Michèle Willson

Glycolysis and proteases as targets for the design of new anti-trypanosome drugs.

Glycolysis is considered as a promising target for new drugs against parasitic trypanosomatid protozoa, because this pathway plays an essential role in their ATP supply. Trypanosomatid glycolysis is unique in that it is compartmentalised, and many of its enzymes display specific structural and kinetic features. Structure- and catalytic mechanism-based approaches are applied to design compounds that inhibit the glycolytic enzymes of the parasites without affecting the corresponding proteins of the human host. For some trypanosomatid enzymes, potent and selective inhibitors have already been developed that affect only the growth of cultured trypanosomatids, and not mammalian cells. Examples are developed concerning all enzymes in the hexoses part with also others concerning glyceraldehyde-phosphate dehydrogenase and pyruvate-kinase for the trioses part. Concerning cysteine protease inhibitor development, a great number of irreversible alkylating agents have shown their efficacy towards the active site cysteine of parasite proteases. This includes fluoromethylketones, epoxides, diazomethylketones, vinylsulfones to mention a few. These functional groups are activated electrophiles that react with the nucleophilic cysteine of the active site and are generally quite selective for cysteine versus serine. They are thought to be also reactive to numerous other nucleophiles in the body, especially other thiols. This potentially hampering property seems not to be detrimental for two reasons: first a recent report has shown that cysteine protease inhibitors containing a vinylsulfone electrophile are unreactive towards thiols such as glutathione and can be considered to be inert in the absence of catalytic machinery. Secondly, irreversible inhibitors are shown to be less toxic than presumed in the parasite treatment, owing to some bioselectivity displayed by the parasite itself.

Inhibition of the Glycolytic-enzymes in the Trypanosome - An Approach in the Development of New Leads in the Therapy of Parasitic Diseases

Glycolysis in the trypanosome represents an important target for the development of new therapeutic agents due to the fact that this metabolism is essential for the parasite, glucose being its sole source of energy. In addition, different features of this metabolism and those associated with glycolytic enzymes offer opportunities for the development of efficient and selective compounds. Examples are given in this work of inhibitors directed to the enzymes aldolase and glyceraldehyde-phosphate-dehydrogenase and also of molecules acting specifically on the clusters of basic amino-acids present at the surfaces of the glycolytic enzymes in the parasite.

Sequencing, Modeling, and Selective Inhibition of Trypanosoma brucei Hexokinase

For Trypanosoma brucei, a parasite responsible for African sleeping sickness, carbohydrate metabolism is the only source of ATP, and glycolytic enzymes are localized within membrane-bound organelles called glycosomes. Hexokinase, the first enzyme of the glycolytic pathway, was chosen as a target for selective drug design. We have cloned and sequenced the hexokinase gene of T. brucei. In parallel, we have synthesized several inhibitors. Kinetic analysis revealed differences in the binding mode of these compounds toward yeast and T. brucei hexokinases, while the m-bromophenyl glucosamide was found to be selective for T. brucei. The modeled structure of T. brucei hexokinase-inhibitor complex (using the crystal structure of the Schistosoma mansoni hexokinase as a template) allows us to propose a mode of action of this inhibitor for the trypanosome hexokinase and to account for the observed selectivity.

Involvement of deacylation in activation of substrate hydrolysis by Drosophila acetylcholinesterase.

Insect acetylcholinesterase (AChE), an enzyme whose catalytic site is located at the bottom of a gorge-like structure, hydrolyzes its substrate over a wide range of concentrations (from 2 μm to 300 mm). AChE is activated at low substrate concentrations and inhibited at high substrate concentrations. Several rival kinetic models have been developed to try to describe and explain this behavior. One of these models assumes that activation at low substrate concentrations partly results from an acceleration of deacetylation of the acetylated enzyme. To test this hypothesis, we used a monomethylcarbamoylated enzyme, which is considered equivalent to the acylated form of the enzyme and a non-hydrolyzable substrate analog, 4-oxo-N,N,N-trimethylpentanaminium iodide. It appears that this substrate analog increases the decarbamoylation rate by a factor of 2.2, suggesting that the substrate molecule bound at the activation site (K d = 130 ± 47 μm) accelerates deacetylation. These two kinetic parameters are consistent with our analysis of the hydrolysis of the substrate. The location of the active site was investigated byin vitro mutagenesis. We found that this site is located at the rim of the active site gorge. Thus, substrate positioning at the rim of the gorge slows down the entrance of another substrate molecule into the active site gorge (Marcel, V., Estrada-Mondaca, S., Magné, F., Stojan, J., Klaébé, A., and Fournier, D. (2000) J. Biol. Chem. 275, 11603–11609) and also increases the deacylation step. This results in an acceleration of enzyme turnover.

