Synthesis of quinone imine and sulphur-containing compounds with antitumor and trypanocidal activities: redox and biological implications.

Ortho-Quinones represent a special class of redox active compounds associated with a spectrum of pronounced biological activities, including selective cytotoxicity and antimicrobial actions. The modification of the quinone ring by simple nitrogen and sulphur substitutions leads to several new classes of compounds with their own, distinct redox behaviour and equally distinct activities against cancer cell lines and Trypanosoma cruzi. Some of the compounds investigated show activity against T. cruzi at concentrations of 24.3 and 65.6 µM with a selectivity index of around 1. These results demonstrate that simple chemical modifications on the ortho-quinone ring system, in particular, by heteroatoms such as nitrogen and sulphur, transform these simple redox molecules into powerful cytotoxic agents with considerable "potential", not only in synthesis and electrochemistry, but also, in a broader sense, in health sciences.

Synthesis of quinones with highlighted biological applications: A critical update on the strategies towards bioactive compounds with emphasis on lapachones.

Naphthoquinones are of key importance in organic synthesis and medicinal chemistry. In the last few years, various synthetic routes have been developed to prepare bioactive compounds derived or based on lapachones. In this sense, this review is mainly focused on the synthetic aspects and strategies used for the design of these compounds on the basis of their biological activities for the development of drugs against the neglected diseases leishmaniases and Chagas disease and also cancer. Three strategies used to develop bioactive quinones are discussed and categorized: (i) C-ring modification, (ii) redox centre modification and (iii) A-ring modification. Framed within these strategies for the development of naphthoquinoidal compounds against T. cruzi. Leishmania and cancer, reactions including copper-catalyzed azide-alkyne cycloaddition (click chemistry), palladium-catalysed cross couplings, C-H activation reactions, Ullmann couplings and heterocyclisations reported up to July 2019 will be discussed. The aim of derivatisation is the generation of novel molecules that can potentially inhibit cellular organelles/processes, generate reactive oxygen species and increase lipophilicity to enhance penetration through the plasma membrane. Modified lapachones have emerged as promising prototypes for the development of drugs against leishmaniases, Chagas disease and cancer.

Rhodium-catalyzed C-H bond activation for the synthesis of quinonoid compounds: Significant Anti-Trypanosoma cruzi activities and electrochemical studies of functionalized quinones.

Thirty four halogen and selenium-containing quinones, synthesized by rhodium-catalyzed C-H bond activation and palladium-catalyzed cross-coupling reactions, were evaluated against bloodstream trypomastigotes of T. cruzi. We have identified fifteen compounds with IC50/24 h values of less than 2 µM. Electrochemical studies on A-ring functionalized naphthoquinones were also performed aiming to correlate redox properties with trypanocidal activity. For instance, (E)-5-styryl-1,4-naphthoquinone 59 and 5,8-diiodo-1,4-naphthoquinone 3, which are around fifty fold more active than the standard drug benznidazole, are potential derivatives for further investigation. These compounds represent powerful new agents useful in Chagas disease therapy.

Effect of 9-hydroxy-α- and 7-hydroxy-ß-pyran naphthoquinones on Trypanosoma cruzi and structure-activity relationship studies.

The available treatment for the prevention and cure of Chagas disease, caused by the protozoan Trypanosoma cruzi, is still unsatisfactory. Thus, there is an urgent need to develop new drugs. In the last few years, our research group has focused on finding a new chemical entity able to target the infectious bloodstream trypomastigotes. In this study, we assayed 16 ß-lapachone analogous with modifications in the pyran and aromatic ring to find a new prototype with high trypanocidal activity. Interestingly, two ortho-naphthoquinones presented the best trypanocidal profile (8c and 8d with an IC50/24 h of 26.9 ± 1.3 and 23.5 ± 2.5 µM, respectively), which were 4 to 17 times more effective than ß-lapachone (391.5 ± 16.5 µM) and the standard drug benznidazole (103.6 ± 0.6 µM). The introduction of a hydroxyl group on the compounds' aromatic ring modulated their biological profile by increasing their activity not only for cancer cells (MDAMB435), as previously described in literature, but also against T. cruzi. The Structure-Activity Relationship (SAR) study indicated that this introduction modulated HOMO and MEP parameters, improving the trypanocidal activity.

