Phylogenomics of Ligand-Gated Ion Channels Predicts Monepantel Effect

Abstract

The recently launched veterinary anthelmintic drench for sheep (Novartis Animal Health Inc., Switzerland) containing the nematocide monepantel represents a new class of anthelmintics: the amino-acetonitrile derivatives (AADs), much needed in view of widespread resistance to the classical drugs. Recently, it was shown that the ACR-23 protein in Caenorhabditis elegans and a homologous protein, MPTL-1 in Haemonchus contortus, are potential targets for AAD action. Both proteins belong to the DEG-3 subfamily of acetylcholine receptors, which are thought to be nematode-specific, and different from those targeted by the imidazothiazoles (e.g. levamisole). Here we provide further evidence that Cel-ACR-23 and Hco-MPTL-1-like subunits are involved in the monepantel-sensitive phenotype. We performed comparative genomics of ligand-gated ion channel genes from several nematodes and subsequently assessed their sensitivity to anthelmintics. The nematode species in the Caenorhabditis genus, equipped with ACR-23/MPTL-1-like receptor subunits, are sensitive to monepantel (EC50<1.25 µM), whereas the related nematodes Pristionchus pacificus and Strongyloides ratti, which lack an ACR-23/MPTL-1 homolog, are insensitive (EC50>43 µM). Genome sequence information has long been used to identify putative targets for therapeutic intervention. We show how comparative genomics can be applied to predict drug sensitivity when molecular targets of a compound are known or suspected.

The cys-loop ligand-gated ion channel gene family of Tetranychus urticae: Implications for acaricide toxicology and a novel mutation associated with abamectin resistance

“…Remarkably, Tua3 has an atypical FxCC amino acid motif ( Figure S1), instead of the highly conserved YxCC in loop C. A study of the chicken a7 nAChR receptor expressed in Xenopus oocytes showed that changing the YxCC motif to FxCC, resulted in a tenfold decrease in ACh affinity (Galzi et al, 1991). The unusual FxCC motif was previously also identified in nAChR(s) of Tribolium confusum, N. vitripennis and the nematodes C. elegans and Haemonchus contortus Rufener et al, 2010). Future functional studies should point out if the presence of this motif in arthropod and nematode nAChRs also results into a similar decrease in ACh affinity.…”

Monepantel Irreversibly Binds to and Opens Haemonchus contortus MPTL-1 and Caenorhabditis elegans ACR-20 Receptors

“…When choline was coapplied with monepantel, the threshold of potentiation differed markedly between the different receptors. Whereas it was about 100 nM in ACR-23 channels (Rufener et al, 2013), MPTL-1 channels were about 100 times more sensitive, a difference of sensitivity toward monepantel that is also observed in vivo on worm viability: the calculated LC 50 for C. elegans is 100 nM (Rufener et al, 2010b) and 7.5 nM (data not shown) for H. contortus. This difference can be explained by the fact that monepantel has been optimized based on H. contortus efficacy in vitro and in vivo and not on C. elegans.…”

“…Recent phylogenetic studies (Rufener et al, 2010b) have shown that mptl-1 is more closely related to the C. elegans acr-20, another member of the nematode-specific deg-3 subfamily. This similarity suggests that it may function as a secondary target for monepantel.…”

Biogenic amines and the control of neuromuscular signaling in schistosomes

“…Virtually all therapeutics currently in use for nematode control, ivermectin, levamisole and, most recently, monepantel all act through neuroreceptors of the worm's neuromuscular system (see Holden-Dye and Walker 2007;Rufener et al 2010). Praziquantel also acts, in part, by disrupting normal muscle function and causing paralysis (Greenberg 2005;Jeziorski and Greenberg 2006).…”