An update on small molecule strategies targeting leishmaniasis

1,2,4-Oxadiazole Derivatives: Physicochemical Properties, Antileishmanial Potential, Docking and Molecular Dynamic Simulations of Leishmania infantum Target Proteins

Visceral leishmaniasis (VL), caused by protozoa of the genus Leishmania, remains a significant public health concern due to its potentially lethal nature if untreated. Current chemotherapy options are limited by severe toxicity and drug resistance. Derivatives of 1,2,4-oxadiazole have emerged as promising drug candidates due to their broad biological activity. This study investigated the effects of novel 1,2,4-oxadiazole derivatives (Ox1-Ox7) on Leishmania infantum, the etiological agent of VL. In silico predictions using SwissADME suggest that these compounds have high oral absorption and good bioavailability. Among them, Ox1 showed the most promise, with higher selectivity against promastigotes and lower cytotoxicity towards L929 fibroblasts and J774.G8 macrophages. Ox1 exhibited selectivity indices of 18.7 and 61.7 against L. infantum promastigotes and amastigotes, respectively, compared to peritoneal macrophages. Ultrastructural analyses revealed severe morphological damage in both parasite forms, leading to cell death. Additionally, Ox1 decreased the mitochondrial membrane potential in promastigotes, as shown by flow cytometry. Molecular docking and dynamic simulations indicated a strong affinity of Ox1 for the L. infantum CYP51 enzyme. Overall, Ox1 is a promising and effective compound against L. infantum.

Revisiting the dipeptidyl carboxypeptidase inhibitor captopril as a source of pan anti-trypanosomatid agents

The protozoan parasites Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. are responsible for continued propagation of neglected tropical diseases such as African sleeping sickness, Chagas disease and leishmaniasis respectively. Following a report that captopril targets Leishmania donovani dipeptidyl carboxypeptidase, a series of simple proline amides and captopril analogues were synthesized and found to exhibit 1-2 μM in vitro inhibition and selectivity against Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. The results were corroborated with computational docking studies. Arguably, the synthetic proline amides represent the structurally simplest examples of in vitro pan antiprotozoal compounds.

Thiourea-functionalized aminoglutethimide derivatives as anti-leishmanial agents

Aim: We aim to develop new anti-leishmanial agents against Leishmania major and Leishmania tropica.Materials & methods: A total of 23 thiourea derivatives of (±)-aminoglutethimide were synthesized and evaluated for in vitro activity against promastigotes of L. major and L. tropica.Results & conclusion: The N-benzoyl analogue 7p was found potent (IC50 = 12.7 μM) against L. major and non toxic to normal cells. The docking studies, indicates that these inhibitors may target folate and glycolytic pathways of the parasite. The N-hexyl compound 7v was found strongly active against both species, and lacked cytotoxicity against normal cells, whereas compound 7r, with a 3,5-bis-(tri-fluoro-methyl)phenyl unit, was active against Leishmania, but was cytotoxic in nature. Compound 7v was thus identified as a hit for further studies.

Effectiveness In Vivo and In Vitro of Polymeric Nanoparticles as a Drug Release System in the Treatment of Leishmaniasis

Leishmaniasis is a neglected disease caused by the parasite of the genus Leishmania. Current treatment regimens are obsolete and cause several side effects, promoting poor patient compliance, in addition to the vast majority already having the potential for resistance. Therefore, polymeric nanoparticles emerge as one of the viable alternatives to overcome existing limitations, through passive or active vectorization. This review aims to summarize the latest studies of polymeric nanoparticles as an alternative treatment for leishmaniasis. In the first section, the main pharmacokinetic and pharmacodynamic challenges of current drugs are reported. The second section details how nanoparticles with and without functionalization are efficient in the treatment of leishmaniasis, discussing the characteristics of the polymer in the formulation. In this way, polymeric nanoparticles can improve the physicochemical properties of leishmanicidal drugs, improving solubility and stability, as well as improve the release of these drugs, directly or indirectly reaching monocytes/macrophages. 64.28% drugs were focused on the treatment of visceral leishmaniasis, and 28.57% on cutaneous leishmaniasis. The most chosen polymers in the literature are chitosan (35.71%) and PLGA (35.71%), the others represented 14.30% drugs, with all able to manage the drug release and increase the in vitro and/or in vivo efficacy of the original molecule. However, there are several barriers for these nanoformulations to cross laboratory research and is necessary more in-depth studies about the metabolites and degradation pathways of the polymers used in the formulations and plasma proteomics studies.

Design, synthesis, and biological evaluation of quinoline-piperazine/pyrrolidine derivatives as possible antileishmanial agents

In pursuance of our efforts to expand the scope of novel antileishmanial entities, a series of thirty-five quinoline-piperazine/pyrrolidine, and other heterocyclic amine derivatives were synthesized via a molecular hybridization approach and examined against intracellular amastigotes of luciferase-expressing Leishmania donovani. The preliminary in vitro screening suggests that twelve compounds in the series exhibited better inhibition against amastigote form with good IC50 values ranging from 2.09 to 8.89 μM and lesser cytotoxicity in contrast to the standard drug miltefosine (IC50 9.25 ± 0.17 μM). Based on the satisfactory selectivity index (SI), two compounds were tested for in vivo leishmanicidal efficacy against Leishmania donovani/golden hamster model. Compounds 33 and 46 have shown significant inhibition of 56.32%, and 49.29%, respectively, in vivo screening at a daily dose of 50 mg/kg for 5 days. The pharmacokinetic results confirmed that 33 and 46 have satisfactory IP exposure with adequate parameters. Collectively, Compound 33 was identified as the most significant potential lead that could be employed as a prototype for future optimizations.

