nature of agonism at these receptors.
|Number of pages||9|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|Publication status||Published - 29 Aug 2001|