Differences in growth of Trypanoplasma borreli in carp serum is dependent on transferrin genotype

Kinetoplastid parasites require transferrin (Tf), being the main source of iron, for growth and multiplication. This group of parasites developed a unique receptor-mediated system for acquiring host Tf which bears no structural homology with the host transferrin receptor. Trypanoplasma borreli, a blood parasite of common carp, probably uses a similar mechanism to sequester iron from host transferrin. In this study, we demonstrate a critical role of Tf for parasite growth. For in vitro studies we isolated and purified Tf from carp homozygous for the D or G allele of Tf. We obtained Tf-depleted serum using specific antibodies to carp Tf and studied gene expression in vivo during T. borreli infection with Real Time-quantitative PCR. We demonstrate that T. borreli cannot survive in medium supplemented with Tf-depleted serum while reconstitution with Tf restores normal growth. The critical role of Tf for parasite survival was shown in incomplete medium (medium without serum): addition of purified Tf significantly increased parasite survival. We also demonstrate that Tf polymorphism has a significant impact on T. borreli multiplication. Cultured parasites die more quickly in an environment containing D-typed Tf, as compared to medium with G-typed Tf. Gene expression during T. borreli infection in carp did not show an acute phase response. We could, however, observe an increased transcription of Tf in the head kidney, which may be associated with an immunological function of the Tf protein.

Antikinetoplastid Activity of Indolocarbazoles from Streptomyces sanyensis

Chagas disease and leishmaniasis are neglected tropical diseases caused by kinetoplastid parasites of Trypanosoma and Leishmania genera that affect poor and remote populations in developing countries. These parasites share similar complex life cycles and modes of infection. It has been demonstrated that the particular group of phosphorylating enzymes, protein kinases (PKs), are essential for the infective mechanisms and for parasite survival. The natural indolocarbazole staurosporine (STS, 1) has been extensively used as a PKC inhibitor and its antiparasitic effects described. In this research, we analyze the antikinetoplastid activities of three indolocarbazole (ICZs) alkaloids of the family of staurosporine STS, 2-4, and the commercial ICZs rebeccamycin (5), K252a (6), K252b (7), K252c (8), and arcyriaflavin A (9) in order to establish a plausive approach to the mode of action and to provide a preliminary qualitative structure-activity analysis. The most active compound was 7-oxostaurosporine (7OSTS, 2) that showed IC₅₀ values of 3.58 ± 1.10; 0.56 ± 0.06 and 1.58 ± 0.52 µM against L. amazonensis; L. donovani and T. cruzi, and a Selectivity Index (CC₅₀/IC₅₀) of 52 against amastigotes of L. amazonensis compared to the J774A.1 cell line of mouse macrophages.

Small Molecule Inhibitors Targeting the Heat Shock Protein System of Human Obligate Protozoan Parasites

Obligate protozoan parasites of the kinetoplastids and apicomplexa infect human cells to complete their life cycles. Some of the members of these groups of parasites develop in at least two systems, the human host and the insect vector. Survival under the varied physiological conditions associated with the human host and in the arthropod vectors requires the parasites to modulate their metabolic complement in order to meet the prevailing conditions. One of the key features of these parasites essential for their survival and host infectivity is timely expression of various proteins. Even more importantly is the need to keep their proteome functional by maintaining its functional capabilities in the wake of physiological changes and host immune responses. For this reason, molecular chaperones (also called heat shock proteins)-whose role is to facilitate proteostasis-play an important role in the survival of these parasites. Heat shock protein 90 (Hsp90) and Hsp70 are prominent molecular chaperones that are generally induced in response to physiological stress. Both Hsp90 and Hsp70 members are functionally regulated by nucleotides. In addition, Hsp70 and Hsp90 cooperate to facilitate folding of some key proteins implicated in cellular development. In addition, Hsp90 and Hsp70 individually interact with other accessory proteins (co-chaperones) that regulate their functions. The dependency of these proteins on nucleotide for their chaperone function presents an Achille's heel, as inhibitors that mimic ATP are amongst potential therapeutic agents targeting their function in obligate intracellular human parasites. Most of the promising small molecule inhibitors of parasitic heat shock proteins are either antibiotics or anticancer agents, whose repurposing against parasitic infections holds prospects. Both cancer cells and obligate human parasites depend upon a robust protein quality control system to ensure their survival, and hence, both employ a competent heat shock machinery to this end. Furthermore, some inhibitors that target chaperone and co-chaperone networks also offer promising prospects as antiparasitic agents. The current review highlights the progress made so far in design and application of small molecule inhibitors against obligate intracellular human parasites of the kinetoplastida and apicomplexan kingdoms.

