Ritonavir does not directly inhibit caspase-1, -3, and -8 activity.

Protein extracts prepared from activated PBMCs, triggered to undergo apoptosis by CD95 agonistic mAb CH11 (0.5 mg/mL), were assayed for activity of caspase-1 (A), caspase-3 (B), and caspase-8 (C) using specific fluorogenic substrates. Ritonavir (▪) was added to the enzymatic reactions at the concentrations indicated and substrate conversion was recorded at the saturation points of the reactions. Because ritonavir did not inhibit these caspases directly, the assays were validated using specific inhibitors (●) for the respective caspases as controls. Uninhibited reactions are depicted as open circles (○). Values shown represent means of triplicate determinations ± SD. For caspase-1, the ritonavir-treated group did not differ significantly from the control group, but differed from the inhibitor group (P = .0019). P values for differences between inhibitor and ritonavir-treated groups for caspase-3 and caspase-8 were .011 and 019, respectively. The ritonavir-treated group did not differ significantly from the control group for these as well. Wilcoxon rank-sum tests were performed for all comparisons of the means. Results from one experiment are shown of 3 performed using cells from 3 different donors, with similar results.