LBH589 and bortezomib induce synergistic cytotoxicity against MM cell lines sensitive and resistant to Dex, as well as freshly isolated CD138⁺ patient MM cells. (A-D) Synergistic cytotoxicity of LBH589 and bortezomib was observed in RPMI8226 and MM.1S, patient cells, and OPM1 (4-20 nM), as well as in MM.1R cells (10-50 nM), as determined by MTS assay and presented as a fraction of cells affected (left panels) and combination indices (right panels).