Augmentation of cognitive function by NS9283, a stoichiometry-dependent positive allosteric modulator of α2- and α4-containing nicotinic acetylcholine receptors.

BACKGROUND AND PURPOSE: Positive allosteric modulation of α4ß2 nicotinic acetylcholine (nACh) receptors could add a new dimension to the pharmacology and therapeutic approach to these receptors. The novel modulator NS9283 was therefore tested extensively. EXPERIMENTAL APPROACH: Effects of NS9283 were evaluated in vitro using fluorescence-based Ca(2+) imaging and electrophysiological voltage clamp experiments in Xenopus oocytes, mammalian cells and thalamocortical neurons. In vivo the compound was tested in models covering a range of cognitive domains in mice and rats. KEY RESULTS: NS9283 was shown to increase agonist-evoked response amplitude of (α4)(3) (ß2)(2) nACh receptors in electrophysiology paradigms. (α2)(3) (ß2)(2) , (α2)(3) (ß4)(2) and (α4)(3) (ß4)(2) were modulated to comparable extents, but no effects were detected at α3-containing or any 2α : 3ß stoichiometry nACh receptors. Native nACh receptors in thalamocortical neurons similarly displayed DHßE-sensitive currents that were receptive to modulation. NS9283 had favourable effects on sensory information processing, as shown by reversal of PCP-disrupted pre-pulse inhibition. NS9283 further improved performance in a rat model of episodic memory (social recognition), a rat model of sustained attention (five-choice serial reaction time task) and a rat model of reference memory (Morris water maze). Importantly, the effects in the Morris water maze could be fully reversed with mecamylamine, a blocker of nACh receptors. CONCLUSIONS AND IMPLICATIONS: These results provide compelling evidence that positive allosteric modulators acting at the (α4)(3) (ß2)(2) nACh receptors can augment activity across a broad range of cognitive domains, and that α4ß2 nACh receptor allosteric modulation therefore constitutes a promising therapeutic approach to symptomatic treatment of cognitive impairment.

Selective positive modulation of the SK3 and SK2 subtypes of small conductance Ca2+-activated K+ channels.

BACKGROUND AND PURPOSE: Positive modulators of small conductance Ca(2+)-activated K(+) channels (SK1, SK2, and SK3) exert hyperpolarizing effects that influence the activity of excitable and non-excitable cells. The prototype compound 1-EBIO or the more potent compound NS309, do not distinguish between the SK subtypes and they also activate the related intermediate conductance Ca(2+)-activated K(+) channel (IK). This paper demonstrates, for the first time, subtype-selective positive modulation of SK channels. EXPERIMENTAL APPROACH: Using patch clamp and fluorescence techniques we studied the effect of the compound cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA) on recombinant hSK1-3 and hIK channels expressed in HEK293 cells. CyPPA was also tested on SK3 and IK channels endogenously expressed in TE671 and HeLa cells. KEY RESULTS: CyPPA was found to be a positive modulator of hSK3 (EC(50) = 5.6 +/- 1.6 microM, efficacy 90 +/- 1.8 %) and hSK2 (EC(50) = 14 +/- 4 microM, efficacy 71 +/- 1.8 %) when measured in inside-out patch clamp experiments. CyPPA was inactive on both hSK1 and hIK channels. At hSK3 channels, CyPPA induced a concentration-dependent increase in the apparent Ca(2+)-sensitivity of channel activation, changing the EC(50)(Ca(2+)) from 429 nM to 59 nM. CONCLUSIONS AND IMPLICATIONS: As a pharmacological tool, CyPPA may be used in parallel with the IK/SK openers 1-EBIO and NS309 to distinguish SK3/SK2- from SK1/IK-mediated pharmacological responses. This is important for the SK2 and SK1 subtypes, since they have overlapping expression patterns in the neocortical and hippocampal regions, and for SK3 and IK channels, since they co-express in certain peripheral tissues.