DREADD agonist 21 dihydrochloride is a potent agonist of human muscarinic acetylcholine M3 receptors (hM3Dq) with an EC50 of 1.7 nM [1].

DREADD agonist 21 acts as a highly potent and selective agonist for human muscarinic acetylcholine M3 receptors (hM3Dq), with no activation observed on the native human M3 receptor (hM3). Exhibiting an EC50 of 1.7 nM for hM3Dq, it demonstrates preferential selectivity, being 3.5 times more selective for hM3Dq over the H1 histamine receptor, 40 times over the 5HT2A serotonin receptor, 100 times over the 5HT2C serotonin receptor, and 165 times over the α1A adrenergic receptor. Furthermore, DREADD agonist 21 showcases high binding affinities to the aforementioned receptors, with Ki values of 66 nM for 5HT2A, 170 nM for 5HT2C, 280 nM for α1A, and 6 nM for H1. It also effectively activates the hM1Dq, hM3Dq, and hM4Di receptors, demonstrating considerable efficacy in Chinese hamster ovary (CHO) cells transfected with these receptors, and holds high selectivity and potency as an agonist for muscarinic DREADDs, evidenced by its compelling performance in pERK assays with a pEC50 of 6.54 for hM1Dq and 7.77 for hM4Di.

DREADD agonist 21, administered intraperitoneally (i.p.) at dosages of 0.3, 1.0, and 3.0 mg/kg, effectively activates the neuronal hM3Dq in mice [2]. It exhibits outstanding bioavailability, pharmacokinetic properties, and brain penetrability. Furthermore, at concentrations of 0.1, 1, and 10 mg/kg (i.p.), DREADD agonist 21 demonstrates high plasma and brain protein binding efficiencies in mice, at 95.1% and 95% respectively [2].