<i>In Vitro</i> Activities of Quinine and Other Antimalarials and <i>pfnhe</i> Polymorphisms in <i>Plasmodium</i> Isolates from Kenya

ABSTRACT Resistance to the amino alcohol quinine has been associated with polymorphisms in pfnhe , a sodium hydrogen exchanger. We investigated the role of this gene in quinine resistance in vitro in isolates from Kenya. We analyzed pfnhe whole-gene polymorphisms, using capillary sequencing, and pfcrt at codon 76 ( pfcrt -76) and pfmdr1 at codon 86 ( pfmdr1 -86), using PCR-enzyme restriction methodology, in 29 isolates from Kilifi, Kenya, for association with the in vitro activities of quinine and 2 amino alcohols, mefloquine and halofantrine. In vitro activity was assessed as the drug concentration that inhibits 50% of parasite growth (IC 50 ). The median IC 50 s of quinine, halofantrine, and mefloquine were 92, 22, and 18 nM, respectively. The presence of 2 DNNND repeats in microsatellite ms4760 of pfnhe was associated with reduced susceptibility to quinine (60 versus 227 nM for 1 and 2 repeats, respectively; P < 0.05), while 3 repeats were associated with restoration of susceptibility. The decrease in susceptibility conferred by the 2 DNNND repeats was more pronounced in parasites harboring the pfmdr1 -86 mutation. No association was found between susceptibility to quinine and the pfcrt -76 mutation or between susceptibility to mefloquine or halofantrine and the pfnhe gene and the pfcrt -76 and pfmdr1 -86 mutations. Using previously published data on the in vitro activities of chloroquine, lumefantrine, piperaquine, and dihydroartemisinin, we investigated the association of their activities with pfnhe polymorphism. With the exception of a modulation of the activity of lumefantrine by a mutation at position 1437, pfnhe did not modulate their activities. Two DNNND repeats combined with the pfmdr1 -86 mutation could be used as an indicator of reduced susceptibility to quinine.