RG3487, a Novel Nicotinic alpha 7 Receptor Partial Agonist, Improves Cognition and Sensorimotor Gating in Rodents

Neuronal nicotinic alpha 7 acetylcholine receptors (alpha 7nAChRs) are expressed primarily in the brain and are implicated in modulating many cognitive functions (e.g., attention, working and episodic memory). Not surprisingly, much effort has been committed to the development of molecules acting at alpha 7nAChRs as potential therapies for a variety of central nervous system diseases (e.g., Alzheimer's). N-[(3S)-1-azabicyclo[2.2.2] oct-3-yl]-1H-indazole-3-carboxamide hydrochloride (RG3487) binds potently to the human alpha 7nAChR (K(i) = 6 nM), in which it acts as a partial agonist (63-69% of acetylcholine) as assessed by whole-cell patch-clamp recordings in both oocytes and QM7 cell lines. RG3487 activates human alpha 7nAChRs with an EC(50) of 0.8 mu M (oocytes) and 7.7 mu M (QM7 cells). RG3487 also exhibits antagonist properties at the serotonin 3 receptor [IC(50) = 2.8 nM (oocytes), 32.7 nM (N1E-115 cells)]. In vivo, RG3487 improved object recognition memory in rats after acute [minimally effective dose (MED) 1.0 mg/kg p.o.] or repeated (10 day) administration at brain and plasma concentrations in the low-nanomolar range. Spatial learning deficits in age-impaired rats were reversed after RG3487 administration (MED: 0.03 mg/kg i.p.) as evaluated in the Morris water maze task. In the prepulse inhibition (PPI) of startle model of sensorimotor gating, RG3487 improved apomorphine-induced deficits in PPI performance (MED: 0.03 mg/kg i.p.) and reversed phencyclidine-induced impairments in an attentional set-shifting model of executive function (MED: <= 0.03 mg/kg i.p.). Cumulative evidence from these studies indicates RG3487 is a novel and potent alpha 7nAChR partial agonist that improves cognitive performance and sensorimotor gating.