Synthesis, biological assessment, and computational investigations of nifedipine and monastrol analogues as anti-leishmanial major and anti-microbial agents

Leishmaniasis includes a range of parasitic diseases caused by numerous types of the protozoan kinetoplastid parasite. Fungal and bacterial pathogens have led to infectious illnesses causing some main public health problem in current years. A series of dihydropyridine and tetrahydropyrimidine derivatives having fluoro, bromo, and nitro substituents at para-phenyl ring on C4 of dihydropyridine and tetrahydropyrimidine rings were synthesized. Then, anti-leishmanial and antimicrobial potencies of compounds were assessed. All compounds were synthesized via Hantzsch and Biginelli reactions. All derivatives were evaluated for their anti-leishmanial and antimicrobial activities. Moreover, docking and molecular dynamics simulation calculations of the compounds in PRT1 binding site were performed to report the results of anti-leishmanial and antimicrobial activities. Compounds 4a and 4b showed the highest anti-amastigote and anti-promastigote activities. Compound 4a revealed the highest antimicrobial activity against E. coli, P. aeruginosa, and C. albicans strains. In addition, compound 4c showed the highest activity against S. aureus. The fluoro, bromo, and nitro substituents in para-position of phenyl group at C4 of dihydropyridine and tetrahydropyrimidine moieties as well as the bulk and length of the chain linking to the ester moieties are essential for anti-leishmanial and anti-microbial activities of these derivatives. Low cytotoxicity was shown by most of derivatives against macrophages. The molecular docking studies were in agreement with in vitro assay. Moreover, hydrogen binds, RMSF, RMSD, and Rg, strongly showed the steady binding of 4a and 4b compounds in PRT1 active site.

Optimization of the 2-arylquinazoline-4(3H)one scaffold for a selective and potent antitrypanosomal agent: modulation of the mechanism of action through chemical functionalization

We sought to identify a potent and selective antitrypanosomal agent through modulation of the mechanism of action of a 2-arylquinazoline scaffold as an antitrypanosomal agent via chemical functionalization at the 4-position. We wished to use the: (i) susceptibility of trypanosomatids towards nitric oxide (NO) and reactive oxygen species (ROS); (ii) capacity of the 4-substituted quinazoline system to act as an antifolate agent. Three quinazolin-based moieties that differed from each other by having at the 4-position key pharmacophores targeting the induction of NO and ROS production were evaluated in vitro against Leishmania infantum and Trypanosoma cruzi parasites and their modes of action were explored. Replacement of an oxygen moiety at the 4-position of the antifolate 2-arylquinazolin-4(3H)one by hydrazinyl and 5-nitrofuryl-hydrazinyl pharmacophores enhanced antitrypanosomatid activity significantly due to promotion of an additional mechanism beyond the antifolate response such as NO or ROS production, respectively. Among the three types of chemical functionalization, the 5-nitrofuryl-hydrazinyl moiety generated the most potent compounds. Compound 3b was a potential candidate thanks to its sub-micromolar response against the promastigotes/amastigotes of L. infantum and epimastigote of T. cruzi, moderate toxicity on macrophages (J774.1), good selectivity index (∼15.1-17.6) and, importantly, non-mutagenic effects. 2-Arylquinazoline could be an attractive platform to design new anti-trypanosomatid agents with the use of key pharmacophores.

Synthesis of new 3-acetyl-1,3,4-oxadiazolines combined with pyrimidines as antileishmanial and antiviral agents

A new series of 3-acetyl-1,3,4-oxadiazoline hybrid molecules was designed and synthesized using a condensation between acyclonucleosides and substituted phenylhydrazone. All intermediates and final products were screened against Leishmania donovani, a Protozoan parasite and against three viruses SARS-CoV-2, HCMV and VZV. While no significant activity was observed against the viruses, the intermediate with 6-azatymine as thymine and 5-azathymine-3-acetyl-1,3,4-oxadiazoline hybrid exhibited a significant antileishmanial activity. The later compound was the most promising, exhibiting an IC50 value at 8.98 µM on L. donovani intramacrophage amastigotes and a moderate selectivity index value at 2.4.

Synthesis, characterization and evaluation of prenylated chalcones ethers as promising antileishmanial compounds

Drug therapy for leishmaniasis remains a major challenge as currently available drugs have limited efficacy, induce serious side-effects and are not accessible to everyone. Thus, the discovery of affordable drugs is urgently needed. Chalcones present a great potential as bioactive agents due to simple structure and functionalization capacity. The antileishmanial activity of different natural and synthetic chalcones have been reported. Here we report the synthesis of twenty-five novel prenylated chalcones that displayed antiparasitic activity in Leishmania mexicana. All the chalcones were evaluated at 5 µg/mL and eleven compounds exhibited a metabolic inhibition close to or exceeding 50%. Compounds 49, 30 and 55 were the three most active with IC50 values < 10 μM. These chalcones also showed the highest selectivity index (SI) values. Interestingly 49 and 55 possessing a substituent at a meta position in the B ring suggests that the substitution pattern influences antileishmanial activity. Additionally, a tridimensional model of fumarate reductase of L. mexicana was obtained by homology modeling. Docking studies suggest that prenylated chalcones could modulate fumarate reductase activity by binding with good affinity to two binding sites that are critical for the target. In conclusion, the novel prenylated chalcones could be considered as promising antileishmanial agents.

