Nitro drugs for the treatment of trypanosomatid diseases: past, present, and future prospects

Metal (Au, Pt, Pd, Ni) Bis(dithiolene) complexes as dual-action agents combating cancer and trypanosomatid infections

Cancer and infection diseases pose severe threats to public health worldwide stressing the need for more effective and efficient treatments. Thus, the search for broad-spectrum activity drugs seems justifiable and urgent. Herein, we investigate the anticancer and antitrypanosomatid (anti-Trypanosoma cruzi) activities of eight monoanionic metal bis(dithiolene) complexes, [Ph4P][M(R-thiazdt)2] with Mn+ = Au3+, Pt2+, Pd2+, Ni2+, containing N-alkyl-1,3-thiazoline-2-thione dithiolene ligands (R-thiazdt) with different alkyl groups (R = Et, tBu). Compared to auranofin (AF) and cisplatin (CP), two reference drugs in clinical use, all complexes showed high anticancer activities against A2780 ovarian cancer cells (IC50 values of 0.6-3.8 μM) some also being able to overcome CP resistance in A2780cisR cells. The selectivity index (SI), the IC50 values on normal cells (HDF) vs. A2780 cells, indicated good anticancer specificity (SI > 3) for most of the complexes but with clinical relevance for [Ph4P][Pd(tBu-thiazdt)2] (SI = 10). All complexes showed relevant antitrypanosomatid activities (IC50 values of 2.6-5.8 μM) some even exhibiting lower IC50 values than the reference drug nifurtimox (NFX). The mechanism of cell death seemed to be mediated mainly by the formation of reactive oxygen species (ROS), although to lesser extent for the gold complexes but superior to AF. Although ROS play a role in the main apoptotic pathways, cell death by apoptosis was not evident as shown by the caspase-3/7 assay and the morphological cell features studies by electron microscopy (SEM). Results obtained evidenced that [Ph4P][Pt(tBu-thiazdt)2] and [Ph4P][Pd(tBu-thiazdt)2] complexes might have potential as novel anticancer and antitrypanosomatid agents as alternatives to current therapeutics.

Rhenium(I) and technetium(I) complexes with megazol derivatives: towards the development of a theranostic platform for Chagas disease

The diagnosis and treatment of Chagas disease (CD) in the chronic phase remains a challenge. With that in mind, a potential theranostic device based on the trypanocidal agent known as megazol and the fac-M(CO)3+ (M = Re or 99mTc) fragment is proposed in the present work. The peripheral structure of megazol (LH,H) was modified to obtain the compounds LR1,R2 (R1 = H, R2 = Me and R1 = R2 = Me), which were used in the syntheses of complexes of composition [ReBr(CO)3LR1,R2]. These compounds were studied by elemental analysis, FTIR, UV-vis, NMR (1H and 13C), HR-ESI-MS, HPLC/UPLC and single-crystal XRD. The trypanocidal activity of the rhenium complexes was evaluated in vitro against the intracellular form of Trypanosoma cruzi. With exception of the [ReBr(CO)3LMe,Me] complex, all compounds are more active than the standard drug, benznidazole (Bzn), while [ReBr(CO)3LH,H] also exhibited a much higher selectivity index. In addition, the interaction of megazol and its ReI complex was evaluated with the T. cruzi Old Yellow Enzyme (TcOYE) by both experimental and computational methods. The data showed that megazol as well as its metal complex exhibited a higher affinity for TcOYE compared to Bzn. Finally, the labelling of megazol with 99mTc was successfully carried out. However, the results indicated that the Re complexes used as standards were not homologous with the 99mTc complexes. Despite this discrepancy, this research suggests that the investigation into Re and 99mTc complexes with megazol could lead to the development of a theranostic device for CD in a near future.

A Cytochrome P450 TxtE Model System with Mechanistic and Theoretical Evidence for a Heme Peroxynitrite Active Species

The cytochrome P450 homolog, TxtE, efficiently catalyzes the direct and regioselective aromatic nitration of the indolyl moiety of L-tryptophan to 4-nitro-L-tryptophan, using nitric oxide (NO) and dioxygen (O2) as co-substrates. Pathways for such direct and selective nitration of heteroaromatic motifs present platforms for engineering new nitration biocatalysts for pharmacologically beneficial targets, among a medley of other pivotal industrial applications. Precise mechanistic details concerning this pathway are only weakly understood, albeit a heme iron(III)-peroxynitrite active species has been postulated. To shed light on this unique reaction landscape, we investigated the indole nitration pathway of a series of biomimetic ferric heme superoxide mimics, [(Por)FeIII(O2 -⋅)], in the presence of NO. Therein, our model systems gave rise to three distinct nitroindole products, including 4-nitroindole, the product analogous to that obtained with TxtE. Moreover, 15N and 18O isotope labeling studies, along with meticulously designed control experiments lend credence to a heme peroxynitrite active nitrating agent, drawing close similarities to the tryptophan nitration mechanism of TxtE. All organic and inorganic reaction components have been fully characterized using spectroscopic methods. Theoretical investigation into several mechanistic possibilities deem a unique indolyl radical based reaction pathway as the most energetically favorable, products of which, are in excellent agreement with experimental findings.

Effects of Free and Nanoencapsulated Benznidazole in Acute Trypanosoma cruzi Infection: Role of Cholinergic Pathway and Redox Status

Background/Objectives: The Trypanosoma cruzi infection promotes an intense inflammatory process that affects several tissues. The cholinergic system may exert a regulatory immune response and control the inflammatory process. This study aimed to evaluate the comparative effect of free and nanoencapsulated benznidazole in acute T. cruzi infection to assess hematological, biochemical, and oxidative status triggered by the cholinergic system. Methods: For this, fifty female Swiss mice were distributed in eight groups, i.e., uninfected and infected animals under four treatment protocols: untreated (control-CT); vehicle treatment (Eudragit L 100-EL-100); benznidazole treatment (BNZ); and nanoencapsulated benznidazole treatment (NBNZ). After eight treatment days, the animals were euthanized for sample collection. Results: The peak of parasitemia was at day 7 p.i., and the BNZ and NBNZ controlled and reduced the parasite rate but showed no efficacy in terms of total elimination of parasites analyzed by RT-PCR in both infected groups. The infection promotes significant anemia, leukopenia, and thrombocytopenia, which the BNZ improves. There was an increase in AChE activity during infection, leading to a pro-inflammatory response and an increase in M1 and M2 mACh receptors in the BNZ group, showing that the treatment interacted with the cholinergic pathway. In addition, a pro-oxidative response was characterized in the infection and mainly in the infected BNZ and NBNZ groups. The histopathological analysis showed significative splenomegaly and inflammatory infiltrate in the heart, liver, and spleen. Conclusions: The administration of the BNZ or NBNZ reverses hematological, hepatic, and renal alterations through cholinergic signaling and stimulates a pro-inflammatory response during acute T. cruzi infection.

A Novel Concept for Cleavable Linkers Applicable to Conjugation Chemistry - Design, Synthesis and Characterization

Linkers with disulfide bonds are the only cleavable linkers that utilize physiological thiol gradients as a trigger to initiate the intracellular drug release cascade. Herein, we present a novel concept exploiting the thiol gradient phenomena to design a new class of cleavable linker with no disulfide bond. To support the concept, an electron-deficient sulfonamide-based cleavable linker amenable to conjugation of drug molecules with targeting agents, was developed. Modulating the electron-withdrawing nature of the aryl sulfonamide was critical to the balance between the stability and drug release. Favorable stability and payload release in human serum under physiologically relevant thiol concentrations was demonstrated with two potent cytotoxics. Intracellular payload release was further validated in cell-based assay in context of antibody-drug conjugate generated from monoclonal antibody and sulfonamide containing linker. To support the proposed release mechanism, possible downstream by-products formed from the drug-linker adduct were characterized.

