Development of binding assays to screen ligands for Plasmodium falciparum thioredoxin and glutathione reductases by ultrafiltration and liquid chromatography/mass spectrometry

• Published in: Journal of chromatography. B, Analytical technologies in the biomedical and life sciences Analytical technologies in the biomedical and life sciences, 2010-04, Vol.878 (13), p.987-993
• Main Authors: Mulabagal, Vanisree, Calderón, Angela I.
• Format: Article
• Language: English
• Subjects: Affinity; Analysis; Analytical, structural and metabolic biochemistry; Assaying; Binding; Biological and medical sciences; Chromatography, Liquid - methods; Enzymes; Fundamental and applied biological sciences. Psychology; General pharmacology; Glutathione reductase; Glutathione Reductase - metabolism; Inhibitors; Ligands; Liquid chromatography; Liquid chromatography/mass spectrometry; Mass Spectrometry - methods; Medical sciences; Pharmacology. Drug treatments; Plasmodium falciparum; Plasmodium falciparum - metabolism; Reductases; Thioredoxin reductase; Thioredoxins - metabolism; Ultrafiltration; Ultrafiltration - methods
• ISSN: 1570-0232; 1873-376X
• DOI: 10.1016/j.jchromb.2010.02.030

To identify potential lead compounds for malaria drug discovery, ultrafiltration and liquid chromatography and mass spectrometry (UF and LC/MS) based binding assays were developed for the first time for Plasmodium falciparum thioredoxin ( PfTrxR) and glutathione ( PfGR) reductases. In the binding assays, curcuminoids (bis-demethoxycurcumin 1, demethoxycurcumin 2, and curcumin 3) were used to study the binding affinity for PfTrxR and PfGR enzymes. The optimum binding was observed when the curcumimoids mixture (1 μM) was incubated with 1 μM PfTrxR and 0.5 μM PfGR enzymes separately for 60 min at 25 °C. The peak areas of the ligands in the chromatogram corresponding to incubation with active PfTrxR and PfGR enzymes increased by 1.6- and 2.0-fold respectively compared to the chromatogram of test compounds incubated with denatured enzymes. Further, binding assay experiments were carried out for compound 2 under non-competitive and competitive incubation conditions with 1 μM PfTrxR and 0.5 μM PfGR enzymes, separately. The binding affinity of compound 2 was higher for both the enzymes under non-competitive incubation conditions. To validate the binding assay developed, we have tested bis-2,4-dinitrophenyl sulfide (4) which is reported as an inhibitor of PfTrxR and PfGR enzymes. Compound 4 showed greater binding affinity for both enzymes under competitive incubation conditions. The relative peak area of compound 4 increased by 3.2- and 6-fold when incubated with active PfTrxR (1 μM) and PfGR (0.5 μM) enzymes respectively compared to the peak areas of the compound in control experiments. The current method developed has a potential for automated high-throughput screening to rapidly determine the binding affinity of ligands for these enzymes.