Purification of a recombinant histidine-tagged lactate dehydrogenase from the malaria parasite, Plasmodium vivax, and characterization of its properties.

Lactate dehydrogenase (LDH) of the malaria parasite, Plasmodium vivax (Pv), serves as a drug target and immunodiagnostic marker. The LDH cDNA generated from total RNA of a clinical isolate of the parasite was cloned into pRSETA plasmid. Recombinant his-tagged PvLDH was over-expressed in E. coli Rosetta2DE3pLysS and purified using Ni(2+)-NTA resin giving a yield of 25-30 mg/litre bacterial culture. The recombinant protein was enzymatically active and its catalytic efficiency for pyruvate was 5.4 × 10(8) min(-1) M(-1), 14.5 fold higher than a low yield preparation reported earlier to obtain PvLDH crystal structure. The enzyme activity was inhibited by gossypol and sodium oxamate. The recombinant PvLDH was reactive in lateral flow immunochromatographic assays detecting pan- and vivax-specific LDH. The soluble recombinant PvLDH purified using heterologous expression system can facilitate the generation of vivax LDH-specific monoclonals and the screening of chemical compound libraries for PvLDH inhibitors.

A knowledge-based approach for identification of drugs against vivapain-2 protein of Plasmodium vivax through pharmacophore-based virtual screening with comparative modelling.

Malaria is one of the most infectious diseases in the world. Plasmodium vivax, the pathogen causing endemic malaria in humans worldwide, is responsible for extensive disease morbidity. Due to the emergence of resistance to common anti-malarial drugs, there is a continuous need to develop a new class of drugs for this pathogen. P. vivax cysteine protease, also known as vivapain-2, plays an important role in haemoglobin hydrolysis and is considered essential for the survival of the parasite. The three-dimensional (3D) structure of vivapain-2 is not predicted experimentally, so its structure is modelled by using comparative modelling approach and further validated by Qualitative Model Energy Analysis (QMEAN) and RAMPAGE tools. The potential binding site of selected vivapain-2 structure has been detected by grid-based function prediction method. Drug targets and their respective drugs similar to vivapain-2 have been identified using three publicly available databases: STITCH 3.1, DrugBank and Therapeutic Target Database (TTD). The second approach of this work focuses on docking study of selected drug E-64 against vivapain-2 protein. Docking reveals crucial information about key residues (Asn281, Cys283, Val396 and Asp398) that are responsible for holding the ligand in the active site. The similarity-search criterion is used for the preparation of our in-house database of drugs, obtained from filtering the drugs from the DrugBank database. A five-point 3D pharmacophore model is generated for the docked complex of vivapain-2 with E-64. This study of 3D pharmacophore-based virtual screening results in identifying three new drugs, amongst which one is approved and the other two are experimentally proved. The ADMET properties of these drugs are found to be in the desired range. These drugs with novel scaffolds may act as potent drugs for treating malaria caused by P. vivax.

Transgenic Plasmodium parasites stably expressing Plasmodium vivax dihydrofolate reductase-thymidylate synthase as in vitro and in vivo models for antifolate screening.

BACKGROUND: Plasmodium vivax is the most prevalent cause of human malaria in tropical regions outside the African continent. The lack of a routine continuous in vitro culture of this parasite makes it difficult to develop specific drugs for this disease. To facilitate the development of anti-P. vivax drugs, bacterial and yeast surrogate models expressing the validated P. vivax target dihydrofolate reductase-thymidylate synthase (DHFR-TS) have been generated; however, they can only be used as primary screening models because of significant differences in enzyme expression level and in vivo drug metabolism between the surrogate models and P. vivax parasites. METHODS: Plasmodium falciparum and Plasmodium berghei parasites were transfected with DNA constructs bearing P. vivax dhfr-ts pyrimethamine sensitive (wild-type) and pyrimethamine resistant (mutant) alleles. Double crossover homologous recombination was used to replace the endogenous dhfr-ts of P. falciparum and P. berghei parasites with P. vivax homologous genes. The integration of Pvdhfr-ts genes via allelic replacement was verified by Southern analysis and the transgenic parasites lines validated as models by standard drug screening assays. RESULTS: Transgenic P. falciparum and P. berghei lines stably expressing PvDHFR-TS replacing the endogenous parasite DHFR-TS were obtained. Anti-malarial drug screening assays showed that transgenic parasites expressing wild-type PvDHFR-TS were pyrimethamine-sensitive, whereas transgenic parasites expressing mutant PvDHFR-TS were pyrimethamine-resistant. The growth and sensitivity to other types of anti-malarial drugs in the transgenic parasites were otherwise indistinguishable from the parental parasites. CONCLUSION: With the permanent integration of Pvdhfr-ts gene in the genome, the transgenic Plasmodium lines expressing PvDHFR-TS are genetically stable and will be useful for screening anti-P. vivax compounds targeting PvDHFR-TS. A similar approach could be used to generate transgenic models specific for other targets of interest, thus facilitating the development of anti-P. vivax drugs in general.

