Effect of the alkyl-lysophospholipids on the proliferation and differentiation of Trypanosoma cruzi

Assessing nystatin cream treatment efficacy against Leishmania (L.) amazonensis infection in BALB/c model

The current scenario for cutaneous leishmaniasis treatment includes the use of first and second-choice drugs, both therapeutic strategies presenting several adverse effects and being related to an increment of treatment-refractory parasite strains. These facts encourage the search for new treatment approaches, including repositioning drugs, such as nystatin. Although some in vitro assays show that this polyene macrolide compound has leishmanicidal activity, no in vivo evidence for a similar activity has been shown so far for the commercial nystatin cream formulation (25,000 IU/g). This work assessed the effects of nystatin cream administered on mice in an amount to completely cover the paw surface of BALB/c mice infected with L. (L.) amazonensis once a day, until a total of up to 20 doses. The data presented herein points to unequivocal evidence that this formulation is related to a statistically significant reduction of swelling/edema in mice paws when compared to animal groups not submitted to this treatment regimen after the fourth week of infection: lesion sizes at the sixth (p = 0.0159), seventh (p = 0.0079) and eighth (p = 0.0079) week. Furthermore, infection reduction relates to a decrease in parasite load in the footpad (∼48%) and in draining lymph nodes (∼68%) at 8th weeks post-infection. This is the first report of the effectiveness of nystatin cream used as a topical treatment in BALB/c model for cutaneous leishmaniasis.

Miltefosine and Benznidazole Combination Improve Anti-Trypanosoma cruzi In Vitro and In Vivo Efficacy

Drug repurposing and combination therapy have been proposed as cost-effective strategies to improve Chagas disease treatment. Miltefosine (MLT), a synthetic alkylphospholipid initially developed for breast cancer and repositioned for leishmaniasis, is a promising candidate against Trypanosoma cruzi infection. This study evaluates the efficacy of MLT as a monodrug and combined with benznidazole (BZ) in both in vitro and in vivo models of infection with T. cruzi (VD strain, DTU TcVI). MLT exhibited in vitro activity on amastigotes and trypomastigotes with values of IC_{50 =} 0.51 µM (0.48 µM; 0,55 µM) and LC_{50 =} 31.17 µM (29.56 µM; 32.87 µM), respectively. Drug interaction was studied with the fixed-ration method. The sum of the fractional inhibitory concentrations (ΣFICs) resulted in ∑FIC= 0.45 for trypomastigotes and ∑FIC= 0.71 for amastigotes, suggesting in vitro synergistic and additive effects, respectively. No cytotoxic effects on host cells were observed. MLT efficacy was also evaluated in a murine model of acute infection alone or combined with BZ. Treatment was well tolerated with few adverse effects, and all treated animals displayed significantly lower mean peak parasitemia and mortality than infected non-treated controls (p<0.05). The in vivo studies showed that MLT led to a dose-dependent parasitostatic effect as monotherapy which could be improved by combining with BZ, preventing parasitemia rebound after a stringent immunosuppression protocol. These results support MLT activity in clinically relevant stages from T. cruzi, and it is the first report of positive interaction with BZ, providing further support for evaluating combined schemes using MLT and exploring synthetic alkylphospholipids as drug candidates.

Phospholipid Analogues as Chemotherapeutic Agents Against Trypanosomatids

BACKGROUND

Neglected tropical diseases (NTDs) represent a serious problem in a number of countries around the world and especially in Africa and South America, affecting mostly the poor population which has limited access to the healthcare system. The drugs currently used for the treatment of NTDs are dated many decades ago and consequently, present in some cases very low efficacy, high toxicity and development of drug resistance. In the search for more efficient chemotherapeutic agents for NTDs, a large number of different compound classes have been synthesized and tested. Among them, ether phospholipids, with their prominent member miltefosine, are considered one of the most promising.

OBJECTIVE

This review summarizes the literature concerning the development of antiparasitic phospholipid derivatives, describing the efforts towards more efficient and less toxic analogues while providing an overview of the mechanism of action of this compound class against trypanosomatids.

CONCLUSION

Phospholipid analogues are already known for their antiprotozoal activity. Several studies have been conducted in order to synthesize novel derivatives with the aim to improve current treatments such as miltefosine, with promising results. Photolabeling and fluorescent alkyl phospholipid analogues have contributed to the clarification of the mode of action of this drug family.

Related Pentacyclic Triterpenes Have Immunomodulatory Activity in Chronic Experimental Visceral Leishmaniasis

Leishmaniasis is a neglected tropical disease caused by the flagellated protozoa of the genus Leishmania that affects millions of people around the world. Drugs employed in the treatment of leishmaniasis have limited efficacy and induce local and systemic side effects to the patients. Natural products are an interesting alternative to treat leishmaniasis, because some purified molecules are selective toward parasites and not to the host cells. Thus, the aim of the present study was to compare the in vitro antileishmanial activity of the triterpenes betulin (Be), lupeol (Lu), and ursolic acid (UA); analyze the physiology and morphology of affected organelles; analyze the toxicity of selected triterpenes in golden hamsters; and study the therapeutic activity of triterpenes in hamsters infected with L. (L.) infantum as well as the cellular immunity induced by studied molecules. The triterpenes Lu and UA were active on promastigote (IC₅₀ = 4.0 ± 0.3 and 8.0 ± 0.2 μM, respectively) and amastigote forms (IC₅₀ = 17.5 ± 0.4 and 3.0 ± 0.2 μM, respectively) of L. (L.) infantum, and their selectivity indexes (SI) toward amastigote forms were higher (≥13.4 and 14, respectively) than SI of miltefosine (2.7). L. (L.) infantum promastigotes treated with Lu and UA showed cytoplasmic degradation, and in some of these areas, cell debris were identified, resembling autophagic vacuoles, and parasite mitochondria were swelled, fragmented, and displayed membrane potential altered over time. Parasite cell membrane was not affected by studied triterpenes. Studies of toxicity in golden hamster showed that Lu did not alter blood biochemical parameters associated with liver and kidney functions; however, a slight increase of aspartate aminotransferase level in animals treated with 2.5 mg/kg of UA was detected. Lu and UA triterpenes eliminated amastigote forms in the spleen (87.5 and 95.9% of reduction, respectively) and liver of infected hamster (95.9 and 99.7% of reduction, respectively); and UA showed similar activity at eliminating amastigote forms in the spleen and liver than amphotericin B (99.2 and 99.8% of reduction). The therapeutic activity of both triterpenes was associated with the elevation of IFN-γ and/or iNOS expression in infected treated animals. This is the first comparative work showing the in vitro activity, toxicity, and therapeutic activity of Lu and UA in the chronic model of visceral leishmaniasis caused by L. (L.) infantum; additionally, both triterpenes activated cellular immune response in the hamster model of visceral leishmaniasis.