Tunic extract of the host ascidian attracts the causal agent of soft tunic syndrome, Azumiobodo hoyamushi (Kinetoplastea: Neobodonida)

Azumiobodo hoyamushi, a kinetoplastid flagellate, is the causative agent of soft tunic syndrome, an infectious disease of the edible ascidian Halocynthia roretzi. The flagellate is thought to invade the tunic matrix via a damaged area of the tunic on the siphon wall. We hypothesized that the flagellate locates the tunic entry site by a chemotactic response to soluble substances diffused from the host ascidians. To investigate this hypothesis, we examined whether the flagellate shows a chemotactic response to tissue extracts (tunic and other tissues) from the host ascidian H. roretzi. We tested extracts from 5 tissues as well as hemolymph. Only the tunic extract showed significant positive chemotactic activity, and the activity decreased with increasing dilution. Furthermore, autoclaved tunic extract, extracts from diseased individuals, and extract from the styelid ascidian Styela clava also had chemotactic activity, although the activities were lower than that of tunic extract from healthy H. roretzi. Ultrafiltration of the tunic extract through a 3 kDa cutoff membrane completely abrogated the activity; the ultrafiltration retentate still showed activity. Thus, the soluble factors that attract the flagellate are present exclusively in the tunic extract, and the chemotactic factors are larger than 3 kDa. Our experiments also suggested that the tunic extract contains both heat-stable and heat-labile factors. We conclude that the flagellate locates the tunic entry site by chemotaxis toward soluble factors that diffuse from a damaged area of the tunic on the siphon wall.

Everybody needs sphingolipids, right! Mining for new drug targets in protozoan sphingolipid biosynthesis

Sphingolipids (SLs) are an integral part of all eukaryotic cellular membranes. In addition, they have indispensable functions as signalling molecules controlling a myriad of cellular events. Disruption of either the de novo synthesis or the degradation pathways has been shown to have detrimental effects. The earlier identification of selective inhibitors of fungal SL biosynthesis promised potent broad-spectrum anti-fungal agents, which later encouraged testing some of those agents against protozoan parasites. In this review we focus on the key enzymes of the SL de novo biosynthetic pathway in protozoan parasites of the Apicomplexa and Kinetoplastidae, outlining the divergence and interconnection between host and pathogen metabolism. The druggability of the SL biosynthesis is considered, alongside recent technology advances that will enable the dissection and analyses of this pathway in the parasitic protozoa. The future impact of these advances for the development of new therapeutics for both globally threatening and neglected infectious diseases is potentially profound.

Screening a Natural Product-Based Library against Kinetoplastid Parasites

Kinetoplastid parasites cause vector-borne parasitic diseases including leishmaniasis, human African trypanosomiasis (HAT) and Chagas disease. These Neglected Tropical Diseases (NTDs) impact on some of the world's lowest socioeconomic communities. Current treatments for these diseases cause severe toxicity and have limited efficacy, highlighting the need to identify new treatments. In this study, the Davis open access natural product-based library was screened against kinetoplastids (Leishmania donovani DD8, Trypanosoma brucei brucei and Trypanosoma cruzi) using phenotypic assays. The aim of this study was to identify hit compounds, with a focus on improved efficacy, selectivity and potential to target several kinetoplastid parasites. The IC50 values of the natural products were obtained for L. donovani DD8, T. b. brucei and T. cruzi in addition to cytotoxicity against the mammalian cell lines, HEK-293, 3T3 and THP-1 cell lines were determined to ascertain parasite selectivity. Thirty-one compounds were identified with IC50 values of ≤ 10 µM against the kinetoplastid parasites tested. Lissoclinotoxin E (1) was the only compound identified with activity across all three investigated parasites, exhibiting IC50 values < 5 µM. In this study, natural products with the potential to be new chemical starting points for drug discovery efforts for kinetoplastid diseases were identified.

Novel scaffolds for inhibition of Cruzipain identified from high-throughput screening of anti-kinetoplastid chemical boxes

American Trypanosomiasis or Chagas disease is a prevalent, neglected and serious debilitating illness caused by the kinetoplastid protozoan parasite Trypanosoma cruzi. The current chemotherapy is limited only to nifurtimox and benznidazole, two drugs that have poor efficacy in the chronic phase and are rather toxic. In this scenario, more efficacious and safer drugs, preferentially acting through a different mechanism of action and directed against novel targets, are particularly welcome. Cruzipain, the main papain-like cysteine peptidase of T. cruzi, is an important virulence factor and a chemotherapeutic target with excellent pre-clinical validation evidence. Here, we present the identification of new Cruzipain inhibitory scaffolds within the GlaxoSmithKline HAT (Human African Trypanosomiasis) and Chagas chemical boxes, two collections grouping 404 non-cytotoxic compounds with high antiparasitic potency, drug-likeness, structural diversity and scientific novelty. We have adapted a continuous enzymatic assay to a medium-throughput format and carried out a primary screening of both collections, followed by construction and analysis of dose-response curves of the most promising hits. Using the identified compounds as a starting point a substructure directed search against CHEMBL Database revealed plausible common scaffolds while docking experiments predicted binding poses and specific interactions between Cruzipain and the novel inhibitors.

