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Trypanosoma cruzi is a protozoan parasite that causes Chagas disease, a neglected tropical disease that is endemic in Latin America and spreading worldwide due to globalization. The current treatments are based on benznidazole and nifurtimox; however, these drugs have important limitations and limited efficacy during the chronic phase, reinforcing the necessity of an alternative chemotherapy. For the last 30 years, our group has been evaluating the biological activity of naphthoquinones and derivatives on T. cruzi, and of the compounds tested, N1, N2 and N3 were found to be the most active in vitro. Here, we show the synthesis of a novel β-lapachone-derived naphthoimidazolium named N4 and assess its activity on T. cruzi stages and the mechanism of action. The new compound was very active on all parasite stages (IC50/24 h in the range of 0.8–7.9 μM) and had a selectivity index of 5.4. Mechanistic analyses reveal that mitochondrial ROS production begins after short treatment starts and primarily affects the activity of complexes II-III. After 24 h treatment, a partial restoration of mitochondrial physiology (normal complexes II-III and IV activities and controlled H2O2 release) was observed; however, an extensive injury in its morphology was still detected. During treatment with N4, we also observed that trypanothione reductase activity increased in a time-dependent manner and concomitant with increased oxidative stress. Molecular docking calculations indicated the ubiquinone binding site of succinate dehydrogenase as an important interaction point with N4, as with the FMN binding site of dihydroorotate dehydrogenase. The results presented here may be a good starting point for the development of alternative treatments for Chagas disease and for understanding the mechanism of naphthoimidazoles in T. cruzi.

BACKGROUND Chagas disease, which is caused by the protozoan Trypanosoma cruzi, is endemic to Latin America and mainly affects low-income populations. Chemotherapy is based on two nitrocompounds, but their reduced efficacy encourages the continuous search for alternative drugs. Our group has characterised the trypanocidal effect of naphthoquinones and their derivatives, with naphthoimidazoles derived from β-lapachone (N1, N2 and N3) being the most active in vitro. OBJECTIVES In the present work, the effects of N1, N2 and N3 on acutely infected mice were investigated. METHODS in vivo activity of the compounds was assessed by parasitological, biochemical, histopathological, immunophenotypical, electrocardiographic (ECG) and behavioral analyses. FINDINGS Naphthoimidazoles led to a decrease in parasitaemia (8 dpi) by reducing the number of bloodstream trypomastigotes by 25-50% but not by reducing mortality. N1 protected mice from heart injury (15 dpi) by decreasing inflammation. Bradycardia was also partially reversed after treatment with N1 and N2. Furthermore, the three compounds did not reverse hepatic and renal lesions or promote the improvement of other evaluated parameters. MAIN CONCLUSION N1 showed moderate trypanocidal and promising immunomodulatory activities, and its use in combination with benznidazole and/or anti-arrhythmic drugs as well as the efficacy of its alternative formulations must be investigated in the near future.

Abstract Chagas disease is caused by the hemoflagellate protozoa Trypanosoma cruzi and is one of the most important neglected tropical diseases, especially in Latin American countries, where there is an association between low-income populations and mortality. The nitroderivatives used in current chemotherapy are far from ideal and present severe limitations, justifying the continuous search for alternative drugs. Since the1990s, our group has been investigating the trypanocidal activity of natural naphthoquinones and their derivatives, and three naphthoimidazoles (N1, N2 and N3) derived from β-lapachone were found to be most effective in vitro. Analysis of their mechanism of action via cellular, molecular and proteomic approaches indicates that the parasite mitochondrion contains one of the primary targets of these compounds, trypanothione synthetase (involved in trypanothione production), which is overexpressed after treatment with these compounds. Here, we further evaluated the participation of the mitochondria and reactive oxygen species (ROS) in the anti- T. cruzi action of naphthoimidazoles. Preincubation of epimastigotes and trypomastigotes with antioxidants (α-tocopherol and urate) strongly protected the parasites from the trypanocidal effect of naphthoimidazoles, decreasing the ROS levels produced and reverting the mitochondrial swelling phenotype. The addition of pro-oxidants (menadione and H 2 O 2) before the treatment induced an increase in parasite lysis. Despite the O 2 uptake and mitochondrial complex activity being strongly reduced by N1, N2 and N3, urate partially restored the mitochondrial metabolism only in N1-treated parasites. In parallel, MitoTEMPO, a mitochondrial-targeted antioxidant, protected the functionality of the mitochondria in N2- and N3-treated parasites. In addition, the trypanothione reductase activity was remarkably increased after treatment with N1 and N3, and molecular docking demonstrated that these two compounds were positioned in pockets of this enzyme. Based on our findings, the direct impairment of the mitochondrial electron transport chain by N2 and N3 led to an oxidative misbalance, which exacerbated ROS generation and led to parasite death. Although other mechanisms cannot be discounted, mainly in N1-treated parasites, further investigations are required. Graphical abstract fx1 Highlights • Naphthoimidazoles promote ROS production and mitochondrial respiration impairment. • Antioxidants reverted oxidative and mitochondrial phenotypes. • The compounds led to an increase in trypanothione reductase activity. [ABSTRACT FROM AUTHOR]

