Leishmaniasis: current status of available drugs and new potential drug targets

(Post-) Genomic approaches to tackle drug resistance in Leishmania

Leishmaniasis, like other neglected diseases is characterized by a small arsenal of drugs for its control. To safeguard the efficacy of current drugs and guide the development of new ones it is thus of utmost importance to acquire a deep understanding of the phenomenon of drug resistance and its link with treatment outcome. We discuss here how (post-)genomic approaches may contribute to this purpose. We highlight the need for a clear definition of the phenotypes under consideration: innate and acquired resistance versus treatment failure. We provide a recent update of our knowledge on the Leishmania genome structure and dynamics, and compare the contribution of targeted and untargeted methods for the understanding of drug resistance and show their limits. We also present the main assays allowing the experimental validation of the genes putatively involved in drug resistance. The importance of analysing information downstream of the genome is stressed and further illustrated by recent metabolomics findings. Finally, the attention is called onto the challenges for implementing the acquired knowledge to the benefit of the patients and the population at risk.

Noncovalent complexation of amphotericin-B with Poly(α-glutamic acid)

A noncovalent complex of amphotericin B (AmB) and poly(α-glutamic acid) (PGA) was prepared to develop a safe and stable formulation for the treatment of leishmaniasis. The loading of AmB in the complex was in the range of ∼20-50%. AmB was in a highly aggregated state with an aggregation ratio often above 2.0. This complex (AmB-PGA) was shown to be stable and to have reduced toxicity to human red blood cells and KB cells compared to the parent compound; cell viability was not affected at an AmB concentration as high as 50 and 200 μg/mL respectively. This AmB-PGA complex retained AmB activity against intracellular Leishmania major amastigotes in the differentiated THP-1 cells with an EC50 of 0.07 ± 0.03-0.08 ± 0.01 μg/mL, which is similar to Fungizone (EC50 of 0.06 ± 0.01 μg/mL). The in vitro antileishmanial activity of the complex against Leishmania donovani was retained after storage at 37 °C for 7 days in the form of a solution (EC50 of 0.27 ± 0.03 to 0.35 ± 0.04 μg/mL) and for 30 days as a solid (EC50 of 0.41 ± 0.07 to 0.63 ± 0.25 μg/mL). These encouraging results indicate that the AmB-PGA complex has the potential for further development.

Leishmania donovani-specific 25- and 28-kDa urinary proteins activate macrophage effector functions, lymphocyte proliferation and Th1 cytokines production

Growing incidence of drug resistance against leishmaniasis in endemic areas and limited drug options necessitates the need for a vaccine. Notwithstanding significant leishmanial research in the past decades, a vaccine candidate is far from reality. In this study, we report the potential of two urinary leishmanial proteins to induce macrophage effector functions, inflammatory cytokines production and human lymphocytes proliferation. A total four proteins of molecular mass 25, 28, 54 and 60 kDa were identified in human urine samples. The 25 and 28 kDa proteins significantly induced NADPH oxidase (p<0.001), superoxide dismutase (p<0.001) and inducible nitric oxide synthase (p<0.001) activities in stimulated RAW264.7 macrophages. The release of nitric oxide, tumor necrosis factor-alpha and interleukin (IL)-12 was also significantly (p<0.001) higher in 25 and 28 kDa activated macrophages as compared with cells activated with other two proteins. These two proteins also induced significant (p<0.001) proliferation and release of IFN-γ and IL-12 in human peripheral blood mononuclear cells.

Identification and functional characterization of Leishmania donovani secretory peroxidase: delineating its role in NRAMP1 regulation

Leishmania silently evades host immune system and establish in the hostile environment of host macrophage phagolysosomes. For differentiation, growth and division parasite acquires divalent cations especially iron from the host nutritive pool. Natural resistance associated with macrophage protein1 (NRAMP1), a cation transporter that effluxes out divalent cations specifically iron from phagosomal milieu to the cytosol, to create ions deprived status for pathogenic microorganisms. The mechanisms of NRAMP1 regulation are largely unknown in leishmanial infections. In the present study, we identified a secretory Leishmania donovani peroxidase (Prx) that showed peroxidoxin like peroxidase activity and significantly reduced H₂O₂, O₂.⁻ and NO levels in LPS activated macrophages. Further, we also observed down regulated Nramp1 expression and concomitantly declined labile iron pool in activated macrophages treated with identified peroxidase. Prx also decreased levels of TNF-α, IFN-γ and IL-12 in LPS activated macrophages. These observations indicate a bifunctional protective role of secretory Prx; first it reduces redox activation of macrophages, and secondly it allows iron access to Leishmania by down regulating NRAMP1 expression.

Different susceptibilities of Leishmania spp. promastigotes to the Annona muricata acetogenins annonacinone and corossolone, and the Platymiscium floribundum coumarin scoparone

Leishmaniasis is a zoonotic disease that can manifest itself in visceral and cutaneous form. The aim of this study was to search for new leishmanicidal compounds. Preliminarily, Artemia salina assay was applied to compounds from two plants found in Northeastern Brazil, Platymiscium floribundum and Annona muricata. Then these compounds were tested against three Leishmania species (Leishmania donovani, Leishmania mexicana and Leishmania major). A screening assay using luciferase-expressing promastigote form were used to measure the viability of promastigote One coumarin, scoparone, isolated from P. floribundum and two acetogenins, annonacinone and corossolone isolated from A. muricata showed leishmanicidal activity in all species tested. Nevertheless, Leishmania species indicated different susceptibilities in relation to the tested compounds: L. mexicana was more sensitive to scoparone followed by L. major and L. donovani. The three species presented similar inhibition to corossolone and annonacinone. Acetogenin annonacinone (EC(50)=6.72-8.00 μg/mL) indicated high leishmanicidal activity; corossolone (EC(50)=16.14-18.73 μg/mL) and scoparone (EC(50)=9.11-27.51 μg/mL) moderate activity. A. saline larvae were less sensitive to the coumarin scoparone and acetogenin corossolone was the most toxic. In conclusion, the leishmanicidal activity demonstrated by the coumarin and acetogenins indicate these compounds for further studies aiming the development of new leishmanicidal agents.

Synthesis and structure-activity relationships of lansine analogues as antileishmanial agents

Clear and rational thinking: A series of rationally designed, lansine-derived carbazoles was synthesized and evaluated for activity against promastigotes and amastigotes of Leishmania donovani, the causative agent of leishmaniasis. Some structural modifications gave rise to compounds with enhanced activity and selectivity over lansine, allowing structure-activity relationships to be elucidated and providing a foundation for the further development of this pharmacophore.

Developments in diagnosis and antileishmanial drugs

Leishmaniasis ranks the third in disease burden in disability-adjusted life years caused by neglected tropical diseases and is the second cause of parasite-related deaths after malaria; but for a variety of reasons, it is not receiving the attention that would be justified seeing its importance. Leishmaniasis is a diverse group of clinical syndromes caused by protozoan parasites of the genus Leishmania. It is estimated that 350 million people are at risk in 88 countries, with a global incidence of 1–1.5 million cases of cutaneous and 500,000 cases of visceral leishmaniasis. Improvements in diagnostic methods for early case detection and latest combitorial chemotherapeutic methods have given a new hope for combating this deadly disease. The cell biology of Leishmania and mammalian cells differs considerably and this distinctness extends to the biochemical level. This provides the promise that many of the parasite's proteins should be sufficiently different from hosts and can be successfully exploited as drug targets. This paper gives a brief overview of recent developments in the diagnosis and approaches in antileishmanial drug discovery and development.