HPLC-DAD phenolic profile, cytotoxic and anti-kinetoplastidae activity of Melissa officinalis

Context Melissa officinalis subsp. inodora Bornm. (Lamiaceae) has been used since ancient times in folk medicine against various diseases, but it has not been investigated against protozoa. Objective To evaluate the activities of M. officinalis against Leishmania braziliensis, Leishmania infantum and Trypanosoma cruzi as well as its cytotoxicity in fibroblast cell line. Materials and methods The fresh leaves were chopped into 1 cm(2) pieces, washed and macerated with 99.9% of ethanol for 72 h at room temperature. Antiparasitic activity of M. officinalis was accessed by direct counting of cells after serial dilution, while the cytotoxicity of M. officinalis was evaluated in fibroblast cell line (NCTC929) by measuring the reduction of resazurin. The test duration was 24 h. High-performance liquid chromatography (HPLC) was used to characterise the extract. Results The extract at concentrations of 250 and 125 μg/mL inhibited 80.39 and 54.27% of promastigote (LC50  value = 105.78 μg/mL) form of L. infantum, 80.59 and 68.61% of L. brasiliensis (LC50 value  = 110.69 μg/mL) and against epimastigote (LC50 value  = 245.23 μg/mL) forms of T. cruzi with an inhibition of 54.45 and 22.26%, respectively, was observed. The maximum toxicity was noted at 500 μg/mL with 95.41% (LC50  value = 141.01 μg/mL). The HPLC analysis identified caffeic acid and rutin as the major compounds. Discussion The inhibition of the parasites is considered clinically relevant (< 500 μg/mL). Rutin and caffeic acids may be responsible for the antiprotozoal effect of the extract. Conclusion The ethanol extract of M. officinalis can be considered a potential alternative source of natural products with antileishmania and antitrypanosoma activities.

Disinfection of fertilized eggs of the edible ascidian Halocynthia roretzi for prevention of soft tunic syndrome

Azumiobodo hoyamushi, the causative agent of soft tunic syndrome, was likely introduced to farming sites of the edible ascidian Halocynthia roretzi via ascidian spat. The source of infection is thought to be cysts of A. hoyamushi that reside in the substrates on which the ascidian spat are attached, but not the spat themselves. Thus, there is a need to develop methods to prevent contamination of the substrates with A. hoyamushi during seed production of the ascidian. We evaluated the protozoacidal effects of sodium hypochlorite and povidone-iodine against the flagellate and temporary cyst forms of A. hoyamushi. Additionally, we evaluated the effects of these disinfectants on the development of fertilized ascidian eggs. The flagellate form of A. hoyamushi was completely inactivated by povidone-iodine (5 ppm, 1 min) and sodium hypochlorite (1 ppm, 1 min). The temporary cysts of A. hoyamushi were completely inactivated by both disinfectants (5 ppm, 1 min). Disinfection with 50 ppm povidone-iodine for 15 min or 5 ppm sodium hypochlorite for 15 min had no effect on ascidian embryogenesis. Thus, horizontal transmission of A. hoyamushi via the substrates can be efficiently prevented by disinfecting ascidian eggs or tools used for spawning with povidone-iodine baths ranging from 5 ppm for 1 min to 50 ppm for 15 min without any side effects.

Targeting Lysine Deacetylases (KDACs) in Parasites

Due to an increasing problem of drug resistance among almost all parasites species ranging from protists to worms, there is an urgent need to explore new drug targets and their inhibitors to provide new and effective parasitic therapeutics. In this regard, there is growing interest in exploring known drug leads of human epigenetic enzymes as potential starting points to develop novel treatments for parasitic diseases. This approach of repurposing (starting with validated targets and inhibitors) is quite attractive since it has the potential to reduce the expense of drug development and accelerate the process of developing novel drug candidates for parasite control. Lysine deacetylases (KDACs) are among the most studied epigenetic drug targets of humans, and a broad range of small-molecule inhibitors for these enzymes have been reported. In this work, we identify the KDAC protein families in representative species across important classes of parasites, screen a compound library of 23 hydroxamate- or benzamide-based small molecules KDAC inhibitors, and report their activities against a range of parasitic species, including the pathogen of malaria (Plasmodium falciparum), kinetoplastids (Trypanosoma brucei and Leishmania donovani), and nematodes (Brugia malayi, Dirofilaria immitis and Haemonchus contortus). Compound activity against parasites is compared to that observed against the mammalian cell line (L929 mouse fibroblast) in order to determine potential parasite-versus-host selectivity). The compounds showed nanomolar to sub-nanomolar potency against various parasites, and some selectivity was observed within the small panel of compounds tested. The possible binding modes of the active compounds at the different protein target sites within different species were explored by docking to homology models to help guide the discovery of more selective, parasite-specific inhibitors. This current work supports previous studies that explored the use of KDAC inhibitors in targeting Plasmodium to develop new anti-malarial treatments, and also pioneers experiments with these KDAC inhibitors as potential new anthelminthics. The selectivity observed begins to address the challenges of targeting specific parasitic diseases while limiting host toxicity.

