We created neutral antimalarial prodrugs that deliver bisthiazolium compounds with antimalarial activity in the nanomolar range. These drugs primarily affect early intraerythrocytic stages through rapid, nonreversible cytotoxicity. The compounds are suitable for both parenteral and oral use and plasma promotes rapid conversion of the prodrug into the drug. We demonstrate that very low doses offer protection in a murine model of malaria. The drugs show great potential for curing high parasitemia with short-course treatments. Oral administration of the TE3 prodrug completely cures Plasmodium cynomolgi infection in rhesus monkeys. The drugs specifically accumulate inside infected erythrocytes, block phosphatidylcholine biosynthesis, and interact with hemozoin. To our knowledge, this class of compounds represents one of the most potent antimalarials tested to date. These unique properties signal a promising future for this class of antimalarial.M alaria is a public health problem affecting Ͼ40% of the world's population. It causes up to 2 million deaths, mostly young children, in Africa, and Ͼ300 million clinical cases each year (1), with major consequent impact on economic productivity and livelihood (2). Currently, there are no licensed vaccines and the spread of drug-resistant parasites and insecticideresistant mosquitoes is an increasing problem. New antimalarial compounds, particularly those based on compounds structurally unrelated to existing antimalarial drugs with new mechanisms of action, are urgently needed (3-5).We have developed classes of antimalarial drugs targeting membrane biogenesis during intraerythrocytic Plasmodium falciparum development. We have focused on mono-and bisquaternary ammonium compounds for their potent antimalarial activity in vitro and in vivo (6, 7). These compounds mimic choline structure; they potently inhibit the low-affinity choline carrier related to phospholipid biosynthesis in eukaryotic cells and the high-affinity carrier involved in biosynthesis of the neurotransmitter acetylcholine in the CNS (8, 9). These compounds have exceptional in vitro and in vivo antimalarial properties devoid of mutagenic activity (10 -12).G25 [1,16-hexadecamethylenebis(N-methylpyrrolidinium) dibromide] and other drugs in this class possess a permanently charged cationic group (7, 13) that is essential for activity but detrimental to oral absorption. This action prejudiced development for the clinic. Oral administration is essential for treatment in dispensaries in endemic countries and for prophylactic or curative treatment for travelers. A targeting carrier system is unsuitable because, in the absence of carrier-mediated specific processes, quaternary ammonium compounds are intrinsically incapable of crossing bilayered cellular membranes. Designing drugs that mask the ionizable groups was therefore the most attractive solution. This was the rationale behind development of a chemically modified form of drug that is converted into an active ionized form by enzymes present in plasma. Here, we repo...

Three new series comprising 24 novel cationic choline analogues and consisting of mono- or bis (N or C-5-duplicated) thiazolium salts have been synthesized. Bis-thiazolium salts showed potent antimalarial activity (much superior to monothiazoliums). Among them, bis-thiazolium salts 12 and 13 exhibited IC(50) values of 2.25 nM and 0.65 nM, respectively, against P. falciparum in vitro. These compounds also demonstrated good in vivo activity (ED(50)