Structural analysis and shape-based identification of novel inhibitors targeting the Trypanosoma cruzi proteasome

There is an urgent need to develop new, safer, and more effective drugs against Chagas disease (CD) as well as related kinetoplastid diseases. Targeting and inhibiting the Trypanosoma cruzi proteasome has emerged as a promising therapeutic approach in this context. To expand the chemical space for this class of inhibitors, we performed virtual screening campaigns with emphasis on shape-based similarity and ADMET prioritization. We describe the ideation and application of robustly validated shape queries for these campaigns, which furnished 44 compounds for biological evaluation. Five hit compounds demonstrated in vitro antitrypanosomal activity by potential inhibition of T. cruzi proteasome and notable chemical diversities, particularly, LCQFTC11. Structural insights were achieved by homology modeling, sequence/structure alignment, proteasome-species comparison, docking, molecular dynamics, and MMGBSA binding affinity estimations. These methods confirmed key interactions as well as the stability of LCQFTC11 at the β4/β5 subunits' binding site of the T. cruzi proteasome, consistent with known inhibitors. Our results warrant future assay confirmation of our hit as a T. cruzi proteasome inhibitor. Importantly, we also shed light into dynamic details for a proteasome inhibition mechanism that shall be further investigated. We expect to contribute to the development of viable CD drug candidates through such a relevant approach.

Synthesis and activity of benzimidazole N-Acylhydrazones against Trypanosoma cruzi, Leishmania amazonensis and Leishmania infantum

In this study, we present the design, synthesis, and cytotoxic evaluation of a series of benzimidazole N-acylhydrazones against strains of T. cruzi (Y and Tulahuen) and Leishmania species (L. amazonensis and L. infantum). Compound (E)-N'-((5-Nitrofuran-2-yl)methylene)-1H-benzo[d]imidazole-2-carbohydrazide demonstrated significant activity against both trypomastigote and amastigote forms (Tulahuen strain), with an IC50/120 h of 0.033 μM and a selectivity index (SI) of 7680. This represents a potency 46 times greater than that of benznidazole (IC50/120 h = 1.520 μM, SI = 1390). Another compound (E)-N'-(2-Hydroxybenzylidene)-1H-benzo[d]imidazole-2-carbohydrazide showed promising activity against both trypomastigote and amastigote forms (Tulahuen strain), with an IC50/120 h of 3.600 μM and an SI of 14.70. However, its efficacy against L. infantum and L. amazonensis was comparatively lower. These findings provide valuable insights for the development of more effective treatments against Trypanosoma cruzi.

Synthesis of Hybrid Molecules with Imidazole-1,3,4-thiadiazole Core and Evaluation of Biological Activity on Trypanosoma cruzi and Leishmania donovani

The aim of this work was to obtain and evaluate, as antiprotozoals, new derivatives of benzoate imidazo-1,3,4-thiadiazole 18-23 based on the concepts of molecular repositioning and hybridization. In the design of these compounds, two important pharmacophoric subunits of the fexnidazole prototype were used: metronidazole was used as a repositioning molecule, p-aminobenzoic acid was incorporated as a bridge group, and 1,3,4-thiadiazole group was incorporated as a second pharmacophore, which at position 5 has an aromatic group with different substituents incorporated. The final six compounds were obtained through a five-step linear route with moderate to good yields. The biological results demonstrated the potential of this new class of compounds, since three of them 19-21 showed inhibitory activity on proliferation, in the order of 50%, in the in vitro assay against epimastigotes of T. cruzi (Strain Y sensitive to nifurtimox and benznidazole) and promastigotes of L. donovani, at a single concentration of 50 μM.

Free Radical Production Induced by Nitroimidazole Compounds Lead to Cell Death in Leishmania infantum Amastigotes

Leishmania infantum is the vector-borne trypanosomatid parasite causing visceral leishmaniasis in the Mediterranean basin. This neglected tropical disease is treated with a limited number of obsolete drugs that are not exempt from adverse effects and whose overuse has promoted the emergence of resistant pathogens. In the search for novel antitrypanosomatid molecules that help overcome these drawbacks, drug repurposing has emerged as a good strategy. Nitroaromatic compounds have been found in drug discovery campaigns as promising antileishmanial molecules. Fexinidazole (recently introduced for the treatment of stages 1 and 2 of African trypanosomiasis), and pretomanid, which share the nitroimidazole nitroaromatic structure, have provided antileishmanial activity in different studies. In this work, we have tested the in vitro efficacy of these two nitroimidazoles to validate our 384-well high-throughput screening (HTS) platform consisting of L. infantum parasites emitting the near-infrared fluorescent protein (iRFP) as a biomarker of cell viability. These molecules showed good efficacy in both axenic and intramacrophage amastigotes and were poorly cytotoxic in RAW 264.7 and HepG2 cultures. Fexinidazole and pretomanid induced the production of ROS in axenic amastigotes but were not able to inhibit trypanothione reductase (TryR), thus suggesting that these compounds may target thiol metabolism through a different mechanism of action.

DprE1 and Ddn as promising therapeutic targets in the development of novel anti-tuberculosis nitroaromatic drugs

Tuberculosis remains the second deadliest infectious disease in humans and a public health threat due to the emergence of multidrug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) strains. Therefore, it is urgent to identify new anti-tuberculosis treatments and novel therapeutic targets to prevent the emergence of resistance. In recent years, the study of anti-tuberculosis properties of nitroaromatic compounds has led to the identification of two novel biological targets, the deazaflavin (F420)-dependent nitroreductase Ddn and the decaprenylphosphoryl-β-d-ribose 2'-epimerase DprE1. This review aims to show why Ddn and DprE1 are promising therapeutic targets and highlight nitroaromatic compounds interest in developing new anti-tuberculosis treatments active against MDR-TB and XDR-TB. Despite renewed interest in the development of new anti-tuberculosis nitroaromatic compounds, pharmaceutical companies often exclude nitro-containing molecules from their drug discovery programs because of their toxic and mutagenic potential. This exclusion results in missed opportunities to identify new nitroaromatic compounds and promising therapeutic targets.

Tackling the challenges of human Chagas disease: A comprehensive review of treatment strategies in the chronic phase and emerging therapeutic approaches

Chagas disease (CD), caused by the flagellated protozoan Trypanosoma cruzi (T. cruzi), affects approximately 7 million people worldwide and is endemic in Latin America, especially among socioeconomically disadvantaged populations. Since the 1960s, only two drugs have been commercially available for treating this illness: nifurtimox (NFX) and benznidazole (BZN). Although these drugs are effective in the acute phase (AP) of the disease, in which parasitemia is usually high, their cure rates in the chronic phase (CP) are low and often associated with several side effects. The CP is characterized by a subpatent parasitaemia and absence of clinical symptoms in the great majority of infected individuals. However, at least 30 % of the individuals will develop potentially lethal symptomatic forms, including cardiac and digestive manifestations. For such reason, in the CP the treatment is usually symptomatic and typically focuses on managing complications such as arrhythmias, heart failure, or digestive problems. Therefore, the need for new drugs or therapeutic approaches using BZN or NFX is extremely urgent. This review presents the main clinical trials, especially in the CP, which involve BZN and NFX in different treatment regimens. Additionally, other therapies using combinations of these drugs with other substances such as allopurinol, itraconazole, ravuconazole, ketoconazole, posaconazole and amiodarone are also reported. The importance of early diagnosis, especially in pediatric patients, is also discussed, emphasizing the need to identify the disease in its early stages to improve the chances of successful treatment.

Synthesis of Nitrostyrylthiazolidine-2,4-dione Derivatives Displaying Antileishmanial Potential

A series of 61 thiazolidine-2,4-diones bearing a styryl group at position 5 was synthesized in 2-5 steps and their structure was proved by elemental and spectral analyses. The compounds obtained were evaluated in vitro against the promastigote stage of the kinetoplastid parasite Leishmania infantum and the human HepG2 cell line, to determine selectivity indices and to compare their activities with those of antileishmanial reference drugs. The study of structure-activity relationships indicated the potential of some derivatives bearing a nitro group on the phenyl ring, especially when located at the meta position. Thus, among the tested series, compound 14c appeared as a hit compound with good antileishmanial activity (EC50 = 7 µM) and low cytotoxicity against both the hepatic HepG2 and macrophage THP-1 human cell lines (CC50 = 101 and 121 µM, respectively), leading to good selectivity indices (respectively, 14 and 17), in comparison with the reference antileishmanial drug compound miltefosine (EC50 = 3.3 µM, CC50 = 85 and 30 µM, SI = 26 and 9). Regarding its mechanism of action, among several possibilities, it was demonstrated that compound 14c is a prodrug bioactivated, predominantly by L. donovani nitroreductase 1, likely leading to the formation of cytotoxic metabolites that form covalent adducts in the parasite. Finally, compound 14c is lipophilic (measured CHI LogD7.7 = 2.85) but remains soluble in water (measured PBS solubility at pH7.4 = 16 µM), highlighting the antileishmanial potential of the nitrostyrylthiazolidine-2,4-dione scaffold.