Due to pandemic drug resistance in the treatment of parasitic infections, there is an urgent need to identify novel drug targets and their associated drug compounds. Although “drug repurposing”, i.e. the application of known drugs and compounds to new indications such as infectious diseases, provides a cost effective approach in the development of novel therapeutics, selectivity is one of the major obstacles to overcome in getting such compounds into clinical trials as anti-parasitic drugs. Using the lysine deacetylases (KDACs) as an example, we explored the activities of a panel of known inhibitors against the KDAC targets in a range of parasitic organisms. The computational study of their binding modes to the targets (by docking the compounds to the homology models within different organisms in comparison with the human proteins) helps to rationalize the different activities observed and provide insight on the optimization of lead compounds to improve selectivity. Our work provides support of “drug repurposing” in the treatment of parasitic diseases, and demonstrates the necessity of optimizing these leads for the ultimate goal of preparing them for clinical use.

In vitro and in vivo efficacy of drugs against the protozoan parasite Azumiobodo hoyamushi that causes soft tunic syndrome in the edible ascidian Halocynthia roretzi (Drasche)

It was discovered recently that infection by a protozoan parasite, Azumiobodo hoyamushi, is the most probable cause for soft tunic syndrome in an edible ascidian, Halocynthia roretzi (Drasche). In an attempt to develop measures to eradicate the causative parasite, various drugs were tested for efficacy in vitro and in vivo. Of the 20 antiprotozoal drugs having different action mechanisms, five were found potent (24-h EC50  < 10 mg L(-1) ) in their parasite-killing effects: formalin, H2 O2 , bithionol, ClO2 and bronopol. Moderately potent drugs (10 < 24-h EC50  < 100 mg L(-1) ) were quinine, fumagillin, amphotericin B, ketoconazole, povidone-iodine, chloramine-T and benzalkonium chloride. Seven compounds, metronidazole, albendazole, paromomycin, nalidixic acid, sulfamonomethoxine, KMnO4 , potassium monopersulphate and citric acid, exhibited EC50  > 100 mg L(-1) . When ascidians were artificially infected with A. hoyamushi, treated using 40 mg L(-1) formalin, bronopol, ClO2 , or H2 O2 for 1 h and then monitored for 24 h, very low mortality was observed. However, the number of surviving parasite cells in the ascidian tunic tissues was significantly reduced by treating with 40 mg L(-1) formalin or ClO2 for 1 h. The data suggest that we might be able to develop a disinfection measure using a treatment regimen involving commonly available drugs.

Glucocorticoid receptors on and in a unicellular organism, Cryptobia salmositica

This is the first report to our knowledge that demonstrates a functional steroid hormone receptor in a protozoon. The study used Cryptobia salmositica, a pathogenic haemoflagellate found in salmonid fishes. It has been previously shown that cortisol and dexamethasone (a synthetic glucocorticoid) enhanced the multiplication of C. salmositica under in vitro conditions indicating the presence of glucocorticoid receptors on/in the parasite. Also, the glucocorticoid receptor antagonist, mifepristone (RU486), inhibited the stimulatory effect of the two glucocorticoids on parasite multiplication. In the present study, we used an antibody (produced in a rabbit against glucocorticoid receptor protein) agglutination test and confocal microscopy with immunohistofluorescence staining to demonstrate cortisol-glucocorticoid receptor-like protein receptors on the plasma membrane and in the cytoplasm of the parasite. In two in vitro studies, the addition of 50ngml(-1) of RU486 was more effective in inhibiting parasite replication in cultures with 7,000parasitesml(-1) than in cultures with 14,000parasitesml(-1). Also, 100ngml(-1) of RU486/ml was more effective than 50ngml(-1) in inhibiting parasite multiplication in the 14,000 parasitesml(-1) cultures. These in vitro studies indicate that the number of binding sites on/in the parasite is finite. The findings may be important in future studies especially on steroid receptor signalling pathways and dissection of ligand-receptor interactions, and for evaluating the adaptations that develop in pathogens as part of the host-parasite interaction.

