Miltefosine (hexadecylphosphocholine) inhibits cytochrome c oxidase in Leishmania donovani promastigotes

Anti-Parasitics with a Triple Threat: Targeting Parasite Enzymes, the Proton Motive Force, and Host Cell-Mediated Killing

We investigated the effects of the tuberculosis drug candidate SQ109 (8a) and of its analog MeSQ109 (8b) against Leishmania mexicana in promastigote and amastigote forms and against host cell macrophages finding potent activity (1.7 nM) for MeSQ109 against the intracellular forms, as well as low toxicity (∼61 μM) to host cells, resulting in a selectivity index of ∼36,000. We then investigated the mechanism of action of MeSQ109, finding that it targeted parasite mitochondria, collapsing the proton motive force, as well as targeting acidocalcisomes, rapidly increasing the intracellular Ca2+ concentration. Using an E. coli inverted membrane vesicle assay, we investigated the pH gradient collapse for SQ109 and 17 analogs, finding that there was a significant correlation (on average, R = 0.67, p = 0.008) between pH gradient collapse and cell growth inhibition in Trypanosoma brucei, T. cruzi, L. donovani, and Plasmodium falciparum. We also investigated pH gradient collapse with other antileishmanial agents: azoles, antimonials, benzofurans, amphotericin B, and miltefosine. The enhanced activity against intracellular trypanosomatids is seen with Leishmania spp. grown in macrophages but not with Trypanosoma cruzi in epithelial cells and is proposed to be due in part to host-based killing, based on the recent observation that SQ109 is known to convert macrophages to a pro-inflammatory (M1) phenotype.

The binuclear cyclopalladated complex CP2 is targeting ubiquinol-cytochrome c reductase (complex III) of Leishmania amazonensis

Leishmaniasis is a neglected disease that remains with a limited number of drugs available for chemotherapy and has an increased drug resistance that affects treatment outcomes. Metal-based drugs such as cyclopalladated complex [Pd(dmba)(μ-N3)]2 (CP2), a Leishmania topoisomerase IB inhibitor involved in calcium dysregulation and mitochondrial dysfunction of the parasite, had been an alternative to outline the appearance of chemoresistance. To identify new molecular targets and point out possible resistance mechanisms, a CP2-resistant Leishmania amazonensis (LaR) was selected by stepwise exposure to increasing drug pressure until a line capable of growth in 13.3 μM CP2. LaR IC50 value was 52.4 μM (4-fold higher than L. amazonensis-wild type, La). LaR promastigotes were cross-resistant to other DNA topoisomerase I inhibitors (camptothecin) and more susceptible to anti-leishmanial drugs pentamidine and miltefosine. A protective effect on cell viability was observed by pretreating the parasite with Ca2+ channel blockers followed by CP2 in La but not in LaR. Analyses of the cell viability of La and LaR using electron transport chain (ETC) inhibitors demonstrated that La is more sensitive than LaR. The studies of mitochondrial oxygen consumption demonstrated that LaR is less susceptible to complex III (ubiquinol-cytochrome c reductase - CcR) inhibitor, antimycin A (AA). CcR activities of La and LaR were equal for both strains in the absence of CP2 and significantly decreased, 69 % for La and 51 % for LaR, in the presence of CP2. This resistance is attributed to overexpression of CcR, confirmed by the RT-qPCR. CcR inhibition by CP2 leads the parasite to increase the reactive oxygen species (ROS) production, principally in La. Therefore, in this work, we suggested that CcR is the main target of CP2 in the mitochondria, acting to inhibit mitochondria respiratory, and the LaR mutant has increased activity of CcR, which reduces the formation of ROS.

Characterization of differentially regulated carboxypeptidase (metallopeptidase M32) protein in Miltefosine resistant Leishmania donovani parasites

INTRODUCTION

Carboxypeptidase, a member of the metallopeptidase M32 family, catalyses the C-terminal hydrolysis of a variety of peptides and proteins in the presence of metal ions.

OBJECTIVE

To characterize Leishmania donovani carboxypeptidase (LdCP) in miltefosine (MIL) drug-resistant parasites.

METHODS

We performed the MTT assay and cell cycle analysis to confirm the MIL resistance of clinical isolates. LdCP gene was cloned and expressed in E. coli Artic strain. The purified LdCP protein was used for antibody generation and biochemical characterization.

RESULTS

MTT assay and cell cycle analysis revealed that all three isolates exhibit MIL resistance. LdCP constitutively expressed in both promastigote and amastigote stages of parasites, and its activity increased 2-3 fold in MIL-resistant parasites. LdCP has high α-helical content at physiological pH and temperature. The protein is quite thermostable with a Tm of 63 °C and susceptible to chemical denaturation, with 50 % unfolding induced by 3.59 M urea or 0.31 M guanidine hydrochloride (GdmCl). LC-MS/MS study reveals that LdCP interacts with membrane-associated proteins that have ATP binding sites and involved in protein phosphorylation.

CONCLUSION

To our knowledge, this is the first study to characterize the carboxypeptidase of L. donovani that appears to contribute to the development of MIL resistance parasites.

Epoxy-a-lapachone in nanosystem: a prototype drug for leishmaniasis assessed in the binomial BALB/c - Leishmania (Leishmania) amazonensis

This perspective presents and supports arguments for a new formulation of epoxy-α-lapachone loaded microemulsion (ELAP-ME), a nanosystem, as a prototype drug for the treatment of leishmaniasis. The benefits of ELAP as a multitarget compound, with properties that affect key physiological pathways of Leishmania spp. are discussed. ELAP-ME demonstrated efficacy in murine infection models, particularly with the binomial BALB/c-Leishmania (Leishmania) amazonensis. Furthermore, it is proposed that the technological maturity of ELAP-ME be classified as Technology Readiness Level 4 (TLR 4) within the context of innovative drugs for American Cutaneous Leishmaniasis (ACL).

Miltefosine impacts small molecule transport in Gram-positive bacteria

Miltefosine (MLT) is an alkylphosphocholine with clinical success as an anticancer and antiparasitic drug. Although the mechanism of action of MLT is highly debated, the interaction of MLT with the membrane, specifically lipid rafts of eukaryotes, is well-documented. Recent reports suggest MLT impacts the functional membrane microdomains in bacteria - regions of the membrane structurally and functionally similar to lipid rafts. There have been conflicting reports, however, as to whether MLT impacts the overall fluidity of cellular plasma membranes. Here, we apply steady-state fluorescence techniques, generalized polarization of laurdan and anisotropy of diphenylhexatriene, to discern how MLT impacts the global ordering and lipid packing of Staphylococcus aureus membranes. Additionally, we investigate how the transport of a range of small molecules is impacted by MLT for S. aureus and Bacillus subtilis by employing time-resolved second harmonic scattering. Overall, we observe MLT does not have an influence on the overall ordering and packing of S. aureus membranes. Additionally, we show that the transport of small molecules across the membrane can be significantly altered by MLT - although this is not the case for all molecules studied. The results presented here illustrate the potential use of MLT as an adjuvant to assist in the delivery of drug molecules in bacteria.

Miltefosine induces reproductive toxicity during sperm capacitation by altering PI3K/AKT signaling pathway

Miltefosine is the first and only drug approved for the treatment of leishmaniasis. It is also known as a PI3K/AKT signaling pathway inhibitor utilized in anti-cancer or anti-viral therapies. However, the impact of miltefosine on male fertility has not been fully understood. Therefore, this study was performed to investigate the effects of miltefosine on sperm function during capacitation. Duroc spermatozoa were exposed to 0, 2.5, 5, 10, 20, 40, and 80 μM miltefosine and induced for capacitation. Our results showed that miltefosine dramatically increased the expression of PI3K/AKT signaling pathway-associated proteins. Sperm motility, motion kinetics, capacitation, and tyrosine phosphorylation were significantly suppressed by miltefosine. However, intracellular ATP levels and cell viability were not significantly affected. Our findings suggest that miltefosine may disrupt sperm function by abnormally increasing the levels of PI3K/AKT signaling pathway-associated proteins. Therefore, the harmful effects of miltefosine on male reproduction should be considered when using this drug.