A QSAR Study for Antileishmanial 2-Phenyl-2,3-dihydrobenzofurans †

Leishmaniasis, a parasitic disease that represents a threat to the life of millions of people around the globe, is currently lacking effective treatments. We have previously reported on the antileishmanial activity of a series of synthetic 2-phenyl-2,3-dihydrobenzofurans and some qualitative structure-activity relationships within this set of neolignan analogues. Therefore, in the present study, various quantitative structure-activity relationship (QSAR) models were created to explain and predict the antileishmanial activity of these compounds. Comparing the performance of QSAR models based on molecular descriptors and multiple linear regression, random forest, and support vector regression with models based on 3D molecular structures and their interaction fields (MIFs) with partial least squares regression, it turned out that the latter (i.e., 3D-QSAR models) were clearly superior to the former. MIF analysis for the best-performing and statistically most robust 3D-QSAR model revealed the most important structural features required for antileishmanial activity. Thus, this model can guide decision-making during further development by predicting the activity of potentially new leishmanicidal dihydrobenzofurans before synthesis.

Label-Free Mass Spectrometry Proteomics Reveals Different Pathways Modulated in THP-1 Cells Infected with Therapeutic Failure and Drug Resistance Leishmania infantum Clinical Isolates

As the world is facing increasing difficulties to treat leishmaniasis with current therapies, deeper investigation into the molecular mechanisms responsible for both drug resistance and treatment failure (TF) is essential in drug discovery and development. So far, few available drugs cause severe side effects and have developed several resistance mechanisms. Drug resistance and TF parasite strains from clinical isolates may have acquired altered expression of proteins that characterize specific mechanisms leading to therapy inefficacy. This work aims to identify the biochemical pathways of THP-1 human monocytes infected by different Leishmania infantum clinical isolates from patients with either resistance or with TF outcome, using whole cell differential Mass Spectrometry proteomics. We have adopted network enrichment analysis to integrate the transcriptomics and the proteomic results of infected cells studies. Transferrin receptor C (TFRC) and nucleoside diphosphate kinase 3 (NDK3) were discovered as overexpressed proteins in THP-1 cells infected with paromomycin, antimony, and miltefosine resistant L. infantum lines. The overall achievements represent founding concepts to confirm new targets involved in the parasitic drug resistance and TF mechanisms, and to consider in perspective the importance of a dual host-guest pharmacological approach to treat the acute stage of the disease.

Antileishmanial Activity and In Silico Molecular Docking Studies of Malachra alceifolia Jacq. Fractions against Leishmania mexicana Amastigotes

Malachra alceifolia Jacq. (family Malvaceae), known as "malva," is a medicinal plant used as a traditional therapy in many regions of America, Africa and Asia. Traditionally, this plant is used in the form of extracts, powder and paste by populations for treating fever, stomachache, inflammation, and parasites. However, the ethnopharmacological validation of M. alceifolia has been scarcely researched. This study showed that the chloroform fraction (MA-IC) and subfraction (MA-24F) of the leaves of M. alceifolia exhibited a potential antileishmanial activity against axenic amastigotes of Leishmania mexicana pifanoi (MHOM/VE/60/Ltrod) and had high and moderate cytotoxic effects on the viability and morphology of macrophages RAW 264.7. This study reports, for the first time, possible terpenoid metabolites and derivatives present in M. alceifolia with activity against some biosynthetic pathways in L. mexicana amastigotes. The compounds from the subfractions MA-24F were highly active and were analyzed by gas chromatography-mass spectrometry (GC-MS) and by a molecular docking study in L. mexicana target protein. This study demonstrates the potential modes of interaction and the theoretical affinity energy of the metabolites episwertenol, α-amyrin and methyl commate A, which are present in the active fraction MA-24F, at allosteric sites of the pyruvate kinase, glyceraldehyde-3-phosphate dehydrogenase, triose phosphate isomerase, aldolase, phosphoglucose isomerase, transketolase, arginase and cysteine peptidases A, target proteins in some vital biosynthetic pathways were responsible for the survival of L. mexicana. Some phytoconstituents of M. alceifolia can be used for the search for potential new drugs and molecular targets for treating leishmaniases and infectious diseases. Furthermore, contributions to research and the validation and conservation of traditional knowledge of medicinal plants are needed globally.

Pyrimido[5,4-d]pyrimidine-Based Compounds as a Novel Class of Antitrypanosomal and Antileishmanial Agents

Sleeping sickness and leishmaniasis are neglected tropical diseases that threaten millions of people. The currently available therapies present several limitations, including high toxicity, lack of efficacy, and emerging drug resistance, prompting a search for novel therapeutic agents. In this work, we designed, synthesized, and in vitro evaluated the activity of new pyrimido[5,4-d]pyrimidines against Trypanosoma brucei and Leishmania infantum (promastigote and amastigote forms). The cytotoxicity of the compounds against the THP1 cell line was also assessed. Most tested compounds presented low micromolar activity against T. brucei with IC50 values in the range between 0.9 and 13.4 μM, and one compound also showed activity against L. infantum (IC50 = 3.13 μM). Several molecules presented a selectivity index higher than 10. The most active compound against booth parasites is derivative 4c, with IC50 = 0.94 μM (SI > 107) against T. brucei and IC50 = 3.13 μM (SI > 32) against L. infantum. This data enabled the identification of a new promising molecular scaffold for developing a novel class of antitrypanosomal and antileishmanial agents.