In vitro antimalarial activity tests play a pivotal role in malaria drug research or for monitoring drug resistance in field isolates. We applied two isotopic tests, two enzyme-linked immunosorbent assays (ELISA) and the SYBR green I fluorescence-based assay, to test artesunate and chloroquine, the metabolic inhibitors atovaquone and pyrimethamine, our fast-acting choline analog T3/SAR97276, and doxycycline, which has a delayed death profile. Isotopic tests based on hypoxanthine and ethanolamine incorporation are the most reliable tests provided when they are applied after one full 48-h parasite cycle. The SYBR green assay, which measures the DNA content, usually requires 72 h of incubation to obtain reliable results. When delayed death is suspected, specific protocols are required with increasing incubation times up to 96 h. In contrast, both ELISA tests used (pLDH and HRP2) appear to be problematic, leading to disappointing and even erroneous results for molecules that do not share an artesunatelike profile. The reliability of these tests is linked to the mode of action of the drug, and the conditions required to get informative results are hard to predict. Our results suggest some minimal conditions to apply these tests that should give rise to a standard 50% inhibitory concentration, regardless of the mechanism of action of the compounds, and highlight that the most commonly used in vitro antimalarial activity tests do not have the same potential. Some of them might not detect the antimalarial potential of new classes of compounds with innovative modes of action, which subsequently could become promising new antimalarial drugs.Malaria is a major global health problem, with an estimated 250 to 300 million clinical cases annually and 3.3 billion people at risk, causing nearly a million deaths, mostly among children under 5 years old in sub-Saharan Africa (18, 47). The resistance of Plasmodium falciparum, the most deadly malaria parasite to most antimalarial drugs, is a major obstacle to the eradication of this disease (46). It is also of considerable concern in the light of a recent report on decreased sensitivity to artemesinin drugs in Southeast Asia (14, 28). New chemotherapeutic approaches are thus urgently needed, based on optimization of current drugs and, more importantly, on the discovery of new antimalarial drugs. The latter implies systematic screening of drug libraries, a series of natural compounds, or a structure-based drug design targeting novel targets. In all cases, in vitro evaluation of the thousands of new molecules for their antimalarial activity is an early and necessary step. This early step aims at detecting the antimalarial potential of individual or series of compounds. It is performed in vitro against P. falciparum laboratory strains and, at a later stage, against field isolates, including multidrug-resistant strains. Assays must provide a first indication on the potency of the pharmacological activity, usually expressed as the concentration required to inhibit the parasite viability ...

The malaria parasite, Plasmodium falciparum, develops and multiplies in the human erythrocyte. It needs to synthesize considerable amounts of phospholipids (PLs), principally phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS). Several metabolic pathways coexist for their de novo biosynthesis, involving a dozen enzymes. Given the importance of these PLs for the survival of the parasite, we sought to determine their sources and to understand the connections and dependencies between the multiple pathways. We used three deuterated precursors (choline-d9, ethanolamine-d4, and serine-d3) to follow and quantify simultaneously their incorporations in the intermediate metabolites and the final PLs by LC/MS/MS. We show that PC is mainly derived from choline, itself provided by lysophosphatidylcholine contained in the serum. In the absence of choline, the parasite is able to use both other precursors, ethanolamine and serine. PE is almost equally synthesized from ethanolamine and serine, with both precursors being able to compensate for each other. Serine incorporated in PS is mainly derived from the degradation of host cell hemoglobin by the parasite. P. falciparum thus shows an unexpected adaptability of its PL synthesis pathways in response to different disturbances. These data provide new information by mapping the importance of the PL metabolic pathways of the malaria parasite and could be used to design future therapeutic approaches.

Malaria is a disease caused by an intraerythrocytic protozoan parasite of the genus Plasmodium , which is transmitted by dipterans and affects vertebrates such as reptiles, birds, and mammals, including humans (see supplementary Table I). By contrast with other Apicomplexa parasite species that can infect a broad range of metazoans, Plasmodium species have a narrow specifi city range regarding insect and vertebrate hosts ( 1 ). Plasmodium falciparum is, thus, responsible for the most severe form of malaria in humans only. Other species, such as P. vivax , two P. ovale subspecies ( 2 ), P. malariae , and, according to recent reports, P. knowlesi ( 3 ) cause less complicated forms of human malaria. The host specifi city of P. knowlesi is not restricted to humans because it also infects monkeys.The evolutionary history of Plasmodium species has been highly debated, especially the position of P. falciparum , either grouped with avian parasites ( 4, 5 ) or placed as a sister species to other mammalian parasites including rodent parasites. The fi ndings of most recent analyses using three classes of rare genomic changes and mitochondrial RNA genes unambiguously support a mammalian clade and no Abstract Malaria, a disease affecting humans and other animals, is caused by a protist of the genus Plasmodium . At the intraerythrocytic stage, the parasite synthesizes a high amount of phospholipids through a bewildering number of pathways. In the human Plasmodium falciparum species, a plant-like pathway that relies on serine decarboxylase and phosphoethanolamine N-methyltransferase activities diverts host serine to provide additional phosphatidylcholine and phosphatidylethanolamine to the parasite. This feature of parasitic dependence toward its host was investigated in other Plasmodium species. In silico analyses led to the identifi cation of phosphoethanolamine N-methyltransferase gene orthologs in primate and bird parasite genomes. However, the gene was not detected in the rodent P. berghei , P. yoelii , and P. chabaudi species. Biochemical experiments with labeled choline, ethanolamine, and serine showed marked differences in biosynthetic pathways when comparing rodent P. berghei and P. vinckei , and human P. falciparum species. Notably, in both rodent parasites, ethanolamine and serine were not signifi cantly incorporated into phosphatidylcholine, indicating the absence of phosphoethanolamine N-methyltransferase activity. To our knowledge, this is the fi rst study to highlight a crucial difference in phospholipid metabolism between Plasmodium species. The fi ndings should facilitate efforts to develop more rational approaches to identify and evaluate new targets for antimalarial therapy.

