Identification of functional MKK3/6 and MEK1/2homologs from Echinococcus granulosus and investigation of protoscolecidal activity of MAPK signaling pathway inhibitors in vitro and in vivo [Experimental Therapeutics]

Cystic echinococcosis is a zoonosis caused by the larval stage of Echinococcus granulosus sensu lato. There is an urgent need to develop new drugs for the treatment of this disease. In this study, we identified two new members of MAPK cascades, MKK3/6 and MEK1/2 homologs (termed EgMKK1 and EgMKK2, respectively), from E. granulosus sensu stricto. Both EgMKK1 and EgMKK2 were expressed at the larval stages. As shown by yeast two-hybrid and co-immunoprecipitation analyses, EgMKK1 interacted with the previously identified Egp38 but not with EgERK. EgMKK2, on the other hand, interacted with EgERK. In addition, EgMKK1 and EgMKK2 displayed kinase activity toward the substrate, myelin basic protein. When sorafenib tosylate, PD184352 or U0126-EtOH were added to the medium for in vitro culture of E. granulosus protoscoleces (PSCs) or cysts, an inhibitory and cytolytic effect was observed via suppressed phosphorylation of EgMKKs and EgERK. Non-viability of PSCs treated with sorafenib tosylate or U0126-EtOH, and not with PD184352, was confirmed through bioassay, i.e. inoculation of treated and untreated protoscoleces into mice. In vivo treatment with sorafenib tosylate or U0126-EtOH for 4 weeks of E. granulosus s.s.-infected mice demonstrated a reduction in parasite weight, but the results did not show significant difference. In conclusion, the MAPK cascades were identified as new targets for drug development and E. granulosus was efficiently inhibited by their inhibitors in vitro. The translation of these findings into in vivo efficacy requires further adjustment of treatment regimens using sorafenib tosylate or, possibly, other kinase inhibitors.

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