Naftifine-analogues as anti-Trypanosoma cruzi agents.

Chagas disease represents a relevant health problem in Central and South America. The first line of treatment is Nifurtimox and Benznidazole which have a great deal of disadvantages that demands the rapid generation of therapeutic alternatives. Based in our research on aza-thiaheterocycles as anti-Trypanosoma cruzi agents we identified pharmacophores that act through oxidative stress. Here, we describe the synthesis and the activity of new containing bioactive-heterocycles analogues of naftifine as potential T. cruzi membrane sterol biosynthesis inhibitors. Benzimidazole 1,3-dioxides (11 and 13) and quinoxaline 1,4-dioxides (22 and 23) displayed excellent parasite/mammal selectivity indexes. Analysis of the free sterols from parasite incubated with the compounds showed that any of them are able to accumulate squalene suggesting that in the anti-T. cruzi mechanism of action is not involved the inhibition of sterol biosynthesis. Some derivatives were also tested as antifungal agents. The results obtained in the present work open potential therapeutic possibilities of new compounds for these infectious diseases.

New heteroaryl nitrones with spin trap properties: Identification of a 4-furoxanyl derivative with excellent properties to be used in biological systems.

A new series of heteroaryl nitrones, 1-7, bearing furoxanyl and thiadiazolyl moieties, were evaluated for their free radical-trapping properties. The physicochemical characterization by electron paramagnetic resonance (EPR) demonstrated its capability to trap and stabilize oxygen-, carbon-, sulfur-, and nitrogen-centered free radicals. The 4-furoxanyl nitrone 3 (FxBN), alpha(Z)-(3-methylfuroxan-4-yl)-N-tert-butylnitrone, showed appropriate solubility in aqueous solution and taking into account that this physicochemical property is very important for biological applications, we studied it deeply in terms of its trapping and kinetic behaviors. For this, kinetic studies of the hydroxyl adduct decay gave rate constants k(ST) of 1.22x10(10)dm(3)mol(-1)s(-1) and half-live up to 7200s at physiological pH, without any artifactual signals. The ability of FxBN to directly traps and stabilizes superoxide free radical, with a half-life of 1620s at physiological pH, was also demonstrated. Besides, FxBN-hydroxyl and -superoxide adducts exhibited distinct and characteristic EPR spectral patterns. Finally, we confirmed the ability of FxBN to act as spin trap in a specific biological system, that is, in the free radical production of experimental anti-trypanosomatid drugs using Trypanosoma cruzi microsomes as biological system. Moreover, previous observations of low FxBN toxicity transform it in a good candidate for in vivo spin trapping.

5-Nitrofuranes and 5-nitrothiophenes with anti-Trypanosoma cruzi activity and ability to accumulate squalene.

Chagas disease represents a serious public health problem in South America. The first line of treatment is Nifurtimox and Benznidazole which generate toxic effects in treated patients. We have recently shown that a number of 5-nitrofuranes possess activity against Trypanosoma cruzi through oxidative stress and inhibition of parasite ergosterol biosynthesis, specifically at the level of squalene epoxidase. Here, we identify new 5-nitrofuranes and the thia-analogues with excellent effects on the viability of T. cruzi and adequate parasite/mammal selectivity indexes. Analysis of the free sterols from parasite incubated, during 120h, with the compounds showed that some of them accumulated squalene suggesting the squalene epoxidase activity inhibition of the parasite. Nifurtimox was able to accumulate squalene only at lower incubation times. Due to this fact some derivatives were also tested as antifungal agents. Quantitative structure-activity relationship studies were also performed showing relevant features for further new derivatives design. Taken together, the results obtained in the present work point to a more general effect of 5-nitrofuranes and 5-nitrothiophenes in trypanosomatids, opening potential therapeutic possibilities of them for these infectious diseases.

Cytotoxic, mutagenic and genotoxic effects of new anti-T. cruzi 5-phenylethenylbenzofuroxans. Contribution of phase I metabolites on the mutagenicity induction.

5-Phenylethenylbenzofuroxans have displayed in vitro and in vivo activity against Trypanosoma cruzi, the etiologic agent of American Trypanosomiasis. On the basis of benzofuroxans pre-clinical studies we evaluated the potential of six 5-phenylethenyl derivatives to induce cytotoxicity, mutagenicity and genotoxicity using different in vitro models. Cytotoxic effects were evaluated using a set of cells, mammal pre-monocytic macrophages, V-79 lung fibroblast from Chinese hamster, and colorectal adenocarcinoma Caco-2 cells, in the MTT viability assay. Mutagenicity was tested in the Ames assay using Salmonella typhimurium TA98 strain with and without metabolic activation by S9-rat liver homogenate. The genotoxic potentials were evaluated with the alkaline single cell gel electrophoresis (comet assay) in V-79 cells. In view of the Ames test results we study whether the main mammals' phase I metabolites, the corresponding o-nitroanilines, are involved in the mechanism of mutagenicity. These metabolites are produced by NADPH-dependent enzymes in cytosol and by xanthine oxidase and cytochrome P450 in microsomes from rat liver. Among them, the electronic property of phenyl substituent seems to be responsible for this effect. It could be pointed out that the equimolecular mixture of compounds 1 and 2 (5E- and 5Z-(2-phenylethenyl)benzofuroxan, respectively) could be used in further clinical studies as anti-T. cruzi drug.

