Ivermectin Fluorescent drug to decipher molecular mechanism of P-glycoproteins mediated RESistance – Fluo-RES

Parasitic nematodes infecting humans and animals are major public health problems worldwide. Ivermectin (IVM) anthelmintic is the most widely used antiparasitic drug in veterinary and human medicine; a powerful example of “One-Health” drug. Most grazing ruminants are infected by a variety of helminth parasites which negatively impact their welfare and consequently their production. IVM has been first marketed for use in farmed animals mainly against gastrointestinal nematodes. It is also used in companion animals, to treat dogs and cats to prevent Dirofilaria immitis infection, a filarial nematode causing heartworm disease. Thanks to its remarkable broad-spectrum activity, IVM has been promptly used in humans in mass treatment programs for onchocerciasis and lymphatic filariasis. It is also used in the treatment for strongylosis and is now the drug of choice against scabies, and difficult-to-treat lice. IVM also reduces malaria transmission through its action against Anopheles mosquito vectors. The discovery of the IVM was awarded a Nobel Prize in 2015 for its major impact on human health. Inevitably, intensive use of the anthelmintic has selected drug-resistant parasite populations globally in many animal species. This is now a major global problem in small livestock, increasing in cattle, and well described in parasites of companion animals. Nowadays, the inevitable losses in productivity and problems of animal welfare result from failure to control resistant worms adequately. The rapid spread of IVM resistance may compromises not only the control of parasites in animals but parasites in humans. In that context, actions are needed to detect drug resistance early, and to preserve efficacy as much as possible. This requires an in-depth understanding of the mechanisms of resistance. There is now considerable evidence that IVM resistance is a polygenic trait in various species of nematode but the mechanisms of resistance that allow some pathogens to survive remain to be resolved. Detoxification systems involving ABC transporters, particularly P-glycropoteins (Pgp), and to a lesser extend cytochromes P450, control the drug quantity and distribution in the host and the final concentration of IVM arriving at the drug receptor sites in the worm; the glutamate-gated chloride channels. The induction of detoxification systems upon exposure to IVM appears to be a precursor event that helps to decrease the amount of drug reaching the target, and to allow organisms that contain resistance genes to survive, which ultimately leads to the loss of drug activity. Thus, the amount of drug in the target organism is a key parameter for assessing drug efficacy and identifying resistant organisms. Nowadays very little is known about the factors that control the bioavailability of IVM in the target worms, and sensitive tools to explore these aspects are lacking. Recently, our laboratory synthesized a fluorescent probe: IVM-Fluo. It is stable and suitable for use as a probe in the nematode model Caenorhabditis elegans. Preliminary results, with microscopy applications in C. elegans, revealed a higher IVM accumulation in wild-type animals compared to IVM-resistant worms, in line with a link between IVM concentration (e.g. induced efflux and/or induced metabolism) in the worm and IVM resistance status. Our fluorescent probe offers new perspectives to evaluate resistance status in parasite nematodes and more widely to pinpoint tissues/cells that accumulate IVM and link this with Pgp expression. Deciphering where IVM accumulates in nematodes will reveal much about how the drug works in the worm and it should advance our understanding of IVM resistance in nematodes. In that context, the objectives of Fluo-RES project are to use a fluorescent IVM probe to understand the link between detoxification systems, IVM accumulation/localization and resistance in (i) various cell models, (ii) the nematode model C. elegans and (iii) resistant parasitic nematodes.