HDAC9 and cancer: Both PC-3 and DU145 cells displayed a basal expression of HR gene products (Rauh‐Adelmann et al., 2000[34]), but they varied in their PTEN expression status as DU145 displayed higher mRNA levels of PTEN. The precise anti-neoplastic mechanism of action for HDAC inhibitors, such as VPA, has not been completely understood, but their role in down-regulating proteins of NHEJ and HR pathways in cancer cells are well explained (Munshi et al., 2006[29]).