RT Journal Article
SR Electronic
T1 Characterization of a Novel M<sub>1</sub> Muscarinic Acetylcholine Receptor Positive Allosteric Modulator (PAM) Radioligand, [<sup>3</sup>H]PT-1284
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP mol.116.104737
DO 10.1124/mol.116.104737
A1 Deborah L Smith
A1 Jennifer E Davoren
A1 Jeremy R Edgerton
A1 John T Lazzaro
A1 Che-Wah Lee
A1 Sarah Neal
A1 Lei Zhang
A1 Sarah Grimwood
YR 2016
UL http://molpharm.aspetjournals.org/content/early/2016/07/05/mol.116.104737.abstract
AB Selective activation of the M1 muscarinic acetylcholine receptor (mAChR) via a positive allosteric modulator (PAM) is a new approach for the treatment of the cognitive impairments associated with schizophrenia and Alzheimer's disease. Herein, we describe the characterization of an M1 PAM radioligand, 8-((1S,2S)-2-hydroxycyclohexyl)-5-((6-(methyl-t3)pyridin-3-yl)methyl)-8,9-dihydro-7H-pyrrolo[3,4-h]quinolin-7-one ([3H]PT-1284), as a tool for characterizing the M1 allosteric binding site, as well as profiling novel M1 PAMs. 8-((1S,2S)-2-hydroxycyclohexyl)-5-((6-meth ylpyridin-3-yl)methyl)-8,9-dihydro-7H-pyrrolo[3,4-h]quinolin-7-one (PT-1284 (1)) was shown to potentiate acetylcholine (ACh) in a M1 FLIPR functional assay (EC50: 36 nM), and carbachol in a hippocampal slice electrophysiology assay (EC50: 165 nM). PT-1284 (1) also reduced the concentration of ACh required to inhibit [3H]N-methylscopolamine ([3H]NMS) binding to M1, left-shifting the ACh Ki approximately 19-fold at 10 μM. Saturation analysis of a human M1 mAChR stable cell line showed that [3H]PT-1284 bound to M1 mAChR in the presence of 1 mM ACh with Kd: 4.23 nM; Bmax: 6.38 pmol/mg protein. M1 selective PAMs were shown to inhibit [3H]PT-1284 binding in a concentration-responsive manner, while M1 allosteric and orthosteric agonists showed weak affinity (&gt;30 μM). A strong positive correlation (R2= 0.86) was found to exist between affinity values generated for nineteen M1 PAMs in the [3H]PT-1284 binding assay and the EC50 values of these ligands in a FLIPR functional potentiation assay. These data indicate that there is a strong positive correlation between M1 PAM binding affinity and functional activity and that [3H]PT-1284 can serve as a tool for pharmacological investigation of M1 mAChR PAMs.