The Neglected Tropical Diseases (NTDs) include the soil-transmitted helminthiases (STHs) which are caused by diverse groups of intestinal nematodes. The parasites include Ascaris, Trichuris and hookworms. These infections are common. Ascariasis for example, affects 1.4 billion people worldwide and is most common in children between the ages of 3 and 8. Control of these nematode parasites relies on an effective supply of anthelmintics. Taking veterinary medicine as an example, we know that continued use of anthelmintic compounds for mass chemotherapy will lead to drug resistance. There is a need to identify novel target sites for anthelmintic development. Once such site is the nicotinic acetylcholine receptor on the nematode pharynx. We have discovered this receptor does not respond to currently used anrthelmintic drugs. Approach:
The specific aims of this application are: 1. Optimize expression of C. elegans eat-2 and eat 18 and pharmacologically characterize the resulting receptor. We will investigate optimal conditions for receptor expression and characterize the resulting receptor responses using a range of agonists, antagonists and potential allosteric modulators. 2. Clone and express A. suum eat-2 and eat-18. Are other subunits required for the pharyngeal receptor? We will identify orthologs of eat-2 and eat-18 from Ascaris suum, clone, and express them in Xenopus oocytes for characterization. Additionally we will test the hypothesis that other subunit genes are required to form the receptor. 3. Do eat-2 and eat 18 combine to form the mature receptor? We will test the novel hypothesis that eat-2 and eat-18 combine to form a functional nAChR. On completion of this project we will have expressed in a heterologous system an important new potential drug target from a parasitic nematode. We will have characterized an extremely novel nAChR (one that lacks any alpha subunits). We will have identified the genes that encode these receptors in the parasitic nematode Ascaris suum. Finally, we will have determined whether the small (71 a.a.) protein eat-18 is required in the mature ion channel receptor.
The Neglected Tropical Diseases (NTDs) include soil transmitted nematode parasites like ascariasis, trichuriasis and hookworm. Ascariasis, for example, is one of the most common human parasitic infections. 1.5 billion people worldwide have ascariasis, and the disease is most common in children between the ages of 3 and 8. Treatment of helminthiasis includes use of nicotinic anthelmintics like pyrantel and oxantel which selectively paralyze nematodes by activating cholinergic ion-channels (nAChRs) on their muscle. However, resistance to anthelmintics drugs is a real concern. We have identified a novel potential target site for new anthelmintics, the nAChR on the nematode pharynx, which is not sensitive to currently used drugs. We have recapitulated a similar receptor in Xenopus oocytes and plan to confirm this is responsible for the response to nicotine in the nematode pharynx. Of great interest is this receptor contains no alpha subunits- thought to be essential for nAChR formation. The receptor is composed of a only a non- alpha subunit (eat-2) and also of note requires the co-expression of eat-18 (a small 71 aa protein) to form the functional ion channel.
|Zheng, Fudan; Robertson, Alan P; Abongwa, Melanie et al. (2016) The Ascaris suum nicotinic receptor, ACR-16, as a drug target: Four novel negative allosteric modulators from virtual screening. Int J Parasitol Drugs Drug Resist 6:60-73|