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Several novel N-type voltage sensitive calcium channel blockers showed high affinity in the IMR32 assay and efficacy in the anti-writhing model. Herein, we describe the design, synthesis, SAR studies, biological data, physicochemical properties and pharmacokinetics of this 4-piperidinylaniline series.

Exploration of the SAR around the leucine side chain in a series of N,N-dialkyldipeptidylamines with potent functional activity at N-type VSCC is presented. A novel analog is disclosed which possesses improved aqueous solubility, in vivo activity in an audiogenic seizure model, and reversible blockade in electrophysiological assays.

Several polyamines have been shown to interact with a site on the N-methyl-D-aspartate (NMDA) receptor that regulates the binding of open channel blockers. Spermine (SP) and spermidine (SD), polyamine agonists, enhanced binding of open channel blockers, whereas arcaine (ARC), diethylenetriamine (DET), and putrescine (PUT), polyamine antagonists, reduced the polyamine enhancement of open channel blocker binding. We previously showed that SP had multiple actions on NMDA receptor single-channel currents that underlie its effect on whole-cell NMDA receptor current. At high concentrations, SP produced a voltage-dependent decrease in NMDA receptor single-channel conductance and average open time. In the present study, another polyamine agonist (SD) produced a similar reduction of NMDA receptor single-channel conductance at higher concentrations. The polyamine antagonists (ARC, DET, and PUT), however, produced a voltage-dependent reduction in NMDA receptor whole-cell currents and reductions in single-channel conductance and average open time, even in the absence of polyamine agonists. The rank order of potency for reduction of NMDA receptor single-channel conductance by polyamines was ARC greater than SP greater than SD greater than PUT = DET, a rank order similar to that for the inhibitory actions of polyamines in receptor binding assays and for the effects of the antagonists on NMDA receptor whole-cell currents. The polyamine antagonist DET did not block the reduction of single-channel conductance by the polyamine agonist SP. In fact, the effects of SP and DET on single-channel conductance were additive. DET also showed a variable enhancement of NMDA receptor whole-cell currents in some neurons, suggesting polyamine agonist-like properties. These results are not consistent with the standard pharmacological profile for agonists and antagonists acting at the same site. Potential mechanisms for the effects of the polyamines on single-channel conductance are discussed.

Spermine potentiates the action of N-methyl-D-aspartate (NMDA) at micromolar concentrations but is less effective at millimolar concentrations. In cultured cortical neurons we demonstrate that spermine enhances NMDA receptor currents in a unique manner. At low concentrations (1-10 microM) spermine enhances NMDA receptor current by increasing channel opening frequency, and at higher concentrations (greater than 10 microM) it produces, in addition, a voltage-dependent decrease in channel amplitude and average open time that limits its enhancing action. It is likely that these two actions of spermine, due to differences in concentration and voltage dependence, are mediated by independent sites on the NMDA receptor complex.

Recent in vitro and in vivo experiments have suggested that excitatory amino acid antagonists, particularly those active at the N-methyl-D-aspartate receptor subtype, are effective in ameliorating ischemic injury due to their antiexcitotoxic activity. However, these drugs are also potent and effective in vivo anticonvulsants. The present experiments compared the noncompetitive N-methyl-D-aspartate antagonists phencyclidine and MK-801 with the anticonvulsant phenytoin in a model of focal brain ischemia. Fisher F-344 rats were subjected to tandem occlusion of the middle cerebral and ipsilateral common carotid arteries under halothane anesthesia. Compounds were administered intravenously 30 minutes and 24 hours after arterial occlusion; infarct size was assessed at 48 hours after occlusion. Phencyclidine had no effect on infarct volume at 1 mg/kg, significantly reduced (by 36%) infarct volume at 3 mg/kg, and produced a nonsignificant 26% decrease at 10 mg/kg. The more potent and selective noncompetitive antagonist MK-801 reduced (by 32%) infarct volume significantly at 0.1 mg/kg, produced a nonsignificant 23% decrease at 0.3 mg/kg, and had no effect at 0.5 mg/kg. Phenytoin, which is not a glutamate antagonist, reduced the infarct volume by 45% at 28 mg/kg. A single dose of phenytoin (28 mg/kg) administered 30 minutes after occlusion was neuroprotective, but delaying drug administration for more than 2 hours was ineffective. These data suggest that blockade of the N-methyl-D-aspartate receptor is effective in reducing the infarct size after focal cerebral ischemia. The neuroprotective activity of phenytoin suggests that this may be related to the common anticonvulsant action.