Comparative structural, kinetic and inhibitor studies of Trypanosoma brucei trypanothione reductase with T. cruzi (original) (raw)
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Structure, 1999
Background: Trypanothione reductase (TR) helps to maintain an intracellular reducing environment in trypanosomatids, a group of protozoan parasites that afflict humans and livestock in tropical areas. This protective function is achieved via reduction of polyamine-glutathione conjugates, in particular trypanothione. TR has been validated as a chemotherapeutic target by molecular genetics methods. To assist the development of new therapeutics, we have characterised the structure of TR from the pathogen Trypanosoma cruzi complexed with the substrate trypanothione and have used the structure to guide database searches and molecular modelling studies.
According to World Health Organization (WHO), trypanosomiasis and leishmaniasis are the most challenging among the neglected tropical diseases. Comparative studies between Leishmania spp and Trypanosoma cruzi have been conducted aiming to find a broad spectrum antiprotozoal agent acting against both parasites. Among the potential molecular target, Trypanothione reductase (TR) is considered an ideal enzyme since it is involved in the unique thiol-based metabolism observed in the Trypanosomatidae family and is a validated target for the search of antitrypanosomatidae drugs. In this review we intend to describe the currently available therapy to treat trypanosomatidae diseases and to highlight important aspects of trypanothione reductase as a target for the search of new and selective inhibitors, such as tricyclic, diphenylsulfide, bicyclic and heterocyclic, polyamine, natural product, N-oxide and nitroheterocyclic, aryl β- aminocarbonyl and α,β-unsaturated carbonyl derivatives
Chemistry – A European Journal, 2019
Trypanothione reductase (TR) plays a key role in the unique redox metabolism of trypanosomatids, the causative agents of human African trypanosomiasis (HAT), Chagas' disease, and leishmaniases. Introduction of a new, lean propargylic vector to a known class of TR inhibitors resulted in the strongest reported competitive inhibitor of Trypanosoma (T.) brucei TR, with an inhibition constant K i of 73 nm, which is fully selective against human glutathione reductase (hGR). The best ligands exhibited in vitro IC 50 values (half-maximal inhibitory concentration) against the HAT pathogen, T. brucei rhodesiense, in the mid-nanomolar range, reaching down to 50 nm. X-Ray co-crystal structures confirmed the binding mode of the ligands and revealed the presence of a HEPES buffer molecule in the large active site. Extension of the propargylic vector, guided by structure-based design, to replace the HEPES buffer molecule should give inhibitors with low nanomolar K i and IC 50 values for in vivo studies.
Validation of Trypanosoma brucei trypanothione synthetase as drug target
Free radical biology & medicine, 2004
In trypanosomes, the parasite-specific thiol trypanothione [T(SH)2] fulfills various functions, the best established being detoxification of H2O2 and organic hydroperoxides and ribonucleotide reduction. Recently, a trypanothione synthetase (Tb-TryS) gene from Trypanosoma brucei was isolated and the heterologously expressed Tb-TryS catalyzed the entire synthesis of T(SH)2 from glutathione (GSH) and spermidine in vitro. To confirm the in situ function of the complex Tb-TryS activities and to evaluate the importance of T(SH)2 metabolism in T. brucei, TryS suppression by double-stranded RNA interference was performed. Knockdown of TryS led to depletion of both T(SH)2 and glutathionylspermidine (Gsp) and accumulation of GSH, while concomitantly impairment of viability and arrest of proliferation were observed. TryS-downregulated cells displayed a significantly increased sensitivity to H2O2 and tert.-butyl hydroperoxide. These data verify the hypothesis that in T. brucei, a single enzyme ...
Journal of Medicinal Chemistry, 2011
Trypanothione reductase (TryR) is a genetically validated drug target in the parasite Trypanosoma brucei, the causative agent of human African trypanosomiasis. Here we report the discovery, synthesis, and development of a novel series of TryR inhibitors based on a 3,4-dihydroquinazoline scaffold. In addition, a high resolution crystal structure of TryR, alone and in complex with substrates and inhibitors from this series, is presented. This represents the first report of a high resolution complex between a noncovalent ligand and this enzyme. Structural studies revealed that upon ligand binding the enzyme undergoes a conformational change to create a new subpocket which is occupied by an aryl group on the ligand. Therefore, the inhibitor, in effect, creates its own small binding pocket within the otherwise large, solvent exposed active site. The TryRÀligand structure was subsequently used to guide the synthesis of inhibitors, including analogues that challenged the induced subpocket. This resulted in the development of inhibitors with improved potency against both TryR and T. brucei parasites in a whole cell assay.
