A new nanoemulsion formulation improves antileishmanial activity and reduces toxicity of amphotericin B

This work aimed to optimise a new nanoemulsion (NE) formulation loaded with Amphotericin B (AmB) and to evaluate its in vivo antileishmanial activity and in vitro haemolytic toxicity. The influence of gradual increases in pressure, using a high-pressure homogeniser, was evaluated. The NE was characterised for droplet size, polydispersity index, zeta potential and encapsulation efficiency (EE). For antileishmanial activity studies, AmB-NE was administered intravenously in mice infected by Leishmania infantum chagasi, which causes Visceral Leishmaniasis (VL). When the NE was submitted to gradual increases in pressure, the PI values and droplet size decreased. The droplet size (～145?nm) was lower than that obtained in previous studies. The zeta potential was negative and the EE was almost 100%. The haemolytic toxicity, evaluated on human red blood cells, for AmB-loaded NE was lower than that observed for the conventional AmB (C-AmB). C-AmB at 2?mg/kg was very toxic. In contrast, administration of the AmB-loaded NE, at same dose, did not result in any sign of acute toxicity, promoting a significant reduction in parasite burden as compared to the C-AmB. These findings suggest that this new AmB-loaded NE constitutes an attractive alternative for the treatment of VL due to improved efficacy and lower toxicity.     

Antileismanial activity,mechanism of action study and molecular docking of 1,4‐bis(substituted benzalhydrazino)phthalazines

To identify new agents for the treatment of American cutaneous leishmaniasis, a series of eight 1,4‐bis(substituted benzalhydrazino)phthalazines was evaluated against Leishmania braziliensis and Leishmania mexicana parasites. These compounds represent a disubstituted version of the 1‐chloro‐4‐(monoaryl/heteroarylhydranizyl)phthalazine that exhibited a significant response against L. braziliensis according to our previous findings. Two disubstituted phthalazines 3b and 3f were identified as potential antileishmanial agents against L. braziliensis parasites, exhibiting a submicromolar IC₅₀ response of 2.37 and 7.90 µM on the promastigote form, and of 1.82 and 4.56 µM against intracellular amastigotes, respectively. In particular, compound 3b showed interesting responses against amastigote isolates from reference, glucantime‐resistant and clinical human strains, which were by far superior to the biological response found for the glucantime drug. With regard to the toxicity results, both 3b and 3f exhibited moderate LD₅₀ values against murine macrophages (BMDM), with good selectivity indexes on promastigotes and intracellular amastigotes of L. braziliensis. A comparison of biological response was established between the monosubstituted and disubstituted versions of these benzalhydrazino‐phthalazines. Easy synthetic procedure and significant response against amastigote strains including against resistant lines made compound 3b a potential candidate for further pharmacokinetic and in vivo experiments as antileishmanial agent, and as a platform for further structural optimization. Mechanism‐of‐action studies and molecular docking simulations discarded to inhibition of superoxide dismutase as possible mode of action.     

Design,synthesis, and in vitro biological evaluation of novel thiazolopyrimidine derivatives as antileishmanial compounds

A series of thiazolopyrimidine derivatives was designed and synthesized as a Leishmania major pteridine reductase 1 (LmPTR1) enzyme inhibitor. Their LmPTR1 inhibitor activities were evaluated using the enzyme produced by Escherichia coli in a recombinant way. The antileishmanial activity of the selected compounds was tested in vitro against Leishmania sp. Additionally, the compounds were evaluated for cytotoxic activity against the murine macrophage cell line RAW 264.7. According to the results, four compounds displayed not only a potent in vitro antileishmanial activity against promastigote forms but also low cytotoxicity. Among them, compound L16 exhibited an antileishmanial activity for both the promastigote and amastigote forms of L. tropica, with IC₅₀ values of 7.5 and 2.69 µM, respectively. In addition, molecular docking studies and molecular dynamics simulations were also carried out in this study. In light of these findings, the compounds provide a new potential scaffold for antileishmanial drug discovery.     