Identification of Trypanosoma cruzi Growth Inhibitors with Activity In Vivo within a Collection of Licensed Drugs

Chagas disease, caused by the parasite Trypanosoma cruzi (T. cruzi), affects more than six million people worldwide, with its greatest burden in Latin America. Available treatments present frequent toxicity and variable efficacy at the chronic phase of the infection, when the disease is usually diagnosed. Hence, development of new therapeutic strategies is urgent. Repositioning of licensed drugs stands as an attractive fast-track low-cost approach for the identification of safer and more effective chemotherapies. With this purpose we screened 32 licensed drugs for different indications against T. cruzi. We used a primary in vitro assay of Vero cells infection by T. cruzi. Five drugs showed potent activity rates against it (IC₅₀ < 4 µmol L⁻¹), which were also specific (selectivity index >15) with respect to host cells. T. cruzi inhibitory activity of four of them was confirmed by a secondary anti-parasitic assay based on NIH-3T3 cells. Then, we assessed toxicity to human HepG2 cells and anti-amastigote specific activity of those drugs progressed. Ultimately, atovaquone-proguanil, miltefosine, and verapamil were tested in a mouse model of acute T. cruzi infection. Miltefosine performance in vitro and in vivo encourages further investigating its use against T. cruzi.

Resolution of Acanthamoeba Keratitis with Adjunctive Use of Oral Miltefosine

Purpose: To report a series of cases demonstrating the resolution of Acanthamoeba keratitis (AK) with adjunctive use of oral miltefosine.Methods: Retrospective case series.Results: The first case was a 27-year-old female who presented with severe pain and photophobia. The diagnosis of AK was made with confocal microscopy, which revealed a significant burden of stromal cysts. After approximately 2 weeks of adjunctive oral miltefosine therapy, there was a severe inflammatory response within the cornea followed by quick resolution of the AK. The second case was a 31-year-old male in whom the diagnosis of AK was confirmed by culture and polymerase chain reaction. Adjunctive oral miltefosine was started 3 months after presentation, leading to a quick resolution.Conclusions: Oral miltefosine may have cysticidal properties and should be considered as adjunctive therapy for the treatment of AK, particularly in cases with a significant burden of cysts or in cases recalcitrant to other treatments.

Oral miltefosine for refractory Acanthamoeba keratitis

Purpose

To report the first case of Acanthamoeba keratitis treated with oral miltefosine in the United States.

Observations

A 17-year-old female with a history of orthokeratology contact lens wear presented after five months of left eye pain, redness, and photophobia. She was previously treated with antivirals and topical corticosteroids for presumed herpetic disease. She was found to have a large central ring infiltrate and corneal cultures were positive for Acanthamoeba. The infection progressed despite hourly PHMB 0.02% and chlorhexidine 0.02%, and oral vorizonazole. The patient was started on oral miltefosine 50 mg 3 times per day. Following one week of treatment, repeat cultures were positive for Acanthamoeba and therefore, the concentration of chlorhexidine was increased from 0.02% to 0.06% and PHMB was changed to propamidine isetionate (Brolene 0.1%). There was definite clinical improvement after five weeks of treatment with oral miltefosine, topical chlorhexidine 0.06% and propamidine isetionate 0.1%.

Conclusions and importance

Acanthamoeba keratitis is a challenging entity to treat and often associated with a poor prognosis. Oral miltefosine may offer additional therapeutic benefit in cases of refractory Acanthamoeba keratitis.

In vitro activities of adamantylidene-substituted alkylphosphocholine TCAN26 against Trypanosoma cruzi: Antiproliferative and ultrastructural effects

Phospholipids are the main component of membranes and are responsible for cell integrity. Alkylphospholipid analogues (APs) were first designed as antitumoral agents and were later tested against different cell types. Trypanosoma cruzi, the Chagas disease etiological agent, is sensitive to APs (edelfosine, miltefosine and ilmofosine) in vitro. We investigated the effect of synthetic ring substituted AP against epimastigotes, amastigotes and trypomastigotes. TCAN26, could inhibit the in vitro growth of epimastigotes and amastigotes with the 50% inhibitory concentrations (IC50) in the nanomolar range. Trypomastigotes lysis was also induced with 24-h treatment and a LC50 of 2.3 μM. Ultrastructural analysis by electron microscopy demonstrated that TCAN26 mainly affected the parasite's membranes leading to mitochondrial and Golgi cisternae swelling, membrane blebs, and autophagic figures in the different parasite developmental stages. While the Golgi of the parasites was significantly affected, the Golgi complex of the host cells remained normal suggesting a specific mechanism of action. In summary, our results suggest that TCAN 26 is a potent and selective inhibitor of T. cruzi growth probably due to disturbances of phospholipid biosynthesis.

3-Hydroxykynurenine, a Tryptophan Metabolite Generated during the Infection, Is Active Against Trypanosoma cruzi

The antiparasitic activity of 3-hydroxykynurenine (3-HK), one of the major tryptophan catabolites of the kynurenine pathway, against both Trypanosoma cruzi evolutive forms that are important for human infection, trypomastigotes (Tps) and amastigotes (Am), possible targets in the parasite and the drug toxicity to mammalian cells have been investigated. 3-HK showed a potent activity against Am with IC₅₀ values in the micromolar concentration range, while the IC₅₀ values to cause Tps death was ∼6000-times higher, indicating that the replicative form present in the vertebrate hosts is much more susceptible to 3-HK than bloodstream Tps. In addition, 3-HK showed activity against Tps and Am, at concentrations that did not exhibit toxicity to mammalian cells. Ultrastructural analysis and flow cytometry studies indicated that Am and Tps mitochondrion and nuclei contain 3-HK targets. The potency and selectivity of 3-HK, which is generated during T. cruzi infection in human and mice, suggest that 3-HK may be a suitable candidate for drug research and development for Chagas disease.

In vitro drug susceptibility of two strains of the wildlife trypanosome, Trypanosoma copemani: A comparison with Trypanosoma cruzi

Trypanosomes are blood protozoan parasites that are capable of producing illness in the vertebrate host. Within Australia, several native Trypanosoma species have been described infecting wildlife. However, only Trypanosoma copemani has been associated with pathological lesions in wildlife hosts and more recently has been associated with the drastic decline of the critically endangered woylie (Bettongia penicillata). The impact that some trypanosomes have on the health of the vertebrate host has led to the development of numerous drug compounds that could inhibit the growth or kill the parasite. This study investigated and compared the in vitro susceptibility of two strains of T. copemani (G1 and G2) and one strain of Trypanosoma cruzi (10R26) against drugs that are known to show trypanocidal activity (benznidazole, posaconazole, miltefosine and melarsoprol) and against four lead compounds, two fenarimols and two pyridine derivatives (EPL-BS1937, EPL-BS2391, EPL-BS0967, and EPL-BS1246), that have been developed primarily against T.cruzi. The in vitro cytotoxicity of all drugs against L6 rat myoblast cells was also assessed. Results showed that both strains of T. copemani were more susceptible to all drugs and lead compounds than T. cruzi, with all IC50 values in the low and sub-μM range for both species. Melarsoprol and miltefosine exhibited the highest drug activity against both T. copemani and T. cruzi, but they also showed the highest toxicity in L6 cells. Interestingly, both fenarimol and pyridine derivative compounds were more active against T. copemani and T. cruzi than the reference drugs benznidazole and posaconazole. T. copemani strains exhibited differences in susceptibility to all drugs demonstrating once again considerable differences in their biological behaviour.

