Meclonazepam sensitivity of parasitic flatworms correlates with TRPMMCLZ sensitivity to meclonazepam

The ionotropic portfolio of parasitic flatworms affords considerable opportunity for development of new anthelmintics. In this regard, transient receptor potential ion channels (TRP channels), cation channels responsive to various physiochemical cues, have emerged as promising druggable targets. This is based on the recent discovery that two members of a TRP channel subfamily (TRP melastatin or TRPM channels) are selectively activated by the clinical drug praziquantel (TRPM_PZQ), or the anthelmintic benzodiazepine meclonazepam (TRPM_MCLZ). Here, the efficacy of meclonazepam was investigated in a trematode (the liver fluke, Fasciola hepatica) and a cestode (Echinococcus multilocularis) model, in which an observed lack of meclonazepam sensitivity correlated with the lack of efficacy of meclonazepam on TRPM_MCLZ in these different parasites. Such correlations support assignment of TRPM_MCLZ as the meclonazepam target. Bioinformatic analysis of all available parasitic flatworm genomes allowed prediction of the meclonazepam binding pocket in over sixty different TRPM_MCLZ orthologs. Mutagenesis and functional profiling analyses highlighted the importance of a key residue in the S4 transmembrane helix of TRPM_MCLZ that impacts meclonazepam potency and efficacy. Variation of this residue and overall binding pocket architecture between different parasitic flatworm TRPM_MCLZ orthologs restricts meclonazepam action to a subset of schistosome species.