 Histone deacetylase HDAC inhibitors, including Panobinostat, radiosensitize tumor cells both in vitro and in vivo. HDAC inhibitors modify the expression of approximately 8 of the transcriptome83. In particular, they have been shown to down regulate expression of the DNA repair enzyme rad51, possibly explaining their radiosensitization properties. It is thought that Panobinostat radiosensitizes through an epigenetic mechanism. Since the target of HDAC inhibitors includes many proteins beyond histones, many prefer the name deacetylase inhibitors, DAC. 