Anti-plasmodial activity of proteasome inhibitors against various Plasmodium species: a preclinical evaluation.

The discovery of novel anti-malarial drugs has become urgent due to increasing drug resistance. Our previous work identified ONX-0914, which targets parasite proteolytic systems, as promising against Plasmodium falciparum. This study aims to further evaluate the antiplasmodial activity of ONX-0914 and related proteasome inhibitors (PIs) against various Plasmodium strains. The in vitro antimalarial activity of the inhibitors was evaluated against the Plasmodium knowlesi A1H1 strain and compared with that against the chloroquine (CQ)-sensitive P. falciparum 3D7 strain. Potent synergistic interactions between compounds and artemisinin (ART) were analyzed against PkA1H1 and ART-resistant PfDd2R539T(+) using an isobologram. To explore the mode of action, the disruption of the ubiquitin-proteasome system (UPS) in PkA1H1 and Pf3D7 was investigated. In vivo efficacy of ONX-0914 was further validated against CQ-resistant Plasmodium yoelii. PIs significantly inhibited PkA1H1 proliferation with low-nanomolar IC50 values; ONX-0914 and LU-005i were more potent against PkA1H1 than Pf3D7, and effectively blocked multiple blood stages. Inhibition of parasite growth correlated with potent disruption of UPS at nanomolar concentrations (IC50 < 50 nM). ONX-0914 demonstrated strong synergistic activity with ART and other PIs (∑FIC50 < 0.8). In vivo, ONX-0914 significantly suppressed P. yoelii infection, improving lifespan, with ⁓84% efficacy at an intraperitoneal (IP) dose of 20 mg/kg, and ⁓90% in combination with artemisinin at a dose of 10 mg/kg (IP). Further optimization of the structure and dosing regimen is able to enhance the therapeutic potential of PIs as potential antimalarial drug candidates.