In vitro evaluation of the activity of aromatic nitrocompounds against Trypanosoma cruzi

Fourteen compounds were evaluated for their activity against Trypanosoma cruzi blood stream forms at the concentration of 500 g/ml. Six compounds were active and re-tested at lower concentrations.     

Design, synthesis and evaluation of 2,4-diaminoquinazolines as inhibitors of trypanosomal and leishmanial dihydrofolate reductase

This paper describes the design, synthesis and evaluation of a series of 2,4-diaminoquinazolines as inhibitors of leishmanial and trypanosomal dihydrofolate reductase. Compounds were designed by a generating virtual library of compounds and docking them into the enzyme active site. Following their synthesis, they were found to be potent and selective inhibitors of leishmanial dihydrofolate reductase. The compounds were also found to have potent activity against Trypanosoma brucei rhodesiense, a causative organism of African trypanosomiasis and also against Trypanosoma cruzi, the causative organism of Chagas disease. There was significantly lower activity against Leishmania donovani, one of the causative organisms of leishmaniasis.     

Novel 3-nitro-1H-1,2,4-triazole-based piperazines and 2-amino-1,3-benzothiazoles as antichagasic agents

We have previously shown that 3-nitro-1H-1,2,4-triazole-based amines demonstrate significant trypanocidal activity, in particular against Trypanosoma cruzi, the causative parasite of Chagas disease. In the present work we further expanded our research by evaluating in vitro the trypanocidal activity of nitrotriazole-based piperazines and nitrotriazole-based 2-amino-1,3-benzothiazoles to establish additional SARs. All nitrotriazole-based derivatives were active or moderately active against T. cruzi; however two of them did not fulfill the selectivity criteria. Five derivatives were active or moderately active against Trypanosoma brucei rhodesiense while one derivative was moderately active against Leishmania donovani. Active compounds against T. cruzi demonstrated selectivity indexes (toxicity to host cells/toxicity to T. cruzi amastigotes) from 117 to 1725 and 12 of 13 compounds were up to 39-fold more potent than the reference compound benznidazole. Detailed SARs are discussed.     

Quinoxaline derivatives as potential antitrypanosomal and antileishmanial agents

Continuous efforts have been made to discover new drugs for the treatment of Chagas’ disease, human African trypanosomiasis, and leishmaniasis. We have previously reported the synthesis and antileishmanial and antitrypanosomal (Y strain) properties of 2,3-disubstituted quinoxalines. Considering their promising antiparasitic potential, the present study was conducted to expand our search and take advantage of high-throughput assays to investigate the effects of quinoxaline derivatives against Leishmania donovani, Trypanosoma brucei, and Trypanosoma cruzi (Tulahuen strain). These compounds were active against the kinetoplastid parasites that were evaluated. The 2-chloro-3-methylsulfoxylsulfonyl and 2-chloro-3-methylsulfinyl quinoxalines were the most potent, and some of these derivatives were even more active than the reference drugs. Although the 2,3-diaryl-substituted quinoxalines were not active against all of the parasites, they were active against T. brucei and intracellular amastigotes of T. cruzi, without interfering with mammalian cell viability. These compounds presented encouraging results that will guide our future studies on in vivo bioassays towards the mode of action.     

Dicationic DNA-targeted antiprotozoal agents: naphthalene replacement of benzimidazole

A series of naphthalene analogues of highly active benzimidazole diamidines were synthesized using sequential Stille and Suzuki coupling reactions for preparation of the bis-nitrile intermediates. All of the diamidines showed strong DNA affinities as judged by high DeltaTm values with poly(dA-dT). The dicationic compounds were quite active in vitro versus Trypanosoma brucei rhodesiense (T. b. r.) exhibiting IC50 values ranging from 4 to 98 nM. These compounds were also active versus Plasmodium falciparum (P. f.) giving IC50 values ranging from 4 to 33 nM. Two of the compounds showed good activity in vivo in the STIB900 model for acute African trypanosomiasis; one gave 3/4 cures and the other gave 4/4 cures on ip dosage of 20 mg/kg for 4 days. The amidoxime prodrugs of the naphthalene analogues were essentially ineffective.     

Comparative antiplasmodial, leishmanicidal and antitrypanosomal activities of several biflavonoids

The antiplasmodial, leishmanicidal and antitrypanosomal activities of eight natural biflavonoids were estimated in vitro on a chloroquine-resistant strain of Plasmodium falciparum, axenically grown Leishmania donovani amastigotes and Trypanosoma cruzi trypomastigotes and Trypanosoma brucei rhodesiense bloodstream forms. Lanaroflavone showed the highest antiplasmodial activity (IC(50) = 0.48 microM), isoginkgetin was the most active leishmanicidal compound (IC(50) = 1.9 microM), whereas ginkgetin (IC(50) = 11 microM) and isoginkgetin (IC(50) = 13 microM) showed the best antitrypanosomal activity in our assays. The cytotoxicity and the selectivity indices for the most active compounds were also estimated. Lanaroflavone exhibited a high selectivity index value (SI = 159), indicating selective antiplasmodial activity.     

