A potent inhibitor of HDAC6 (IC50 = 0.40 nM); selective for HDAC6 over HDAC3 (IC50 = 51.61 nM); induces α-tubulin acetylation, an HDAC6-dependent process, with minimal effect on global lysine acetylation; inhibits growth of patient-derived multiple myeloma cell lines (IC50s = 1.5-4.7 μM); enhances cytotoxicity of bortezomib and carfilzomib against patient-derived multiple myeloma cells; decreases tumor size in a human MM.1S multiple myeloma mouse xenograft model when administered in combination with bortezomib at doses of 50 and 0.5 mg/kg, respectively