Regional binding of 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP) to muscarinic receptors in rat brain and comparative analysis of minimum energy conformations.
The binding of the muscarinic antagonist 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP), which has been suggested as an M3-selective antagonist in peripheral tissues, was examined through quantitative autoradiographic techniques in brain. The ability of 4-DAMP to displace [3H](R)-quinuclindinyl benzilate (QNB) binding to rat brain sections was compared with the known distribution of M1 and M2 muscarinic receptor subtypes as measured previously with pirenzepine and AF-DX 116 (Messer et al., 1989a). 4-DAMP displayed a high affinity for [3H](R)-QNB binding sites in rat brain sections. Analysis of 4-DAMP binding to various brain regions revealed heterogeneous binding profiles, suggesting an interaction with multiple receptor sites. Quantification of the autoradiograms indicated that 4-DAMP bound with the highest affinity to muscarinic receptors in the midline thalamus (IC50 values < 30 nM), and had a slightly lower affinity for hippocampal receptors (IC50 values between 30 and 46 nM). 4-DAMP also displayed a lower affinity for cortical receptors with IC50 values between 30 and 50 nM. The binding profile of the putative M3 muscarinic antagonist did not exhibit a marked selectivity for any single region of brain. The data suggest that whereas 4-DAMP may be selective for M3 receptors in peripheral tissues, it has limited selectivity in the CNS. Minimum energy conformations for 4-DAMP were calculated using molecular mechanics calculations. 4-DAMP displayed two global minimum energy conformations, differing in the relative position of the piperidine ring with respect to the aromatic rings. The minimum energy conformations of 4-DAMP were compared with conformations generated for pirenzepine (Messer et al., 1989a). The lowest energy conformation of 4-DAMP was superimposable on the lowest energy conformation of pirenzepine (RMS = 0.297 A). It is suggested that the conformations available to 4-DAMP permit binding to several muscarinic receptors in the CNS.
Collins
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Department of Medicinal & Biological Chemistry, College of Pharmacy, University of Toledo, OH 43606.
Smith
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DA
Messer
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WS
D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D008968:Molecular Conformation; D010880:Piperidines / Q000737:chemistry* / Q000378:metabolism*; D010890:Pirenzepine / Q000737:chemistry / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D051381:Rats; D011976:Receptors, Muscarinic / Q000378:metabolism*; D014018:Tissue Distribution
D010880:Piperidines; D011976:Receptors, Muscarinic; D010890:Pirenzepine; D011813:Quinuclidinyl Benzilate; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium