Investigation of thiazolyl-benzothiophenamides as potential agents for African sleeping sickness.

African sleeping sickness is a potentially fatal neglected disease affecting sub-Saharan Africa. High-throughput screening identified the thiazolyl-benzothiophenamide 1 to be active against the causative parasite, Trypanosoma brucei. This work establishes structure-activity relationships of 1, guiding the design of second generation derivatives. After screening against the clinically relevant species T. b. rhodesiense, the derivative 16 was identified as a suitable candidate for further investigation.

Design, Synthesis, and Biological Evaluation of 2-Nitroimidazopyrazin-one/-es with Antitubercular and Antiparasitic Activity.

Tuberculosis and parasitic diseases, such as giardiasis, amebiasis, leishmaniasis, and trypanosomiasis, all urgently require improved treatment options. Recently, it has been shown that antitubercular bicyclic nitroimidazoles such as pretomanid and delamanid have potential as repurposed therapeutics for the treatment of visceral leishmaniasis. Here, we show that pretomanid also possesses potent activity against Giardia lamblia and Entamoeba histolytica, thus expanding the therapeutic potential of nitroimidazooxazines. Synthetic analogues with a novel nitroimidazopyrazin-one/-e bicyclic nitroimidazole chemotype were designed and synthesized, and structure-activity relationships were generated. Selected derivatives had potent antiparasitic and antitubercular activity while maintaining drug-like properties such as low cytotoxicity, good metabolic stability in liver microsomes and high apparent permeability across Caco-2 cells. The kinetic solubility of the new bicyclic derivatives varied and was found to be a key parameter for future optimization. Taken together, these results suggest that promising subclasses of bicyclic nitroimidazoles containing different core architectures have potential for further development.

Screening a Natural Product-Based Library against Kinetoplastid Parasites.

Kinetoplastid parasites cause vector-borne parasitic diseases including leishmaniasis, human African trypanosomiasis (HAT) and Chagas disease. These Neglected Tropical Diseases (NTDs) impact on some of the world's lowest socioeconomic communities. Current treatments for these diseases cause severe toxicity and have limited efficacy, highlighting the need to identify new treatments. In this study, the Davis open access natural product-based library was screened against kinetoplastids (Leishmania donovani DD8, Trypanosoma brucei brucei and Trypanosoma cruzi) using phenotypic assays. The aim of this study was to identify hit compounds, with a focus on improved efficacy, selectivity and potential to target several kinetoplastid parasites. The IC50 values of the natural products were obtained for L. donovani DD8, T. b. brucei and T. cruzi in addition to cytotoxicity against the mammalian cell lines, HEK-293, 3T3 and THP-1 cell lines were determined to ascertain parasite selectivity. Thirty-one compounds were identified with IC50 values of ≤ 10 µM against the kinetoplastid parasites tested. Lissoclinotoxin E (1) was the only compound identified with activity across all three investigated parasites, exhibiting IC50 values < 5 µM. In this study, natural products with the potential to be new chemical starting points for drug discovery efforts for kinetoplastid diseases were identified.

Screening the Medicines for Malaria Venture Pathogen Box across Multiple Pathogens Reclassifies Starting Points for Open-Source Drug Discovery.

Open-access drug discovery provides a substantial resource for diseases primarily affecting the poor and disadvantaged. The open-access Pathogen Box collection is comprised of compounds with demonstrated biological activity against specific pathogenic organisms. The supply of this resource by the Medicines for Malaria Venture has the potential to provide new chemical starting points for a number of tropical and neglected diseases, through repurposing of these compounds for use in drug discovery campaigns for these additional pathogens. We tested the Pathogen Box against kinetoplastid parasites and malaria life cycle stages in vitro Consequently, chemical starting points for malaria, human African trypanosomiasis, Chagas disease, and leishmaniasis drug discovery efforts have been identified. Inclusive of this in vitro biological evaluation, outcomes from extensive literature reviews and database searches are provided. This information encompasses commercial availability, literature reference citations, other aliases and ChEMBL number with associated biological activity, where available. The release of this new data for the Pathogen Box collection into the public domain will aid the open-source model of drug discovery. Importantly, this will provide novel chemical starting points for drug discovery and target identification in tropical disease research.

Biological characterization of chemically diverse compounds targeting the Plasmodium falciparum coenzyme A synthesis pathway.

