Critical role of P-Glycoprotein-9 in ivermectin tolerance in nematodes.

Helminth infections in grazing ruminants are of major concern for animal welfare and cause substantial economic losses, prompting the widespread use of ivermectin (IVM). The emergence of IVM resistance, driven by complex and poorly understood mechanisms, increasingly compromises treatment efficacy. Drug efflux transporters, particularly P-glycoproteins (PGPs), are suspected to contribute to resistance. Yet, the study of their individual and functional role is hindered by their diversity in nematodes. This study aimed to dissect the role of specific PGPs in mediating IVM resistance. Thus, the Caenorhabditis elegans strain IVR10, selected for IVM resistance and reported to overexpress pgps, was used as a model. We generated different IVR10 strains each lacking one of six key pgps, and assessed changes in IVM tolerance. Remarkably, only the deletion of pgp-9 significantly increased IVM sensitivity. Furthermore, transgenic expression of Haemonchus contortus pgp-9.1 rescued the resistant phenotype, demonstrating a conserved function across species. To explore drug dynamics, we developed a fluorescent IVM analog, which revealed reduced drug accumulation in IVR10, a phenotype reversed by pgp-9 deletion. Altogether, these findings show that nematode PGP-9 modulates IVM tolerance in IVR10 by controlling drug efflux and highlight it as a potential therapeutic target.