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2.  Structure-Based Design of Pteridine Reductase Inhibitors Targeting African Sleeping Sickness and the Leishmaniases† 
Journal of Medicinal Chemistry  2009;53(1):221-229.
Pteridine reductase (PTR1) is a target for drug development against Trypanosoma and Leishmania species, parasites that cause serious tropical diseases and for which therapies are inadequate. We adopted a structure-based approach to the design of novel PTR1 inhibitors based on three molecular scaffolds. A series of compounds, most newly synthesized, were identified as inhibitors with PTR1-species specific properties explained by structural differences between the T. brucei and L. major enzymes. The most potent inhibitors target T. brucei PTR1, and two compounds displayed antiparasite activity against the bloodstream form of the parasite. PTR1 contributes to antifolate drug resistance by providing a molecular bypass of dihydrofolate reductase (DHFR) inhibition. Therefore, combining PTR1 and DHFR inhibitors might improve therapeutic efficacy. We tested two new compounds with known DHFR inhibitors. A synergistic effect was observed for one particular combination highlighting the potential of such an approach for treatment of African sleeping sickness.
doi:10.1021/jm901059x
PMCID: PMC2804273  PMID: 19916554
3.  Structure-based Ligand Design and the Promise Held for Antiprotozoan Drug Discovery* 
The Journal of Biological Chemistry  2009;284(18):11749-11753.
The development of the pharmaceutical industry, driven by progress in chemistry, biology, and technology, ranks as one of the most successful of human endeavors. However, serious health problems persist, among which are diseases caused by protozoan parasites, largely ignored in modern times. Advances in genomic sciences, molecular and structural biology, and computational and medicinal chemistry now set the scene for a renewed assault on such infections. A structure-centric approach to support discovery of antiparasitic compounds promises much. Current strategies and benefits of a structure-based approach to support early stage drug discovery will be described.
doi:10.1074/jbc.R800072200
PMCID: PMC2673241  PMID: 19103598
4.  Geobacillus stearothermophilus 6-phosphogluconate dehydrogenase complexed with 6-phosphogluconate 
The structure of 6-phosphogluconate dehydrogenase from a moderate thermophile, G. stearothermophilus, is presented and compared with those of orthologous enzymes.
Two crystal structures of recombinant Geobacillus stearothermophilus 6-phosphogluconate dehydrogenase (Gs6PDH) in complex with the substrate 6-­phosphogluconate have been determined at medium resolution. Gs6PDH shares significant sequence identity and structural similarity with the enzymes from Lactococcus lactis, sheep liver and the protozoan parasite Trypanosoma brucei, for which a range of structures have previously been reported. Comparisons indicate that amino-acid sequence conservation is more pronounced in the two domains that contribute to the architecture of the active site, namely the N-terminal and C-terminal domains, compared with the central domain, which is primarily involved in the subunit–subunit associations required to form a stable dimer. The active-site residues are highly conserved, as are the interactions with the 6-phosphogluconate. There is interest in 6PDH as a potential drug target for the protozoan parasite T. brucei, the pathogen responsible for African sleeping sickness. The recombinant T. brucei enzyme has proven to be recalcitrant to enzyme–ligand studies and a surrogate protein might offer new opportunities to investigate and characterize 6PDH inhibitors. The high degree of structural similarity, efficient level of expression and straightforward crystallization conditions mean that Gs6PDH may prove to be an appropriate model system for structure-based inhibitor design targeting the enzyme from Trypanosoma species.
doi:10.1107/S1744309109012767
PMCID: PMC2675582  PMID: 19407374
pentose phosphate pathway; 6-phosphogluconate dehydrogenase; Geobacillus stearothermophilus
5.  A Structure-Based Approach to Ligand Discovery for 2C-Methyl-d-erythritol-2,4-cyclodiphosphate Synthase: A Target for Antimicrobial Therapy† 
Journal of Medicinal Chemistry  2009;52(8):2531-2542.
