Inhibition of Trypanosoma cruzi hexokinase by bisphosphonates

Hexokinase is the first enzyme involved in glycolysis in most organisms, including the etiological agents of Chagas disease (Trypanosoma cruzi) and African sleeping sickness (Thypanosoma brucei). The T. cruzi enzyme is unusual since, unlike the human enzyme, it is inhibited by inorganic diphosphate (PPi). Here, we show that non-hydrolyzable analogues of PPi, bisphosphonates, are potent inhibitors of T. cruzi hexokinase (TcHK). We determined the activity of 42 bisphosphonates against TcHK, and the IC50 values were used to construct pharmacophore and comparative molecular similarity indices analysis (CoMSIA) models for enzyme inhibition. Both models revealed the importance of electrostatic, hydrophobic, and steric interactions, and the IC50 values for 17 active compounds were predicted with an average error of 2.4x by using the CoMSIA models. The Compound most active against T cruzi hexokinase was found to have a 2.2 mu M IC50 versus the clinically relevant intracellular amastigote form of T cruzi, but only a similar to 1-2 mM IC50 versus Dictyostelium discoideum and a human cell line, indicating selective activity versus T. cruzi.