Antimalarial screening via large-scale purification of Plasmodium falciparum Ca2+-ATPase 6 and in vitro studies

ATP2, The essential P4-ATPase of malaria parasites, catalyzes lipid-stimulated ATP hydrolysis in complex with a Cdc50 β-subunit

Gene targeting approaches have demonstrated the essential role for the malaria parasite of membrane transport proteins involved in lipid transport and in the maintenance of membrane lipid asymmetry, representing emerging oportunites for therapeutical intervention. This is the case of ATP2, a Plasmodium-encoded 4 P-type ATPase (P4-ATPase or lipid flippase), whose activity is completely irreplaceable during the asexual stages of the parasite. Moreover, a recent chemogenomic study has situated ATP2 as the possible target of two antimalarial drug candidates. In eukaryotes, P4-ATPases assure the asymmetric phospholipid distribution in membranes by translocating phospholipids from the outer to the inner leaflet. In this work, we have used a recombinantly-produced P. chabaudi ATP2 (PcATP2), to gain insights into the function and structural organization of this essential transporter. Our work demonstrates that PcATP2 associates with two of the three Plasmodium-encoded Cdc50 proteins: PcCdc50B and PcCdc50A. Purified PcATP2/PcCdc50B complex displays ATPase activity in the presence of either phosphatidylserine or phosphatidylethanolamine. In addition, this activity is upregulated by phosphatidylinositol 4-phosphate. Overall, our work describes the first biochemical characterization of a Plasmodium lipid flippase, a first step towards the understanding of the essential physiological role of this transporter and towards its validation as a potential antimalarial drug target.

Identification of Antifungal H+-ATPase Inhibitors with Effect on Plasma Membrane Potential

The plasma membrane H⁺-ATPase (Pma1) is an essential fungal protein and a proposed target for new antifungal medications. The compounds in a small-molecule library containing ∼191,000 commercially available compounds were screened for their ability to inhibit Saccharomyces cerevisiae plasma membranes containing Pma1. The overall hit rate was 0.2%, corresponding to 407 compounds. These hit compounds were further evaluated for ATPase selectivity and broad-spectrum antifungal activity. Following this work, one Pma1 inhibitor series based on compound 14 and analogs was selected for further evaluation. This compound series was able to depolarize the membrane and inhibit extracellular acidification in intact fungal cells concomitantly with a significant increase in intracellular ATP levels. Collectively, we suggest that these effects may be a common feature of Pma1 inhibitors. Additionally, the work uncovered a dual mechanism for the previously identified cationic peptide BM2, revealing fungal membrane disruption, in addition to Pma1 inhibition. The methods presented here provide a solid platform for the evaluation of Pma1-specific inhibitors in a drug development setting. The present inhibitors could serve as a starting point for the development of new antifungal agents with a novel mode of action.

SC83288 is a clinical development candidate for the treatment of severe malaria

Severe malaria is a life-threatening complication of an infection with the protozoan parasite Plasmodium falciparum, which requires immediate treatment. Safety and efficacy concerns with currently used drugs accentuate the need for new chemotherapeutic options against severe malaria. Here we describe a medicinal chemistry program starting from amicarbalide that led to two compounds with optimized pharmacological and antiparasitic properties. SC81458 and the clinical development candidate, SC83288, are fast-acting compounds that can cure a P. falciparum infection in a humanized NOD/SCID mouse model system. Detailed preclinical pharmacokinetic and toxicological studies reveal no observable drawbacks. Ultra-deep sequencing of resistant parasites identifies the sarco/endoplasmic reticulum Ca2+ transporting PfATP6 as a putative determinant of resistance to SC81458 and SC83288. Features, such as fast parasite killing, good safety margin, a potentially novel mode of action and a distinct chemotype support the clinical development of SC83288, as an intravenous application for the treatment of severe malaria.