A comparison of the activities of three amphotericin B lipid formulations against experimental visceral and cutaneous leishmaniasis

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.

Comparison of a high-throughput high-content intracellular Leishmania donovani assay with an axenic amastigote assay

Visceral leishmaniasis is a neglected tropical disease with significant health impact. The current treatments are poor, and there is an urgent need to develop new drugs. Primary screening assays used for drug discovery campaigns have typically used free-living forms of the Leishmania parasite to allow for high-throughput screening. Such screens do not necessarily reflect the physiological situation, as the disease-causing stage of the parasite resides inside human host cells. Assessing the drug sensitivity of intracellular parasites on scale has recently become feasible with the advent of high-content screening methods. We describe here a 384-well microscopy-based intramacrophage Leishmania donovani assay and compare it to an axenic amastigote system. A panel of eight reference compounds was tested in both systems, as well as a human counterscreen cell line, and our findings show that for most clinically used compounds both axenic and intramacrophage assays report very similar results. A set of 15,659 diverse compounds was also screened using both systems. This resulted in the identification of seven new antileishmanial compounds and revealed a high false-positive rate for the axenic assay. We conclude that the intramacrophage assay is more suited as a primary hit-discovery platform than the current form of axenic assay, and we discuss how modifications to the axenic assay may render it more suitable for hit-discovery.

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

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

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.

Immunoadjuvant chemotherapy of visceral leishmaniasis in hamsters using amphotericin B-encapsulated nanoemulsion template-based chitosan nanocapsules

The accessible treatment options for life-threatening neglected visceral leishmaniasis (VL) disease have problems with efficacy, stability, adverse effects, and cost, making treatment a complex issue. Here we formulated nanometric amphotericin B (AmB)-encapsulated chitosan nanocapsules (CNC-AmB) using a polymer deposition technique mediated by nanoemulsion template fabrication. CNC-AmB exhibited good steric stability in vitro, where the chitosan content was found to be efficient at preventing destabilization in the presence of protein and Ca(2+). A toxicity study on the model cell line J774A and erythrocytes revealed that CNC-AmB was less toxic than commercialized AmB formulations such as Fungizone and AmBisome. The results of in vitro (macrophage-amastigote system; 50% inhibitory concentration [IC(50)], 0.19 ± 0.04 μg AmB/ml) and in vivo (Leishmania donovani-infected hamsters; 86.1% ± 2.08% parasite inhibition) experiments in conjunction with effective internalization by macrophages illustrated the efficacy of CNC-AmB at augmenting antileishmanial properties. Quantitative mRNA analysis by real-time PCR (RT-PCR) showed that the improved effect was synergized with the upregulation of tumor necrosis factor alpha (TNF-α), interleukin-12 (IL-12), and inducible nitric oxide synthase and with the downregulation of transforming growth factor β (TGF-β), IL-10, and IL-4. These research findings suggest that a cost-effective CNC-AmB immunoadjuvant chemotherapeutic delivery system could be a viable alternative to the current high-cost commercial lipid-based formulations.

Review of the current treatments for leishmaniases

Leishmaniases are vector-borne zoonotic diseases that are prevalent in tropical and subtropical areas in the world, with two million new cases occurring yearly. Visceral and tegumentary forms of leishmaniasis are known. The latter form may present as localized cutaneous or mucosal forms, disseminated, diffuse forms, or leishmaniasis recidiva cutis. Visceral leishmaniasis is caused by parasites of the species Leishmania (Leishmania) donovani and L. (L.) infantum, and tegumentary leishmaniasis is caused by 15 other species, with distinct distributions in the Old and New World. The varied clinical manifestations, the multitude of Leishmania species, and the increasing incidence of HIV coinfection make the diagnosis and treatment of leishmaniases complex. Since there are no solid data relating clinical manifestations, treatment outcomes and Leishmania species the decision regarding the best therapeutic option is almost entirely based on clinical manifestations. Because most of the literature is focused on leishmaniasis in the Old World, in this review we present data on the treatment of New World leishmaniasis in more detail. Ranked therapeutic options, clinical trials, and also observations, even with a restricted number of subjects, on treatment outcome of visceral and different forms of tegumentary leishmaniasis, are presented. Treatment for leishmaniasis in HIV-coinfected patients is addressed as well. Some of these data strongly suggest that the differences in the outcome of the treatment are related to the Leishmania species. Therefore, although it is not possible at most points of care to identify the species causing the infection - a process that requires a well equipped laboratory - the infecting species should be identified whenever possible. More recent approaches, such as the use of immunomodulators and immunotherapy, and the lines for development of new candidate drugs are mentioned.

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

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

Cutaneous leishmaniasis in a Japanese returnee from West Africa successfully treated with liposomal amphotericin B

Leishmaniasis has been occasionally reported in returnees from endemic areas. Here, we report a case of cutaneous leishmaniasis in a 33-year-old Japanese man who presented with a skin nodule after returning from an 8-year stay in West Africa including Burkina Faso. He was successfully treated with liposomal amphotericin B with no significant adverse effects. This is the first Japanese case of cutaneous leishmaniasis treated successfully with liposomal amphotericin B.

Plant derived therapeutics for the treatment of Leishmaniasis

Diseases caused by insect borne trypanosomatid parasites are significant, yet remain a neglected public health problem. Leishmania, a unicellular protozoan parasite is the causative organism of Leishmaniasis and is transmitted by female phlebotamine sandflies affecting millions of people worldwide. In the wake of resistance to pentavalent antimonial drugs, new therapeutic alternatives are desirable. The plant kingdom has in the past provided several affordable compounds and this review aims to provide an overview of the current status of available leishmanicidal plant derived compounds that are effective singly or in combination with conventional anti-leishmanial drugs, yet are non toxic to mammalian host cells. Furthermore, delineation of the contributory biochemical mechanisms involved in mediating their effect would help develop new chemotherapeutic approaches.

