Novel bisbenzamidines and bisbenzimidazolines as noncompetitive NMDA receptor antagonists.

A series of novel bisbenzamidines and bisbenzimidazolines with different linkers connecting the aromatic groups was tested in vitro for NMDA receptor antagonist activity. IC50 values for these compounds ranged from 1.2 to >200 microM. The bisbenzamidine with a homopiperazine ring as the central linker was found to be the most potent NMDA receptor antagonist among all the pentamidine analogues tested so far.

Characterization of the effects of polyamines on [125I]MK-801 binding to recombinant N-methyl-D-aspartate receptors.

The assembly of heterogeneous populations of native N-methyl-D-aspartate receptors results in receptors with multiple pharmacological properties dependent on subunit combinations. Using stably transfected ML(tk-) mouse fibroblasts expressing N-methyl-D-aspartate R1a and either R2A or R2B, we evaluated polyamine effects on [125I]dizocilpine (MK-801) binding to determine subunit-specific pharmacological characteristics. The polyamine agonists spermine and spermidine produced biphasic concentration response curves in rat brain membrane: low concentrations (<100 microM) enhanced [125I]MK-801 binding and higher concentrations (>100 microM) inhibited binding. Polyamine agonists did not affect [125I]MK-801 binding in NR1a/NR2A, whereas spermine and spermidine did produce enhancement, and, at higher concentrations, inhibition of binding in NR1a/NR2B. The polyamine 1,5-(diethylamino)piperidine is thought to be selective for the agonist polyamine site and only enhanced [125I]MK-801 binding in brain membranes (EC50 = 9.6 microM). However, 1,5-(diethylamino)piperidine inhibited [125I]MK-801 binding (IC50 = 8.0 microM) in NR1:NR2A receptors and produced a small increase followed by a modest decrease in binding to NR1a/NR2B receptors. In brain membranes, the polyamine antagonist arcaine inhibited [125I]MK-801 binding (IC50 = 4.6 microM). Similar effects were demonstrated in both NR1:NR2A and NR1:NR2B receptors (IC50 = 8. 4 and 14.1 microM, respectively) and agonists decreased the affinity of arcaine in both receptor preparations. These results suggest that the stimulatory effects of polyamines on recombinant receptors are influenced by the NR2 subunit, and that NR1:NR2A does not contain a positive modulatory site. However, the inhibitory effects of polyamine antagonists are similar in both subunit combinations. Furthermore, native NMDA receptors pharmacology cannot be modeled by simple NR1:NR2A or NR1:NR2B combinations.

Complex polyamine effects on [3H]MDL 105,519 binding to the NMDA receptor glycine site.

Several studies have suggested that polyamines modulate the interaction of glycine with the NMDA receptor. We have further investigated the effects of polyamines using the NMDA receptor glycine site antagonist [(E)-3-(2-phenyl-2-carboxyethenyl)-4,6-dichloro-1H-indole-2-carbox ylic acid] ([3H]MDL 105,519). [3H]MDL 105,519 binding assays were performed using well washed membranes prepared from frozen rat brains. The polyamines spermine and spermidine increased the fraction of non-specific binding (determined by the addition of 1 mM glycine) in the [3H]MDL 105,519 binding assay from 40-60% when spermine or spermidine concentration was increased from 1 to 100 microM. Polyamine agonists spermine, spermidine and 1,5-(diethylamino)piperidine (30 microM) did not have a significant effect on displacement of [3H]MDL 105,519 binding by glycine or glycine site antagonists. Similarly, the polyamine antagonist arcaine did not have a significant effect on displacement of [3H]MDL 105,519 binding by glycine or glycine site antagonists. However, spermidine significantly depressed the potency of MDL 105,519 in displacing [3H]dizocilpine binding. These data suggest that [3H]MDL 105,519 may preferentially bind to a polyamine insensitive form of the NMDA receptor.

Aromatic analogs of arcaine inhibit MK-801 binding to the NMDA receptor.

Aromatic analogs of arcaine were shown to have inhibitory effects on the binding of the channel blocking drug [3H]MK-801 to the NMDA receptor complex. The most potent compound of the series was an N,N'-bis(propyl)guanidinium which inhibited [3H]MK-801 binding with an IC50 of 0.58 microM and an IC50 of 12.17 microM upon addition of 100 microM spermidine. The increase in IC50 upon addition of spermidine suggests competitive antagonism between the inhibitor and spermidine at the arcaine-sensitive polyamine site of the NMDA receptor complex.

Synthesis of a potent wide-spectrum serotonin-, norepinephrine-, dopamine-reuptake inhibitor (SNDRI) and a species-selective dopamine-reuptake inhibitor based on the gamma-amino alcohol functional group.

A series of gamma-amino alcohols were synthesized and screened for reuptake inhibition and noncompetitive NMDA antagonism. Compound (+/-)-3f simultaneously and potently inhibits reuptake of 5-HT, NE, and DA, representing a potential wide-spectrum reuptake inhibitor antidepressant. In addition, comparative rat and human studies uncovered a species-selective DA reuptake inhibitor (+/-)-2e, KD(hDAT)/KD(rDAT) = 97.

Trifluoperazine and dibucaine-induced inhibition of glutamate-induced mitochondrial depolarization in rat cultured forebrain neurones.

1. Glutamate receptor activation has been previously shown to result in mitochondrial depolarization and activation of the mitochondrial permeability transition pore in cultured neurones. In this study, we characterized the effects of two putative permeability transition inhibitors, namely trifluoperazine and dibucaine, on mitochondrial depolarization in rat intact, cultured forebrain neurones. 2. Permeability transition was monitored by following mitochondrial depolarization in neurones loaded with the mitochondrial membrane potential-sensitive fluorescent indicator, JC-1. Trifluoperazine (10 20 microM) and dibucaine (50-100 microM) inhibited or delayed the onset of glutamate-induced permeability transition. 3. We also investigated the effects of trifluoperazine and dibucaine on neuronal recovery from glutamate-induced Ca2+ loads. Trifluoperazine affected Ca2+ recovery in a manner similar to the mitochondrial Na+/Ca2+ exchange inhibitor, CGP-37157, while dibucaine had no apparent effect on Ca2+ recovery. Therefore, inhibition of permeability transition does not appear to be involved in Ca2+ recovery from glutamate-induced Ca2+ loads. 4. Trifluoperazine and dibucaine did not inhibit [3H]-dizocilpine binding at the concentrations that prevented mitochondrial depolarization. 5. These studies suggest that trifluoperazine and dibucaine inhibit permeability transition in intact neurones. Trifluoperazine also appears to inhibit mitochondrial Na+/Ca2+ exchange. These drugs should prove to be valuable tools in the further study of the role of mitochondrial permeability transition in glutamate-induced neuronal death.