Effect of the microtubule stabilising agent taxol on leishmanial protozoan parasites in vitro

Evolutionarily diverse fungal zoospores show contrasting swimming patterns specific to ultrastructure

Zoosporic fungi, also called chytrids, produce single-celled motile spores with flagellar swimming tails (zoospores).1,2 These fungi are key components of aquatic food webs, acting as pathogens, saprotrophs, and prey.3,4,5,6,7,8 Little is known about the swimming behavior of fungal zoospores, a crucial factor governing dispersal, biogeographical range, ecological function, and infection dynamics.6,9 Here, we track the swimming patterns of zoospores from 12 evolutionarily divergent species of zoosporic fungi from across seven orders of the Chytridiomycota and the Blastocladiomycota. We report two major swimming patterns that correlate with the cytoskeletal ultrastructure of these zoospores. Specifically, we show that species without major cytoplasmic tubulin components swim in a circular fashion, while species with prominent cytoplasmic tubulin structures swim in a pattern akin to a random walk (move-stop-redirect-move). We confirm cytoskeletal architecture by performing fluorescence confocal microscopy across all 12 species. We then treat representative species with variant swimming behaviors and cytoplasmic-cytoskeletal arrangements with tubulin-stabilizing (Taxol) and depolymerizing (nocodazole) pharmacological compounds. We observed that when treating the "random walk" species with nocodazole, their swimming behavior changed to a circular-swimming pattern. Confocal imaging of the nocodazole-treated zoospores demonstrates that these cells maintain flagellum tubulin structures but lack their characteristic cytoplasmic tubulin structures. Our data demonstrate that the capability of zoospores to perform "complex" random-walk movement is linked to the presence of prominent cytoplasmic tubulin structures and suggest a link between cytology, sensory systems, and swimming behavior in a diversity of zoosporic fungi.

Repurposing as a strategy for the discovery of new anti-leishmanials: the-state-of-the-art

Leishmaniasis is a vector-borne neglected tropical disease caused by protozoan parasites of the genus Leishmania for which there is a paucity of effective viable non-toxic drugs. There are 1·3 million new cases each year causing considerable socio-economic hardship, best measured in 2·4 million disability adjusted life years, with greatest impact on the poorest communities, which means that desperately needed new antileishmanial treatments have to be both affordable and accessible. Established medicines with cheaper and faster development times may hold the cure for this neglected tropical disease. This concept of using old drugs for new diseases may not be novel but, with the ambitious target of controlling or eradicating tropical diseases by 2020, this strategy is still an important one. In this review, we will explore the current state-of-the-art of drug repurposing strategies in the search for new treatments for leishmaniasis.

Wnt5a Signaling Promotes Host Defense against Leishmania donovani Infection

Leishmania donovani infects macrophages, disrupting immune homeostasis. The underlying mechanism that sustains infection remains unresolved. In view of the potential of Wnt5a signaling to support immune homeostasis, we evaluated the interrelationship of Wnt5a signaling and Leishmania donovani infection. Upon infecting macrophages separately with antimony drug-sensitive and -resistant L. donovani, we noted disruption in the steady-state level of Wnt5a. Moreover, inhibition of Wnt5a signaling by small interfering RNA transfection in vitro or by use of inhibitor of Wnt production in vivo led to an increase in cellular parasite load. In contrast, treatment of macrophages with recombinant Wnt5a caused a decrease in the load of antimony-sensitive and -resistant parasites, thus confirming that Wnt5a signaling antagonizes L. donovani infection. Using inhibitors of the Wnt5a signaling intermediates Rac1 and Rho kinase, we demonstrated that Wnt5a-mediated inhibition of parasite infection in macrophages is Rac1/Rho dependent. Furthermore, phalloidin staining and reactive oxygen species estimation of Wnt5a-treated macrophages suggested that a Wnt5a-Rac/Rho-mediated decrease in parasite load is associated with an increase in F- actin assembly and NADPH oxidase activity. Moreover, live microscopy of L. donovani-infected macrophages treated with Wnt5a demonstrated increased endosomal/lysosomal fusions with parasite-containing vacuoles (parasitophorous vacuoles [PV]). An increase in PV-endosomal/lysosomal fusion accompanied by augmented PV degradation in Wnt5a-treated macrophages was also apparent from transmission electron microscopy of infected cells. Our results suggest that, although L. donovani evades host immune response, at least in part through inhibition of Wnt5a signaling, revamping Wnt5a signaling can inhibit L. donovani infection, irrespective of drug sensitivity or resistance.

