Fig. 4.

Intracellular proteasome inhibition by PKS21221 and its cytotoxicity against transformed cell lines. a Karpas 1106P lymphoma cells (white and black symbols) or HepG2 cells (blue symbols) were treated with PKS21221 for 2 h at the concentrations indicated prior to incubation with substrate (Ac-ANW)₂R110 for β5i (Karpas cells) or suc-LLVY-luciferin for β5 (Karpas cells and HepG2 cells). IC50s were 0.154 and 0.149 µM for the two substrates in Karpas cells. b Cytotoxicity of PKS21221 against multiple myeloma cell lines MM.1S (solid circle) and RPMI 8226 (solid square), Karpas (solid triangle) and HepG2 (blue triangle). Cell viability was determined by CellTiter-glo. Values of IC50 of intracellular proteasome inhibition and EC50 of cytotoxicity are listed in the Table 3. Data are means ± SEM of three to four independent experiments