Based on the notion that HDAC inhibitors may reactivate the expression of genes favoring cell response to drugs, the aim of this study was to investigate the interaction between the HDAC6-specific inhibitor ricolinostat (ACY1215) and the MEK-inhibitor selumetinib (AZD6244) to identify effective combinations in prostate cancer models. The gene discussed is HDAC9; the disease is prostate cancer.