New method developed to track the emergence of resistance to partner drugs

Artemisinin drug resistance is firmly established in many regions in Southeast Asia, but resistance to the commonly used antimalarial partner drug piperaquine is not well characterised in regions where artemisinin drug resistance is commonly found. Unlike artemisinin resistance, there is currently no genetic marker that can be used to identify the presence of resistance to piperaquine.

The WWARN In Vitro team lead by Institut Pasteur, Cambodia, have designed a new piperaquine survival assay (PSA) that can now be used to capture the outcomes of antimalarial drug resistance to piperaquine in the laboratory. This study was published recently in BMC Medicine.

Resistance to artemisinin drugs is reflected in the slow clearance of malaria from the blood after three days of treatment, however resistance to the partner drug is reflected in later recrudescence or re-emergence of the malaria infection in the patient. This new assay is crucial to identify and track malaria parasites resistant to the piperaquine partner drug as the resistant parasites are selected and become common in various locations.

“This assay is an extremely useful way to track and assess resistance to the artemisinin partner drug piperaquine in the field. It will be especially useful in areas where artemisinin resistance is established, such as Southeast Asia, where dihydroartemisinin-piperaquine (DP) is commonly used as a treatment against malaria infection,” says Dr Benoit Witkowski, co-lead author of the study and PI researcher in the Malaria Molecular Epidemiology Unit at the Institut Pasteur, Cambodia.

The assay mimics the exposure of the malaria parasite to piperaquine in the patient’s body. The assay is based on the detection of viable parasites after exposure to 200 nM of the drug for 48 hours.

Results from this study strongly reinforce recent recommendations from the Cambodian national malaria control programmes to use the ACT, artesunate mefloquine, as the first line of treatment for uncomplicated malaria in regions where resistance to DP is firmly established.

“The gains we’ve made against malaria over the past decade are coming under jeopardy as ACTs decline in efficacy across Cambodia and other parts of Southeast Asia. It is critical that we are able to provide timely evidence of resistance to artemisinin and partner drugs such as piperaquine, to inform policy makers of the risks and complement therapeutic efficacy studies,” adds Dr Didier Ménard, Head of the Malaria Molecular Epidemiology Unit at the Institut Pasteur, Cambodia.

The study also investigated the association between candidate molecular markers and in vitro PSA survival rates. This new assay, in conjunction with genetic testing for the K13 mutation known to be associated with artemisinin drug resistance in the Mekong region, will be important in providing governments and national control programmes with the ability to assess the spread or emergence of resistance to artemisinin and piperaquine.

Prof Philippe Guérin, Director of WWARN adds: “This new assay builds on the success of the artemisinin Ring Stage Survival Assay developed in 2014. Both assays work on the basis of parasite clearance – a key indicator of the presence of antimalarial drug resistance – and both enable us to better understand the threat of antimalarial drug resistance.”

Research publication:

Duru, V., et al. (2015). "Plasmodium falciparum dihydroartemisinin-piperaquine failures in Cambodia are associated with mutant K13 parasites presenting high survival rates in novel piperaquine in vitro assays: retrospective and prospective investigations." BMC Medicine 13(1): 1-11.