Sensitivity of HMCLs to PRIMA-1^Met was independent from TP53 status, p53 expression, and myeloma heterogeneity. (A) Sensitivity of HMCLs to PRIMA-1^Met was independent of TP53 status. The LD₅₀ values were defined by incubating cells (100 000 cells/0.2 mL) for 72 hours in the presence of a serial dilution of PRIMA-1^Met (starting dose, 200 μM). Cell death was determined using Apo2.7 staining, as described previously.^24,27  The LD₅₀ values (defined as the mean of at least 3 independent experiments) were plotted against the TP53 status (supplemental Table 1). (B) Silencing of p53 in TP53^wt (XG6, NCI-H929) and TP53^R282W XG5 HMCLs did not inhibit PRIMA-1^Met-induced cell death. Stable shTP53 HMCLs were previously reported.²⁴  (Left) Cells were incubated for 72 hours, with serial dilutions of PRIMA-1^Met (starting dose, 80 μM), and cell death was assessed as described in the legend of Figure 1A. The data represent the mean ± standard error of the mean (SEM) of 3 independent experiments. (Right) Western blot analysis of p53 expression in shCont and shp53 myeloma cells. (C) Sensitivity of HMCLs to PRIMA-1^Met was independent of myeloma heterogeneity. The LD₅₀ values were plotted against myeloma heterogeneity, characterized by recurrent 14q32, leading to overexpression of CCND1, (C-MAF or MAF-B) MAF, and MMSET.²³