Unusual case of resistance to amphotericin B in visceral leishmaniasis in a region in India where leishmaniasis is not endemic

The case of a patient with visceral leishmaniasis showing inadequate response to amphotericin B from a region where leishmaniasis is not endemic is reported, with the Leishmania donovani isolate showing increased tolerance to amphotericin B in vivo. Four single nucleotide polymorphisms (SNPs) detected in the cysteine proteinase B gene resulted in changes to the deduced amino acid sequence: valine→alanine and arginine→leucine. Overexpression and underexpression of proteins were observed in the 65- to 80-kDa range and at 20 kDa, respectively.

Recent advances in leishmaniasis treatment

About 1.5 million new cases of cutaneous leishmaniasis and 500,000 new cases of visceral leishmaniasis occur each year around the world. For over half a century, the clinical forms of the disease have been treated almost exclusively with pentavalent antimonial compounds. In this review, we describe the arsenal available for treating Leishmania infections, as well as recent advances from research on plants and synthetic compounds as source drugs for treating the disease. We also review some new drug-delivery systems for the development of novel chemotherapeutics. We observe that the pharmaceutical industry should employ its modern technologies, which could lead to better use of plants and their extracts, as well as to the development of synthetic and semi-synthetic compounds. New studies have highlighted some biopharmaceutical technologies in the design of the delivery strategy, such as nanoparticles, liposomes, cochleates, and non-specific lipid transfer proteins. These observations serve as a basis to indicate novel routes for the development and design of effective anti-Leishmania drugs.

A species-specific approach to the use of non-antimony treatments for cutaneous leishmaniasis

We used a species-specific approach to treat 10 patients with cutaneous leishmaniasis diagnosed using polymerase chain reaction. Non-antimony treatments (oral miltefosine, ketoconazole, and liposomal amphotericin B) were chosen as an alternative to pentavalent antimony drugs based on likely or proven drug efficacy against the infecting species. Leishmania Viannia panamensis was diagnosed in three patients and treated successfully with oral ketoconazole. Miltefosine treatment cured two patients with L. infantum chagasi. A wide variety of Leishmania responded to liposomal amphotericin B administered for 5-7 days. Three patients with L. V. braziliensis, one patient with L. tropica, and two patients with L. infantum chagasi were treated successfully. One person with L. V. braziliensis healed slowly because of a resistant bacterial superinfection, and a second patient with L. infantum chagasi relapsed and was retreated with miltefosine. These drugs were reasonably well-tolerated. In this limited case series, alternative non-antimony-based regimens were convenient, safe, and effective.

Characterization of the colloidal properties, in vitro antifungal activity, antileishmanial activity and toxicity in mice of a di-stigma-steryl-hemi-succinoyl-glycero-phosphocholine liposome-intercalated amphotericin B

1,2-Di-stigma-steryl-hemi-succinoyl-sn-glycero-3-phosphocholine (DSHemsPC) is a new lipid in which two molecules of stigmasterol (an inexpensive plant sterol) are covalently linked via a succinic acid to glycerophosphocholine. Since amphotericin B (AmB) interacts with sterols, we postulated that DSHemsPC could be used in AmB liposome formulations. Thirty-two DSHemsPC-AmB formulations were prepared using various mole ratios of DSHemsPC, phosphatidylcholine and phosphatidylglycerol at different pH. Most formulations had physical properties similar to AmBisome™: a particle diameter of about 100 nm, a monomodal distribution and a negative zeta potential. The red blood cell potassium release (RBCPR) IC50s for formulations spanned a range, with some being comparable to or greater than the IC50 observed using AmBisome™. A number of formulations had superior in vitro antifungal activity compared to AmBisome™ against all of the tested pathogenic yeasts and molds. The IC50s of formulations against Leishmania major promastigotes and amastigotes for certain formulations were comparable with AmBisome™ and Fungizone™. Most formulations had maximum tolerated intravenous doses (MTD) of less than 10 mg/kg. However the formulation consisting of DSHemsPC/DMPC/DMPG/AmB mole ratio 1.25/5.0/1.5/1.0 (prepared at pH 5.5) had excellent colloidal properties, a high IC50 for RBCPR, antifungal and antileishmanial activity similar to AmBisome™ and an MTD of 60 mg/kg. The characteristics of this DSHemsPC/DMPC/DMPG/AmB formulation make it suitable for further investigation to treat AmB-responsive pathogens.

Lipsosomal amphotericin B for treatment of cutaneous leishmaniasis

Treatment options for cutaneous leishmaniasis in the United States are problematic because the available products are either investigational, toxic, and/or of questionable effectiveness. A retrospective review of patients receiving liposomal amphotericin B through the Walter Reed Army Medical Center for the treatment of cutaneous leishmaniasis during 2007-2009 was conducted. Twenty patients who acquired disease in five countries and with five different strains of Leishmania were treated, of whom 19 received a full course of treatment. Sixteen (84%) of 19 experienced a cure with the initial treatment regimen. Three patients did not fully heal after an initial treatment course, but were cured with additional dosing. Acute infusion-related reactions occurred in 25% and mild renal toxicity occurred in 45% of patients. Although the optimum dosing regimen is undefined and the cost and toxicity may limit widespread use, liposomal amphotericin B is a viable treatment alternative for cutaneous leishmaniasis.

