Distinct activation mechanisms trigger the trypanocidal activity of DNA damaging prodrugs.

Quinone-based compounds have been exploited to treat infectious diseases and cancer, with such chemicals often functioning as inhibitors of key metabolic pathways or as prodrugs. Here, we screened an aziridinyl 1,4-benzoquinone (ABQ) library against the causative agents of trypanosomiasis, and cutaneous leishmaniasis, identifying several potent structures that exhibited EC50 values of <100 nM. However, these compounds also displayed significant toxicity towards mammalian cells indicating that they are not suitable therapies for systemic infections. Using anti-T. brucei ABQs as chemical probes, we demonstrated that these exhibit different trypanocidal modes of action. Many functioned as type I nitroreductase (TbNTR) or cytochrome P450 reductase (TbCPR) dependent prodrugs that, following activation, generate metabolites which promote DNA damage, specifically interstrand crosslinks (ICLs). Trypanosomes lacking TbSNM1, a nuclease that specifically repairs ICLs, are hypersensitive to most ABQ prodrugs, a phenotype exacerbated in cells also engineered to express elevated levels of TbNTR or TbCPR. In contrast, ABQs that contain substituent groups on the biologically active aziridine do not function as TbNTR or TbCPR-activated prodrugs and do not promote DNA damage. By unravelling how ABQs mediate their activities, features that facilitate the desired anti-parasitic growth inhibitory effects could be incorporated into new, safer compounds targeting these neglected tropical diseases.

Pharmacodynamics and cellular accumulation of amphotericin B and miltefosine in Leishmania donovani-infected primary macrophages.

Objectives: We examined the in vitro pharmacodynamics and cellular accumulation of the standard anti-leishmanial drugs amphotericin B and miltefosine in intracellular Leishmania donovani amastigote-macrophage drug assays. Methods: Primary mouse macrophages were infected with L. donovani amastigotes. In time-kill assays infected macrophages were exposed to at least six different concentrations of serially diluted drugs and the percentage of infected macrophages was determined after 6, 12, 24, 48, 72 and 120 h of exposure. Cellular drug accumulation was measured following exposure to highly effective drug concentrations for 1, 6, 24, 48 and 72 h. Data were analysed through a mathematical model, relating drug concentration to the percentage of infected cells over time. Host cell membrane damage was evaluated through measurement of lactate dehydrogenase release. The effect of varying the serum and albumin concentrations in medium on the cellular accumulation levels of miltefosine was measured. Results: Amphotericin B was more potent than miltefosine (EC50 values of 0.65 and 1.26 µM, respectively) and displayed a wider therapeutic window in vitro. The kinetics of the cellular accumulation of amphotericin B was concentration- and formulation-dependent. At an extracellular concentration of 10 µM miltefosine maximum cellular drug levels preceded maximum anti-leishmanial kill. Miltefosine induced membrane damage in a concentration-, time- and serum-dependent manner. Its cellular accumulation levels increased with decreasing amounts of protein in assay medium. Conclusions: We have developed a novel approach to investigate the cellular pharmacology of anti-leishmanial drugs that serves as a model for the characterization of new drug candidates.

Snapshot Profiling of the Antileishmanial Potency of Lead Compounds and Drug Candidates against Intracellular Leishmania donovani Amastigotes, with a Focus on Human-Derived Host Cells.

This study characterized the in vitro potencies of antileishmanial agents against intracellular Leishmania donovani amastigotes in primary human macrophages, obtained with or without CD14-positive monocyte enrichment, phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 cells, and mouse peritoneal exudate macrophages (PEMs). Host cell-dependent potency was confirmed for pentavalent and trivalent antimony. Fexinidazole was inactive against intracellular amastigotes across the host cell panel. Fexinidazole sulfone, (R)-PA-824, (S)-PA-824, and VL-2098 displayed similar potency in all of the host cells tested.

Pharmacodynamics and Biodistribution of Single-Dose Liposomal Amphotericin B at Different Stages of Experimental Visceral Leishmaniasis.