New 2-nitroimidazole-N-acylhydrazones, analogs of benznidazole, as anti-Trypanosoma cruzi agents

Chagas disease is a neglected tropical parasitic disease caused by the protozoan Trypanosoma cruzi. Worldwide, an estimated 8 million people are infected with T. cruzi, causing more than 10,000 deaths per year. Currently, only two drugs, nifurtimox and benznidazole (BNZ), are approved for its treatment. However, both are ineffective during the chronic phase, show toxicity, and produce serious side effects. This work aimed to obtain and evaluate novel 2-nitroimidazole-N-acylhydrazone derivatives analogous to BNZ. The design of these compounds used the two important pharmacophoric subunits of the BNZ prototype, the 2-nitroimidazole nucleus and the benzene ring, and the bioisosterism among the amide group of BNZ and N-acylhydrazone. The 27 compounds were obtained by a three-step route in 57%-98% yields. The biological results demonstrated the potential of this new class of compounds, since eight compounds were potent and selective in the in vitro assay against T. cruzi amastigotes and trypomastigotes using a drug-susceptible strain of T. cruzi (Tulahuen) (IC50 = 4.3-6.25 µM) and proved to be highly selective with low cytotoxicity on L929 cells. The type I nitroreductase (TcNTR) assay suggests that the new compounds may act as substrates for this enzyme.

In vitro evaluation of the selective cytotoxicity and genotoxicity of three synthetic ortho-nitrobenzyl derivatives in human cancer cell lines, with and without metabolic activation

Although the presence of nitro groups in chemicals can be recognized as structural alerts for mutagenicity and carcinogenicity, nitroaromatic compounds have attracted considerable interest as a class of agents that can serve as source of potential new anticancer agents. In the present study, the in vitro cytotoxicity, genotoxicity, and mutagenicity of three synthetic ortho-nitrobenzyl derivatives (named ON-1, ON-2 and ON-3) were evaluated by employing human breast and ovarian cancer cell lines. A series of biological assays was carried out with and without metabolic activation. Complementarily, computational predictions of the pharmacokinetic properties and druglikeness of the compounds were performed in the Swiss ADME platform. The MTT assay showed that the compounds selectively affected selectively the cell viability of cancer cells in comparison with a nontumoral cell line. Additionally, the metabolic activation enhanced cytotoxicity, and the compounds affected cell survival, as demonstrated by the clonogenic assay. The comet assay, the cytokinesis-block micronucleus assay, and the immunofluorescence of the γ-H2AX foci formation assay have that the compounds caused chromosomal damage to the cancer cells, with and without metabolic activation. The results obtained in the present study showed that the compounds assessed were genotoxic and mutagenic, inducing double-strand breaks in the DNA structure. The high selectivity indices observed for the compounds ON-2 and ON-3, especially after metabolic activation with the S9 fraction, must be highlighted. These experimental biological results, as well as the theoretical properties predicted for the compounds have shown that they are promising anticancer candidates to be exploited in additional studies.

Chagas disease in immunocompromised patients

SUMMARYAs Chagas disease remains prevalent in the Americas, it is important that healthcare professionals and researchers are aware of the screening, diagnosis, monitoring, and treatment recommendations for the populations of patients they care for and study. Management of Trypanosoma cruzi infection in immunocompromised hosts is challenging, particularly because, regardless of antitrypanosomal treatment status, immunocompromised patients with Chagas disease are at risk for T. cruzi reactivation, which can be lethal. Evidence-based practices to prevent and manage T. cruzi reactivation vary depending on the type of immunocompromise. Here, we review available data describing Chagas disease epidemiology, testing, and management practices for various populations of immunocompromised individuals, including people with HIV and patients undergoing solid organ and hematopoietic stem cell transplantation.

Biological Activity of Complexes Involving Nitro-Containing Ligands and Crystallographic-Theoretical Description of 3,5-DNB Complexes

Drug resistance in infectious diseases developed by bacteria and fungi is an important issue since it is necessary to further develop novel compounds with biological activity that counteract this problem. In addition, new pharmaceutical compounds with lower secondary effects to treat cancer are needed. Coordination compounds appear to be accessible and promising alternatives aiming to overcome these problems. In this review, we summarize the recent literature on coordination compounds based on nitrobenzoic acid (NBA) as a ligand, its derivatives, and other nitro-containing ligands, which are widely employed owing to their versatility. Additionally, an analysis of crystallographic data is presented, unraveling the coordination preferences and the most effective crystallization methods to grow crystals of good quality. This underscores the significance of elucidating crystalline structures and utilizing computational calculations to deepen the comprehension of the electronic properties of coordination complexes.

Drug repurposing for parasitic protozoan diseases

Protozoan parasites are major hazards to human health, society, and the economy, especially in equatorial regions of the globe. Parasitic diseases, including leishmaniasis, malaria, and others, contribute towards majority of morbidity and mortality. Around 1.1 million people die from these diseases annually. The lack of licensed vaccinations worsens the worldwide impact of these diseases, highlighting the importance of safe and effective medications for their prevention and treatment. However, the appearance of drug resistance in parasites continuously affects the availability of medications. The demand for novel drugs motivates global antiparasitic drug discovery research, necessitating the implementation of many innovative ways to maintain a continuous supply of promising molecules. Drug repurposing has come out as a compelling tool for drug development, offering a cost-effective and efficient alternative to standard de novo approaches. A thorough examination of drug repositioning candidates revealed that certain drugs may not benefit significantly from their original indications. Still, they may exhibit more pronounced effects in other disorders. Furthermore, certain medications can produce a synergistic effect, resulting in enhanced therapeutic effectiveness when given together. In this chapter, we outline the approaches employed in drug repurposing (sometimes referred to as drug repositioning), propose novel strategies to overcome these hurdles and fully exploit the promise of drug repurposing. We highlight a few major human protozoan diseases and a range of exemplary drugs repurposed for various protozoan infections, providing excellent outcomes for each disease.

Privileged small molecules against neglected tropical diseases: A perspective from structure activity relationships

Neglected tropical diseases (NTDs) comprise diverse infections with more incidence in tropical/sub-tropical areas. In spite of preventive and therapeutic achievements, NTDs are yet serious threats to the public health. Epidemiological reports of world health organization (WHO) indicate that more than 1.5 billion people are afflicted with at least one NTD type. Among NTDs, leishmaniasis, chagas disease (CD) and human African trypanosomiasis (HAT) result in substantial morbidity and death, particularly within impoverished countries. The statistical facts call for robust efforts to manage the NTDs. Currently, most of the anti-NTD drugs are engaged with drug resistance, lack of efficient vaccines, limited spectrum of pharmacological effect and adverse reactions. To circumvent the issue, numerous scientific efforts have been directed to the synthesis and pharmacological development of chemical compounds as anti-infectious agents. A survey of the anti-NTD agents reveals that the majority of them possess privileged nitrogen, sulfur and oxygen-based heterocyclic structures. In this review, recent achievements in anti-infective small molecules against parasitic NTDs are described, particularly from the SAR (Structure activity relationship) perspective. We also explore current advocating strategies to extend the scope of anti-NTD agents.

