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

Targeting effective treatment to cutaneous Leishmaniasis: A preclinical investigation on photodynamic therapy mediated by the water-soluble Zn(II) porphyrin, ZnTnHex-2-PyP4

The current chemotherapy for cutaneous leishmaniasis (CL) is accompanied by side effects and drug resistance emergence, encouraging the proposal of new treatment approaches for this disease. ZnTnHex-2-PyP4+ (ZnP hexyl) is a water-soluble Zn(II) porphyrin that exhibits remarkable potential for photodynamic therapy (PDT). This study aimed to investigate the ZnP hexyl-PDT against CL in vivo. As far as we know, this is the first investigation with this Zn(II) porphyrin in an animal model. The influence of the number and time interval of sessions on photodynamic effects was also investigated. BALB/c mice infected with Leishmania amazonensis were divided in 4 groups (untreated control, 1, 2, or 3 PDT sessions). In PDT groups, animals received ZnP hexyl (5 μM, 0.17 μg, 30 μL per animal/session) and were irradiated with blue LED. Parasite burden was quantified by bioluminescence for up to 21 days. The infected paw thickness and nociceptive analyses were also assessed. In treated groups, parasite burden showed an over time decrease compared to the control, indicating ZnP hexyl-PDT efficiency, mainly after 3 sessions, achieving about 91% reduction. Overall, no differences in infected paw thickness and nociceptive sensibility were observed among the groups. Results also indicated the importance of tuning the time interval between sessions to enhance therapeutic outcomes and diminish adverse effects. Under the conditions studied, weekly PDT sessions were superior, as intervals ≤ 72-h led to a temporary increase in infected paw thickness and nociceptive sensibility at day 7. This study pointed out that ZnP hexyl-PDT holds promise as an ally for CL treatment.

Photodynamic therapy offers a novel approach to managing miltefosine-resistant cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is a neglected disease caused by Leishmania parasites. The oral drug miltefosine is effective, but there is a growing problem of drug resistance, which has led to increasing treatment failure rates and relapse of infections. Photodynamic therapy (PDT) combines a light source and a photoactive drug to promote cell death by oxidative stress. Although PDT is effective against several pathogens, its use against drug-resistant Leishmania parasites remains unexplored. Herein, we investigated the potential of organic light-emitting diodes (OLEDs) as wearable light sources, which would enable at-home use or ambulatory treatment of CL. We also assessed its impact on combating miltefosine resistance in Leishmania amazonensis-induced CL in mice. The in vitro activity of OLEDs combined with 1,9-dimethyl-methylene blue (DMMB) (OLED-PDT) was evaluated against wild-type and miltefosine-resistant L. amazonensis strains in promastigote (EC50 = 0.034 μM for both strains) and amastigote forms (EC50 = 0.052 μM and 0.077 μM, respectively). Cytotoxicity in macrophages and fibroblasts was also evaluated. In vivo, we investigated the potential of OLED-PDT in combination with miltefosine using different protocols. Our results demonstrate that OLED-PDT is effective in killing both strains of L. amazonensis by increasing reactive oxygen species and stimulating nitric oxide production. Moreover, OLED-PDT showed great antileishmanial activity in vivo, allowing the reduction of miltefosine dose by half in infected mice using a light dose of 7.8 J/cm2 and 15 μM DMMB concentration. In conclusion, OLED-PDT emerges as a new avenue for at-home care and allows a combination therapy to overcome drug resistance in cutaneous leishmaniasis.

Amphotericin B resistance in Leishmania amazonensis: In vitro and in vivo characterization of a Brazilian clinical isolate

In Brazil, Leishmania amazonensis is the etiological agent of cutaneous and diffuse cutaneous leishmaniasis. The state of Maranhão in the Northeast of Brazil is prevalent for these clinical forms of the disease and also has high rates of HIV infection. Here, we characterized the drug susceptibility of a L. amazonensis clinical isolate from a 46-year-old man with diffuse cutaneous leishmaniasis coinfected with HIV from this endemic area. This patient underwent several therapeutic regimens with meglumine antimoniate, liposomal amphotericin B, and pentamidine, without success. In vitro susceptibility assays against promastigotes and intracellular amastigotes demonstrated that this isolate had low susceptibility to amphotericin B, when compared with the reference strain of this species that is considered susceptible to antileishmanial drugs. Additionally, we investigated whether the low in vitro susceptibility would affect the in vivo response to amphotericin B treatment. The drug was effective in reducing the lesion size and parasite burden in mice infected with the reference strain, whereas those infected with the clinical isolate and a resistant line (generated experimentally by stepwise selection) were refractory to amphotericin B treatment. To evaluate whether the isolate was intrinsically resistant to amphotericin B in animals, infected mice were treated with other drugs that had not been used in the treatment of the patient (miltefosine, paromomycin, and a combination of both). Our findings demonstrated that all drug schemes were able to reduce lesion size and parasite burden in animals infected with the clinical isolate, confirming the amphotericin B-resistance phenotype. These findings indicate that the treatment failure observed in the patient may be associated with amphotericin B resistance, and demonstrate the potential emergence of amphotericin B-resistant L. amazonensis isolates in an area of Brazil endemic for cutaneous leishmaniasis.

Clemastine/tamoxifen hybrids as easily accessible antileishmanial drug leads

A library of hybrid molecules is developed based on the common chemical features shared by clemastine and tamoxifen both of which are well known for their antileishmanial activities. In the initial screening against Leishmania major and L. amazonensis promastigotes, as well as cytotoxicity assays using HepG2 cells, several hybrids showed submicromolar activity against the parasite and no toxicity against human cells. The compounds with an EC50 < 2 μM against promastigotes of both species and a selectivity index >10 were further characterized against intracellular amastigotes as well as promastigotes of species that cause both visceral and cutaneous leishmaniasis, such as L. infantum and L. braziliensis, respectively. These sequential screenings revealed the high pan-activity of this class of molecules against these species, with several compounds displaying an EC50 ≤ 2 μM against both promastigotes and intracellular amastigotes. Two of them were identified as the potential templates for lead optimization of this series having shown the highest activities against all species in both stages of parasite. The present findings can serve as a good starting point in the search for novel antileishmanial compounds that are easy to access and highly active.

