Resistance to melphalan in mutant RAS MM cells is partially regulated by cox-2. (A) WT, N-RAS–, and K-RAS–containing ANBL-6 cells were cultured with 0μM, 5 μM, and 20 μM melphalan for 48 hours and nonviable cells were then quantified. The results are reported as percent of nonviable cells in each population, mean ± SE of 3 experiments (except the 20-μM treated group, which was performed once). Results from WT cells challenged with 5 μM melphalan are significantly different from N-RAS and K-RAS cells (P < .05). (B) Oncogenic N-RAS– and K-RAS–containing ANBL-6 cells were cultured with or without NS398 (10 μM) for 24 hours and then challenged with melphalan (5 μM). After an additional 48 hours in culture, nonviable cells were quantified. Results are presented as percent cell death, mean ± SE of 4 separate experiments. *Significantly different from corresponding groups without added cox-2 inhibitor (P < .05). (C) Mutant N-RAS and K-RAS cells were cultured without antibody or with 5 μg/mL mouse IgG or 5 μg/mL PGE2 mouse neutralizing antibodies for 24 hours and melphalan was then added at 5 μM. The cells were maintained for an additional 48 hours and the percent of cell death was determined. The data are reported as the percent cell death in each population above untreated group. (D) WT cells were cultured without IL-6 and with or without PGE2 (μM) for 24 hours and 5 μM melphalan was then added. After 48 hours of melphalan treatment, nonviable cells were quantified with trypan blue uptake, mean ± SD, n = 2.