The effect of herbicides as novel antimalarial drugs on the transcriptome and proteome of Plasmodium falciparum

Abstract

The Apicomplexan parasite, P. falciparum, is one of the causative agents of the morbidity and mortality in sub-Saharan Africa, especially children under 5 years of age and pregnant women (1). The parasite harbours a non-photosynthetic plastid believed to have been acquired from blue-green algae (2, 3). The presence of this apicoplast in the parasite and its connection to plants opens many doors for to the development of novel antimalarials not harmful to the human host. In this study, a herbicide-derived compound (A51B1C1_1) with structural similarities to 1,2-diacylglycerol (DAG) was tested against P. falciparum. It was anticipated that this herbicide would target similar pathways of the malaria parasite as was shown for Arabidopsis. One such pathway is the synthesis of the glycerolipids. Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the two most studied galactolipids. MGDG is synthesised by MGDG synthase and DGDG is synthesised by DGDG synthase from DAG. Morphological studies after inhibition of P. falciparum parasites with A51B1C1_1 confirmed that the compound does have an effect on the parasites. The determined IC50 value, the drug-like properties conforming to Lipinski’s rule of five and the specificity of the compound towards the parasite makes A51B1C1_1 a possible antimalarial compound. Transcriptomic data of A51B1C1_1 P. falciparum treated parasites revealed 1504 differentially affected transcripts, of which 579 transcripts were unique to this treatment. The differentially affected processes included apicoplastassociated metabolic pathways such as glycerolipid and glycerophospholipid metabolism. These results thus indicated that enzymes involved in glycerolipid synthesis, especially those responsible for the metabolism of DAG, are affected in P. falciparum parasites treated with A51B1C1_1. Proteome analysis indicated that similar processes as shown for the transcriptomic data were affected by the herbicide treatment. At the assay time-point, a total of 276 Plasmodial proteins were uniquely expressed in the A51B1C1_1 treated sample whereas 204 Plasmodial proteins were uniquely expressed in the control sample. Interestingly, the direction of the change in the abundance of these affected proteins did not necessarily correlate with the change of abundance observed in the transcriptomic data, as seen numerous times before in other reported Plasmodial perturbations. Global functional genomics aid in the confirmation that compound A51B1C1_1 does affect glycerolipid and glycerophospholipid metabolism in P. falciparum as seen in Arabidopsis after treatment with the parent compound Galvestine-1. Overall, this study demonstrated the importance of functional genomics in the investigation for potential antimalarial compounds and contributed in the progress of A51B1C1_1 from an early hit to an early lead in the antimalarial drug discovery pipeline.