Proline transport inhibitors trigger differential responses in Trypanosoma cruzi growth inhibition

Background: Proline is a fundamental amino acid for Trypanosoma cruzi, the etiological agent of Chagas disease. Proline is mainly incorporated from the extracellular medium by amino acid transport systems. Different proline analogues proved to interact with the proline permease TcAAAP069 and inhibit the proline uptake by T. cruzi. Methods: Decyl- (1), oleyl- (2) and farnesyl- (3) substituted proline analogues were evaluated on six T. cruzi DTUs. Cell death type was determined by flow cytometry, and the effect on the parasite metabolism was analysed by directed NMR exometabolomics. Structural modifications of 1 (compounds 4 – 6) were implemented to have more information on the mode of action (MoA). Results: The compounds showed broad-spectrum activity against all DTUs. Compound 3 at high concentration (116 µM) induced necrosis. The removal of the triazole from 1 proved to be important for the activity. Compounds 1 and 2 induced deep changes in the exometabolome, diminishing the amounts of succinate, lactate, acetate, and ethanol excreted. The fluorescent labelling and subsequent microscopy showed that compound 1 can be taken up by epimastigotes. Conclusions: Two different MoA related to proline transport for decyl and farnesyl-substituted proline analogues are proposed. The former presented an in-cell action while the latter was not taken up by the parasites but interacted with the extracellular side of the proline permease. General Significance: Subtle structural variations in the compounds determine differences in the MoA. This finding opens new perspectives that should be examined on the development of new drugs targeting metabolite permeases.