Trematode flatworms of the genus Schistosoma are the causative agents of schistosomiasis. One potential physiological target for new anti-schistosoma drugs is the worm's system for excretion of wastes and xenobiotics. P-glycoprotein (Pgp), a member of the ATP-binding cassette superfamily of proteins, is an ATP-dependent efflux pump involved in transport of toxins and xenobiotics from cells. In vertebrates, Pgp is the product of the multi-drug-resistance 1 gene, which is amplified and over-expressed in tumor cells that show broad drug resistance. Pgp may also play a role in drug resistance in helminths. A schistosome Pgp cDNA (SMDR2) was sequenced several years ago, but has not been functionally characterized. The long-term goal of this proposal is to dissect the functional role and pharmacological sensitivities of SMDR2 and other schistosome drug transporters. We will adapt a calcein fluorescence assay to examine the substrate and inhibitor specificities of expressed SMDR2 and other transporters. We will also examine the effects of praziquantel, the current antischistosomal of choice, on expression of SMDR2, and whether praziquantel-resistant isolates have altered expression of this or other transporters. Finally, we will examine the effect on the parasite of genetic or pharmacological disruption of SMDR2.
The specific aims of the project are to answer the following questions: 1. What are the biochemical properties and substrate specificities of SMDR2 and other schistosome drug transporters expressed in mammalian cells? 2. What is the tissue distribution and developmental profile of SMDR2 and other schistosome multi-drug transporters? 3. Does exposure to agents such as PZQ result in changes in SMDR2 expression or distribution? 4. Do isolates of worms with reduced susceptibility to PZQ show differences in expression levels of SMDR2 or other multidrug transporters? 5. What effects do genetic and pharmacological disruption of SMDR2 have on parasite survival, physiology and pharmacological sensitivities/relevance: Schistosomiasis is a major tropical disease caused by parasitic flatworms called schistosomes. Potential physiological targets for new drugs against schistosomiasis might be the transporters that remove wastes and toxins from schistosome cells. We propose to use several approaches to determine the properties of one such schistosome molecule, P-glycoprotein, which, in vertebrates, is also involved in resistance to a broad array of drugs.
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