Optimization of topical therapy for Leishmania major localized cutaneous leishmaniasis using a reliable C57BL/6 Model

Comparison of Bioluminescent Substrates in Natural Infection Models of Neglected Parasitic Diseases

The application of in vivo bioluminescent imaging in infectious disease research has significantly increased over the past years. The detection of transgenic parasites expressing wildtype firefly luciferase is however hampered by a relatively low and heterogeneous tissue penetrating capacity of emitted light. Solutions are sought by using codon-optimized red-shifted luciferases that yield higher expression levels and produce relatively more red or near-infrared light, or by using modified bioluminescent substrates with enhanced cell permeability and improved luminogenic or pharmacokinetic properties. In this study, the in vitro and in vivo efficacy of two modified bioluminescent substrates, CycLuc1 and AkaLumine-HCl, were compared with that of D-luciferin as a gold standard. Comparisons were made in experimental and insect-transmitted animal models of leishmaniasis (caused by intracellular Leishmania species) and African trypanosomiasis (caused by extracellular Trypanosoma species), using parasite strains expressing the red-shifted firefly luciferase PpyRE9. Although the luminogenic properties of AkaLumine-HCl and D-luciferin for in vitro parasite detection were comparable at equal substrate concentrations, AkaLumine-HCl proved to be unsuitable for in vivo infection follow-up due to high background signals in the liver. CycLuc1 presented a higher in vitro luminescence compared to the other substrates and proved to be highly efficacious in vivo, even at a 20-fold lower dose than D-luciferin. This efficacy was consistent across infections with the herein included intracellular and extracellular parasitic organisms. It can be concluded that CycLuc1 is an excellent and broadly applicable alternative for D-luciferin, requiring significantly lower doses for in vivo bioluminescent imaging in rodent models of leishmaniasis and African trypanosomiasis.

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.

An Antiparasitic Compound from the Medicines for Malaria Venture Pathogen Box Promotes Leishmania Tubulin Polymerization

The few frontline antileishmanial drugs are poorly effective and toxic. To search for new drugs for this neglected tropical disease, we tested the activity of compounds in the Medicines for Malaria Venture (MMV) "Pathogen Box" against Leishmania amazonensis axenic amastigotes. Screening yielded six discovery antileishmanial compounds with EC50 values from 50 to 480 nM. Concentration-response assays demonstrated that the best hit, MMV676477, had mid-nanomolar cytocidal potency against intracellular Leishmania amastigotes, Trypanosoma brucei, and Plasmodium falciparum, suggesting broad antiparasitic activity. We explored structure-activity relationships (SAR) within a small group of MMV676477 analogs and observed a wide potency range (20-5000 nM) against axenic Leishmania amastigotes. Compared to MMV676477, our most potent analog, SW41, had ∼5-fold improved antileishmanial potency. Multiple lines of evidence suggest that MMV676477 selectively disrupts Leishmania tubulin dynamics. Morphological studies indicated that MMV676477 and analogs affected L. amazonensis during cell division. Differential centrifugation showed that MMV676477 promoted partitioning of cellular tubulin toward the polymeric form in parasites. Turbidity assays with purified Leishmania and porcine tubulin demonstrated that MMV676477 promoted leishmanial tubulin polymerization in a concentration-dependent manner. Analogs' antiparasitic activity correlated with their ability to facilitate purified Leishmania tubulin polymerization. Chemical cross-linking demonstrated binding of the MMV676477 scaffold to purified Leishmania tubulin, and competition studies established a correlation between binding and antileishmanial activity. Our studies demonstrate that MMV676477 is a potent antiparasitic compound that preferentially promotes Leishmania microtubule polymerization. Due to its selectivity for and broad-spectrum activity against multiple parasites, this scaffold shows promise for antiparasitic drug development.

In Vivo Bioluminescent Monitoring of Parasites in BALB/c Mouse Models of Cutaneous Leishmaniasis Drug Discovery

Confirming the in vivo efficacy of potential antileishmanial compounds that display in vitro potency and good chemical characteristics is one of the most important steps in preclinical research drug discovery before human clinical trials begin. Here we describe the use of the in vivo bioluminescent monitoring of high and low inocula of luciferase-expressing Leishmania major (L. major) parasites in traditional and more innovative rodent models of in vivo cutaneous leishmaniasis (CL) drug discovery.

Novel benzoxaborole, nitroimidazole and aminopyrazoles with activity against experimental cutaneous leishmaniasis

OBJECTIVES

Drugs for Neglected Diseases initiative (DNDi) has identified three chemical lead series, the nitroimidazoles, benzoxaboroles and aminopyrazoles, as innovative treatments for visceral leishmaniasis. The leads discovered using phenotypic screening, were optimised following disease- and compound-specific criteria. Several leads of each series were progressed and preclinical drug candidates have been nominated. Here we evaluate the efficacy of the lead compounds of each of these three chemical classes in in vitro and in vivo models of cutaneous leishmaniasis.

METHODS

The in vitro activity of fifty-five compounds was evaluated against the intracellular amastigotes of L. major, L. aethiopica, L. amazonensis, L. panamensis, L. mexicana and L. tropica. The drugs demonstrating potent activity (EC50 < 5 μM) against at least 4 of 6 species were subsequently evaluated in vivo in different L. major - BALB/c mouse models using a 5 or 10-day treatment with either the oral or topical formulations. Efficacy was expressed as lesion size (measured daily using callipers), parasite load (by quantitative PCR - DNA) and bioluminescence signal reduction relative to the untreated controls.

RESULTS

The selected drug compounds (3 nitroimidazoles, 1 benzoxaborole and 3 aminopyrazoles) showed consistent and potent activity across a range of Leishmania species that are known to cause CL with EC50 values ranging from 0.29 to 18.3 μM. In all cases, this potent in vitro antileishmanial activity translated into high levels of efficacy with a linear dose-response against murine CL. When administered at 50 mg/kg/day, DNDI-0690 (nitroimidazole), DNDI-1047 (aminopyrazole) and DNDI-6148 (benzoxaborole) all resulted in a significant lesion size reduction (no visible nodule) and an approximate 2-log-fold reduction of the parasite load as measured by qPCR compared to the untreated control.

CONCLUSIONS

The lead compounds DNDI-0690, DNDI-1047 and DNDI-6148 showed excellent activity across a range of Leishmania species in vitro and against L. major in mice. These compounds offer novel potential drugs for the treatment of CL.

