Natural products, and phytochemicals in particular, constitute a huge potential for drug discovery and medical use against parasitic diseases. Novel drugs and safer and more efficacious treatment options are urgently needed to fight neglected tropical diseases such as Chagas disease, caused by Trypanosoma cruzi.
So far, antichagasic drug discovery was marked by the lack of financial resources and restricted by low throughput. Research subsequently fell back on drug repurposing and target-based approaches, which did not translate to new drugs against Chagas disease. Understanding drug action and discovering potential mechanisms of action is vital in finding alternative, safe, and efficacious treatment options.
Waltheriones are a group of natural compounds isolated from the plant Waltheria indica, a plant occurring in tropical and subtropical area. Their activity against T. cruzi observed in protozoan phenotypic screens and the high selectivity towards the parasitic cells make the waltheriones very attractive for research, potentially leading to a candidate drug or advancing the knowledge about a novel drug target in T. cruzi.
In my Ph.D. thesis, I have investigated drug action of the waltheriones against T. cruzi by using cell biological and molecular approaches. Untargeted exposure metabolomics of extracellular epimastigote T. cruzi with waltherione revealed an accumulation of acylcarnitines, indicating an effect on fatty acid metabolism downstream of carnitine palmitoyltransferase 1 (CPT1). This finding was further investigated using isotopically labelled palmitate and NMR or mass spectrometry. This demonstrated that β-oxidation is functional in the vector form of T. cruzi. However, no effect of waltherione on β-oxidation or TCA metabolites was observed.
In vitro drug resistance selection was used as a starting point for finding possible mechanisms of resistance and possible mechanisms of action. Selecting for drug resistance in T. cruzi toward waltheriones proved to be difficult. Waltherione-resistant T. cruzi were generated and analysed with comparative transcriptomics revealing a candidate resistance mutation in a mitoribosomal protein.
In conclusion, untargeted exposure metabolomics and comparative transcriptomics point to a mitochondrial involvement in waltherione drug action and a possible drug resistance mechanism. Stage-specific waltherione sensitivity profiles in different protozoan parasites further consolidate the hypothesis that the mode of action of waltheriones against T. cruzi involves interference with mitochondrial metabolism.