Alkyl-linked bis-THTT derivatives as potent in vitro trypanocidal agents

The effect of several alkyl-linked bis tetrahydro-(2H)-1,3,5-thiadiazine-2-thione (bis-THTT) on Leishmania donovani, Trypanosoma brucei rhodesiense, and Plasmodium falciparum is reported. Most of the compounds exhibited a potent activity against the three parasitic strains but the best in vitro activity profiles were found against T. b. rhodesiense with IC(50) values ranging between 0.3 and 4 microM for the most active compounds.     

Synthesis of a small library of 2-phenoxy-1,4-naphthoquinone and 2-phenoxy-1,4-anthraquinone derivatives bearing anti-trypanosomal and anti-leishmanial activity

Taking advantage of the structural features of natural products showing anti-trypanosomatid activity, we designed and synthesized a small library of 2-phenoxy-1,4-naphthoquinone and 2-phenoxy-1,4-anthraquinone derivatives. The library was obtained following a parallel approach and using readily available synthons. All the derivatives showed inhibitory activity toward either Trypanosoma or Leishmania species, with 8, 10, and 16 being the most active compounds against Trypanosoma brucei rhodesiense, Leishmania donovani, and Trypanosoma cruzi cells (IC(50)=50nM, IC(50)=0.28microM, and IC(50)=1.26microM, respectively).     

Arylfurans as potential trypanosoma cruzi trypanothione reductase inhibitors

The natural lignans veraguensin and grandisin have been reported to be active against Trypanosoma cruzi bloodstream forms. Aiming at the total synthesis of these and related compounds, we prepared three 2-arylfurans and eight 2,5-diarylfurans. They were evaluated for their potential as T. cruzi trypanothione reductase (TR) inhibitors as well against the parasite's intracellular (amastigote) and bloodstream (trypomastigote) forms. Compound 12 was the most effective against TR with an IC50 of 48.5 microM while 7 and 14 were active against amastigotes, inhibiting the parasite development by 60% at 20 microg/ml (59 and 90 microM, respectively). On the other hand, none of the compounds was significantly active against the parasite bloodstream forms even at 250 microg/ml (0.6-1.5 mM).     

Antimalarial and antitrypanosomal activity of a series of amide and sulfonamide derivatives of a 2,5-diaminobenzophenone

Here, we describe a series of readily obtainable benzophenone derivatives with antimalarial and antitrypanosomal activity. The most active compounds display submicromolar activity against Plasmodium falciparum. Micromolar activity is obtained against Trypanosoma brucei. Main problem of the compounds is low selectivity. However, there are indications that separation of antimalarial and cytotoxic activity might by possible. In addition, some compounds inhibit human ABC transporter with nanomolar activity.     

The activity of diguanidino and 'reversed' diamidino 2,5-diarylfurans versus Trypanosoma cruzi and Leishmania donovani

The in vitro activity of 20 dicationic molecules containing either diguanidino or reversed amidine cationic groups were evaluated versus Trypanosoma cruzi and Leishmania donovani. The most active compounds were in the reversed amidine series and six exhibited IC(50) values of less than 1 micro mol versus T. cruzi and five gave similar values versus L. donovani.     

2,4-Diaminopyrimidines as inhibitors of Leishmanial and Trypanosomal dihydrofolate reductase

This paper describes the synthesis of 4'-substituted and 3',4'-disubstituted 5-benzyl-2,4-diaminopyrimidines as selective inhibitors of leishmanial and trypanosomal dihydrofolate reductase. Compounds were then assayed against the recombinant parasite and human enzymes. Some of the compounds showed good activity. They were also tested against the intact parasites using in vitro assays. Good activity was found against Trypanosoma cruzi, moderate activity against Trypanosoma brucei and Leishmania donovani. Molecular modeling was undertaken to explain the results. The leishmanial enzyme was found to have a more extensive lipophilic binding region in the active site than the human enzyme. Compounds which bound within the pocket showed the highest selectivity.     

New ligand-based approach for the discovery of antitrypanosomal compounds

The antitrypanosomal activity of 10 already synthesized compounds was in silico predicted as well as in vitro and in vivo explored against Trypanosoma cruzi. For the computational study, an approach based on non-stochastic linear fingerprints to the identification of potential antichagasic compounds is introduced. Molecular structures of 66 organic compounds, 28 with antitrypanosomal activity and 38 having other clinical uses, were parameterized by means of the TOMOCOMD-CARDD software. A linear classification function was derived allowing the discrimination between active and inactive compounds with a confidence of 95%. As predicted, seven compounds showed antitrypanosomal activity (%AE>70) against epimastigotic forms of T. cruzi at a concentration of 100mug/mL. After an unspecific cytotoxic assay, three compounds were evaluated against amastigote forms of the parasite. An in vivo test was carried out for one of the studied compounds.     

