title: N-desmethylclozapine (NDMC) is an antagonist at the human native muscarinic M(1) receptor.
abstract: N-desmethylclozapine (NDMC) has been reported to display partial agonism at the human recombinant and rat native M(1) mAChR, a property suggested to contribute to the clinical efficacy of clozapine. However, the profile of action of NDMC at the human native M(1) mAChR has not been reported. The effect of NDMC on M(1) mAChR function was investigated in human native tissues by assessing its effect on (1) M(1) mAChR-mediated stimulation of [(35)S]-GTPgammaS-G(q/11)alpha binding to human post mortem cortical membranes and (2) the M(1) mAChR-mediated increase in neuronal firing in human neocortical slices. NDMC displayed intrinsic activities of 46+/-9%, compared to oxo-M, at the human recombinant M(1) receptor, in FLIPR studies and 35+/-4% at rat native M(1) receptors in [(35)S]-GTPgammaS-G(q/11)alpha binding studies. In [(35)S]-GTPgammaS-G(q/11)alpha binding studies in human cortex, oxo-M stimulated binding by 240+/-26% above basal with a pEC(50) of 6.56+/-0.05. In contrast, NDMC did not stimulate [(35)S]-GTPgammaS-G(q/11)alpha binding to human cortical membranes but antagonised the response to oxo-M (2microM) showing a pK(B) of 6.8, comparable to its human recombinant M(1) mAChR affinity (pK(i)=6.9) derived from [(3)H]-NMS binding studies. In human, contrary to the rat neocortical slices, NDMC did not elicit a significant increase in M(1) mAChR-mediated neuronal firing, and attenuated a carbachol-induced increase in neuronal firing when pre-applied. These data indicate that, whereas NDMC displays moderate to low levels of partial agonism at the human recombinant and rat native M(1) mAChR, respectively, it acts as an antagonist at the M(1) mAChR in human cortex.
authors.affiliation: Neurosciences Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park (North), Harlow, Essex CM19 5AW UK.
authors.forename: David R
authors.initials: DR
authors.lastname: Thomas
authors.forename: Adeshola
authors.initials: A
authors.lastname: Dada
authors.forename: Gareth A
authors.initials: GA
authors.lastname: Jones
authors.forename: Rudolf A
authors.initials: RA
authors.lastname: Deisz
authors.forename: Sylvain
authors.initials: S
authors.lastname: Gigout
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Langmead
authors.forename: Tim D
authors.initials: TD
authors.lastname: Werry
authors.forename: Nicola
authors.initials: N
authors.lastname: Hendry
authors.forename: Jim J
authors.initials: JJ
authors.lastname: Hagan
authors.forename: Ceri H
authors.initials: CH
authors.lastname: Davies
authors.forename: Jeannette M
authors.initials: JM
authors.lastname: Watson
mesh_terms: D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003024:Clozapine / Q000031:analogs & derivatives* / Q000494:pharmacology; D054333:Drug Partial Agonism; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D019579:Neocortex / Q000187:drug effects / Q000502:physiology; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000494:pharmacology; D011485:Protein Binding; D011869:Radioligand Assay; D051381:Rats; D043643:Receptor, Muscarinic M1 / Q000819:agonists / Q000037:antagonists & inhibitors*; D011994:Recombinant Proteins / Q000819:agonists
chemical_list: D043643:Receptor, Muscarinic M1; D011994:Recombinant Proteins; C058272:norclozapine; D010095:Oxotremorine; C042743:oxotremorine M; D003024:Clozapine; D002118:Calcium