Novel tick glutathione transferase inhibitors as promising acaricidal compounds

Ticks are important ectoparasites with a worldwide distribution. The most commonly used method for tick control involves the use of acaricides. The main problem is that its indiscriminate use has led to the selection of resistant tick populations. Glutathione transferases (GSTs) are enzymes that play an important role in the detoxification of several types of compounds used in commercial tick control products. This work aims to find new bioactive molecules through in vitro assays with a panel of 160 molecules with putative inhibitory activity on the Rhipicephalus microplus GST enzyme (RmGST). Also, selected molecules were tested against GSTs from other tick species; Rhipicephalus decoloratus, Amblyomma variegatum, Rhipicephalus appendiculatus, and Haemaphysalis longicornis. The first screening on RmGST identified 30 compounds with the ability to modify the enzymatic activity of this enzyme. These compounds included different chemical families, like chalcones, diarylideneketones, flavone, thiazoles, thiourea, steroids, thiadiazines, indazoles, and hydrazine. The most potent compounds against RmGST belong to the diarylideneketones family with an inhibition concentration of 50% of activity (IC50) between 7-50 μM. Interestingly, one of the most potent compounds was also an inhibitor of the GST from other tick species. Experiments with R. microplus adults and larvae showed toxicity at 150 μM, suggesting a potential acaricidal effect of these molecules.