Treatment of Pediatric Cutaneous Leishmaniasis with Liposomal Amphotericin B

BACKGROUND

The use of liposomal amphotericin B (L-AmB) in the treatment of cutaneous leishmaniasis (CL) is increasing. However, few data are available regarding the efficacy and safety of L-AmB in pediatric CL patients.

AIMS

Our aim in this study is to evaluate the efficacy and safety of L-AmB in pediatric CL patients.

METHODS

Pediatric patients admitted to a tertiary training and research hospital in a hyperendemic region for CL between January 2019 and May 2021 and receiving L-AmB therapy for CL were included in this retrospective study. L-AmB treatment was administered as 3 mg/kg for 5 consecutive days and on the 10th day, in a total of 6 doses (18 mg/kg total dose).

RESULT

Fifty-two pediatric patients who received L-AmB therapy for CL were included in the study. In the follow-up 3 months after L-AmB treatment, 16 (31%) patients showed complete clinical recovery, while treatment failure was detected in 36 (69%) patients.

CONCLUSION

In conclusion, considering the low treatment success rate in our study, we think that the L-AmB dose used in our study is not an appropriate treatment option for the treatment of pediatric CL patients. However, we think that prospective studies with a large number of patients treated with higher doses of L-AmB and in whom the causative agents of CL were determined are needed. This article is protected by copyright. All rights reserved.

In Silico Research of New Therapeutics Rotenoids Derivatives against Leishmania amazonensis Infection

Yearly, 1,500,000 cases of leishmaniasis are diagnosed, causing thousands of deaths. To advance in its therapy, we present an interdisciplinary protocol that unifies ethnobotanical knowledge of natural compounds and the latest bioinformatics advances to respond to an orphan disease such as leishmaniasis and specifically the one caused by Leishmania amazonensis. The use of ethnobotanical information serves as a basis for the development of new drugs, a field in which computer-aided drug design (CADD) has been a revolution. Taking this information from Amazonian communities, located in the area with a high prevalence of this disease, a protocol has been designed to verify new leads. Moreover, a method has been developed that allows the evaluation of lead molecules, and the improvement of their affinity and specificity against therapeutic targets. Through this approach, deguelin has been identified as a good lead to treat the infection due to its potential as an ornithine decarboxylase (ODC) inhibitor, a key enzyme in Leishmania development. Using an in silico-generated combinatorial library followed by docking approaches, we have found deguelin derivatives with better affinity and specificity against ODC than the original compound, suggesting that this approach could be adapted for developing new drugs against leishmaniasis.

Hyaluronic acid-Amphotericin B Nanocomplexes: a Promising Anti-Leishmanial Drug Delivery System

The development of an effective amphotericin B (AmB) formulation to replace actual treatments available for leishmaniasis, which present serious drawbacks, is a challenge. Here we report the development of hyaluronic...

Synthesis and structure-activity relationship of L-methionine-coupled 1,3,4-thiadiazole derivatives with activity against influenza virus

In previous investigations, we identified a class of 1,3,4-thiadiazole derivatives with antiviral activity. N-{3-(Methylsulfanyl)-1-[5-(phenylamino)-1,3,4-thiadiazole-2-yl]propyl}benzamide emerged as a relevant lead compound for designing novel influenza A virus inhibitors. In the present study, we elaborated on this initial lead by performing chemical synthesis and antiviral evaluation of a series of structural analogues. During this research, thirteen novel 1,3,4-thiadiazole derivatives were synthesized by the cyclization of the corresponding thiosemicarbazides as synthetic precursors. The structures and the purities of the synthesized compounds were confirmed through chromatographic and spectral data. Four L-methionine-based 1,3,4-thiadiazole derivatives displayed activity against influenza A virus, the two best compounds being 24 carrying a 5-(4-chlorophenylamino)-1,3,4-thiadiazole moiety and 30 possessing a 5-(benzoylamino)-1,3,4-thiadiazole structure [antiviral EC₅₀ against influenza A/H3N2 virus: 4.8 and 7.4 µM, respectively]. The 1,3,4-thiadiazole derivatives were inactive against influenza B virus and a wide panel of unrelated DNA and RNA viruses. Compound 24 represents a new class of selective influenza A virus inhibitors acting during the virus entry process, as evidenced by our findings in a time-of-addition assay. Molecular descriptors and in silico prediction of ADMET properties of the active compounds were calculated. According to in silico ADMET and drug similarity studies, active compounds have been estimated to be good candidates for oral administration with no apparent toxicity considerations.

