Roles for mitochondria in pentamidine susceptibility and resistance in Leishmania donovani

Repurposing the anti-parasitic agent pentamidine for cancer therapy; a novel approach with promising anti-tumor properties

Pentamidine (PTM) is an aromatic diamidine administered for infectious diseases, e.g. sleeping sickness, malaria, and Pneumocystis jirovecii pneumonia. Due to similarities of cellular mechanisms between human cells and such infections, PTM has also been proposed for repurposing in non-infectious diseases such as cancer. Indeed, by modulating different signaling pathways such as PI3K/AKT, MAPK/ERK, p53, PD-1/PD-L1, etc., PTM has been shown to inhibit different properties of cancer, including proliferation, invasion, migration, hypoxia, and angiogenesis, while inducing anti-tumor immune responses and apoptosis. Given the promising implications of PTM for cancer treatment, however, the clinical translation of PTM in cancer is not without certain challenges. In fact, clinical trials have shown that systemic administration of PTM can be concurrent with serious adverse effects, e.g. hypoglycemia. Therefore, to reduce the administered doses of PTM, lower the risk of adverse effects, and prevent any potential drug resistance, while maintaining the anti-tumor efficacy, two main strategies have been suggested. One is combination therapy that employs PTM in conjunction with other anti-cancer modalities, such as chemotherapy and radiotherapy, and attacks tumor cells with significant additive or synergistic anti-tumor effects. The other is developing PTM-loaded nanocarrier drug delivery systems e.g. pegylated liposomes, chitosan-coated niosomes, squalene-based nanoparticles, hyaluronated lipid-polymer hybrid nanoparticles, etc., that offer enhanced pharmacokinetic characteristics, including increased bioavailability, sit-targeting, and controlled/sustained drug release. This review highlights the anti-tumor properties of PTM that favor its repurposing for cancer treatment, as well as, PTM-based combination therapies and nanocarrier delivery systems which can enhance therapeutic efficacy and simultaneously reduce toxicity.

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.

Treatment of Refractory Mucosal Leishmaniasis Is Associated with Parasite Overexpression of HSP70 and ATPase and Reduced Host Hydrogen Peroxide Production (Brief Report)

BACKGROUND

Mucosal leishmaniasis (ML) is a deforming type of American Tegumentary Leishmaniasis caused by Leishmania (Viannia) braziliensis that frequently does not respond to treatment. Despite its relapsing clinical course, few parasites are usually found in mucosal lesions. Host and parasite factors may be responsible for this paradox in the pathogenesis of the disease, allowing for both a low parasite burden and the inability of the host to clear and eliminate the disease.

METHODS AND RESULTS

In this work, we present a clinical case of relapsing ML that was treated for 25 years without success with SbV, N-methyl glucamine, sodium stibogluconate, amphotericin B deoxycholate, gabromycin, antimonial plus thalidomide, liposomal amphotericin B, Leishvacin (a vaccine made in Brazil) and miltefosine. In a comparative analysis using nanoscale liquid chromatography coupled with tandem mass spectrometry of protein extracts of L. (V.) braziliensis promastigotes isolated from the patient and from the reference strain (MHOM/BR/94/M15176), we observed increases in ATPase and HSP70 protein levels in the parasite. We also observed an impairment in the production of hydrogen peroxide by peripheral mononuclear blood monocytes (PBMCs), as assessed by the horseradish peroxidase-dependent oxidation of phenol red.

CONCLUSIONS

We hypothesise that these parasite molecules may be linked to the impairment of host parasiticidal responses, resulting in Leishmania persistence in ML patients.

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.

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.

Toxoplasma gondii infection: novel emerging therapeutic targets

INTRODUCTION

Toxoplasmosis constitutes a challenge for public health, animal production, and welfare. So far, only a limited panel of drugs has been marketed for clinical applications. In addition to classical screening, the investigation of unique targets of the parasite may lead to the identification of novel drugs.

AREAS COVERED

Herein, the authors describe the methodology to identify novel drug targets in Toxoplasma gondii and review the literature with a focus on the last two decades.

EXPERT OPINION

Over the last two decades, the investigation of essential proteins of T. gondii as potential drug targets has fostered the hope of identifying novel compounds for the treatment of toxoplasmosis. Despite good efficacies in vitro, only a few classes of these compounds are effective in suitable rodent models, and none has cleared the hurdle to applications in humans. This shows that target-based drug discovery is in no way better than classical screening approaches. In both cases, off-target effects and adverse side effects in the hosts must be considered. Proteomics-driven analyses of parasite- and host-derived proteins that physically bind drug candidates may constitute a suitable tool to characterize drug targets, irrespectively of the drug discovery methods.

Binding to the DNA Minor Groove by Heterocyclic Dications: from AT Specific to GC Recognition Compounds

Compounds that bind in the DNA minor groove have provided critical information on DNA molecular recognition, have found extensive uses in biotechnology, and are providing clinically useful drugs against diseases as diverse as cancer and sleeping sickness. This review focuses on the development of clinically useful heterocyclic diamidine minor groove binders. These compounds show that the classical model for minor groove binding in AT DNA sequences must be expanded in several ways: compounds with nonstandard shapes can bind strongly to the groove, water can be directly incorporated into the minor groove complex in an interfacial interaction, compounds can be designed to recognize GC and mixed AT/GC base pair sequences, and stacked dimers can form to recognize specific sequences. © 2023 Wiley Periodicals LLC.

