Figure 1.

Relationship between cytotoxicity and proteasome β-subunit activity. AMO-1 cells and its derivatives adapted to bortezomib (AMO-BTZ) and carfilzomib (AMO-CFZ) have been cultured for 2 weeks without proteasome inhibitors. Then AMO-1, AMO-BTZ and AMO-CFZ were treated for a 1-h pulse with different concentrations of (a) bortezomib (Btz) or (b) carfilzomib (Cfz). Proteasome activity after drug exposure was measured directly using activity-specific, fluorescent chemical probes.²³ Cell viability was determined after cells were grown in fresh medium for 48 h following the 1-h drug exposure. Panels represent (in the order from left to right): cell viability determined by MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) test, activity of the proteasome β5c/5i, β1c/1i and β2c/2i subunits, respectively, as assessed by activity-based labeling, for each cell type (AMO-1, AMO-BTZ, AMO-CFZ, horizontal rows) and for each proteasome inhibitor (bortezomib, carfilzomib, panels a and b). Data are presented as a mean±s.d. of three independent replicates.