title: Trypanosoma brucei: chemical evidence that cathepsin L is essential for survival and a relevant drug target.
abstract: The protozoan parasite causing human African trypanosomiasis, Trypanosoma brucei, displays cysteine peptidase activity, the chemical inhibition of which is lethal to the parasite. This activity comprises a cathepsin B (TbCATB) and a cathepsin L (TbCATL). Previous RNA interference (RNAi) data suggest that TbCATB rather than TbCATL is essential to survival even though silencing of the latter was incomplete. Also, chemical evidence supporting the essentiality of either enzyme which would facilitate a target-based drug development programme is lacking. Using specific peptidyl inhibitors and substrates, we quantified the contributions of TbCATB and TbCATL to the survival of T. brucei. At 100 μM, the minimal inhibitory concentration that kills all parasites in culture, the non-specific cathepsin inhibitors, benzyloxycarbonyl-phenylalanyl-arginyl-diazomethyl ketone (Z-FA-diazomethyl ketone) and (l-3-trans-propylcarbamoyloxirane-2-carbonyl)-l-isoleucyl-l-proline methyl ester (CA-074Me) inhibited TbCATL and TbCATB by >99%. The cathepsin L (CATL)-specific inhibitor, ((2S,3S)-oxirane-2,3-dicarboxylic acid 2-[((S)-1-benzylcarbamoyl-2-phenyl-ethyl)-amide] 3-{[2-(4-hydroxy-phenyl)-ethyl]-amide}) (CAA0225), killed parasites with >99% inhibition of TbCATL but only 70% inhibition of TbCATB. Conversely, the cathepsin B (CATB)-specific inhibitor, (l-3-trans-propylcarbamoyloxirane-2-carbonyl)-l-isoleucyl-l-proline (CA-074), did not affect survival even though TbCATB inhibition at >95% was statistically indistinguishable from the complete inhibition by Z-FA-diazomethyl ketone and CA-074Me. The observed inhibition of TbCATL by CA-074 and CA-074Me was shown to be facilitated by the reducing intracellular environment. All inhibitors, except the CATB-specific inhibitor, CA-074, blockaded lysosomal hydrolysis prior to death. The results suggest that TbCATL, rather than TbCATB, is essential to the survival of T. brucei and an appropriate drug target.
authors.affiliation: Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich NR4 7TJ, UK. dsteverding@hotmail.com
authors.forename: Dietmar
authors.initials: D
authors.lastname: Steverding
authors.forename: Darren W
authors.initials: DW
authors.lastname: Sexton
authors.forename: Xia
authors.initials: X
authors.lastname: Wang
authors.forename: Sebastian S
authors.initials: SS
authors.lastname: Gehrke
authors.forename: Gerd K
authors.initials: GK
authors.lastname: Wagner
authors.forename: Conor R
authors.initials: CR
authors.lastname: Caffrey
mesh_terms: D000981:Antiprotozoal Agents / Q000494:pharmacology; D056668:Cathepsin L / Q000235:genetics / Q000502:physiology*; D002470:Cell Survival; D008826:Microbial Sensitivity Tests; D011480:Protease Inhibitors / Q000494:pharmacology; D015800:Protozoan Proteins / Q000235:genetics / Q000502:physiology*; D014346:Trypanosoma brucei brucei / Q000472:pathogenicity / Q000502:physiology*; D037521:Virulence Factors / Q000235:genetics / Q000502:physiology*
chemical_list: D000981:Antiprotozoal Agents; D011480:Protease Inhibitors; D015800:Protozoan Proteins; D037521:Virulence Factors; D056668:Cathepsin L