A Potential New Source of Therapeutic Agents for the Treatment of Mucocutaneous Leishmaniasis: The Essential Oil of Rhaphiodon echinus

Weeds are an important source of natural products; with promising biological activity. This study investigated the anti-kinetoplastida potential (in vitro) to evaluate the cytotoxicity (in vitro) and antioxidant capacity of the essential oil of Rhaphiodon echinus (EORe), which is an infesting plant species. The essential oil was analyzed by GC/MS. The antioxidant capacity was evaluated by reduction of the DPPH radical and Fe3+ ion. The clone Trypanosoma cruzi CL-B5 was used to search for anti-epimastigote activity. Antileishmanial activity was determined using promastigotes of Leishmania braziliensis (MHOM/CW/88/UA301). NCTC 929 fibroblasts were used for the cytotoxicity test. The results showed that the main constituent of the essential oil was γ-elemene. No relevant effect was observed concerning the ability to reduce the DPPH radical; only at the concentration of 480 μg/mL did the essential oil demonstrate a high reduction of Fe3+ power. The oil was active against L. brasiliensis promastigotes; but not against the epimastigote form of T. cruzi. Cytotoxicity for mammalian cells was low at the active concentration capable of killing more than 70% of promastigote forms. The results revealed that the essential oil of R. echinus showed activity against L. brasiliensis; positioning itself as a promising agent for antileishmanial therapies.

Balancing de novo synthesis and salvage of lipids by Leishmania amastigotes

Leishmania parasites replicate as flagellated, extracellular promastigotes in the sand fly vector and then differentiate into non-flagellated, intracellular amastigotes in the vertebrate host. Promastigotes rely on de novo synthesis to produce the majority of their lipids including glycerophospholipids, sterols and sphingolipids. In contrast, amastigotes acquire most of their lipids from the host although they retain some capacity for de novo synthesis. The switch from de novo synthesis to salvage reflects the transition of Leishmania from fast-replicating promastigotes to slow-growing, metabolically quiescent amastigotes. Future studies will reveal the uptake and remodeling of host lipids by amastigotes at the cellular and molecular levels. Blocking the lipid transfer from host to parasites may present a novel strategy to control Leishmania growth.

Nano-Leish-IL: A novel iron oxide-based nanocomposite drug platform for effective treatment of cutaneous leishmaniasis

Kinetoplastids are infamous parasites that include trypanosomes and Leishmania species. Here, we developed an anti-Leishmania nano-drug using ultra-small functional maghemite (γ-Fe₂O₃) nanoparticles (NPs) that were surface-doped by [CeL_n]^3/4+ to enable effective binding of the polycationic polyethylenebyimine (PEI) polymer by coordinative chemistry. This resulting nano-drug is cytolytic in-vitro to both Trypanosoma brucei parasites, the causative agent of sleeping sickness, as well as to three Leishmania species. The nano-drug induces the rupture of the single lysosome present in these parasites attributed to the PEI, leading to cytolysis. To evaluate the efficacy of a "cream-based" version of the nano-drug, which was termed "Nano-Leish-IL" for topical treatment of cutaneous leishmaniasis (CL), we developed a rapid screening method utilizing T. brucei parasites involved in social motility and demonstrated that functional NPs arrested the migration of the parasites. This assay presents a surrogate system to rapidly examine the efficacy of "cream-based" drugs in topical preparations against leishmaniasis, and possibly other dermal infectious diseases. The resulting Nano-Leish-IL topical preparation eliminated L. major infection in mice. Thus, this study presents a novel efficient nano-drug targeting the single lysosome of kinetoplastid parasites.

A "Golden Age" for the discovery of new antileishmanial agents: Current status of leishmanicidal gold complexes and prospective targets beyond the trypanothione system

Leishmaniasis is one of the most neglected diseases worldwide and is considered a serious public health issue. The current therapeutic options have several disadvantages that make the search for new therapeutics urgent. Gold compounds are emerging as promising candidates based on encouraging in vitro and limited in vivo results for several Au^I and Au^III complexes. The antiparasitic mechanisms of these molecules remain only partially understood. However, a few studies have proposed the trypanothione redox system as a target, similar to the mammalian thioredoxin system, pointed out as the main target for several gold compounds with significant antitumor activity. In this review, we present the current status of the investigation and design of gold compounds directed at treating leishmaniasis. In addition, we explore potential targets in Leishmania parasites beyond the trypanothione system, taking into account previous studies and structure modulation performed for gold-based compounds.

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.

Sterol 14-α-demethylase is vital for mitochondrial functions and stress tolerance in Leishmania major

Sterol 14-α-demethylase (C14DM) is a key enzyme in the biosynthesis of sterols and the primary target of azoles. In Leishmania major, genetic or chemical inactivation of C14DM leads to accumulation of 14-methylated sterol intermediates and profound plasma membrane abnormalities including increased fluidity and failure to maintain ordered membrane microdomains. These defects likely contribute to the hypersensitivity to heat and severely reduced virulence displayed by the C14DM-null mutants (c14dm‾). In addition to plasma membrane, sterols are present in intracellular organelles. In this study, we investigated the impact of C14DM ablation on mitochondria. Our results demonstrate that c14dm‾ mutants have significantly higher mitochondrial membrane potential than wild type parasites. Such high potential leads to the buildup of reactive oxygen species in the mitochondria, especially under nutrient-limiting conditions. Consistent with these mitochondrial alterations, c14dm‾ mutants show impairment in respiration and are heavily dependent on glucose uptake and glycolysis to generate energy. Consequently, these mutants are extremely sensitive to glucose deprivation and such vulnerability can be rescued through the supplementation of glucose or glycerol. In addition, the accumulation of oxidants may also contribute to the heat sensitivity exhibited by c14dm‾. Finally, genetic or chemical ablation of C14DM causes increased susceptibility to pentamidine, an antimicrobial agent with activity against trypanosomatids. In summary, our investigation reveals that alteration of sterol synthesis can negatively affect multiple cellular processes in Leishmania parasites and make them vulnerable to clinically relevant stress conditions.

