Paclitaxel (Taxol)-induced killing of Leishmania major in murine macrophages

Antileishmanial Effects of Bunium Persicum Crude Extract, Essential Oil, and Cuminaldehyde on Leishmania Major: In Silico and In Vitro Properties

PURPOSE

Cuminaldehyde (CA), an oxidized aldehyde monoterpene, is a major essential oil component in cumin seeds, which has shown different promising medical effects. In this study, we comprehensively evaluated the antileishmanial potential of Bunium persicum (Boiss) B. Fedtsch (Apiaceae) and one of its main essential oil constituents, CA, focus on the mechanisms of action.

METHODS

We used a molecular docking approach to examine the capability of CA for binding to IL-12P40 and TNF-α. The colorimetric assay was performed to assess the effect of B. persicum crude extract, essential oil, and CA, against Leishmania major promastigotes and intracellular amastigotes. The expression of IFN-γ, IL-12P40, TNF-α, and IL-10 genes was detected using quantitative real-time polymerase chain reaction qPCR.

RESULTS

Docking analyses in the current study indicated CA binds to IL-12P40 and TNF-α. These products were safe, extremely antileishmanial, and significantly promoted Th1-related cytokines (IFN-γ, IL-12P40, TNF-α), while downregulating the Th2 phenotype (IL-10).

CONCLUSION

Cumin essential oil and its major component, CA, possessed powerful antileishmanial activity. The primary mechanism of activity involves an immunomodulatory role toward Th1 cytokine response. Therefore, cumin essential oil and CA deserve further explorations as promising medications for treating leishmaniasis.

Morphogenesis Dynamics in Leishmania Differentiation

Leishmania, the causative agent of leishmaniasis, is an obligatory intracellular parasite that cycles between phagolysosome of mammalian macrophages, where it resides as round intracellular amastigotes, and the midgut of female sandflies, where it resides as extracellular elongated promastigotes. This protozoan parasite cytoskeleton is composed of stable and abundant subpellicular microtubules (SPMT). This study aims to determine the kinetics of developmental morphogenesis and assess whether microtubules remodelling is involved in this process. Using image-streaming technology, we observed that rounding of promastigotes during differentiation into amastigotes was initiated promptly after exposure to the differentiation signal. Stabilizing microtubules with taxol sped rounding, but later killed differentiating parasites if taxol was not removed. Microtubule destabilizers such as vinblastine had no effect on the rate of rounding, nor on the viability of differentiating parasites. In the reverse process, elongation is initiated after a delay of 7.5 and completed 72 h after exposure to the amastigote to the promastigote differentiation signal. During the delay, parasites became highly sensitive to treatment with microtubule destabilizers. The addition of vinblastine during the first 7.5 h halted differentiation and killed parasites. Between 8 and 24 h, parasites gradually became resistant to vinblastine and, in parallel, started to elongate. In contrast, taxol had no effect on parasite elongation, nor on the viability of these cells. In a parallel study, we showed that the Leishmania-specific protein kinase A (PKA) holoenzyme containing the LdPKAR3-C3 complex is essential for promastigote elongation. Mutant promastigotes lacking either of these proteins are round, but maintain their flagella. Here, we observed that during differentiation into amastigotes, these mutants round at the same rate as the wild type, but never exceed the WT density of round amastigotes. In the reverse process, these mutants undergo the same initial delay and then elongate at the same rate as the WT. They stop elongating when they reach 20% of elongated cells in mature promastigotes. Our analysis indicates that while promastigote rounding into amastigotes did not require microtubule remodelling, morphogenesis of round amastigotes into elongated promastigotes required microtubule rearrangement before elongation was initiated. This is the first study that investigates the dynamics of microtubules during parasite development.

Ex Vivo Phenotypic Screening of Two Small Repurposing Drug Collections Identifies Nifuratel as a Potential New Treatment against Visceral and Cutaneous Leishmaniasis

Leishmaniases are vector-borne neglected diseases caused by single-celled parasites. The search for new antileishmanial drugs has experienced a strong boost thanks to the application of bioimaging to phenotypic screenings based on intracellular amastigotes. Mouse splenic explants infected with fluorescent strains of Leishmania are proven tools of drug discovery, where hits can be easily transferred to preclinical in vivo models. We have developed a two-staged platform for antileishmanial drugs. First, we screened two commercial collections of repurposing drugs with a total of 1769 compounds in ex vivo mouse splenocytes infected with an infrared emitting Leishmania infantum strain. The most active and safest compounds were scaled-up to in vivo models of chronic Leishmania donovani visceral leishmaniasis and Leishmania major cutaneous leishmaniasis. From the total of 1769 compounds, 12 hits with selective indices >35 were identified, and 4 of them were tested in vivo in a model of L. donovani visceral leishmaniasis. Nifuratel, a repurposed synthetic nitrofuran, when administered orally at 50 mg/kg bw once or twice a day for 10 days, caused >80% reduction in the parasitic load. Furthermore, the intralesional administration of nifuratel in a model of cutaneous leishmaniasis by L. major produced the parasitological cure. From the previous results we have deduced the great capacity of mouse splenic explants to identify new hits, a model which could be easily transferred to in vivo models, as well as the potential use of nifuratel as an alternative to the current treatment of cutaneous leishmaniasis.

