Unraveling the molecular mechanism of DII, a new anthelmintic drug

Abstract

Nematode parasites cause substantial morbidity to billions of people and considerable losses in livestock and food crops. The repertoire of effective anthelmintic compounds is very limited, as drug development has been delayed for decades. By using C. elegans as a model for parasitic nematodes, we previously identified a new imidazole derivative, diisopropylphenyl-imidazole (DII), as a promising candidate for anthelmintic agent. DII lethal effects rely on a previously unidentified muscle nicotinic receptor (AChR), different from the classical levamisole-sensitive AChR. This novel AChR is composed by UNC-29 (a non-alpha subunit incapable of forming homomeric receptors) and other unidentified subunits. To elucidate its stoichiometry, we performed an initial screening of strains containing null mutations in different AChR subunits. By exposing these animals to DII (600 m), we found a null mutant in acr-23 (an alpha nicotinic subunit) that is even more resistant to DII than UNC-29 null mutants. Since the mutants used in the initial screening had not been outcrossed to the wild-type (wt), we performed this outcross four times, selecting (by genotyping) those animals that contain the deletion in acr-23. Surprisingly, these outcrossed animals are as sensitive to DII as the wt. Moreover, when we outcrossed the original mutant strain to the wt selecting by their resistance to DII, we obtained animals that contain wild-type acr-23 alleles. This strongly suggests that another mutation, different from acr-23 deletion, causes the DII resistance. The drug resistance of these mutants appears to be DII-specific, as it is as sensitive to the classic anthelmintic levamisole as the wt. We are now focused on determining the gene that underlies this DII resistant phenotype. Parasite resistance to traditional nematocidal drugs has become a global concern. Therefore, the identification of new anthelmintics with novel targets, as DII, is mandatory to circumvent this growing problem.