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.

An Overview of Drug Resistance in Protozoal Diseases

Protozoan diseases continue to be a worldwide social and economic health problem. Increased drug resistance, emerging cross resistance, and lack of new drugs with novel mechanisms of action significantly reduce the effectiveness of current antiprotozoal therapies. While drug resistance associated to anti-infective agents is a reality, society seems to remain unaware of its proportions and consequences. Parasites usually develops ingenious and innovative mechanisms to achieve drug resistance, which requires more research and investment to fight it. In this review, drug resistance developed by protozoan parasites Plasmodium, Leishmania, and Trypanosoma will be discussed.

Anti-leishmanial Nanotherapeutics: A Current Perspective

Background:

Leishmaniasis is a dreaded disease caused by protozoan parasites belonging to the genus Leishmania which results in significant morbidity and mortality worldwide. There are no vaccines available currently for the treatment of Leishmaniasis and chemotherapy still remains the mainstay for anti-leishmanial therapeutics. However, toxicity, reduced bioavailability, high cost and chemoresistance are the principal problems which limit the use of the available drugs. In this context, anti-leishmanial nanotherapeutics may show the way for effective treatment of this dreaded disease.

Methods:

We carried out extensive literature search of bibliographic database using keywords strictly within the scope of the present study for peer reviewed research articles. We focused specifically on articles related to the application of nanotechnology in drug development, drug delivery and vaccine delivery for anti-leishmanial therapeutics.

Results:

This study shows the immense potential of the application of nanotechnology in the field of anti-leishmanial therapeutics. This will aid the targeted delivery of different drugs which is expected to increase the bioavailability, reduce toxicity and also address the problem of chemoresistance.

Conclusion:

We surmise that exciting research in the field of anti-leishmanial nanotherapeutics is already showing the promise for effective applicability. Though direct use of nanoparticles as therapeutic agents does not seem to be a good option, the application of nanotechnology in this field for vaccine development is still in its early days. The nano based drug delivery system for anti-leishmanial therapeutics has evolved considerably over the past ten years and holds the potential to drastically change the landscape of anti-leishmanial therapeutics.

In vitro 4-Aryloxy-7-chloroquinoline derivatives are effective in mono- and combined therapy against Leishmania donovani and induce mitocondrial membrane potential disruption

The present study evaluates in vitro the effect of two synthetic compounds of the 7-chloro-4-aryloxyquinoline series, QI (C₁₇H₁₂ClNO₃) and QII (C₁₈H₁₅ClN₄O₂S), on Leishmania donovani parasites. The results obtained demonstrate that these compounds are able to inhibit the proliferation of L. donovani promastigotes in a dose-dependent way (QI IC₅₀ = 13.03 ± 3.4 and QII IC₅₀ = 7.90 ± 0.6 μM). Likewise, these compounds significantly reduced the percentage of macrophage infection by amastigotesand the number of amastigotes within macrophage phagolysosomes, the clinical relevant phase of these parasites. Compound QI showed an IC₅₀ value of 0.66 ± 0.2 μM, while for derivative QII, the corresponding IC₅₀ was 1.02 ± 0.17 μM. Interestingly, the amastigotes were more susceptible to the drug treatment when compared to promastigotes. Furthermore, no cytotoxic effect of these compounds was observed on the macrophage cell line at the concentrations tested. The combination of these compounds with miltefosine and amphotericin B on both parasite morphotypes was evaluated. The isobolograms showed a synergistic effect for both combinations; with a Fractional Inhibitory Concentration (FIC) Index lower than 1 for promastigotes and less than 0.3 for intracellular amastigotes. The effect of QI and QII on mitochondrial membrane potential was also studied. The combination of quinolone derivatives compounds with miltefosine and amphotericin B showed 5-8-fold stronger depolarization of membrane mitochondrial potential when compared to drugs alone. The present work validates the combination of drugs as an effective alternative to potentiate the action of anti-Leishmania agents and points to the quinoline compounds studied here as possible leishmanicidal drugs.

Phloroglucinol derivatives from Hypericum species trigger mitochondrial dysfunction in Leishmania amazonensis

Bioactive molecules isolated from plants are promising sources for the development of new therapies against leishmaniasis. We investigated the leishmanicidal activity of cariphenone A (1), isouliginosin B (2) and uliginosin B (3) isolated from Hypericum species. Promastigotes and amastigotes of Leishmania amazonensis were incubated with compounds 1-3 at concentrations 1-100 µm for 48 h. The anti-promastigote effect of compounds was also tested in combinations. The cytotoxicity against macrophages and human erythrocytes were determined using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) method and hemolysis assay, respectively. The compounds 1-3 showed high leishmanicidal activity against promastigotes, IC50 values of 10.5, 17.5 and 11.3 µm, respectively. Synergistic interactions were found to the associations of compounds 1 and 2 [Σ fractional inhibitory concentration (FIC) = 0.41], and 2 and 3 (ΣFIC = 0.28) on promastigotes. All Hypericum compounds induced mitochondrial hyperpolarization and reactive oxygen species production in promastigotes. The compounds showed low cytotoxicity toward mammalian cells, high selectivity index and killed intracellular amastigotes probably mediated by oxidative stress. These results indicate that these compounds are promising candidates for the development of drugs against leishmaniasis.