Synthesis of new trypanocidal agents from the hybridisation of metronidazole and eugenol analogues

Nitroimidazole compounds are well-known bioactive substances, and the structural activity relationship has been reported whereby the position of the nitro group within the imidazole ring has a large influence on the activity. This study focuses on synthesising new trypanocidal agents from the hybridisation of metronidazole with different natural phenols (eugenol, dihydroeugenol and guaiacol). Two different coupling methodologies have been explored in order to analyse the influence of the connector on bioactivity: i) classic direct esterification (AD compounds) and ii) "click" chemistry using a triazole connector (AC compounds). The in vitro trypanocidal tests show good results for both AC and AD hybrid compounds against both epimastigote and trypomastigote forms of T. cruzi. In silico studies showed positive data for most of the synthesised compounds and, in general present low toxicological risks. The AC compounds present lower ClogP (lipophilicity) values than those found for the AD series and higher TPSA (topological polar surface area) values, suggesting lower lipophilicity may be related to the presence of the triazole connector. The AD series compounds have higher Drug Score values than the AC series derivatives, suggesting better general properties for a pharmacological action.

In vitro antitrypanosomal activity of synthesized nitrofurantoin-triazole hybrids against Trypanosoma species causing animal African trypanosomosis

Animal African trypanosomosis (AAT) is a disease caused by Trypanosoma brucei brucei, T. vivax, T. evansi and T. congolense which are mainly transmitted by tsetse flies (maybe the family/genus scientific name for the tsetse flies here?). Synthetic trypanocidal drugs are used to control AAT but have reduced efficacy due to emergence of drug resistant trypanosomes. Therefore, there is a need for the continued development of new safe and effective drugs. The aim of this study was to evaluate the in vitro anti-trypanosomal activity of novel nitrofurantoin compounds against trypanosomes (Trypanosoma brucei brucei, T. evansi and T. congolense) causing AAT. This study assessed previously synthesized nineteen nitrofurantoin-triazole (NFT-TZ) hybrids against animal trypanosomes and evaluated their cytotoxicity using Madin-Darby bovine kidney cells. The n-alkyl sub-series hybrids, 8 (IC50 0.09 ± 0.02 μM; SI 686.45) and 9 (IC50 0.07 ± 0.04 μM; SI 849.31) had the highest anti-trypanosomal activity against T. b. brucei. On the contrary, the nonyl 6 (IC50 0.12 ± 0.06 μM; SI 504.57) and nitrobenzyl 18 (IC50 0.11 ± 0.03 μM; SI 211.07) displayed the highest trypanocidal activity against T. evansi. The nonyl hybrid 6 (IC50 0.02 ± 0.01 μM; SI 6328.76) was also detected alongside the undecyl 8 (IC50 0.02 ± 0.01 μM; SI 3454.36) and 3-bromobenzyl 19 (IC50 0.02 ± 0.01 μM; SI 2360.41) as the most potent hybrids against T. congolense. These hybrids had weak toxicity effects on the mammalian cells and highly selective submicromolar antiparasitic action efficacy directed towards the trypanosomes, hence they can be regarded as potential trypanocidal leads for further in vivo investigation.

Lead Optimization of the 5-Phenylpyrazolopyrimidinone NPD-2975 toward Compounds with Improved Antitrypanosomal Efficacy

Human African trypanosomiasis (HAT) still faces few therapeutic options and emerging drug resistance, stressing an urgency for novel antitrypanosomal drug discovery. Here, we describe lead optimization efforts aiming at improving antitrypanosomal efficacy and better physicochemical properties based on our previously reported optimized hit NPD-2975 (pIC50 7.2). Systematic modification of the 5-phenylpyrazolopyrimidinone NPD-2975 led to the discovery of a R4-substituted analogue 31c (NPD-3519), showing higher in vitro potency (pIC50 7.8) against Trypanosoma brucei and significantly better metabolic stability. Further, in vivo pharmacokinetic evaluation of 31c and experiments in an acute T. brucei mouse model confirmed improved oral bioavailability and antitrypanosomal efficacy at 50 mg/kg with no apparent toxicity. With good physicochemical properties, low toxicity, improved pharmacokinetic features, and in vivo efficacy, 31c may serve as a promising candidate for future drug development for HAT.

Prodrugs as empowering tools in drug discovery and development: recent strategic applications of drug delivery solutions to mitigate challenges associated with lead compounds and drug candidates

The delivery of a drug to a specific organ or tissue at an efficacious concentration is the pharmacokinetic (PK) hallmark of promoting effective pharmacological action at a target site with an acceptable safety profile. Sub-optimal pharmaceutical or ADME profiles of drug candidates, which can often be a function of inherently poor physicochemical properties, pose significant challenges to drug discovery and development teams and may contribute to high compound attrition rates. Medicinal chemists have exploited prodrugs as an informed strategy to productively enhance the profiles of new chemical entities by optimizing the physicochemical, biopharmaceutical, and pharmacokinetic properties as well as selectively delivering a molecule to the site of action as a means of addressing a range of limitations. While discovery scientists have traditionally employed prodrugs to improve solubility and membrane permeability, the growing sophistication of prodrug technologies has enabled a significant expansion of their scope and applications as an empowering tool to mitigate a broad range of drug delivery challenges. Prodrugs have emerged as successful solutions to resolve non-linear exposure, inadequate exposure to support toxicological studies, pH-dependent absorption, high pill burden, formulation challenges, lack of feasibility of developing solid and liquid dosage forms, first-pass metabolism, high dosing frequency translating to reduced patient compliance and poor site-specific drug delivery. During the period 2012-2022, the US Food and Drug Administration (FDA) approved 50 prodrugs, which amounts to 13% of approved small molecule drugs, reflecting both the importance and success of implementing prodrug approaches in the pursuit of developing safe and effective drugs to address unmet medical needs.

The Potential Use of Peptides in the Fight against Chagas Disease and Leishmaniasis

Chagas disease and leishmaniasis are both neglected tropical diseases that affect millions of people around the world. Leishmaniasis is currently the second most widespread vector-borne parasitic disease after malaria. The World Health Organization records approximately 0.7-1 million newly diagnosed leishmaniasis cases each year, resulting in approximately 20,000-30,000 deaths. Also, 25 million people worldwide are at risk of Chagas disease and an estimated 6 million people are infected with Trypanosoma cruzi. Pentavalent antimonials, amphotericin B, miltefosine, paromomycin, and pentamidine are currently used to treat leishmaniasis. Also, nifurtimox and benznidazole are two drugs currently used to treat Chagas disease. These drugs are associated with toxicity problems such as nephrotoxicity and cardiotoxicity, in addition to resistance problems. As a result, the discovery of novel therapeutic agents has emerged as a top priority and a promising alternative. Overall, there is a need for new and effective treatments for Chagas disease and leishmaniasis, as the current drugs have significant limitations. Peptide-based drugs are attractive due to their high selectiveness, effectiveness, low toxicity, and ease of production. This paper reviews the potential use of peptides in the treatment of Chagas disease and leishmaniasis. Several studies have demonstrated that peptides are effective against Chagas disease and leishmaniasis, suggesting their use in drug therapy for these diseases. Overall, peptides have the potential to be effective therapeutic agents against Chagas disease and leishmaniasis, but more research is needed to fully investigate their potential.

Repositioning FDA-Approved Drug Against Chagas Disease and Cutaneous Leishmaniosis by Structure-Based Virtual Screening

BACKGROUND

Chagas disease and cutaneous leishmaniasis, two parasitic diseases caused by Trypanosoma cruzi (T. cruzi) and Leishmania mexicana (L. mexicana), respectively, have a major global impact. Current pharmacological treatments for these diseases are limited and can cause severe side effects; thus, there is a need for new antiprotozoal drugs.

METHODS

Using molecular docking, this work describes a structure-based virtual screening of an FDA-approved drug library against Trypanosoma cruzi and Leishmania mexicana glycolytic enzyme triosephosphate isomerase (TIM), which is highly conserved in these parasites. The selected compounds with potential dual inhibitory activity were tested in vitro to confirm their biological activity.

RESULTS

The study showed that five compounds: nilotinib, chlorhexidine, protriptyline, cyproheptadine, and montelukast, were more active against T. cruzi, than the reference drugs, nifurtimox and benznidazole while chlorhexidine and protriptyline were the most active against L. mexicana.

CONCLUSIONS

The analysis of these compounds and their structural characteristics may provide the basis for the development of new antiprotozoal agents.

