No abstract

KCNQ2 (Kv7.2) and KCNQ3 (Kv7.3) are voltage-gated K ϩ channel subunits that underlie the neuronal M current. In humans, mutations in these genes lead to a rare form of neonatal epilepsy (Biervert et al., 1998;Singh et al., 1998), suggesting that KCNQ2/Q3 channels may be attractive targets for novel antiepileptic drugs. In the present study, we have identified the compound N- (6-chloro-pyridin-3-yl)-3,4-difluoro-benzamide (ICA-27243) as a selective activator of the neuronal M current and KCNQ2/Q3 channels. In SH-SY5Y human neuroblastoma cells, ICA-27243 produced membrane potential hyperpolarization that could be prevented by coadministration with the M-current inhibitors 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone dihydrochloride (XE-991) and linopirdine. ICA-27243 enhanced both 86 Rb ϩ efflux (EC 50 ϭ 0.2 M) and whole-cell currents in Chinese hamster ovary cells stably expressing heteromultimeric KCNQ2/Q3 channels (EC 50 ϭ 0.4 M). Activation of KCNQ2/Q3 channels was associated with a hyperpolarizing shift of the voltage dependence of channel activation (V 1/2 shift of Ϫ19 mV at 10 M). In contrast, ICA-27243 was less effective at activating KCNQ4 and KCNQ3/Q5 and was selective over a wide range of neurotransmitter receptors and ion channels such as voltagedependent sodium channels and GABA-gated chloride channels. ICA-27243 (1-10 M) was found to reversibly suppress seizure-like activity in an ex vivo hippocampal slice model of epilepsy and demonstrated in vivo anticonvulsant activity (ED 50 ϭ 8.4 mg/kg) in the mouse maximal electroshock epilepsy model. In conclusion, ICA-27243 represents the first member of a novel chemical class of selective KCNQ2/Q3 activators with anticonvulsant-like activity in experimental models of epilepsy.

A series of phthalimide and isoindolinone derivatives bridged to 4-(1,2-benzisothiazol-3-yl)-1-piperazinyl was prepared. The compounds were evaluated in vitro at dopamine D2 and serotonin 5-HT1a and 5-HT2 receptors and in vivo for their ability to antagonize the apomorphine-induced climbing response in mice. The effects of bridge length and conformation on the biological activity of these potential antipsychotic agents are discussed. A four-carbon spacer provided optimal activity within the two homologous series. Conformational investigations of the lead compound, isoindolinone 2, were conducted in an attempt to account for the superior activity observed for the butyl derivatives. On the basis of NMR and molecular modeling studies, two types of folded structures were proposed and several conformationally restrained analogues were synthesized. In general, restrictions incorporated within the linking bridge were detrimental to activity.

Apomorphine disruption of prepulse inhibition (PPI) has been proposed as an animal model of sensorimotor gating deficits exhibited by schizophrenics. The effects of apomorphine on PPI of the acoustic startle reflex in male rats of Wistar and CD (Sprague-Dawley derived) strains were compared under identical test conditions. In Wistar rats, subcutaneous administration of 0.25-1.0 mg/kg apomorphine blocked PPI without affecting startle amplitude. In CD rats, apomorphine (0.3-3.0 mg/kg, SC) had no effect on PPI, but increased startle amplitude. Therefore, choice of rat strain is an important factor in the design of experiments studying apomorphine effects on PPI.

Openers or activators of neuronal KCNQ2/Q3 potassium channels decrease neuronal excitability and may provide benefit in the treatment of disorders of neuronal excitability such as epilepsy. In the present study, we evaluate the effects of ICA-27243 [N-(6-chloro-pyridin-3-yl)-3,4-difluoro-benzamide], an orally bioavailable, potent, and selective KCNQ2/Q3 opener, in a broad range of rodent seizure models. ICA-27243 was effective against maximal electroshock (MES) and pentylenetetrazole (PTZ)-induced seizures in both rats (MES, ED 50 ϭ 1.5 mg/kg p.o.; PTZ, ED 50 ϭ 2.2 mg/kg p.o.) and mice (MES, ED 50 ϭ 8.6 mg/kg p.o.; PTZ, ED 50 ϭ 3.9 mg/kg p.o.) in the rat amygdala kindling model of partial seizures (full protection from seizure at 9 mg/kg p.o.) and in the 6-Hz model of psychomotor seizures in mice (active at 10 mg/kg i.p.). Antiseizure efficacy in all models was observed at doses significantly less than those shown to effect open-field locomotor activity (rat ED 50 ϭ 40 mg/kg p.o.) or ability to remain on a Rotorod (no effect in rat at doses up to 100 mg/kg p.o.). There was no evidence of cognition impairment as measured in the Morris water maze in the rat (10 and 30 mg/kg p.o.), nor was there evidence of the development of tolerance after multiple doses of ICA-27243. Our findings suggest that selective KCNQ2/Q3 opening activity in the absence of effects on KCNQ3/Q5 or GABA-activated channels may be sufficient for broad-spectrum antiepileptic activity in rodents.KCNQ2-5 (Kv7.2-7.5) voltage-dependent potassium channels are potentially attractive targets for novel antiepileptic drugs. These channels are expressed at high levels in the brain, including regions linked to seizure disorders, such as cortex, hippocampus, and thalamus. They represent the molecular correlate of the neuronal M current