In vivo interference of paromomycin with mitochondrial activity of Leishmania

Antiprotozoal potential of Vismia species (Hypericaceae), medicinal plants used to fight cutaneous leishmaniasis

ETHNOPHARMACOLOGICAL RELEVANCE

Species of Vismia (Hypericaceae), known in Brazil as "lacre", are commonly used in traditional Amazonian medicine for the treatment of skin lesions, including those caused by Leishmania infection.

AIM OF THE STUDY

Hexane extracts from the leaves of Vismia cayennensis, V. gracilis, V. sandwithii and V. guianensis, as well as from the fruits of the latter, in addition to the anthraquinones vismiaquinone, physcion and chrysophanol isolated from these species were explored for their anti-promastigote and anti-amastigote activity on Leishmania amazonensis.

MATERIALS AND METHODS

Extracts were prepared by static maceration with n-hexane. The compounds, isolated by chromatographic techniques, were identified by spectroscopic methods (1H and 13C NMR). Promastigotes of L.amazonensis were incubated with hexane extracts (1-50 μg/mL) or anthraquinones (1-50 μM) and the parasite survival analyzed. The action of compounds on reactive oxygen species (ROS) production, mitochondrial membrane potential, and membrane integrity of promastigotes were evaluated by flow cytometer, and the cytotoxicity on mammalian cells using MTT assay. Furthermore, the activity of compounds against amastigotes and nitric oxide production were also investigated.

RESULTS

Vismiaquinone and physcion were obtained from the leaves of V. guianensis. Physcion, as well as chrysophanol, were isolated from V. sandwithii. Vismia cayennensis and V. gracilis also showed vismiaquinone, compound detected in lower quantity in the fruits of V. guianensis. All extracts were active against the parasite, corroborating the popular use. The greatest activity against promastigotes was achieved with V. guianensis extract (IC50 4.3 μg/mL), precisely the most used Vismia species for treating cutaneous leishmaniasis. Vismiaquinone and physcion exhibited relevant activity with IC50 12.6 and 2.6 μM, respectively. Moreover, all extracts and anthraquinones tested induced ROS production, mitochondrial dysfunction, membrane disruption and were able to kill intracellular amastigote forms, being worthy of further in vivo studies as potential antileishmanial drugs.

CONCLUSIONS

The overall data achieved in the current investigation scientifically validate the traditional use of Vismia species, mainly V. guianensis, as an anti-Leishmania agent. Furthermore, the promising results presented here indicate species of Vismia as potentially useful resources of Brazilian flora for the discovery of therapeutic solutions for neglected diseases.

A novel chemically defined medium for the biotechnological and biomedical exploitation of the cell factory Leishmania tarentolae

The development of media for cell culture is a major issue in the biopharmaceutical industry, for the production of therapeutics, immune-modulating molecules and protein antigens. Chemically defined media offer several advantages, as they are free of animal-derived components and guarantee high purity and a consistency in their composition. Microorganisms of the genus Leishmania represent a promising cellular platform for production of recombinant proteins, but their maintenance requires supplements of animal origin, such as hemin and fetal bovine serum. In the present study, three chemically defined media were assayed for culturing Leishmania tarentolae, using both a wild-type strain and a strain engineered to produce a viral antigen. Among the three media, Schneider's Drosophila Medium supplemented with Horseradish Peroxidase proved to be effective for the maintenance of L. tarentolae promastigotes, also allowing the heterologous protein production by the engineered strain. Finally, the engineered strain was maintained in culture up to the 12th week without antibiotic, revealing its capability to produce the recombinant protein in the absence of selective pressure.

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.

Antileishmanial Activity, Toxicity and Mechanism of Action of Complexes of Sodium Usnate with Lanthanide Ions: Eu(III), Sm(III), Gd(III), Nd(III), La(III) and Tb(III)

Leishmaniases are neglected diseases with limited therapeutic options. Diffuse cutaneous leishmaniasis can occur in Brazil due to Leishmania amazonensis. This study details the antileishmanial activity and cytotoxicity of complexes of sodium usnate (SAU) with lanthanide ions ([LnL3 (H2O)x] (Ln = La(III), Nd(III), Gd(III), Tb(III), Eu(III) and Sm(III); L = SAU). All lanthanide complexes were highly active and more potent than SAU against L. amazonensis promastigotes and intracellular amastigotes (Pro: IC50 < 1.50 μM; Ama: IC50 < 7.52 μM). EuL3·3H2O and NdL3·3H2O were the most selective and effective on intracellular amastigotes, with a selectivity index of approximately 7.0. In silico predictions showed no evidence of mutagenicity, tumorigenicity or irritation for all complexes. Treatment with EuL3·3H2O triggered NO release even at the lowest concentration, indicating NO production as a mechanism of action against the parasite. Incubating promastigotes with the lanthanide complexes, particularly with SmL3·4H2O and GdL3·3H2O, led to a change in the mitochondrial membrane potential, indicating the ability of these complexes to target this essential organelle. The same complexes caused cell death through cell membrane disruption, but their relationship with early or late apoptotic processes remains unclear. Thus, the inclusion of lanthanide ions in SAU improves selectivity with a promising mechanism of action targeting the mitochondria.

In Silico Exploration of the Trypanothione Reductase (TryR) of L. mexicana

Human leishmaniasis is a neglected tropical disease which affects nearly 1.5 million people every year, with Mexico being an important endemic region. One of the major defense mechanisms of these parasites is based in the polyamine metabolic pathway, as it provides the necessary compounds for its survival. Among the enzymes in this route, trypanothione reductase (TryR), an oxidoreductase enzyme, is crucial for the Leishmania genus' survival against oxidative stress. Thus, it poses as an attractive drug target, yet due to the size and features of its catalytic pocket, modeling techniques such as molecular docking focusing on that region is not convenient. Herein, we present a computational study using several structure-based approaches to assess the druggability of TryR from L. mexicana, the predominant Leishmania species in Mexico, beyond its catalytic site. Using this consensus methodology, three relevant pockets were found, of which the one we call σ-site promises to be the most favorable one. These findings may help the design of new drugs of trypanothione-related diseases.

