Drug combinations for visceral leishmaniasis

Efficacy of the treatment using a microemulsion loaded with epoxy-α-lapachone in combination with meglumine antimoniate against murine infection by Leishmania (Leishmania) amazonensis

Leishmaniasis is a disease caused by Leishmania spp., affecting millions of people around the world. For decades, its treatment has been based on pentavalent antimonials, which notoriously cause toxic side effects in patients. In this study, epoxy-α-lapachone incorporated into an oil-in-water-type microemulsion (ELAP-ME) and meglumine antimoniate (MA) were assayed in monotherapy and in combination (ELAP-ME/MA) in BALB/c mice infected with Leishmania (Leishmania) amazonensis. In general, there was a reduction in paw lesion size (up to 37% reduction) and decreases of parasite loads in the footpad (∼40%) and lymph nodes (∼31%) of animals treated with ELAP-ME/MA, when compared to the non-treated control groups. Analyses of serum biochemical parameters revealed that the ELAP-ME/MA showed lower renal and hepatic toxicity when compared to MA 2-doses/week monotherapy. These findings indicate that the ELAP-ME/MA combination may be a promising approach for the treatment of cutaneous leishmaniasis.

Nitazoxanide and quercetin co-loaded nanotransfersomal gel for topical treatment of cutaneous leishmaniasis with macrophage targeting and enhanced anti-leishmanial effect

Purpose

Anti-leishmanial medications administered by oral and parenteral routes are less effective for treatment of cutaneous leishmaniasis (CL) and cause toxicity, hence targeted drug delivery is an efficient way to improve drug availability for CL with reduced toxicity. This study aimed to develop, characterize and evaluate nitazoxanide and quercetin co-loaded nanotransfersomal gel (NTZ-QUR-NTG) for the treatment of CL.

Methods

NTZ-QUR-NT were prepared by thin film hydration method and were statistically optimized using Box-Behnken design. To ease the topical delivery and enhance the retention time, the NTZ-QUR-NT were dispersed in 2 % chitosan gel. Moreover, in-vitro drug release, ex-vivo permeation, macrophage uptake, cytotoxicity and anti-leishmanial assays were performed.

Results

The optimized formulation indicated mean particle size 210 nm, poly dispersity index (PDI) 0.16, zeta potential (ZP) -15.1 mV and entrapment efficiency (EE) of NTZ and QUR was 88 % and 85 %, respectively. NTZ-QUR-NT and NTZ-QUR-NTG showed sustained release of the incorporated drugs as compared to the drug dispersions. Skin permeation of NTZ and QUR in NTZ-QUR-NTG was 4 times higher in comparison to the plain gels. The NTZ-QUR-NT cell internalization was almost 10-folds higher than NTZ-QUR dispersion. The cytotoxicity potential (CC50) of NTZ-QUR-NT (71.95 ± 3.32 μg/mL) was reduced as compared to NTZ-QUR dispersion (49.77 ± 2.15 μg/mL. A synergistic interaction was found between NTZ and QUR. Moreover, in-vitro anti-leishmanial assay presented a lower IC50 value of NTZ-QUR-NT as compared to NTZ-QUR dispersion. Additionally, a significantly reduced lesion size was observed in NTZ-QUR-NTG treated BALB/c mice, indicating its antileishmanial potential.

Conclusion

It can be concluded that nanotransfersomal gel has the capability to retain and permeate the incorporated drugs through stratum corneum and induce synergetic anti-leishmanial effect of NTZ and QUR against cutaneous leishmaniasis.

Epoxy-α-lapachone (2,2-Dimethyl-3,4-dihydro-spiro[2H-naphtho[2,3-b]pyran-10,2'-oxirane]-5(10H)-one): a promising molecule to control infections caused by protozoan parasites

Natural products and their derivatives have been sources of search and research for new drugs for the treatment of neglected diseases. Naphthoquinones, a special group of quinones, are products of natural metabolites with a wide spectrum of biological activities and represent a group of interesting molecules for new therapeutic propositions. Among these compounds, lapachol stands out as a molecule from the heartwood of Tabebuia sp. whose structural changes resulted in compounds considered promising, such as epoxy-α-lapachone (ELAP). The biological activity of ELAP has been demonstrated, so far, for parasitic protozoa such as Leishmania spp., Trypanosoma cruzi and Plasmodium spp., species causing diseases needing new drug development and adequate health policy. This work gathers in vitro and in vivo studies on these parasites, as well as the toxicity profile, and the probable mechanisms of action elucidated until then. The potential of ELAP-based technology alternatives for a further drug is discussed here.

Antileishmanial Efficacy of the Calpain Inhibitor MDL28170 in Combination with Amphotericin B

The necessity of drug combinations to treat leishmaniasis came to the surface mainly because of the toxicity of current treatments and the emergence of resistant strains. The calpain inhibitor MDL28170 has previously shown anti-Leishmania activity, therefore its use in association with standard drugs could provide a new alternative for the treatment strategy against leishmaniasis. In this study, we analyzed the potential of the combination of MDL28170 and the antileishmanial drug amphotericin B against Leishmania amazonensis and Leishmania chagasi. The compounds were tested in the combination of the ½ × IC50 value of MDL28170 plus the ¼ × IC50 value of amphotericin B, which led to an increment in the anti-promastigote activity when compared to the single drug treatments. This drug association revealed several and severe morphophysiological changes on parasite cells, such as loss of plasma membrane integrity, reduced size of flagellum, and depolarization of mitochondrial membrane potential besides increased reactive oxygen species production. In addition, the combination of both drugs had a deleterious effect on the Leishmania–macrophage interaction, reflecting in a significant anti-amastigote action, which achieved a reduction of 50% in the association index. These results indicate that the combination treatment proposed here may represent a new alternative for leishmaniasis chemotherapy.

