In Vitro Sensitivities of Plasmodium falciparum Isolates from the China-Myanmar Border to Piperaquine and Association with Polymorphisms in Candidate Genes

The recent reports of resistance in Plasmodium falciparum to artemisinin derivatives and their partner drugs demand intensive studies toward understanding the molecular mechanisms of resistance. In this study, we examined the in vitro susceptibility of 63 P. falciparum field isolates collected from the China-Myanmar border area to chloroquine (CQ) and piperaquine (PPQ). Parasite isolates remained highly resistant to CQ, with the geometric mean 50% inhibitory concentration (IC50) of 252.7 nM and a range of 51.9 to 1,052.0 nM. In comparison, these parasites had a geometric mean IC50 of 28.4 nM for PPQ, with a fairly wide range of 5.3 to 132.0 nM, suggesting that certain parasite isolates displayed relatively high levels of resistance to PPQ. Interestingly, within the 4 years of study, the parasites exhibited a continuous decline in susceptibilities to both CQ and PPQ, and there was a significant correlation between responses to CQ and PPQ (Pearson correlation coefficient = 0.79, P 22%, and the I876V mutation was associated with reduced sensitivity to CQ. However, we could not establish a link between PPQ responses and the polymorphisms in the three genes associated with quinoline drug resistance.