Drug Discovery for Cutaneous Leishmaniasis: A Review of Developments in the Past 15 Years

Leishmaniasis is a group of vector-borne, parasitic diseases caused by over 20 species of the protozoan Leishmania spp. The three major disease classifications, cutaneous, visceral, and mucocutaneous, have a range of clinical manifestations from self-healing skin lesions to hepatosplenomegaly and mucosal membrane damage to fatality. As a neglected tropical disease, leishmaniasis represents a major international health challenge, with nearly 350 million people living at risk of infection a year. The current chemotherapeutics used to treat leishmaniasis have harsh side effects, prolonged and costly treatment regimens, as well as emerging drug resistance, and are predominantly used for the treatment of visceral leishmaniasis. There is an undeniable need for the identification and development of novel chemotherapeutics targeting cutaneous leishmaniasis (CL), largely ignored by concerted drug development efforts. CL is mostly non-lethal and the most common presentation of this disease, with nearly 1 million new cases reported annually. Recognizing this unaddressed need, substantial yet fragmented progress in early drug discovery efforts for CL has occurred in the past 15 years and was outlined in this review. However, further work needs to be carried out to advance early discovery candidates towards the clinic. Importantly, there is a paucity of investment in the translation and development of therapies for CL, limiting the emergence of viable solutions to deal with this serious and complex international health problem.

Organogold(III)-dithiocarbamate compounds and their coordination analogues as anti-tumor and anti-leishmanial metallodrugs

The limited chemical stability of gold(III)-based compounds in physiological environment has been a challenge in drug discovery, and organometallic chemistry might provide the solution to overcome this issue. In this work, four novel cationic organogold(III)-dithiocarbamate complexes of general structure [(C^N)AuIIIDTC]PF6 (C1a - C4a, DTC = dithiocarbamate, L1 - L4, C^N = 2-anilinopyridine) are presented, and compared to their coordination gold(III)-dithiocarbamate analogues [AuIIIDTCCl2] (C1b - C4b), as potential anti-cancer and anti-leishmanial drugs. Most of the complexes effectively inhibited cancer cell growth, notably C3a presented anti-proliferative effect in the nanomolar range against breast cancer (MCF-7 and MDA-MB-231 cells with moderate selectivity. Pro-apoptotic studies on treated MCF-7 cells showed a high population of cells in early apoptosis. Reactivity studies of C3a towards model thiols (N-acetyl-L-cysteine) refer to a possible mode of action involving bonding between the organogold(III)-core and the thiolate. In the scope of neglected diseases, gold complexes are emerging as promising therapeutic alternatives against leishmaniasis. In this regard, all gold(III)-dithiocarbamate complexes presented anti-leishmanial activity against at least one Leishmania species. Complexes C1a, C4a, C1b, C4b were active against all tested parasites with IC50 values varying between 0.12 and 42 μM, and, overall, organometallic compounds presented more intriguing inhibition profiles. For C4a selectivity over 500-fold for L. braziliensis; even higher than the reference anti-leishmanial drug amphotericin B. Overall, our findings revealed that the organogold(III) moiety significantly amplified the anti-cancer and anti-leishmanial effects with respect to the coordination analogues; thus, showing the great potential of organometallic chemistry in metallodrug-based chemotherapy for cancer and leishmaniasis.

Towards effective natural anthraquinones to mediate antimicrobial photodynamic therapy of cutaneous leishmaniasis

BACKGROUND

Cutaneous leishmaniasis (CL) is an important tropical neglected disease with broad geographical dispersion. The lack of effective drugs has raised an urgent need to improve CL treatment, and antimicrobial photodynamic therapy (APDT) has been investigated as a new strategy to face it with positive outcomes. Natural compounds have emerged as promising photosensitizers (PSs), but their use in vivo remains unexplored.

PURPOSE

In this work, we investigated the potential of three natural anthraquinones (AQs) on CL induced by Leishmania amazonensis in BALB/c mice.

STUDY DESIGN/METHODS

ANIMALS WERE INFECTED AND RANDOMLY DIVIDED INTO FOUR GROUPS: CG (control, non-treated group), G5ClSor-gL (treated with 5-chlorosoranjidiol and green LED, 520±10 nm), GSor-bL and GBisor-bL (treated with soranjidiol and bisoranjidiol, respectively, exposed to violet-blue LED, 410±10 nm). All AQs were assayed at 10 μM and LEDs delivered a radiant exposure of 45 J/cm² with an irradiance of 50 mW/cm². We assessed the parasite burden in real time for three consecutive days. Lesion evolution and pain score were assessed over 3 weeks after a single APDT session.

RESULTS

G5ClSor-gL was able to sustain low levels of parasite burden over time. Besides, GSor-bL showed a smaller lesion area than the control group, inhibiting the disease progression.

CONCLUSION

Taken together, our data demonstrate that monoAQs are promising compounds for pursuing the best protocol for treating CL and helping to face this serious health problem. Studies involving host-pathogen interaction as well as monoAQ-mediated PDT immune response are also encouraged.

Development of a Fluorescent Assay to Search New Drugs Using Stable tdTomato-Leishmania, and the Selection of Galangin as a Candidate With Anti-Leishmanial Activity

Antimonials continue to be considered the first-line treatment for leishmaniases, but its use entails a wide range of side effects and serious reactions. The search of new drugs requires the development of methods more sensitive and faster than the conventional ones. We developed and validated a fluorescence assay based in the expression of tdTomato protein by Leishmania, and we applied this method to evaluate the activity in vitro of flavonoids and reference drugs. The pIR1SAT/tdTomato was constructed and integrated into the genome of Leishmania (Leishmania) amazonensis. Parasites were selected with nourseothricin (NTC). The relation of L. amaz/tc3 fluorescence and the number of parasites was determined; then the growth in vitro and infectivity in BALB/c mice was characterized. To validate the fluorescence assay, the efficacy of miltefosine and meglumine antimoniate was compared with the conventional methods. After that, the method was used to assess in vitro the activity of flavonoids; and the mechanism of action of the most active compound was evaluated by transmission electron microscopy and ELISA. A linear correlation was observed between the emission of fluorescence of L. amaz/tc3 and the number of parasites (r2 = 0.98), and the fluorescence was stable in the absence of NTC. No differences were observed in terms of infectivity between L. amaz/tc3 and wild strain. The efficacy of miltefosine and meglumine antimoniate determined by the fluorescence assay and the microscopic test showed no differences, however, in vivo the fluorescence assay was more sensitive than limiting dilution assay. Screening assay revealed that the flavonoid galangin (GAL) was the most active compound with IC50 values of 53.09 µM and 20.59 µM in promastigotes and intracellular amastigotes, respectively. Furthermore, GAL induced mitochondrial swelling, lipid inclusion bodies and vacuolization in promastigotes; and up-modulated the production of IL-12 p70 in infected macrophages. The fluorescence assay is a useful tool to assess the anti-leishmanial activity of new compounds. However, the assay has some limitations in the macrophage-amastigote model that might be related with an interfere of flavanol aglycones with the fluorescence readout of tdTomato. Finally, GAL is a promising candidate for the development of new treatment against the leishmaniasis.

