FIG 6.

(A) Effect of alisporivir on the ring survival of the artemisinin-resistant parasite strain. (i) Light microscopic images of Giemsa-stained parasites treated with DHA, alisporivir, and DHA plus alisporivir. For RSA, early-ring-stage parasites (0 to 3 h) were incubated with DHA (700 nM), alisporivir (4 μM), or DHA+alisporivir (700 nM + 4 μM) for 6 h. Postincubation, the drug was removed by extensive washing, and the parasites were allowed to grow for 72 h. (ii) Bar graph representing the percent parasitemia in untreated, DHA-treated, alisporivir-treated, and DHA+alisporivir-treated samples. The combination of alisporivir with DHA enhances the antiparasitic activity of DHA against an artemisinin-resistant strain (*, P < 0.05). Scale bar, 5 μm. The data represent the means ± the SD of three independent experiments. The statistical significance was calculated using an unpaired t test. (Bi) Effect of alisporivir (1 μM) on a 700 nM DHA-treated ring-stage culture of the artemisinin-resistant strain. The culture was incubated with DHA for 6 h and then washed with culture medium; alisporivir (1 μM) was added, and the culture was allowed to grow for 72 h. (ii) Significant reduction in the parasitemia of a DHA-treated ring-stage culture of an artemisinin-resistant strain was observed after treatment with 1 μM alisporivir. The data represent the means ± the SD of three independent experiments. The statistical significance was calculated using an unpaired t test. (C) Checkerboard combination assay showing synergistic antiparasitic activity of alisporivir with DHA against an artemisinin-resistant strain at three different combinations of DHA and alisporivir with an FIC of <1.