Discovery of 2-iminobenzimidazoles as a new class of trypanothione reductase inhibitor by high-throughput screening

Abstract

A high-throughput screening campaign of a library of 100,000 lead-like compounds identified 2-iminobenzimidazoles as a novel class of trypanothione reductase inhibitors. These 2-iminobenzimidazoles display potent trypanocidal activity against Trypanosoma brucei rhodesiense, do not inhibit closely related human glutathione reductase and have low cytotoxicity against mammalian cells. KeywordsTropical diseases; Trypanosomiasis therapeutics; Trypanothione reductase inhibitors; Highthroughput screening; Medicinal chemistry; Imino benzimidazoles Parasitic protozoa of the family Trypanosomatidae are the causative agent of many significant tropical diseases including African trypanosomiasis, Chagas disease and Leishmaniasis. In the 2004 world health report 1 African trypanosomiasis was reported to cause 48 thousand deaths and a disease burden of 1525 thousand DALYs (disability adjusted life years) annually, Chagas disease 14 thousand deaths and a disease burden of 667 thousand DALYs and Leishmaniasis 51 thousand deaths and a disease burden of 2090 DALYs. There are currently nine key drugs in use for the treatment of these disease states ( Fig. 1): suramin and pentamidine against early stage African trypanosomiasis, and eflornithine and melarsoprol against late stage disease; nifurtimox and benznidazole against early stage Chagas disease; meglumine antimonite and sodium stibogluconate against Leishmaniasis, and amphotericin B against anti-mony-resistant strains. All of these drugs have severe limitations including administration diffculties, long treatment regimes, lifethreatening side effects, varied parasitological cure rates for different strains, lack of effcacy against late stage diseases, and increasing incidence of drug resistance. [2][3][4][5] The intracellular reducing environment of trypanosomatids is maintained by a unique thiol redox system where the glutathione/glutathione reductase (GR) couple found in mammalian cells is replaced by the (bis-glutathionyl)spermidine trypanothione/trypanothione reductase (TR) couple. 6 TR is a key enzyme of the parasite antioxidant defence, 7,8 does not occur in the mammalian host and has been found to be essential for all trypanosomatids currently studied. 9 Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts TR and human GR have similar catalytic mechanisms with 14 of the 19 amino acid residues close to the substrate binding site being conserved. However, they are specific to their respective disulfide substrates (Fig. 2). 11 GR has a hydrophilic, positively charged region in its active site that interacts with the glycine carboxylates of glutathione disulfide, while TR has a larger binding site with a negatively charged region with which the spermidine moiety of trypanothione disulfide binds. 12 The absence of TR from the mammalian host and the sensitivity of trypanosomatids to oxidative stress makes TR an attractive target for trypanosomiasis therapeutics. 13 The objective of this work, therefore, was to identify novel classes of TR inhibit...

Trypanothione Reductase High-Throughput Screening Campaign Identifies Novel Classes of Inhibitors with Antiparasitic Activity

“…A K m app of 1.5 M was determined ( (See an early publication by this group [23] for more details about the screen.) An automated screening protocol for GR, based on our TR assay, was also developed.…”

“…Their purity was also analyzed by liquid chromatographymass spectrometry, and all samples were found to be Ͼ90% pure. See Holloway et al (23) for a summary of this screening campaign and details of the discovery of the 2-iminobenzimidazole class of TR inhibitors.…”

Inhibitors of Leishmania GDP-Mannose Pyrophosphorylase Identified by High-Throughput Screening of Small-Molecule Chemical Library

“…We have successfully screened the activities of compounds against other parasitic targets, with the guiding philosophy behind the selection criteria for the design of the on May 12, 2018 by guest http://aac.asm.org/ chemical library being that lead-like simplicity rather than drug-like complexity is better for furnishing more optimizable screening hits, which are better starting points for drug development and better cover diversity space. We have commented in more detail on this elsewhere (17,18). Lead-like chemical structures have been defined as having simple molecular structures that are chemically unreactive, that are synthetically accessible, that have drug-like properties, and that might bind only relatively weakly in the low-micromolar range to target proteins but that are also highly optimizable.…”

Discovery of novel and potent benzhydryl-tropane trypanocides highly selective for Trypanosoma cruzi

“…We have previously reported on a high-throughput screening campaign conducted to identify inhibitors of trypanothione reductase (TR) that might consequently be toxic to trypanosomatids. 4,5 Amongst the identified hits was a benzhydryl tropinone oxime that was found to be potently toxic towards T. cruzi with an EC 50 of 110 nM and highly selective for this organism relative to other trypanosomatids such as Leishmania donovani and Trypanosoma brucei. 5 These data are summarized in Figure 2.…”