Vorinostat inhibits the enzymatic activity of histone deacetylases HDAC1, HDAC2 and HDAC3 (Class I) and HDAC6 (Class II) at nanomolar concentrations (IC5_
The major pathways of vorinostat metabolism involve glucuronidation and hydrolysis followed by _-oxidation. Human serum levels of two metabolites, O-glucuronide of vorinostat and 4-anilino-4-oxobutanoic acid were measured. Both metabolites are pharmacologically inactive. Compared to vorinostat, the mean steady state serum exposures in humans of the O-glucuronide of vorinostat and 4-anilino-4-oxobutanoic acid were 4-fold and 13-fold higher, respectively. In vitro studies using human liver microsomes indicate negligible biotransformation by cytochromes P450 (CYP).