Development of novel strategies to fill the empty drug pipeline for schistosomiasis: from drug sensitivity assay development to preclinical studies

Schistosomiasis is a neglected tropical disease caused by Schistosoma spp. parasites. It affects more than 200 million people and 700 million more are at risk. Over 10’000 people die every year because of the disease, but this number might be a big underestimation. While the disease is endemic in 78 countries and affects mostly poor communities without access to clean water, the highest prevalence for the disease is found in sub-Saharan Africa with over 85% of the overall occurrences. Children are at especially high risk of exposure through activities such as playing or bathing in infested water bodies. Schistosomiasis is a debilitating disease; the loss of productivity and mortality associated with the disease have a negative effect on the emerging countries' economies, which causes people to be stuck in a negative feedback loop of poverty and public health problems. Poor sanitation and unawareness of the general population are the main reasons for the transmission of schistosomiasis. The first symptoms of the disease are red bumps on the skin, usually appearing a few hours after infection and sometimes followed by mild fever and nausea. However, the chronic effects are more serious. In fact, children affected by the disease often show developmental delays and adults may develop chronic hepatic damage and eventually liver failure. There is only one drug available for mass drug administration (MDA) campaigns: praziquantel. There is growing evidence of a decreasing efficacy of praziquantel against Schistosoma spp. There is no vaccine available and the drug pipeline to treat schistosomiasis is empty. The overwhelming prevalence of schistosomiasis in the developing world and the absence of novel drug candidates against the disease are provoking fear of resistance emergence among the handful of laboratories involved in the fight against this neglected tropical disease (NTD). The research of novel compounds moves slowly and one of the main reasons for this is the difficulty in finding a reliable and faster drug screening method that would increase the drug screening output and the concordance between laboratories involved in the drug screening process. During my PhD, I worked on different projects tackling schistosomiasis, searching for ways to speed up drug screening processes and to contribute to the currently empty drug pipeline. I worked on a protocol, in which we detail all the aspects of the drug screening procedure, with the aim to familiarize new laboratories with the procedures as we do them here at Swiss TPH, in order to decrease the methodological fragmentation in the field. I worked on the development of novel drug screening platforms and new methods to identify potential drug candidates. In collaboration with the Department of Biosystems Science and Engineering (D-BSSE) of ETH located in Basel, we developed a novel platform for antischistosomal drug screening based on microfluidic electrical impedance spectroscopy (EIS). Also, I worked on a human liver microtissue-based system to assess the liver metabolism for extending the standard drug screening assays in vitro on NTS to prodrugs, and to evaluate the liver metabolism's effect on the compounds’ activity on NTS in vitro. I first validated the system with praziquantel and then quantified the amount of compound metabolised and tested the effect of the liver metabolites on NTS in vitro with other compounds that are approved for human medicine. Finally, in an attempt to resolve the issue of praziquantel's low solubility, I collaborated with the University of Trieste in the development and testing of a novel formulation of praziquantel. This novel praziquantel formulation was based on a polymorph co-crystal provided by the University of Trieste. I tested this formulation derivative in vivo and in vitro to compare it to the standard praziquantel to evaluate its activity. I quantified praziquantel enantiomers by LC-MS/MS in mice plasma and compared the pharmacokinetics of the standard praziquantel with the polymorph praziquantel derivative. In this thesis, all of the above-mentioned projects are contextualised and discussed.