Modulation of TRAIL-induced cytotoxicity in MM.1S myeloma cells by selective inhibition of caspases.

(A) TRAIL-sensitive MM.1S myeloma cells were pretreated 1 hour before overnight incubation with TRAIL (100, 200, and 300 ng/mL) with or without the pancaspase inhibitor ZVAD-FMK, the caspase-8 inhibitor IETD-FMK, the caspase-3 and -7 inhibitor DEVD-FMK, the caspase-9 inhibitor LEHD-FMK, or the caspase-6 inhibitor VEID-FMK. Cell survival was determined using the MTT colorimetric assay. Bars represent mean ± SD values. (B-D) Caspase-3 enzymatic activity was measured by a caspase-3 intracellular activity assay in TRAIL-sensitive MM.1S cells as in Figure 2. (B) Control MM.1S cells. (C) MM.1S cells were treated with TRAIL (300 ng/mL) for 5 hours. (D) MM.1S cells were treated with TRAIL in the presence of DEVD-FMK (1 hour before treatment). DEVD-FMK inhibits caspase-3 activity, confirming that it is indeed internalized by MM cells and is functional.