Development of PTLS-209 for treatment for giardiasis

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Project Summary: This project focuses on the development of treatment to combat giardiasis resistance to standard care drugs. Giardia lamblia is a highly infective waterborne parasite that causes severe diarrhea. Current antigiardiasis drugs fail in about 20% of cases, and they all have undesirable side effects. Additionally, drug-resistant G. lamblia strains can be readily raised in the laboratory, increasing the risk of this category B bioterrorism organism. Chronic infection of giardiasis and lack of treatment in developing countries lead to malnutrition, growth retardation in children, and death. Thus, the prevalence of giardiasis impacts global health profoundly, and the World Health Organization has included giardiasis in its Neglected Diseases Initiative. Our collaborators and NCATS/NIH investigators identified fumagillin as a lead compound through screening an approved drug library. Fumagillin kills Giardia trophozoites in vitro with high potency via MetAP2 inhibition. It has also shown excellent efficacy in an in vivo mouse model; however, it has two liabilities: heat and humidity instability, as well as potential toxicity in humans. These liabilities hamper the further development of fumagillin. We addressed these issues during our lead optimization process and identified PTLS-209, which has high potency for MetAP2, low bioavailability, improved efficacy, and enhanced stability. Thus, PTLS-209 has the ideal attributes to be an effective and safe intestinal targeting drug for treating giardiasis, particularly drug-resistant giardiasis. The arsenal of drugs available for treating giardiasis belongs to only a few chemical classes, primarily nitroimidazoles, thiazolides, and benzimidazoles. G. lamblia drug resistance already exists for each of these classes of compounds. None of the currently used drugs to treat giardiasis act on the MetAP2 enzyme. Thus, PTLS-209, a fumagillin analog, will not be subject to the current drug resistance mechanisms that result in treatment failures. PTLS-209 has an excellent safety profile, while other analogs of the fumagillin class, beloranib, ZGN-1061, and ZGN-1258, have shown adverse effects in preclinical studies and clinical trials. Note that these analogs were administered subcutaneously, whereas PTLS-209 is administered orally and has a very low oral bioavailability in mice (which may be the cause of its low toxicity). In order to mitigate the risks early, we have adopted the “Fail Early, Fail Cheap” approach. We propose two critical tests to evaluate these toxicity concerns in our SBIR Phase I portion of the Fast-Track application. Once we meet our Phase I milestones, we will continue IND-enabling studies to ensure that PTLS-209 has all the attributes to be a successful treatment for giardiasis and will file an IND application.