Nootropic alpha7 nicotinic receptor allosteric modulator derived from GABAA receptor modulators

Abstract

Activation of brain alpha7 nicotinic acetylcholine receptors (alpha7 nAChRs) has broad therapeutic potential in CNS diseases related to cognitive dysfunction, including Alzheimer's disease and schizophrenia. In contrast to direct agonist activation, positive allosteric modulation of alpha7 nAChRs would deliver the clinically validated benefits of allosterism to these indications. We have generated a selective alpha7 nAChR-positive allosteric modulator (PAM) from a library of GABAA receptor PAMs. Compound 6 (N-(4-chlorophenyl)-alpha-[[(4-chloro-phenyl)amino]methylene]-3-methyl-5-isoxazoleacet-amide) evokes robust positive modulation of agonist-induced currents at alpha7 nAChRs, while preserving the rapid native characteristics of desensitization, and has little to no efficacy at other ligand-gated ion channels. In rodent models, it corrects sensory-gating deficits and improves working memory, effects consistent with cognitive enhancement. Compound 6 represents a chemotype for allosteric activation of alpha7 nAChRs, with therapeutic potential in CNS diseases with cognitive dysfunction.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Compound 6 selectively enhances wild-type human α7 nAChR-mediated currents in Xenopus oocytes. (a) Typical recording illustrating positive modulation of submaximal (EC5) nicotine-evoked currents by compound 6 at human α7 nAChRs. Pretreatments with compound 6 (30 sec) were followed by coapplication with nicotine (5 sec). Nic, nicotine. (b) Concentration–response relationships for compound 6-evoked modulation of ACh, choline, and nicotine (EC5) elicited currents at human α7 nAChRs. (c) ACh concentration–response curves in the presence or absence of compound 6 (Cmpd 6). (d) Comparison of maximal modulation evoked by compound 6 (10 μM) at α7, α4β2, α3β4, and α1β1γδ nACh; GABAA α1β2γ2L and 5-HT3A receptors. All data in each experiment are from four oocytes.

Fig. 2.

Maintenance of rapid native kinetics and desensitization after modulation by compound 6 at human α7 nAChRs expressed in Xenopus oocytes. Experiments were performed on four oocytes. (a and b) Comparison of macroscopic kinetics after positive modulation of (EC5) nicotine-evoked currents by compound 6 and PNU-120596 at concentrations displaying similar extent of modulation (a) and 10 μM (b). (c) Effect of compound 6 (Left) and PNU-120596 (Right) on a timed sequence of brief (1-sec duration) exposures to nicotine. (d) Effect of compound 6 (Left) and PNU-120596 (Right) exposures (2.5-min duration) after desensitization by a prolonged exposure to nicotine (30 sec). Cmpd 6, compound 6; PNU, PNU-120596; Nic, nicotine.

Fig. 3.

Compound 6 does not change SH-SY5Y-α7 cell viability. SH-SY5Y-α7 cells were exposed to compound 6 (Cmpd 6) (a), PNU-120596 (PNU) (b), and the positive control, 10 μM thapsigargin (10 Thaps), for 24 h. Data represent mean ± SEM; n = 4 per group. ∗, P < 0.01 compared with control; †, P < 0.01 compared with PNU-120596 (3 μM), one-way ANOVA, Bonferroni's post hoc test. M, 10μM methylcaconitine.

Fig. 4.

Normalization of sensory-gating deficits in DBA/2 mice by compound 6. Data are presented as evoked responses (Upper) of conditioning amplitude (closed circles), test amplitude (open circles), and TC ratio (Lower). Statistically significant normalization of sensory gating by compound 6 (Cmpd 6) at 0.3 mg/kg, i.v., was observed in the TC ratio. Data are the mean ± SEM; n = 8 per group. ∗, P < 0.05; ∗∗, P < 0.01, Fisher's least significant difference.

Fig. 5.

Compound 6 improves memory acquisition of rats in the eight-arm radial maze. Compound 6 (Cmpd 6) at 0.3 mg/kg, i.p., significantly increases the entries to repeat (ETR) (a and b) and percent correct performance (c and d) measures compared with vehicle controls for both individual (Left) and averaged (first six trials) (Right) trial blocks. Data are mean ± SEM; n = 6–7 per group. ∗, P < 0.05 compared with vehicle control, one-way ANOVA, Dunnett's post hoc test.