Abstract:
Chemotherapy remains central in the control of malaria. However, the rapid emergence and spread of antimalarial
drugs remains a public health problem. To date, resistance to almost all available antimalarials has been reported. To
counter this problem the resistance markers to existing drugs need to be fully understood. Pyramax®, a combination of
artesunate (ASN)-pyronaridine (PRD) was recently prequalified by WHO drug as a potential alternative for treatment of
malaria in Africa. Artesunate is however partnered with a drug against which resistance may arise relatively quickly. We
thus used rodent malaria parasite Plasmodium berghei as a surrogate for Plasmodium falciparum to study pyronaridine
resistance. We selected resistance by submitting P. berghei ANKA in vivo to increasing pyronaridine concentration for
twenty successive passages over a period of 6 months. The effective doses that reduces parasitaemia by 50% (ED50) and
90% (ED90) determined in the standard 4-Day Suppressive Test for the parent line were 1.83mgkg-1 and 4.79mgkg-1. After
twenty drug pressure passages the ED50 and ED90 increased by 66 and 40 folds respectively. We then assessed the
stability of the resistant phenotypes by i) dilution cloning (ED50=145.5mgkg-1, ED90 =193.1mgkg-1) ii) after growing them
in absence of drug for five passages (ED50=107.5mgkg-1, ED90=146.1mgkg-1) and iii) after freezing the parasite at -80
degree 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. The
stability of the resistant phenotypes indicates that resistance mechanisms may be encoded in the cell genome.
