Prodrugs of bisthiazolium salts are orally potent antimalarials

Abstract

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...

Lipidomics of host–pathogen interactions

“…Lysobisphosphatidic acid and phosphoinositides regulate release of VSV nucleocapsid into cytoplasm [13] SigD/SopB is a type III bacterial derived phosphoinositide phosphatase [29,112] Molecular species of phosphatidylcholine and phosphatidylethanolamine are altered in host plasmamembrane after Plasmodium infection [116] GP Ethanolamine phospholipids required for Sindbis virus production [111] Intracellular mycobacteria release a heterogeneous mixture of lipids [27,113] Growth arrest of Plasmodium [117] and Toxoplasma [85] by disruption of phosphatidylcholine synthesis Semliki Forest virus mRNA capping enzyme requires association with anionic membrane phospholipids for activity [14] Phosphatidylinositol mannosides stimulate fusion of early endosomes with mycobacterial phagosomes [30] Glycosylated phosphatidylinositol causes phagosome maturation arrest [114] SapM, a mycobacterial derived phosphatase hydrolyses PI3P contributing to inhibition of phagolysosome maturation [115] Sphingosine 1-kinase is recruited to nascent phagosomes [118] Inhibition of sphingolipid biosynthesis in T. gondii blocks replication [119] SP Sphingomyelin metabolism important for P. falciparum development [120] Inhibition of cholesterol biosynthesis inhibits Hepatitis C virus RNA replication [15] Inhibition of cholesterol acquisition by the host lowers T. gondii replication [40] ST Cholesterol esterification essential for optimal T. gondii proliferation [121,122] Isopreonoid synthesis inhibitors with anti-malarial [123] and anti-T. gondii activity [124] PR Block of protein farnesylation as antiapicomplexan therapies [125] 5…”

Rodent and nonrodent malaria parasites differ in their phospholipid metabolic pathways

“…The biosynthesis of phosphatidylcholine (PC), the most abundant membrane phospholipid (PL) in P. falciparum , is a remarkable example of the level of parasitic adaptation and dependence toward its host and represents a promising target for novel chemotherapies ( 8,9 ).…”

Quantification of Antimalarial Bisthiazolium Compounds and Their Neutral Bioprecursors in Plasma by Liquid Chromatography-Electrospray Mass Spectrometry

“…The lower limit of quantification (LLOQ) was defined as the lowest concentration that could be determined with an accuracy within 80 -120% and an imprecision Յ20% on a day-to-day basis (11)(12)(13)(14). To determine the analytical error in the LLOQ, we used QC samples containing the compounds of interest.…”

“…The bisquaternary ammonium salts showed the highest activities. The third generation consists of neutral prodrugs that deliver bisthiazolium salts with antimalarial activity when present in nanomolar concentrations (11 ). In plasma, the prodrug is rapidly converted into the active drug, and the prodrugs have also been found to offer protection in a murine model of malaria as well as in P. cynomolgi-infected Rhesus monkeys (11 ).…”

“…The third generation consists of neutral prodrugs that deliver bisthiazolium salts with antimalarial activity when present in nanomolar concentrations (11 ). In plasma, the prodrug is rapidly converted into the active drug, and the prodrugs have also been found to offer protection in a murine model of malaria as well as in P. cynomolgi-infected Rhesus monkeys (11 ). The rapid clearance of parasitemia, the absence of recrudescence, and the capacity of curing highly infected animals at a moderate dose (11 ) highlight that the bisthiazolium compounds T3 and T4 and their bioprecursors have very promising clinical potential for malaria treatment and need to be monitored.…”