Therapeutic response to artemisinin combination therapies among individuals with Plasmodium falciparum single infection vs mixed Plasmodium species infections: a retrospective posthoc analysis in Kisumu County, western Kenya.

OBJECTIVES: This study examined the treatment response of mixed vs single-species Plasmodium falciparum infections to artemisinin-based combination therapies (ACTs). METHODS: A total of 1211 blood samples collected on days 0, 7, 14, 21, 28, 35, and 42 from 173 individuals enrolled in two randomized ACT efficacy studies were tested for malaria using 18s ribosomal RNA-based real-time polymerase chain reaction. All recurrent parasitemia were characterized for Plasmodium species composition and time to reinfection during 42-day follow-up compared across ACTs. RESULTS: Day 0 samples had 71.1% (116/163) single P. falciparum infections and 28.2% (46/163) coinfections. A total of 54.0% (88/163) of individuals tested positive for Plasmodium at least once between days 7-42. A total of 19.3% (17/88) of individuals with recurrent infections were infected with a different Plasmodium species than observed at day 0, with 76.5% (13/17) of these "hidden" infections appearing after clearing P. falciparum present at day 0. Artesunate-mefloquine (16.4 hours) and dihydroartemisinin-piperaquine (17.6 hours) had increased clearance rates over artemether-lumefantrine (21.0 hours). Dihydroartemisinin-piperaquine exhibited the longest duration of reinfection prophylaxis. Cure rates were comparable across each species composition. CONCLUSION: No differences in clearance rates were found depending on whether the infection contained species other than P. falciparum. Significantly longer durations of protection were observed for individuals treated with dihydroartemisinin-piperaquine.

Characterization of sulfated polysaccharide activity against virulent Plasmodium falciparum PHISTb/RLP1 protein.

Background: The emergence of artemisinin resistance in South East Asia calls for urgent discovery of new drug compounds that have antiplasmodial activity. Unlike the classical compound screening drug discovery methods, the rational approach involving targeted drug discovery is less cumbersome and therefore key for innovation of new antiplasmodial compounds.  Plasmodium falciparum (Pf) utilizes the process of host erythrocyte remodeling using Plasmodium-helical interspersed sub-telomeric domain (PHIST) containing proteins, which are amenable drug targets. The aim of this study is to identify inhibitors of PHIST from sulfated polysaccharides as new antimalarials. Methods: 251 samples from an ongoing study of epidemiology of malaria and drug resistance sensitivity patterns in Kenya were sequenced for PHISTb/RLP1 gene using Sanger sequencing. The sequenced reads were mapped to the reference Pf3D7 protein sequence of PHISTb/RLP1 using CLC Main Workbench. Homology modeling of both reference and mutant protein structures was achieved using the LOMETs tool. The models were refined using ModRefiner for energy minimization. Ramachandran plot was generated by ProCheck to assess the conformation of amino acids in the protein model. Protein binding sites predictions were assessed using FT SITE software. We searched for prospective antimalarials from PubChem. Docking experiments were achieved using AutoDock Vina and analysis results visualized in PyMOL. Results: Sanger sequencing generated 86 complete sequences. Upon mapping of the sequences to the reference, 12 non-synonymous single nucleotide polymorphisms were considered for mutant protein structure analysis. Eleven drug compounds with antiplasmodial activity were identified. Both modelled PHISTb/RLP1 reference and mutant structures had a Ramachandran score of >90% of the amino acids in the favored region. Ten of the drug compounds interacted with amino acid residues in PHISTb and RESA domains, showing potential activity against these proteins. Conclusion: These interactions provide lead compounds for new anti-malarial molecules. Further in vivo testing is recommended.