The malaria parasite cation ATPase PfATP4 and its role in the mechanism of action of a new arsenal of antimalarial drugs

Abstract

The intraerythrocytic malaria parasite, Plasmodium falciparum, maintains a low cytosolic Na+ concentration and the plasma membrane P-type cation translocating ATPase ‘PfATP4’ has been implicated as playing a key role in this process. PfATP4 has been the subject of significant attention in recent years as mutations in this protein confer resistance to a growing number of new antimalarial compounds, including the spiroindolones, the pyrazoles, the dihydroisoquinolones, and a number of the antimalarial agents in the Medicines for Malaria Venture's ‘Malaria Box’. On exposure of parasites to these compounds there is a rapid disruption of cytosolic Na+. Whether, and if so how, such chemically distinct compounds interact with PfATP4, and how such interactions lead to parasite death, is not yet clear. The fact that multiple different chemical classes have converged upon PfATP4 highlights its significance as a potential target for new generation antimalarial agents. A spiroindolone (KAE609, now known as cipargamin) has progressed through Phase I and IIa clinical trials with favourable results. In this review we consider the physiological role of PfATP4, summarise the current repertoire of antimalarial compounds for which PfATP4 is implicated in their mechanism of action, and provide an outlook on translation from target identification in the laboratory to patient treatment in the field.

Plasmodium falciparum Cyclic Amine Resistance Locus (PfCARL), a Resistance Mechanism for Two Distinct Compound Classes

“…54 For each of the PfDHODH, PfATP4, cytochrome bc 1 , and PfPI4K inhibitors, there is functional and/or biochemical validation that these unrelated chemotypes directly interact with the mutated target, indicating common targets instead of multidrug-resistance mechanisms. 39,40,42,43,45−50,52−54 Diverse chemotypes hitting the same targets may indicate that such common targets play critical biological roles and that there are a limited number of accessible drug targets in Plasmodium . Recent in silico target profiling indeed showed that only 4% of the P. falciparum genome is druggable.…”

Comparative chemical genomics reveal that the spiroindolone antimalarial KAE609 (Cipargamin) is a P-type ATPase inhibitor

“…However, its use has mostly relied on the availability of rapid methods for mapping the resistance locus to a given chromosomal position. The advent of whole-genome tiling arrays and whole-genome sequencing has made the method more practical in other single-celled organisms such as Mycobacterium tuberculosis bacilli35, malaria parasites36, trypanosomes37, and yeast383940. Unlike other essential gene products that are often described as possible drug targets, drug targets discovered through directed evolution are known from the outset to be druggable and are considered “chemically validated.” The method has been successfully used to identify the targets of several antimalarial compounds initially found through phenotypic screens, as well as to identify genes contributing to the resistome24142.…”

“…38), raising the possibility that PfATP4 is a general drug resistance gene. The finding that a single amino acid change in Sc Pma1p sensitizes the cell to edelfosine by 750% suggests that these mutations confer a fitness cost to the protein, reducing either the ability to pump hydrogen ions or to stay associated with plasma-membrane lipid rafts.…”

“…The alignments of Pf Atp4p amino acids 314–429 and Sc Pma1p 252–356 are shown below. Residues that confer resistance in Plasmodium when mutated are colored based on the compound class used: red for dihydroisoquinolones and blue for spiroindolones (see38 for a review).…”

Phenotypic Screens in Antimalarial Drug Discovery

“…Several compounds identified from these screens have been evaluated and optimized in hit-to-lead programs, with a few advancing into clinical trials. The spiroindolone KAE609, thought to target P-type cation-transporter ATPase4 (PfATP4, reviewed in [25]), works rapidly with a median parasite clearance half life of 0.9 hours [26]. In contrast, less than <1% of P. falciparum malaria patients treated with oral artesunate showed a parasite clearance half-life of less than 1 hour [26].…”