6). A modification of the fluorescence protease assay also was performed in which freshly prepared protease from replicons was used in place of recombinant protease, as described by Yu et al.21 (Fig. 5D). The results of these experiments were similar to those with the recombinant enzyme, although inhibition of the endogenous AP24534 cost protease required slightly higher concentrations of BV than the recombinant enzyme, possibly because of conversion of BV to BR by endogenous BVR in the microsomes. The kinetics of BV inhibition of NS3/4A protease was assessed on Lineweaver-Burk plots (Fig. 6A). These data indicated that

BV competitively inhibits NS3/4A protease, based on the characteristic increase in slope with higher concentrations of inhibitor. Slopes (Km/V) and y intercepts (1/Vmax) of the primary reciprocal plots were then used to make secondary plots (Fig. 6B, C)

to estimate Ki and Ki′, respectively, as general indices of competitive and noncompetitive inhibition. Note that plots of BV versus 17-AAG concentration either 1/Vap or Km/V showed highly significant linearity, (r1 = 0.975 and r2 = 0.979 respectively, p < 0.005), suggesting that BV has both noncompetitive and competitive inhibitor activity for NS3/4A protease (Ki′ = 1.1 and Ki = 0.6 μM, respectively). BV is rapidly reduced to BR by the soluble enzyme BVR (Fig. 1). We hypothesized that knockdown of BVR expression would result in increased antiviral activity for BV by diminishing its conversion to the less potent BR. Preliminary WB showed that knockdown of BVR was highly efficient and led to more than 80% reduction of BVR expression in both replicon lines (Fig. 7A). The antiviral activity of BV was significantly enhanced by BVR knockdown compared with control (scramble) RNA knockdown (Fig. 7B, left panel, p < 0.01). In contrast, knockdown of BVR before incubation of replicons with BR had no significant effect on the relatively modest antiviral

activity of BR (Fig. 7B, right panel). Taken together, these data support the concept that BVR knockdown augments the check details antiviral activity of BV by arresting its conversion to BR and thereby maintaining higher intracellular levels of BV. Because interferon remains a cornerstone of HCV therapy, we examined the effects of BV on the antiviral activity of α-interferon. As shown in Fig. 8, BV had a clear additive effect when exposed to cells in the presence of interferon. These findings indicate that BV does not appear to compromise the action of interferon, but rather to enhance it. They also raise the possibility that the BV or stable derivatives could be used as antiprotease agents in combination with interferon. Heme oxygenase catalyzes the breakdown of heme to equimolar quantities of BV, iron, and carbon monoxide.