Axenic amastigotes of Leishmania species as a suitable model for in vitro studies

Antimicrobial activity of nanoparticles based on carboxymethylated cashew gum and epiisopiloturine: In vitro and in silico studies

Epiisopiloturine (EPI) is a compound found in jaborandi leaves with antiparasitic activity, which can be enhanced when incorporated into nanoparticles (NP). Cashew Gum (CG), modified by carboxymethylation, is used to produce polymeric nanomaterials with biological activity. In this study, we investigated the antimicrobial potential of carboxymethylated CG (CCG) NP containing EPI (NPCCGE) and without the alkaloid (NPCCG) against bacteria and parasites of the genus Leishmania. We conducted theoretical studies, carboxymethylated CG, synthesized NP by nanoprecipitation, characterized them, and tested them in vitro. Theoretical studies confirmed the stability of modified carbohydrates and showed that the EPI-4A30 complex had the best interaction energy (-8.47 kcal/mol). CCG was confirmed by FT-IR and presented DSabs of 0.23. NPCCG and NPCCGE had average sizes of 221.94 ± 144.086 nm and 247.36 ± 3.827 nm, respectively, with homogeneous distribution and uniform surfaces. No NP showed antibacterial activity or cytotoxicity to macrophages. NPCCGE demonstrated antileishmanial activity against L. amazonensis, both in promastigote forms (IC50 = 9.52 μg/mL, SI = 42.01) and axenic amastigote forms (EC50 = 6.6 μg/mL, SI = 60.60). The results suggest that nanostructuring EPI in CCG enhances its antileishmanial activity.

Effect of the aggregated protein dye YAT2150 on Leishmania parasite viability

The problems associated with the drugs currently used to treat leishmaniasis, including resistance, toxicity, and the high cost of some formulations, call for the urgent identification of new therapeutic agents with novel modes of action. The aggregated protein dye YAT2150 has been found to be a potent antileishmanial compound, with a half-maximal inhibitory concentration (IC50) of approximately 0.5 µM against promastigote and amastigote stages of Leishmania infantum. The encapsulation in liposomes of YAT2150 significantly improved its in vitro IC50 to 0.37 and 0.19 µM in promastigotes and amastigotes, respectively, and increased the half-maximal cytotoxic concentration in human umbilical vein endothelial cells to >50 µM. YAT2150 became strongly fluorescent when binding intracellular protein deposits in Leishmania cells. This fluorescence pattern aligns with the proposed mode of action of this drug in the malaria parasite Plasmodium falciparum, the inhibition of protein aggregation. In Leishmania major, YAT2150 rapidly reduced ATP levels, suggesting an alternative antileishmanial mechanism. To the best of our knowledge, this first-in-class compound is the only one described so far having significant activity against both Plasmodium and Leishmania, thus being a potential drug for the treatment of co-infections of both parasites.

Next generation of selenocyanate and diselenides with upgraded leishmanicidal activity

Nowadays, leishmaniasis is still treated with outdated drugs that present several obstacles related to their high toxicity, long duration, parenteral administration, high costs and drug resistance. Therefore, there is an urgent demand for safer and more effective novel drugs. Previous studies indicated that selenium compounds are promising derivatives for innovative therapy in leishmaniasis treatment. With this background, a new library of 20 selenocyanate and diselenide derivatives were designed based on structural features present in the leishmanicidal drug miltefosine. Compounds were initially screened against promastigotes of L. major and L. infantum and their cytotoxicity was evaluated in THP-1 cells. Compounds B8 and B9 were the most potent and less cytotoxic and were further screened for the intracellular back transformation assay. The results obtained revealed that B8 and B9 showed EC50 values of 7.7 µM and 5.7 µM, respectively, in L. major amastigotes, while they presented values of 6.0 µM and 7.4 µM, respectively, against L. infantum amastigotes. Furthermore, they exerted high selectivity (60 < SI > 70) towards bone marrow-derived macrophages. Finally, these compounds exhibited higher TryR inhibitory activity than mepacrine (IC50 7.6 and 9.2 µM, respectively), and induced nitric oxide (NO) and reactive oxygen species (ROS) production in macrophages. These results suggest that the compounds B8 and B9 could not only exert a direct leishmanicidal activity against the parasite but also present an indirect action by activating the microbicidal arsenal of the macrophage. Overall, these new generation of diselenides could constitute promising leishmanicidal drug candidates for further studies.

