Profound Activity of the Anti-cancer Drug Bortezomib against Echinococcus multilocularis Metacestodes Identifies the Proteasome as a Novel Drug Target for Cestodes

Abstract

A library of 426 FDA-approved drugs was screened for in vitro activity against E. multilocularis metacestodes employing the phosphoglucose isomerase (PGI) assay. Initial screening at 20 µM revealed that 7 drugs induced considerable metacestode damage, and further dose-response studies revealed that bortezomib (BTZ), a proteasome inhibitor developed for the chemotherapy of myeloma, displayed high anti-metacestodal activity with an EC50 of 0.6 µM. BTZ treatment of E. multilocularis metacestodes led to an accumulation of ubiquinated proteins and unequivocally parasite death. In-gel zymography assays using E. multilocularis extracts demonstrated BTZ-mediated inhibition of protease activity in a band of approximately 23 kDa, the same size at which the proteasome subunit beta 5 of E. multilocularis could be detected by Western blot. Balb/c mice experimentally infected with E. multilocularis metacestodes were used to assess BTZ treatment, starting at 6 weeks post-infection by intraperitoneal injection of BTZ. This treatment led to reduced parasite weight, but to a degree that was not statistically significant, and it induced adverse effects such as diarrhea and neurological symptoms. In conclusion, the proteasome was identified as a drug target in E. multilocularis metacestodes that can be efficiently inhibited by BTZ in vitro. However, translation of these findings into in vivo efficacy requires further adjustments of treatment regimens using BTZ, or possibly other proteasome inhibitors.

Bortezomib initiates endoplasmic reticulum stress, elicits autophagy and death in Echinococcus granulosus larval stage

“…The Echinococcus genome decoding [ 19 – 20 ] has provided powerful tools to find new drug targets with potential use in chemo-treatment. In accordance with the findings reported by Tsai et al [ 19 ], Stadelmann et al [ 18 ] have described in vitro and in vivo anthelmintic activity of Bz in metacestodes of E . multilocularis .…”

“…Interestingly, Bz was also tested for in vitro activity against different protozoan parasites such as Plasmodium and Trypanosoma [ 16 – 17 ]. Recently, Bz was assayed as a potential candidate against the metacestode life-stage of Echinococcus multilocularis (fox tapeworm), the causative cestode of alveolar echinococcosis, a zoonosis limited to the northern hemisphere [ 18 ]. Previously, Tsai et al [ 19 ] had identified all proteasome subunits as a top predicted targets based on proteome data in this cestode.…”

Treatment of echinococcosis: albendazole and mebendazole – what else?

“…More recently, screening of a commercially available FDA-approved drug library comprised of over 400 drugs that are currently in use against different diseases resulted in the identification of the profound activity of bortezomib, a proteasome inhibitor used as an anti-cancer drug, against E. multilocularis metacestodes. Detailed studies on the activity of bortezomib in Echinococcus showed that indeed the proteasome represents a promising drug target that should be exploited in more detail in the future [ 57 ].…”

Targeting proteasomes in infectious organisms to combat disease

“…Echinococcus multilocularis causes parasitic tumors in many human organs and are often treated with benzimidazoles . In one study, E. multilocularis metacestodes were incubated with 426 FDA‐approved drugs and bortezomib was identified as the most potent drug with EC 50 of 0.6 μ m . Metacestode treatment with bortezomib induced serious morphological alterations resembling apoptotic cells at concentrations as low as 50 n m .…”

“…In addition, chymotrypsin‐like proteasome activity in cellular lysates was inhibited in a dose‐dependent manner. Despite good in vitro efficacy against larvae, bortezomib had poor efficacy in a mouse model of secondary alveolar echinococcosis . However, future improvement of the animal model could lead to a better understanding and validation of proteasome inhibitors in vivo .…”