Combination Therapy for Post-Kala-Azar Dermal Leishmaniasis: A Literature Review of Current Evidence

Post-kala-azar dermal leishmaniasis (PKDL) is a neglected skin disease that has tremendous epidemiological significance as a reservoir of Leishmania parasites. Relapse, drug resistance, non-compliance to prolonged treatment, poor health-seeking behaviour, along with limited therapeutic options pose a significant impact on the management of PKDL. In this study, we aimed to review the efficacy, safety and tolerability data of combination therapies for PKDL in the published literature. We have also described patients' compliance with treatment and associated co-infections in PKDL. A comprehensive literature search was conducted in PubMed, Scopus and Google Scholar to identify the relevant articles. A total of nine studies were eligible for inclusion in this review. Drug combinations used in India were miltefosine-liposomal amphotericin-B, miltefosine-paromomycin, miltefosine-amphotericin-B, sodium stibogluconate (SSG)-immunotherapy and SSG-rifampicin. However, in Sudan, except one, all studies have used SSG-based combinations viz. SSG-rifampicin, SSG-paromomycin and SSG-immunotherapy. The efficacy and safety of miltefosine in combination with liposomal amphotericin-B as well as conventional amphotericin-B were found to be excellent in a limited number of patients. These combinations are said to have better patient compliance and shorter treatment duration. Another combination of miltefosine and paromomycin was found to be satisfactory with a final cure rate of 83.3%. SSG in combination with paromomycin had a good clinical outcome among severe PKDL patients in Sudan, though pain at the injection site was experienced by all patients. There is a lack of data on combination therapies for PKDL through large-scale randomised controlled trials (RCTs). Therefore, multicentric randomized controlled trials with a sufficiently large sample size are urgently needed to verify the efficacy, safety, and other advantages of combination therapies for PKDL. With the availability of liposomal amphotericin-B, miltefosine and immunotherapy, clinical management of PKDL appears promising.

Synergistic Effects of Artesunate in Combination with Amphotericin B and Miltefosine against Leishmania infantum: Potential for Dose Reduction and Enhanced Therapeutic Strategies

Leishmaniasis is a tropical infectious disease caused by Leishmania parasites. The disease can be spread by the bite of an infected sand fly. Currently, five chemotherapeutic drugs are available in leishmaniasis treatment. However, these drugs exhibit toxicity and serious adverse effects on infected individuals, necessitating alternative treatment strategies. One such strategy involves using combinations of existing antileishmanial drugs. In this study, we evaluated the interaction between artesunate (AS) and three antileishmanial drugs-amphotericin B (AmB), miltefosine (MF), and paromomycin (PM) against Leishmania infantum. This evaluation marks the first time such an assessment has been conducted. The Chou-Talalay combination index method was employed to analyze the drug interaction. The findings revealed that the interaction between AS and AmB ranged from antagonistic to synergistic, while the interaction between AS and MF showed moderate to strong synergism. In contrast, the interaction between AS and PM resulted in an antagonistic interaction, which differs from the combinations with AmB or MF. This study provides valuable insights for developing novel drug regimens for leishmaniasis treatment, emphasizing the potential of AS and its combination with existing antileishmanial drugs. Further research is necessary to optimize drug combinations and minimize adverse effects, leading to more effective therapeutic outcomes.

High-throughput prioritization of target proteins for development of new antileishmanial compounds

Leishmaniasis, a vector-borne disease, is caused by the infection of Leishmania spp., obligate intracellular protozoan parasites. Presently, human vaccines are unavailable, and the primary treatment relies heavily on systemic drugs, often presenting with suboptimal formulations and substantial toxicity, making new drugs a high priority for LMIC countries burdened by the disease, but a low priority in the agenda of most pharmaceutical companies due to unattractive profit margins. New ways to accelerate the discovery of new, or the repositioning of existing drugs, are needed. To address this challenge, our study aimed to identify potential protein targets shared among clinically-relevant Leishmania species. We employed a subtractive proteomics and comparative genomics approach, integrating high-throughput multi-omics data to classify these targets based on different druggability metrics. This effort resulted in the ranking of 6502 ortholog groups of protein targets across 14 pathogenic Leishmania species. Among the top 20 highly ranked groups, metabolic processes known to be attractive drug targets, including the ubiquitination pathway, aminoacyl-tRNA synthetases, and purine synthesis, were rediscovered. Additionally, we unveiled novel promising targets such as the nicotinate phosphoribosyltransferase enzyme and dihydrolipoamide succinyltransferases. These groups exhibited appealing druggability features, including less than 40% sequence identity to the human host proteome, predicted essentiality, structural classification as highly druggable or druggable, and expression levels above the 50th percentile in the amastigote form. The resources presented in this work also represent a comprehensive collection of integrated data regarding trypanosomatid biology.

Compounds with potentialities as novel chemotherapeutic agents in leishmaniasis at preclinical level

Leishmaniasis are neglected infectious diseases caused by kinetoplastid protozoan parasites from the genus Leishmania. These sicknesses are present mainly in tropical regions and almost 1 million new cases are reported each year. The absence of vaccines, as well as the high cost, toxicity or resistance to the current drugs determines the necessity of new treatments against these pathologies. In this review, several compounds with potentialities as new antileishmanial drugs are presented. The discussion is restricted to the preclinical level and molecules are organized according to their chemical nature, source and molecular targets. In this manner, we present antimicrobial peptides, flavonoids, withanolides, 8-aminoquinolines, compounds from Leish-Box, pyrazolopyrimidines, and inhibitors of tubulin polymerization/depolymerization, topoisomerase IB, proteases, pteridine reductase, N-myristoyltransferase, as well as enzymes involved in polyamine metabolism, response against oxidative stress, signaling pathways, and sterol biosynthesis. This work is a contribution to the general knowledge of these compounds as antileishmanial agents.

Unmasking the Mechanism behind Miltefosine: Revealing the Disruption of Intracellular Ca2+ Homeostasis as a Rational Therapeutic Target in Leishmaniasis and Chagas Disease

Originally developed as a chemotherapeutic agent, miltefosine (hexadecylphosphocholine) is an inhibitor of phosphatidylcholine synthesis with proven antiparasitic effects. It is the only oral drug approved for the treatment of Leishmaniasis and American Trypanosomiasis (Chagas disease). Although its precise mechanisms are not yet fully understood, miltefosine exhibits broad-spectrum anti-parasitic effects primarily by disrupting the intracellular Ca2+ homeostasis of the parasites while sparing the human hosts. In addition to its inhibitory effects on phosphatidylcholine synthesis and cytochrome c oxidase, miltefosine has been found to affect the unique giant mitochondria and the acidocalcisomes of parasites. Both of these crucial organelles are involved in Ca2+ regulation. Furthermore, miltefosine has the ability to activate a specific parasite Ca2+ channel that responds to sphingosine, which is different to its L-type VGCC human ortholog. Here, we aimed to provide an overview of recent advancements of the anti-parasitic mechanisms of miltefosine. We also explored its multiple molecular targets and investigated how its pleiotropic effects translate into a rational therapeutic approach for patients afflicted by Leishmaniasis and American Trypanosomiasis. Notably, miltefosine's therapeutic effect extends beyond its impact on the parasite to also positively affect the host's immune system. These findings enhance our understanding on its multi-targeted mechanism of action. Overall, this review sheds light on the intricate molecular actions of miltefosine, highlighting its potential as a promising therapeutic option against these debilitating parasitic diseases.