Antileishmanial Mechanism of Diamidines Involves Targeting Kinetoplasts

Leishmaniasis is a disease caused by pathogenic Leishmania parasites; current treatments are toxic and expensive, and drug resistance has emerged. While pentamidine, a diamidine-type compound, is one of the treatments, its antileishmanial mechanism of action has not been investigated in depth. Here we tested several diamidines, including pentamidine and its analog DB75, against Leishmania donovani and elucidated their antileishmanial mechanisms. We identified three promising new antileishmanial diamidine compounds with 50% effective concentrations (EC₅₀s) of 3.2, 3.4, and 4.5 μM, while pentamidine and DB75 exhibited EC₅₀s of 1.46 and 20 μM, respectively. The most potent antileishmanial inhibitor, compound 1, showed strong DNA binding properties, with a shift in the melting temperature (ΔT_m) of 24.2°C, whereas pentamidine had a ΔT_m value of 2.1°C, and DB75 had a ΔT_m value of 7.7°C. Additionally, DB75 localized in L. donovani kinetoplast DNA (kDNA) and mitochondria but not in nuclear DNA (nDNA). For 2 new diamidines, strong localization signals were observed in kDNA at 1 μM, and at higher concentrations, the signals also appeared in nuclei. All tested diamidines showed selective and dose-dependent inhibition of kDNA, but not nDNA, replication, likely by inhibiting L. donovani topoisomerase IB. Overall, these results suggest that diamidine antileishmanial compounds exert activity by accumulating toward and blocking replication of parasite kDNA.

DDX3 DEAD-box RNA helicase plays a central role in mitochondrial protein quality control in Leishmania

DDX3 is a highly conserved member of ATP-dependent DEAD-box RNA helicases with multiple functions in RNA metabolism and cellular signaling. Here, we describe a novel function for DDX3 in regulating the mitochondrial stress response in the parasitic protozoan Leishmania. We show that genetic inactivation of DDX3 leads to the accumulation of mitochondrial reactive oxygen species (ROS) associated with a defect in hydrogen peroxide detoxification. Upon stress, ROS production is greatly enhanced, causing mitochondrial membrane potential loss, mitochondrial fragmentation, and cell death. Importantly, this phenotype is exacerbated upon oxidative stress in parasites forced to use the mitochondrial oxidative respiratory machinery. Furthermore, we show that in the absence of DDX3, levels of major components of the unfolded protein response as well as of polyubiquitinated proteins increase in the parasite, particularly in the mitochondrion, as an indicator of mitochondrial protein damage. Consistent with these findings, immunoprecipitation and mass-spectrometry studies revealed potential interactions of DDX3 with key components of the cellular stress response, particularly the antioxidant response, the unfolded protein response, and the AAA-ATPase p97/VCP/Cdc48, which is essential in mitochondrial protein quality control by driving proteosomal degradation of polyubiquitinated proteins. Complementation studies using DDX3 deletion mutants lacking conserved motifs within the helicase core support that binding of DDX3 to ATP is essential for DDX3's function in mitochondrial proteostasis. As a result of the inability of DDX3-depleted Leishmania to recover from ROS damage and to survive various stresses in the host macrophage, parasite intracellular development was impaired. Collectively, these observations support a central role for the Leishmania DDX3 homolog in preventing ROS-mediated damage and in maintaining mitochondrial protein quality control.

New Approaches to Overcome Transport Related Drug Resistance in Trypanosomatid Parasites

Leishmania and Trypanosoma are members of the Trypanosomatidae family that cause severe human infections such as leishmaniasis, Chagas disease, and sleeping sickness affecting millions of people worldwide. Despite efforts to eradicate them, migrations are expanding these infections to developing countries. There are no vaccines available and current treatments depend only on chemotherapy. Drug resistance is a major obstacle for the treatment of these diseases given that existing drugs are old and limited, with some having severe side effects. Most resistance mechanisms developed by these parasites are related with a decreased uptake or increased efflux of the drug due to mutations or altered expression of membrane transporters. Different new approaches have been elaborated that can overcome these mechanisms of resistance including the use of inhibitors of efflux pumps and drug carriers for both active and passive targeting. Here we review new formulations that have been successfully applied to circumvent resistance related to drug transporters, opening alternative ways to solve drug resistance in protozoan parasitic diseases.

An Aromatic Diamidine That Targets Kinetoplast DNA, Impairs the Cell Cycle in Trypanosoma cruzi, and Diminishes Trypomastigote Release from Infected Mammalian Host Cells

