Target-based discovery of antagonists of the tick (Rhipicephalus microplus) kinin receptor identifies small molecules that inhibit midgut contractions

Rhipicephalus microplus>, the southern cattle tick, cattle fever tick, or Asian blue tick, is the vector of pathogenic microorganisms causing the deadly bovine babesiosis and anaplasmosis. The widespread resistance to acaricides in tick populations worldwide emphasizes that exploring novel targets for effective tick control is imperative. A GPCR target-based approach was applied to identify antagonists of the arthropod-specific tick kinin receptor. Fifty-three structural analogs of previously identified tick kinin antagonists were screened in a "dual-addition" calcium fluorescence assay using a CHO-K1 cell line expressing the tick kinin receptor. Seven molecules were validated as non-cytotoxic antagonists, four of which were partial and three were full antagonists. Four of these antagonists also inhibited the tick midgut contractions induced by the myotropic kinin agonist analog 1728, verifying their antagonistic bioactivity. The small molecules were tested on recombinant human neurokinin (NK) receptors, the one most similar to the invertebrate kinin receptors. Most molecules were inhibitors of the NK1 receptor, except one, a previously identified tick kinin receptor antagonist, which inhibited the NK1 receptor only at the highest concentration tested (25 µM). None of the molecules inhibited the NK3 human receptor. Molecules identified through this approach could be useful probes for studying the tick kinin signaling system and midgut physiology.
Acknowledgment: This project was supported by the Agriculture and Food Research Initiative Competitive Grant no. 2022-67015-36336 from the USDA National Institute of Food and Agriculture.