title: Trypanocidal and cysteine protease inhibitory activity of isopentyl caffeate is not linked in Trypanosoma brucei.
abstract: Previously, it was reported that caffeic acid esters inhibit the growth of bloodstream forms of Trypanosoma brucei and the activity of its major lysosomal cathepsin L-like cysteine protease, TbCATL. However, whether this trypanocidal activity is due to inactivation of TbCATL has not so far been demonstrated. Caffeic acid isopentyl ester (isopentyl caffeate) displayed antitrypanosomal activity against T. brucei bloodstream forms with minimum inhibitory concentration (MIC) and 50 % growth inhibition (GI50) values of 1 and 0.31 μg/ml, respectively. The ester also inhibited the activity of purified TbCATL but with a 27-fold higher half maximal inhibitory concentration (IC50) value of 8.5 μg/ml compared to its GI50value. In contrast to previous suggestion, isopentyl caffeate did not interact with the active site of TbCATL but inhibited the enzyme in a non-competitive way. In addition, the ester was ineffective in blocking the proteolysis in the lysosome of the parasite, which, however, is a hallmark for inhibitors whose trypanocidal action is through inactivation of TbCATL. These results suggest that the antitrypanosomal activity of isopentyl caffeate (and probably of other caffeic acid esters) cannot be attributed to inhibition of TbCATL. Nevertheless, caffeic acid esters are interesting compounds with promising antitrypanosomal activity. This is supported by a more than 100 times less sensitivity of human HL-60 cells to isopentyl caffeate indicating that the ester has a favourable selectivity profile.
authors.affiliation: Bob Champion Research and Education Building, Norwich Medical School, University of East Anglia, Norwich Research Park, James Watson Road, Norwich, NR4 7UQ, UK. dsteverding@hotmail.com.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Steverding
authors.affiliation: Department of Pharmaceutical Sciences, Laboratory of Pharmaceutical Chemistry, Federal University of Paraiba, João Pessoa, Brazil.
authors.forename: Flávio Rogério
authors.initials: FR
authors.lastname: da Nóbrega
authors.affiliation: Bob Champion Research and Education Building, Norwich Medical School, University of East Anglia, Norwich Research Park, James Watson Road, Norwich, NR4 7UQ, UK.
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Rushworth
authors.affiliation: Department of Pharmaceutical Sciences, Laboratory of Pharmaceutical Chemistry, Federal University of Paraiba, João Pessoa, Brazil.
authors.forename: Damião Pergentino
authors.initials: DP
authors.lastname: de Sousa
mesh_terms: D000818:Animals; D002109:Caffeic Acids / Q000494:pharmacology*; D056668:Cathepsin L / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D008826:Microbial Sensitivity Tests; D014344:Trypanocidal Agents / Q000494:pharmacology*; D014346:Trypanosoma brucei brucei / Q000187:drug effects*
chemical_list: D002109:Caffeic Acids; D014344:Trypanocidal Agents; C000619453:isopentyl caffeate; D056668:Cathepsin L
keywords: Cysteine protease; Isopentyl caffeate; Non-competitive inhibition; Trypanosoma brucei