Sterol profiling of Leishmania parasites using a new HPLC-tandem mass spectrometry-based method and antifungal azoles as chemical probes reveals a key intermediate sterol that supports a branched ergosterol biosynthetic pathway

Human leishmaniasis is an infectious disease caused by Leishmania protozoan parasites. Current chemotherapeutic options against the deadly disease have significant limitations. The ergosterol biosynthetic pathway has been identified as a drug target in Leishmania. However, remarkable differences in the efficacy of antifungal azoles that inhibit ergosterol biosynthesis have been reported for the treatment of leishmaniasis. To better understand the sterol biosynthetic pathway in Leishmania and elucidate the mechanism underlying the differential efficacy of antifungal azoles, we developed a new LC-MS/MS method to study sterol profiles in promastigotes of three Leishmania species, including two L. donovani, one L. major and one L. tarentolae strains. A combination of distinct precursor ion masses and LC retention times allowed for specific detection of sixteen intermediate sterols between lanosterol and ergosterol using the newly developed LC-MS/MS method. Although both posaconazole and fluconazole are known inhibitors of fungal lanosterol 14α-demethylase (CYP51), only posaconazole led to a substantial accumulation of lanosterol in azole-treated L. donovani promastigotes. Furthermore, a key intermediate sterol accumulated by 40- and 7-fold when these parasites were treated with posaconazole and fluconazole, respectively, which was determined as 4α,14α-dimethylzymosterol by high resolution mass spectrometry and NMR spectroscopy. The identification of 4α,14α-dimethylzymosterol supports a branched ergosterol biosynthetic pathway in Leishmania, where lanosterol C4- and C14-demethylation reactions occur in parallel rather than sequentially. Our results suggest that selective inhibition of leishmanial CYP51 is insufficient to effectively prevent parasite growth and dual inhibitors of both CYP51 and the unknown sterol C4-demethylase may be required for optimal antiparasitic effect.

Genome-wide analysis reveals allelic variation and chromosome copy number variation in paromomycin-resistant Leishmania donovani

In the absence of adequate diagnosis and treatment, leishmaniasis remains a major public health concern on a global scale. Drug resistance remains a key obstacle in controlling and eliminating visceral leishmaniasis. The therapeutic gap due to lack of target-specific medicine and vaccine can be minimized by obtaining parasite's genomic information. This study compared whole-genome sequence of paromomycin-resistant parasite (K133PMM) developed through in vitro adaptation and selection with sensitive Leishmania clinical isolate (K133WT). We found a large number of upstream and intergenic gene variations in K133PMM. There were 259 single nucleotide polymorphisms (SNPs), 187 insertion-deletion (InDels), and 546 copy number variations (CNVs) identified. Most of the genomic variations were found in the gene's upstream and non-coding regions. Ploidy estimation revealed chromosome 5 in tetrasomy and 6, 9, and 12 in trisomy, uniquely in K133PMM. These contain the genes for protein degradation, parasite motility, autophagy, cell cycle maintenance, and drug efflux membrane transporters. Furthermore, we also observed reduction in ploidy of chromosomes 15, 20, and 23, in the resistant parasite containing mostly the genes for hypothetical proteins and membrane transporters. We chronicled correlated genomic conversion and aneuploidy in parasites and hypothesize that this led to rapid evolutionary changes in response to drug induced pressure, which causes them to become resistant.

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.

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.

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.

Experimental Selection of Paromomycin Resistance in Leishmania donovani Amastigotes Induces Variable Genomic Polymorphisms

The relatively high post-treatment relapse rates of paromomycin (PMM) in visceral leishmaniasis treatment and the swift emergence of experimental drug resistance challenge its broad application and urge for rational use and monitoring of resistance. However, no causal molecular mechanisms to Leishmania PMM resistance have been identified so far. To gain insights into potential resistance mechanisms, twelve experimentally selected Leishmania donovani clonal lines and the non-cloned preselection population, with variable degrees of PMM resistance, were subjected to whole genome sequencing. To identify genomic variations potentially associated with resistance, SNPs, Indels, chromosomal somy and gene copy number variations were compared between the different parasite lines. A total of 11 short nucleotide variations and the copy number alterations in 39 genes were correlated to PMM resistance. Some of the identified genes are involved in transcription, translation and protein turn-over (transcription elongation factor-like protein, RNA-binding protein, ribosomal protein L1a, 60S ribosomal protein L6, eukaryotic translation initiation factor 4E-1, proteasome regulatory non-ATP-ase subunit 3), virulence (major surface protease gp63, protein-tyrosine phosphatase 1-like protein), mitochondrial function (ADP/ATP mitochondrial carrier-like protein), signaling (phosphatidylinositol 3-related kinase, protein kinase putative and protein-tyrosine phosphatase 1-like protein) and vesicular trafficking (ras-related protein RAB1). These results indicate that, in Leishmania, the aminoglycoside PMM affects protein translational processes and underlines the complex and probably multifactorial origin of resistance.

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.

Perspectives From Systems Biology to Improve Knowledge of Leishmania Drug Resistance

Neglected Tropical Diseases include a broad range of pathogens, hosts, and vectors, which represent evolving complex systems. Leishmaniasis, caused by different Leishmania species and transmitted to humans by sandflies, are among such diseases. Leishmania and other Trypanosomatidae display some peculiar features, which make them a complex system to study. Leishmaniasis chemotherapy is limited due to high toxicity of available drugs, long-term treatment protocols, and occurrence of drug resistant parasite strains. Systems biology studies the interactions and behavior of complex biological processes and may improve knowledge of Leishmania drug resistance. System-level studies to understand Leishmania biology have been challenging mainly because of its unusual molecular features. Networks integrating the biochemical and biological pathways involved in drug resistance have been reported in literature. Antioxidant defense enzymes have been identified as potential drug targets against leishmaniasis. These and other biomarkers might be studied from the perspective of systems biology and systems parasitology opening new frontiers for drug development and treatment of leishmaniasis and other diseases. Our main goals include: 1) Summarize current advances in Leishmania research focused on chemotherapy and drug resistance. 2) Share our viewpoint on the application of systems biology to Leishmania studies. 3) Provide insights and directions for future investigation.

Leishmaniasis: where are we and where are we heading?

