Arylpyrrole and fipronil analogues that inhibit the motility and/or development of Haemonchus contortus in vitro

Abstract

Due to widespread drug resistance in parasitic nematodes, there is a need to develop new anthelmintics. Given the cost and time involved in developing a new drug, the repurposing of known chemicals can be a promising, alternative approach. In this context, we tested a library (n = 600) of natural product-inspired pesticide analogues against exsheathed third stage-larvae (xL3s) of Haemonchus contortus (barber's pole worm) using a whole-organism, phenotypic screening technique that measures the inhibition of motility and development in treated larvae. In the primary screen, we identified 32 active analogues derived from chemical scaffolds of arylpyrrole or fipronil. The seven most promising compounds, selected based on their anthelmintic activity and/or limited cytotoxicity, are arylpyrroles that reduced the motility of fourth-stage larvae (L4s) with significant potency (IC50 values ranged from 0.04 ± 0.01 μM to 4.25 ± 0.82 μM, and selectivity indices ranged from 10.6 to 412.5). Since the parent structures of the active compounds are uncouplers of oxidative phosphorylation, we tested the effect of selected analogues on oxygen consumption in xL3s using the Seahorse XF24 flux analyser. Larvae treated with the test compounds showed a significant increase in oxygen consumption compared with the untreated control, demonstrating their uncoupling activity. Overall, the results of the present study have identified natural product-derived molecules that are worth considering for chemical optimisation as anthelmintic drug leads.

Phenotypic screening of the ‘Kurz-box’ of chemicals identifies two compounds (BLK127 and HBK4) with anthelmintic activity in vitro against parasitic larval stages of Haemonchus contortus

“…Therefore, the discovery of novel chemical entities with unique modes of action against drug-resistant nematodes of livestock is critical. In this context, we have commenced a programme to screen several distinct compound libraries [10–16] against H. contortus , a representative strongylid nematode, using a whole-organism phenotypic screening technique established in our laboratory [10]. In the present study, we expand this work by screening a set of compounds ( n = 236) representing distinct classes of chemicals, including heterocyclic compounds (e.g.…”

A phenotypic screen of the Global Health Priority Box identifies an insecticide with anthelmintic activity

“…Of the seven compounds that inhibited H. contortus xL3 motility by ≥ 70%, three compounds, MMV1577458 (chlorfenapyr), MMV688934 (tolfenpyrad) and MMV0002519 (rotenone), had been previously assessed for motility inhibition on H. contortus larvae (cf. [ 49 , 63 , 64 ]). Thus, the remaining four compounds (MMV1794214, MMV1794206, MMV1577463 and MMV027339) were prioritised for further potency assessment on H. contortus larval motility inhibition.…”

“…Compounds with previously identified activity on H. contortus —chlorfenapyr (MMV1577458) [ 64 ], tolfenpyrad (MMV688934) [ 49 ] and rotenone (MMV0002519) [ 63 ]—were all reidentified as hit compounds in this study. Two compounds—MMV1577463 and MMV027339—were initially identified as hits (83 and 72% motility reduction, respectively), but upon further potency evaluation were found to display IC 50 values (against H. contortus ) of > 40 μM.…”

“…The conserved 5-chloropyrimidin-4-amine motif does suggest that pyrimidifen and flufenerim share a similar mode of action, namely, as METIs. Several METI insecticides have been previously identified to display anthelmintic activity—notably, the pyrazole compounds tebufenpyrad and tolfenpyrad [ 75 ], and the rotenoid compound, rotenone [ 64 ]. In addition, a preliminary study [ 75 ] suggested that tolfenpyrad may indeed disrupt or interrupt mitochondrial function in H. contortus .…”