An amphotericin B-based drug for treating experimental Leishmania major infection

There is an urgent need for a non-toxic and low-cost treatment for cutaneous leishmaniasis. We synthesised and tested in vivo an amphotericin B-poly(methacrylic acid) drug (AmB-PMA) that had previously shown in-vitro activity against Leishmania major and L. donovani parasites. Efficacy was determined using L. major footpad infection in 30 non-healing BALB/c mice. Three subcutaneous injections of AmB-PMA at days 7, 14 and 21 post-infection resulted in a reduction of ∼80% in lesion size by day 35 post-infection in 18 treated mice compared with six untreated controls, and complete healing of lesions by day 50 with no lesion relapse seen at day 80 post-infection in six treated mice. Healing was associated with decreased IL-10 (P=0.002) and increased IFN-γ (P=0.005) in the footpad.

Antileishmanial and antitrypanosomal activities of the 8-aminoquinoline tafenoquine

The 8-aminoquinoline tafenoquine showed significant in vitro activity against Leishmania species, including L. donovani amastigotes in macrophages, with 50% inhibitory concentrations (IC(50)s) between 0.1 and 4.0 μM for both pentavalent antimony (SbV)-sensitive and SbV-resistant strains and by oral administration in BALB/c mice, with 50% effective dose (ED(50)) values of 1.2 to 3.5 mg/kg for 5 days. Tafenoquine was less active against intracellular Trypanosoma cruzi amastigotes, with an IC(50) of 21.9 μM.

Flow cytometric screening for anti-leishmanials in a human macrophage cell line

High-throughput drug screening methods against the intracellular stage of Leishmania have been facilitated by the development of in vitro models of infection. The use of cell lines rather than primary cells facilitates these methods. Peripheral blood mononuclear cell (PBMC) derived macrophages and THP-1 cells were infected with stationary phase egfp transfected Leishmania amazonensis parasites and then treated with anti-leishmanial compounds. Drug activity was measured using a flow cytometric approach, and toxicity was assessed using either the MTT assay or trypan blue dye exclusion. Calculated EC(50)'s for amphotericin B, sodium stibogluconate, and miltefosine were 0.1445±0.0005μg/ml, 0.1203±0.018mg/ml, and 26.71μM using THP-1 cells, and 0.179±0.035μg/ml, 0.1948±0.0364mg/ml, and 13.77±10.74μM using PBMC derived macrophages, respectively. We conclude that a flow cytometric approach using egfp transfected Leishmania species can be used to evaluate anti-leishmanial compounds against the amastigote stage of the parasite in THP-1 cells with excellent concordance to human PBMC derived macrophages.

Efficacy of artemisinin in experimental visceral leishmaniasis

Visceral leishmaniasis (VL), caused by the protozoan Leishmania sp., affects 500000 people annually, with the Indian subcontinent contributing a significant proportion of these cases. Emerging refractoriness to conventional antimony therapy has emphasised the need for safer yet effective antileishmanial drugs. Artemisinin, a widely used antimalarial, demonstrated anti-promastigote activity and the 50% inhibitory concentration (IC(50)) ranged from 100 microM to 120 microM irrespective of Leishmania species studied. Leishmania donovani-infected macrophages demonstrated decreased production of nitrite as well as mRNA expression of inducible nitric oxide synthase, which was normalised by artemisinin, indicating that it exerted both a direct parasiticidal activity as well as inducing a host protective response. Furthermore, in a BALB/c model of VL, orally administered artemisinin (10mg/kg and 25mg/kg body weight) effectively reduced both splenic weight and parasite burden, which was accompanied by a restoration of Th1 cytokines (interferon-gamma and interleukin-2). Taken together, these findings have delineated the therapeutic potential of artemisinin in experimental VL.

Topical buparvaquone formulations for the treatment of cutaneous leishmaniasis

As the part of a study to develop buparvaquone (BPQ) formulations for the treatment of cutaneous leishmaniasis, the topical delivery of BPQ and one of its prodrugs from a range of formulations was evaluated. In previous studies, BPQ and its prodrugs were shown to be potent antileishmanials in-vitro, with ED50 values in the nanomolar range. 3-Phosphono-oxymethyl-buparvaquone (3-POM-BPQ) was the most potent antileishmanial and was chosen, together with the parent drug, for further investigation. The ability of the parent and prodrug formulations to cross human and murine skin was tested in-vitro using the Franz diffusion cells. Formulations intended for topical application containing either BPQ or 3-POM-BPQ were developed using excipients that were either acceptable for topical use (GRAS or FDA inactive ingredients) or currently going through the regulatory process. BPQ was shown to penetrate both human epidermal membranes and full thickness BALB/c skin from a range of formulations (gels, emulsions). Similarly, 3-POM-BPQ penetrated full-thickness BALB/c skin from several gel formulations. In-vitro binding studies showed that BPQ bound melanin in a dose-dependent manner and preferably bound to delipidized skin over untreated BALB/c skin (on a weight to weight basis). The results confirm that BPQ and its prodrug 3-POM-BPQ can penetrate the skin from several formulations, making them potentially interesting candidates for further investigation of topical formulations using in-vivo models of cutaneous leishmaniasis.