Visceral leishmaniasis is a neglected tropical disease that causes significant morbidity and mortality worldwide. Characterization of the pharmacokinetics and pharmacodynamics of antileishmanial drugs in preclinical models is important for drug development and use. Here we investigated the pharmacodynamics and drug distribution of liposomal amphotericin B (AmBisome) in Leishmania donovani-infected BALB/c mice at three different dose levels and two different time points after infection. We additionally compared drug levels in plasma, liver, and spleen in infected and uninfected BALB/c mice over time. At the highest administered dose of 10 mg/kg AmBisome, >90% parasite inhibition was observed within 2 days after drug administration, consistent with drug distribution from blood to tissue within 24 h and a fast rate of kill. Decreased drug potency was observed in the spleen when AmBisome was administered on day 35 after infection, compared to day 14 after infection. Amphotericin B concentrations and total drug amounts per organ were lower in liver and spleen when AmBisome was administered at the advanced stage of infection and compared to those in uninfected BALB/c mice. However, the magnitude of difference was lower when total drug amounts per organ were estimated. Differences were also noted in drug distribution to L. donovani-infected livers and spleens. Taken together, our data suggest that organ enlargement and other pathophysiological factors cause infection- and organ-specific drug distribution and elimination after administration of single-dose AmBisome to L. donovani-infected mice. Plasma drug levels were not reflective of changes in drug levels in tissues.

Metabolic, immune, and gut microbial signals mount a systems response to Leishmania major infection.

Parasitic infections such as leishmaniasis induce a cascade of host physiological responses, including metabolic and immunological changes. Infection with Leishmania major parasites causes cutaneous leishmaniasis in humans, a neglected tropical disease that is difficult to manage. To understand the determinants of pathology, we studied L. major infection in two mouse models: the self-healing C57BL/6 strain and the nonhealing BALB/c strain. Metabolic profiling of urine, plasma, and feces via proton NMR spectroscopy was performed to discover parasite-specific imprints on global host metabolism. Plasma cytokine status and fecal microbiome were also characterized as additional metrics of the host response to infection. Results demonstrated differences in glucose and lipid metabolism, distinctive immunological phenotypes, and shifts in microbial composition between the two models. We present a novel approach to integrate such metrics using correlation network analyses, whereby self-healing mice demonstrated an orchestrated interaction between the biological measures shortly after infection. In contrast, the response observed in nonhealing mice was delayed and fragmented. Our study suggests that trans-system communication across host metabolism, the innate immune system, and gut microbiome is key for a successful host response to L. major and provides a new concept, potentially translatable to other diseases.

Sequential chemoimmunotherapy of experimental visceral leishmaniasis using a single low dose of liposomal amphotericin B and a novel DNA vaccine candidate.

Combination therapies for leishmaniasis, including drugs and immunomodulators, are one approach to shorten treatment courses and to improve the treatment of complex manifestations of the disease. We evaluated a novel T-cell-epitope-enriched DNA vaccine candidate (LEISHDNAVAX) as host-directed immunotherapy in combination with a standard antileishmanial drug in experimental visceral leishmaniasis. Here we show that the DNA vaccine candidate can boost the efficacy of a single suboptimal dose of liposomal amphotericin B in C57BL/6 mice.

An essential type I nitroreductase from Leishmania major can be used to activate leishmanicidal prodrugs.

Nitroaromatic prodrugs are used to treat a range of microbial infections with selectivity achieved by specific activation reactions. For trypanosomatid parasites, this is mediated by type I nitroreductases. Here, we demonstrate that the causative agent of leishmaniasis, Leishmania major, expresses an FMN-containing nitroreductase (LmNTR) that metabolizes a wide range of substrates, and based on electron donor and acceptor preferences, it may function as an NADH:quinone oxidoreductase. Using gene deletion approaches, we demonstrate that this activity is essential to L. major promastigotes, the parasite forms found in the insect vector. Intriguingly, LmNTR(+/-) heterozygote promastigote parasites could readily differentiate into infectious metacyclic cells but these were unable to establish infections in cultured mammalian cells and caused delayed pathology in mice. Furthermore, we exploit the LmNTR activity evaluating a library of nitrobenzylphosphoramide mustards using biochemical and phenotypic screens. We identify a subset of compounds that display significant growth inhibitory properties against the intracellular parasite form found in the mammalian hosts. The leishmanicidal activity was shown to be LmNTR-specific as the LmNTR(+/-) heterozygote promastigotes displayed resistance to the most potent mustards. We conclude that LmNTR can be targeted for drug development by exploiting its prodrug activating property or by designing specific inhibitors to block its endogenous function.