Applications of bioluminescence in biotechnology and beyond

Bioluminescent probes have hugely benefited from the input of synthetic chemistry and protein engineering. Here we review the latest applications of these probes in biotechnology and beyond, with an eye on current limitations and future directions.

Activity of paromomycin against Leishmania amazonensis: Direct correlation between susceptibility in vitro and the treatment outcome in vivo

Paromomycin is an aminoglycoside antibiotic approved in 2006 for the treatment of visceral leishmaniasis caused by Leishmania donovani in Southeast Asia. Although this drug is not approved for the treatment of visceral and cutaneous leishmaniasis in Brazil, it is urgent and necessary to evaluate the potential of this drug as alternative for the treatment against species responsible for these clinical forms of the disease. In Brazil, Leishmania amazonensis is responsible for cutaneous and diffuse cutaneous leishmaniasis. The diffuse cutaneous form of the disease is difficult to treat and frequent relapses are reported, mainly when the treatment is interrupted. Here, we evaluated paromomycin susceptibility in vitro of a L. amazonensis clinical isolate from a patient with cutaneous leishmaniasis and the reference strain L. amazonensis M2269, as well as its in vivo efficacy in a murine experimental model. Although never exposed to paromomycin, a significant differential susceptibility between these two lines was found. Paromomycin was highly active in vitro against the clinical isolate in both forms of the parasite, while its activity against the reference strain was less active. In vivo studies in mice infected with each one of these lines demonstrated that paromomycin reduces lesion size and parasite burden and a direct correlation between the susceptibility in vitro and the effectiveness of this drug in vivo was found. Our findings indicate that paromomycin efficacy in vivo is dependent on intrinsic susceptibility of the parasite. Beyond that, this study contributes for the evaluation of the potential use of paromomycin in chemotherapy of cutaneous leishmaniasis in Brazil caused by L. amazonensis.

Repurposing topical triclosan for cutaneous leishmaniasis: Preclinical efficacy in a murine Leishmania (L.) amazonensis model

Leishmaniasis remains an important neglected tropical infection caused by the protozoan Leishmania and affects 12 million people in 98 countries. The treatment is limited with severe adverse effects. In the search for new therapies, the drug repositioning and combination therapy have been successfully applied to neglected diseases. The aim of the present study was to evaluate the in vitro and in vivo anti-Leishmania (Leishmania) amazonensis potential of triclosan, an approved topical antimicrobial agent used for surgical procedures. in vitro phenotypic studies of drug-treated parasites were performed to evaluate the lethal action of triclosan, accompanied by an isobolographic ex-vivo analysis with the association of triclosan and miltefosine. The results showed that triclosan has activity against L. (L.) amazonensis intracellular amastigotes, with a 50% inhibitory concentration of 16 μM. By using fluorescent probes and transmission electron microscopy, a pore-forming activity of triclosan toward the parasite plasma membrane was demonstrated, leading to depolarization of the mitochondrial membrane potential and reduction of the reactive oxygen species levels in the extracellular promastigotes. The in vitro interaction between triclosan and miltefosine in the combination therapy assay was classified as additive against intracellular amastigotes. Leishmania-infected mice were treated with topical triclosan (1% base cream for 14 consecutive days), and showed 89% reduction in the parasite burden. The obtained results contribute to the investigation of new alternatives for the treatment of cutaneous leishmaniasis and suggest that the coadministration of triclosan and miltefosine should be investigated in animal models.

Evaluation of NanoLuc, RedLuc and Luc2 as bioluminescent reporters in a cutaneous leishmaniasis model

New drugs for the treatment of human leishmaniasis are urgently needed, considering the limitations of current available options. However, pre-clinical evaluation of drug candidates for leishmaniasis is challenging. The use of luciferase-expressing parasites for parasite load detection is a potentially powerful tool to accelerate the drug discovery process. We have previously described the use of Leishmania amazonensis mutants expressing firefly luciferase (Luc2) for drug testing. Here, we describe three new mutant L. amazonensis lines that express different variants of luciferases: NanoLuc, NanoLuc-PEST and RedLuc. These mutants were evaluated in drug screening protocols. NanoLuc-parasites, in spite of high bioluminescence intensity in vitro, were shown to be inadequate in discriminating between live and dead parasites. Bioluminescence detection from intracellular amastigotes expressing NanoLuc-PEST, RedLuc or Luc2 proved more reliable than microscopy to determine parasite killing. Increased sensitivity was observed in vivo with RedLuc-expressing parasites as compared to NanoLuc-expressing L. amazonensis. Our data indicates that NanoLuc is not suitable for in vivo parasite burden determination. Additionally, RedLuc and the conventional luciferase Luc2 demonstrated equivalent sensitivity in an in vivo model of cutaneous leishmaniasis.

Preclinical Gold Complexes as Oral Drug Candidates to Treat Leishmaniasis Are Potent Trypanothione Reductase Inhibitors

The drugs currently used to treat leishmaniases have limitations concerning cost, efficacy, and safety, making the search for new therapeutic approaches urgent. We found that the gold(I)-derived complexes were active against L. infantum and L. braziliensis intracellular amastigotes with IC₅₀ values ranging from 0.5 to 5.5 μM. All gold(I) complexes were potent inhibitors of trypanothione reductase (TR), with enzyme IC₅₀ values ranging from 1 to 7.8 μM. Triethylphosphine-derived complexes enhanced reactive oxygen species (ROS) production and decreased mitochondrial respiration after 2 h of exposure, indicating that gold(I) complexes cause oxidative stress by direct ROS production, by causing mitochondrial damage or by impairing TR activity and thus accumulating ROS. There was no cross-resistance to antimony; in fact, SbR (antimony-resistant mutants) strains were hypersensitive to some of the complexes. BALB/c mice infected with luciferase-expressing L. braziliensis or L. amazonensis and treated orally with 12.5 mg/kg/day of AdT Et (3) or AdO Et (4) presented reduced lesion size and parasite burden, as revealed by bioimaging. The combination of (3) and miltefosine allowed for a 50% reduction in miltefosine treatment time. Complexes 3 and 4 presented favorable pharmacokinetic and toxicity profiles that encourage further drug development studies. Gold(I) complexes are promising antileishmanial agents, with a potential for therapeutic use, including in leishmaniasis caused by antimony-resistant parasites.

