3-Trifluoromethylquinoxaline N,N'-dioxides as anti-trypanosomatid agents. Identification of optimal anti-T. cruzi agents and mechanism of action studies

For a fourth approach of quinoxaline N,N'-dioxides as anti-trypanosomatid agents against T. cruzi and Leishmania, we found extremely active derivatives. The present study allows us to state the correct requirements for obtaining optimal in vitro anti-T. cruzi activity. Derivatives possessing electron-withdrawing substituents in the 2-, 3-, 6-, and 7-positions were the most active compounds. With regard to these features and taking into account their mammal cytotoxicity, some trifluoromethylquinoxaline N,N'-dioxides have been proposed as candidates for further clinical studies. Consequently, mutagenicity and in vivo analyses were performed with the most promising derivatives. In addition, with regard to the mechanism of action studies, it was demonstrated that mitochondrial dehydrogenases are involved in the anti-T. cruzi activity of the most active derivatives.

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.

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 potent imidazoisoquinolinone derivatives as anti-Trypanosoma cruzi agents: biological evaluation and structure-activity relationships

A series of novel benzoimidazo and N-aryl-5-oxo-imidazo[1,2-b]isoquinoline-10-carbothioamides was developed. All the compounds were evaluated for their in vitro action against the epimastigote form of Trypanosoma cruzi. Four of them showed higher activity than Nifurtimox. Their unspecific cytotoxicity was evaluated using HeLa and L6 cells, being non-toxic at concentrations at least 15 and 200 times higher than that of T. cruzi IC(50.) To gain insight into the mechanism of action, their DNA binding properties and reactivity with glutathione were studied, and QSAR study was performed.

New trypanocidal hybrid compounds from the association of hydrazone moieties and benzofuroxan heterocycle

Hybrid compounds containing hydrazones and benzofuroxan pharmacophores were designed as potential Trypanosoma cruzi-enzyme inhibitors. The majority of the designed compounds was successfully synthesized and biologically evaluated displaying remarkable in vitro activity against different strains of T. cruzi. Unspecific cytotoxicity was evaluated using mouse macrophages, displaying isothiosemicarbazone 10 and thiosemicarbazone 12 selectivity indexes (macrophage/parasite) of 21 and 27, respectively. In addition, the mode of anti-trypanosomal action of the derivatives was investigated. Some of these derivatives were moderate inhibitors of cysteinyl active site enzymes of T. cruzi, cruzipain and trypanothione reductase. ESR experiments using T. cruzi microsomal fraction suggest that the main mechanism of action of the trypanocidal effects is the production of oxidative stress into the parasite.

Seminiferous epithelium cycle of a hantavirus reservoir, the long-tailed mouse Oligoryzomys flavescens (Rodentia-Cricetidae)

Oligoryzomys flavescens, a common rodent of the temperate regions of South America, has been identified as a Hantavirus reservoir. There is still little information concerning its reproductive biology, which is essential to devise effective control measurement of natural populations. This rodent is a seasonal breeder and adult males exhibit a short period of testicular regression during winter months (June-August). In the present study we provided a histological and ultrastructural analysis of the composition of the testis of sexually mature O. flavescens during the breeding season. Over 95% of the testicular parenchyma was occupied by the seminiferous tubules and less than 5% by the interstitial tissue. The mean tubular diameter and epithelium height were 147.2 and 57.8 microm, respectively. The spermatogenic wave was characterized and eight spermatogenesis stages were identified according to the tubular morphology method. Their length, estimated as their relative frequencies, were (I-VIII) 8.8, 14.9, 4.0, 5.0, 10.4, 5.8, 27.0, and 23.9. Ultrastructural features of spermiogenesis are shown for the first time in a sigmodontine rodent.

