MOD-1 receptor as a novel drug target for anthelmintic therapy

Abstract

Caenorhabditis elegans (Nematoda) contains a homomeric 5HT-gated chloride channel, MOD-1, that belongs to the Cys-loop receptor family and modulates locomotor behavior. Although it binds 5-HT, MOD-1 is not present in vertebrates, and it therefore emerges as a possible anthelmintic target. We deciphered MOD-1 pharma- cological properties and searched for novel modulators with poten- tial anthelmintic activity by performing patch-clamp recordings from mammalian cells heterologously expressing MOD-1 and locomotor activity assays in C. elegans. Whole-cell recordings showed that MOD-1 desensitizes slowly and recovers from desensitization with a time constant of about 1 s. Compared to the vertebrate 5-HT3 A receptor, dose-response curves were similar for 5-HT but very differ- ent for the orthosteric agonists tryptamine and 2-Me-5HT. The an- thelmintic drugs ivermectin (IVM), levamisole, and piperazine (PZE), which are agonists of other Cys-loop receptors, did not activate MOD-1. However, IVM produced a slight and irreversible inhibition and PZE produced a profound and reversible inhibition of MOD-1 currents elicited by 5-HT. The analysis indicated that PZE is a non- competitive antagonist of MOD-1, revealing a novel function of this drug. To relate the molecular effects to behavioral actions of these compounds, we performed locomotor activity assays in C. elegans. We found that 5-HT produces rapid and reversible paralysis of wild- type (WT) worms while MOD-1 mutants are partially resistant under similar conditions, thus indicating that MOD-1 is the main 5-HT tar- get in this type of assays. Additional assays using drug combinations in WT and mutant strains confirmed the inhibition of MOD-1 activity by IVM and PZE. The elucidation of the molecular pharmacology of MOD-1 enhances our knowledge of function and drug selectivity of Cys-loop receptors and contributes to determine its potential as a novel target for anthelmintic therapy.