Evaluating aziridinyl nitrobenzamide compounds as leishmanicidal prodrugs.

Many of the nitroaromatic agents used in medicine function as prodrugs and must undergo activation before exerting their toxic effects. In most cases, this is catalyzed by flavin mononucleotide (FMN)-dependent type I nitroreductases (NTRs), a class of enzyme absent from higher eukaryotes but expressed by bacteria and several eukaryotic microbes, including trypanosomes and Leishmania. Here, we utilize this difference to evaluate whether members of a library of aziridinyl nitrobenzamides have activity against Leishmania major. Biochemical screens using purified L. major NTR (LmNTR) revealed that compounds containing an aziridinyl-2,4-dinitrobenzyl core were effective substrates for the enzyme and showed that the 4-nitro group was important for this activity. To facilitate drug screening against intracellular amastigote parasites, we generated leishmanial cells that expressed the luciferase reporter gene and optimized a mammalian infection model in a 96-well plate format. A subset of aziridinyl-2,4-dinitrobenzyl compounds possessing a 5-amide substituent displayed significant growth-inhibitory properties against the parasite, with the most potent agents generating 50% inhibitory concentrations of <100 nM for the intracellular form. This antimicrobial activity was shown to be LmNTR specific since L. major NTR(+/-) heterozygote parasites were slightly resistance to most aziridinyl dinitrobenzyl agents tested. When the most potent leishmanicidal agents were screened against the mammalian cells in which the amastigote parasites were propagated, no growth-inhibitory effect was observed at concentrations of up to 100 µM. We conclude that the aziridinyl nitrobenzamides represent a new lead structure that may have the potential to treat leishmanial infections.

Antileishmanial activity, uptake, and biodistribution of an amphotericin B and poly(α-Glutamic Acid) complex.

A noncovalent, water-soluble complex of amphotericin B (AMB) and poly(α-glutamic acid) (PGA), with AMB loadings ranging from 25 to 55% (wt/wt) using PGA with a molecular weight range of 50,000 to 70,000, was prepared as a potential new treatment for visceral leishmaniasis (VL). The AMB-PGA complex was shown to be as active as Fungizone (AMB deoxycholate) against intracellular Leishmania donovani amastigotes in differentiated THP-1 cells. The in vitro uptake of the AMB-PGA complex by differentiated THP-1 cells was similar to that of Fungizone and higher than that of AmBisome (liposomal AMB). The AMB-PGA complex also displayed a dose-response profile similar to that of AmBisome in vivo in BALB/c mice against L. donovani, with 50% effective doses (ED50s) of 0.24 ± 0.03 mg/kg of body weight for the AMB-PGA complex and 0.24 ± 0.06 mg/kg for AmBisome. A biodistribution study with mice indicated that the AMB-PGA complex cleared more rapidly from plasma than AmBisome, with a comparable low level of distribution to the kidneys.

Noncovalent complexation of amphotericin-B with Poly(α-glutamic acid).

A noncovalent complex of amphotericin B (AmB) and poly(α-glutamic acid) (PGA) was prepared to develop a safe and stable formulation for the treatment of leishmaniasis. The loading of AmB in the complex was in the range of ∼20-50%. AmB was in a highly aggregated state with an aggregation ratio often above 2.0. This complex (AmB-PGA) was shown to be stable and to have reduced toxicity to human red blood cells and KB cells compared to the parent compound; cell viability was not affected at an AmB concentration as high as 50 and 200 µg/mL respectively. This AmB-PGA complex retained AmB activity against intracellular Leishmania major amastigotes in the differentiated THP-1 cells with an EC50 of 0.07 ± 0.03-0.08 ± 0.01 µg/mL, which is similar to Fungizone (EC50 of 0.06 ± 0.01 µg/mL). The in vitro antileishmanial activity of the complex against Leishmania donovani was retained after storage at 37 °C for 7 days in the form of a solution (EC50 of 0.27 ± 0.03 to 0.35 ± 0.04 µg/mL) and for 30 days as a solid (EC50 of 0.41 ± 0.07 to 0.63 ± 0.25 µg/mL). These encouraging results indicate that the AmB-PGA complex has the potential for further development.