In Vitro and Ex Vivo Synergistic Effect of Pyrvinium Pamoate Combined with Miltefosine and Paromomycin against Leishmania

One of the major drawbacks of current treatments for neglected tropical diseases is the low safety of the drugs used and the emergence of resistance. Leishmaniasis is a group of neglected diseases caused by protozoa of the trypanosomatidae family that lacks preventive vaccines and whose pharmacological treatments are scarce and unsafe. Combination therapy is a strategy that could solve the above-mentioned problems, due to the participation of several mechanisms of action and the reduction in the amount of drug necessary to obtain the therapeutic effect. In addition, this approach also increases the odds of finding an effective drug following the repurposing strategy. From the previous screening of two collections of repositioning drugs, we found that pyrvinium pamoate had a potent leishmanicidal effect. For this reason, we decided to combine it separately with two clinically used leishmanicidal drugs, miltefosine and paromomycin. These combinations were tested in axenic amastigotes of Leishmania infantum obtained from bone marrow cells and in intramacrophagic amastigotes obtained from primary cultures of splenic cells, both cell types coming from experimentally infected mice. Some of the combinations showed synergistic behavior, especially in the case of the combination of pyrvinium pamoate with paromomycin, and exhibited low cytotoxicity and good tolerability on intestinal murine organoids, which reveal the potential of these combinations for the treatment of leishmaniasis.

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.

Recent Advances in Chemotherapeutics for Leishmaniasis: Importance of the Cellular Biochemistry of the Parasite and Its Molecular Interaction with the Host

Leishmaniasis, a category 1 neglected protozoan disease caused by a kinetoplastid pathogen called Leishmania, is transmitted through dipteran insect vectors (phlebotomine, sand flies) in three main clinical forms: fatal visceral leishmaniasis, self-healing cutaneous leishmaniasis, and mucocutaneous leishmaniasis. Generic pentavalent antimonials have long been the drug of choice against leishmaniasis; however, their success is plagued with limitations such as drug resistance and severe side effects, which makes them redundant as frontline therapy for endemic visceral leishmaniasis. Alternative therapeutic regimens based on amphotericin B, miltefosine, and paromomycin have also been approved. Due to the unavailability of human vaccines, first-line chemotherapies such as pentavalent antimonials, pentamidine, and amphotericin B are the only options to treat infected individuals. The higher toxicity, adverse effects, and perceived cost of these pharmaceutics, coupled with the emergence of parasite resistance and disease relapse, makes it urgent to identify new, rationalized drug targets for the improvement in disease management and palliative care for patients. This has become an emergent need and more relevant due to the lack of information on validated molecular resistance markers for the monitoring and surveillance of changes in drug sensitivity and resistance. The present study reviewed the recent advances in chemotherapeutic regimens by targeting novel drugs using several strategies including bioinformatics to gain new insight into leishmaniasis. Leishmania has unique enzymes and biochemical pathways that are distinct from those of its mammalian hosts. In light of the limited number of available antileishmanial drugs, the identification of novel drug targets and studying the molecular and cellular aspects of these drugs in the parasite and its host is critical to design specific inhibitors targeting and controlling the parasite. The biochemical characterization of unique Leishmania-specific enzymes can be used as tools to read through possible drug targets. In this review, we discuss relevant metabolic pathways and novel drugs that are unique, essential, and linked to the survival of the parasite based on bioinformatics and cellular and biochemical analyses.

The Antileishmanial Activity of Eugenol Associated with Lipid Storage Reduction Rather Than Membrane Properties Alterations

Leishmaniasis is a neglected tropical disease that still infects thousands of people per year throughout the world. The occurrence of resistance against major treatments for this disease causes a healthcare burden in low-income countries. Eugenol is a phenylpropanoid that has shown in vitro antileishmanial activity against Leishmania mexicana mexicana (Lmm) promastigotes with an IC₅₀ of 2.72 µg/mL and a high selectivity index. Its specific mechanism of action has yet to be studied. We prepared large unilamellar vesicles (LUVs), mimicking Lmm membranes, and observed that eugenol induced an increase in membrane permeability and a decrease in membrane fluidity at concentrations much higher than IC₅₀. The effect of eugenol was similar to the current therapeutic antibiotic, amphotericin B, although the latter was effective at lower concentrations than eugenol. However, unlike amphotericin B, eugenol also affected the permeability of LUVs without sterol. Its effect on the membrane fluidity of Lmm showed that at high concentrations (≥22.5× IC₅₀), eugenol increased membrane fluidity by 20-30%, while no effect was observed at lower concentrations. Furthermore, at concentrations below 10× IC₅₀, a decrease in metabolic activity associated with the maintenance of membrane integrity revealed a leishmaniostatic effect after 24 h of incubation with Lmm promastigotes. While acidocalcisomes distribution and abundance revealed by Trypanosoma brucei vacuolar H⁺ pyrophosphatase (TbVP1) immunolabeling was not modified by eugenol, a dose-dependent decrease of lipid droplets assessed by the Nile Red assay was observed. We hereby demonstrate that the antileishmanial activity of eugenol might not directly involve plasma membrane sterols such as ergosterol, but rather target the lipid storage of Lmm.

Quinolinyl β-enaminone derivatives exhibit leishmanicidal activity against Leishmania donovani by impairing the mitochondrial electron transport chain complex and inducing ROS-mediated programmed cell death

OBJECTIVES

Previously, a series of side chain-modified quinolinyl β-enaminones was identified to possess significant activity against chloroquine-sensitive or -resistant Plasmodium falciparum and Brugia malayi microfilariae. The present study evaluates in vitro and in vivo activity of the series against Leishmania donovani and reports their mode of action.

METHODS

The in vitro activity of 15 quinolinyl β-enaminone derivatives against Leishmania promastigotes and amastigotes was assessed by luciferase assay. The reduction of organ parasite burden was assessed by Giemsa staining in L. donovani-infected BALB/c mice and hamsters. Intracellular Ca2+ and ATP level in active derivative (3D)-treated promastigotes were determined by fluorescence and luminescence assays. Flow cytometry was performed to determine loss of mitochondrial membrane potential (MMP) using JC-1 dye, reactive oxygen species (ROS) generation using 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) dye, phosphatidylserine externalization by Annexin V-FITC staining and cell-cycle arrest by propidium iodide (PI) staining.

RESULTS

Compounds 3A, 3B and 3D showed significant in vitro efficacy against L. donovani with IC50 < 6 µM and mild cytotoxicity (∼75% viability) at 25 µM on J774 macrophages. 3A and 3D at 50 mg/kg and 100 mg/kg reduced parasite burden (>84%) in infected mice and hamsters, respectively, whereas 3D-treated animals demonstrated maximum parasite burden reduction without organ toxicity. Mode-of-action analysis revealed that 3D induced apoptosis by inhibiting mitochondrial complex II, reducing MMP and ATP levels, increasing ROS and Ca2+ levels, ultimately triggering phosphatidylserine externalization and sub-G0/G1 cell-cycle arrest in promastigotes.

CONCLUSIONS

Compound 3D-mediated inhibition of L. donovani mitochondrial complex induces apoptosis, making it a promising therapeutic candidate for visceral leishmaniasis.

A new immunochemotherapy schedule for visceral leishmaniasis in a hamster model

The purpose of the present study was to evaluate the efficacy of the treatment with a recombinant cysteine proteinase from Leishmania, rldccys1, associated with allopurinol or miltefosine on Leishmania (Leishmania) infantum chagasi-infected hamsters. Golden Syrian hamsters infected with L. (L.) infantum chagasi were treated with either miltefosine (46 mg/kg) or allopurinol (460 mg/kg) alone by oral route or associated with rldccys1 (150 µg/hamster) by subcutaneous route for 30 days. Infected hamsters were also treated with miltefosine (46 mg/kg) plus rldccys1 (150 µg/hamster) for 30 days (phase 1) followed by two additional doses of rldccys1 (250 µg/hamster) (phase 2). After the end of treatment, the animals were analyzed for parasite load, body weight, serum levels of immunoglobulins, cytokine expression, and drug toxicity. The data showed a significant decrease of parasite load in infected hamsters treated with allopurinol or miltefosine alone or associated with rldccys1, as well as in those treated with rldccys1 alone. Significantly lower levels of serum IgG were detected in hamsters treated with allopurinol plus rldccys1. The treatment with miltefosine associated with rldccys1 prevented relapse observed in animals treated with miltefosine alone. A significant loss of body weight was detected only in some hamsters treated with miltefosine for 1 month and deprived of this treatment for 15 days. There were no significant differences in transcript expression of IFN-γ and IL-10 in any of treated groups. Neither hepatotoxicity nor nephrotoxicity was observed among controls and treated groups. These findings open perspectives to further explore this immunochemotherapeutic schedule as an alternative for treatment of visceral leishmaniasis.