Second generation of 5-ethenylbenzofuroxan derivatives as inhibitors of Trypanosoma cruzi growth: Synthesis, biological evaluation, and structure–activity relationships

In vitro growth inhibitory activity of 21 new 5-ethenylbenzofuroxan derivatives against the protozoan parasite Trypanosoma cruzi, the causative agent of American trypanosomiasis, was studied. The designed compounds possess the previously described exigencies for optimal anti-parasite activity, the 5-ethenylbenzofuroxanyl moiety with different substituents. The synthetic key for preparing the derivatives was the Wittig procedure, that when 5-formylbenzofuroxan was used as the electrophile the corresponding deoxygenated products were marginally generated. Four of the new derivatives displayed remarkable in vitro activities against the epimastigote form of three strains of T. cruzi, Tulahuen 2, CL Brener, and Y. While the three deoxygenated analogues biologically assayed resulted inactives. Unspecific cytotoxicity was evaluated using human macrophages and active derivatives were not toxic at a concentration at least 13 times that of its IC(50) against T. cruzi (CL Brener strain). From the preliminary structure-activity relationship studies lipophilicity and electronic requirements were found relevant to anti-T. cruzi activity. Active compounds are more lipophilic than inactive ones and it was also identified that an optimum value of R Swain-Lupton's descriptor is required for optimal activity.

Nitrofurylsemicarbazone Rhenium and Ruthenium Complexes as Anti-trypanosomal Agents

Rhenium and ruthenium complexes of the type [Re(V)OCl(2)(PPh(3))L] and [Ru(II)Cl(2)(DMSO)(2)L], where L are 5-nitrofurylsemicarbazone derivatives, were prepared in an effort to obtain new anti-trypanosomal agents combining the recognized biological activity of these metals and the trypanocidal activity of the free ligands. Rhenium complexes resulted unstable in aqueous solution not allowing their use as potential drugs. On the other hand, complexation to ruthenium of the bioactive ligands lead to the lack of antiprotozoa activity even though free radical production and redox cycling induction were detected when the compounds were incubated in presence of Trypanosoma cruzi cells. The lack of anti-trypanosomal activity of ruthenium complexes could be explained on the basis of their high protein binding capacity and their high hydrophilicity.

2H-Benzimidazole 1,3-Dioxide Derivatives: A New Family of Water-Soluble Anti-Trypanosomatid Agents†

Three series of benzimidazole N-oxide derivatives were developed and were examined for their activity against trypanosomatid parasites (Trypanosoma cruzi and Leishmania spp.). 2H-benzimidazole 1,3-dioxides displayed remarkable in vitro activities against both parasites, with derivatives 28, 29, and 32 being the most potent (IC50 < 5 microM) against the epimastigote form of T. cruzi and 28, 33, and 35 the most potent against the promastigote form of Leishmania spp. Unspecific cytotoxicity was evaluated using murine macrophages, and derivative 33 was not toxic at a concentration 30 times that of its IC50 against T. cruzi that was completely toxic for Leishmania spp., implying that the series of 2H-benzimidazole 1,3-dioxides is selective toward both trypanosomatid parasites. Derivatives 33 and 35 were submitted to an in vivo assay using an acute model of Chagas' disease and a short-term treatment (30 mg/kg/day orally administrated as aqueous solution, during 10 days). While in the control (untreated) and Benznidazole (50 mg/kg/day) groups survival fraction was 60.0% and 87.5%, respectively, none of the animals treated with derivatives 33 and 35 died. From the preliminary structure-activity relationship studies reduction potential and electrophilicity were found relevant to anti-T. cruzi activity. Active compounds are better electrophiles and more easily reduced than inactive ones.

Novel Antitrypanosomal Agents Based on Palladium Nitrofurylthiosemicarbazone Complexes: DNA and Redox Metabolism as Potential Therapeutic Targets

In the search for new therapeutic tools against American Trypanosomiasis palladium complexes with bioactive nitrofuran-containing thiosemicarbazones as ligands were obtained. Sixteen novel palladium (II) complexes with the formulas [PdCl2(HL)] and [Pd(L)2] were synthesized, and the crystal structure of [Pd(5-nitrofuryl-3-acroleine thiosemicarbazone)2] x 3DMSO was solved by X-ray diffraction methods. Most complexes showed higher in vitro growth inhibition activity against Trypanosoma cruzi than the standard drug Nifurtimox. In most cases, the activity of the ligand was maintained or even increased as a result of palladium complexation. In addition, the complexes' mode of antitrypanosomal action was investigated. Although the complexes showed strong DNA binding, all data strongly suggest that the main trypanocidal mechanism of action is the production of oxidative stress as a result of their bioreduction and extensive redox cycling. Moreover, the complexes were found to be irreversible inhibitors of trypanothione reductase.

