Claudia M. Rohr

Praziquantel (PZQ) is an essential medicine used to treat schistosomiasis and other infectious diseases caused by parasitic flatworms. The parasite target of PZQ is a transient receptor potential ion channel of the melastatin subfamily, TRPM _PZQ . As little is currently known about the native role of TRPM _PZQ in schistosomes, we developed and validated TRPM _PZQ specific antibodies to immunolocalize TRPM _PZQ across various S. mansoni life cycle stages (adult worms, juvenile worms, miracidia and cercariae). TRPM _PZQ was expressed in muscle, nervous tissues, as well as various sensory structures on the surface of the parasite across all these life cycle stages. In adult male worms, TRPM _PZQ positive neurons innervated the oral and ventral suckers as well as sensory papillae covering the head of the worm. TRPM _PZQ was also present in papillae throughout the body, and within tubercles. In a S. mansoni strain selected in the laboratory for resistance to PZQ, reduced expression and immunostaining of TRPM _PZQ was apparent. In immature worms, which can recover from PZQ exposure, TRPM _PZQ expression was predominantly found within the musculature compared with the neuronal localization evident in adult worms. A developmental transition of TRPM _PZQ from muscle to nervous tissues during schistosome maturation was also supported from single cell RNAseq data. Because muscle buffers Ca ²⁺ transients more effectively than neurons, the transition of TRPM _PZQ away from muscle during schistosome maturation may increase the sensitivity of adult male worms to PZQ.

Schistosomiasis, a neglected tropical disease caused by infection with parasitic blood flukes of the genus Schistosoma , affects more than 250 million people worldwide. Currently, patients rely on a single medicine, praziquantel (PZQ), discovered half a century ago. To combat drug resistance and reach elimination of the schistosome parasite, alternative drugs to PZQ are required that treat and prevent disease. Here, we describe a drug candidate, M5493, with potent activity against multiple parasite life cycle stages. The target is a parasite transient receptor potential ion channel, distinct from the target of PZQ. To circumvent its limited bioavailability, the active agent was converted to prodrug M5493, which displayed robust activity against the schistosome parasite at doses as low as 5 milligrams per kilogram in mice infected with Schistosoma mansoni . Unlike the benzodiazepine meclonazepam, which displays clinical antihelminthic activity through the same target, M5493 showed no sedating side effects given that it did not engage GABA _A receptors. Overall, this compound has the potential to provide single-dose treatment, broad-spectrum efficacy against schistosome parasites at different life cycle stages, and transmission blocking activity.

The anthelmintic praziquantel (PZQ) has been used for decades as the clinical therapy for schistosomiasis, and remains the only available drug. As a cheap and effective drug therapy for all human disease-causing Schistosoma species, usage of PZQ underpins mass drug administration strategies aimed at eliminating schistosomiasis as a public health problem by 2030. Concern over the potential emergence of resistance to PZQ is therefore warranted, as it would constitute a major threat to this approach. In terms of molecular adaptations conferring PZQ resistance, variation in the sequence and/or expression of the drug target is an obvious mechanism and should be a priority for surveillance efforts. The target of PZQ is a transient receptor potential ion channel, TRPM _PZQ , which is established as a locus that regulates schistosome sensitivity to PZQ. Here, we describe the establishment of a community resource, ‘TRPtracker’, which coalesces data on TRPM _PZQ natural variants together with measurements of individual variant sensitivity to PZQ. A compendium of laboratory-generated mutants in TRPM _PZQ is also compiled in TRPtracker to map regions within TRPM _PZQ critical for PZQ sensitivity. Aggregation of data from multiple research groups into TRPtracker permits rapid community-wide exchange of data, cataloguing which TRPM _PZQ variants have been functionally profiled, where geographically these variants have been found, their frequency within populations and their potential impact on PZQ sensitivity.

Diseases caused by parasitic flatworms impart a considerable healthcare burden worldwide. Many of these diseases—for example, the parasitic blood fluke infection schistosomiasis—are treated with the drug praziquantel (PZQ). However, PZQ is ineffective against disease caused by liver flukes from the genus Fasciola because of a single amino acid change within the target of PZQ, a transient receptor potential ion channel in the melastatin family (TRPM_PZQ), in Fasciola species. Here, we identify benzamidoquinazolinone analogs that are active against Fasciola TRPM_PZQ. Structure–activity studies define an optimized ligand (BZQ) that caused protracted paralysis and tegumental damage to these liver flukes. BZQ also retained activity against Schistosoma mansoni comparable to PZQ and was active against TRPM_PZQ orthologs in all profiled species of parasitic fluke. This broad-spectrum activity manifests as BZQ adopts a pose within the binding pocket of TRPM_PZQ that is dependent on a ubiquitously conserved residue. BZQ therefore acts as a universal activator of trematode TRPM_PZQ and a first-in-class, broad-spectrum flukicide.

Diseases caused by parasitic flatworms impart a considerable healthcare burden worldwide. Many of these diseases – for example, the parasitic blood fluke infection, schistosomiasis – are treated with the drug praziquantel (PZQ). However, PZQ is ineffective against disease caused by liver flukes from the genus Fasciola . This is due to a single amino acid change within the target of PZQ, a transient receptor potential ion channel (TRPM _PZQ ), in Fasciola species. Here we identify benzamidoquinazolinone analogs that are active against Fasciola TRPM _PZQ . Structure-activity studies define an optimized ligand (BZQ) that caused protracted paralysis and damage to the protective tegument of these liver flukes. BZQ also retained activity against Schistosoma mansoni comparable to PZQ and was active against TRPM _PZQ orthologs in all profiled species of parasitic fluke. This broad spectrum activity was manifest as BZQ adopts a pose within the binding pocket of TRPM _PZQ dependent on a ubiquitously conserved residue. BZQ therefore acts as a universal activator of trematode TRPM _PZQ and a first-in-class, broad spectrum flukicide.

The drug praziquantel (PZQ) is the key clinical therapy for treating schistosomiasis and other infections caused by parasitic flatworms. A schistosome target for PZQ was recently identified— a transient receptor potential ion channel in the melastatin subfamily (TRPM _PZQ )—however, little is known about the properties of TRPM _PZQ in other parasitic flatworms. Here, TRPM _PZQ orthologs were scrutinized from all currently available parasitic flatworm genomes. TRPM _PZQ is present in all parasitic flatworms, and the consensus PZQ binding site was well conserved. Functional profiling of trematode, cestode, and a free-living flatworm TRPM _PZQ ortholog revealed differing sensitives (~300-fold) of these TRPM _PZQ channels toward PZQ, which matched the varied sensitivities of these different flatworms to PZQ. Three loci of variation were defined across the parasitic flatworm TRPM _PZQ pocketome with the identity of an acidic residue in the TRP domain acting as a gatekeeper residue impacting PZQ residency within the TRPM _PZQ ligand binding pocket. In trematodes and cyclophyllidean cestodes, which display high sensitivity to PZQ, this TRP domain residue is an aspartic acid which is permissive for potent activation by PZQ. However, the presence of a glutamic acid residue found in other parasitic and free-living flatworm TRPM _PZQ was associated with lower sensitivity to PZQ. The definition of these different binding pocket architectures explains why PZQ shows high therapeutic effectiveness against specific fluke and tapeworm infections and will help the development of better tailored therapies toward other parasitic infections of humans, livestock, and fish.

Parasitic flatworm sensitivity to praziquantel is determined by amino acid variation in the binding pocket of a TRP channel.