In vitro interactions between sitamaquine and amphotericin B, sodium stibogluconate, miltefosine, paromomycin and pentamidine against Leishmania donovani.

OBJECTIVES: To evaluate in vitro interactions between sitamaquine and the current antileishmanial drugs amphotericin B, sodium stibogluconate, miltefosine, paromomycin and pentamidine against intracellular Leishmania donovani amastigotes in peritoneal mouse macrophages. A second objective was to evaluate the susceptibility of antimony-resistant L. donovani isolates to sitamaquine. METHODS: Mouse peritoneal macrophages were infected with L. donovani amastigotes. Drug susceptibility was assessed in a standard 5 day assay and drug interactions with a modified fixed ratio isobologram method. Fractional inhibitory concentrations (FICs), sum FICs (∑FICs) and an overall mean ∑FIC were calculated for each combination. The nature of interaction was classified on the basis of the mean ∑FIC as follows: synergy as mean ∑FIC≤0.5, indifference as mean ∑FIC between >0.5 and ≤4 and antagonism as mean ∑FIC>4. RESULTS: Interactions between sitamaquine and amphotericin B, sodium stibogluconate, paromomycin and miltefosine were classified as indifferent at the 50% and 90% effective concentration (EC50 and EC90, respectively) levels. The sitamaquine/pentamidine combination was synergistic, with overall mean ∑FICs from 0.5 to 0.6 at the EC50 level and from 0.3 to 0.7 at the EC90 level. Sitamaquine displayed in vitro activity against L. donovani isolates resistant to sodium stibogluconate. CONCLUSIONS: This study expands the preclinical data on drug combinations and provides the basis for further studies as antileishmanial chemotherapy is moving towards multidrug treatment regimens.

Pharmacokinetic / pharmacodynamic relationships of liposomal amphotericin B and miltefosine in experimental visceral leishmaniasis.

BACKGROUND: There is a continued need to develop effective and safe treatments for visceral leishmaniasis (VL). Preclinical studies on pharmacokinetics and pharmacodynamics of anti-infective agents, such as anti-bacterials and anti-fungals, have provided valuable information in the development and dosing of these agents. The aim of this study was to characterise the pharmacokinetic and pharmacodynamic properties of the anti-leishmanial drugs AmBisome and miltefosine in a preclinical disease model of VL. METHODOLOGY / PRINCIPAL FINDINGS: BALB/c mice were infected with L. donovani (MHOM/ET/67/HU3) amastigotes. Groups of mice were treated with miltefosine (orally, multi-dose regimen) or AmBisome (intravenously, single dose regimen) or left untreated as control groups. At set time points groups of mice were killed and plasma, livers and spleens harvested. For pharmacodynamics the hepatic parasite burden was determined microscopically from tissue impression smears. For pharmacokinetics drug concentrations were measured in plasma and whole tissue homogenates by LC-MS. Unbound drug concentrations were determined by rapid equilibrium dialysis. Doses exerting maximum anti-leishmanial effects were 40 mg/kg for AmBisome and 150 mg/kg (cumulatively) for miltefosine. AmBisome displayed a wider therapeutic range than miltefosine. Dose fractionation at a total dose of 2.5 mg/kg pointed towards concentration-dependent anti-leishmanial activity of AmBisome, favouring the administration of large doses infrequently. Protein binding was >99% for miltefosine and amphotericin B in plasma and tissue homogenates. CONCLUSION / SIGNIFICANCE: Using a PK/PD approach we propose optimal dosing strategies for AmBisome. Additionally, we describe pharmacokinetic and pharmacodynamic properties of miltefosine and compare our findings in a preclinical disease model to available knowledge from studies in humans. This approach also presents a strategy for improved use of animal models in the drug development process for VL.

In vitro activity of anti-leishmanial drugs against Leishmania donovani is host cell dependent.