Anti-toxoplasma activity and DNA-binding of copper(II) and zinc(II) coordination compounds with 5-nitroimidazole-based ligands

Tetrahedral copper(II) and zinc(II) coordination compounds from 5-nitroimidazole derivatives, viz. 1-(2-chloroethyl)-2-methyl-5-nitroimidazole (cenz) and ornidazole 1-(3-chloro-2-hydroxypropyl)-2-methyl-5-nitroimidazole (onz), were synthesized and spectroscopically characterized. Their molecular structures were determined by X-ray diffraction studies. The complexes [Cu(onz)2X2], [Zn(onz)2X2], [Cu(cenz)2X2] and [Zn(cenz)2X2] (X- = Cl, Br), are stable in solution and exhibit positive LogD7.4 values that are in the range for molecules capable of crossing the cell membrane via passive difussion. Their biological activity against Toxoplasma gondi was investigated, and IC50 and lethal dose (LD50) values were determined. The ornidazole copper(II) compounds showed very good antiparasitic activity in its tachyzoite morphology. The interaction of the coordination compounds with DNA was examined by circular dichroism, fluorescence (using intercalating ethidium bromide and minor groove binding Hoechst 33258) and UV-Vis spectroscopy. The copper(II) compounds interact with the minor groove of the biomolecule, whereas weaker electrostatic interactions take place with the zinc(II) compounds. The spectroscopic data achieved for the two series of complexes (namely with copper(II) and zinc(II) as metal center) agree with the respective DNA-damage features observed by gel electrophoresis.

Antigiardial and antiamebic activities of fexinidazole and its metabolites: new drug leads for giardiasis and amebiasis

The intestinal parasites Giardia lamblia and Entamoeba histolytica are major causes of morbidity and mortality associated with diarrheal diseases. Metronidazole is the most common drug used to treat giardiasis and amebiasis. Despite its efficacy, treatment failures in giardiasis occur in up to 5%-40% of cases. Potential resistance of E. histolytica to metronidazole is an increasing concern. Therefore, it is critical to search for more effective drugs to treat giardiasis and amebiasis. We identified antigiardial and antiamebic activities of the rediscovered nitroimidazole compound, fexinidazole, and its sulfone and sulfoxide metabolites. Fexinidazole is equally active against E. histolytica and G. lamblia trophozoites, and both metabolites were 3- to 18-fold more active than the parent drug. Fexinidazole and its metabolites were also active against a metronidazole-resistant strain of G. lamblia. G. lamblia and E. histolytica cell extracts exhibited decreased residual nitroreductase activity when metabolites were used as substrates, indicating nitroreductase may be central to the mechanism of action of fexinidazole. In a cell invasion model, fexinidazole and its metabolites significantly reduced the invasiveness of E. histolytica trophozoites through basement membrane matrix. A q.d. oral dose of fexinidazole and its metabolites at 10 mg/kg for 3 days reduced G. lamblia infection significantly in mice compared to control. The newly discovered antigiardial and antiamebic activities of fexinidazole, combined with its FDA-approval and inclusion in the WHO Model List of Essential Medicines for the treatment of human African trypanosomiasis, offer decreased risk and a shortened development timeline toward clinical use of fexinidazole for treatment of giardiasis or amebiasis.

Discovery of an orally active nitrothiophene-based antitrypanosomal agent

Human African Trypanosomiasis (HAT), caused by Trypanosoma brucei gambiense and rhodesiense, is a parasitic disease endemic to sub-Saharan Africa. Untreated cases of HAT can be severely debilitating and fatal. Although the number of reported cases has decreased progressively over the last decade, the number of effective and easily administered medications is very limited. In this work, we report the antitrypanosomal activity of a series of potent compounds. A subset of molecules in the series are highly selective for trypanosomes and are metabolically stable. One of the compounds, (E)-N-(4-(methylamino)-4-oxobut-2-en-1-yl)-5-nitrothiophene-2-carboxamide (10), selectively inhibited the growth of T. b. brucei, T. b. gambiense and T. b. rhodesiense, have excellent oral bioavailability and was effective in treating acute infection of HAT in mouse models. Based on its excellent bioavailability, compound 10 and its analogs are candidates for lead optimization and pre-clinical investigations.

Design and synthesis of imidazo[1,2-a]pyridine-chalcone conjugates as antikinetoplastid agents

A library of imidazo[1,2-a]pyridine-appended chalcones were synthesized and characterized using 1 H NMR, 13 C NMR and HRMS. The synthesized analogues were screened for their antikinetoplastid activity against Trypanosoma cruzi, Trypanosoma brucei brucei, Trypanosoma brucei rhodesiense and Leishmania infantum. The analogues were also tested for their cytotoxicity activity against human lung fibroblasts and primary mouse macrophages. Among all screened derivatives, 7f was found to be the most active against T. cruzi and T. b. brucei exhibiting IC50 values of 8.5 and 1.35 μM, respectively. Against T. b. rhodesiense, 7e was found to be the most active with an IC50 value of 1.13 μM. All synthesized active analogues were found to be non-cytotoxic against MRC-5 and PMM with selectivity indices of up to more than 50.

Organocatalytic Michael Addition of Unactivated α-Branched Nitroalkanes to Afford Optically Active Tertiary Nitrocompounds

The direct, asymmetric conjugate addition of unactivated α-branched nitroalkanes is developed based on the combined use of chiral amine/ureidoaminal bifunctional catalysts and a tunable acrylate template to provide tertiary nitrocompounds in 55-80% isolated yields and high enantioselectivity (e.r. up to 96:4). Elaboration of the ketol moiety in thus obtained adducts allows a fast entry to not only carboxylic and aldehyde derivatives but also nitrile compounds and enantioenriched 5,5-disubstituted γ-lactams.

Design, synthesis and antitrypanosomatid activity of 2-nitroimidazole-3,5-disubstituted isoxazole compounds based on benznidazole

Chagas disease and leishmaniasis are neglected diseases of high priority as a public health problem. Pharmacotherapy is based on the administration of a few drugs, which exhibit hazardous adverse effects and toxicity to the patients. Thus, the search for new antitrypanosomatid drugs is imperative to overcome the limitations of the treatments. In this work, 46 2-nitroimidazole 3,5-disubstituted isoxazole compounds were synthesized in good yields by [3 + 2] cycloaddition reaction between terminal acetylene (propargyl-2-nitroimidazole) and chloro-oximes. The compounds were non-toxic to LLC-MK2 cells. Compounds 30, 35, and 44 showed in vitro antichagasic activity, 15-fold, 12-fold, and 10-fold, respectively, more active than benznidazole (BZN). Compounds 30, 35, 44, 45, 53, and 61 acted as substrates for the TcNTR enzyme, indicating that this might be one of the mechanisms of action involved in their antiparasitic activity. Piperazine series and 4-monosubstituted compounds were potent against T. cruzi parasites. Besides the in vitro activity observed in compound 45, the in vivo assay showed that the compound only reduced the parasitemia levels by the seventh-day post-infection (77%, p > 0.001) compared to the control group. However, 45 significantly reduced the parasite load in cardiac tissue (p < 0.01) 11 days post-infection. Compounds 49, 52, and 54 showed antileishmanial activity against intracellular amastigotes of Leishmania (L.) amazonensis at the same range as amphotericin B. These findings highlight the antitrypanosomatid properties of 2-nitroimidazole 3,5-disubstituted isoxazole compounds and the possibility in using them as antitrypanosomatid agents in further studies.

