Miguel A. Gallo

Inhibition of neuronal nitric oxide synthase activity by N1-acetyl-5-methoxykynuramine, a brain metabolite of melatonin.

We assessed the effects of melatonin, N1‐acetyl‐N 2‐formyl‐5‐methoxykynuramine (AFMK) and N1‐acetyl‐5‐methoxykynuramine (AMK) on neuronal nitric oxide synthase (nNOS) activity in vitro and in rat striatum in vivo. Melatonin and AMK (10−11−10−3 m), but not AFMK, inhibited nNOS activity in vitro in a dose–response manner. The IC50 value for AMK (70 µm) 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 Ca2+‐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 and its brain metabolite N1‐acetyl‐5‐methoxykynuramine prevent mitochondrial nitric oxide synthase induction in parkinsonian mice

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 Parkinsons 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, N1‐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.

Cellular mechanisms involved in the melatonin inhibition of HT-29 human colon cancer cell proliferation in culture

Abstract:  The antiproliferative and proapoptotic properties of melatonin in human colon cancer cells in culture were recently reported. To address the mechanisms involved in these actions, HT‐29 human colon cancer cells were cultured in RPMI 1640 medium supplemented with fetal bovine serum at 37°C. Cell proliferation was assessed by the incorporation of [3H]‐thymidine into DNA. Cyclic nucleotide levels, nitrite concentration, glutathione peroxidase and reductase activities, and glutathione levels were assessed after the incubation of these cells with the following drugs: melatonin membrane receptor agonists 2‐iodo‐melatonin, 2‐iodo‐N‐butanoyl‐5‐methoxytryptamine, 5‐methoxycarbonylamino‐N‐acetyltryptamine (GR‐135,531), and the antagonists luzindole, 4‐phenyl‐2‐propionamidotetralin, and prazosin; the melatonin nuclear receptor agonist CGP 52608, and four synthetic kynurenines analogs to melatonin 2‐acetamide‐4‐(3‐methoxyphenyl)‐4‐oxobutyric acid, 2‐acetamide‐4‐(2‐amino‐5‐methoxyphenyl)‐4‐oxobutyric acid, 2‐butyramide‐4‐(3‐methoxyphenyl)‐4‐oxobutyric acid and 2‐butyramide‐4‐(2‐amino‐5‐methoxyphenyl)‐4‐oxobutyric acid. The results show that the membrane receptors are not necessary for the antiproliferative effect of melatonin and the participation of the nuclear receptor in this effect is suggested. Moreover, the antioxidative and anti‐inflammatory actions of melatonin, counteracting the oxidative status and reducing the production of nitric oxide by cultured HT‐29 cells seem to be directly involved in the oncostatic properties of melatonin. Some of the synthetic kynurenines exert higher antiproliferative effects than melatonin. The results reinforce the clinical interest of melatonin due to the different mechanisms involved in its oncostatic role, and suggest a new synthetic pathway to obtain melatonin agonists with clinical applications to oncology.

Modification of Nitric Oxide Synthase Activity and Neuronal Response in Rat Striatum by Melatonin and Kynurenine Derivatives

Tryptophan is mainly metabolized in the brain through methoxyindole and kynurenine pathways. The methoxyindole pathway produces (among other compounds) melatonin, which displays inhibitory effects on human and animal central nervous systems, including a significant attenuation of excitatory, glutamate‐mediated responses. The kynurenine pathway produces kynurenines that interact with brain glutamate‐mediated responses. Nitric oxide (NO) increases glutamate release, and melatonin and kynurenines may act via modification of NO synthesis. In the present study, the effects of melatonin and four synthetic kynurenines were studied on the activity of rat striatal nitric oxide synthase (NOS) and on the response of rat striatal neurons to sensorimotor cortex (SMCx) stimulation, a glutamate‐mediated response. Melatonin inhibited both NOS activity and the striatal glutamate response, and these effects were dose‐related. Compound A (2‐acetamide‐4‐(3‐methoxyphenyl)‐4‐oxobutyric acid) did not inhibit NOS activity but inhibited the striatal response similarly to melatonin. Compound B (2‐acetamide‐4‐(2‐amino‐5‐methoxyphenyl)‐