Trypanosoma cruzi is the etiological agent of Chagas disease, affecting approximately 10 million people in the Americas and with some 40 million people at risk. The objective of this study was to evaluate the anti-T. cruzi activity of three new diamidines that have a 3,4-ethylenedioxy extension of the thiophene core, designated MB17, MB19, and MB38. All three diamidines exhibited dose-dependent inhibition of epimastigote replication. The mechanisms of action of these diamidines were investigated. Unlike MB17 and MB19, MB38 exhibited a significant increase in the number of annexin-propidium iodide double-labeled cells compared to levels in control parasites. As MB17 had shown a lower 50% inhibitory concentration (IC50) against epimastigote growth, the mechanism of action of this drug was studied in more detail. MB17 triggered a decrease in the intracellular ATP levels. As a consequence, MB17 affected the genomic DNA and kinetoplast DNA (kDNA) and impaired the parasite cell cycle. Moreover, MB17 caused DNA fragmentation, with a more severe effect on kDNA than on nuclear DNA, resulting in dyskinetoplastic cells. MB17 was tested for toxicity and effectiveness for the treatment of infected CHO-K1 cells, exhibiting a 50% cytotoxic concentration (CC50) of 13.47 ± 0.37 μM and an IC50 of 0.14 ± 0.12 μM against trypomastigote release. MB17 also diminished the infection index by 60% at 0.5 μM. In conclusion, despite belonging to the same family, these diamidines have different efficiencies. To summarize, MB17 was the most potent of these diamidines against epimastigotes, producing DNA damage preferentially in kDNA, impairing the parasite cell cycle, and decreasing the infection index and trypomastigote release from infected mammalian host cells, with a high selectivity index (SI) (<90). These data suggest that MB17 could be an interesting lead compound against T. cruzi.

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.

Leishmania is not prone to develop resistance to tamoxifen

Tamoxifen, an antineoplastic agent, is active in vitro and in vivo against the parasitic protozoa Leishmania. As part of our efforts to unravel this drug's mechanisms of action against the parasite and understand how resistance could arise, we tried to select tamoxifen-resistant Leishmania amazonensis. Three different strategies to generate tamoxifen resistant mutants were used: stepwise increase in drug concentration applied to promastigote cultures, chemical mutagenesis followed by drug selection and treatment of infected mice followed by selection of amastigotes. For amastigote selection, we employed a method with direct plating of parasites recovered from lesions into semi-solid media. Tamoxifen resistant parasites were not rescued by any of these methods. Miltefosine was used as a control in selection experiments and both stepwise selection and chemical mutagenesis allowed successful isolation of miltefosine resistant mutants. These findings are consistent with a multi-target mode of action to explain tamoxifen's leishmanicidal properties. Considering that drug resistance is a major concern in anti-parasitic chemotherapy, these findings support the proposition of using tamoxifen as a partner in drug combination schemes for the treatment of leishmaniasis.

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Tamoxifen is effective in the treatment of cutaneous and visceral leishmaniasis.

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Resistance to tamoxifen was not found in promastigotes upon mutagenesis/selection.

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Resistance to tamoxifen was not detected in amastigotes after in vivo selection.

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Tamoxifen may be a good partner in drug combination schemes for leishmaniasis.

A hyaluronic acid–pentamidine bioconjugate as a macrophage mediated drug targeting delivery system for the treatment of leishmaniasis

A new HA–Pent bioconjugate was synthetized and proposed as drug targeting delivery system for the treatment of leishmaniasis, exploiting the specific biological recognition of HA by the macrophage.

Activity of melatonin against Leishmania infantum promastigotes by mitochondrial dependent pathway

Visceral leishmaniasis, a potentially fatal disease, remains a major international health problem. Only a limited number of effective antileishmanial agents are available for chemotherapy, and many of them are expensive with severe side effects or have a markedly reduced effectiveness due to the development of drug resistance. Hence, there is a genuine need to develop a novel effective and less toxic antileishmanial drug. Melatonin, a neurohormone found in animals, plants, and microbes, can participate in various biological and physiological functions. Several in vitro or in vivo studies have reported the inhibitory effect of melatonin against many parasites via various mechanisms, including modulation of intracellular concentrations of calcium in the parasite and/or any other suggested mechanism. Importantly, many of available antileishmanial drugs have been reported to exert their effects by disrupting calcium homeostasis in the parasite. The objective of the present study was to test the efficacy of exogenous melatonin against Leishmania infantum promastigotes in vitro. Interestingly, melatonin not only demonstrated a significant antileishmanial activity of against promastigote viability in tested cultures but was also accompanied by an alteration of the calcium homeostasis of parasite mitochondrion, represented by earlier mitochondrial permeability transition pore opening, and by changes in some mitochondrial parameters are critical to parasite survival. These pioneering findings suggest that melatonin may be a candidate for the development of novel effective antileishmanial agents either alone or in associations with other drugs.

Comparative analysis of the omics technologies used to study antimonial, amphotericin B, and pentamidine resistance in leishmania

Leishmaniasis is a serious threat in developing countries due to its endemic nature and debilitating symptoms. Extensive research and investigations have been carried out to learn about the mechanism of drug resistance in Leishmania but results obtained in the laboratory are not in agreement with those obtained from the field. Also the lack of knowledge about the mode of action for a number of drugs makes the study of drug resistance more complex. A major concern in recent times has been regarding the role of parasitic virulence in drug resistance for Leishmania. Researchers have employed various techniques to unravel the facts about resistance and virulence in Leishmania. With advent of advanced and more specific means of detection, further hints about probable mechanisms of conferring resistance are expected. This review aims to provide a consolidated picture along with a comparative account of the work done so far to study the mechanism of antimony, amphotericin B, and pentamidine resistance using various techniques.