Development of a topical liposomal formulation of Amphotericin B for the treatment of cutaneous leishmaniasis

BACKGROUND

Currently, there is no topical treatment available for any form of cutaneous leishmaniasis (CL) in most of the endemic areas. The aim of the current study was to develop a topical nano-liposomal Amphotericin B (AmB) for the treatment of CL.

METHODOLOGY/PRINCIPAL FINDINGS

Liposomes containing 0.1, 0.2 and 0.4% AmB (Lip-AmB) were formulated and characterized for the size, entrapment efficiency, long term stability, and skin penetration properties using Franz diffusion cells. Liposomes diameters were around 100 nm with no change during more than 20 months' storage either at 4 °C or at room temperature. Franz diffusion cells studies showed that almost 4% of the applied formulations penetrated across the skin and the highest skin retention (73.92%) observed with Lip-AmB 0.4%. The median effective doses (ED₅₀), the doses of AmB required to kill 50% of L. major amastigotes were 0.151, 0.151, and 0.0856 (μg/mL) in Lip-AmB 0.1, 0.2, 0.4%, respectively. Lip-AmB 0.4% caused 80% reduction in fluorescence intensity of GFP+ L. tropica infected macrophages at 5 μg/mL of AmB concentration. Topical Lip-AmB was applied twice a day for 4 weeks to the skin of BALB/c mice to treat lesions caused by L. major. Results showed the superiority of Lip-AmB 0.4% compared to Lip-AmB 0.2 and 0.1%. The parasite was completely cleared from the skin site of infection and spleens at week 8 and 12 post-infection in mice treated with Lip-AmB 0.4%. The results suggest that topical Lip-AmB 0.4% may be a useful tool in the treatment of CL and merits further investigation.

Route map for the discovery and pre-clinical development of new drugs and treatments for cutaneous leishmaniasis

Although there have been significant advances in the treatment of visceral leishmaniasis (VL) and several novel compounds are currently in pre-clinical and clinical development for this manifestation of leishmaniasis, there have been limited advances in drug research and development (R & D) for cutaneous leishmaniasis (CL). Here we review the need for new treatments for CL, describe in vitro and in vivo assays, models and approaches taken over the past decade to establish a pathway for the discovery, and pre-clinical development of new drugs for CL. These recent advances include novel mouse models of infection using bioluminescent Leishmania, the introduction of PK/PD approaches to skin infection, and defined pre-clinical candidate profiles.

Walking a tightrope: drug discovery in visceral leishmaniasis

The current commitment of the pharma industry, nongovernmental organizations and academia to find better treatments against neglected tropical diseases should end decades of challenge caused by these global scourges. The initial result of these efforts has been the introduction of enhanced combinations of drugs, currently in clinical use, or formulations thereof. Phenotypic screening based on intracellular parasite infections has been revealed as the first key tool of antileishmanial drug discovery, because most first-in-class drugs entering Phase I trials were discovered this way. The professional commitment among stakeholders has enabled the availability of a plethora of new chemical entities that fit the target product profile for these diseases. However, the rate of hit discovery in leishmaniasis is far behind that for other neglected diseases. This review defends the need to develop new screening methods that consider the part played not only by intracellular parasites but also by the host's immune system to generate disease-relevant assays and improve clinical outcomes.

Anilinoquinoline based inhibitors of trypanosomatid proliferation

We recently reported the medicinal chemistry re-optimization of a series of compounds derived from the human tyrosine kinase inhibitor, lapatinib, for activity against Plasmodium falciparum. From this same library of compounds, we now report potent compounds against Trypanosoma brucei brucei (which causes human African trypanosomiasis), T. cruzi (the pathogen that causes Chagas disease), and Leishmania spp. (which cause leishmaniasis). In addition, sub-micromolar compounds were identified that inhibit proliferation of the parasites that cause African animal trypanosomiasis, T. congolense and T. vivax. We have found that this set of compounds display acceptable physicochemical properties and represent progress towards identification of lead compounds to combat several neglected tropical diseases.

As part of our efforts to identify compounds that are active against the parasite that causes malaria (P. falciparum), we employed a “parasite hopping” approach in our drug discovery efforts. This involved screening a library of demonstrated antiparasitic agents against other parasites responsible for a host of neglected tropical diseases (NTDs) including Chagas disease (T. cruzi), human African trypanosomiasis (T. brucei) and cutaneous leishmaniasis (L. major). The compounds we identified generally show improved selectivity for the parasite of interest over the mammalian cell lines tested and, from this work, we have made progress towards the identification of lead compounds against multiple NTDs.

Series of Alkynyl-Substituted Thienopyrimidines as Inhibitors of Protozoan Parasite Proliferation

Discovery of new chemotherapeutic lead agents can be accelerated by optimizing chemotypes proven to be effective in other diseases to act against parasites. One such medicinal chemistry campaign has focused on optimizing the anilinoquinazoline drug lapatinib (1) and the alkynyl thieno[3,2-d]pyrimidine hit GW837016X (NEU-391, 3) into leads for antitrypanosome drugs. We now report the structure-activity relationship studies of 3 and its analogs against Trypanosoma brucei, which causes human African trypanosomiasis (HAT). The series was also tested against Trypanosoma cruzi, Leishmania major, and Plasmodium falciparum. In each case, potent antiparasitic hits with acceptable toxicity margins over mammalian HepG2 and NIH3T3 cell lines were identified. In a mouse model of HAT, 3 extended life of treated mice by 50%, compared to untreated controls. At the cellular level, 3 inhibited mitosis and cytokinesis in T. brucei. Thus, the alkynylthieno[3,2-d]pyrimidine chemotype is an advanced hit worthy of further optimization as a potential chemotherapeutic agent for HAT.

A phase II study to evaluate the safety and efficacy of topical 3% amphotericin B cream (Anfoleish) for the treatment of uncomplicated cutaneous leishmaniasis in Colombia

BACKGROUND

Pentavalent antimonials (Sb5) are the first-line drugs for treating cutaneous leishmaniasis in Colombia; however, given problems with toxicity, compliance, availability, and cost, it is imperative to look for better therapeutic options. Intravenous amphotericin B (AmB) has been used extensively to treat visceral leishmaniasis; however, evidence on its topical use for cutaneous leishmaniasis is limited. Anfoleish is a topical formulation based on 3% AmB, which was developed following GMP standards by HUMAX and PECET. Anfoleish was shown to be safe and efficacious in animal model and in an open label study in CL patients. Hereafter we show the results of the first controlled and randomized study assessing the safety and efficacy of Anfoleish administered topically, two or three times per day for 28 days, for the treatment of non-complicated cutaneous leishmaniasis in Colombia.