Recent advances in functional research in Giardia intestinalis

This review considers current advances in tools to investigate the functional biology of Giardia, it's coding and non-coding genes, features and cellular and molecular biology. We consider major gaps in current knowledge of the parasite and discuss the present state-of-the-art in its in vivo and in vitro cultivation. Advances in in silico tools, including for the modelling non-coding RNAs and genomic elements, as well as detailed exploration of coding genes through inferred homology to model organisms, have provided significant, primary level insight. Improved methods to model the three-dimensional structure of proteins offer new insights into their function, and binding interactions with ligands, other proteins or precursor drugs, and offer substantial opportunities to prioritise proteins for further study and experimentation. These approaches can be supplemented by the growing and highly accessible arsenal of systems-based methods now being applied to Giardia, led by genomic, transcriptomic and proteomic methods, but rapidly incorporating advanced tools for detection of real-time transcription, evaluation of chromatin states and direct measurement of macromolecular complexes. Methods to directly interrogate and perturb gene function have made major leaps in recent years, with CRISPr-interference now available. These approaches, coupled with protein over-expression, fluorescent labelling and in vitro and in vivo imaging, are set to revolutionize the field and herald an exciting time during which the field may finally realise Giardia's long proposed potential as a model parasite and eukaryote.

Generation and Characterization of a Dual-Reporter Transgenic Leishmania braziliensis Line Expressing eGFP and Luciferase

In this study, we generated a transgenic strain of Leishmania braziliensis, an etiological agent associated with a diversity of clinical manifestations of leishmaniasis ranging from localized cutaneous to mucocutaneous to disseminated disease. Transgenic parasites expressing reporter proteins are valuable tools for studies of parasite biology, host-pathogen interactions, and anti-parasitic drug development. To this end, we constructed an L. braziliensis line stably expressing the reporters eGFP and luciferase (eGFP-LUC L. braziliensis). The integration cassette co-expressing the two reporters was targeted to the ribosomal locus (SSU) of the parasite genome. Transgenic parasites were characterized for their infectivity and stability both in vitro and in vivo. Parasite maintenance in axenic long-term culture in the absence of selective drugs did not alter expression of the two reporters or infection of BALB/c mice, indicating stability of the integrated cassette. Infectivity of eGFP-LUC, L. braziliensis, both in vivo and in vitro was similar to that obtained with the parental wild type strain. The possibility of L. braziliensis tracking and quantification using fluorescence and luminescence broadens the scope of research involving this neglected species, despite its importance in terms of public health concerning the leishmaniasis burden.

Assessment of Leishmania cell lines expressing high levels of beta-galactosidase as alternative tools for the evaluation of anti-leishmanial drug activity

Leishmaniasis, caused by protozoa belonging to the genus Leishmania, is an important public health problem found in >90 countries and with still limited options for treatment. Development of new anti-leishmanial drugs is an urgent need and the identification of new active compounds is a limiting factor that can be accelerated through large scale drug screening. This requires multiple steps and can be expensive and time consuming. Here, we propose an alternative approach for the colorimetric assessment of anti-Leishmania drug activity that can be easily scaled up. L. amazonensis and L. infantum cell lines were generated having the β-galactosidase (β-gal) gene integrated into their chromosomal 18S rRNA (ssu) locus. Both cell lines expressed high levels of β-gal and had their growth easily monitored and quantified colorimetrically. These two cell lines were then evaluated as tools to assess drug susceptibility and their use was validated through in vitro assays with Amphotericin B, which is routinely used against leishmaniasis. β-gal expression was also confirmed through flow-cytometry, another method of phenotypic detection. With these recombinant parasites, an alternative in vitro model of drug screening against cutaneous and visceral leishmaniasis is now available.

Natural anthraquinones as novel photosentizers for antiparasitic photodynamic inactivation

BACKGROUND

Cutaneous leishmaniasis (CL) is a vector-borne disease caused by obligate protist parasites from the genus Leishmania. The potential toxicity as well as the increased resistance of standard treatments has encouraged the development of new therapeutical strategies. Photodynamic inactivation (PDI) combines the use of a photosensitizer and light to generate reactive oxygen species and kill cells, including microorganisms. Vegetal kingdom constitutes an important source of bioactive compounds that deserve to be investigated in the search of naturally occurring drugs with leishmanicidal activity.

PURPOSE

The purpose of this study was to test the antiparasitic activity of PDI (ApPDI) of five natural anthraquinones (AQs) obtained from Heterophyllaea lycioides (Rusby) Sandwith (Rubiacae). To support our results, effect of AQ mediated-PDI on parasite´s morphology and AQ uptake were studied. Cytotoxicity on fibroblasts was also evaluated.

STUDY DESIGN/METHODS

Two monomers, soranjidiol (Sor) and 5-chlorosoranjidiol (5-ClSor) plus three bi-anthraquinones (bi-AQs), bisoranjidiol (Bisor), 7-chlorobisoranjidiol (7-ClBisor) and Lycionine (Lyc) were selected for this study. Recombinant L. amazonensis promastigote strain expressing luciferase was subjected to AQs and LED treatment. Following irradiation with variable light parameters, cell viability was quantified by bioluminescence. Alteration on parasite's morphology was analyzed by scanning electron microscopy (SEM). In addition, we verified the AQ uptake in Leishmania cells by fluorescence and their toxicity on fibroblasts by using MTT assay.

RESULTS

Bisor, Sor and 5-ClSor exhibited photodynamic effect on L. amazonensis. SEM showed that promastigotes treated with Bisor-mediated PDI exhibited a significant alteration in shape and size. Sor and 5-ClSor presented higher uptake levels than bi-AQs (Bisor, Lyc and 7-ClBisor). Finally, Sor and Bisor presented the lowest toxic activity against fibroblasts.

CONCLUSION

Taking together, our results indicate that Sor presents the highest specificity towards Leishmania cells with no toxicity on fibroblasts.

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.

In-vivo monitoring of infectious diseases in living animals using bioluminescence imaging

Traditional methods of localizing and quantifying the presence of pathogenic microorganisms in living experimental animal models of infections have mostly relied on sacrificing the animals, dissociating the tissue and counting the number of colony forming units. However, the discovery of several varieties of the light producing enzyme, luciferase, and the genetic engineering of bacteria, fungi, parasites and mice to make them emit light, either after administration of the luciferase substrate, or in the case of the bacterial lux operon without any exogenous substrate, has provided a new alternative. Dedicated bioluminescence imaging (BLI) cameras can record the light emitted from living animals in real time allowing non-invasive, longitudinal monitoring of the anatomical location and growth of infectious microorganisms as measured by strength of the BLI signal. BLI technology has been used to follow bacterial infections in traumatic skin wounds and burns, osteomyelitis, infections in intestines, Mycobacterial infections, otitis media, lung infections, biofilm and endodontic infections and meningitis. Fungi that have been engineered to be bioluminescent have been used to study infections caused by yeasts (Candida) and by filamentous fungi. Parasitic infections caused by malaria, Leishmania, trypanosomes and toxoplasma have all been monitored by BLI. Viruses such as vaccinia, herpes simplex, hepatitis B and C and influenza, have been studied using BLI. This rapidly growing technology is expected to continue to provide much useful information, while drastically reducing the numbers of animals needed in experimental studies.

