Centrally Active Allosteric Potentiators of the M4 Muscarinic Acetylcholine Receptor Reverse Amphetamine-Induced Hyperlocomotor Activity in Rats

Previous clinical and animal studies suggest that selective activators of M-1 and/or M-4 muscarinic acetylcholine receptors (mAChRs) have potential as novel therapeutic agents for treatment of schizophrenia and Alzheimer's disease. However, highly selective centrally penetrant activators of either M 1 or M 4 have not been available, making it impossible to determine the in vivo effects of selective activation of these receptors. We previously identified VU10010 [3-amino-N-(4-chlorobenzyl)-4,6-dimethylthieno[2,3-b]pyridine-2-carboxamide] as a potent and selective allosteric potentiator of M 4 mAChRs. However, unfavorable physiochemical properties prevented use of this compound for in vivo studies. We now report that chemical optimization of VU10010 has afforded two centrally penetrant analogs, VU0152099 [3-amino-N-(benzo[d][1,3]dioxol-5-ylmethyl)-4,6-dimethylthieno[2,3-b]pyridine carboxamide] and VU0152100 [3-amino-N-(4-methoxybenzyl)-4,6-dimethylthieno[2,3-b]pyridine carboxamide], that are potent and selective positive allosteric modulators of M-4. VU0152099 and VU0152100 had no agonist activity but potentiated responses of M-4 to acetylcholine. Both compounds were devoid of activity at other mAChR subtypes or at a panel of other GPCRs. The improved physiochemical properties of VU0152099 and VU0152100 allowed in vivo dosing and evaluation of behavioral effects in rats. Interestingly, these selective allosteric potentiators of M-4 reverse amphetamine-induced hyperlocomotion in rats, a model that is sensitive to known antipsychotic agents and to nonselective mAChR agonists. This is consistent with the hypothesis that M-4 plays an important role in regulating midbrain dopaminergic activity and raises the possibility that positive allosteric modulation of M-4 may mimic some of the antipsychotic-like effects of less selective mAChR agonists.