The Effectiveness of Natural Diarylheptanoids against Trypanosoma cruzi: Cytotoxicity, Ultrastructural Alterations and Molecular Modeling Studies

Curcumin (CUR) is the major constituent of the rhizomes of Curcuma longa and has been widely investigated for its chemotherapeutic properties. The well-known activity of CUR against Leishmania sp., Trypanosoma brucei and Plasmodium falciparum led us to investigate its activity against Trypanosoma cruzi. In this work, we tested the cytotoxic effects of CUR and other natural curcuminoids on different forms of T. cruzi, as well as the ultrastructural changes induced in epimastigote form of the parasite. CUR was verified as the curcuminoid with more significant trypanocidal properties (IC₅₀ 10.13 μM on epimastigotes). Demethoxycurcumin (DMC) was equipotent to CUR (IC₅₀ 11.07 μM), but bisdemethoxycurcumin (BDMC) was less active (IC₅₀ 45.33 μM) and cyclocurcumin (CC) was inactive. In the experiment with infected murine peritoneal macrophages all diarylheptanoids were more active than the control in the inhibition of the trypomastigotes release. The electron microscopy images showed ultrastructural changes associated with the cytoskeleton of the parasite, indicating tubulin as possible target of CUR in T. cruzi. The results obtained by flow cytometry analysis of DNA content of the parasites treated with natural curcuminoids suggested a mechanism of action on microtubules related to the paclitaxel`s mode of action. To better understand the mechanism of action highlighted by electron microscopy and flow cytometry experiments we performed the molecular docking of natural curcuminoids on tubulin of T. cruzi in a homology model and the results obtained showed that the observed interactions are in accordance with the IC₅₀ values found, since there CUR and DMC perform similar interactions at the binding site on tubulin while BDMC do not realize a hydrogen bond with Lys163 residue due to the absence of methoxyl groups. These results indicate that trypanocidal properties of CUR may be related to the cytoskeletal alterations.

Miltefosine increases lipid and protein dynamics in Leishmania amazonensis membranes at concentrations similar to those needed for cytotoxicity activity

Miltefosine (MT) is a membrane-active alkylphospholipid licensed for the topical treatment of breast cancer skin metastases and the oral treatment of leishmaniasis, although its mechanism of action remains unclear. Electron paramagnetic resonance (EPR) spectroscopy of a spin-labeled lipid and a thiol-specific spin label in the plasma membrane of Leishmania promastigotes showed that MT causes dramatic increases in membrane dynamics. Although these alterations can be detected using a spin-labeled lipid, our experimental results indicated that MT interacts predominantly with the protein component of the membrane. Cell lysis was also detected by analyzing the supernatants of centrifuged samples for the presence of spin-labeled membrane fragments and cytoplasmic proteins. Using a method for the rapid incorporation of MT into the membrane, these effects were measured immediately after treatment under the same range of MT concentrations that cause cell growth inhibition. Cytotoxicity, estimated via microscopic counting of living and dead cells, indicated ∼70% cell death at the concentration of MT at which EPR spectroscopy detected a significant change in membrane dynamics. After this initial impact on the number of viable parasites, the processes of cell death and growth continued during the first 4 h of incubation. The EPR spectra of spin-labeled membrane-bound proteins were consistent with more expanded and solvent-exposed protein conformations, suggesting a detergent-like action. Thus, MT may form micelle-like structures around polypeptide chains, and proteins with a higher hydrophobicity may induce the penetration of hydrophilic groups of MT into the membrane, causing its rupture.

The expected outcome of the Trypanosoma cruzi proteomic map: a review of its potential biological applications for drug target discovery

Chagas disease is a neglected tropical illness endemic to Latin America, and its treatment remains unsatisfactory. This disease is caused by the hemoflagellate protozoan Trypanosoma cruzi, which has a complex life cycle involving three evolutive forms in both vertebrate and invertebrate hosts. Targeting metabolic pathways in the parasite for rational drug design represents a promising research field. This research area requires high performance techniques and proteomics become a powerful tool in this context. Here, we review advances in the construction of proteomic maps of the different forms of T. cruzi, emphasizing their biological applications towards the identification of alternative candidates for drug intervention.

Miltefosine resistance in Leishmania donovani involves suppression of oxidative stress-induced programmed cell death

Miltefosine (MIL), an alkylphospholipid, is the first orally administrable anti-leishmanial drug. But due to its long half-life, miltefosine is highly vulnerable for resistance. Hence it is important to understand the mechanism of resistance and to elucidate its action on Leishmania. Here we investigate the miltefosine induced process of programmed cell death in wild type (miltefosine sensitive) and in laboratory generated resistant strains of Leishmania donovani. Results indicate that miltefosine induced apoptosis like death in a time and dose dependent manner in wild-type cells, but not in MIL-resistant cell line. The miltefosine resistant cells remained protected against miltefosine-induced loss of mitochondrial membrane potential, gradual ATP loss and cytochrome C release from mitochondria into the cytosol. Comparative transcriptomic study showed significantly increased expression of FeSODA and SIR2 genes, putatively involved in oxidative stress associated apoptotic cell death. We hypothesize that oxidative stress mediated apoptosis as an alternative mechanism of miltefosine resistance.

A novel alkyl phosphocholine-dinitroaniline hybrid molecule exhibits biological activity in vitro against Leishmania amazonensis

Parasitic protozoa of the Leishmania genus cause leishmaniasis, an important complex of tropical diseases that affect about 12 million people around the world. The drugs used to treat leishmaniasis are pentavalent antimonials, miltefosine, amphotericin B and pentamidine. In the present study, we evaluated the effect of a novel alkyl phosphocholine-dinitroaniline hybrid molecule, TC95, against Leishmania amazonensis promastigotes and intracellular amastigotes. Antiproliferative assays indicated that TC95 is a potent inhibitor of promastigotes and intracellular amastigotes with IC50 values of 2.6 and 1.2 μM, respectively. Fluorescence microscopy with anti-α-tubulin antibody revealed changes in the cytoskeleton, whilst scanning electron microscopy showed alterations in the shape, plasma membrane, length of the flagellum, and cell cycle. Flow cytometry confirmed the cell cycle arrest mainly in G1 phase, however a significant population appeared in sub G0/G1 and super-G2. The alterations in the plasma membrane integrity were confirmed by fluorometric analysis using Sytox Blue. Transmission electron microscopy also revealed an accumulation of lipid bodies, confirmed by fluorescence microscopy and fluorometric analysis using Nile Red. Important lesions were also observed in organelles such as mitochondrion, endoplasmic reticulum and Golgi complex. In summary, our study suggests that TC95, an alkyl phosphocholine-trifluralin hybrid molecule, is a promising novel compound against L. amazonensis.