Energy metabolism as a target for cyclobenzaprine: A drug candidate against Visceral Leishmaniasis

Leishmaniases have a broad spectrum of clinical manifestations, ranging from a cutaneous to a progressive and fatal visceral disease. Chemotherapy is nowadays the almost exclusive way to fight the disease but limited by its scarce therapeutic arsenal, on its own compromised by adverse side effects and clinical resistance. Cyclobenzaprine (CBP), an FDA-approved oral muscle relaxant drug has previously demonstrated in vitro and in vivo activity against Leishmania sp., but its targets were not fully unveiled. This study aimed to define the role of energy metabolism as a target for the leishmanicidal mechanisms of CBP. Methodology to assess CBP leishmanicidal mechanism variation of intracellular ATP levels using living Leishmania transfected with a cytoplasmic luciferase. Induction of plasma membrane permeability by assessing depolarization with DiSBAC(2)3 and entrance of the vital dye SYTOX® Green. Mitochondrial depolarization by rhodamine 123 accumulation. Mapping target site within the respiratory chain by oxygen consumption rate. Reactive oxygen species (ROS) production using MitoSOX. Morphological changes by transmission electron microscopy. CBP caused on L. infantum promastigotes a decrease of intracellular ATP levels, with irreversible depolarization of plasma membrane, the collapse of the mitochondrial electrochemical potential, mild uncoupling of the respiratory chain, and ROS production, with ensuing intracellular Ca²⁺ imbalance and DNA fragmentation. Electron microscopy supported autophagic features but not a massive plasma membrane disruption. The severe and irreversible mitochondrial damage induced by CBP endorsed the bioenergetics metabolism as a relevant target within the lethal programme induced by CBP in Leishmania. This, together with the mild-side effects of this oral drug, endorses CBP as an appealing novel candidate as a leishmanicidal drug under a drug repurposing strategy.

Transcriptome Analysis of Intracellular Amastigotes of Clinical Leishmania infantum Lines from Therapeutic Failure Patients after Infection of Human Macrophages

Leishmaniasis is considered to be one of the most neglected tropical diseases affecting humans and animals around the world. Due to the absence of an effective vaccine, current treatment is based on chemotherapy. However, the continuous appearance of drug resistance and therapeutic failure (TF) lead to an early obsolescence of treatments. Identification of the factors that contribute to TF and drug resistance in leishmaniasis will constitute a useful tool for establishing future strategies to control this disease. In this manuscript, we evaluated the transcriptomic changes in the intracellular amastigotes of the Leishmania infantum parasites isolated from patients with leishmaniasis and TF at 96 h post-infection of THP-1 cells. The adaptation of the parasites to their new environment leads to expression alterations in the genes involved mainly in the transport through cell membranes, energy and redox metabolism, and detoxification. Specifically, the gene that codes for the prostaglandin f2α synthase seems to be relevant in the pathogenicity and TF since it appears substantially upregulated in all the L. infantum lines. Overall, our results show that at the late infection timepoint, the transcriptome of the parasites undergoes significant changes that probably improve the survival of the Leishmania lines in the host cells, contributing to the TF phenotype as well as drug therapy evasion.

Tackling Drug Resistance and Other Causes of Treatment Failure in Leishmaniasis

Leishmaniasis is a tropical infectious disease caused by the protozoan Leishmania parasite. The disease is transmitted by female sand flies and, depending on the infecting parasite species, causes either cutaneous (stigmatizing skin lesions), mucocutaneous (destruction of mucous membranes of nose, mouth and throat) or visceral disease (a potentially fatal infection of liver, spleen and bone marrow). Although more than 1 million new cases occur annually, chemotherapeutic options are limited and their efficacy is jeopardized by increasing treatment failure rates and growing drug resistance. To delay the emergence of resistance to existing and new drugs, elucidating the currently unknown causes of variable drug efficacy (related to parasite susceptibility, host immunity and drug pharmacokinetics) and improved use of genotypic and phenotypic tools to define, measure and monitor resistance in the field are critical. This review highlights recent progress in our understanding of drug action and resistance in Leishmania, ongoing challenges (including setbacks related to the COVID-19 pandemic) and provides an overview of possible strategies to tackle this public health challenge.

Unraveling of interacting protein network of chaperonin TCP1 gamma subunit of Leishmania donovani

T-complex polypeptide-1 (TCP1) is a group II chaperonin that folds various cellular proteins. About 10% of cytosolic proteins in yeast have been shown to flux through the TCP1 protein complex indicating that it interacts and folds a plethora of substrate proteins that perform essential functions. In Leishmania donovani, the gamma subunit of TCP1 (LdTCP1γ) has been shown to form a homo-oligomeric complex and exhibited ATP-dependent protein folding activity. LdTCP1γ is essential for the growth and infectivity of the parasite. The interacting partners of L. donovani TCP1γ, involved in many cellular processes, are far from being understood. In this study, we utilized co-immunoprecipitation assay coupled with liquid chromatography-mass spectrometry (LC-MS) to unravel protein-protein interaction (PPI) networks of LdTCP1γ in the L. donovani parasite. Label-free quantification (LFQ) proteomic analysis revealed 719 interacting partners of LdTCP1γ. String analysis showed that LdTCP1γ interacts with all subunits of TCP1 complex as well as other proteins belonging to pathways like metabolic process, ribosome, protein folding, sorting, and degradation. Trypanothione reductase, identified as one of the interacting partners, is refolded by LdTCP1γ. In addition, the differential expression of LdTCP1γ modulates the trypanothione reductase activity in L. donovani parasite. The study provides novel insight into the role of LdTCP1γ that will pave the way to better understand parasite biology by identifying the interacting partners of this chaperonin.

FRB domain of human TOR protein induces compromised proliferation and mitochondrial dysfunction in Labrus donovani promastigotes

Visceral leishmaniasis (VL) or Kala-azar, the second-largest parasitic killer worldwide, is caused by Leishmania donovani. The drugs to treat VL are toxic and expensive. Moreover, their indiscriminate use gave rise to resistant strains. The high rate of parasite proliferation within the host macrophage cells causes pathogenesis. In the proliferative pathway, FRB domain of TOR protein is ubiquitously essential. Although orthologues of mTOR protein are reported in trypanosomatids and Leishmania but therein depth molecular characterization is yet to be done. Considerable protein sequence homology exists between the TOR of kinetoplastidas and mammals. Interestingly, exogenous human FRB domain was shown to block G1 to S transition in mammalian cancer cells. Thus, we hypothesized that expression of human FRB domain would inhibit the proliferation of Labrus donovani. Indeed, promastigotes stably expressing wild type human FRB domain show 4.7 and 1.5 folds less intra- and extra-cellular proliferations than that of untransfected controls. They also manifested 2.65 times lower rate of glucose stimulated oxygen consumption. The activities of all respiratory complexes were compromised in the hFRB expressing promastigotes. In these cells, depolarized mitochondria were 2-fold more than control cells. However, promastigotes expressing its mutant version (Trp²⁰²⁷-Phe) has shown similar characteristics like untransfected cells. Thus, this study reveals greater insights on the conserved role of TOR in the regulation of the respiratory complexes in L. donovani. The slow growing variant of FRB expressing promastigotes will have great potential to be exploited as a prophylactic agent against leishmaniasis.

