In blood and liver there was an accumulation of polyubiquitin conjugates observed that correlated with proteasome inhibition displayed in Figure 3. In the brain, however, a constitutive high amount of polyubiquitin conjugates was detected that did not increase upon administration of inhibitors. A moderate accumulation of polyubiquitin was only found in brain homogenates after 24 hours of BSc2118 treatment. Proteasome inhibitors are approved for use in the treatment Natural Product Library of multiple myeloma and mantle cell lymphoma. Moreover, a number of clinical studies investigated the anti-tumor effects of bortezomib in patients with solid tumors. Therefore, we decided to compare potential anti-tumor
effects of BSc2118 to bortezomib in the B16F10 melanoma model in mice (Figure 6). First, we compared the efficiency selleck of BSc2118 to inhibit the 20S activity directly within tumor tissues after i.t. or i.p. administration. The inhibition in tumor tissues was compared to the inhibition in red blood cells. After i.p. administration of BSc2118 (30 mg/kg),the activity of 20S proteasomes was reduced by up to 65% within tumors when measured at 1 hour post-injection. However, the 20S proteasome activity recovered to control levels within 24 hours (Figure 6). BSc2118 when given i.t. (10 mg/kg) almost completely inhibited 20S proteasome activity at 1 hour after administration. Activities also
remained inhibited by 90% during the following 24 hours. BSc2118 given i.p. reduced the 20S activity
in blood cells of mice bearing melanoma (Figure 6) similarly to healthy ones (Figure 3), i.e. there was an initial reduction of 20S activity in the 1-hour group that increased in the 24-hour group. After i.t. injection of BSc2118, the initial inhibition of the 20S proteasome in the 1 hour groups was 40% and it dropped towards 50% in the 24-hour groups. Taken together with proteasome inhibition within erythrocytes after i.t. injection of BSc2118, Morin Hydrate there is an evidence that at least half of the initial proteasome activity is still inhibited within the tumor after 24 hours post-injection and that the inhibitor is slowly released from the place of injection. The activity data correlated with accumulation of polyubiquitin conjugates within tumors that are shown in Figure 6E. Tumor size or survival of treated mice after i.p. administration with either BSc2118 or bortezomib was, however, not affected by the inhibitors (data not shown). On the contrary, when BSc2118 was administered i.t. at a 5mg/kg dose, a complete tumor regression was observed, which led to prolonged animal survival for up to two months (Figure 7, A–B). Unexpectedly, when BSc2118 was injected i.t. at 10 or 15 mg/kg doses, a significant local toxicity (edema and ischemia) was observed in 30% of animals that precluded further analysis of tumor growth ( Figure 7, A–B).