Miltefosine and polyhexamethylene biguanide: a new drug combination for the treatment of Acanthamoeba keratitis

BACKGROUND

In this study, a series of compounds - miltefosine, polyhexamethylene biguanide, chlorhexidine and propamidine isethionate - and combinations of the latter three agents with miltefosine were prepared and used in a rat model for the topical treatment of Acanthamoeba keratitis.

METHODS

The corneas of rats were infected with Acanthamoeba hatchetti. On the fifth day, all corneas were microscopically examined in order to determine the grade of infections. Nine groups were then prepared: miltefosine (65.12 μg/mL); chlorhexidine (0.02%); polyhexamethylene biguanide (0.02%), propamidine isethionate (0.1%), miltefosine plus chlorhexidine, miltefosine plus polyhexamethylene biguanide; miltefosine plus propamidine isethionate; infected control; and a non-infected control group. The treatment was continued for 28 days. After the treatment, the corneas were excised and used for Acanthamoeba culture to investigate the presence of Acanthamoeba growth. For the determination of cytotoxicity of the drugs on L929 cells, colorimetric assays were performed.

RESULTS

The best treatment results were obtained from the polyhexamethylene biguanide plus miltefosine group; the ratio of fully recovered eyes was 28.4%. It was proven that the miltefosine-polyhexamethylene biguanide combination yielded the highest anti-acanthamoebal activity in that approximately 86% of the eyes were cleared from amoebae. The cytotoxicity values of the miltefosine and the control groups were compared with other groups and found to be statistically different (P < 0.05).

CONCLUSION

This in vivo study demonstrates that a miltefosine-polyhexamethylene biguanide combination is highly effective for the treatment of Acanthamoeba keratitis.

Giardia lamblia: a new target for miltefosine

Giardia lamblia, the causative agent of giardiasis, is an intestinal infection with worldwide distribution and high rates of prevalence. Increased resistance of the parasite and the side effects of the reference drugs employed in the treatment of giardiasis make it necessary to seek new therapeutic agents. Therefore,the aim of this study was to examine the activity of hexadecylphosphocholine (miltefosine), a membrane active alkylphospholipid, that is licensed as an antileishmanial agent against giardiasis. The efficacy of miltefosine was evaluated both in vitro and in vivo in Swiss albino mice. Results of the in vitro testing revealed susceptibility of G. lamblia trophozoites to miltefosine with the following effective concentrations:EC50s of between 20 and 40 lM, and EC90s of between 20 and 80 lM. Immediate total lysis of the organisms was achieved by 100 lM. In vivo testing showed that oral administration of miltefosine,in a daily dose regimen course of 20 mg/kg for three successive days, to infected mice resulted in total elimination of the parasite from the intestine and amelioration of intestinal pathology. Scanning and transmission electron microscopy studies revealed that miltefosine induced severe morphological alterations to G. lamblia trophozoites, mainly at the level of cell membrane and adhesive disc. In conclusion,we believe that this is the first study highlighting G. lamblia as a possible new target for miltefosine.

Miltefosine: a review of its pharmacology and therapeutic efficacy in the treatment of leishmaniasis

Miltefosine is an alkylphosphocholine drug with demonstrated activity against various parasite species and cancer cells as well as some pathogenic bacteria and fungi. For 10 years it has been licensed in India for the treatment of visceral leishmaniasis (VL), a fatal neglected parasitic disease. It is the first and still the only oral drug that can be used to treat VL and cutaneous leishmaniasis (CL). The standard 28 day miltefosine monotherapy regimen is well tolerated, except for mild gastrointestinal side effects, although its teratogenic potential severely hampers its general use in the clinic and roll-out in national elimination programmes. The pharmacokinetics of miltefosine are mainly characterized by its long residence time in the body, resulting in extensive drug accumulation during treatment and long elimination half-lives. At the moment, different combination therapy strategies encompassing miltefosine are being tested in multiple controlled clinical trials in various geographical areas of endemicity, both in South Asia and East Africa. We here review the most salient pre-clinical and clinical pharmacological aspects of miltefosine, its mechanism of action against Leishmania parasites and other pathogens, and provide a systematic overview of the efficacy and safety data from all clinical trials of miltefosine, either alone or in combination, in the treatment of VL and CL.

Dihydrofolate reductase as a therapeutic target for infectious diseases: opportunities and challenges

Infectious diseases caused by parasites continue to take a massive toll on human health in the poor regions of the world. Filling the anti-infective drug-discovery pipeline has never been as challenging as it is now. The organisms responsible for these diseases have interesting biology with many potential biochemical targets. Inhibition of metabolic enzymes has been established as an attractive strategy for anti-infectious drug development. In this field, dihydrofolate reductase (DHFR) is an important enzyme in nucleic and amino acid synthesis and an extensively studied drug target over the past 50 years. The challenges for novel DHFR inhibition-based chemotherapeutics for the treatment of infectious diseases are now focused on overcoming the resistance problem as well as cost–effectiveness. Each year, the large number of literature citations attest the continued popularity of DHFR. It becomes truly the ‘enzyme of choice for all seasons and almost all reasons’. Herein, we summarize the opportunities and challenges in developing novel lead based on this target.

The biological in vitro effect and selectivity of aromatic dicationic compounds on Trypanosoma cruzi

Trypanosoma cruzi is a parasite that causes Chagas disease, which affects millions of individuals in endemic areas of Latin America. One hundred years after the discovery of Chagas disease, it is still considered a neglected illness because the available drugs are unsatisfactory. Aromatic compounds represent an important class of DNA minor groove-binding ligands that exhibit potent antimicrobial activity. This study focused on the in vitro activity of 10 aromatic dicationic compounds against bloodstream trypomastigotes and intracellular forms of T. cruzi. Our data demonstrated that these compounds display trypanocidal effects against both forms of the parasite and that seven out of the 10 compounds presented higher anti-parasitic activity against intracellular parasites compared with the bloodstream forms. Additional assays to determine the potential toxicity to mammalian cells showed that the majority of the dicationic compounds did not considerably decrease cellular viability. Fluorescent microscopy analysis demonstrated that although all compounds were localised to a greater extent within the kinetoplast than the nucleus, no correlation could be found between compound activity and kDNA accumulation. The present results stimulate further investigations of this class of compounds for the rational design of new chemotherapeutic agents for Chagas disease.