METHODS

An open-label, randomized, non-comparative phase Ib/II clinical trial was performed. Adult volunteers with a parasitologically confirmed diagnosis of cutaneous leishmaniasis were randomly allocated to receive Anfoleish cream either 3 (TID group) or 2 (BID group) times per day for 4 weeks.

RESULTS

80 out of 105 subjects screened were included in the study. In intention to treat analysis, final cure was observed in 13 (32.5%) out of 40 subjects (IC 95% = 20.1-48) and in 12 (30%) out of 40 subjects (IC 95% = 18.1-45.5) in the BID and TID group respectively. In the per protocol analysis, cure rates were 39.4% (n = 13) (IC 95% = 24.7-56.3) and 35.3% (n = 12) (IC 95% = 21.5-52.1) in the BID and TID groups respectively. Anfoleish proved to be safe, and the few adverse events reported were local, around the area of application of the cream, and of mild intensity.

CONCLUSION

Anfoleish showed to be a safe and well-tolerated intervention. Its efficacy results however do not support at this time continuing with its clinical development or recommending it for the treatment of CL. Additional, studies to improve its current formulation are needed before thinking in conducting additional studies in patients.

TRIAL REGISTRATION

Registered in clinicaltrials.gov NCT01845727.

Use of In Vivo Imaging System Technology in Leishmania major BALB/c Mouse Ear Infection Studies

Novel treatments for cutaneous leishmaniasis (CL) are needed, due to current lack of effective universal treatments, increasing resistance among the parasite, and toxic effects or impracticality of the current therapeutics. Models of direct infection with high number of Leishmania parasites in the current research of CL involving the BALB/c mouse or Golden Syrian Hamster are considered not suitable for the assessment of antileishmanial drug efficacy because of the lack of disease similarities with humans. The saliva of the sand fly vector is known to affect the host response to infection by the Leishmania parasite. Here, we build upon a previous BALB/c model infected with luciferase-expressing Leishmania major parasites. In the present study, we infect the ear dermis instead of the foot pad or base of the tail, and compare multiple methods of infection, using parasites alone or mixed with either bites from uninfected sand flies (Phlebotomus duboscqi Diptera Psychodidae:Neveu-Lemaire) or salivary gland sonicate from sand flies. Our data show a dose-response of bioluminescent signal (which represents the parasite load at the infection site), dermal lesion development, and Leishmania Donovan Units in liver and spleen. This in vivo L. major ear infection model, once optimized, can be used for assessing the efficacy of drug compounds that have been determined as very effective in the other, high inoculum CL models.

Use of Optical Imaging Technology in the Validation of a New, Rapid, Cost-Effective Drug Screen as Part of a Tiered In Vivo Screening Paradigm for Development of Drugs To Treat Cutaneous Leishmaniasis

In any drug discovery and development effort, a reduction in the time of the lead optimization cycle is critical to decrease the time to license and reduce costs. In addition, ethical guidelines call for the more ethical use of animals to minimize the number of animals used and decrease their suffering. Therefore, any effort to develop drugs to treat cutaneous leishmaniasis requires multiple tiers of in vivo testing that start with higher-throughput efficacy assessments and progress to lower-throughput models with the most clinical relevance. Here, we describe the validation of a high-throughput, first-tier, noninvasive model of lesion suppression that uses an in vivo optical imaging technology for the initial screening of compounds. A strong correlation between luciferase activity and the parasite load at up to 18 days postinfection was found. This correlation allows the direct assessment of the effects of drug treatment on parasite burden. We demonstrate that there is a strong correlation between drug efficacy measured on day 18 postinfection and the suppression of lesion size by day 60 postinfection, which allows us to reach an accurate conclusion on drug efficacy in only 18 days. Compounds demonstrating a significant reduction in the bioluminescence signal compared to that in control animals can be tested in lower-throughput, more definitive tests of lesion cure in BALB/c mice and Golden Syrian hamsters (GSH) using Old World and New World parasites.

Experimental infection of Phlebotomus perniciosus by bioluminescent Leishmania infantum using murine model and artificial feeder

Leishmaniasis is a vector-borne disease that is transmitted by sandflies and caused by obligate intracellular protozoa of the genus Leishmania. In the present study, we carried out a screening on the experimental infection of Phlebotomus pernioucus by bioluminescent Leishmania infantum using murine model and artificial feeder. We developed a real-time polymerase chain reaction (RT-PCR)-based method to determine individually the number of Leishmania promastigotes fed by infected flies. Among 1840 new emerged female sand flies, 428 were fed on the infected mice. After their death, they were analysed individually by RT-PCR. Our results demonstrated just a single Leishmania positive female at sixth day post meal. A total of 1070 female sand flies were exposed in contact with artificial feeder containing the human blood with two different quantities of Leishmania parasites: 2.10⁶/mL and 1.10⁷/mL. A blood meal including 1.10⁷/mL LUC-promastigotes was proposed to 270 females and 75 (28%) flies were engorged. Among them, 44 (59%) were positive by RT-PCR analysis, with a relative average of 50551 Leishmania parasites. In case of blood feeding of females with 2.10⁶/mL promastigotes, 57 out of 800 (7%) females succeed to feed from artificial feeder which 22 (39%) were positive with a relative average of 6487 parasites.

Conditional gene deletion with DiCre demonstrates an essential role for CRK3 in Leishmania mexicana cell cycle regulation

Leishmania mexicana has a large family of cyclin‐dependent kinases (CDKs) that reflect the complex interplay between cell cycle and life cycle progression. Evidence from previous studies indicated that Cdc2‐related kinase 3 (CRK3) in complex with the cyclin CYC6 is a functional homologue of the major cell cycle regulator CDK1, yet definitive genetic evidence for an essential role in parasite proliferation is lacking. To address this, we have implemented an inducible gene deletion system based on a dimerised Cre recombinase (diCre) to target CRK3 and elucidate its role in the cell cycle of L. mexicana. Induction of diCre activity in promastigotes with rapamycin resulted in efficient deletion of floxed CRK3, resulting in G2/M growth arrest. Co‐expression of a CRK3 transgene during rapamycin‐induced deletion of CRK3 resulted in complementation of growth, whereas expression of an active site CRK3^T178E mutant did not, showing that protein kinase activity is crucial for CRK3 function. Inducible deletion of CRK3 in stationary phase promastigotes resulted in attenuated growth in mice, thereby confirming CRK3 as a useful therapeutic target and diCre as a valuable new tool for analyzing essential genes in Leishmania.

