Development of an in-vitro assay for the screening of antischistosomal drugs
Duration: 1 year Project Completion: 2010
Background and Aim
Schistosomiasis is a so-called neglected tropical disease, but it affects over 200 million people and is of considerable public health significance.
Method and Results
We have compared 4 different published methods (mechanical, chemical and skin transformation of cercariae) (3, 4) for the production of schistosomula (Figure 2) with regard to quantity of schistosomula obtained, quality (worm motor activity and morphology of schistosomula) and its ease of use. We found that the most successful and convenient transformation method to artificially produce large amounts of schistosomula was the vortex transformation method. Schistosomula obtained by vortex transformation are now an important part of our drug screening cascade. For example, we have successfully used vortex produced schistosomula to describe the antischistosomal properties of mefloquine and its isomers (6, 7). In line with our findings, Abdulla and colleagues have also recently described the development of a medium throughput assay based on schistosomula, which they describe as an attractive parasite stage since adaptable to the 96-well plate format and quickly and easily transformed from cercariae that are harvestable in great numbers from vector snails (8).
Conclusions and Relevance for 3R
In conclusion, we have achieved our goal and developed a drug sensitivity test based on schistosomula, which can be obtained from infected snails, which is able to replace the adult schistosome in vitro assay. Hence, our technique reduces and replaces live animals in experimental methods in accordance with the 3Rs animal protection principles. In addition, the schistosomula screen is cost-effective and allows screening a large set of compounds (medium throughput assay), hence shortens the duration of assay turnaround times, a distinctively advantageous feature of an ideal screening assay given the urgency in discovery of new compounds.
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6. Manneck T., Y. Haggenmüller, J. Keiser (2010). Morphological effects and tegumental alterations induced by mefloquine on schistosomula and adult flukes of Schistosoma mansoni. Parasitology 137:85-98.
7. Manneck T., O. Braissant, W. Ellis, et al. (2010). Schistosoma mansoni: Antischistosomal activity of the four optical isomers and the two racemates of mefloquine on schistosomula and adult worms in vitro and in vivo. Experimental Parasitology 127: 260-269.
8. Abdulla M.H., D.S. Ruelas, B. Wolff, et al. (2009). Drug discovery for schistosomiasis: hit and lead compounds identified in a library of known drugs by medium-throughput phenotypic screening. PLoS Negl Trop Dis. 3:e478.
9. Manneck T., O. Braissant, Y. Haggenmüller, et al. Isothermal microcalorimetry to study drugs against Schistosoma mansoni. J Clin Microbiol (in press).
10. Mansour N.R., Q.D. Bickle (2010). Comparison of microscopy and Alamar blue reduction in a larval based assay for schistosome drug screening. PLoS Negl Trop Dis. 4:e795.