Tuberculosis (TB) is the cause of more than one million deaths worldwide, and despite being a curable disease, some factors can make therapy difficult, emphasizing the need for the development of new drugs that may potentiate the action of the classic anti-TB antimicrobials. Naphthoimidazoles show a broad spectrum of biological activities, including antimycobacterial activity. The aim of this study was to evaluate the anti- Mycobacterium tuberculosis activity of nine naphthoimidazoles, alone and combined with isoniazid (INH) and rifampicin (RIF). We evaluated the minimum inhibitory concentration (MIC) of the compounds, the fractional inhibitory concentration of the combinations of the naphthoimidazoles with INH or RIF, and the cytotoxicity of these compounds. Eight compounds showed MICs ranging from 1.56 to 25 μg/mL and the presence of substituents on phenyl groups shown to be essential for antimycobacterial activity. Four compounds showed additivity with both INH and RIF and showed SI values higher than 10, indicating safety. Thus, considering the antimycobacterial activity and the absence of antagonism between naphthoimidazoles and the two main drugs for TB treatment, these compounds could be scaffolds for the development of new anti-TB drugs. [ABSTRACT FROM AUTHOR]

Several disubstituted angular naphthoimidazoles have been synthesized by a new domino reaction from (1,4-dimethoxynaphthalen-2-yl)amine ( 1) and imines (obtained from 1 and aromatic aldehydes) in the presence of Sc(OTf)3. A plausible pathway for the reaction involves attack of the nucleophilic amine on the imine and further reaction of the resulting intermediate by intramolecular cyclization with loss of a methoxy group and subsequent oxidation to yield the final naphthoimidazole. These naphthoimidazoles were also obtained in lower yields from aromatic aldehydes, Sc(OTf)3 and 2 equiv. of 1 through an ABB′ domino process. Post-condensation transformations allowed direct access to several derivatives. [ABSTRACT FROM AUTHOR]

Abstract: Chagas'' disease, caused by the protozoan Trypanosoma cruzi, is endemic in Latin America, which current treatment presents variable efficacy and serious side effects. A previous screening of naphthoquinone derivatives pointed to the naphthoimidazoles N1, N2 and N3 as the most active compounds against T. cruzi. In this study, a proteomic approach was employed to identify proteins involved in the N1, N2 and N3 trypanocidal activity. In epimastigotes, the naphthoimidazoles are involved in multiple mechanisms: (a) redox metabolism; (b) energy production; (c) ergosterol biosynthesis; (d) cytoskeleton assembly; (e) protein metabolism and biosynthesis; and (f) chaperones modulation. They induce an imbalance in crucial pathways of the parasite, leading to the loss of metabolic homeostasis and T. cruzi death. [Copyright &y& Elsevier]

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Abstract: Four new naphthofuranquinones, obtained from 2-hydroxy-3-allyl-naphthoquinone (1) and nor-lapachol (2), have their structures established by physical and X-ray analysis and their activity evaluated against Trypanosoma cruzi. Compounds 3 and 4 were obtained by addition of iodine to 1 followed by cyclization generating a furan ring. Compound 5 was obtained through the acid-catalyzed reaction by dissolution of 1 in sulfuric acid. Compound 6 was synthesized by addition of bromine and aniline to 2. The IC50/24 h for 3–6 in assays with T. cruzi trypomastigotes was between 157 and 640 μM, while the value for crystal violet was 536.0±3.0 μM. Compounds 3–5 also inhibited epimastigote proliferation. The trypanocidal activity of the new naphthofuranquinones endowed with redox properties reinforces a rational approach in the chemotherapy of Chagas'' disease. [Copyright &y& Elsevier]

