Further and new target-based benzimidazole anthelmintics active against Teladorsagia circumcincta

Abstract

Helminth infections are one of the most prevalent parasitic diseases affecting animals and humans worldwide. Anthelmintic resistance to the main drugs used to control these infections in animals, especially ruminants, is a major global problem that needs urgent solutions. The purpose of this study was to design and obtain new benzimidazole (BZ) derivatives to evaluate their in vitro ovicidal and larvicidal activities. Based on previous results from 2-phenylbenzimidazoles and new docking studies of different BZ-containing scaffolds in Teladorsagia circumcincta tubulin four structural groups of BZs were selected. In addition to several new members of those previously reported 2-phenylBZs (type I), some twenty 2-aminoBZ derivatives (type II) and twenty-five BZ amides (types III and IV) were prepared and evaluated for their ability to inhibit egg hatching and larval motility of T. circumcincta with results superior to those previously achieved. Nine of the fifty-five BZs tested displayed ovicidal activity higher than 90%, and fourteen induced more than 30% larval death in the assays at 50 µM. The benzamide BZ 42 showed the best ovicidal EC50 value of 0.92 µM with a selectivity index > 100 respecting HepG2 cells, while the benzylamine BZ 13 attained a higher than 50% larvicidal activity. Notably, the amide BZ 39 displayed both ovicidal (100%) and larvicidal (>50%) activities. The SAR analysis and the docking studies carried out led to the conclusion that, in addition to the effects on tubulin, pending experimental confirmation, there must be other mechanisms by which the evaluated BZs prevent hatching and limit the mobility of the parasitic larvae.