Trypanosoma brucei: β2-selective proteasome inhibitors do not block the proteasomal trypsin-like activity but are trypanocidal

Abstract

Please cite this article as: Steverding D, Florea BI, Overkleeft HS, Trypanosoma brucei: ␤2-selective proteasome inhibitors do not block the proteasomal trypsin-like activity but are trypanocidal, Molecular and amp; Biochemical Parasitology (2018), https://doi.

Trypanosoma brucei: Inhibition of cathepsin L is sufficient to kill bloodstream forms

“…LU-102 showed a dose-dependent effect on the growth of trypanosomes with a MIC (minimum inhibitory concentration, i.e., that concentration of a compound at which all cells were killed) value of 25 µM and a GI50 (50% growth inhibition, i.e., that concentration of a compound necessary to reduce the growth rate of cells by 50% to that of controls) value 10.2 μM ( Fig 2B). Whereas a MIC value was not determined previously, the GI50 value was comparable to that recently published (6.9 µM [8]). Based on the findings that LU-102 does not inhibit TbCATB (see above) and the trypsin-like activity of the trypanosomal proteasome [8], the trypanocidal activity of the compound seems to be solely due to inhibition of TbCATL, indicating that blocking the activity of TbCATL is sufficient to kill bloodstream forms of T. brucei.…”

“…Whereas a MIC value was not determined previously, the GI50 value was comparable to that recently published (6.9 µM [8]). Based on the findings that LU-102 does not inhibit TbCATB (see above) and the trypsin-like activity of the trypanosomal proteasome [8], the trypanocidal activity of the compound seems to be solely due to inhibition of TbCATL, indicating that blocking the activity of TbCATL is sufficient to kill bloodstream forms of T. brucei.…”

“…Although we have recently shown that LU-102 at 10 µM did not significantly inhibit the trypsin-like activity of the trypanosomal proteasome in cell extracts [8], there might be the possibility that at the higher concentration of 25 µM the compound inhibits the proteasomal trypsin-like activity more readily facilitated by the intracellular reducing environment. To exclude this possibility, bloodstream forms of T. brucei were incubated with 25 µM LU-102 for 2 h and the proteasomal trypsin-like activity in cell extracts was subsequently measured using the fluorogenic trypsin-like peptide substrate Boc-LSTR-AMC.…”

“…The compound LU-102 is a peptidyl vinyl sulfone and was initially developed as an inhibitor of the trypsin-like activity of the mammalian proteasome [7]. By contrast, LU-102 was recently shown not to inhibit the trypsin-like activity of the proteasome of T. brucei [8].…”

“…The observed trypanocidal activity of LU-102 was subsequently attributed to the activity of the compound to inhibit also cathepsins [7,8]. Other targets could be excluded because peptidyl vinyl sulfones react exclusively with active site cysteine sulfhydryl and threonine hydroxyl; they do not react with the serine hydroxyl of serine proteases [9].…”