Homochiral Drugs: A Demanding Tendency of the Pharmaceutical Industry

The issue of drug chirality is now a major theme in the design and development of new drugs, underpinned by a new understanding of the role of molecular recognition in many pharmacologically relevant events. In general, three methods are utilized for the production of a chiral drug: the chiral pool, separation of racemates, and asymmetric synthesis. Although the use of chiral drugs predates modern medicine, only since the 1980s has there been a significant increase in the development of chiral pharmaceutical drugs. An important commercial reason is that as patents on racemic drugs expire, pharmaceutical companies have the opportunity to extend patent coverage through development of the chiral switch enantiomers with desired bioactivity. Stimulated by the new policy statements issued by the regulatory agencies, the pharmaceutical industry has systematically begun to develop chiral drugs in enantiometrically enriched pure forms. This new trend has caused a tremendous change in the industrial small- and large-scale production to enantiomerically pure drugs, leading to the revisiting and updating of old technologies, and to the development of new methodologies of their large-scale preparation (as the use of stereoselective syntheses and biocatalyzed reactions). The final decision whether a given chiral drug will be marketed in an enantiomerically pure form, or as a racemic mixture of both enantiomers, will be made weighing all the medical, financial and social proficiencies of one or other form. The kinetic, pharmacological and toxicological properties of individual enantiomers need to be characterized, independently of a final decision.

Medium benzene-fused oxacycles with the 5-fluorouracil moiety: synthesis, antiproliferative activities and apoptosis induction in breast cancer cells

Abstract On the basis of the increase in lipophilicity, novel benzannelated six- and seven-membered derivatives have been synthesized, starting from 2-hydroxybenzyl alcohols, 2-hydroxybenzaldehydes, and catechol. The X-ray structure of (RS)-1-(2,3-dihydro-5H-1,4-benzodioxepin-3-yl)-5-fluorouracil ( 5 ) is presented and compared with its conformational analysis at the semiempirical (AM1) and ab initio (6-31G∗) levels and NOE effects. A good agreement between both experimental and theoretical data was found showing a chair conformation for the 2,3-dihydro-5H-1,4-dioxepin ring and an axial orientation of the 5-FU moiety on the C3 position. Compounds 5 and (RS)-1-(7-methoxy-2,3-dihydro-5H-1,4-benzodioxepin-3-yl)-5-fluorouracil ( 6 ) were found to be the most potent inhibitor of MCF-7 cells growth. (RS)-1-(2,3-Dihydrobenzoxepin-2-yl)-5-fluorouracil ( 8 ) induced apoptosis up to 57.33% of cell population after 24 h.

Synthesis and anticancer activity of (RS)-9-(2,3-dihydro-1,4-benzoxaheteroin-2-ylmethyl)-9H-purines.

Herein are reported the synthesis and anticancer activity against the human breast cancer cell line MCF-7 of a series of substituted (RS)-9-(2,3-dihydro-1,4-benzoxathiin-2-ylmethyl)-9H-purine derivatives and (RS)-9-(2,3-dihydro-1,4-benzodioxin-2-ylmethyl)-9H-purine derivatives. When the Mitsunobu reaction was carried out between (RS)-2,3-dihydro-1,4-benzoxathiin-3-methanol and the heterocyclic bases 6-chloro-, 2,6-dichloro, and 6-bromo-purines under microwave-assisted conditions, a formal 1,4-sulfur migration takes place through two consecutive oxyranium and episulfonium rings, giving rise to the corresponding (RS)-9-(2,3-dihydro-1,4-benzodioxin-3-ylmethyl)-9H-purine derivatives, previously reported by us. The most active compound (RS)-2,6-dichloro-9-(2,3-dihydro-1,4-benzoxathiin-2-ylmethyl)-9H-purine shows an IC(50) = 2.75 ± 0.02 μM. When the cancerous cells were treated with this compound, a significant increase of apoptotic cells (70.08 ± 0.33%) was obtained in relation to the control ones. The induction of the G(2)/M cell cycle arrest and apoptosis by the three most active compounds is associated with increased phosphorylation of eIF2α in human breast cancer cells.

