Loss of p53 enhances the drug resistance of clonogenic MM cells. (A) Primary (1°) and secondary (2°) colony formation of MM.1S p53-wt (Scr) and p53-KO cells after treatment with melphalan (1 uM), bortezomib (1.5nM), dexamethasone (1.5 nM), or lenalidomide (62.5 nM) (n = 3). (B) Colony formation of p53-wt (Scr) and p53-KO MOLP8 cells with melphalan (1 uM) or bortezomib (5 nM) (n = 3). (C) Colony formation of p53-wt (Scr) and p53-KO NCI-H929 cells after treatment with melphalan (0.5 uM) or bortezomib (2 nM) (n = 3).