Long non-coding RNAs as possible therapeutic targets in protozoa, and in Schistosoma and other helminths

Long non-coding RNAs (lncRNAs) emerged in the past 20 years due to massive amounts of scientific data regarding transcriptomic analyses. They have been implicated in a plethora of cellular processes in higher eukaryotes. However, little is known about lncRNA possible involvement in parasitic diseases, with most studies only detecting their presence in parasites of human medical importance. Here, we review the progress on lncRNA studies and their functions in protozoans and helminths. In addition, we show an example of knockdown of one lncRNA in Schistosoma mansoni, SmLINC156349, which led to in vitro parasite adhesion, motility, and pairing impairment, with a 20% decrease in parasite viability and 33% reduction in female oviposition. Other observed phenotypes were a decrease in the proliferation rate of both male and female worms and their gonads, and reduced female lipid and vitelline droplets that are markers for well-developed vitellaria. Impairment of female worms' vitellaria in SmLINC156349-silenced worms led to egg development deficiency. All those results demonstrate the great potential of the tools and methods to characterize lncRNAs as potential new therapeutic targets. Further, we discuss the challenges and limitations of current methods for studying lncRNAs in parasites and possible solutions to overcome them, and we highlight the future directions of this exciting field.

Development of new combination anti-leishmanial complexes: Triphenyl Sb(V) mono-hydroxy mono-quinolinolates

In seeking to develop single entity combination anti-Leishmanial complexes six heteropletic organometallic Sb(V) hydroxido quinolinolate complexes of general formula [SbPh₃(C₉H₄NORR')(OH)] have been synthesised and characterised, derived from a series of halide substituted quinolinols (8-hydroxyquinolines). Single crystal X-ray diffraction on all the complexes show a common distorted six-coordinate octahedral environment at the Sb(V) centre, with the aryl groups and nitrogen atom of quinolinolate ligand bonding in the equatorial planes, with the two oxygen atoms (hydroxyl and quinolinolate) occupying the axial plane in an almost linear configuration. Each complex was tested for their anti-promastigote activity and mammalian cytotoxicity and a selectivity indices established. The complexes displayed excellent anti-promastigote activity (IC₅₀: 2.03-3.39 μM) and varied mammalian cytotoxicity (IC₅₀: 12.7-46.9 μM), leading to a selectivity index range of 4.52-16.7. All complexes displayed excellent anti-amastigote activity with a percentage infection range of 2.25%-9.00%. All complexes performed substantially better than the parent quinolinols and comparable carboxylate complexes [SbPh₃(O₂CRR')₂] indicating the synergistic role of the Sb(V) and quinolinol moieties in increasing parasite mortality. Two of the complexes [SbPh₃(C₉H₄NOBr₂)(OH)] 4, [SbPh₃(C₉H₄NOI₂)(OH)] 5, provide an ideal combination of high selective and good activity towards the leishmanial amastigotes and offer the potential as good lead compounds.

Ethanolic Extract of the Fungus Trichoderma asperelloides Induces Ultrastructural Effects and Death on Leishmania amazonensis

The Trichoderma genus comprises several species of fungi whose diversity of secondary metabolites represents a source of potential molecules with medical application. Because of increased pathogen resistance and demand for lower production costs, the search for new pharmacologically active molecules effective against pathogens has become more intense. This is particularly evident in the case of American cutaneous leishmaniasis due to the high toxicity of current treatments, parenteral administration, and increasing rate of refractory cases. We have previously shown that a fungus from genus Trichoderma can be used for treating cerebral malaria in mouse models and inhibit biofilm formation. Here, we evaluated the effect of the ethanolic extract of Trichoderma asperelloides (Ext-Ta) and its fractions on promastigotes and amastigotes of Leishmania amazonensis, a major causative agent of cutaneous leishmaniasis in the New World. Ext-Ta displayed leishmanicidal action on L. amazonensis parasites, and its pharmacological activity was associated with the low-molecular-weight fraction (LMWF) of Ext-Ta. Ultrastructural analysis demonstrated morphological alterations in the mitochondria and the flagellar pocket of promastigotes, with increased lipid body and acidocalcisome formation, microtubule disorganization of the cytoplasm, and intense vacuolization of the cytoplasm when amastigotes were present. We suggest the antiparasitic activity of Trichoderma fungi as a promising tool for developing chemotherapeutic leishmanicidal agents.

In vitro effectivity of three approved drugs and their synergistic interaction against Leishmania infantum

Introduction:

Leishmaniasis remains one of the neglected tropical diseases. Repurposing existing drugs has proven to be successful for treating neglected tropical diseases while combination therapy is a strategic alternative for the treatment of infectious diseases.

Auranofin, lopinavir/ritonavir, and sorafenib are FDA approved drugs used in the treatment of diverse diseases by acting on different essential biological enzymes.

Objective:

To evaluate the effects of monotherapy and combined therapies with the three drugs against Leishmania infantum.

Materials and methods:

We compared the leishmanicidal effects of the three drugs on promastigotes in vitro as regards the parasite count, the drug concentration providing a half-maximal response, and the ultrastructural changes of the parasite. We determined the fractional inhibitory concentration index of combined drugs in two ways, as well as the activity of the three drugs together to establish their synergetic effect.

Results:

The monotherapy with the three drugs was effective with auranofin showing the best leishmanicidal effect (EC50=1.5 µM), whereas sorafinib reduced parasite growth at EC50=2.5 µM. The scanning electron microscopy of promastigotes from all treated media showed distortion in the shape with loss of flagella and bleb formation. Acidocalcinosis was evident by transmission electron microscopy with all treatments suggesting apoptosis.

Treatment with lopinavir/ritonavir showed signs of autophagy. The two-way combination of the drugs led to additive interactions while the combination of the three drugs showed synergistic action.

Conclusion:

Each drug when used as monotherapy against Leishmania spp. was effective, but the combination therapy was more effective than the individual drugs due to the additive or synergistic effects.

