Reversal of Chloroquine Resistance of Plasmodium vivax in Aotus Monkeys.

Chloroquine-resistant (CQR) vivax malaria has emerged as a threat to the malaria elimination agenda. The objective of this study was to assess if a combination of chloroquine (CQ) and prochlorperazine was able to reverse CQ resistance of the Plasmodium vivax AMRU-1 strain from Papua New Guinea in infected Aotus monkeys. For this purpose, in two independent experimental drug efficacy trials, a total of 18 Aotus monkeys infected with blood obtained from donor animals were randomly assigned to treatment and control groups and orally administered CQ at 10 mg/kg or prochlorperazine at 20 mg/kg, alone or in combination, for five consecutive days. Reversal of CQR was achieved in animals that received the drug combination, whereas neither drug alone produced cures. This same drug combination reverses CQR in P. falciparum and could be an alternative for treatment in humans with chloroquine-resistant P. vivax infections.

Adaptation of a Thai multidrug-resistant C2A clone of Plasmodium falciparum to Aotus monkeys and its preliminary in vivo antimalarial drug efficacy-resistance profile.

A multidrug-resistant (MDR) clone of Plasmodium falciparum (C2A) from Thailand was adapted through serial passage to Aotus monkeys. During adaptation, the parasite showed resistance to a single 20 or 40 mg/kg oral dose of mefloquine (MQ). Infection was only cured when MQ was administered orally at 40 mg/kg once in combination with intravenous artesunic acid at 20 mg/kg for 3 days. Similarly, the parasite clone was found to be resistant to quinine, failing at 20 mg/kg orally for 5 days in combination with an experimental dihydrofolate reductase (DHFR) inhibitor (WR297608) at 10, 20, or 40 mg/kg orally for 3 days, and with atovaquone/proguanil at 25 mg/kg for 3 days. This new model will allow in vivo testing of new antimalarial compounds or their combinations against a currently circulating MDR P. falciparum strain.

Effects of point mutations in Plasmodium falciparum dihydrofolate reductase and dihydropterate synthase genes on clinical outcomes and in vitro susceptibility to sulfadoxine and pyrimethamine.

BACKGROUND: Sulfadoxine-pyrimethamine was a common first line drug therapy to treat uncomplicated falciparum malaria, but increasing therapeutic failures associated with the development of significant levels of resistance worldwide has prompted change to alternative treatment regimes in many national malaria control programs. METHODOLOGY AND FINDING: We conducted an in vivo therapeutic efficacy trial of sulfadoxine-pyrimethamine at two locations in the Peruvian Amazon enrolling 99 patients of which, 86 patients completed the protocol specified 28 day follow up. Our objective was to correlate the presence of polymorphisms in P. falciparum dihydrofolate reductase and dihydropteroate synthase to in vitro parasite susceptibility to sulfadoxine and pyrimethamine and to in vivo treatment outcomes. Inhibitory concentration 50 values of isolates increased with numbers of mutations (single [108N], sextuplet [BR/51I/108N/164L and 437G/581G]) and septuplet (BR/51I/108N/164L and 437G/540E/581G) with geometric means of 76 nM (35-166 nM), 582 nM (49-6890- nM) and 4909 (3575-6741 nM) nM for sulfadoxine and 33 nM (22-51 nM), 81 nM (19-345 nM), and 215 nM (176-262 nM) for pyrimethamine. A single mutation present in the isolate obtained at the time of enrollment from either dihydrofolate reductase (164L) or dihydropteroate synthase (540E) predicted treatment failure as well as any other single gene alone or in combination. Patients with the dihydrofolate reductase 164L mutation were 3.6 times as likely to be treatment failures [failures 85.4% (164L) vs 23.7% (I164); relative risk = 3.61; 95% CI: 2.14 - 6.64] while patients with the dihydropteroate synthase 540E were 2.6 times as likely to fail treatment (96.7% (540E) vs 37.5% (K540); relative risk = 2.58; 95% CI: 1.88 - 3.73). Patients with both dihydrofolate reductase 164L and dihydropteroate synthase 540E mutations were 4.1 times as likely to be treatment failures [96.7% vs 23.7%; RR = 4.08; 95% CI: 2.45 - 7.46] compared to patients having both wild forms (I164 and K540). CONCLUSIONS: In this part of the Amazon basin, it may be possible to predict treatment failure with sulfadoxine-pyrimethamine equally well by determination of either of the single mutations dihydrofolate reductase 164L or dihydropteroate synthase 540E. TRIAL REGISTRATION: ClinicalTrials.gov NCT00951106.

Evaluation of artemisone combinations in Aotus monkeys infected with Plasmodium falciparum.

Artemisone (single oral dose, 10 mg/kg of body weight) cured nonimmune Aotus monkeys of their Plasmodium falciparum infections when combined with mefloquine (single oral dose, 5 and 10 mg/kg but not 2.5 mg/kg). In combination with amodiaquine (20 mg/kg/day), artemisone (10 mg/kg/day) given orally for 3 days cured all infected monkeys. Three days of treatment with artemisone (30 mg/kg/day) and clindamycin (100 mg/kg/day) was also curative.

Current treatment and drug discovery against Leishmania spp. and Plasmodium spp.: a review.

Malaria and leishmaniasis are the most prevalent tropical diseases caused by protozoan parasites. Half of world's population is at risk of malaria and more than 2 million of new cases of leishmaniasis occur annually. There are no vaccines available for these diseases and current treatments suffer from several limitations. Therefore, novel drugs for malaria and leishmaniasis are much-needed. This article reviews the agents currently in use for treatment of these diseases, their known mechanisms of action and weaknesses. We present an overview of the main strategies for drug discovery and the relevance of these parasites genomics/proteomics data for a rational search of molecular targets and matching leads. In this direction, we emphasize the importance of the highly integrated partnerships and networks between scientists in academic institutions and industry involving several countries that promise to increase the chances of success and enhance cost-effectiveness in drug discovery against these parasitic diseases. In addition, we approach the available assays for testing lead compounds in large scale and their limitations for they represent one of the bottlenecks in the pipeline for novel drug discovery. We conclude the article presenting a recent coordinated initiative (TDR Transfection Network) established to overcome some of these limitations by the generation of Plasmodium and Leishmania transgenic parasites better suited for HTS platforms.

World Antimalarial Resistance Network (WARN) II: in vitro antimalarial drug susceptibility.

Intrinsic resistance of Plasmodium falciparum is clearly a major determinant of the clinical failure of antimalarial drugs. However, complex interactions between the host, the parasite and the drug obscure the ability to define parasite drug resistance in vivo. The in vitro antimalarial drug susceptibility assay determines ex-vivo growth of parasite in the presence of serial drug concentrations and, thus, eliminates host effects, such as drug metabolism and immunity. Although the sensitivity of the parasite to various antimalarials provided by such a test provides an important indicator of intrinsic parasite susceptibility, there are fundamental methodological issues that undermine comparison of in vitro susceptibility both between laboratories and within a single laboratory over time. A network of laboratories is proposed that will agree on the basic parameters of the in vitro test and associated measures of quality control. The aim of the network would be to establish baseline values of sensitivity to commonly used antimalarial agents from key regions of the world, and create a global database, linked to clinical, molecular and pharmacology databases, to support active surveillance to monitor temporal trends in parasite susceptibility. Such a network would facilitate the rapid detection of strains with novel antimalarial resistance profiles and investigate suitable alternative treatments with retained efficacy.