A murine malaria protocol for characterizing transmission blocking benefits of antimalarial drug combinations

Background. Current efforts towards malaria elimination include the discovery of new transmission blocking (TB) drugs and identification of compounds suitable to replace primaquine, recommended as transmission blocking post treatment after artemisinin combination therapy (ACT). High through put screening of compound libraries has allowed to identify numerous compounds active in vitro against gametocytes and insect early sporogonic stages, but few studies have been performed to characterize TB compounds in vivo. Here we propose a double TB drug Direct Feeding Assay (2TB-DFA), suitable to assess the combined effects of TB compounds. Materials and methods. Plasmodium berghei GFPcon (PbGFPcon), BALB/c mice and Anopheles stephensi mosquitoes were used. Artemisinin (ART) and artesunate (AS) served as examples of artemisinins, NeemAzal® (NA), as a known TB-product with sporontocidal activity. DFA experiments were performed to assess the appropriate time point of administration before mosquito feeding and estimate suitable sub-optimal doses of the three compounds that allow combination effects to be appreciated. Results. Suboptimal dosages, that reduce about 50% of oocyst development, were recorded with ART in the range of 16-30 mg/kg, AS 14-28 mg/kg and NA 31-38mg/kg. Ten hours before mosquito feeding (corresponding to 3.5 days after mouse infection) was determined as a suitable time point for mouse treatment with ART and AS and 1 hour for post-treatment with NA. ART given at 35 mg/kg in combination with NA at 40 mg/kg reduced oocyst density by 94% and prevalence of infection by 59%. Similarly, the combination of ART at 25 mg/kg plus NA at 35 mg/kg decreased oocyst density by 95% and prevalence of infection by 34%. In the 2TB-DFA, conducted with AS (20 mg/kg) and NA (35 mg/kg) the combination treatment reduced oocyst density by 71% and did not affect prevalence of infection. Applying ‘Highest Single Agent’ analysis and considering as readout oocyst density and prevalence of infection, cooperative effects of the combination treatments, compared with the single compound treatments emerged. Conclusion. This study suggests the 2TB-DFA to be suitable for the profiling of new TB candidates that could substitute primaquine as a post-treatment to ACT courses

In vitro multistage malaria transmission blocking activity of selected Malaria Box compounds

Purpose: Continuous efforts into the discovery and development of new antimalarials are required to face the emerging resistance of the parasite to available treatments. Thus, new effective drugs, ideally able to inhibit the Plasmodium life-cycle stages that cause the disease as well as those responsible for its transmission, are needed. Eight compounds from the Medicines for Malaria Venture (MMV) Malaria Box, potentially interfering with the parasite polyamine biosynthesis were selected and assessed in vitro for activity against malaria transmissible stages, namely mature gametocytes and early sporogonic stages. Methods: Compound activity against asexual blood stages of chloroquine-sensitive 3D7 and chloroquine-resistant W2 strains of Plasmodium falciparum was tested measuring the parasite lactate dehydrogenase activity. The gametocytocidal effect was determined against the P. falciparum 3D7elo1-pfs16-CBG99 strain with a luminescent method. The murine P. berghei CTRP.GFP strain was employed to assess compounds activities against early sporogonic stage development in an in vitro assay simulating mosquito midgut conditions. Results: Among the eight tested molecules, MMV000642, MMV000662 and MMV006429, containing a 1,2,3,4-tetrahydroisoquinoline-4-carboxamide chemical skeleton substituted at N-2, C-3 and C-4, displayed multi-stage activity. Activity against asexual blood stages of both strains was confirmed with values of IC50 (50% inhibitory concentration) in the range of 0.07-0.13 µM. They were also active against mature stage V gametocytes with IC50 values below 5 µM (range: 3.43-4.42 µM). These molecules exhibited moderate effects on early sporogonic stage development, displaying IC50 values between 20 and 40 µM. Conclusion: Given the multi-stage, transmission-blocking profiles of MMV000642, MMV000662, MMV006429, and their chemical characteristics, these compounds can be considered worthy for further optimisation toward a TCP5 or TCP6 target product profile proposed by MMV for transmission-blocking antimalarials

Assessment of attitudes and practices of rural women towards malaria in Western Region, Cameroon: Strategic implications for prevention programs

M. Sanou Sobze1, J. Fokam2, J.-F. Onohiol1,∗, G.B. Djeunang Dongho1, P.M. Nkamedjie Pete1, A. Tenoh Guedoung1, G. Temgue1, V. Colizzi3, G. Russo4 1 Faculty of Sciences; University of Dschang, Dschang, Cameroon 2 Chantal Biya International Reference Centre (CIRCB) for research on HIV/AIDS prevention and management, Yaounde, Cameroon 3 University of Rome "Tor Vergata", Rome, Italy 4 Sapienza University of Rome, Rome, Ital

Plasmodium stage-selective antimalarials from Lophira lanceolata stem bark

Targeting the transmissible stages of the Plasmodium parasite that develop in the human and mosquito host is a crucial strategy for malaria control and elimination. Medicinal plants offer a prolific source for the discovery of new antimalarial compounds. The recent identification of the gametocytocidal activity of lophirone E, obtained from the African plant Lophira lanceolata (Ochnaceae), inspired the evaluation of the plant also against early sporogonic stages of the parasite development. The bioassay-guided phytochemical study led to the isolation of two known lanceolins and of a new glycosylated bichalcone, named glucolophirone C. Its stereostructure, including absolute configuration of the bichalcone moiety, was elucidated by means of NMR, HRMS, ECD and computational calculations. Lanceolin B proved to be a potent inhibitor of the development of Plasmodium early sporogonic stages indicating that the plant produces two different stage-specific antimalarial agents acting on transmissible stages in the human and mosquito host