A short-term method to evaluate anti-leishmania drugs by inhibition of stage differentiation in Leishmania mexicana using flow cytometry

Leishmaniasis is a vector-borne neglected tropical disease caused by the Leishmania spp. Parasite. The disease is transmitted to humans and animals by the bite of infected female sandflies during the ingestion of bloodmeal. Because current drug treatments induce toxicity and parasite resistance, there is an urgent need to evaluate new drugs. Most therapeutics target the differentiation of promastigotes to amastigotes, which is necessary to maintain Leishmania infection. However, in vitro assays are laborious, time-consuming, and depend on the experience of the technician. In this study, we aimed to establish a short-term method to assess the differentiation status of Leishmania mexicana (L. mexicana) using flow cytometry. Here, we showed that flow cytometry provides a rapid means to quantify parasite differentiation in cell culture as reliably as light microscopy. Interestingly, we found using flow cytometry that miltefosine reduced promastigote-to-amastigote differentiation of L. mexicana. We conclude that flow cytometry provides a means to rapidly assay the efficacy of small molecules or natural compounds as potential anti-leishmanials.

Generation of Aurachin Derivatives by Whole-Cell Biotransformation and Evaluation of Their Antiprotozoal Properties

The natural product aurachin D is a farnesylated quinolone alkaloid, which is known to possess activity against the causative agent of malaria, Plasmodium spp. In this study, we show that aurachin D inhibits other parasitic protozoa as well. While aurachin D had only a modest effect on Trypanosoma brucei rhodesiense, two other trypanosomatids, T. cruzi and Leishmania donovani, were killed at low micromolar and nanomolar concentrations, respectively, in an in vitro assay. The determined IC₅₀ values of aurachin D were even lower than those of the reference drugs benznidazole and miltefosine. Due to these promising results, we set out to explore the impact of structural modifications on the bioactivity of this natural product. In order to generate aurachin D derivatives with varying substituents at the C-2, C-6 and C-7 position of the quinolone ring system, we resorted to whole-cell biotransformation using a recombinant Escherichia coli strain capable of aurachin-type prenylations. Quinolone precursor molecules featuring methyl, methoxy and halogen groups were fed to this E. coli strain, which converted the substrates into the desired analogs. None of the generated derivatives exhibited improved antiprotozoal properties in comparison to aurachin D. Obviously, the naturally occurring aurachin D features already a privileged structure, especially for the inhibition of the causative agent of visceral leishmaniasis.

Assessing the effect of antimony pressure on trypanothione reductase activity in Leishmania (Viannia) braziliensis

Leishmania parasites have an oxidative and chemical defense mechanism called trypanothione system (T[SH]₂), the most abundant thiol system in trypanosomatids. This system has a central role in processing pentavalent antimony and resistance has been related to a better capacity to metabolize it through the activation of T[SH]₂ enzymatic cascade. A biochemical approach was applied to assess the effect of trivalent (Sb^III) and pentavalent antimony (Sb^V) on Trypanothione Reductase (TR) activity of two Leishmania (Viannia) braziliensis clinical isolates, which were labeled as responder (R) and non-responder (NR) after patient treatment with Glucantime®. Both isolates were characterized based on in vitro susceptibility to Sb^III and Sb^V and trypanothione reductase (TR) activity. Sb^III and Sb^V discriminated susceptibility profiles in all parasite forms, since isolate NR had significantly higher EC₅₀ values than isolate R. Differences were observed in TR activity between promastigotes, axenic amastigotes and intracellular amastigotes: R (0.439 ± 0.009, 0.103 ± 0.01 and 0.185 ± 0.01AU.min^-1.μg of protein^-1) and NR (1.083 ± 0.04, 0.914 ± 0.04 and 0.343 ± 0.04 AU. min^-1.μg of protein^-1), respectively. Incubation with Sb^III and Sb^V using each form EC₅₀ value caused a time-dependent differential effect on TR activity suggesting that oxidative defense is related to the antimony susceptibility phenotype. Data gathered here shows a biochemical approach able to discriminate two L. (V.) braziliensis clinical isolates measurements TR activity of promastigotes, axenic amastigotes and intracellular amastigotes.

An RNA Interference (RNAi) Toolkit and Its Utility for Functional Genetic Analysis of Leishmania (Viannia)