An easy stereospecific synthesis of 1-amino-2,5-anhydro-1-deoxy-D-mannitol and arylamino derivatives.

1-Amino-2,5-anhydro-1-deoxy-D-mannitol and a series of arylamino derivatives were prepared by nitrous acid deamination of 2-amino-2-deoxy-D-glucose and subsequent reductive amination of the resulting 2,5-anhydro-D-mannose. Some of these compounds showed an enhanced affinity for the hexose transporter of Trypanosoma brucei as compared to D-fructose.

Mecanisme de formation et de transformation des spirophosphoranes—I : Synthese de phosphites cycliques de structure et etude de leurs reactions avec les alcools et les glycols

Abstract The preparations of three cyclic diphosphites and their reactions with alcohols and diols are described. A nucleophilic attack on the P atoms gives compounds with either tricoordinated or pentacoordinated phosphorous. These reactions have confirmed previous results on the stability of dioxaphospholane cycles.

Specific inhibitors for the glycolytic enzymes of Trypanosoma brucei

Abstract The selective inhibition of four glycolytic enzymes from Trypanosoma brucei by α-ω difunctionalized compounds at clusters of amino acids exhibit higher activity than the trypanocidal drug suramin.

A Convenient Synthesis of Dibenzyl α,α‐Difluoromethyl‐β‐ketophosphonates

The first synthesis of dibenzyl α,α-difluoro-β-ketophosphonates has been accomplished by an original fluorination reaction, namely addition of the F+ ion to the enolate form of the corresponding dibenzyl β-ketophosphonate. After an easy cleavage of the benzyloxy protecting groups on the phosphorus atom, α-fluoro-β-ketophosphonic acids were subsequently obtained as stable carboxyphosphate mimics. This approach enables α,α-difluoro-β-ketophosphonate moieties to be introduced into multiply functionalised molecules, thus making the previously described diethyl phosphonate route no longer relevant. Moreover, study of their stability under neutral and basic conditions showed the importance of the keto-enol equilibrium in the decomposition pathway of these molecules. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Selective inhibition of Trypanosoma brucei GAPDH by 1,3-bisphospho-D-glyceric acid (1,3-diPG) analogues.

Various phosphono-phosphates and diphosphonates were synthesized as 1,3-diphosphoglycerate (1,3-diPG) analogues by using a beta-ketophosphonate, an alpha-fluoro,beta-ketophosphonate or a beta-ketophosphoramidate to mimic the unstable carboxyphosphate part of the natural substrate. The inhibitory effect of these analogues on glyceraldehyde-3-phosphate dehydrogenases (GAPDH) from Trypanosoma brucei (Tb) and rabbit muscle were measured with respect to both substrates, glyceraldehyde-3-phosphate (GAP) and 1,3-diPG. Interestingly, all 1,5-diphosphono,2-oxopentanes without substitution at the C-3 position selectively inhibit the Tb GAPDH with respect to 1,3-diPG and are without effect on Rm GAPDH. All 1-phospho,3-oxo,4-phosphonobutanes show themselves to be non-selective inhibitors either with regard to substrates or organisms, but they will be of a great interest as 1,3-diPG stable models for structural studies of co-crystals with GAPDHs.

Inhibition of yeast hexokinase: a kinetic and phosphorus nuclear magnetic resonance study

Abstract Glucosamine analogues are inhibitors of yeast hexokinase (HK); kinetic analysis with respect to glucose and ATP suggests a pseudo-substrate behaviour for these compounds. However, a spectroscopy study by 31P NMR indicates that they are not phosphorylated but that, in fact, they enhance the ATPase activity of HK; this result gives a further insight into the phosphorylation or ATP hydrolysis process in HK.