Discovery of SyntheticLeishmaniaInhibitors by Screening of a 2-Arylbenzothiophene Library

A New Class of Benzo[b]thiophene-chalcones as Cholinesterase Inhibitors: Synthesis, Biological Evaluation, Molecular Docking and ADME Studies

In this study, heterocyclic compounds containing a benzothiophene scaffold were designed and synthetized, and their inhibitory activity against cholinesterases (ChE) and the viability of SH-SY5Y cells have been evaluated. Benzothiophenes 4a-4i and benzothiophene-chalcone hybrids 5a-5i were tested against both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), revealing interesting structure-activity relationships. In general, benzothiophene-chalcone hybrids from series 5 proved to be better inhibitors of both enzymes, with compound 5f being the best AChE inhibitor (IC50 = 62.10 μM) and compound 5h being the best BChE inhibitor (IC50 = 24.35 μM), the last one having an IC50 similar to that of galantamine (IC50 = 28.08 μM), the reference compound. The in silico ADME profile of the compounds was also studied. Molecular docking calculations were carried out to analyze the best binding scores and to elucidate enzyme-inhibitors' interactions.

Chemotherapy of leishmaniasis: present challenges

Cutaneous and visceral leishmaniasis are amongst the most devastating infectious diseases of our time, affecting millions of people worldwide. The treatment of these serious diseases rely on a few chemotherapeutic agents, most of which are of parenteral use and induce severe side-effects. Furthermore, rates of treatment failure are high and have been linked to drug resistance in some areas. Here, we reviewed data on current chemotherapy practice in leishmaniasis. Drug resistance and mechanisms of resistance are described as well as the prospects for applying drug combinations for leishmaniasis chemotherapy. It is clear that efforts for discovering new drugs applicable to leishmaniasis chemotherapy are essential. The main aspects on the various steps of drug discovery in the field are discussed.

Novel Amino-pyrazole Ureas with Potent In Vitro and In Vivo Antileishmanial Activity

Visceral leishmaniasis is a severe parasitic disease that is one of the most neglected tropical diseases. Treatment options are limited, and there is an urgent need for new therapeutic agents. Following an HTS campaign and hit optimization, a novel series of amino-pyrazole ureas has been identified with potent in vitro antileishmanial activity. Furthermore, compound 26 shows high levels of in vivo efficacy (>90%) against Leishmania infantum, thus demonstrating proof of concept for this series.

Leishmania is not prone to develop resistance to tamoxifen

Tamoxifen, an antineoplastic agent, is active in vitro and in vivo against the parasitic protozoa Leishmania. As part of our efforts to unravel this drug's mechanisms of action against the parasite and understand how resistance could arise, we tried to select tamoxifen-resistant Leishmania amazonensis. Three different strategies to generate tamoxifen resistant mutants were used: stepwise increase in drug concentration applied to promastigote cultures, chemical mutagenesis followed by drug selection and treatment of infected mice followed by selection of amastigotes. For amastigote selection, we employed a method with direct plating of parasites recovered from lesions into semi-solid media. Tamoxifen resistant parasites were not rescued by any of these methods. Miltefosine was used as a control in selection experiments and both stepwise selection and chemical mutagenesis allowed successful isolation of miltefosine resistant mutants. These findings are consistent with a multi-target mode of action to explain tamoxifen's leishmanicidal properties. Considering that drug resistance is a major concern in anti-parasitic chemotherapy, these findings support the proposition of using tamoxifen as a partner in drug combination schemes for the treatment of leishmaniasis.

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Tamoxifen is effective in the treatment of cutaneous and visceral leishmaniasis.

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Resistance to tamoxifen was not found in promastigotes upon mutagenesis/selection.

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Resistance to tamoxifen was not detected in amastigotes after in vivo selection.

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Tamoxifen may be a good partner in drug combination schemes for leishmaniasis.

Antileishmanial activity of the estrogen receptor modulator raloxifene

Background

The treatment of leishmaniasis relies mostly on parenteral drugs with potentially serious adverse effects. Additionally, parasite resistance in the treatment of leishmaniasis has been demonstrated for the majority of drugs available, making the search for more effective and less toxic drugs and treatment regimens a priority for the control of leishmaniasis. The aims of this study were to evaluate the antileishmanial activity of raloxifene in vitro and in vivo and to investigate its mechanism of action against Leishmania amazonensis.

Methodology/Principal Findings

Raloxifene was shown to possess antileishmanial activity in vitro against several species with EC₅₀ values ranging from 30.2 to 38.0 µM against promastigotes and from 8.8 to 16.2 µM against intracellular amastigotes. Raloxifene's mechanism of action was investigated through transmission electron microscopy and labeling with propidium iodide, DiSBAC₂(3), rhodamine 123 and monodansylcadaverine. Microscopic examinations showed that raloxifene treated parasites displayed autophagosomes and mitochondrial damage while the plasma membrane remained continuous. Nonetheless, plasma membrane potential was rapidly altered upon raloxifene treatment with initial hyperpolarization followed by depolarization. Loss of mitochondrial membrane potential was also verified. Treatment of L. amazonensis – infected BALB/c mice with raloxifene led to significant decrease in lesion size and parasite burden.

Conclusions/Significance

The results of this work extend the investigation of selective estrogen receptor modulators as potential candidates for leishmaniasis treatment. The antileishmanial activity of raloxifene was demonstrated in vitro and in vivo. Raloxifene produces functional disorder on the plasma membrane of L. amazonensis promastigotes and leads to functional and morphological disruption of mitochondria, which culminate in cell death.

Cutaneous and visceral leishmaniasis are part of the group we call neglected diseases. They are serious conditions that afflict millions in vast regions of the world. These diseases are very difficult to treat. This is due to the scanty choice of effective drugs together with their potentially severe side effects. One way of finding new treatments for these neglected conditions is to repurpose drugs that are already in use to treat other diseases. In this paper, we show that raloxifene, a drug that is used for the treatment of osteoporosis and also as an alternative in the treatment of breast cancer, is active against the causative agents of leishmaniasis and is effective in the treatment of cutaneous leishmaniasis in an experimental model. We also show that the antileishmanial mechanism of action of raloxifene is related to damage to the cell membrane and to the mitochondrion of the parasite.