Background

The potentially lethal zoonosis alveolar echinococcosis (AE) is caused by the metacestode larval stage of the tapeworm Echinococcus multilocularis . Current AE treatment options are limited and rely on surgery as well as on chemotherapy involving benzimidazoles (BZ). BZ treatment, however, is parasitostatic only, must be given for prolonged time periods, and is associated with adverse side effects. Novel treatment options are thus urgently needed.

Methodology/Principal findings

By applying a broad range of kinase inhibitors to E. multilocularis stem cell cultures we identified the proto-oncogene PIM kinase as a promising target for anti-AE chemotherapy. The gene encoding the respective E. multilocularis ortholog, EmPIM, was characterized and in situ hybridization assays indicated its expression in parasite stem cells. By yeast two-hybrid assays we demonstrate interaction of EmPIM with E. multilocularis CDC25, indicating an involvement of EmPIM in parasite cell cycle regulation. Small molecule compounds SGI-1776 and CX-6258, originally found to effectively inhibit human PIM kinases, exhibited detrimental effects on in vitro cultured parasite metacestode vesicles and prevented the formation of mature vesicles from parasite stem cell cultures. To improve compound specificity for EmPIM, we applied a high throughput in silico modelling approach, leading to the identification of compound Z196138710. When applied to in vitro cultured metacestode vesicles and parasite cell cultures, Z196138710 proved equally detrimental as SGI-1776 and CX-6258, but displayed significantly reduced toxicity towards human HEK293T and HepG2 cells.

Conclusions/Significance

Repurposing of kinase inhibitors initially designed to affect mammalian kinases for helminth disease treatment is often hampered by adverse side effects of respective compounds on human cells. Here we demonstrate the utility of high throughput in silico approaches to design small molecule compounds of higher specificity for parasite cells. We propose EmPIM as a promising target for respective approaches towards AE treatment.

Author summary

The larva of the tapeworm E. multilocularis grows tumor-like within the host liver, thus causing the lethal disease alveolar echinococcosis (AE). Anti-parasitic treatment relies on chemotherapy with benzimidazoles, which do not kill the parasite and must be applied for years. As druggable enzymes with key functions in growth control, protein kinases are promising drug targets and many kinase inhibitors have been identified during cancer research. Optimized for binding to human kinases, however, repurposing of such drugs for parasitic disease treatment is associated with adverse side effects. Herein, the authors applied an in silico approach to identify small molecule compounds that show higher specificity for a parasite kinase, EmPIM, over its mammalian homologs. The authors demonstrate expression of EmPIM in Echinococcus stem cells, which are the drivers of parasite growth, and show that mammalian PIM kinase inhibitors SGI-1776 and CX-6258 also affect parasite development in vitro . Finally, they show that one of the in silico screened compounds is equally effective against the parasite as SGI-1776 and CX-6258, but significantly less toxic to human cells. These results demonstrate the utility of in silico approaches to identify parasite-specific kinase inhibitors.