We assessed the effects of melatonin, N 1 -acetyl-N 2 -formyl-5-methoxykynuramine (AFMK) and N 1 -acetyl-5-methoxykynuramine (AMK) on neuronal nitric oxide synthase (nNOS) activity in vitro and in rat striatum in vivo. Melatonin and AMK (10)10 )3 M), but not AFMK, inhibited nNOS activity in vitro in a dose-response manner. The IC 50 value for AMK (70 lM) was significantly lower than for melatonin (>1 mM). A 20% nNOS inhibition was reached with either 10 )9 M melatonin or 10 )11 M AMK. AMK inhibits nNOS by a non-competitive mechanism through its binding to Ca 2+-calmodulin (CaCaM). The inhibition of nNOS elicited by melatonin, but not by AMK, was blocked with 0.05 mM norharmane, an indoleamine-2,3-dioxygenase inhibitor.In vivo, the potency of AMK to inhibit nNOS activity was higher than that of melatonin, as a 25% reduction in rat striatal nNOS activity was found after the administration of either 10 mg/kg of AMK or 20 mg/kg of melatonin. Also, in vivo, the administration of norharmane blocked the inhibition of nNOS produced by melatonin administration, but not the inhibition produced by AMK. These data reveal that AMK rather than melatonin is the active metabolite against nNOS, which may be inhibited by physiological levels of AMK in the rat striatum.

Melatonin prevents mitochondrial failure in models of sepsis through its ability to inhibit the expression and activity of both cytosolic (iNOS) and mitochondrial (i-mtNOS) inducible nitric oxide synthases. Because Parkinson's disease (PD), like sepsis, is associated with iNOS induction, we assessed the existence of changes in iNOS/i-mtNOS and their relation with mitochondrial dysfunction in the MPTP model of PD, which also displays increased iNOS expression. We also evaluated the role of melatonin (aMT) and its brain metabolite, N(1)-acetyl-5-methoxykynuramine (AMK), in preventing i-mtNOS induction and mitochondrial failure in this model of PD. Mitochondria from substantia nigra (SN) and, to a lesser extent, from striatum (ST) showed a significant increase in i-mtNOS activity, nitrite levels, oxidative stress, and complex I inhibition after MPTP treatment. MPTP-induced i-mtNOS was probably related to mitochondrial failure, because its prevention by aMT and AMK reduced oxidative/nitrosative stress and restored complex I activity. These findings represent the first experimental evidence of a potential role for i-mtNOS in the mitochondrial failure of PD and support a novel mechanism in the neuroprotective effects of aMT and AMK.

Two new series of inhibitors of tubulin polymerization based on the 2-amino-3-(3,4,5-trimethoxybenzoyl)benzo[b]thiophene molecular skeleton and its 3-amino positional isomer were synthesized and evaluated for antiproliferative activity, inhibition of tubulin polymerization, and cell cycle effects. Although many more 3-amino derivatives have been synthesized so far, the most promising compound in this series was 2-amino-6-methyl-3-(3,4,5-trimethoxybenzoyl)benzo[b]thiophene, which inhibits cancer cell growth at subnanomolar concentrations and interacts strongly with tubulin by binding to the colchicine site.

A series of 1-aryl-5-(3′,4′,5′-trimethoxyphenyl) derivatives and their related 1-(3′,4′,5′-trimethoxyphenyl)-5-aryl-1,2,4-triazoles, designed as cis-restricted combretastatin analogues, were synthesized and evaluated for antiproliferative activity, inhibitory effects on tubulin polymerization, cell cycle effects, and apoptosis induction. Their activity was greater than, or comparable with, that of the reference compound CA-4. Flow cytometry studies showed that HeLa and Jurkat cells treated with the most active compounds 4l and 4o were arrested in the G2/M phase of the cell cycle in a concentration dependent manner. This effect was accompanied by apoptosis of the cells, mitochondrial depolarization, generation of reactive oxygen species, activation of caspase-3, and PARP cleavage. Compound 4l was also shown to have potential antivascular activity, since it induced endothelial cell shape change in vitro and disrupted the sprouting of endothelial cells in the chick aortic ring assay.