BG45 is a potent, selective and cell permeable HDAC3 inhibitor. It inhibits HDAC3 with IC50 of 289 nM. It has IC50 of 2.0 μM, 2.2 μM and >20 μM for HDAC1, HDAC2, and HDAC6 in cell-free assays, respectively. BG45 triggers significant MM cell growth inhibition via apoptosis, evidenced by caspase and poly (ADP-ribose) polymerase cleavage. BG45 alone and in combination with bortezomib triggers significant tumor growth inhibition in vivo in a murine xenograft model of human MM.