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Biomedical subjects

M Willson

Publications and source records attributed to M Willson.

At least 19 recordsLinked to original sources
PubMed2002

Modified berberine and protoberberines from Enantia chlorantha as potential inhibitors of Trypanosoma brucei.

Phytochemical study of the stem bark of Enantia chlorantha resulted in the isolation of two protoberberines 1 and 2. These alkaloids as well as commercially available berberine were modified chemically and tested in vitro against Typanosoma brucei proliferation as well as on three targeted glycolytic enzymes. The inhibitory activities observed were in the range of 20 microM (ED50 values).

Animals↗
PubMed2001

Indazolylamino quinazolines and pyridopyrimidines as inhibitors of the EGFr and C-erbB-2.

Described herein is the design and synthesis of indazolylaminopyridopyrimidines and quinazolines as inhibitors of the class 1 tyrosine kinase receptor family. Data is presented for N(4)-(1-benzyl-1H-indazol-5-yl)-N(6),N(6)-dimethylpyrido[3,4-d]pyrimidine-4,6-diamine 3B. This compound inhibited EGFr and c-erbB-2 enzymes selectively over other kinases. It inhibited the proliferation of a range of tumour cell lines in vitro and the growth of BT474 xenografts in SCID mice.

Animals↗
PubMed2001

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 microm 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 microm) 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 by in 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.

Acetylcholinesterase↗
PubMed2001

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.

Animals↗
PubMed2001

Glycolysis as a target for the design of new anti-trypanosome drugs.

Glycolysis is perceived 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 compartmentalized, and many of its enzymes display unique 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.

Animals↗
PubMed1998

Analysis of the kinetics of reversible enzyme inhibition by a general algebraic method. Application to multisite inhibition of the phosphoglycerate kinase from Trypanosoma brucei.

The action of an inhibitor on a stationary enzyme reaction is described by a simple equation, which reflects how the progressive binding of inhibitor molecules influences the existence and the productivity of the enzyme forms. This allows deduction of the structure of the enzyme system from the experimental results, using new type of plots (1/[I], 1/[I](a)v) where a = 0,1,2,... in complement to the usual graphs. A reaction scheme is thereby logically built. This method may be used without any theoretical calculation. It is valid whatever the inhibitor, when the association reactions of the substrates and the inhibitor to the enzyme are in rapid equilibrium, and with dead end inhibitors, more generally for steady state enzyme reactions. This method may be adapted to enzyme activation. An original inhibition mode is described with particular bifunctional molecules: cooperative binding of the inhibitor to the enzyme, outside the active site, by direct mutual interaction of two inhibitor molecules, and locking of the conformational changes that normally precede the release of the products.

Animals↗
PubMed1997

Yeast hexokinase inhibitors designed from the 3-D enzyme structure rebuilding.

This work describes a search for hexokinase inhibitors based on the interactions analysis at the active site of the X-ray resolved o-tolulyl-glucosamine-hexokinase (OTG-HK) complex structure. As the actual enzyme sequence was unknown when the X-ray structure was made (only 30% homology), the structure of the complex was rebuilt by modelling on the X-ray structure frame which allowed residues in close vicinity to the inhibitor to be defined, particularly Glu249 and Gln278. Compounds with inhibitor-bearing groups able to interact with these residues were synthesized and assayed. Some of them revealed strong affinities, in the Km range for glucose. Kinetic analysis of their behaviour towards glucose and ATP together with spectroscopic studies using NMR, allowed the determination of the corresponding inhibition patterns and provided complementary information on HK.

Amino Acid Sequence↗
PubMed1995

Inhibition of platelet type II phospholipase A2 by an acylamino phospholipid does not alter arachidonate liberation.

An acylamino phospholipid analogue (2-(R)-N-palmitoylnorleucinol-1-phosphoglycol or (R)-PNPG) was examined for its inhibitory effects against type II phospholipase A2 (PLA2) acting on membranes from Escherichia coli. Using two enzyme sources (rat platelet membranes or recombinant human type II PLA2), (R)-PNPG inhibited phospholipid hydrolysis to a maximal value of 80-85%, half-maximal effect being attained at a substrate/inhibitor molar ratio of 80-250. In contrast, (S)-PNPG was 12-fold less potent and thus provided a control for possible non-specific effects of these polar lipids. However, both analogues exerted only marginal effects on the liberation of [3H]arachidonic acid from rat platelets challenged with calcium ionophore A23187. Since, among various animal species, rat platelets contain by far the highest amounts of this enzyme, our data rule out any possible involvement of secretory PLA2 in arachidonic acid liberation from platelet phospholipids, cytosolic PLA2 appearing in this case as the best candidate able to regulate eicosanoid biosynthesis.

Animals↗
PubMed1994

Inhibition of glyceraldehyde-3-phosphate dehydrogenase by phosphorylated epoxides and alpha-enones.

Pentalenolactone and koningic acid are antibiotics known for their potent inhibition of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. The reactive groups present in these antibiotics are, respectively, an epoxide and an alpha-enone, which form covalent bonds with an active-site cysteine residue of the enzyme. This information was used for the design of two series of glyceraldehyde 3-phosphate analogues with similar reactive groups that could function as potential irreversible inhibitors of glyceraldehyde-3-phosphate dehydrogenase. Inactivation kinetics, NMR analysis, protection experiments, and titration of free cysteine residues together indicate that the inhibitors bind to the active site of the enzyme and form a covalent bond with the active-site cysteine residue of the enzyme. Binding probably takes place at the inorganic phosphate site of the enzyme and may lead to a conformational change. Comparison of the reactivities of the inhibitors for the glycosomal enzyme from the protozoan parasite Trypanosoma brucei and the rabbit muscle enzyme revealed that some of them had a preference for the trypanosome enzyme. When their effect was measured on the multiplication of trypanosome in vitro cultures, one inhibitor appeared to exhibit an inhibitory effect at a concentration significantly lower than the trypanocidal drugs, pentamidin and (difluoromethyl)ornithine, that are routinely used in the treatment of African sleeping sickness.

Animals↗
PubMed1993

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.

Amino Acid Sequence↗
PubMed1993

Synthesis and activity of inhibitors highly specific for the glycolytic enzymes from Trypanosoma brucei.

Most glycosomal enzymes of Trypanosoma brucei carry a relatively high number of positive charges. In at least 3 of the enzymes some of the charges unique to these enzymes are concentrated in 2 distinct areas on the enzymes' surface, about 4 nm apart [4] and these positively charged structural elements have been suggested to be the site of interaction with the trypanocidal drug Suramin. We have synthesized a series of symmetrical long chain molecules with negative charges or strong dipoles at each end. Several of these compounds inhibited the glycosomal enzymes more strongly than Suramin. They also exhibited a specificity for the trypanosome enzymes, when compared with homologous enzymes from other organisms. By varying the chain length of the active compounds, a 4-nm distance between the molecules' extremes proved optimal for inhibition. Tetra-substituted compounds were better than di-substituted. Modifications introduced at the two ends indicated that a planar orientation, with an amide bond linking a phenyl ring to the chain, is preferred. Inhibition kinetics for some of the enzymes indicated the existence of multi-site interactions with the inhibitors.

Animals↗