Histone deacetylase 6 (HDAC6) is a class II HDAC that represses transcription by removing acetyl groups from histones. In addition, HDAC6 deacetylases tubulin, which is important in regulating microtubule stability and function. CAY10603 is a potent and selective inhibitor of HDAC6 (IC50 = 0.002 nM, as compared with 271, 252, 0.42, 6851, and 90.7 nM for HDAC1, 2, 3, 8, and 10, respectively). Also, CAY10603 prevents the growth of several pancreatic cancer cell lines (IC50 = 0.1-1 μM). The HDAC6 inhibitor is more active in inhibiting cell growth than the broad spectrum HDAC inhibitor suberoylanilide hydroxamic acid (SAHA).