Breaking beta: deconstructing the parasite transmission function

Transmission is a fundamental step in the life cycle of every parasite but it is also one of the most challenging processes to model and quantify. In most host–parasite models, the transmission process is encapsulated by a single parameter β. Many different biological processes and interactions, acting on both hosts and infectious organisms, are subsumed in this single term. There are, however, at least two undesirable consequences of this high level of abstraction. First, nonlinearities and heterogeneities that can be critical to the dynamic behaviour of infections are poorly represented; second, estimating the transmission coefficient β from field data is often very difficult. In this paper, we present a conceptual model, which breaks the transmission process into its component parts. This deconstruction enables us to identify circumstances that generate nonlinearities in transmission, with potential implications for emergent transmission behaviour at individual and population scales. Such behaviour cannot be explained by the traditional linear transmission frameworks. The deconstruction also provides a clearer link to the empirical estimation of key components of transmission and enables the construction of flexible models that produce a unified understanding of the spread of both micro- and macro-parasite infectious disease agents.

This article is part of the themed issue ‘Opening the black box: re-examining the ecology and evolution of parasite transmission’.

The power of bioluminescence imaging in understanding host-pathogen interactions

Infectious diseases are one of the leading causes of death worldwide. Modelling and understanding human infection is imperative to developing treatments to reduce the global burden of infectious disease. Bioluminescence imaging is a highly sensitive, non-invasive technique based on the detection of light, produced by luciferase-catalysed reactions. In the study of infectious disease, bioluminescence imaging is a well-established technique; it can be used to detect, localize and quantify specific immune cells, pathogens or immunological processes. This enables longitudinal studies in which the spectrum of the disease process and its response to therapies can be monitored. Light producing transgenic rodents are emerging as key tools in the study of host response to infection. Here, we review the strategies for identifying biological processes in vivo, including the technology of bioluminescence imaging and illustrate how this technique is shedding light on the host-pathogen relationship.

Giardia Colonizes and Encysts in High-Density Foci in the Murine Small Intestine

Giardia is a single-celled parasite causing significant diarrheal disease in several hundred million people worldwide. Due to limited access to the site of infection in the gastrointestinal tract, our understanding of the dynamics of Giardia infections in the host has remained limited and largely inferred from laboratory culture. To better understand Giardia physiology and colonization in the host, we developed imaging methods to quantify Giardia expressing bioluminescent physiological reporters in two relevant animal models. We discovered that parasites primarily colonize and encyst in the proximal small intestine in discrete, high-density foci. We also show that high parasite density contributes to encystation initiation.

Giardia lamblia is a highly prevalent yet understudied protistan parasite causing significant diarrheal disease worldwide. Hosts ingest Giardia cysts from contaminated sources. In the gastrointestinal tract, cysts excyst to become motile trophozoites, colonizing and attaching to the gut epithelium. Trophozoites later differentiate into infectious cysts that are excreted and contaminate the environment. Due to the limited accessibility of the gut, the temporospatial dynamics of giardiasis in the host are largely inferred from laboratory culture and thus may not mirror Giardia physiology in the host. Here, we have developed bioluminescent imaging (BLI) to directly interrogate and quantify the in vivo temporospatial dynamics of Giardia infection, thereby providing an improved murine model to evaluate anti-Giardia drugs. Using BLI, we determined that parasites primarily colonize the proximal small intestine nonuniformly in high-density foci. By imaging encystation-specific bioreporters, we show that encystation initiates shortly after inoculation and continues throughout the duration of infection. Encystation also initiates in high-density foci in the proximal small intestine, and high density contributes to the initiation of encystation in laboratory culture. We suggest that these high-density in vivo foci of colonizing and encysting Giardia likely result in localized disruption to the epithelium. This more accurate visualization of giardiasis redefines the dynamics of the in vivo Giardia life cycle, paving the way for future mechanistic studies of density-dependent parasitic processes in the host.

IMPORTANCEGiardia is a single-celled parasite causing significant diarrheal disease in several hundred million people worldwide. Due to limited access to the site of infection in the gastrointestinal tract, our understanding of the dynamics of Giardia infections in the host has remained limited and largely inferred from laboratory culture. To better understand Giardia physiology and colonization in the host, we developed imaging methods to quantify Giardia expressing bioluminescent physiological reporters in two relevant animal models. We discovered that parasites primarily colonize and encyst in the proximal small intestine in discrete, high-density foci. We also show that high parasite density contributes to encystation initiation.

Transcriptomic Profiling of High-Density Giardia Foci Encysting in the Murine Proximal Intestine

Giardia is a highly prevalent, understudied protistan parasite causing significant diarrheal disease worldwide. Its life cycle consists of two stages: infectious cysts ingested from contaminated food or water sources, and motile trophozoites that colonize and attach to the gut epithelium, later encysting to form new cysts that are excreted into the environment. Current understanding of parasite physiology in the host is largely inferred from transcriptomic studies using Giardia grown axenically or in co-culture with mammalian cell lines. The dearth of information about the diversity of host-parasite interactions occurring within distinct regions of the gastrointestinal tract has been exacerbated by a lack of methods to directly and non-invasively interrogate disease progression and parasite physiology in live animal hosts. By visualizing Giardia infections in the mouse gastrointestinal tract using bioluminescent imaging (BLI) of tagged parasites, we recently showed that parasites colonize the gut in high-density foci. Encystation is initiated in these foci throughout the entire course of infection, yet how the physiology of parasites within high-density foci in the host gut differs from that of cells in laboratory culture is unclear. Here we use BLI to precisely select parasite samples from high-density foci in the proximal intestine to interrogate in vivo Giardia gene expression in the host. Relative to axenic culture, we noted significantly higher expression (>10-fold) of oxidative stress, membrane transporter, and metabolic and structural genes associated with encystation in the high-density foci. These differences in gene expression within parasite foci in the host may reflect physiological changes associated with high-density growth in localized regions of the gut. We also identified and verified six novel cyst-specific proteins, including new components of the cyst wall that were highly expressed in these foci. Our in vivo transcriptome data support an emerging view that parasites encyst early in localized regions in the gut, possibly as a consequence of nutrient limitation, and also impact local metabolism and physiology.

Topical tamoxifen in the therapy of cutaneous leishmaniasis

The aims of the present work were to test the effect of tamoxifen administered topically and the therapeutic efficacy of tamoxifen and pentavalent antimonial combinations in an experimental model of cutaneous leishmaniasis. BALB/c mice infected with a luciferase expressing line of Leishmania amazonensis were treated with topical tamoxifen in two different formulations (ethanol or oil-free cream) as monotherapy or in co-administration with pentavalent antimonial. Treatment efficacy was evaluated by lesion size and parasite burden, quantified through luminescence, at the end of treatment and 4 weeks later. Topical tamoxifen, formulated in ethanol or as a cream, was shown to be effective. The interaction between tamoxifen and pentavalent antimonial was additive in vitro. Treatment with combined schemes containing tamoxifen and pentavalent antimonial was effective in reducing lesion size and parasite burden. Co-administration of tamoxifen and pentavalent antimonial was superior to monotherapy with antimonial.