Identification of potent chemotypes targeting Leishmania major using a high-throughput, low-stringency, computationally enhanced, small molecule screen

Patients with clinical manifestations of leishmaniasis, including cutaneous leishmaniasis, have limited treatment options, and existing therapies frequently have significant untoward liabilities. Rapid expansion in the diversity of available cutaneous leishmanicidal chemotypes is the initial step in finding alternative efficacious treatments. To this end, we combined a low-stringency Leishmania major promastigote growth inhibition assay with a structural computational filtering algorithm. After a rigorous assay validation process, we interrogated ∼200,000 unique compounds for L. major promastigote growth inhibition. Using iterative computational filtering of the compounds exhibiting >50% inhibition, we identified 553 structural clusters and 640 compound singletons. Secondary confirmation assays yielded 93 compounds with EC₅₀s ≤ 1 µM, with none of the identified chemotypes being structurally similar to known leishmanicidals and most having favorable in silico predicted bioavailability characteristics. The leishmanicidal activity of a representative subset of 15 chemotypes was confirmed in two independent assay formats, and L. major parasite specificity was demonstrated by assaying against a panel of human cell lines. Thirteen chemotypes inhibited the growth of a L. major axenic amastigote-like population. Murine in vivo efficacy studies using one of the new chemotypes document inhibition of footpad lesion development. These results authenticate that low stringency, large-scale compound screening combined with computational structure filtering can rapidly expand the chemotypes targeting in vitro and in vivo Leishmania growth and viability.

Leishmaniasis is a parasitic disease with cutaneous, mucocutaneous and visceral clinical manifestations, depending on the Leishmania spp. and human host. Globally, there are 350 million people at risk of leishmaniasis, but current treatment options rely predominantly on ancient pentavalent antimonials, which have the potential to cause serious systemic toxicity. Our research focuses on the rapid expansion of potential anti-leishmanial compounds that could function as novel chemical structures for future drug development and offer additional therapeutic options to patients with leishmaniasis. We combined high throughput screening methodologies with computational algorithms and multiple confirmatory assay formats to identify and characterize new potent L. major promastigote growth inhibitors, including one that displays in vivo activity without toxicity to human cells. Our use of a large, broadly distributed compound library enabled the identification of these new chemotypes. In addition, since this chemical library is publicly available and annotated, we were able to cross-query archived bioassays and to identify new molecular targets that may be involved in L. major growth and viability as well as identify new protein targets for future leishmanicidal drug discovery.

Effect of topical liposomes containing paromomycin sulfate in the course of Leishmania major infection in susceptible BALB/c mice

The aim of this study was to evaluate the antileishmanial effects of topical liposomal paromomycin sulfate (PM) in Leishmania major-infected BALB/c mice. Liposomes containing 10 or 15% PM (Lip-PM-10 and Lip-PM-15, respectively) were prepared by the fusion method and were characterized for their size and encapsulation efficiency. The penetration of PM from the liposomal PM formulations (LPMFs) through and into skin was evaluated in vitro with Franz diffusion cells fitted with mouse skin at 37 degrees C for 8 h. The in vitro permeation data showed that almost 15% of the LPMFs applied penetrated the mouse skin, and the amount retained in the skin was about 60% for both formulations. The 50% effective doses of Lip-PM-10 and Lip-PM-15 against L. major promastigotes in culture were 65.32 and 59.73 microg/ml, respectively, and those against L. major amastigotes in macrophages were 24.64 and 26.44 microg/ml, respectively. Lip-PM-10 or Lip-PM-15 was used topically twice a day for 4 weeks to treat L. major lesions on BALB/c mice, and the results showed a significantly (P < 0.001) smaller lesion size in the mice in the treated groups than in the mice in the control group, which received either empty liposomes or phosphate-buffered saline (PBS). Eight weeks after the beginning of the treatment, every mouse treated with LPMFs was completely cured. The spleen parasite burden was significantly (P < 0.001) lower in mice treated with Lip-PM-10 or Lip-PM-15 than in mice treated with PBS or control liposomes, but no significant difference was seen between the two groups treated with either Lip-PM-10 or Lip-PM-15. The results suggest that topical liposomal PM may be useful for the treatment of cutaneous leishmaniasis.

N-(2-hydroxypropyl)methacrylamide-amphotericin B (HPMA-AmB) copolymer conjugates as antileishmanial agents

Leishmaniasis is a major health problem in many parts of the world, caused by various species of Leishmania. Amastigotes are the clinically relevant form of the parasite in the human host and reside in the parasitophorous vacuole within macrophages. Polymer-drug conjugates have been used for lysosomotropic drug delivery and have already shown potential in anticancer and antileishmanial chemotherapy. We synthesised N-(2-hydroxypropyl)methacrylamide-amphotericin B (HPMA-AmB) copolymer conjugates in which the AmB was attached to the polymer through a degradable GlyPheLeuGly linker. Antileishmanial activity was assessed in vitro against intracellular amastigotes in host macrophages [murine peritoneal exudate macrophages (PEMs), murine bone marrow-derived macrophages (BMMs) and differentiated THP-1 cells]. The most potent copolymers had 50% effective concentration (EC(50)) values of 0.03 microg/mL AmB equivalent against Leishmania donovani amastigotes in PEMs and BMMs and an EC(50) of 0.57 microg/mL AmB equivalent against L. donovani in THP-1 cells. This activity was comparable with free AmB (EC(50)=0.03-0.07 microg/mL against L. donovani in PEMs and BMMs and 0.24-0.42 microg/mL against amastigotes in THP-1 cells) and Fungizone (EC(50)=0.04-0.07 microg/mL against amastigotes in PEMs). Conjugates also showed potent in vivo activity with ca. 50% inhibition of parasite burden at 1mg/kg body weight.

Synthesis and Antileishmanial Activity of 3-Imidazolylalkylindoles. Part I

The present study was designed to investigate conazoles as new antileishmanial agents. Several 3-imidazolylalkyl-indoles were prepared under mild reaction conditions and pharmacomodulation at N1 and C5 of the indole ring and at the level of the alkyl chain (R) was carried out starting from the corresponding 3-formylindoles 7-10. All target imidazolyl compounds 38-52 were evaluated in vitro against Leishmania mexicana promastigotes; ketoconazole, amphotericin B and meglumine antimoniate were used as references. Eight out of fifteen compounds (40,43,44,47,48, 50, 51 and 52) exerted similar activity to ketoconazole, with IC50 values in the range of 2.10-3.30 microg/mL. However the most potent compound, 1-(2-bromobenzyl)-3-(1H-imidazol-1-ylmethyl)-1H-indole (38), exhibited IC50 value (0.011+/-0.003 microg/mL) 270-fold lower than that of ketoconazole. Four compounds (38, 43, 50 and 52) were also tested against intracellular amastigotes of L. mexicana; compound 38 exhibited the highest activity with an IC50 value of 0.018+/-0.004 microg/mL.