Effects of linalool and eugenol on the survival of Leishmania (L.) infantum chagasi within macrophages

The most commonly used drugs against visceral leishmaniasis are based on pentavalent antimonial compounds, which have played a fundamental role in therapy for over 70 years. However, the treatment is painful and has severe toxic side effects that can be fatal. Antimonial resistance is spreading and reaching alarming proportions. Linalool and eugenol have been shown to kill Leishmania (L.) amazonensis and Trypanosoma cruzi at low doses. In the present study, we demonstrate the effects of linalool and eugenol, components of essential oils, on Leishmania (L.) infantum chagasi, one of the causative agents of visceral leishmaniasis. We compared the effects of those compounds to the effects of glucantime, a positive control. In L. infantum chagasi killing assays, the LD₅₀ for eugenol was 220μg/ml, and that for linalool was 550μg/ml. L. infantum chagasi was added to cultures of peritoneal mouse macrophages for four hours prior to drug treatment. Eugenol and linalool significantly decreased the number of parasites within the macrophages. Eugenol and linalool enhanced the activities of the L. infantum chagasi protein kinases PKA and PKC. Linalool also decreased L. infantum chagasi oxygen consumption. In conclusion, both linalool and eugenol promoted a decrease in the proliferation and viability of L. infantum chagasi. These effects were more pronounced during the interaction between the parasites and peritoneal mouse macrophages.

Microtubule drugs: action, selectivity, and resistance across the kingdoms of life

Microtubule drugs such as paclitaxel, colchicine, vinblastine, trifluralin, or oryzalin form a chemically diverse group that has been reinforced by a large number of novel compounds over time. They all share the ability to change microtubule properties. The profound effects of disrupted microtubule systems on cell physiology can be used in research as well as anticancer treatment and agricultural weed control. The activity of microtubule drugs generally depends on their binding to α- and β-tubulin subunits. The microtubule drugs are often effective only in certain taxonomic groups, while other organisms remain resistant. Available information on the molecular basis of this selectivity is summarized. In addition to reviewing published data, we performed sequence data mining, searching for kingdom-specific signatures in plant, animal, fungal, and protozoan tubulin sequences. Our findings clearly correlate with known microtubule drug resistance determinants and add more amino acid positions with a putative effect on drug-tubulin interaction. The issue of microtubule network properties in plant cells producing microtubule drugs is also addressed.

Dolabelladienetriol, a compound from Dictyota pfaffii algae, inhibits the infection by Leishmania amazonensis

BACKGROUND

Chemotherapy for leishmaniasis, a disease caused by Leishmania parasites, is expensive and causes side effects. Furthermore, parasite resistance constitutes an increasing problem, and new drugs against this disease are needed. In this study, we examine the effect of the compound 8,10,18-trihydroxy-2,6-dolabelladiene (Dolabelladienetriol), on Leishmania growth in macrophages. The ability of this compound to modulate macrophage function is also described.

METHODOLOGY/PRINCIPAL FINDINGS

Leishmania-infected macrophages were treated with Dolabelladienetriol, and parasite growth was measured using an infectivity index. Nitric oxide (NO), TNF-α and TGF-β production were assayed in macrophages using specific assays. NF-kB nuclear translocation was analyzed by western blot. Dolabelladienetriol inhibited Leishmania in a dose-dependent manner; the IC(50) was 44 µM. Dolabelladienetriol diminished NO, TNF-α and TGF-β production in uninfected and Leishmania-infected macrophages and reduced NF-kB nuclear translocation. Dolabelladienetriol inhibited Leishmania infection even when the parasite growth was exacerbated by either IL-10 or TGF-β. In addition, Dolabelladienetriol inhibited Leishmania growth in HIV-1-co-infected human macrophages.

CONCLUSION

Our results indicate that Dolabelladienetriol significantly inhibits Leishmania in macrophages even in the presence of factors that exacerbate parasite growth, such as IL-10, TGF-β and HIV-1 co-infection. Our results suggest that Dolabelladienetriol is a promising candidate for future studies regarding treatment of leishmaniasis, associated or not with HIV-1 infection.

Leishmanicidal effect of LLD-3 (1), a nor-triterpene isolated from Lophanthera lactescens

Leishmanicidal activity of 6alpha, 7alpha, 15beta, 16beta, 24-pentacetoxy-22alpha-carbometoxy-21beta,22beta-epoxy-18beta-hydroxy-27,30-bisnor-3,4-secofriedela-1,20 (29)-dien-3,4 R-olide (LLD-3 (1)) isolated from Lophanthera lactescens Ducke, a member of the Malpighiaceae, was demonstrated against intramacrophage amastigote forms (IC(50) of 0.41mug/mL). The in vitro leishmanicidal effect of Glucantime, the first choice drug for leishmaniasis treatment, was increased by LLD-3 (1) association. The leishmanicidal effect of LLD-3 (1) was not due to stimulation of nitric oxide production by macrophages. LLD-3 (1) was also not cytotoxic for mouse peritoneal macrophages or B cells as assessed by the XTT and Trypan blue exclusion assays. LLD-3 (1) was unable to affect proliferation of naïve or activated B and T cells, as well as the B cells immunoglobulin synthesis. Cellularity of different tissues, liver and kidney functions were not altered in mice treated with LLD-3 (1), as well as the histology pattern of different organs. Our results add LLD-3 (1) as a potential drug candidate for treatment of leishmaniasis.