Antileishmanial Activity of Compounds Derived from the Medicines for Malaria Venture Open Access Box Against Intracellular Leishmania major Amastigotes

Leishmaniasis is a complex tropical disease caused by kinetoplastid parasitic protozoa of the genus Leishmania and is transmitted by the sand fly insect vector. Cutaneous leishmaniasis (CL) is the most common form of this disease, and CL infections often result in serious skin lesions and scars. CL remains a public health problem in many endemic countries worldwide because of the absence of effective, safe, and cost-effective drugs for treatment. One of the strategies we chose to use to find novel chemical entities worthy of further development as antileishmanials involved screening synthetic and natural products libraries. In our study, we developed a Leishmania major intracellular amastigote assay that uses the activity of luciferase as a measure of parasite proliferation and used this assay to screen a collection of 400 compounds obtained from Medicines for Malaria Venture (MMV) for their antileishmanial activity. Our results showed that 14 compounds identified by MMV as antimalarial drugs have antileishmanial activity and can potentially be optimized for CL drug development.

Generation of stable L. major(+EGFP-LUC) and simultaneous comparison between EGFP and luciferase sensitivity

Because of the lack of an accurate and sensitive tool to evaluate the parasitemia level, treatment or prevention of leishmaniasis remains an important challenge worldwide. To monitor and track leishmanial infection by two parameters in real time, we generated stably transgenic Leishmania that express a bi-reporter protein as fused EGFP and firefly luciferase. Using two reporter genes (egfp-luc) simultaneously increases the experimental sensitivity for detection/diagnosis, and in vitro quantification of parasites as well as real-time infection in mice. Through different specific tools, EGFP and LUC signals from the parasite were detectable and measurable within a mammalian host and promastigotes. Here, the LUC protein provided a higher level of sensitivity than did EGFP, so that infection was detectable at an earlier stage of the disease in the footpad (injection site) and lymph nodes by bioluminescence. These results depicted that: (1) both quantitative reporter genes, EGFP and LUC, could be simultaneously used to detect parasitemia in vitro and in vivo and (2) sensitivity of firefly luciferase was 10-fold higher than that of EGFP in promastigotes.

Simultaneous multi-parametric analysis of Leishmania and of its hosting mammal cells: A high content imaging-based method enabling sound drug discovery process

Leishmaniasis is a vector-borne disease for which only limited therapeutic options are available. The disease is ranked among the six most important tropical infectious diseases and represents the second-largest parasitic killer in the world. The development of new therapies has been hampered by the lack of technologies and methodologies that can be integrated into the complex physiological environment of a cell or organism and adapted to suitable in vitro and in vivo Leishmania models. Recent advances in microscopy imaging offer the possibility to assess the efficacy of potential drug candidates against Leishmania within host cells. This technology allows the simultaneous visualization of relevant phenotypes in parasite and host cells and the quantification of a variety of cellular events. In this review, we present the powerful cellular imaging methodologies that have been developed for drug screening in a biologically relevant context, addressing both high-content and high-throughput needs. Furthermore, we discuss the potential of intra-vital microscopy imaging in the context of the anti-leishmanial drug discovery process.

Trypanosomatids see the light: recent advances in bioimaging research

The use of genetically engineered pathogens that express fluorescent or luminescent proteins represents a huge stride forward in the understanding of trypanosomatid-borne tropical diseases. Nowadays, such modified microorganisms are being used to screen thousands of compounds under a target-free (phenotypic) approach. In addition, experimental infections with transgenic parasites drastically reduce the number of animals required for preclinical studies, because no animal needs to be put down to assess its parasite load. Finally, the use of fluorescent parasites is contributing to unraveling genetic exchange events between trypanosomatid strains. This phenomenon is important for understanding the mechanism by which traits such as virulence, tissue tropism, and drug resistance are transferred, as well as the emergence of novel strains.

Imaging host-Leishmania interactions: significance in visceral leishmaniasis

Leishmaniasis is a neglected disease that is associated with a spectrum of clinical manifestations ranging from self-healing cutaneous lesions to fatal visceral infections, which primarily depends on the parasite species. In visceral leishmaniasis (VL), as opposed to cutaneous leishmaniasis (CL), parasites that infect host cells at the sand fly bite site have the striking ability to disseminate to visceral organs where they proliferate and persist for long periods of time. Imaging the dynamics of the host-Leishmania interaction in VL provides a powerful approach to understanding the mechanisms underlying host cell invasion, Leishmania dissemination and persistence within visceral organs and, to dissecting the immune responses to infection. Therefore, by allowing the visualization of the critical steps involved in the pathogenesis of VL, state-of-the-art microscopy technologies have the great potential to aid in the identification of better intervention strategies for this devastating disease. In this review, we emphasize the current knowledge and the potential significance of imaging technologies in understanding the infection process of visceralizing Leishmania species. Then, we discuss how application of innovative microscopy technologies to the study of VL will provide rich opportunities for investigating host-parasite interactions at a previously unexplored level and elucidating visceral disease-promoting mechanisms.

Nanoparticles as multifunctional devices for the topical treatment of cutaneous leishmaniasis

INTRODUCTION

Cutaneous and mucocutaneous leishmaniasis are major tropical skin diseases. Topical treatment is currently limited to the least severe forms of cutaneous leishmaniasis (CL) without risk of dissemination. It is also recommended in combination with systemic therapy for more severe forms. Progresses in this modality of treatment are hindered by the heterogeneity of the disease and shortcomings in the clinical trials.

AREAS COVERED

This review overlooks three major modalities of topical therapies in use or under investigation against CL: chemotherapy, photodynamic therapy and immunotherapy; either with older compounds such as paramomycin or more recent nitric oxide donors, antimicrobial peptides or silver derivatives. The advantages and limitations of their administration with newer formulation strategies such as nanoparticles (NPs) are discussed.

EXPERT OPINION

The efficacy of a topical treatment against CL depends not only on the intrinsic antileishmanial activity of the drug but also on the amount of drug available in the dermis. NPs as sustained release systems and permeation enhancers could favour the creation of a drug reservoir in the dermis. Additionally, certain NPs have immunomodulatory properties or wound healing capabilities of benefit in CL treatment. Pending task is the selective delivery of active compounds to intracellular amastigotes, because even small NPs are unable to penetrate deeply into the skin to encounter infected macrophages (except in ulcerative lesions).