BACKGROUND AND PURPOSE Choline analogues, a new type of antimalarials, exert potent in vitro and in vivo antimalarial activity. This has given rise to albitiazolium, which is currently in phase II clinical trials to cure severe malaria. Here we dissected its mechanism of action step by step from choline entry into the infected erythrocyte to its effect on phosphatidylcholine (PC) biosynthesis. EXPERIMENTAL APPROACH We biochemically unravelled the transport and enzymatic steps that mediate de novo synthesis of PC and elucidated how albitiazolium enters the intracellular parasites and affects the PC biosynthesis. KEY RESULTS Choline entry into Plasmodium falciparum‐infected erythrocytes is achieved both by the remnant erythrocyte choline carrier and by parasite‐induced new permeability pathways (NPP), while parasite entry involves a poly‐specific cation transporter. Albitiazolium specifically prevented choline incorporation into its end‐product PC, and its antimalarial activity was strongly antagonized by choline. Albitiazolium entered the infected erythrocyte mainly via a furosemide‐sensitive NPP and was transported into the parasite by a poly‐specific cation carrier. Albitiazolium competitively inhibited choline entry via the parasite‐derived cation transporter and also, at a much higher concentration, affected each of the three enzymes conducting de novo synthesis of PC. CONCLUSIONS AND IMPLICATIONS Inhibition of choline entry into the parasite appears to be the primary mechanism by which albitiazolium exerts its potent antimalarial effect. However, the pharmacological response to albitiazolium involves molecular interactions with different steps of the de novo PC biosynthesis pathway, which would help to delay the development of resistance to this drug.

Malaria still affects around 200 million people and is responsible for more than 400,000 deaths per year, mostly children in subequatorial areas. This disease is caused by parasites of the Plasmodium genus. Only a few WHO-recommended treatments are available to prevent or cure plasmodial infections, but genetic mutations in the causal parasites have led to onset of resistance against all commercial antimalarial drugs. New drugs and targets are being investigated to cope with this emerging problem, including enzymes belonging to the main metabolic pathways, while nucleoside and nucleotide analogues are also a promising class of potential drugs. This review highlights the main metabolic pathways targeted for the development of potential antiplasmodial therapies based on nucleos(t)ide analogues, as well as the different series of purine-containing nucleoside and nucleotide derivatives designed to inhibit Plasmodium falciparum purine metabolism.

Mechanisms of transcriptional control in malaria parasites are still not fully understood. The positioning patterns of G-quadruplex (G4) DNA motifs in the parasite's AT-rich genome, especially within the var gene family which encodes virulence factors, and in the vicinity of recombination hotspots, points towards a possible regulatory role of G4 in gene expression and genome stability. Here, we carried out the most comprehensive genome-wide survey, to date, of G4s in the Plasmodium falciparum genome using G4Hunter, which identifies G4 forming sequences (G4FS) considering their G-richness and G-skewness. We show an enrichment of G4FS in nucleosome-depleted regions and in the first exon of var genes, a pattern that is conserved within the closely related Laverania Plasmodium parasites. Under G4-stabilizing conditions, i.e., following treatment with pyridostatin (a high affinity G4 ligand), we show that a bona fide G4 found in the non-coding strand of var promoters modulates reporter gene expression. Furthermore, transcriptional profiling of pyridostatin-treated parasites, shows large scale perturbations, with deregulation affecting for instance the ApiAP2 family of transcription factors and genes involved in ribosome biogenesis. Overall, our study highlights G4s as important DNA secondary structures with a role in Plasmodium gene expression regulation, sub-telomeric recombination and var gene biology.