| Summary: | Increasing levels of resistance to currently available anthelmintic drugs has created an urgent need to develop new compounds with the potential to eliminate parasitic worm infections. Amidantel and its derivatives, Bay d9216 and tribendimidine, have previously been reported to act by disrupting transmission at the nematode neuromuscular junction. It is not known whether this activity is mediated by levamisole gated acetylcholine receptors or a novel molecular target. We have used Caenorhabditis elegans as a model organism to investigate the effects of these compounds in wild type worms. A reverse genetic approach was then undertaken, using strains carrying mutations in genes expressing nicotinic acetylcholine receptor (nAChR) subunits or related proteins. We clearly demonstrate that the predominant action of amidantel, Bay d9216 and tribendimidine was an inhibition of locomotion shown on both solid and in liquid media. This activity is in agreement with the previously reported mode of action of these compounds as agonists acting at nAChRs. The level of inhibition was comparable to the widely used anthelmintic, levamisole. Other effects included stimulation of egg laying and reduction in brood size. No effects on the timing of development were observed. A levamisole resistant strain was inhibited by Bay d9216, suggesting a distinct receptor subtype is targeted by this compound. Only a minimal inhibition of locomotion and no reduction in brood size was observed when worms carrying a mutation in the gene expressing the ACR-16 subunit were exposed to Bay d9216. The inhibitory effects of the remaining compounds on this strain were comparable to those of wild type worms. Strains carrying mutations in ACR-12 and ACR-8 subunits showed a reduced susceptibility to Bay d9216. This data suggests that this compound acts by targeting nAChRs containing the ACR-16, ACR-12 and ACR-8 subunits. Susceptibility to Bay d9216 was restored in a strain which was generated to express wild type copies of acr-16 under a body wall muscle specific promoter in an acr-16 mutant background. These data confirmed that the ACR-16 subunit is a key target for the action of Bay d9216. ACR-16 nAChRs have previously been shown to be levamisole resistant. Bay d9216 has also been shown to have activity in economically important parasitic species of worm. Taken together these data provide strong evidence that Bay d9216 has the potential to act as an anthelmintic compound and the molecular target of Bay d9216 is distinct to that of levamisole and therefore has the potential to break resistance.
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