[Importance of a regional observatory of malarial chemoresistance, an emerging public health problem in the Guyanas region]. / Intérêt d'un observatoire régional de la chimiorésistance du paludisme, problème émergent de santé publique dans la région des Guyanes.

A regular implementation of prophylactic and therapeutic decision trees was organized on a consensus basis in Cayenne, French Guiana in 1990, 1995 and 2002. The updated recommendations were based on the knowledge of the in vitro chemosensitivity profiles of the local isolates, mainly coming from big rivers (Maroni and Oyapock, frontiers with Suriname and Brazil, respectively; and more recently Approuague). Most of the patients infected by Plasmodium falciparum were followed by the medical staff of the main hospitals (Cayenne and Saint-Laurent) and of the peripheral health centers in remote areas. Consequently the epidemiological situation and evolution of chemoresistance have been widely observed on a long-term (since 1994) basis in the Maroni region. Yet, we have only partial information coming from the Oyapock valley, even though an important (most of the time) illegal immigration has been developing since the 90s' leading to a notable modification of the epidemiological status of malaria in this eastern region, including a regular increase of P. vivax infections. Presently very little P. vivax chloroquine (and mefloquine) resistance has been identified but this result could lead to a real public health problem in a near future. As such, the National Reference Center on Plasmodium Chemoresistance in the French West Indies and Guiana (CNRCP-AG in French) is a unique observatory of malaria chemoresistance in the Guyanese shield which works with research laboratories of the Institut Pasteur, Paris. This network strategy offers a very attractive perspective for applications of modern tools, including the validation of chemoresistance molecular markers, for malaria control at both medical and public health levels. Some examples related to chloroquine and artemether resistance are given.

Therapeutic efficacies of artesunate-sulfadoxine-pyrimethamine and chloroquine-sulfadoxine-pyrimethamine in vivax malaria pilot studies: relationship to Plasmodium vivax dhfr mutations.

Artemisinin-derivative combination therapies (ACT) are highly efficacious against multidrug-resistant Plasmodium falciparum malaria. Few efficacy data, however, are available for vivax malaria. With high rates of chloroquine (CQ) resistance in both vivax and falciparum malaria in Papua Province, Indonesia, new combination therapies are required for both species. We recently found artesunate plus sulfadoxine-pyrimethamine (ART-SP) to be highly effective (96%) in the treatment of falciparum malaria in Papua Province. Following a preliminary study of CQ plus sulfadoxine-pyrimethamine (CQ-SP) for the treatment of Plasmodium vivax infection, we used modified World Health Organization criteria to evaluate the efficacy of ART-SP for the treatment of vivax malaria in Papua. Nineteen of 22 patients treated with ART-SP could be evaluated on day 28, with no early treatment failures. Adequate clinical and parasitological responses were found by day 14 in all 20 (100%) of the patients able to be evaluated and by day 28 in 17 patients (89.5%). Fever and parasite clearance times were short, with hematological improvement observed in 70.6% of the patients. Double (at positions 58 and 117) and quadruple (at positions 57, 58, 61, and 117) mutations in the P. vivax dihydrofolate reductase (PvDHFR) were common in Papuan P. vivax isolates (46 and 18%, respectively). Treatment failure with SP-containing regimens was significantly higher with isolates with this PvDHFR quadruple mutation, which included a novel T-->M mutation at residue 61 linked to an S-->T (but not an S-->N) mutation at residue 117. ART-SP ACT resulted in a high cure rate for both major Plasmodium species in Papua, though progression of DHFR mutations in both species due to the continued use of SP monotherapy for clinically diagnosed malaria threatens the future utility of this combination.

Delaying antimalarial drug resistance with combination chemotherapy.

Resistance to antimalarial drugs arises when spontaneously occurring mutants with gene mutations or amplifications which confer reduced drug susceptibility are selected, and are then transmitted. Simultaneous use of two or more antimalarials with different modes of action and which therefore do not share the same resistance mechanisms will reduce the chance of selection, because the chance of a resistant mutant surviving is the product of the parasite mutation rates for the individual drugs, multiplied by the number of parasites in an infection that are exposed to the drugs. The artemisinin derivatives are very active antimalarials, which produce large reductions in parasite biomass per asexual cycle, and reduce malaria transmissibility. To date no resistance to these drugs has been reported. These drugs therefore make particularly effective combination partners. This suggests that antimalarial drugs should not be used alone in treatment, but always in combination, as in the treatment of tuberculosis or HIV, and that the combination should include artemisinin or one of its derivatives.