The Proteasome as a Drug Target in the Metazoan Pathogen, Schistosoma mansoni

ACS Infect Dis. 2019 Oct 11;5(10):1802-1812. doi: 10.1021/acsinfecdis.9b00237. Epub 2019 Aug 12.


Proteases are fundamental to successful parasitism, including that of the schistosome flatworm parasite, which causes the disease schistosomiasis in 200 million people worldwide. The proteasome is receiving attention as a potential drug target for treatment of a variety of infectious parasitic diseases, but it has been understudied in the schistosome. Adult Schistosoma mansoni were incubated with 1 μM concentrations of the proteasome inhibitors bortezomib, carfilzomib, and MG132. After 24 h, bortezomib and carfilzomib decreased worm motility by more than 85% and endogenous proteasome activity by >75%, and after 72 h, they increased caspase activity by >4.5-fold. The association between the engagement of the proteasome target and the phenotypic and biochemical effects recorded encouraged the chromatographic enrichment of the S. mansoni proteasome (Sm20S). Activity assays with fluorogenic proteasome substrates revealed that Sm20S contains caspase-type (β1), trypsin-type (β2), and chymotrypsin-type (β5) activities. Sm20S was screened with 11 peptide epoxyketone inhibitors derived from the marine natural product carmaphycin B. Analogue 17 was 27.4-fold less cytotoxic to HepG2 cells than carmaphycin B and showed equal potency for the β5 subunits of Sm20S, human constitutive proteasome, and human immunoproteasome. However, this analogue was 13.2-fold more potent at targeting Sm20S β2 than it was at targeting the equivalent subunits of the human enzymes. Furthermore, 1 μM 17 decreased both worm motility and endogenous Sm20S activity by more than 90% after 24 h. We provide direct evidence of the proteasome's importance to schistosome viability and identify a lead for which future studies will aim to improve the potency, selectivity, and safety.

Keywords: MG132; Schistosoma; bortezomib; carfilzomib; carmaphycin; proteasome; schistosomiasis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / pharmacology
  • Bortezomib / pharmacology
  • Caspases / metabolism
  • Cysteine Proteinase Inhibitors / pharmacology
  • Drug Delivery Systems / methods*
  • Hep G2 Cells
  • Humans
  • Leupeptins
  • Oligopeptides / pharmacology
  • Proteasome Endopeptidase Complex / drug effects*
  • Proteasome Inhibitors / pharmacology*
  • Schistosoma mansoni / drug effects*


  • Antineoplastic Agents
  • Cysteine Proteinase Inhibitors
  • Leupeptins
  • Oligopeptides
  • Proteasome Inhibitors
  • carmaphycin B
  • Bortezomib
  • carfilzomib
  • Caspases
  • Proteasome Endopeptidase Complex
  • benzyloxycarbonylleucyl-leucyl-leucine aldehyde