In vitro and in vivo antitrypanosomatid activity of 5-nitroindazoles.

Previously, we have identified a series of 5-nitroindazoles with good antiprotozoal activities, against Trypanosoma cruzi epimastigotes and Trichomonas vaginalis. Most of them have shown very low unspecific toxicity on macrophage cell lines. In the present work, we assayed these compounds on T. cruzi bloodstream trypomastigotes and Leishmania promastigotes (Leishmania amazonensis, Leishmania braziliensis and Leishmania infantum). Derivatives 1, 2, 7 and 8 displayed remarkable trypanocidal activity (>80% lysis) equivalent to gentian violet. Derivatives 2 and 10, as Pentamidine, caused the complete lysis of promastigotes of Leishmania. An oxidative stress-mediated mechanism of action was confirmed for derivatives 1, 10 and 12 on T. cruzi epimastigotes. Supported by the in vitro activities, derivatives 1 and 2 were submitted to in vivo assays using an acute model of Chagas' disease and a short-term treatment. None of the animals treated with derivatives 1 and 2 died, unlike the untreated control and Benznidazole groups.

Study of 5-nitroindazoles' anti-Trypanosoma cruzi mode of action: electrochemical behaviour and ESR spectroscopic studies.

New indazole derivatives have been developed to know about structural requirements for adequate anti-Trypanosoma cruzi activity. In relation to position 1 of indazole ring, we have observed that a butylaminopentyl substituent (14) affords good activity, but N-oxidation of omega-tertiary amino moiety yields completely inactive compounds (17, 18); the substituent at position 3 of indazole ring affects drastically the in vitro activity, 3-OH derivative 13 being completely inactive. On the other hand, since compound 22, denitro-analogue of active compound 4, does not show activity, the 5-nitro substituent of indazole ring seems to be essential. Intramolecular cyclization of side chain at position 1 also affords inactive compounds (19, 20). The electrochemical studies showed that the trypanocidal 5-nitroindazole derivatives yielded nitro-anion radical via one-electron process at physiological pH. This electrochemical behaviour occurs in the parasite according to ESR experiment with the T. cruzi microsomal fraction showing that 5-nitroindazole derivatives suffer bio-reduction without reactive oxygen species generation.

In vivo studies of 5-arylethenylbenzofuroxans in acute murine models of Chagas' disease.

5-arylethenylbenzofuroxan derivatives with high in vitro anti-Trypanosoma cruzi activity were studied in vivo using acute murine models of Chagas' disease. The selected compounds, as pure isomeric forms, 1, 2, 3 and 4, or as equimolecular mixture of geometric isomers, 1:2, 3:4, 5:6 were studied against different T. cruzi strains. Consequently, Tulahuen 2 strain, Colombiana strain (resistant to Nifurtimox and Benznidazole), and two different wild strains, one isolated from the wild reservoir Didelphis marsupialis and another one from Uruguayan patients, were selected. No relevant signs of in vivo toxicity were observed with the benzofuroxans orally administered. Compound 1 and the mixture of isomers 1:2 were the best for treating infection against the four studied strains.

Development of a HPLC method for the determination of antichagasic phenylethenylbenzofuroxans and its major synthetic secondary products in the chemical production processes.

A simple isocratic reverse-phase HPLC method for the determination of six antichagasic phenylethenylbenzofuroxans and its major synthetic secondary products, the corresponding geometric isomers and the benzofurazans, was developed and validated for use in the analysis of pre-clinical studies. Separation was achieved on a reverse-phase Supelco LC-18 column using either methanol-acetonitrile-water or acetonitrile-water, in different proportions, as mobile phase. The compounds were eluted isocratically at a flow rate of either 0.8 or 1.0 mLmin(-1). The compounds were analyzed with UV detection at 210 and 300 nm. The validation characteristics included linearity, accuracy, precision, specificity, limit of detection and quantification and robustness. Validation acceptance criteria were met in all cases. This method was used successfully for the quality assessment of the drugs production in the scale-up procedures.

Comparative spectroscopic and electrochemical study of nitroindazoles: 3-alcoxy, 3-hydroxy and 3-oxo derivatives.