Fexinidazole induced cytotoxicity is distinct from related anti-trypanosome nitroaromatic drugs

Nitroaromatic drugs are of critical importance for the treatment of trypanosome infections in Africa and the Americas. Fexinidazole recently joined benznidazole and nifurtimox in this family when it was approved as the first oral therapy against Human African trypanosomiasis (HAT). Nitroaromatic prodrugs are bioactivated by the trypanosome-specific type I nitroreductase (NTR) enzyme that renders the compounds trypanocidal. A caveat to the specificity of NTR activation is the potential for drug resistance and cross-resistance that can arise if NTR expression or functionality is altered through mutation. The outcomes of NTR bioactivation of nitroaromatic compounds is variable but can include the formation highly reactive open chain nitriles that can damage biomolecules including DNA. A proposed mechanism of action of nitroaromatic compounds is the formation of reactive oxygen species (ROS) resulting in the formation of trypanocidal levels of DNA damage. Fexinidazole made its way to clinical approval without a significant interrogation of its effects on trypanosome biology and a limited understanding of its mechanism of action. Early reports mentioned fexinidazole potentially affects DNA synthesis but without supporting data. In this study, we evaluated and compared the cytotoxic effects of nifurtimox, benznidazole, and fexinidazole on Trypanosoma brucei using in vitro analyses. Specifically, we sought to differentiate between the proposed effects of nitroaromatics on DNA damage and DNA synthesis. Toward this goal we generated a novel γH2A-based flow cytometry assay that reports DNA damage formation in conjunction with cell cycle progression. Here we report that fexinidazole's cytotoxic outcomes are distinct from the related drugs nifurtimox and benznidazole. Specifically, we show that fexinidazole treatment results in a pronounced defect in DNA synthesis that reduces the population of parasites in S phase. In contrast, treatment with nifurtimox and benznidazole appear accumulate DNA damage early in cell cycle and result in a defective G 2 population. The findings presented here bring us closer to understanding the anti-trypanosomatid mechanisms of action of nitroaromatic compounds, which will promote improved drug design and help combat potential drug resistance in the future. Our findings also highlight DNA synthesis inhibition as a powerful anti-parasitic drug target.

A new approach to study semi-coordination using two 2-methyl-5-nitroimidazole copper(ii) complexes of biological interest as a model system

Two novel copper(ii) complexes [Cu(2mni)2(H2O)2](NO3)2·2H2O (1) and [Cu(2mni)2(NO3)2] (2), where 2mni is 2-methyl-5-nitroimidazole, were prepared and characterized in the solid state using single-crystal and powder X-ray diffraction analyses, EPR, electronic and vibrational spectroscopies (FTIR and Raman), and thermogravimetric methods. Both products present an elongated distorted octahedral geometry with axial Cu-O bond lengths of 2.606(14) and 2.593(15) Å, indicating semi-coordination. Density functional theory (DFT) calculations at the B3LYP/LANL2DZ theory level were used to study the electronic properties of 1 and 2. The Independent Gradient Model (IGM) was employed to determine the Intrinsic Bond Strength Index (IBSI) of the semi-coordination and to plot δg isosurfaces for the electronic sharing between the metal center and ligands. A moderate to weak antibacterial activity against Escherichia coli cultures was found for 1 with a 50% growth inhibition (GI50) value of 0.25 mmol L-1. To the best of our knowledge, this is the first time that the semi-coordination analysis using IGM was carried out for a copper(ii) complex with axial elongation, finding a good correlation between the bond length and the IBSI, and the study was extended for a series of analogous complexes described in the literature.

Regioselective synthesis of 3-nitroindoles under non-acidic and non-metallic conditions

An electrophilic substitution reaction, without acid and metal, of indole with ammonium tetramethylnitrate for accessing 3-nitroindole has been developed. In this protocol, trifluoroacetyl nitrate (CF3COONO2) was produced by metathesis of ammonium tetramethyl nitrate and trifluoroacetic anhydride at sub-room temperature. Trifluoroacetyl nitrate (CF3COONO2) is an electrophilic nitrating agent for a variety of indoles, aromatic and heterocyclic aromaticity. Meanwhile, this strategy could be applied to construct the skeleton structure of many kinds of bioactive molecules. Interestingly, 3-nitroindole can be further derivatived as a pyrrolo[2,3-b]indole.

Ferrocene-based nitroheterocyclic sulfonylhydrazones: design, synthesis, characterization and trypanocidal properties

A series of new ferrocenyl nitroheterocyclic sulfonylhydrazones (1a-4a and 1b-2b) were prepared by the reaction between formyl (R = H) or acetyl (R = CH3) nitroheterocyclic precursors [4/5-NO2(C5H2XCOR), where X = O, S)] and ferrocenyl tosyl hydrazine [(η5-C5H5)Fe(η5-C5H4SO2-NH-NH2)]. All compounds were characterized by conventional spectroscopic techniques. In the solid state, the molecular structures of compounds 1a, 2b, and 3a were determined by single-crystal X-ray diffraction. The compounds showed an E-configuration around the C=N moiety. Evaluation of trypanocidal activity, measured in vitro against the Trypanosoma cruzi and Trypanosoma brucei strains, indicated that all organometallic tosyl hydrazones displayed activity against both parasite species with a higher level of potency toward T. brucei than T. cruzi. Moreover, the biological evaluation showed that the 5-nitroheterocyclic derivatives were more efficient trypanocidal agents than their 4-nitroheterocyclic counterparts.

Tackling Sleeping Sickness: Current and Promising Therapeutics and Treatment Strategies

Human African trypanosomiasis is a neglected tropical disease caused by the extracellular protozoan parasite Trypanosoma brucei, and targeted for eradication by 2030. The COVID-19 pandemic contributed to the lengthening of the proposed time frame for eliminating human African trypanosomiasis as control programs were interrupted. Armed with extensive antigenic variation and the depletion of the B cell population during an infectious cycle, attempts to develop a vaccine have remained unachievable. With the absence of a vaccine, control of the disease has relied heavily on intensive screening measures and the use of drugs. The chemotherapeutics previously available for disease management were plagued by issues such as toxicity, resistance, and difficulty in administration. The approval of the latest and first oral drug, fexinidazole, is a major chemotherapeutic achievement for the treatment of human African trypanosomiasis in the past few decades. Timely and accurate diagnosis is essential for effective treatment, while poor compliance and resistance remain outstanding challenges. Drug discovery is on-going, and herein we review the recent advances in anti-trypanosomal drug discovery, including novel potential drug targets. The numerous challenges associated with disease eradication will also be addressed.

Cysteine synthase: multiple structures of a key enzyme in cysteine synthesis and a potential drug target for Chagas disease and leishmaniasis

Chagas disease is a neglected tropical disease (NTD) caused by Trypanosoma cruzi, whilst leishmaniasis, which is caused by over 20 species of Leishmania, represents a group of NTDs endemic to most countries in the tropical and subtropical belt of the planet. These diseases remain a significant health problem both in endemic countries and globally. These parasites and other trypanosomatids, including T. theileri, a bovine pathogen, rely on cysteine biosynthesis for the production of trypanothione, which is essential for parasite survival in hosts. The de novo pathway of cysteine biosynthesis requires the conversion of O-acetyl-L-serine into L-cysteine, which is catalysed by cysteine synthase (CS). These enzymes present potential for drug development against T. cruzi, Leishmania spp. and T. theileri. To enable these possibilities, biochemical and crystallographic studies of CS from T. cruzi (TcCS), L. infantum (LiCS) and T. theileri (TthCS) were conducted. Crystal structures of the three enzymes were determined at resolutions of 1.80 Å for TcCS, 1.75 Å for LiCS and 2.75 Å for TthCS. These three homodimeric structures show the same overall fold and demonstrate that the active-site geometry is conserved, supporting a common reaction mechanism. Detailed structural analysis revealed reaction intermediates of the de novo pathway ranging from an apo structure of LiCS and holo structures of both TcCS and TthCS to the substrate-bound structure of TcCS. These structures will allow exploration of the active site for the design of novel inhibitors. Additionally, unexpected binding sites discovered at the dimer interface represent new potential for the development of protein-protein inhibitors.