Amphotericin B lipid preparations: what are the differences?

To reduce the in-vivo toxicity of the broad-spectrum antifungal drug amphotericin B, various lipid formulations of amphotericin B, ranging from lipid complexes to small unilamellar liposomes, have been developed and subsequently commercialized. These structurally diverse formulations differ in their serum pharmacokinetics as well as their tissue localisation, tissue retention and toxicity. These differences can affect the choice of formulation for a given infection, the time of initiation of treatment, and the dosing regimen. Although preclinical studies have shown similarities in the in-vitro and in-vivo antifungal activity of the formulations with comparable dosing, their acute and chronic toxicity profiles are not the same, and this has a significant impact on their therapeutic indices, especially in high-risk, immunosuppressed patients. With the recent introduction of new antifungal drugs to treat the increasing numbers of infected patients, the amphotericin B lipid formulations are now being studied to evaluate their potential in combination drug regimens. With proven efficacy demonstrated during the past decade, it is expected that amphotericin B lipid formulations will remain an important part of antifungal drug therapy.

Amphotericin B Formulations and Drug Targeting

Amphotericin B is a low-soluble polyene antibiotic which is able to self-aggregate. The aggregation state can modify its activity and pharmacokinetical characteristics. In spite of its high toxicity it is still widely employed for the treatment of systemic fungal infections and parasitic disease and different formulations are marketed. Some of these formulations, such as liposomal formulations, can be considered as classical examples of drug targeting. The pharmacokinetics, toxicity and activity are clearly dependent on the type of amphotericin B formulation. New drug delivery systems such as liposomes, nanospheres and microspheres can result in higher concentrations of AMB in the liver and spleen, but lower concentrations in kidney and lungs, so decreasing its toxicity. Moreover, the administration of these drug delivery systems can enhance the drug accessibility to organs and tissues (e.g., bone marrow) otherwise inaccessible to the free drug. During the last few years, new AMB formulations (AmBisome, Abelcet, and Amphotec) with an improved efficacy/toxicity ratio have been marketed. This review compares the different formulations of amphotericin B in terms of pharmacokinetics, toxicity and activity and discusses the possible drug targeting effect of some of these new formulations.

Antileishmanial activity of nano-amphotericin B deoxycholate

OBJECTIVES

The aim of the present study was to compare the efficacy of a nano form of amphotericin B deoxycholate with that of conventional amphotericin B deoxycholate for the treatment of visceral leishmaniasis.

METHODS

We have formulated nanoparticles (10-20 nM) from amphotericin B deoxycholate (1-2 microM) by applying high-pressure (150 argon) milling homogenization and have tested their efficacy in a J774A cell line and in hamsters. Parasite survival and tissue burden in spleen were evaluated for nano-amphotericin B and conventional amphotericin B. Both nano-amphotericin B and conventional amphotericin B were injected intraperitoneally at 5 mg/kg per day for 5 days.

RESULTS

The inhibition of amastigotes in the splenic tissue with nano-amphotericin B was significantly more than with conventional amphotericin B (92.18% versus 74.57%, P = 0.005). Similarly, the suppression of parasite replication in the spleen was also found to be significant (99.18% versus 97.17%, P = 0.05). In a cytotoxicity test, nano-amphotericin B against the J774A cell line had a CC(50) of 12.67 mg/L in comparison with 10.61 mg/L for amphotericin B, far higher than the doses used for ED(50).

CONCLUSIONS

Nanoparticles of amphotericin B had significantly greater efficacy than conventional amphotericin B. This formulation may have a favourable safety profile, and if production costs are low, it may prove to be a feasible alternative to conventional amphotericin B.

In vitro and in vivo activity of Aloe vera leaf exudate in experimental visceral leishmaniasis

The leishmanicidal activity of Aloe vera leaf exudate (AVL) has been demonstrated in promastigotes and axenic amastigotes, but its effectiveness in animal models has not been evaluated. The presence of alkaloids, triterpenes, cyanidines, proanthocyanidines, tannins, and saponins in AVL was identified. Its effectiveness in four Leishmania donovani strains was studied both in promastigotes (IC50 ranged from 70-115 microg/ml) and amastigotes (IC50 ranged from 3.1-11.4 microg/ml). In amastigotes, the killing by AVL was facilitated through its induction of nitric oxide in leishmania-infected macrophages. The safety index was good as AVL up to 300 microg/ml remained non-toxic to monocytes and macrophages. In a L. donovani BALB/c mouse model, oral or subcutaneous administration of AVL (15 mg/kg body weight x 5 days) reduced parasitemia by >90% in the liver, spleen, and bone marrow without impairment of hepatic and renal functions. Collectively, we conclude that AVL shows promising antileishmanial activity and may provide a new lead agent in the treatment of Leishmaniasis.

Fishing for anti-leishmania drugs: principles and problems

To date, there are no vaccines against any of the major parasitic diseases including leishmaniasis, and chemotherapy is the main weapon in our arsenal. Current drugs are toxic and expensive, and are losing their effectiveness due to parasite resistance. The availability of the genome sequence of two species of Leishmania, Leishmania major and Leishmania infantum, as well as that of Trypanosoma brucei and Trypanosoma cruzi should provide a cornucopia of potential new drug targets. Their exploitation will require a multi-disciplinary approach that includes protein structure and function and high throughput screening of random and directed chemical libraries, followed by in vivo testing in animals and humans. We outline the opportunities that are made possible by recent technologies, and potential problems that need to be overcome.