Selective lead compounds against kinetoplastid tubulin

Kinetoplastid parasites are responsible for the potentially fatal diseases leishmaniasis, African sleeping sickness and Chagas disease. The current treatments for these diseases are far from ideal and new compounds are needed as antiparasitic drug candidates. Tubulin is the accepted target for treatments against cancer and helminths, suggesting that kinetoplastid tubulin is also a suitable target for antiprotozoal compounds. Selective lead compounds against kinetoplastid tubulin have been identified that could represent a starting point for the development of new drug candidates against these parasites.

Molecular basis for resistance of acanthamoeba tubulins to all major classes of antitubulin compounds

Tubulin is essential to eukaryotic cells and is targeted by several antineoplastics, herbicides, and antimicrobials. We demonstrate that Acanthamoeba spp. are resistant to five antimicrotubule compounds, unlike any other eukaryote studied so far. Resistance correlates with critical amino acid differences within the inhibitor binding sites of the tubulin heterodimers.

Confocal microscopic investigation of tubulin distribution and effect of paclitaxel on posttranslationally modified tubulins in sodium arsenite resistant Leishmania donovani

The affinity of arsenic towards the cytoskeleton leading to disturbance of tubulin polymerization is well known. Tubulin undergoes extensive posttranslational modifications which effect stability and dynamics of microtubules but little is known about the effect of antimicrotubule drugs on their distribution and function in kinetoplastid parasites such as Leishmania. The current study was undertaken to investigate the effect of continuous sodium arsenite exposure on the tubulin distribution profile in wild type and sodium arsenite resistant Leishmania donovani together with effect of paclitaxel, a tubulin-polymerizing agent, on that distribution using confocal microscopy. Immunofluorescence studies using specific monoclonal antibodies against alpha-tubulin and posttranslationally modified tubulins (acetylated and tyrosinated) have revealed distinct differences in the organization of microtubule arrays in wild type and sodium arsenite resistant L. donovani that is further affected by paclitaxel treatment. Microtubules are arranged in spiral arrays in wild type as compared to the longitudinal arrays in arsenite resistant L. donovani. The difference in microtubular structure organization may explain the parasite response to continuous drug pressure and illustrate the fundamental impact of arsenite on microtubules in arsenite resistant L. donovani.

Functional expression of a multidrug P-glycoprotein transporter of Leishmania

P-glycoprotein (Pgp) transporters play an important role in multidrug resistance in eukaryotic cells and in protozoan parasites such as Leishmania. To search for new reversal agents of the Leishmania tropica Pgp, we developed a screening assay using the Baculovirus-insect cell expression system. We demonstrated a MgATP-dependent, vanadate-sensitive transport of Hoechst 33342 in membrane preparations of Sf9 insect cells expressing Pgp. We have found that dihydro-beta-agarofuran sesquiterpenes from Maytenus cuzcoina inhibited Hoechst 33342 transport that correlates with their reversal effect in a multidrug-resistant L. tropica line overexpressing Pgp. The results suggest that Sf9 cell membrane Hoechst 33342 transport system represents an efficient tool for examining the interactions of Leishmania Pgp with pharmacological agents.

High-affinity binding of silybin derivatives to the nucleotide-binding domain of a Leishmania tropica P-glycoprotein-like transporter and chemosensitization of a multidrug-resistant parasite to daunomycin

In order to overcome the multidrug resistance mediated by P-glycoprotein-like transporters in Leishmania spp., we have studied the effects produced by derivatives of the flavanolignan silybin and related compounds lacking the monolignol unit on (i) the affinity of binding to a recombinant C-terminal nucleotide-binding domain of the L. tropica P-glycoprotein-like transporter and (ii) the sensitization to daunomycin on promastigote forms of a multidrug-resistant L. tropica line overexpressing the transporter. Oxidation of the flavanonol silybin to the corresponding flavonol dehydrosilybin, the presence of the monolignol unit, and the addition of a hydrophobic substituent such as dimethylallyl, especially at position 8 of ring A, considerably increased the binding affinity. The in vitro binding affinity of these compounds for the recombinant cytosolic domain correlated with their modulation of drug resistance phenotype. In particular, 8-(3,3-dimethylallyl)-dehydrosilybin effectively sensitized multidrug-resistant Leishmania spp. to daunomycin. The cytosolic domains are therefore attractive targets for the rational design of inhibitors against P-glycoprotein-like transporters.