Dual-stage inhibition of Plasmodium falciparum by a Skeletocutis-derived fungal metabolite targeting pyruvate kinase II.

Plasmodium falciparum resistance to current first-line treatments is threatening at-risk populations and underscores the urgent need for novel therapeutic targets and drugs. P. falciparum pyruvate kinases I and II are two essential enzymes with distinct roles and subcellular localizations within the parasite. PfPyrKI is cytosolic, while PfPyrKII is found in the apicoplast, a specific organelle of Apicomplexa, where it is required for the production of (d)NTPs essential for apicoplast maintenance. We identify skeletocutin E, a basidiomycete-derived metabolite, as a specific inhibitor of PfPyrKII. Skeletocutin E inhibits in vitro the activity of PfPyrKII with an IC50 of 0.52 ± 0.08 µM through a mixed inhibition mechanism and does not affect the activities of three human pyruvate kinases. Structure-activity relationship analyses using synthetic skeletocutin E analogs allowed us to identify the molecular determinants of this inhibition. Furthermore, determination of the quaternary structure of PfPyrKII by mass photometry showed that skeletocutin E does not alter the distribution of the complexes, indicating that it does not interact at the subunit interfaces. We addressed the expression of PfPyrKII in liver stages and confirmed its apicoplast localization. Importantly, skeletocutin E inhibits P. falciparum growth in both blood and liver stages, with IC₅₀ values of 3.56 ± 0.50 µM in red blood cells and 3.70 ± 0.74 µM in primary human hepatocytes. Together, these findings establish PfPyrKII as a druggable antimalarial target and identify skeletocutin E as a promising lead compound for the rational development of dual-stage antimalarial therapies.