Antipromastigote activity of the malabaricones of Myristica malabarica (rampatri)

A major problem in the management of visceral leishmaniasis, especially in the Indian subcontinent, is the growing unresponsiveness to conventional antimonial therapy, indicating the urgent need to identify new antileishmanial compounds. This study was undertaken to evaluate the antileishmanial activity of the fruit rind of Myristica malabarica that is used as a spice and is also credited with medicinal properties. The antipromastigote activity of different extracts/fractions of M. malabarica and its constituent diarylnonanoids were evaluated in Leishmania donovani promastigotes (MHOM/IN/83/AG83) using the MTS-PMS assay. Preliminary screening of the ether extract (R1) with its crude methanol fraction (R2) and two fractions (R3 and R4) revealed that R2 had potent leishmanicidal activity (IC(50) 31.0 microg/mL), whereas R3 and R4 showed poor activity. Fractionation of R2 yielded four diarylnonanoids (malabaricones A-D, designated as Mal A, Mal B, Mal C and Mal D, respectively). The IC(50) values of Mal A-D were 16, 22, 27 and >50 microg/mL, respectively. Taken together, the data suggest that the methanol extract of M. malabarica, especially its constituent compounds, Mal A and Mal B, have promising antileishmanial activity meriting further investigations regarding the underlying molecular mechanism(s) of action with a view towards future drug development.     

Chromene-Based Synthetic Chalcones as Potent Antileishmanial Agents: Synthesis and Biological Activity

Two types of regioisomeric chromene-based chalcones namely, 1-(6-methoxy-2H-chromen-3-yl)-3-phenylpropen-1-ones and 3-(6-methoxy-2H-chromen-3-yl)-1-phenylpropen-1-ones were prepared and investigated for their antileishmanial activity against promastigotes form of Leishmania major. The obtained results from in vitro biological assays indicated that chloro-substituted 1-(6-methoxy-2H-chromen-3-yl)-3-phenylpropen-1-ones exhibited excellent activity against Leishmania major at non-cytotoxic concentrations.     

16α-Hydroxycleroda-3,13 (14)Z-dien-15,16-olide from Polyalthia longifolia: a safe and orally active antileishmanial agent

Background and purpose:

New antileishmanials from natural products are urgently needed due to the emergence of drug resistance complicated by severe cytotoxic effects. 16α-Hydroxycleroda-3,13 (14)Z-dien-15,16-olide (Compound 1) from Polyalthia longifolia was found to be a potential antileishmanial and non-cytotoxic, as evidenced by long-term survival (>6 months) of treated animals. This prompted us to determine its target and, using molecular modelling, identify the interactions responsible for its specific antileishmanial activity.

Experimental approach:

In vitro activity of compound was assessed using intracellular transgenic green fluorescent protein-stably expressed Leishmania donovani parasites. In vivo activity and survival of animals post-treatment were evaluated in L. donovani-infected hamsters. Known property of clerodane diterpenes as potent human DNA topoisomerase inhibitors led us to evaluate the inhibition of recombinant L. donovani topoisomerase I using relaxation assay. Mode of cell death induced by Compound 1 was assessed by phosphotidylserine exposure post-treatment. Molecular modelling studies were conducted with DNA topoisomerase I to identify the binding interactions responsible for its activity.

Key results:

Bioassay-guided fractionation led to isolation of Compound 1 as a non-cytotoxic, orally active antileishmanial. Compound 1 inhibited recombinant DNA topoisomerase I which, ultimately, induced apoptosis. Molecular docking studies indicated that five strong hydrogen-bonding interactions and hydrophobic interactions of Compound 1 with L. donovani DNA-topoisomerase are responsible for its antileishmanial activity.

Conclusions and implications:

The data reveal Compound 1 is a potent and safe antileishmanial. The study further exploited the structural determinants responsible for its non-cytotoxic and potent activity, to raise the feasibility of specifically targeting the target enzyme responsible for its activity through rational drug design.     

7‐Chloro‐4‐quinolinyl Hydrazones: A Promising and Potent Class of Antileishmanial Compounds

In this work, we report the antileishmanial evaluation of twenty 7‐chloro‐4‐quinolinyl hydrazone derivatives ( 1 – 20 ). Firstly, the compounds were tested against promastigotes of four different Leishmania species. After that, all derivatives were assayed against L. braziliensis amastigotes and murine macrophages. Furthermore, it was investigated whether the antiamastigote L. braziliensis effect of the compounds could be associated with nitric oxide production. Compounds 6 and 7 showed a strong leishmanicidal activity against intracellular parasite with IC₅₀ in nanogram levels (30 and 20 ng/mL, respectively). Appreciable activity of three compounds tested can be considered an important finding for the rational design of new leads for antileishmanial compounds.