Different Drugs, Same End: Ultrastructural Hallmarks of Autophagy in Pathogenic Protozoa

Protozoan parasites interact with a wide variety of organisms ranging from bacteria to humans, representing one of the most common causes of parasitic diseases and an important public health problem affecting hundreds of millions of people worldwide. The current treatment for these parasitic diseases remains unsatisfactory and, in some cases, very limited. Treatment limitations together with the increased resistance of the pathogens represent a challenge for the improvement of the patient’s quality of life. The continuous search for alternative preclinical drugs is mandatory, but the mechanisms of action of several of these compounds have not been described. Electron microscopy is a powerful tool for the identification of drug targets in almost all cellular models. Interestingly, ultrastructural analysis showed that several classes of antiparasitic compounds induced similar autophagic phenotypes in trypanosomatids, trichomonadids, and apicomplexan parasites as well as in Giardia intestinalis and Entamoeba spp. with the presence of an increased number of autophagosomes as well as remarkable endoplasmic reticulum profiles surrounding different organelles. Autophagy is a physiological process of eukaryotes that maintains homeostasis by the self-digestion of nonfunctional organelles and/or macromolecules, limiting redundant and damaged cellular components. Here, we focus on protozoan autophagy to subvert drug effects, discussing its importance for successful chemotherapy.

In-Depth Quantitative Proteomics Characterization of In Vitro Selected Miltefosine Resistance in Leishmania infantum

Visceral leishmaniasis (VL) is a neglected disease caused by Leishmania parasites. Although significant morbidity and mortality in tropical and subtropical regions of the world are associated with VL, the low investment for developing new treatment measures is chronic. Moreover, resistance and treatment failure are increasing for the main medications, but the emergence of resistance phenotypes is poorly understood at the protein level. Here, we analyzed the development of resistance to miltefosine upon experimental selection in a L. infantum strain. Time to miltefosine resistance emergence was ~six months and label-free quantitative mass-spectrometry-based proteomics analyses revealed that this process involves a remodeling of components of the membrane and mitochondrion, with significant increase in oxidative phosphorylation complexes, particularly on complex IV and ATP synthase, accompanied by increased energy metabolism mainly dependent on β-oxidation of fatty acids. Proteins canonically involved in ROS detoxification did not contribute to the resistant process whereas sterol biosynthesis enzymes could have a role in this development. Furthermore, changes in the abundance of proteins known to be involved in miltefosine resistance such as ABC transporters and phospholipid transport ATPase were detected. Together, our data show a more complete picture of the elements that make up the miltefosine resistance phenotype in L. infantum.

Lipid and fatty acid metabolism in trypanosomatids

Trypanosomiases and leishmaniases are neglected tropical diseases that have been spreading to previously non-affected areas in recent years. Identification of new chemotherapeutics is needed as there are no vaccines and the currently available treatment options are highly toxic and often ineffective. The causative agents for these diseases are the protozoan parasites of the Trypanosomatidae family, and they alternate between invertebrate and vertebrate hosts during their life cycles. Hence, these parasites must be able to adapt to different environments and compete with their hosts for several essential compounds, such as amino acids, vitamins, ions, carbohydrates, and lipids. Among these nutrients, lipids and fatty acids (FAs) are essential for parasite survival. Trypanosomatids require massive amounts of FAs, and they can either synthesize FAs de novo or scavenge them from the host. Moreover, FAs are the major energy source during specific life cycle stages of T. brucei, T. cruzi, and Leishmania. Therefore, considering the distinctive features of FAs metabolism in trypanosomatids, these pathways could be exploited for the development of novel antiparasitic drugs. In this review, we highlight specific aspects of lipid and FA metabolism in the protozoan parasites T. brucei, T. cruzi, and Leishmania spp., as well as the pathways that have been explored for the development of new chemotherapies.

The Search for Putative Hits in Combating Leishmaniasis: The Contributions of Natural Products Over the Last Decade

Despite advancements in the areas of omics and chemoinformatics, potent novel biotherapeutic molecules with new modes of actions are needed for leishmaniasis. The socioeconomic burden of leishmaniasis remains alarming in endemic regions. Currently, reports from existing endemic areas such as Nepal, Iran, Brazil, India, Sudan and Afghanistan, as well as newly affected countries such as Peru, Bolivia and Somalia indicate concerns of chemoresistance to the classical antimonial treatment. As a result, effective antileishmanial agents which are safe and affordable are urgently needed. Natural products from both flora and fauna have contributed immensely to chemotherapeutics and serve as vital sources of new chemical agents. This review focuses on a systematic cross-sectional view of all characterized anti-leishmanial compounds from natural sources over the last decade. Furthermore, IC50/EC50, cytotoxicity and suggested mechanisms of action of some of these natural products are provided. The natural product classification includes alkaloids, terpenes, terpenoids, and phenolics. The plethora of reported mechanisms involve calcium channel inhibition, immunomodulation and apoptosis. Making available enriched data pertaining to bioactivity and mechanisms of natural products complement current efforts geared towards unraveling potent leishmanicides of therapeutic relevance.

Screening of Chemical Libraries for New Antifungal Drugs against Aspergillus fumigatus Reveals Sphingolipids Are Involved in the Mechanism of Action of Miltefosine

Aspergillus fumigatus is an important fungal pathogen and the main etiological agent of aspergillosis, a disease characterized by a noninvasive process that can evolve to a more severe clinical manifestation, called invasive pulmonary aspergillosis (IPA), in immunocompromised patients. The antifungal arsenal to threat aspergillosis is very restricted. Azoles are the main therapeutic approach to control IPA, but the emergence of azole-resistant A. fumigatus isolates has significantly increased over recent decades. Therefore, new strategies are necessary to combat aspergillosis, and drug repurposing has emerged as an efficient and alternative approach for identifying new antifungal drugs. Here, we used a screening approach to analyze A. fumigatus in vitro susceptibility to 1,127 compounds. A. fumigatus was susceptible to 10 compounds, including miltefosine, a drug that displayed fungicidal activity against A. fumigatus. By screening an A. fumigatus transcription factor null library, we identified a single mutant, which has the smiA (sensitive to miltefosine) gene deleted, conferring a phenotype of susceptibility to miltefosine. The transcriptional profiling (RNA-seq) of the wild-type and ΔsmiA strains and chromatin immunoprecipitation coupled to next-generation sequencing (ChIP-Seq) of an SmiA-tagged strain exposed to miltefosine revealed genes of the sphingolipid pathway that are directly or indirectly regulated by SmiA. Sphingolipid analysis demonstrated that the mutant has overall decreased levels of sphingolipids when growing in the presence of miltefosine. The identification of SmiA represents the first genetic element described and characterized that plays a direct role in miltefosine response in fungi. IMPORTANCE The filamentous fungus Aspergillus fumigatus causes a group of diseases named aspergillosis, and their development occurs after the inhalation of conidia dispersed in the environment. Very few classes of antifungal drugs are available for aspergillosis treatment, e.g., azoles, but the emergence of global resistance to azoles in A. fumigatus clinical isolates has increased over recent decades. Repositioning or repurposing drugs already available on the market is an interesting and faster opportunity for the identification of novel antifungal agents. By using a repurposing strategy, we identified 10 different compounds that impact A. fumigatus survival. One of these compounds, miltefosine, demonstrated fungicidal activity against A. fumigatus. The mechanism of action of miltefosine is unknown, and, aiming to get more insights about it, we identified a transcription factor, SmiA (sensitive to miltefosine), important for miltefosine resistance. Our results suggest that miltefosine displays antifungal activity against A. fumigatus, interfering in sphingolipid biosynthesis.

Miltefosine enhances infectivity of a miltefosine-resistant Leishmania infantum strain by attenuating its innate immune recognition

Background

Miltefosine (MIL) is currently the only oral drug available to treat visceral leishmaniasis but its use as first-line monotherapy has been compromised by an increasing treatment failure. Despite the scarce number of resistant clinical isolates, MIL-resistance by mutations in a single aminophospholipid transporter gene can easily be selected in a laboratory environment. These mutations result in a reduced survival in the mammalian host, which can partially be restored by exposure to MIL, suggesting a kind of drug-dependency.