Particularities of mitochondrial structure in parasitic protists (Apicomplexa and Kinetoplastida)

Without mitochondria, eukaryotic cells would depend entirely on anaerobic glycolysis for ATP generation. This also holds true for protists, both free-living and parasitic. Parasitic protists include agents of human and animal diseases that have a huge impact on world populations. In the phylum Apicomplexa, several species of Plasmodium cause malaria, whereas Toxoplasma gondii is a cosmopolite parasite found on all continents. Flagellates of the order Kinetoplastida include the genera Leishmania and Trypanosoma causative agents of human leishmaniasis and (depending on the species) African trypanosomiasis and Chagas disease. Although clearly distinct in many aspects, the members of these two groups bear a single and usually well developed mitochondrion. The single mitochondrion of Apicomplexa has a dense matrix and many cristae with a circular profile. The organelle is even more peculiar in the order Kinetoplastida, exhibiting a condensed network of DNA at a specific position, always close to the flagellar basal body. This arrangement is known as Kinetoplast and the name of the order derived from it. Kinetoplastids also bear glycosomes, peroxisomes that concentrate enzymes of the glycolytic cycle. Mitochondrial volume and activity is maximum when glycosomal is low and vice versa. In both Apicomplexa and trypanosomatids, mitochondria show particularities that are absent in other eukaryotic organisms. These peculiar features make them an attractive target for therapeutic drugs for the diseases they cause.

Differential cytotoxicity of phospholipid analogues to pathogenic Acanthamoeba species and mammalian cells

OBJECTIVES

Previous studies have reported the ability of several phospholipid analogues to successfully inhibit the growth of Acanthamoeba species in vitro. This study tests further phospholipid analogues, either as free drug or in liposomal formulations, and unlike previous studies, examines their comparative toxicities to mammalian cells.

METHODS

The relative cytotoxic activities of the phospholipid derivatives hexadecyl-PC, octadecyl-PC, elaidyl-PC, erucyl-PC and edelfosine, against Acanthamoeba castellanii, Acanthamoeba polyphaga and a rabbit corneal epithelial (RCE) cell line, was determined by the alamarBlue assay. Free and liposomal formulations were compared for hexadecyl-PC and elaidyl-PC.

RESULTS

Both hexadecyl-PC and octadecyl-PC (IC50 values between 3.9 and 7.8 microM) demonstrated considerable activity against A. castellanii, as did elaidyl-PC (IC50 values between 15.6 and 31.25 microM). Both hexadecyl-PC and elaidyl-PC also proved effective against A. polyphaga (IC50 values between 15.6 and 31.25 and between 31.25 and 62.5 microM, respectively). In contrast, neither erucyl-PC nor edelfosine was inhibitory against either Acanthamoeba species. The growth of RCE cells was inhibited by octadecyl-PC, erucyl-PC and edelfosine (octadecyl-PC and erucyl-PC IC50 values between 7.8 and 15.6 microM and edelfosine IC50 values between 31.25 and 62.5 microM). Liposomal formulations of hexadecyl-PC and elaidyl-PC were less effective than free drug against both Acanthamoeba species.

CONCLUSIONS

These results demonstrate that hexadecyl-PC has the highest therapeutic index and is the most promising for the treatment of acanthamoebiasis.

Mitochondrial disruption and DNA fragmentation in Trypanosoma cruzi induced by naphthoimidazoles synthesized from beta-lapachone

Three naphthoimidazoles presenting aromatic groups attached to the imidazole ring were the most active against trypomastigotes of Trypanosoma cruzi between 45 derivatives from beta-lapachone. N1 is active against the three forms of the parasite. In this work, we investigated N2 and N3 and analyzed the effect of the three derivatives on metacyclogenesis, endocytosis, and cell cycle. In epimastigotes, N2 and N3 blocked the cell cycle, inhibited succinate cytochrome c reductase, metacyclogenesis, and induced damage to mitochondrion, Golgi, and reservosomes. In treated trypomastigotes, there were alterations in the mitochondrion, nucleus and kinetoplast, and DNA fragmentation. Preincubation with cysteine protease inhibitors reversed the effect of N1, N2, and N3. Such reversion and ultrastructural alterations suggest the involvement of autophagy in parasite death. Ultrastructural, flow cytometry, and biochemical studies suggest that naphthoimidazoles interferes with the energetic metabolism and induces DNA fragmentation.

Activity of “reversed” diamidines against Trypanosoma cruzi “in vitro”

Chagas' disease is an important parasitic illness caused by the flagellated protozoan Trypanosoma cruzi. The disease affects nearly 17 million individuals in endemic areas of Latin America and the current chemotherapy is quite unsatisfactory based on nitroheterocyclic agents (nifurtimox and benznidazol). The need for new compounds with different modes of action is clear. Due to the broad-spectrum antimicrobial activity of the aromatic dicationic compounds, this study focused on the activity of four such diamidines (DB811, DB889, DB786, DB702) and a closely related diguanidine (DB711) against bloodstream trypomastigotes as well as intracellular amastigotes of T. cruzi in vitro. Additional studies were also conducted to access the toxicity of the compounds against mammalian cells in vitro. Our data show that the four diamidines compounds presented early and high anti-parasitic activity (IC50 in low-micromolecular range) exhibiting trypanocidal dose-dependent effects against both trypomastigote and amastigote forms of T. cruzi 2h after drug treatment. Most of the diamidines compounds (except the DB702) exerted high anti-parasitic activity and low toxicity to the mammalian cells. Our results show the activity of reversed diamidines against T. cruzi and suggested that the compounds merit in vivo studies.

Inward Translocation of the Phospholipid Analogue Miltefosine across Caco-2 Cell Membranes Exhibits Characteristics of a Carrier-mediated Process

Miltefosine (hexadecylphosphocholine, HePC) is the first effective oral agent for the treatment of visceral leishmaniasis. The characteristics of HePC incorporation into the human intestinal epithelial cell line Caco-2 were investigated in order to understand its oral absorption mechanism. The results provide evidence for the involvement of a carrier-mediated mechanism, since the association of HePC at the apical pole of Caco-2 cells was (1) saturable as a function of time with a rapid initial incorporation over 5 min followed by a more gradual increase; (2) saturable as a function of concentration over the range studied (2-200 microM) with a saturable component which followed Michaelis-Menten kinetics (apparent K (m) 15.7 micromol/L, V (max) 39.2 nmol/mg protein/h) and a nonspecific diffusion component; (3) partially inhibited by low temperature and ATP depletion, indicating the temperature and energy-dependence of the uptake process. Moreover, we demonstrated, by an albumin back-extraction method, that HePC is internalized via translocation from the outer to the inner leaflet of the plasma membrane and that HePC may preferentially diffuse through intact raft microdomains. In conclusion, our results suggest that incorporation of HePC at the apical membrane of Caco-2 cells may occur through a passive diffusion followed by a translocation in the inner membrane leaflet through an active carrier-mediated mechanism.