Leishmaniasis is a zoonotic disease in humans caused by the bite of a parasite-infected sandfly. The disease, widely referred to as "poor man's disease," affects millions of people worldwide. The clinical manifestation of the disease depends upon the species of the parasite and ranges from physical disfigurement to death if left untreated. Here, we review the past, present, and future of leishmaniasis in detail. The life cycle of Leishmania sp., along with its epidemiology, is discussed, and in addition, the line of therapeutics available for treatment currently is examined. The current status of the disease is critically evaluated, keeping emerging threats like human immunodeficiency virus (HIV) coinfection and post kala-azar dermal leishmaniasis (PKDL) into consideration. In summary, the review proposes a dire need for new therapeutics and reassessment of the measures and policies concerning emerging threats. New strategies are essential to achieve the goal of leishmaniasis eradication in the next few decades.

An Overview on the Therapeutics of Neglected Infectious Diseases-Leishmaniasis and Chagas Diseases

Neglected tropical diseases (NTDs) as termed by WHO include twenty different infectious diseases that are caused by bacteria, viruses, and parasites. Among these NTDs, Chagas disease and leishmaniasis are reported to cause high mortality in humans and are further associated with the limitations of existing drugs like severe toxicity and drug resistance. The above hitches have rendered researchers to focus on developing alternatives and novel therapeutics for the treatment of these diseases. In the past decade, several target-based drugs have emerged, which focus on specific biochemical pathways of the causative parasites. For leishmaniasis, the targets such as nucleoside analogs, inhibitors targeting nucleoside phosphate kinases of the parasite’s purine salvage pathway, 20S proteasome of Leishmania, mitochondria, and the associated proteins are reviewed along with the chemical structures of potential drug candidates. Similarly, in case of therapeutics for Chagas disease, several target-based drug candidates targeting sterol biosynthetic pathway (C14-ademethylase), L-cysteine protease, heme peroxidation, mitochondria, farnesyl pyrophosphate, etc., which are vital and unique to the causative parasite are discussed. Moreover, the use of nano-based formulations towards the therapeutics of the above diseases is also discussed.

Can We Harness Immune Responses to Improve Drug Treatment in Leishmaniasis?

Leishmaniasis is a vector-borne parasitic disease that has been neglected in priority for control and eradication of malaria, tuberculosis, and HIV/AIDS. Collectively, over one seventh of the world’s population is at risk of being infected with 0.7–1.2 million new infections reported annually. Clinical manifestations range from self-healing cutaneous lesions to fatal visceral disease. The first anti-leishmanial drugs were introduced in the 1950′s and, despite several shortcomings, remain the mainstay for treatment. Regardless of this and the steady increase in infections over the years, particularly among populations of low economic status, research on leishmaniasis remains under funded. This review looks at the drugs currently in clinical use and how they interact with the host immune response. Employing chemoimmunotherapeutic approaches may be one viable alternative to improve the efficacy of novel/existing drugs and extend their lifespan in clinical use.

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.

The Novel Serine/Threonine Protein Kinase LmjF.22.0810 from Leishmania major may be Involved in the Resistance to Drugs such as Paromomycin

The identification and clarification of the mechanisms of action of drugs used against leishmaniasis may improve their administration regimens and prevent the development of resistant strains. Herein, for the first time, we describe the structure of the putatively essential Ser/Thr kinase LmjF.22.0810 from Leishmania major. Molecular dynamics simulations were performed to assess the stability of the kinase model. The analysis of its sequence and structure revealed two druggable sites on the protein. Furthermore, in silico docking of small molecules showed that aminoglycosides preferentially bind to the phosphorylation site of the protein. Given that transgenic LmjF.22.0810-overexpressing parasites displayed less sensitivity to aminoglycosides such as paromomycin, our predicted models support the idea that the mechanism of drug resistance observed in those transgenic parasites is the tight binding of such compounds to LmjF.22.0810 associated with its overexpression. These results may be helpful to understand the complex machinery of drug response in Leishmania.

Elucidation of role of an acetyltransferase like protein in paromomycin resistance in Leishmania donovani using in silico and in vitro approaches

Paromomycin, an aminoglycoside antibiotic, is an effective treatment for VL (visceral leishmaniasis) in India. The modification of aminoglycoside antibiotics by enzymes such as aminoglycoside acetyltransferases is the predominant mechanism of resistance to antibiotics in bacterial system. In the present study, we identified and characterized LdATLP (an acetyltransferase-like protein) and elucidated its role in paromomycin resistance in Leishmania donovani. Gene encoding LdATLP was consistently up-regulated (>2fold) in three distinct paromomycin resistant in comparison with sensitive parasites, although the gene sequence was identical in the two. In silico analysis revealed that LdATLP consisted of conserved GNAT (GCN5-related N-Acetyltransferase) domain which is characteristic of aminoglycoside N-acetyltransferases. Evolutionary relationship among LdATLP of Leishmania and aminoglycoside acetyltransferases of bacteria was established by phylogenetic analysis. The 3D structure of LdATLP, predicted by ab-initio modeling, constituted 6 α-helices and 6 β-sheets. A few residues, such as R175, R177, E196, R197, V198, V200, K202, R205, C206, D208, G210, R211, R215, A234, S237, S238, K239, D240, F241 and Y242 of GNAT domain were predicted to be present at active site. Molecular docking of LdATLP with paromomycin or indolicidin (broad spectrum inhibitor of aminoglycoside modifying enzymes), followed by molecular dynamics simulation of docked complex suggested that both paromomycin and indolicidin bind to LdATLP with comparable free energy of binding. In vitro studies revealed that in the presence of indolicidin, paromomycin resistant parasites exhibited reversion of phenotype into sensitive parasites with marked increase in paromomycin susceptibility, suggesting the role of LdATLP in paromomycin resistance.Communicated by Ramaswamy H. Sarma.