RNA interference (RNAi) is a powerful tool whose efficacy against a broad range of targets enables functional genetic tests individually or systematically. However, the RNAi pathway has been lost in evolution by a variety of eukaryotes including most Leishmania sp. RNAi was retained in species of the Leishmania subgenus Viannia, and here we describe the development, optimization, and application of RNAi tools to the study of L. (Viannia) braziliensis (Lbr). We developed vectors facilitating generation of long-hairpin or "stem-loop" (StL) RNAi knockdown constructs, using Gateway^TM site-specific recombinase technology. A survey of applications of RNAi in L. braziliensis included genes interspersed within multigene tandem arrays such as quinonoid dihydropteridine reductase (QDPR), a potential target or modulator of antifolate sensitivity. Other tests include genes involved in cell differentiation and amastigote proliferation (A600), and essential genes of the intraflagellar transport (IFT) pathway. We tested a range of stem lengths targeting the L. braziliensis hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and reporter firefly luciferase (LUC) genes and found that the efficacy of RNAi increased with stem length, and fell off greatly below about 128 nt. We used the StL length dependency to establish a useful 'hypomorphic' approach not possible with other gene ablation strategies, with shorter IFT140 stems yielding viable cells with compromised flagellar morphology. We showed that co-selection for RNAi against adenine phosphoryl transferase (APRT1) using 4-aminopyrazolpyrimidine (APP) could increase the efficacy of RNAi against reporter constructs, a finding that may facilitate improvements in future work. Thus, for many genes, RNAi provides a useful tool for studying Leishmania gene function with some unique advantages.

Monomethylsulochrin isolated from biomass extract of Aspergillus sp. against Leishmania amazonensis: In vitro biological evaluation and molecular docking

Leishmaniasis represents a serious world health problem, with 1 billion people being exposed to infection and a broad spectrum of clinical manifestations with a potentially fatal outcome. Based on the limitations observed in the treatment of leishmaniasis, such as high cost, significant adverse effects, and the potential for drug resistance, the aim of the present study was to evaluate the leishmanicidal activity of the compounds pseurotin A and monomethylsulochrin isolated from the biomass extract of Aspergillus sp. The chromatographic profiles of the extract were determined by high-performance liquid chromatography coupled with a diode-array UV-Vis detector (HPLC-DAD-UV), and the molecular identification of the pseurotin A and monomethylsulochrin were carried out by electrospray ionization mass spectrometry in tandem (LC-ESI-MS-MS) and nuclear magnetic resonance (NMR). Antileishmanial activity was assayed against promastigote and intracellular amastigote of Leishmania amazonensis. As a control, cytotoxicity assays were performed in non-infected BALB/c peritoneal macrophages. Ultrastructural alterations in parasites were evaluated by transmission electron microscopy. Changes in mitochondrial membrane potential were determined by flow cytometry. Only monomethylsulochrin inhibited the promastigote growth (IC₅₀ 18.04 ± 1.11 µM), with cytotoxicity to peritoneal macrophages (CC₅₀ 5.09 91.63 ± 1.28 µM). Activity against intracellular amastigote forms (IC₅₀ 5.09 ± 1.06 µM) revealed an increase in antileishmanial activity when compared with promastigotes. In addition to a statistically significant reduction in the evaluated infection parameters, monomethylsulochrin altered the ultrastructure of the promastigote forms with atypical vacuoles, electron-dense corpuscles in the cytoplasm, changes at the mitochondria outer membrane and abnormal disposition around the kinetoplast. It was showed that monomethylsulochrin leads to a decrease in the mitochondrial membrane potential (25.9%, p = 0.0286). Molecular modeling studies revealed that monomethylsulochrin can act as inhibitor of sterol 14-alpha-demethylase (CYP51), a therapeutic target for human trypanosomiasis and leishmaniasis. Assessed for its drug likeness, monomethylsulochrin follows the Lipinski Rule of five and Ghose, Veber, Egan, and Muegge criteria. Furthermore, monomethylsulochrin can be used as a reference in the development of novel and therapeutically useful antileishmanial agents.

Challenges and Tools for In Vitro Leishmania Exploratory Screening in the Drug Development Process: An Updated Review

Leishmaniases are a group of vector-borne diseases caused by infection with the protozoan parasites Leishmania spp. Some of them, such as Mediterranean visceral leishmaniasis, are zoonotic diseases transmitted from vertebrate to vertebrate by a hematophagous insect, the sand fly. As there is an endemic in more than 90 countries worldwide, this complex and major health problem has different clinical forms depending on the parasite species involved, with the visceral form being the most worrying since it is fatal when left untreated. Nevertheless, currently available antileishmanial therapies are significantly limited (low efficacy, toxicity, adverse side effects, drug-resistance, length of treatment, and cost), so there is an urgent need to discover new compounds with antileishmanial activity, which are ideally inexpensive and orally administrable with few side effects and a novel mechanism of action. Therefore, various powerful approaches were recently applied in many interesting antileishmanial drug development programs. The objective of this review is to focus on the very first step in developing a potential drug and to identify the exploratory methods currently used to screen in vitro hit compounds and the challenges involved, particularly in terms of harmonizing the results of work carried out by different research teams. This review also aims to identify innovative screening tools and methods for more extensive use in the drug development process.