(S)-5-ethynyl-anabasine, a novel compound, is a more potent agonist than other nicotine alkaloids on the nematode Asu-ACR-16 receptor

Abstract

Nematode parasites infect ∼2 billion people world-wide. Infections are treated and prevented by anthelmintic drugs, some of which act on nicotinic acetylcholine receptors (nAChRs). There is an unmet need for novel therapeutic agents because of concerns about the development of resistance. We have selected Asu-ACR-16 from a significant nematode parasite genus, Ascaris suum, as a pharmaceutical target and nicotine as our basic moiety (EC₅₀ 6.21 ± 0.56 μM, I_max 82.39 ± 2.52%) to facilitate the development of more effective anthelmintics. We expressed Asu-ACR-16 in Xenopus oocytes and used two-electrode voltage clamp electrophysiology to determine agonist concentration-current-response relationships and determine the potencies (EC₅₀s) of the agonists. Here, we describe the synthesis of a novel agonist, (S)-5-ethynyl-anabasine, and show that it is more potent (EC₅₀ 0.14 ± 0.01 μM) than other nicotine alkaloids on Asu-ACR-16. Agonists acting on ACR-16 receptors have the potential to circumvent drug resistance to anthelmintics, like levamisole, that do not act on the ACR-16 receptors.

Keywords: Agonist-binding site; Anthelmintic; Ascaris suum; Asu-ACR-16; Nicotine alkaloids; Xenopus expression.