These experiments make it clear that one can

These experiments make it clear that one can study the effect of antimalaria drugs that target the DHFR enzyme of P. falciparum by transferring the malaria enzyme into S. cerevisiae. The ease of growth and manipulation of the yeast make it easy to measure the sensitivity of any particular dhfr allele to potential inhibitors of Pf-DHFR. More important, it will allow us now to measure the efficiency with which resistant mutants to any particular DHFR inhibitors are selected. A drug or combination of drugs that show a very low capacity to select resistant populations in the yeast system will be a valuable lead in the development of drugs of this class that remain clinically useful for treatment of P. falciparum over much longer periods than those observed for pyrimethamine and cycloguanil.
Acknowledgements
For many years, Nitroglycerin (NTG) and other organic nitrates have been the mainstay of cardiovascular therapy and of particular benefit in the treatment of diangina pectoris, unstable cancer and the early stages of acute myocardial infarction. They have shown real efficacy in coronary atherosclerosis, hypercholesterolemia or other blood vessel wall disorders involving endothelial dysfunction, and reduced vasodilator capacity of the coronary arteries (). Glutathione reductase (GR; NADPH: oxidized glutathione oxidoreductase, EC 1.6.4.2), a flavoprotein, is an important enzyme which catalyzes the conversion of oxidized glutathione into the reduced form. GR enables several vital functions of the cell, such as the detoxification of free radicals and reactive oxygen species as well as protein and DNA biosynthesis, by maintaining a high ratio of GSH/GSSG., It is a target enzyme for antimalarial and antitumor drugs, and studies on the enzyme are therefore important for drug development. One may expect an increase in the antiplasmodial activity of nitroaromatic and quinoidal compounds with their redox potential. However, the antimalarial activity of some redox active compounds, such as 10-arylizoalloxazines and methylene blue, was also attributed to their inhibition of antioxidant flavoenzyme glutathione reductase, which catalyzes the reduction of glutathione disulfide (GSSG) at the expense of NADPH. It is assumed that both human erythrocyte and GR play important roles for the intraerythrocyte growth of parasites, protecting them from oxidative stress., , Since nitroaromatic and quinoidal compounds may efficiently inhibit GR from various sources,, , it is necessary to assess the relative importance of redox cycling and GR inhibition in their antiplasmodial activity., , , , , In our work, toward the discovery of novel GR inhibitors, we synthesized novel organic nitrate derivatives (). Compounds were evaluated for their ability to inhibit human erythrocyte GR. Inhibition is reported as IC and (μM) and the results are the average of at least three independent experiments (). The rationale of investigating nitro compounds as GR inhibitors is due to the fact that the simple molecules have been shown to be inhibitor of human GR. Grellier et al. showed the antiplasmodial activity of a series of homologous nitroaromatic compounds, which were either strong or weak inhibitors of erythrocyte GR. For this purpose, that study selected the derivatives of 2-(59-nitrofurylvinyl)-quinoline-4-carbonic acid, which possess a broad spectrum of bactericidal and antiparasitic activities, and inhibit yeast GR and trypanothione reductase. The purification of human erythrocyte GR was performed using simple two-step method by 2′,5′-ADP Sepharose-4B affinity gel chromatography and Sephadex G-200 gel filtration chromatography., Human erythrocyte glutathione reductase was purified, 2633-fold with a specific activity of 26.33EUmg and overall yield of 32.., , , , , β-hydroxy nitrates were synthesized using ring-opening reaction of epoxides with Bi(NO)·5HO, which was used both as catalyst and reagent. Some of the nitrate derivatives have previously been synthesized by other groups as well. Inhibitory effects of organic nitrates on the enzyme activity were tested under in vitro conditions; values were calculated from Lineweaver–Burk graphs and given in .