Cortisol and dexamethasone increase the in vitro multiplication of the haemoflagellate, Cryptobia salmositica, possibly by interaction with a glucocorticoid receptor-like protein

Cryptobia salmositica is a pathogenic haemoflagellate of Pacific salmon, Oncorhynchus spp., on the west coast of North America. The in vitro multiplication of the parasite was significantly enhanced by the addition of cortisol (within a range consistent with physiological levels in salmonid fishes; 10-50 ng ml(-1)) to the culture medium (MEM supplemented with FBS). However, higher cortisol concentrations (100 and 200 ng ml(-1)) either had no enhancing effects or resulted in lower replication rates compared with the controls. The synthetic glucocorticoid, dexamethasone (Dex), also stimulated the replication of the parasite and mifepristone (RU486), a synthetic steroid that has glucocorticoid receptor (GR) antagonist properties, inhibited the stimulatory actions of both cortisol and Dex, when added to the medium at a concentration of 100 ng ml(-1) co-culture with cortisol or Dex. Furthermore, the dose-dependent effects of glucocorticoids (cortisol and Dex) on the multiplication of the haemoflagellate were correlated with the initial size of the inocula. The study revealed a novel relationship between the parasite and its host, in which the host's cortisol is used by the parasite to enhance its replication. Also, since C. salmositica responds to both native and synthetic glucocorticoids and to the GR antagonist, RU486, and exhibits a biphasic (hormetic) response to the amount of cortisol in the medium, we propose that the glucocorticoid exerts its effects via an interaction with GR-like proteins in C. salmositica that are functionally similar to those present in vertebrate cells.

Comparison of tank treatments with copper sulfate and potassium permanganate for sunshine bass with ichthyobodosis

The biflagellated, single-celled parasite Ichthyobodo necator can cause significant losses among fish populations, particularly those cultured in tanks. Treatments of KMnO4 and CuSO4 were evaluated against a naturally occurring I. necator infestation on sunshine bass (female white bass Morone chrysops x male striped bass M. saxatilis) raised in tanks. Four-hour static treatments with 3 mg of KMnO4/L of water (2.5 mg/L above the determined KMnO4 demand) or 2 mg of CuSO4/L of water (total alkalinity = 207 mg/L; total hardness = 95 mg/L) were randomly applied to 4 tanks/treatment (23 fish/tank); the same treatments were reapplied 2 d later. Four tanks were used as positive controls. By 2 d posttreatment (after the second treatment), only 17.4% of the untreated control fish survived, and a sample of the remaining fish was heavily infested with I. necator. All remaining control fish were dead by 5 d posttreatment. The KMnO4 treatment significantly curtailed the initial mortality (survival = 92.4%) and slightly reduced the high parasite loads at 2 d posttreatment. However, fish mortalities increased dramatically over the next 3 d (survival at 5 d posttreatment = 37.5%), and parasite loads from sampled fish remained high. The CuSO4 treatment was effective in significantly lowering the parasite load (almost eliminating I. necator) and maintaining a high fish survival (87.5%) by 5 d posttreatment. The findings in this study clearly demonstrate that CuSO4 is a viable treatment for ichthyobodosis in tanks.

Synthesis, biological evaluation, and molecular modeling of 3,5-substituted-N1-phenyl-N4,N4-di-n-butylsulfanilamides as antikinetoplastid antimicrotubule agents

Dinitroanilines are of interest as antiprotozoal lead compounds because of their selective activity against the tubulin of these organisms, but concern has been raised due to the potentially mutagenic nitro groups. Analogues of N(1)-phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (GB-II-150, compound 2b), a selective antimitotic agent against African trypanosomes and Leishmania, have been prepared where the nitro groups are replaced with amino, chloro, cyano, carboxylate, methyl ester, amide, and methyl ketone moieties. Dicyano compound 5 displays IC(50) values that are comparable to 2b against purified leishmanial tubulin assembly (6.6 vs 7.4 microM), Trypanosoma brucei brucei growth in vitro (0.26 vs 0.18 microM), Leishmania donovani axenic amastigote growth in vitro (4.4 vs 2.3 microM), and in vitro toxicity against Vero cells (16 vs 9.7 microM). Computational studies provide a rationale for the antiparasitic order of activity of these analogues and further insight into the role of the substituents at the 3 and 5 positions of the sulfanilamide ring.

Topoisomerases of kinetoplastid parasites: why so fascinating?

DNA topoisomerases are the key enzymes involved in carrying out high precision DNA transactions inside the cells. However, they are detrimental to the cell when a wide variety of topoisomerase-targeted drugs generate cytotoxic lesions by trapping the enzymes in covalent complexes on the DNA. The discovery of unusual heterodimeric topoisomerase I in kinetoplastid family added a new twist in topoisomerase research related to evolution, functional conservation and their preferential sensitivity to Camptothecin. On the other hand, structural and mechanistic studies on kinetoplastid topoisomerase II delineate some distinguishing features that differentiate the parasitic enzyme from its prokaryotic and eukaryotic counterparts. This review summarizes the recent advances in research in kinetoplastid topoisomerases, their evolutionary significance and the death of the unicellular parasite Leishmania donovani induced by topoisomerase I inhibitor camptothecin.

