The Fasciola TRPM_PZQ channel, a new druggable target

Abstract text

Introduction

Milestones have recently been achieved in clarifying the mechanism of action of praziquantel (PZQ), the drug of choice to fight schistosomes. PZQ acts as an agonist of a transient receptor potential (TRP) channel within the melastatin family (SmTRPM_PZQ), which leads to rapid contraction of the worms and death. Mutagenesis of residues within the binding pocket of SmTRPM_PZQ identified an asparagine (Asn) residue as crucial factor for PZQ-sensitivity. While the TRPM channel of other PZQ-sensitive helminths harbor the same Asn, natural variation at this residue renders TRPM_PZQ of the liver fluke Fasciola hepatica (FhTRPM_PZQ) resistant to PZQ (Park et al. 2021). Exploring FhTRPM_PZQ as drug target opens new avenues to find new fasciolicidal compounds. This is particularly pressing against the wide spread of triclabendazole resistance.

Objectives

In this study, we aim for a de novo discovery of agonists for the F. hepatica TRPM_PZQ channel and to test if such agonists have fasciolicidal activity.

Materials and Methods

A high throughput drug screen using a Ca²⁺-based reporter assay (Chulkov et al. 2021) was used to identify FhTRPM_PZQ-activating chemotypes. One of these chemotypes was tested against FhTRPM_PZQ and different stages of F. hepatica in vitro. Further characterization of FhTRPM_PZQ is envisaged by RNA interference and gene expression analysis.

Results

The reporter assay identified several chemotypes triggering Ca²⁺ influx in FhTRPM_PZQ-transfected cells. One series was selected and optimized to yield a ligand that activated FhTRPM_PZQ with high sensitivity in vitro (EC50=855±151nM). The same chemotype killed adult and immature F. hepatica at concentrations of 6.25-12.5 µM within 24 h-72 h. The TRPM agonists, therefore, outcompeted triclabendazole, which was lethal at 50 µM within 48 h. Contraction of the worms resembled the phenotype observed for PZQ-treated schistosomes. Finally, our single-cell transcriptomics data suggest a neuronal expression of FhTRPM.

Conclusion

Our study proves that TRPM_PZQ is a druggable target also in a PZQ-resistant helminth. The successful screening approach may be translated to other PZQ-resistant helminths in the future.

Park et al. Mechanism of praziquantel action at a parasitic flatworm ion channel. Sci Transl Med. 2021;13(625):eabj5832.

Chulkov et al. Identification of novel modulators of a schistosome transient receptor potential channel targeted by praziquantel. PLoS Negl Trop Dis. 2021;15(11):e0009898.