 |
3R-Project 110-08
Development of an in-vitro assay for the screening of antischistosomal drugs
Jennifer Keiser
Swiss Tropical Institute, University Basel, CH-4002 Basel, Switzerland
jennifer.keiser@unibas.ch
Keywords: human; rodents; infectious diseases; cell cultures: parasites; replacement; drug screening
Duration: 1 year End of the Project: 2009
Background and Aim
Schistosomiasis is a so-called neglected tropical disease, but it affects over 250 million people and is of considerable public health significance.
The treatment and control of schistosomiasis virtually relies on a single drug: praziquantel. The pressing need to develop new antischistosomal compounds has been stressed, particularly in view of the blanket application of praziquantel within the frame of preventive chemotherapy, a strategy that might select for drug-resistant parasites (1). The current in-vitro screening protocols are based on juvenile and adult schistosomes, obtained by portal perfusion from the mouse or hamster, hence rely on infected rodents and allow only a small number of molecules to be tested (2). Our goal is to develop a reliable in-vitro antischistosomal drug sensitivity assay, with high sensitivity for screening large numbers of compounds based on schistosomula, which can be obtained from infected snails, as depicted in Figure 1.
Method and Results
in progress (present status)
In a first step we will compare different published methods (mechanical, chemical and skin transformation of cercariae) (3, 4) for the production of schistosomula (Fig.2) with regard to quantity of schistosomula obtained, quality (worm motor activity and morphology of schistosomula) and its ease of use. In a next step, a series of media will be tested and compared as it is necessary for our drug screening assay to maintain schistosomula for at least 4 days in vitro without loss of activity and morphological changes of schistosomula. In order to determine whether the effect of drugs on schistosomula is similar to the effect on juvenile and adult schistosomes (the two stages in the human body, hence the worm stages which need to be targeted by drugs) in vitro, we will test the effect of a variety of compounds, with known in vivo antischistosomal activity (e.g. praziquantel, oxamniquine, artemether, artesunate, different synthetic trioxolanes) and compounds that possess no antischistosomal activity (e.g. sulfadoxine, pyrimethamine) against schistosomula. The effect of drugs will be analyzed based primarily on motility disturbances (e.g. activity or paralysis), morphological changes (relaxation, shrinkage, curling, tegumental disruption, worm disintegration) and worm death, but we will also search for a biochemical indicator.
Conclusions and Relevance for 3R
Our ultimate goal is to replace the adult schistosome in vitro assay with a drug sensitivity test based on schistosomula, which can be obtained from infected snails. While schistosomula have been used to answer various biological research questions, they have never been used for the discovery and characterization of novel antischistosomal drugs. Hence, our technique would reduce and replace live animals in experimental methods in accordance with the 3Rs animal protection principles. In addition, a schistosomula screen will definitely shorten the duration of assay turnaround times, a distinctively advantageous feature of an ideal screening assay given the urgency in discovery of new compounds. As a large number of schistosomula can be obtained it would allow screening a large set of compounds and it would be cost-effective.
References
1. Keiser J, Utzinger J. Advances in the discovery and development of novel trematocidal drugs. Expert Opin Drug Discov 2007; 2: 9-23.
2. Ramirez B, Bickle Q, Yousif F, et al. Schistosomes: Challenges in drug screening. Exp Opin Drug Discov 2007; 2: 53-61.
3. Brink LH, McLaren DJ, Smithers SR. Schistosoma mansoni: a comparative study of artificially transformed schistosomula and schistosomula recovered after cercarial penetration of isolated skin. Parasitology 1977; 74: 73-86.
4. Ramalho-Pinto FJ, Gazzinelli G, Howells RE, et al. Schistosoma mansoni: defined system for stepwise transformation of cercaria to schistosomule in vitro. Exp Parasitol 1974; 36: 360-72.
Figures
Figure 1: Schistosomiasis - Life Cycle: Human-Snail phase.
Figure 2: Picture of schistosomula
| Dernières modifications: 29.08.2010 |  |