Antiparasitic Activity of Plumbago auriculata Extracts and Its Naphthoquinone Plumbagin against Trypanosoma cruzi

Chagas disease (CD) caused by the protozoan Trypanosoma cruzi affects more than six million people worldwide. Treatment is restricted to benznidazole (Bz) and nifurtimox (Nf) that display low activity in the later chronic stage besides triggering toxic events that result in treatment abandonment. Therefore, new therapeutic options are necessary. In this scenario, natural products emerge as promising alternatives to treat CD. In the family Plumbaginaceae, Plumbago sp. exhibits a broad spectrum of biological and pharmacological activities. Thus, our main objective was to evaluate, in vitro and in silico, the biological effect of crude extracts of root and of aerial parts of P. auriculata, as well as its naphthoquinone Plumbagin (Pb) against T. cruzi. The phenotypic assays revealed potent activity of the root extract against different forms (trypomastigote and intracellular forms) and strains (Y and Tulahuen), with a compound concentration that reduced 50% of the number of the parasite (EC₅₀) values ranging from 1.9 to 3.9 µg/mL. In silico analysis showed that Pb is predicted to have good oral absorption and permeability in Caco2 cells, besides excellent probability of absorption by human intestinal cells, without toxic or mutagenic potential effects, not being predicted as a substrate or inhibitor of P-glycoprotein. Pb was as potent as Bz against intracellular forms and displayed a superior trypanosomicidal effect (about 10-fold) in bloodstream forms (EC₅₀ = 0.8 µM) as compared to the reference drug (8.5 µM). The cellular targets of Pb on T. cruzi were evaluated using electron microscopy assays and the findings on bloodstream trypomastigotes showed several cellular insults related to the autophagic process. Regarding toxicity in mammalian cells, the root extracts and the naphthoquinone present a moderate toxic profile on fibroblasts and cardiac cell lines. Then, aiming to reduce host toxicity, the root extract and Pb were tested in combination with Bz, and the data showed additive profiles with the sum of the fractional inhibitory concentration indexes (ΣFICIs) being 1.45 and 0.87, respectively. Thus, our work reveals the promising antiparasitic activity of Plumbago auriculata crude extracts and its purified naphthoquinone Plumbagin against different forms and strains of Trypanosoma cruzi in vitro.

Arylimidamides Have Potential for Chemoprophylaxis against Blood-Transmitted Chagas Disease

Chagas disease (CD) affects over 6 million people worldwide and can be transmitted iatrogenically. Crystal violet (CV) was previously used for pathogen reduction but has harmful side-effects. In the present study, three arylimidamides (AIAs) and CV were used to sterilize mice blood samples experimentally contaminated with bloodstream trypomastigotes (BT) of Trypanosoma cruzi, at non hemolytic doses. All AIAs were not toxic to mouse blood cells until the highest tested concentration (96 µM). The previous treatment of BT with the AIAs impaired the infection establishment of cardiac cell cultures. In vivo assays showed that pre-incubation of mouse blood samples with the AIAs and CV (96 µM) significantly suppressed the parasitemia peak, but only the AIA DB1831 gave ≥90% animal survival, while vehicle treated samples reached 0%. Our findings support further studies regarding the potential use of AIAs for blood bank purposes.

Molecular-level strategic goals and repressors in Leishmaniasis - Integrated data to accelerate target-based heterocyclic scaffolds

Leishmaniasis is a complex of neglected tropical diseases caused by various species of leishmanial parasites that primarily affect the world's poorest people. A limited number of standard medications are available for this disease that has been used for several decades, these drugs have many drawbacks such as resistance, higher cost, and patient compliance, making it difficult to reach the poor. The search for novel chemical entities to treat leishmaniasis has led to target-based scaffold research. Among several identified potential molecular targets, enzymes involved in the purine salvage pathway include polyamine biosynthetic process, such as arginase, ornithine decarboxylase, S-adenosylmethionine decarboxylase, spermidine synthase, trypanothione reductase as well as enzymes in the DNA cell cycle, such as DNA topoisomerases I and II plays vital role in the life cycle survival of leishmanial parasite. This review mainly focuses on various heterocyclic scaffolds, and their specific inhibitory targets against leishmaniasis, particularly those from the polyamine biosynthesis pathway and DNA topoisomerases with estimated activity studies of various heterocyclic analogs in terms of their IC₅₀ or EC₅₀ value, reported molecular docking analysis from available published literatures.

Further Investigations of Nitroheterocyclic Compounds as Potential Antikinetoplastid Drug Candidates

Due to the lack of specific vaccines, management of the trypanosomatid-caused neglected tropical diseases (sleeping sickness, Chagas disease and leishmaniasis) relies exclusively on pharmacological treatments. Current drugs against them are scarce, old and exhibit disadvantages, such as adverse effects, parenteral administration, chemical instability and high costs which are often unaffordable for endemic low-income countries. Discoveries of new pharmacological entities for the treatment of these diseases are scarce, since most of the big pharmaceutical companies find this market unattractive. In order to fill the pipeline of compounds and replace existing ones, highly translatable drug screening platforms have been developed in the last two decades. Thousands of molecules have been tested, including nitroheterocyclic compounds, such as benznidazole and nifurtimox, which had already provided potent and effective effects against Chagas disease. More recently, fexinidazole has been added as a new drug against African trypanosomiasis. Despite the success of nitroheterocycles, they had been discarded from drug discovery campaigns due to their mutagenic potential, but now they represent a promising source of inspiration for oral drugs that can replace those currently on the market. The examples provided by the trypanocidal activity of fexinidazole and the promising efficacy of the derivative DNDi-0690 against leishmaniasis seem to open a new window of opportunity for these compounds that were discovered in the 1960s. In this review, we show the current uses of nitroheterocycles and the novel derived molecules that are being synthesized against these neglected diseases.

Heterologous Expression and Characterization of a Full-length Protozoan Nitroreductase from Leishmania orientalis isolate PCM2

Leishmaniasis, a parasitic disease found in parts of the tropics and subtropics, is caused by Leishmania protozoa infection. Nitroreductases (NTRs), enzymes involved in nitroaromatic prodrug activation, are attractive targets for leishmaniasis treatment development. In this study, a full-length recombinant NTR from the Leishmania orientalis isolate PCM2 (LoNTR), which causes severe leishmaniasis in Thailand, was successfully expressed in soluble form using chaperone co-expression in Escherichia coli BL21(DE3). The purified histidine-tagged enzyme (His₆-LoNTR) had a subunit molecular mass of 36 kDa with no cofactor bound; however, the addition of exogenous flavin (either FMN or FAD) readily increased its enzyme activity. Bioinformatics analysis found that the unique N-terminal sequences of LoNTR is only present in Leishmania where the addition of this region might result in the loss of flavin binding. Either NADH or NADPH can serve as an electron donor to transfer electrons to nitrofurazone; however, NADPH was preferred. Molecular oxygen was identified as an additional electron acceptor resulting in wasteful electrons from NADPH for the main catalysis. Steady-state kinetic experiments revealed a ping-pong mechanism for His₆-LoNTR with K_m,NADPH, K_m,NFZ, and k_cat of 28 µM, 68 µM, and 0.84 min^-1, respectively. Besides nitroreductase activity, His₆-LoNTR also has the ability to reduce quinone derivatives. The properties of full-length His₆-LoNTR were different from previously reported protozoa and bacterial NTRs in many respects. This study provides information of NTR catalysis to be developed as a potential future therapeutic target to treat leishmaniasis.

Engineering Cytochrome P450BM3 Enzymes for Direct Nitration of Unsaturated Hydrocarbons

Applications of the peroxidase activity of cytochrome P450 enzymes in synthetic chemistry remain largely unexplored. We present herein a protein engineering strategy to increase cytochrome P450BM3 peroxidase activity for the direct nitration of aromatic compounds and terminal aryl-substituted olefins in the presence of a dual-functional small molecule (DFSM). Site-directed mutations of key active-site residues allowed the efficient regulation of steric effects to limit substrate access and, thus, a significant decrease in monooxygenation activity and increase in peroxidase activity. Nitration of several phenol and aniline compounds also yielded ortho- and para-nitration products with moderate-to-high total turnover numbers. Besides direct aromatic nitration by P450 variants using nitrite as a nitrating agent, we also demonstrated the use of the DFSM-facilitated P450 peroxidase system for the nitration of the vinyl group of styrene and its derivatives.

Emerging compounds and therapeutic strategies to treat infections from Trypanosoma brucei: an overhaul of the last 5-years patents

INTRODUCTION

Human African Trypanosomiasis is a neglected disease caused by infection from parasites belonging to the Trypanosoma brucei species. Only six drugs are currently available and employed depending on the stage of the infection: pentamidine, suramin, melarsoprol, eflornithine, nifurtimox, and fexinidazole. Joint research projects were launched in an attempt to find new therapeutic options for this severe and often lethal disease.

AREAS COVERED

After a brief description of the recent literature on the parasite and the disease, we searched for patents dealing with the proposal of new anti-trypanosomiasis agents and, following the PRISMA guidelines, we filtered the results to those published from 2018onwards returning suitable entries, which represent the contemporary landscape of compounds/strategies against Trypanosoma brucei. In addition, some relevant publications from the overall scientific literature were also discussed.