Delivery systems to increase the selectivity of antibiotics in phagocytic cells

Many infectious diseases are caused by facultative organisms that are able to survive in phagocytic cells. The intracellular location of these microorganisms protects them from the host defence systems and from some antibiotics with poor penetration into phagocytic cells. One strategy used to improve the penetration of antibiotics into phagocytic cells is the use of carrier systems that deliver these drugs directly to the target cell. Delivery systems such as liposomes, micro/nanoparticles, lipid systems, conjugates, and biological carriers such as erythrocyte ghosts may contribute to increasing the therapeutic efficacy of antibiotics and antifungal agents in the treatment of infections caused by intracellular microorganisms. The main objective of this review is to analyze recent advances and current perspectives in the use of antibiotic delivery systems in the treatment of intracellular infections such as mycobacterial infections, brucellosis, salmonellosis, listeriosis, fungal infections, visceral leishmaniasis, and HIV.

Racemoside A, an anti-leishmanial, water-soluble, natural steroidal saponin, induces programmed cell death in Leishmania donovani

Leishmaniasis remains a major health problem of the tropical and subtropical world. The visceral form causes the most fatalities if left untreated. Dramatic increases in the rates of infection and drug resistance and the non-availability of safe vaccines have highlighted the need for identification of novel and inexpensive anti-leishmanial agents. This study reports that racemoside A, a water-soluble steroidal saponin purified from the fruits of Asparagus racemosus, is a potent anti-leishmanial molecule effective against antimonial-sensitive (strain AG83) and -unresponsive (strain GE1F8R) Leishmania donovani promastigotes, with IC(50) values of 1.15 and 1.31 microg ml(-1), respectively. Incubation of promastigotes with racemoside A caused morphological alterations including cell shrinkage, an aflagellated ovoid shape and chromatin condensation. This compound exerts its leishmanicidal effect through the induction of programmed cell death mediated by the loss of plasma membrane integrity as detected by binding of annexin V and propidium iodide, loss of mitochondrial membrane potential culminating in cell-cycle arrest at the sub-G(0)/G(1) phase, and DNA nicking shown by deoxynucleotidyltransferase-mediated dUTP end labelling (TUNEL). Racemoside A also showed significant activity against intracellular amastigotes of AG83 and GE1F8R at a 7-8-fold lower dose, with IC(50) values of 0.17 and 0.16 microg ml(-1), respectively, and was non-toxic to murine peritoneal macrophages up to a concentration of 10 microg ml(-1). Hence, racemoside A is a potent anti-leishmanial agent that merits further pharmacological investigation.

Cutaneous leishmaniasis

Cutaneous leishmaniasis is endemic in the tropics and neotropics. It is often referred to as a group of diseases because of the varied spectrum of clinical manifestations, which range from small cutaneous nodules to gross mucosal tissue destruction. Cutaneous leishmaniasis can be caused by several Leishmania spp and is transmitted to human beings and animals by sandflies. Despite its increasing worldwide incidence, but because it is rarely fatal, cutaneous leishmaniasis has become one of the so-called neglected diseases, with little interest by financial donors, public-health authorities, and professionals to implement activities to research, prevent, or control the disease. In endemic countries, diagnosis is often made clinically and, if possible, by microscopic examination of lesion biopsy smears to visually confirm leishmania parasites as the cause. The use of more sophisticated diagnostic techniques that allow for species identification is usually restricted to research or clinical settings in non-endemic countries. The mainstays of cutaneous leishmaniasis treatment are pentavalent antimonials, with new oral and topical treatment alternatives only becoming available within the past few years; a vaccine currently does not exist. Disease prevention and control are difficult because of the complexity of cutaneous leishmaniasis epizoology, and the few options available for effective vector control.

Cutaneous leishmaniasis treatment

The causative species of cutaneous leishmaniasis determines the clinical features and courses, and treatments. Intralesional or systemic antimonials are the gold standard for the treatment of these diseases. However, as for visceral leishmaniasis, other therapeutic options appear promising. Paromomycin ointments are effective in Leishmania major, L. tropica, L. mexicana, and L. panamensis lesions. In L. braziliensis localized leishmaniasis, both paromomycin and imiquimod may be topically applied. Oral fluconazole and zinc sulfate are useful in L. major. Oral azithromycin, effective in vitro and in mice, needs further investigation in human leishmaniasis. On the contrary, data with oral itraconazole are disappointing. Oral miltefosine, which is very effective in visceral leishmaniasis caused by L. donovani, appears ineffective in L. major and L. braziliensis infections. Intramuscular pentamidine is required for L. guyanensis cutaneous leishmaniasis, for which systemic antimony is not effective. Liposomal amphotericin B could be an alternative to antimony in south American cutaneous leishmaniasis with mucosal involvement (especially L. braziliensis and L. guyanensis infections).