Genomic and transcriptomic alterations in Leishmania donovani lines experimentally resistant to antileishmanial drugs

Leishmaniasis is a serious medical issue in many countries around the World, but it remains largely neglected in terms of research investment for developing new control and treatment measures. No vaccines exist for human use, and the chemotherapeutic agents currently used are scanty. Furthermore, for some drugs, resistance and treatment failure are increasing to alarming levels. The aim of this work was to identify genomic and trancriptomic alterations associated with experimental resistance against the common drugs used against VL: trivalent antimony (Sb^III, S line), amphotericin B (AmB, A line), miltefosine (MIL, M line) and paromomycin (PMM, P line). A total of 1006 differentially expressed transcripts were identified in the S line, 379 in the A line, 146 in the M line, and 129 in the P line. Also, changes in ploidy of chromosomes and amplification/deletion of particular regions were observed in the resistant lines regarding the parental one. A series of genes were identified as possible drivers of the resistance phenotype and were validated in both promastigotes and amastigotes from Leishmania donovani, Leishmania infantum and Leishmania major species. Remarkably, a deletion of the gene LinJ.36.2510 (coding for 24-sterol methyltransferase, SMT) was found to be associated with AmB-resistance in the A line. In the P line, a dramatic overexpression of the transcripts LinJ.27.T1940 and LinJ.27.T1950 that results from a massive amplification of the collinear genes was suggested as one of the mechanisms of PMM resistance. This conclusion was reinforced after transfection experiments in which significant PMM-resistance was generated in WT parasites over-expressing either gene LinJ.27.1940 (coding for a D-lactate dehydrogenase-like protein, D-LDH) or gene LinJ.27.1950 (coding for an aminotransferase of branched-chain amino acids, BCAT). This work allowed to identify new drivers, like SMT, the deletion of which being associated with resistance to AmB, and the tandem D-LDH-BCAT, the amplification of which being related to PMM resistance.

Transcriptome profiling identifies genes/pathways associated with experimental resistance to paromomycin in Leishmania donovani

Widespread resistance towards antimony and reports of relapses following miltefosine treatment has severely affected the management of visceral leishmaniasis (VL) in the Indian subcontinent. Paromomycin (PMM), an aminoglycoside antibiotic, has been licensed for VL treatment in India in 2007. Although its use is still restricted in the field, unraveling the molecular mechanism of resistance towards PMM is the key to preserve the drug. In this study, PMM resistant lines were selected up to 100 μM of PMM in three distinct field isolates of Leishmania donovani at promastigote stage. The resistance induced at promastigote level was also evident in amastigotes which showed 6 fold decreases in PMM susceptibility. Comparative transcriptome profiling of PMM resistant (PMM-R) and the corresponding PMM sensitive (PMM-S) parasites revealed modulated expression of 500 genes (1.5 fold cut off) in PMM-R parasites. Selected genes were validated for their modulated expression by quantitative real-time PCR. Functional classification and pathway analysis of modulated genes indicated probable adaptations in drug resistant lines which included a) reduced oxidative phosphorylation; b) increased glycosomal succinate fermentation and substrate level phosphorylation; c) dependency on lipids and amino acids for energy generation; d) reduced DNA synthesis and increased DNA damage repair and e) decreased protein synthesis and degradation. Interestingly, PMM-R parasites showed a marked increase in PMM susceptibility in presence of verapamil and amlodipine, antagonists of Ca2+ channel that are also modulators of ABC transporters. Moreover, infection of macrophages by PMM-R parasites led to modulated nitric oxide (NO) levels while reactive oxygen species (ROS) level remained unaltered. The present study highlights the putative mechanisms of PMM resistance in Leishmania.

Atomic resolution snapshot of Leishmania ribosome inhibition by the aminoglycoside paromomycin

Leishmania is a single-celled eukaryotic parasite afflicting millions of humans worldwide, with current therapies limited to a poor selection of drugs that mostly target elements in the parasite's cell envelope. Here we determined the atomic resolution electron cryo-microscopy (cryo-EM) structure of the Leishmania ribosome in complex with paromomycin (PAR), a highly potent compound recently approved for treatment of the fatal visceral leishmaniasis (VL). The structure reveals the mechanism by which the drug induces its deleterious effects on the parasite. We further show that PAR interferes with several aspects of cytosolic translation, thus highlighting the cytosolic rather than the mitochondrial ribosome as the primary drug target. The results also highlight unique as well as conserved elements in the PAR-binding pocket that can serve as hotspots for the development of novel therapeutics.

Carbonic anhydrases from Trypanosoma and Leishmania as anti-protozoan drug targets

Trypanosoma cruzi and Leishmania spp. are protozoa of the Trypanosomatidae family, being the etiological agents of two widespread parasitic diseases, Chagas disease and leishmaniasis, respectively. Both parasites are the focus of worldwide research with the aim to find effective and less toxic drugs than the few ones available so far, and for controlling the spread of the diseases. Carbonic anhydrases (CAs, EC 4.2.1.1) belonging to the α- and β-class were recently identified in these protozoans and several studies suggested that they could be new targets for drug development. Sulfonamide, thiol and hydroxamate inhibitors effectively inhibited the α-CA from T. cruzi (TcCA) and the β-CA from L. donovani chagasi (LdccCA) in vitro, and some of them also showed in vivo efficacy in inhibiting the growth of the parasites in animal models of Chagas disease and leishmaniasis. As few therapeutic options are presently available for these orphan diseases, protozoan CA inhibition may represent a novel strategy to address this stringent health problem.

Chemotherapy of leishmaniasis: present challenges

Cutaneous and visceral leishmaniasis are amongst the most devastating infectious diseases of our time, affecting millions of people worldwide. The treatment of these serious diseases rely on a few chemotherapeutic agents, most of which are of parenteral use and induce severe side-effects. Furthermore, rates of treatment failure are high and have been linked to drug resistance in some areas. Here, we reviewed data on current chemotherapy practice in leishmaniasis. Drug resistance and mechanisms of resistance are described as well as the prospects for applying drug combinations for leishmaniasis chemotherapy. It is clear that efforts for discovering new drugs applicable to leishmaniasis chemotherapy are essential. The main aspects on the various steps of drug discovery in the field are discussed.

