Potential role of Plasmodium falciparum exported protein 1 in the chloroquine mode of action

Abstract

In the human malaria parasite Plasmodium falciparum, membrane glutathione S-transferases (GST) have recently emerged as potential cellular detoxifying units and as drug target candidates with the artemisinin (ART) class of antimalarials inhibiting their activity at single-digit nanomolar potency when activated by iron sources such as cytotoxic hematin. Here we put forward the hypothesis that the membrane GST Plasmodium falciparum exported protein 1 (PfEXP1, PF3D7_1121600) might be directly involved in the mode of action of the unrelated antimalarial 4-aminoquinoline drug chloroquine (CQ). Along this line we report potent biochemical inhibition of membrane glutathione S-transferase activity in recombinant PfEXP1 through CQ at half maximal inhibitory CQ concentrations of 9.02 nM and 19.33 nM when using hematin and the iron deficient 1-chloro-2,4-dinitrobenzene (CDNB) as substrate, respectively. Thus, in contrast to ART, CQ may not require activation through an iron source such as hematin for a potent inhibition of membrane GST activity. Arguably, these data represent the first instance of low nanomolar inhibition of an essential Plasmodium falciparum enzyme through a 4-aminoquinoline and might encourage further investigation of PfEXP1 as a potential CQ target candidate.

Insights in Chloroquine Action: Perspectives and Implications in Malaria and COVID‐19

“…This mechanism was proposed as explanation to the substantial portion of free heme that escapes the FV, hence also biocrystallization into hemozoin. At the same time, it is known that minor concentrations in the micromolar range already effectively kill the parasite, suggesting additional mechanisms to be involved in heme detoxification (14).…”

“…In 2018, Lisewski and colleagues reported a direct inhibition of Pf EXP1 by CQ at nanomolar levels, which may indicate a heme/hematin‐unrelated complementary effect of the drug (14) (Fig. 1).…”

“…It belongs to the class of amino alcohols and is, like ADQ, still in use, as a partner drug for ACTs. Further, mefloquine is still effective against CQ‐resistant strains, in which an increased expression of Pf EXP1 upon mefloquine treatment was observed (2, 5, 14).…”

Structure-Based Screening of Plasmodium berghei Glutathione S-Transferase Identifies CB-27 as a Novel Antiplasmodial Compound

“…Plasmodium GST can also bind ferriprotoporphyrin IX (FPIX) produced during hemoglobin digestion to mediate its detoxification (Hiller et al, 2006). Eukaryotic organisms usually have multiple GSTs while the human malaria parasite P. falciparum and the rodent malaria P. berghei have only one cytosolic GST (Harwaldt et al, 2002;Liebau, 2002;Fritz-Wolf et al, 2003), and membrane-bound GST, known as P. falciparum exported protein 1 (PF3D7_1121600) (Lisewski et al, 2014(Lisewski et al, , 2018.…”