Protozoan and helminth parasites of humans are common in areas of extreme poverty. Treatment of these infections relies on often antiquated drugs that are toxic and/or for which resistance has developed. New drugs are needed. Microtubule-(MT) modulators are established treatments for cancer and, more recently, as experimental treatments for neurodegenerative indications such as Alzheimer’s disease. Further, tubulin is a known molecular target in both parasitic protozoa and helminths. Herein, I first developed and optimized a robust automated assay to measure the motility of C. elegans, the nematode which is often used as a convenient parasite surrogate for the screening of anthelmintics. This assay was augmented by a visual assay to measure egg-hatching. Next, a collection of 38 MT-modulators was then screened at 50 µM in both assays and a number of ‘hits’ were discovered. Further optimization of the egg-hatching assay and additional screening of MT-modulators will be pursued. Lastly, in relation to Human African Trypanosomiasis (HAT), one MT-modulator was tested in a mouse model of Trypanosoma brucei infection for anti-parasite efficacy. After intraperitoneal administration at 5, 7.5 and 10 mg/kg to infected mice, the compound decreased parasitemia in the blood to below detectable levels and significantly extended the survival of mice relative to vehicle-treated infected controls. The data encourage the further pursuit of MT-modulators for the therapy of HAT.

Worldwide, there are about 1,400 pathogens that infect humans. In particular, for the neglected diseases of poverty that are caused by eukaryotic pathogens, chemotherapy often relies on a small number of antiquated drugs that can be toxic, and for which resistance is either established or a concern. Chapter 1 introduces the 20S proteasome, its biology and the use of small molecule inhibitors to treat various cancers, such as multiple myeloma. The chapter then describes the current state-of-the-art regarding 20S proteasome inhibitor development for a range of parasitic diseases, not least, malaria and leishmaniasis, with the key point being that in spite of its conservation in life, inhibitor specificity to a particular 20S target can be achieved to deliver exciting new treatments. Chapter 2 focuses on the synthesis and application of two novel activity-based probes, LJL-1 and LJL-2, each with a different specificity for the 20 proteasome of two parasitic organisms, Leishmania donovani and Trichomonas vaginalis. The probes were designed to enable the attachment of a bifunctional fluorescent-biotin handle via click chemistry to visualize and formally identify the component catalytic β subunits for each proteasome. Also, the probes are more specific to the 20S target and offer greater functionality compared to a well-described and commercially-available product. Chapter 3 focuses on the whole-organism screening of T. brucei with and the development of a structure activity relationship (SAR) for a series of peptidyl, epoxyketone 20S inhibitors derived from the marine natural product, carmaphycin B (CPB). The compound collection stems from a campaign to develop Plasmodium falciparum 20S (Pf20S) inhibitors and the SAR arising is similar to that described for Pf20S. Not least is the strong toxicity differential between T. brucei and mammalian cells generated by the introduction of D stereochemistry at the P3 position of the CPB backbone. In a mouse model of T. brucei infection, one such inhibitor extended the survival of mice, thus, supporting the further development of this compound class as a potential treatment for African trypanosomiasis.

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Conclusions