Specific peptide inhibitors of trypanothione reductase with backbone structures unrelated to that of substrate: potential rational drug design lead frameworks

By introducing cationic charge sites novel peptide lead inhibitor structures for trypanothione reductase have been designed using molecular modelling methods. The inhibitors showed reversible, linear competitive inhibition and the strongest peptide inhibitor to date was found to be N-benzyloxycarbonyl-Ala-Arg-Arg-4-methoxy-beta-naphthylamide with a Ki value of 2.4 microM and a selectivity for parasitic enzyme (trypanothione reductase) over the host enzyme (human glutathione reductase) of over 3 orders of magnitude.

Magnetic water treatment for scale prevention

A home-made magnetic device was built with permanent magnets for treating scaling waters. Its efficiency was evaluated by measuring the remaining ionic calcium at the output of the device by means of an ion selective electrode. The scaling power of the treated water was estimated through an electrochemical scaling test. Chroamperometric curves and chronoelectrogravimetric curves were plotted to obtain the scaling time and the nucleation time of the scale deposition. The variation of the efficiency of the magnetic treatment was studied when the length of treatment, the flow velocity of the scaling water in the device, the material of the pipe where the scaling water flowed were changed. An empirical relationship, which gives the value of the efficiency in function of the length of treatment and the flow velocity, was proposed. Possible mechanisms of action of the magnetic treatment were discussed.

Synthesis and enzymology of modified N-benzyloxycarbonyl-L-cysteinylglycyl-3,3-dimethylaminopropylamide++ + disulphides as alternative substrates for trypanothione reductase from Trypanosoma cruzi: Part 3

Kinetic data for alternative substrates of recombinant trypanothione reductase from Trypanosoma cruzi were measured for a series of N-substituted-L-cysteinylglycyl-3-dimethylaminopropylamides, in which the cysteine N-substituent was either a variant of the benzyloxycarbonyl group or was L-phenylalanine or L-tryptophan. Replacing the benzylic ether oxygen atom by CH2 or NH had relatively minor effects on kcat, but raised the value of K(m) 4.5- and 10-fold, respectively. Similarly, relative to the carbobenzoxy group, an N-L-phenylalanyl or N-L-tryptophanyl replacement on the cysteine hardly altered kcat, but increased K(m) values by 16.6 and 7.4 fold, respectively. These observations were consistent with the K(m) values referring primarily to binding for this series of nonspecific substrates.

Phenothiazine inhibitors of trypanothione reductase as potential antitrypanosomal and antileishmanial drugs

Given the role of trypanothione in the redox defenses of pathogenic trypanosomal and leishmanial parasites, in contrast to glutathione for their mammalian hosts, selective inhibitors of trypanothione reductase are potential drug leads against trypanosomiasis and leishmaniasis. In the present study, the rational drug design approach was used to discover tricyclic neuroleptic molecular frameworks as lead structures for the development of inhibitors, selective for trypanothione reductase over host glutathione reductase. From a homology-modeled structure for trypanothione reductase, replaced in the later stages of the study by the X-ray coordinates for the enzyme from Crithidia fasciculata, a series of inhibitors based on phenothiazine was designed. These were shown to be reversible inhibitors of trypanothione reductase from Trypanosoma cruzi, linearly competitive with trypanothione as substrate and noncompetitive with NADPH, consistent with ping-pong bi bi kinetics. Analogues, synthesized to define structure-activity relationships for the active site, included N-acylpromazines, 2-substituted phenothiazines, and trisubstituted promazines. Analysis of Ki and I50 data, on the basis of calculated log P and molar refractivity values, provided evidence of a specially favored fit of small 2-substituents (especially 2-chloro and 2-trifluoromethyl), with a remote hydrophobic patch on the enzyme accessible for larger, hydrophobic 2-substituents. There was also evidence of an additional hydrophobic enzymic region available to suitable N-substituents of the promazine nucleus. Ki data also indicated that the phenothiazine nucleus can adopt more than one inhibitory orientation in its binding site. Selected compounds were tested for in vitro activity against Trypanosoma brucei, T. cruzi, and Leishmania donovani, with selective activities in the micromolar range being determined for a number of them.

Use of transferred nuclear-Overhauser-effect spectroscopy to measure the bound conformation of a disulphide-replaced analogue of glutathione disulphide as an inhibitor of yeast glutathione reductase

The analogue of glutathione disulphide (GSSG) in which the disulphide bridge of GSSG is replaced by -CH2-S- was synthesised from L-cystathionine using t-butoxycarbonyl and t-butyl ester protection with triethylsilane-promoted deprotection. This analogue (GCSG) was found to be a linear, competitive inhibitor of yeast glutathione reductase (Ki value 981 microM at pH 7.0), a very poor substrate and not to act as an irreversible inhibitor of glutathione reductase. The weak binding of GCSG to glutathione reductase permitted the use of transferred nuclear Overhauser effect spectroscopy (TRNOESY) to investigate the bound conformation of GCSG in its complex with glutathione reductase. The solution structure of free GCSG was investigated by NMR spectroscopy using a range of NMR techniques. The TRNOESY experiment allowed a range of conformations to be determined for the central bridge region (containing the -CH2-S- replacement) of GCSG bound to yeast glutathione reductase. Using the nuclear Overhauser effect constraints thus derived, in combination with molecular graphics and energy minimisation based on the known crystal coordinates of glutathione disulphide (GSSG) bound to human erythrocyte glutathione reductase, allowed an explanation of the lack of substrate activity of GCSG, its inactivity as a suicide inactivator and its relatively weak binding in terms of the enforced mislocation of the -CH2-S- bridge with respect to the catalytic residues (relative to GSSG). Thus, the simple replacement of -S- by -CH2-, common in medicinal chemistry, can lead to poor receptor binding if the replacement occurs in a central, rather than peripheral, part of the ligand under modification.

A molecular model for cinnamyl alcohol dehydrogenase, a plant aromatic alcohol dehydrogenase involved in lignification

The plant aromatic alcohol dehydrogenase, cinnamyl alcohol dehydrogenase (CAD2 from Eucalyptus) was found by sequence analysis of its cloned gene to be homologous to a range of dehydrogenases including alcohol dehydrogenases, L-threonine-3-dehydrogenase, D-xylose reductase and sorbitol dehydrogenase. A homology model of CAD2 was built using the X-ray crystallographic coordinates of horse-liver alcohol dehydrogenase to provide the template, with additional modelling input from other analogous regions of structure from similar enzymes where necessary. The structural model thus produced rationalised the Zn-binding properties of CAD2, indicated the possession of a Rossmann fold (GXGXXG motif), and explained the class A stereospecificity (pro-R hydrogen removal from substrate alcohol) and aromatic substrate specificity of the enzyme. A range of potential ligands was designed based on the homology model and tested as inhibitors of CAD2 and horse liver alcohol dehydrogenase.