Cytotoxic activity of HDAC inhibitors in the presence of an antiherpes virus drug. (A) Three hundred thousand P3HR1 cells were exposed to either 40μM GCV or vehicle, and the indicated concentrations of individual HDAC inhibitors in a 1-mL volume in 24-well plates in triplicate. Three days later, 800 μL of the medium was removed without disturbing the settled cells, 1 mL of fresh growth medium containing GCV (40μM) was added, and the cells were allowed to grow for another 3 days. HDAC inhibitors used included butyrate, valproate, apicidin, largazole and its analogs, MS275, oxamflatin, LBH589, SAHA, and Scriptaid. The number above the HDAC + GCV bar represents the percentage of cells surviving relative to the cultures exposed to that particular HDAC inhibitor alone (assigned a value of 100%). Error bars represent SDs in individual experiments. (B) Cytotoxic activity of selected HDAC inhibitors (butyrate, MS275, and LBH589) in the presence of GCV in the EBV⁻ B-lymphoma lines BJAB and Toledo. Experiments were carried out essentially as in panel A. The right panel shows detection of EBER1- and β-actin–specific PCR products generated from cellular DNA of BJAB, P3HR1, and Toledo cells analyzed in a 2% agarose gel. A vertical line has been inserted to indicate a repositioned gel lane.