A Novel Niosomal Combination of Selenium Coupled with Glucantime against Leishmania tropica

There is no effective treatment modality available against different forms of leishmaniasis. Therefore, the aim of this study was to improve the penetration and efficacy of selenium and glucantime coupled with niosomes and compared them with their simple forms alone on in vitro susceptibility assays. In this study, the niosomal formulations of selenium and in combination with glucantime were prepared. The size and morphology of the niosomal formulations were characterized and the effectivity of the new formulation was also evaluated using in vitro MTT assay, intra-macrophage model, and gene expression profile. From the results obtained, no cytotoxicity effect was observed for niosomal and simple forms of drugs, as alone or in combination. Niosomal formulations of the drugs significantly showed more inhibitory effects (P ≤ 0.001) than the simple drugs when the selectivity index was considered. The gene expression levels of Interleukin (IL-10) significantly decreased, while the level of IL-12 and metacaspase significantly increased (P ≤ 0.001). The results of the present study showed that selenium plus glucantime niosome possess a potent anti-leishmanial effect and enhanced their lethal activity as evidenced by the in vitro experiments.

Cell death pathways in pathogenic trypanosomatids: lessons of (over)kill

Especially in tropical and developing countries, the clinically relevant protozoa Trypanosoma cruzi (Chagas disease), Trypanosoma brucei (sleeping sickness) and Leishmania species (leishmaniasis) stand out and infect millions of people worldwide leading to critical social-economic implications. Low-income populations are mainly affected by these three illnesses that are neglected by the pharmaceutical industry. Current anti-trypanosomatid drugs present variable efficacy with remarkable side effects that almost lead to treatment discontinuation, justifying a continuous search for alternative compounds that interfere with essential and specific parasite pathways. In this scenario, the triggering of trypanosomatid cell death machinery emerges as a promising approach, although the exact mechanisms involved in unicellular eukaryotes are still unclear as well as the controversial biological importance of programmed cell death (PCD). In this review, the mechanisms of autophagy, apoptosis-like cell death and necrosis found in pathogenic trypanosomatids are discussed, as well as their roles in successful infection. Based on the published genomic and proteomic maps, the panel of trypanosomatid cell death molecules was constructed under different experimental conditions. The lack of PCD molecular regulators and executioners in these parasites up to now has led to cell death being classified as an unregulated process or incidental necrosis, despite all morphological evidence published. In this context, the participation of metacaspases in PCD was also not described, and these proteases play a crucial role in proliferation and differentiation processes. On the other hand, autophagic phenotype has been described in trypanosomatids under a great variety of stress conditions (drugs, starvation, among others) suggesting that this process is involved in the turnover of damaged structures in the protozoa and is not a cell death pathway. Death mechanisms of pathogenic trypanosomatids may be involved in pathogenesis, and the identification of parasite-specific regulators could represent a rational and attractive alternative target for drug development for these neglected diseases.

Effective Tetradentate Compound Complexes against Leishmania spp. that Act on Critical Enzymatic Pathways of These Parasites

The spectrum and efficacy of available antileishmanial drugs is limited. In the present work we evaluated in vitro the antiproliferative activity of 11 compounds based on tetradentate polyamines compounds against three Leishmania species (L. braziliensis, L. donovani and L. infantum) and the possible mechanism of action. We identified six compounds (3, 5, 6, 7, 8 and 10) effective against all three Leishmania spp both on extracellular and intracellular forms. These six most active leishmanicidal compounds also prevent the infection of host cells. Nevertheless, only compound 7 is targeted against the Leishmania SOD. Meanwhile, on the glucose metabolism the tested compounds have a species-specific effect on Leishmania spp.: L. braziliensis was affected mainly by 10 and 8, L. donovani by 7, and L. infantum by 5 and 3. Finally, the cellular ultrastructure was mainly damaged by 11 in the three Leishmania spp. studied. These identified antileishmania candidates constitute a good alternative treatment and will be further studied.

Chemoprevention of Leishmaniasis: In-vitro antiparasitic activity of dibenzalacetone, a synthetic curcumin analog leads to apoptotic cell death in Leishmania donovani

Curcumin is the major phenolic compound found in turmeric, a dry powder of rhizomes and roots of the plant, Curcuma longa L., which is widely used as spice and food colorant around the world, and in herbal medicinal practice in Asian countries. The present study reports the leishmanicidal activity of trans-dibenzalacetone (DBA), a synthetic monoketone analog of curcumin, against Leishmania donovani parasites. We for the first time report the antiproliferative effect of a curcumin analog (DBA) on the intracellular amastigotes of L. donovani, the clinically more relevant stage of the parasite than its promastigotes stage. The leishmanicidal effect of DBA was further confirmed by scanning and transmission electron microscopies. Cell growth was arrested in G0/G1 phase with increased concentration of cytosolic calcium and dissipation of mitochondrial membrane potential. Further, the unique trypanothione/trypanothione reductase (TR) system of Leishmania cells was significantly inhibited by DBA. This economically synthesizable simple monoketone analog of curcumin has the potential for field use against visceral leishmaniasis which is currently widespread in tropical and subtropical developing countries of the world. In conclusion, we have identified an analog of curcumin for potential applications against leishmaniasis, based on its strong antiparasitic activity and low toxicity. This curcumin analog compares favorably, at least in vitro, with the existing medication miltefosine.

Towards elimination of visceral leishmaniasis in the Indian subcontinent-Translating research to practice to public health

BACKGROUND

The decade following the Regional Strategic Framework for Visceral Leishmaniasis (VL) elimination in 2005 has shown compelling progress in the reduction of VL burden in the Indian subcontinent. The Special Programme for Research and Training in Tropical Diseases (TDR), hosted by the World Health Organization (WHO) and other stakeholders, has coordinated and financed research for the development of new innovative tools and strategies to support the regional VL elimination initiative. This paper describes the process of the TDR's engagement and contribution to this initiative.