Cyclic voltammetry and electron spin resonance techniques were used in the investigation of novel 3-alkoxy- and 3-hydroxy-1-[omega-(dialkylamino)alkyl]-5-nitroindazole derivatives. A self-protonation process involving the protonation of the nitro group was observed. The reactivity of the nitro-anion radical for these derivatives with glutathione, a biological relevant thiol, was also studied by cyclic voltammetry. These studies demonstrated that glutathione could react with radical species from 5-nitroindazole system. Also we demonstrated that nitro-anion radicals show three different patterns of delocalization where the indazole 1-lateral chain does not have major influence.

Heteroallyl-containing 5-nitrofuranes as new anti-Trypanosoma cruzi agents with a dual mechanism of action.

New heteroallyl-containing 5-nitrofuranes were synthesized as potential anti-Trypanosoma cruzi agents with a dual mechanism of action, oxidative stress and inhibition of membrane sterol biosynthesis. Some of the derivatives were found to have high and selective activity against the proliferative stages of the parasite, with IC(50) values against the clinically relevant intracellular amastigote forms in the low micromolar to sub-micromolar range. Oxidative stress was verified measuring cyanide dependent respiration. Inhibition of the de novo sterol biosynthesis at the level of squalene epoxidase was confirmed, using high-resolution gas-liquid chromatography coupled to mass spectrometry, by the disappearance of the parasite's mature sterols and the concomitant accumulation of squalene. The in vitro activities of these novel compounds were superior to that of nifurtimox, a nitrofuran currently used in the treatment of human Chagas' disease, and terbinafine, a commercially available allylamine-based squalene epoxidase inhibitor. The results support further in vivo studies of some of these nitrofuran derivatives.

Indazole N-oxide derivatives as antiprotozoal agents: synthesis, biological evaluation and mechanism of action studies.

A series of indazole N-oxide derivatives have been synthesized and their antichagasic and leishmanocidal properties studied. 3-Cyano-2-(4-iodophenyl)-2H-indazole N1-oxide exhibited interesting antichagasic activity on the two parasitic strains and the two parasitic stages evaluated. Furthermore, besides its trypanocidal activity, 3-cyano-2-(4-nitrophenyl)-2H-indazole N1-oxide showed leishmanocidal activity in the three parasitic strains evaluated. To gain insight into the mechanism of action, electrochemical behaviour, ESR experiment, inhibition of parasitic respiration and QSAR were performed.

ESR and electrochemical study of 5-nitroindazole derivatives with antiprotozoal activity.

The electrochemistry of 3-alkoxy- and 3-hydroxy-1-[omega-(dialkylamino)alkyl]-5-nitroindazole derivatives were characterized using cyclic voltammetry in DMSO. The nitro reduction process was studied and this was affected by the acid moieties present in these compounds. A nitro anion self-protonation process was observed. This phenomenon was studied by cyclic voltammetry in presence of increasing amount of NaOH. The reactivity of the nitro anion radical of these derivatives with glutathione was also studied by cyclic voltammetry. The oxidizing effect of glutathione is supported by the parallel decrease of the anodic peak current and increase of the cathodic peak in the cyclic voltammograms, corresponding to the wave of the nitro anion radical from uncharged species with the addition of glutathione. Nitro anion radicals obtained by electrolytic reduction of these derivatives were measured and analyzed in DMSO using electron spin resonance spectroscopy.

Pharmacological properties of indazole derivatives: recent developments.

The chemistry of indazole and its N-oxide derivatives is very well-known. Indazole derivatives were extensively studied as bioactive compounds, such as anti-aggregatory and vasorelaxant activity by NO release and increase of cGMP levels and anticancer effects, antimicrobial and antiparasitic properties, among others. Recently, the research and development in the medicinal chemistry of these systems have produced compounds with contraceptive activities for men, for the treatment of osteoporosis, inflammatory disorders and neurodegenerative diseases. On the other hand, indazole N-oxide derivatives were poorly studied as bioactive compounds, but recently compounds with antiparasitic properties were produced. In this presentation, recent developments in the chemistry and medicinal chemistry of indazole and its N-oxide derivatives will be reviewed.

Novel antiprotozoal products: imidazole and benzimidazole N-oxide derivatives and related compounds.

The syntheses and biological evaluation of the first anti-protozoa imidazole N-oxide and benzimidazole N-oxide and their derivatives are reported. They were tested in vitro against two different protozoa, Trypanosoma cruzi and Trichomonas vaginalis. Derivative 7c, ethyl-1-(i-butyloxycarbonyloxy)-6-nitrobenzimid-azole-2-carboxylate, displayed activity on both protozoa. Lipophilicity and redox potential were experimentally determined in order to study the relationship with activity of the compounds. These properties are well related with the observed bioactivity. Imidazole and benzimidazole N-oxide derivatives are becoming leaders for further chemical modifications and advanced biological studies.