A novel function for kojic acid, a secondary metabolite from Aspergillus fungi, as antileishmanial agent

Kojic acid (KA) is a fungal metabolite used as a topical treatment skin-whitening cosmetic agent for melasma in humans; however its potential as an anti-leishmanial agent is unknown. Chemotherapy is one of the most effective treatments for Leishmaniasis. However, the drugs available are expensive, invasive, require long-term treatment and have severe side effects. Thus, the development of new effective leishmanicidal agents is a necessity. In this study we investigated the anti-leishmanial effect of KA on L. amazonensis, following in vitro and in vivo infections. KA (50 μg/mL) was found to decrease the growth by 62% (IC₅₀ 34 μg/mL) and 79% (IC₅₀ 27.84 μg/mL) of promastigotes and amastigotes in vitro, respectively. Ultrastructural analysis of KA-treated amastigotes showed the presence of vesicles bodies into the flagellar pocket, and an intense intracellular vacuolization and swelling of the mitochondrion. During the in vitro interaction of parasites and the host cell, KA reverses the superoxide anions (O₂^-) inhibitory mechanism promoted by parasite. In addition, 4 weeks after KA-topical formulation treatment of infected animals, a healing process was observed with a high production of collagen fibers and a decrease in parasite burden. Thus, these results demonstrated the great potential of KA as an anti-leishmanial compound.

[Leishmania epidemiology, diagnosis, chemotherapy and vaccination approaches in the international network of Pasteur Institutes]

Protozoan parasites of the genus Leishmania generate severe human diseases termed leishmaniases. Due to their frequency and the severity of certain clinical forms, these diseases represent a major public health problem and limit the economic growth in various developing countries. The presence of Pasteur Institutes in countries with endemic leishmaniasis has provided important incentives to develop a strong public health agenda in the Pasteur scientific community with respect to this important disease. A concerted effort is now coordinated through the recently created LeishRIIP platform (www.leishriip.org), which aims to identify synergies and complementary expertise between the eleven members of the international network of Pasteur Institutes working on various aspects of the disease including epidemiology, diagnosis, chemotherapy and vaccination.

A combined luciferase-expressing Leishmania imaging/RT-qPCR assay provides new insights into the sequential bilateral processes deployed in the ear pinna of C57BL/6 mice

Leishmania/L. major was identified as the etiological agent of human localized cutaneous leishmaniasis. L. major metacyclic promastigotes/MP - the infectious form transmitted by sand flies - were enriched from axenically-derived cultures and inoculated into the dermis of mice (10(3) or 10(4) luciferase-expressing L. major MP inoculated into the C57BL/6 mouse ear pinna). Quantitative readout assays were then combined with imaging of this L. major-hosting skin site and established i) that a specific period of time - depending upon the L. major load used for the inoculation - is required for the L. major-hosting ear pinna to be continuously populated by a balanced population of functional regulatory and effector T lymphocytes, and that ii) this balance coincides with persisting low numbers of amastigotes in more or less rapidly healing skin. This approach also established that, whatever the MP inoculum load delivered to the primary site, the immune processes that reduce the L. major amastigote population also account for concomitant immunity, namely remodelling of the secondary site - where 10(4) MP were delivered - as a clinically silent niche hosting a small L. major population.

Dressings combined with injection of meglumine antimoniate in the treatment of cutaneous leishmaniasis: a randomized controlled clinical trial

BACKGROUND

Cutaneous leishmaniasis (CL) is a neglected infectious disease and a major health problem in several developing countries. Despite some reasonable explanation for their potential benefits, there is only trace evidence regarding the role of dressings in the treatment of CL.

METHODS

This randomized, assessor-blind, controlled, clinical trial was conducted in an endemic area for CL caused by Leishmania major in Iran to assess the efficacy of administration of weekly intralesional meglumine antimoniate (i.l.MA) either alone or combined with application of a silver or a non-silver polyester dressing on their lesions for 6 weeks. After screening of 241 patients with CL lesions, 83 eligible patients with 158 lesions were randomly allocated in three arms of the study. Eligibility criteria included parasitologically confirmed CL, age of 12 to 60 years; willingness to participate, duration of lesion<3 months, number of lesions<5, largest ulcer diameter<5 cm. Pregnant or lactating women were excluded. The primary outcome was absolute risk reduction (ARR) based on the proportion of complete healing, which was defined as more than 75% reduction in the size of the lesion compared with baseline in each group at the termination of treatment and 1 month later.

FINDINGS

ARR (95% Confidence Interval [CI]) in i.l.MA versus i.l.MA+non-silver dressing groups was 5.98% (-7.07% to 20.25%), between i.l.MA versus i.l.MA+silver dressing groups was -0.23% (-13.53% to 14.82%), and between i.l.MA+non-silver dressing versus i.l.MA+silver dressing groups was -6.21%(-18.28% to 6.52%) after 6 weeks of treatment. ARR (95% CI) in i.l.MA versus i.l.MA+non-silver dressing groups was -2.22% (-22.12% to 18.10%), between i.l.MA versus i.l.MA+silver dressing groups was 3.64% (-15.36% to 22.82%), and between i.l.MA+non-silver dressing versus i.l.MA+silver dressing groups was 5.86% (-12.86% to 24.31%) 1 month later.

CONCLUSION

It could not be demonstrated that the efficacy of i.l.MA was improved by either dressing.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials (IRCT.ir) IRCT138707201166N2.

Parasite burden in Leishmania (Leishmania) amazonensis-infected mice: validation of luciferase as a quantitative tool

Given the lack of effective and safe alternatives to the drugs already in use, considerable efforts are being applied to the search of new therapeutic options to treat leishmaniasis. A necessary step in the discovery of antileishmanial drugs is the validation of drug candidates in mouse models. The standard methods to quantify the parasite burden in animal models, mainly culture-based, are time consuming and expensive. In recent years, in vivo imaging systems have been proposed as a tool to overcome these problems, allowing parasite detection in living organisms. Here we compared different treatment efficacy evaluation approaches. Recombinant Leishmania (L.) amazonensis lines expressing the luciferase gene (La-LUC) were obtained and characterized for biological properties as compared with the wild type (WT) parental line. Bioluminescence generated by La-LUC was shown to correlate with the number of promastigotes in vitro. La-LUC promastigotes and intracellular amastigotes were equally sensitive to amphotericin B (AmB) as the WT parasites. The clinical pattern of lesion development upon infection with the transgenic lines was similar to lesions observed after infection with the WT strain. The half maximal effective dose (ED50) of AmB was determined in La-LUC infected mice through quantification of bioluminescence in vivo and ex vivo, by limiting dilution and using clinical parameters. There was agreement in the ED50 determined by all methods. Quantification of bioluminescence in vivo and/or ex vivo was elected as the best tool for determining parasite burden to assess drug efficacy in infected mice. Furthermore, the detailed analysis of AmB effectiveness in this model generated useful data to be used in drug combination experiments.