Methodology/Principal findings

To enable a combined study of the infection dynamics and underlying immunological events for differential in vivo survival, firefly luciferase (PpyRE9) / red fluorescent protein (DsRed) double-reporter strains were generated of MIL-resistant (MIL-R) and syngeneic MIL-sensitive (MIL-S) Leishmania infantum. Results in C57Bl/6 and BALB/c mice show that MIL-R parasites induce an increased innate immune response that is characterized by enhanced influx and infection of neutrophils, monocytes and dendritic cells in the liver and elevated serum IFN-γ levels, finally resulting in a less efficient establishment in liver macrophages. The elevated IFN-γ levels were shown to originate from an increased response of hepatic NK and NKT cells to the MIL-R parasites. In addition, we demonstrated that MIL could increase the in vivo fitness of MIL-R parasites by lowering NK and NKT cell activation, leading to a reduced IFN-γ production.

Conclusions/Significance

Differential induction of innate immune responses in the liver was found to underlie the attenuated phenotype of a MIL-R parasite and its peculiar feature of drug-dependency. The impact of MIL on hepatic NK and NKT activation and IFN-γ production following recognition of a MIL-R strain indicates that this mechanism may sustain infections with resistant parasites and contribute to treatment failure.

Visceral leishmaniasis is a neglected tropical disease that is fatal if left untreated. Miltefosine is currently the only oral drug available but is increasingly failing to cure patients, resulting in its discontinuation as first-line drug in some endemic areas. To understand these treatment failures, we investigated the complex interplay of the parasite with the host immune system in the presence and absence of miltefosine. Our data indicate that miltefosine-resistant Leishmania parasites become severely hampered in their in vivo infectivity, which could be attributed to the induction of a pronounced innate immune response. Interestingly, the infection deficit was partially restored in the presence of miltefosine. Our results further indicate that miltefosine can exacerbate infections with resistant parasites by reducing innate immune recognition. This study provides new insights into the complex interplay between parasite, drug and host and discloses an immune-related mechanism of treatment failure.

In vivo evaluation of anti-Leishmania activity of alkyltriazoles and alkylphosphocholines by oral route

The failures in the treatment of leishmaniasis is an increasing problem around the world, especially related to resistance. Thus, we describe the synthesis and in vivo anti-Leishmania activity of alkylphosphocholine and alkyltriazoles; besides, their likely action mechanisms stem from some eventual inhibition of parasite enzymes using computational tools. These compounds were tested in an in vivo hamster model infected with Leishmania Leishmania infantum chagasi. Fifty days after parasite inoculation, the two compounds 12-azidedodecylphosphocholine (3) and 3-(1-(12-fluorododecyl)-1H-1,2,3-triazol-1-yl)propano-1-ol (9), were separately administered once a day as oral suspensions (25 and 12.5 mg/kg/day, respectively) during ten days, and their efficacy was compared to the reference compound pentavalent antimonial Glucantime (GLU). Compound 3 significantly reduced the number of parasites in the spleen (4.93 × 10² amastigotes/g) and liver (4.52 × 10³ amastigotes/g). Compound 9 reduced the number of amastigotes in the spleen to 1.30 × 10⁴ and 1.36 × 10³ amastigotes/g in the liver. GLU was the most effective overall treatment (7.50 × 10¹ and 2.28 × 10² amastigotes/g in the spleen and liver, respectively). The high activity levels of these compounds in vivo may stem from their high in vitro leishmanicidal activity and lipophilicity. The in silico absorption, distribution, metabolism, and excretion studies also showed some anti-Leishmania potential. Compound 9 had more lipophilic characteristics than those of compound 3. In silico studies of the nine enzymes of compounds 3 and 9 showed significant evidence of interactions with nicotimidase and tyrosine aminotransferase, demonstrating possible inhibition enzymes present in L. (L.) infantum chagasi. These compounds could be a promising template for developing a new class of leishmanicidal agents, by oral route, and deserve further investigation to explore different therapeutic regimens.

De Novo Synthesis of Phosphatidylcholine Is Essential for the Promastigote But Not Amastigote Stage in Leishmania major

Phosphatidylcholine (PC) is the most abundant type of phospholipids in eukaryotes constituting ~30% of total lipids in Leishmania. PC synthesis mainly occurs via the choline branch of the Kennedy pathway (choline ⇒ choline-phosphate ⇒ CDP-choline ⇒ PC) and the N-methylation of phosphatidylethanolamine (PE). In addition, Leishmania parasites can acquire PC and other lipids from the host or culture medium. In this study, we assessed the function and essentiality of choline ethanolamine phosphotransferase (CEPT) in Leishmania major which is responsible for the final step of the de novo synthesis of PC and PE. Our data indicate that CEPT is localized in the endoplasmic reticulum and possesses the activity to generate PC from CDP-choline and diacylglycerol. Targeted deletion of CEPT is only possible in the presence of an episomal CEPT gene in the promastigote stage of L. major. These chromosomal null parasites require the episomal expression of CEPT to survive in culture, confirming its essentiality during the promastigote stage. In contrast, during in vivo infection of BALB/c mice, these chromosomal null parasites appeared to lose the episomal copy of CEPT while maintaining normal levels of virulence, replication and cellular PC. Therefore, while the de novo synthesis of PC/PE is indispensable for the proliferation of promastigotes, intracellular amastigotes appear to acquire most of their lipids through salvage and remodeling.

The ultimate fate determinants of drug induced cell-death mechanisms in Trypanosomatids

Chemotherapy constitutes a major part of modern-day therapy for infectious and chronic diseases. A drug is said to be effective if it can inhibit its target, induce stress, and thereby trigger an array of cell death pathways in the form of programmed cell death, autophagy, necrosis, etc. Chemotherapy is the only treatment choice against trypanosomatid diseases like Leishmaniasis, Chagas disease, and sleeping sickness. Anti-trypanosomatid drugs can induce various cell death phenotypes depending upon the drug dose and growth stage of the parasites. The mechanisms and pathways triggering cell death in Trypanosomatids serve to help identify potential targets for the development of effective anti-trypanosomatids. Studies show that the key proteins involved in cell death of trypanosomatids are metacaspases, Endonuclease G, Apoptosis-Inducing Factor, cysteine proteases, serine proteases, antioxidant systems, etc. Unlike higher eukaryotes, these organisms either lack the complete set of effectors involved in cell death pathways, or are yet to be deciphered. A detailed summary of the existing knowledge of different drug-induced cell death pathways would help identify the lacuna in each of these pathways and therefore open new avenues for research and thereby new therapeutic targets to explore. The cell death pathway associated complexities in metazoans are absent in trypanosomatids; hence this summary can also help understand the trigger points as well as cross-talk between these pathways. Here we provide an in-depth overview of the existing knowledge of these drug-induced trypanosomatid cell death pathways, describe their associated physiological changes, and suggest potential interconnections amongst them.

Association of miltefosine with granulocyte and macrophage colony-stimulating factor (GM-CSF) in the treatment of cutaneous leishmaniasis in the Amazon region: A randomized and controlled trial

OBJECTIVES

To compare topical granulocyte and macrophage colony-stimulating factor (GM-CSF) and miltefosine (G + M) versus placebo and miltefosine (P + M) or parenteral meglumine antimoniate (MA) in the treatment of 150 patients with cutaneous leishmaniasis (CL) caused by Leishmania guyanensis in the Amazon.

DESIGN

A randomized and double-blinded clinical trial.

RESULTS

At 90 days after the initiation of therapy, the cure rates were 66%, 58%, and 52% for the groups P + M, G + M, and MA, respectively (p > 0.05). Cure rates at 180 days did not differ. Healing time was similar in the 3 groups, but faster in the MA group as compared to the G + M group (p = 0.04). Mild and transitory systemic adverse events were frequent in all groups (above 85%). Nausea (85%) and vomiting (39%) predominated in the miltefosine groups and arthralgia (51%) and myalgia (48%) in the MA group. One patient (group MA) stopped treatment after presenting with fever, exanthema, and severe arthralgia.

CONCLUSIONS

Miltefosine did not present a higher cure rate than MA, and the association of GM-CSF did not improve the therapeutic response. Nevertheless, because of its less toxicity, easier administration, and a similar cure rate when compared with MA, miltefosine should remain as one of the main drugs for treating CL due to L. guyanensis. (Clinicaltrials.gov Identifier NCT03023111).