METHODOLOGY/PRINCIPAL FINDINGS

Multiple databases were searched to identify 152 scientific papers and reports with WHO funding or authorship affiliation around the following 3 framework strategies: detection of new cases, morbidity reduction, and prevention of infection. TDR has played a critical role in the evaluation and subsequent use of the 39-aminoacid-recombinant kinesin antigen (rK39) rapid diagnostic test (RDT) as a confirmatory test for VL in the national program. TDR has supported the clinical research and development of miltefosine and single-dose liposomal amphotericin B as a first-line treatment against VL. TDR has engaged with in-country researchers, national programme managers, and partners to generate evidence-based interventions for early detection and treatment of VL patients. TDR evaluated the quality, community acceptance, and cost effectiveness of indoor residual spraying, insecticide-treated bed nets, insecticide-impregnated durable wall linings, insecticidal paint, and environmental management as tools for integrated vector management in reducing sandfly density.

CONCLUSIONS/SIGNIFICANCE

TDR's engagement with country policy makers, scientists, and clinicians in the development of effective diagnosis, treatment, case detection, and vector control represents an important example of TDR's stewardship toward the elimination of VL in the Indian subcontinent.

Meglumine antımoniate-TiO2@Ag nanoparticle combinations reduce toxicity of the drug while enhancing its antileishmanial effect

Currently, the treatment of leishmaniasis is increasingly insufficient as current antileishmanial drugs have many disadvantages such as toxic side effects, high cost, and growing drug resistance. In order to overcome these disadvantages, researchers have recently focused on combination therapy by using pentavalent antimonials in conjunction with other antileihmanial compounds. Our previous study found that TiO2@Ag nanoparticles (TiAgNps) demonstrated significant antileishmanial effects. However, a lethal dose of TiAgNps on L. topica promastigotes was found to be toxic for macrophage cells. Moreover, non-toxic concentrations of TiAgNps were ineffective in inhibiting L. topica promastigotes and amastigotes. Thus, we propose the use of TiAgNps in combination with other antileishmanial compounds like meglumine antimoniate (MA) at non-toxic concentrations, which may increase the efficacies of both agents and decrease their toxicities. Therefore, the aim of this study was to determine in vitro and in vivo antileishmanial efficacies of TiAgNps-MA combinations at non-toxic concentrations and develop a new approach for treatment that lowers the toxicities of pentavalent antimonials to minimal levels and enhances their effectiveness. In vitro screening was performed on L. topica promastigote and amastigote-macropage culture by using MTT assay to determine proliferation, perform infection index analysis, and to conduct a Griess reaction for nitric oxide production, while in vivo antileishmanial assays were applied on Balb/c mice with CL models. The results demonstrated that combinations including TiAgNps and MA at non-toxic concentrations were highly efficacious against both promastigotes and amastigotes, while MA application alone did not show any inhibitory effects. It was determined that combination applications decreased the proliferation of L. topica promastigotes 2- to 5-fold in contrast to use of MA alone, and was dependent on concentrations. Moreover, the use of combinations led to inhibition of L. topica amastigotes at rates ranging between 80% and 95%. Additionally, combinations were found to decrease metabolic activities of each form of the parasite at ranges between 7- to 20-fold, causing programmed-cell death and stimulation of macrophages for intensive production of nitric oxide, which is accepted as an important antileishmanial agent (p<0.05). Furthermore, Σ FIC analysis demonstrated that the tested combinations composed little additive, but mostly synergistic effects for inhibition of promastigotes and amastigotes. According to in vivo screening results, the combinations displayed high antileishmanial activities by successfully healing lesions and significantly reducing parasite burdens. Combined, these results show that TiAgNps-MA combinations were much more effective than use of MA alone at non-toxic concentrations and they possess high potential for development of new antileishmanial drugs to fight against leishmaniasis.

Nanotized Curcumin and Miltefosine, a Potential Combination for Treatment of Experimental Visceral Leishmaniasis

Leishmaniasis chemotherapy remains very challenging due to high cost of the drug and its associated toxicity and drug resistance, which develops over a period of time. Combination therapies (CT) are now in use to treat many diseases, such as cancer and malaria, since it is more effective and affordable than monotherapy. CT are believed to represent a new explorable strategy for leishmaniasis, a neglected tropical disease caused by the obligate intracellular parasite Leishmania In the present study, we investigated the effect of a combination of a traditional Indian medicine (ayurveda), a natural product curcumin and miltefosine, the only oral drug for visceral leishmaniasis (VL) using a Leishmania donovani-hamster model. We developed an oral nanoparticle-based formulation of curcumin. Nanoformulation of curcumin alone exhibited significant leishmanicidal activity both in vitro and in vivo In combination with miltefosine, it exhibited a synergistic effect on both promastigotes and amastigotes under in vitro conditions. The combination of these two agents also demonstrated increased in vivo leishmanicidal activity accompanied by increased production of toxic reactive oxygen/nitrogen metabolites and enhanced phagocytic activity. The combination also exhibited increased lymphocyte proliferation. The present study thus establishes the possible use of nanocurcumin as an adjunct to antileishmanial chemotherapy.

DETC-based bacterial cellulose bio-curatives for topical treatment of cutaneous leishmaniasis

The treatment of leishmaniasis still relies on drugs with potentially serious adverse effects. Herein, we tested a topical formulation of bacterial cellulose (BC) membranes containing Diethyldithiocarbamate (DETC), a superoxide dismutase 1 inhibitor. Leishmania-infected macrophages exposed to BC-DETC resulted in parasite killing, without pronounced toxic effects to host cells. This outcome was associated with lower SOD1 activity and higher production of superoxide and cytokine mediators. Topical application of BC-DETC significantly decreased lesion size, parasite load and the inflammatory response at the infection site, as well as the production of both IFN-γ and TNF. Combination of topical BC-DETC plus intraperitoneal Sb^v also significantly reduced disease development and parasite load. The leishmanicidal effect of BC-DETC was extended to human macrophages infected with L. braziliensis, highlighting the feasibility of BC-DETC as a topical formulation for chemotherapy of cutaneous leishmaniasis caused by L. braziliensis.