An appraisal of the scientific current situation and new perspectives in the treatment of cutaneous leishmaniasis

Leishmaniasis is a Neglected Tropical Diseases caused by protozoan parasites of the genus Leishmania. It is a major health problem in many tropical and subtropical regions of the world and can produce three different clinical manifestations, among which cutaneous leishmaniasis has a higher incidence in the world than the other clinical forms. There are no recognized and reliable means of chemoprophylaxis or vaccination against infections with different forms of leishmaniasis. In addition, chemotherapy, unfortunately, remains, in many respects, unsatisfactory. Therefore, there is a continuing and urgent need for new therapies against leishmaniasis that are safe and effective in inducing a long-term cure. This review summarizes the latest advances in currently available treatments and improvements in the development of drug administration. In addition, an analysis of the in vivo assays was performed and the challenges facing promising strategies to treat CL are discussed. The treatment of leishmaniasis will most likely evolve into an approach that uses multiple therapies simultaneously to reduce the possibility of developing drug resistance. There is a continuous effort to discover new drugs to improve the treatment of leishmaniasis, but this is mainly at the level of individual researchers. Undoubtedly, more funding is needed in this area, as well as greater participation of the pharmaceutical industry to focus efforts on the development of chemotherapeutic agents and vaccines for this and other neglected tropical diseases.

ENTPDases from Pathogenic Trypanosomatids and Purinergic Signaling: Shedding Light towards Biotechnological Applications

ENTPDases are enzymes known for hydrolyzing extracellular nucleotides and playing an essential role in controlling the nucleotide signaling via nucleotide/purinergic receptors P2. Moreover, ENTPDases, together with Ecto-5´-nucleotidase activity, affect the adenosine signaling via P1 receptors. These signals control many biological processes, including the immune system. In this context, ATP is considered as a trigger to inflammatory signaling, while adenosine (Ado) induces anti-inflammatory response. The trypanosomatids Leishmania and Trypanosoma cruzi, pathogenic agents of Leishmaniasis and Chagas Disease, respectively, have their own ENTPDases named "TpENTPDases," which can affect the nucleotide signaling, adhesion and infection, in order to favor the parasite. Besides, TpENTPDases are essential for the parasite nutrition, since the Purine De Novo synthesis pathway is absent in them, which makes these pathogens dependent on the intake of purines and nucleopurines for the Salvage Pathway, in which TpENTPDases also take place. Here, we review information regarding TpNTPDases, including their known biological roles and their effect on the purinergic signaling. We also highlight the roles of these enzymes in parasite infection and their biotechnological applications, while pointing to future developments.

Recent advancements in anti-leishmanial research: Synthetic strategies and structural activity relationships

Leishmaniasis is a parasitic neglected tropical disease caused by various species of Leishmania parasite. Despite tremendous advancements in the therapeutic sector and drug development strategies, still the existing anti-leishmanial agents are associated with some clinical issues like drug resistance, toxicity and selectivity. Therefore, several research groups are continuously working towards the development of new therapeutic candidates to overcome these issues. Many potential heterocyclic moieties have been explored for this purpose including triazoles, chalcones, chromone, thiazoles, thiosemicarbazones, indole, quinolines, etc. It is evident from the literature that the majority of anti-leishmanial agents act by interacting with key regulators including PTR-I, DHFR, LdMetAP1, MAPK, 14 α-demethylase and pteridine reductase-I, etc. Also, these tend to induce the production of ROS which causes damage to parasites. In the present compilation, authors have summarized various significant synthetic procedures for anti-leishmanial agents reported in recent years. A brief description of the pharmacological potentials of synthesized compounds along with important aspects related to structural activity relationship has been provided. Important docking outcomes highlighting the possible mode of interaction for the reported compounds have also been included. This review would be helpful to the scientific community to design newer strategies and also to develop novel therapeutic candidates against leishmaniasis.

A MEDT computational study of the mechanism, reactivity and selectivity of non-polar [3+2] cycloaddition between quinazoline-3-oxide and methyl 3-methoxyacrylate

The Molecular Electron Density Theory (MEDT) was used for the study of the mechanism and the selectivity of the [3+2] cycloaddition reaction between quinazoline-3-oxide and methyl 3-methoxyacrylate, using the B3LYP/6-31G(d,p) DFT method. In gas phase, this [3+2] cycloaddition reaction is characterized by a completely ortho regioselectivity and a moderate exo stereoselectivity. Dichloroethane solvent did not modify the selectivities obtained in gas phase but increase the activation energies and decrease the exothermic character. Analysis of thermodynamic characters indicates that by the inclusion of the experimental conditions, the reaction becomes endergonic and thereby under thermodynamic control favouring the formation of the most stable product as observed experimentally, explaining the exo stereoselectivity. The analysis of the global electron density transfer (GEDT) at the transition states and bond order (BO) show that this reaction takes place via a very slightly synchronous and non-polar one-step mechanism. Conceptual DFT reactivity indices analysis accounts for the electrophilic character of the reagents, explaining the high obtained free activation energies, while local Parr functions analysis allows us to explain the ortho regioselectivity observed experimentally. ELF topological analysis of the most favoured reactive pathways indicates that mechanism of this 32CA reaction is one stage, one step, synchronous and non-concerted. The stability of the favourable cycloadduct is attributed to the presence of different non-conventional hydrogen bonds interactions as indicated by NCI and QTAIM analyses. Graphical Abstract.

