Altered expression of cruzipain and a cathepsin B-like target in a Trypanosoma cruzi cell line displaying resistance to synthetic inhibitors of cysteine-proteinases.

The therapeutic potential of synthetic inhibitors to the major cysteine-proteinase from Trypanosoma cruzi (cruzain or cruzipain) was recently demonstrated in animal models of Chagas' disease. A possible limitation of this strategy would be the emergence of parasite populations developing resistance to cysteine-proteinase inhibitors. Here, we describe the properties of a phenotypically stable T. cruzi cell line (R-Dm28) that displays increased resistance to Z-(SBz)Cys-Phe-CHN2, an irreversible cysteine-proteinase inhibitor which preferentially inactivates cathepsin L-like enzymes. Isolated from axenic cultures of the parental cells (IC50 1.5 microM), R-Dm28 epimastigotes exhibited 13-fold (IC50) 20 microM) higher resistance to this inhibitor and did not display cross-resistance to unrelated trypanocidal drugs, such as benznidazol and nifurtimox. Western blotting (with mAb), affinity labeling (with biotin-LVG-CHN2) and FACS analysis of R-Dm28 log-phase epimastigotes revealed that the cruzipain target was expressed at lower levels, as compared with Dm28c. Interestingly, this deficit was paralleled by increased expression of an unrelated Mr 30 000 cysteine-proteinase whose activity was somewhat refractory to inhibition by Z-(SBz)Cys-Phe-CHN,. N-terminal sequencing of the affinity-purified biotin-LVG-proteinase complex allowed its identification as a cathepsin B-like enzyme. Increased antigenic deposits of this proteinase were found in the grossly enlarged and electron dense reservosomes from R-Dm28 epimastigotes. Our data suggest that R-Dm28 resistance to toxic effects induced by the synthetic inhibitor may result from decreased availability of the most sensitive cysteine-proteinase target, cruzipain. The deficit in metabolic functions otherwise mediated by this cathepsin L-like proteinase is likely compensated by increased expression/accumulation of a cathepsin B-like target.