The effect of Bulgarian propolis against Trypanosoma cruzi and during its interaction with host cells

Propolis has shown activity against pathogenic microorganisms that cause diseases in humans and animals. The ethanol (Et-Blg) and acetone (Ket-Blg) extracts from a Bulgarian propolis, with known chemical compositions, presented similar activity against tissue culture-derived amastigotes. The treatment of Trypanosoma cruzi-infected skeletal muscle cells with Et-Blg led to a decrease of infection and of the intracellular proliferation of amastigotes, while damage to the host cell was observed only at concentration 12.5 times higher than those affecting the parasite. Ultrastructural analysis of the effect of both extracts in epimastigotes revealed that the main targets were the mitochondrion and reservosomes. Et-Blg also affected the mitochondrion-kinetoplast complex in trypomastigotes, offering a potential target for chemotherapeutic agents.

Mechanisms of action of lysophospholipid analogues against trypanosomatid parasites

Lysophospholipid analogues (LPAs) comprise a class of metabolically stable compounds that have been developed as anticancer agents for over two decades, but which have also potent and selective antiparasitic activity, particularly against trypanosomatid parasites such as Leishmania and Trypanosoma cruzi, both in vitro and in vivo. The in vivo activities of LPAs result from direct effects on their target cells and are not dependent on a functional immune system. Because of their chemical nature, LPAs have a potential for interaction with a variety of subcellular structures and biochemical pathways. However, in mammalian cells LPA-induced growth inhibition and programmed cell death is usually associated with a blockade of phosphatidylcholine (PC) biosynthesis at the level of CTP: phosphocholine citidyltransferase, probably through an increase of cellular ceramide levels due to depressed sphingomyelin synthesis. Although in trypanosomatid parasites much less information is available, inhibition of PC biosynthesis by LPA has also been documented but at the level of phosphatidylethanolamine N-methyl-transferase, as well as LPA-induced classical apoptotic phenomena. The higher activity of LPAs as inhibitors of PC biosynthesis in parasites than in mammalian cells, probably due to different biochemical pathways involved in the two types of cells, could explain their selective antiparasitic action in vivo.

Ultrastructural analysis of edelfosine-treated trypomastigotes and amastigotes of Trypanosoma cruzi

We have previously reported that epimastigote forms of Trypanosoma cruzi treated with the lysophospholipid analogues (LPAs) edelfosine (ET-18), ilmofosine, and miltefosine suffered alterations in plasma membrane, mitochondrion, and lipid synthesis. In this work, ET-18 induced membrane damage in trypomastigotes and amastigotes. Incubation of epimastigotes and trypomastigotes with the three LPAs led to membrane permeabilization, which was abolished by serum addition. Treatment for 24 h in culture medium interfered the with mitochondrial status of epimastigotes, with no effect in trypomastigotes, in agreement with ultrastructural data. LPAs induced alterations in the plasma membrane of the three forms of T. cruzi and in the mitochondria of epimastigotes, suggesting that these organelles are potential targets of these analogues.

Ultrastructural alterations induced by the neolignan dihydrobenzofuranic eupomatenoid-5 on epimastigote and amastigote forms of Trypanosoma cruzi

Eupomatenoid-5, a compound isolated from leaves of Piper regnellii var. pallescens, showed antiprotozoal activity against the epimastigote proliferative stages and intracellular amastigote forms of Trypanosoma cruzi Y strain. Eupomatenoid-5, at 7.0 microg/ml (50% growth inhibition concentration) produced morphological changes in epimastigote forms of the parasite, such as intense cytoplasmic vacuolization, mitochondrial swelling, kinetoplast alteration, presence of myelin-like figures, and mitochondrial damage, as observed by transmission electron microscopy. In amastigote forms in LLCMK(2) cells, at 7.0-microg/ml concentration, the compound induced a decrease in the number of cells with internalized parasites and in the number of internalized parasites per LLCMK(2) cell, compared with untreated cells. Furthermore, intense cytoplasmic vacuolization and autophagic vacuoles were observed in T. cruzi intracellular amastigotes after 72 h of incubation. Scanning electron microscopy confirmed the alterations in the shape of the parasites.

Novel antitrypanosomal agents

Trypanosomes are the causative agents of Chagas' disease in Central and South America and sleeping sickness in sub-Saharan Africa. The current chemotherapy of the human trypanosomiases relies on only six drugs, five of which were developed > 30 years ago. In addition, these drugs display undesirable toxic side effects and the emergence of drug-resistant trypanosomes has been reported. Therefore, the development of new drugs in the treatment of Chagas' disease and sleeping sickness is urgently required. This article summarises the recent progress in identifying novel lead compounds for antitrypanosomal chemotherapy. Particular emphasis is placed on those agents showing promising, selective antitrypanosomal activity.

In vitro activity of hexadecylphosphocholine (miltefosine) against metronidazole-resistant and -susceptible strains of Trichomonas vaginalis

OBJECTIVES

Trichomonas vaginalis is the causative agent of trichomoniasis, a sexually transmitted disease with worldwide significance. Trichomoniasis can be treated with metronidazole; however, resistant strains of T. vaginalis have been isolated and there is a lack of useful alternative drugs. The aim of the present study was to examine the activity of hexadecylphosphocholine (HePC; miltefosine), a membrane-active alkylphospholipid, that is licensed as an antileishmanial agent against T. vaginalis.

METHODS

The efficacy of HePC after 30 min, 1 h, 16 h and 24 h against four different T. vaginalis strains (with varying resistance to metronidazole) was evaluated.

RESULTS

It was shown that all isolates, including the metronidazole-resistant strains, were susceptible to HePC, with EC50s of between 8 and 40 microM and EC90s of between 8 and 80 microM depending on time and on the medium used for the experiments. Treatment of trichomonads with HePC resulted in rounding up and, at concentrations of >or=40 microM, in subsequent total lysis of the organisms.

CONCLUSIONS

HePC may be a promising new candidate for the treatment of trichomoniasis.

Antiproliferative and ultrastructural effects of BPQ-OH, a specific inhibitor of squalene synthase, on Leishmania amazonensis

Parasites of the Leishmania genus require for the growth and viability the de novo synthesis of specific sterols as such as episterol and 5-dehydroepisterol because cholesterol, which is abundant in their mammalian hosts, does not fulfill the parasite sterol requirements. Squalene synthase catalyzes the first committed step in the sterol biosynthesis and has been studied as a possible target for the treatment of high cholesterol levels in humans. In this work we investigated the antiproliferative and ultrastructural effects induced by 3-(biphenyl-4-yl)-3-hydroxyquinuclidine (BPQ-OH), a specific inhibitor of squalene synthase, on promastigote and amastigote forms of Leishmania amazonensis. BPQ-OH had a potent dose-dependent growth inhibitory effect against promastigotes and amastigotes, with IC(50) values 0.85 and 0.11 microM, respectively. Ultrastructural analysis of the treated parasites revealed several changes in the morphology of promastigote forms. The main ultrastructural change was found in the plasma membrane, which showed signs of disorganization, with the concomitant formation of elaborated structures. We also observed alterations in the mitochondrion-kinetoplast complex such as mitochondrial swelling, rupture of its internal membrane and an abnormal compaction of the kinetoplast. Other alterations included the appearance of multivesicular bodies, myelin-like figures, alterations of the flagellar membrane and presence of parasites with two or more nuclei and kinetoplasts. We conclude that the BPQ-OH was a potent growth inhibitor of L. amazonensis, which led to profound changes of the parasite's ultrastructure and might be a valuable lead compound for the development of novel anti-Leishmania agents.

