Characterization and inhibition of a p38-like mitogen-activated protein kinase (MAPK) from Echinococcus multilocularis: antiparasitic activities of p38 MAPK inhibitors.

Alveolar echinococcosis (AE), caused by the metacestode larval stage of the fox-tapeworm Echinococcus multilocularis, is a life-threatening disease with very limited treatment options. In search for novel drug targets, we concentrate on factors of the cellular signaling machinery and report herein the characterization of a novel gene, Emmpk2, which is expressed in the parasite's larval stage and which codes for a member of the mitogen-activated protein kinase (MAPK) family. On the amino acid sequence level, the encoded protein, EmMPK2, shares considerable homologies with p38 MAPKs from a wide variety of animal organisms but also displays several distinct differences, particularly in amino acid residues known to be involved in the regulation of enzyme activity. Upon heterologous expression in Escherichia coli, purified EmMPK2 showed prominent autophosphorylation activity and strongly elevated basal activity towards a MAPK substrate, when compared to the closest human orthologue, p38-alpha. EmMPK2 activity could be effectively inhibited in the presence of ML3403 and SB202190, two ATP-competitive pyridinyl imidazole inhibitors of p38 MAPKs, in a concentration-dependent manner. When added to in vitro cultivated metacestode vesicles, SB202190 and particularly ML3403 led to dephosphorylation of EmMPK2 in the parasite and effectively killed parasite vesicles at concentrations that did not affect cultivated mammalian cells. Taken together, these results identify pyridinyl imidazoles as a novel class of anti-Echinococcus compounds and EmMPK2 as a promising target for the development of drugs against alveolar echinococcosis.