OBJECTIVES: To evaluate the in vitro activity of anti-leishmanial drugs against intracellular Leishmania donovani amastigotes in different types of macrophages. METHODS: Mouse peritoneal macrophages (PEMs), mouse bone marrow-derived macrophages (BMMPhi), human peripheral blood monocyte-derived macrophages (PBM Phi) and differentiated THP-1 cells were infected with L. donovani. Cultures were incubated with sodium stibogluconate, amphotericin B deoxycholate (Fungizone), miltefosine or paromomycin sulphate over six concentrations in 3-fold serial dilutions for 5 days. Analysis was based on percentage inhibition of infected macrophages and EC(50)/EC(90) values estimated using sigmoidal curve-fitting. RESULTS: The rank order of drug activity was the same in the different macrophage populations: amphotericin B > miltefosine > sodium stibogluconate > paromomycin. However, significant (P < 0.05) differences were observed between populations. Amphotericin B was more active in PEMs and BMM Phi (EC(50) 0.02-0.06 microM) compared with PBM Phi and differentiated THP-1 cells (EC(50) 0.08-0.40 microM) and miltefosine was more active in PBM Phi (EC(50) 0.16-0.74 microM) compared with PEMs and BMM Phi (EC(50) 2.60-7.67 microM). Sodium stibogluconate displayed highest activity in PBM Phi (EC(50) 1.38-1.89 microg Sb(v)/mL), followed by PEMs (EC(50) 21.75-27.79 microg Sb(v)/mL) and BMM Phi and differentiated THP-1 cells (EC(50) 28.96-112.77 microg Sb(v)/mL). Paromomycin showed highest activity in PBM Phi (EC(50) 80.03-104.38 microM) and PEMs (EC(50) 75.42-201.63 microM). CONCLUSIONS: In vitro activity of anti-leishmanial drugs is host cell dependent. This has implications for: (i) the evaluation of in vitro drug activity; (ii) the evaluation of drug susceptibility of clinical isolates; and (iii) the standardization of anti-leishmanial drug assays.

Water-soluble polymer-drug conjugates for combination chemotherapy against visceral leishmaniasis.

There is a need for new safe, effective and short-course treatments for leishmaniasis; one strategy is to use combination chemotherapy. Polymer-drug conjugates have shown promise for the delivery of anti-leishmanial agents such as amphotericin B. In this paper, we report on the preparation and biological evaluation of polymer-drug conjugates of N-(2-hydroxypropyl)methacrylamide (HPMA), amphotericin B and alendronic acid. The combinatorial polymer-drug conjugates were effective anti-leishmanial agents in vitro and in vivo, but offered no advantage over the single poly(HPMA)-amphotericin B conjugates.

Impact of individual-level factors on Ex vivo mycobacterial growth inhibition: Associations of immune cell phenotype, cytomegalovirus-specific response and sex with immunity following BCG vaccination in humans.

Understanding factors associated with varying efficacy of Bacillus Calmette-Guérin (BCG) would aid the development of improved vaccines against tuberculosis (TB). In addition, investigation of individual-level factors affecting mycobacterial-specific immune responses could provide insight into confounders of vaccine efficacy in clinical trials. Mycobacterial growth inhibition assays (MGIA) have been developed to assess vaccine immunogenicity ex vivo and provide a measure of immune function against live mycobacteria. In this study, we assessed the impact of immune cell phenotype, cytomegalovirus (CMV)-specific response and sex on ex vivo growth inhibition following historical BCG vaccination in a cohort of healthy individuals (n = 100). A higher frequency of cytokine-producing NK cells in peripheral blood was associated with enhanced ex vivo mycobacterial growth inhibition following historical BCG vaccination. A CMV-specific response was associated with T-cell activation, a risk factor for TB disease and we also observed an association between T-cell activation and ex vivo mycobacterial growth. Interestingly, BCG-vaccinated females in our cohort controlled mycobacterial growth better than males. In summary, our present study has shown that individual-level factors influence capacity to control mycobacterial growth following BCG vaccination and the MGIA could be used as a tool to assess how vaccine candidates may perform in different populations.

Historical BCG vaccination combined with drug treatment enhances inhibition of mycobacterial growth ex vivo in human peripheral blood cells.

