| Summary: | Human African trypanosomiasis (HAT) and Chagas disease are caused by infection with the protozoan parasites Trypanosoma brucei and T. cruzi, respectively. There has historically been a lack of investment into measures to control these diseases. As a result, few drugs are available to treat HAT and Chagas disease, and there is an urgent need for novel alternatives. The enzyme L-threonine 3-dehydrogenase (TDH) initiates the conversion of L-threonine into acetyl-coenzyme A and glycine. This pathway has been shown to play a vital role in T. brucei, particularly in fatty acid synthesis. Exposure of T. brucei in culture to a potent TDH inhibitor, has been shown to be lethal(1) and dual blockade of the TDH pathway and a second pathway for acetyl-coenzyme A production, terminated by pyruvate dehydrogenase, completely inhibits the growth of T. brucei(2,3). Multiple three-dimensional structures of TDH, alone and in complex with ligands, were determined by X-ray crystallography. In parallel, enzyme assays were carried out to investigate the kinetic behaviour of TDH and the modes of action of known TDH inhibitors. The structural information on TDH was used in a virtual screen to predict the binding interactions between the enzyme and a library of around 3000 ligands. These ligands were mainly selected for their diversity and for their inhibition of proteins related to TDH. Subsequently, an in vitro screen was performed to test compounds identified by virtual screening, along with small molecules and fragments from commercial libraries. In total, 27 compounds were identified as TDH inhibitors. Of these compounds, four were found to potently inhibit T. brucei growth. This study has demonstrated the effectiveness of combining structural and functional data in rational drug discovery. Novel aspects of TDH have been discovered, in addition to novel inhibitors that will aid in the design of a new class of antitrypanosomal drugs.
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