Polymeric Nanoparticles of Brazilian Red Propolis Extract: Preparation, Characterization, Antioxidant and Leishmanicidal Activity

The ever-increasing demand for natural products and biotechnology derived from bees and ultra-modernization of various analytical devices has facilitated the rational and planned development of biotechnology products with a focus on human health to treat chronic and neglected diseases. The aim of the present study was to prepare and characterize polymeric nanoparticles loaded with Brazilian red propolis extract and evaluate the cytotoxic activity of "multiple-constituent extract in co-delivery system" for antileishmanial therapies. The polymeric nanoparticles loaded with red propolis extract were prepared with a combination of poly-ε-caprolactone and pluronic using nanoprecipitation method and characterized by different analytical techniques, antioxidant and leishmanicidal assay. The red propolis nanoparticles in aqueous medium presented particle size (200-280 nm) in nanometric scale and zeta analysis (-20 to -26 mV) revealed stability of the nanoparticles without aggregation phenomenon during 1 month. After freeze-drying method using cryoprotectant (sodium starch glycolate), it was possible to observe particles with smooth and spherical shape and apparent size of 200 to 400 nm. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and thermal analysis revealed the encapsulation of the flavonoids from the red propolis extract into the polymeric matrix. Ultra performance liquid chromatography coupled with diode array detector (UPLC-DAD) identified the flavonoids liquiritigenin, pinobanksin, isoliquiritigenin, formononetin and biochanin A in ethanolic extract of propolis (EEP) and nanoparticles of red propolis extract (NRPE). The efficiency of encapsulation was determinate, and median values (75.0 %) were calculated using UPLC-DAD. 2,2-Diphenyl-1-picryhydrazyl method showed antioxidant activity to EEP and red propolis nanoparticles. Compared to negative control, EEP and NRPE exhibited leishmanicidal activity with an IC50 value of ≅38.0 μg/mL and 31.3 μg/mL, 47.2 μg/mL, 154.2μg/mL and 193.2 μg/mL for NRPE A1, NRPE A2, NRPE A3 and NRPE A4, respectively. Nanoparticles loaded with red propolis extract in co-delivery system and EEP presented cytotoxic activity on Leishmania (V.) braziliensis. Red propolis extract loaded in nanoparticles has shown to be potential candidates as intermediate products for preparation of various pharmaceutical dosage forms containing red propolis extract in the therapy against negligible diseases such as leishmaniasis. Graphical Abstract Some biochemical mechanisms of cellular debridement of Leishmania (V.) braziliensis species by the flavonoids of red propolis extract (EEP) or NRPE loaded with red propolis extract.

Mammalian host defense peptides and their implication on combating Leishmania infection

Infection with parasites of the genus Leishmania is a health problem in many countries around the world. No effective vaccine is available against leishmaniasis, so chemotherapy is the only alternative for treatment of all forms of the disease. However, drawbacks including toxicity and severe adverse reactions restrain the use of currently available chemotherapeutics. Therefore development of new drugs and therapeutic approaches is highly demanded. Mammalian host defense peptides (mHDP) and/or mammalian antimicrobial peptides (mAMP) are among promising compounds considered effective to control the infectious diseases. These are potential multifunctional molecules that modulate the immune response besides direct killing of pathogens. Here we have reviewed the hallmark characteristics of the mHDPs in respect to the potential role they can play against leishmaniasis.

Visceral leishmaniasis: Revisiting current treatments and approaches for future discoveries

The current treatments for visceral leishmaniasis are old and toxic with limited routes of administration. The emergence of drug-resistant Leishmania threatens the efficacy of the existing reservoir of antileishmanials, leading to an urgent need to develop new treatments. It is particularly important to review and understand how the current treatments act against Leishmania in order to identify valid drug targets or essential pathways for next-generation antileishmanials. It is equally important to adapt newly emerging biotechnologies to facilitate the current research on the development of novel antileishmanials in an efficient fashion. This review covers the basic background of the current visceral leishmaniasis treatments with an emphasis on the modes of action. It briefly discusses the role of the immune system in aiding the chemotherapy of leishmaniasis, describes potential new antileishmanial drug targets and pathways, and introduces recent progress on the utilization of high-throughput phenotypic screening assays to identify novel antileishmanial compounds.

Structural basis for selective targeting of leishmanial ribosomes: aminoglycoside derivatives as promising therapeutics

Leishmaniasis comprises an array of diseases caused by pathogenic species of Leishmania, resulting in a spectrum of mild to life-threatening pathologies. Currently available therapies for leishmaniasis include a limited selection of drugs. This coupled with the rather fast emergence of parasite resistance, presents a dire public health concern. Paromomycin (PAR), a broad-spectrum aminoglycoside antibiotic, has been shown in recent years to be highly efficient in treating visceral leishmaniasis (VL)—the life-threatening form of the disease. While much focus has been given to exploration of PAR activities in bacteria, its mechanism of action in Leishmania has received relatively little scrutiny and has yet to be fully deciphered. In the present study we present an X-ray structure of PAR bound to rRNA model mimicking its leishmanial binding target, the ribosomal A-site. We also evaluate PAR inhibitory actions on leishmanial growth and ribosome function, as well as effects on auditory sensory cells, by comparing several structurally related natural and synthetic aminoglycoside derivatives. The results provide insights into the structural elements important for aminoglycoside inhibitory activities and selectivity for leishmanial cytosolic ribosomes, highlighting a novel synthetic derivative, compound 3, as a prospective therapeutic candidate for the treatment of VL.

Antileishmanial drug discovery: comprehensive review of the last 10 years

This review covers the current aspects of leishmaniasis including marketed drugs, new antileishmanial agents, and possible drug targets of antileishmanial agents.

