Gabriela Aguirre

Synthesis, trypanocidal activity and docking studies of novel quinoxaline-N-acylhydrazones, designed as cruzain inhibitors candidates

In this paper, we report the structural design, synthesis, trypanocidal activity and docking studies of novel quinoxaline-N-acylhydrazone (NAH) derivatives, planned as cruzain inhibitors candidates, a cysteine protease essential for the survival of Trypanosoma cruzi within the host cell. The salicylaldehyde N-acylhydrazones 7a and 8a presented IC(50) values of the same magnitude order than the standard drug nifurtimox (Nfx), when tested in vitro against epimastigote forms of Trypanosoma cruzi (Tulahuen 2 strain) and were non-toxic at the highest assayed doses rendering selectivity indexes (IC(50) (macrophages)/IC(50) (Trypanosoma cruzi)) of >25 for 7a and >20 for 8a, with IC(50) values in macrophages >400 microM.

Platinum-based complexes of bioactive 3-(5-nitrofuryl)acroleine thiosemicarbazones showing anti-Trypanosoma cruzi activity.

Eight new platinum(II) complexes with 3-(5-nitrofuryl)acroleine thiosemicarbazones showing anti-trypanosomal activity were synthesized, characterized and in vitro evaluated. Most of the complexes showed IC(50) values in the micromolar range against two different strains of Trypanosoma cruzi, causative agent of Chagas disease (American Trypanosomiasis). In addition, most of the newly developed complexes, together with the analogous platinum 5-nitrofuraldehyde containing thiosemicarbazones previously reported, resulted more active than the reference trypanocidal drug nifurtimox on the infective trypomastigote form of the parasite. Their capacity to produce free radicals that could lead to parasite death was evaluated by ESR experiments in the parasite and by respiration measurements. Compounds were tested for their DNA interaction ability. Results showed that some of the compounds could act as dual inhibitors in the parasite, through production of toxic free radicals and interaction with DNA. All the results were compared with those previously reported for the free ligands, the analogous palladium(II) compounds and the previously reported series of platinum(II) compounds.

Potent in vitro anti-Trypanosoma cruzi activity of pyridine-2-thiol N-oxide metal complexes having an inhibitory effect on parasite-specific fumarate reductase.

In the search for new therapeutic tools against Chagas disease (American trypanosomiasis) palladium and platinum complexes of the bioactive ligand pyridine-2-thiol N-oxide were exhaustively characterized and evaluated in vitro. Both complexes showed high in vitro growth inhibition activity (IC50 values in the nanomolar range) against Trypanosoma cruzi, the causative agent of the disease. They were 39–115 times more active than the antitrypanosomal drug Nifurtimox. The palladium complex showed an approximately threefold enhancement of the activity compared with the parent compound. In addition, owing to their low unspecific cytotoxicity on mammalian cells, the complexes showed a highly selective antiparasite activity. To get an insight into the mechanism of action of these compounds, DNA, redox metabolism (intraparasite free-radical production) and two parasite-specific enzymes absent in the host, namely, trypanothione reductase and NADH-fumarate reductase, were evaluated as potential parasite targets. Additionally, the effect of metal coordination on the free radical scavenger capacity previously reported for the free ligand was studied. All the data strongly suggest that trypanocidal action of the complexes could mainly rely on the inhibition of the parasite-specific enzyme NADH-fumarate reductase.

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.

Benzo[1,2-c]1,2,5-oxadiazole N-oxide derivatives as potential antitrypanosomal drugs. Structure-activity relationships. Part II.

The preparation of new derivatives of benzo[1, 2‐c]1, 2, 5‐oxadiazole N‐oxide is described. These derivatives were chosen in order to investigate and confirmprevious structural features found necessary to display an adequate antitrypanosomal activity. The compounds synthesized were tested in vitro against epimastigote forms of Trypanosoma cruzi.The presence of a bromine atom in the benzo system produced compounds less active than the corresponding de‐halo analogues. However, 5‐(bromomethyl)‐7‐bromobenzo[1, 2‐c]oxadiazole N‐oxide (23) was the most cytotoxic compound against T. cruzi. For this, the 50% inhibitory dose (ID50) was determined, it was of the same order as that of Nifurtimox. From statistical analysis we could establish a relationship between lipophilic‐hydrophilic balance of the derivatives with their effectiveness as antichagasic compounds.

Furoxan-, alkylnitrate-derivatives and related compounds as anti-trypanosomatid agents: Mechanism of action studies

A series of over a hundred furoxans, alkylnitrates and related compounds were studied as growth inhibitors of the two major kinetoplastids of Latin America, Trypanosoma cruziand Leishmania spp., in in vitro assays. The most active compounds showed 50% inhibitory doses of the same order of that of Nifurtimox and Miltefosine, reference drugs used to treat Chagas Disease and Leishmaniasis respectively. Among the studied compounds derivative 4, presenting excellent inhibitory activity against the tryposmastigote and amastigote forms of T. cruzi, has emerged as a lead compound. Mechanism of action seems to involve mitochondrial dehydrogenases as a distinct effect with respect to Nifurtimox. Excreted metabolites, studied by NMR, showed a significant decrease in succinate, confirming the observed effect on the mitochrondrial dehydrogenases.

ESR AND SPIN TRAPPING STUDIES OF TWO NEW POTENTIAL NTITRYPANOSOMAL DRUGS

The Electron Spin Resonance (ESR) spectra of radicals obtained from two new potential antitrypanosomal drugs by Trypanosoma cruzi reduction were analyzed. DMPO Spin Trapping was used to investigate the possible formation of free radicals in the trypanosome microsomal system. The Nitro 2 (4-(n-butyl)-1-(5-nitrofurfurylidene)semicarbazide) analogue of Nifurtimox showed better antiparasitic activity than N-oxide 1 (4-(n-butyl)-1-[(7-bromo-N1-oxidebenzo[1,2-c]1,2,5-oxadiazole-5-yl)methylidene]semicarbazide). Only Nitro 2 could produce oxygen redox cycling in T. cruzi epimastigotes. The ESR signal intensities were consistent with the trapping of hydroxyl radical. These results are in agreement with the biological observation that Nitro 2 showed antichagasic activity by an oxidative stress mechanism