Valdiation of Trypanosoma brucei trypanothione synthetase as drug target
Free Radical Biology and Medicine, 2004
In trypanosomes, the parasite-specific thiol trypanothione [T(SH) 2 ] fulfills various functions, the best established being detoxification of H 2 O 2 and organic hydroperoxides and ribonucleotide reduction. Recently, a trypanothione synthetase (Tb-TryS) gene from Trypanosoma brucei was isolated and the heterologously expressed Tb-TryS catalyzed the entire synthesis of T(SH) 2 from glutathione (GSH) and spermidine in vitro. To confirm the in situ function of the complex Tb-TryS activities and to evaluate the importance of T(SH) 2 metabolism in T. brucei, TryS suppression by double-stranded RNA interference was performed. Knockdown of TryS led to depletion of both T(SH) 2 and glutathionylspermidine (Gsp) and accumulation of GSH, while concomitantly impairment of viability and arrest of proliferation were observed. TryS-downregulated cells displayed a significantly increased sensitivity to H 2 O 2 and tert.butyl hydroperoxide. These data verify the hypothesis that in T. brucei, a single enzyme synthesizes the spermidineconjugated thiols (Gsp and T(SH) 2 ) and further confirms the significance of trypanothione in the defense against oxidative stress and the maintenance of viability and proliferation in unstressed parasites. D 2004 Elsevier Inc. All rights reserved.
In Vitro and In Vivo Activity of Multi-Target Inhibitors Against Trypanosoma brucei
ACS Infectious Diseases, 2015
We tested a series of amidine and related compounds against Trypanosoma brucei. The most active compound was a biphenyldiamidine that had an EC 50 of 7.7 nM against bloodstream-form parasites. There was little toxicity against two human cell lines with CC 50 > 100 μM. There was also good in vivo activity in a mouse model of infection with 100% survival at 3 mg/kg i.p. The most potent lead blocked replication of kinetoplast DNA (k-DNA), but not nuclear DNA, in the parasite. Some compounds also inhibited the enzyme farnesyl diphosphate synthase (FPPS), and some were uncouplers of oxidative phosphorylation. We developed a computational model for T. brucei cell growth inhibition (R 2 = 0.76) using DNA ΔT m values for inhibitor binding combined with T. brucei FPPS IC 50 values. Overall, the results suggest that it may be possible to develop multitarget drug leads against T. brucei that act by inhibiting both k-DNA replication and isoprenoid biosynthesis.
Molecular Microbiology, 2006
The protozoan Trypanosoma brucei has a functional pteridine reductase (TbPTR1), an NADPH-dependent short-chain reductase that participates in the salvage of pterins, which are essential for parasite growth. PTR1 displays broad-spectrum activity with pterins and folates, provides a metabolic bypass for inhibition of the trypanosomatid dihydrofolate reductase and therefore compromises the use of antifolates for treatment of trypanosomiasis. Catalytic properties of recombinant TbPTR1 and inhibition by the archetypal antifolate methotrexate have been characterized and the crystal structure of the ternary complex with cofactor NADP + and the inhibitor determined at 2.2 Å resolution. This enzyme shares 50% amino acid sequence identity with Leishmania major PTR1 (LmPTR1) and comparisons show that the architecture of the cofactor binding site, and the catalytic centre are highly conserved, as are most interactions with the inhibitor. However, specific amino acid differences, in particular the placement of Trp221 at the side of the active site, and adjustment of the b6-a6 loop and a6 helix at one side of the substrate-binding cleft significantly reduce the size of the substrate binding site of TbPTR1 and alter the chemical properties compared with LmPTR1. A reactive Cys168, within the active site cleft, in conjunction with the C-terminus carboxyl group and His267 of a partner subunit forms a triad similar to the catalytic component of cysteine proteases. TbPTR1 therefore offers novel structural features to exploit in the search for inhibitors of therapeutic value against African trypanosomiasis.
Discovery of Trypanocidal Compounds by Whole Cell HTS of Trypanosoma brucei
Chemical Biology <html_ent glyph="@amp;" ascii="&"/> Drug Design, 2006
Chemotherapy against human African trypanosomiasis relies on four drugs that cause frequent and occasionally severe side-effects. Because human African trypanosomiasis is a disease of poor people in Africa, the traditional market-driven pathways to drug development are not available. One potentially rapid and cost-effective approach to identifying and developing new trypanocidal drugs would be high throughput-screening of existing drugs already approved for other uses, as well as clinical candidates in late development. We have developed an ATP-bioluminescence assay that could be used to rapidly and efficiently screen compound libraries against trypanosomes in a high throughput-screening format to validate this notion. We screened a collection of 2160 FDAapproved drugs, bioactive compounds and natural products to identify hits that were cytotoxic to cultured Trypanosoma brucei at a concentration of 1 lM or less. This meant that any hit identified would be effective at a concentration readily achievable by standard drug dosing in humans. From the screen, 35 hits from seven different drug categories were identified. These included the two approved trypanocidal drugs, suramin and pentamidine, several other drugs suspected but never validated as trypanocidal, and 17 novel trypanocidal drugs.