Non-invasive in vivo study of the Trypanosoma vivax infectious process consolidates the brain commitment in late infections

Trypanosoma vivax, one of the leading parasites responsible for Animal African Trypanosomosis (Nagana), is generally cyclically transmitted by Glossina spp. but in areas devoid of the tsetse flies in Africa or in Latin American countries is mechanically transmitted across vertebrate hosts by other haematophagous insects, including tabanids. We followed on from our recent studies on the maintenance of this parasite in vivo and in vitro, and its genetic manipulation, by constructing a West African IL1392 T. vivax strain that stably expresses firefly luciferase and is fully virulent for immunocompetent mice. We report here on a study where murine infection with this strain was monitored in vivo using a non-invasive method. Study findings fully support the use of this strain in the assessment of parasite dynamics in vivo since a strong correlation was found between whole body light emission measured over the course of the infection and parasitemia determined microscopically. In addition, parasitemia and survival rates were very similar for mice infected by the intraperitoneal and sub-cutaneous routes, except for a longer prepatent period following sub-cutaneous inoculation with the parasite. Our results clearly show that when administered by the subcutaneous route, the parasite is retained few days in the skin close to the inoculation site where it multiplies before passing into the bloodstream. Ex vivo bioluminescence analyses of organs isolated from infected mice corroborated our previous histopathological observations with parasite infiltration into spleen, liver and lungs. Finally, our study reinforces previous observations on the presence of the parasite in the central nervous system and consequently the brain commitment in the very late phases of the experimental infection.

Appraisal of a Leishmania major strain stably expressing mCherry fluorescent protein for both in vitro and in vivo studies of potential drugs and vaccine against cutaneous leishmaniasis

BACKGROUND

Leishmania major cutaneous leishmaniasis is an infectious zoonotic disease. It is produced by a digenetic parasite, which resides in the phagolysosomal compartment of different mammalian macrophage populations. There is an urgent need to develop new therapies (drugs) against this neglected disease that hits developing countries. The main goal of this work is to establish an easier and cheaper tool of choice for real-time monitoring of the establishment and progression of this pathology either in BALB/c mice or in vitro assays. To validate this new technique we vaccinated mice with an attenuated Δhsp70-II strain of Leishmania to assess protection against this disease.

METHODOLOGY

We engineered a transgenic L. major strain expressing the mCherry red-fluorescent protein for real-time monitoring of the parasitic load. This is achieved via measurement of fluorescence emission, allowing a weekly record of the footpads over eight weeks after the inoculation of BALB/c mice.

RESULTS

In vitro results show a linear correlation between the number of parasites and fluorescence emission over a range of four logs. The minimum number of parasites (amastigote isolated from lesion) detected by their fluorescent phenotype was 10,000. The effect of antileishmanial drugs against mCherry+L. major infecting peritoneal macrophages were evaluated by direct assay of fluorescence emission, with IC(50) values of 0.12, 0.56 and 9.20 µM for amphotericin B, miltefosine and paromomycin, respectively. An experimental vaccination trial based on the protection conferred by an attenuated Δhsp70-II mutant of Leishmania was used to validate the suitability of this technique in vivo.

CONCLUSIONS

A Leishmania major strain expressing mCherry red-fluorescent protein enables the monitoring of parasitic load via measurement of fluorescence emission. This approach allows a simpler, faster, non-invasive and cost-effective technique to assess the clinical progression of the infection after drug or vaccine therapy.

Accelerated healing of cutaneous leishmaniasis in non-healing BALB/c mice using water soluble amphotericin B-polymethacrylic acid

Cutaneous leishmaniasis (CL) is a neglected tropical disease that causes prominent skin scaring. No water soluble, non-toxic, short course and low cost treatment exists. We developed a new water soluble amphotericin B-polymethacrylic acid (AmB-PMA) using established and scalable chemistries. AmB-PMA was stable for 9 months during storage. In vitro, it was effective against Leishmania spp. promastigotes and amastigote infected macrophages. It was also less toxic and more effective than deoxycholate-AmB, and similar to liposomal AmB. Its in vivo activity was determined in both early and established CL lesion models of Leishmania major infection in genetically susceptible non-healing BALB/c mice. Intradermal AmB-PMA at a total dose of 18 mg of AmB/kg body weight led to rapid parasite killing and lesion healing. No toxicity was seen. No parasite relapse occurred after 80 days follow-up. Histological studies confirmed rapid parasite clearance from macrophages followed by accelerated fibroblast mediated tissue repair, regeneration and cure of the infection. Quantitative mRNA studies of the CL lesions showed that accelerated healing was associated with increased Tumour Necrosis Factor-α and Interferon-γ, and reduced Interleukin-10. These results suggest that a cost-effective AmB-PMA could be used to pharmacologically treat and immuno-therapeutically accelerate the healing of CL lesions.

Natural killer cells support the induction of protective immunity during dendritic cell-mediated vaccination against Leishmania major

Dendritic cell (DC)-mediated vaccination against Leishmania major induces a parasite-specific T helper 1 (Th1) response and long-lasting protective immunity in susceptible mice. As the cytokine interleukin-12 required for induction of this Th1 response is not derived from the transferred DC, but has to be produced by the vaccinated host, we examined cross-presentation of transferred DC via resident DC of the host and cross-activation with natural killer (NK) cells as mechanisms supporting the induction of protective immunity after DC-mediated vaccination. Co-culture with DC that had been conditioned ex vivo by loading with L. major lysate and stimulation with CpG-containing oligodeoxynucleotides did not result in the activation of naive DC in vitro. Furthermore, L. major antigen from conditioned DC was not cross-presented to a significant extent in vivo. In contrast, co-culture of DC with NK cells led to cross-activation of both cell populations with induction of interferon-γ, which was dependent on the activation status of the conditioned DC. Transient depletion of NK cells during vaccination of L. major-susceptible mice with conditioned DC resulted in reduced protection. Our findings indicate that cross-presentation of conditioned DC after DC-based vaccination against L. major plays a minor role in the induction of protective immunity. However, we demonstrated for the first time that the capacity of DC to mediate protection against L. major is supported by cross-activation with NK cells of the host and NK-cell-derived interferon-γ.