Mechanisms of action of substituted β-amino alkanols on Leishmania donovani

Leishmaniasis is the protozoan disease second in importance for human health, superseded only by malaria; however, the options for chemotherapeutic treatment are increasingly limited due to drug resistance and toxicity. Under this perspective, a quest for new chemical compounds is urgently needed. An N-substituted 2-aminoalkan-1-ol scaffold has been shown to be a versatile scaffold for antiparasitic activity. Knowledge about its mechanism of action is still rather limited. In this work, we endeavored to define the leishmanicidal profile of such β-amino alkanol derivatives using a set of 15 N-mono- and disubstituted surrogates, tested on Leishmania donovani promastigotes and intracellular amastigotes. The best compound (compound 5), 2-ethylaminododecan-1-ol, had a 50% effective concentration (EC50) of 0.3 μM and a selectivity index of 72 for infected THP-1 cells and was selected for further elucidation of its leishmanicidal mechanism. It induced fast depletion of intracellular ATP content in promastigotes in the absence of vital dye intracellular entry, ruling out plasma membrane permeabilization as its origin. Confocal and transmission electron microscopy analyses showed that compound 5 induced severe mitochondrial swelling and vesiculation. Polarographic analysis using an oxygen electrode demonstrated that complex II of the respiratory chain (succinate reductase) was strongly inhibited by compound 5, identifying this complex as one of the primary targets. Furthermore, for other β-amino alkanols whose structures differed subtly from that of compound 5, plasma membrane permeabilization or interference with membrane traffic was also observed. In all, N-substituted β-amino alkanols were shown as appealing leishmanicidal candidates deserving further exploration.

Initial studies on mechanism of action and cell death of active N-oxide-containing heterocycles in Trypanosoma cruzi epimastigotes in vitro

Chagas disease, endemic in 21 countries across Latin America, kills more people in the region each year than any other parasite-borne disease. Therapeutic options have problems ranging from toxicity, poor efficacy, drug resistance and high cost. Thus, cheaper and less toxic treatments are necessary. From our in-house chemical library of agents against Trypanosoma cruzi the most relevant N-oxide-containing heterocycles were selected for mode of action and type of death studies. Also included in these studies were two active nitrofuranes. Epimastigotes of T. cruzi were used as the biological model in this study. The metabolic profile was studied by 1H NMR in association with the MTT assay. Excreted catabolites data, using 1H NMR spectroscopy, showed that most of the studied N-oxides were capable of decreasing both the release of succinate and acetate shedding, the compounds therefore possibly acting on mitochondria. Only quinoxalines and the nitrofurane Nf1 showed significant mitochondrial dehydrogenase inhibitions, but with different dose-time profiles. In the particular case of quinoxaline Qx2 the glucose uptake study revealed that the integrity of some pathways into the glycosome could be affected. Optic, fluorescence (TUNEL and propidium iodide) and transmission electron microscopy (TEM) were employed for type of death studies. These studies were complemented with 1H NMR to visualize mobile lipids. At low concentrations none of the selected compounds showed a positive TUNEL assay. However, both quinoxalines, one furoxan and one benzofuroxan showed a necrotic effect at high concentrations. Curiously, one furoxan, Fx1, one benzofuroxan, Bfx1, and one nitrofurane, Nf1, caused a particular phenotype, with a big cytoplasmatic vacuole being observed while the parasite was still alive. Studies of TEM and employing a protease inhibitor (3-methyladenine) suggested an autophagic phenotype for Bfx1 and Nf1 and a 'BigEye' phenotype for Fx1.

Natural product based leads to fight against leishmaniasis

The growing incidence of parasitic resistance against generic pentavalent antimonials, specifically for visceral disease in Indian subcontinent, is a serious issue in Leishmania control. Notwithstanding the two treatment alternatives, that is amphotericin B and miltefosine are being effectively used but their high cost and therapeutic complications limit their use in endemic areas. In the absence of a vaccine candidate, identification, and characterization of novel drugs and targets is a major requirement of leishmanial research. This review describes current drug regimens, putative drug targets, numerous natural products that have shown promising antileishmanial activity alongwith some key issues and strategies for future research to control leishmaniasis worldwide.

Leishmania donovani develops resistance to drug combinations

Drug combinations for the treatment of leishmaniasis represent a promising and challenging chemotherapeutic strategy that has recently been implemented in different endemic areas. However, the vast majority of studies undertaken to date have ignored the potential risk that Leishmania parasites could develop resistance to the different drugs used in such combinations. As a result, this study was designed to elucidate the ability of Leishmania donovani to develop experimental resistance to anti-leishmanial drug combinations. The induction of resistance to amphotericin B/miltefosine, amphotericin B/paromomycin, amphotericin B/Sb^III, miltefosine/paromomycin, and Sb^III/paromomycin was determined using a step-wise adaptation process to increasing drug concentrations. Intracellular amastigotes resistant to these drug combinations were obtained from resistant L. donovani promastigote forms, and the thiol and ATP levels and the mitochondrial membrane potential of the resistant lines were analysed. Resistance to drug combinations was obtained after 10 weeks and remained in the intracellular amastigotes. Additionally, this resistance proved to be unstable. More importantly, we observed that promastigotes/amastigotes resistant to one drug combination showed a marked cross-resistant profile to other anti-leishmanial drugs. Additionally, the thiol levels increased in resistant lines that remained protected against the drug-induced loss of ATP and mitochondrial membrane potential. We have therefore demonstrated that different resistance patterns can be obtained in L. donovani depending upon the drug combinations used. Resistance to the combinations miltefosine/paromomycin and Sb^III/paromomycin is easily obtained experimentally. These results have been validated in intracellular amastigotes, and have important relevance for ensuring the long-term efficacy of drug combinations.

Leishmania is a protozoan parasite that infects human macrophages to produce the neglected tropical disease known as leishmaniasis. Chemotherapy is currently the only treatment option for leishmaniasis. First-line therapies include pentavalent antimonials, except in some regions in the Indian subcontinent, the liposomal formulation of amphotericin B, miltefosine and paromomycin. The WHO has recently recommended a combined therapy in order to extend the life expectancy of these compounds. However, resistance could be induced in Leishmania if this approach is not applied in a controlled and regulated way, thus resulting in a rapid loss of efficacy of not one but two therapeutic options. In light of this, we have designed relevant experimental studies in order to determine whether Leishmania parasites are able to develop resistance to the different potential anti-leishmanial drug combinations that will be used in the near future. The results obtained could help us to predict the success of drug combination therapy. Experimental resistance of Leishmania donovani promastigotes to drug combinations was obtained after 10 weeks and remained in the intracellular amastigotes. We therefore conclude that L. donovani can easily develop resistance to drug combinations mainly miltefosine/paromomycin and Sb^III/paromomycin. These results have been validated in intracellular amastigotes and are of considerable interest for future prediction of the success of drug combination therapy.

