Trypanosoma brucei: Killing of bloodstream forms in vitro and in vivo by the cysteine proteinase inhibitor Z-Phe-Ala-CHN2

Cysteine proteinases were tested for their suitability as targets for chemo therapy of sleeping sickness using the peptidyl inhibitor Z-Phe-Ala-diazome thyl ketone (Z-Phe-Ala-CHN2). In vitro, the inhibitory concentration of Z-P he-Ala-CHN2 required to reduce the growth rate by 50% was 400 times lower f or culture-adapted bloodstream forms of trypanosoma brucei than for a mouse myeloma cell line. At an inhibitor concentration of 10 mu M the parasites were lysed within 48 h of incubation. Parasitemia of mice infected with I: brucei decreased to undetectable levels for 3 days following treatment with 250 mg/kg Z-Phe-Ala-CHN2 on days 3 to 6 after infection. Although parasite mia returned thereafter to control levels, infected mice treated with the i nhibitor survived approximately twice as long as those treated with placebo . Z-Phe-Ala-CHN2 inhibited proteinolysis in lysosomes in vitro and almost c ompletely blocked cysteine proteinase activity in vivo. The results demonst rate the importance of cysteine proteinase activity for survival of T. bruc ei and suggest that such activity is an appropriate target for antitrypanos omal chemotherapy. (C) 1999 Academic Press.