Discovery of highly potent and selective antiparasitic new oxadiazole and hydroxy-oxindole small molecule hybrids

A series of highly active hybrids were discovered as novel antiparasitic agents. Two heterocyclic scaffolds (1,2,4-oxadiazole and 3-hydroxy-2-oxindole) were linked, and the resulting compounds showed in vitro activities against intracellular amastigotes of two protozoan parasites, Trypanosoma cruzi and Leishmania infantum. Their cytotoxicity was assessed using HFF-1 fibroblasts and HepG2 hepatocytes. Compounds 5b, 5d, 8h and 8o showed selectivity against L. infantum (IC₅₀ values of 3.89, 2.38, 2.50 and 2.85 μM, respectively). Compounds 4c, 4q, 8a and 8k were the most potent against T. cruzi, exhibiting IC₅₀ values of 6.20, 2.20, 2.30 and 2.20 μM, respectively. Additionally, the most potent anti-T. cruzi compounds showed in vitro efficacies comparable or superior to that of benznidazole. These easy-to-synthesize molecules represent novel chemotypes for the design of potent and selective lead compounds for Chagas disease and leishmaniasis drug discovery.

Three Alkaloids from an Apocynaceae Species, Aspidosperma spruceanum as Antileishmaniasis Agents by In Silico Demo-case Studies

This paper is focused on demonstrating with a real case that Ethnobotany added to Bioinformatics is a promising tool for new drugs search. It encourages the in silico investigation of "challua kaspi", a medicinal kichwa Amazonian plant (Aspidosperma spruceanum) against a Neglected Tropical Disease, leishmaniasis. The illness affects over 150 million people especially in subtropical regions, there is no vaccination and conventional treatments are unsatisfactory. In attempts to find potent and safe inhibitors of its etiological agent, Leishmania, we recovered the published traditional knowledge on kichwa antimalarials and selected three A. spruceanum alkaloids, (aspidoalbine, aspidocarpine and tubotaiwine), to evaluate by molecular docking their activity upon five Leishmania targets: DHFR-TS, PTR1, PK, HGPRT and SQS enzymes. Our simulation results suggest that aspidoalbine interacts competitively with the five targets, with a greater affinity for the active site of PTR1 than some physiological ligands. Our virtual data also point to the demonstration of few side effects. The predicted binding free energy has a greater affinity to Leishmania proteins than to their homologous in humans (TS, DHR, PKLR, HGPRT and SQS), and there is no match with binding pockets of physiological importance. Keys for the in silico protocols applied are included in order to offer a standardized method replicable in other cases. Apocynaceae having ethnobotanical use can be virtually tested as molecular antileishmaniasis new drugs.

Targeting of the mitochondrion by dinuclear thiolato-bridged arene ruthenium complexes in cancer cells and in the apicomplexan parasite Neospora caninum

A library of 18 dinuclear-thiolato bridged arene ruthenium complexes, some of which with demonstrated activity against cancer cells, was screened for activity against a transgenic Neospora caninum strain that constitutively expresses beta-galactosidase. Initial assessments were done at concentrations of 2500, 250, 25 and 2.5 nM, and 5 compounds were further evaluated with regard to their half maximal proliferation-inhibiting concentration (IC50). Among those, [(η6-p-MeC6H4Pri)2Ru2(μ2-SC6H4-p-CH3)3]Cl (1), [(η6-p-MeC6H4Pri)2Ru2(μ2-SC6H4-p-But)3]Cl (2) and [(η6-p-MeC6H4Pri)2Ru2(μ2-SCH2C6H4-p-But)2(μ2-SC6H4-p-OH)]BF4 (9) inhibited N. caninum proliferation with low C50 values of 15, 5 and 1 nM, respectively, while [(η6-p-MeC6H4Pri)2Ru2(μ2-SC6H4-p-OH)3]Cl (3) and [(η6-p-MeC6H4Pri)2Ru2(μ2-SC6H4-p-mco)3]Cl (5, mco = 4-methylcoumarinyl) were less active (IC50 = 280 and 108 nM, respectively). These compounds did not affect human foreskin fibroblast (HFF) host cells at dosages of 5 μM and above, but impaired proliferation of the human ovarian carcinoma cell line A2780 (IC50 values of 130 nM (1), 30 nM (2), 530 nM (3), 7730 nM (5), 130 nM (9)). A2780 cancer cells were treated with complexes 1, 2, and 5, and biodistribution analysis using inductively coupled plasma mass spectrometry (ICP-MS) showed that most of the drugs accumulated in the mitochondrial fractions. Transmission electron microscopy showed that the parasite mitochondrion is the primary target also in N. caninum tachyzoites, but these compounds, when applied at 200 nM for 15 days in vitro, did not act parasiticidal. Complexes 1, 2 and 9 applied orally at 2 and 10 mg kg-1 day-1 during 5 days in a neosporosis mouse model did not reduce parasite load and did not limit parasite dissemination to the central nervous system. In accordance with these results, ICP-MS carried out on different organs of mice orally administrated with complexes 1 and 9, demonstrated that the drugs were readily absorbed, and after 3 and 48 h, were mainly detected in liver and kidney, but were largely absent from the brain. Thus, dinuclear thiolato-bridged arene ruthenium complexes exhibit interesting activities against N. caninum in vitro, but further modifications of these promising molecules are required to improve their bioavailability and pharmacokinetic properties in order to exert a pronounced and selective effect against N. caninum in vivo.