Different Mutations in a P-type ATPase Transporter in Leishmania Parasites are Associated with Cross-resistance to Two Leading Drugs by Distinct Mechanisms

Leishmania infantum is an etiological agent of the life-threatening visceral form of leishmaniasis. Liposomal amphotericin B (AmB) followed by a short administration of miltefosine (MF) is a drug combination effective for treating visceral leishmaniasis in endemic regions of India. Resistance to MF can be due to point mutations in the miltefosine transporter (MT). Here we show that mutations in MT are also observed in Leishmania AmB-resistant mutants. The MF-induced MT mutations, but not the AmB induced mutations in MT, alter the translocation/uptake of MF. Moreover, mutations in the MT selected by AmB or MF have a major impact on lipid species that is linked to cross-resistance between both drugs. These alterations include changes of specific phospholipids, some of which are enriched with cyclopropanated fatty acids, as well as an increase in inositolphosphoceramide species. Collectively these results provide evidence of the risk of cross-resistance emergence derived from current AmB-MF sequential or co-treatments for visceral leishmaniasis.

Apoptotic protein profile in Leishmania donovani after treatment with hexaazatrinaphthylenes derivatives

Two hexaazatrinaphthylene derivatives, DGV-B and DGV-C previously known to induce an apoptotic-like process in Leishmania donovani parasites were used in this study. For this purpose, two different human protein commercial arrays were used to determine the proteomic profile of the treated parasites compared to non-treated ones. One of the commercial arrays is able to detect the relative expression of 35 human apoptosis-related proteins and the other one is able to identify 9 different human kinases. The obtained results showed that the two tested molecules were able to activate a programmed cell death process by different pathways in the promastigote stage of the parasite. The present study reports the potential application of two commercialised human apoptotic arrays to evaluate the action mechanism of active compounds at least against Leishmania donovani. The obtained data would be useful to establish the putative activated apoptosis pathways in the treated parasites and to further support the use of hexaazatrinaphthylene derivatives for the treatment of leishmaniasis in the near future. Nevertheless, further molecular studies should be developed in order to design and evaluate specific apoptotic arrays for Leishmania genus.

Leptin augments protective immune responses in murine macrophages and enhances potential of miltefosine against experimental visceral leishmaniasis

Adverse side effects and drug resistance issues are the two most important drawbacks which influence the widespread use of existing antileishmanial drugs. Use of immune stimulating agent with standard antileishmanial might be helpful to minimize the toxic effect of drug, shorten the dose regimen and delay the emergence of resistance. In the present study, we explored the in vitro immunomodulatory potential of an immunomodulator, leptin with lower concentration of standard drug, miltefosine. The level of Th1/Th2 cytokines, production of nitric oxide and reactive oxygen species and phagocytic activity was assessed by ELISA, Griess reaction and flow cytometric analysis, respectively. Leptin at a concentration of 15μg/mL showed heightened level of Th1 cytokines and nitric oxide generation from murine macrophages (J-774A.1 cells). Leptin (15μg/mL) also reduces the effective concentration of miltefosine by 2-folds from 7.5μM to 3.7μM. When given in conjunction with lower concentration of miltefosine (4μM), leptin (15μg/mL) significantly (***p<0.001) elevated the level of IL-12 (7.7 fold), TNF-α (8.1 fold) and nitric oxide (6.6 fold) along with markedly (***p<0.001) suppressed level of IL-10 and TGF-β when compared with untreated infected macrophages. Leptin plus miltefosine also induces the phagocytic ability (**p<0.01) of macrophages in comparison to leptin alone and miltefosine alone treated groups. These finding illustrate that leptin activates host macrophages to generate protective immune response for the successful elimination of Leishmania parasite at lower concentration of miltefosine and has potential for further exploration in experimental animal model of visceral leishmaniasis (VL).

Three-dimensional structures in the design of therapeutics targeting parasitic protozoa: reflections on the past, present and future

Parasitic protozoa cause a range of diseases which threaten billions of human beings. They are responsible for tremendous mortality and morbidity in the least-developed areas of the world. Presented here is an overview of the evolution over the last three to four decades of structure-guided design of inhibitors, leads and drug candidates aiming at targets from parasitic protozoa. Target selection is a crucial and multi-faceted aspect of structure-guided drug design. The major impact of advances in molecular biology, genome sequencing and high-throughput screening is touched upon. The most advanced crystallographic techniques, including XFEL, have already been applied to structure determinations of drug targets from parasitic protozoa. Even cryo-electron microscopy is contributing to our understanding of the mode of binding of inhibitors to parasite ribosomes. A number of projects have been selected to illustrate how structural information has assisted in arriving at promising compounds that are currently being evaluated by pharmacological, pharmacodynamic and safety tests to assess their suitability as pharmaceutical agents. Structure-guided approaches are also applied to incorporate properties into compounds such that they are less likely to become the victim of resistance mechanisms. A great increase in the number of novel antiparasitic compounds will be needed in the future. These should then be combined into various multi-compound therapeutics to circumvent the diverse resistance mechanisms that render single-compound, or even multi-compound, drugs ineffective. The future should also see (i) an increase in the number of projects with a tight integration of structural biology, medicinal chemistry, parasitology and pharmaceutical sciences; (ii) the education of more `medicinal structural biologists' who are familiar with the properties that compounds need to have for a high probability of success in the later steps of the drug-development process; and (iii) the expansion of drug-development capabilities in middle- and low-income countries.

Fitness of Leishmania donovani parasites resistant to drug combinations

Drug resistance represents one of the main problems for the use of chemotherapy to treat leishmaniasis. Additionally, it could provide some advantages to Leishmania parasites, such as a higher capacity to survive in stress conditions. In this work, in mixed populations of Leishmania donovani parasites, we have analyzed whether experimentally resistant lines to one or two combined anti-leishmanial drugs better support the stress conditions than a susceptible line expressing luciferase (Luc line). In the absence of stress, none of the Leishmania lines showed growth advantage relative to the other when mixed at a 1:1 parasite ratio. However, when promastigotes from resistant lines and the Luc line were mixed and exposed to different stresses, we observed that the resistant lines are more tolerant of different stress conditions: nutrient starvation and heat shock-pH stress. Further to this, we observed that intracellular amastigotes from resistant lines present a higher capacity to survive inside the macrophages than those of the control line. These results suggest that resistant parasites acquire an overall fitness increase and that resistance to drug combinations presents significant differences in their fitness capacity versus single-drug resistant parasites, particularly in intracellular amastigotes. These results contribute to the assessment of the possible impact of drug resistance on leishmaniasis control programs.