Leishmanicidal activity of edelfosine, miltefosine and ilmofosine

The anti-proliferative action of three alkyl-lysophospholipid derivatives, edelfosine (ET-OCH), miltefosine (Hexadecylphosphocholine), and ilmofosine (BM 14.440) has been studied on the promastigotes and amastigotes of Leishmania donovani. The effect of the three drugs has previously been studied, but the action mode was not clearly elucidated. In this study the effect on the intracellular amastigote forms was evaluated by two different methods: the traditional method, counting the amastigotes within the macrophages stained with Giemsa; and by a new method, staining the nuclear macrophages and amastigotes with ethidium bromide and counting the different population by flow cytometry. This new method, based on the flow cytometry, shows an advantage for evaluating the anti-proliferative effects in intracellular parasites. The ED50 were calculated for the drug activity after 72 hr, and for the three alkyl-lysophospholipid derivatives it were in the range of 26.73-33.31 microM against promastigotes and in the range of 16.46-23.16 against amastigotes. Also, studying the effect against macrophages J774A1, the ED50 were in the range of 24.28-26.38 microM. The effect of the alkyl-lysophospholipids in the macromolecular biosynthesis of the Leishmania donovani, was studied comparing the incorporation of labelled analogues ([3H] thymidine, [3H] uridine and [3H] leucine), respectively, in the DNA, RNA, and proteins of the flagellates treated. Miltefosine was the most active of the alkyl-lysophospholipids, especially in the inhibition of the RNA synthesis. The three compounds studied show high in vitro activity against L. donovani promastigotes and amastigotes.

Anti-proliferative synergy of lysophospholipid analogues and ketoconazole against Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae): cellular and ultrastructural analysis

OBJECTIVES

Investigation of the antiproliferative synergy of the lysophospholipid analogues (LPAs) edelfosine, ilmofosine and miltefosine with the ergosterol biosynthesis inhibitor ketoconazole against Trypanosoma cruzi.

METHODS

The effect of LPAs, ketoconazole and their combination was evaluated against epimastigotes and intracellular amastigotes by the parameter IC50 leading to construction of isobolograms, for determination of a synergic effect. For epimastigotes, ultrastructural damage induced by these treatments was evaluated by transmission and scanning electron microscopy.

RESULTS

Synergy was confirmed against both epimastigotes and amastigotes of the parasite. Edelfosine or ketoconazole alone induced morphological alterations in the plasma membrane and reservosomes of the parasites, while in combination, they also led to severe mitochondrial damage, formation of autophagic structures and multinucleation. Scanning electron microscopy confirmed the effect at the plasma membrane and also revealed alterations in the shape of the parasites.

CONCLUSIONS

Our results describe the synergic anti-proliferative effect of LPAs and ketoconazole against epimastigotes and intracellular amastigotes and suggest that in epimastigotes, plasma membrane, reservosomes and mitochondria are targets of these drugs, possibly by interference with lipid metabolism.

Effect of the lysophospholipid analogues edelfosine, ilmofosine and miltefosine against Leishmania amazonensis

OBJECTIVES

Analysis of the effect of edelfosine, ilmofosine and miltefosine on Leishmania amazonensis and of potential targets of these lysophospholipid analogues.

METHODS

Quantification and ultrastructural analysis of the effect of lysophospholipid analogues on promastigote forms and on infected peritoneal macrophages, and flow cytometry analysis of treated promastigotes labelled with propidium iodide and rhodamine 123 (Rh123).

RESULTS

The lysophospholipid analogues presented potent antiproliferative activity with IC50/3 days of 1.9-3.4 microM for promastigotes and 4.2-9.0 microM for intracellular amastigotes. Treatment with these analogues in Schneider medium for 1 day led to a dose-dependent decrease in Rh123 fluorescence, an effect more accentuated in edelfosine-treated parasites, suggesting interference with the potential of the mitochondrial membrane. In both forms of L. amazonensis, edelfosine induced extensive mitochondrial damage, multinucleation and, in promastigotes, also led to plasma membrane alterations, formation of autophagic structures and membranous arrangements inside the flagellar pocket.

CONCLUSIONS

The alkylglycerophosphocholines edelfosine and ilmofosine were more active than the alkylphosphocholine miltefosine against promastigotes and intracellular amastigotes of L. amazonensis, and ultrastructural and flow cytometry data indicate the mitochondrion as a target of edelfosine.

Miltefosine induces apoptosis-like death in Leishmania donovani promastigotes

Miltefosine (hexadecylphosphocholine [HePC]) has proved to be a potent oral treatment for human visceral leishmaniasis due to Leishmania donovani. The molecular mechanisms that contribute to the antileishmanial activity of HePC are still unknown. We report that in wild-type promastigotes of Leishmania donovani HePC is able to induce a cell death process with numerous cytoplasmic, nuclear, and membrane features of metazoan apoptosis, including cell shrinkage, DNA fragmentation into oligonucleosome-sized fragments, and phosphatidylserine exposure. None of these changes were detected in an HePC-resistant clone treated with the same drug concentration. Therefore, HePC does not appear to kill L. donovani promastigotes by a direct toxic mechanism but, rather, kills the promastigotes by an indirect one. Pretreatment of wild-type promastigotes with two broad caspase inhibitors, z-Val-Ala-DL-Asp(methoxy)-fluoromethylketone and Boc-Asp(methoxy)-fluoromethylketone, as well as a broad protease inhibitor, calpain inhibitor I, prior to drug exposure interfered with DNA fragmentation but did not prevent cell shrinkage or phosphatidylserine externalization. These data suggest that at least part of the apoptotic machinery operating in wild-type promastigotes involves proteases. Identification of the death-signaling pathways activated in HePC-sensitive parasites appears to be essential for a better understanding of the molecular mechanisms of action and resistance in these parasites.

Characterisation of Leishmania donovani promastigotes resistant to hexadecylphosphocholine (miltefosine)

Leishmania donovani promastigote lines resistant to hexadecylphosphocholine (HePC, miltefosine) at 2.5, 5.0, 10.0, 20.0 and 40.0 microM were developed in vitro by continuous step-wise drug pressure. The 40 microM line was 15 times more resistant to HePC than the wild-type clone and showed cross-resistance to the ether lipid ET-18-OCH3 (edelfosine) but not to the standard anti-leishmanial drugs. Resistance was stable up to 12 weeks in drug-free culture medium. No amplification of specific genes, including the multidrug resistance P-glycoprotein gene, could be detected in the resistant parasites.

