Mini Reviews in Medicinal Chemistry - Volume 15, Issue 3, 2015

Despite affecting around 8 million people worldwide and representing an economic burden above $7 billion/ year, currently approved medications to treat Chagas disease are still limited to two drugs, nifurtimox and benznidazole, which were developed more than 40 years ago and present important efficacy and safety limitations. Drug repositioning (i.e. finding second or further therapeutic indications for known drugs) has raised considerable interest within the international drug development community. There are many explanations to the current interest on drug repositioning including the possibility to partially circumvent clinical trials and the consequent saving in time and resources. It has been suggested as a particular attractive approach for the development of novel therapeutics for neglected diseases, which are usually driven by public or non-profit organizations. Here we review current computer-guided approaches to drug repositioning and reports on drug repositioning stories oriented to Chagas disease, with a focus on computer-guided drug repositioning campaigns.

Neglected diseases are infections that thrive mainly among underdeveloped countries, particularly those belonging to regions found in Asia, Africa, and America. One of the most complex diseases is noma, a dangerous health condition characterized by a polymicrobial and opportunistic nature. The search for potent and safer antibacterial agents against this disease is therefore a goal of particular interest. Chemoinformatics can be used to rationalize the discovery of drug candidates, diminishing time and financial resources. However, in the case of noma, there is no in silico model available for its use in the discovery of efficacious antibacterial agents. This work is devoted to report the first mtk-QSBER model, which integrates dissimilar kinds of chemical and biological data. The model was generated with the aim of simultaneously predicting activity against bacteria present in noma, and ADMET (absorption, distribution, metabolism, elimination, toxicity) parameters. The mtk-QSBER model was constructed by employing a large and heterogeneous dataset of chemicals and displayed accuracies higher than 90% in both training and prediction sets. We confirmed the practical applicability of the model by predicting multiple profiles of the investigational antibacterial drug delafloxacin, and the predictions converged with the experimental reports. To date, this is the first model focused on the virtual search for desirable anti-noma agents.

Leishmaniasis affects more than 12 million people in 98 countries, the infection being caused by more than 20 species of protozoan parasites belonging to the genus Leishmania and spread by sandflies bite. Poor sanitary conditions, malnutrition, deforestation and urbanization increase the risk for leishmaniasis. Leishmaniasis is the only tropical disease treated with non-anti-leishmanial drugs, among which liposomal amphotericin B, a combination of pentavalent antimonials and paromomycin and miltefosine, that are highly toxic, represent the most used ones. Drug resistance is now widespread and the search for new molecular targets is open. Topoisomerase 1B, that controls the topological state of DNA and is essential for the parasites viability, has been detected as a promising target for antileishmaniasis therapy. The enzyme presents structural/functional differences with the human counterpart, making it unique among Eukarya. Here we review the structural features of this enzyme and the drugs that can be developed and used for this specific targeting.

Entamoeba being an internal parasite is the causative organism of many human and animal infections with lethal consequences. Chemotherapy against Entamoeba was well established by both synthetic and natural products. Vigorous attainments were made by different researchers all over the world for discovering better chemical entities and the potent formulations. Preexisting compounds were developed into non-cytotoxic and with an enhanced therapeutic compounds by usage of multiparametric optimization techniques like QSAR, and molecular docking. The present review is therefore an aerial perspective of importance of medicinal chemistry in anti-amoebic chemotherapy. The review elucidates the existing synthetic compounds, their analogues, natural products, in silico studies and some novel methods adopted for the drug design as anti-amoebic agents which would be of assured benefit in the future drug design.

Neglected tropical diseases (NTD) are a group of 17 diseases transmitted by virus, protozoa, helminthes and bacteria. These illnesses are responsible for millions of deaths per year, affecting mainly the poorest populations in the world. The therapeutic drugs available are obsolete, toxic, have questionable efficacy and there are reports of resistance. Therefore, the discovery of new, safe, effective and affordable active molecules is urgently needed. Considering that, the main purpose of this mini-review is to show the current scenario concerning drug design for neglected disease in Brazil. NTD are a very broad topic. Thus, we selected four infections for discussion: Chagas disease, leishmaniasis, malaria and tuberculosis. According to CNPq (National Counsel of Technological and Scientific Development) directories, there are many Brazilian groups studying these respective diseases. The papers published possess high quality and some of them, the most recent, are briefly discussed here. Medicinal chemistry approaches such as synthesis of novel series of molecules and biological activity evaluation, studies of structure-activity relationships (qualitative and quantitative), molecular modeling calculations and electrochemistry are some of the tools applied in the design of the compounds.

Leishmaniasis is a neglected disease affecting more than 12 million people worldwide. The most used drugs are pentavalent antimonials that are very toxic and display the problem of drug resistance, especially in endemic regions such as Bihar in India. For this reason, it is urgent to find new and less toxic drugs against leishmaniasis. To this end, the understanding of pathways affecting parasite survival is of prime importance for targeted drug discovery. The parasite survival inside the macrophage is strongly dependent on polyamine metabolism. Polyamines are, in fact, very important for cell growth and proliferation. In particular, spermidine (Spd), the final product of the polyamine biosynthesis pathway, serves as a precursor for trypanothione (N1,N8- bis(glutathionyl)spermidine, T(SH)2) and hypusine (Nε-(4-amino-2-hydroxybutyl)lysine). T(SH)2 is a key molecule for parasite defense against the hydrogen peroxide produced by macrophages during the infection. Hypusination is a posttranslational modification occurring exclusively in the eukaryotic initiation factor 5A (eIF5A), which has an important role in avoiding the ribosome stalling during the biosynthesis of protein containing polyprolines sequences. The enzymes, belonging to the spermidine metabolism, i.e. arginase (ARG), ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (AdoMetDC), spermidine synthase (SpdS), trypanothione synthetase (TryS or TSA), trypanothione reductase (TryR or TR), tryparedoxin peroxidase (TXNPx), deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH) are promising targets for the development of new drugs against leishmaniasis. This minireview furnishes a picture of the structural, functional and inhibition studies on polyamine metabolism enzymes that could guide the discovery of new drugs against leishmaniasis.

Natural products are compounds that are isolated from plants, provide a variety of lead structures for the development of new drugs by the pharmaceutical industry. The interest in these substances increases because of their beneficial effects on human health, which include antiviral, antiallergic, antiplatelet, anti-inflammatory, antitumor, antioxidant, and antiparasitic activities. Leishmaniasis is the infection caused by protozoa of the genus Leishmania, which affects mainly people who live in poor countries, and can cause chronic fever, liver problems, anemia, and other blood problems. Current chemotherapies against the disease cause side effects, and are ineffective. There are no vaccines, and new chemotherapeutic agents for the treatment of leishmaniasis are greatly needed. This work reports on some of the enzymatic targets studied in the development of new drugs using natural products as inhibitors for the treatment of leishmaniasis. We applied ligand-based-virtual screening using Random Forest, associated with structure-based-virtual screening (docking), of a small dataset of 683 flavonoids and derivatives from an in-house data bank to select structures with potential inhibitory activity against pyruvate kinase, an important enzyme in Leishmania mexicana’s energy production chemistry. The computer-aided drug design studies revealed good results against Leishmaniasis for flavones.