Anticancer activity of (1,2,3,5-tetrahydro-4,1-benzoxazepine-3-yl)-pyrimidines and -purines against the MCF-7 cell line: Preliminary cDNA microarray studies

Completing a SAR study, a series of (RS)-1- or 3-(1,2,3,5-tetrahydro-4,1-benzoxazepine-3-yl)-pyrimidines and (RS)-6-substituted-7- or 9-(1,2,3,5-tetrahydro-4,1-benzoxazepine-3-yl)-7H- or 9H-purines have been prepared. Their antiproliferative activities on MCF-7 cells are here presented and discussed. (RS)-6-Chloro-9-[1-(9H-9-fluorenylmethoxycarbonyl)-1,2,3,5-tetrahydro-4,1-benzoxazepine-3-yl]-9H-purine (28) is the most active (IC(50)=0.67+/-0.18 microM) of the series so far described. cDNA microarray technology reveals potential drug targets, which are mainly centred on apoptosis regulatory pathway genes.

Growth inhibition, G1-arrest, and apoptosis in MCF-7 human breast cancer cells by novel highly lipophilic 5-fluorouracil derivatives

In this study we evaluate the antitumour activity, the cell cycle arrest and apoptotic properties of novel lipophilic benzene-fused seven-membered 5-fluorouracil (5-FU) analogs in comparison to 5-FU on MCF-7 human breast cancer cells. The lipophilicities of ESB-786B, ESB-252A and ESB-928A were predicted by using the CDR option of the PALLAS 2.0 program. Cytotoxic assays were evaluated in MCF-7 cells treated with the sulforhodamine B colorimetric method. Cell cycle perturbations were studied by flow cytometry. Apoptosis was determined by both DNA fragmentation and annexin V-FITC and propidium iodide staining. The novel derivatives were more lipophilic than 5-FU and induced a marked growth inhibition, in a dose-dependent manner. After treatment with IC50 value (ranged from 2.5 to 22 μM) for each compound, light microscopy observation showed modifications in the morphology of MCF-7 cells. In addition, the 5-FU analogs arrest cells in the G0/G1 phase of the cell cycle whereas 5-FU induced arrest in S-phase. Moreover, induction of apoptosis was demonstrated by the annexin-V-based assay and confirmed using DNA fragmentation analysis on MCF-7 cells, a cell line in which the induction of DNA laddering is very difficult. The novel benzannelated seven-membered 5-FU analogs can be considered as specific apoptotic inducers. These experimental findings provide support for the use of these novel compounds as new weapons in the fight against breast cancer.

Homodimeric bis-quaternary heterocyclic ammonium salts as potent acetyl- and butyrylcholinesterase inhibitors: a systematic investigation of the influence of linker and cationic heads over affinity and selectivity.

A molecular library of quaternary ammonium salts (QASs), mainly composed of symmetrical bis-quaternary heterocyclic bromides exhibiting choline kinase (ChoK) inhibitory activity, were evaluated for their ability to inhibit acetyl- and butyrylcholinesterase (AChE and BChE, respectively). The molecular framework of QASs consisted of two positively charged heteroaromatic (pyridinium or quinolinium) or sterically hindered aliphatic (quinuclidinium) nitrogen rings kept at an appropriate distance by lipophilic rigid or semirigid linkers. Many homodimeric QASs showed AChE and BChE inhibitory potency in the nanomolar range along with a low enzymatic selectivity. Computational studies on AChE, BChE, and ChoK allowed identification of the key molecular determinants for high affinity and selectivity over either one of the three enzymes and guided the design of a hybrid bis-QAS (56) exhibiting the highest AChE affinity (IC(50) = 15 nM) and selectivity over BChE and ChoK (SI = 50 and 562, respectively) and a promising pharmacological potential in myasthenia gravis and neuromuscular blockade.