Plasmodium falciparum glucose‐6‐phosphate dehydrogenase 6‐phosphogluconolactonase is a potential drug target

Abstract

The malarial parasite Plasmodium falciparum is exposed to substantial redox challenges during its complex life cycle. In intraerythrocytic parasites, haemoglobin breakdown is a major source of reactive oxygen species. Deficiencies in human glucose‐6‐phosphate dehydrogenase, the initial enzyme in the pentose phosphate pathway (PPP), lead to a disturbed redox equilibrium in infected erythrocytes and partial protection against severe malaria. In P. falciparum, the first two reactions of the PPP are catalysed by the bifunctional enzyme glucose‐6‐phosphate dehydrogenase 6‐phosphogluconolactonase (PfGluPho). This enzyme differs structurally from its human counterparts and represents a potential target for drugs. In the present study we used epitope tagging of endogenous PfGluPho to verify that the enzyme localises to the parasite cytosol. Furthermore, attempted double crossover disruption of the PfGluPho gene indicates that the enzyme is essential for the growth of blood stage parasites. As a further step towards targeting PfGluPho pharmacologically, ellagic acid was characterised as a potent PfGluPho inhibitor with an IC50 of 76 nm. Interestingly, pro‐oxidative drugs or treatment of the parasites with H2O2 only slightly altered PfGluPho expression or activity under the conditions tested. Furthermore, metabolic profiling suggested that pro‐oxidative drugs do not significantly perturb the abundance of PPP intermediates. These data indicate that PfGluPho is essential in asexual parasites, but that the oxidative arm of the PPP is not strongly regulated in response to oxidative challenge.

Oxidative stress and protein damage responses mediate artemisinin resistance in malaria parasites

“…Here we focused on three genes on the 6A-R chromosome 14 amplification that are likely to be involved in adaptive responses against cellular damage within the parasite. These include 6-phosphogluconate dehydrogenase (PF3D7_1454700, pf6pgd ) and thioredoxin 1 (PF3D7_1457200, pftrx1 )—both of which are involved in antioxidant defense[ 77 , 78 , 79 ], and an ER-resident signal peptide peptidase (PF3D7_1457000, pfspp) [ 80 ] that is a component of ER associated degradation (ERAD)[ 81 ]. All three candidate genes were found to be significantly overexpressed in 6A-R compared throughout the IDC ( Fig 5A and S6 Table ).…”

A high susceptibility to redox imbalance of the transmissible stages of Plasmodium falciparum revealed with a luciferase‐based mature gametocyte assay

“…This compound is a specific inhibitor of the parasite bifunctional enzyme PfGluPho, which catalyzes the first two steps of the pentose phosphate pathway (PPP) that produces >80% of the NADPH in infected erythrocytes, as determined in P. falciparum asexual stages (Atamna et al, 1994). PfGluPho is structurally different from the two separate isofunctional human host enzymes and has recently been validated as an antimalarial drug target (Allen et al ., 2015). As the redox cycling activity of MB leads to a depletion of intracellular NADPH levels, the most likely explanation for the observed synergy of MB and ML304 is that the consumption of the parasite reducing power caused by MB is augmented by the concomitant inhibition of PfGluPho-dependent NADPH production by ML304 (Fig.…”

Hydrogen peroxide dynamics in subcellular compartments of malaria parasites using genetically encoded redox probes

“…NADPH in parasite-infected red blood cells (iRBCs) is generated by human G6PD, but also by P. falciparum glucose-6-phosphate dehydrogenase 6-phosphogluconolactonase ( Pf GluPho) with G6PD activity. Pf GluPho is essential for Plasmodium proliferation and propagation and differs structurally and mechanistically from the human ortholog 67 , 68 . Therefore, developing Pf GluPho inhibitors is a promising way to kill the parasite and treat malaria.…”