Antikinetoplastid antimitotic activity and metabolic stability of dinitroaniline sulfonamides and benzamides

N(1)-Phenyl-3,5-dinitro-N(4),N(4)-di-n-propylsulfanilamide (1) and N(1)-phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (2) show potent in vitro antimitotic activity against kinetoplastid parasites but display poor in vivo activity. Seventeen new dinitroaniline sulfonamide and eleven new benzamide analogs of these leads are reported here. Nine of the sulfonamides display in vitro IC(50) values under 500 nM against African trypanosomes, and the most active antikinetoplastid compounds also inhibit the in vitro assembly of purified leishmanial tubulin with potencies similar to that of 2. While several of the potent compounds are rapidly degraded by rat liver S9 fractions in vitro, N(1)-(3-hydroxy)phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (21) displays an IC(50) value of 260 nM against African trypanosomes in vitro and is more stable than 2 in the in vitro metabolism assay.

Pre-systemic metabolism prevents in vivo antikinetoplastid activity of N1,N4-substituted 3,5-dinitro sulfanilamide, GB-II-150

We previously showed that N1-phenyl-3,5-dinitro-N4,N4-di-n-butylsulfanilamide (denoted GB-II-150) possesses selective antimicrotubule activity against Leishmania donovani and Trypanosoma brucei in vitro [Bhattacharya, G., Herman, J., Delfin, D., Salem, M.M., Barszcz, T., Mollet, M., Riccio, G., Brun, R., Werbovetz, K.A., 2004. Synthesis and antitubulin activity of N(1)- and N(4)-substituted 3,5-dinitro sulfanilamides against African trypanosomes and Leishmania. Journal of Medicinal Chemistry 47, 1823-1832]. When GB-II-150 was administered orally to male Sprague-Dawley rats, extensive first-pass metabolism of the compound was observed and the oral bioavailability was zero. GB-II-150 displayed a half-life of 170 min and a clearance of 31.5 mL/min/kg in rats when administered intravenously. In vitro metabolism studies indicated that less than 5% of GB-II-150 remained intact after a 60-min incubation with rat liver S9 fraction. As expected, the compound was extensively metabolized, with the major products resulting from N1-ring oxidation, N4-alkane oxidation, N4-oxidation, and nitro reduction. These data indicate that GB-II-150 undergoes rapid and extensive first-pass metabolism, precluding the attainment of effective systemic drug concentrations and explaining the lack of in vivo antitrypanosomal activity of this compound.

DNA topoisomerases in life and death: implications in kinetoplastid protozoa

Current biomedical research has its focus on the search for newer intervention strategies to control public health impact of parasitic diseases. The dramatic advances of molecular and cellular biology in recent times have provided opportunities for discovering and evaluating molecular targets for drug designing, which now form a rational basis for the development of improved anti parasitic therapy. DNA topoisomerases, the "cellular magicians" involved in nearly all biological processes governing DNA, have emerged as one such biological target. Over the last two decades, interest in topoisomerases has expanded beyond the realm of the basic science laboratory into the clinical arena. This review aims at providing a comprehensive insight into the biology of DNA topoisomerases and also focus on its evolution as a drug target in the unicellular kinetoplastids.

Selective antimicrotubule activity of N1-phenyl-3,5-dinitro-N4,N4-di-n-propylsulfanilamide (GB-II-5) against kinetoplastid parasites

Analogs of the antimitotic herbicide oryzalin (3,5-dinitro-N4,N4-di-n-propylsulfanilamide) were recently prepared that were more potent in vitro than the parent compound against the kinetoplastid parasite Leishmania donovani (Bioorg Med Chem Lett 12:2395-2398, 2002). In the present work, we show that the most active molecule in the group, N1-phenyl-3,5-dinitro-N4,N4-di-n-propylsulfanilamide (GB-II-5), is a potent, selective antimitotic agent against kinetoplastid parasites. GB-II-5 possesses IC50 values of 0.41 and 0.73 microM in vitro against two strains of the related parasite Trypanosoma brucei but is much less toxic to J774 murine macrophages and PC3 prostate cancer cells, exhibiting IC50 values of 29 and 35 microM against these lines, respectively. Selectivity is also observed for GB-II-5 with purified leishmanial and mammalian tubulin. The assembly of 15 microM leishmanial tubulin is completely inhibited by 10 microM GB-II-5, whereas 40 microM GB-II-5 inhibits the assembly of 15 microM porcine brain tubulin by only 17%. In cultured L. donovani and T. brucei, treatment with 5 and 0.5 microM GB-II-5, respectively, causes a striking increase in the fraction of G2M cells compared with control. Given the potency and selectivity of this agent against kinetoplastid tubulin, GB-II-5 emerges as an exciting new antitrypanosomal and antileishmanial lead compound.