[Therapy of leishmaniasis in France: consensus on proposed guidelines]

Because it relies on potentially toxic, difficult-to-handle, or expensive compounds the therapy of leishmaniasis is still a complex issue in 2010, especially for visceral leishmaniasis in immuno-suppressed subjects, or in patients with cutaneous and mucosal involvement. This induces a wide diversity of observed therapeutic practices, some being sub-optimal. The Société de Pathologie Exotique organised a meeting dedicated to the therapy of leishmaniasis in France that led to the first consensus on therapeutic guidelines. Liposomal amphotericin B is the first-line option for visceral leishmaniasis both in immunocompetent, and immunosuppressed patients (cumulated doses of 20 mg/kg and 30-40 mg/kg, respectively). Secondary prophylaxis with either liposomal amphotericin B, pentamidine or meglumine antimoniate is proposed to patients with heavy immunosuppression until immunity has been restored for at least 6 months. While the efficacy of new topical formulations of paromomycin is being tested, patients with Old World cutaneous leishmaniasis may be left untreated, or be administered a combination of superficial cryotherapy plus intralesional antimony, or even--in complex situations--receive systemic therapy. The efficacy of a short course of pentamidine (L. guyanensis/L. panamensis) and a 20-day schedule of meglumine antimoniate (L. braziliensis) is solidly established. However, in well-defined situations, local therapy of New World cutaneous leishmaniasis is now considered acceptable.

Imaging of the host/parasite interplay in cutaneous leishmaniasis

An understanding of host-parasite interplay is essential for the development of therapeutics and vaccines. Immunoparasitologists have learned a great deal from 'conventional'in vitro and in vivo approaches, but recent developments in imaging technologies have provided us (immunologists and parasitologists) with the ability to ask new and exciting questions about the dynamic nature of the parasite-immune system interface. These studies are providing us with new insights into the mechanisms involved in the initiation of a Leishmania infection and the consequent induction and regulation of the immune response. Here, we review some of the recent developments and discuss how these observations can be further developed to understand the immunology of cutaneous Leishmania infection in vivo.

Noninvasive biophotonic imaging for studies of infectious disease

According to World Health Organization estimates, infectious organisms are responsible for approximately one in four deaths worldwide. Animal models play an essential role in the development of vaccines and therapeutic agents but large numbers of animals are required to obtain quantitative microbiological data by tissue sampling. Biophotonic imaging (BPI) is a highly sensitive, nontoxic technique based on the detection of visible light, produced by luciferase-catalysed reactions (bioluminescence) or by excitation of fluorescent molecules, using sensitive photon detectors. The development of bioluminescent/fluorescent microorganisms therefore allows the real-time noninvasive detection of microorganisms within intact living animals. Multiple imaging of the same animal throughout an experiment allows disease progression to be followed with extreme accuracy, reducing the number of animals required to yield statistically meaningful data. In the study of infectious disease, the use of BPI is becoming widespread due to the novel insights it can provide into established models, as well as the impact of the technique on two of the guiding principles of using animals in research, namely reduction and refinement. Here, we review the technology of BPI, from the instrumentation through to the generation of a photonic signal, and illustrate how the technique is shedding light on infection dynamics in vivo.

In vivo imaging of transgenic Leishmania parasites in a live host

Distinct species of Leishmania, a protozoan parasite of the family Trypanosomatidae, typically cause different human disease manifestations. The most common forms of disease are visceral leishmaniasis (VL) and cutaneous leishmaniasis (CL). Mouse models of leishmaniasis are widely used, but quantification of parasite burdens during murine disease requires mice to be euthanized at various times after infection. Parasite loads are then measured either by microscopy, limiting dilution assay, or qPCR amplification of parasite DNA. The in vivo imaging system (IVIS) has an integrated software package that allows the detection of a bioluminescent signal associated with cells in living organisms. Both to minimize animal usage and to follow infection longitudinally in individuals, in vivo models for imaging Leishmania spp. causing VL or CL were established. Parasites were engineered to express luciferase, and these were introduced into mice either intradermally or intravenously. Quantitative measurements of the luciferase driving bioluminescence of the transgenic Leishmania parasites within the mouse were made using IVIS. Individual mice can be imaged multiple times during longitudinal studies, allowing us to assess the inter-animal variation in the initial experimental parasite inocula, and to assess the multiplication of parasites in mouse tissues. Parasites are detected with high sensitivity in cutaneous locations. Although it is very likely that the signal (photons/second/parasite) is lower in deeper visceral organs than the skin, but quantitative comparisons of signals in superficial versus deep sites have not been done. It is possible that parasite numbers between body sites cannot be directly compared, although parasite loads in the same tissues can be compared between mice. Examples of one visceralizing species (L. infantum chagasi) and one species causing cutaneous leishmaniasis (L. mexicana) are shown. The IVIS procedure can be used for monitoring and analyzing small animal models of a wide variety of Leishmania species causing the different forms of human leishmaniasis.

Early curative applications of the aminoglycoside WR279396 on an experimental Leishmania major-loaded cutaneous site do not impair the acquisition of immunity

Topical therapy is an attractive approach for the treatment of Leishmania major cutaneous leishmaniasis (CL). WR279396, an expanded-spectrum aminoglycoside ointment, is now in phase 3 trials. Because the application of a cream is easier than the injection of pentavalent antimony, many patients with CL will likely be treated with WR279396 soon after the onset of a lesion. However, this new therapeutic approach may impair the acquisition of immunity. We evaluated the impact of early topical therapy on acquired immunity in an optimized mouse model of L. major-induced CL. The efficacy of the WR279396 ointment in this model has been established previously. Acquired immunity was defined as the absence of lesions upon reinoculation of the same parasite isolate at a different skin site. Bioluminescence-based follow-up of luciferase-expressing L. major loads was also performed. In this model, the control of L. major loads at the initial inoculation site and the acquisition of immunity are simultaneous (day 22 postinoculation). The clinical and parasitological efficacies of WR279396 applied as early as day 11 postinoculation, i.e., during the L. major multiplication phase, did not impair the acquisition of immunity to a second L. major challenge. This is reassuring from the perspective of the wide deployment of WR279396-based therapy in foci where L. major is endemic.

