: Cryptosporidium parvum is an enteric pathogen causing diarrheal disease of humans. The disease causes chronic illness in children, the elderly, and immunocompromised individuals. The number of cases have soared since the emergence of the Acquired Immune Deficiency Syndrome (AIDS) pandemic, and cryptosporidiosis is now recognized as one of the most common human enteric infections. Since the infamous outbreak in Milwaukee, WI, of water borne cryptosporidiosis affecting over 400,000 people, there have been at least 20 other smaller outbreaks associated with this parasite in the USA. A major issue is the unusual degree of resistance that Cryptosporidium has shown to antiprotozoan and antimicrobial agents. We have demonstrated the presence of a plant- like polyamine biosynthetic pathway in C. parvum that is inhibited by difluoromethylarginine, a specific irreversible inhibitor of arginine decarboxylase. We have also shown that C. parvum transports polyamines avidly and has the ability to back-convert spermine to spermidine and putrescine via a coupled spermidine:spermine N about-acetyltransferase (SSAT)/polyamine oxidase (PAO) pathway. We have tested a number of bis ethyl conformationally restricted and unrestricted polyamine analogues as potential regulators of the polyamine backconversion pathway. Our results demonstrate that certain conformationally restricted polyamine analogues are very effective uncompetitive inhibitors of the C. parvum SSAT. Members of this class of inhibitor were also found to be effective at curing an immunosuppressed mouse model infection. We propose to extend these studies to examine the structural requirements of the polyamine analogues that will result in the most effective inhibition of SSAT activity.
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