Review of the current treatments for leishmaniases

Leishmaniases are vector-borne zoonotic diseases that are prevalent in tropical and subtropical areas in the world, with two million new cases occurring yearly. Visceral and tegumentary forms of leishmaniasis are known. The latter form may present as localized cutaneous or mucosal forms, disseminated, diffuse forms, or leishmaniasis recidiva cutis. Visceral leishmaniasis is caused by parasites of the species Leishmania (Leishmania) donovani and L. (L.) infantum, and tegumentary leishmaniasis is caused by 15 other species, with distinct distributions in the Old and New World. The varied clinical manifestations, the multitude of Leishmania species, and the increasing incidence of HIV coinfection make the diagnosis and treatment of leishmaniases complex. Since there are no solid data relating clinical manifestations, treatment outcomes and Leishmania species the decision regarding the best therapeutic option is almost entirely based on clinical manifestations. Because most of the literature is focused on leishmaniasis in the Old World, in this review we present data on the treatment of New World leishmaniasis in more detail. Ranked therapeutic options, clinical trials, and also observations, even with a restricted number of subjects, on treatment outcome of visceral and different forms of tegumentary leishmaniasis, are presented. Treatment for leishmaniasis in HIV-coinfected patients is addressed as well. Some of these data strongly suggest that the differences in the outcome of the treatment are related to the Leishmania species. Therefore, although it is not possible at most points of care to identify the species causing the infection - a process that requires a well equipped laboratory - the infecting species should be identified whenever possible. More recent approaches, such as the use of immunomodulators and immunotherapy, and the lines for development of new candidate drugs are mentioned.

Experimental induction of paromomycin resistance in antimony-resistant strains of L. donovani: outcome dependent on in vitro selection protocol

Paromomycin (PMM) has recently been introduced for treatment of visceral leishmaniasis in India. Although no clinical resistance has yet been reported, proactive vigilance should be warranted. The present in vitro study compared the outcome and stability of experimental PMM-resistance induction on promastigotes and intracellular amastigotes. Cloned antimony-resistant L. donovani field isolates from India and Nepal were exposed to stepwise increasing concentrations of PMM (up to 500 µM), either as promastigotes or intracellular amastigotes. One resulting resistant strain was cloned and checked for stability of resistance by drug-free in vitro passage as promastigotes for 20 weeks or a single in vivo passage in the golden hamster. Resistance selection in promastigotes took about 25 weeks to reach the maximal 97 µM inclusion level that did not affect normal growth. Comparison of the IC₅₀ values between the parent and the selected strains revealed a 9 to 11-fold resistance for the Indian and 3 to 5-fold for the Nepalese strains whereby the resistant phenotype was also maintained at the level of the amastigote. Applying PMM pressure to intracellular amastigotes produced resistance after just two selection cycles (IC₅₀ = 199 µM) compared to the parent strain (IC₅₀ = 45 µM). In the amastigote-induced strains/clones, lower PMM susceptibilities were seen only in amastigotes and not at all in promastigotes. This resistance phenotype remained stable after serial in vitro passage as promastigote for 20 weeks and after a single in vivo passage in the hamster. This study clearly demonstrates that a different PMM-resistance phenotype is obtained whether drug selection is applied to promastigotes or intracellular amastigotes. These findings may have important relevance to resistance mechanism investigations and the likelihood of resistance development and detection in the field.

Leishmaniasis is caused by protozoan parasites of the genus Leishmania and is transmitted by inoculation of infective promastigotes by the female sand fly. In the mammalian host, amastigotes live inside macrophage cells which may lead to various clinical symptoms. First-line treatment relies mainly on antimonials and miltefosine; however, drug resistance is a growing problem. The antibiotic paromomycin (PMM) has recently been added as treatment option, but it is now essential to proactively assess the likelihood of resistance development to safeguard its long term effectiveness. Since ‘resistant’ patient isolates are not yet available, we artificially selected for PMM resistance using two different in vitro protocols with drug pressure on either the extracellular promastigote or on the intracellular amastigote stage. Resistance in promastigotes was obtained after about 25 weeks and persisted in the intracellular amastigote. High levels of resistance were obtained within two selection cycles on amastigotes, but with the unexpected observation that the promastigotes remained fully susceptible. In addition, the resistance proved to be stable. We could clearly demonstrate that a different PMM-resistance is obtained dependent on the ‘stage-selection’ protocol. These findings have important relevance to resistance mechanism investigations and the likelihood of resistance development and detection in the field.

Paromomycin affects translation and vesicle-mediated trafficking as revealed by proteomics of paromomycin -susceptible -resistant Leishmania donovani

Leishmania donovani is a protozoan parasite that causes visceral leishmaniasis (VL) and is responsible for significant mortality and morbidity. Increasing resistance towards antimonial drugs poses a great challenge in chemotherapy of VL. Paromomycin is an aminoglycosidic antibiotic and is one of the drugs currently being used in the chemotherapy of cutaneous and visceral leishmaniasis. To understand the mode of action of this antibiotic at the molecular level, we have investigated the global proteome differences between the wild type AG83 strain and a paromomycin resistant (PRr) strain of L. donovani. Stable isotope labeling of amino acids in cell culture (SILAC) followed by quantitative mass spectrometry of the wild type AG83 strain and the paromomycin resistant (PRr) strain identified a total of 226 proteins at ≥95% confidence. Data analysis revealed upregulation of 29 proteins and down-regulation of 21 proteins in the PRr strain. Comparative proteomic analysis of the wild type and the paromomycin resistant strains showed upregulation of the ribosomal proteins in the resistant strain indicating role in translation. Elevated levels of glycolytic enzymes and stress proteins were also observed in the PRr strain. Most importantly, we observed upregulation of proteins that may have a role in intracellular survival and vesicular trafficking in the PRr strain. Furthermore, ultra-structural analysis by electron microscopy demonstrated increased number of vesicular vacuoles in PRr strain when compared to the wild-type strain. Drug affinity pull-down assay followed by mass spectrometery identified proteins in L. donovani wild type strain that were specifically and covalently bound to paromomycin. These results provide the first comprehensive insight into the mode of action and underlying mechanism of resistance to paromomycin in Leishmania donovani.