4-amino bis-pyridinium derivatives as novel antileishmanial agents

The antileishmanial activity of a series of bis-pyridinium derivatives that are analogues of pentamidine have been investigated, and all compounds assayed were found to display activity against promastigotes and intracellular amastigotes of Leishmania donovani and Leishmania major, with 50% effective concentrations (EC50s) lower than 1 μM in most cases. The majority of compounds showed similar behavior in both Leishmania species, being slightly more active against L. major amastigotes. However, compound VGP-106 {1,1'-(biphenyl-4,4'-diylmethylene)bis[4-(4-bromo-N-methylanilino)pyridinium] dibromide} exhibited significantly higher activity against L. donovani amastigotes (EC50, 0.86 ± 0.46 μM) with a lower toxicity in THP-1 cells (EC50, 206.54 ± 9.89 μM). As such, VGP-106 was chosen as a representative compound to further elucidate the mode of action of this family of inhibitors in promastigote forms of L. donovani. We have determined that uptake of VGP-106 in Leishmania is a temperature-independent process, suggesting that the compound crosses the parasite membrane by diffusion. Transmission electron microscopy analysis showed a severe mitochondrial swelling in parasites treated with compound VGP-106, which induces hyperpolarization of the mitochondrial membrane potential and a significant decrease of intracellular free ATP levels due to the inhibition of ATP synthesis. Additionally, we have confirmed that VGP-106 induces mitochondrial ROS production and an increase in intracellular Ca(2+) levels. All these molecular events can activate the apoptotic process in Leishmania; however, propidium iodide assays gave no indication of DNA fragmentation. These results underline the potency of compound VGP-106, which may represent a new avenue for the development of novel antileishmanial compounds.

The double-edged sword in pathogenic trypanosomatids: the pivotal role of mitochondria in oxidative stress and bioenergetics

The pathogenic trypanosomatids Trypanosoma brucei, Trypanosoma cruzi, and Leishmania spp. are the causative agents of African trypanosomiasis, Chagas disease, and leishmaniasis, respectively. These diseases are considered to be neglected tropical illnesses that persist under conditions of poverty and are concentrated in impoverished populations in the developing world. Novel efficient and nontoxic drugs are urgently needed as substitutes for the currently limited chemotherapy. Trypanosomatids display a single mitochondrion with several peculiar features, such as the presence of different energetic and antioxidant enzymes and a specific arrangement of mitochondrial DNA (kinetoplast DNA). Due to mitochondrial differences between mammals and trypanosomatids, this organelle is an excellent candidate for drug intervention. Additionally, during trypanosomatids' life cycle, the shape and functional plasticity of their single mitochondrion undergo profound alterations, reflecting adaptation to different environments. In an uncoupling situation, the organelle produces high amounts of reactive oxygen species. However, these species role in parasite biology is still controversial, involving parasite death, cell signalling, or even proliferation. Novel perspectives on trypanosomatid-targeting chemotherapy could be developed based on better comprehension of mitochondrial oxidative regulation processes.

Independence from Kinetoplast DNA maintenance and expression is associated with multidrug resistance in Trypanosoma brucei in vitro

It is well known that several antitrypanosomatid drugs accumulate in the parasite's mitochondrion, where they often bind to the organellar DNA, the kinetoplast. To what extent this property relates to the mode of action of these compounds has remained largely unquantified. Here we show that single point mutations that remove the dependence of laboratory strains of the sleeping sickness parasite Trypanosoma brucei on a functional kinetoplast result in significant resistance to the diamidine and phenanthridine drug classes.

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.

Developments in diagnosis and treatment of visceral leishmaniasis during the last decade and future prospects

Human visceral leishmaniasis (VL) continues to be a life-threatening neglected tropical disease, with close to 200 million people at risk of infection globally. Epidemics and resurgence of VL are associated with negligence by the policy makers, economic decline and population movements. Control of the disease is hampered by the lack of proficient vaccination, rapid diagnosis in a field setting and severe side effects of current drug therapies. The diagnosis of VL relied largely on invasive techniques of detecting parasites in splenic and bone marrow aspirates. rK39 and PCR, despite problems related to varying sensitivities and specificities and field adaptability, respectively, are considered the best options for VL diagnosis today. No single therapy of VL currently offers satisfactory efficacy along with safety. The field of VL research only recently shifted toward actively identifying new drugs for safe and affordable treatment. Oral miltefosine and safe AmBisome along with better use of amphotericin B have been rapidly implemented in the last decade. A combination therapy will substantially reduce the required dose and duration of drug administration and reduce the chance of the development of resistance. In addition, identification of asymptomatic cases, vector control and treatment of post-kala-azar dermal leishmaniasis would allow new perspectives in VL control and management.

Role of efflux pumps and intracellular thiols in natural antimony resistant isolates of Leishmania donovani

BACKGROUND

In view of the recent upsurge in the phenomenon of therapeutic failure, drug resistance in Leishmania, developed under natural field conditions, has become a great concern yet little understood. Accordingly, the study of determinants of antimony resistance is urgently warranted. Efflux transporters have been reported in Leishmania but their role in clinical resistance is still unknown. The present study was designed to elucidate the mechanism of natural antimony resistance in L. donovani field isolates by analyzing the functionality of efflux pump(s) and expression profiles of known genes involved in transport and thiol based redox metabolism.

METHODOLOGY/PRINCIPAL FINDINGS

We selected 7 clinical isolates (2 sensitive and 5 resistant) in addition to laboratory sensitive reference and SbIII resistant mutant strains for the present study. Functional characterization using flow cytometry identified efflux pumps that transported substrates of both P-gp and MRPA and were inhibited by the calmodulin antagonist trifluoperazine. For the first time, verapamil sensitive efflux pumps for rhodamine 123 were observed in L. donovani that were differentially active in resistant isolates. RT-PCR confirmed the over-expression of MRPA in isolates with high resistance index only. Resistant isolates also exhibited consistent down regulation of AQP1 and elevated intracellular thiol levels which were accompanied with increased expression of ODC and TR genes. Interestingly, γ-GCS is not implicated in clinical resistance in L. donovani isolates.

