Enhancement of tumor cell death by PS-341 plus TRAIL combinations. (A) C1498 cells labeled with [¹¹¹In] Ox and then incubated with PS-341 at 0 (▪), 10 nM (○), 20 nM (♦), or 30 nM (□) for 2 hours prior to the addition of various concentrations of TRAIL. After a further 16 hours, lysis (± SEM) was estimated as described in “Materials and methods.” (B) Renca cells were incubated with PS-341 at 0 (▪), 10 nM (○), 20 nM (♦), and 40 nM (▴) for 2 hours prior to the addition of various concentrations of TRAIL. After a further 16 hours, cell viability (± SEM) was assessed by the uptake of the MTS dye as described in “Materials and methods.” *P < .01 and **P < .001 by Student t test.