Leishmanicidal Activity of Isoselenocyanate Derivatives

Conventional chemotherapy against leishmaniasis includes agents exhibiting considerable toxicity. In addition, reports of drug resistance are not uncommon. Thus, safe and effective therapies are urgently needed. Isoselenocyanate compounds have recently been identified with potential antitumor activity. It is well known that some antitumor agents demonstrate effects against Leishmania In this study, the in vitro leishmanicidal activities of several organo-selenium and organo-sulfur compounds were tested against Leishmania major and Leishmania amazonensis parasites, using promastigotes and intracellular amastigote forms. The cytotoxicity of these agents was measured in murine peritoneal macrophages and their selectivity indexes were calculated. One of the tested compounds, the isoselenocyanate derivative NISC-6, showed selectivity indexes 2- and 10-fold higher than those of the reference drug amphotericin B when evaluated in L. amazonensis and L. major, respectively. The American strain (L. amazonensis) was less sensitive to NISC-6 than L. major, showing a trend similar to that observed previously for amphotericin B. In addition, we also observed that NISC-6 significantly reduced the number of amastigotes per infected macrophage. On the other hand, we showed that NISC-6 decreases expression levels of Leishmania genes involved in the cell cycle, such as topoisomerase-2 (TOP-2), PCNA, and MCM4, therefore contributing to its leishmanicidal activity. The effect of this compound on cell cycle progression was confirmed by flow cytometry. We observed a significant increase of cells in the G₁ phase and a dramatic reduction of cells in the S phase compared to untreated cells. Altogether, our data suggest that the isoselenocyanate NISC-6 may be a promising candidate for new drug development against leishmaniasis.

Analysis of structure activity relationships for LPS-mimetic activities of taxane analogs in murine macrophages

The anti-tumor agent, paclitaxel (active ingredient of Taxol®), is best recognized for its ability to bind to microtubules and to block cell division. However, it has more recently been demonstrated to mimic the varied effects of bacterial lipopolysaccharide (LPS) in murine macrophages, actions that appear to be dissociable from its well-characterized β-tubulin binding capacity. Secretion of tumor necrosis factor alpha (TNFα) and induction of TNFα gene expression were assessed in macrophages treated with paclitaxel analogs. Two structural modifications resulted in elevated TNFα mRNA and protein secretion: (i) the presence of a cyclopropane carboxylate ester at C-4 rather than an acetate; or (ii) deoxygenation of the C-7 position. Certain modifications essentially eliminated activity: derivatization of the side chain 2′ hydroxy group to form an ethyl carbonate, the presence of a benzoate at C-4 rather than an acetate, or de-acetylization to leave a free hydroxy group at the C-10 position. Substitution of the phenyl group at the 3′ carbon position of the side chain with a 2-furyl group or the presence of a 2- or 3-pyridine carboxylate moiety at C-2 rather than a benzoate also resulted in a significant reduction in TNFα. These structure—activity relationships can be distinguished from those that affect the cytotoxic effects of paclitaxel which are attributable to its microtubule binding activity.

Identification of CD18 as a novel Taxol binding/signaling protein in murine macrophage membranes

The anti-tumor agent, Taxol, is a potent LPS mimetic in murine macrophages, an activity that is dissociable from its well-characterized anti-mitotic activity which is mediated by microtubule hyperstabilization. A photoactivatable Taxol analog was used to identify components of a putative, shared LPS signaling apparatus in murine macrophage membranes. We report here that CD18, the β chain of the β2-integrin, Mac-1, represents a major Taxol binding protein in murine macrophages.

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.

Metabolic network analysis predicts efficacy of FDA-approved drugs targeting the causative agent of a neglected tropical disease

Background

Systems biology holds promise as a new approach to drug target identification and drug discovery against neglected tropical diseases. Genome-scale metabolic reconstructions, assembled from annotated genomes and a vast array of bioinformatics/biochemical resources, provide a framework for the interrogation of human pathogens and serve as a platform for generation of future experimental hypotheses. In this article, with the application of selection criteria for both Leishmania major targets (e.g. in silico gene lethality) and drugs (e.g. toxicity), a method (MetDP) to rationally focus on a subset of low-toxic Food and Drug Administration (FDA)-approved drugs is introduced.

Results

This metabolic network-driven approach identified 15 L. major genes as high-priority targets, 8 high-priority synthetic lethal targets, and 254 FDA-approved drugs. Results were compared to previous literature findings and existing high-throughput screens. Halofantrine, an antimalarial agent that was prioritized using MetDP, showed noticeable antileishmanial activity when experimentally evaluated in vitro against L. major promastigotes. Furthermore, synthetic lethality predictions also aided in the prediction of superadditive drug combinations. For proof-of-concept, double-drug combinations were evaluated in vitro against L. major and four combinations involving the drug disulfiram that showed superadditivity are presented.