CONCLUSIONS/SIGNIFICANCE

Here we demonstrate for the first time, the role of P-gp type plasma membrane efflux transporter(s) in antimony resistance in L. donovani field isolates. Further, decreased levels of AQP1 and elevated thiols levels have emerged as biomarkers for clinical resistance.

Binding to the DNA minor groove by heterocyclic dications: from AT-specific monomers to GC recognition with dimers

Compounds that bind in the DNA minor groove have provided critical information on DNA molecular recognition, have found extensive uses in biotechnology, and are providing clinically useful drugs against diseases as diverse as cancer and sleeping sickness. This review focuses on the development of clinically useful heterocyclic diamidine minor groove binders. These compounds have shown us that the classical model for minor groove binding in AT DNA sequences must be expanded in several ways: compounds with nonstandard shapes can bind strongly to the groove, water can be directly incorporated into the minor groove complex in an interfacial interaction, and the compounds can form cooperative stacked dimers to recognize GC and mixed AT/GC base pair sequences.

Involvement of mitochondrial genes of Babesia gibsoni in resistance to diminazene aceturate

The stability of the characteristics of the diminazene aceturate (DA)-resistant B. gibsoni isolate was initially determined in vitro. Part of the DA-resistant B. gibsoni isolate was cultured without DA for 4 weeks, and then newly exposed to 200 ng/ml DA. As a result, this isolate could proliferate the same as the DA-resistant isolate, indicating that the characteristic of DA resistance was stable in the DA-resistant isolate. Additionally, the level of parasitemia in the DA-resistant isolate was comparatively lower than in the wild-type, suggesting that the proliferation potential of the DA-resistant isolate would be lower than that of the wild-type. Subsequently, to investigate the involvement of mitochondrial DNA (mtDNA) in DA resistance in B. gibsoni, the nucleotide sequences and deduced amino acid sequences of mitochondrial genes such as COXI, COXIII, and CYTb genes of the DA-resistant isolate, were compared with those of the wild-type. As a result, these three genes were not altered in the DA-resistant B. gibsoni isolate. Moreover, the transcription levels of COXI, COXIII, and CYTb genes were observed by semi-quantitative RT-PCR. As a result, the gene transcription of those genes in the DA-resistant isolate was not significantly altered. These results indicated that DA did not affect mtDNA directly in DA-resistant B. gibsoni. Thus, it is suggested that mtDNA should not be deeply involved in DA resistance in B. gibsoni.

New insights in staging and chemotherapy of African trypanosomiasis and possible contribution of medicinal plants

Human African trypanosomiasis (HAT) is a fatal if untreated fly-borne neuroinflammatory disease caused by protozoa of the species Trypanosoma brucei (T.b.). The increasing trend of HAT cases has been reversed, but according to WHO experts, new epidemics of this disease could appear. In addition, HAT is still a considerable burden for life quality and economy in 36 sub-Saharan Africa countries with 15-20 million persons at risk. Following joined initiatives of WHO and private partners, the fight against HAT was re-engaged, resulting in considerable breakthrough. We present here what is known at this day about HAT etiology and pathogenesis and the new insights in the development of accurate tools and tests for disease staging and severity monitoring in the field. Also, we elaborate herein the promising progresses made in the development of less toxic and more efficient trypanocidal drugs including the potential of medicinal plants and related alternative drug therapies.

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.

Symmetrical choline-derived dications display strong anti-kinetoplastid activity

OBJECTIVES

to investigate the anti-kinetoplastid activity of choline-derived analogues with previously reported antimalarial efficacy.

METHODS

from an existing choline analogue library, seven antimalarial compounds, representative of the first-, second- and third-generation analogues previously developed, were assessed for activity against Trypanosoma and Leishmania spp. Using a variety of techniques, the effects of choline analogue exposure on the parasites were documented and a preliminary investigation of their mode of action was performed.

RESULTS

the activities of choline-derived compounds against Trypanosoma brucei and Leishmania mexicana were determined. The compounds displayed promising anti-kinetoplastid activity, particularly against T. brucei, to which 4/7 displayed submicromolar EC(50) values for the wild-type strain. Low micromolar concentrations of most compounds cleared trypanosome cultures within 24-48 h. The compounds inhibit a choline transporter in Leishmania, but their entry may not depend only on this carrier; T. b. brucei lacks a choline carrier and the mode of uptake remains unclear. The compounds had no effect on the overall lipid composition of the cells, cell cycle progression or cyclic adenosine monophosphate production or short-term effects on intracellular calcium levels. However, several of the compounds, displayed pronounced effects on the mitochondrial membrane potential; this action was not associated with production of reactive oxygen species but rather with a slow rise of intracellular calcium levels and DNA fragmentation.

CONCLUSIONS

the choline analogues displayed strong activity against kinetoplastid parasites, particularly against T. b. brucei. In contrast to their antimalarial activity, they did not act on trypanosomes by disrupting choline salvage or phospholipid metabolism, instead disrupting mitochondrial function, leading to chromosomal fragmentation.