We synthesized new naphthoimidazoles from β-lapachone with an aromatic moiety linked to the imidazole ring, using phenylic and heterocyclic aldehydes. The most active compound against Trypanosoma cruzi had a p-methyl group linked to the phenyl ring, presenting an EC50 value of 15.5 ± 2.9 μM. No reliable correlation could be established with the biological activity and the structure of in the phenylic series. For the heterocyclic series, activity was associated with a three bond-distance from nitrogen to the imidazole ring, in accordance with our previous work. [Copyright &y& Elsevier]

• β-lapachone-derived naphthoimidazolium N4 is very active on all T. cruzi stages. • Complexes II-III inhibition and mitochondrial ROS production was showed after 2 h. • Mitochondrial swelling and some physiology alterations were showed at 24 h. • Trypanothione reductase activity is time-dependent increased. • N4 interacts with succinate dehydrogenase and dihydroorotate dehydrogenase. Trypanosoma cruzi is a protozoan parasite that causes Chagas disease, a neglected tropical disease that is endemic in Latin America and spreading worldwide due to globalization. The current treatments are based on benznidazole and nifurtimox; however, these drugs have important limitations and limited efficacy during the chronic phase, reinforcing the necessity of an alternative chemotherapy. For the last 30 years, our group has been evaluating the biological activity of naphthoquinones and derivatives on T. cruzi , and of the compounds tested, N1, N2 and N3 were found to be the most active in vitro. Here, we show the synthesis of a novel β-lapachone-derived naphthoimidazolium named N4 and assess its activity on T. cruzi stages and the mechanism of action. The new compound was very active on all parasite stages (IC 50 /24 h in the range of 0.8–7.9 μM) and had a selectivity index of 5.4. Mechanistic analyses reveal that mitochondrial ROS production begins after short treatment starts and primarily affects the activity of complexes II-III. After 24 h treatment, a partial restoration of mitochondrial physiology (normal complexes II-III and IV activities and controlled H 2 O 2 release) was observed; however, an extensive injury in its morphology was still detected. During treatment with N4, we also observed that trypanothione reductase activity increased in a time-dependent manner and concomitant with increased oxidative stress. Molecular docking calculations indicated the ubiquinone binding site of succinate dehydrogenase as an important interaction point with N4, as with the FMN binding site of dihydroorotate dehydrogenase. The results presented here may be a good starting point for the development of alternative treatments for Chagas disease and for understanding the mechanism of naphthoimidazoles in T. cruzi. [ABSTRACT FROM AUTHOR]

Chagas disease, Sleeping sickness and Leishmaniasis, caused by trypanosomatids Trypanosoma cruzi, Trypanosoma brucei and Leishmania spp., respectively, are considered neglected tropical diseases, and they especially affect impoverished populations in the developing world. The available chemotherapies are very limited, and a search for alternatives is still necessary. In folk medicine, natural naphthoquinones have been employed for the treatment of a great variety of illnesses, including parasitic infections. This review is focused on the anti-trypanosomatid activity and mechanistic analysis of naphthoquinones and derivatives. Among all the series of derivatives tested in vitro, naphthoquinone-derived 1,2,3-triazoles were very active on T. cruzi infective forms in blood bank conditions, as well as in amastigotes of Leishmania spp. naphthoquinones containing a CF 3 on a phenyl amine ring inhibited T. brucei proliferation in the nanomolar range, and naphthopterocarpanquinones stood out for their activity on a range of Leishmania species. Some of these compounds showed a promising selectivity index (SI) (30 to 1900), supporting further analysis in animal models. Indeed, high toxicity to the host and inactivation by blood components are crucial obstacles to be overcome to use naphthoquinones and/or their derivatives for chemotherapy. Multidisciplinary initiatives embracing medicinal chemistry, bioinformatics, biochemistry, and molecular and cellular biology need to be encouraged to allow the optimization of these compounds. Large scale automated tests are pivotal for the efficiency of the screening step, and subsequent evaluation of both the mechanism of action in vitro and pharmacokinetics in vivo is essential for the development of a novel, specific and safe derivative, minimizing adverse effects., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)