Miltefosine (Impavido): the first oral treatment against leishmaniasis

Miltefosine is a novel antileishmanial drug that has significant selectivity in both in vitro and in vivo models. Clinical efficacy was demonstrated for the treatment of visceral leishmaniasis with the advantage of oral administration over the currently recommended antileishmanial drugs that require parenteral administration. Miltefosine produces high cure rates also in patients resistant to the standard antimonial therapy.

Leishmania donovani resistance to miltefosine involves a defective inward translocation of the drug

Miltefosine (hexadecylphosphocholine [HePC]) is the first drug approved for the oral treatment of visceral leishmaniasis. As part of a study on the mechanisms of action of this drug and on the rates of resistance to this drug, we have been working in vitro with an Leishmania donovani line that was previously shown to be 15-fold more resistant to HePC. We have studied the accumulation of [(14)C]HePC by L. donovani promastigotes and have found a drastic reduction (>95%) in the ability of the resistant line to internalize the drug. Binding of HePC to the plasma membrane and drug efflux from preloaded cells were similar in both drug-sensitive and -resistant lines, and no [(14)C]HePC metabolism was evident in either line. Resistant parasites were also unable to take up other short-chain phospholipid analogs, independently of their polar head group, even though endocytosis remained unaltered. Finally, HePC uptake was temperature and energy dependent and sensitive to the thiol-reactive agent N-ethylmaleimide. We propose that inward translocation of a short-chain phospholipid across the plasma membrane may exist in Leishmania promastigotes and that such activity is defective in the resistant line.

Antiprotozoal activities of phospholipid analogues

The antiprotozoal activity of phospholipid analogues, originally developed as anti-cancer drugs, has been determined in the past decade. The most susceptible parasites are Leishmania spp. and Trypanosoma cruzi with activity also shown against Trypanosoma brucei spp., Entamoeba histolytica and Acanthamoeba spp. Miltefosine, an alkylphosphocholine, was registered for the oral treatment of visceral leishmaniasis (VL) in India in March 2002. This review will focus on the biological activities of phospholipid analogues. Biochemical and molecular targets and mechanism(s) of action have been studied extensively in tumor cells but have not been determined in protozoa.

Proinflammatory and cytotoxic effects of hexadecylphosphocholine (miltefosine) against drug-resistant strains of Trypanosoma cruzi

The increased resistance of the protozoan parasite Trypanosoma cruzi to nitro derivatives is one of the major problems for the successful treatment of Chagas' disease. In the present study, we have tested the effects of 1-O-hexadecylphosphocholine (miltefosine) against strains of T. cruzi that are partially resistant (strain Y) and highly resistant (strain Colombiana) to the drugs in clinical use. As expected, epimastigotes of strain Colombiana showed higher levels of resistance to benznidazole than those of strain Y. However, the level of resistance to miltefosine was the same for both strains. This alkylphospholipid was also extremely toxic against intracellular amastigotes of both strains. This ether-lipid analogue induced in a dose-dependent manner the production of tumor necrosis factor alpha and nitric oxide (NO) radicals by infected and noninfected macrophages, suggesting that miltefosine may activate macrophages in vitro. Nevertheless, the cytotoxic effect of miltefosine against intracellular amastigotes was independent of the amount of NO produced by the infected macrophages since the same dose-response curves for miltefosine were observed when the NO production was blocked by the NO synthase inhibitor N(G)-monomethyl-L-arginine monoacetate. Preliminary in vivo studies with BALB/c mice infected with strain Y indicated that oral miltefosine promoted survival and reduced the parasitemia to levels comparable to those observed when benznidazole was used. Four months after treatment, no parasites were detected in the blood or spleen tissue sections maintained in culture. Together, these results support the hypothesis that miltefosine may be used for the treatment of Chagas' disease, including cases caused by resistant strains of T. cruzi.

Cytotoxic activities of alkylphosphocholines against clinical isolates of Acanthamoeba spp

Free-living amoebae of the genus Acanthamoeba are causing serious chronic conditions such as destructive keratitis in contact lens wearers or granulomatous amoebic encephalitis in individuals with compromised immune systems. Both are characterized by the lack of availability of sufficiently effective and uncomplicated, manageable treatments. Hexadecylphosphocholine (miltefosine) is licensed for use as a topical antineoplastic agent, but it is also active in vitro against several protozoan parasites, and it was applied very successfully for the treatment of human visceral leishmaniasis. The aim of our study was to evaluate the efficacy of hexadecylphosphocholine and other alkylphosphocholines (APCs) against Acanthamoeba spp. The in vitro activities of eight different APCs against three Acanthamoeba strains of various pathogenicities were determined. All substances showed at least amoebostatic effects, and some of them disrupted the amoebae, as shown by the release of cytoplasmic enzyme activity. Hexadecylphosphocholine exhibited the highest degree of cytotoxicity against trophozoites, resulting in complete cell death at a concentration as low as 40 microM, and also displayed significant cysticidal activity. Hexadecylphosphocholine may be a promising new candidate for the topical treatment of Acanthamoeba keratitis and, conceivably, even for the oral treatment of granulomatous amoebic encephalitis.

Sensitivities of Leishmania species to hexadecylphosphocholine (miltefosine), ET-18-OCH(3) (edelfosine) and amphotericin B

The sensitivities of both promastigote and amastigote stages of six species of Leishmania, L. donovani, L. major, L. tropica, L. aethiopica, L. mexicana and L. panamensis, were determined in vitro to the phospholipid drugs hexadecylphosphocholine (HPC, miltefosine) and ET-18-OCH(3) (edelfosine). In all assays L. donovani was the most sensitive species, with ED(50) values in the range of 0.12-1.32 microM against promastigotes and 1.2-4.6 microM against amastigotes. L. major was the least sensitive species in the majority of assays with ED(50) values for HPC in the range of 4.8-13.1 microM against promastigotes and for HPC and ET-18-OCH(3) in the range of 7.5-37.1 microM against amastigotes. Amphotericin B deoxycholate was used as the standard drug and gave submicromolar ED(50) values in all assays; L. mexicana was the least sensitive species to this drug.

A critical review on Chagas disease chemotherapy

In this "Critical Review" we made a historical introduction of drugs assayed against Chagas disease beginning in 1912 with the works of Mayer and Rocha Lima up to the experimental use of nitrofurazone. In the beginning of the 70s, nifurtimox and benznidazole were introduced for clinical treatment, but results showed a great variability and there is still a controversy about their use for chronic cases. After the introduction of these nitroheterocycles only a few compounds were assayed in chagasic patients. The great advances in vector control in the South Cone countries, and the demonstration of parasite in chronic patients indicated the urgency to discuss the etiologic treatment during this phase, reinforcing the need to find drugs with more efficacy and less toxicity. We also review potential targets in the parasite and present a survey about new classes of synthetic and natural compounds studied after 1992/1993, with which we intend to give to the reader a general view about experimental studies in the area of the chemotherapy of Chagas disease, complementing the previous papers of Brener (1979) and De Castro (1993).