Tafenoquine, an antiplasmodial 8-aminoquinoline, targets leishmania respiratory complex III and induces apoptosis

Tafenoquine (TFQ), an 8-aminoquinoline analogue of primaquine, which is currently under clinical trial (phase IIb/III) for the treatment and prevention of malaria, may represent an alternative treatment for leishmaniasis. In this work, we have studied the mechanism of action of TFQ against Leishmania parasites. TFQ impaired the overall bioenergetic metabolism of Leishmania promastigotes, causing a rapid drop in intracellular ATP levels without affecting plasma membrane permeability. TFQ induced mitochondrial dysfunction through the inhibition of cytochrome c reductase (respiratory complex III) with a decrease in the oxygen consumption rate and depolarization of mitochondrial membrane potential. This was accompanied by ROS production, elevation of intracellular Ca(2+) levels and concomitant nuclear DNA fragmentation. We conclude that TFQ targets Leishmania mitochondria, leading to an apoptosis-like death process.

Uptake of T-2307, a novel arylamidine, in Candida albicans

OBJECTIVES

T-2307, a novel arylamidine synthesized at Toyama Chemical Co., Ltd, has in vitro and in vivo broad-spectrum activities against pathogenic fungi. T-2307 particularly exhibits potent in vitro and in vivo activity against Candida albicans, suggesting that its uptake might be mediated by a transport system. In this report, we studied the uptake of T-2307 in C. albicans.

METHODS

C. albicans cells and rat hepatocytes were exposed to 0.02 microM [(14)C]T-2307. After incubation, the reaction mixture was concentrated and layered on a silicon layer (mixture of silicon oil and liquid paraffin) inside a tube. The tube was then centrifuged to transfer cells into the bottom layer (sodium hydroxide) for solubilization. The bottom layer was neutralized and measured for radioactivity.

RESULTS

T-2307 was concentrated from the extracellular medium by C. albicans cells in 10 mM phosphate buffer solution supplemented with 1% glucose by 3200- to 5100-fold. The accumulation was approximately two orders of magnitude greater than that achieved with a rat hepatocyte preparation. T-2307 uptake was sensitive to temperature and extracellular pH, and was reduced in the presence of inhibitors of mitochondrial respiration, oxidative phosphorylation and plasma membrane proton pump, and by an uncoupler. Furthermore, T-2307 uptake was concentration dependent and an Eadie-Hofstee plot suggested the involvement of two transport systems.

CONCLUSIONS

The considerably higher concentrations of T-2307 were selectively accumulated in C. albicans via transporter-mediated systems, as compared with the concentrations in rat hepatocytes. This transporter-mediated uptake of T-2307 contributes to its potent anticandidal activity.

Protein composition of Trypanosoma brucei mitochondrial membranes

Mitochondria consist of four compartments, outer membrane, intermembrane space, inner membrane, and matrix; each harboring specific functions and structures. In this study, we used LC-MS/MS to characterize the protein composition of Trypanosoma brucei mitochondrial (mt) membranes, which were enriched by different biochemical fractionation techniques. The analyses identified 202 proteins that contain one or more transmembrane domain(s) and/or positive GRAVY scores. Of these, various criteria were used to assign 72 proteins to mt membranes with high confidence, and 106 with moderate-to-low confidence. The sub-cellular localization of a selected subset of 13 membrane assigned proteins was confirmed by tagging and immunofluorescence analysis. While most proteins assigned to mt membrane have putative roles in metabolic, energy generating, and transport processes, approximately 50% have no known function. These studies result in a comprehensive profile of the composition and sub-organellar location of proteins in the T. brucei mitochondrion thus, providing useful information on mt functions.

The role of ATP-binding cassette (ABC) proteins in protozoan parasites

The ATP-binding cassette (ABC) superfamily is one of the largest protein families with representatives in all kingdoms of life. Members of this superfamily are involved in a wide variety of transport processes with substrates ranging from small ions to relatively large polypeptides and polysaccharides, but also in cellular processes such as DNA repair, translation or regulation of gene expression. For many years, the role of ABC proteins was mainly investigated for their implication in drug resistance. However, recent studies focused rather on their physiological functions for the parasite. In this review, we present an overview of ABC proteins in major protozoan parasites including Leishmania, Trypanosoma, Plasmodium, Toxoplasma, Cryptosporidium and Entamoeba species. We will also discuss the role of characterized ABC transporters in the biology of the parasite and in drug resistance.

Flow cytometric determination of intracellular non-protein thiols in Leishmania promastigotes using 5-chloromethyl fluorescein diacetate

Leishmania parasites lack catalase and therefore, their anti-oxidant system hinges primarily upon non-protein thiols; accordingly, depletion of thiols could potentially serve as an effective drug target. We have developed a flow cytometry based assay using 5-chloromethyl fluorescein diacetate based upon its selective staining of non-protein thiols. Its specificity was confirmed using buthionine sulphoximine (a gamma-glutamyl cysteine synthetase inhibitor), diamide (an oxidizing agent of intracellular thiols) and N-ethylmaleimide (a covalent modifier of cysteine residues) as evidenced by reduction in fluorescence; furthermore, restoration of fluorescence by N-acetyl cysteine corroborated specificity of 5-chloromethyl fluorescein diacetate to measure non-protein thiols. Differences in basal level of thiols in antimony sensitive and antimony resistant Leishmania field isolates were detected. The depletion of non-protein thiols by conventional anti-leishmanial drugs e.g. antimony and miltefosine was demonstrated. Furthermore, fluorescence was unaffected by depletion of ATP in majority of the strains studied, indicating that 5-chloromethyl fluorescein diacetate is not a substrate for the pump operative in most Leishmania donovani strains. Taken together, measurement of 5-chloromethyl fluorescein diacetate fluorescence is an effective method for monitoring non-protein thiols in Leishmania promastigotes.