Identifying new transmission-blocking agents
Several of the molecules progressing through clinical development and translational research have demonstrated that they can kill the sexual stages or the gametocytes in vitro. Over the last year using a Standard Membrane Feeding Assay (SMFA) in collaboration with scientists at TropIQ in the Netherlands and GSK in Spain we have shown that many of these molecules also have the potential to block the transmission of malaria in the laboratory (OZ439,1 KAE609,2 KAF156, DDD498, SJ733, PA92 and GSK030).
The assay works by allowing mosquitoes to feed on malaria-infected blood cultured in vitro, combined with a compound and then dissecting the mosquitoes to see if the parasite was able to develop. This assay has enabled us to rank compounds in terms of activity.
Dr Janneth Rodrigues, Insectary Supervisor at GSK-Tres Cantos, explains her work to establish the assay in an industrial setting.
1. What were the challenges you faced in setting up the assay and how did you overcome them?
One of the key challenges is ensuring the results remain robust and reproducible. We have a highly efficient and well trained team of people and have standardized our protocols to obtain an efficient parasite read out in the mosquito, enabling us to screen around 40 molecules per year. A key priority when working with infected mosquitoes is biosafety – we need to ensure no infected mosquitoes escape. The insectary at GSK is a Biosafety Level 33 facility, which means we are extremely careful about this.
Another challenge is to keep the mosquito breeding environment as close to real life as possible. In industry, we work in extremely clean and sterile environments and we observed that from generation to generation the mosquitoes lose their natural bacterial flora – even mosquitoes have bacteria in their guts just like you and I. This flora is actually important for transmission. We have now changed the breeding protocol to make it more realistic.
2. How many molecules have you been able to analyze and what did you find?
So far, we have analyzed 40 molecules, 15 of which have been fully profiled, meaning that we have assessed them in different concentrations to understand the dose and response relationship. Some molecules are extremely promising and are in clinical development, for example, OZ439 and KAE609. GSK assets like the dione, thiotriazole and aminoindole series have also shown transmissionblocking potential in the assay. GSK030 from the thiotriazole series was declared a preclinical candidate in 2014. This is something we are really excited about.
We also want to increase the efficiency of the assay by decreasing the number of mosquitoes per assay, as well as minimizing the labour intensive mosquito dissections and parasite counting postinfection. We are looking at several options. Lots of progress is being made so it’s an exciting time to be involved!
1. Delves M et al. “The activities of current antimalarial drugs on the life cycle stages of Plasmodium: a comparative study with human and rodent parasites.” PLoS Med. 9(2):e1001169 (2012).
2. van Pelt-Koops JC et al. “The spiroindolone drug candidate NITD609 potently inhibits gametocytogenesis and blocks Plasmodium falciparum transmission to anopheles mosquito vector.” Antimicrob Agents Chemother. 56(7):3544-8 (2012).
3. Biosafety level: level of the biocontainment precautions required to isolate dangerous biological agents in an enclosed laboratory facility. The levels of containment range from the lowest biosafety level 1 to the highest at level 4.
Dr Janneth Rodrigues, Insectary Supervisor at GSK-Tres Cantos