Cysteine Proteinase Inhibitors Kill Cultured Bloodstream Forms ofTrypanosoma brucei brucei

Abstract

Troeberg, L., Morty, R. E., Pike, R. N., Lonsdale-Eccles, J. D., Palmer, J. T., McKerrow, J. H., and Coetzer, T. H. T. 1999. Cysteine proteinase inhibitors kill cultured bloodstream forms ofTrypanosoma brucei brucei. Experimental Parasitology91, 349–355.Trypanosoma brucei bruceiis a causative agent of bovine trypanosomiasis (nagana), a disease of considerable economic significance in much of Africa. Here we report investigations on the effects of various irreversible cysteine proteinase inhibitors, including vinyl sulfones (VS), peptidyl chloromethylketones (CMK), diazomethylketones, and fluoromethyl ketones, on the major lysosomal cysteine proteinase (trypanopain-Tb) ofT. b. bruceiand onin vitro-cultured bloodstream forms of the parasite. Many of the tested inhibitors were trypanocidal at low micromolar concentrations. Methylpiperazine urea-Phe-homoPhe-VS was the most effective trypanocidal agent, killing 50% of test populations at a work ing concentration of 0.11 μM, while carbobenzoxy-Phe-Phe-CMK was the most trypanocidal of the methylketones with an IC50of 3.6 μM. Labelling of live and lysedT. b. bruceiwith biotinylated inhibitor derivatives suggests that trypanopain-Tb is the likely intracellular target for these inhibitors. Kinetic analysis of the inhibition of purified trypanopain-Tb by the inhibitors showed that most hadkassvalues in the 106M−1s−1range. We conclude that cysteine proteinase inhibitors have potential as trypanocidal agents and that a major target of these compounds is the lysosomal enzyme trypanopain-Tb.