Chemotherapy is currently the only treatment option for leishmaniasis, a neglected tropical disease produced by the protozoan parasite Leishmania. However, first-line drugs have different types of limitations including toxicity, price, efficacy and mainly emerging resistance. The WHO has recently recommended a combined therapy in order to extend the life expectancy of these compounds. The emergence and spread of Leishmania antimonial-resistant parasites have led to a high rate of antimonial failure in India and have raised questions about the selection and propagation risk of drug resistant parasites. The spread of drug-resistant parasites in the field probably depends on their transmission potential, which is influenced by, among other factors, the relative fitness of drug-resistant versus drug-susceptible parasites. In light of this, we have designed experimental studies to determine whether Leishmania donovani parasites resistant to single and combinations of anti-leishmanial drugs present any advantages in their ability to bear the different stress conditions versus a susceptible L. donovani line. Our results suggest that resistant parasites acquire an overall fitness increase and that resistance to drug combinations presents significant differences in their fitness capacity, particularly in intracellular amastigotes.

In vitro activities of hexaazatrinaphthylenes against Leishmania spp

The in vitro activity of a novel group of compounds, hexaazatrinaphthylene derivatives, against two species of Leishmania is described in this study. These compounds showed a significant dose-dependent inhibition effect on the proliferation of the parasites, with 50% inhibitory concentrations (IC(50)s) ranging from 1.23 to 25.05 μM against the promastigote stage and 0.5 to 0.7 μM against intracellular amastigotes. Also, a cytotoxicity assay was carried out to in order to evaluate the possible toxic effects of these compounds. Moreover, different assays were performed to determine the type of cell death induced after incubation with these compounds. The obtained results highlight the potential use of hexaazatrinaphthylene derivatives against Leishmania species, and further studies should be undertaken to establish them as novel leishmanicidal therapeutic agents.

Experimental resistance to drug combinations in Leishmania donovani: metabolic and phenotypic adaptations

Together with vector control, chemotherapy is an essential tool for the control of visceral leishmaniasis (VL), but its efficacy is jeopardized by growing resistance and treatment failure against first-line drugs. To delay the emergence of resistance, the use of drug combinations of existing antileishmanial agents has been tested systematically in clinical trials for the treatment of visceral leishmaniasis (VL). In vitro, Leishmania donovani promastigotes are able to develop experimental resistance to several combinations of different antileishmanial drugs after 10 weeks of drug pressure. Using an untargeted liquid chromatography-mass spectrometry (LC-MS) metabolomics approach, we identified metabolic changes in lines that were experimentally resistant to drug combinations and their respective single-resistant lines. This highlighted both collective metabolic changes (found in all combination therapy-resistant [CTR] lines) and specific ones (found in certain CTR lines). We demonstrated that single-resistant and CTR parasite cell lines show distinct metabolic adaptations, which all converge on the same defensive mechanisms that were experimentally validated: protection against drug-induced and external oxidative stress and changes in membrane fluidity. The membrane fluidity changes were accompanied by changes in drug uptake only in the lines that were resistant against drug combinations with antimonials, and surprisingly, drug accumulation was higher in these lines. Together, these results highlight the importance and the central role of protection against oxidative stress in the different resistant lines. Ultimately, these phenotypic changes might interfere with the mode of action of all drugs that are currently used for the treatment of VL and should be taken into account in drug development.

New perspectives for leishmaniasis chemotherapy over current anti-leishmanial drugs: a patent landscape

INTRODUCTION

Although leishmaniasis is estimated to cause the ninth largest disease burden among individual infectious diseases, it is still one of the most neglected diseases in terms of drug development. Current drugs are highly toxic, resistance is common and compliance of patients to treatment is low, as treatment is long and drug price is high.

AREAS COVERED

In this review, the authors carried out a patent landscape in search for new perspectives for leishmaniasis therapy. This search encompassed patent documents having priority date between 1994 and 2014. Selected compounds were compared to current anti-leishmanial drugs regarding efficacy and toxicity, when experimental data were available.

EXPERT OPINION

Most patents related to drugs for leishmaniasis have not been produced by the pharmaceutical industry but rather by public research institutes or by universities, and the majority of the inventions disclosed are still in preclinical phase. There is an urgent need to find new ways of funding research for leishmaniasis drugs, incentivizing product development partnerships and pushing forward innovation.

Drug resistance analysis by next generation sequencing in Leishmania

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WGS revealed the complexity of resistance which is often polyclonal in Leishmania.

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An impressive variation in chromosome copy numbers exist between Leishmania species.

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The genotype heterogeneity complicates the analysis of resistance in field isolates.

The use of next generation sequencing has the power to expedite the identification of drug resistance determinants and biomarkers and was applied successfully to drug resistance studies in Leishmania. This allowed the identification of modulation in gene expression, gene dosage alterations, changes in chromosome copy numbers and single nucleotide polymorphisms that correlated with resistance in Leishmania strains derived from the laboratory and from the field. An impressive heterogeneity at the population level was also observed, individual clones within populations often differing in both genotypes and phenotypes, hence complicating the elucidation of resistance mechanisms. This review summarizes the most recent highlights that whole genome sequencing brought to our understanding of Leishmania drug resistance and likely new directions.