BACKGROUND: In the fight against malaria, the discovery of chemical compounds with a novel mode of action and/or chemistry distinct from currently used drugs is vital to counteract the parasite's known ability to develop drug resistance. Another desirable aspect is efficacy against gametocytes, the sexual developmental stage of the parasite which enables the transmission through Anopheles vectors. Using a chemical rescue approach, we previously identified compounds targeting Plasmodium falciparum coenzyme A (CoA) synthesis or utilization, a promising target that has not yet been exploited in anti-malarial drug development. RESULTS: We report on the outcomes of a series of biological tests that help to define the species- and stage-specificity, as well as the potential targets of these chemically diverse compounds. Compound activity against P. falciparum gametocytes was determined to assess stage-specificity and transmission-reducing potential. Against early stage gametocytes IC50 values ranging between 60 nM and 7.5 µM were obtained. With the exception of two compounds with sub-micromolar potencies across all intra-erythrocytic stages, activity against late stage gametocytes was lower. None of the compounds were specific pantothenate kinase inhibitors. Chemical rescue profiling with CoA pathway intermediates demonstrated that most compounds acted on either of the two final P. falciparum CoA synthesis enzymes, phosphopantetheine adenylyltransferase (PPAT) or dephospho CoA kinase (DPCK). The most active compound targeted either phosphopantothenoylcysteine synthetase (PPCS) or phosphopantothenoylcysteine decarboxylase (PPCDC). Species-specificity was evaluated against Trypanosoma cruzi and Trypanosoma brucei brucei. No specific activity against T. cruzi amastigotes was observed; however three compounds inhibited the viability of trypomastigotes with sub-micromolar potencies and were confirmed to act on T. b. brucei CoA synthesis. CONCLUSIONS: Utilizing the compounds we previously identified as effective against asexual P. falciparum, we demonstrate for the first time that gametocytes, like the asexual stages, depend on CoA, with two compounds exhibiting sub-micromolar potencies across asexual forms and all gametocytes stages tested. Furthermore, three compounds inhibited the viability of T. cruzi and T. b. brucei trypomastigotes with sub-micromolar potencies and were confirmed to act on T. b. brucei CoA synthesis, indicating that the CoA synthesis pathway might represent a valuable new drug target in these parasite species.

Hit-to-Lead Optimization of a Novel Class of Potent, Broad-Spectrum Trypanosomacides.

The parasitic trypanosomes Trypanosoma brucei and T. cruzi are responsible for significant human suffering in the form of human African trypanosomiasis (HAT) and Chagas disease. Drugs currently available to treat these neglected diseases leave much to be desired. Herein we report optimization of a novel class of N-(2-(2-phenylthiazol-4-yl)ethyl)amides, carbamates, and ureas, which rapidly, selectively, and potently kill both species of trypanosome. The mode of action of these compounds is unknown but does not involve CYP51 inhibition. They do, however, exhibit clear structure-activity relationships, consistent across both trypanosome species. Favorable physicochemical parameters place the best compounds in CNS drug-like chemical space but, as a class, they exhibit poor metabolic stability. One of the best compounds (64a) cleared all signs of T. cruzi infection in mice when CYP metabolism was inhibited, with sterile cure achieved in one mouse. This family of compounds thus shows significant promise for trypanosomiasis drug discovery.

Identification and Characterization of FTY720 for the Treatment of Human African Trypanosomiasis.

The screening of a focused library identified FTY720 (Fingolimod; Gilenya) as a potent selective antitrypanosomal compound active against Trypanosoma brucei gambiense and T. brucei rhodesiense, the causative agents of human African trypanosomiasis (HAT). This is the first report of trypanocidal activity for FTY720, an oral drug registered for the treatment of relapsing multiple sclerosis, and the characterization of sphingolipids as a potential new class of compounds for HAT.

Future treatment options for human African trypanosomiasis.

Over the past 17 years, the number of reported cases of human African trypanosomiasis (HAT) has declined by over 90%, a significant result since the disease was highlighted as a public health problem by the WHO in 1995. However, if the goal of eliminating HAT by 2020 is to be achieved, then new treatments need to be identified and developed. A plethora of compound collections has been screened against Trypanosoma brucei spp, the etiological agents of HAT, resulting in three compounds progressing to clinical development. However, due to the high attrition rates in drug discovery, it is essential that research continues to identify novel molecules. Failure to do so, will result in the absence of molecules in the pipeline to fall back on should the current clinical trials be unsuccessful. This could seriously compromise control efforts to date, resulting in a resurgence in the number of HAT cases.