Synthesis of quinoidal molecules: strategies towards bioactive compounds with an emphasis on lapachones.

Naphthoquinoidal compounds are of great interest in medicinal chemistry. In recent years, several synthetic routes have been developed to obtain bioactive molecules derived from lapachones. In this mini-review, we focus on the synthetic aspects and strategies used to design these compounds and on the biological activities of these substances for the development of drugs against the neglected diseases leishmaniasis and Chagas disease as well as malaria, tuberculosis and cancer. Three strategies used to develop bioactive naphthoquinoidal compounds are discussed: (i) C-ring modification, (ii) redox centre modification and (iii) A-ring modification. Among these strategies, reactions such as copper-catalysed azide-alkyne cycloaddition (click chemistry), palladium-catalysed cross couplings, and heterocyclisations will be discussed for the development of naphthoquinoidal compounds against Trypanosoma cruzi, Leishmania and cancer. The aim of derivatisation is the generation of novel molecules that inhibit cellular organelles/processes, generate reactive oxygen species (ROS) and increase lipophilicity to enhance penetration through the plasma membrane. Modified lapachones have emerged as promising prototypes for the development of drugs against neglected diseases and cancer.

Trypanosoma cruzi mitochondrial swelling and membrane potential collapse as primary evidence of the mode of action of naphthoquinone analogues.

BACKGROUND: Naphthoquinones (NQs) are privileged structures in medicinal chemistry due to the biological effects associated with the induction of oxidative stress. The present study evaluated the activities of sixteen NQs derivatives on Trypanosoma cruzi. RESULTS: Fourteen NQs displayed higher activity against bloodstream trypomastigotes of T. cruzi than benznidazole. Further assays with NQ1, NQ8, NQ9 and NQ12 showed inhibition of the proliferation of axenic epimastigotes and intracelulluar amastigotes interiorized in macrophages and in heart muscle cells. NQ8 was the most active NQ against both proliferative forms of T. cruzi. In epimastigotes the four NQs induced mitochondrial swelling, vacuolization, and flagellar blebbing. The treatment with NQs also induced the appearance of large endoplasmic reticulum profiles surrounding different cellular structures and of myelin-like membranous contours, morphological characteristics of an autophagic process. At IC50 concentration, NQ8 totally disrupted the ΔΨm of about 20% of the parasites, suggesting the induction of a sub-population with metabolically inactive mitochondria. On the other hand, NQ1, NQ9 or NQ12 led only to a discrete decrease of TMRE + labeling at IC50 values. NQ8 led also to an increase in the percentage of parasites labeled with DHE, indicative of ROS production, possibly the cause of the observed mitochondrial swelling. The other three NQs behaved similarly to untreated controls. CONCLUSIONS: NQ1, NQ8, NQ9 and NQ12 induce an autophagic phenotype in T. cruzi epimastigoted, as already observed with others NQs. The absence of oxidative stress in NQ1-, NQ9- and NQ12-treated parasites could be due to the existence of more than one mechanism of action involved in their trypanocidal activity, leaving ROS generation suppressed by the detoxification system of the parasite. The strong redox effect of NQ8 could be associated to the presence of the acetyl group in its structure facilitating quinone reduction, as previously demonstrated by electrochemical analysis. Further experiments using biochemical and molecular approaches are needed to better characterize ROS participation in the mechanism of action of these NQs.

Design and synthesis of new (E)-cinnamic N-acylhydrazones as potent antitrypanosomal agents.

We report herein the synthesis and trypanocidal profile of new (E)-cinnamic N-acylhydrazones (NAHs) designed by exploiting molecular hybridization between the potent cruzain inhibitors (E)-1-(benzo[d][1,3]dioxol-5-yl)-3-(4-bromophenyl)prop-2-en-1-one and (E)-3-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene)-7-methoxy-2-naphthohydrazide. These derivatives were evaluated against both amastigote and trypomastigote forms of Trypanosoma cruzi and lead us to identify two compounds that were approximately two times more active than the reference drug, benznidazole, and with good cytotoxic index. Although designed as cruzain inhibitors, the weak potency displayed by the best cinnamyl NAH derivatives indicated that another mechanism of action was likely responsible for their trypanocide action.

Different cell death pathways induced by drugs in Trypanosoma cruzi: an ultrastructural study.

