SAHA (suberoylanilide hydroxamic acid, Vorinostat, Zolinza?) is a histone deacetylase (HDAC) inhibitor that binds directly to the catalytic site of the enzyme thereby blocking substrate access. Sirt activator based on a dihydropyridine structural scaffold. EC150 (effective concentration able to increase enzyme activity by 150%) is 1 uM for Sirt1, 25 uM for Sirt2, and 50 uM for Sirt3. The compound is active in whole cells and arrests cell cycle at G1/S phase in U937 cells. SAHA inhibits class I and class II HDACs at around 50 nM and arrests cell growth in a wide variety of transformed cells in culture at 2.5-5.0 uM.