Chemotherapy of leishmaniasis: present challenges

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

A Luciferase-Expressing Leishmania braziliensis Line That Leads to Sustained Skin Lesions in BALB/c Mice and Allows Monitoring of Miltefosine Treatment Outcome

Background

Leishmania braziliensis is the most prevalent species isolated from patients displaying cutaneous and muco-cutaneous leishmaniasis in South America. However, there are difficulties for studying L. braziliensis pathogenesis or response to chemotherapy in vivo due to the natural resistance of most mouse strains to infection with these parasites. The aim of this work was to develop an experimental set up that could be used to assess drug efficacy against L. braziliensis. The model was tested using miltefosine.

Methodology/Principal Findings

A L. braziliensis line, originally isolated from a cutaneous leishmaniasis patient, was passaged repeatedly in laboratory rodents and further genetically manipulated to express luciferase. Once collected from a culture of parasites freshly transformed from amastigotes, 10⁶ wild type or luciferase-expressing stationary phase promastigotes were inoculated subcutaneously in young BALB/c mice or golden hamsters. In both groups, sustained cutaneous lesions developed at the site of inoculation, no spontaneous self- healing being observed 4 months post-inoculation, if left untreated. Compared to the wild type line features, no difference was noted for the luciferase-transgenic line. Infected animals were treated with 5 or 15 mg/kg/day miltefosine orally for 15 days. At the end of treatment, lesions had regressed and parasites were not detected. However, relapses were observed in animals treated with both doses of miltefosine.

Conclusions/Significance

Here we described experimental settings for a late-healing model of cutaneous leishmaniasis upon inoculation of a luciferase-expressing L. braziliensis line that can be applied to drug development projects. These settings allowed the monitoring of the transient efficacy of a short-term miltefosine administration.

Leishmania braziliensis is the most prevalent species isolated from patients displaying either cutaneous or mucocutaneous leishmaniasis in South America. In this study, we developed a transgenic luciferase-expressing L. braziliensis line. These parasites were passaged in hamsters and mice and then transformed back into promastigotes. Once inoculated subcutaneously in the footpad of young laboratory animals—BALB/c mice or golden hamsters, rapid and sustained footpad thickness increase developed. This experimental model was used to monitor the parasite load fluctuations and the response to miltefosine treatment. Mice were treated orally over a two-week period, starting at week 4 post-inoculation. Though such a regimen was shown to display efficacy, the effect was not sustained and both parasite re-expansion and delayed footpad thickness increase were noticed.

Evaluation of the in vivo leishmanicidal activity of amphotericin B emulgel: An alternative for the treatment of skin leishmaniasis

The American Cutaneous Leishmaniasis (ACL) is an infectious disease that can be fatal. The first line of treatment is pentavalent antimonies. However, due to its potential to develop resistance, Amphotericin B (AmB) started to be used as an alternative medicine. Current treatments are limited, a fact that has led to a growing interesting in developing new therapies. This study aims to evaluate the therapeutic potential in vivo of an amphotericin B + oleic acid (OA) emulgel in the treatment of cutaneous leishmaniasis in an experimental model. Strains of Leishmania major MHOM/IL/80/Friendlin of Leishmania major were used. The animals were inoculated subcutaneously. After the development of leishmanial, nodular or ulcerative lesions, the animals were divided into three groups (control, Group A and Group B) and treated twice a day for twelve days. The weight of the animals was measured and the size of the lesions was observed. A histopathological analysis was performed with skin fragments of lesions and with the spleen of animals treated with different treatments (emulgel, AmB 3% emulgel and AmB 3% plus OA 5% emulgel). It was observed that when subjected to treatment with AmB 3% emulgel during the study period using both formulations, with enhancer and without enhancer, ulcerative lesions regress gradually or even complete cure. The quantification of the average number of parasites recovered from the inoculation site was made after the treatment in each group and the differences were considered significant. The treatment with AmB 3% and OA 5% emulgel had the best in vivo therapeutic response, showing good prospects for cutaneous leishmaniasis therapy as an alternative therapy.

Distinct courses of infection with Leishmania (L.) amazonensis are observed in BALB/c, BALB/c nude and C57BL/6 mice

Leishmania (L.) amazonensis [L. (L.) amazonensis] is widely distributed in Brazil and its symptomatic infections usually lead to few localized lesions and sometimes to diffuse cutaneous form, with nodules throughout the body, anergy to parasite antigens and poor therapeutic response. The variability of these manifestations draws attention to the need for studies on the pathophysiology of infection by this species. In this study, we analysed the course and immunological aspects of L. (L.) amazonensis infection in BALB/c and C57BL/6 strains, both susceptible, but displaying different clinical courses, and athymic BALB/c nude, to illustrate the role of T cell dependent responses. We analysed footpad thickness and parasite burden by in vivo imaging. Furthermore, we evaluated the cellular profile and cytokine production in lymph nodes and the inflammatory infiltrates of lesions. Nude mice showed delayed lesion development and less inflammatory cells in lesions, but higher parasite burden than BALB/c and C57BL/6. BALB/c and C57BL/6 mice had similar parasite burdens, lesion sizes and infiltrates until 6 weeks after infection, and after that C57BL/6 mice controlled the infection. Small differences in parasite numbers were observed in C57BL/6 macrophages in vitro, indicating that in vivo milieu accounts for most differences in infection. We believe our results shed light on the role of host immune system in the course of L. (L.) amazonensis infection by comparing three mouse strains that differ in parasitaemia and inflammatory cells.

EGFP reporter protein: its immunogenicity in Leishmania-infected BALB/c mice

Optical reporter genes such as green fluorescent protein (GFP) and luciferase are efficiently and widely used in monitoring and studying the protective/therapeutic potential of candidate agents in leishmaniasis. But several observations and controversial reports have generated a main concern, whether enhanced GFP (EGFP) affects immune response. To address this issue, we studied the immunogenicity of EGFP in vivo by two lines of stably transfected parasites (Leishmania major (EGFP) or L. major (EGFP-LUC)) in BALB/c model and/or as a recombinant protein (rEGFP) produced in vitro by bacteria in parallel. Disease progression was followed by footpad swelling measurements and parasite burden in draining lymph nodes using microtitration assay and real-time PCR, and immune responses were also evaluated in spleen. EGFP-expressing parasites generated larger swellings in comparison with wild-type (L. major) while mice immunized with rEGFP and challenged with wild-type parasite were quite comparable in footpad swelling with control group without significant difference. However, both conventional and molecular approaches revealed no significant difference in parasite load between different groups. More importantly, no significant inflammatory responses were detected in groups with higher swelling size measured by interferon-γ (IFN-γ), interleukin (IL)-10, IL-5, and nitric oxide against frozen and thawed lysate of parasite as stimulator. Altogether, these results clearly revealed that EGFP protein expressed in prokaryotic and eukaryotic hosts is not an immunological reactive molecule and acts as a neutral protein without any side effects in mice. So, EGFP expressing Leishmania could be a safe and reliable substitution for wild-types that simplifies in situ follow-up and eliminates the animal scarification wherever needed during the study.