The nonmevalonate route to isoprenoid biosynthesis is essential in Gram-negative bacteria and apicomplexan parasites. The enzymes of this pathway are absent from mammals, contributing to their appeal as chemotherapeutic targets. One enzyme, 2C-methyl-d-erythritol-2,4-cyclodiphosphate synthase (IspF), has been validated as a target by genetic approaches in bacteria. Virtual screening against Escherichia coli IspF (EcIspF) was performed by combining a hierarchical filtering methodology with molecular docking. Docked compounds were inspected and 10 selected for experimental validation. A surface plasmon resonance assay was developed and two weak ligands identified. Crystal structures of EcIspF complexes were determined to support rational ligand development. Cytosine analogues and Zn2+-binding moieties were characterized. One of the putative Zn2+-binding compounds gave the lowest measured KD to date (1.92 ± 0.18 μM). These data provide a framework for the development of IspF inhibitors to generate lead compounds of therapeutic potential against microbial pathogens.
doi:10.1021/jm801475n
PMCID: PMC2669732  PMID: 19320487
6.  One Scaffold, Three Binding Modes: Novel and Selective Pteridine Reductase 1 Inhibitors Derived from Fragment Hits Discovered by Virtual Screening† 
Journal of Medicinal Chemistry  2009;52(14):4454-4465.
The enzyme pteridine reductase 1 (PTR1) is a potential target for new compounds to treat human African trypanosomiasis. A virtual screening campaign for fragments inhibiting PTR1 was carried out. Two novel chemical series were identified containing aminobenzothiazole and aminobenzimidazole scaffolds, respectively. One of the hits (2-amino-6-chloro-benzimidazole) was subjected to crystal structure analysis and a high resolution crystal structure in complex with PTR1 was obtained, confirming the predicted binding mode. However, the crystal structures of two analogues (2-amino-benzimidazole and 1-(3,4-dichloro-benzyl)-2-amino-benzimidazole) in complex with PTR1 revealed two alternative binding modes. In these complexes, previously unobserved protein movements and water-mediated protein−ligand contacts occurred, which prohibited a correct prediction of the binding modes. On the basis of the alternative binding mode of 1-(3,4-dichloro-benzyl)-2-amino-benzimidazole, derivatives were designed and selective PTR1 inhibitors with low nanomolar potency and favorable physicochemical properties were obtained.
doi:10.1021/jm900414x
PMCID: PMC2966039  PMID: 19527033
7.  The ethanolamine branch of the Kennedy pathway is essential in the bloodstream form of Trypanosoma brucei 
Molecular Microbiology  2009;73(5):826-843.
Phosphatidylethanolamine (GPEtn), a major phospholipid component of trypanosome membranes, is synthesized de novo from ethanolamine through the Kennedy pathway. Here the composition of the GPEtn molecular species in the bloodstream form of Trypanosoma brucei is determined, along with new insights into phospholipid metabolism, by in vitro and in vivo characterization of a key enzyme of the Kennedy pathway, the cytosolic ethanolamine-phosphate cytidylyltransferase (TbECT). Gene knockout indicates that TbECT is essential for growth and survival, thus highlighting the importance of the Kennedy pathway for the pathogenic stage of the African trypanosome. Phosphatiylserine decarboxylation, a potential salvage pathway, does not appear to be active in cultured bloodstream form T. brucei, and it is not upregulated even when the Kennedy pathway is disrupted. In vivo metabolic labelling and phospholipid composition analysis by ESI-MS/MS of the knockout cells confirmed a significant decrease in GPEtn species, as well as changes in the relative abundance of other phospholipid species. Reduction in GPEtn levels had a profound influence on the morphology of the mutants and it compromised mitochondrial structure and function, as well as glycosylphosphatidylinositol anchor biosynthesis. TbECT is therefore genetically validated as a potential drug target against the African trypanosome.
doi:10.1111/j.1365-2958.2009.06764.x
PMCID: PMC2784872  PMID: 19555461

Results 1-7 (7)