DISCOVERY OF A NOVEL TARGET FOR GIARDIASIS

Project SummaryThe waterborne pathogen, Giardia lamblia, is a major cause of parasite-induceddiarrheal diseases worldwide, including the U.S. Giardia has a biphasic life cycle?i.e.,replicative trophozoites and relatively dormant but viable cysts. While cysts areresponsible for the transmission of Giardia through sewage-contaminated water,trophozoites colonize the upper portion of the human small intestine and cause theinfection (called ?giardiasis?), which can be symptomatic or non-symptomatic. Thesymptoms of giardiasis include diarrhea, irritable bowel syndrome (IBS), indigestion andgastro-intestinal discomfort. Children in low-resource settings are especially vulnerableto the infection and often suffer from malnutrition and age-specific development. Clinicalresistance has been reported for all prescribed anti-giardial agents, includingmetronidazole with reports of treatment failure rates increasing from 15% in 2008 to40% in 2013. We recently reported that oseltamivir was active against Giardia in culture.This led to our discovery that the active metabolite of oseltamivir (oseltamivir-free acidor OFA) is a potent inhibitor of trophozoite growth and cyst formation in laboratoryculture. Because oseltamivir inhibits neuraminidases, our further investigation led to thediscovery of a previously unreported giardial sialidase (gSial). This application isfocused on exploitation of the abovementioned discoveries. Specifically, we aim toexamine if this novel non-metronidazole class of anti-giardial agents has clinicalpotential for treatment of giardiasis, as well as to elucidate their mechanism of action.These anti-giardia agents are likely to have a different mode of action from currentagents (inhibition of giardial sialidase) and therefore should be active against strains ofGiardia resistant to current therapeutics. In Specific Aim-1, we will synthesize and testseveral OFA analogues on giardial growth and encystation in vitro (in culture) and invivo (in mice). In Specific Aim-2, we seek to characterize gSial (a presumed target ofOFAs in Giardia) by biochemical and molecular methodologies. The interactionsbetween OFAs and gSial will also be investigated. Thus, the successful completion ofthis project?s aims should lead to the discovery of a novel lead for further developmentagainst giardiasis and validation of giardia sialidase as a novel drug target for giardiasis.Much is known about oseltamivir and its active metabolite and this should facilitaterepositioning of this class of drugs for giardiasis.