Mechanisms mediating the anti-MM activity of FK866 plus bortezomib. (A) MM-1S, U266, ANBL6/WT, and ANBL6/BR cells were pretreated with or without low-dose FK866 (3 nM) for 24 hours, and then bortezomib (2 nM) was added for an additional 24 hours. Cells were then harvested, and whole-cell lysates were subjected to immunoblot analysis using anti-PARP, anti-caspase 3, anti-caspase 8, anti-caspase 9, anti-Mcl-1, anti bcl-2, or anti-actin antibodies. (B) Bortezomib-sensitive (ANBL6/WT) and bortezomib-resistant (ANBL6/BR) cells were treated with FK866 (3 nM), bortezomib (2 nM), or combined therapy for 72 hours, followed by Annexin V/PI staining and flow cytometry analysis. CF, cleaved fragment; FL, full length.