EXPERT OPINION

This review comprehensively covers and analyzes the most recent advances not only in the discovery of new inhibitors and their structure-activity relationships but also in the assessment of innovative biological targets opening new scenarios in the MedChem field. Lastly, also new vaccines and formulations recently patented were described. However, natural and synthetic compounds were analyzed in terms of inhibitory activity and selective toxicity against human cells.

Major benznidazole metabolites in patients treated for Chagas disease: Mass spectrometry-based identification, structural analysis and detoxification pathways

Benznidazole is the drug of choice for the treatment of Chagas disease, but its metabolism in humans is unclear. Here, we identified and characterized the major benznidazole metabolites and their biosynthetic mechanisms in humans by analyzing the ionic profiles of urine samples from patients and untreated donors through reversed-phase UHPLC-ESI-QTOF-MS and UHPLC-ESI-QqLIT-MS. A strategy for simultaneous detection and fragmentation of characteristic positive and negative ions was employed using information-dependent acquisitions (IDA). Selected precursor ions, neutral losses, and MS³ experiments complemented the study. A total of six phase-I and ten phase-II metabolites were identified and structurally characterized in urine of benznidazole-treated patients. Based on creatinine-corrected ion intensities, nitroreduction to amino-benznidazole (M1) and its subsequent N-glucuronidation to M5 were the main metabolic pathways, followed by imidazole-ring cleavage, oxidations, and cysteine conjugations. This extensive exploration of benznidazole metabolites revealed potentially toxic structures in the form of glucuronides and glutathione derivatives, which may be associated with recurrent treatment adverse events; this possibility warrants further exploration in future clinical trials. Incorporation of this knowledge of the benznidazole metabolic profile into clinical pharmacology trials could lead to improved treatments, facilitate the study of possible drug-drug interactions, and even mitigation of adverse drug reactions.

Ligand-based virtual screening, molecular dynamics, and biological evaluation of repurposed drugs as inhibitors of Trypanosoma cruzi proteasome

Chagas disease is a well-known Neglected Tropical Disease, mostly endemic in continental Latin America, but that has spread to North America and Europe. Unfortunately, current treatments against such disease are ineffective and produce known and undesirable side effects. To find novel effective drug candidates to treat Chagas disease, we uniquely explore the Trypanosoma cruzi proteasome as a recent biological target and, also, apply drug repurposing through different computational methodologies. For this, we initially applied protein homology modeling to build a robust model of proteasome β4/β5 subunits, since there is no crystallographic structure of this target. Then, we used it on a drug repurposing via a virtual screening campaign starting with more than 8,000 drugs and including the methodologies: ligand-based similarity, toxicity predictions, and molecular docking. Three drugs were selected concerning their favorable interactions at the protein binding site and subsequently submitted to molecular dynamics simulations, which allowed us to elucidate their behavior and compare such theoretical results with experimental ones, obtained in biological assays also described in this paper.Communicated by Ramaswamy H. Sarma.

Structure-activity relationship of dibenzylideneacetone analogs against the neglected disease pathogen, Trypanosoma brucei

Trypanosoma brucei is a protozoan parasite that causes Human African Trypanosomiasis (HAT), a neglected tropical disease (NTD) that is endemic in 36 countries in sub-Saharan Africa. Only a handful drugs are available for treatment, and these have limitations, including toxicity and drug resistance. Using the natural product, curcumin, as a starting point, several curcuminoids and related analogs were evaluated against bloodstream forms of T. b. brucei. A particular subset of dibenzylideneacetone (DBA) compounds exhibited potent in vitro antitrypanosomal activity with sub-micromolar EC₅₀ values. A structure-activity relationship study including 26 DBA analogs was initiated, and several compounds exhibited EC₅₀ values as low as 200 nM. Cytotoxicity counter screens in HEK293 cells identified several compounds having selectivity indices above 10. These data suggest that DBAs offer starting points for a new small molecule therapy of HAT.

Miltefosine and Nifuratel Combination: A Promising Therapy for the Treatment of Leishmania donovani Visceral Leishmaniasis

Visceral leishmaniasis is a neglected vector-borne tropical disease caused by Leishmania donovani and Leishmania infantum that is endemic not only in East African countries, but also in Asia, regions of South America and the Mediterranean Basin. For the pharmacological control of this disease, there is a limited number of old and, in general, poorly adherent drugs, with a multitude of adverse effects and low oral bioavailability, which favor the emergence of resistant pathogens. Pentavalent antimonials are the first-line drugs, but due to their misuse, resistant Leishmania strains have emerged worldwide. Although these drugs have saved many lives, it is recommended to reduce their use as much as possible and replace them with novel and more friendly drugs. From a commercial collection of anti-infective drugs, we have recently identified nifuratel-a nitrofurantoin used against vaginal infections-as a promising repurposing drug against a mouse model of visceral leishmaniasis. In the present work, we have tested combinations of miltefosine-the only oral drug currently used against leishmaniasis-with nifuratel in different proportions, both in axenic amastigotes from bone marrow and in intracellular amastigotes from infected Balb/c mouse spleen macrophages, finding a potent synergy in both cases. In vivo evaluation of oral miltefosine/nifuratel combinations using a bioimaging platform has revealed the potential of these combinations for the treatment of this disease.

Effect of B-NIPOx in Experimental Trypanosoma cruzi Infection in Mice

Chagas disease is caused by Trypanosoma cruzi and represents a major public health problem, which is endemic in Latin America and emerging in the rest of the world. The two drugs that are currently available for its treatment, Benznidazole and Nifurtimox, are partially effective in the chronic phase of the disease. In this study, we designed and synthesized the benzyl ester of N-isopropyl oxamic acid (B-NIPOx), which is a non-polar molecule that crosses cell membranes. B-NIPOx is cleaved inside the parasite by carboxylesterases, releasing benzyl alcohol (a molecule with antimicrobial activity), and NIPOx, which is an inhibitor of α-hydroxy acid dehydrogenase isozyme II (HADH-II), a key enzyme in T. cruzi metabolism. We evaluated B-NIPOx cytotoxicity, its toxicity in mice, and its inhibitory activity on purified HADH-II and on T. cruzi homogenates. We then evaluated the trypanocidal activity of B-NIPOx in vitro and in vivo and its effect in the intestine of T. cruzi-infected mice. We found that B-NIPOx had higher trypanocidal activity on epimastigotes and trypomastigotes than Benznidazole and Nifurtimox, that it was more effective to reduce blood parasitemia and amastigote nests in infected mice, and that, in contrast to the reference drugs, it prevented the development of Chagasic enteropathy.

Giardia lamblia G6PD::6PGL Fused Protein Inhibitors Decrease Trophozoite Viability: A New Alternative against Giardiasis

Treatments to combat giardiasis have been reported to have several drawbacks, partly due to the drug resistance and toxicity of current antiparasitic agents. These constraints have prompted many researchers to investigate new drugs that act against protozoan parasites. Enzyme inhibition is an important means of regulating pathogen metabolism and has recently been identified as a significant alternative target in the search for new treatments. Glucose-6-phosphate dehydrogenase and 6-phosphogluconolactonase (G6PD::6PGL) is a bifunctional enzyme involved in the pentose phosphate pathway (PPP) in Giardia lamblia (G. lamblia). The G. lamblia enzyme is unusual since, unlike the human enzyme, it is a fused enzyme. Here, we show, through inhibition assays, that an in-house chemical library of 120 compounds and four target compounds, named CNZ-7, CNZ-8, CMC-1, and FLP-2, are potent inhibitors of the G. lamblia G6PD::6PGL fused enzyme. With a constant (k2) of 2.3, 3.2, and 2.8 M−1 s−1, respectively, they provoke alterations in the secondary and tertiary protein structure and global stability. As a novel approach, target compounds show antigiardial activity, with IC50 values of 8.7, 15.2, 15.3, and 24.1 µM in trophozoites from G. lamblia. Moreover, these compounds show selectivity against G. lamblia, since, through counter-screening in Caco-2 and HT29 human cells, they were found to have low toxicity. This finding positions these compounds as a potential and attractive starting point for new antigiardial drugs.