In vitro Multistage Malaria Transmission Blocking Activity of Selected Malaria Box Compounds

Abstract

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.

Keywords:

• Plasmodium
• multi-stage antimalarials
• transmission blocking drugs
• malaria elimination

Acknowledgments

The authors would like to thank the Medicines for Malaria Venture (MMV), Geneva, Switzerland, for their generous funding for this project. This research work was also supported by the Italian MIUR, PRIN2015, project 20154JRJPP “Towards multi-stage drugs to fight poverty related and neglected parasitic diseases: synthetic and natural compounds directed against Leishmania, Plasmodium and Schistosoma life stages and assessment of their mechanisms of action“ and by the Italian Ministries of Health and of Foreign Affairs/International Cooperation (MAECI), ISARP grant “New generation drugs against Plasmodium falciparum transmission for malaria eradication” PGR00948. MCule (https://mcule.com/), a pharma and biotech company is acknowledged for providing high-quality MMV Malaria Box Compounds that were used in this study.

The authors would also like to recognize the crucial research infrastructure provided by the Department of Traditional Medicine Research at the National Institute for Medical Research (NIMR) in Tanzania; the National Centre for Research and Training on Malaria (CNRFP), Ouagadougou, Burkina Faso; the Department of Pharmacological and Biomolecular Sciences and the Department of Biomedical, Surgical and Dental Sciences at the University of Milan and the School of Pharmacy at the University of Camerino, both in Italy.

The authors thank Rina Righi for her precious assistance in rearing and handling the mice used as P. berghei gametocyte donors and Paolo Rossi for his assistance in mosquito rearing and maintenance of the P. berghei model.

Author Contributions

HMM, AH and DT conceived the study, coordinated the study and were involved in all stages of the investigation. SDA, SP, SJK and HS carried out the in vitro phenotypic screening of MMV Malaria Box compounds against Plasmodium falciparum asexual and gametocyte stages. YAE, ARTG, and HS carried out activity evaluation against early sporogonic development in vitro on Plasmodium berghei Pb.CTRPp.GFP strain. All authors contributed to the data interpretation and writing of the manuscript. HMM, AH, DT and SP prepared the final version of the manuscript. All authors contributed to data analysis, drafting or revising the article, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.