In vitro efficacy of cyclooctadepsipepdtides and aminophenylamidines alone and in combination against third-stage larvae and adult worms of Nippostrongylus brasiliensis and first-stage larvae of Trichinella spiralis

The present study investigates the in vitro efficacy of derivatives of the cyclooctadepsipeptides and the aminophenylamidines, which are promising candidates for the evaluation of the treatment of human soil-transmitted helminthiases. The effects of emodepside and PF1022A as well as of amidantel, deacylated amidantel and tribendimidine were evaluated in a concentration range between 0.01 and 100 mu g/ml against third-stage larvae (L3) and adult worms of Nippostrongylus brasiliensis and first-stage larvae (L1) of Trichinella spiralis. Furthermore, drug combinations of PF1022A plus deacylated amidantel or tribendimidine and of tribendimidine plus levamisole were tested for any potential additive or even synergistic interactions. Emodepside had a significantly lower EC50 value than PF1022A in the T. spiralis (0.02788 vs. 0.05862 mu g/ml) and the N. brasiliensis (0.06188 vs. 0.1485 mu g/ml) motility assays but not in the acetylcholine esterase secretion assay with adult N. brasiliensis (0.05650 vs. 0.06886 mu g/ml). While amidantel showed only minimal or at best partial inhibition of nematode motility and acetylcholine esterase secretion, tribendimidine was nearly as potent as deacylated amidantel. Whereas deacylated amidantel had a significantly lower EC50 than tribendimidine in the N. brasiliensis L3 motility assay (0.05492 vs. 0.2080 mu g/ml), differences were not significant in the T. spiralis L1 motility assay (0.7766 vs. 1.145 mu g/ml). Surprisingly, none of the combinations showed improved efficacy when compared to the individual drugs including levamisole/tribendimidine, which have previously been reported to act synergistically against Ancylostoma ceylanicum.