Targeting of toxic compounds to the trypanosome's interior

Drugs can be targeted into African trypanosomes by exploiting carrier proteins at the surface of these parasites. This has been clearly demonstrated in the case of the melamine-based arsenical and the diamidine classes of drug that are already in use in the treatment of human African trypanosomiasis. These drugs can enter via an aminopurine transporter, termed P2, encoded by the TbAT1 gene. Other toxic compounds have also been designed to enter via this transporter. Some of these compounds enter almost exclusively through the P2 transporter, and hence loss of the P2 transporter leads to significant resistance to these particular compounds. It now appears, however, that some diamidines and melaminophenylarsenicals may also be taken up by other routes (of yet unknown function). These too may be exploited to target new drugs into trypanosomes. Additional purine nucleoside and nucleobase transporters have also been subverted to deliver toxic agents to trypanosomes. Glucose and amino acid transporters too have been investigated with a view to manipulating them to carry toxins into Trypanosoma brucei, and recent work has demonstrated that aquaglyceroporins may also have considerable potential for drug-targeting. Transporters, including those that carry lipids and vitamins such as folate and other pterins also deserve more attention in this regard. Some drugs, for example suramin, appear to enter via routes other than plasma-membrane-mediated transport. Receptor-mediated endocytosis has been proposed as a possible way in for suramin. Endocytosis also appears to be crucial in targeting natural trypanocides, such as trypanosome lytic factor (TLF) (apolipoprotein L1), into trypanosomes and this offers an alternative means of selectively targeting toxins to the trypanosome's interior. Other compounds may be induced to enter by increasing their capacity to diffuse over cell membranes; in this case depending exclusively on selective activity within the cell rather than selective uptake to impart selective toxicity. This review outlines studies that have aimed to exploit trypanosome nutrient uptake routes to selectively carry toxins into these parasites.

Nanodisk-associated amphotericin B clears Leishmania major cutaneous infection in susceptible BALB/c mice

Nanometer-scale, apolipoprotein-stabilized phospholipid bilayer disk complexes (nanodisks [ND]) harboring the toxic and poorly soluble antileishmanial agent amphotericin B (AMB) were examined for efficacy in treatment of Leishmania major-infected BALB/c mice (Mus musculus). L. major-infected mice were intraperitoneally (i.p.) treated with AMB-ND in 0-, 1-, and 5-mg/kg doses at 24 h, 48 h, and 4, 7, 14, and 21 days postinfection in two experiments. L. major-infected mice were i.p. treated with phosphate-buffered saline, 5 mg/kg AMB-ND, or 5 mg/kg lipid-associated amphotericin B (liposomal amphotericin B, AmBisome) at 24 h, 48 h, and 10, 20, 30, and 40 days postinfection in one experiment. Parasite numbers, footpad lesion size progression, and development of cytokine responses were assayed at days 7, 15, 30, 50, 140, and 250 or at days 14, 30, 50, 95, and 140 postinfection. Mice administered AMB-ND in 1- or 5-mg/kg doses were significantly protected from L. major, displaying decreases in lesion size and parasite burden, particularly at the 5-mg/kg dosage level. In contrast to the i.p. treated AmBisome group, BALB/c mice treated with i.p. AMB-ND completely cleared an L. major infection by 140 to 250 days postinfection, with no lesions remaining and no parasites isolated from infected animals. Restimulated mixed lymphocyte culture cytokine responses (interleukin-4 [IL-4], IL-12, IL-10, NO, and gamma interferon) were unchanged by AMB-ND administration compared to controls. The marked clearance of Leishmania parasites from a susceptible strain of mice without an appreciable change in the cytokine response suggests that AMB-ND represent a potentially useful formulation for treatment of intrahistiocytic organisms.

Amphotericin B Colloidal Dispersion for the Treatment of Indian Visceral Leishmaniasis

BACKGROUND

In Bihar, India, where visceral leishmaniasis (VL) is hyperendemic and refractory to antimony, amphotericin B is the most effective option for the treatment of VL. Lipid formulations of amphotericin B are able to circumvent the toxic effect of conventional amphotericin B, and the total dose of these formulations can be administered over a short duration. However, cost is a major constraint in the use of lipid formulations of amphotericin B. Amphotericin B colloidal dispersion (ABCD), which is a less expensive lipid formulation, has not been tested for the treatment of VL in India.

METHODS

In an open-label, randomized clinical trial, we evaluated the efficacy and safety of a 6-day course of ABCD administered to 3 different dose groups (total dose: 7.5 mg/kg [group A], 10 mg/kg [group B], and 15 mg/kg [group C]), each of which included a cohort of 135 patients.

RESULTS

Although infusion-related fever and chills occurred in 56%-68% of patients in the 3 different dose groups, 401 of 405 patients completed the treatment. All 135 patients in group A completed treatment, and the final cure rate for this group was 97%. In the group that received the highest dose of ABCD (group C), severe backache, an unusual side effect, was observed in 8 patients (5.92%). Serious adverse effects led to the withdrawal of 2 patients (1.48%) each from group B and group C.

CONCLUSIONS

Although the cost of ABCD is prohibitive, the high level of efficacy associated with short-term treatment with low-dose ABCD provides another alternative for the treatment of VL, especially in regions where VL is antimony refractory.

Purine nucleobase transport in amastigotes of Leishmania mexicana: involvement in allopurinol uptake

Nucleobase and nucleoside transporters play central roles in the biochemistry of parasitic protozoa, as they lack the ability to synthesize purines de novo and are absolutely reliant upon purine salvage from their hosts. Furthermore, such transporters are potentially critical to the pharmacology of these important human pathogens, because they mediate the uptake of purine analogues, as well as some nonpurine drugs, that can be selectively cytotoxic to the parasites. We here report the first identification and characterization of a purine nucleobase transporter in Leishmania amastigotes. Uptake of [3H]hypoxanthine by Leishmania mexicana amastigotes was mediated by a single high-affinity transporter, LmexNBT1, with a Km of 1.6 +/- 0.4 microM and high affinity for adenine, guanine, and xanthine but low affinity for nucleosides and pyrimidine nucleobases. Allopurinol, an antileishmanial hypoxanthine analogue, was apparently taken up by the same transporter. Using [3H]allopurinol, a Km value of 33.6 +/- 6.0 microM was obtained. All evidence was compatible with a model of a single purine nucleobase transporter being expressed in amastigotes. Using various purine nucleobase analogues, a model for the interactions between hypoxanthine and the transporter's permeant binding site was constructed. The binding interactions were compared with those of the LmajNBT1 transporter in Leishmania major promastigotes and found to be very similar.

