Drugs targeting parasite lysosomes.

Lysosomes were first described as vacuolar structures containing various hydrolytic enzymes at acidic pH. Subsequent studies revealed that the lysosome/vacuolar system is complex and composed of distinct membrane-enclosed vesicles including endosomes, primary and mature lysosomes, autophagic vesicles, residual bodies, multivesicular bodies, and digestive lysosomes. Lysosomes express a battery of hydrolytic enzymes including proteases, acid phosphatases, glycosidases, and lipases. Parasitic protozoa also possess complex intracellular lysosomes/endosomes/vesicles involved in digestion, transport and recycling of molecules similar to those of mammalian cells. Unique characteristics are ascribed to lysosomes of different parasites and may even differ between parasite stages. Transport of hydrolases and proteins to parasite lysosomes is directed either from the Golgi complex via endosomal vesicles or from endocytic vesicles originated in the cell surface. Inhibition of lysosomal proteases demonstrated that different proteolytic machineries catabolize distinct classes of proteins, and this selectivity may be exploited for the development of effective antiparasitic drugs. This review describes lysosomal molecules that are either validated or potential drug targets for Chagas' disease, sleeping sickness, leishmaniasis, toxoplasmosis, malaria, amebiasis, and giardiasis.

RNA interference of Trypanosoma brucei cathepsin B and L affects disease progression in a mouse model.

We investigated the roles played by the cysteine proteases cathepsin B and cathepsin L (brucipain) in the pathogenesis of Trypansoma brucei brucei in both an in vivo mouse model and an in vitro model of the blood-brain barrier. Doxycycline induction of RNAi targeting cathepsin B led to parasite clearance from the bloodstream and prevent a lethal infection in the mice. In contrast, all mice infected with T. brucei containing the uninduced Trypanosoma brucei cathepsin B (TbCatB) RNA construct died by day 13. Induction of RNAi against brucipain did not cure mice from infection; however, 50% of these mice survived 60 days longer than uninduced controls. The ability of T. b. brucei to cross an in vitro model of the human blood-brain barrier was also reduced by brucipain RNAi induction. Taken together, the data suggest that while TbCatB is the more likely target for the development of new chemotherapy, a possible role for brucipain is in facilitating parasite entry into the brain.