6-Arylpyrazine-2-carboxamides: A New Core for Trypanosoma brucei Inhibitors.

From a whole-organism high throughput screen of approximately 87000 compounds against Trypanosoma brucei brucei, we recently identified eight new unique compounds for the treatment of human African trypanosomiasis. In an effort to understand the structure-activity relationships around these compounds, we report for the first time our results on a new class of trypanocides, the pyrazine carboxamides. Attracted by the low molecular weight (270 g·mol(-1)) of our starting hit (9) and its potency (0.49 µM), the SAR around the core was explored, leading to compounds having an EC50 as low as 25 nM against T. b. brucei and being more than 1500 times less toxic against mammalian L6 and HEK293 cell lines. The most potent compounds in the series were exquisitely selective for T. brucei over a panel of other protozoan parasites, showing an excellent correlation with the human infective parasite Trypanosoma brucei rhodesiense, the most potent compound (65) having an EC50 of 24 nM. The compounds are highly drug-like and are able to penetrate the CNS, their only limitation currently being their rate of microsomal metabolism. To that effect, efforts to identify potential metabolites of selected compounds are also reported.

Profiling the anti-protozoal activity of anti-cancer HDAC inhibitors against Plasmodium and Trypanosoma parasites.

Histone deacetylase (HDAC) enzymes work together with histone acetyltransferases (HATs) to reversibly acetylate both histone and non-histone proteins. As a result, these enzymes are involved in regulating chromatin structure and gene expression as well as other important cellular processes. HDACs are validated drug targets for some types of cancer, with four HDAC inhibitors clinically approved. However, they are also showing promise as novel drug targets for other indications, including malaria and other parasitic diseases. In this study the in vitro activity of four anti-cancer HDAC inhibitors was examined against parasites that cause malaria and trypanosomiasis. Three of these inhibitors, suberoylanilide hydroxamic acid (SAHA; vorinostat(®)), romidepsin (Istodax(®)) and belinostat (Beleodaq(®)), are clinically approved for the treatment of T-cell lymphoma, while the fourth, panobinostat, has recently been approved for combination therapy use in certain patients with multiple myeloma. All HDAC inhibitors were found to inhibit the growth of asexual-stage Plasmodium falciparum malaria parasites in the nanomolar range (IC50 10-200 nM), while only romidepsin was active at sub-µM concentrations against bloodstream form Trypanosoma brucei brucei parasites (IC50 35 nM). The compounds were found to have some selectivity for malaria parasites compared with mammalian cells, but were not selective for trypanosome parasites versus mammalian cells. All compounds caused hyperacetylation of histone and non-histone proteins in P. falciparum asexual stage parasites and inhibited deacetylase activity in P. falciparum nuclear extracts in addition to recombinant PfHDAC1 activity. P. falciparum histone hyperacetylation data indicate that HDAC inhibitors may differentially affect the acetylation profiles of histone H3 and H4.

Design and Synthesis of a Screening Library Using the Natural Product Scaffold 3-Chloro-4-hydroxyphenylacetic Acid.

The fungal metabolite 3-chloro-4-hydroxyphenylacetic acid (1) was utilized in the generation of a unique drug-like screening library using parallel solution-phase synthesis. A 20-membered amide library (3-22) was generated by first converting 1 to methyl (3-chloro-4-hydroxyphenyl)acetate (2), then reacting this scaffold with a diverse series of primary amines via a solvent-free aminolysis procedure. The structures of the synthetic analogues (3-22) were elucidated by spectroscopic data analysis. The structures of compounds 8, 12, and 22 were confirmed by single X-ray crystallographic analysis. All compounds were evaluated for cytotoxicity against a human prostate cancer cell line (LNCaP) and for antiparasitic activity toward Trypanosoma brucei brucei and Plasmodium falciparum and showed no significant activity at 10 µM. The library was also tested for effects on the lipid content of LNCaP and PC-3 prostate cancer cells, and it was demonstrated that the fluorobenzyl analogues (12-14) significantly reduced cellular phospholipid and neutral lipid levels.

