Interaction of benzylidene-anabaseine analogues with agonist and allosteric sites on muscle nicotinic acetylcholine receptors.

BACKGROUND AND PURPOSE: Benzylidene-anabaseines (BAs) are partial agonists of the alpha7 nicotinic acetylcholine receptor (nAChR) but their mechanism(s) of action are unknown. Our study explores several possibilities, including direct interactions of BAs with the nAChR channel. EXPERIMENTAL APPROACH: Functional and radioligand-binding assays were used to examine the interaction of two BA analogues, 3-(2,4-dimethoxybenzylidene)-anabaseine (DMXBA) and its primary metabolite 3-(4-hydroxy-2-methoxybenzylidene)-anabaseine (4OH-DMXBA) with both agonist and non-competitive antagonist (NCA)-binding sites on muscle-type nAChRs. KEY RESULTS: Both BAs non-competitively inhibited ACh activation of human fetal muscle nAChRs and sterically inhibited the specific binding of the NCAs [piperidyl-3,4-3H(N)]-(N-(1-(2-thienyl)cyclohexyl)-3,4-piperidine ([(3)H]TCP) and [(3)H]dizocilpine to Torpedo nAChRs in the desensitized state. These compounds modulated [(3)H]tetracaine, [(14)C]amobarbital and [(3)H]TCP binding to resting nAChRs by allosteric mechanisms. Both BAs enhanced [(3)H]TCP binding when the nAChR was initially in the resting but activatable state, suggesting that both compounds desensitized the Torpedo nAChR. Although DMXBA failed to activate human fetal muscle nAChRs, 4OH-DMXBA was found to be a partial agonist. [(3)H]Nicotine competition-binding experiments confirmed that 4OH-DMXBA has higher affinity than DMXBA for the agonist sites, and that DMXBA is also a competitive antagonist. CONCLUSIONS AND IMPLICATIONS: 3-(4-hydroxy-2-methoxybenzylidene)-anabaseine is a partial agonist for human fetal muscle nAChRs, whereas DMXBA only has competitive and NCA activities. The NCA-binding site for BAs overlaps both the phencyclidine- and dizocilpine-binding sites in the desensitized Torpedo nAChR ion channel. The desensitizing property of BAs suggests another possible mode of non-competitive inhibition in addition to direct channel-blocking mechanisms.

Benzylidene analogs of anabaseine display partial agonist and antagonist properties at the mouse 5-hydroxytryptamine(3A) receptor.

The nicotinic receptor drug candidate, 3-(2,4-dimethoxybenzylidene)-anabaseine (also known as GTS-21; DMXBA), its hydroxy metabolites, and some related analogs were evaluated with the two-electrode voltage-clamp technique in mouse 5-hydroxytryptamine (5-HT)(3A) receptors expressed in Xenopus oocytes. Although DMXBA lacked partial agonist activity, its hydroxy-benzylidene metabolites and related analogs were partial agonists, displaying the following rank order of potency (EC(50)) and apparent efficacy: 5-HT, 0.9 +/- 0.06 microM (100% efficacy) > 3-(2-hydroxy,4-methoxybenzylidene)-anabaseine (2-OH-MBA), 2.0 +/- 0.3 microM (63% efficacy) > 3-(2,4-dihydroxybenzylidene)-anabaseine, 2.6 +/- 0.3 microM (63% efficacy) > 3-(2-methoxy,4-hydroxybenzylidene)-anabaseine, 17.2 +/- 1.0 microM (30% efficacy). To examine the influence of a benzylidene ring hydroxy substituent, the agonist actions of the three possible monohydroxy isomers were examined. The rank order of potency, based on EC(50) determinations, and apparent efficacy was: 3-(2-hydroxybenzylidene)-anabaseine, 20.3 +/- 2.6 microM (63% efficacy) > 3-(4-hydroxybenzylidene)-anabaseine, 32.3 +/- 5.9 microM (14% efficacy) > 3-(3-hydroxybenzylidene)-anabaseine (3-OH-BA) (no agonist activity). Both DMXBA and 3-OH-BA antagonized 5-HT-mediated currents, with IC(50) values of 15.7 +/- 0.9 and 27.5 +/- 4.7 microM, respectively. DMXBA demonstrated both competitive and noncompetitive forms of antagonism over the range of concentrations tested. These results suggest that a hydroxy substituent at the 2' position of the benzene ring is necessary and sufficient for partial agonist activity; substitution at the 4' position with a hydroxy or methoxy group further enhances agonist potency. Because 2-OH-MBA is a primary metabolite of DMXBA, it may contribute to the physiological, biochemical, and behavioral effects of the parent compound when administered in vivo.

Derivatives of dexanabinol. II. Salts of amino acid esters containing tertiary and quaternary heterocyclic nitrogen with increased water-solubility.

PURPOSE: Amino acid esters containing tertiary or quaternary nitrogen heterocycles were synthesized for dexanabinol (1) and evaluated as water-soluble prodrugs or congeners. METHODS: Syntheses were performed by conventional methods; stability studies in water, blood (rat, dog, human) and assay-media were performed by HPLC; NMDA receptor binding was determined by [3H] MK-801 displacement; neuroprotection and neurotoxicity studies were performed in cortical cell cultures. RESULTS: 7-morpholino and N-methylpiperazino acetates and butyrates and the respective N-methylmorpholinium and piperazinium iodides as well as a 3'-N-methyl morpholino butyrate and the corresponding N-methyl quaternary type derivative were synthesized. All compounds were relatively soluble in water or 10% aqueous ethanol. The examined derivatives were stable in water and generally less stable in blood and assay media. Quaternary derivatives of dexanabinol were found to hydrolyze faster. All examined compounds inhibited NMDA receptor and protected neurons against NMDA induced toxicity. Neuroprotection (with one exception) is however attributed to the parent 1 released by hydrolysis during the assay. CONCLUSIONS: Some of the examined derivatives could be further evaluated as prodrugs on congeners of 1.

Synthesis of vinca alkaloids and related compounds, XLIV: Synthesis of trifluoro-apovincaminic acid ester.

Via the intermediate iminium salt 8 the 21,21,21-trifluoro-apovincaminic acid ethyl ester (2), a derivative of CAVINTONR (1) was synthesized. The pharmacological effect of 2 changed dramatically compared with the parent compound.