Amphotericin B

Invasive fungal infections are a major cause of morbidity and mortality in immunodeficient individuals (such as AIDS patients) and in transplant recipients or tumor patients undergoing immunosuppressive chemotherapy. Amphotericin B is one of the oldest, yet most efficient antimycotic agents. However, its usefulness is limited due to dose-dependent side-effects, notably nephrotoxicity. In order to improve its safety margin, new pharmaceutical formulations of amphotericin B have been designed especially to reduce its detrimental effects on the kidneys. Since the 1980s, a wide variety of new amphotericin B formulations have been brought forward for clinical testing, many of which were approved and reached market value in the 1990s. This review describes and discusses the molecular genetics, pharmacological, toxicological, and clinical aspects of amphotericin B itself and many of its innovative formulations.

Activity of a paromomycin hydrophilic formulation for topical treatment of infections by Leishmania (Leishmania) amazonensis and Leishmania (Viannia) braziliensis

Studies on in vitro skin permeation and in vivo anti-leishmanial activity in mice experimentally infected with Leishmania (Leishmania) major pointed out to the potential of a new paromomycin (PA) formulation (hydrophilic gel) for treatment of cutaneous leishmaniasis (CL). In this study, the activity of this formulation was evaluated in animals experimentally infected by Leishmania species that prevail in the New World. PA gel activity was compared to antimony treatment, since it is still the first choice treatment to the different clinical forms of leishmaniasis. The topical treatment activity with 10% PA gel in BALB/c mice infected by Leishmania (Leishmania) amazonensis was higher than that observed for parenteral antimony treatment, while the efficacy of these two regimes in hamsters infected by Leishmania (Viannia) braziliensis was similar. These results suggest that this formulation could be suitable for clinical studies and may represent an alternative novel formulation for topical treatment of CL.

Amphotericin B lipid complex: in visceral leishmaniasis

Amphotericin B lipid complex is a lipid formulation of amphotericin B, an antifungal drug with activity against Leishmania spp. Amphotericin B lipid complex appears to enhance uptake of amphotericin B by infected macrophages in patients with visceral leishmaniasis (VL). In randomised, open-label, dose-ranging studies, short-course treatment with once-daily amphotericin B lipid complex (5-15 mg/kg total cumulative dose over 5 days), administered by intravenous infusion, produced high rates of apparent (day 19) [93-100%] and definitive (6 months) [79-100%] cures in Indian patients with antimonial-resistant VL. Amphotericin B lipid complex appeared to be as effective as liposomal amphotericin B or the conventional deoxycholate formulation in a randomised, open-label study conducted in India in a mixed population of patients with previously untreated or antimonial-resistant VL. In patients with HIV infection and VL, amphotericin B lipid complex 3 mg/kg/day for 5 or 10 days appeared to be as effective as meglumine antimonate 20 mg/kg/day for 28 days in a small randomised pilot study in southern Europe. Amphotericin B lipid complex was generally well tolerated in patients with VL. Infusion-related reactions were the most common adverse events associated with amphotericin B lipid complex.

Successful treatment of cutaneous leishmaniasis with lipid formulations of amphotericin B in two immunocompromised patients

Pentavalent antimonial drugs are habitually the first choice for treating leishmaniasis, although they possess well-known toxicity and may present some therapeutic failure. Lipid formulations of amphotericin B (LFAB) have been increasingly used for treating several types of leishmaniasis. However, the administration of such lipid formulations specifically to patients with cutaneous leishmaniasis (CL) is still rare, including immunocompromised patients to whom standard treatments are more frequently contraindicated. We describe here two cases of immunocompromised patients with CL, one of them with AIDS, representing the first case of AIDS and CL co-infection treated with LFAB described in the literature. The patient achieved therapeutic success with a total 1.500 mg dose of amphotericin B colloidal dispersion. The other had diabetes mellitus as well as kidney failure and was under dialysis, having obtained the healing of lesion with a total dose of 600 mg of liposomal amphotericin B. Thus, the authors suggest that LFAB can represent a safe, efficient and less toxic therapeutic alternative to pentavalent antimonials, as well as to the so-called second line drugs, pentamidine and amphotericin B deoxycholate.

Anti-leishmanial activity of a new formulation of amphotericin B

The effectiveness of albumin microspheres loaded with amphotericin B was tested in an in vivo model of visceral leishmaniasis using the golden hamster. Free and encapsulated amphotericin B was tested at the dose of 1 mg/kg given by the intracardiac route on days 25, 26 and 27 post-infection (p.i.) to treat animals previously infected with 10(7) stationary promastigotes by the intracardiac route. Encapsulated amphotericin was highly effective against infection causing a reduction of 88.8% and 87.2% in the early stage of infection (day 32 p.i.) and of 66.7% and 54% in a later stage of infection (day 135 p.i.) in liver and spleen parasite load respectively, compared with untreated animals, whereas free amphotericin was inactive. Lymphocyte proliferation was restored together with an increase in CD4(+) subsets in animals treated with encapsulated amphotericin B, but not in those treated with the non-encapsulated compound. Antibody responses did not increase after treatment with encapsulated amphotericin B with antibody levels remaining at base levels for most animals in contrast to those of untreated or treated with free amphotericin, where in most animals the antibody levels sharply increased. This new formulation could be a more economical alternative to liposomes for the treatment of visceral leishmaniasis with amphotericin B.