A Novel Anti-Microbial Peptide from Pseudomonas, REDLK Induced Growth Inhibition of Leishmania tarentolae Promastigote In Vitro

Leishmaniasis is a prevalent cause of death and animal morbidity in underdeveloped countries of endemic area. However, there is few vaccine and effective drugs. Antimicrobial peptides are involved in the innate immune response in many organisms and are being developed as novel drugs against parasitic infections. In the present study, we synthesized a 5-amino acid peptide REDLK, which mutated the C-terminus of Pseudomonas exotoxin, to identify its effect on the Leishmania tarentolae. Promastigotes were incubated with different concentration of REDLK peptide, and the viability of parasite was assessed using MTT and Trypan blue dye. Morphologic damage of Leishmania was analyzed by light and electron microscopy. Cellular apoptosis was observed using the annexin V-FITC/PI apoptosis detection kit, mitochondrial membrane potential assay kit and flow cytometry. Our results showed that Leishmania tarentolae was susceptible to REDLK in a dose-dependent manner, disrupt the surface membrane integrity and caused parasite apoptosis. In our study, we demonstrated the leishmanicidal activity of an antimicrobial peptide REDLK from Pseudomonas aeruginosa against Leishmania tarentolae in vitro and present a foundation for further research of anti-leishmanial drugs.

Structural characterization by scattering and spectroscopic methods and biological evaluation of polymeric micelles of poloxamines and TPGS as nanocarriers for miltefosine delivery

Miltefosine (MF), an alkylphospholipid originally developed for breast cancer treatment, is a highly active drug for the treatment against leishmaniasis, a neglected tropical disease considered the world's second leading cause of death by a parasitic agent after malaria. MF exhibits dose-limiting gastrointestinal side effects in patients and its penetration through lipophilic barriers is reduced. In this work we propose a reformulation of MF by incorporating the drug to poly(ethylene)oxide (PEO)-based polymeric micelles, specifically, D-α-tocopheryl polyethylene glycol succinate (TPGS) and Tetronic block copolymers (T904 and T1107). A full structural characterization of the aggregates has been carried out by SANS (small-angle neutron scattering) and dynamic light scattering (DLS), in combination with proton 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, to determine the precise location of the drug. The structure of MF micelles has been characterized as a function of the temperature and concentration. In the presence of the block-copolymers, MF forms mixed micelles in a wide range of temperatures, TPGS being the co-surfactant that incorporates more MF unimers. The hydrophobic tail of MF and those of the block copolymers are in close contact within the micelles, which present a core-shell structure with a hydrophilic corona formed by the PEG blocks of the TPGS and the zwitterion head group of the MF. In order to identify the best carrier, the antileishmanicidal activity of MF in the different formulations has been tested on macrophages, promastigotes and intracellular amastigotes. The combination of the three vehicles with MF makes the formulated drug more active than MF alone against L. major promastigotes, however, only the combination with T904 increases the MF activity against intracellular amastigotes. With the aim of exploring gel-based formulations of the drug, the combination of MF and T1107 under gelation conditions has also been investigated.

Synthesis, study of antileishmanial and antitrypanosomal activity of imidazo pyridine fused triazole analogues

Thirty-five novel 1,2,3-triazole analogues of imidazo-[1,2-a]-pyridine-3-carboxamides were designed, synthesized and evaluated for in vitro antileishmanial and antitrypanosomal activity against L. major and T. brucei parasites, respectively.

Structure based designing of benzimidazole/benzoxazole derivatives as anti-leishmanial agents

Folates are essential biomolecules required to carry out many crucial processes in leishmania parasite. Dihydrofolate reductase-thymidylate synthase (DHFR-TS) and pteridine reductase 1 (PTR1) involved in folate biosynthesis in leishmania have been established as suitable targets for development of chemotherapy against leishmaniasis. In the present study, various computational tools such as homology modelling, pharmacophore modelling, docking, molecular dynamics and molecular mechanics have been employed to design dual DHFR-TS and PTR1 inhibitors. Two designed molecules, i.e. 2-(4-((4-nitrobenzyl)oxy)phenyl)-1H-benzo[d]imidazole and 2-(4-((2,4-dichlorobenzyl)oxy)phenyl)-1H-benzo[d]oxazolemolecules were synthesized. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay was performed to evaluate in vitro activity of molecules against promastigote form of Leishmania donovani using Miltefosine as standard. 2-(4-((4-nitrobenzyl)oxy)phenyl)-1H-benzo[d]imidazole and 2-(4-((2,4-dichlorobenzyl)oxy)phenyl)-1H-benzo[d]oxazolemolecules were found to be moderately active with showed IC₅₀ = 68 ± 2.8 µM and 57 ± 4.2 µM, respectively.

Leishmania mexicana Trypanothione Reductase Inhibitors: Computational and Biological Studies

Leishmanicidal drugs have many side effects, and drug resistance to all of them has been documented. Therefore, the development of new drugs and the identification of novel therapeutic targets are urgently needed. Leishmania mexicana trypanothione reductase (LmTR), a NADPH-dependent flavoprotein oxidoreductase important to thiol metabolism, is essential for parasite viability. Its absence in the mammalian host makes this enzyme an attractive target for the development of new anti-Leishmania drugs. Herein, a tridimensional model of LmTR was constructed and the molecular docking of 20 molecules from a ZINC database was performed. Five compounds (ZINC04684558, ZINC09642432, ZINC12151998, ZINC14970552, and ZINC11841871) were selected (docking scores -10.27 kcal/mol to -5.29 kcal/mol and structurally different) and evaluated against recombinant LmTR (rLmTR) and L. mexicana promastigote. Additionally, molecular dynamics simulation of LmTR-selected compound complexes was achieved. The five selected compounds inhibited rLmTR activity in the range of 32.9% to 40.1%. The binding of selected compounds to LmTR involving different hydrogen bonds with distinct residues of the molecule monomers A and B is described. Compound ZINC12151998 (docking score -10.27 kcal/mol) inhibited 32.9% the enzyme activity (100 µM) and showed the highest leishmanicidal activity (IC₅₀ = 58 µM) of all the selected compounds. It was more active than glucantime, and although its half-maximal cytotoxicity concentration (CC₅₀ = 53 µM) was higher than that of the other four compounds, it was less cytotoxic than amphotericin B. Therefore, compound ZINC12151998 provides a promising starting point for a hit-to-lead process in our search for new anti-Leishmania drugs that are more potent and less cytotoxic.