Conclusions

A direct metabolic network-driven method that incorporates single gene essentiality and synthetic lethality predictions is proposed that generates a set of high-priority L. major targets, which are in turn associated with a select number of FDA-approved drugs that are candidate antileishmanials. Additionally, selection of high-priority double-drug combinations might provide for an attractive and alternative avenue for drug discovery against leishmaniasis.

A review of natural products with antileishmanial activity

Infections caused by protozoa of the genus Leishmania are a major worldwide health problem, with high endemicity in developing countries. The incidence of the disease has increased since the emergence of AIDS. In the absence of a vaccine, there is an urgent need for effective drugs to replace/supplement those in current use. The plant kingdom is undoubtedly valuable as a source of new medicinal agents. The present work constitutes a review of the literature on plant extracts and chemically defined molecules of natural origin showing antileishmanial activity. The review refers to 101 plants, their families, and geographical distribution, the parts utilized, the type of extract and the organism tested. It also includes 288 compounds isolated from higher plants and microorganisms, classified into appropriate chemical groups. Some aspects of recent antileishmanial-activity-directed research on natural products are discussed.

Reactive oxygen and reactive nitrogen intermediates in innate and specific immunity

Nitric oxide, nitric oxide derivatives and reactive oxygen intermediates are toxic molecules of the immune system which contribute to the control of microbial pathogens and tumors. There is recent evidence for additional functions of these oxygen metabolites in innate and adaptive immunity; these functions include the modulation of the cytokine response of lymphocytes and the regulation of immune cell apoptosis, as well as immunodeviating effects. Components of several signal transduction pathways have been identified as intracellular targets for reactive nitrogen and oxygen intermediates.

Regulation of IFN Consensus Sequence Binding Protein Expression in Murine Macrophages

Recent work has demonstrated that the transcription factor, IFN consensus sequence binding protein (ICSBP), plays a critical role in the capacity of mice to control infection with Toxoplasma gondii and Leishmania major, agents that require highly activated macrophages for their elimination. In this report the regulation of ICSBP mRNA and protein were analyzed in murine macrophages stimulated with LPS and/or IFN-γ. Like induction of leishmaniacidal activity, LPS and IFN-γ synergize to induce ICSBP mRNA and protein. Deletion analysis of the ICSBP promoter identified regions that were IFN-γ responsive, regions that mediate the ability of LPS and IFN-γ to activate this promoter synergistically, as well as regions that normally repress ICSBP transcription. Finally, exogenous expression of ICSBP, found in previous studies to down-regulate MHC I gene expression, failed to repress basal or IFN-γ-induced ICSBP transcription. This demonstrates that ICSBP can selectively suppress the expression of IFN-responsive genes. These findings extend in a significant way our understanding of the regulation of ICSBP by LPS and IFN-γ and provide important clues as to its role in macrophage activation.

Use of a Photoactivatable Taxol Analogue to Identify Unique Cellular Targets in Murine Macrophages: Identification of Murine CD18 as a Major Taxol-Binding Protein and a Role for Mac-1 in Taxol-Induced Gene Expression

Taxol, a potent antitumor agent that binds β-tubulin and promotes microtubule assembly, results in mitotic arrest at the G2/M phase of the cell cycle. More recently, Taxol was shown to be a potent LPS mimetic in murine, but not in human macrophages, stimulating signaling pathways and gene expression indistinguishably from LPS. Although structurally unrelated to LPS, Taxol’s LPS-mimetic activities are blocked by inactive structural analogues of LPS, indicating that despite the species-restricted effects of Taxol, LPS and Taxol share a common receptor/signaling complex that might be important in LPS-induced human diseases. To identify components of the putatively shared Taxol/LPS receptor, a novel, photoactivatable Taxol analogue was employed to identify unique Taxol-binding proteins in murine macrophage membranes. Seven major Taxol-binding proteins, ranging from ∼50 to 200 kDa, were detected. Although photoactivatable Taxol analogue failed to bind to CD14, the prominent Taxol-binding protein was identified as CD18, the ∼96-kDa common component of the β2 integrin family. This finding was supported by the concomitant failure of macrophage membranes from Mac-1 knockout mice to express immunoreactive CD18 and the major Taxol-binding protein. In addition, Taxol-induced IL-12 p40 mRNA was markedly reduced in Mac-1 knockout macrophages and anti-Mac-1 Ab blocked secretion of IL-12 p70 in Taxol- and LPS-stimulated macrophages. Since CD18 has been described as a participant in LPS-induced binding and signal transduction, these data support the hypothesis that the interaction of murine CD18 with Taxol is involved in its proinflammatory activity.