The Plasmodium falciparum lactate dehydrogenase enzyme (PfLDH) has been considered as a potential molecular target for antimalarials due to this parasite's dependence on glycolysis for energy production. Because the LDH enzymes found in P. vivax, P. malariae and P. ovale (pLDH) all exhibit ∼90% identity to PfLDH, it would be desirable to have new anti-pLDH drugs, particularly ones that are effective against P. falciparum, the most virulent species of human malaria. Our present work used docking studies to select potential inhibitors of pLDH, which were then tested for antimalarial activity against P. falciparum in vitro and P. berghei malaria in mice. A virtual screening in DrugBank for analogs of NADH (an essential cofactor to pLDH) and computational studies were undertaken, and the potential binding of the selected compounds to the PfLDH active site was analyzed using Molegro Virtual Docker software. Fifty compounds were selected based on their similarity to NADH. The compounds with the best binding energies (itraconazole, atorvastatin and posaconazole) were tested against P. falciparum chloroquine-resistant blood parasites. All three compounds proved to be active in two immunoenzymatic assays performed in parallel using monoclonals specific to PfLDH or a histidine rich protein (HRP2). The IC50 values for each drug in both tests were similar, were lowest for posaconazole (<5 µM) and were 40- and 100-fold less active than chloroquine. The compounds reduced P. berghei parasitemia in treated mice, in comparison to untreated controls; itraconazole was the least active compound. The results of these activity trials confirmed that molecular docking studies are an important strategy for discovering new antimalarial drugs. This approach is more practical and less expensive than discovering novel compounds that require studies on human toxicology, since these compounds are already commercially available and thus approved for human use.

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.

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.

dMost antimalarial drugs target asexual parasites without reducing gametocyte formation or development. Drugs with dual roles, i.e., those that can target both asexual parasites and gametocytes, would improve the control of malaria. In the current study, MEFAS, a hybrid drug derived from mefloquine and artesunate that has been shown to be an active blood schizonticidal drug, was assessed to determine its ability to block the infectivity of Plasmodium falciparum gametocytes. MEFAS was 280 and 15 times more effective than mefloquine alone and artesunate alone, respectively. D espite significant recent advances in the treatment of malaria, the eradication of this disease, which is a goal of the World Health Organization, has not yet been achieved. An ideal drug should have dual effects, i.e., it should cure the disease and should reduce the infectivity of gametocytes in mosquitoes, thereby limiting transmission (1). Reports of delayed parasite clearance rates in patients treated with artemisinin derivatives have triggered the development of novel antimalarials that target multiple stages of the parasite life cycle, thus blocking infection and transmission (2). Gametocytes, the sexual forms of the parasite that are responsible for parasite development in mosquito vectors, are affected by a few drugs, such as primaquine (PQ), that prevent parasite transmission. This is especially important in Plasmodium falciparum, because the gametocytes of this species survive longer than the asexual forms (3). Although the initial gametocyte stages (stages I to III) are sensitive to most schizonticidal antimalarials, the mature stages (stages IV and V) are sensitive only to PQ (4-6).Single-dose PQ is used as a P. falciparum transmission-blocking drug; long-term PQ treatments (14 days) are used for Plasmodium vivax. In this case, PQ blocks transmission and prevents late relapse (7). However, prolonged use of PQ requires medical supervision, because this drug may cause gastrointestinal problems and severe hemolytic anemia in patients who lack the glucose-6-phosphate dehydrogenase (G6PD) enzyme (8, 9).New antimalarial drugs with different biological functions and distinct pharmacophores include hybrids that are covalently linked to single compounds (10). MEFAS, a hybrid salt derived from artesunate (AS) and mefloquine (MQ), was synthesized on a large scale and evaluated for chemical purity (N. Boechat, M. V. N. de Souza, A. L. Valverde, and A. U. Krettli, international patent application WO 2005/100370 A1). MEFAS was less toxic and more effective than AS and MQ applied separately against chloroquine-resistant (clone W2) and chloroquine-sensitive (3D7 strain) P. falciparum in vitro. Additionally, MEFAS was able to cure Plasmodium berghei malaria in experimentally infected mice (11). In this work, the ability of MEFAS to interfere with gametocyte infectivity, male gamete exflagellation, and female gamete activation was evaluated using mature P. falciparum gametocytes cultured in vitro.Two gametocyte-producing P. falciparum strains, 3D7...

No abstract

No abstract

No abstract