Bortezomib induces DNA synthesis. (A) RPMI 8226 cells were treated with bortezomib (10 and 20 nM) for 8 hours. Cells were labeled with BrdU for an additional 2 hours and assessed for growth by DNA synthesis. (B) RPMI 8226 cells were incubated with bortezomib (20 nM) for 8 hours. Cells were washed with media to remove bortezomib, and then cultured for another 24 hours or 48 hours. Cell survival was determined by MTT assay. (C) Immunohistochemical analysis for p65 expression was performed on tumor tissue from RPMI 8226 xenograft mice, untreated and treated with bortezomib. *P < .01.