For these assays, BSc2118 had to be i.p. administered Fulvestrant for technical reasons, yielding no optimal inhibition of the 20S proteasome within the 24-hour animal groups. Nevertheless,

animals treated with BSc2118 at 30 mg/kg revealed a tendency to reduce the number of metastases as compared to controls (Figure 7C). In spite of a tendency of BSc2118 (30 mg/kg) to reduce angiogenesis, significant results were lacking ( Figure 7D; P = 0.06). Taken together, BSc2118 exerts local antitumor activity in a mouse melanoma model. Novel proteasome inhibitors are intensively developed and studied in order to find more specific and safer inhibitors with a broad spectrum of therapeutic applications [15], [33], [34] and [35]. IDH inhibitor drugs In this context, we studied for the first time the biodistribution of the novel proteasome inhibitor BSc2118 In Vivo followed by an analysis of its therapeutic potential and therapeutic safety in the context of malignant melanoma. For inhibitor tracking in living organisms, the fluorescent variant of BSc2118, BSc2118-FL, was synthesized. BSc2118-FL was cell-permeable, targets the proteasome specifically, co-localizes with the proteasome

and had a similar inhibition profile in comparison to its non-fluorescent variant. The bright fluorescence signal facilitated rapid and sensitive detection of proteasomes by fluorescence-based microscopy in living cells and in tissues. Because the proteasome inhibitor BSc2118 had a low toxicity, even the use of higher concentrations that allows monitoring of inhibitor biodistribution, was well tolerated in experimental models. The biodistribution and inhibition profile of proteasomes inhibited by BSc2118 in a mouse model was compared to bortezomib and was similar in equivalent concentrations. BSc2118 was given daily at maximal doses of 60 mg/kg

body weight for 7 days, which was well tolerated by mice with no signs of toxicity. Using this application schedule, no lethality was observed. Moreover as it was shown in a different publication, BSc2118 up to 60 mg/kg daily dose did not affect peripheral blood morphology in C57BL/6 mouse [36]. In contrast, bortezomib had to be given with at least a one-day break, whereas daily injection of 1 Amobarbital mg/kg body weight was lethal in most animals. As such, BSc2118 might serve as a potential, low toxic and well tolerated novel drug [30]. Therefore, we analyzed the potential for BSc2118 usage in different application forms to be considered for proteasome inhibition. These typically include anti-tumor effects based on cell cycle arrest and on inducing apoptosis [34] and [35]. Although Bortezomib was developed and approved for therapy of multiple myeloma and mantle cell lymphoma only, therapeutic potential for other tumors was investigated within the last years as well [37]. However, bortezomib was not effective in treatment of solid tumors until recently [38].