Fig 4.

(A) Effects of compounds on parasite motility. C1 and C5 completely blocked parasite motility, while C3 and C12 slightly enhanced it. V, vehicle control. (B) Effects of four inhibitors and four enhancers on parasite invasion. Cytochalasin D (Cyt-D) was used as a positive control for invasion inhibition. Effects on invasion were assessed by comparing the mean number of invading or uninvading parasites per field of view to that for the vehicle control. Cytochalasin D and C1 significantly decreased the number of invading parasites, while C1 also decreased the number of uninvading (i.e., attached) parasites, although this difference was not significant (P = 0.08). (C) Effect of pretreatment of extracellular parasites for 16 h on parasite growth after washing out the compound. Compounds C1, C2, C3, and C5 significantly inhibited parasite growth after pretreatment, while C8 significantly enhanced parasite growth. On the basis of the invasion assay results, it is likely that very few, if any, parasites attached to the monolayer after C1 treatment. (D) Effects of host cell pretreatment on parasite growth. Host cells were pretreated with the compounds or vehicle for 24 h and extensively washed prior to parasite invasion and 3 days of growth. Assays where the compound was present for the entire 3-day incubation period were also run in parallel. C8 and C11 resulted in significantly enhanced parasite growth after pretreatment that was comparable to that observed when the compound was present for the entire 3-day growth period. *, P < 0.05; **, P < 0.01; ***, P < 0.001 (compared to the vehicle-treated control for all comparisons).