A Review: The Current In Vivo Models for the Discovery and Utility of New Anti-leishmanial Drugs Targeting Cutaneous Leishmaniasis

The current in vivo models for the utility and discovery of new potential anti-leishmanial drugs targeting Cutaneous Leishmaniasis (CL) differ vastly in their immunological responses to the disease and clinical presentation of symptoms. Animal models that show similarities to the human form of CL after infection with Leishmania should be more representative as to the effect of the parasite within a human. Thus, these models are used to evaluate the efficacy of new anti-leishmanial compounds before human clinical trials. Current animal models aim to investigate (i) host–parasite interactions, (ii) pathogenesis, (iii) biochemical changes/pathways, (iv) in vivo maintenance of parasites, and (v) clinical evaluation of drug candidates. This review focuses on the trends of infection observed between Leishmania parasites, the predictability of different strains, and the determination of parasite load. These factors were used to investigate the overall effectiveness of the current animal models. The main aim was to assess the efficacy and limitations of the various CL models and their potential for drug discovery and evaluation. In conclusion, we found that the following models are the most suitable for the assessment of anti-leishmanial drugs: L. major–C57BL/6 mice (or–vervet monkey, or–rhesus monkeys), L. tropica–CsS-16 mice, L. amazonensis–CBA mice, L. braziliensis–golden hamster (or–rhesus monkey). We also provide in-depth guidance for which models are not suitable for these investigations.

In Vitro Infectivity Assessment by Drug Susceptibility Comparison of Recombinant Leishmania major Expressing Enhanced Green Fluorescent Protein or EGFP-Luciferase Fused Genes with Wild-Type Parasite

Leishmaniasis is a worldwide uncontrolled parasitic disease due to the lack of effective drug and vaccine. To speed up effective drug development, we need powerful methods to rapidly assess drug effectiveness against the intracellular form of Leishmania in high throughput assays. Reporter gene technology has proven to be an excellent tool for drug screening in vitro. The effects of reporter proteins on parasite infectivity should be identified both in vitro and in vivo. In this research, we initially compared the infectivity rate of recombinant Leishmania major expressing stably enhanced green fluorescent protein (EGFP) alone or EGFP-luciferase (EGFP-LUC) with the wild-type strain. Next, we evaluated the sensitivity of these parasites to amphotericin B (AmB) as a standard drug in 2 parasitic phases, promastigote and amastigote. This comparison was made by MTT and nitric oxide (NO) assay and by quantifying the specific signals derived from reporter genes like EGFP intensity and luciferase activity. To study the amastigote form, both B10R and THP-1 macrophage cell lines were infected in the stationary phase and were exposed to AmB at different time points. Our results clearly revealed that the 3 parasite lines had similar in vitro infectivity rates with comparable parasite-induced levels of NO following interferon-γ/lipopolysaccharide induction. Based on our results we proposed the more reporter gene, the faster and more sensitive evaluation of the drug efficiency.

In vivo bioimaging with tissue-specific transcription factor activated luciferase reporters

The application of transcription factor activated luciferase reporter cassettes in vitro is widespread but potential for in vivo application has not yet been realized. Bioluminescence imaging enables non-invasive tracking of gene expression in transfected tissues of living rodents. However the mature immune response limits luciferase expression when delivered in adulthood. We present a novel approach of tissue-targeted delivery of transcription factor activated luciferase reporter lentiviruses to neonatal rodents as an alternative to the existing technology of generating germline transgenic light producing rodents. At this age, neonates acquire immune tolerance to the conditionally responsive luciferase reporter. This simple and transferrable procedure permits surrogate quantitation of transcription factor activity over the lifetime of the animal. We show principal efficacy by temporally quantifying NFκB activity in the brain, liver and lungs of somatotransgenic reporter mice subjected to lipopolysaccharide (LPS)-induced inflammation. This response is ablated in Tlr4(-/-) mice or when co-administered with the anti-inflammatory glucocorticoid analogue dexamethasone. Furthermore, we show the malleability of this technology by quantifying NFκB-mediated luciferase expression in outbred rats. Finally, we use somatotransgenic bioimaging to longitudinally quantify LPS- and ActivinA-induced upregulation of liver specific glucocorticoid receptor and Smad2/3 reporter constructs in somatotransgenic mice, respectively.

Generation of luciferase-expressing Leishmania infantum chagasi and assessment of miltefosine efficacy in infected hamsters through bioimaging

Background

The only oral drug available for the treatment of leishmaniasis is miltefosine, described and approved for visceral leishmaniasis in India. Miltefosine is under evaluation for the treatment of cutaneous leishmaniasis in the Americas although its efficacy for the treatment of human visceral leishmaniasis caused by Leishmania infantum chagasi has not been described. Drug efficacy for visceral leishmaniasis is ideally tested in hamsters, an experimental model that mimics human disease. Luciferase has been validated as a quantitative tool for the determination of parasite burden in experimental leishmaniasis. However, there are no reports of luciferase detection in the model of progressive visceral leishmaniasis in hamsters. Therefore, the aims of this study were to generate recombinant Leishmania infantum chagasi expressing the luciferase gene (Lc-LUC), characterize the biological properties of this transgenic line as compared with the wild-type parasites and evaluate miltefosine effectiveness in Lc-LUC infected hamsters.

Methodology/Principal Findings

A transgenic line containing a luciferase encoding gene integrated into the ribosomal DNA locus was obtained and shown to produce bioluminescence which correlated with the number of parasites. Lc-LUC growth curves and susceptibility to pentavalent antimony and miltefosine in vitro were indistinguishable from the wild-type parasites. The effectiveness of pentavalent antimony was evaluated in Lc-LUC infected hamsters through bioimaging and determination of Leishman Donovan Units. Both methods showed concordant results. Miltefosine was effective in the treatment of Lc-LUC-infected hamsters, as demonstrated by the reduction in parasite burden in a dose-dependent manner and by prolongation of animal survival.

