Planta Med 2015; 81 - SL5A_03
DOI: 10.1055/s-0035-1565343

2, 3-dehydrosilybin: A new potent inhibitor of Glyceraldehyde-3-phosphate-dehydrogenase from Trypanosoma brucei identified by in silico screening and an enzyme inhibition assay

FC Herrmann 1, TJ Schmidt 1
  • 1Institute of Pharmaceutical Biology and Phytochemistry, Münster, Germany

In continuation of our screening [1] aimed at the identification of natural inhibitors of Glyceraldehyde-3-phosphate-dehydrogenase from Trypanosoma brucei (TbGAPDH), a commercial natural product database (Phytolab GmbH) was examined in silico by pharmacophore based virtual screening and molecular docking. Experimental validation of the in silico hits was carried out by a photometric enzyme inhibition assay with recombinant TbGAPDH [1]. Virtual screening of the mentioned database (1100 molecules) against GAPDH of various parasites resulted in the identification of 18 potential hits. Noteworthy, six silybin-related flavolignans occurring in Silybum marianum (Asteraceae) were among the in silico hits. The enzyme assay proved one of them, 2, 3-dehydrosilybin A 1 to inhibit the enzyme quite efficiently (≈50% inhibition at 75 µM) while most others (silybin B, isosilybins A and B as well as silychristin) did not show any inhibition. The fact that 1, and only to a lesser extent its enantiomer 2 (Fig. 1), showed inhibitory activity, promises insight into a highly specific mechanism of inhibition. The EC50 values for 1 and 2 were determined at 31.6 and 43.7 µM. Maximum inhibition by higher concentrations of 1 was about 60% but only about 25% by 2, due to poor solubility. 2,3-dehydrosilybin A may thus be a potential lead structure for further inhibitor design and mechanistic studies. Evaluation of the antitrypanosomal activity in cellular tests is in progress.

Fig. 1: Structures of dehydrosilybins A and B

Acknowledgements: Test compounds were kindly donated by Phytolab GmbH, Vestenbergsgreuth, Germany. Bacteria containing the expression plasmid for TbGAPDH were kindly provided by M.L. Bolognesi and S. Piretti (Bologna, Italy) and P. Michels (Edinburgh, U.K.). Support of CCG, Montreal, Canada, is gratefully acknowledged.

This work is part of the activities of ResNetNPND: http://www. ResNetNPND.org/

References:

[1] Herrmann F, Schmidt T J. Planta Med. 2013; 79 1132