Tuberculosis (TB) is a leading infectious cause of death globally. Drug treatment and vaccination, in particular with Bacillus Calmette-Guérin (BCG), remain the main strategies to control TB. With the emergence of drug resistance, it has been proposed that a combination of TB vaccination with pharmacological treatment may provide a greater therapeutic value. We implemented an ex vivo mycobacterial growth inhibition assay (MGIA) to discriminate vaccine responses in historically BCG-vaccinated human volunteers and to assess the contribution of vaccine-mediated immune response towards the killing effect of mycobacteria in the presence of the antibiotics isoniazid (INH) and rifampicin (RIF), in an attempt to develop the assay as a screening tool for therapeutic TB vaccines. BCG vaccination significantly enhanced the ability of INH to control mycobacterial growth ex vivo. The BCG-vaccinated group displayed a higher production of IFN-γ and IP-10 when peripheral blood mononuclear cells (PBMC) were co-cultured with INH, with a similar trend during co-culture with RIF. A higher frequency of IFN-γ+ and TNF-α+ CD3- CD4- CD8- cells was observed, suggesting the contribution of Natural Killer (NK) cells in the combined effect between BCG vaccination and INH. Taken together, our data indicate the efficacy of INH can be augmented following historical BCG vaccination, which support findings from previous observational and animal studies.

RUTI Vaccination Enhances Inhibition of Mycobacterial Growth ex vivo and Induces a Shift of Monocyte Phenotype in Mice.

Tuberculosis (TB) is a major global health problem and there is a dire need for an improved treatment. A strategy to combine vaccination with drug treatment, termed therapeutic vaccination, is expected to provide benefit in shortening treatment duration and augmenting treatment success rate. RUTI candidate vaccine has been specifically developed as a therapeutic vaccine for TB. The vaccine is shown to reduce bacillary load when administered after chemotherapy in murine and guinea pig models, and is also immunogenic when given to healthy adults and individuals with latent TB. In the absence of a validated correlate of vaccine-induced protection for TB vaccine testing, mycobacterial growth inhibition assay (MGIA) has been developed as a comprehensive tool to evaluate vaccine potency ex vivo. In this study, we investigated the potential of RUTI vaccine to control mycobacterial growth ex vivo and demonstrated the capacity of MGIA to aid the identification of essential immune mechanism. We found an association between the peak response of vaccine-induced growth inhibition and a shift in monocyte phenotype following RUTI vaccination in healthy mice. The vaccination significantly increased the frequency of non-classical Ly6C- monocytes in the spleen after two doses of RUTI. Furthermore, mRNA expressions of Ly6C--related transcripts (Nr4a1, Itgax, Pparg, Bcl2) were upregulated at the peak vaccine response. This is the first time the impact of RUTI has been assessed on monocyte phenotype. Given that non-classical Ly6C- monocytes are considered to play an anti-inflammatory role, our findings in conjunction with previous studies have demonstrated that RUTI could induce a balanced immune response, promoting an effective cell-mediated response whilst at the same time limiting excessive inflammation. On the other hand, the impact of RUTI on non-classical monocytes could also reflect its impact on trained innate immunity which warrants further investigation. In summary, we have demonstrated a novel mechanism of action of the RUTI vaccine, which suggests the importance of a balanced M1/M2 monocyte function in controlling mycobacterial infection. The MGIA could be used as a screening tool for therapeutic TB vaccine candidates and may aid the development of therapeutic vaccination regimens for TB in the near future.

Histopathological and immunohistochemical characterisation of hepatic granulomas in Leishmania donovani-infected BALB/c mice: a time-course study.