The in vitro effects of isometamidium chloride (Samorin) on the piscine hemoflagellate Cryptobia salmositica (Kinetoplastida, Bodonina)

Isometamidium chloride (Samorin) is therapeutic in rainbow trout (Oncorhynchus mykiss) during preclinical and chronic cryptobiosis. However, the toxic mechanism of isometamidium on Cryptobia salmositica has not been elucidated. The objective of the present study was to examine the in vitro effects of isometamidium on C. salmositica. Under in vitro conditions, isometamidium chloride reduced the infectivity of C. salmositica suspended in whole fish blood. It accumulated rapidly in the kinetoplast (within 1 min) and caused disruption and decantenation of kinetoplast DNA. The in vitro cryptobiacidal activity of isometamidium was reduced when parasites were incubated in medium containing serum supplement, suggesting that isometamidium also binds to plasma proteins. Isometamidium altered glycoprotein receptors (epitopes) for antibodies on the surface of C. salmositica and thus protected some of the parasites from lysis by complement-fixing antibodies. In vitro oxygen consumption and carbon dioxide production decreased in drug-exposed C. salmositica, with increased products of glycolysis, i.e., lactate and pyruvate, after exposure to isometamidium. This suggests that some C. salmositica switched from aerobic respiration to glycolysis when the mitochondrion was damaged by isometamidium.

Identification of glycosomes and metabolic end products in pathogenic and nonpathogenic strains of Cryptobia salmositica (Kinetoplastida: Bodonidae)

Whole cell lysates of pathogenic and nonpathogenic strains of Cryptobia salmositica were subjected to subcellular fractionation using differential and isopycnic centrifugation in sucrose. The glycolytic enzymes hexokinase, fructose-1,6-biphosphate aldolase, triosephosphate isomerase, glucosephosphate isomerase and glyceraldehyde-3-phosphate-dehydrogenase and the peroxisomal enzyme catalase were associated with a microbody that had a buoyant density in sucrose of 1.21 g cm-3. Lactate dehydrogenase was detected in whole cell lysates, but not in purified organelles. A microbody with a positive reaction for catalase was detected in electron microscope sections of the pathogenic and nonpathogenic strains. These catalase-containing microbodies fused with lipid bodies and vacuoles, arose by division from pre-existing microbodies and expelled their contents into the cytoplasm of the cell. Both strains also modified the catalase content in their microbodies. Under aerobic conditions, they metabolized glucose to pyruvate and lactate. We conclude that part of the glycolytic pathway in C. salmositica is compartmentalized in a microbody called the glycosome.

Suramin blocks nucleotide triphosphate binding to ribosomal protein L3 from Trypanoplasma borreli

Ribosomal protein L3 (L3) has been demonstrated to participate in formation of the peptidyltransferase center and is essential for its catalytic activity. In the present study we show that L3 is able to bind nucleotide triphosphates with high and specific affinity in vitro. L3 was serendipitously identified by screening of a genomic phage library from a primitive kinetoplastid flagellate Trypanoplasma borreli with the ATPase domain of the topoisomerase II gene as a probe. The cloned gene was overexpressed and purified as a his-tag fusion protein in E. coli. Radioligand binding experiments, using [gamma-35S]ATP, showed that L3 is able to bind ATP but also GTP and UTP with similar high affinity (IC50 50-100 nM), while it has no ATPase activity. Furthermore, we showed that L3 has more than 500-fold higher affinity for nucleotide triphosphates compared to the corresponding nucleotide monophosphates and diphosphates. Molecular genetic and biochemical analyses allowed us to localize the NTP binding domain of L3 to the N-terminal 296 residues. Suramin, a polysulfonated naphthylamine derivative of urea, known for its chemotherapeutic effects completely inhibited the binding of [gamma-35S]ATP at subclinical levels. Results obtained with surface plasmon resonance technology showed that suramin both forms weak multimolecular complexes with L3 and binds strongly to L3 in nearly stoichiometric amounts.

The in vitro effects of crystal violet on the pathogenic haemoflagellate Cryptobia salmositica Katz, 1951 (Sarcomastigophora: Kinetoplastida)

Crystal violet does not inhibit in vitro multiplication of a nonpathogenic strain of Cryptobia salmositica at low concentrations (0.01 microM and 0.001 microM) but multiplication is inhibited at higher concentrations (> or = 0.05 microM). In contrast, the pathogenic strain of C. salmositica does not multiply in vitro when incubated with crystal violet (0.001 microM, 0.01 microM and 0.05 microM). The infectivity of the pathogenic strain is significantly reduced after in vitro exposure to crystal violet. Crystal violet lyses C. salmositica (100.0 microM) and causes lesions on mitochondrial and nuclear membranes of the parasite. Pathogenic strains of Cryptobia salmositica and C. bullocki are more susceptible to lysis after in vitro exposure to crystal violet than are nonpathogenic strains of Cryptobia salmositica and C. catostomi.

