Caspase inhibitors z-VAD-fmk and z-IETD-fmk prevent HGS-ETR1– and HGS-ETR2–induced myeloma killing and Mcl-1L cleavage. (A) NAN-1 and MDN (125 000 cells/0.25 mL in 96-well plates) were cultured for 48 hours with or without (control) 0.6 mg/mL HGS-ETR1 or HGS-ETR2 mAb in the presence or absence of 50 mM caspase inhibitors. (B) Myeloma cells (4 million/8 mL) cultured with (NAN-1) or without (KMS12PE) 3 ng/mL IL-6 were treated for 7 hours with 0.6 μg/mL HGS-ETR1 mAb in the presence or absence of 50 μM caspase inhibitors.