Conclusions/Significance

Luciferase expressing parasites are a reliable alternative for parasite burden quantification in hamsters with advantages such as the possibility of estimating parasite load before drug treatment and therefore allowing distribution of animals in groups with equivalent mean parasite burden. Miltefosine was effective in vivo in an L. infantum chagasi experimental model of infection.

Studies to determine drug efficacy in experimental models of leishmaniasis involve several difficulties. Parasite quantification in tissues is generally done by techniques that are laborious and time consuming, such as limiting dilution and microscopic counting of amastigotes in imprinting of infected organs. To overcome some of these problems, we described in this study an experimental model of visceral leishmaniasis (VL) using parasites expressing luciferase. Leishmania infantum chagasi, the etiologic agent of VL in Latin America, was genetically manipulated to express the luciferase gene in order to produce light upon addition of luciferin. We inoculated these parasites in hamsters and, about one month post-infection, we detected light in the abdominal and/or pelvic region, indicating widespread infection. We compared the data obtained by bioluminescence with microscopic counting of amastigotes in imprinting of infected spleens and both methods showed concordant results. Aiming to validate our model to be used in drug effectiveness experiments, we performed the experimental treatment with pentavalent antimony, the first choice drug for VL treatment in Latin America. We also treated infected hamsters with miltefosine, the only oral drug used for leishmaniasis treatment and for which effectiveness against L. infantum chagasi infected hamsters had not yet been reported.

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.

In vitro and in vivo miltefosine susceptibility of a Leishmania amazonensis isolate from a patient with diffuse cutaneous leishmaniasis

Miltefosine was the first oral compound approved for visceral leishmaniasis chemotherapy, and its efficacy against Leishmania donovani has been well documented. Leishmania amazonensis is the second most prevalent species causing cutaneous leishmaniasis and the main etiological agent of diffuse cutaneous leishmaniasis in Brazil. Driven by the necessity of finding alternative therapeutic strategies for a chronic diffuse cutaneous leishmaniasis patient, we evaluated the susceptibility to miltefosine of the Leishmania amazonensis line isolated from this patient, who had not been previously treated with miltefosine. In vitro tests against promastigotes and intracellular amastigotes showed that this parasite isolate was less susceptible to miltefosine than L. amazonensis type strains. Due to this difference in susceptibility, we evaluated whether genes previously associated with miltefosine resistance were involved. No mutations were found in the miltefosine transporter gene or in the Ros3 or pyridoxal kinase genes. These analyses were conducted in parallel with the characterization of L. amazonensis mutant lines selected for miltefosine resistance using a conventional protocol to select resistance in vitro, i.e., exposure of promastigotes to increasing drug concentrations. In these mutant lines, a single nucleotide mutation G852E was found in the miltefosine transporter gene. In vivo studies were also performed to evaluate the correlation between in vitro susceptibility and in vivo efficacy. Miltefosine was effective in the treatment of BALB/c mice infected with the L. amazonensis type strain and with the diffuse cutaneous leishmaniasis isolate. On the other hand, animals infected with the resistant line bearing the mutated miltefosine transporter gene were completely refractory to miltefosine chemotherapy. These data highlight the difficulties in establishing correlations between in vitro susceptibility determinations and response to chemotherapy in vivo. This study contributed to establish that the miltefosine transporter is essential for drug activity in L. amazonensis and a potential molecular marker of miltefosine unresponsiveness in leishmaniasis patients.

Leishmania amazonensis is the etiological agent of diffuse cutaneous leishmaniasis. The disease is extremely difficult to treat and frequently relapses once the treatment is interrupted. Although not yet approved in Brazil, miltefosine is an attractive alternative for leishmaniasis treatment due to its oral administration and low incidence of side effects. Here, we evaluated the efficacy of miltefosine against a L. amazonensis line that was isolated from a chronic diffuse cutaneous leishmaniasis patient to ascertain whether miltefosine could be considered as a therapeutic option in this case. Parasites isolated from this patient were less susceptible to miltefosine than a reference strain in vitro. The mechanisms underlying this decreased susceptibility were studied in this natural parasite isolate in parallel with mutant strains selected in vitro for miltefosine resistance. A mutation in the gene encoding the miltefosine transporter was identified in the mutants selected in vitro but not in the line isolated from the patient. Notwithstanding the decreased susceptibility in vitro, when used to treat infected mice, miltefosine was equally effective against the isolate from the patient and the type strain, but completely ineffective against the resistant line.

Antileishmanial activity of the estrogen receptor modulator raloxifene

Background

The treatment of leishmaniasis relies mostly on parenteral drugs with potentially serious adverse effects. Additionally, parasite resistance in the treatment of leishmaniasis has been demonstrated for the majority of drugs available, making the search for more effective and less toxic drugs and treatment regimens a priority for the control of leishmaniasis. The aims of this study were to evaluate the antileishmanial activity of raloxifene in vitro and in vivo and to investigate its mechanism of action against Leishmania amazonensis.

Methodology/Principal Findings

Raloxifene was shown to possess antileishmanial activity in vitro against several species with EC₅₀ values ranging from 30.2 to 38.0 µM against promastigotes and from 8.8 to 16.2 µM against intracellular amastigotes. Raloxifene's mechanism of action was investigated through transmission electron microscopy and labeling with propidium iodide, DiSBAC₂(3), rhodamine 123 and monodansylcadaverine. Microscopic examinations showed that raloxifene treated parasites displayed autophagosomes and mitochondrial damage while the plasma membrane remained continuous. Nonetheless, plasma membrane potential was rapidly altered upon raloxifene treatment with initial hyperpolarization followed by depolarization. Loss of mitochondrial membrane potential was also verified. Treatment of L. amazonensis – infected BALB/c mice with raloxifene led to significant decrease in lesion size and parasite burden.

Conclusions/Significance

The results of this work extend the investigation of selective estrogen receptor modulators as potential candidates for leishmaniasis treatment. The antileishmanial activity of raloxifene was demonstrated in vitro and in vivo. Raloxifene produces functional disorder on the plasma membrane of L. amazonensis promastigotes and leads to functional and morphological disruption of mitochondria, which culminate in cell death.

Cutaneous and visceral leishmaniasis are part of the group we call neglected diseases. They are serious conditions that afflict millions in vast regions of the world. These diseases are very difficult to treat. This is due to the scanty choice of effective drugs together with their potentially severe side effects. One way of finding new treatments for these neglected conditions is to repurpose drugs that are already in use to treat other diseases. In this paper, we show that raloxifene, a drug that is used for the treatment of osteoporosis and also as an alternative in the treatment of breast cancer, is active against the causative agents of leishmaniasis and is effective in the treatment of cutaneous leishmaniasis in an experimental model. We also show that the antileishmanial mechanism of action of raloxifene is related to damage to the cell membrane and to the mitochondrion of the parasite.

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.

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.