Combination therapy with tamoxifen and amphotericin B in experimental cutaneous leishmaniasis

Leishmaniasis chemotherapy remains very challenging. The high cost of active drugs, along with the severity of their side effects and the increasing failure rate of the current therapeutic schemes, calls for the discovery of new active drugs and schemes of treatment. The use of combination therapy has gained much attention in recent years as a possible strategy for overcoming the various shortcomings in the present arsenal. We recently described the effectiveness of tamoxifen in murine models of leishmaniasis, and here, we investigated the interactions between tamoxifen and amphotericin B, one of the most potent drugs used in leishmaniasis treatment. The in vitro interactions were indifferent for the association of tamoxifen and amphotericin B. The association was also assayed in vivo in Leishmania amazonensis-infected BALB/c mice and was found to yield at least additive effects at low doses of both drugs.

Elucidation of cellular mechanisms involved in experimental paromomycin resistance in Leishmania donovani

Leishmania donovani is the causative agent of the potentially fatal disease visceral leishmaniasis (VL). Chemotherapeutic options available to treat VL are limited and often face parasite resistance, inconsistent efficacy, and toxic side effects. Paromomycin (PMM) was recently introduced to treat VL as a monotherapy and in combination therapy. It is vital to understand the mechanisms of PMM resistance to safeguard the drug. In the present study, we utilized experimentally generated PMM-resistant L. donovani to elucidate the mechanisms of resistance and parasite biology. We found increased membrane fluidity accompanied by decreased intracellular drug accumulation in the PMM-resistant parasites. There were marked increases in gene expression of ATP-binding cassette (ABC) transporters (MDR1 and MRPA) and protein phosphatase 2A that evince increased drug efflux. Further, evaluation of parasite tolerance toward host leishmanicidal mechanisms revealed PMM-resistant parasites as being more tolerant to nitrosative stress at the promastigote and amastigote stages. The PMM-resistant parasites also predicted a better survival capacity, as indicated by resistance to complement-mediated lysis and increased stimulation of host interleukin-10 (IL-10) expression. The susceptibilities of PMM-resistant isolates to other antileishmanial agents (sodium antimony gluconate and miltefosine) remained unchanged. The data implicated the roles of altered membrane fluidity, decreased drug accumulation, increased expression of ABC transporters, and greater tolerance of parasites to host defense mechanisms in conferring PMM resistance in Leishmania.

In vitro synergistic effect of amphotericin B and allicin on Leishmania donovani and L. infantum

Current monotherapy against visceral leishmaniasis has serious side effects, and resistant Leishmania strains have been identified. Amphotericin B (AmB) has shown an extraordinary antileishmanial efficacy without emergence of resistance; however, toxicity has limited its general use. Results obtained showed, using a fixed-ratio analysis, that the combination of diallyl thiosulfinate (allicin) and AmB ranged from moderately synergic to synergic at low concentrations (0.07 μM AmB plus 35.45 μM allicin induced 95% growth inhibition). None of the treatments, alone or in combination, had noticeable adverse effects on macrophages (M) in the concentration range examined (allicin, 0.5, 1, 5 and 10 μM; AmB, 0.05, 0.075, and 0.1 μM). Allicin, AmB, or the combination did not affect the infection rate (percentage of infected M) of Leishmania. Allicin enhanced the activity of AmB on intracellular amastigotes of Leishmania donovani and L. infantum (ca. 45% reduction of amastigote burden with 0.05 μM AmB plus 10 μM allicin); this represented nearly a 2-fold reduction in the 50% inhibitory concentration (IC50) of the antibiotic added alone. Results point toward the possible utility of testing this combination in vivo to reduce the toxicity associated with monotherapy with AmB.

A new ABC half-transporter in Leishmania major is involved in resistance to antimony

The characterization of ABCI4, a new intracellular ATP-binding cassette (ABC) half-transporter in Leishmania major, is described. We show that ABCI4 is involved in heavy metal export, thereby conferring resistance to Pentostam, to Sb(III), and to As(III) and Cd(II). Parasites overexpressing ABCI4 showed a lower mitochondrial toxic effect of antimony by decreasing reactive oxygen species production and maintained higher values of both the mitochondrial electrochemical potential and total ATP levels with respect to controls. The ABCI4 half-transporter forms homodimers as determined by a coimmunoprecipitation assay. A combination of subcellular localization studies under a confocal microscope and a surface biotinylation assay using parasites expressing green fluorescent protein- and FLAG-tagged ABCI4 suggests that the transporter presents a dual localization in both mitochondria and the plasma membrane. Parasites overexpressing ABCI4 present an increased replication in mouse peritoneal macrophages. We have determined that porphyrins are substrates for ABCI4. Consequently, the overexpression of ABCI4 confers resistance to some toxic porphyrins, such as zinc-protoporphyrin, due to the lower accumulation resulting from a significant efflux, as determined using the fluorescent zinc-mesoporphyrin, a validated heme analog. In addition, ABCI4 has a significant ability to efflux thiol after Sb(III) incubation, thus meaning that ABCI4 could be considered to be a potential thiol-X-pump that is able to recognize metal-conjugated thiols. In summary, we have shown that this new ABC transporter is involved in drug sensitivity to antimony and other compounds by efflux as conjugated thiol complexes.

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.

Interest in paromomycin for the treatment of visceral leishmaniasis (kala-azar)

Leishmaniasis is an important vector-borne disease, and it is classified as one of the most important tropical fly-borne infections. This disease can cause two types of clinical manifestations: cutaneous forms and visceral forms. Visceral leishmaniasis, which is also called kala-azar, is a very serious infection that can be fatal. The management of visceral leishmaniasis requires informed diagnostic and therapeutic approaches. Continuous research and development regarding the treatment of visceral leishmaniasis had led to many improvements. Paromomycin is a relatively new antibiotic drug that has been used for the treatment of visceral leishmaniasis for several years. This article reviews and discusses the use of paromomycin for visceral leishmaniasis therapy.

Visceral leishmaniasis treatment: What do we have, what do we need and how to deliver it?

