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

## TL;DR

This study shows that P-Glycoprotein-9 helps nematodes resist the drug ivermectin by pumping it out of their cells, suggesting a new target to combat drug resistance in parasites.

## Contribution

The study identifies PGP-9 as a key player in ivermectin resistance in nematodes through functional analysis and fluorescent drug tracking.

## Key findings

- Deletion of pgp-9 in IVR10 nematodes significantly increased ivermectin sensitivity.
- Transgenic expression of Haemonchus contortus pgp-9.1 restored resistance in IVR10 nematodes.
- Fluorescent ivermectin analog showed reduced drug accumulation in IVR10, reversed by pgp-9 deletion.

## Abstract

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.

The intensive use of macrocyclic lactones such as ivermectin to control gastrointestinal parasitic nematodes in livestock has led to the emergence of widespread resistance. Understanding the multifaceted processes underlying resistance remains an urgent challenge. In our study, we focus on a family of ATP-binding cassette transporter proteins, P-Glycoproteins, which can actively pump drugs out of cells. To explore their role, we relied on a model of an ivermectin-resistant nematode, the Caenorhabditis elegans IVR10 strain. We used gene knock-out and knock-down approaches to abolish or reduce protein expression, together with a fluorescent derivative of ivermectin that allowed us to visualize drug distribution in the worm. We found that one member of this family, PGP-9, plays an important role in drug response. We show that PGP-9 is expressed at key physiological barriers, such as the intestine, thereby preventing drug accumulation in the nematode. Our work provides new insights into how resistant worms can tolerate treatment, which may help in developing strategies to slow the spread of drug resistance in the future.