WR279,396, a third generation aminoglycoside ointment for the treatment of Leishmania major cutaneous leishmaniasis: a phase 2, randomized, double blind, placebo controlled study

Background

Cutaneous leishmaniasis (CL) is a disfiguring disease that confronts clinicians with a quandary: leave patients untreated or engage in a complex or toxic treatment. Topical treatment of CL offers a practical and safe option. Accordingly, the treatment of CL with WR279,396, a formulation of paromomycin and gentamicin in a hydrophilic base, was investigated in a phase 2 clinical study in Tunisia and France.

Methods

A phase 2, randomized, double blind, vehicle-controlled study was conducted to assess the safety and efficacy of topical WR279,396 when applied twice a day for 20 days as treatment for parasitologically confirmed CL. The study protocol established the primary efficacy end point as complete clinical response (CCR) defined as 50% or greater reduction in the ulceration size of an index lesion by day 50 (D50) followed by complete re-epithelialization by D100, and no relapse through D180.

Results

Ninety-two subjects were randomized. Leishmania major was identified in 66 of 68 isolates typed (97%). In the intent-to-treat population, 47 of 50 WR279,396 treated participants (94%) met the definition of CCR, compared with 30 of 42 vehicle-placebo participants (71%) [p = 0.0045]. Erythema occurred in 30% and 24% of participants receiving WR279,396 and placebo, respectively [p = 0.64]. There was no clinical or laboratory evidence of systemic toxicity.

Conclusion

Application of WR279,396 for 20 days was found to be safe and effective in treating L. major CL, and offers great potential as a new, simple, easily applicable, and inexpensive topical therapy for this neglected disease.

Trial Registration

ClinicalTrials.gov NCT00703924

Cutaneous leishmaniasis is due to a small parasite (Leishmania) that creates disfiguring sores, and affects more than one million persons (mainly children) each year. Treating lesions with a cream—instead of with injections as currently done—would greatly improve the well-being of affected patients. No cream formulation that would be efficient and would not create important skin irritation has been identified yet. Here, we tested a new cream formulation (WR279,396) containing paromomycin and gentamicin, two members of a well-known family of antibacterial antibiotics (aminoglycosides). Injectable paromomycin is efficient in other forms of the disease (visceral leishmaniasis). This was a carefully monitored study (phase 2) involving mainly children in Tunisia and France. The cream was applied twice a day for 20 days. The proportion of patients treated with the paromomycin-containing cream (active formulation) that cured (94%) was higher than that observed (71%) in patients treated with a cream that did not contain the active product (placebo formulation). Local irritation affected less than one-third of the patients and was usually mild. This new cream formulation was safe and effective in treating cutaneous leishmaniasis, thereby providing a new, simple, easily applicable, and inexpensive treatment for this neglected disease.

Is paromomycin an effective and safe treatment against cutaneous leishmaniasis? A meta-analysis of 14 randomized controlled trials

Background

High cost, poor compliance, and systemic toxicity have limited the use of pentavalent antimony compounds (SbV), the treatment of choice for cutaneous leishmaniasis (CL). Paromomycin (PR) has been developed as an alternative to SbV, but existing data are conflicting.

Methodology/Principal Findings

We searched PubMed, Scopus, and Cochrane Central Register of Controlled Trials, without language restriction, through August 2007, to identify randomized controlled trials that compared the efficacy or safety between PR and placebo or SbV. Primary outcome was clinical cure, defined as complete healing, disappearance, or reepithelialization of all lesions. Data were extracted independently by two investigators, and pooled using a random-effects model. Fourteen trials including 1,221 patients were included. In placebo-controlled trials, topical PR appeared to have therapeutic activity against the old world and new world CL, with increased local reactions, when used with methylbenzethonium chloride (MBCL) compared to when used alone (risk ratio [RR] for clinical cure, 2.58 versus 1.01: RR for local reactions, 1.60 versus 1.07). In SbV-controlled trials, the efficacy of topical PR was not significantly different from that of intralesional SbV in the old world CL (RR, 0.70; 95% confidence interval, 0.26–1.89), whereas topical PR was inferior to parenteral SbV in treating the new world CL (0.67; 0.54–0.82). No significant difference in efficacy was found between parenteral PR and parenteral SbV in the new world CL (0.88; 0.56–1.38). Systemic side effects were fewer with topical or parenteral PR than parenteral SbV.

Conclusions/Significance

Topical PR with MBCL could be a therapeutic alternative to SbV in selected cases of the old world CL. Development of new formulations with better efficacy and tolerability remains to be an area of future research.

Millions of people worldwide are suffering from cutaneous leishmaniasis that is caused by parasites of the genus Leishmania. Although pentavalent antimony compounds are the treatment of choice, their use is limited by high cost, poor compliance, and systemic toxicity. Paromomycin was developed to overcome such limitations. However, there is no consensus on its efficacy. This meta-analysis assessed the efficacy and safety of paromomycin compared with placebo and pentavalent antimony compounds. Fourteen randomized controlled trials, including 1,221 patients, met our selection criteria. Topical paromomycin appeared to have therapeutic activity against the old world and new world cutaneous leishmaniasis, with increased local reactions, when combined with methylbenzethonium chloride. Topical paromomycin was not significantly different from intralesional pentavalent antimony compounds in treating the old world form, whereas it was inferior to parenteral pentavalent antimony compounds in treating the new world form. However, a similar efficacy was found between parenteral paromomycin and pentavalent antimony compounds in treating the new world form. Fewer systemic side effects were observed with topical and parenteral paromomycin than pentavalent antimony compounds. These results suggest that topical paromomycin with methylbenzethonium chloride could be a therapeutic alternative to pentavalent antimony compounds for selected cases of the old world cutaneous leishmaniasis.

Leishmania parasites: could we consider them as living organisms per se?

Over the last 10 years - in Microbes and Infection - the publications dealing with protozoan parasites were mainly providing insights on the pathogenic processes leading to the local or systemic damages in the mammals, these parasitic organisms exploit/subvert as hosts. As a result, many investigators introduced the objectives of their analysis by referring to "host-pathogen" interactions. Though we, as investigators, are all determined to decipher the pathogenic processes which can indeed be coupled to the parasite uncontrolled development, I think that the parasites - alike the living organisms they subvert as hosts - need to be considered as living organisms per se, instead of being considered as "pathogens". Such a conceptual frame will promote research on the processes on which relies their perpetuation whatever the level under investigations - individual and/or population level. Only the unicellular protozoan parasites of the genus Leishmania known to be hosted by blood-feeding insects and mammals will be further considered in this brief contribution.