ABSTRACT
In previous studies, we have shown that mefloquine disrupts calcium homeostasis in neurons by depletion of endoplasmic reticulum (ER) stores, followed by an influx of external calcium across the plasma membrane. In this study, we explore two hypotheses concerning the mechanism(s) of action of mefloquine. First, we investigated the possibility that mefloquine activates non-N-methyl-d-aspartic acid receptors and the inositol phosphate 3 (IP3) signaling cascade leading to ER calcium release. Second, we compared the disruptive effects of mefloquine on calcium homeostasis to those of ionomycin in neuronal and nonneuronal cells. Ionomycin is known to discharge the ER calcium store (through an undefined mechanism), which induces capacitative calcium entry (CCE). In radioligand binding assays, mefloquine showed no affinity for the known binding sites of several glutamate receptor subtypes. The pattern of neuroprotection induced by a panel of glutamate receptor antagonists was dissimilar to that of mefloquine. Both mefloquine and ionomycin exhibited dose-related and qualitatively similar disruptions of calcium homeostasis in both neurons and macrophages. The influx of external calcium was blocked by the inhibitors of CCE in a dose-related fashion. Both mefloquine and ionomycin upregulated the IP3 pathway in a manner that we interpret to be secondary to CCE. Collectively, these data suggest that mefloquine does not activate glutamate receptors and that it disrupts calcium homeostasis in mammalian cells in a manner similar to that of ionomycin.
Subject(s)
Antimalarials/adverse effects , Calcium/metabolism , Ionomycin/adverse effects , Macrophages/drug effects , Mefloquine/adverse effects , Neurons/drug effects , Animals , Cell Line , Cells, Cultured , Cerebral Cortex/cytology , Homeostasis/drug effects , Macrophages/cytology , Macrophages/metabolism , Neurons/cytology , Neurons/metabolism , RatsABSTRACT
Mefloquine has been one of the more valuable antimalarial drugs but has never reached its full clinical potential due to concerns about its neurologic side effects, its greater expense than that of other antimalarials, and the emergence of resistance. The commercial development of mefloquine superseded that of another quinolinyl methanol, WR030090, which was used as an experimental antimalarial drug by the U.S. Army in the 1970s. We evaluated a series of related 2-phenyl-substituted alkylaminoquinolinyl methanols (AAQMs) for their potential as mefloquine replacement drugs based on a series of appropriate in vitro and in vivo efficacy and toxicology screens and the theoretical cost of goods. Generally, the AAQMs were less neurotoxic and exhibited greater antimalarial potency, and they are potentially cheaper than mefloquine, but they showed poorer metabolic stability and pharmacokinetics and the potential for phototoxicity. These differences in physiochemical and biological properties are attributable to the "opening" of the piperidine ring of the 4-position side chain. Modification of the most promising compound, WR069878, by substitution of an appropriate N functionality at the 4 position, optimization of quinoline ring substituents at the 6 and 7 positions, and deconjugation of quinoline and phenyl ring systems is anticipated to yield a valuable new antimalarial drug.
Subject(s)
Antimalarials/pharmacology , Mefloquine/analogs & derivatives , Mefloquine/pharmacology , 3T3 Cells , Animals , Antimalarials/chemical synthesis , Antimalarials/chemistry , Antimalarials/economics , Antimalarials/metabolism , Antimalarials/pharmacokinetics , Antimalarials/toxicity , Aotidae , Computer Simulation , Drug Evaluation, Preclinical , Erythrocytes/parasitology , Female , Hydrogen-Ion Concentration , Inhibitory Concentration 50 , Male , Mefloquine/chemical synthesis , Mefloquine/chemistry , Mefloquine/economics , Mefloquine/metabolism , Mefloquine/pharmacokinetics , Mefloquine/toxicity , Mice , Microscopy, Confocal , Molecular Structure , Neurons/drug effects , Neurons/metabolism , Parasitemia/drug therapy , Plasmodium berghei/drug effects , Plasmodium falciparum/drug effects , Plasmodium vivax/drug effects , Solubility , Structure-Activity RelationshipABSTRACT
Mefloquine is one of the drugs approved by the FDA for malaria chemoprophylaxis. Mefloquine is also approved for the treatment of malaria and is widely used for this purpose in combination with artesunate. However, the clinical utility of the compound has been compromised by reports of adverse neurological effects in some patients. In the present study, the potential neurological effects of mefloquine were investigated with six 7-week-old female rats given a single oral dose of the compound. Potential mefloquine-induced neurological effects were monitored using a standard functional observational battery, automated open field tests, automated spontaneous activity monitoring, a beam traverse task, and histopathology. Plasma mefloquine concentrations were determined 72 h after dosing by using liquid chromatography-mass spectrometry. Mefloquine induced dose-related changes in endpoints associated with spontaneous activity and impairment of motor function and caused degeneration of specific brain stem nuclei (nucleus gracilis). Increased spontaneous motor activity was observed only during the rats' normal sleeping phase, suggesting a correlate to mefloquine-induced sleep disorders. The threshold dose for many of these effects was 187 mg/kg of body weight. This dose yielded plasma mefloquine concentrations after 72 h that are similar to those observed in humans after the treatment dose. Collectively, these data suggest that there may be a biological basis for some of the clinical neurological effects associated with mefloquine.