BACKGROUND: Visceral leishmaniasis (VL) is a neglected tropical disease (NTD), caused by the intracellular protozoan parasites Leishmania donovani and Leishmania infantum. Symptomatic VL is considered fatal when left untreated. At present, there is no effective vaccine licensed for human use and available chemotherapies have limitations. Understanding the local immune mechanisms required for the control of infection is a key factor for developing effective vaccines and therapeutics. METHODS: We have investigated the development of the typical granulomatous lesions in the liver in experimental VL over time, together with the local immune responses. BALB/c mice were infected intravenously with a dose of 2 × 107 L. donovani amastigotes (MHOM/ET/67/HU3) and sacrificed at 15, 35 and 63 days post-infection (dpi). Histopathology and immunohistochemical techniques were used for the detection of Leishmania antigen, selected cell types including B and T lymphocytes, macrophages and neutrophils (CD45R-B220+, CD3+, F4/80+ and Ly-6G+) and iNOS. RESULTS: Granulomatous lesions were identified as early as 15 dpi in the livers of all infected animals. Three categories were used to classify liver granulomas (immature, mature and clear). Clear granulomas were exclusively detected from 35 dpi onwards. Kupffer cells (F4/80+) were predominant in immature granulomas, regardless of the dpi. Nonetheless, the highest expression was found 63 dpi. Positive staining for iNOS was mainly observed in the cytoplasm of fused Kupffer cells and the highest expression observed at 35 dpi. T cells (CD3+) and B cells (CD45R-B220+) were predominant in more advanced granuloma stages, probably related to the establishment of acquired immunity. Neutrophils (Ly-6G+) were predominantly observed in mature granulomas with the highest expression at 15 dpi. Neutrophils were lower in numbers compared to other cell types, particularly at later time points. CONCLUSIONS: Our results reflect the role of macrophages during the early stage of infection and the establishment of a lymphocytic response to control the infection in more advanced stages.

Tissue and host species-specific transcriptional changes in models of experimental visceral leishmaniasis.

Background: Human visceral leishmaniasis, caused by infection with Leishmania donovani or L. infantum, is a potentially fatal disease affecting 50,000-90,000 people yearly in 75 disease endemic countries, with more than 20,000 deaths reported. Experimental models of infection play a major role in understanding parasite biology, host-pathogen interaction, disease pathogenesis, and parasite transmission. In addition, they have an essential role in the identification and pre-clinical evaluation of new drugs and vaccines. However, our understanding of these models remains fragmentary. Although the immune response to Leishmania donovani infection in mice has been extensively characterized, transcriptomic analysis capturing the tissue-specific evolution of disease has yet to be reported. Methods: We provide an analysis of the transcriptome of spleen, liver and peripheral blood of BALB/c mice infected with L. donovani. Where possible, we compare our data in murine experimental visceral leishmaniasis with transcriptomic data in the public domain obtained from the study of L. donovani-infected hamsters and patients with human visceral leishmaniasis. Digitised whole slide images showing the histopathology in spleen and liver are made available via a dedicated website, www.leishpathnet.org. Results: Our analysis confirms marked tissue-specific alterations in the transcriptome of infected mice over time and identifies previously unrecognized parallels and differences between murine, hamster and human responses to infection. We show commonality of interferon-regulated genes whilst confirming a greater activation of type 2 immune pathways in infected hamsters compared to mice. Cytokine genes and genes encoding immune checkpoints were markedly tissue specific and dynamic in their expression, and pathways focused on non-immune cells reflected tissue specific immunopathology. Our data also addresses the value of measuring peripheral blood transcriptomics as a potential window into underlying systemic disease.  Conclusions: Our transcriptomic data, coupled with histopathologic analysis of the tissue response, provide an additional resource to underpin future mechanistic studies and to guide clinical research.

Inactivation of the miltefosine transporter, LdMT, causes miltefosine resistance that is conferred to the amastigote stage of Leishmania donovani and persists in vivo.

Miltefosine (hexadecylphosphocholine) is the first oral antileishmanial drug. In this study, we addressed the question whether miltefosine-resistant Leishmania donovani promastigotes transform to miltefosine-resistant amastigotes. A promastigote line, M-mutR, showed defective internalisation of miltefosine owing to mutations in LdMT, similar to previously described resistant lines. M-mutR parasites were infective to macrophages in vitro as well as in BALB/c mice in vivo. There was good correlation of in vitro resistance indices between promastigotes and intracellular amastigotes. Most importantly, M-mutR parasites retained the resistant phenotype in vivo, with no decrease of hepatic burden in BALB/c mice following miltefosine treatment up to 30 mg/kg (ca. 90% inhibition in wild-type infections). No cross-resistance to other antileishmanial drugs was observed in M-mutR amastigotes.