Differential blocking of apoptosis by caspase-specific blocking peptides in myeloma cells expressing wt or mutated p53.

U266 cells (mutated p53, upper panel) and HS-Sultan (wt p53, lower panel) cells were cultured for 48 hours with 7.5 μM ATO, with or without 2 μM of each caspase inhibitory peptide, or control peptide (FA-FMK). Nonspecific toxicity of the control peptide (CP) was around 5%. The toxicity of the blocking peptides was 2% to 5% above untreated control cells (results not shown). Apoptosis was determined by the annexin V method. Ar is ATO alone; Ar+1 is ATO plus caspase-1 inhibitor; Ar+2 is ATO plus caspase-2 inhibitor; and so on. For more experimental details, see “Materials and methods.” Bars are ± SD of at least 3 experiments. Note the differential blocking of apoptosis by caspase-9 and caspase-8 and -10, depending on the status of p53.