Therefore, the search for new effective and low toxic inhibitors of the proteasome system is urgently needed. Another proteasome inhibitor that has been frequently used in Buparlisib in vitro various experimental designs is MG132 (zLLL-CHO). In the present project, we characterized the novel inhibitor
BSc2118 (patent no T30305), which is an analogue of MG132 with a better proteasome inhibition profile than MG132 [27]. Previously, BSc2118 has been shown to inhibit the ChTL activity of the proteasome, induce G2/M cell cycle arrest and promote apoptosis. BSc2118 further stabilizes IκBα and prevents NF-κB activation [27]. In the current work, we analyzed the distribution pattern of Bsc2118 both in various tumor cell lines and in mice as well as the inhibition profile in selected mice organs after intraperitoneal administration. We finally show that application of BSc2118 in mice induces local anti-tumor effects and is tolerated at higher doses as compared to bortezomib. BSc2118 and fluorescent Bodipy-BSc2118 was dissolved in DMSO at 20 mM and kept at − 20°C. Bortezomib (Lilly, Germany) was dissolved in distilled water at 4 mM and kept at − 20°C
until usage. BSc2118 was synthesized as described previously [28]. The fluorescent variant of BSc2118 (further named as BSc2118-FL) was synthesized as follows: a solution of 10 mg of the peptide NH2-Leu-Asp(tBu)-Leu-CHO (BSc2118) in 1 ml dimethylformamide DMF (pH = 
was given to 10 mg of Bodipy-FL, SE (Molecular Probes, Germany). The ABT 737 reaction mixture was stirred overnight in darkness. Preparative purification by high-pressure
liquid chromatography (HPLC) was carried out on a Shimadzu LC-8A system with an Agilent Zorbax, C18 SE column (250 × 21.2 mm), 7 μl, (buffer A: 0.2% trifluoroacetic acid TFA in water, buffer B: 0.2% TFA in water: acetonitrile, 1:4). The peptides were purified with a gradient of 60% B to 95% B in 50 min. HeLa cells and C26 murine colon cancer cells were cultured in RPMI-1640 (Biochrom AG, Germany) with stable glutamax, both supplemented with 10% heat-inactivated FBS (Invitrogen, Germany), 100 μg/ml streptomycin and 250 ng/ml amphotericin much B (Invitrogen, Germany). For assessment of In Vitro cytostatic/cytotoxic activity of BSc2118, established human and mouse tumor cell lines were used. These cells were in particular: HCT116, PC3, LoVo, CaPan2, MDA435, Panc02, EMT6, C26, B16F10 (all ATCC) MeWo, MeWoCis, MeWoVin, MeWoEto, MeWoFote (obtained from Dr. H. Roekmann [29]), Mel-6, Mel-15, Mel-18, Mel-21, MaMel-63a (obtained from Dr. D. Schadendorf, Skin Cancer Unit Deutsches Krebsforschungszentrum, Heidelberg, Germany), WM35, WM902B, WM9 (obtained from Dr. M.