Inhibition or Knockdown of ABC Transporters Enhances Susceptibility of Adult and Juvenile Schistosomes to Praziquantel

Abstract

Parasitic flatworms of the genus Schistosoma cause schistosomiasis, a neglected tropical disease that affects hundreds of millions. Treatment of schistosomiasis depends almost entirely on the drug praziquantel (PZQ). Though essential to treating and controlling schistosomiasis, a major limitation of PZQ is that it is not active against immature mammalian-stage schistosomes. Furthermore, there are reports of field isolates with heritable reductions in PZQ susceptibility, and researchers have selected for PZQ-resistant schistosomes in the laboratory. P-glycoprotein (Pgp; ABCB1) and other ATP binding cassette (ABC) transporters remove a wide variety of toxins and xenobiotics from cells, and have been implicated in multidrug resistance (MDR). Changes in ABC transporter structure or expression levels are also associated with reduced drug susceptibility in parasitic helminths, including schistosomes. Here, we show that the activity of PZQ against schistosome adults and juveniles ex vivo is potentiated by co-administration of either the highly potent Pgp inhibitor tariquidar or combinations of inhibitors targeting multiple ABC multidrug transporters. Adult worms exposed to sublethal PZQ concentrations remain active, but co-administration of ABC transporter inhibitors results in complete loss of motility and disruption of the tegument. Notably, juvenile schistosomes (3–4 weeks post infection), normally refractory to 2 µM PZQ, become paralyzed when transporter inhibitors are added in combination with the PZQ. Experiments using the fluorescent PZQ derivative (R)-PZQ-BODIPY are consistent with the transporter inhibitors increasing effective intraworm concentrations of PZQ. Adult worms in which expression of ABC transporters has been suppressed by RNA interference show increased responsiveness to PZQ and increased retention of (R)-PZQ-BODIPY consistent with an important role for these proteins in setting levels of PZQ susceptibility. These results indicate that parasite ABC multidrug transporters might serve as important targets for enhancing the action of PZQ. They also suggest a potentially novel and readily-available strategy for overcoming reduced PZQ susceptibility of schistosomes.

Effects of third generation P-glycoprotein inhibitors on the sensitivity of drug-resistant and -susceptible isolates of Haemonchus contortus to anthelmintics in vitro

“…Lifschitz et al (2010a,b); Lifschitz et al (2010a,b) showed that P-gp inhibitors could increase the efficacy of macrocyclic lactones against several species of GIN in sheep and cattle. With regard to the third generation MDRIs, Kasinathan et al (2014) recently reported that tariquidar, zosuquidar and elacridar enhanced the susceptibility of adult Schistosoma mansoni to praziquantel in vitro. However, to our knowledge, there are no reports on the effects of these third generation inhibitors on any life stage of GINs.…”

The role of drug efflux systems in anthelmintic resistance in parasitic nematodes

“…The synergistic effects of third-generation inhibitors (zosuquidar, elacridar, and tariquidar) in increasing the efficacy of praziquantel had only been reported for adult Schistosoma mansoni (Kasinathan et al, 2014). The present study, therefore, has significantly extended these earlier reported studies by highlighting the synergistic effects of a number of third generation MDRIs in an economically-important species of GIN.…”

“…The disruption of parasite egg deposition in worms due to SMDR2 and SmMRP1 genetic knockdown suggests that MDR transporters play an important physiological role in egg production, hence it could be ventured that the absence of egg production was due to the effects of tariquidar on MDR transporters. Later on, Kasinathan et al (2014) reported that tariquidar, zosuquidar and elacridar enhanced the susceptibility of adult S. mansoni to praziquantel in vitro. However, there are no reports on the effects of these third-generation inhibitors on any life stage of GINs.…”

“…Lifschitz et al (2010a, b) showed that P-gp inhibitors could increase the efficacy of macrocyclic lactones against several species of GIN in sheep and cattle. With regard to the third generation MDRIs, Kasinathan et al (2014) recently reported that tariquidar, zosuquidar and elacridar enhanced the susceptibility of adult Schistosoma mansoni to praziquantel in vitro.…”

Characterising granuloma regression and liver recovery in a murine model of schistosomiasis japonica

“…The transcriptional response of the parasite to PZQ has advanced the understanding of its mode of action (Gobert, 2010). While some insights have been made in regards to the anti-parasite response of PZQ for both S. japonicum (You et al, 2013) and S. mansoni (Aragon et al, 2009;Hines-Kay et al, 2012;Kasinathan et al, 2014), less is understood regarding the impact of the drug on host tissues, particularly in the main organ of pathology, the liver.…”