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.

New potent 5-substituted benzofuroxans as inhibitors of Trypanosoma cruzi growth: Quantitative structure–activity relationship studies

Benzofuroxan derivatives have been shown to inhibit the growth of Trypanosoma cruzi, the etiological agent of Chagas' disease. Therefore, 2D- and 3D-QSAR models of their in vitro antichagasic activity were developed. Six new derivatives were synthesized to complete a final set of 26 structurally diverse benzofuroxans. The 2D-QSAR model (r = 0.939, r(adj)(2) = 0.849) was generated using multiple regression analysis of tabulated substituents' physicochemical properties and indicator variables. In addition, a 3D-QSAR model (r(2) = 0.997, q(2) = 0.802) was obtained using a comparative molecular field analysis (CoMFA). Due to the well-known benzofuroxan tautomerism, in both approaches (2D- and 3D-QSAR) it was necessary to include an indicator variable to consider the N-oxide position (I(6)). This parameter was established using low-temperature NMR experiments. Both QSAR models identified the electrophilic character of the substituent alpha-atom as a requirement for activity. Further support was found using a density functional theory (DFT) approach.

Benzo[1,2-c]1,2,5-oxadiazole N-oxide derivatives as potential antitrypanosomal drugs. Part 3: Substituents-clustering methodology in the search for new active compounds

The results of a study on the use of Hansch's series design, cluster methodology, for the generation of new benzo[1,2-c]1,2,5-oxadiazole N-oxide derivatives as antitrypanosomal compounds are described. In vitro activity of these compounds was tested against Tulahuen 2 strain of Trypanosoma cruzi. Clearly, the Hansch methodology allowed identifying two cluster-substituents suitable for further structural modifications. The most effective drugs, derivatives 11, 18, and 21, with 50% inhibitory concentration (IC(50)) of the same order as that of the reference drug, represent an excellent structural point of chemical modifications for the design of future drugs. Preliminary results from the study of the mechanism of action of these benzofuroxans point to perturbation of the mitochondrial electron chain, inhibiting parasite respiration.

Synthesis and biological properties of new 5-nitroindazole derivatives

A series of new 3-alkoxy- or 3-hydroxy-1-[omega-(dialkylamino)alkyl]-5-nitroindazoles have been synthesized and their trichomonacidal, antichagasic and antineoplastic properties studied. Five derivatives (5, 6, 8, 9 and 17) showed remarkable trichomonacidal activity against Trichomonas vaginalis at 10 microg/mL concentration. Three compounds (8, 10, 11) exhibited interesting antichagasic activity and these same compounds moderate antineoplastic activity against TK-10 and HT-29 cell lines. Unspecific cytotoxicity against macrophages has also been evaluated and only compounds 9, 10 and 11 resulted cytotoxic at the higher dose evaluated (100 microg/mL), loosing cytotoxicity at lower doses. QSAR studies have been carried out. X-ray crystallographic study of compound 8 has been performed.

In vitro activity and mechanism of action against the protozoan parasite Trypanosoma cruzi of 5-nitrofuryl containing thiosemicarbazones

The in vitro growth inhibition activity of new thiosemicarbazone derivatives against the protozoan parasite Trypanosoma cruzi, the causative agent of American trypanosomiasis, are described. The designed compounds combine in the same molecule the thiosemicarbazone function, recently described as a potent cruzain-inhibitor moiety, and the recognised 5-nitrofuryl group, an oxidative stress promoter. Some of the derivatives were found to be very active against the cultured (epimastigote) form of the parasite, being 1.5-1.7-fold more active than the reference compound, Nifurtimox. Free radicals production was detected when the compounds were incubated in presence of mammalian-liver microsomes. The thiosemicarbazones' capacity to act as pharmacophore in the cruzain inhibition process was theoretically analysed. Frontier molecular orbital HOMO was found as an adequate descriptor in this process. Acute in vivo toxicity of two of the more active derivatives was evaluated. The results showed that these compounds are among the most potent 5-nitrofuryl derivatives tested against this parasite thus support further in vivo studies of some of these thiosemicarbazones.