Crystal structure of Trypanosoma cruzi glyceraldehyde-3-phosphate dehydrogenase complexed with an analogue of 1,3-bisphospho-d-glyceric acid.

We report here the first crystal structure of a stable isosteric analogue of 1,3-bisphospho-d-glyceric acid (1,3-BPGA) bound to the catalytic domain of Trypanosoma cruzi glycosomal glyceraldehyde-3-phosphate dehydrogenase (gGAPDH) in which the two phosphoryl moieties interact with Arg249. This complex possibly illustrates a step of the catalytic process by which Arg249 may induce compression of the product formed, allowing its expulsion from the active site. Structural modifications were introduced into this isosteric analogue and the respective inhibitory effects of the resulting diphosphorylated compounds on T. cruzi and Trypanosoma brucei gGAPDHs were investigated by enzymatic inhibition studies, fluorescence spectroscopy, site-directed mutagenesis, and molecular modelling. Despite the high homology between the two trypanomastid gGAPDHs (> 95%), we have identified specific interactions that could be used to design selective irreversible inhibitors against T. cruzi gGAPDH.     

Antitrypanosomal activity of quaternary naphthalimide derivatives

Sleeping sickness caused by Trypanosoma brucei gambiense and rhodesiense is fatal if left untreated. Due to the toxicity of drugs currently used and the emerging resistance against these drugs new lead compounds are urgently needed. Within the frame of a broad screening program for drugs with antitrypanosomal activity, some highly potent tertiary and quaternary mono- and bisnaphthalimides being active in the lower micromolar and nanomolar range of concentration have been identified. These compounds are easily available via a two- or three-step microwave-driven synthesis with high yield.     

Evaluation of some organic compounds on bloodstream forms of Trypanosoma cruzi.

Accidental transmission of Chagas' disease to man by blood transfusion is a serious problem in Latin-America. This paper describes the testing of several synthetic, semi-synthetic, and natural compounds for their activity against blood trypomastigotes in vitro at 4 degrees C. The compounds embody several types of chemical structures: benzoquinone, naphthoquinone, anthracenequinone, phenanthrenequinone, imidazole, piperazine, quinoline, xanthene, and simple benzenic and naphthalenic derivatives. Some of them are for the first time tested against Trypanosoma cruzi. The toxic effect of these compounds on this parasite was done by two quite distinct sets of experiments. In one set, the compounds were added to infected blood as ethanolic solution. In this situation the most active one was a furan-1,2-naphthoquinone, in the same range as gentian violet, a new fact to be considered in the assessment of structure-activity relationships in this class of compounds. In other set, we tentatively evaluated the biological activity of water insoluble compounds by adding them in a pure form without solvent into infected blood. In this way some appear to be very active and it was postulated that the effectiveness of such compounds must result from interactions between them and specific blood components.     

Anti-Trypanosoma activity of some natural stilbenoids and synthetic related heterocyclic compounds

We report the anti-Chagasic activity of the natural dihydrostilbenoid isonotholaenic acid and several simple derivatives, as well as that of some representative compounds of related synthetic series, with basic structures of benzalphthalides, dihydrostilbamides, isoindoles, phthalazin-1-ones, imidazo[2,1-a]isoindoles and pyrimido[2,1-a]isoindoles. The evaluation was performed in vitro on cultures of epimastigote and trypomastigote forms of Trypanosoma cruzi. Some of the tested compounds resulted to be as potent as benznidazole (epimastigotes), and others were shown to be more active than gentian violet (trypomastigotes), used as reference drugs.     

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.     

New antiprotozoal agents: Their synthesis and biological evaluations

Here we report identification of new lead compounds based on quinoline and indenoquinolines with variable side chains as antiprotozoal agents. Quinolines 32, 36 and 37 (Table 1) and indenoquinoline derivatives 14 and 23 (Table 2) inhibit the in vitro growth of the Trypanosoma cruzi, Trypanosoma brucei, Trypanosoma brucei rhodesiense subspecies and Leishmania infantum with IC₅₀ = 0.25 μM. These five compounds have superior activity to that of the front-line drugs such as benznidazole, nifurtimox and comparable to amphotericin B. Thus these compounds constitute new ‘leads’ for further structure–activity studies as potential active antiprotozoal agents.     

In vitro evaluation of antitrypanosomal activity and molecular docking of benzoylthioureas

A series of sixteen benzoylthioureas derivatives were initially evaluated in vitro against the epimastigote form of Trypanosoma cruzi. All of the tested compounds inhibited the growth of this form of the parasite, and due to the promising anti-epimastigote activity from three of these compounds, they were also assayed against the trypomastigote and amastigote forms. ADMET-Tox in silico predictions and molecular docking studies with two main enzymatic targets (cruzain and CYP-51) were performed for the three compounds with the highest activity. The docking studies showed that these compounds can interact with the active site of cruzain by hydrogen bonds and can be coordinated with Fe-heme through the carbonyl oxygen atom of the CYP51. These findings can be considered an important starting point for the proposal of the benzoylthioureas as potent, selective, and multi-target antitrypanosomal agents.