Development of topical liposomes containing miltefosine for the treatment of Leishmania major infection in susceptible BALB/c mice

Herein, we investigated the efficacy of liposomes for the topical delivery of miltefosine (ML) to treat cutaneous leishmaniasis (CL). Liposomes containing varying concentrations of ML (0.5, 1, 2 and 4%) were prepared and characterized by their size and entrapment efficiency. The liposome diameters were between 100-150 nm. The penetration of ML from liposomal formulations through and in the skin was assessed using ex-vivo Franz diffusion cells fitted with mouse skin at 37 °C for 24 h. Data indicated that Lip-ML-4% showed the highest percent of retention across mouse skin (82%). in vitro promastigote and amastigote assays showed that ML and Lip-ML inhibit the growth of parasites either in the culture medium or intracellularly. Lip-ML formulations were topically applied twice a day for 4 weeks to the skin of BALB/c mice infected with L. major. Results showed a significantly (p < 0.001) smaller lesion size in Lip-ML-2 and 4% when compared to controls. At week 8 post-infection, the number of parasites was higher in Lip-ML-0.5% compared to Lip-ML-2 and 4%, however, the difference was not significant. At week 12, the splenic parasite burden was significantly (p < 0.001) lower in mice treated with different Lip-ML formulations when compared to controls. The lesion parasite burden was significantly (p < 0.001) lower in mice treated with either Lip-ML-2 and 4% compared to Lip-ML-0.5% at week 12 post-infection. The results suggested that topical Lip-ML-4% showed optimal ex-vivo penetration and in vivo anti-leishmanial activity against CL caused by L. major when compared to ML cream and other liposomes and thus, merits further investigation.

Screening diagnostic candidates from Leishmania infantum proteins for human visceral leishmaniasis using an immunoproteomics approach

There is no suitable vaccine against human visceral leishmaniasis (VL) and available drugs are toxic and/or present high cost. In this context, diagnostic tools should be improved for clinical management and epidemiological evaluation of disease. However, the variable sensitivity and/or specificity of the used antigens are limitations, showing the necessity to identify new molecules to be tested in a more sensitive and specific serology. In the present study, an immunoproteomics approach was performed in Leishmania infantum promastigotes and amastigotes employing sera samples from VL patients. Aiming to avoid undesired cross-reactivity in the serological assays, sera from Chagas disease patients and healthy subjects living in the endemic region of disease were also used in immunoblottings. The most reactive spots for VL samples were selected, and 29 and 21 proteins were identified in the promastigote and amastigote extracts, respectively. Two of them, endonuclease III and GTP-binding protein, were cloned, expressed, purified and tested in ELISA experiments against a large serological panel, and results showed high sensitivity and specificity values for the diagnosis of disease. In conclusion, the identified proteins could be considered in future studies as candidate antigens for the serodiagnosis of human VL.

Untargeted LC-MS metabolomic studies of Asteraceae species to discover inhibitors of Leishmania major dihydroorotate dehydrogenase

INTRODUCTION

Interesting data about the family Asteraceae as a new source of Leishmania major dihydroorotate dehydrogenase (LmDHODH) inhibitors are presented. This key macromolecular target for parasites causing neglected diseases catalyzes the fourth reaction of the de novo pyrimidine biosynthetic pathway, which takes part in major cell functions, including DNA and RNA biosynthesis.

OBJECTIVES

We aimed to (1) determine LmDHODH inhibitor candidates, revealing the type of chemistry underlying such bioactivity, and (2) predict the inhibitory potential of extracts from new untested plant species, classifying them as active or inactive based on their LC-MS based metabolic fingerprints.

METHODS

Extracts from 150 species were screened for the inhibition of LmDHODH, and untargeted UHPLC-(ESI)-HRMS metabolomic studies were carried out in combination with in silico approaches.

RESULTS

The IC₅₀ values determined for a subset of 59 species ranged from 148 µg mL^-1 to 9.4 mg mL^-1. Dereplication of the metabolic fingerprints allowed the identification of 48 metabolites. A reliable OPLS-DA model (R² > 0.9, Q² > 0.7, RMSE_CV < 0.3) indicated the inhibitor candidates; nine of these metabolites were identified using data from isolated chemical standards, one of which-4,5-di-O-E-caffeoylquinic acid (IC₅₀ 73 µM)-was capable of inhibiting LmDHODH. The predictive OPLS model was also effective, with 60% correct predictions for the test set.

CONCLUSION

Our approach was validated for (1) the discovery of LmDHODH inhibitors or interesting starting points for the optimization of new leishmanicides from Asteraceae species and (2) the prediction of extracts from untested species, classifying them as active or inactive.