Control of gene expression in viruses and protozoan parasites by antisense oligonucleotides

Chemically-modified oligonucleotides are now routinely used to prevent gene expression in cell-free media and in cultured cells. The binding of an antisense sequence to a complementary RNA target may lead to the selective inhibition of the encoded information. This may occur at different levels: splicing; transport of the mature RNA from the nucleus to the cytoplasm; translation. Antisense oligonucleotides constitute an interesting tool to shed some light on gene function. They are also potential new therapeutic agents against pathogenic organisms. This review discusses the rules that guide the design of an antisense oligomer and the choice of a target sequence. Examples of the potential use of antisense oligonucleotides in the fields of virology and parasitology, in particular in relation to trypanosomatids, are described.

Lipid biosynthesis pathways as chemotherapeutic targets in kinetoplastid parasites

Inhibitors of sterol and phospholipid biosynthesis in kinetoplastid parasites such as Trypanosoma cruzi, the causative agent of Chagas' disease, and different species of Leishmania have potent and selective activity as chemotherapeutic agents in vitro and in vivo. Recent work with the sterol C14 alpha-demethylase inhibitor D0870, a bis triazole derivative, showed that this compound is capable of inducing radical parasitological cure in murine models of both acute and chronic Chagas' disease. Other inhibitors of this type, such as SCH 56592, have also shown curative, rather than suppressive, activity against T. cruzi in these models. Leishmania species have different susceptibilities to sterol biosynthesis inhibitors, both in vitro and in vivo. Leishmania braziliensis promastigotes, naturally resistant to C14 alpha-demethylase inhibitors such as ketoconazole and D0870, were susceptible to these drugs when used in combination with the squalene epoxidase inhibitor terbinafine. Inhibitors of delta 24(25) sterol methyl transferase have been shown to act as potent antiproliferative agents against Trypanosoma cruzi, both in vitro and in vivo. New inhibitors of this type which show enhanced activity and novel mechanisms of action have been synthesized. Recent work has also demonstrated that this type of enzyme inhibitors can block sterol biosynthesis and cell proliferation in Pneumocystis carinii, a fungal pathogen which had previously been found resistant to other sterol biosynthesis inhibitors. Ajoene, an antiplatelet compound derived from garlic, was shown to have potent antiproliferative activity against epimastigotes and amastigotes of Trypanosoma cruzi in vitro; this activity was associated with a significant alteration of the phospholipid composition of the cells with no significant effects on the sterol content. In addition, alkyllsophospholipids such as ilmofosine, miltefosine and edelfosine have been shown to block the proliferation of T. cruzi and Leishmania and alter both the phospholipid and sterol composition. These results indicate the potential of lipid biosynthesis inhibitors as useful therapeutic agents in the treatment of leishmaniasis and Chagas' disease.

Hydroxyurea-induced synchrony of DNA replication in the Kinetoplastida

We have developed a reliable and reproducible method to induce synchrony of the DNA synthetic cycle in the Kinetoplastida. The method involves treatment of cultures with 20 mM hydroxyurea (HU) and fetal bovine serum. Both stationary-phase and exponential-phase cultures can be synchronized. However, in the case of exponential-phase cultures the population doubling time and rate of DNA synthesis of the population influenced the time of exposure to HU. The treatment of kinetoplastids with 20 mM HU did not adversely affect the cells as judged by oxygen consumption, RNA, and protein content. We postulate that the requirement for high HU levels, which would be toxic to vertebrate cells, may be due to a lower affinity of kinetoplastid ribonucleotide reductase, the target enzyme for HU. Some of the kinetoplastids are pathogens of man and his food chain. Consequently, the development of a reliable technique for synchronization of the kinetoplastids should not only permit a detailed analysis of their cellular and molecular biology but provide a means to collect and characterize biochemical and immunochemical substances relevant to the infectious process.

In vitro oxygen consumption and motility of Cryptobia salmositica, Cryptobia bullocki, and Cryptobia catostomi (Sarcomastigophora: Kinetoplastida)

Cryptobia salmositica (pathogenic and vaccine strains), Cryptobia bullocki (pathogenic), and Cryptobia catostomi (nonpathogenic) have similar oxygen consumption rates (0.17 +/- 0.01 nm O2/10(6) parasites). Incubation with sodium azide (5 microliters of a 1-M solution to 1 ml of parasite suspension, i.e., a 5-mM final concentration) reduced the oxygen consumption by approximately 4.5-fold. Motility of the parasites was also greatly reduced in sodium azide. The oxygen consumption and motility of the parasites returned to preazide treatment levels when the azide was removed even after 24 hr of incubation in sodium azide. The activities of hexokinase, pyruvate kinase, and cytochrome C oxidase were not detected in the 3 species of Cryptobia.