MEFAS, a hybrid of artesunate-mefloquine active against asexual stages of Plasmodium vivax in field isolates, inhibits malaria transmission

Human malaria continues to be a public health problem and an important cause of morbidity and mortality in the world. Malaria control is achieved through both individual protection against mosquito bites and drug treatment, which is hampered by the spread of Plasmodium falciparum resistance to most antimalarials, including artemisinin derivatives. One of the key pharmacological strategies for controlling malaria is to block transmission of the parasites to their mosquito vectors. Following this rational, MEFAS, a synthetic hybrid salt derived from artesunate (AS) and mefloquine has been previously reported for its activity against asexual P. falciparum parasites in vitro, in addition to a pronounced reduction in the viability of mature gametocytes. Herein, MEFAS was tested against asexual forms of Plasmodium vivax and for its ability to block malaria transmission in Anopheles darlingi mosquitoes in a membrane feeding assay using P. vivax field isolates. MEFAS demonstrated high potency, with a IC50 of 6.5 nM against asexual forms of P. vivax. At 50 μM, MEFAS completely blocked oocyst formation in mosquitoes, regardless of the oocyst number in the control group. At lower doses, MEFAS reduced oocyst prevalence by greater than 20%. At equivalent doses, AS irregularly reduced oocyst formation and caused only slight inhibition of mosquito infections. These results highlight the potential of MEFAS as a novel transmission-blocking molecule, as well as its high blood schizonticidal activity against P. vivax and P. falciparum field isolates, representing a starting point for further development of a new drug with dual antimalarial activity.

Commercial drugs containing flavonoids are active in mice with malaria and in vitro against chloroquine-resistant Plasmodium falciparum

BACKGROUND The main strategy to control human malaria still relies on specific drug treatment, limited now by Plasmodium falciparum-resistant parasites, including that against artemisinin derivatives. Despite the large number of active compounds described in the literature, few of them reached full development against human malaria. Drug repositioning is a fast and less expensive strategy for antimalarial drug discovery, because these compounds are already approved for human use. OBJECTIVES To identify new antimalarial drugs from compounds commercially available and used for other indications. METHODS Accuvit^®, Ginkgo^® and Soyfit^®, rich in flavonoids, and also the standard flavonoids, hesperidin, quercetin, and genistein were tested against blood cultures of chloroquine-resistant P. falciparum, as well as chloroquine, a reference antimalarial. Inhibition of parasite growth was measured in immunoenzymatic assay with monoclonal anti-P. falciparum antibodies, specific to the histidine-rich protein II. Tests in mice with P. berghei malaria were based on percent of parasitaemia reduction. These compounds were also evaluated for in vitro cytotoxicity. FINDINGS The inhibition of parasite growth in vitro showed that Accuvit^® was the most active drug (IC₅₀ 5 ± 3.9 μg/mL). Soyfit^® was partially active (IC₅₀ 13.6 ± 7.7 μg/mL), and Ginkgo^® (IC₅₀ 38.4 ± 14 μg/mL) was inactive. All such compounds were active in vivo at a dose of 50 mg/kg body weight. Accuvit^® and quercetin induced the highest reduction of P. berghei parasitaemia (63% and 53%, respectively) on day 5 after parasite inoculation. As expected, the compounds tested were not toxic. MAIN CONCLUSIONS The antimalarial activity of Accuvit^® was not related to flavonoids only, and it possibly results from synergisms with other compounds present in this drug product, such as multivitamins. Multivitamins in Accuvit^® may explain its effect against the malaria parasites. This work demonstrated for the first time the activity of these drugs, which are already marketed.

Theoretical and experimental studies of new modified isoflavonoids as potential inhibitors of topoisomerase I from Plasmodium falciparum

DNA topoisomerase I from Plasmodium falciparum (PfTopoI), a potential selective target for chemotherapy and drug development against malaria, is used here, together with human Topo I (HssTopoI), for docking, molecular dynamics (MD) studies and experimental assays. Six synthetic isoflavonoid derivatives and the known PfTopoI inhibitors camptothecin and topotecan were evaluated in parallel. Theoretical results suggest that these compounds dock in the binding site of camptothecin and topotecan inside both enzymes and that LQB223 binds selectively in PfTopoI. In vitro tests against P. falciparum blood parasites corroborated the theoretical findings. The selectivity index (SI) of LQB223 ≥ 98 suggests that this molecule is the most promising in the group of compounds tested. In vivo experiments in mice infected with P. berghei showed that LQB223 has an antimalarial activity similar to that of chloroquine.