Activity of carfilzomib and bortezomib against myeloma models. (A) Several MM cell lines were treated with a 1-hour pulse of increasing concentrations of carfilzomib or bortezomib. After 24 hours, the number of live cells was determined with a WST-1 assay. (B) Activation of the stress response in RPMI 8226 cells pulse treated for 1 hour with proteasome inhibitors and allowed to recover for the indicated time points is shown. Protein expression levels of activated JNK were examined after treatment with carfilzomib or bortezomib. (C) ANBL-6 cells were exposed to a 1-hour pulse of 100 nM carfilzomib or bortezomib and allowed to recover for 8 hours. Cellular lysates (30 μg per reaction) were then incubated with 40-μM fluorogenic substrates specific for caspase-3, caspase-8, and caspase-9 activity. Results are expressed as fold relative fluorescence units over DMSO control and determined as described in Figure 1. Error bars for panels A and C are SD.