Leishmaniasis is one of the most neglected tropical disease in terms of drug discovery and development. Most antileishmanial drugs are highly toxic, present resistance issues or require hospitalization, being therefore not adequate to the field. Recently improvements have been achieved by combination therapy, reducing the time and cost of treatment. Nonetheless, new drugs are still urgently needed. In this review, we describe the current visceral leishmaniasis (VL) treatments and their limitations. We also discuss the new strategies in the drug discovery field including the development and implementation of high-throughput screening (HTS) assays and the joint efforts of international teams to deliver clinical candidates.

Leishmaniasis chemotherapy--challenges and opportunities

Although there have been significant advances in the treatment of visceral leishmaniasis (VL), there remain challenges to ensure that treatments effective in India are also effective in other regions of the world and to identify treatment for post kala-azar dermal leishmaniasis as well as the opportunity to develop a safe oral short-course treatment. At the same time, there have been few advances for the treatment of simple or complex forms of cutaneous leishmaniasis (CL), other than topical paromomycin formulations. The main challenge for CL is to ensure that this disease is on the research and development agenda, so that new drugs are evaluated or compounds are screened in appropriate models, and that the standardization of quality of clinical trials is guaranteed. Problems also remain in the treatment of HIV/leishmaniasis co-infected patients. We are some way from having the ideal treatments for VL and CL and drug research and development for these diseases must remain focused.

Inhibitory effects of decavanadate on several enzymes and Leishmania tarentolae in vitro

Multiple studies report apparent effects of vanadium on various systems in vivo and in vitro. Vanadium species may be possible deterrents for the growth of the Leishmania parasite, which causes the sometimes deadly diseases known as leishmaniasis. The current studies focus specifically on decavanadate V(10)O(28)(6-) (V10), which has a potential to be a potent effector for disease treatment. The X-ray structure of a new solvate salt of V10, namely (NH(4))(6)V(10)O(28)·5H(2)O, is also reported. Other vanadium complexes with imidazole carboxylate, anthranilate, or picolinate were also evaluated. The yellow-orange oxoanion, used as the (NH(4))(6)V(10)O(28)·6H(2)O salt, was tested (at 1-100 μM) directly with two strains of Leishmania tarentolae promastigotes in culture to evaluate the effect on cell viability. Vanadium coordination complexes are known effective inhibitors of phosphatases. Using the artificial phosphatase substrate para-nitrophenylphosphate in the presence of a bovine calf intestine alkaline phosphatase enzyme, V10 (from 5 to 100 μM) was shown to be a mixed inhibitor for this enzyme and decreased the activity of the other two phosphatases tested. The effect of V10 and the other vanadium complexes on the activity of phosphoglycerate mutase B (PGAM), an important enzyme in glycolysis and gluconeogenesis, was also evaluated. At 10 μM, V10 was the most potent inhibitor of PGAM, with an apparent reduction of about 50%. Taken together, we speculate that V10 could have a role in treating Leishmania diseases.

Leishmaniasis: new insights from an old and neglected disease

Leishmaniases are a clinically heterogeneous group of diseases caused by protozoa of the genus Leishmania. There is growing evidence that the true incidence of the disease is underestimated, especially in hyperendemic regions. Moreover, climate changes together with the increasing movement of humans and animals raise concerns about the possible introduction of Leishmania infection in previously spared areas. The disease is emerging in immunocompromised patients undergoing bone marrow or solid organ transplantation or treatment with biologic drugs. Furthermore, the deployment of military troops and travel to endemic areas are associated with the observation of a growing number of patients with cutaneous disease. Improvement in diagnostic methods, both in the field and in specialized laboratories, has been obtained through the implementation of molecular amplification methods and using the rK39 antigen as the substrate. Finally, new therapeutic approaches are gaining attention, such as the use of miltefosine for cutaneous leishmaniasis and paromomycin for visceral leishmaniasis, as well as the use of various antileishmanial drugs in combination.

Therapy with sodium stibogluconate in stearylamine-bearing liposomes confers cure against SSG-resistant Leishmania donovani in BALB/c mice

Background

Resistance of Leishmania donovani to pentavalent antimonials, the first-line treatment of visceral leishmaniasis (VL), has become a critical issue worldwide. Second-line and new drugs are also not devoid of limitations. Suitable drug-delivery systems can improve the mode of administration and action of the existing antimonials, thus increasing their clinical life.

Methodology/Principal Findings

We investigated the efficacy of sodium stibogluconate (SSG) in phosphatidylcholine (PC)–stearylamine-bearing liposomes (PC-SA-SSG), PC-cholesterol liposomes (PC-Chol-SSG) and free amphotericin B (AmB) against SSG-resistant L. donovani strains in 8-wk infected BALB/c mice. Animals were sacrificed and parasites in liver, spleen and bone marrow were estimated 4-wk post-treatment by microscopic examination of stamp smears and limiting dilution assay. A set of PC-SA-SSG and AmB treated mice were further studied for protection against reinfection. Serum antibodies and cytokine profiles of ex-vivo cultured splenocytes were determined by ELISA. Uptake of free and liposomal SSG in intracellular amastigotes was determined by atomic absorption spectroscopy. Rhodamine 123 and 5-carboxyfluorescein, known substrates of Pgp and MRP transporter proteins, respectively, were used in free and liposomal forms for efflux studies to estimate intracellular drug retention. Unlike free and PC-Chol-SSG, PC-SA-SSG was effective in curing mice infected with two differentially originated SSG-unresponsive parasite strains at significantly higher levels than AmB. Successful therapy correlated with complete suppression of disease-promoting IL-10 and TGF-β, upregulation of Th1 cytokines and expression of macrophage microbicidal NO. Cure due to elevated accumulation of SSG in intracellular parasites, irrespective of SSG-resistance, occurs as a result of increased drug retention and improved therapy when administered as PC-SA-SSG versus free SSG.

Conclusions/Significance

The design of this single-dose combination therapy with PC-SA-SSG for VL, having reduced toxicity and long-term efficacy, irrespective of SSG-sensitivity may prove promising, not only to overcome SSG-resistance in Leishmania, but also for drugs with similar resistance-related problems in other diseases.