Tolerance to drug-induced cell death favours the acquisition of multidrug resistance in Leishmania

The control of the protozoan parasite Leishmania relies on few drugs with unknown cellular targets and unclear mode of action. Several antileishmanials, however, were shown to induce apoptosis in Leishmania and this death mechanism was further studied in drug-sensitive and drug-resistant Leishmania infantum. In sensitive parasites, antimonials (SbIII), miltefosine (MF) and amphotericin B (AMB), but not paromomycin (PARO), triggered apoptotic cell death associated with reactive oxygen species (ROS). In contrast, Leishmania mutants resistant to SbIII, MF or AMB not only failed to undergo apoptosis following exposure to their respective drugs, but also were more tolerant towards apoptosis induced by other antileishmanials, provided that these killed Leishmania via ROS production. Such tolerance favored the rapid acquisition of multidrug resistance. PARO killed Leishmania in a non-apoptotic manner and failed to produce ROS. PARO resistance neither protected against drug-induced apoptosis nor provided an increased rate of acquisition of resistance to other antileishmanials. However, the PARO-resistant mutant, but not SbIII-, MF- or AMB-resistant mutants, became rapidly cross-resistant to methotrexate, a model drug also not producing ROS. Our results therefore link the mode of killing of drugs to tolerance to cell death and to a facilitated emergence of multidrug resistance. These findings may have fundamental implications in the field of chemotherapeutic interventions.

Drug resistance in leishmaniasis

The treatment options of leishmaniasis are limited and far from satisfactory. For more than 60 years, treatment of leishmaniasis has centered around pentavalent antimonials (Sb^v). Widespread misuse has led to the emergence of Sb^v resistance in the hyperendemic areas of North Bihar. Other antileishmanials could also face the same fate, especially in the anthroponotic cycle. The HIV/ visceral leishmaniasis (VL) coinfected patients are another potential source for the emergence of drug resistance. At present no molecular markers of resistance are available and the only reliable method for monitoring resistance of isolates is the technically demanding in vitro amastigote-macrophage model. As the armametrium of drugs for leishmaniasis is limited, it is important that effective monitoring of drug use and response should be done to prevent the spread of resistance. Regimens of simultaneous or sequential combinations should be seriously considered to limit the emergence of resistance.

3-Trifluoromethylquinoxaline N,N'-dioxides as anti-trypanosomatid agents. Identification of optimal anti-T. cruzi agents and mechanism of action studies

For a fourth approach of quinoxaline N,N'-dioxides as anti-trypanosomatid agents against T. cruzi and Leishmania, we found extremely active derivatives. The present study allows us to state the correct requirements for obtaining optimal in vitro anti-T. cruzi activity. Derivatives possessing electron-withdrawing substituents in the 2-, 3-, 6-, and 7-positions were the most active compounds. With regard to these features and taking into account their mammal cytotoxicity, some trifluoromethylquinoxaline N,N'-dioxides have been proposed as candidates for further clinical studies. Consequently, mutagenicity and in vivo analyses were performed with the most promising derivatives. In addition, with regard to the mechanism of action studies, it was demonstrated that mitochondrial dehydrogenases are involved in the anti-T. cruzi activity of the most active derivatives.

Structures, targets and recent approaches in anti-leishmanial drug discovery and development

Recent years have seen a significant improvement in available treatment options for leishmaniasis. Two new drugs, miltefosine and paromomycin, have been registered for the treatment of visceral leishmaniasis (VL) in India since 2002. Combination therapy is now explored in clinical trials as a new treatment approach for VL to reduce the length of treatment and potentially prevent selection of resistant parasites. However there is still a need for new drugs due to safety, resistance, stability and cost issues with existing therapies. The search for topical treatments for cutaneous leishmaniasis (CL) is ongoing. This review gives a brief overview of recent developments and approaches in anti-leishmanial drug discovery and development.

Reductions in skin and systemic parasite burdens as a combined effect of topical paromomycin and oral miltefosine treatment of mice experimentally infected with Leishmania (Leishmania) amazonensis

This study aimed to investigate the activity of a combination of topical paromomycin gel and oral miltefosine for the treatment of experimental cutaneous leishmaniasis caused by Leishmania (Leishmania) amazonensis. The efficacy of the combination, evaluated by measuring lesion size and parasite burden in the skin and spleen, was assessed in BALB/c mice infected by L. (L.) amazonensis. The miltefosine was administered orally at 10 mg/kg of body weight/day for 10 days, while 10% paromomycin gel was applied topically twice a day for 20 days. Treatment of the experimentally infected animals with a topical paromomycin-oral miltefosine combination induced a statistically significant reduction in lesion size and parasite burden in the skin and spleen, with complete healing of ulcers, compared with those treated with a placebo group. A combination of topical paromomycin gel and oral miltefosine provided enhanced efficacy in the treatment of L. (L.) amazonensis-infected mice, showing activity higher than that observed for the monotherapeutic regimens.

Drug delivery strategies for therapy of visceral leishmaniasis

IMPORTANCE OF THE FIELD

Visceral leishmaniasis (VL) is the most overwhelming type of leishmaniasis associated with the poverty of developing countries and usually mortal if untreated. Most of the conventionally used dosage forms offer us the shortcomings of toxic side effects and emergence of drug resistance. Several efforts have been made to overcome the barriers involved in the treatment of VL. Colloidal carriers extensively represent the drug delivery systems (DDSs) for intracellular localization of antileishmanial compounds in macrophage-rich organs such as liver, spleen and bone marrow. These DDSs offer superior therapeutic efficacy over the conventional treatment in terms of site-specific drug delivery with reduced side effects. However, after 35 years of research in the field, AmBisome (Amphotericin B liposome for injection, Astellas Pharma US, Inc.) is the only DDS used against the VL.

AREAS COVERED IN THIS REVIEW

A literature search was performed (for drugs and DDSs against VL) on PubMed and through Google.

WHAT THE READER WILL GAIN

This review aims to describe the pathophysiology of VL and its current conventional treatment with special reference to DDSs designed against VL.

TAKE HOME MESSAGE

On reviewing the conventional drugs and DDSs developed against VL, it is concluded that advances in the field of targeted drug delivery can result in more efficient strategies for the therapy of VL.