Evaluation of the Ability of Miltefosine Associated with Topical GM-CSF in Modulating the Immune Response of Patients with Cutaneous Leishmaniasis

Cutaneous leishmaniasis (CL) due to L. braziliensis is associated with an exaggerated inflammatory response and tissue damage. Miltefosine is more effective than pentavalent antimony (Sb^v) in the treatment of CL, and here, we evaluate the ability of Sb^v, miltefosine, and GM-CSF administered intravenously, orally, or topically, respectively, to modify the immune response. Patients were treated with miltefosine plus GM-CSF, miltefosine plus placebo, or Sb^v. Mononuclear cells were stimulated with soluble Leishmania antigen (SLA) on day 0 and day 15 of therapy, and cytokine levels were determined in supernatants by ELISA. The lymphocyte proliferation and oxidative burst were evaluated by flow cytometry, and the degree of infection and Leishmania killing by optical microscopy. Proliferation of CD4⁺ T cells were enhanced in patients using miltefosine and in CD8⁺ T cells when GM-CSF was associated. Enhancement in the oxidative burst occurred in the miltefosine plus GM-CSF group on day 15 of therapy. Moreover, the number of L. braziliensis in infected monocytes on day 15 as well as the percentage of infected cells was lower after 48- and 72-hour culture in cells from patients treated with miltefosine plus GM-CSF. In addition to the ability of miltefosine to kill Leishmania, the changes in the immune response caused by miltefosine and GM-CSF may increase the cure rate of CL patients using these drugs.

Mode of action of a formulation containing hydrazones and saponins against leishmania spp. Role in mitochondria, proteases and reinfection process

Toxicity and poor adherence to treatment that favors the generation of resistance in the Leishmania parasites highlight the need to develop better alternatives. Here, we evaluated the in vitro effectiveness of hydrazone derived from chromanes 2-(2,3-dihydro-4H-1-benzothiopyran-4-ylidene) hydrazide (TC1) and 2-(2,3-dihydro-4H-1-benzopyran-4-ylidene) hydrazide (TC2) and the mixture of triterpene saponin hederagenin-3-O-(3,4-O-diacetyl-ß-D-xylopyranosyl-(1à3)-a-L- rhamnopyranosyl-(1à2)-a-L-arabinofuranoside, hederagenin-3-O-(3,4-O-diacetyl-a-L- arabinopyranosyl-(1à3)-a-L-rhamnopyranosyl-(1à2)-a-L-arabinofuranoside and, hederagenin-3-O-(4-O-acetyl-ß-D-xylopyranosyl-(1à3)-a-L-rhamnopyranosyl-(1à2)-a-L-arabinofuranoside from Sapindus saponaria (SS) on L. braziliensis and L. pifanoi. Mixtures of TC1 or TC2 with saponin were formulated for topical application and the therapeutic effectiveness was evaluated in the model for cutaneous leishmaniasis (CL) in golden hamster. The mode of action of these compounds was tested on various parasite processes and ultrastructural parasite modifications. TC1, TC2 and SS showed moderate cytotoxicity when tested independently but toxicity was improved when tested in combination. The compounds were more active against intracellular Leishmania amastigotes. In vivo studies showed that combinations of TC1 or TC2 with SS in 1:1 ratio (w/w) cured 100% of hamsters with no signs associated with toxicity. The compounds did cause changes in the mitochondrial activity of the parasite with a decrease in ATP levels and depolarization of membrane potential and overproduction of reactive oxygen species; nevertheless, these effects were not related to alterations in membrane permeability. The phagolysosome ultrastructure was also affected impacting the survival of Leishmania but the function of the lysosome nor the pH inside the phagolysosome did not change. Lastly, there was a protease inhibition which was directly related to the decrease in the ability of Leishmania to infect and multiply inside the macrophage. The results suggest that the combination of TC1 and TC2 with SS in a 1:1 ratio is capable of curing CL in hamsters. This effect may be due to the ability of these compounds to affect parasite survival and the ability to infect new cells.

Antileishmanial Drugs Modulate IL-12 Expression and Inflammasome Activation in Primary Human Cells

Leishmaniases are neglected tropical diseases. The treatment of leishmaniasis relies exclusively on chemotherapy including amphotericin B (AmB), miltefosine (hexadecylphosphocholine), and pentamidine. Besides the fact that these molecules are harmful for patients, little is known about the impact of such antileishmanial drugs on primary human cells in relation to immune function. The present study demonstrates that all antileishmanial drugs inhibit CD4 and CD8 T cell proliferation at the doses that are not related to increased cell death. Our results highlight that antileishmanial drugs have an impact on monocytes by altering the expression of IL-12 induced by LPS, whereas only AmB induced IL-10 secretion; both cytokines are essential in regulating Th1 cell-mediated immunity. Interestingly, IL-12 and anti-IL-10 Abs improved T cell proliferation inhibited by AmB. Furthermore, our results show that in contrast to hexadecylphosphocholine and pentamidine, AmB induced gene expression of the inflammasome pathway. Thus, AmB induced IL-1β and IL-18 secretions, which are reduced by specific inhibitors of caspase activation (Q-VD) and NLRP3 activation (MCC950). Our results reveal previously underestimated effects of antileishmanial drugs on primary human cells.

The preclinical discovery and development of oral miltefosine for the treatment of visceral leishmaniasis: a case history

INTRODUCTION

Visceral leishmaniasis (VL) is a vector-borne disease caused by Leishmania donovani or Leishmania infantum. Closely related to poverty, VL is fatal and represents one of the main burdens on public health in developing countries. Treatment of VL relies exclusively on chemotherapy, a strategy still experiencing numerous limitations. Miltefosine (MF) has been used in the chemotherapy of VL in some endemic areas, and has been expanded to other regions, being considered crucial in eradication programs.

AREAS COVERED

This article reviews the most relevant preclinical and clinical aspects of MF, its mechanism of action and resistance to Leishmania parasites, as well as its limitations. The authors also give their perspectives on the treatment of VL.

EXPERT OPINION

The discovery of MF represented an enormous advance in the chemotherapy of VL, since it was the first oral drug for this neglected disease. Beyond selection of resistant parasites due to drug pressure, several other factors can lead to treatment failure such as, for example, factors intrinsic to the host, parasite and the drug itself. Although its efficacy as a monotherapy has reduced over recent years, MF is still an important alternative in VL chemotherapy, especially when used in combination with other drugs.

Discovery and Pharmacological Studies of 4-Hydroxyphenyl-Derived Phosphonium Salts Active in a Mouse Model of Visceral Leishmaniasis

We report the discovery of new 4-hydroxyphenyl phosphonium salt derivatives active in the submicromolar range (EC₅₀ from 0.04 to 0.28 μM, SI > 10) against the protozoan parasite Leishmania donovani. The pharmacokinetics and in vivo oral efficacy of compound 1 [(16-(2,4-dihydroxyphenyl)-16-oxohexadecyl)triphenylphosphonium bromide] in a mouse model of visceral leishmaniasis were established. Compound 1 reduced the parasite load in spleen (98.9%) and liver (95.3%) of infected mice after an oral dosage of four daily doses of 1.5 mg/kg. Mode of action studies showed that compound 1 diffuses across the plasma membrane, as designed, and targets the mitochondrion of Leishmania parasites. Disruption of the energetic metabolism, with a decrease of intracellular ATP levels as well as mitochondrial depolarization together with a significant reactive oxygen species production, contributes to the leishmanicidal effect of 1. Importantly, this compound was equally effective against antimonials and miltefosine-resistant clinical isolates of Leishmania infantum, indicating its potential as antileishmanial lead.

