FIG. 1.

In vitro synergy of cysteine and aspartic protease inhibitors. Parasites grown in microwell cultures were incubated with different concentrations of protease inhibitors, and the effects of combinations of inhibitors were compared to the effects of each inhibitor used alone. Results were plotted by using an isobologram analysis based on the IC₅₀ for each inhibitor. Assays measured the metabolism (uptake of [³H]hypoxanthine) (A and B) and development (formation of new ring-stage parasites) (C) of cultured parasites. Inhibitor concentrations yielding 50% inhibition of control values with each assay were plotted. The concave slopes of the isobologram plots indicate synergistic interactions of the inhibitors.