Pyridyl benzamides as a novel class of potent inhibitors for the kinetoplastid Trypanosoma brucei.

A whole-organism screen of approximately 87000 compounds against Trypanosoma brucei brucei identified a number of promising compounds for medicinal chemistry optimization. One of these classes of compounds we termed the pyridyl benzamides. While the initial hit had an IC50 of 12 µM, it was small enough to be attractive for further optimization, and we utilized three parallel approaches to develop the structure-activity relationships. We determined that the physicochemical properties for this class are generally favorable with particular positions identified that appear to block metabolism when substituted and others that modulate solubility. Our most active compound is 79, which has an IC50 of 0.045 µM against the human pathogenic strain Trypanosoma brucei rhodesiense and is more than 4000 times less active against the mammalian L6 cell line.

Facile Synthesis and Preliminary Structure-Activity Analysis of New Sulfonamides Against Trypanosoma brucei.

The high throughput screening of a library of over 87,000 drug-like compounds against the African sleeping sickness parasite resulted in the discovery of hits with a wide range of molecular diversity. We report here the medicinal chemistry development of one such hit, a tetrahydroisoquinoline disulfonamide, with the synthesis and testing of 26 derivatives against the trypanosome subspecies. Activities in the 2-4 µM range were revealed with a selectivity index suitable for further development.

Trypanocidal activity of marine natural products.

Marine natural products are a diverse, unique collection of compounds with immense therapeutic potential. This has resulted in these molecules being evaluated for a number of different disease indications including the neglected protozoan diseases, human African trypanosomiasis and Chagas disease, for which very few drugs are currently available. This article will review the marine natural products for which activity against the kinetoplastid parasites; Trypanosoma brucei brucei, T.b. rhodesiense and T. cruzi has been reported. As it is important to know the selectivity of a compound when evaluating its trypanocidal activity, this article will only cover molecules which have simultaneously been tested for cytotoxicity against a mammalian cell line. Compounds have been grouped according to their chemical structure and representative examples from each class were selected for detailed discussion.

3-(Oxazolo[4,5-b]pyridin-2-yl)anilides as a novel class of potent inhibitors for the kinetoplastid Trypanosoma brucei, the causative agent for human African trypanosomiasis.

A whole organism high-throughput screen of approximately 87,000 compounds against Trypanosoma brucei brucei led to the recent discovery of several novel compound classes with low micromolar activity against this organism and without appreciable cytotoxicity to mammalian cells. Herein we report a structure-activity relationship (SAR) investigation around one of these hit classes, the 3-(oxazolo[4,5-b]pyridin-2-yl)anilides. Sharp SAR is revealed, with our most active compound (5) exhibiting an IC50 of 91 nM against the human pathogenic strain T.b. rhodesiense and being more than 700 times less toxic towards the L6 mammalian cell line. Physicochemical properties are attractive for many compounds in this series. For the most potent representatives, we show that solubility and metabolic stability are key parameters to target during future optimisation.

Whole-organism high-throughput screening against Trypanosoma brucei brucei.

INTRODUCTION: Human African trypanosomiasis (HAT) occurs as a result of infection with the protozoan parasites Trypanosoma brucei gambiense and T.b. rhodesiense and is nearly always fatal without treatment. However, current therapeutic options are severely limited and there is a desperate need for new compounds to treat the disease. Whole-cell high-throughput screening (HTS) is a technique frequently used to identify compounds with trypanocidal activity. AREAS COVERED: The authors examine the development of whole-organism HTS assays for T.b. brucei. The authors describe the successes achieved through HTS and discuss the advantages and disadvantages of whole-organism HTS. EXPERT OPINION: Despite hundreds of trypanocidal molecules being identified by whole-organism HTS, very few have progressed into preclinical development. The failure of molecules identified by HTS to progress along the drug development pathway is due to a multitude of factors including undrug-like molecules and molecules having poor pharmacodynamics/kinetic properties. Future studies should focus on screening libraries that contain drug-like molecules that possess some of the properties required in the final compound.

Letting the ghosts out of the closet.

This pastoral case study is a reflection on intimidating personalities and how those personalities can effect the leadership style and emotional responses of clergy. When a clergy person finds that he or she is caught in an emotional triangle because of intimidating factors, it becomes necessary to develop a strategy to "unhook" through changing the clergy's behavior. This case study is a reflection regarding a personal experience.