SELECTION OF PYRONARIDINE RESISTANCE IN PLASMODIUM BERGHEI IN A MOUSE MODEL

Abstract

Chemotherapy remains central in the control of malaria. However, the rapid emergence and spread of antimalarialdrugs remains a public health problem. To date, resistance to almost all available antimalarials has been reported. Tocounter this problem the resistance markers to existing drugs need to be fully understood. Pyramax®, a combination ofartesunate (ASN)-pyronaridine (PRD) was recently prequalified by WHO drug as a potential alternative for treatment ofmalaria in Africa. Artesunate is however partnered with a drug against which resistance may arise relatively quickly. Wethus used rodent malaria parasite Plasmodium berghei as a surrogate for Plasmodium falciparum to study pyronaridineresistance. We selected resistance by submitting P. berghei ANKA in vivo to increasing pyronaridine concentration fortwenty successive passages over a period of 6 months. The effective doses that reduces parasitaemia by 50% (ED50) and90% (ED90) determined in the standard 4-Day Suppressive Test for the parent line were 1.83mgkg-1 and 4.79mgkg-1. Aftertwenty drug pressure passages the ED50 and ED90 increased by 66 and 40 folds respectively. We then assessed thestability of the resistant phenotypes by i) dilution cloning (ED50=145.5mgkg-1, ED90 =193.1mgkg-1) ii) after growing themin absence of drug for five passages (ED50=107.5mgkg-1, ED90=146.1mgkg-1) and iii) after freezing the parasite at -80degree for at least 1 month (ED50=73.48, ED90=107.10mgkg-1). We concluded that stable pyronaridine resistant P.berghei lines were selected and could be used for elucidation of markers associated with pyronaridine resistance. Thestability of the resistant phenotypes indicates that resistance mechanisms may be encoded in the cell genome.