Electron microscopy has proven to be a reliable and essential tool to determine morphological alterations and target organelles in the investigation of new drugs for Chagas disease. In this review, we focused on evaluating different agents that induce death of Trypanosoma cruzi, i.e. lysophospholipids analogues, naphthoquinones and derivatives, cytoskeletal inhibitors and natural products. Apoptosis-like presents as morphological characteristics DNA fragmentation, membrane blebbing and apoptotic body formation. Autophagy involves autophagosome formation, with the appearance of membranes surrounding organelles and cytosolic structures. Necrosis causes the loss of osmotic balance, an increase of cytoplasmic vacuolization and plasma membrane disruption. Mitochondrion appears as a central checkpoint in both apoptosis and necrosis. Our evidences of ultrastructural changes to T. cruzi treated with the different classes of compounds point to dramatic mitochondrial alterations and similar autophagic phenotypes. Lysophospholipid analogues interfere in the lipid biosynthesis in epimastigotes, altering the amount of both phospholipids and sterols, and consequently the physical properties of the membrane. Naphthoquinone derivatives led to a strong DNA fragmentation in trypomastigotes and to the release of cysteine proteases from reservosomes to cytosol in epimastigotes, starting a proteolytic process which results in parasite death. The susceptibility of reservosomes was also observed in parasites treated with propolis, suggesting impairment of lipid metabolism, compromising membrane fluidity and leading to lysis. The cytoskeletal agents blocked mitosis of epimastigotes, arresting cell cycle and impairing the parasite proliferation. The variety of drug stimuli converge to the same pathway of death suggests an intense cross-talking between the three types of PCD in the protozoa.

Trypanosoma cruzi targets for new chemotherapeutic approaches.

BACKGROUND: Strategies for development of anti-parasite chemotherapy involve identification of active principles of plants, investigation of drugs already licensed for other pathologies, or validation of specific targets identified within key metabolic pathways. OBJECTIVE: To review the state of the art of drug targets against Trypanosoma cruzi with emphasis on sterol metabolism, kinetoplast DNA (kDNA) sites, trypanothione reductase, cysteine proteinase, hypoxanthine-guanine phosphoribosyltransferase, dihydrofolate reductase and glyceraldehyde-3-phosphate dehydrogenase. METHODS: Current knowledge, accumulated over the last three decades, on targets for design and development of new trypanocidal compounds is described. RESULTS/CONCLUSION: There is an urgent need for better drugs to treat chagasic patients. Since the introduction of benznidazole and nifurtimox only allopurinol and a few sterol inhibitors have moved to clinical trials, despite the long list of natural and synthetic compounds assayed against T. cruzi. This reflects, at least in part, the absence of well-established universal protocols to screen and compare drug activity associated with a lack of definitive preclinical evidence of parasitological cure in animal models.

Effect of a beta-lapachone-derived naphthoimidazole on Trypanosoma cruzi: identification of target organelles.

OBJECTIVES: Investigation of the mode of action of the naphthoimidazole N1, obtained from the reaction of beta-lapachone with benzaldehyde, which among 45 semi-synthetic derivatives of naphthoquinones isolated from Tabebuia sp. was one of the most active compounds against Trypanosoma cruzi trypomastigotes. METHODS: Quantification of the effect of N1 against the proliferative forms of T. cruzi, and investigation of potential targets in the parasite using electron microscopy and flow cytometry techniques. RESULTS: N1 presented the following order of activity: amastigotes > trypomastigotes > epimastigotes. The effect on intracellular forms was approximately 25 times higher than on macrophages and heart muscle cells. N1-treated parasites presented an abnormal chromatin condensation and mitochondrial damage. In epimastigotes, alterations of reservosomes were observed, and in trypomastigotes, a decrease in the electron density of acidocalcisomes was observed. In epimastigotes, the naphthoimidazole inhibited the activity of succinate cytochrome c reductase. Labelling with rhodamine 123 or Acridine Orange was decreased in both forms treated with N1. CONCLUSIONS: The results suggest that epimastigotes, reservosomes, mitochondrion, and nucleus contain N1 targets. In trypomastigotes, in which reservosomes are absent, the organelles affected by the compound were also the mitochondrion and nucleus, as well as acidocalcisomes, in which the decrease in electron density could be due to the use of polyphosphate as an alternative energy supply.