β-Amino acid derivatives as mitochondrial complex III inhibitors of L. donovani: A promising chemotype targeting visceral leishmaniasis

β-amino acids and their analogues are gathering increased attention not only because of their antibacterial and antifungal activity, but also for their use in designing peptidomimetics with increased oral bioavailability and resistance to metabolic degradation. In this study, a series of α-phenyl substituted chalcones, α-phenyl, β-amino substituted dihydrochalcones and β-amino acid derivatives were synthesized and evaluated for their antileishmanial efficacy against experimental visceral leishmaniasis (VL). Among all synthesized derivatives, 10c showed promising antileishmanial efficacy against both extracellular promastigote and intracellular amastigote (IC₅₀ 8.2 μM and 20.5 μM respectively) of L. donovani with negligible cytotoxic effect towards J774 macrophages and Vero cells. 10c effectively reduced spleen and liver parasite burden (>90%) in both hamster and Balb/c model of VL without any hepatotoxicity. In vitro pharmacokinetic analysis showed that 10c was stable in gastric fluid and plasma of Balb/c mice at 10 μg/ml. Further analysis of the molecular mechanism revealed that 10c entered into the parasite by depolarizing the plasma membrane rather than forming nonspecific pores and induced molecular events like loss in mitochondrial membrane potential with a gradual decline in ATP production. This, in turn, did not induce programmed cell death of the parasite; rather 10c induced bioenergetic collapse of the parasite by decreasing ATP synthesis through specific inhibition of mitochondrial complex III activity. Altogether, our results allude to the therapeutic potential of β-amino acid derivatives as novel antileishmanials, identifying them as lead compounds for further exploration in the design of potent candidates for the treatment of visceral leishmaniasis.

Multi-target drugs active against leishmaniasis: A paradigm of drug repurposing

This mini-review focuses on leishmanicidal drugs that were sourced from small molecules previously approved for other diseases. The mechanisms of action of these molecules are herein explored, to probe the origins of their inter-species growth inhibitory activities. It is shown how the transversal action of the azoles - fluconazole, posaconazole and itraconazole - in both fungi and Leishmania is due to the occurrence of the same target, lanosterol 14-α-demethylase, in these two groups of species. In turn, the drugs miltefosine and amphotericin B are presented as truly multi-target agents, acting on small molecules, proteins, genes and even organelles. Steps towards future leishmanicidal drug candidates based on the multi-target strategy and on drug repurposing are also briefly presented.

Current and promising novel drug candidates against visceral leishmaniasis

Leishmaniasis is a group of zoonotic diseases caused by a trypanosomatid parasite mostly in impoverished populations of low-income countries. In their different forms, leishmaniasis is prevalent in more than 98 countries all over the world and approximately 360-million people are at risk. Since no vaccine is currently available to prevent any form of the disease, the control strategy of leishmaniasis mainly relies on early case detection followed by adequate pharmacological treatment that may improve the prognosis and can reduce transmission. A handful of compounds and formulations are available for the treatment of leishmaniasis in humans, but only few of them are currently in use since most of these agents are associated with toxicity problems such as nephrotoxicity and cardiotoxicity in addition to resistance problems. In recent decades, very few novel drugs, new formulations of standard drugs or combinations of them have been approved against leishmaniasis. This review highlights the current drugs and combinations that are used medical practice and recent advances in new treatments against leishmaniasis that were pointed out in the recent 2nd Conference, Global Challenges in Neglected Tropical Diseases, held in San Juan, Puerto Rico in June 2018, emphasizing the plethora of new families of molecules that are bridging the gap between preclinical and first-in-man trials in next future.

Exploiting knowledge on pharmacodynamics-pharmacokinetics for accelerated anti-leishmanial drug discovery/development

Introduction: Being on the top list of neglected tropical diseases, leishmaniasis has been marked for elimination by 2020. In the light of small armamentarium of drugs and their associated drawbacks, the understanding of pharmacodynamics and/or pharmacokinetics becomes a priority to achieve and sustain disease elimination. Areas covered: The authors have looked into pharmacological aspects of existing and emerging drugs for treatment of leishmaniasis. An in-depth understanding of pharmacodynamics and pharmacokinetics (PKPD) provides a rationale for drug designing and optimizing the treatment strategies. It forms a key to prevent drug resistance and avoid drug-associated adverse effects. The authors have compiled the researches on the PKPD of different anti-leishmanial formulations that have the potential for improved and/or effective disease intervention. Expert opinion: Understanding the pharmacological aspects of drugs forms the basis for the clinical application of novel drugs. Tailoring drug dosage and individualized treatment can avoid the adverse events and bridge gap between the in vitro models and their clinical application. An integrated approach, with pragmatic use of technological advances can improve phenotypic screening and physiochemical properties of novel drugs. Concomitantly, this can serve to improve clinical efficacies, reduce the incidence of relapse and accelerate the drug discovery/development process for leishmaniasis elimination.

A randomized, open-label clinical trial comparing the long-term effects of miltefosine and meglumine antimoniate for mucosal leishmaniasis

INTRODUCTION

The treatment of mucosal leishmaniasis (ML) is difficult due to the toxicity and route of administration of standard drugs. Miltefosine is an oral agent used for leishmaniasis treatment; however, no data exist regarding its use for ML in Brazil. In this study, we aimed to evaluate the efficacy of miltefosine for ML treatment compared to that of pentavalent antimonial in a pilot study.

METHODS

We performed a randomized clinical trial with two parallel groups. The tested intervention consisted of miltefosine 1.3-2 mg/kg/day (two capsules) for 28 days or intravenous 20 mg SbV/kg/day of meglumine antimoniate (N-MA) for 30 days. The final endpoint was defined as complete healing of the lesion four years after treatment. We also analyzed an early endpoint at 90 days after treatment.

RESULTS

Forty patients were included in this study: each experimental group comprised 20 patients. Applying a multivariate model in an intention-to-treat analysis, we observed that patients treated with miltefosine had a cure probability 2.08 times greater (95% confidence interval [CI] = 1.03-4.18) than those treated with N-MA at 90 days after treatment. At the final endpoint, we observed no differences in cure probability between miltefosine and N-MA (relative risk = 0.66; 95% CI = 0.33-1.32). With respect to adverse reactions, significant differences between groups were related to gastrointestinal effects, which were more frequent in the miltefosine group.

CONCLUSIONS

Miltefosine may be an interesting alternative for treating ML because of its oral administration and cure rate after long-term follow-up.

Investigation of the pathways related to intrinsic miltefosine tolerance in Leishmania (Viannia) braziliensis clinical isolates reveals differences in drug uptake

In Brazil, cutaneous leishmaniasis is caused predominantly by L. (V.) braziliensis. The few therapeutic drugs available exhibit several limitations, mainly related to drug toxicity and reduced efficacy in some regions. Miltefosine (MF), the only oral drug available for leishmaniasis treatment, is not widely available and has not yet been approved for human use in Brazil. Our group previously reported the existence of differential susceptibility among L. (V.) braziliensis clinical isolates. In this work, we further characterized three of these isolates of L. (V.) braziliensis chosen because they exhibited the lowest and the highest MF half maximal inhibitory concentrations and were therefore considered less tolerant or more tolerant, respectively. Uptake of MF, and also of phosphocholine, were found to be significantly different in more tolerant parasites compared to the less sensitive isolate, which raised the hypothesis of differences in the MF transport complex Miltefosine Transporter (MT)-Ros3. Although some polymorphisms in those genes were found, they did not correlate with the drug susceptibility phenotype. Drug efflux and compartmentalization were similar in the isolates tested, and amphotericin B susceptibility was retained in MF tolerant parasites, suggesting that increased fitness was also not the basis of observed differences. Transcriptomic analysis revealed that Ros3 mRNA levels were upregulated in the sensitive strain compared to the tolerant ones. Increased mRNA abundance in more tolerant isolates was validated by quantitative PCR. Our results suggest that differential gene expression of the MT transporter complex is the basis of the differential susceptibility in these unselected, naturally occurring parasites.

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Brazilian L. (V.) braziliensis isolates vary in mitefosine susceptibility.

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Diminished drug internalization was observed in more tolerant isolates.

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Drug susceptibility did not correlate with SNPs in MT-Ros3 genes.

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Drug efflux and compartmentalization were similar in the isolates tested.

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Increased drug sensitivity is accompanied by Ros3 mRNA upregulation.