Monepantel Allosterically Activates DEG-3/DES-2 Channels of the Gastrointestinal NematodeHaemonchus contortus

Abstract

Monepantel is the first drug of a new family of anthelmintics, the amino acetonitrile derivatives (AAD), presently used to treat ruminants infected with gastrointestinal nematodes such as Haemonchus contortus. Monepantel shows an excellent tolerability in mammals and is active against multidrug-resistant parasites, indicating that its molecular target is absent or inaccessible in the host and is different from those of the classic anthelmintics. Genetic approaches with mutant nematodes have suggested acetylcholine receptors of the DEG-3 subfamily as the targets of AADs, an enigmatic clade of ligand-gated ion channels that is specific to nematodes and does not occur in mammals. Here we demonstrate direct interaction of monepantel, its major active metabolite monepantel sulfone, and other AADs with potential targets of the DEG-3 subfamily of acetylcholine receptors. H. contortus DEG-3/DES-2 receptors were functionally expressed in Xenopus laevis oocytes and were found to be preferentially activated by choline, to permeate monovalent cations, and to a smaller extent, calcium ions. Although monepantel and monepantel sulfone did not activate the channels by themselves, they substantially enhanced the late currents after activation of the channels with choline, indicating that these AADs are type II positive allosteric modulators of H. contortus DEG-3/DES-2 channels. It is noteworthy that the R-enantiomer of monepantel, which is inactive as an anthelmintic, inhibited the late currents after stimulation of H. contortus DEG-3/DES-2 receptors with choline. In summary, we present the first direct evidence for interaction of AADs with DEG-3-type acetylcholine receptors and discuss these findings in the context of anthelmintic action of AADs.

Monepantel Irreversibly Binds to and Opens Haemonchus contortus MPTL-1 and Caenorhabditis elegans ACR-20 Receptors

“…We previously found that currents mediated by choline-activated H. contortus DEG-3/DES-2 channels (Rufener et al, 2010a), but not ACR-23 (Rufener et al, 2013) channels, permeated calcium (Ca 21 ) in addition to monovalent cations. This was detected indirectly by activation of a Ca 21 -activated chloride channel endogenous to the oocyte, resulting in a shift of the reversal potential toward the chloride reversal potential.…”

“…In this respect, the target of monepantel in H. contortus, MPTL-1, and its closest homolog in C. elegans, ACR-20, were expressed in Xenopus oocytes, and their function was characterized. Previous attempts to reconstitute the MPTL-1 receptor were unsuccessful (Rufener et al, 2010a). In the present study, we have subcloned the open reading frame of MPTL-1 from pcDNA3.1 to the pT7-TS vector.…”

“…The C. elegans ACR-23 and the H. contortus DES-2/DEG-3 receptors have recently been characterized (Rufener et al, 2010a(Rufener et al, , 2013, and we compare in the following discussion their functional properties with those of MPTL-1 and ACR-20, determined in this work. As ACR-23, both channels were preferentially gated by betaine compared with choline or acetylcholine.…”

“…This similarity suggests that it may function as a secondary target for monepantel. Monepantel has also been shown to potentiate the H. contortus DES-2/DEG-3 receptor at micromolar concentrations when coapplied with choline chloride (Rufener et al, 2010a). A genetic screen of C. elegans (Kaminsky et al, 2008) identified mutations in acr-23, but no other member of the deg-3 family, including acr-20, des-2, and deg-3.…”

EVOLUTION IN CHEMOTHERAPY OF HUMAN AND ANIMAL HELMINTHIASES (review)

“…The most active metabolite is monepantel sulfone (81,82); this substance is effective in low doses (2.5-3.5 mg/kg) against a broad spectrum of gastro-intestinal helminths in larval and adult stages resistant to conventional anthelmintics (83). Interaction of monepantel with nematode-specific nAChR Hco-MPTL-1 leads to dysfunction of this receptor which paralyzes helminth's muscles (84,85). Derquantel is semisynthetic derivative of paraherquamide A isolated from natural spiroindoles -products of Penicillium paraherquei (86,87).…”