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      N-Myristoyltransferase inhibitors as new leads to treat sleeping sickness

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          Abstract

          African sleeping sickness or human African trypanosomiasis (HAT), caused by Trypanosoma brucei spp., is responsible for ~30,000 deaths each year. Available treatments for this neglected disease are poor, with unacceptable efficacy and safety profiles, particularly in the late stage of the disease, when the parasite has infected the central nervous system. Here, we report the validation of a molecular target and discovery of associated lead compounds with potential to address this unmet need. Inhibition of this target, T. brucei N-myristoyltransferase (TbNMT), leads to rapid killing of trypanosomes both in vitro and in vivo and cures trypanosomiasis in mice. These high affinity inhibitors bind into the peptide substrate pocket of the enzyme and inhibit protein N-myristoylation in trypanosomes. The compounds identified have very promising pharmaceutical properties and represent an exciting opportunity to develop oral drugs to treat this devastating disease. Our studies validate TbNMT as a promising therapeutic target for HAT.

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          Most cited references35

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          The Alamar Blue assay to determine drug sensitivity of African trypanosomes (T.b. rhodesiense and T.b. gambiense) in vitro.

          Alamar Blue, an indicator for metabolic cell function, was evaluated as a fluorescent and as a colorimetric dye in drug sensitivity assays for human pathogenic African trypanosomes, Trypanosoma brucei rhodesiense and T.b. gambiense. The experimental conditions were adjusted to find those where the relationship between trypanosome number and Alamar Blue signal was linear over the widest possible range. Fluorescent signals correlated to trypanosome numbers from 10(4) trypanosomes/ml (T.b. rhodesiense) and 10(5) trypanosomes/ml (T.b. gambiense) up to 2-3 x 10(6) trypanosomes/ml when trypanosomes were incubated for 2 h with 10% Alamar Blue. Trypanocidal activity of common drugs (melarsoprol, DFMO, suramin, pentamidine and diminazene aceturate) was determined employing this assay. The IC50 values obtained were comparable to those obtained with another fluorochrome, BCECF-AM. The Alamar Blue assay can be applied for drug screening, since it is simple, reproducible and economical. The assay can also be used in field sites with less equipped laboratories, because in addition to fluorometric endpoint determination, a colorimetric reading is possible.
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            Lessons Learnt from Assembling Screening Libraries for Drug Discovery for Neglected Diseases

            To enable the establishment of a drug discovery operation for neglected diseases, out of 2.3 million commercially available compounds 222 552 compounds were selected for an in silico library, 57 438 for a diverse general screening library, and 1 697 compounds for a focused kinase set. Compiling these libraries required a robust strategy for compound selection. Rules for unwanted groups were defined and selection criteria to enrich for lead-like compounds which facilitate straightforward structure–activity relationship exploration were established. Further, a literature and patent review was undertaken to extract key recognition elements of kinase inhibitors (“core fragments”) to assemble a focused library for hit discovery for kinases. Computational and experimental characterisation of the general screening library revealed that the selected compounds 1) span a broad range of lead-like space, 2) show a high degree of structural integrity and purity, and 3) demonstrate appropriate solubility for the purposes of biochemical screening. The implications of this study for compound selection, especially in an academic environment with limited resources, are considered.
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              Hydrodynamic flow-mediated protein sorting on the cell surface of trypanosomes.

              The unicellular parasite Trypanosoma brucei rapidly removes host-derived immunoglobulin (Ig) from its cell surface, which is dominated by a single type of glycosylphosphatidylinositol-anchored variant surface glycoprotein (VSG). We have determined the mechanism of antibody clearance and found that Ig-VSG immune complexes are passively sorted to the posterior cell pole, where they are endocytosed. The backward movement of immune complexes requires forward cellular motility but is independent of endocytosis and of actin function. We suggest that the hydrodynamic flow acting on swimming trypanosomes causes directional movement of Ig-VSG immune complexes in the plane of the plasma membrane, that is, immunoglobulins attached to VSG function as molecular sails. Protein sorting by hydrodynamic forces helps to protect trypanosomes against complement-mediated immune destruction in culture and possibly in infected mammals but likewise may be of functional significance at the surface of other cell types such as epithelial cells lining blood vessels.
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                Author and article information

                Journal
                0410462
                6011
                Nature
                Nature
                Nature
                0028-0836
                1476-4687
                5 July 2010
                1 April 2010
                01 October 2010
                : 464
                : 7289
                : 728-732
                Affiliations
                [1 ]Drug Discovery Unit, Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
                [2 ]Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
                [3 ]Structural Biology Laboratory, Department of Chemistry University of York, Heslington, York YO10 5YW, UK
                [4 ]Centre for Immunology and Infection, Department of Biology and Hull York Medical School, University of York, Heslington, York YO10 5YW, UK
                [5 ]Structural Genomics Consortium, University of Toronto, MaRS South Tower, 7th Floor, 101 College St, Toronto, Ontario, Canada M5G 1L7
                Author notes
                Correspondence and request for materials should be addressed to P.G.W. ( pgwyatt@ 123456dundee.ac.uk ).

                Author Contributions The project management team responsible for experimental design and coordination of research activities at the University of Dundee comprised S.B., R.B., A.H.F., M.A.J.F., J.A.F., I.H.G., K.D.R., D.M.F.vA and P.G.W. and D.F.S. at the University of York. J.A.B., M.H. and A.J.W. optimized expression and produced the active TbNMT used for screening in the Drug Discovery Unit. Biological studies were carried out by S.P.M., O.S, L.S.T, M.L.S.G., I.H., H.P.P. and chemical syntheses by L.C. and S.B.; structural biology and modelling by D.A.R., O.G.R. and C.P.M. at Dundee and R.H. and W.Q. at University of Toronto; and pharmacological studies by L.S.

                Author Information Atomic coordinates and structure factors for the crystal structures have been deposited with the Protein Data Bank under accession codes 3H5Z and 2WSA for LmNMT with bound myristoyl CoA and DDD85646, respectively. A patent relating to this work has been filed (PCT/GB2009/002084).

                Article
                UKMS31238
                10.1038/nature08893
                2917743
                20360736
                5dcaafed-1fe2-4d7a-876b-11fee285db09
                History
                Funding
                Funded by: Wellcome Trust :
                Award ID: 087590 || WT
                Funded by: Wellcome Trust :
                Award ID: 077705 || WT
                Funded by: Wellcome Trust :
                Award ID: 077503 || WT
                Funded by: Medical Research Council :
                Award ID: G0900138(90614) || MRC_
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